to the vehicle are publicly planned. In May 2018, ahead of the first flight of Falcon 9 Block 5, SpaceX announced that the goal had been achieved. The Merlin 1D is now close to the sea-level thrust of the retired Rocketdyne H-1 / RS-27 engines used on Saturn I, Saturn IB, and Delta II. Anomalies The March 18, 2020, launch of Starlink satellites on board a Falcon 9 experienced an early engine shutdown on ascent. The shutdown occurred 2 minutes 22 seconds into the flight and was accompanied with an "event" seen on camera. The rest of the Falcon 9 engines burned longer and did deliver the payload to orbit. However, the first stage was not successfully recovered. In a subsequent investigation SpaceX found that isopropyl alcohol, used as cleaning fluid, was trapped and ignited, causing the engine to be shut down. To address the issue, in a following launch SpaceX indicated that the cleaning process was not done. On October 2, 2020, the launch of a GPS-III satellite was aborted at T-2 seconds due to a detected early startup on 2 of the 9 engines on the first stage. The engines were removed for further testing and it was found that a port in the gas generator was blocked. After removing the blockage the engines started as intended. After this, SpaceX inspected other engines across its fleet and found that two of the engines on the Falcon 9 rocket intended for the Crew-1 launch also had this problem. Those engines were replaced with new M1D engines. On February 16, 2021, on Falcon 9 flight 108 launching Starlink satellites, an engine shut down early due to hot exhaust gasses passing through a damaged heat-shielding cover. The mission was a success, but the booster could not be recovered. Merlin 1D Vacuum A vacuum version of the Merlin 1D engine was developed for the Falcon 9 v1.1 and the Falcon Heavy second stage. As of 2020, the thrust of the Merlin 1D Vacuum is with a specific impulse of 348 seconds, the highest specific impulse ever for a U.S. hydrocarbon rocket engine. The increase is due to the greater expansion ratio afforded by operating in vacuum, now 165:1 using an updated nozzle extension. The engine can throttle down to 39% of its maximum thrust, or . Design Engine control SpaceX uses a triple-redundant design in the Merlin engine computers. The system uses