SpaceX reusable launch system development program
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 back 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.
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. 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. The reusable technology will also be extended to the future launch vehicle for the Mars Colonial Transporter.
- 1 History
- 2 Technologies
- 3 Economic issues
- 4 Technical feasibility
- 5 Test program
- 6 Popular culture
- 7 References
- 8 External links
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. As of March 2014[update], a prototype reusable first stage is being flight tested by SpaceX with the suborbital Grasshopper rocket.
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. 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.
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. 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. In early March 2013, SpaceX successfully tested Grasshopper for a fourth time when it flew to an altitude of over 80 meters (260 ft).
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. 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. 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 2014, 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 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. 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."
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.
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.
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 Restarts are required at both supersonic velocities in the upper atmosphere—in order to decelerate 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.
- new attitude control technology—for 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 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.
- throttleable rocket engine technology is required to reduce engine thrust because the full thrust of even a single Merlin 1D engine exceeds the weight of the nearly empty booster core.
- 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 is approximately 18 meters (60 ft), and they weigh less than 2,100 kilograms (4,600 lb); the deployment system uses 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, requiring around a 30 percent reduction of the maximum payload to orbit in comparison with the expendable Falcon 9. 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.
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. 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." 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.
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." 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.
However, even if SpaceX is successful with the technology, they could lose profits due to reduced demand for their rockets as fewer new launch vehicles are ordered from their factory. Additional demand to make up for this loss would need to come from new markets, and it is uncertain whether such demand would emerge.
As of March 2014[update] 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.
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.
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" is dependent on achieving both complete and rapid reusability.
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."
The return and rapid reuse of an orbital launch system has never been accomplished. In fact, the physics of the Tsiolkovsky rocket equation that describes the forces and physical movement of rockets nearly precludes it. 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. 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.
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.
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), 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
- 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), very-high-velocity (approximately 2.0 km/s; 6,500 km/h; 4,100 mph; Mach 6) 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. 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
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. 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.
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. F9R Dev will be tested at both the Texas facility and also at Spaceport America in New Mexico, 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.
In 2011 when SpaceX initially announced its test program, it projected it would begin flight tests in 2012. In the event, 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 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). Five additional test flights were made in 2013 before Grasshopper v1.0 was retired in October 2013. F9R-Dev flight testing began in April 2014.
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. 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. 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. 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. 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. The Grasshopper test vehicle is now retired.
Falcon 9 Reusable Development Vehicle (F9R Dev)
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. 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. F9R Dev1 will be used for low-altitude test flights in the McGregor, Texas area with projected maximum altitude below 3,000 meters (10,000 ft).
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.
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.
The DragonFly test vehicle is powered by eight SuperDraco engines, arranged in a redundant pattern to support fault-tolerance in the propulsion system design. 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. 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.
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.
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 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.
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]". 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."
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. 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.
Reusability test plan for post-mission testing
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. 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. 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.
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. 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[update], SpaceX said the experiment had approximately a ten percent chance of success. 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.
Test flight history
- 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". 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. The company 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 the company now believes it has "all the pieces of the puzzle".
- Test flight 2
The second test of controlled-descent hardware and software on the first-stage booster occurred on April 18, 2014, and became the first successful controlled ocean soft touchdown of a liquid-rocket-engine orbital booster. 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.
During the second test, the booster was traveling at a velocity of Mach 10 (6,300 mph; 10,000 km/h) at an altitude of 80,000 meters (260,000 ft) 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. 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.
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.
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. The company was careful to label the entire flight test as "an experiment". 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.
- Test flight 3
The third test flight and another attempt at recovery of the returned booster is planned for July 2014 on Falcon 9 Flight 10. Whereas the previous test did its "soft landing" some hundreds of kilometers off the Florida coast, this flight is aiming for a boost-back trajectory that will attempt the simulated ocean landing much nearer the coast, and closer to the original launch location at Cape Canaveral.
- Simberg, Rand (February 8, 2012). "Elon Musk on SpaceX's Reusable Rocket Plans". Popular Mechanics. Retrieved February 7, 2012.
- Belluscio, Alejandro G. (March 7, 2014). "SpaceX advances drive for Mars rocket via Raptor power". NASAspaceflight.com. Retrieved April 3, 2014.
- "SpaceX chief details reusable rocket". Washington Post. September 30, 2011. "Both of the rocket's stages would return to the launch site and touch down vertically, under rocket power, on landing gear after delivering a spacecraft to orbit."
- Wall, Mike (September 30, 2011). "SpaceX Unveils Plan for World's First Fully Reusable Rocket". Space.com. Retrieved October 11, 2011.
- "Falcon 9 Return to Launch Site" (video). SpaceX.com. Archived from the original on June 15, 2011.
- Mark Hamrick, Elon Musk (September 29, 2011). "National Press Club: The Future of Human Spaceflight". NPC video repository (video) (in English) (National Press Club). "(@18:15 It is a very tough engineering problem—and it wasn't something that I thought, wasn't sure it could be solved for a while. But then, just relatively recently, in the last 12 months or so, I've come to the conclusion that it can be solved. And SpaceX is going to try to do it. Now, we could fail. I am not saying we are certain of success here, but we are going to try to do it. And we have a design that, on paper, doing the calculations, doing the simulations, it does work. Now we need to make sure that those simulations and reality agree, because generally when they don't, reality wins. So that's to be determined.)"
- Boyle, Alan (December 24, 2012). "SpaceX launches its Grasshopper rocket on 12-story-high hop in Texas". NBC News / Cosmic Log. Retrieved December 25, 2012.
- "Draft Environmental Assessment for Issuing an Experimental Permit to SpaceX for Operation of the Grasshopper Vehicle at the McGregor Test Site, Texas". Federal Aviation Administration. September 22, 2011. Retrieved November 21, 2013.
- Mohney, Doug (September 26, 2011). "SpaceX Plans to Test Reusable Suborbital VTVL Rocket in Texas". Satellite Spotlight. Retrieved November 21, 2013.
- "NASA Finishes Wind-tunnel Testing of Falcon 9 1st Stage". Space News. May 28, 2012. Retrieved June 26, 2012.
- Coppinger, Rod (November 23, 2012). "Huge Mars Colony Eyed by SpaceX Founder Elon Musk". Space.com. Retrieved November 25, 2012. "much bigger [than Falcon 9], but I don’t think we’re quite ready to state the payload. We’ll speak about that next year."
- "More on Grasshopper's "Johnny Cash hover slam" test". NewSpace Journal. March 9, 2013. Retrieved February 28, 2014.
- Messier, Doug (March 28, 2013). "Dragon Post-Mission Press Conference Notes". Parabolic Arc. Retrieved March 30, 2013. "Q. What is strategy on booster recover? Musk: Initial recovery test will be a water landing. First stage continue in ballistic arc and execute a velocity reduction burn before it enters atmosphere to lessen impact. Right before splashdown, will light up the engine again. Emphasizes that we don’t expect success in the first several attempts. Hopefully next year with more experience and data, we should be able to return the first stage to the launch site and do a propulsion landing on land using legs. Q. Is there a flight identified for return to launch site of the booster? Musk: No. Will probably be the middle of next year."
- Lindsey, Clark (March 28, 2013). "SpaceX moving quickly towards fly-back first stage". NewSpace Watch. Archived from the original on April 11, 2013. Retrieved March 29, 2013. (subscription required (. ))
- Nield, George C. (April 2013). Draft Environmental Impact Statement: SpaceX Texas Launch Site (Report). 1. Federal Aviation Administration / Office of Commercial Space Transportation. http://1.usa.gov/YtxBzo.
- Musk, Elon (April 28, 2013). "First test of the Falcon 9-R (reusable) ignition system". Twitter.com.
- Belfiore, Michael (December 9, 2013). "The Rocketeer". Foreign Policy. Retrieved December 11, 2013.
- Belfiore, Michael (September 30, 2013). "Musk: SpaceX Now Has "All the Pieces" For Truly Reusable Rockets". Popular Mechanics. Retrieved October 17, 2013.
- Amos, Jonathan (September 30, 2013). "Recycled rockets: SpaceX calls time on expendable launch vehicles". BBC News. Retrieved October 2, 2013.
- Messier, Doug (September 29, 2013). "Falcon 9 Launches Payloads into Orbit From Vandenberg". Parabolic Arc. Retrieved September 30, 2013.
- Norris, Guy (April 28, 2014). "SpaceX Plans For Multiple Reusable Booster Tests". Aviation Week. Retrieved May 17, 2014. "The April 17 F9R Dev 1 flight, which lasted under 1 min., was the first vertical landing test of a production-representative recoverable Falcon 9 v1.1 first stage, while the April 18 cargo flight to the ISS was the first opportunity for SpaceX to evaluate the design of foldable landing legs and upgraded thrusters that control the stage during its initial descent."
- Kremer, Ken (April 19, 2014). "SpaceX Makes Strides Towards 1st Stage Falcon Rocket Recovery during Space Station Launch". Universe Today. Retrieved April 19, 2014.
- Gannes, Liz (May 30, 2013). 36:03. "Tesla CEO and SpaceX Founder Elon Musk: The Full D11 Interview (Video)". All Things D (Video interview). Retrieved May 31, 2013. "hopeful that sometime in the next couple of years we'll be able to achieve full and rapid reusability of the first stage—which is about three-quarters of the cost of the rocket—and then with a future design architecture, achieve full reusability."
- Junod, Tom (November 15, 2012). "Triumph of His Will". Esquire. Retrieved April 5, 2014.
- Boyle, Alan (2015-05-21). "Elon Musk's SpaceX Plans DragonFly Landing Tests". NBC News. Retrieved 2015-05-22.
- Shotwell, Gwynne (June 4, 2014). Discussion with Gwynne Shotwell, President and COO, SpaceX. Atlantic Council. Event occurs at 22:35–26:20. Retrieved June 9, 2014. "This technology element [reusable launch vehicle technology] all this innovation is being done by SpaceX alone, no one is paying us to do it. The government is very interested in the data we are collecting on this test series. ... This is the kind of thing that entrepreneurial investment and new entrants/innovators can do for an industry: fund their own improvements, both in the quality of their programs and the quality of their hardware, and the speed and cadence of their operations."
- Shotwell, Gwynne (January 14, 2014). Shotwell statement on reusable technology development. Parabolic Arc. Event occurs at 16:15–17:05. Retrieved January 15, 2014. "[Rocket stages are not passively stable on rentry from orbit], ... so there is a lot of software involved, a lot of guidance navigation and control involved, and a lot of thermal protection required; so we have to make advances in all those areas. We also have to restart the engines supersonically."
- Gwynne Shotwell (March 21, 2014). Broadcast 2212: Special Edition, interview with Gwynne Shotwell (mp3) (audio file) (in English). The Space Show. Event occurs at 51;50–52;55. 2212. Archived from the original on March 22, 2014. Retrieved March 22, 2014.
- Rosenberg, Zach (March 21, 2013). "SpaceX Merlin 1D qualified for flight". Flightglobal. Retrieved March 18, 2014.
- "SpaceX Falcon 9 v1.1 Data Sheet". Space Launch Report. March 12, 2014. Retrieved March 18, 2014.
- Boyle, Alan (May 2, 2013). "SpaceX's Elon Musk shows off Grasshopper test rocket's latest hop". NBC News. Retrieved March 9, 2013.
- "Woo-hoo! Awesome SpaceX Grasshopper "Hover-Slam" Rocket Launch Doubles Previous Height". Daily Kos. March 9, 2013.
- "Grasshopper 325m Test | Single Camera (Hexacopter)". YouTube.com (SpaceX). June 14, 2013. Retrieved July 6, 2013.
- "Landing Legs". SpaceX.com. July 29, 2013. Retrieved December 4, 2013. "The Falcon 9 first stage carries landing legs which will deploy after stage separation and allow for the rocket’s soft return to Earth. The four legs are made of state-of-the-art carbon fiber with aluminum honeycomb. Placed symmetrically around the base of the rocket, they stow along the side of the vehicle during liftoff and later extend outward and down for landing."
- "Falcon Heavy Landing Legs". SpaceX.com. April 12, 2013. Retrieved December 4, 2013. "The Falcon Heavy first stage center core and boosters each carry landing legs, which will land each core safely on Earth after takeoff. After the side boosters separate, the center engine in each will burn to control the booster’s trajectory safely away from the rocket. The legs will then deploy as the boosters turn back to Earth, landing each softly on the ground. The center core will continue to fire until stage separation, after which its legs will deploy and land it back on Earth as well. The landing legs are made of state-of-the-art carbon fiber with aluminum honeycomb. The four legs stow along the sides of each core during liftoff and later extend outward and down for landing."
- Lindsey, Clark (May 2, 2013). "SpaceX shows a leg for the "F-niner"". NewSpace Watch. Archived from the original on June 30, 2013. Retrieved May 2, 2013. (subscription required (. "F9R (pronounced F-niner) shows a little leg. Design is a nested, telescoping piston w A frame... High pressure helium. Needs to be ultra light." ))
- Bergin, Chris (2014-02-28). "SpaceX outlines CRS-3 landing legs plan toward first stage recovery ambitions". NASAspaceflight.com. Retrieved 2014-05-10.
- Foust, Jeff (March 24, 2014). "Reusability and other issues facing the launch industry". The Space Review. Retrieved April 1, 2014.
- Boozer, R.D. (March 10, 2014). "Rocket reusability: a driver of economic growth". The Space Review. Retrieved March 25, 2014.
- Belfiore, Michael (April 22, 2014). "SpaceX Brings a Booster Safely Back to Earth". MIT Technology Review. Retrieved April 25, 2014.
- Kothari, Ajay P. (April 14, 2014). "Robust and reusable?". The Space Review. Retrieved April 14, 2014.
- Messier, Doug (January 14, 2014). "Shotwell: Reusable Falcon 9 Would Cost $5 to $7 Million Per Launch". Parabolic Arc. Retrieved January 15, 2014.
- Belfiore, Michael (March 13, 2014). "SpaceX Set to Launch the World's First Reusable Booster". MIT Technology Review. Retrieved March 14, 2014. "SpaceX is counting on lower launch costs to increase demand for launch services. But Foust cautions that this strategy comes with risk. 'It's worth noting,' he says, 'that many current customers of launch services, including operators of commercial satellites, aren't particularly price sensitive, so thus aren't counting on reusability to lower costs.' That means those additional launches, and thus revenue, may have to come from markets that don't exist yet. 'A reusable system with much lower launch costs might actually result in lower revenue for that company unless they can significantly increase demand,' says Foust. 'That additional demand would likely have to come from new markets, with commercial human spaceflight perhaps the biggest and best-known example.'"
- Gwynne Shotwell (March 21, 2014). Broadcast 2212: Special Edition, interview with Gwynne Shotwell (mp3) (audio file) (in English). The Space Show. Event occurs at 08:15–11:20. 2212. Archived from the original on March 22, 2014. Retrieved March 22, 2014. "[Falcon 9 v1.1] vehicle has thirty percent more performance than what we put on the web and that extra performance is reserved for us to do our reusability and recoverability [tests] ... current vehicle is sized for reuse."
- Bergin, Chris (April 22, 2014). "Rockets that return home – SpaceX pushing the boundaries". NASAspaceflight.com. Retrieved April 23, 2014.
- "SpaceX’s Plan Shows Aggressive Investment In R&D". Aviation Week. 2014-04-28. Retrieved 2014-05-17.
- "Methods and apparatus for reusable launch platform and reusable spacecraft". USPTO. Retrieved March 18, 2014.
- "National Press Club: The Future of Human Spaceflight". September 29, 2011.
- Abbott, Joseph (May 8, 2013). "SpaceX's Grasshopper leaping to NM spaceport". Waco Tribune. Retrieved October 25, 2013.
- Foust, Jeff (May 5, 2014). "Following up: reusability, B612, satellite servicing". The Space Review. Retrieved May 6, 2014.
- Wang, Brian (March 23, 2013). "Spacex May try to "land / recover" the first stage of it next Falcon 9 v1.1 launch this summer". Next Big Future. Retrieved April 6, 2013.
- Klotz, Irene (February 24, 2014). "SpaceX Falcon Rocket to Test Landing Legs". Discovery News. Retrieved February 25, 2014.
- Klotz, Irene (September 27, 2011). "A rocket that lifts off—and lands—on launch pad". NBC News. Retrieved November 23, 2011.
- Lindsey, Clark (October 2, 2012). "A 2nd-gen Grasshopper + A new video of first hop". NewSpace Watch. Archived from the original on January 4, 2013. Retrieved November 4, 2012. (subscription required (. ))
- Lindsey, Clark (May 7, 2013). "SpaceX to test Grasshopper reusable booster at Spaceport America in NM". NewSpace Watch. Archived from the original on June 16, 2013. Retrieved May 7, 2013. (subscription required (. ))
- "Grasshopper flies to its highest height to date". Facebook.com. SpaceX. October 12, 2013. Retrieved October 14, 2013. "WATCH: Grasshopper flies to its highest height to date - 744 m (2441 ft) into the Texas sky. http://youtu.be/9ZDkItO-0a4 This was the last scheduled test for the Grasshopper rig; next up will be low altitude tests of the Falcon 9 Reusable (F9R) development vehicle in Texas followed by high altitude testing in New Mexico."
- Lindsey, Clark (October 12, 2011). "Space law panel + Grasshopper news". HobbySpace.com. Archived from the original on November 18, 2011. Retrieved November 23, 2011.
- Clark, Stephen (July 9, 2012). "Reusable rocket prototype almost ready for first liftoff". Spaceflight Now. Retrieved July 13, 2012. "SpaceX has constructed a half-acre concrete launch facility in McGregor, and the Grasshopper rocket is already standing on the pad, outfitted with four insect-like silver landing legs."
- Clark, Stephen (September 24, 2012). "SpaceX's reusable rocket testbed takes first hop". Spaceflight Now. Retrieved September 25, 2012.
- Klotz, Irene (October 17, 2013). "SpaceX Retires Grasshopper, New Test Rig To Fly in December". Space News. Retrieved October 21, 2013.
- "Grasshopper Completes Highest Leap to Date". SpaceX.com. March 10, 2013. Retrieved April 21, 2013.
- Boyle, Alan (August 14, 2013). "SpaceX's Grasshopper test rocket flies sideways successfully". NBC News. Retrieved August 15, 2013.
- Abbott, Joseph (April 17, 2014). "Grasshopper's successor flies at SpaceX's McGregor site". Waco Tribune. Retrieved April 18, 2014.
- James, Michael; Salton, Alexandria; Downing, Micah (November 12, 2013). "Draft Environmental Assessment for Issuing an Experimental Permit to SpaceX for Operation of the Dragon Fly Vehicle at the McGregor Test Site, Texas, May 2014 – Appendices". Blue Ridge Research and Consulting, LCC. p. 12.
- Abbott, Joseph (2014-05-22). "Grasshopper to DragonFly: SpaceX seeks approval for new McGregor testing". Waco Tribune. Retrieved 2014-05-23.
- Messier, Doug (September 10, 2013). "A Preview of Falcon 9′s Flight From Vandenberg". Parabolic Arc. Retrieved September 11, 2013.
- Klotz, Irene (September 6, 2013). "Musk Says SpaceX Being "Extremely Paranoid" as It Readies for Falcon 9's California Debut". Space News. Retrieved September 13, 2013.
- de Selding, Peter B. (November 27, 2013). "Why the World's 2nd Largest Satellite Fleet Operator Agreed To Be SpaceX's 1st Customer for a Launch to Geo". Space News. Retrieved November 28, 2013.
- Wall, Mike (October 17, 2013). "SpaceX Hit Huge Reusable Rocket Milestone with Falcon 9 Test". Space.com. Retrieved December 5, 2013.
- Vaughan, Adam (October 25, 2013). "12 interesting things we learned from Tesla's Elon Musk this week". The Guardian. Retrieved October 26, 2013. "we managed to re-enter the atmosphere, not break up like we normally do, and get all way down to sea level."
- "SpaceX CRS-3 Mission Press Kit: Cargo Resupply Services Mission". NASA. March 2014. Retrieved March 15, 2014.
- Boyle, Alan (April 18, 2014). "Cargo Launch and Rocket Test Add Up to 'Happy Day' for SpaceX". NBC News. Retrieved April 20, 2014.
- Clark, Stephen (April 14, 2014). "Recovery crews positioned to retrieve Falcon 9 first stage". Spaceflight Now. Retrieved April 14, 2014.
- Amos, Jonathan (April 25, 2014). "SpaceX rocket stage in 'soft landing'". BBC News. Retrieved April 26, 2014.
- Musk, Elon (April 25, 2014). "SpaceX Press Conference at the National Press Club". YouTube.com (National Press Club). Retrieved April 26, 2014.
- "SpaceX Continues its Quest to Create a "Buck Rogers" Reusable Rocket". 21st Century Tech. March 15, 2013. Retrieved March 24, 2014.
- Elon Musk, Scott Pelley (March 30, 2014). Tesla and SpaceX: Elon Musk's industrial empire (video and transcript). CBS. Event occurs at 03:50–04:10. Retrieved March 31, 2014. "Only four entities have launched a space capsule into orbit and successfully brought it back: the United States, Russia, China, and Elon Musk. This Buck Rogers dream started years ago"
- SpaceX Reusable Launch System, concept video released prior to completion of the system design, 3:58, September 29, 2011.
- Video of Grasshopper low-altitude, low-velocity landing test, 4th test flight, March 8, 2013.
- Video of 7th Grasshopper low-altitude test flight, including a 100-meter lateral maneuver, August 13, 2013.
- Video of 8th and final low-altitude Grasshopper v1.0 test flight, to 744 meters (0.462 miles), October 7, 2013.
- Low-resolution photograph of the Falcon 9 booster controlled-descent test on September 29, 2013, just moments before impacting the Atlantic ocean.
- Video of Falcon 9 Reusable (F9R) test flight, to 250 meters (0.16 miles), hovering and then landing just next to the launch stand, April 18, 2014.
- Video of CRS-3 Booster Stage Landing, Low Quality