SpaceX reusable rocket launching system
The SpaceX reusable rocket launching system is a set of orbital launch system technologies being developed by SpaceX over a number of years in order to facilitate full and rapid reusability of space launch vehicles. The privately funded development effort aims to bring a launch vehicle first stage back to the launch site in minutes—and a second stage back to the launch pad, following orbital realignment with the launch site and atmospheric reentry, in up to 24 hours—with both stages designed to be available for reuse within "single-digit hours" after return.
The design for "bringing the rocket back to launchpad using only thrusters" was completed in February 2012. SpaceX is currently in an active test program, begun in late 2012, where they are testing both low-altitude, low-speed aspects of the landing technology, as well as testing high-velocity, high-altitude aspects of the booster atmospheric return technology.
The first return and vertical landing of a booster stage from a launch vehicle on an orbital trajectory is planned to occur no earlier than February 2014, assuming all licensing issues and safety issues can be worked out with various US regulatory authorities.
The reusable launch system technology is under consideration for both the Falcon 9 and the Falcon Heavy launch vehicles. It is particularly well suited to the Falcon Heavy where the two outer cores separate from the rocket much earlier in the flight profile, and are therefore moving at slower velocity at stage separation. If the technology is used on a reusable Falcon 9 rocket, the first stage separation would occur at 6,546 km/h (4,067 mph; Mach 6) rather than the much faster 11,200 km/h (6,960 mph; Mach 10) for an expendable Falcon 9, in order to provide the residual fuel necessary to complete the deceleration and turnaround maneuver, as well as the controlled descent and landing.
- 1 History
- 2 Technologies
- 3 Economic issues
- 4 Test program
- 5 See also
- 6 References
- 7 External links
The broad outline of the reusable launch system was first publicly described on September 29, 2011. SpaceX indicated that they would attempt to develop powered descent and recovery of both Falcon 9 stages – a fully vertical takeoff, vertical landing (VTVL) rocket.  Included was a computer-animation video said to be an approximation depicting the first stage returning tail-first for a powered descent and the second stage, with heat shield, reentering head first before rotating for a powered descent. A reusable first stage is now being flight tested by SpaceX with the suborbital Grasshopper rocket.
Initial word of the new test rocket had actually become public a bit earlier in September, when the US Federal Aviation Administration released a draft Environmental Impact Assessment for the SpaceX Test Site in Texas, and the space media picked up on it and wrote about by September 26.
In May 2012, SpaceX obtained a re-entry database 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 for by SpaceX under a reimburseable Space Act Agreement with NASA.
In November 2012, CEO Elon Musk made public SpaceX has plans to build a much-larger second reusable rocket system that will be powered by LOX/methane, "an evolution of SpaceX's Falcon 9 booster" and reiterated SpaceX' commitment to development of a vertical landing breakthrough technology to achieve "extreme, rapid reusability ... as close to aircraft-like dispatch capability as one can achieve. "
By the end of 2012, the demonstration test vehicle, Grasshopper, had made three VTVL test flights including a 29-second hover flight to 40 meters (130 ft) on December 17, 2012, and in early March 2013, SpaceX successfully tested Grasshopper for a fourth time with a 24 story hop.
In March 2013, SpaceX announced that they would instrument and equip all subsequent Falcon 9 first-stages as controlled descent test vehicles, with plans to do over-water propulsively decelerated simulated landings beginning in mid-2013, with the intent to bring the vehicle back to the launch site for a powered landing, perhaps as early as mid-2014.
The April 2013 draft Environmental Impact Statement for the proposed SpaceX private launch facility in south Texas 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.
A key milestone was reached in September 2013, when with the data collected from the first flight test of a booster controlled descent from high-altitude—coupled with the technology advancements made on the Grasshopper low-altitude landing demonstrator—SpaceX announced that they now believe they are 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 objective by which they would like to accomplish the first land-return booster test from mid-2014 to early-2014, with a public goal of doing so on the next Space Station cargo resupply flight scheduled in February 2014, pending regulatory approvals.
Musk stated in May 2013 that the goal of the program is to achieve full and rapid reusability of the first stage by 2015, with full launch vehicle reusability to be worked on following that as "part of a future design architecture. "
Several new technologies need to be developed and tested to facilitate successful launch and recovery of both stages of the SpaceX reusable rocket launching system, including:
- restartable ignition system for the first-stage booster
- new attitude control technology—for both the booster stage and second stage—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 outside 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.
- throttleable rocket engine technology
- 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
- 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 will be approximately 18 meters (60 ft), and weigh less than 2,100 kilograms (4,600 lb); the deployment system will use high-pressure Helium as the working fluid.
- large-surface-area thermal protection system to absorb the heat load of deceleration of the second stage from orbital velocity to terminal velocity
In order to make the Falcon 9 reusable and return to the launch site, extra propellant and landing gear must be carried on the first stage. This necessitates a reduction of about 30 percent to the maximum payload to orbit when compared to the expendable Falcon 9.
Reflight of a previously-used stage on a subsequent flight is dependent on the condition of the landed stage, as well as introducing space launch customers to the novel idea of putting a payload in space with a used stage. If all aspects of the test program go very well, and if a customer is interested, SpaceX said in September 2013 that the first reflight of a Falcon 9 booster stage could be no earlier than late 2014.
If SpaceX is successful in developing the reusable technology, it would be expected to "have a major impact on the cost of access to space", and change the increasingly competitive market in space launch services.
- low-altitude (less than 3.5 kilometers (11,500 ft)), low-velocity testing of their Grasshopper technology-demonstrator at their Texas test site,
- high-altitude, mid-velocity testing of a much-larger second-generation Grasshopper test vehicle with all nine engines at Spaceport America in New Mexico, as well as
- high-altitude (91 kilometers (300,000 ft),) very high-velocity (6,546 km/h (4,067 mph; Mach 6)) ballistic reentry, controlled-deceleration and controlled-descent tests of post-mission (spent) Falcon 9 booster stages on Falcon 9 commercial missions that began in September 2013.
Grasshopper is a set of experimental technology-demonstrator, suborbital reusable launch vehicles (RLV). Two vertical takeoff, vertical landing (VTVL) rockets are being built. The first, Grasshopper v1.0, was built in 2011/2012 for low-altitude, low-velocity hover testing in Texas that began in September 2012 and concluded in October 2013 after eight test flights. The second, Grasshopper v1.1, is currently being built in 2013 for higher-altitude and higher-velocity flight testing in New Mexico.
A multiphase, multiyear flight test program is currently underway. The low-altitude, low-speed flights of the first test vehicle—Grasshopper v1.0—were conducted at the SpaceX Rocket Test Facility in McGregor, Texas. Test plans call for the v1.1 Grasshopper to be flight tested at Spaceport America, New Mexico, at altitudes up to approximately 91,000 meters (300,000 ft), although initial low-altitude flight tests of the vehicle are to occur in Texas.
SpaceX projected it would begin its flight test program in 2012, and did so. Grasshopper began flight testing in September 2012 with a brief, three-second hop at the company's Texas test site, followed by a second hop in November 2012 with an 8-second flight that took the testbed approximately 5.4 meters (18 ft) off the ground, and a third flight in December 2012 of 29 seconds duration, with extended hover under rocket engine power, in which it ascended to an altitude of 40 meters (130 ft). Four additional test flights have been made through August 2013.
The initial test vehicle, Grasshopper version 1.0, consisted of a "Falcon 9 [v1.0] first stage tank, a single Merlin-1D engine, four steel landing legs and a support structure, plus other pressurization tanks attached to the support structure" and is 106 feet (32 m) tall. SpaceX "constructed a half-acre concrete launch facility" at the SpaceX Rocket Development and Test Facility, McGregor, Texas, to support the Grasshopper test flight program.
In addition to the three test flights in 2012, five additional flight tests were successfully flown through October 2013, including the fourth test overall, in March 2013, where Grasshopper v1.0 doubled its highest leap to rise to 80.1 meters (263 ft) with a 34 second flight duration, and the seventh test, in August, when it flew to 250 meters (820 ft) altitude on a 60-second duration flight which also executed a 100 meters (330 ft) lateral maneuver before returning back to the pad. Additional flight test details may be found in the main Grasshopper (rocket) article.
Grasshopper v1.0 made its eighth, and final, test flight on October 7, 2013, flying to an altitude of 744 meters (2,441 ft) (0.46 miles) before making its eighth successful landing. The v1.0 test vehicle is now retired.
Beginning in October 2012, SpaceX discussed development of a second-generation Grasshopper test vehicle, one that would have lighter-weight landing legs that fold up on the side of the rocket, would have a different engine bay, and would be nearly 50% longer than the first Grasshopper vehicle. In March 2013, SpaceX announced that the Grasshopper v1.1 suborbital flight vehicle will be constructed out of the Falcon 9 v1.1 first-stage tank that was used for qualification testing at the SpaceX Rocket Development and Test Facility in early 2013. It has been rebuilt as the v1.1 Grasshopper "with flight-like landing legs. "
In August 2013, SpaceX announced that the Grasshopper v1.1 test vehicle would fly in New Mexico with all nine engines of the fully loaded Falcon 9-R, whereas Grasshopper v1.0 had flown exclusively with only a single Merlin 1D engine in place, the center engine planned to be used to complete each landing.
Falcon 9 booster post-mission, controlled-descent tests
In an arrangement unusual for launch vehicles, some first stages of the SpaceX Falcon 9 v1.1 versions of the rocket are conducting propulsive-return over-water tests to test various aspects of the SpaceX reusable rocket technology. The over-water tests will occur in both the Pacific and Atlantic oceans, south of Vandenberg Air Force Base and east of Cape Canaveral Air Force Station. The first flight test occurred on September 29, 2013 after the second stage with the CASSIOPE and nanosat payloads separated from the booster. These descent and simulated landing tests are planned to continue in 2014.
Following analysis of the flight test data from the first booster controlled descent in September 2013, SpaceX announced that they had successfully tested a large amount of new technology on the flight, and that—coupled with the technology advancements made on the Grasshopper low-altitude landing demonstrator—they now believe they are ready to test a full recovery of the booster stage. The first flight test was successful. SpaceX was "able to successfully transition from vacuum through hypersonic, through supersonic, through transonic, and light the engines all the way and control the stage all the way through [the atmosphere]. "
Musk said "the next attempt to recovery [sic] the Falcon 9 first stage will be on the fourth flight of the upgraded rocket. This would be [the] third commercial Dragon cargo flight to ISS", scheduled for 2014. The test plan for that second flight test includes a test objective of a landing on land at Cape Canaveral, assuming all the licensing issues and safety issues can be worked out with various regulatory authorities.
Reusability test plan for post-mission testing
As part of the test program for the SpaceX reusable rocket launching system, the post-mission test plan calls for the first stage booster —both on Falcon 9 Flight 6 and on a number of subsequent flights—to do a burn to slow it down and then a second burn just before it reaches the water. SpaceX had said in March 2013 that they intend to conduct such tests on every Falcon 9 v1.1 launch vehicle and would "continue doing such tests until they can do a return to the launch site and a powered landing ... [and that they expect several] failures before they 'learn how to do it right. '" In September 2013, SpaceX announced a slight modification to this plan: the second and third flights of the Falcon 9 v1.1 rocket will not conduct booster controlled descent tests, and the fourth flight may attempt a vertical landing on land.
In detailed information disclosed in the Falcon 9 Flight 6 launch license for the CASSIOPE mission, SpaceX indicated they would fire three of the nine Merlin 1D engines initially to slow the horizontal velocity of the rocket and begin the attempt at a controlled descent. Then, shortly before impacting the ocean, a single engine would be relighted in an attempt to reduce the stage's speed to an extent where it could be recovered. As of 10 September 2013[update], SpaceX had projected an approximately ten percent chance that this would be successful.
SpaceX is not performing controlled-descent tests on all Falcon 9 v1.1 flights. For example, in order to maximize the propellant available for the launch of SES-8 into a Geosynchronous transfer orbit in November 2013, SpaceX did not attempt a booster controlled descent test on the second Falcon 9 v1.1 flight.
Test flight history
After the three-minute boost phase of September 29 launch—the first flight of the v1.1 version of the Falcon 9—the booster stage attitude was reversed, and three of the nine Merlin 1D engines reignited at high altitude, as planned, to initiate a deceleration and controlled descent trajectory to the surface of the ocean. The first phase of the test "worked well and the first stage re-entered safely. " However, the stage began to roll due to aerodynamic forces during the descent through the atmosphere, and the roll rate exceeded the capabilities of the booster attitude control system (ACS) to null it out. The fuel in the tanks "centrifuged" to the outside of the tank and the single engine involved in the low-altitude deceleration maneuver shut down. SpaceX was able to retrieve some first stage debris from the ocean. SpaceX did not expect a successful booster recovery on this flight and, as of March 2013[update], had said that they did not expect booster recovery following the first several powered-descent tests. The test was successful—with substantial test milestones achieved and a great deal of engineering test data collected—but the booster was not successfully recovered from the ocean.
SpaceX tested a large amount of new technology on the flight, and that—coupled with the technology advancements made on the Grasshopper technology demonstrator—means they now believe they have "all the pieces of the puzzle, ... [they] were able to successfully transition from vacuum through hypersonic, through supersonic, through transonic, and light the engines all the way and control the stage all the way through—we have all the pieces necessary to achieve a full recovery of the boost stage. "
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