Breadboard Testing of the ESA ExoMars Airbag Landing Systems
Bown, N¹; Glynn, S¹; Giovangrossi, G²; Tenore, A³; Mercurio, U⁴; Dellantonio, D⁵; Laine, B^5
1Vorticity Ltd.; ²Aero Sekur SpA; ³Thales Alenia Space - Italy; ⁴CIRA; ⁵ESTEC

ExoMars is the next ESA mission to Mars and will include a lander of 480 kg to 600kg. The lander will be delivered to the surface of Mars using a heat shield, parachutes, retro-rockets and an airbag landing system to cushion the final impact to the Martian terrain. Two designs of airbag landing system were initially under consideration for the mission.

The first was a conventional sealed airbag, roughly based on the NASA Pathfinder/MER geometry. This system transfers the kinetic energy inherited from the descent system to the gas within the airbag by compression. The energy is subsequently returned to the payload during the rebound but due to irreversibilities in the system the kinetic energy after impact is less than that before. The airbag therefore experiences a number of impacts, at different orientations, during which the energy is dissipated until the payload is at rest.

The second system considered was a new technology for extra-terrestrial applications and uses vents in the airbag to release the compressed gas. Correct timing of the venting allows the kinetic energy of the payload to be absorbed, bring the payload to rest but releases the absorbed energy with the gas preventing a rebound. Further, by compartmentalising the airbag and employing differential venting the rotational dynamics of the payload can be controlled.

Vented airbags potentially offer significant mass savings over the sealed, rebounding systems employed on extra-terrestrial missions to date. With the intention of bringing the payload to rest during the first impact, only one side of the payload requires protection, significantly reducing the quantity of material required and reducing the mass of the associated sub-systems. In addition the airbag is not required to retain gas following the impact, so protection of the inflatable can be minimised. However, the vented airbag is more sensitive to the impact conditions, particularly the lateral velocity and pitch attitude and requires more complex systems for vent activation and control.

In order to select the flight design for the ExoMars mission a "breadboarding" activity has been carried out to assess the technological and programmatic risks associated with each design. Designs for the two systems for the ExoMars mission have been formulated, hardware manufactured and tested under Earth ambient pressure. Test conditions were adjusted to compensate for the Earth environment with the aim of exercising the critical aspects of each design. Testing yielded valuable data to compare with analytical models and progress the design towards the flight system. The vented airbag design is now the baseline landing system for the ExoMars mission. The designs of the two airbag landing systems will be described and the results of the breadboard testing presented.