About this Research Topic
Fifty years ago, space astronomy and space science began to use satellites for scientific observations. By the 1990s NASA had begun its series of “Great Observatories”. These were 10,000-kg class, multibillion-dollar facilities and they did impressive science. But the cost to build the next generation of space-based observatories such as the James Webb Space Telescope (JWST) is an order of magnitude larger at $10B or more. As a result, there has been pressure for NASA, and other space agencies to built more frequent, smaller missions – the Medium Class and Small Explorers (MIDEX and SMEX). Impressive results were obtained from such missions as the Transiting Exoplanet Survey Satellite (TESS) launched in 2018. TESS cost in the hundreds of millions and weighed just 362 kg.
Can we go smaller than TESS for astronomy missions? In the last decade 10 kg-class cubesats have matured. They are being used for space-physics, earth observation and now, planetary sciences. In astrophysics its often said that, due to the requirement for large optics, cubesats have limited use. Conversely, in ultraviolet and X-ray spectral regions sensors have gotten quite small. NASA is development at least one cubesat equipped with x-ray detectors, HALOSAT. It is designed to study the hot galactic halo. The cost of these missions are in the few million-dollar range.
One of the exciting new possibilities of cubesats is the potential for having a distributed constellation that is a phased-array receiver, particularly in the lower radio frequencies. The low radio frequencies mean that simple time tagging approaches can be used on a large number of cubesats to synthesize an arbitrarily large aperture. Such a system could be useful to observe small scale structures on the sun and perhaps investigate the early universe.
What about much smaller, cheaper satellites? Gram class satellites, called “chipsats” or “nanocraft” are real and have been launched. The chips in our electronic watches do most functions a satellite does – so chipsats can be built cheaply. The Breakthrough StarShot concept envisages gram-class nanocraft accelerated to 0.2c by high-powered lasers against a gram-class light sail 5-10 meters in diameter. This rapidly-maturing approach would use the chipsat and the associated lightsail as an imaging element when flying by nearby star systems such as Alpha Centauri. It’s likely that earlier versions could conduct significant astrophysical observations – either independently or in an ensemble.
The Topic Editors would like to acknowledge Dillon O'Reilly, who has acted as coordinator and contributed to the preparation of this Research Topic.
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