ASTERIA (Arcsecond Space Telescope Enabling Research in Astrophysics) was a technology demonstration and opportunistic science mission to conduct astrophysical measurements using a CubeSat. ASTERIA was the first JPL-built CubeSat to have been successfully operated in space. Originally envisioned as a project for training early career scientists and engineers, ASTERIA's technical goal was to achieve arcsecond-level line-of-sight pointing error and highly stable focal plane temperature control. These technologies are important for precision photometry, i.e., the measurement of stellar brightness over time. Precision photometry, in turn, provides a way to study stellar activity, transiting exoplanets, and other astrophysical phenomena.
ASTERIA was a 6U CubeSat (roughly 10 x 20 x 30 cm, 10 kg) that operated in low-Earth orbit. The payload consisted of a lens and baffle assembly, a CMOS imager, and a two-axis piezoelectric positioning stage on which the focal plane was mounted. A set of commercial reaction wheels provided coarse attitude control. Fine pointing control was achieved by tracking a set of guide stars on the CMOS sensor and moving the piezoelectric stage to compensate for residual pointing errors. Precision thermal control was achieved by isolating the payload from the spacecraft bus, passively cooling the detector, and using trim heaters to perform small temperature corrections over the course of an observation.
In June 2017, the flight spacecraft was delivered for integration into the Nanoracks CubeSat Deployer. ASTERIA was launched to the International Space Station (ISS) with the SpaceX Falcon-9 Commercial Resupply Services 12 (CRS-12) mission on August 14, 2017. The spacecraft was deployed from the ISS on November 20, 2017 to begin the 90-day ASTERIA technology demonstration mission.
As of February 2018, ASTERIA had met its primary mission requirements by demonstrating pointing stability better than 0.5 arcseconds RMS over 20 minutes and pointing repeatability of 1 milliarcsecond RMS from orbit-to-orbit. The mission also demonstrated thermal stability of +/-0.01 K as measured at a single point on the focal plane.
Since completing its primary mission objectives, ASTERIA continued operating through three mission extensions until loss of contact. The last successful communication with ASTERIA occurred on December 5, 2019. Mission operators continued attempts at contacting the spacecraft through the end of February 2020, at which point the end of mission was declared. During these mission extensions, the spacecraft was used as an in-space platform to test various capabilities that aim to make CubeSats more autonomous, some of which are based on artificial intelligence programs. ASTERIA also made opportunistic observations of the Earth, a comet, Vesta, Uranus, other spacecraft in geo-synchronous orbit, and stars that might host transiting exoplanets.
Extended Mission Overview
The ASTERIA mission was extended almost two years beyond its successful prime mission. During its extended mission, ASTERIA conducted precision photometric monitoring (precise recording of the brightness of objects such as stars over time). The star 55 Cancri (55 Cnc) is known to host multiple exoplanets, one of which is known to transit (pass in front of) the star. This planet, 55 Cnc e, is a "super-Earth," about twice the diameter of Earth. When the planet passes in front of the star it blocks only about 0.04% of the star's light. ASTERIA detected this minute temporary dimming, making it the smallest spacecraft ever to detect an exoplanet (paper; press release). ASTERIA also monitored the stars HD219134 and Alpha Centauri AB for potential new transiting exoplanets, various bright calibration stars, and Uranus. Image data from the precision photometric monitoring campaigns will be released on the NASA Exoplanet Archive on a rolling basis from Fall 2020 through Spring 2021.
During the extended mission, ASTERIA also was used as an in-space platform to demonstrate and mature three autonomy-related technologies. The first of these was JPL's autonomous optical navigation software (AutoNav). The AutoNav software computes a spacecraft's position and velocity in inertial space using only optical images of navigation targets. These targets can be asteroids, planets, comets or even other spacecraft. This software had been previously flown with great success on two of JPL's comet missions, Deep Space 1 and Deep Impact. The ASTERIA mission provided an opportunity to operate the AutoNav software on a CubeSat form factor, and to apply the algorithms to execute in Low Earth Orbit instead of the previous deep space applications. With its visible light astrometric camera and stable attitude control system, the ASTERIA spacecraft promised to be a capable platform for the imaging of navigation targets. The AutoNav software was successfully operated on board ASTERIA in November 2019, using sequenced images of the asteroid Vesta. Several images of geosynchronous spacecraft were successfully imaged by ASTERIA and processed on the ground using an updated version of AutoNav, demonstrating the viability of AutoNav to use such targets for navigation.
Another autonomy experiment demonstrated the capabilities of spacecraft activity planning, scheduling and execution as a more flexible way to command a spacecraft at a higher task-level than time-based sequences. In the fall of 2019, the ASTERIA CubeSat was commanded with task networks using MEXEC (Multi-mission EXECutive), an integrated, task-based, planning and execution library developed at JPL. Task networks model spacecraft constraints and behavior, checking that conditions are satisfied prior to executing a command. When used in conjunction with smart, on-board planning and execution systems like MEXEC, Task networks enable the ability to re-plan on-board with the most up to date information, which can increase science return and be more robust to unexpected changes. In this on-board experiment, MEXEC and task networks replicated the behavior of traditional sequences to perform nominal science observations and pass setups. This was an important first step to show the viability of spacecraft commanding through task networks and to lay the foundation for more robust and autonomous behavior. All task networks executed as expected, including successful observations of the Moon, the asteroid Vesta, the star HD219134, and New York City.
Additional MEXEC capabilities were exercised using the ground-based testbed, including the ability to react to events by establishing MEXEC maintenance goals such as managing momentum. External torques acting on the spacecraft cause momentum buildup, which can result in attitude control loss. In the prime mission, science observations were scheduled to avoid times when the predicted momentum or reaction wheel zero crossings were unfavorable. When the momentum magnitude of the spacecraft increased above an acceptable limit, the original fault protection response was to reset the spacecraft, requiring reset recovery procedures and causing upcoming observations to be lost. MEXEC monitors momentum and reacts with commands to dump momentum before the fault protection limit is reached, avoiding costly reset recovery procedures and lost science. MEXEC will reschedule and resume science observations once the momentum has returned to an acceptable magnitude. In this experiment, MEXEC scheduled activities to dump momentum and recovered the planned observations four times. This demonstrated that MEXEC can responds to on-board state information to maintain goals such as momentum management.
A third experiment focused on model-based fault diagnosis, which offers a system health estimation approach by continuously analyzing system performance, verifying expected behavior and diagnosing off-nominal behavior against a system model. This effort teamed with Okean Solutions, applying Model-based Off-Nominal State Identification and Detection (MONSID) product. A MONSID behavior model of the ASTERIA XACT Attitude Control Subsystem (ACS) was built using project documentation and high-rate ACS data captured from the ASTERIA spacecraft to represent the ACS as a series of model components, capturing physical relationships and behaviors as mathematical constraints between system state variables. In parallel, the reusable MONSID engine was integrated into a special ASTERIA Flight Software build, using a new, modular F Prime software component to handle all required interfaces. The early end-of-mission prohibited the in-flight experiment; however, the team conducted MONSID functional and sensitivity testing on the ground-based system testbed using captured flight data, testbed data generated with ACS and environmental emulators, and seeded fault data. Technology maturation included reviews of the MONSID model and flight software implementation. The MONSID flight software met all goals for sensitivity and accuracy, both against injected faults and unexpected behavior of the actual ASTERIA spacecraft, and proved its ability to support closed-loop autonomous fault management, without challenging the computational resources available on ASTERIA.
Each of these autonomy technologies was checked for software bugs using static analyzers, integrated with the ASTERIA F Prime software and approved for uplink through a Software Review Certification Record process. A final experiment was performed on the ground after the end of the mission, in which an integration of the three technologies demonstrated successful and persistent autonomous orbit determination even in the presence of faults.
The ASTERIA project was a collaboration with the Massachusetts Institute of Technology (MIT) and was funded at JPL through the Phaeton Program for training early career employees. JPL was responsible for overall project management, systems engineering, spacecraft implementation, integration and test, and mission operations. The main spacecraft subsystem suppliers were Blue Canyon Technologies (Attitude Control Subsystem), Vulcan Wireless (Telecommunications Subsystem), MMA Design LLC (Solar Arrays), GomSpace (Power Subsystem and Batteries), Spaceflight Industries (Flight Computer), Ecliptic Enterprises (Focal Plane), Physik Instrumente (Piezo Stage), and Thermotive (Thermal Hardware). Morehead State University (MSU) provided spacecraft tracking, telemetry, and control services to the Mission Operations team at JPL. MIT and the University of Bern (Switzerland) performed target selection and analysis of stellar photometry data. ASTERIA traced its origins back to the ExoplanetSat concept developed at MIT in collaboration with Draper Laboratory (ScD Thesis by C. Pong, US Patent by M. W. Smith, C. Pong, et al.).
M. Knapp, S. Seager, B.-O. Demory, A. Krishnamurthy, M. W. Smith, C. M. Pong, V. P. Bailey, A. Donner, P. Di Pasquale, B. Campuzano, C. Smith, J. Luu, A. Babuscia, R. L. Bocchino Jr., J. Loveland, C. Colley, T. Gedenk, T. Kulkarni, K. Hughes, M. White, J. Krajewski, L. Fesq, “Demonstrating High-Precision Photometry with a CubeSat: ASTERIA Observations of 55 Cancri e,” Astronomical Journal, 160, 23 (2020). Download from AJ or from arXiv.
Smith, M. W., “An Efficient Focal Plane Alignment Methodology with Application to the ASTERIA Nanosatellite Space Telescope”, 2020 IEEE Aerospace Conference, Big Sky, MT, March 2020.
Babuscia, A., Di Pasquale, P., Smith, M. W., Taylor, J., “Arcsecond Space Telescope Enabling Research in Astrophysics (ASTERIA) Telecommunications”, JPL DESCANSO Near Earth Design and Performance Summary Series, Pasadena, CA, June 2019, https://descanso.jpl.nasa.gov/NEDSummary/summary.html.
Pong, C. M., Smith, M.W., "Camera Modeling, Centroiding Performance, and Geometric Camera Calibration on ASTERIA", 2019 IEEE Aerospace Conference, Big Sky, MT, March 2019, https://doi.org/10.1109/AERO.2019.8741842.
Fesq, L., Beauchamp, P., Donner, A., Bocchino, R., Kennedy, B., Mirza, F., Mohan, S., Sternberg, D., Smith, M.W., Troesch, M, Knapp, M., “Extended Mission Technology Demonstrations Using the ASTERIA Spacecraft,” IEEE Aerospace Conference, Big Sky, MT, March 2019, https://ieeexplore.ieee.org/document/8742020/.
Pong, C. M., Sternberg, D. C., and Chen, G. T., “Adaptations of Guidance, Navigation, and Control Verification and Validation Philosophies for Small Spacecraft,” Guidance and Control 2019, Advances in the Astronautical Sciences, Breckenridge, CO, February 2019.https://trs.jpl.nasa.gov/handle/2014/46649
Donner, A., Smith, M.W., "ASTERIA Lessons Learned", Small Satellite Reliability Initiative (SSRI), Technical Interchange Meeting 4 (TIM-4), Boulder, CO, November 2018, https://www.nasa.gov/smallsat-institute/reliability-working-group-4.
Donner, A. Di Pasquale, P., Smith, M.W., Pong, C. M., Campuzano, B., Knapp, M., "ASTERIA Operations Demonstrates the Value of Combining the Mission Assurance and Fault Protection Roles on CubeSats", 69th International Astronautical Congress, IAF, Bremen, Germany, October 2018. https://iafastro.directory/iac/archive/browse/IAC-18/B4/3/46796/
Smith, M. W., Donner, A., Knapp, M., Pong, C. M., Smith, C., Luu, J., Di Pasquale, P., Bocchino, R. L., Jr., Campuzano, B., Loveland, J., Colley, C., Babuscia, A., White, M., Krajewski, J., Seager, S., “On-Orbit Results and Lessons Learned from the ASTERIA Space Telescope Mission,” Proceedings of the 32rd Annual AIAA/USU Conference on Small Satellites, Logan, UT, August 2018, SSC18-I-08, https://digitalcommons.usu.edu/smallsat/2018/all2018/255/.
Pong, C. M., "On-Orbit Performance & Operation of the Attitude & Pointing Control Subsystems on ASTERIA", Proceedings of the 32rd Annual AIAA/USU Conference on Small Satellites, Logan, UT, August 2018, SSC18-PI-34, https://digitalcommons.usu.edu/smallsat/2018/all2018/361/.
Bocchino, R., Canham, T., Watney, G., Reder, L., Levison, J., "F Prime: An Open-Source Framework for Small-Scale Flight Software Systems," Proceedings of the 32rd Annual AIAA/USU Conference on Small Satellites, Logan, UT, August 2018, SSC-18-XII-04, https://digitalcommons.usu.edu/smallsat/2018/all2018/328/.
Knapp, M., Seager, S., Smith, M.W., Pong, C.M., Donner, A., Campuzano, B., Di Pasquale, P., Smith, C., Krajewski, J., White, M., "ASTERIA: A CubeSat Enabling High Precision Photometry in a Small Package", 42nd COSPAR Scientific Assembly, Pasadena, CA, July 2018, E4.1-0004-18, https://www.cospar-assembly.org/abstractcd/COSPAR-18/abstracts/E4.1-0004-18.pdf.