“Of Course I Still Love You, we have a Falcon 9 on board!” were the words met with exhilaration by thousands of SpaceX employees on Friday when the company finally achieved a successful Falcon 9 booster landing at sea. Returning from the edge of space and a speed over five times the speed of sound, the Falcon 9 booster came to rest on its four landing legs nine minutes after taking off from Florida and dispatching the Dragon resupply craft on its way into orbit.
Elon Musk, SpaceX CEO and Chief Designer, outlined ambitious plans for the recovered booster after its expected Sunday return to the Space Coast. First on the agenda will be a series of ground based firings to attest the vehicle a clean bill of health before readying it for re-flight – possibly with a paying customer’s satellite payload sitting atop. Musk said the re-flight of the booster could go ahead as early as June.
SpaceX had decided to attempt a landing at sea on this flight despite available margins for a return to land. This decision was prompted by the need to master the landing sequence for sea-based recoveries which will be needed for about half of Falcon 9’s flights when lifting heavy satellites to high-energy orbits.
Having a mission with healthy propellant margins to attempt a landing on the Drone Ship was hoped to deliver valuable data needed to perfect the landing sequence for all missions, including those challenged by a limited surplus in vehicle performance.
Recovering the majority of boosters is an essential part of lowering the cost for access to space as SpaceX envisions its boosters to fly over and over again with minimal effort and time needed for refurbishment. Musk said he expects boosters to easily fly 20 times with only minimal refurbishment and up to 100 times with regular maintenance and refurbishment on the rockets.
SpaceX already celebrated a successful booster landing in December on the very first flight of the Falcon 9 Full Thrust variant that saw the booster flying back to Landing Zone 1 a few Kilometers south of SLC-40, lighting up the night before landing dead center on its concrete landing pad. While landing back at the Cape was met with great celebration, SpaceX was also facing up to the fact that landing at sea would be more difficult as multiple close calls had shown, starting with the first ASDS landing attempt in January 2015.
Musk likened landing on the small drone ship to landing on an aircraft carrier and targeting the small pad from space to touching down on a postage stamp. Only a few meters of margin exist for the rocket’s landing accuracy and the stationkeeping precision of the GPS-guided drone ship as all four landing legs need to be on deck for Falcon 9 to stand upright.
Falcon 9 lifted off from Space Launch Complex 40 at Cape Canaveral Air Force Station on time at 4:43p.m. local time, 20:43 UTC. Ascending under the power of its nine Merlin 1D engines, the 70-meter tall Falcon 9 swung to the north-east for a quick flight across the Atlantic to lift Dragon into orbit for its return to the Space Station after the June 2015 Falcon 9 failure.
The first stage executed a flawless burn of two minutes and 34 seconds and sent the second stage off to finish the job of boosting the Dragon spacecraft into orbit with a seven-minute burn of its MVac engine. Main Engine Cutoff on the first stage occurred 68 Kilometers in altitude at a speed of Mach 5.45.
Immediately after separation, the first stage began a busy sequence of events comprising its return to the ground beginning with a maneuver to flip around to point its engines to the direction of travel for a 38-second boost back maneuver with three of the rocket’s engines.
Next was a short coast towards the atmosphere to set up for a re-entry burn of 24 seconds to slow the booster down and shield its engine section against the aerodynamic forces at entry interface. Back in the atmosphere, the vehicle used its four actuated grid fins to guide itself to the Autonomous Spaceport Drone Ship – battling strong winds in the upper atmosphere to reach the precise coordinates of the ship, located 300 Kilometers from the launch site.
Impressive airborne video of the landing showed the booster arcing towards the ship with its Center Engine going through some heavy throttling and gimbaling action to transition the booster to a vertical descent with only meters to spare. The four landing legs sprung into place seconds before the vehicle made a successful touchdown – a few meters off center.
In the seconds after landing, all eyes were on the top of the booster to sense whether it was tipping over or remaining upright while the engine went through shutdown. Loud cheers and celebration emerged at the Control Center in Hawthorne, California where hundreds of SpaceX employees had gathered on the factory floor to witness their company make another leap towards an operational reusability of the rocket stage.
With the first stage resting on its four legs, the SpaceX Launch Team could not break out in celebration as one part of the team was still overseeing the successful orbital delivery of the Dragon while the other part headed into post-landing safing of the booster.
Steps completed immediately after landing were to safe the propellant system and vent the pressurized propellant tanks to safe pressures. Crews were expected to approach the Drone Ship some time after landing, starting with a careful inspection of the booster before getting close to it to weld the landing legs to the steel deck of the ASDS using steel shoes. The booster is secured to the pad to prevent it from tipping over in the event of rough seas and strong winds which are expected for its return to shore.
The Autonomous Spaceport Drone Ship is expected at the Space Coast on Sunday, Musk was unsure whether Port Canaveral would be its first destination, but said the ASDS was ultimately headed there.
At the post-flight press conference, Musk said this recovered booster would be the first to fly again – the vehicle returned to Landing Zone 1 in December has finished its active duty after a post-landing Static Fire Test and will be put on display in front of the company’s headquarters in California.
But before re-flying the rocket, SpaceX will complete a rigorous testing campaign comprised of an initial inspection of the booster and putting it through ten consecutive Static Fire Tests. These tests are hoped to be completed at Cape Canaveral, either using SpaceX’s new facility at Pad 39A at the Kennedy Space Center or further south at SLC-40.
Musk expects the booster to be re-flown on an operational mission with a paying customer as early as June, though discussions are still to be finalized.
SpaceX will not get much of a pause after Friday’s successful mission as the company ramps up its launch pace to tackle a busy manifest for the remainder of 2016. The next two Falcon 9 missions will lift satellites to Geostationary Transfer Orbit and rely on the Drone Ship for the return of the first stage due to performance limitations in these flights – putting to use lessons learned in Friday’s successful landing at sea and attempting to manage a more challenging landing.
Musk said he fully expects future landing failures given the difference of Low Earth Orbit and GTO missions with the first stage separating at higher speed and further downrange, only with very limited propellant reserves for a re-entry burn. This creates a much more extreme re-entry environment in terms of heating experienced by the vehicle and also puts limitations on margins for the final landing burn.
The next opportunity to land a Falcon 9 at Landing Zone 1 will come on the third flight from now, likely the Dragon SpX-9 mission currently looking at a launch target in late June – though subject to change given the fluidity in Space Station schedules and potential changes to the SpaceX manifest.
SpaceX’s future plans to further expand reusability of launch vehicle components will focus on Falcon’s 13-meter long payload fairing which costs several million Dollars to produce. Experimentation was already conducted on an earlier flight with stabilization systems on the fairing and early SpaceX concepts called for the fairing halves to be recovered in mid-air using helicopters.