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

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