Lunar Landing Simulations With Tosca

Abstract

In the frame of the ROBEX project (Robotic Exploration of Extreme Environments) funded by the Helmholtz association, DLR is designing a robotic mission to the Moon. Amongst other a transportation system should be designed. For this, trajectory analyses have to be performed to simulate soft lunar landings, ascent from the Moon. The SART (Space Launcher System Analysis) division of DLR is regularly doing the sizing of vehicle launched from Earth, orbiting around Earth or returning to Earth. Trajectory simulation and optimisation are usually performed with the help of the in-house Tosca program. In the past Tosca has already been modified to calculate trajectory on Saturn’s moon Titan. For the particular case of ROBEX a new version of Tosca, version 1.253 has been created. Different gravity models are now available for the Earth, Mars, Titan and the Moon. This new version is also able to manage the characteristic energy C3. This new version of tosca needed however to be validated. For this purpose it has been decided to simulate historic lunar missions. The purpose of this document is to provide all the information gathered during a literature study, to provide an analysis of the simulation results and to discuss the problems that were found in the program. To validate the program, flight data has been used. Only successful soft landing lunar missions were investigated. The programmes considered were Surveyor, Luna, Apollo and Chang’e, however, since there was practically no information to be found on the Luna missions and the Chinese Chang’e mission, the focus was put on Surveyor and Apollo. The considered Surveyor missions were Surveyor 1, 3, 5, 6 and 7 because they made a soft landing on the Moon. The considered Apollo missions were Apollo 11, 12, 14, 15, 16 and 17. Of these missions, Apollo 11 and Surveyor 6 were used to perform the series of simulations. Surveyor 6 was used to simulate two stage descent using two propulsion systems; a solid rocket motor and 3 liquid rocket engines and Apollo 11 was used for a single stage descent and ascent simulation. The objective for the simulation was to match the simulation output to the actual flight data. The Apollo 11 descent simulation results looked promising; they followed the same curve as the flight data, but still need some improvement due to inconsistencies in data available. The Surveyor 6 simulations showed a problem in the separation part of the descent, where the solid rocket engine was supposed to separate. In the simulation it failed to do so leading to a higher final mass. This problem could not be solved yet but the simulation could be performed in two parts with a manual separation. Eventually, the results for the Surveyor 6 simulations fit well to the flight data curves but can still be improved. The Apollo 11 ascent simulation results are still deviating from the actual trajectory and require some additional changes to the input file, in order to properly be able to optimize the output. In the end 7 issues were found and most of them have been dealt with. It would be recommended to perform extra simulations in order to have a perfect fit with the flight data curves, however the flight data are not always reliable, as proved by the many inconsistencies found during the literature study.