VTXO: the virtual telescope for x-ray observations

Abstract

The Virtual Telescope for X-ray Observations (VTXO) will use lightweight Phase Frensel Lenses (PFLs) in a virtual X-ray telescope with 1 km focal length and with nearly 50 milli-arcsecond angular resolution. Laboratory characterization of PFLs have demonstrated near diffraction-limited angular resolution in the X-ray band, but they require long focal lengths to achieve this quality of imaging. VTXO is formed by using precision formation flying of two SmallSats: a smaller, 6U OpticsSat that houses the PFLs and navigation beacons while a larger, ESPA-class DetectorSat contains an X-ray camera, a charged-particle radiation monitor, a precision star tracker, and the propulsion for the formation flying. The baseline flight dynamics uses a highly-elliptical supersynchronous geostationary transfer orbit to allow the inertial formation to form and hold around the 90,000 km apogee for 10 hours of the 32.5-hour orbit with nearly a year mission lifetime. The guidance, navigation, and control (GN&C) for the formation flying uses standard CubeSat avionics packages, a precision star tracker, imaging beacons on the OpticsSat, and a radio ranging system that also serves as an inter-satellite communication link. VTXO's fine angular resolution enables measuring the environments nearly an order of magnitude closer to the central engines of bright compact X-ray sources compared to the current state of the art. This X-ray imaging capability allows for the study of the effects of dust scattering nearer to the central objects such as Cyg X-3 and GX 5-1, for the search for jet structure nearer to the compact object in X-ray novae such as Cyg X-1 and GRS 1915+105, and for the search for structure in the termination shock of in the Crab pulsar wind nebula. The In this paper, the VTXO science performance, SmallSat and instrument designs, and mission description is be described. The VTXO development was supported as one of the selected 2018 NASA Astrophysics SmallSat Study (AS3) missions.

Practical Limits on Nanosatellite Telescope Pointing: The Impact of Disturbances and Photon Noise

“…Improving nanosatellite pointing enables a range of applications beyond the transformative photometry recently demonstrated by the ASTERIA mission (Knapp et al, 2020b). These applications span from direct exoplanet detection by interferometry (Dandumont et al, 2020) or starshades (Macintosh et al, 2019) to X-rays (Krizmanic et al, 2020) and the ultraviolet (Shkolnik, 2018).…”

Designing Monte Carlo Simulation and an Optimal Machine Learning to Optimize and Model Space Missions

“…Formation flying, as a key factor in virtual spacecraft formation [2], and rendezvous [3], is investigated in missions including virtual telescope for X-ray observation (VTXO) [4], Proba 3 [5], MASSIM X-ray virtual telescope [6], PRISMA [7], and SIMBOL-X [8]. Making a formation of spacecraft for astrophysics observation and optimizing the science mission lifetime of VTXO by 50% is studied in [9]- [12]. Making a formation of distributed telescope to observe exoplanet AEgir and optimizing the energy consumption of the mission is studied in [13].…”

“…Formation has been studied as leader-follower approach, behavior-based method, potential field approach, and generalized coordinates [14]. In VTXO, leader-follower approach is taken [12], [15], [16] where the leader holds the lens, known as the optics spacecraft (OS), and the follower holds the X-ray camera, known as the imaging spacecraft (IS).…”

“…VTXO uses a lightweight Phased Fresnel Lens (PFL) to obtain near diffraction-limited angular resolution in the X-ray band [4], [10], [12], [15]- [18]. PFL provides the VTXO mission with nearly 55 milli-arcsecond (mas) (FWHM) imaging resolution of astrophysical sources in the X-ray band for a 1 km focal length.…”

“…55 milli-arcsecond (mas) (FWHM) imaging resolution provided by PFL requires VTXO to hold a minimum 55 milli-arcsecond (mas) (FWHM) 1 km precision formation of IS and OS with a sub millimeter transverse alignment accuracy. The imaging resolution of around 55 mas is approximately 10 fold higher than the state-of-theart Chandra X-ray 0.5 arcsecond pointing resolution [12] and James Webb space telescope 0.5 arcsecond pointing resolution [19]. With the VTXO's high resolution, the search for exoplanets [20] and high-energy environments around space objects including black holes, neutron stars, and stellar systems at the smallest spatial details is possible for the first time.…”