Design and Performance of the AERO-VISTA Magnetometer

We describe the design and performance of the magnetometer instrument for the CubeSat mission AERO-VISTA. AERO-VISTA requires in-situ vector magnetic measurements with magnetic precision and repeatability better than 100 nT at a minimum rate of 10 Hz. Our magnetometer system uses the three-axis Honeywell HMC1053 anisotropic magnetoresistive (AMR) sensor. As built, our instrument exhibits intrinsic magnetic noise better than 10 nTrms from 0.1 to 10 Hz, though self-interference effects degrade performance to about 50 nT to 200 nT uncertainty. The analog and mixed signal portion of each magnetometer occupies about 8 square centimeters of circuit board space and draws about 100 mW. We describe the selection of major components, detail the schematic design of the analog electronics, and derive a noise budget from datasheet component specifications. The theoretical noise budget matches experimental results to better than 20%. We also describe the digital electronics and software which operates an analog to digital converter interface and implements a sampling method that allows for improved separation of offset and magnetic field signal contributions. We show the spectral characteristics of the magnetic field noise floor including self-interference effects. Our magnetometer design can be used in whole or in part on other small satellites which plan to use similar AMR magnetic sensors

Demonstrating high-precision photometry with a CubeSat: ASTERIA observations of 55 Cancri e

ASTERIA (Arcsecond Space Telescope Enabling Research In Astrophysics) is a 6U CubeSat space telescope (10 cm x 20 cm x 30 cm, 10 kg). ASTERIA's primary mission objective was demonstrating two key technologies for reducing systematic noise in photometric observations: high-precision pointing control and high-stabilty thermal control. ASTERIA demonstrated 0.5 arcsecond RMS pointing stability and $\pm$10 milliKelvin thermal control of its camera payload during its primary mission, a significant improvement in pointing and thermal performance compared to other spacecraft in ASTERIA's size and mass class. ASTERIA launched in August 2017 and deployed from the International Space Station (ISS) November 2017. During the prime mission (November 2017 -- February 2018) and the first extended mission that followed (March 2018 - May 2018), ASTERIA conducted opportunistic science observations which included collection of photometric data on 55 Cancri, a nearby exoplanetary system with a super-Earth transiting planet. The 55 Cancri data were reduced using a custom pipeline to correct CMOS detector column-dependent gain variations. A Markov Chain Monte Carlo (MCMC) approach was used to simultaneously detrend the photometry using a simple baseline model and fit a transit model. ASTERIA made a marginal detection of the known transiting exoplanet 55 Cancri e ($\sim2$~\Rearth), measuring a transit depth of $374\pm170$ ppm. This is the first detection of an exoplanet transit by a CubeSat. The successful detection of super-Earth 55 Cancri e demonstrates that small, inexpensive spacecraft can deliver high-precision photometric measurements.Comment: 23 pages, 9 figures. Accepted in A

Aurora: A Software Radio for Electromagnetic Vector Sensors in Space

The AERO (Auroral Emission Radio Observer) and VISTA (Vector Interferometry Space Technology using AERO) missions will advance auroral radio science and radio interferometry technology. AERO is intended to qualify and validate electromagnetic vector sensor technology in space while also answering key scientific questions about the nature and sources of auroral radio emissions. These questions cannot be addressed from the ground due to shielding by the ionosphere. VISTA, together with AERO, will provide the first demonstration of interferometric imaging, beamforming, and nulling using electromagnetic vector sensors at low frequencies (100 kHz – 15 MHz) using Space based sensors. A key component of the AERO-VISTA joint mission is the Aurora software radio system which forms the primary mission payload when combined with an electromagnetic vector sensor antenna (VSA). This radio combines the analog, digital, and signal processing necessary to detect and digitize the signals associated with the radio aurora. We provide a detailed discussion of the radio design, implementation, and performance results from early testing of our engineering model units

HD 219134 Revisited: Planet d Transit Upper Limit and Planet f Transit Nondetection with ASTERIA and TESS

HD 219134 is a K3V dwarf star with six reported radial-velocity discovered planets. The two innermost planets b and c show transits, raising the possibility of this system to be the nearest (6.53 pc), brightest (V = 5.57) example of a star with a compact multiple transiting planet system. Ground-based searches for transits of planets beyond b and c are not feasible because of the infrequent transits, long transit duration (~5 hr), shallow transit depths (<1%), and large transit time uncertainty (~half a day). We use the space-based telescopes the Arcsecond Space Telescope Enabling Research in Astrophysics (ASTERIA) and the Transiting Exoplanet Survey Satellite (TESS) to search for transits of planets f (P = 22.717 days and M sin i = 7.3 ± 0.04M_⊕) and d (P = 46.859 days and M sin i = 16.7 ± 0.64M_⊕). ASTERIA was a technology demonstration CubeSat with an opportunity for science in an extended program. ASTERIA observations of HD 219134 were designed to cover the 3σ transit windows for planets f and d via repeated visits over many months. While TESS has much higher sensitivity and more continuous time coverage than ASTERIA, only the HD 219134 f transit window fell within the TESS survey's observations. Our TESS photometric results definitively rule out planetary transits for HD 219134 f. We do not detect the Neptune-mass HD 219134 d transits and our ASTERIA data are sensitive to planets as small as 3.6 R_⊕. We provide TESS updated transit times and periods for HD 219134 b and c, which are designated TOI 1469.01 and 1469.02 respectively

Transit Search for Exoplanets around Alpha Centauri A and B with ASTERIA

Alpha Centauri is a triple star system with two Sun-like stars, α Cen A (V = 0.01) and B (V = 1.33), and a third fainter red dwarf star, Proxima Centauri. Most current transit missions cannot produce precision photometry of α Cen A and B as their detectors saturate for these very bright stars. The Arcsecond Space Telescope Enabling Research in Astrophysics (ASTERIA) was a technology demonstration mission that successfully demonstrated two key technologies necessary for precision photometry achieving line-of-sight fine-pointing stability of 0.5'' rms and focal plane temperature control of ±0.01 K over a period of 20 minutes. The payload consisted of a 6.7 cm aperture diameter refractive camera and used a scientific complementary metal-oxide semiconductor detector that enabled monitoring of the brightest stars without saturating. We obtained spatially unresolved (blended) observations of α Cen A and B during opportunistic science campaigns as part of ASTERIA's extended mission. The resulting 1σ photometric precision for the blended α Cen A and B data is 250 ppm (parts per million) per 9 s exposure. We do not find evidence of transits in the blended data. We establish limits for transiting exoplanets around both α Cen A and B using transit signal injection and recovery tests. We find that ASTERIA is sensitive to planets with radii as small as 3.0 R⊕ around α Cen A and 3.7 R⊕ around α Cen B, corresponding to signals of ∼500 ppm (signal-to-noise ratio = 5.0) in the blended data, with periods ranging from 0.5 to 6 days