Foust Forward | The next giant leap for space observatories

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On Jan. 30, NASA will send the final commands to the Spitzer Space Telescope, shutting down the infrared space observatory. NASA decided last year to end the mission, launched in 2003, as it drifts away from the Earth, making communications and spacecraft operations more challenging.

The end of Spitzer means half of NASA’s original “Great Observatories” will be defunct. The Compton Gamma-Ray Observatory, launched in 1991, was deorbited in 2000 after suffering failures of several of its gyroscopes. The other two, the Chandra X-Ray Observatory and Hubble Space Telescope, remain operational, but are aging: Chandra marked 20 years in orbit last year while Hubble turns 30 in April.

Both Chandra and Hubble should continue to operate through much of the 2020s. “Right now we’re in the middle of what I think is a very good news story about Hubble,” said Jennifer Wiseman, an astronomer at NASA’s Goddard Space Flight Center, during the 235th Meeting of the American Astronomical Society (AAS) in Honolulu in early January. The telescope shows no signs of serious problems that could impair its use.

But she and other scientists at the conference acknowledged that, sooner or later, Hubble will come to an end. “We don’t know how long Hubble’s going to last,” she said.

The ultimate demise of the remaining Great Observatories has some astronomers worried about gaps in coverage of the universe. NASA’s next two flagship space telescopes, the James Webb Space Telescope and WideField Infrared Survey Telescope, are both intended for infrared observations, with limited capabilities at visible light wavelengths and none in the ultraviolet, like Hubble.

Astronomers have proposed several large space telescopes that could serve as true successors to Chandra or Hubble and are under consideration by the ongoing astrophysics decadal survey. However, even if NASA agreed to develop the mission recommended by the survey’s final report next January, it’s unlikely to be in space before the mid-2030s.

“Without a concerted effort to maintain some sort of coverage, there will be some very large gaps in our wavelength coverage that will inhibit progress and erode expertise,” said Lee Armus of Caltech at the conference.

Armus co-chaired a study completed last fall that examined whether it was beneficial to maintain the “panchromatic” coverage, from infrared to gamma rays, that the Great Observatories provided, and how to do so. The answer to the first question was a resounding yes: astronomers argued that having space telescopes observing at different wavelengths can be beneficial for everything from the search for habitable exoplanets to studying the formation and evolution of galaxies.

The report argued for a program of “Giant Leap Observatories” to maintain that panchromatic coverage. Doing so, astronomers argued, could be done in a way that doesn’t bust NASA’s astrophysics budget. “It can be achieved with a range of mission sizes and costs,” Armus said. “If you’re smart, you can do it with a mix.”

Indeed, not all of the Great Observatories had great price tags. While Hubble cost more than $9 billion in present-day dollars, Spitzer cost just $1 billion, about the size of a “probe-class” astrophysics mission. While the report didn’t recommend any specific missions, it concluded that smaller missions could help maintain that wavelength coverage without a major increase in NASA’s budget.

NASA hasn’t endorsed the report, and will likely wait until after the decadal survey is complete before committing to a specific strategy. However, NASA’s long-term budget projections include starting a probe-class astrophysics mission as soon as 2022, one that would likely be ready in the latter half of the decade.

In the meantime, Spitzer is working up until the very end. Joseph Rodriguez of the Harvard-Smithsonian Center for Astrophysics was part of a team that used Spitzer to confirm the discovery of an Earth-sized exoplanet announced at the conference. He was already worried, though, about how to do similar work after this month. “The options are a bit limited without Spitzer,” he said.


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Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews.

His Foust Forward column appears in every issue of the magazine. This column ran in the Jan. 20, 2020 issue.