Jason-CS Satellite Design, Configuration and Expected Performances
Junginger, Heinz1; Barthern, Bjoern1; Köble, Klaus-Peter1; Francis, Richard2; Cullen, Robert2

The Jason-CS spacecraft, currently in the design and development phase at Astrium in Friedrichshafen provides continuity of ocean topography data services following the well-recognized series of TOPEX/Poseidon and Jason-1, 2 and Jason-3.
ESA's choice to rely on the CryoSat platform design for Jason-CS permits re-use of a well established product and proven processes. An industrial consortium led by Astrium GmbH, with ThalesAleniaSpace of France as major core team member providing the radar instrument, has built the satellite CryoSat-2. Since more than two and a half years CryoSat-2 successfully provides altimeter measurements of the polar ice cap thickness evolutions and, more recently, even provides important altimeter data over ocean, serving the ocean surface topography science community.
The CryoSat-2 platform deploys unique design features which are perfectly suited for accommodation of the Jason-CS instruments furnished both from European and US sources and to ensure the mission performance even beyond the pure continuation of services.
Jason-CS will orbit Earth at an altitude of 1336 km with an inclination of 66°. This orbit exposes the spacecraft to a harsh radiation environment especially considering the extended lifetime of 7.5 years. The orbit is non-sun-synchronous leading to varying Sun illumination, which drives the design of the body-mounted solar array arrangement.
Unlike CryoSat-2, Jason-CS is required to perform a post-mission disposal according to the ESA Requirements for Space Debris Mitigation, asking for atmospheric capture within 25 years after end of mission. This proves to be challenging in view of the mission altitude, significantly higher than typical Earth Observation LEO satellite.
Due to the required change in velocity for de-orbiting Jason-CS, a mono-propellant system with a large tank of at least 210 kg propellant loading capacity has to be introduced. In addition, the required Centre of Mass knowledge of better than 1 mm requires a special tank design as the uncertainty of the gas location in the tank is a main driver for this requirement.
The operation of the POSEIDON-4 altimeter and some of the other instruments requires Earth surface orientation and accurate pointing in order to ensure the science data acquisition. Based on the proven CS-2 design the satellite geometry is arranged such that the solar panels, rigidly fixed to the satellite body, form a 'roof' with a carefully optimised angle, which will provide adequate power under all orbital conditions and still fit within the launch vehicle.
Other design drivers described in the paper cover the tight thermal stability constraints of the system needed to ensure that mission requirements on long-term drifts are met concerning, in particular, the microwave radiometer. In addition, the large volume of data acquired by the POSEIDON-4 altimeter creates a large power demand and needs to be carefully handled to meet NRT objectives.
This paper describes the finally selected design and configuration of the Jason-CS spacecraft and provides the expected platform/satellite performance.