ESA has used a robotic arm to simulate a spacecraft's final approach to an asteroid. The laboratory test, which took place recently at the Madrid headquarters of the GMV company in Spain, is part of the preparation for the proposed Asteroid Impact Mission (AIM), which would be man's first visit to a double asteroid system.
The simulation involved a model asteroid and a real spacecraft's navigation camera mounted on a robotic arm that was controlled by dedicated navigation software. The purpose was to provide a real-world test of the AIM spacecraft's new navigation algorithm. This is designed to enable an approach close enough to the smaller of the two asteroids for the release of the Mascot-2 instrument package, making for a soft landing on the surface without the lander being destroyed or bouncing back into space.
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In seeking a successful approach to its target, the near-Earth double asteroid system of Didymos, ESA will look to avoid usingexpensive proximity sensors and instead put down its lander using very limited resources. This not only requires some sophisticated navigation, but onboard autonomy on the part of the spacecraft due to the interplanetary distances separating the probe from mission control on Earth.
As a more cost-effective approach, the space agency us using its Navigation for Planetary Approach and Landing (NPAL) camera backed by smart visual navigation software.
In the test, this system took multiple images of the target and measured motion across its surface by selecting and tracking landmark "feature points" and then comparing them against the onward and rotational motion of the spacecraft to monitor its position and orientation. ESA says that the NPAL camera stores the images and carries out the image tracking before sending the results to the guidance and navigation computer. ESA says AIM may also utilize its laser communication package to measure the spacecraft's distance to the surface.
Still awaiting approval from ESA's Ministerial Council by December 2016, AIM is one of two spacecraft that make up the Asteroid Impact & Deflection Assessment (AIDA) mission, which is a joint project by ESA, the German Aerospace Center, Observatoire de la Côte d'Azur, NASA, and the Johns Hopkins University Applied Physics Laboratory.
AIDA consists of the NASA-developed Double Asteroid Redirection Test (DART) and AIM. This deep-space technology demonstration mission is designed to not only be the first to explore a double asteroid, but also to test the feasibility of deflecting an asteroid should it prove a menace to Earth or a general hazard to space navigation.
If approval is given, the mission is scheduled to launch in October 2020, with a view to touching down in October 2022. In the meantime, the first major design review is set for January and detailed design work will begin in February.
"The ultimate goal for AIM is to demonstrate new ways to explore small Solar System bodies in the future," says Ian Carnelli, AIM project manager, "So we are testing this approach as fully as possible. In effect, the test bench is a fully fledged optical and robotic laboratory, testing AIM's approach and the lander descent right down to deployment altitude."
The video below shows the simulation test.