SpaceX reusable launch system development program

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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. The company SpaceX is developing the technologies over a number of 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. Both stages will be designed to allow reuse a few hours after return.[1]

The program was publicly announced in 2011 and the design for returning the rocket to its launchpad using only thrusters was completed in February 2012.[1] SpaceX's active test program began in late 2012 with testing low-altitude, low-speed aspects of the landing technology. High-velocity, high-altitude aspects of the booster atmospheric return technology began testing in late 2013.

The reusable launch system technology is under development for the Falcon family of rockets. It is particularly well-suited to the Falcon Heavy where the two outer cores separate from the rocket earlier in the flight, and are therefore moving more slowly at stage separation. If the technology is used on a reusable Falcon 9 rocket, the first-stage separation would occur at a velocity of approximately 2.0 km/s (6,500 km/h; 4,100 mph; Mach 6) rather than the 3.4 km/s (11,000 km/h; 7,000 mph; Mach 10) for an expendable Falcon 9, to provide the residual fuel necessary for the deceleration and turnaround maneuver and the controlled descent and landing.[1] The reusable technology will also be extended to the future launch vehicle for the Mars Colonial Transporter.[2]

History[edit]

From left to right, Falcon 1, Falcon 9 v1.0, three versions of Falcon 9 v1.1, and two versions of Falcon Heavy. The SpaceX reusable rocket technology is being developed for both Falcon 9 v1.1 and Falcon Heavy.

The broad outline of the reusable launch system was first publicly described on September 29, 2011. SpaceX said it would attempt to develop powered descent and recovery of both Falcon 9 stages—a fully vertical takeoff, vertical landing (VTVL) rocket. The company produced a computer-animated video depicting a notional view 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.[3][4][5][6] As of March 2014, a prototype reusable first stage is being flight tested by SpaceX with the suborbital Grasshopper rocket.[7]

News of the test rocket become public earlier in September 2011, 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 by September 26.[8][9] 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 for by SpaceX under a reimburseable Space Act Agreement with NASA.[10]

In November 2012, CEO Elon Musk announced SpaceX's plans to build a second, much larger, reusable rocket system, this one to be powered by LOX/methane rather than LOX/RP-1 used on Falcon 9 and Falcon Heavy. The new system will be "an evolution of SpaceX's Falcon 9 booster", and SpaceX reiterated their commitment to develop a breakthrough in vertical landing technology.[11] 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.[7] In early March 2013, SpaceX successfully tested Grasshopper for a fourth time when it flew to an altitude of over 80 meters (260 ft).[12]

In March 2013, SpaceX announced that it would instrument and equip all subsequent Falcon 9 first-stages as controlled descent test vehicles, with plans for over-water propulsion-decelerated simulated landings beginning in mid-2013, with the intent to return the vehicle to the launch site for a powered landing—possibly by mid-2014.[13][14] The April 2013 draft Environmental Impact Statement for the proposed SpaceX private launch site in south Texas includes specific accommodations for return of the Falcon 9 first-stage boosters to the launch site.[15] Elon Musk first publicly referred to the reusable Falcon 9 as the Falcon 9-R in April 2013.[16]

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.[17] 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.[18] 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 2014, with the intention of doing so on the next Space Station cargo resupply flight pending regulatory approvals.[19][20] That flight took place on April 18, 2014.[21][22]

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".[23]

In February 2014, SpaceX made explicit that the newly defined super-heavy launch vehicle for the Mars Colonial Transporter would also make use of the reusable technology.[2] This is 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."[24]

Also in May 2014, SpaceX publicly announced an extensive test program for a related reusable technology: a propulsively-landed space capsule called DragonFly. The tests will be run in Texas at the McGregor Rocket Test Facility in 2014–2015.[25]

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 by the US government.[26] SpaceX has not publicly disclosed the cost of the development program.[27]

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."[28]

Technologies[edit]

Several new technologies needed to be developed and tested to facilitate successful launch and recovery of both stages of the SpaceX reusable rocket launching system. Following the completion of the third high-altitude controlled-descent test, and the completion of the third low-altitude flight of the second-generation prototype test vehicle (plus eight flights of the first-generation Grasshopper prototype flight test vehicle), SpaceX indicated that they are now able to consistently "reenter from space at hypersonic velocity, restart main engines twice, deploy landing legs and touch down at near zero velocity."[28]

The technologies that were developed for this program, some of which are still being refined, include::

Economic issues[edit]

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, requiring around a 30 percent reduction of the maximum payload to orbit in comparison with the expendable Falcon 9.[19] Reflight of a previously used stage on a subsequent flight is dependent on the condition of the landed stage, and upon introducing space launch customers to the very novel idea of putting a payload in space with a used stage. In September 2013, SpaceX said that if all aspects of the test program are successful and if a customer is interested, the first reflight of a Falcon 9 booster stage could happen as early as late 2014.[19]

If SpaceX is successful in developing the reusable technology, it is expected to significantly reduce the cost of access to space, and change the increasingly competitive market in space launch services.[19][41] Michael Belfiore wrote in Foreign Policy that at a published cost of US$56.5 million per launch to low Earth orbit, "Falcon 9 rockets are already the cheapest in the industry. Reusable Falcon 9s could drop the price by an order of magnitude, sparking more space-based enterprise, which in turn would drop the cost of access to space still further through economies of scale."[17] Even for military launches, which have a number of contractual requirements for additional launch services to be provided, SpaceX's price is under US$100 million.[42]

Space industry analyst Ajay Kothari has noted that SpaceX reusable technology could do for space transport "what jet engines did for air transportation sixty years ago when people never imagined that more than 500 million passengers would travel by airplanes every year and that the cost could be reduced to the level it is—all because of passenger volume and reliable reusability."[43] SpaceX has said that if they are successful in developing the reusable technology, launch prices of around US$5 to 7 million for a reusable Falcon 9 are possible.[44]

As of March 2014 launch service providers who compete with SpaceX are not planning to develop similar technology or offer competing reusable launcher options. Neither ILS, which markets launches of the Russian Proton rocket; Arianespace; nor SeaLaunch are planning on developing and marketing reusable launch vehicle services. SpaceX is the only competitor that currently sees a sufficiently elastic market on the demand side that justifies the costly development of reusable rocket technology and the expenditure of private capital to develop options for that theoretical market opportunity.[40]

SpaceX pricing and payload specifications published for the non-reusable Falcon 9 v1.1 rocket actually include about 30 percent more performance than the published price list indicates; the additional performance is reserved for SpaceX to do reusability booster demonstration flight tests while still achieving the specified payloads for customers.[45]

In order to achieve the full economic benefit of the reusable technology, it is necessary that the reuse be both rapid and complete—without the long and costly refurbishment period or partially reusable design that plagued earlier attempts at reusable launch vehicles. SpaceX has been explicit that the "huge potential to open up space flight"[46] is dependent on achieving both complete and rapid reusability.[21][42] CEO Musk has publicly stated that success with the technology development effort could reduce "the the cost of spaceflight by a factor of 100."[47]

Separate from the market competition brought about by SpaceX lower launch prices and the potential future of even more radically lower launch prices if the technology can be completed successfully, Aviation Week has said that "SpaceX reusable launch work is an R&D model"—"The audacity of the concept and speed of the program’s progress make it an exemplar. ... [the] breakneck pace of development has been almost Apollo-like in its execution... [even while] success is far from guaranteed."[48]

Technical feasibility[edit]

The return and rapid reuse of an orbital launch system has never been accomplished. The challenge of creating a reusable rocket is almost impossible due to the small percentage of a rocket's mass that can make it to orbit.[4][dubious ] Typically, a rocket's payload is only about 3% of the mass of the rocket which is also roughly the amount of mass in fuel that is required for the vehicle's re-entry.[49]

Elon Musk said that he believes return, vertical landing and recovery is possible because the SpaceX manufacturing methodologies result in a rocket efficiency exceeding the typical 3% margin. A SpaceX rocket operating in the reusable configuration will have approximately 30% less payload lift capacity than the same rocket in an expendable configuration.[18]

Test program[edit]

SpaceX is currently testing reusable technologies both for its first-stage booster launch vehicle designs—with three test vehicles—and for its new reusable Dragon V2 space capsule—with a low-altitude test vehicle called DragonFly.

SpaceX has publicly disclosed a multi-element, incremental test program for booster stages that includes four aspects:

  • low-altitude (less than 760 m/2,500 ft[8][50]), low-velocity testing of its single-engine Grasshopper technology-demonstrator at its Texas test site
  • low-altitude (less than 3,000 m/9,800 ft), low-velocity testing of a much larger, second-generation, three-engine test vehicle called F9R Dev1. The second generation vehicle includes extensible landing legs and will be tested at the Texas test site[51]
  • high-altitude, mid-velocity testing of another of the second-generation test vehicles (F9R Dev2) at a SpaceX leased facility at Spaceport America in New Mexico. The number of engines on F9R Dev2 has not yet been made public.
  • high-altitude (91 km/300,000 ft[52]), very-high-velocity (approximately 2.0 km/s; 6,500 km/h; 4,100 mph; Mach 6[1]) ballistic reentry, controlled-deceleration and controlled-descent tests of post-mission (spent) Falcon 9 booster stages following a subset of Falcon 9 launches beginning in 2013

Eight low-altitude booster flight tests were made by Grasshopper in 2012 and 2013. The first booster return controlled-descent test from high-altitude was made in September 2013, and a second test took place in April 2014.[19][22][53] Three low-altitude booster flight tests have been made with F9R Dev1 in 2014.

The DragonFly flight tests will begin after the completion of the Texas F9R Dev1 test flights.

Prototype vehicle flight testing[edit]

Main article: Grasshopper (rocket)
Grasshopper vehicle in September 2012.

Grasshopper is a set of experimental technology-demonstrator, suborbital reusable launch vehicles (RLV). Two versions of the prototype reusable test vehicles have been built, the 106-foot tall Grasshopper (formerly designated as Grasshopper v1.0) and the 160-foot tall Falcon 9 Reusable Development Vehicle, or F9R Dev—formerly known as Grasshopper v1.1.[46] Grasshopper 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 prototype vehicle design, F9R Dev, is built on the much larger Falcon 9 v1.1 booster stage form factor, and will include at least two test vehicles—designated F9R Dev1 and F9R Dev2—to be used for higher-altitude and higher-velocity flight testing.[46][54][55]

The flight test program is currently underway. The low-altitude, low-speed flights of the first test vehicle—Grasshopper—were conducted at the SpaceX Rocket Test Facility in McGregor, Texas.[8][9] F9R Dev will be tested at both the Texas facility and also at Spaceport America in New Mexico,[56] with the initial and low-altitude flight tests of the vehicle occurring in Texas, and the high-altitude—approximately 91,000 meters (300,000 ft)—flights in New Mexico.[46][52][57]

In 2011 when SpaceX initially announced its test program, it projected it would begin flight tests in 2012.[58][59] In the event, Grasshopper began flight testing in September 2012 with a brief, three-second hop at the company's Texas test site,[60] followed by a second hop in November 2012 with an eight-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 40 meters (130 ft).[7] Five additional test flights were made in 2013 before Grasshopper v1.0 was retired in October 2013.[61] F9R-Dev flight testing began in April 2014.[46]

Grasshopper[edit]

Grasshopper, the company's first VTVL test vehicle, consisted of a Falcon 9 v1.0 first-stage tank, a single Merlin-1D engine, and four permanently attached steel landing legs. It stood 106 feet (32 m) tall.[9] SpaceX built a 0.5 acres (0.20 ha) concrete launch facility at its Rocket Development and Test Facility in McGregor, Texas to support the Grasshopper flight test program.[59] Grasshopper was also known as Grasshopper version 1.0, or Grasshopper v1.0, prior to 2014 during the time the followon Grasshopper-class test vehicles were being built.

In addition to three test flights in 2012, five additional tests were successfully flown by the end of October 2013—including the fourth test overall in March 2013—in which Grasshopper doubled its highest leap to rise to 80.1 meters (263 ft) with a 34-second flight.[62] In the seventh test, in August 2013, the vehicle flew to 250 meters (820 ft) during a 60-second flight and executed a 100 meters (330 ft) lateral maneuver before returning to the pad.[63] Grasshopper made its eighth and final test flight on October 7, 2013, flying to 744 meters (2,441 ft) (0.46 miles) before making its eighth successful landing.[57] The Grasshopper test vehicle is now retired.[61]

Falcon 9 Reusable Development Vehicle (F9R Dev)[edit]

Beginning in October 2012, SpaceX discussed development of a second-generation Grasshopper test vehicle, which would have lighter landing legs that fold up on the side of the rocket, a different engine bay, and would be nearly 50% longer than the first Grasshopper vehicle.[55] In March 2013, SpaceX announced that the larger Grasshopper-class suborbital flight vehicle would 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 F9R Dev1 with extensible landing legs.

The second VTVL flight test vehicle—F9R Dev1, built on the much longer Falcon 9 v1.1 first-stage tank, and with retractable landing legs—made its first test flight on April 17, 2014.[46][64] F9R Dev1 was used for low-altitude test flights in the McGregor, Texas area with projected maximum altitude below 3,000 meters (10,000 ft).[46] This vehicle self-destructed as a safety measure during a test flight on 22 August 2014.[65]

A third flight test vehicle—F9R Dev2—is currently being built and will be flown at the high-altitude test range available at Spaceport America in New Mexico. It will be flown at altitudes up to 91,000 meters (300,000 ft)-plus.[46]

DragonFly[edit]

Main article: DragonFly (rocket)

DragonFly is a prototype test article for a propulsively-landed version of the SpaceX Dragon space capsule, a suborbital reusable launch vehicle (RLV), intended for low-altitude flight testing. It will undergo a test program in Texas at the McGregor Rocket Test Facility, in 2014–2015.[25][66]

The DragonFly test vehicle is powered by eight SuperDraco engines, arranged in a redundant pattern to support fault-tolerance in the propulsion system design.[67] SuperDracos utilize a storable propellant mixture of monomethyl hydrazine (MMH) fuel and nitrogen tetroxide oxidizer (NTO), the same propellants used in the much smaller Draco thrusters used for attitude control and maneuvering on the first-generation Dragon spacecraft.[66] While SuperDraco engines are capable of 73,000 newtons (16,400 lbf) of thrust, during use on DragonFly flight test vehicle each will be throttled to less than 68,170 newtons (15,325 lbf) to maintain vehicle stability.[66]

A test flight program of thirty flights has been proposed, including two propulsive assist (parachutes plus thrusters) and two propulsive landing (no parachutes) on flights dropped from a helicopter at an altitude of approximately 3,000 meters (10,000 ft). The other 26 test flights are projected to take off from a pad: eight to be propulsive assist hops (landing with parachutes plus thrusters) and 18 to be full propulsive hops, similar to the Grasshopper and F9R Dev booster stage test flights.[66][67]

The DragonFly test program is not expected to start until after the completion of the F9R Dev1 booster testing at the McGregor facility.[67]

Falcon 9 booster post-mission, controlled-descent tests[edit]

Falcon 9 v.1.1 vehicle during launch ascent on September 29, 2013, three minutes before the first-ever retro-deceleration and descent flight test of the first-stage booster.

In an arrangement unusual for launch vehicles, some first stages of the SpaceX Falcon 9 v1.1 rockets are being used for propulsive-return controlled-descent flight tests after they complete the boost phase of an orbital flight. These boosters would ordinarily just be discarded in the ocean once boost phase is complete. The over-water tests are occurring in 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 continuing in 2014, with the second flight having occurred on April 18.[19][22][53]

Following analysis of the flight test data from the first booster-controlled descent in September 2013, SpaceX announced it 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 were ready to test a full recovery of the booster stage. The first flight test was successful; SpaceX said it 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]".[18] 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."[20]

This second flight test took place during the April 2014 Dragon flight to the ISS. SpaceX attached landing legs to the first stage, decelerated it over the ocean and attempt a simulated landing over the water, following the ignition of the second stage on the third cargo resupply mission contracted to NASA. The first stage was successfully slowed down enough for a soft landing over the Atlantic Ocean.[22] SpaceX announced in February 2014 that they intend to continue the tests to land the first-stage booster in the ocean until precision control from hypersonic all the way through subsonic regimes has been proven.[53]

Reusability test plan for post-mission testing[edit]

The post-mission Falcon 9 test plan for these flights calls for the first-stage booster to do a retro-propulsion burn in the upper atmosphere to slow it down and put it on a descent ballistic trajectory to its target landing location, followed by a second burn in the lower atmosphere before the booster reaches the water.[68] SpaceX said in March 2013 that it intended 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". The company said it expected several failures before it can land the vehicle correctly.[14][39][53] 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 that the fourth v1.1 flight would be the second test of the booster controlled descent test profile.[19]

In detailed information disclosed in the Falcon 9 Flight 6 launch license for the CASSIOPE mission, SpaceX said it 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.[68] Then, shortly before hitting the ocean, one engine would be relighted in an attempt to reduce the stage's speed so that it could be recovered. As of 10 September 2013, SpaceX said the experiment had approximately a ten percent chance of success.[69] SpaceX is not performing controlled-descent tests on all Falcon 9 v1.1 flights. For example, to maximize the propellant available for the launch of SES-8 into a Geosynchronous transfer orbit in November 2013, SpaceX did not attempt a full booster-controlled descent test on the second Falcon 9 v1.1 flight.[70]

Test flights[edit]

Ocean test water "landings"[edit]
Test flight 1

After the three-minute boost phase of the September 29 launch—the first flight of the v1.1 version of the Falcon 9—the first stage was reoriented, and three of the nine Merlin 1D engines reignited at high altitude 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".[20] However, the stage began to roll because of 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.[19][20] The company did not expect a successful booster recovery on this flight[71] and, as of March 2013, had said that they did not expect booster recovery following the first several powered-descent tests.[13] 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.[71]

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 the company now believes it has "all the pieces of the puzzle".[18][71][72]

Test flight 2

The second test of controlled-descent hardware and software on the first-stage booster occurred on April 18, 2014,[22] and became the first successful controlled ocean soft touchdown of a liquid-rocket-engine orbital booster.[42] The booster included landing legs for the first time which were extended for the simulated "landing", and the test utilized more powerful gaseous Nitrogen control thrusters to control the aerodynamic-induced rotation that had occurred on the first test flight. The booster stage successfully approached the water surface with no spin and at zero vertical velocity, as designed.[21][73][53]

During the second test, the booster was traveling at a velocity of Mach 10 (6,300 mph; 10,000 km/h)[21] at an altitude of 80,000 meters (260,000 ft)[74] at the time of the high-altitude turn-around maneuver, followed by ignition of three of the nine main engines for the initial deceleration and placement onto its descent trajectory.[73] The "first stage executed a good re-entry burn and was able to stabilize itself on the way down. ... [The] landing in [the] Atlantic [ocean] was good! ... Flight computers continued transmitting [telemetry data] for 8 seconds after reaching the water" and stopped only after the booster went horizontal.[75]

The major modifications for the second booster controlled-descent test flight included changes to both the reentry burn and the landing burn as well as adding increased attitude control system (ACS) capabilities.[30]

SpaceX had projected a low probability of stage recovery following the flight test due to complexity of the test sequence and the large number of steps that would need to be carried out perfectly.[53] The company was careful to label the entire flight test as "an experiment".[76] In an press conference at the National Press Club on April 25, Elon Musk said that the first stage achieved soft landing on the ocean but due to rough seas, the stage was destroyed.[77][78]

Test flight 3

The third test flight of a returned booster was July 14, 2014 on Falcon 9 Flight 10. Whereas the previous test did its "soft landing" some hundreds of kilometers off the Florida coast, this flight aimed for a boost-back trajectory that would attempt the simulated ocean landing much nearer the coast, and closer to the original launch location at Cape Canaveral. Following the third controlled-descent test flight, SpaceX expressed confidence in their ability to successfully land in the future on a "floating launch pad or back at the launch site and refly the rocket with no required refurbishment."[79]

Following the booster loft of the second stage and payload on its orbital trajectory, SpaceX conducted a successful flight test on the spent first stage. The first stage successfully decelerated from hypersonic velocity in the upper atmosphere, made a successful reentry, landing burn, deployment of its landing legs, and touched down on the ocean surface. The first stage was not recovered for analysis as the hull integrity was breached, either on landing or on the subsequent "tip over and body slam".[80] Results of the post-landing analysis showed that the hull integrity was lost as the 46-metre (150 ft)-tall booster rocket body fell horizontally, as planned, onto the ocean surface following the landing.[79]

Test flight 4

The fourth test flight of a returned booster, with a planned water landing, occurred on Falcon 9 Flight 13 which was launched on 21 September 2014.[28] SpaceX has not yet announced the results of the test.

Solid-surface test landings[edit]

The fifth and sixth controlled-descent test flights are projected to attempt a landing on a solid surface, merging the lessons from the high-altitude envelope expansion of the first four controlled-descent flights over water with the low-altitude lessons of the F9R Dev testing in Texas.[28] As of July 2014, the flights were planned for Falcon 9 Flight 14 and Falcon 9 Flight 15, respectively. The "solid surface" was later revealed to be a barge,[79] but the barge has not been named, nor clarified as to whether it will be a jack-up barge or a floating barge.

Popular culture[edit]

The SpaceX reusable rockets have sometimes been referred to as a "Quest to Create a 'Buck Rogers' Reusable Rocket", after the 1920s–1950s comic book character Buck Rogers.[81][82]

References[edit]

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