ESA exoplanet hunter CHEOPS set to depart Spain for pre-launch testing

by Chris Bergin

The CHEOPS (CHaracterising ExOPlanet Satellite) spacecraft has completed integration work at Airbus’ Madrid-Barajas site and is now set to be shipped around Europe for testing.  This spacecraft will be the first mission dedicated to searching for exoplanetary transits by performing ultra-high precision photometry on bright stars already known to host planets.

Nearly eight years ago, CHEOPS was selected for study as the first S-class mission in Cosmic Vision 2015-2025. The mission was formally adopted in early February 2014, with the launch planned for early 2019.

It is set to be launched by an Arianespace Soyuz rocket from the Guiana Space Centre to a sun-synchronous orbit with a 650-800 km altitude and is set to spend at least 3.5 years collecting science. It will ride along with  CSG-1 (COSMO-SkyMed Second Generation-1) via the Soyuz ST-B/Fregat-MT combination.

Arianespace’s Soyuz rocket – via Arianespace

The mission’s main science goals are to measure the bulk density of super-Earths and Neptunes orbiting bright stars and provide suitable targets for future in-depth characterization studies of exoplanets in these mass and size ranges.

Effectively, the mission will be able to identify if targeted planets are rocky, a water world, or gaseous.

CHEOPS will provide the unique capability of determining radii within ~10% accuracy for a subset of those planets, in the super-Earth to Neptune mass range, for which the mass has already been estimated using ground-based spectroscopic surveys.

A render of CHEOPS – via Airbus

It will also provide accurate radii for new planets discovered by the next generation of ground-based or space transits surveys (from super-Earth to Neptune-size). By unveiling transiting exoplanets with high potential for in-depth characterization, CHEOPS will provide suitable targets for future instruments suited to the spectroscopic characterization of exoplanetary atmospheres.

Knowing where to look and at what time to observe makes CHEOPS the most efficient instrument to search for shallow transits and to determine accurate radii for planets in the super-Earth to Neptune mass range.

Cheops will study these planets using a Ritchey-Chrétien Telescope supplied by the University of Bern, in Switzerland.

CHEOPS has one instrument – a photometer with a single CCD, operating mainly in the visible, that is at the focal plane of the on-axis Ritchey-Chrétien telescope of 32cm diameter (clear aperture diameter of 30cm).

A cutaway view of the CHEOPS flight instrument – via ESA

The spacecraft will be three-axis stabilized to aid the stability of the instrument as it takes observations.

In the latest reported milestone, it was integrated last month at Airbus’ Madrid-Barajas site on the already-finished platform.

This took place after the science instrument arrived from Bern, allowing for the alignment of the baffle and cover assembly with the optical telescope assembly. The baffle serves to prevent stray light from off-axis sources entering the telescope aperture.

Following successful integration the spacecraft will be sent to France, back to Switzerland and then on to The Netherlands for a comprehensive test campaign on July 9.

The campaign will include a complete set of functional and environmental tests to ensure that the spacecraft is fit for launch. The satellite will then return to Madrid for final functional tests and a final inspection before it is shipped to Kourou, French Guiana, for launch.

The satellite – which only has a total launch mass of between 250 and 300 kg – is a partnership between Switzerland and ESA’s Science Programme, with contributions from Austria, Belgium, France, Germany, Hungary, Italy, Portugal, Spain, Sweden, and the United Kingdom.

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