SpaceX Drone Ship ASDS
A SpaceX drone ship is a floating landing pad that sails out into the open ocean and waits for a rocket to come down and land on it. The official name is an Autonomous Spaceport Drone Ship, or ASDS.
Quick facts
- What it is: An uncrewed (no people aboard) ocean barge fitted with a rocket-landing deck, built and operated by SpaceX.
- Job: Catch and recover the reusable first-stage booster of Falcon 9 and Falcon Heavy rockets at sea.
- Deck size: Roughly 91 m by 52 m (about 300 ft by 170 ft). For comparison, a Falcon 9’s landing legs span about 18 m (60 ft), so the deck is large compared with the rocket’s footprint.
- Holding position: Originally stated to stay within about 3 m (10 ft) of its target spot, even in storms, using GPS satellite navigation.
- Propulsion: Four diesel-powered steerable “azimuth” thrusters (about 300 horsepower each), made by Thrustmaster of Texas.
- Names: All borrowed from sentient starships in Iain M. Banks’ Culture science-fiction novels.
- First success: April 8, 2016, on the ship Of Course I Still Love You, during the CRS-8 cargo mission to the International Space Station.
How it works
After a rocket lifts off, its first stage (the large bottom section that does the early heavy lifting) separates and begins falling back toward Earth. The drone ship is already waiting “downrange” — out in the ocean along the booster’s flight path. To stay in one spot despite waves and wind, the ship uses GPS and its four steerable thrusters in a technique called dynamic positioning: small, constant adjustments that hold a fixed point like a hovering helicopter.
Meanwhile, the booster steers itself home. It fires its engines in a “boostback” and re-entry burn to slow down and aim, uses grid fins (small steerable metal panels) and gentle gas jets to guide its descent, then fires a single engine in a final “landing burn” to slow almost to a stop just as it touches the deck on its landing legs. Both sides act on their own — the rocket flies itself, and the ship holds station by itself, though human operators can take remote control if needed. The deck carries cameras (including off-the-shelf GoPros) to record each landing and is protected by a steel blast wall to survive the rocket’s exhaust.
Why it matters
The drone ship is the key to reusing rockets, which is the heart of SpaceX’s lower launch costs. Landing at sea is a middle path. Flying all the way back to a land pad costs the most fuel, because the booster must reverse course and travel home. Throwing the booster away recovers nothing. Landing downrange on a ship lets the booster keep moving forward, saving fuel and preserving more of the rocket’s payload capacity while still bringing the hardware back to fly again.
That trade-off matters most for “high-energy” missions — the demanding flights that leave little spare fuel. Sea recovery is used on roughly three-quarters of booster-recovery missions, while lower-energy flights return to land instead. This is what lets SpaceX recover boosters from Starlink deployments, heavy satellites bound for distant orbits, and both side boosters and the center core of a Falcon Heavy. The April 2016 landing was a historic first: the first vertical rocket landing on a floating platform by any organization, proving an idea many had thought impractical.
The fleet and notable flights
SpaceX has operated four named ships, all built from Marmac deck barges: the original Just Read the Instructions (retired after two failed attempts), Of Course I Still Love You (OCISLY, 2015), a second Just Read the Instructions (JRTI, 2016), and A Shortfall of Gravitas (ASOG, in service since 2021). Today ASOG and JRTI support Atlantic launches from Florida out of Port Canaveral, while OCISLY moved to the Port of Long Beach for Pacific launches from Vandenberg.
- CRS-8 (April 8, 2016): First fully successful drone-ship landing, on OCISLY about 300 km off Florida, after four near-miss attempts.
- Demo-2 (May 30, 2020): The booster that launched the first crewed Dragon flight from U.S. soil was recovered on OCISLY.
- Falcon Heavy test flight (Feb 6, 2018): The two side boosters landed on land, but the center core struck the ocean near OCISLY at about 300 mph after two of its three landing engines failed to fire — a reminder of how hard center-core recovery is.
- Jason-3 (Jan 17, 2016): The booster reached the original Just Read the Instructions in the Pacific, but a leg latch failed, the stage tipped over and exploded — an early reliability challenge.
- CRS-23 (Aug 29, 2021): First operational landing on the newest ship, A Shortfall of Gravitas.
