SpaceX outlines CRS-3 landing legs plan toward first stage recovery ambitions
SpaceX believes they have “all the necessary pieces” to achieve a full recovery of the booster stage, with the next launch of their Falcon 9 v1.1 set to test another key technology towards that aim, via the debut of landing legs on the aft of the first stage. While there is a low likelihood SpaceX will be able to recover the first stage of the CRS-3 Falcon 9 from the water, the returning booster will attempt to deploy its landing legs during its descent.
The NET (No Earlier Than) March 16 launch of the Falcon 9 v1.1 has a primary objective of lofting the next Dragon spacecraft (CRS-3/SpX-3) into orbit for her journey to the International Space Station (ISS).
Preparations are continuing with the processing and integration of the spacecraft and launch vehicle at SpaceX’s SLC-40 facility located at Cape Canaveral in Florida.
Milestones in the upcoming flow include the potential of a static fire (hot fire) on the launch pad, currently penciled in for March 7, per L2 KSC/Cape scheduling documentation.
As recently revealed by NASASpaceFlight.com – via comments made by Tom Mueller, Co-Founder and VP Propulsion for SpaceX – the decision was taken to install four landing legs on to the aft of the F9 v1.1 first stage. The potential for this launch to include the innovative legs was known for some time. However, the actual decision to integrate the legs on the CRS-3 F9 was not confirmed until deep into the rocket’s flow.
Just days later, SpaceX CEO Elon Musk tweeted a couple of photos showing the legs as installed on the rocket, confirming the company is ready for the next milestone towards the rocket becoming fully reusable.
Both NASA sources, and SpaceX officials, note the addition of the legs on the rocket will incur no impact to the primary goal of lofting Dragon into orbit on its resupply mission to the ISS.
The debut of the Falcon 9 v1.1 on September 29, 2013 - carrying the CASSIOPE satellite – involved the first in space test objectives toward the ultimate goal of returning the first stage back to Earth for reuse.
These events occur after staging, with the first stage booster rotating 180 degrees via Reaction Control System (RCS) thrusters, prior to the re-ignition of three of the booster’s nine Merlin 1D engines.
This “boost back” maneuver, as it will be known when the stages eventually return to a designated landing site, currently targets an area over water, allowing a safe testing zone to refine control of the returning stage, prior to the eventual landing attempts on terra firma.
“Extended and precise high altitude reentry burns have occurred (on previous Falcon 9 v1.1 missions) that are similar to a boost back, but we did not attempt to bring the rocket close to land,” noted SpaceX Spokesperson Emily Shanklin in a series of responses to NASASpaceFlight.com
The first stage of the Falcon 9 v1.1 that successfully lofted the CASSIOPE satellite managed to conduct its three engine burn, allowing for reentry.
However, the stage started to spin during its return, causing the fuel to centrifuge. According to Mr. Mueller, the baffles in the tanks were not designed for those stresses, causing debris to get into the engines, resulting in them shutting down prematurely. The stage was lost when it impacted the Pacific Ocean.
The next advance in the testing will come during the March launch of the Falcon 9 on the CRS-3 mission. Not only will SpaceX attempt to bring the stage back down over water, but they will also attempt to test the deployment of the landing legs.
“During this test, SpaceX will attempt to execute first a reentry burn and then a landing burn with the Falcon 9 first stage. For the first burn, we will relight three engines to do a supersonic retro propulsion burn to slow the vehicle down and help ensure it survives atmospheric reentry,” Ms. Shanklin added.
“Assuming successful reentry, SpaceX will relight the center engine to stabilize the stage and reduce the vehicle’s velocity prior to contact with the water. About 10 seconds into the landing burn, SpaceX will attempt to demonstrate successful deployment of the legs in preparation for future land landings.”
While the successful execution of the aforementioned test objectives may still result in the first stage being unrecoverable from its watery touchdown, SpaceX is confident they are on the right track to eventually gaining the confidence that will allow them to return a booster stage to land.
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“It’s important to note the probability of recovering the first stage is low, maybe 30-40 percent. SpaceX is getting closer, but it is not likely that we will recover the stage during this attempt,” Ms. Shanklin continued.
“With the data from the recovered portions of the stage and the now complete Grasshopper program, SpaceX believes we have all the necessary pieces to achieve a full recovery of the boost stage.”
Grasshopper to F9R:
The Grasshopper program provided tantalizing visuals of what a first stage looks like as it gracefully heads back to its landing site.
The Grasshopper testing was conducted at SpaceX’s McGregor facility in Texas, ahead of a new phase of testing is scheduled to take place in New Mexico, utilizing the larger F9R rocket.
Numerous tests have involved the Grasshopper showing its ability to carry out incremental objectives, opening with a short hop of just six feet during Test 1, through to a massive 1,066 foot leap during Test 6.
The seventh test proved to be the most stunning, as the Grasshopper did much more than rise upwards before returning to its concrete pad.
That leap completed a divert test, flying to a 250 meter altitude with a 100 meter lateral maneuver before returning for a landing on the center of the pad.
The test demonstrated the vehicle’s ability to perform more aggressive steering maneuvers than have been attempted in previous flights.
Preparations for testing with the next system, a test vehicle called Falcon 9 Reusable (F9R-Dev1), have already begun in Texas, with the rocket already sporting its own set of landing legs. Its Merlin 1D engines have already been test fired in preparation for its shipping to Spaceport America in New Mexico.
“Grasshopper was a vertical landing test rig designed to test some of the technologies necessary to return a vehicle from orbit. The last flight under the Grasshopper program was completed last year,” noted Ms. Shanklin.
“Future testing, including that in New Mexico, will be conducted using the first stage of a Falcon 9 Reusable (F9R), which is essentially a Falcon 9 v1.1 first stage with legs.
“F9R test flights in New Mexico will allow us to test at higher altitudes than we are permitted for at our test site in Texas, to do more with unpowered guidance and to prove out landing cases that are more-flight like.”
The incremental test approach will eventually move on to testing the tricky return of the second (upper) stage of the Falcon 9 v1.1, while work has already begun on the propulsive landing capability for the Dragon spacecraft.
Once all three elements sport the ability to return to land for reuse, SpaceX will be able to boast a fully reusable launch system, which will in turn drive down manufacturing costs and allow for a more aggressive launch manifest.
(Images: SpaceX, Spaceport America and L2)
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