ASTERIA (spacecraft)

Did You Know?

• ASTERIA was launched on board a SpaceX Falcon-9 rocket (mission SpaceX CRS-12).
• A crew member in the ISS transferred the satellite from the cargo vehicle to the Japanese Experiment Module airlock for deployment.
• The Principal Investigator was Canadian-American astronomer and planetary scientist Sara Seager.

Overview

The Arcsecond Space Telescope Enabling Research in Astrophysics (ASTERIA) was a six-unit CubeSat space telescope deployed from the International Space Station to test new technologies for detecting exoplanets via the transit method. Funded through JPL's Phaeton Program for training early career employees, its target mission lasted 90 days, after which it was extended until loss of contact. ASTERIA's capabilities enabled precision photometry on an opportunistic basis to study stellar activity, transiting exoplanets, and other astrophysical phenomena.

The technological objectives were to achieve arcsecond-level line-of-sight pointing error and highly stable focal plane temperature control for precision photometry, with pointing stability demonstrated over 20-minute observations. This mission may serve as a pathfinder for a fleet of low-cost space telescopes observing multiple targets simultaneously, and the miniaturization of a photometric detection system into a CubeSat could enable a constellation of orbiting observatories for continuous study of bright Sun-like stars.

Design

The ASTERIA concept followed the proposed 3U CubeSat mission ExoplanetSat from the early 2010s. The spacecraft measured 10 × 20 × 30 cm with a mass of 12 kg, powered by deployable fixed solar panels and rechargeable batteries. Commercial reaction wheels provided coarse attitude control, while fine pointing control used guide stars tracked on a CMOS active pixel sensor and a piezoelectric positioning stage to compensate for residual errors, aiming to keep the target star image within a fraction of a pixel over long durations.

Pointing accuracy was better than 60 arcseconds, optimally as precise as 5 arcseconds over 20 minutes. The second objective was milliKelvin-level temperature stability of the imaging detector. The telescope payload comprised an f/1.4 85 mm Zeiss lens with a 28.6-degree field of view and six elements, focusing a 43 mm diameter image onto the focal plane. The focal plane array housed two active detector areas: a larger CMOS detector for science and a smaller CMOS sensor acting as a rapid-cadence star camera for attitude control.

After its 90-day planned mission, the extended mission targeted bright stars with known low-mass planets discovered by radial velocity that were not yet known to transit.