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SpaceX - F9R Development Updates
F9R Launch Vehicle Overview, Grasshopper Updates
SpaceX CEO Elon Musk jokingly said that if Grasshopper did not crash, teams were not pushing it hard enough. "But do I think there will be a few craters along the way," Musk said in 2012. "I think that's a likely outcome. We'll be very lucky if there's no craters along the way in creating a vertical landing rocket."
Video Credit: KWTX-TV News
A flight following a similar profile was conducted on May 1st with a maximum altitude of 1,000 meters.
The next flight of F9R Dev1 on June 17 saw the addition of four grid fins mounted in the uppermost portion of the vehicle to solve the problem of flight control in atmospheric flight without active propulsion which is an absolute requirement in achieving the accuracy needed for guiding a rocket stage back to a landing pad. During the May 1 test, F9R Dev1 again flew to 1,000 meters, but used the grid fins during the descent to control the vehicle by rotating and tilting them at the same time indicating a two-degree of freedom type design allowing for complex guidance and control during atmospheric flight. F9R Dev1 made another test on August 1, but no video or other information was provided by SpaceX.
F9R Dev1 is equipped with a Flight Termination System used to intentionally destroy the vehicle to prevent it from veering off-course and endangering life and property.
The Flight Termination System can be activated via remote radio commands or by the onboard computers when detecting off-nominal flight parameters exceeding pre-set limits. In Friday's case, the vehicle automatically triggered the termination when its computers sensed a situation from which the vehicle could not recover. As part of a terminated flight, the vehicle would immediately shut down its engines - as seen in the video of Friday's test, and then trigger the explosion of the vehicle. The cause of the loss of control is not known at this point. Failures of this type can be due to a malfunction of the flight control system, the attitude sensors or the thrust vector control system. SpaceX said that Friday's "test was particularly complex, pushing the limits of the vehicle further than any previous test. As our practice, the company will be reviewing the flight record details to learn more about the performance of the vehicle prior to our next test."
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Falcon 9 Test-Rig demonstrates Steering Fins for Future Precision Landings
June 19, 2014 |
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SpaceX has completed the third test flight of its F9R test rig at the McGregor testing facility in Texas following up on two successful tests in April in May. In contrast to previous tests, Wednesday's 1000-meter flight demonstrated four deployable and steerable grid fins for vehicle control during descent. These grid fins will likely become the primary control mechanism used during Falcon 9 first stage boost back missions as the first stages travel through the atmosphere on the way to a targeted landing back at the launch site.
The F9R test rig is a Falcon 9 first stage with flight-like landing legs and three Merlin 1D engines. It is 3.66 meters in diameter and about 42 meters tall. F9R rockets & F9R-Dev1 are equipped with a cold gas reaction control system consisting of various nitrogen thrusters that are used to control the orientation of the vehicle during unpowered flight. The ACS was also the only control mechanism of the previous boost back & soft-splashdown demonstrations made by Falcon 9. Using only the cold gas system to keep the vehicle stable throughout the flight from stage separation at 80 Kilometers in altitude back to a landing pad at the launch site would require excessive fuel and strong thrusters to keep roll momentum from building up - as demonstrated last September during the Cassiope launch. Also, the vehicle would run into problems when encountering winds in the lower atmosphere as the cold gas reaction system could not keep the vehicle on target by itself. A non-propulsive control system is therefore highly desirable as it reduces the demand on the reaction control system thus potentially reducing the overall mass of the stage while increasing the accuracy of the landing. F9R's newest addition - four grid fins mounted in the uppermost portion of the vehicle - show that SpaceX has been working on developing a solution for flight control in atmospheric flight without active propulsion. Grid-fins have been widely used as a stabilizer on missiles & bombs and are shaped like miniature wings consisting of a lattice structure. |
The Russian Soyuz employs grid-fins in its launch abort system which would deploy when the launch escape rockets start firing in an abort scenario to stabilize the vehicle, but the fins used by SpaceX take it one step further as they can be moved independently to actively control the vehicle's flight and not only act as a stabilizer.
Grid-fins perform well in all velocity ranges including supersonic and subsonic speeds with the exception of the trans-sonic regime due to the shock wave enveloping the grid. These properties make them ideally suitable for the Falcon 9 first stage that starts out at supersonic speeds and returns to subsonic velocity as it travels through the atmosphere, en-route to the landing site.
Wednesday's F9R test flight was the first time the vehicle tested the grid-fins which were installed after the last test that took place in early May. Video published by SpaceX shows the vehicle igniting one of its three Merlin 1D engines and lifting off from its launch mount. After an initial vertical ascent, the Merlin engine was gimbaled to perform a divert maneuver that appeared more aggressive than the maneuver conducted on the last flight. Afterwards, the vehicle ascended to 1,000 meters in altitude.
At the start of the descent, the four grid-fins were deployed and F9R intentionally introduced a roll rate on the vehicle as it started descending to demonstrate that the fins could compensate the roll. On the way down, the fins were moving to guide the vehicle back to the pad and eliminate the roll.
The video clearly showed the fins rotating and tilting at the same time indicating a two-degree of freedom type design allowing for complex guidance and control during atmospheric flight. After two minutes of flight, the vehicle safely touched down and returned its grid-fins to their stowed position. Wednesday's test again used the legs in their deployed configuration from the start, but SpaceX will soon transition to testing with the legs folded up for liftoff and then deploying them shortly before touchdown. Visible in the video of the test is significant smoke rising from the legs during flight and after landing it appeared that the ablative coating of the legs was on fire for a brief moment before self-extinguishing. In the operational landing scenario, the legs are subjected to the heat only for a short period of time after deployment during the landing burn. SpaceX will most likely continue testing the grid-fins in Texas as F9R continues flights in the low-altitude, low-velocity regime before beginning boost-back demonstrations with flights up 90 Kilometers from Spaceport America. Testing at the lower altitudes can only serve as a verification of the flight control software before the complete potential of the grid-fins will be used in unpowered flight at higher altitudes and speeds. When the grid-fins will be first seen in flight aboard the operational Falcon 9 rocket is unknown at this point. |
Deployed steering fins seen from an onboard camera
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The first attempt of a propulsive landing of the first stage on a pad at Cape Canaveral is expected later in 2014 or early in 2015 depending on the results of the ambitious testing campaign ongoing with the F9R-Dev vehicles and the operational Falcon 9 launcher that will demonstrate a soft-splashdown landing closer to the coast on its next launch coming up this weekend. This twofold effort of splashing down closer to land will increase the odds of a recovery of the stage and demonstrate a more precise targeting of the landing spot which will be crucial for landings on land which will eventually be supported by the new fins tested on Wednesday.
Progress has also been made by SpaceX as the company has secured a suitable landing site at Cape Canaveral that is close to the launch site but also meets the strict safety requirements for the propulsive landing of the first stage of the Falcon 9.
Progress has also been made by SpaceX as the company has secured a suitable landing site at Cape Canaveral that is close to the launch site but also meets the strict safety requirements for the propulsive landing of the first stage of the Falcon 9.
Flying to new Heights - SpaceX F9R completes highest Test Flight to Date
May 2, 2014 |
SpaceX has conducted the second flight test with its F9R-Dev1 test rig currently undergoing low-altitude testing at the company's McGregor Test Site, Texas. Flying to new heights, Thursday's test took the F9R test rig to an altitude of 1000 meters, quadrupling the height of its first test that was performed two weeks earlier.
The previous testbed known as Grasshopper reached an altitude of 744 meters in its highest flight. This also marked the quickest turnaround in between flight tests performed with Grasshopper or F9R showing that SpaceX is making progress with fast post flight processing and preparation for the next flight. Ultimately, SpaceX plans for an efficient and fast processing campaign in between missions of the reusable Falcon 9 rocket performing orbital missions. Thursday's test was just over two minutes in duration as the vehicle ignited one of its three Merlin 1D engines that throttled up while the vehicle was restrained on the launch mount via a hold down system - although the landing legs were deployed for liftoff, the stage did not rest on the legs prior to the flight. After liftoff, the vehicle ascended to 1,000 meters in altitude. On its way up, F9R performed its divert maneuver to avoid the launch pad for landing. While ascending, the vehicle initiated a slow roll of more than 180 degrees before reaching its target altitude of 1,000 meters where it hovered for a few seconds before it started descending again. During descent, the vehicle reversed the roll indicating that the roll was part of the test, likely to verify the roll control ability of the vehicle during the final stages of its descent. |
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In the final portion of the descent to the landing pad, the vehicle showed a small attitude disturbance that could have been the result of winds catching the vehicle or a sign of the throttle-up of the Merlin 1D engine for the hoverslam landing - that is landing the vehicle at a thrust to weight ratio greater than one, throttling the engine up to slow the vehicle down to nearly zero when it reached the ground.
At contact, the vehicle shut its engine down to rest on its four landing legs. A small shift of the vehicle was visible at landing showing that F9R did not touch down on all of its four legs at one - whether intentional or not, landing the vehicle with some offset or horizontal velocity is a good simulation of the conditions to be encountered during first-stage boost back landings.
At contact, the vehicle shut its engine down to rest on its four landing legs. A small shift of the vehicle was visible at landing showing that F9R did not touch down on all of its four legs at one - whether intentional or not, landing the vehicle with some offset or horizontal velocity is a good simulation of the conditions to be encountered during first-stage boost back landings.
The 1,000-meter test again used the legs in their deployed configuration from the start, but SpaceX will soon transition to testing with the legs folded up for liftoff and then deploying them shortly before touchdown. Visible in the video of the test is significant smoke rising from the legs during the two-minute test as they encountered significant heating from the engine. In the operational landing scenario, the legs are subjected to the heat only short a short period of time after deployment during the landing burn.
Per the current FAA Permit, testing at the McGregor site will continue with the F9R-Dev1 test rig up to an altitude of 3,000 meters. In parallel, SpaceX is continuing preparations to begin testing of the F9R-Dev2 vehicle at Spaceport America, however, no reports on its progress have been provided by SpaceX. Testing at Spaceport America is expected to begin later this year to demonstrate the high-altitude, high-velocity component of the flight regime of the first stage boost-back landing. For these tests, F9R would lift off powered by more than one engine and its legs folded followed by an ascent to up to 90 Kilometers reaching hypersonic speeds encountered at the point of stage separation in a nominal Falcon 9 flight. F9R would then conduct the boost-back burn to put itself onto a trajectory to the landing pad for a short landing burn using the center engine only with leg deployment in the final seconds ahead of touchdown. Performing low-altitude tests at McGregor, high-altitude tests at Spaceport America and continuing first-stage boost-back attempts during operational Falcon 9 launches allows SpaceX to proceed at full speed to the ultimate goal of first stage re-usability. The next Falcon 9 launch currently planned for May 10 tasked with orbiting six Orbcomm G2 satellites will again feature a soft splashdown test of the first stage - building on the success of the recent splashdown after the launch of the Dragon SpX-3 mission. Following the successful and intact return of the rocket stage to the Ocean downrange from the launch site, it succumbed to heavy seas and was destroyed as ships could not reach the stage that touched down in the middle of a storm. SpaceX recovered a large portion of the interstage and some other fragments and hopes the next attempt will yield more recoverable hardware - in addition to the data obtained during descent which is the real goal of these soft splashdown attempts. The Orbcomm G2 launch will see an attempt of actually boosting the first stage back for a splashdown closer to Cape Canaveral in a twofold effort of increasing the odds of a recovery of the stage and demonstrating a more precise targeting of the landing spot which will be crucial for landings on land. The first attempt of a propulsive landing of the first stage on a pad at Cape Canaveral is expected later in 2014 or early in 2015 depending on the results of the ambitious testing campaign ongoing with the F9R-Dev vehicles and the operational Falcon 9 launcher. |
SpaceX reaches for Reusability - Soft-Splashdown Success & 1st F9R Test
April 19, 2014
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Making steady progress on their path to the development of re-usable launch vehicles, SpaceX have successfully flown their F9R-Dev test rig for the first time last week and succeeded in bringing the first stage of their operational Falcon 9 v1.1 rocket back for a soft-splashdown in the Ocean after the launch of the Dragon spacecraft on Friday.
The F9R-Dev test rig builds on the Grasshopper program that was completed by SpaceX between September 2012 and October 2013 to test the basic architecture of a landing system for the first stage. The Grasshopper vehicle consisted of a Falcon 9 v1.0 first stage, an early version of the Merlin 1D engine and prototype landing legs. Making increasingly high and more complex flights, Grasshopper demonstrated navigation sensors and landing algorithms, and the vehicle's ability to perform lateral maneuvers, maintain stability in wind and land with a thrust to weight ratio greater than one. Taking it to the next level, SpaceX began construction of the F9R-Dev test article - a v1.1 first stage that would use the operational Merlin 1D engine and actual landing legs to test the real flight equipment. F9R-Dev is set to begin with tests of the low-altitude, low-velocity regime of the landing sequence building on the tests already performed with Grasshopper. |
Built to fly higher and faster than Grasshopper, F9R will also demonstrate the high-altitude, high-velocity aspect of the first stage return with supersonic flights up to 90 Kilometers.
Construction of the first F9R-Dev vehicle got underway in 2013 using a Falcon 9 v1.1 qualification test article used at the McGregor Rocket Development and Test Facility. F9R-Dev uses a Falcon 9 v1.1 first stage with three Merlin 1D engines and deployable landing legs, standing approximately 42 meters tall with a diameter of 3.66 meters. The stage is equipped with a cold gas reaction control system for three-axis control during coast phases and roll control during single-engine burns.
The F9R-Dev test rig went through the usual testing all SpaceX vehicles go through consisting of an acceptance firing of each engine followed by a firing of the integrated stage. In 2014, the rig was moved to its pad at the McGregor test site. Unlike the pad used for the now retired Grasshopper, the modified pad consists of two zones - a launch zone featuring a launch mount and a flat landing pad to allow F9R to touch down on its landing legs.
On March 28, 2014, a short static firing of the F9R-Dev rig was performed to validate all systems for the first test flight that was completed on April 17. Lifting off with its landing legs already extended, F9R started ascending powered by a single Merlin 1D engine up to about 250 meters. The flight included a lateral divert maneuver before F9R began its descent to the landing zone. Video of the test shows the stage flew with a partial fuel load as condensation on the Liquid Oxygen tank extended less than a quarter up the total tank length. The hover ahead of landing appeared to be relatively long in duration when compared with previous hover-slam landings of Grasshopper. Presumably, SpaceX was testing the throttle capability of the Merlin 1D in close proximity to the ground or simply programmed the vehicle to perform a landing as soft as possible. The flight was just under a minute in duration. Flying with the legs extended subjected them to heating from the engine illustrated by smoke rising from the legs halfway into the flight. The first test flights of the F9R will launch with the legs deployed followed by the transition to launching with the legs stowed against the rocket body and deploying them shortly before landing. When deployed, the legs have a span of about 18 meters consisting of a carbon fiber and aluminum honeycomb structure with a mass of about 2,000 Kilograms. Deployment is accomplished through the use of a pneumatic system utilizing high-pressure helium. SpaceX has an FAA permit to perform low-altitude testing of the F9R at McGregor up to about three Kilometers in altitude. For the high-altitude tests, SpaceX will move to Spaceport America where a 30 by 30-meter pad was built in 2013. Revealed by SpaceX CEO Elon Musk this week, F9R testing will continue in parallel with tests at McGregor using F9R-Dev1 and Spaceport America using a different test rig, F9R-Dev2. |
Tests performed at Spaceport America are expected to start later in 2014.
For the high-altitude tests, F9R would lift off using three engines, accelerating the rocket stage to supersonic speeds approaching 90 Kilometers in altitude before the boost-back to the landing pad followed by a short landing burn using the center engine only with leg deployment in the final seconds ahead of touchdown.
Performing low-altitude tests at McGregor, high-altitude tests at Spaceport America and continuing first-stage boost-back attempts during operational Falcon 9 launches allows SpaceX to proceed at full speed to the ultimate goal of first stage re-usability.
For the high-altitude tests, F9R would lift off using three engines, accelerating the rocket stage to supersonic speeds approaching 90 Kilometers in altitude before the boost-back to the landing pad followed by a short landing burn using the center engine only with leg deployment in the final seconds ahead of touchdown.
Performing low-altitude tests at McGregor, high-altitude tests at Spaceport America and continuing first-stage boost-back attempts during operational Falcon 9 launches allows SpaceX to proceed at full speed to the ultimate goal of first stage re-usability.
A major milestone was achieved on Friday when the first stage of the Falcon 9 v1.1 that launched the Dragon SpX-3 spacecraft en-route to the Space Station made a successful soft-splashdown in the Atlantic Ocean.
Blasting off from Space Launch Complex 40 at Cape Canaveral on Friday at 19:25 UTC, Falcon 9 embarked on an ambitious mission with the primary goal of delivering Dragon to orbit, and the secondary objective of a first stage splashdown and a second stage re-light for re-entry. Sending the second stage on its way to complete the trip to orbit, Falcon 9's first stage separated at T+2 minutes and 43 seconds at an altitude of about 80 Kilometers traveling at Mach 10. Shortly after separation, the first stage used its cold-gas attitude control system to turn to an engine-forward position for a braking maneuver using three of its nine Merlin 1D engines. This burn utilizing three engines was to slow the vehicle down ahead of re-entry in order to reduce forces occurring during entry, ensuring the stage could survive the entry sequence. By T+ 8 minutes and 25 seconds, the first stage had completed its entry burn and teams were receiving telemetry and video from the stage. Telemetry was transmitted in real-time to the TEL-4 ground station at Cape Canaveral and a SpaceX plane circling above the landing area in the Atlantic Ocean. |
As the vehicle's altitude decreased, it disappeared behind the horizon as seen from the Cape causing an expected loss of signal. The plane was recording telemetry for later playback - there was no real time insight into the crucial landing maneuver of the first stage.
The expectations of the experimental maneuver were kept low by SpaceX as the company stressed that these first stage landing attempts are primarily performed to gather data and improve the return sequence for future attempts. Another contributing factor to the slim probability of success were rough seas in the landing area on Friday. Seven-meter seas prevented the recovery boats from reaching the landing zone and waves were expected to cause some trouble during the final landing maneuver of the first stage. Overall, Elon Musk issued a 30 to 40% chance of an intact return of the first stage.
The expectations of the experimental maneuver were kept low by SpaceX as the company stressed that these first stage landing attempts are primarily performed to gather data and improve the return sequence for future attempts. Another contributing factor to the slim probability of success were rough seas in the landing area on Friday. Seven-meter seas prevented the recovery boats from reaching the landing zone and waves were expected to cause some trouble during the final landing maneuver of the first stage. Overall, Elon Musk issued a 30 to 40% chance of an intact return of the first stage.
Stage Separation
F9R First Stage with Landing Legs
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After receiving the last data point before losing the signal from the Cape, Musk Tweeted: "Last known state for rocket boost stage is 360 m/s, Mach 1.1, 8.5 km altitude and roll rate close to zero (v important!)"
That last part was of particular importance because an excessive roll rate occurred during the first Falcon 9 splashdown attempt last September. On that flight, an uncontrollable roll caused the landing burn of the center engine to be cut short because the propellant was being centrifuged up the tank walls, damaging the tank baffles & leading to debris entering the engines. Teams made adjustments to the attitude control system of the first stage to better cope with roll-rates and to be able to reduce them during the flight through the atmosphere. Also, SpaceX hoped that the landing legs would add stability to the vehicle during the final burn to prevent a roll. Additional adjustments included modifications to the initial entry burn and the timing of the landing burn. During re-entry, the stage was expected to fly in a stable posture due to its low center of gravity caused by the nearly empty fuel tanks and the heavy engines in the aft section. Once falling vertically and closing in on the ocean, Falcon 9 was to ignite the center engine for the final landing burn of under ten seconds. With the legs deployed and engine firing, Falcon 9 was to pretend that the ocean was firm ground to land on and make a soft splashdown in the Atlantic. As the second stage arrived in orbit, the first stage was scheduled to reach the Ocean - hopefully in one piece, but it took several hours to confirm the outcome of the landing attempt since telemetry acquired by the plane had to be sent back for analysis and a bulk of the team was focused on Dragon's mission to the Space Station. "Data upload from tracking plane shows landing in Atlantic was good! Several boats enroute through heavy seas. Flight computers continued transmitting for 8 seconds after reaching the water. Stopped when booster went horizontal," Musk Tweeted just after midnight UTC. The fact that the computers kept sending data after contact with the water until the stage had fallen to a horizontal position confirms a successful soft-splashdown of the first stage. Musk did not explicitly confirm a good deployment of the landing legs. Whether recovery boats managed to reach the stage and if the recovery of the stage or individual components was successful has not been announced. Still, the successful landing of the stage on the second attempt marks a milestone for SpaceX having managed to obtain one more piece in the puzzle leading to operational boost-back capability of the Falcon 9 first stage. With a busy F9R development plan laid out for 2014, Elon Musk stated he was hopeful to see the first attempt to bring the first stage back to land by late 2014 or early 2015 to begin working on the rapid re-usability of the first stage which may still be a long way down the road. |