SpaceX reusable launch system development program


has privately funded the development of orbital launch systems that can be reused many times, similar to the reusability of aircraft. SpaceX has developed technologies since the 2010s to facilitate full and rapid reuse of space launch vehicles. The project's long-term objectives include returning a launch vehicle first stage to the launch site within 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 would have been reusability of both stages of their orbital launch vehicle, and the first stage would be designed to allow reuse a few hours after return. Development of reusable second stages for Falcon 9 was later abandoned in favor of developing Starship. However, SpaceX still developed reusable payload fairings for the Falcon 9.
The program was 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. Reflights of refurbished first stages then became routine. In May 2021, B1051 became the first booster to launch ten missions.
The reusable launch system technology was initially developed for the first stage of Falcon 9. After stage separation, the booster flips around, a reentry burn sheds gravity-induced speed to prevent stage overheating as the spacecraft reenters the thicker part of the atmosphere, and a landing burn accomplishes the final low-altitude deceleration and touchdown.
SpaceX planned since at least 2014 to develop reusable second stages, a more challenging engineering problem because the vehicle is traveling at orbital velocity. Second stage reuse is considered vital to Elon Musk's plans for settlement of Mars. Initial concepts for a reusable Falcon 9 second stage were abandoned by 2018.
, SpaceX is developing the Starship system to be a fully-reusable two-stage launch vehicle, intended to replace all of its other launch vehicles and spacecraft for satellite delivery and human transport—Falcon 9, Falcon Heavy, and Dragon—and eventually support flights to the Moon and Mars. It could theoretically be used for point-to-point transportation on Earth.

History

SpaceX attempted to land the first stage of the Falcon 1 by parachute, but the stage did not survive atmosphere re-entry. They continued to experiment unsuccessfully with parachutes on the earliest Falcon 9 flights after 2010. SpaceX subsequently switched to developing a powered descent landing system.
A description of the reusable launch system was outlined in September 2011. SpaceX said it would attempt to develop powered descent and recovery of both Falcon 9 stagesa fully vertical takeoff, vertical landing rocket. The company produced an animated video of the first stage returning tail-first for a powered descent and the second stage with a heat shield, reentering head first before rotating for a powered descent. In September 2012, SpaceX began flight tests on a prototype reusable first stage with the suborbital Grasshopper rocket. Those tests continued into 2014, including testing of a second and larger prototype vehicle, F9R Dev1.
News of the Grasshopper test rocket had become public a few days earlier, when the US Federal Aviation Administration released a draft Environmental Impact Assessment for the SpaceX Test Site in Texas, and the space media had reported it. In May 2012, SpaceX obtained a set of atmospheric test data for the recovery of the Falcon 9 first stage based on 176 test runs in the NASA Marshall Space Flight Center wind tunnel test facility. The work was contracted out by SpaceX under a reimbursable Space Act Agreement with NASA.
In 2012, it was projected that the first-stage separation of a reusable Falcon 9 rocket would occur at a velocity of approximately rather than for an expendable Falcon 9, to provide the residual fuel necessary for the deceleration and turnaround maneuver and the controlled descent and landing.
In November 2012, CEO Elon Musk announced plans to build a second, much larger, reusable rocket system powered by LOX/methane rather than LOX/RP-1 used on Falcon 9 and Falcon Heavy. The new system was to be "an evolution of SpaceX's Falcon 9 booster", and SpaceX reiterated their commitment to develop a breakthrough in vertical landing technology. By the end of 2012, the demonstration test vehicle, Grasshopper, had made three VTVL test flightsincluding a 29-second hover flight to on December 17, 2012. In early March 2013, SpaceX successfully tested Grasshopper for a fourth time when it flew to an altitude of over.
In March 2013, SpaceX announced that it would instrument and equip subsequent Falcon 9 first-stages as controlled descent test vehicles, with plans for over-water propulsively decelerated simulated landings beginning in 2013, with the intent to return the vehicle to the launch site for a powered landingpossibly as early as mid-2014. The April 2013 draft Environmental Impact Statement for the proposed SpaceX South Texas Launch Site includes specific accommodations for return of the Falcon 9 first-stage boosters to the launch site. Elon Musk first publicly referred to the reusable Falcon 9 as the Falcon 9-R in April 2013.
In September 2013, SpaceX successfully relit three engines of a spent booster on an orbital launch, and the booster re-entered the atmosphere at hypersonic speed without burning up. With the data collected from the first flight test of a booster-controlled descent from high altitude, coupled with the technological advancements made on the Grasshopper low-altitude landing demonstrator, SpaceX announced it believed it was ready to test a full land-recovery of a booster stage. Based on the positive results from the first high-altitude flight test, SpaceX advanced the expected date of a test from mid-2014 to early 2015, with the intention of doing so on the next Space Station cargo resupply flight pending regulatory approvals. That flight took place on April 18, 2014.
Musk stated in May 2013 that the goal of the program is to achieve full and rapid reusability of the first stage by 2015, and to develop full launch vehicle reusability following that as "part of a future design architecture". In September 2013, SpaceX said that if all aspects of the test program were successful and if a customer is interested, the first reflight of a Falcon 9 booster stage could happen as early as late 2014.
In February 2014, SpaceX made explicit that the newly defined super-heavy launch vehicle for what was then called Mars Colonial Transporter would also make use of the reusable technology. This was consistent with Musk's strategic statement in 2012 that "The revolutionary breakthrough will come with rockets that are fully and rapidly reusable. We will never conquer Mars unless we do that. It'll be too expensive. The American colonies would never have been pioneered if the ships that crossed the ocean hadn't been reusable."
Also in May 2014, SpaceX announced an extensive test program for a reusable, powered landing space capsule called DragonFly. The tests were to be run in Texas at the McGregor Rocket Test Facility in 2014–2015.
In June 2014, COO Gwynne Shotwell clarified that all funding for development and testing of the reusable launch system technology development program is private funding from SpaceX, with no contribution from the US government. As of 2017 SpaceX had spent over a billion dollars on the development program.
For the first time, SpaceX stated in July 2014 that they are "highly confident of being able to land successfully on a floating launch pad or back at the launch site and refly the rocket with no required refurbishment."
By late 2014, SpaceX suspended or abandoned the plan to recover and reuse the Falcon 9 second stage; the additional mass of the required heat shield, landing gear, and low-powered landing engines would incur too great a performance penalty. While the idea was mentioned again later, it was ultimately abandoned as Starship development made progress.
In December 2015, following the recovery of the first stage from December 22 launch, SpaceX projected that the first reflight of a recovered booster would likely occur in 2016, but not using the December 22 recovered stage.
In September 2016, SpaceX announced that development was underway to extend the reusable flight hardware to second stages, a more challenging engineering problem because the vehicle is travelling at orbital velocity. The reusable technology was to have been extended to the 2016 designs of both the tanker and crewed spaceship upper stage variants as well as the first stage of the Interplanetary Transport System, and is considered paramount to the plans Elon Musk is championing to enable the settlement of Mars. In 2016, initial test flights of an Interplanetary Transport System vehicle were expected no earlier than 2020.
In 2017 SpaceX was making test flight progress in incrementally and iteratively developing a fairing recovery system. In July 2017, Musk said "we are quite close to being able to recover the fairing.... We've got a decent shot of recovering a fairing by the end of the year, and reflight by late this year or early next." The cost savings to SpaceX of recovering the fairing is expected to be on the order of. Together, the booster stage and the fairing make up approximately 80 percent of the cost of a launch. The fairings are equipped with a steerable parachute and fall towards a ship equipped with a big net. Intact fairings could be recovered from the ocean starting in 2017, with landings in the net from 2019 on.

Technologies

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 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 have 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. As of 2022, SpaceX built three autonomous spaceport drone ships, one operating the West coast and two on the East 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, and weigh less than. 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.