TOKYO — The Japan Aerospace Exploration Agency has confirmed that its Martian Moons eXploration mission will place the Idefix rover on Phobos by throwing it at the moon from a height of four meters and then, if it bounces, throwing it again from three.
Mission planners say the moon's gravity is so weak that a conventional landing would require the rover to grip the surface with wheels that have never been tested on regolith. «We considered a soft touchdown,» said a JAXA flight dynamics lead. «Then we considered that Phobos is a rubble pile and our rover weighs about as much as a suitcase. The team voted to just drop it and see.»
The revised profile calls for the spacecraft to hover alongside Phobos at walking pace while a spring-loaded tray tips the rover out. Engineers expect it to bounce between two and five times before settling, and have fitted the rover with a small flag that deploys on the first impact so ground crews can count the hops from Earth.
JAXA has also announced a public rehearsal: a full-scale rover model will be dropped from a stepladder in Sagamihara every afternoon until the 2029 arrival, with spectators invited to guess the number of bounces. The agency says the data will help calibrate the final throw, and that the winner will be permitted to name the crater where the rover eventually stops.