Feasibility of utilizing Cherenkov Telescope Array gamma-ray telescopes as free-space optical communication ground stations

Abstract

The signals that will be received on Earth from deep-space probes in future implementations of free-space optical communication will be extremely weak, and new ground stations will have to be developed in order to support these links. This paper addresses the feasibility of using the technology developed in the gamma-ray telescopes that will make up the Cherenkov Telescope Array (CTA) observatory in the implementation of a new kind of ground station. Among the main advantages that these telescopes provide are the much larger apertures needed to overcome the power limitation that ground-based gamma-ray astronomy and optical communication both have. Also, the large number of big telescopes that will be built for CTA will make it possible to reduce costs by economy-scale production, enabling optical communications in the large telescopes that will be needed for future deep-space links.

CTA Telescopes as Deep-Space Lasercom Ground Receivers

“…This is one of the reasons to study the use of other kind of telescopes. This paper completes an initial proposal from the authors about the use of IACTs (Imaging Atmospheric Cherenkov Telescopes) as optical ground terminals in deep-space FSOC [2].…”

“…The authors of this paper presented the original idea of using IACT telescopes for deep-space FSOC in a previous paper [2]. The motivations were explored back then: the big apertures of the telescopes, their native operation as an array, their low costs due to their relaxed requirements, the ideal sky-related conditions, the fast tracking of the telescopes, a suitable communications network infrastructure, etc.…”

“…In [2], the required detector position displacement ε in order to focus at infinity (as a FSOC receiver) instead of at a point 10 km high in the atmosphere (as IACTs are designed to operate, in order to detect the Cherenkov radiation), was studied for the MAGIC (Major Atmospheric Gamma Imaging Cherenkov Telescope) telescope. The same equations of [2], applied to CTA, give ε values ranging from 1.4 cm (SST) to 9 cm (LST) (see table I). In the case of MAGIC II, the camera can be shifted as far as 30 cm in real operations for focusing and maintenance [8], so this is a normal feature in IACTs.…”

“…In [2], a discussion about the relation between the FoV and the SNR was made for MAGIC-II telescope. A deeper discussion needs to be made regarding the concepts of SNR, FoV and their relation with the optical resolution of the CTA telescopes.…”

Long-baseline optical intensity interferometry

“…Of course, it will mainly be devoted to its primary task of observing Cherenkov light in air; however several other applications have been envisioned, to be preferably carried out during nights with bright moonlight which -owing to the faintness of the Cherenkov light flashes -might preclude their efficient observation. Besides intensity interferometry (Dravins et al, 2013), additional uses that have been suggested include searches for rapid astrophysical events (Deil et al, 2009;Hinton et al, 2006;Lacki, 2011), observations of stellar occultations by distant Kuiper-belt objects (Lacki, 2014), or as a terrestrial ground station for optical communication with distant spacecraft (Carrasco-Casado et al, 2013). For practical operations, one proposed concept is to place auxiliary detectors on the outside of the Cherenkov camera cover lid, an approach already realized on some telescopes (Deil et al, 2009;Hinton et al, 2006), and one that should not interfere with regular Cherenkov camera operations.…”