GTOSat is a 6U CubeSat mission that will pave the way for highly reliable, capable CubeSat constellations and missions beyond low Earth orbit (LEO). GTOSat will study Earth’s dynamic radiation belts, acting as a follow-on to NASA’s Van Allen Probe mission and demonstrating the potential utility of SmallSats for both science and space weather monitoring. While a number of previous CubeSats have studied the radiation belts from LEO, GTOSat will launch into a low inclination geosynchronous transfer orbit (GTO) to directly sample the core trapped particle population. From this orbit, it will measure energy spectra and pitch angles of ~hundreds keV - few MeV electrons and ions, with the primary science goal of advancing our quantitative understanding of particle acceleration and loss in the outer radiation belt. High-heritage instrumentation includes the Relativistic Electron Magnetic Spectrometer (REMS), measuring energetic electrons and ions, and a boom-mounted fluxgate magnetometer (MAG) to provide 3-axis knowledge of the local ambient magnetic field. The GTOSat bus consists of a 6U spin-stabilized structure with a Sun-pointing spin axis. Mitigation of radiation effects is accomplished through a multi-pronged systems approach including parts selection and shielding to reduce the total dose for 1 year on orbit to less than ~30 krad. Communication is achieved via an S-band transceiver, enabling high data throughput through the Near-Earth Network (NEN) and low-latency radiation belt monitoring via the Tracking and Data Relay Satellite System (TDRSS).
Far more definitive information on composition is required to resolve the question of origin for the Martian moons Phobos and Deimos. Current infrared spectra of the objects are inconclusive due to the lack of strong diagnostic features. Definitive compositional measurements of Phobos could be obtained using in-situ X-ray, gamma-ray, or neutron spectroscopy or collecting and returning samples to Earth for analysis. We have proposed, in lieu of those methods, to derive Phobos and Deimos compositional data from secondary ion mass spectrometry (SIMS) measurements by calibrating the instrument to elemental abundance measurements made for known samples in the laboratory. We describe the Phobos/Deimos Regolith Ion Sample Mission (PRISM) concept here. PRISM utilizes a high-resolution TOF plasma composition analyzer to make SIMS measurements by observing the sputtered species from various locations of the moons' surfaces. In general, the SIMS technique and ion mass spectrometers complement and expand quadrupole mass spectrometer measurements by collecting ions that have been energized to higher energies, 50-100 eV, and making measurements at very low densities and pressures. Furthermore, because the TOF technique accepts all masses all the time, it obtains continuous measurements and does not require stepping through masses. The instrument would draw less than 10 W and weigh less than 5 kg. The spacecraft, nominally a radiation-hardened 12U CubeSat, would use a low-thrust Solar Electric Propulsion system to send it on a two-year journey to Mars, where it would co-orbit with Deimos and then Phobos at distances as low as 27 km.
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