An asteroid a few hundred metres to a kilometre across has almost no gravity, so a spacecraft can't land and sit on it the way a lander sits on the Moon or Mars — it would barely be held down at all, and a full landing risks tipping or sinking into loose, unconsolidated regolith. Instead, both JAXA's Hayabusa2 (at asteroid Ryugu) and NASA's OSIRIS-REx (at asteroid Bennu) flew a touch-and-go: a slow, controlled descent down a pre-mapped approach corridor, a contact lasting only a few seconds, and an immediate thruster burn back up and away before the vehicle can react with the surface any further.
- Approach — the spacecraft creeps down toward a pre-selected target point, guided by imagery from earlier reconnaissance passes; both real missions found their targets far rockier than expected and had to aim for small clear patches between boulders.
- Contact — for a gas-jet sampler (OSIRIS-REx's TAGSAM), a nitrogen jet fires into the surface at the moment of contact, fluidizing loose material so it flows up into a collector ring. For a projectile sampler (Hayabusa2), a small metal mass is fired into the surface, and the resulting spray of fragments is caught by a collection horn.
- Escape — thrusters fire immediately to pull the spacecraft back up and away, so the whole surface interaction lasts only a handful of seconds — long enough to collect a sample, too short to risk tipping over on the uneven terrain.