Above our heads, higher than volcanic dust or the aurora borealis, thousands of expensive metal objects speed by, 30 times faster than a commercial jet. Contraptions as massive as a Hummer and apparatuses larger than a school bus proudly make their appointed rounds in the sky. And somewhere amongst them lurk a new generation of miniature spacecraft for astrophysics, not much bigger than a box of laundry detergent -- ASTERIA.
Honey, I Shrunk the Telescope
ASTERIA (Arcsecond Space Telescope Enabling Research in Astrophysics) hitched a ride to the International Space Station in August 2017 on a SpaceX Falcon 9, which is a rocket used for crew resupply services. After two months tucked into its comfy sleeve, this compact satellite was deployed into low Earth orbit (which is about 400 km straight up, a little farther than New York City is from Washington, DC).
Also known as a CubeSat, the ASTERIA spacecraft is riding the wave of innovation that has already given the world ever-shrinking technological wonders such as drones, smart phones, and a myriad of life-saving medical applications.
Like every other successful flight project, from Voyager to the Mars rovers, ASTERIA has benefited from that magical coalescence of ideas and talent needed to thrive. Having already exceeded all expectations of its primary mission and currently in an extended mission, some special stardust (and lots of hard work) has clearly enabled ASTERIA’s evolution from concept to state-of-the-art.
In a series of firsts, ASTERIA is:
- The first CubeSat to detect an exoplanet, in this case the known transiting super-Earth 55 Cancri e.
- The first miniature spacecraft to achieve pointing stability performance of better than 0.5 arcseconds RMS over 20 minutes, and a pointing repeatability of 1 milliarcsecond over the same period, which is precision that is on par with other spacecraft that are orders of magnitude larger.
- The best focal plane temperature control achieved by a spacecraft of its size (±0.01K over 20 minutes).
ASTERIA has successfully demonstrated ways of achieving meaningful astrophysics science in a small package. Although it can only observe one star at a time, its success could open the door for launching many more miniature star-monitoring satellites to advance the search for nearby Earth-like worlds.
The Power of an Idea
How did this success story begin? In 2008, future Jet Propulsion Laboratory (JPL) engineers Matthew W. Smith and Christopher Pong were students at the Massachusetts Institute of Technology (MIT), as was Mary Knapp, now a research scientist at MIT’s Haystack Observatory. Professor Sara Seager, already a world-renowned exoplanet researcher, had recently joined the MIT faculty with a joint appointment in Earth, Atmospheric and Planetary Sciences and Physics. Little did they know that they were about to embark on a shared 10-year-long inquiry that would strengthen the valuable working relationship between JPL and MIT.
Seager had a vision for developing techniques for understanding the atmospheres of extrasolar planets. Often referred to as “an astronomical Indiana Jones,” her quest was -- and still is -- to search for alien life, detectable from Earth, by way of exoplanet atmospheric biosignature gases. The first step was devising a low-cost space telescope to find suitable exoplanets using the so-called “transit method.” Pointing at nearby bright stars, this telescope would look for miniscule dips in brightness that occur when an exoplanet passes in front of its host.
When Seager asked David Miller, professor of Aeronautics and Astronautics and director of the MIT Space Systems Laboratory, to suggest some students who might be interested in her nascent project, and he put her in contact with Smith and Pong. Knapp, an engineering undergraduate with a curiosity for science, joined the project through MIT’s Undergraduate Research Opportunities Program. The group was excited to transform Seager’s concept into reality. They called their first collaboration the ExoplanetSat project.
“The early days were all about figuring out if the idea was even possible,” remembers Smith. “CubeSats were relatively new and no one had tried to do transit measurements with such a small spacecraft.”
With funding from MIT and NASA, as well as a research grant from and collaboration with Draper Laboratory, Seager and her three curious students began laying the foundation for what would eventually become ASTERIA.
The group’s efforts received a boost from 2010-2011 thanks to a JPL Strategic University Research Partnership (SURP) grant. The SURP program supports collaborations between researchers at JPL and strategic university partners, to support the development of new science and technology opportunities. Backing from SURP can help accelerate progress and innovation for missions in formulation, a perfect fit for ExoplanetSat. The grant from SURP helped fund MIT’s 16.83x design/build capstone class that was created to give MIT juniors and seniors hands-on project experience, a natural fit for developing ExoplanetSat further. Knapp enrolled, and Pong and Smith, along with future JPL engineer Alessandra Babuscia, served as teaching assistants. Smith and Pong also applied for and received NASA Space Technology Research Fellowship awards. Supported by funding and a vehicle for working together, things progressed rapidly.
Once the work with the SURP grant had completed, Seager and her exoplanet team wanted to take their concept to the next level, and submitted a NASA ROSES Astrophysics Research and Analysis proposal in collaboration with JPL. That’s where they hit their only major snag, when in 2013, their proposal was not selected. Undaunted, the ASTERIA concept found other funding and institutional support at JPL through an early career training program called Phaeton, and rapidly developed the CubeSat over the next 3 years, with Smith and Pong now working at JPL. The payoff for this dynamic partnership between JPL and MIT was the eventual launch of the ASTERIA mission, for which they share the responsibilities of mission operations and data analysis.
Something Old, Something New
Innovative optical design made ASTERIA’s success possible. Using refractive lenses instead of reflective mirrors -- an uncommon approach for telescopes in space -- it is a unique combination of old and new technology. The five-lens configuration of the optical telescope is tried and true, inspired by camera design of the nineteenth century -- the physics governing the properties of light haven’t changed. With only a few modifications, ASTERIA’s multi-lens design is largely the same as those created during the rise of modern photography.
However, the imager/detector, software, and pointing control system of ASTERIA are cutting edge. ASTERIA was able to greatly exceed its required pointing performance with a unique two stage control system. This remarkable system combined reaction wheels to control the spacecraft attitude and a precise piezoelectric positioning stage to achieve a highly stable focal plane. All of this was backed up and powered by very sophisticated computer algorithms, mission operation system (MOS) automation and custom software. What makes ASTERIA’s accomplishment even more notable is that the computer in its electronics assembly is about six times slower than an iPhone 7, and with only 64 MB of RAM (an iPhone 7 has 2 GB!).
ASTERIA has accomplished all of its primary mission objectives of demonstrating precision pointing and highly stable temperature control. The spacecraft has detected a known transiting exoplanet, proving that the miniaturized technologies on board do indeed operate in space as expected and can produce science-worthy measurements. “ASTERIA has taught us a lot, both in terms of technology and how to organize a small mission,” says Smith. “Now we’re taking those lessons and applying them to future projects.” This marks the success of one of the world's first astrophysics CubeSat missions, and shows that small, low-cost satellites could be used to assist in future studies of the universe beyond the solar system.