Falcon 9 booster controlled-descent and landing tests

Falcon 9 Flight 20's first stage successfully landed for the first time. The landing, attempted for the first time on land at Landing Zone 1 at Cape Canaveral Air Force Station, followed a flight of 11 Orbcomm OG2 satellites.

The Falcon 9 first stage landing tests are a series of controlled-descent flight tests conducted by SpaceX beginning in 2013 which continued through December 2015.The program objective was to execute a controlled-descent re-entry into Earth's atmosphere after Falcon 9 rocket first stages complete the boost phase of an orbital flight. Some tests included an attempt at softly landing the first stage of the rocket in the ocean, or on an Autonomous spaceport drone ship—commissioned by SpaceX to provide a hard landing surface on a floating vessel—or on terra firma at Landing Zone 1 on the east coast of Florida.[1] Test flights began in September 2013. As of April 2016, eleven test flights have been conducted, two of which achieved a soft landing and recovery of the booster: Falcon 9 Flight 20 on the ground upon its first attempt and flight 23 finally achieving a vertical landing at sea after four previous attempts.

The first stage descent tests are a part of the larger SpaceX reusable launch system development program, which also includes a number of technology development activities and low-altitude test flights at their McGregor, Texas facility. The program's goal is to privately develop reusable rocket technology, including vertical-landing technology.

The first stages used on orbital launches have been, prior to 2015, typically discarded in the ocean once the ascent is complete. A reusable rocket "would dramatically reduce the cost of launches," according to CNBC.[2] The over-water tests occurred in both the Pacific Ocean, south of Vandenberg Air Force Base, and the Atlantic Ocean, east of Cape Canaveral Air Force Station.

The first flight test occurred on 29 September 2013, after the second stage with the CASSIOPE and nanosat payloads separated from the first stage. Descent and simulated landing tests have continued into 2014 and 2015, with the second flight test having occurred on April 18, 2014,[3][4][5][6] and the fifth, sixth, and seventh tests occurred in January, February, and April 2015, respectively. The first attempt to land a Falcon 9 on land was accomplished, with a successful recovery of the first stage, in December 2015.[7] The next successful landing, the first at sea, occurred on April 8, 2016.

History

SpaceX first announced that it would instrument and equip subsequent Falcon 9 first-stages as controlled descent test vehicles, with plans for over-water propulsively-decelerated simulated landings, in March 2013. They stated at the time that they expected to begin these flight tests in 2013, with an attempt to return the vehicle to the launch site for a powered landing no earlier than mid-2014.[8]

In the event, they did execute the first flight test in 2013, but continued the over-water testing into 2015. Following analysis of the flight test data from the first first stage-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 first 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]".[9] Musk said that "the next attempt to [recover] the Falcon 9 first stage [would] be on the fourth flight of the upgraded rocket. This would be [the] third commercial Dragon cargo flight to ISS."[10]

This second flight test took place during the April 2014 Dragon flight to the ISS. SpaceX attached landing legs to the first stage, decelerated the stage over the ocean and attempted 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 sufficiently for a soft landing over the Atlantic Ocean.[5] SpaceX announced in February 2014 that they intended to continue the tests to land the first stage in the ocean until precision control from hypersonic all the way through subsonic regimes has been proven.[6]

Further tests starting with the first stage of the CRS-5 vehicle have involved the Autonomous Spaceport Drone Ship.[1] The ship has been used for two returning cores as of April 2015: CRS-5 and CRS-6. An attempt was made with the returning first stage from the DSCOVR mission, but the landing was called off due to abnormally high sea conditions.[11]

Reusability test plan for post-mission testing

Falcon 9 v.1.1 thermal imaging of the controlled-descent test of the first stage from stage separation onward, on Falcon 9 Flight 13, 21 September 2014. Includes footage as the first stage maneuvers out of the second stage plume; coasting near peak altitude of approximately 140 km (87 mi); boost-back burn to limit downrange translation; preparing for the reentry burn; and the reentry burn from approximately 70 km (43 mi) to 40 km (25 mi) altitude. Does not include the landing burn as clouds obscured the infrared imaging at low altitude.

The post-mission Falcon 9 test plan for the earliest flight tests called for the first stage 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 first stage reaches the water.[12] SpaceX announced in March 2013 that it intended to conduct such tests on Falcon 9 v1.1 launch vehicles 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.[6][13]

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.[12] 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.[14]

SpaceX would not perform controlled-descent tests on all Falcon 9 v1.1 flights.[15] In September 2013, SpaceX announced that the fourth Falcon 9 v1.1 flight—which occurred in April 2014[16]—would be the second test of the first stage controlled descent test profile.[3]

Whereas the early tests restarted the engines only twice, by the fourth flight test, in September 2014, SpaceX was reigniting the main engines three times to accomplish its controlled-descent test objectives (although only three of the nine engines are reignited each time): a boost-back burn, a reentry burn, and a landing burn. The boost-back burn limits downrange translation of the used stage; the reentry burn (from approximately 70 to 40 km (43 to 25 mi) altitude) is used to control the descent and deceleration profile at atmospheric interface; and the landing burn completes the deceleration from terminal velocity to zero velocity at the landing surface.[17][18]

Test flights

Ocean water test descents

Falcon 9 Flight 6

After the three-minute boost phase of the 29 September 2013 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".[10] 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 first stage 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.[3][10] The company did not expect a successful first stage recovery on this flight[19] and, as of March 2013, had said that they did not expect first stage recovery following the first several powered-descent tests.[8] The test was successful—with substantial test milestones achieved and a great deal of engineering test data collected—but the first stage was not successfully recovered from the ocean.[19]

SpaceX tested a large amount of new technology on the flight, and that—coupled with the technology advancements made on the Grasshopper technology demonstrator—meant the company now believed it had "all the pieces of the puzzle".[9][19][20]

Falcon 9 Flight 9

The second test of controlled-descent hardware and software on the first stage occurred on April 18, 2014,[5] and became the first successful controlled ocean soft touchdown of a liquid-rocket-engine orbital first stage.[21][22] The first stage 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 first stage successfully approached the water surface with no spin and at zero vertical velocity, as designed.[6][23][24]

During the second test, the first stage was traveling at a velocity of Mach 10 (6,300 mph; 10,000 km/h)[23] at an altitude of 80,000 meters (260,000 ft)[25] 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.[24] 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 first stage went horizontal.[26]

The major modifications for the second first stage 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.[27]

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.[6] The company was careful to label the entire flight test as "an experiment".[28] 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.[29][30]

Falcon 9 Flight 10

The third test flight of a returned first stage was 14 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 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."[31]

Following the first stage 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 speed in the upper atmosphere, made a successful reentry, landing burn, and 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".[32] Results of the post-landing analysis showed that the hull integrity was lost as the 46-metre (150 ft)-tall first stage fell horizontally, as planned, onto the ocean surface following the landing.[31]

Falcon 9 Flight 13

Infrared thermal imagery of Falcon 9 SpaceX CRS-4 launch. The larger image was captured shortly after second stage separation from the first stage: the top of the first stage appears as a dim dot below the larger plume. In the inset, the restarted first stage engines power the stage.

The fourth test flight of a returned first stage, with a planned water landing, occurred on Falcon 9 Flight 13 which was launched on 21 September 2014.[33] and the first stage flew a profile approaching a zero-velocity at zero-altitude simulated landing on the sea surface.[18] SpaceX made no attempt to recover the first stage, since earlier tests had confirmed that the 14-story tall first stage would not survive the tip-over event into the sea.

One month later, detailed thermal imaging infrared sensor data and video were released of the controlled-descent test. The data was collected by NASA in a joint arrangement with SpaceX as part of research on retropropulsive deceleration technologies in order to develop new approaches to Mars atmospheric entry. A key problem with propulsive techniques is handling the fluid flow problems and attitude control of the descent vehicle during the supersonic retropropulsion phase of the entry and deceleration. All phases of the nighttime flight test on the first stage were successfully imaged except for the final landing burn, as that occurred below the clouds where the IR data was not visible.[18] The research team is particularly interested in the 70–40-kilometer (43–25 mi) altitude range of the SpaceX "reentry burn" on the Falcon 9 Earth-entry tests as this is the "powered flight through the Mars-relevant retropulsion regime" that models Mars entry and descent conditions.[17]

Falcon 9 Flight 15

Falcon 9 Flight 15 first stage re-entry with grid fins. Onboard camera view

SpaceX had planned to make the sixth controlled-descent test flight and second[34] landing attempt on the floating recovery ship no earlier than 11 February (see below for first attempt). This would be a "potentially historic rocket launch and landing" because the first stage would attempt a test landing on a drone ship, something that "was unheard of" five years earlier.[34][35][36]

According to regulatory paperwork filed in 2014, SpaceX plans had called for the sixth test flight to occur on a late January 2015 launch attempt. However, after the completion of the fifth test flight, and with some damage being incurred by the drone ship in the unsuccessful landing, it was not clear if the sixth test would still be able to occur only a few weeks later.[37] That was resolved within days of the ship's return to Jacksonville, and by 15 January SpaceX was unambiguous about its plans to attempt a landing of the first stage following the boost phase of the Deep Space Climate Observatory mission.[36]

However, in a statement by SpaceX, the drone ship was in conditions "with waves reaching up to three stories in height crashing over the decks". Additionally, one of the four thrusters that keep the barge in a constant position had malfunctioned, making station-keeping difficult. For these reasons, the post-launch flight test did not involve the barge, but instead attempted a soft landing over water.[38]

The test was successful, and the first stage of the Falcon 9 landed "nicely vertical" with an accuracy of 10 meters from the target location in the ocean.[39]

Therefore, this test represented the fifth ocean landing, and the sixth overall Falcon 9 first stage controlled-descent test.

Landing tests

Depiction of Falcon 9 landing trajectory in floating-platform recovery tests

As of April 2016, SpaceX has attempted six landings of a first stage on a solid surface. Many of the test objectives were achieved on the first attempt, including bringing the stage to the specific location of the floating platform. Also a large amount of test data obtained from the first use of grid fin control surfaces used for more precise reentry positioning. However the touchdown on the corner of the barge was a hard landing and most of the rocket body fell into the ocean and sank.

In July 2014, SpaceX had announced that the fifth and sixth controlled-descent test flights would attempt landings 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.[33] At that time, the tests were stated to be planned for the 14th and 15th Falcon 9 flights, and the "solid surface" was not further described. In the event, the 14th Falcon 9 flight became the fifth controlled-descent test and first attempted landing on floating platform, but the 15th F9 flight was redirected to target another over-ocean landing because of excessive sea state conditions.

Falcon 9 Flight 14

In October 2014, SpaceX clarified that the "solid surface" would be a floating platform that was then being built for SpaceX in Louisiana, and confirmed that they would attempt to land the first stage of the fourteenth Falcon 9 flight on the platform.[40] For the landing to be successful, the 18 m (60 ft)-wide span of the rocket landing legs must not only land within the 52 m (170 ft)-wide barge deck, but would need to also deal with large ocean swell and GPS errors.[41] In late November, SpaceX revealed that the barge—now designated the Autonomous spaceport drone ship—would be capable of autonomous operation and would not need to be anchored or moored.[1] The fifth flight of the over-ocean controlled descent test series—referred to as a "historic core return attempt" by NASA SpaceFlight[42]—was the first orbital flight to test the grid fin aerodynamic control surfaces that had previously been tested only on a low-altitude, low-speed test flight on the F9R Dev1 prototype vehicle in early 2014. The addition of grid fins, with continuation of the control authority obtained from gimbaling the engines as on previous test flights, was projected to improve the landing accuracy to 10 m (33 ft); the landing accuracy on the previous 4 controlled-descent test flights was only 10 km (6.2 mi).[43] Prior to the flight, SpaceX projected that the likelihood of successfully landing on the platform on the first try was 50 percent or less.[41]

The first flight attempt for the test hardware occurred on 10 January 2015 on the CRS-5 flight contracted to NASA. The controlled-descent flight started approximately three minutes after launch, following the second stage separation event,[42] when the first stage was approximately 80 km (50 mi) high and moving at a velocity of Mach 10 (6,300 mph; 10,000 km/h).[44]

The SpaceX webcast indicated that the boostback burn and reentry burns for the descending first stage occurred, and that the descending rocket then went "below the horizon," as expected, which eliminated the live telemetry signal. Shortly thereafter, SpaceX released information that the rocket did get to the drone spaceport ship as planned, but "landed hard ... Ship itself is fine. Some of the support equipment on the deck will need to be replaced."[45] Musk later elaborated that the rocket's flight-control surfaces had exhausted their supply of hydraulic fluid prior to impact.[46] Musk posted photos of the impact while talking to John Carmack on Twitter. SpaceX later released a video of the impact on Vine.[47]

Falcon 9 Flight 17

Falcon 9 first stage attempts landing on ASDS after second stage with CRS-6 continued onto orbit. Landing legs are in the midst of deploying.
Falcon 9 Flight 17's first stage attempting a controlled landing on the Autonomous Spaceport Drone Ship following the launch of CRS-6 to the International Space Station.

A seventh test flight of the first stage controlled-descent profile occurred on 14 April 2015 on Falcon 9 Flight 17, which carried CRS-6 to the International Space Station. This was SpaceX's second attempt to land on a floating platform. The first stage was fitted with grid fins and landing legs to facilitate the post-mission test. If successful, this would have been the first time in history that a rocket first stage was returned to a vertical landing.[48]

An early report from Elon Musk suggested that the first stage made a hard landing on the drone ship.[49] Musk later clarified that the bipropellant valve was stuck, and therefore the control system could not react rapidly enough for a successful landing.[50] On 15 April, SpaceX released a video of the terminal phase of the descent, the landing, the tip over, and the resulting deflagration as the stage broke up on the deck of the ASDS.[51]

Flight 20: first landing on ground pad

Main article: Falcon 9 Flight 20
Falcon 9 Flight 20 after landing

The first attempt to land the first stage of the Falcon 9 on land, near the launch site, occurred on Falcon 9 Flight 20—the first launch of the Falcon 9 full thrust version of Falcon 9—on 21 December 2015. The landing was successful, and the first stage was recovered.[7][52][53]

SpaceX applied to the Federal Aviation Administration (FAA) US regulatory authority, to make the on-land landing test, the 8th first stage descent test overall, at the Landing Zone 1 facility—the former CCAFS Launch Complex 13—that SpaceX had recently built at Cape Canaveral Air Force Station.[54] SpaceX received clearance from the FAA to attempt a landing in Landing Zone 1 at Cape Canaveral for this launch attempt following FAA's findings that the landing will have minimal damaging environmental effects.[55][56] Additionally, NASA planned to close the NASA Causeway near the launch and landing site and significantly increase the size of exclusion zones during the launch and landing attempt.[57][58]

Falcon 9 Flight 20 first stage moments before touchdown on Landing Zone 1

The decision to attempt a landing on land, or on the ASDS floating platform, was not made final until the day of the launch. The final decision to attempt a land-based landing was made based on a number of factors, including weather at the potential landing sites.

Flight 20 launched at 20:29 EST on 21 December 2015 (01:29 UTC on 22 December 2015). About 9 minutes and 45 seconds later, the first stage landed successfully.[7][52][59]

As of December 2015, the SpaceX plan is to not fly the Falcon 9 Flight 20 first stage again. Rather, the rocket will be moved to the new SpaceX launch pad several miles to the north leased from the adjacent Kennedy Space Center and a static fire test will be performed. After the hot fire test, the vehicle will be evaluated in detail by SpaceX to assess capabilities for reflight of the launch vehicle design after future landings.[60]

On 31 December, SpaceX announced that no damage had been found on the stage and that it was ready to perform a static fire again.[61][62] On 13 January 2016, Florida Today journalist James Dean reported that SpaceX could run the static fire test on the recovered first stage as early as Thursday, 14 January. SpaceX had initially moved the booster to their hangar at LC 39A, but they moved the stage to LC 40—the pad from which it was launched on 22 December 2015—on 12 January.[63] On 15 January 2016, SpaceX conducted the static fire test on the recovered booster and reported that the test was good overall but one of the outer engines, "engine 9", showed thrust fluctuations. Elon Musk reported that this may have been due to debris ingestion.[64]

Falcon 9 Flight 21

Landing approach of Falcon 9 Flight 21, which touched down at an acceptable velocity

Flight 21, the final launch of a Falcon 9 v1.1, carried the Jason 3 payload. At one point this was the first possible opportunity for an attempt to land the first stage on land,[48] but the launches were reordered following the loss of Falcon 9 Flight 19 in June 2015. Jason-3 was successfully launched on 17 January 2016, and while the first stage successfully slowed to the correct touchdown speed,[65] the lockout collet on one of the landing legs did not latch correctly, which caused the rocket to fall over and explode after touching down.[66] Elon Musk noted that ice buildup on the collet from the high-humidity launch conditions may have led to the failure of the latch.[67][68][69]

Falcon 9 Flight 22

SES-9 massed approximately 5,271 kilograms (12,000 lb) at launch,[70][71] the largest Falcon 9 payload yet to a highly-energetic geosynchronous transfer orbit (GTO). Consequently, the Falcon 9 first stage followed a ballistic trajectory after separation and re-entered the atmosphere at high velocity with very little fuel to mitigate potential aerodynamic damage.

Therefore, SpaceX could only attempt to land its Falcon 9 booster on a sea barge, the Of Course I Still Love You, in the Atlantic Ocean. SpaceX founder and CEO Elon Musk confirmed in a tweet that the landing attempt was unsuccessful.[72] "Rocket landed hard on the droneship. Didn't expect this one to work (v hot reentry), but next flight has a good chance."[73]

Flight 23: first landing on drone ship

Falcon 9 Flight 23 landing successfully on droneship

On April 8, 2016, Falcon 9 Flight 23, the third flight of the full-thrust version, delivered the SpaceX CRS-8 cargo on its way to the International Space Station while the first stage conducted a boostback and re-entry maneuver over the Atlantic ocean. Nine minutes after liftoff, the booster landed vertically on the droneship Of Course I Still Love You, 300 km from the Florida coastline, achieving a long-sought-after milestone for the SpaceX reusability development program.[74]

Flight 24: second landing on drone ship

On May 6, 2016, Falcon 9 Flight 24, the fourth flight of the full-thrust version, delivered the JSAT_Corporation JCSAT-14 satellite on its way to GEO while the first stage conducted re-enty burn without first doing a boostback burn then a landing burn as it approached the droneship Of Course I Still Love You. The booster successfully landed vertically on the droneship . This landing was more difficult than the previous droneship landing due to the launch being to a Geostationary transfer orbit meaning the booster at separation was travelling about 8350 Km/h compared to around 6650km/h on the previous launch to Low Earth orbit.[75][76]

Future tests

SpaceX aims to return a number of first stages in both land and drone ship landings to clarify the procedures needed to re-use flown boosters. The company hopes to be able to begin offering flown Falcon 9 rocket stages by the end of 2016, aiming for a re-flight of a stage.[77] Musk indicated in January 2016 that he thought the likelihood of successful landings for each of the attempted landings in 2016 would be approximately 70 percent, hopefully rising to 90 percent in 2017, and cautioned that we expect "a few more RUDs" (Rapid Unscheduled Disassembly, Musk's euphemism to denote explosion on impact).[78]

See also

References

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  2. ↑ Wells, Jane (13 January 2015). "SpaceX, Elon Musk and the reusable rocket dream". CNBC. Comcast. Retrieved 23 April 2015.
  3. 1 2 3 Amos, Jonathan (September 30, 2013). "Recycled rockets: SpaceX calls time on expendable launch vehicles". BBC News. Retrieved October 2, 2013.
  4. ↑ Boozer, R.D. (March 10, 2014). "Rocket reusability: a driver of economic growth". The Space Review. Retrieved March 25, 2014.
  5. 1 2 3 Kremer, Ken (April 19, 2014). "SpaceX Makes Strides Towards 1st Stage Falcon Rocket Recovery during Space Station Launch". Universe Today. Retrieved April 19, 2014.
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  8. 1 2 Messier, Doug (March 28, 2013). "Dragon Post-Mission Press Conference Notes". Parabolic Arc. Retrieved March 30, 2013. Q. What is strategy on first stage 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 first stage? Musk: No. Will probably be the middle of next year.
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  18. 1 2 3 Morring, Frank, Jr. (October 20, 2014). "NASA, SpaceX Share Data On Supersonic Retropropulsion : Data-sharing deal will help SpaceX land Falcon 9 on Earth and NASA put humans on Mars". Aviation Week. Archived from the original on 27 October 2014. Retrieved March 28, 2015. [The] partnership between NASA and SpaceX is giving the U.S. space agency an early look at what it would take to land multi-ton habitats and supply caches on Mars for human explorers, while providing sophisticated infrared (IR) imagery to help the spacecraft company develop a reusable launch vehicle. After multiple attempts, airborne NASA and U.S. Navy IR tracking cameras ... captured a SpaceX Falcon 9 in flight as its first stage [fell] back toward Earth shortly after second-stage ignition and then reignit[ed] to lower the stage toward a propulsive "zero-velocity, zero-altitude" touchdown on the sea surface.
  19. 1 2 3 Wall, Mike (October 17, 2013). "SpaceX Hit Huge Reusable Rocket Milestone with Falcon 9 Test". Space.com. Retrieved December 5, 2013.
  20. ↑ 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.
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  23. 1 2 Norris, Guy (April 28, 2014). "SpaceX Plans For Multiple Reusable first stage 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.
  24. 1 2 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.'
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  32. ↑ "SpaceX Falcon Rocket Sends Up a Six-Pack of Satellites". NBC. July 14, 2014. Retrieved July 15, 2014. Musk: 'Rocket first stage reentry, landing burn & leg deploy were good, but lost hull integrity right after splashdown (aka kaboom) ... Detailed review of rocket telemetry needed to tell if due to initial splashdown or subsequent tip over and body slam.'
  33. 1 2 Berger, Brian (July 21, 2014). "SpaceX Releases Footage of Falcon 9 First-stage Splashdown". SpaceNews. Retrieved July 23, 2014.
  34. 1 2 Graham, William (February 8, 2015). "SpaceX Falcon 9 ready for DSCOVR mission". NASASpaceFlight.com. Retrieved February 8, 2015.
  35. ↑ Orwig, Jessica (February 5, 2015). "SpaceX will attempt a potentially historic rocket launch and landing this weekend". Business Insider. Retrieved February 7, 2015.
  36. 1 2 Bergin, Chris (January 16, 2015). "DSCOVR and Recover: SpaceX chase the cigar with next Falcon 9 mission". NASASpaceFlight.com. Retrieved January 17, 2015.
  37. ↑ Clark, Stephen (January 10, 2015). "Dragon successfully launched, rocket recovery demo crash lands". Spaceflight Now. Retrieved January 10, 2015.
  38. ↑ Wall, Mike (February 11, 2015). "SpaceX Won't Try Rocket Landing on Drone Ship After Satellite Launch Today". Space.com. Retrieved February 11, 2015.
  39. ↑ Hull, Dana (February 11, 2015). stage-on-ship-amid-rough-seas "SpaceX Launches Satellite as Rocket Recovery Is Scrapped" Check |url= value (help). Bloomberg. Bloomberg. Retrieved February 12, 2015.
  40. ↑ Foust, Jeff (October 25, 2014). "Next Falcon 9 Launch Could See First-stage Platform Landing". Space News. Retrieved October 25, 2014.
  41. 1 2 Bergin, Chris (November 18, 2014). "Pad 39A – SpaceX laying the groundwork for Falcon Heavy debut". NASA SpaceFlight. Retrieved November 21, 2014.
  42. 1 2 Graham, William (January 5, 2015). "SpaceX set for Dragon CRS-5 launch and historic core return attempt". NASASpaceFlight.com. Retrieved January 6, 2015. While the Falcon 9’s second stage continues to orbit with the Dragon spacecraft, its first stage will execute a series of maneuvers which SpaceX hope will culminate in a successful landing atop a floating platform off the coast of Florida. The demonstration follows successful tests during two previous launches where the first stage has been guided to a controlled water landing, however the stage has not been recoverable on either previous attempt. ... Achieving a precision landing on a floating platform is an important milestone for SpaceX as they attempt to demonstrate their planned flyback recovery of the first stage of the Falcon 9.
  43. ↑ "X MARKS THE SPOT: FALCON 9 ATTEMPTS OCEAN PLATFORM LANDING". SpaceX. December 16, 2014. Retrieved December 17, 2014. A key upgrade to enable precision targeting of the Falcon 9 all the way to touchdown is the addition of four hypersonic grid fins placed in an X-wing configuration around the vehicle, stowed on ascent and deployed on reentry to control the stage’s lift vector. Each fin moves independently for roll, pitch and yaw, and combined with the engine gimbaling, will allow for precision landing – first on the autonomous spaceport drone ship, and eventually on land.
  44. ↑ "SpaceX CRS-% Mission: Cargo Resupply Services" (PDF). nasa.gov. NASA. December 2014. Retrieved January 17, 2015. Approximately 157 seconds into flight, the first-stage engines are shut down, an event known as main-engine cutoff, or MECO. At this point, Falcon 9 is 80 kilometers (50 miles) high, traveling at 10 times the speed of sound.
  45. ↑ Musk, Elon. "Post-launch Twitter news releases". SpaceX. Retrieved January 10, 2015. Rocket made it to drone spaceport ship, but landed hard. Close, but no cigar this time. Bodes well for the future tho. ... Ship itself is fine. Some of the support equipment on the deck will need to be replaced... Didn't get good landing/impact video. Pitch dark and foggy. Will piece it together from telemetry and ... actual pieces.
  46. ↑ Musk, Elon. "Twitter @elonmusk". Elon Musk. Retrieved January 13, 2015.
  47. ↑ Watch SpaceX's Vine "Close, but no cigar. This time."
  48. 1 2 Bergin, Chris (April 3, 2015). "SpaceX preparing for a busy season of missions and test milestones". NASASpaceFlight.com. Retrieved April 4, 2015.
  49. ↑ Elon Musk (14 April 2015). "Elon Musk on Twitter".
  50. ↑ Guy Norris (16 April 2015). "SpaceX Checks Throttle Valve After Flawed Falcon 9 Recovery Attempt".
  51. ↑ CRS-6 First Stage Landing, SpaceX, 15 April 2015.
  52. 1 2 Wow! SpaceX Lands Orbital Rocket Successfully in Historic First
  53. ↑ de Selding, Peter B. (2015-10-16). "SpaceX Changes its Falcon 9 Return-to-flight Plans". SpaceNews. Retrieved 8 November 2015.
  54. ↑ Dean, James (2015-12-01). stage-cape-canaveral/76576142/ "SpacexSpaceX wants to land next first stage at Cape Canaveral" Check |url= value (help). Florida Today. Retrieved 2 December 2015.
  55. ↑ Orwig, Jessica (19 December 2015). "SpaceX will attempt a potentially historic rocket landing like never before this weekend". Business Insider. Retrieved 19 December 2015.
  56. ↑ "SpaceX aims for Sunday launch and ground landing". Orlando Sentinel. 2015-12-20. Retrieved 2015-12-20.
  57. ↑ Foust, Jeff (18 December 2015). "FAA Moves Closer to Approving Falcon 9 Landings at Cape Canaveral". SpaceNews. Retrieved 19 December 2015.
  58. ↑ Bergin, Chris (18 December 2015). "SpaceX Falcon 9 Static Fires ahead of OG2 RTF mission". NASASpaceFlight. Retrieved 19 December 2015.
  59. ↑ SpaceX Falcon9 1st Successful Launch/Landing on Target - YouTube
  60. ↑ O'Kane, Sean (2015-12-21). "SpaceX’s 'reusable' Falcon 9 rocket won’t fly again, Elon Musk says". The Verge. Retrieved 2015-12-26.
  61. ↑ "SpaceX Reports No Damage to Falcon 9 First Stage After Landing". 3 January 2016. Retrieved 2016-01-04.
  62. ↑ Falcon 9 back in the hangar at Cape Canaveral. No damage found, ready to fire again., Elon Musk, via Twitter, 31 December 2015, accessed 2 January 2016.
  63. ↑ Dean, James (13 January 2016). "SpaceX poised to test-fire landed Falcon rocket's engines". Florida Today. Retrieved 14 January 2016.
  64. ↑ "SpaceX Tests Recovered Falcon 9 Stage and Prepares for Next Launch". 15 January 2016. Retrieved 2016-01-15.
  65. ↑ "Elon Musk on Twitter". Twitter. Retrieved January 17, 2016.
  66. ↑ "Elon Musk on Instagram: Falcon lands on droneship". Twitter. Retrieved January 17, 2016.
  67. ↑ "SpaceX on Twitter". Twitter. Retrieved January 17, 2016.
  68. ↑ Boyle, Alan (2016-01-17). "SpaceX rocket launches satellite, but tips over during sea landing attempt". GeekWire. Retrieved 2016-01-18.
  69. ↑ "SpaceX: ice buildup may have led rocket to tip over". Washington Post (Washington Post). 2016-01-18. Retrieved 2016-01-18. Musk tweeted that the lockout collet on one of the rocket’s four legs didn’t latch, causing it to tip over after landing. He said the “root cause may have been ice buildup due to condensation from heavy fog at liftoff.”
  70. ↑ Clark, Stephen (2016-02-24). "Falcon 9 rocket to give SES 9 telecom satellite an extra boost". Spaceflight Now. Retrieved 2016-03-07. SES 9’s launch weight is 11,620 pounds, or about 5,271 kilograms ... heavier than the Falcon 9 rocket’s advertised lift capacity to geosynchronous transfer orbit, an elliptical path around Earth that serves as a drop-off point for communications satellites heading for positions 22,300 miles (36,000 kilometers) above the equator, a popular location for powerful broadcast platforms. Geosynchronous transfer orbits targeted by satellite launchers typically have an apogee, or high point, of at least 22,300 miles and a low point a few hundred miles above Earth. ... SES’s contract with SpaceX called for the rocket to deploy SES 9 into a “sub-synchronous” transfer orbit with an apogee around 16,155 miles (26,000 kilometers) in altitude. Such an orbit would require SES 9 to consume its own fuel to reach a circular 22,300-mile-high perch, a trek that Halliwell said was supposed to last 93 days. The change in the Falcon 9’s launch profile [is planned to] put SES 9 into an initial orbit with an apogee approximately 24,419 miles (39,300 kilometers) above Earth, a low point 180 miles (290 kilometers) up, and a track tilted about 28 degrees to the equator
  71. ↑ Klotz, Irene (2016-02-23). "Satellite operator SES says interested in used SpaceX rocket". Reuters. Retrieved 2016-02-24.
  72. ↑ David Szondy (March 4, 2016). "SES-9 mission launch successful, but Falcon 9 landing less so". Gizmag. Retrieved March 4, 2016.
  73. ↑ "Elon Musk on Twitter". Twitter. Retrieved March 5, 2016.
  74. ↑ Drake, Nadia (April 8, 2016). "SpaceX Rocket Makes Spectacular Landing on Drone Ship". National Geographic. Retrieved April 8, 2016. To space and back, in less than nine minutes? Hello, future.
  75. ↑ You tube JCSat 14 hosted webcast
  76. ↑ You tube CRS8 hosted webcast
  77. ↑ "returned falcon 9 booster fires up for static fire test". spaceflight101. January 15, 2016. Retrieved 18 Jan 2016.
  78. ↑ https://twitter.com/elonmusk/status/689299216607232000, 19 January 2016.

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