Autonomous Spacecraft Drone Ship (ASDS) are ocean-going vessels derived from a deck barge, equipped with station-keeping engines and a large landing platform controlled by an autonomous robot. This allows for the recovery of the launch vehicle’s first stages at sea for missions that do not carry enough fuel to return to the launch site after boosting spacecraft onto an orbital or interplanetary trajectory. As of 12 December 2020, 57 Falcon 9 flights have attempted to land on a drone ship, with 48 of them succeeding (84.2%).
Operation
A tug is used to bring the ASDS to its oceanic position, and a support ship stands by some distance away from the crewless ASDS. The vessels initially used on the East Coast were Elsbeth III (tug) and GO Quest (support). Following landing, technicians and engineers typically board the landing platform and secure the rocket’s landing legs to lock the vehicle in place for transport back to port. The first stage is secured to the deck of the drone ship with steel hold-downs welded onto the feet of the landing legs. In June 2017, OCISLY started being deployed with a robot that drives under the rocket and grabs onto the hold-down clamps located on the outside of the Falcon 9’s structure after landing. Fans call the robot “Optimus Prime” or “Roomba”, the latter of which has been turned into a backronym for “Remotely Operated Orientation and Mass Balance Adjustment”. Starting with “A Shortfall of Gravitas”, the drone ship will not need to use a tug to bring the ASDS to the Falcon 9 landing zone, as it is now fully autonomous.
Characteristics
The ASDS is autonomous vessel capable of precision positioning, originally stated to be within 3 m (9.8 ft) even under storm conditions, using GPS position information and four diesel-powered azimuth thrusters. In addition to the autonomous operating mode, the ships may also be telerobotically controlled. The returning first stage must not only land within the confines of the deck surface but must also deal with ocean swells and GPS errors. SpaceX equips the ships with a variety of sensor and measurement technology to gather data on the booster returns and landing attempts, including commercial off-the-shelf GoPro cameras.
Naming
The ASDS is named after spaceships that appear in the Culture series of science fiction novels by Iain M. Banks.
- Just Read the Instructions (II) (JRTI), which operates in the Atlantic for launches from Cape Canaveral
- Of Course I Still Love You, (OCISLY), operates in the Pacific to support missions from Vandenberg.
- A Shortfall of gravitas is undergoing trials.
