Falcon 9 ocean booster landing tests

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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. The stage landed hard and tipped over after landing.

The Falcon 9 ocean booster landing tests are a series of controlled-descent flight tests conducted by SpaceX. The program aims to execute a controlled-descent re-entry into Earth's atmosphere after Falcon 9 v1.1 rocket boosters complete the boost phase of an orbital flight. Some tests include an attempt at softly landing the booster of the rocket in the ocean or on the Autonomous spaceport drone ship, a ship commissioned by SpaceX to provide a hard landing surface for the booster.[1] Test flights began in September 2013. As of April 2015, seven test flights have been conducted.

The ocean booster 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 boosters used on orbital launches are 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 occur 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 September 29, 2013, after the second stage with the CASSIOPE and nanosat payloads separated from the booster. 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.

History[edit]

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.[7]

In the event, they did complete the first flight test in 2013, but continued the over-water testing into 2015. 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]".[8] 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."[9]

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 booster 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.[10]

Reusability test plan for post-mission testing[edit]

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, September 21, 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 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.[11] 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][12]

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.[11] 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.[13]

SpaceX is not performing controlled-descent tests on all Falcon 9 v1.1 flights.[14] In September 2013, SpaceX announced that the fourth Falcon 9 v1.1 flight—which occurred in April 2014[15]—would be the second test of the booster 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.[16][17]

Test flights[edit]

Ocean water test descents[edit]

Falcon 9 Flight 6[edit]

After the three-minute boost phase of the September 29, 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".[9] 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.[3][9] The company did not expect a successful booster recovery on this flight[18] and, as of March 2013, had said that they did not expect booster recovery following the first several powered-descent tests.[7] 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.[18]

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".[8][18][19]

Falcon 9 Flight 9[edit]

The second test of controlled-descent hardware and software on the first-stage booster occurred on April 18, 2014,[5] and became the first successful controlled ocean soft touchdown of a liquid-rocket-engine orbital booster.[20][21] 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.[6][22][23]

During the second test, the booster was traveling at a velocity of Mach 10 (6,300 mph; 10,000 km/h)[22] at an altitude of 80,000 meters (260,000 ft)[24] 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.[23] 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.[25]

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.[26]

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".[27] 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.[28][29]

Falcon 9 Flight 10[edit]

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."[30]

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 speed 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".[31] 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.[30]

Falcon 9 Flight 13[edit]

Infrared thermal imagery of Falcon 9 SpaceX CRS-4 launch on September 21, 2014. 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 with a fading plume within the brighter plume of the second stage rocket exhaust. In the inset, photographed subsequently, the restarted first-stage engines power the stage as it performs a propulsive descent to Earth.

The fourth test flight of a returned booster, with a planned water landing, occurred on Falcon 9 Flight 13 which was launched on September 21, 2014.[32] and the booster flew a profile approaching a zero-velocity at zero-altitude simulated landing on the sea surface.[17] SpaceX made no attempt to recover the first stage, since earlier tests had confirmed that the 14-story tall booster 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 booster were successfully imaged except for the final landing burn, as that occurred below the clouds where the IR data was not visible.[17] 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.[16]

Falcon 9 Flight 15[edit]

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

SpaceX had planned make the sixth controlled-descent test flight and second[33] landing attempt on the floating recovery ship, no earlier than February 11 (see below for first attempt). This would be a "potentially historic rocket launch and landing" because the first stage will attempt a test landing on a droneship, something that "was unheard of" five years ago.[33][34][35]

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.[36] That was resolved within days of the ship returning to Jacksonville, and by January 15 SpaceX was unambiguous about its plans to attempt a landing of the booster following the boost phase of the DSCOVR mission.[35]

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 which keep the barge in a constant position had malfunctioned, making station-keeping difficult. Due to these factors, the post-launch flight test did not involve the barge, but instead attempted a soft landing over water.[37]

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.[38]

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

Floating-platform test landings[edit]

SpaceX has attempted two landings of a test vehicle on a solid surface as of April 2015. Many of the test objectives were achieved, including landing on a floating platform at a specific point in the Atlantic ocean and 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.

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

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.[32] 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 due to excessive sea state conditions.

Falcon 9 Flight 14[edit]

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 14th Falcon 9 flight on the platform.[39] 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.[40] 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 an "historic core return attempt" by NASA SpaceFlight[41]—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, are projected to improve the landing accuracy to 10 m (33 ft); the landing accuracy on the previous four controlled-descent test flights was only 10 km (6.2 mi).[42] Prior to the flight, SpaceX projected that the likelihood of successfully landing on the platform on the first try was 50 percent or less.[40]

The first flight attempt for the test hardware occurred on January 10, 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,[41] when the booster was approximately 80 km (50 mi) high and moving at a velocity of Mach 10 (6,300 mph; 10,000 km/h).[43]

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."[44] Musk later elaborated that the rocket's flight-control surfaces had exhausted their supply of hydraulic fluid prior to impact.[45] Musk posted photos of the impact while talking to John Carmack on Twitter. SpaceX later released a video of the impact on Vine.[46]

Falcon 9 Flight 17[edit]

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.

A seventh test flight of the booster controlled-descent profile occurred on April 14, 2015 on Falcon 9 Flight 17. This was SpaceX's second attempt to land on a floating platform. The booster was fitted with grid fins and landing legs to facilitate the post-mission test. If successful, this would have been first time in history that a rocket booster was returned to a vertical landing.[47]

An early report from Elon Musk suggested that the booster made a hard landing on the drone ship.[48] Musk later clarified that the bipropellant valve was stuck, and therefore the control system could not react rapidly enough for a successful landing.[49] On 15 April, SpaceX released a video of the terminal phase of the descent, the landing, the tip over, and a small deflagration as the stage broke up on the deck of the ASDS.[50]

Future tests[edit]

Falcon 9 Flight 21[edit]

The first attempt to land the first stage of the Falcon 9 at the launch site is tentatively scheduled to occur on Falcon 9 Flight 21, depending on the outcome of prior landing tests.[47] The booster will carry the Jason 3 satellite from NASA; after separation the booster will attempt a return-to-launch-site trajectory. The launch and landing, taking place from Vandenberg Air Force Base, is scheduled for August 8, 2015. [51]

See also[edit]

References[edit]

  1. ^ a b c Bergin, Chris (24 November 2014). "SpaceX’s Autonomous Spaceport Drone Ship ready for action". NASASpaceFlight. Retrieved 23 April 2015. 
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  7. ^ a b 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. 
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  18. ^ a b c Wall, Mike (October 17, 2013). "SpaceX Hit Huge Reusable Rocket Milestone with Falcon 9 Test". Space.com. Retrieved December 5, 2013. 
  19. ^ 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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  21. ^ Orwig, Jessica (November 25, 2014). "Elon Musk Just Unveiled A Game-Changing Ocean Landing Pad For His Reusable Rockets". Business Insider. Retrieved December 11, 2014. The first successful "soft landing" of a Falcon 9 rocket happened in April of this year 
  22. ^ a b 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. 
  23. ^ a b 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.' 
  24. ^ "SpaceX CRS-3 Mission Press Kit: Cargo Resupply Services Mission" (PDF). NASA. March 2014. Retrieved March 15, 2014. 
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  40. ^ a b Bergin, Chris (November 18, 2014). "Pad 39A – SpaceX laying the groundwork for Falcon Heavy debut". NASA SpaceFlight. Retrieved November 21, 2014. 
  41. ^ a b 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 manoeuvres 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. 
  42. ^ "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. 
  43. ^ "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. 
  44. ^ 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. 
  45. ^ Musk, Elon. "Twitter @elonmusk". Elon Musk. Retrieved January 13, 2015. 
  46. ^ https://vine.co/v/OjqeYWWpVWK
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  48. ^ Elon Musk (14 April 2015). https://twitter.com/elonmusk/status/588076749562318849.  Missing or empty |title= (help)
  49. ^ Guy Norris (16 April 2015). "SpaceX Checks Throttle Valve After Flawed Falcon 9 Recovery Attempt". 
  50. ^ CRS-6 First Stage Landing, SpaceX, 15 April 2015.
  51. ^ http://spacexstats.com/mission.php?launch=25

External links[edit]