Lander mission to europa with solar electric propulsion
- Paper number
IAC-06-A3.P.2.06
- Author
Dr. Wolfgang Seboldt, German Aerospace Center (DLR), Germany
- Coauthor
Mr. Joern Streppel, Deutsches Zentrum fur Luft und Raumfahrt e.V. (DLR), Germany
- Coauthor
Dr. Bernd Dachwald, German Aerospace Center (DLR), Germany
- Coauthor
Dr. Horst W. Loeb, University of Giessen, Germany
- Coauthor
Dr. Karl-Heinz Schartner, Giessen University, Germany
- Year
2006
- Abstract
For high-energy solar system exploration missions, electric propulsion may offer clear advantages with respect to Delta-V-capability, flexibility in launch date, payload ratio and even flight time over conventional chemical propulsion with gravity assists. Advanced power supply technologies (solar electric or nuclear electric), however, are indispensable. On behalf of DLR, a robotic mission to Jupiter with the goal to land a small surface module on Europa has been studied using solar electric propulsion. The overall mission was divided into three distinct phases: A) from Earth escape (C3=0) to Jupiter rendezvous (at sphere of influence); B) Jupiter capture and ‘spiral down’ to a ‘relay orbit’, where the mother spacecraft is stationed and the lander released; C) lander transfer to the surface of Europa. For the ‘relay orbit’ different options have been included: i) orbits around Jupiter with distances from 15 to 35 Jupiter radii (to cope with the severe radiation environment near Jupiter) and ii) a 3300 km orbit around Europa (this includes an Europa capture of the spacecraft and ‘spiral down’ to the final orbit). The last option, however, may be less preferable due to long flight times in the inner Jovian system and corresponding radiation degradation problems. The spacecraft design (mass, power, number of engines) and corresponding trajectory calculations have been performed parametrically. For phase A the important spacecraft parameter is the ratio of available power at 1 AU (between 40 and 200 kW) to initial total mass (between 2.5 and 7 tons). This parameter determines the flight time for this phase. A cluster of 5 to 15 ion engines (RIT-22) has been considered so that at 1 AU all engines are operating. Later on, the thrusters are shut down one after the other - due to the decreasing solar power- until at Jupiter only one or a few can be used. This leads to a staging principle for the electric propulsion, where most of the left over electric thrusters and the empty propellant tanks are jettisoned during or at the end of phase A, keeping only a small thruster cluster for the remaining flight phase in accordance with the available power (this includes the option to use engines with different/reduced specific impulse). For phase B the number of operating thrusters and the thrust are assumed to be constant. Therefore, the relevant spacecraft parameter for determining the flight time is the initial acceleration at the beginning of phase B (corresponding to an available power typically between 2 and 8 kW and masses between 2 and 4.5 tons). The lander for phase C is equipped with chemical propulsion only and the landing scenario (using airbags) is similar to the Mercury lander studied for Bepi Colombo by Babakin Space Center and ESA in 2002. To save Delta-V and thus chemical propellant mass for the lander, the options with descent from high Jupiter ‘relay orbits’ to Europa distance are assumed to be performed with gravity assists at Callisto, Ganymede and Europa, so that only a moderate Delta-V has been taken into account. The landed small surface station may weight several ten kilograms and contain a scientific payload of several kilograms. The life time of the lander will be several weeks and its data are relayed to Earth via the mother spacecraft. The paper demonstrates that the overall flight time until landing on Europa strongly depends on the specific power supply mass α (in kg/kW)- if the mass of the power system is kept constant - and also on the ratio of the power supply mass to total spacecraft mass (typically 0.2). For values of α between 5 and 10 kg/kW the flight times are between 7 and 15 years. A comparison with other options (nuclear electric or chemical) has also been performed and will be discussed.
- Abstract document