Technologies for landing on the Moon The NEXT Lunar Lander study

The United States have been to the Moon and want to go again, China and India have recently launched their own lunar missions, and Europe is looking at the possibility of future missions to Earth’s natural satellite. Astrium is working on a European Space Agency (ESA) study: ‘NEXT Lunar Lander with In-Situ Science and Mobility’.

The NEXT Lunar Lander study is in two phases. “In the first phase, we defined the baseline for a mission concept,” explains Dr Peter Kyr, who is leading the study at Astrium Space Transportation. “This mainly concerned the transfer strategy, the descent, landing, mobility, lunar surface operations and the issue of weight distribution between the lander and the Moon rover.” The results of the first phase were presented to ESA in July 2008. In Phase 2, the complete mission concept is now being finalised, and the design of the transfer module, the lander and the Moon rover is being developed.

The concept envisages a Soyuz rocket with a Fregat upper stage for the launch. Following separation of the payload from the upper stage, the two-stage spacecraft (the lander and the lunar module) will enter a transfer orbit before swinging into orbit around the Moon just two kilometres above its surface. At this point, the lander will detach itself from the transfer module and land near the Moon’s south pole. The Moon rover will emerge from the landing module and begin the scientific exploration.

Technological challenges

“There are a number of technological challenges that have to be mastered in order for such a lunar landing manoeuvre to work,” says Peter Kyr, referring to what lies ahead in the second phase of the study. “So far, the Moon has been orbited, but only American astronauts have actually set foot on it. The technologies required for a robotic landing operation, as envisaged in the study, are at present only partially available or still need to be developed.”

The key technologies that make this type of lunar mission so challenging include:

Optical navigation and obstacle avoidance

Even if a suitable landing place can be specified in advance, an autonomous optical navigation system is needed during the landing manoeuvre to ensure that the vehicle does not head for any rocks, slopes or other inaccessible areas. Given that the final phase of the landing approach takes a mere 75 seconds and needs to be executed precisely to within just a few hundred metres, this is a very critical aspect.

Control and propulsion

The idea is for the landing module to use the same types of engines as the ATV automated transfer vehicle: eight 220 N and four 500 N propulsion units. Unlike the ATV, however, the landing module cannot be brought to a standstill in space, so it needs to control and slow down its approach during the entire descent. This is done by pulsed engines that work asynchronously, i.e. that can be switched on and off at alternating times.

Further technological challenges lie in the design of the landing legs which, whatever the lunar surface is like, must ensure that the vehicle lands gently and remains steady on the ground so that the rover and its scientific instruments remain intact and can be unloaded.

Teamwork

The study is an Astrium team effort. The Bremen site in Germany is responsible for the mission architecture, the design of the lunar and landing modules and the cost estimate. Colleagues in Stevenage are contributing the Rover systems concept, while Toulouse in France is investigating the key topic of navigation.

In addition, there are various subcontractors and technology institutes involved, such as the German Aerospace Center (DLR) Space Systems Institute in Bremen and the DLR Institute of Flight Systems in Braunschweig.