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Designing a Gamma-Ray Telescope on a Budget

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CubeSat
Artist’s rendering of a CubeSat, a small, relatively inexpensive satellite cube. [NASA/JPL-Caltech/Montana State University]

Major space-based observatories are imperative in astronomy, but they take a long time to plan, build, and launch — and they aren’t cheap. A new study examines an interesting compromise: a low-cost, space-based gamma-ray detector that we could use while we wait for the next big observatory to launch.

gamma-ray observatories

Coverage and sensitivity of past and future missions for the X-ray to gamma-ray energy range (click for a better look!). The only past mission to explore the 1 MeV region was COMPTEL, on board CGRO. e-ASTROGAM is a proposed future space mission that would explore this range. [Lucchetta et al. 2017]

A Gap in Coverage

In the last few decades, we’ve significantly expanded our X-ray and gamma-ray view of the sky. One part of the electromagnetic spectrum remains poorly explored, however: the approximate transition point between X-rays and gamma rays near 1 MeV.

Space-based gamma-ray telescopes have been proposed for the future to better explore this energy range. But these major observatories have costs of around half a billion Euros and will take roughly a decade to build and launch. Is there a way to get eyes on this energy range sooner?

Scaling Down with CubeSat

A team of scientists led by Giulio Lucchetta (University of Padova and INFN Padova, Italy) has proposed an intriguing solution for the more immediate future: a nano-satellite telescope based on the CubeSat standard.

proposed detector

Structure of the proposed gamma-ray detector, in a 2U CubeSat design. [Lucchetta et al. 2017]

A CubeSat is a miniaturized satellite design that can be easily deployed in space, either from the International Space Station or by hitching a ride as a secondary payload on a large rocket. The size of a CubeSat is a standardized unit of measurement: a single CubeSat unit, or 1U, is a mere 10x10x10 cm and a maximum of 1.33 kg in weight.

The gamma-ray telescope proposed by Lucchetta and collaborators would use a 2U standard for the instrument, so the instrument would be only 10x10x20 cm in size! The design for the telescope as a whole — including the on-board electronics and flight system — would likely require a 4U model.

The team’s proposed nanoscale observatory would be capable of detecting gamma rays from 100 keV up to a few MeV. In comparison to the major space-based observatories, this project would be very low-cost, at only half a million Euros — and such a telescope could go from build to launch in about a year.

Evaluating Performance

estimated sensitivity

Estimated sensitivity of the proposed nanoscale satellite telescope (for tracked, untracked, and pair production events) compared to that of COMPTEL. [Lucchetta et al. 2017]

Cheaper and faster is great, but how would this project do in terms of quality? The authors performed simulations to examine the scientific performance of the proposed detector, evaluating its effective area, energy resolution, and angular resolution. Luchetta and collaborators show that while the scientific performance would be well below that expected for large future missions, it would likely be on par with the last detector to observe this region — COMPTEL, on board the Compton Gamma Ray Observatory.

It seems that a nanoscale satellite like this one would helpfully cover the gap around 1 MeV and allow us to learn more about low-energy gamma rays while we wait for large future missions to launch. As an additional benefit, such a project could serve as a pathfinder mission to test technologies and algorithms to be used in larger missions in the future.

Citation

Giulio Lucchetta et al 2017 AJ 153 237. doi:10.3847/1538-3881/aa6a1b