Cubesats gain broader acceptance for astrophysics missions

HONOLULU — As one astronomy cubesat reaches the end of its mission, scientists and NASA officials argue that such spacecraft have demonstrated they can perform useful science often not feasible with larger missions.

The Jet Propulsion Laboratory announced Jan. 3 that it had lost contact with the Arcsecond Space Telescope Enabling Research in Astrophysics, or ASTERIA, spacecraft. The cubesat last communicated with controllers Dec. 5, and had not responded subsequent efforts to restore contact.

While JPL said it would continue efforts to restore contact until March, one project official doubted ASTERIA would resume normal operations. “It’s likely that we’ve reached the end of the flight portion of the mission,” said Vanessa Bailey of JPL at an astrophysics cubesat workshop during the 235th Meeting of the American Astronomical Society here Jan. 4. The orbit of ASTERIA, deployed from the International Space Station in November 2017, was gradually decaying because of atmospheric drag, and she estimated that even without the loss of communication its “useful scientific lifetime” would have ended between March and May.

ASTERIA launched for an initial 90-day mission to test the ability of cubesats to search for exoplanets by looking for changes in brightness of stars as planets pass in front, or transit, those stars, which requires a high degree of precision in observations. “We need both pointing control and thermal control at a level that hadn’t been demonstrated before in a cubesat platform,” Bailey said.

ASTERIA met or exceeded its thermal control and pointing control goals. “It was significantly better than had been demonstrated before in such a small platform, and good enough to do some high-precision photometry,” she said. After its prime mission, ASTERIA performed some science observations as well as additional technology demonstrations.

NASA is supporting the development of cubesats for astrophysics missions, currently funded at $5 million a year. There was, agency officials said, some initial skepticism about the capabilities of cubesats to perform astrophysics work. “Cubesats are small. Astrophysics is the study of very faint objects, and it’s hard to do that with a small telescope,” said Michael Garcia of NASA Headquarters.

However, he noted that peer review ratings on astrophysics cubesat mission proposals submitted to NASA over the last several years have been steadily improving. “Maybe it’s not so much that we’re flux-starved,” he said, suggesting a combination of more persuasive proposals and improvements in cubesats are leading to better reviews.

Astrophysics cubesats work best when they can find a niche that can’t be filled by larger spacecraft. That includes wide-field observations or the ability to observe transient phenomena. “At the beginning, cubesats were really concentrating on education and technology development, but they are doing real science,” he said.

One example he cited is HaloSat, a cubesat deployed from the ISS in 2018 to measure diffuse X-ray emission from halos of material surrounding galaxies. The cubesat has a much larger field of view than other X-ray observatories and can be dedicated to this particular research project.

Five astrophysics cubesats funded by NASA are in various stages of development. One, the Colorado Ultraviolet Transit Experiment (CUTE), plans to study exoplanet transits at ultraviolet wavelengths to better understand how some “hot Jupiter” exoplanets lose mass from their atmospheres. CUTE is nearing completion and is scheduled to launch in early 2021 as a secondary payload on the Atlas 5 launch of Landsat 9.

Kevin France, the principal investigator for CUTE at the University of Colorado, said they want to study multiple transits by the same planet, as well as increase the number of planets studied, something difficult to do with the ultraviolet capabilities on the Hubble Space Telescope, whose observing time remains in high demand. “We can do this with a dedicated platform,” he said.

Another mission under development is the Star-Planet Activity Research CubeSat (SPARCS) at Arizona State University. It will also perform ultraviolet astronomy, studying the activity of M dwarf stars that host exoplanets, which can adversely affect those planets’ habitability.

Paul Scowen, a professor at Arizona State working on SPARCS, said the improvement in cubesat pointing makes such a mission feasible. “This was something that was very necessary over the last five to ten years, going from ‘tumblers’ to those with the stability necessary to acquire astronomically interesting data,” he said.

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