A study on tethered lander for soft landing on a class of planets with atmosphere

Paper number

IAC-06-A3.4.06

Author

Mr. Zhu Jianfeng, Beijing University of Aeronautics and Astronautics, China

Coauthor

Prof. Xu Shijie, Beijing University of Aeronautics and Astronautics, China

Year

2006

Abstract

It is very complicated to land on the surface of a planet with atmosphere, especially to terminal descending phase because the security of payloads is great important. Some landers have successfully implemented soft landing on planetary surface, such as Viking, Mars, Pathfinder, Spirit and Opportunity on the Mars, and Venera on the Venus. There are two classes of soft landing strategies in past planetary surface missions. The first class uses thrusters and parachute, which requires decelerating thrusters continuously work  until the soft landing conditions are satisfied. Unfortunately, the tail flame of decelerating thrusters would instigate upwards dust which cover planetary surface and damage the payload, even endanger the health of astronauts if the lander is manned. The second class uses thrusters, parachute and airbag. Even though the tail flame of thrusters doesn’t touch the planetary surface in this case, but it is very dangerous to use airbag if these are edgy blocks inside landing areas.

To overcome the forementioned drawbacks, a new soft landing strategy using thrusters, parachute and tether is proposed in this paper. The lander consists of payload and assist module equipped motor, parachute and decelerating thrusters. They are connected by a tether which enwinds around a windlass and fixed together at the beginning. After the lander entering planetary atmosphere, the parachute is opened. The lander starts terminal descent after its horizontal velocity decelerating to small enough. First of all, the lander cruises above planetary surface to find safe landing site. Then, the parachute’s cable is snipped and the lander begins to vertical descent while its horizontal velocity is decelerated to zero. When the lander is above surface at a proper distance, the payload is separated from the assist module. The descent velocity and altitude of the payload is controlled by the tether using motor. The assist module should be above the planetary surface at a sufficient distance to avoid dust and ejecta of thrusters damaging payload. While the altitude and velocity of payload are respectively less than 0.5m and 1m/s, the tether is cut off and the payload completes soft landing successfully. Subsequently, the decelerating thrusters turn off and the lateral thrusters push the assist module to land on a site far from payload.

Numerical simulation for soft landing on the Mars is fulfilled. A fuzzy controller and a variable structure controller are applied respectively to control the decelerating thruster’s turning on or turning off and to control the tether’s length. The touchdown velocity of the payload is less than 1.5m/s. The least distance from planetary surface to decelerating thrusters is 16.8m, and the splash down point of the assist module is 12.3m away from the payload. Simulation results show that the new soft landing strategy is feasible.

Abstract document

IAC-06-A3.4.06.pdf

Manuscript document

IAC-06-A3.4.06.pdf (🔒 authorized access only).

To get the manuscript, please contact IAF Secretariat.