Astronomers say new telescopes should take advantage of “Starship paradigm”

A consensus among leading American astronomers is that NASA's next wave of great observatories should take advantage of game-changing lift capabilities offered by giant new rockets like SpaceX's Starship.

 

Launching a follow-on to the James Webb Space Telescope (JWST) on Starship, for example, could unshackle the mission from onerous mass and volume constraints, which typically drive up complexity and cost, a panel of three astronomers recently told the National Academies' Committee on Astronomy and Astrophysics.

 

"The availability of greater mass and volume capability, at lower cost, enlarges the design space," said Charles Lawrence, the chief scientist for astronomy and physics at NASA's Jet Propulsion Laboratory. "We want to take advantage of that.”

 

Lawrence's presentation dealt with the impact of large, new launch vehicles on future astronomy missions. The presentation was given last week alongside Martin Elvis, an astronomer at the Harvard-Smithsonian Center for Astrophysics, and Sara Seager, an astrophysicist and planetary scientist at MIT. Lawrence, Elvis, and Seager authored a paper earlier this year in the journal Physics Today discussing this topic.

 

It's widely known that the Starship's ability to lift more than 100 metric tons into space, at a fraction of the cost per kilogram of existing rockets, would change how the wider space industry does business. The Starship's 9-meter diameter (8 meters of the diameter would be usable for a payload) is nearly double the width of the payload volume on any existing rocket.

 

But astronomers are starting to get serious in planning for rockets like the Starship, or Blue Origin's New Glenn with a slightly smaller 7-meter payload fairing, to be available to loft the next generation of big space telescopes.

Big telescopes on big launchers

In 2021, the National Academies released a once-in-a-decade review of the top astronomy and astrophysics priorities for the US science community. In this survey, known in shorthand as Astro2020, a distinguished panel of scientists laid out a roadmap for NASA to spend the bulk of the 2020s developing technologies and designs for the next series of "great observatories" that will follow the likes of Hubble, Chandra, James Webb, and the Roman Space Telescope scheduled for launch in 2027.

 

NASA's policy is to follow the science community's recommendations wherever possible. Sometime around the end of the decade, the thinking goes, NASA should be ready to officially kick off development of these new telescopes. First should be a large telescope called the Habitable Worlds Observatory, which would be comparable in size to Webb with a primary mirror around 6 meters (20 feet) across and a coronagraph or a starshade to blot out starlight, enabling direct observations of planets around other stars, or exoplanets. This is a capability not available on Webb.

 

The Habitable Worlds Observatory, with sensitivity to light in infrared, visible, and ultraviolet wavelengths, would be tasked with observing Earth-like exoplanets in search of worlds that have the makeup to support life. Later, NASA should launch similarly ambitious far-infrared and X-ray telescopes to study the formation of stars, black holes, and galaxies, scientists recommended in 2021.

 

 

These big, new multibillion-dollar missions wouldn't start launching until the 2040s. This is a "forbidding timeline," Elvis and his colleagues wrote in their paper published earlier this year. "A newly minted PhD today will be barely a decade from retirement by the time even the first of the observatories launches."

 

NASA doesn't have the budget to launch them any sooner, and the new telescopes require innovations in optics, detectors, and materials to make them feasible.

 

Maybe the arrival of big, new rockets could lower some of these technological hurdles, scientists said. Ultimately, they could lead to simplified designs, reducing costs and perhaps shortening the time needed to develop and build the next great observatories. Maybe they don't have to wait until the 2040s to launch. Those are important factors when the initial estimate from the National Academies is that the Habitable Worlds Observatory will cost some $11 billion.

 

“Designs are highly constrained by the launchers, by the volume and mass available to the orbit you want, and that leads to increased complexity and cost, inevitably," Elvis said.

 

Elvis said engineers working on preliminary designs for these new telescopes should, in the next few years, reassess their assumptions about the kinds of rockets that would be available to launch the missions into space.

 

"We suggest studies of all three of these Astro2020 flagships, and their payloads and their spacecraft, in this new Starship paradigm, or any large launcher paradigm, to take advantage of the design space that’s opened up," Elvis said last week.

 

“The big questions are, are the major cost savings that we’ve outlined really plausible, and as a result, can Astro2020 be accelerated?” he added.

Tyranny of the rocket

To illustrate the limitations imposed by a rocket's capacity, let's revisit the James Webb Space Telescope. Webb had to fit inside the roughly 5-meter-diameter payload fairing of an Ariane 5 rocket, which had the largest payload envelope of any available launch vehicle when engineers were first designing Webb. That meant the telescope's 18 individual primary mirror segments had to fold, and designers devised a five-layer tennis court-size sunshade made of flimsy but effective insulation to block the Sun's heat and light from the telescope. All of that had to bundle up to allow Webb to fit within the confines of its rocket when it launched in 2021.

 

With a larger rocket like Starship or New Glenn, a future telescope could use a monolithic mirror, throwing out the need for segmented mirrors. There are scientific arguments that suggest segmented mirrors may be better for some applications, but the jury is still out. Also, instead of needing a complex deployable sunshade that might be prone to failure, engineers could bolt on a larger rigid sunshade wrapping around the entire telescope.

 

 

If it launched on a huge rocket like Starship, a telescope's mirrors could be thicker and heavier, meaning they would be easier to manufacture and polish, scientists said. A heavier rocket could allow spacecraft designers to add on larger solar panels for additional power. The extra power could allow the spacecraft to use cheaper electronics with more redundancy, Elvis said.

 

“One of the biggest lessons learned from JWST was the importance of understanding the rockets up front, in detail," said Lee Feinberg, Webb's optics manager and a co-chair of the technical assessment group studying the Habitable Worlds Observatory. "One of the key points here is we want flexibility. We’re over 20 years away from a mission."

 

And who knows what rockets will even be flying in the 2040s? For the Roman Space Telescope, set to launch a few years from now, NASA officials thought they would have a choice between several rockets. It turned out new rockets, like United Launch Alliance's Vulcan and Blue Origin's New Glenn, weren't ready when NASA needed to select a launch contractor. By default, the contract went to SpaceX for launch on a Falcon Heavy rocket.

 

"It really highlights the importance of being flexible in rockets," said Feinberg, an engineer at NASA's Goddard Space Flight Center. He recently met with SpaceX and Blue Origin. "Our view right now is both New Glenn and Starship look promising," he said.

 

There are other new rockets. NASA's Space Launch System is too expensive to even consider. "The new Vulcan from ULA does not have a significantly larger fairing, so we did not even think about that," Elvis said.

Is Starship the answer?

Studies have shown the Starship, with its wider diameter, could accommodate a range of telescope designs, such as those under consideration for the Habitable Worlds Observatory. Starship could launch the observatory, with its roughly 6-meter primary mirror, in a folded or unfolded configuration, on its side, or pointing up.

 

"What we have found is that with Starship, you really have a lot of flexibility," Feinberg said at the National Academies committee meeting last week.

 

Of course, Starship and New Glenn haven't made it to orbit yet, and they are many flights away from becoming eligible to launch a NASA flagship mission. But SpaceX and Blue Origin have a couple of decades to prove the reliability of their new rockets before NASA packs one of its new great observatories aboard for launch.

 

"By the time our first great observatory launches, Starship will presumably have launched many, many times and have a record you can judge on," Seager said.

 

 

It's also unclear what the price of a Starship or New Glenn launch might be in the 2030s or 2040s, but it will probably be a small fraction of the overall cost of a multibillion-dollar observatory.

 

In order to send any of these telescopes into deep space toward the L2 Lagrange point, where they would observe the Universe far away from interference from Earth, Starship would need to be refueled in orbit. Feinberg said NASA's optics experts have questions about whether the refueling process could contaminate a telescope's sensitive mirrors. A telescope loitering in low-Earth orbit waiting for its Starship transport to be refueled could also be subjected to extreme temperature swings, potentially putting it at risk of damage.

 

"These are all considerations that we’re going to have to understand over the many years to come," Feinberg said. "When we ask (SpaceX) for details, the sense we get is they will tell us as they figure this stuff out, but they can’t tell us this stuff now. On the New Glenn side, it’s a different thing, where what they plan to launch (on their first flight) potentially could get you to L2, so they're very close."

 

Ultimately, if NASA wants to go even bigger with its next-generation space telescopes, Starship could accommodate a folded mirror as big as 10 to 12 meters wide, according to Feinberg. For New Glenn, the upper limit is probably on the order of about 8 meters. Bigger mirrors increase the collecting area of a telescope, giving it improved resolution to see smaller and fainter objects.

 

“I think we’re in a new situation," Elvis said. "These launchers do change what we can do in space, and at what cost. The way you design the mission is totally changed."

 

Listing image by NASA/GSFC