@inproceedings{99f242e51d794b64a6028570a02c21e2,
title = "SmallSat interferometry for THz astrophysics",
abstract = "While great strides have been made in far-infrared astrophysics with the NASA Spitzer and ESA Herschel missions, subarcsecond spatial resolution from space is still beyond the reach of current technologies. The Atacama Large Millimeter Array has produced stunning images from the ground of planetary systems in the process of formation but cannot observe the key molecules of water or O2, due to the presence of Earth's atmosphere. The concept presented here will enable interferometric imaging with sub-arcsecond resolution of water and other key far infrared molecular species from space at a cost far lower than the flagship class interferometric missions previously proposed (i.e. ESA's ESPRIT). We present a concept for a far infrared interferometer based on a constellation of CubeSat antenna elements with a central ESPA-class correlator satellite optimized for the imaging of water in protoplanetary systems. Such a mission would produce groundbreaking images of newly forming planetary systems in a key astrophysical and astrobiological tracer, the 557 GHz ground state line of water. By leveraging recent developments in CubeSat technology, inflatable reflectors, miniaturized receiver systems and low power CMOS digital electronics, such a mission could be implemented at an Explorer level budget. In addition to the proposed astrophysics application, the developments proposed here could also find application in planetary science (FIR spectroscopy of comets and small bodies) and Earth observing (high resolution imaging of Earth from geostationary orbit).",
keywords = "Cubesat, Interferometry, Mission concept, Terahertz, Water",
author = "Christopher Groppi and Paul Goldsmith and Philip Mauskopf and Jose Siles and Jonathan Hoh and Jeremy Whitton and Gena Pilyavsky and Christopher Walker and Adrian Tang",
note = "Funding Information: This work was supported in part by NASA cooperative agreement NNX16AT65A and JPL award SP.17.0001.003. Funding Information: In this concept, there are ~12x 6U CubeSats. each equipped with a 2-meter diameter spherical inflatable antenna (1m effective aperture) feeding an ambient temperature Schottky diode-based terahertz receiver (See figure 2). This number of elements and reflector size provides the same collecting area as the Herschel space telescope, but with over three orders of magnitude higher spatial resolution. This inflatable spherical antenna concept has been developed as part of a recently completed NASA Innovative Advanced Concepts (NIAC) effort by Co-I Walker and his team and is continuing under a grant awarded to him by the Office of Naval Research (ONR). A laser or mm-wave metrology system used in conjunction with GPS will be used to triangulate and track the position of the CubeSats. In addition, each CubeSat will be equipped with a high-speed laser and/or radio communication system to transmit the received data to a central ESPA-class small spacecraft and receive a centrally generated local oscillator reference signal. An ESPA-class spacecraft is compatible with many different launch vehicles, including Minotaur I, Minotaur IV, Delta IV, Atlas V, Pegasus, Falcon 1/1e, and Falcon 9. This ESPA class spacecraft contains the master oscillator for local oscillator distribution to the CubeSats, the correlator used to process the data received from the CubeSats, and a Ka-band system to transmit the processed data to the ground. The remainder of each CubeSat contains commercial off-the shelf subsystems, which could be built with existing hardware. Each CubeSat would use a system similar to the Blue Canyon XACT platform for attitude determination and control. The XACT unit contains an integrated star tracker, sun-sensor, IMU, reaction-wheels and magneto-torquers to provide a 10-20 arcsecond pointing accuracy. Each CubeSat also contains a camera (e.g. the RocketCam from Ecliptic) for engineering and navigation, a pair of radiation shielded payload computers, (e.g. a Space Micro CSP based on the Xilinx Virtex-5 FPGA fabric and Tyvak Intrepid CD&H computers) and a secondary UHF communication system for spacecraft to ground backup communication. While absolute station keeping is not required, the CubeSat constellation must be kept in the same ~5 km diameter volume throughout the mission. While a detailed study of the propulsion system requirements for the constellation is necessary, simple gas thrusters will likely be adequate to maintain the constellation in formation for reasonable mission durations. Publisher Copyright: {\textcopyright} COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.; Space Telescopes and Instrumentation 2018: Optical, Infrared, and Millimeter Wave ; Conference date: 10-06-2018 Through 15-06-2018",
year = "2018",
doi = "10.1117/12.2312822",
language = "English (US)",
isbn = "9781510619494",
series = "Proceedings of SPIE - The International Society for Optical Engineering",
publisher = "SPIE",
editor = "Fazio, {Giovanni G.} and MacEwen, {Howard A.} and Makenzie Lystrup",
booktitle = "Space Telescopes and Instrumentation 2018",
}