Meet ANYmal, a four-legged dog-like robot designed by researchers at ETH Zürich in Switzerland, in hopes of using such robots for search-and-rescue on building sites or disaster areas, among other applications. Now ANYmal has been upgraded to perform rudimentary parkour moves, aka "free running." Human parkour enthusiasts are known for their remarkably agile, acrobatic feats, and while ANYmal can't match those, the robot successfully jumped across gaps, climbed up and down large obstacles, and crouched low to maneuver under an obstacle, according to a recent paper published in the journal Science Robotics.

The ETH Zürich team introduced ANYmal's original approach to reinforcement learning back in 2019 and enhanced its proprioception (the ability to sense movement, action, and location) three years later. Just last year, the team showcased a trio of customized ANYmal robots, tested in environments as close to the harsh lunar and Martian terrain as possible. As previously reported, robots capable of walking could assist future rovers and mitigate the risk of damage from sharp edges or loss of traction in loose regolith. Every robot had a lidar sensor. but they were each specialized for particular functions and still flexible enough to cover for each other—if one glitches, the others can take over its tasks.

For instance, the Scout model’s main objective was to survey its surroundings using RGB cameras. This robot also used another imager to map regions and objects of interest using filters that let through different areas of the light spectrum. The Scientist model had the advantage of an arm featuring a MIRA (Metrohm Instant Raman Analyzer) and a MICRO (microscopic imager). The MIRA was able to identify chemicals in materials found on the surface of the demonstration area based on how they scattered light, while the MICRO on its wrist imaged them up close. The Hybrid was more of a generalist, helping out the Scout and the Scientist with measurements of scientific targets such as boulders and craters.

As advanced as ANYmal and similar-legged robots have become in recent years, significant challenges still remain before they are as nimble and agile as humans and other animals. “Before the project started, several of my researcher colleagues thought that legged robots had already reached the limits of their development potential,” said co-author Nikita Rudin, a graduate student at ETH Zurich who also does parkour. “But I had a different opinion. In fact, I was sure that a lot more could be done with the mechanics of legged robots.”

Parkour is quite complex from a robotics standpoint, making it an ideal aspirational task for the Swiss team's next step in ANYmal's capabilities. Parkour can involve large obstacles, requiring the robot "to perform dynamic maneuvers at the limits of actuation while accurately controlling the motion of the base and limbs," the authors wrote. To succeed, ANYmal must be able to sense its environment and adapt to rapid changes, selecting a feasible path and sequence of motions from its programmed skill set. And it has to do all that in real time with limited onboard computing.

The Swiss team's overall approach combines machine learning with model-based control. They split the task into three interconnected components: a perception module that processes the data from onboard cameras and LiDAR to estimate the terrain; a locomotion module with a programmed catalog of movements to overcome specific terrains; and a navigation module that guides the locomotion module in selecting which skills to use to navigate different obstacles and terrain using intermediate commands.

Rudin, for example, used machine learning to teach ANYmal some new skills through trial and error, namely, scaling obstacles and figuring out how to climb up and jump back down from them. The robot's camera and artificial neural network enable it to pick the best maneuvers based on its prior training. Another graduate student, Fabian Jenelten, used model-based control to teach ANYmal how to recognize and negotiate gaps in piles of rubble, augmented with machine learning so the robot could have more flexibility in applying known movement patterns to unexpected situations.

Among the tasks ANYmal was able to perform was jumping from one box to a neighboring box up to 1 meter away. This required the robot to approach the gap sideways, place its feet as close as possible to the edge, and then use three legs to jump while extending the fourth to land on the other box. It could then transfer two diagonal legs before bringing the final leg across the gap. This meant ANYmal could recover from any missteps and slippage by transferring its weight between the non-leaping legs.

ANYmal also was able to climb down from a 1-meter-high box to reach a target on the ground, as well as climbing up the box. It can also crouch down to reach a target on the other side of a narrow passage, lowering its base and adapting its gait accordingly. The team also tested ANYmal's walking abilities, in which the robot successfully traversed stairs, slopes, random small obstacles and so forth.

ANYmal still has its limitations when it comes to navigating real-world environments, whether it be a parkour course or the debris of a collapsed building. For instance, the authors note that they have yet to test the scalability of their approach to more diverse and unstructured scenarios that incorporate a wider variety of obstacles; the robot was only tested in a few select scenarios. "It remains to be seen how well these different modules can generalize to completely new scenarios," they wrote. The approach is also time-consuming since it requires eight neural networks that must be tuned separately, and some of the networks are interdependent, so changing one means changing and retraining the others as well.

Still, ANYmal "can now evolve in complex scenes where it must climb and jump on large obstacles while selecting a nontrivial path toward its target location," the authors wrote. Thus, "by aiming to match the agility of free runners, we can better understand the limitations of each component in the pipeline from perception to actuation, circumvent those limits, and generally increase the capabilities of our robots."

Science Robotics, 2024. DOI: 10.1126/scirobotics.adi7566  (About DOIs).

Listing image by ETH Zurich / Nikita Rudin

When we talk about memories in biology, we tend to focus on the brain and the storage of information in neurons. But there are lots of other memories that persist within our cells. Cells remember their developmental history, whether they've been exposed to pathogens, and so on. And that raises a question that has been challenging to answer: How does something as fundamental as a cell hold on to information across multiple divisions?

There's no one answer, and the details are really difficult to work out in many cases. But scientists have now worked out one memory system in detail. Cells are able to remember when their parent had a difficult time dividing—a problem that's often associated with DNA damage and cancer. And, if the problems are substantial enough, the two cells that result from a division will stop dividing themselves.

Setting a timer

In multicellular organisms, cell division is very carefully regulated. Uncontrolled division is the hallmark of cancers. But problems with the individual segments of division—things like copying DNA, repairing any damage, making sure each daughter cell gets the right number of chromosomes—can lead to mutations. So, the cell division process includes lots of checkpoints where the cell makes sure everything has worked properly.

But if a cell makes it through all the checkpoints, it's presumably all good, right? Not entirely, as it turns out.

Mitosis is the portion of cell division where the duplicated chromosomes get separated out to each of the daughter cells. Spending a lot of time in mitosis can mean that the chromosomes have picked up damage, which may cause problems in the future. And prior research found that some cells derived from the retina will register when mitosis takes too long, and the daughter cells will stop dividing.

The new work, done by a team of researchers in Okinawa, Japan, and San Diego, started by showing that this behavior wasn't limited to retinal cells—it seems to be a general response to a slow mitosis. Careful timing experiments showed that the longer cells spent trying to undergo mitosis, the more likely the daughter cells would be to stop dividing. The researchers term this system a "mitotic stopwatch."

So, how does a cell operate a stopwatch? It's not like it can ask Siri to set a timer—it's largely stuck working with nucleic acids and proteins.

It turns out that, like many things relayed to cell division, the answer comes down to a protein named p53. It's a protein that's key to many pathways that detect damage to cells and stop them from dividing if there are problems. (You may recall it from our recent coverage of the development of elephant stem cells.)

A stopwatch made of proteins

The researchers found that, while mitosis was going on, p53 started showing up in a complex with two other proteins (ubiquitin-specific protease 28 and the creatively named p53-binding protein 1). If you made mutations in one of the proteins that blocked this complex from forming, the mitotic stopwatch stopped ticking. This three-protein complex only started building up to significant levels if mitosis took longer than usual, and it remained stable once it formed so that it would get passed on to the daughter cells once cell division was completed.

So, why does this complex form only when mitosis takes longer than usual? The key turned out to be a protein called a kinase, which attaches a phosphate to other proteins. The researchers screened chemicals that inhibit specific kinases that are active during mitosis and DNA repair, and found a specific one that was needed for the mitotic stopwatch. In the absence of this kinase (PLK1, for the curious), the three-protein complex doesn't form.

So, the researchers think that the stopwatch looks like this: during mitosis, the kinase slowly attaches a phosphate to one of the proteins, allowing it to form the three-protein complex. If mitosis gets done quickly enough, the levels of this complex don't get very high, and it has no effect on the cell. But if mitosis goes more slowly, then the complex starts building up, and it's stable enough that it's still around in both daughter cells. The existence of the complex helps stabilize the p53 protein, allowing it to stop future cell divisions once it's present at high enough levels.

Consistent with this idea, all three of the proteins in the complex are tumor suppressors, meaning that mutations in them make tumor formation more likely. The researchers confirmed that the mitotic stopwatch was frequently defective in tumor samples.

So, that's how individual cells manage to store one of their memories—the memory of problems with cell division. The mitotic stopwatch, however, is just one of the memory storage systems, with completely separate systems handling different memories. And, at the same time this is happening, a large number of other pathways also feed into the activity of p53. So, while the mitotic stopwatch may efficiently handle one specific type of problem, it's integrated into a lot of additional, complex systems operating in the cell.

Science, 2024. DOI: 10.1126/science.add9528  (About DOIs).

Welcome to Edition 6.37 of the Rocket Report! The big story this week is the final launch of the Delta IV Heavy rocket, which is one of the biggest spectacles to enjoy lifting away from the planet. Because of a scrub on Thursday, there is still time to clear your calendar for a second attempt on Friday at 1:37 pm ET in Florida.

As always, we welcome reader submissions, and if you don't want to miss an issue, please subscribe using the box below (the form will not appear on AMP-enabled versions of the site). Each report will include information on small-, medium-, and heavy-lift rockets as well as a quick look ahead at the next three launches on the calendar.

Orbex patents reusable rocket tech. The British launch company said this week it has patented a "REFLIGHT" technology that enables the recovery of the first stage of its small Prime rocket. Essentially, Orbex designed an interstage that will function somewhat like grid fins on the Falcon 9 rocket's first stage. "After Stage 1 detaches from Stage 2, the interstage on top of Stage 1 reconfigures into four ‘petals’ which fold out and create drag forces that passively reorients and slows the spent rocket stage’s descent to Earth," the company stated.

Show me, don't tell me ... This petal structure will combine with a parachute to enable a low-speed landing at sea, where Orbex plans to recover its first stage. It all sounds good, but this seems to be something of putting the cart before the horse. Orbex is now nearly 9 years old, and it's not clear when the Prime rocket will take flight for the first time. As with all small launch companies, the focus should really be getting to the first flight, demonstrating a capability, and then ramping up launch cadence. Talk of reuse and recycling is great. But flying is better. (submitted by EllPeaTea)

Boeing sues Virgin Galactic. Boeing and its subsidiary, Aurora Flight Sciences Corporation, have sued Virgin Galactic, alleging the space tourism company has misappropriated trade secrets, The Register reports. In 2022, Virgin Galactic selected Aurora to build new motherships for its spacecraft as replacements for the VMS Eve carrier aircraft. The lawsuit alleges that Virgin Galactic has failed to pay it almost $26 million for work on new craft.

Going forward with just one aircraft ... At the time of the agreement, Virgin Galactic said it needed new motherships to support an increased cadence of spaceflights. Virgin Galactic CEO Michael Colglazier said, "Our next-generation motherships are integral to scaling our operations. They will be faster to produce, easier to maintain, and will allow us to fly substantially more missions each year." The first delivery was due in 2025. After it began work on the project, Aurora concluded that a new mothership would cost nearly twice as much as Virgin Galactic hoped and would not be completed before 2027. Now, Virgin Galactic plans to soldier on with just Eve for the time being. (submitted by EllPeaTea and Ken the Bin)

JAXA inks with Interstellar Technologies, others. Japan’s space agency has selected startup Interstellar Technologies as a priority launch provider as part of a program to advance the commercialization of space, Space News reports. Space One, whose Kairos solid rocket exploded seconds after liftoff earlier this month, was also selected under the small satellite initiative by JAXA, as were Space BD and Mitsui Bussan Aerospace.

Broadening the domestic industry ... The agreements mean the companies will have priority for future contracts. These are designed to support private-sector entities capable of launching satellites developed under JAXA’s small satellite missions and advance the commercialization of space transportation services. Japan is targeting a domestic launch capacity of approximately 30 institutional rockets and private rockets per year by the early 2030s. (submitted by Ken the Bin)

Will the Medium Launch Vehicle be reusable? Earlier this month Northrop Grumman unveiled a new website that provided some additional detail about the "Medium Launch Vehicle" it is developing in conjunction with Firefly. "Carrying more than 16,000 kg to low Earth orbit, MLV serves commercial, civil, national security, and international launch markets with competitive pricing to customers’ preferred orbits," the website stated. MLV will first launch from Virginia’s Mid-Atlantic Regional Spaceport on Wallops Island.

A rare new vehicle without a reuse component ... What was missing from the new information about MLV was any mention of reusability, be it of the first stage, its seven main Miranda engines, or other components. This was a bit surprising, because almost every medium-lift vehicle announced recently in the United States and elsewhere has featured some element of reuse. I asked a spokesperson with Northrop Grumman about this and was told this week, "At the current moment we don’t have more answers to provide other than what’s currently on our website." Read into that what you will.

After rare delay, Soyuz crew mission safely launches. The crewed Soyuz MS-25 mission was scheduled to fly on March 21 from the Baikonur Cosmodrome to the International Space Station. However, an automatic abort command was issued at the T-20 second mark. On its second attempt two days later, the mission lifted off successfully, NASASpaceflight.com reports.

A lower launch cadence ... Once Soyuz MS-25 got off the ground, it took a 48-hour path to the ISS. If it had launched on March 21, it could have taken an “express” path to the station that would take only three hours and 18 minutes to get to docking, which was expected to occur at 16:39 UTC on the same day. Soyuz MS-25 is only the second launch to take place from Baikonur Cosmodrome this year. (submitted by Jay50001)

Don't expect perfection from Starliner. The first crewed launch of Boeing's Starliner spacecraft remains on track for May 1 of this year on board an Atlas V rocket. In a pre-flight interview, the commander of that mission, Butch Wilmore, emphasized to Ars that this would be truly a test flight. "The expectation from the media should not be perfection," Wilmore said. "This is a test flight. Flying and operating in space is hard. It’s really hard, and we’re going to find some stuff. That’s expected. It’s the first flight where we are integrating the full capabilities of this spacecraft."

But it's not going to be bad ... Outside observers, Wilmore said, "don’t realize that there are flights going on with F-18s back in the day, or the T-45s that I flew, where we found stuff and fixed it." More on the mission: "You don’t get visibility in those programs and those flights. This one is visible, especially with some of the things that have transpired. So don’t have that expectation, please. It’s not going to be perfect. But it’s not going to be bad, either. We wouldn’t go if we thought that... It’s going to be things that are rectifiable. And the whole thing is to get up, get to the space station, and get back, and we’re going to show that it has that capability.”

China to increase usage of Long March 6. On Tuesday, a Long March 6A rocket lifted off from Taiyuan Satellite Launch Center, north China, carrying a secretive meteorological satellite. Tuesday’s mission was the fifth launch of the Long March 6A rocket, which has a capacity of 4.5 metric tons to low-Earth orbit and features two kerosene-liquid oxygen stages and four solid propellant side boosters. As Space News notes, this is the first Chinese rocket to use a combination of liquid and solid stages and boosters.

A new generation of rockets ... All of the Long March 6A rocket launches have been successful, dating to March 2022. A new variant of the rocket, the Long March 6C, is due to launch later this year. It uses the same core stage but does not have any boosters. China’s main space contractor, CASC, stated that Tuesday’s launch is the start of the high-frequency launch of the Long March 6 series this year. It is part of China's effort to replace the aging hypergolic and toxic Long March 2, 3, and 4 series of boosters. (submitted by Ken the Bin)

Delta IV Heavy scrubs on Thursday. At just under four minutes to go before liftoff, United Launch Alliance scrubbed the final mission of the Delta IV Heavy rocket on Thursday. According to the company, the launch "was scrubbed due to an issue with the gaseous nitrogen pipeline, which provides pneumatic pressure to the launch vehicle systems." Later on Thursday United Launch Alliance said it needed more time to troubleshoot the pipeline issue, and did not set a new date. The launch is now unlikely to take place before at least Monday.

It's the end of an era ... As Ars reports, the Delta IV Heavy leaves a legacy of launching national security missions, along with NASA's Orion spacecraft, on a test flight in 2014 and NASA's Parker Solar Probe in 2018 on a mission to fly through the Sun's outer atmosphere. Moreover, this is the final flight overall for the Delta rocket family—the 389th rocket with the Delta name—since 1960. But those earlier rockets share virtually nothing in common with the Delta IV, which debuted in 2002. The older generations of Delta rockets could trace at least some of their design lineage to the Thor program, a Cold War-era ballistic missile later converted into a satellite launcher.

Starship fired up for fourth test flight. This week SpaceX conducted two static fire tests of the Starship upper stage that will be used for a fourth test flight of the vehicle later this year, possibly as soon as May. The first test was a "full duration" static fire test of the vehicle's six Raptor engines. The second test, on Wednesday, saw the firing of a single Raptor engine using the header tanks in the vehicle, rather than its main fuel tank.

Seeking a full test flight ... The goal of this fourth flight will be to complete a full test regime, including making a soft landing of the Super Heavy boost stage in the Gulf of Mexico and a series of milestones by the Starship upper stage. This includes an in-space re-light of the Raptor engines, a fully controlled flight, and successfully surviving the fiery reentry process. There will be no Starlink satellites on board. (submitted by Ken the Bin)

Next three launches

March 29: Falcon 9 | Starlink 7-18 | Vandenberg Space Force Base, Calif. | 02:30 UTC

March 29: Delta IV Heavy | NROL-70 | Cape Canaveral Space Force Station, Fla. | 17:37 UTC

March 30: Falcon 9 | Eutelsat 36D | Kennedy Space Center, Fla. | 21:52 UTC

When Chuck Yeager reached Mach 1 on October 14, 1947, the entire frame of his Bell X-1 aircraft suddenly started to shake, and the controls went. A crew observing the flight in a van on the ground reported hearing something like a distant, rolling thunder. They were probably the first people on Earth to hear a boom made by a supersonic aircraft.

The boom felt like an innocent curiosity at first but soon turned into a nightmare. In no time, supersonic jets—F-100 Super Sabers, F-101 Voodoos, and B-58 Hustlers—came to Air Force bases across the US, and with them came the booms. Proper, panes-flying-off-the windows supersonic booms. People filed over 40,000 complaints about nuisance and property damage caused by booming jets, which eventually ended up with the Federal Aviation Administration imposing a Mach 1 speed limit for flights over land in 1973.

Now, NASA wants this ban to go. It has started the Quesst mission to go fast over American cities once more. But this time, it wants to do it quietly.

Breaking the sound barrier

The reason Yeager’s X-1 was so difficult to control at Mach 1 was not an actual “sound barrier” the plane broke. The “barrier” aspect is purely metaphorical. While Yeager’s plane experienced turbulence and shaking, it was due to rising drag and aircraft design.

At subsonic speeds, the airflow around the wings, tail, and fuselage is smooth. But at supersonic speeds, the air going over irregular shapes— the nose, canopy, and wings—accelerates to above the speed of sound. Then, where the curvature of the wing or canopy becomes less pronounced, it starts to build up pressure and decelerate back below Mach 1, a phenomenon known as “adverse pressure.” This creates shockwaves, and those are what cause supersonic booms and change the way wings, flaps, and other control surfaces behave in an airplane. The X-1 started acting so wild at Mach 1 because its aerodynamics weren’t designed for supersonic flight.

Lockheed, Bell, McDonell Douglas, and other companies that built early supersonic planes solved the control issues quickly, which made accelerating to Mach speeds pretty uneventful for the pilot. But that left two decades of booming.

How loud is the boom?

A supersonic jet boom sounds like a thunder strike hitting nearby—a product of the shockwaves generated mainly by the nose and tail of the aircraft. The boom usually falls between 100 and 110 on a perceived level decibel scale (PLdB), which is used to quantify how people experience sound. A car door slam 100 feet away is 60 PLdB; distant thunder, like the one the ground crew heard during Yeager’s first supersonic flight, is around 70 PLdB. A supersonic boom is on par with a nearby thunder strike, which falls at around 105–110 PLdB.

It’s really freaking loud. And you can easily make it even louder.

This 110 PLdB is estimated for an airplane in a steady, level flight at high altitude. These conditions create what’s known as a “carpet boom” that tracks the aircraft on the ground for the entire time it flies supersonic.

Transitions from subsonic to supersonic speeds and vice versa result in so-called “focus booms,” which can be up to three to four times louder than a carpet boom. This likely gave rise to the popular misconception that the boom is heard only when a plane breaks the sound barrier.

Focus booms are also caused by maneuvers like pitch and dive, where an aircraft gains altitude, levels, and flies back down; turns made with aggressive banking angles work as well. Unlike carpet booms, the booms made by transitions and maneuvers are singular events. The military even tested whether those amplified booms could be projected at chosen spots on the ground to weaponize them. As it turned out, you could do targeted booms, but they proved more scary than lethal.

But despite all the problems with booming, the allure of superior speed was irresistible. Supersonic airplanes could cut the time of transatlantic flights by half. So back in the mid-1950s, when the FAA’s Mach 1 speed limit was still many years away, British and French engineers got to the drawing board and conceived one of the most breathtaking airliners to ever pierce the sky: Concorde.

Roar of the Concordes

The first studies conceptualizing Concorde started in 1954. In 1962, France and Britain signed a treaty that created a joint development project to build it—the scale of the effort was so gargantuan that neither country could pull it off on its own. Arguably, building a supersonic airliner in the 1960s and early 1970s was more of a moonshot than an actual Apollo Moon landing.

The plane was built by Sud Aviation and British Aircraft Company, which many corporate mergers later became parts of Airbus and BAE Systems, respectively. The constructors didn’t want it to go only slightly supersonic like the Yeager’s X-1 did. They wanted to go over Mach 2, which was (and remains) crazy fast and made building the plane even harder.

At Mach 2.2, air friction heated up Concorde’s fuselage to 121° Celsius, which made it expand over 12 inches. To keep the passengers and crew from boiling inside, the craft’s air conditioning system used its jet fuel as a heat sink. To accelerate to and maintain Mach 2.2, Concorde used four bespoke Rolls-Royce/Snecma Olympus 593 engines, each generating over 160 kN of thrust.

The engine’s compressor blades and drums were made of titanium to withstand the high temperatures of air coming through the inlets. The signature delta wings needed a super aggressive angle to generate lift at low speeds, which forced the engineers to fit Concorde with its signature nose, which was lowered during takeoff and landing so the crew could see the runway. It was probably the quirkiest airplane ever made.

And then there was the noise. Concorde’s supersonic boom felt like a thunder strike, even when it was flying at its usual cruise altitude of 60,000 feet. You can actually hear how it sounded—within the limitations of over 20-year-old handheld cam, of course. Just get good headphones and crank up the volume (at your own risk).

The landing and takeoff noise was just as bad. Concordes approaching New York’s JFK Airport flew over Queens. People who lived there back then remember shaking furniture followed by “the most deafening roar you’ve ever heard.”

Quieting the boom

Research on supersonic booms started a couple of years after Yeager’s first supersonic flight. Back then, the Air Force wanted to learn if the booms could cause damage on the ground or trouble to nearby airplanes flying in formation. “They started looking into these problems in the 1950s, and NACA, the predecessor of NASA, was there too, right from the beginning,” said Peter Cohen, NASA’s Quesst mission integration manager. The booms were measured with arrays of microphones on the ground, on balloons, towers, and other aircraft following the booming plane at various distances.

“Lots of research, lots of measurements taken,” said Cohen.

The 1960s saw the first designs aimed at reducing the boom tested in wind tunnels. “These were small aircraft models, between an inch and three inches long, used to test shockwave pressures around them to see how changing the design affects boom acoustic signature,” Cohen explained.

The first mathematical concepts describing how low-boom aircraft should be designed were developed in the 1970s; the 1980s brought computers that could run those models in a timely manner. “We also got first programs to simulate fluid dynamics. So we started to identify designs that would not only reduce sonic boom noise but were also practical and looked like real airplanes,” said Cohen. (One of the first of those designs was intended to be a next-gen Concorde.)

The main focus of the High Speed Research (HSR) program was a 300-passenger airliner called High Speed Civil Transport, co-developed with and largely funded by Boeing. The program produced some ideas on how to design engine nozzles to reduce takeoff and landing noise, but Boeing considered boom-mitigation technologies unfeasible at that time. That meant the HSCT airliner would be limited to subsonic speeds over land, just like the Concorde it was supposed to compete with. This ultimately led to Boeing withdrawing its interest and money. The HSR program was canceled in 1999.

“But then DARPA said, ‘What if we could build a small airplane instead, make it quiet, and see where that would get us?’” Cohen said. This led to a new program called Shaped Sonic Boom Demonstration, which used a modified F-5E fighter jet to see if quieting the boom was possible in the real world.

Test flights done in 2003 proved it was.

“It verified the theory. The measurements done on the ground matched the design predictions,” Cohen said. So in the late-2000s, NASA contracted Boeing and Lockheed to develop concept designs for low-boom supersonic airliners, and both concepts seemed viable on paper. “And since we wanted to test those design approaches in a real atmosphere, we started thinking about building a new X-plane,” said Cohen. This plane became known as the X-59, and NASA chose Lockheed to build it.

Low boom design

When earlier designs flew faster than sound, individual shockwaves coming from different features like the nose, canopy, and wings merged into one powerful shockwave as they traveled to the ground. “We designed the X-59 so that those individual shockwaves don’t merge, which makes the boom quieter,” said Mike Buonanno, the X-59 air vehicle lead at Lockheed.

But making the X-59 sonic boom quieter was just one of the two main goals. The other was tuning the boom characteristics of the relatively small jet to resemble those of a full-sized airliner. “The X-59 has roughly 25 thousand pounds takeoff weight, but it makes a sonic boom that sounds similar enough to a much larger airplane,” Buonanno added.

“When you compare the X-59 to conventional supersonic aircraft, it looks very clean. “One of the ways to prevent all those small shocks that merge later is to eliminate them,” said Dave Richardson, a director at Lockheed’s X-59 Program Management.

Like an electric car, the X-59 has a mostly flat underbody. The engine inlet, usually fitted at the bottom of the plane, is installed at the top, just ahead of the tail. Bumps that accommodate control effectors for flaps and so on are on the top of the wings, not the bottom. The engine nozzle has a bathtub-like cover underneath it, again to maintain this featureless underside.

“This way the vast majority of shocks generated by the X-59 are directed upward, and very few go to the ground,” Richardson explained. But perhaps the most unusual victim of eliminating shock-generating features was the canopy. The X-59 has no front-facing windows.

From the pilot’s point of view, forward visibility is provided by a screen fitted where a front window should be, displaying a feed from a front-facing camera. The only real windows are to the sides to give some peripheral vision. “This kind of system has been studied earlier—for example, in the HSR program. Back then, pilots got motion sickness because the displayed image did not match the real world exactly. But the system in the X-59 gives you better visual quality than your eyes,” said Cohen.

According to Cohen, who is also a pilot, the X-59 is a good flying airplane. “We have a simulator, and I have flown it myself. It’s a research airplane, so it does not have some of the pilot-friendly features a production machine would have. It doesn’t loop and roll like a fighter jet, but it is very stable, very controllable,” Cohen said. And it is quiet—the sonic boom it will make should be around 75 PLdB, roughly like a car door slam from 20 feet away.

The push for change

The X-59 is being built to do a series of supersonic test flights over American cities to boom people living there. Then NASA will gather feedback from those on the ground and compile it into a data pack for the aviation authorities, the FAA and the International Civil Aviation Administration. Should things work as expected, that data will be part of a push to lift the ban on supersonic flight over land and replace it with an acceptable noise standard.

“We have labs and rooms with speaker systems that can simulate quiet supersonic booms. But we want to see how people react to them in their communities,” said Cohen. To make the data more variable, the X-59 will generate booms with different intensities.

“We have a requirement for the X-59 to be able to use maneuvering to both make the boom quieter or louder,” said Buonanno. For example, when a supersonic airplane turns, the boom is slightly louder on the inside of the turn and quieter on the outside. There are other maneuvering tricks, too. “By diving a plane very steeply and going briefly supersonic, you can vary the sonic boom sound level by varying the distance between the plane and the listeners on the ground,” said Cohen.

NASA has also figured that this diving maneuver could be used to demonstrate how the X-59’s quiet boom would sound by using a computer model of the X-59. So they brought the members of the ICAO’s Committee on Aviation Environmental Protection (CAEP) out to the Mojave Desert and hit them with an equivalent boom. “I have to tell you, we had a lot of skeptics before we did that,” Cohen said.

According to Cohen, the demonstration went well and managed to convince some skeptical CAEP members. “People do not understand that you can quiet the boom down to a really soft sound. It was very eye-opening for them to realize the sound we were talking about was not a sonic boom, it was very much quieter,” said Cohen.

He said that CAEP is currently working to generate a noise-based standard for supersonic flight over land forward using metrics, measuring procedures, and data from the X-59 mission. Assuming the standard is internationally approved, we should be heading straight to “making commercial supersonic air travel possible for everyone,” as the mission statement on the X-59 website puts it. But there’s a catch.

When asked by Condé Nast Traveler in 2021 what it felt like to fly Concorde, Richard Westray, a Concorde pilot, said, “I’ve always equated it to being a bus driver given a Ferrari to go and play with.” Buses totally are “possible for everyone.” Ferraris are not. And supersonic aircraft, so far at least, have had seating capacities closer to a Ferrari.

First class only

The way sound propagates through air is often compared to waves caused by an object falling into a body of water. “Do an experiment. Take a marble, a wide one, and drop it down into the water. It will make a splash. But take something narrow, even of equal mass, like a pencil, and drop it nose-down, and you’ll see almost no splash at all,” said Richardson. The difference between the splash and no splash is dictated by the fineness ratio, the ratio of the length of the body to its maximum width.

The fineness ratio is also one of the most important design metrics in supersonic airplane construction. To pierce the air at supersonic speeds, you need something that looks more like a needle and less like a truck. Just look at Concorde, the SR-71 Blackbird, or the X-59—all long and very slender. That's why Concorde could take only 100 passengers on board. And this determined who these passengers were.

“The atmosphere in the cabin was one of an exclusive club, and it was because these were the people who controlled the world, controlled the world’s finance and the world’s trade,” Joe Cudy, a Concorde flight attendant, said in the same Condé Nast Traveler Concorde story.

The interior was luxurious. The meals were gourmet. At the front of the cabin, there was a screen showing the current Mach number to let passengers know they were flying faster than bullets. Concorde was not “possible for everyone.” It was a super-high-end air carriage for one-percenters and top-tier celebrities.

And even those one-percenters could not keep Concorde afloat financially. It never paid off its development costs. One of the reasons was its horrible fuel-efficiency.

Supersonic airplanes have arrow-like wings that work well when you fly fast but struggle to keep the plane in the air when you are slow. These small wings mean that supersonic airplanes have a lift-to-drag ratio that is usually about half that of subsonic planes. They need to supply twice the thrust to keep a given mass flying, which in turn means using twice as much fuel. And that's without afterburners, of course.

“Off the top of my head, the efficiency gap between Concorde and subsonic airplanes was 3 or 4 times in terms of fuel efficiency,” said Buonanno. On a New York to Paris flight, Concorde burned through roughly four times more fuel than the Boeing 747 while carrying one-fifth of the passengers.

The problem is that you can’t really do much about both fineness and lift-to-drag ratios—they're limitations imposed by pure physics. If you wanted to keep the right fineness ratio and have enough space for over 500 passengers in a supersonic airliner, you’d just need to make it absurdly long.

And even if you could overcome all the engineering issues with building such a thing, you’d probably have to build dedicated runways and terminals to support it, too. This is why other supersonic airliner concepts, like one Lockheed proposed to NASA in late 2000s, can’t take many passengers (Lockheed’s took about 80 passengers, even fewer than Concorde). The question is whether physics will allow us to make them less elitist.

Transoceanic express

“Subsonic airplanes will always have better fuel efficiency than supersonic airplanes,” said Buonanno.

That said, NASA and Lockheed want to make this efficiency gap smaller by making the X-59 and presumably future supersonic airliners a bit slower. “The goal here is to fly supersonically but do so at a threshold where you are still affordable,” said Richardson.

This threshold is between Mach 1.6 and Mach 1.8, where the plane doesn’t need super complicated engines like Concorde had, Richardson said. “It is slower than Concorde’s Mach 2 but still twice as fast as we fly today,” he added.

Slowing future supersonic airliners down doesn’t solve all the issues. “The sonic boom is one challenge that needs to be overcome. Then landing and takeoff noise is another challenge, fuel efficiency is yet another challenge, and high altitude emissions is a challenge, too. Still, NASA feels that one of the big reasons Concorde did not sell enough airplanes was because it couldn’t fly over land supersonically. When the ban on supersonic flight was put in place, the demand for Concorde evaporated,” said Cohen.

It evaporated because Concorde’s efficiency at lower speeds was even worse, which limited the plane to routes that ran mostly over ocean. In practice, this meant there were only 14 Concordes flying London to New York and Paris to New York. Concorde lacked economies of scale.

“It is not economically efficient to operate a fleet of seven aircraft, which was what British Airways and Air France were doing. With the low-boom technology, you open up the size of the market—you can build more airplanes and amortize your training over a larger fleet and so on,” said Buonanno.

“NASA wants this airplane geared toward business travelers, people who want to put that premium value on time and pay extra money to get there sooner,” Richardson added. “But just like your cell phone, like microwave ovens, like computers, it will become cheaper over time. But it won’t be cheaper than flying subsonically.” The next-gen supersonic flight will still be a first-class experience, just like Concorde, but it will include business class as well, he said.

Still, we’ll have to wait a while before it happens. “We want to bring the new noise standard forward at the CAEP meeting in 2031,” said Cohen. “If it is ratified then, and you factor in a 10-year timeframe to develop the airplane, I think the earliest you could see Concorde 2.0 would be around 2040. It’s gonna take a while, but we have already been patient for 60 years.”

Correction: The original article stated that the Concorde used afterburners in regular, cruising flight. This is an error; afterburners were primarily used for takeoff.

Good morning. It's March 28, and today's photo comes from NASA's Chandra X-ray Observatory as well as a host of other observatories.

It is a composite image of supernova remnant SNR 1181. The name of the object gives us a clue to when this object went supernova: the year 1181. For about half a year, the 'new' star appeared in the constellation Cassiopeia. It took a long time before astronomers using modern telescopes were able to find the remnant of this supernova, but they finally did so in the last decade.

This image combines X-ray, optical, and infrared wavelengths to bring the remnant to life. And in doing so, astronomers have been able to piece together what happened to cause the supernova. It seems to have been quite an incredible bit of astronomical sleuthing:

Studies of the composition of the different parts of the remnant have led scientists to believe that it was formed in a thermonuclear explosion, and more precisely a special kind of supernova called a sub-luminous Type Iax event. During this event two white dwarf stars merged, and typically no remnant is expected for this kind of explosion. But incomplete explosions can leave a kind of ‘zombie’ star, such as the massive white dwarf star in this system. This very hot star, one of the hottest stars in the Milky Way (about 200,000 degrees Celsius), has a fast stellar wind with speeds up to 16,000 km/h. The combination of the star and the nebula makes it a unique opportunity for studying such rare explosions.

The Chandra Observatory, by the way, faces steep budget cuts despite the fact that it remains operational. There is an effort to save the Great Observatory.

Source: Chandra X-Ray Observatory

This is the rocket that literally lights itself on fire before it heads to space. It's the world's largest rocket entirely fueled by liquid hydrogen, a propellant that is vexing to handle but rewarding in its efficiency.

The Delta IV Heavy was America's most powerful launch vehicle for nearly a decade and has been a cornerstone for the US military's space program for more than 20 years. It is also the world's most expensive commercially produced rocket, a fact driven not just by its outsized capability but also its complexity.

Now, United Launch Alliance's last Delta IV Heavy rocket is set to lift off Thursday from Cape Canaveral Space Force Station, Florida, with a classified payload for the National Reconnaissance Office, the US government's spy satellite agency.

"This is such an amazing piece of technology, 23 stories tall, a half-million gallons of propellant and a quarter-million pounds of thrust, and the most metal of all rockets, setting itself on fire before it goes to space," said Tory Bruno, ULA's president and CEO. "Retiring it is (key to) the future, moving to Vulcan, a less expensive higher-performance rocket. But it’s still sad.”

45th and final Delta IV

Weather permitting, the Delta IV Heavy will light up its three hydrogen-fueled RS-68A engines at 1:40 pm EDT (17:40 UTC) Thursday, the opening of a four-hour launch window. The three RS-68s will fire up in a staggered sequence, a permutation designed to minimize the hydrogen fireball that ignites around the base of the rocket during engine startup.

The Delta IV Heavy will certainly have a legacy of launching national security missions, along with NASA's Orion spacecraft on an orbital test flight in 2014 and NASA's Parker Solar Probe in 2018 on a mission to fly through the Sun's outer atmosphere.

But the fireball will leave an indelible mark in the memories of anyone who saw a Delta IV Heavy launch. It all comes down to the choice of super-cold liquid hydrogen as the fuel. The three RS-68 engines burn hydrogen along with liquid oxygen as the oxidizer.

"We like those propellants because they’re very, very high performance," Bruno said. "In order to prepare the RS-68 engines to get that very cold cryogenic propellant flowing through them, before they’re ignited, we start flowing that propellant.

"Hydrogen is lighter than air, so after it flows through the engine and into the flame trench, it then rises. When the engines are finally full and ready to go and we start spinning up the pumps, then we actually drop the main load (of propellant), we ignite it, and that flame carries on up that ... plume of hydrogen, which is clinging to the side of the booster and rising up.”

The Delta IV rocket cores are covered in orange foam insulation. One of the reasons for this is to protect the rocket from the fireball, leading to what Bruno called a "very dramatic effect of a self-immolating booster" that has the appearance of a "toasted marshmallow" as it heads to space.

A few seconds after the engines start, 12 hold-down bolts will blow to release the triple-core rocket from its restraints. More than 2 million pounds of thrust will power the Delta IV Heavy off the launch pad toward the east from Cape Canaveral. The RS-68 on the center core will throttle down to conserve liquid hydrogen and liquid hydrogen propellant, while the rocket's two side boosters will burn through their propellants in less than four minutes.

Once the Delta IV lets go of its side boosters and falls into the Atlantic Ocean, the center core throttles up and burns for another minute and a half. A few moments later, the first stage booster jettisons, and the upper stage's RL10 engine ignites for the first of three burns needed to propel the rocket's classified cargo into an orbit thousands of miles above Earth.

There's just a 30 percent chance of favorable weather for liftoff Thursday. High winds and cumulus clouds are the primary concerns. The weather forecast improves for a backup launch opportunity Friday afternoon.

You can watch the launch on ULA's live broadcast, embedded below.

This is also the final flight overall for the Delta rocket family—the 389th rocket with the Delta name—since 1960. But those earlier rockets share virtually nothing in common with the Delta IV, which debuted in 2002. The older generations of Delta rockets could trace at least some of their design lineage to the Thor program, a Cold War-era ballistic missile later converted into a satellite launcher.

The last of that older family of Delta rockets, the Delta II, launched for the final time in 2018. The Delta IV was a clean-sheet design, initially conceived by McDonnell Douglas, that won a contract from the Air Force in 1998, alongside Lockheed Martin's Atlas V rocket, to become the new workhorse launch vehicles for the military's fleet of satellites.

The Delta IV program became part of Boeing when that company merged with McDonnell Douglas in 1997. In 2006, Boeing merged its Delta rocket program with Lockheed Martin's Atlas V program, creating United Launch Alliance in a 50-50 joint venture.

The launch this week will mark the 45th flight of a Delta IV rocket and the 16th to fly in the Delta IV Heavy configuration. The Delta IV Heavy, in particular, launched the kinds of heavy military and intelligence-gathering satellites that once flew on the Titan IV rocket, which retired in 2005. These payloads have primarily included NRO eavesdropping satellites and the massive bus-size Keyhole imaging platforms, essentially Hubble-class telescopes pointed at Earth.

The Delta IV boasts a nearly perfect success record. The only blemish was on the first flight of the Delta IV Heavy in 2004 when a dummy payload was deployed into a lower-than-planned orbit after the three booster engines shut down a few seconds early.

But the Delta IV Heavy is expensive. At one time, a single launch on this expendable rocket cost as much as much as $400 million, although the government secured a somewhat lower price from ULA for buying in bulk the the final three missions on Delta IV Heavy. The Delta IV launched a commercial satellite on its first flight in 2002, but no more commercial customers ever bought a Delta IV launch.

The Delta IV launch pads in Florida and California were particularly complex, requiring maintenance and sustainment even during years-long lulls in launch activity.

These high prices helped open a path for SpaceX, then a newcomer to the national security launch business, to petition the Pentagon for the right to compete for military launch contracts. With its partially reusable Falcon 9 rocket, SpaceX offered lower prices than ULA. "I don't know how to build a $400 million rocket," Gwynne Shotwell, SpaceX's president and chief operating officer, told Congress in 2015.

The Falcon Heavy rocket debuted in 2018, giving SpaceX the capability to launch nearly all of the military's space missions. There are a few exceptions, like the NRO payloads assigned to the final few Delta IV Heavy rockets. SpaceX is developing a longer payload fairing for the Falcon Heavy to accommodate these types of satellites.

Now, ULA has the less expensive Vulcan rocket, which flew on a problem-free test flight in January. Vulcan will replace the Delta IV and Atlas V rockets in ULA's fleet. There are still 17 Atlas V rockets remaining in ULA's inventory, primarily missions to launch Boeing's Starliner crew capsule and Amazon's Kuiper broadband network.

Under a contract the Pentagon awarded in 2020, ULA's Vulcan rocket and SpaceX's Falcon 9 and Falcon Heavy will launch all of the military's most expensive and sensitive satellites over the next few years. In its heaviest configuration, the Vulcan will outlift the Delta IV Heavy without needing three first-stage boosters to do the job.

"Delta IV Heavy is three rockets bolted together," Bruno said. "With a single core Vulcan, we’re able to collapse that cost (of Delta IV Heavy) by 70 percent and make that mission a lot more practical."

SpaceX has an agreement with the Space Force to take over the former Delta IV launch pad at Vandenberg Space Force Base in California. Falcon 9 and Falcon Heavy rockets will launch from there. And SpaceX has its eye on Space Launch Complex-37 at Cape Canaveral, where the final Delta IV Heavy will take off this week, as a possible future home for the giant Starship rocket.

Launching a listening post

The NRO payload aboard the final Delta IV Heavy launch is likely a sophisticated reconnaissance satellite that will be stationed in geosynchronous orbit, more than 22,000 miles (nearly 36,000 kilometers) over the equator. At that altitude, the spacecraft will orbit Earth in lock-step with the planet's rotation and will operate near numerous satellites owned by US adversaries like China and Russia. This orbital regime is also populated with privately owned satellites, primarily providing communication services.

Experts can make an educated guess based on publicly available information on the trajectory of the Delta IV Heavy as it flies east from Cape Canaveral. Only the largest NRO spy satellites require a launch on a Delta IV Heavy, and the payload on this mission is "almost certainly" a type of satellite known publicly as an "Advanced Orion" or "Mentor" spacecraft, according to Marco Langbroek, an expert Dutch satellite tracker.

The Advanced Orion satellites require the combination of the Delta IV Heavy rocket’s lift capability, long-duration upper stage, and huge 65-foot-long (19.8-meter) trisector payload fairing, the largest payload enclosure of any operational rocket. In 2010, Bruce Carlson, then-director of the NRO, referred to the Advanced Orion platform as the "largest satellite in the world."

When viewed from Earth, these satellites shine with the brightness of an eighth-magnitude star, making them easily visible with small binoculars despite their distant orbits, according to Ted Molczan, a skywatcher who tracks satellite activity.

The final phase of the Delta IV Heavy launch sequence will play out over roughly six hours, enough time for the upper stage and its payload to coast up to geosynchronous altitude, where a final engine burn will circularize the orbit before satellite deployment.

"The satellites feature a very large parabolic unfoldable mesh antenna, with estimates of the size of this antenna ranging from 20 to 100 (!) meters," Langbroek writes on his website, citing information leaked by Edward Snowden.

The purpose of these Advanced Orion satellites is to listen in on communications and radio transmissions from US adversaries and perhaps allies. Six previous Delta IV Heavy missions also likely launched Advanced Orion or Mentor satellites, giving the NRO a global web of listening posts parked high above the planet.

The Advanced Orion-series satellites began launching on Titan IV rockets in 1995, following a pair of earlier NRO Orion payloads that launched in the 1980s on space shuttle missions. The NRO began using Delta IV Heavy rockets for the Advanced Orion missions in 2009 following retirement of the Titan IV.

Bruno, ULA's chief executive, said this is the kind of mission Delta IV Heavy, and now Vulcan, was made for.

"The national security space mission is our core," he said. "This is a unique set of missions that require this high-energy rocket capability, very special orbits. We designed Vulcan specifically for that. Every rocket can do a range of missions, but there’s one mission it's best at. It is literally designed to be the best at the mission we’re going to fly here with this last Delta IV."

When asked why not wait for a cheaper ride on Vulcan or Falcon Heavy, with its still-to-come longer fairing, Scolese said, "We had the spacecraft ready to go, and we had a rocket that we trust, so it made sense to continue on with this. Something has to be last and we’re proud to be on that vehicle, and we have a lot of confidence in the system."

Physicists have been confident since the1980s that there is a supermassive black hole at the center of the Milky Way galaxy, similar to those thought to be at the center of most spiral and elliptical galaxies. It's since been dubbed Sagittarius A* (pronounced A-star), or SgrA* for short. The Event Horizon Telescope (EHT) captured the first image of SgrA* two years ago. Now the collaboration has revealed a new polarized image (above) showcasing the black hole's swirling magnetic fields. The technical details appear in two new papers published in The Astrophysical Journal Letters. The new image is strikingly similar to another EHT image of a larger supermassive black hole, M87*, so this might be something that all such black holes share.

The only way to "see" a black hole is to image the shadow created by light as it bends in response to the object's powerful gravitational field. As Ars Science Editor John Timmer reported in 2019, the EHT isn't a telescope in the traditional sense. Instead, it's a collection of telescopes scattered around the globe. The EHT is created by interferometry, which uses light in the microwave regime of the electromagnetic spectrum captured at different locations. These recorded images are combined and processed to build an image with a resolution similar to that of a telescope the size of the most distant locations. Interferometry has been used at facilities like ALMA (the Atacama Large Millimeter/submillimeter Array) in northern Chile, where telescopes can be spread across 16 km of desert.

In theory, there's no upper limit on the size of the array, but to determine which photons originated simultaneously at the source, you need very precise location and timing information on each of the sites. And you still have to gather sufficient photons to see anything at all. So atomic clocks were installed at many of the locations, and exact GPS measurements were built up over time. For the EHT, the large collecting area of ALMA—combined with choosing a wavelength in which supermassive black holes are very bright—ensured sufficient photons.

In 2019, the EHT announced the first direct image taken of a black hole at the center of an elliptical galaxy, Messier 87, located in the constellation of Virgo some 55 million light-years away. This image would have been impossible a mere generation ago, and it was made possible by technological breakthroughs, innovative new algorithms, and (of course) connecting several of the world's best radio observatories. The image confirmed that the object at the center of M87* is indeed a black hole.

In 2021, the EHT collaboration released a new image of M87* showing what the black hole looks like in polarized light—a signature of the magnetic fields at the object's edge—which yielded fresh insight into how black holes gobble up matter and emit powerful jets from their cores. A few months later, the EHT was back with images of the "dark heart" of a radio galaxy known as Centaurus A, enabling the collaboration to pinpoint the location of the supermassive black hole at the galaxy's center.

SgrA* is much smaller but also much closer than M87*. That made it a bit more challenging to capture an equally sharp image because SgrA* changes on time scales of minutes and hours compared to days and weeks for M87*. Physicist Matt Strassler previously compared the feat to "taking a one-second exposure of a tree on a windy day. Things get blurred out, and it can be difficult to determine the true shape of what was captured in the image."

The EHT collaboration finally announced the first image of SgrA* in 2022, showing that it has a ring structure. But astronomers still didn't know how the Milky Way's supermassive black hole is oriented or how fast it is spinning. That image was based on the same 2017 data as the image of M87*; it just took much longer to process. While M87* was an easier, steadier target, with nearly all images looking the same, that was not the case for SgrA*. The 2022 image was an average of the different images from observational data that the team collected over the course of multiple days. It took five years, multiple supercomputer simulations, and the development of new computational imaging algorithms capable of making inferences to fill in the blanks in the data.

Having EHT images for two black holes—one at the large end and one at the small end of supermassive black holes in the Universe—enables astronomers to compare the two. The 2022 SgrA* image was so remarkably similar to M87* that astronomers wanted to learn more about what else the two objects might have in common on top of their general appearance.  So they set out to capture an image of SgrA* in polarized light—a feat even more challenging than getting that first image in "normal" light.

"We were relieved that polarized imaging was even possible," said co-author Geoffrey Bower of the Institute of Astronomy and Astrophysics at Academia Sinica in Taiwan. To do so, the collaboration linked eight different telescopes around the world, including the aforementioned ALMA and the Atacama Pathfinder Experiment (APEX), also in northern Chile.

"With a sample of two black holes—with very different masses and very different host galaxies—it’s important to determine what they agree and disagree on," said Mariafelicia De Laurentis of the University of Naples Federico II, in Italy. "Since both are pointing us toward strong magnetic fields, it suggests that this may be a universal and perhaps fundamental feature of these kinds of systems.” The EHT will start observing SgrA* again next month, and future expansions should incorporate enough new telescopes to produce high-fidelity movies of the black hole.

Given the similarities, astronomers suspect there could be a hidden jet lurking somewhere in SgrA* and further imaging could reveal it, as well as shed light on how neutrinos or cosmic rays can reach such high energies. "There’s this really exciting hint that there may be some additional structure,” co-author Ziri Younsi of University College London told New Scientist. “There might be something going on that’s quite exciting in the center of the galaxy, and I think that these results we’re going to need to follow up. The magnetic fields are the bedrock of all of this. Anything which gives us more insight into how black holes and magnetic fields interact is just foundationally important for astrophysics.”

Astrophysical Journal Letters, 2024. DOI: 10.3847/2041-8213/ad2df0

Astrophysical Journal Letters, 2024. DOI: 10.3847/2041-8213/ad2df1  (About DOIs).

Listing image by EHT Collaboration

Venus Aerospace conducted its first powered flight last month, reaching Mach 0.9 with a drone.

The 8-foot-long vehicle was dropped from an Aero L-29 Delfín aircraft at 12,000 feet and flew under the power of a hydrogen peroxide monopropellant engine. This engine was not fired at full thrust because the location of the test flight, an unspecified range in the United States, did not permit flight faster than the speed of sound, said Andrew Duggleby, co-founder and chief technology officer of the Houston-based company.

This first powered flight came as the company announced a long-duration test firing of its rotating detonation rocket engine, an experimental approach to propulsion that could be about 15 percent more efficient than a conventional chemical rocket engine. The company's long-term ambition is to develop a commercial aircraft that can travel at Mach 9—far faster than any previous airplane. That's clearly a ways off, but these are important, if early, steps on that path.

"We're doing this one step at a time," Duggleby told Ars.

Engine tests

About three weeks ago the company announced it had completed a "long duration" run of its engine, which uses a mode of propulsion different from a chemical engine. In a traditional rocket engine, propellant and an oxidizer are injected into a combustion chamber where they burn and produce a tremendously energetic exhaust plume. A rotating detonation engine differs in that a wave of detonation travels around a circular channel. This is sustained by the injection of fuel and oxidizer and produces a shockwave that travels outward at supersonic speed.

Venus is developing this engine in concert with the US Defense Advanced Research Projects Agency, or DARPA, for potential use in testing hypersonic weapon and defense technology.

Based on the company's latest tests, Duggleby said Venus is now increasingly confident that it will be able to combine its rocket engine with air-breathing technology—using the forward motion of the engine to ingest air for combustion—to create what is known as a rocket-based combined cycle engine. Such an engine, if it can be realized, will allow Venus to see excellent performance at a wide variety of altitudes and velocities. The idea has been largely theoretical until now, developed mostly in universities rather than pursued for commercial purposes.

"We're now 100 percent compelled by this path," Duggleby said. "I'm convinced that this is going to be the engine that unlocks the hypersonic economy."

A drone flight

Even as the small company is working on engine development, it pursued the drone flight as a means of gaining valuable experience testing telemetry, flight control, and other systems.

Duggleby said Venus is considering a couple of options for its next test. If it can identify a range for supersonic flight, it may attach its existing rotating detonation engine to the 8-foot drone. The current engine, which has a firing ring 4 inches in diameter, produces about 1,200 pounds of thrust. Such a test flight, if Venus opts for this route, could take place later this year. The company would go for Mach 2 or 3 on such a test.

Another option is moving to a larger 12-foot vehicle using the existing engine. This would not be ready for flight until 2025 but would have the advantage of generating revenue in the near term as a hypersonics testbed for the US military, Duggleby said. This larger vehicle should be capable of reaching Mach 4 or Mach 5. Hypersonic flight is defined as speeds of greater than Mach 5.

Beyond that, the company may work with an aircraft developer or build its own planes to use a larger version of this engine for commercial flights. While Mach 9 is the ultimate goal, initially the company is likely to target passenger flights at Mach 3 or Mach 4. This is considerably faster than the Concorde, which maxed out at just above Mach 2.

These are big dreams for a small company, which as yet still has a full-time workforce of about 75 people. But as its recent achievements show, Venus may yet shine brightly like its namesake.

Wild migratory birds likely spread a deadly strain of bird flu to dairy cows in Texas and Kansas, state and federal officials announced this week.

According to the Associated Press, officials with the Texas Animal Health Commission confirmed the flu virus is the Type A H5N1 strain, which has been ravaging bird populations around the globe for several years. The explosive, ongoing spread of the virus has led to many spillover events into mammals, making epidemiologists anxious that the virus could adapt to spread widely in humans.

For now, the risk to the public is low. According to a release from the US Department of Agriculture (USDA), genetic testing by the National Veterinary Services Laboratories indicated that H5N1 strain that spread to the cows doesn't appear to contain any mutations that would make it more transmissible to humans. Though the flu strain was found in some milk samples from the infected cows, the USDA emphasized that all the milk from affected animals is being diverted and destroyed. Dairy farms are required to send only milk from healthy animals to be processed for human consumption. Still, even if some flu-contaminated milk was processed for human consumption, the standard pasteurization process inactivates viruses, including influenza, as well as bacteria.

So far, officials believe the virus is primarily affecting older cows. The virus was detected in milk from sick cows on two farms in Kansas and one in Texas, as well as in a throat swab from a cow on a second Texas farm. The USDA noted that farmers have found dead birds on their properties, indicating exposure to infected birds. Sick cows have also been reported in New Mexico. Symptoms of the bird flu in cows appear to include decreased milk production and low appetite.

But so far, the USDA believes the spread of H5N1 will not significantly affect milk production or the herds. Milk loss has been limited; only about 10 percent of affected herds have shown signs of the infection, and there has been "little to no associated mortality." The USDA suggested it will remain vigilant, calling the infections a "rapidly evolving situation."

While federal and state officials continue to track the virus, Texas officials aim to assure consumers. "There is no threat to the public and there will be no supply shortages," Texas Agriculture Commissioner Sid Miller said in a statement. "No contaminated milk is known to have entered the food chain; it has all been dumped. In the rare event that some affected milk enters the food chain, the pasteurization process will kill the virus."

Good morning. It's March 26, and today's photo comes from the Hubble Space Telescope. It showcases a very young multi-star system known as FS Tau.

This star system is only about 2.8 million years old. In terms of cosmic time, that is but a blink of the eye. It lies about 450-light-years away from Earth.

FS Tau A is the very bright object in the middle of the image. It is a T Tauri binary system, consisting of two young variable stars. FS Tau B is the bright object to the far right that is partially obscured by a dark, vertical lane of dust. It is a protostar, and it's worth taking a moment to look a little bit closer at the dust separating the two halves of the star.

According to astronomers who captured this photo, FS Tau B "is surrounded by a protoplanetary disc, a pancake-shaped collection of dust and gas leftover from the formation of the star that will eventually coalesce into planets. The thick dust lane, seen nearly edge-on, separates what are thought to be the illuminated surfaces of the disc."

That is pretty awesome.

Source: NASA, ESA, K. Stapelfeldt (NASA JPL), G. Kober

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Needle, a cheerful miniature schnauzer I had as a kid, turned into a ball of unspeakable noise and fury each time she saw a dog called Puma. She hated Puma so much she would go ballistic, barking and growling. Merely whispering the name “Puma” set off the same reaction, as though the sound of it and the idea of the dog it represented were clearly connected deep in Needle’s mind.

A connection between a word and a mental representation of its meaning is called “referential understanding,” and for a very long time, we believed dogs lacked this ability. Now, a study published by a team of Hungarian researchers indicates we might have been wrong.

Practice makes perfect

The idea that dogs couldn’t form associations with language in a referential manner grew out of behavioral studies in which dogs were asked to do a selective fetching task. The canines had a few objects placed in front of them (like a toy or a bone) and then had to fetch the one specifically named by their owner.

“In laboratory conditions, the dogs performed at random, fetching whatever they could grab first, even though their owners claimed they knew the names of the objects," said Marianna Boros, a researcher at Neuroethology of Communication Lab at Eötvös Loránd University in Budapest, Hungary. "But the problem is when the dogs are not trained for the task, there are hundreds of things that can disturb them. They can be more interested in one specific toy, they may be bored, or they may not understand the task. So many distractions.”

To get around the issue of distractions, her team checked to see if the dogs could understand words passively using EEG brain monitoring. In humans, the EEG reading that is considered a telltale sign of semantic reasoning is the N400 effect.

“The work on the N400 was first published in 1981, and hundreds of studies replicated it since then with different stimuli. Typically, you show images of objects to the subject and say matching or mismatching names. When you measure EEG brain activity, you will see it looks different in match and mismatch scenarios,” explained Lilla Magyari, also a scientist at Neuroethology of Communication Lab and co-author of the study. (It’s called the N400 effect because the peak of this difference appears around 400 milliseconds after an object is presented, Magyari explained.)

The only change the team made to adapt a standard N400 test to dogs was switching the order of stimuli—the words were uttered first, and the matching or mismatching objects were shown second. “Because when they hear the word which activates mental representation of the object, they are expecting to see it. The sound made them more attentive,” said Magyari.

Timing is everything

In the experiment, the dogs started out lying on a mat with EEG gear on their heads in a room with an experimenter or the owner of a different dog. The owner of the dog being tested was separated by a glass pane with controllable opaqueness. “It was important because EEG studies [can] very precisely time the moment of presentation of your stimulus,” said Boros.

Sentences spoken by the owners that would get the dogs’ attention—things like “Kun-kun, look! The ball!”—were recorded and played to each dog through a loudspeaker. Then, 2,000 milliseconds after each dog heard the sentence, the pane would turn transparent, and the owner would appear holding a matching or mismatching toy. “Each test lasted for as long as the dog was happy to participate. The moment it started to get up or look away, we just stopped the test, and the dog could leave the mat and we just finished by playing sessions. It was all super dog-friendly,” Boros said.

For most dogs in the study, an EEG reading similar to the human N400 appeared between 200 and 600 milliseconds after they saw the object. The mismatch effect was stronger the more they were familiar with the item they saw—a favorite toy that was mentioned but didn’t appear caused a stronger reaction, as measured by the EEG. “It was not only about the association of words with objects. Like, often when I see a ball I also hear the word ‘ball,’ so I know they somehow belong together. Introducing this little bit of delay in presentation led us to think dogs actually had expectations to see the object based on their mental representations,” said Magyari.

In previous referential understanding studies with parrots, bottleneck dolphins, apes, and even some dogs, the animals were always specifically trained to perform in the tests. “We did a study on untrained, very typical dogs,” said Boros. This was to determine whether semantics might only be a feature found in a few exceptional individuals. For the first time, there is strong evidence that it’s a capacity all dogs have as a species. But if so, dogs should have been able to breeze through all those selective fetching tests. So why didn’t they?

You are what you eat

“When you think about their evolution, ever since dogs were domesticated 18,000 to 30,000 years ago, they were selected for specific, action-oriented functions like herding, hunting, etc. These functions were not really connected with objects,” said Boros.

Dogs understand action words like "sit," "come," or "fetch" much better than object words because that’s what they’ve always heard from us. “But today, family dogs are living in a completely different environment than they did through most of their evolutionary history,” Boros added. Modern dogs mostly live with us in our homes, and human homes are full of stuff and full of language. What we see might just be evolution catching up to this. But there is another reason.

“Puma” was among a very small list of words that triggered such an enormous emotional response in my Needle. One of those words referred to the dog she hated, and others referred to the people she loved—to me and my family. None were objects like the ones used in these tests.

“Dogs are very social. They are not really interested in objects. But they are super-interested in humans, especially their owners,” said Boros. It may be that in those selective fetching studies, dogs could tell one bouncy, shiny, plasticky gadget from the other. It just didn’t matter to them when there was a human there to interact with. “Communicating with your dog, you need to keep in mind it understands more than it shows,” said Magyari.

Current Biology, 2024.  DOI: 10.1016/j.cub.2024.02.029.