page_title: SpaceX reusable launch system development program
section_title: Technologies
hierarchical_section_title: SpaceX reusable launch system development program / Technologies
caption_attribution_description: English: SpaceX autonomous spaceport drone ship, previously the barge Marmac 300, now nicknamed Just Read the Instructions. It is a floating landing platform used by SpaceX for landing attempts by the Falcon 9 rocket's first stage.
context_page_description: The SpaceX reusable launch system development program is a privately funded program to develop a set of new technologies for an orbital launch system that may be reused many times in a manner similar to the reusability of aircraft. SpaceX has been developing the technologies over several years to facilitate full and rapid reusability of space launch vehicles. The project's long-term objectives include returning a launch vehicle first stage to the launch site in minutes and to return a second stage to the launch pad following orbital realignment with the launch site and atmospheric reentry in up to 24 hours. SpaceX's long term goal is that both stages of their orbital launch vehicle will be designed to allow reuse a few hours after return.
  The program was publicly announced in 2011. SpaceX first achieved a successful landing and recovery of a first stage in December 2015. The first re-flight of a landed first stage occurred in March 2017 with the second occurring in June 2017, that one only five months after the maiden flight of the booster. The third attempt occurred in October 2017 with the SES-11/EchoStar-105 mission.
context_section_description: Several new technologies needed to be developed and tested to facilitate successful launch and recovery of the first stages of Falcon 9 and Falcon Heavy, and both stages of Starship. Since 2017, recovery and reuse of Falcon rocket boosters has become routine.
  The technologies that were developed for Falcon 9, some of which are still being refined, include:
  Restartable ignition system for the first-stage booster. Restarts are required at both supersonic velocities in the upper atmosphere—in order to reverse the high velocity away from the launch pad and put the booster on a descent trajectory back toward the launch pad—and at high transonic velocities in the lower atmosphere—in order to slow the terminal descent and to perform a soft landing. If the booster returns to a landing site on land another burn is needed shortly after stage separation to reverse the flight direction of the booster, for a total of four burns for the center engine.
  New attitude control technology for the booster to bring the descending rocket body through the atmosphere in a manner conducive both to non-destructive return and sufficient aerodynamic control such that the terminal phase of the landing is possible.  This includes sufficient roll control authority to keep the rocket from spinning excessively as occurred on the first high-altitude flight test in September 2013, where the roll rate exceeded the capabilities of the booster attitude control system (ACS) and the fuel in the tanks "centrifuged" to the side of the tank shutting down the single engine involved in the low-altitude deceleration maneuver. The technology needs to handle the transition from the vacuum of space at hypersonic conditions, decelerating to supersonic velocities and passing through transonic buffet, before relighting one of the main-stage engines at terminal velocity.
  Hypersonic grid fins were added to the booster test vehicle design beginning on the fifth ocean controlled-descent test flight in 2014 in order to enable precision landing.  Arranged in an "X" configuration, the grid fins control the descending rocket's lift vector once the vehicle has returned to the atmosphere to enable a much more precise landing location.  Iteration on the design continued into 2017.  Larger and more robust grid fins, made from forged titanium and left unpainted, were first tested in June 2017, and has been used on all reusable Block 5 Falcon 9 first stages since May 2018.
  The rocket engine needs to be throttleable to achieve zero velocity at the same time the rocket reaches the ground. Even the lowest possible thrust of a single Merlin 1D engine exceeds the weight of the nearly empty Falcon 9 booster core, therefore the rocket cannot hover.
  Terminal guidance and landing capability, including a vehicle control system and a control system software algorithm to be able to land a rocket with the thrust-to-weight ratio of the vehicle greater than one, with closed-loop thrust vector and throttle control
  Navigation sensor suite for precision landing
  A large floating landing platform for launches where the first stage does not have sufficient fuel to return to the launch site. SpaceX built two autonomous spaceport drone ships, one for each coast of the United States.
  A thermal protection system to avoid damage to the first stage when re-entering the atmosphere.
  Lightweight, deployable landing gear for the booster stage. In May 2013, the design was shown to be a nested, telescoping piston on an A-frame.  The total span of the four carbon fiber/aluminum extensible landing legs is approximately 18 meters (60 ft), and weigh less than 2,100 kilograms (4,600 lb). Deployment system uses high-pressure Helium as the working fluid. With Flight 25 it was announced that each landing leg contained a "crush core", to absorb the impact of landing for particularly hard landings.
caption: Autonomous Spaceport Drone Ship, in port in January 2015.
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