New Space and Tech

Capella: A Space-only High-frequency Radio VLBI Network Formed by a Constellation of Small Satellites

By Keith Cowing
Press Release
April 30, 2023
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Capella: A Space-only High-frequency Radio VLBI Network Formed by a Constellation of Small Satellites
Top panels: Simulated uv plane coverage achieved by the reference Capella constellation after 250,000 seconds of observing time, assuming observations of M 87 (left) and Sgr A* (right) at a frequency of 690 GHz, respectively. Black circles mark the uv distance corresponding to an angular resolution of 10 µas. Bottom panels: The corresponding dirty beams, for M 87 (left) and Sgr A* (right), respectively. The pixel scale is 1 µas/pixel. The beams are normalized to a maximum value of 1; contour levels are 1, 0.88, 0.76, …, −0.08. The central maxima both have a FWHM of approximately 7 µas.

Very long baseline radio interferometry (VLBI) with ground-based observatories is limited by the size of Earth, the geographic distribution of antennas, and the transparency of the atmosphere. In this whitepaper, we present Capella, a tentative design of a space-only VLBI system.

Using four small (<500 kg) satellites on two orthogonal polar low-Earth orbits, and single-band heterodyne receivers operating at frequencies around 690 GHz, the interferometer is able to achieve angular resolutions of approximately 7 microarcsec. Within a total observing time of three days, a near-complete uv plane coverage can be reached, with a 1-sigma point source sensitivity as good as about 6~mJy for an instantaneous bandwidth of 1 GHz.

The required downlink data rates of >10 Gbps can be reached through near-infrared laser communication; depending on the actual downlink speed, one or multiple ground communication stations are necessary. We note that all key technologies required for the Capella system are already available, some of them off-the-shelf.

Data can be correlated using dedicated versions of existing Fourier transform (FX) software correlators; dedicated routines will be needed to handle the effects of orbital motion, including relativistic corrections. With the specifications assumed in this whitepaper, Capella will be able to address a range of science cases, including: photon rings around supermassive black holes; the acceleration and collimation zones of plasma jets emitted from the vicinity of supermassive black holes; the chemical composition of accretion flows into active galactic nuclei through observations of molecular absorption lines; mapping supermassive binary black holes; the magnetic activity of stars; and nova eruptions of symbiotic binary stars – and, like any substantially new observing technique, has the potential for unexpected discoveries.

Sascha Trippe, Taehyun Jung, Jung-Won Lee, Wonseok Kang, Jae-Young Kim, Jongho Park, Jeffrey A. Hodgson

Comments: 18 pages, 2 figures, 1 table. Whitepaper version 1.0. Living document, will be updated when necessary
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2304.06482 [astro-ph.IM] (or arXiv:2304.06482v1 [astro-ph.IM] for this version)
Submission history
From: Sascha Trippe
[v1] Sun, 9 Apr 2023 10:56:28 UTC (356 KB)

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