Plummeting through the black sky above Cape Canaveral at supersonic speed, a Falcon 9 rocket completed a historic soft-landing on solid ground after successfully deploying 11 communications satellites on the return to flight mission of SpaceX’s flagship launch vehicle.
In addition to marking the Falcon 9 vehicle’s return-to-flight after the heartbreaking failure of the Dragon CRS-7 space station resupply mission on June 28, the OG2 Mission 2 launch featured important several firsts.
The flight was the first for the “full thrust” version of the rocket, with upgraded Merlin engines providing additional thrust, helped in part by the first use of “densified” cryogenic propellants on an orbital launch vehicle. Traditionally, liquid oxygen is cooled to -289 degrees Fahrenheit, at which point it can be safely stored as a pressurized liquid. SpaceX dropped the temperature another 51 degrees to -340.
Since LOX is denser at the lower temperature – not far from the point it would turn into feezing slush – more of the oxidizer can be stored in the the same size tank and pumped to the engines in the same period of time, resulting in greater thrust. To accomplish this, the kersoene-derived RP-1 fuel was also chilled – to 20 degrees – to increase it’s density as well.
The increase in performance is intended to enable Falcon to carry heavier payloads to orbit and also make it easier for the first stage to fly back either to its ground-based landing zones or the autonomous drone ship for recovery and reuse.
SpaceX also upgraded the vehicle’s second stage, with a larger nozzle on the single Merlin engine and stretching the stage by about 5 feet. After deploying the Orbcomm satellites, the stage coasted before its engine restarted in a crucial test for future missions to geostationary orbit.
Still, it was the dramatic night-time landing of the Falcon first stage that grabbed headlines around the world and thrilled spectators all along Florida’s Space Coast. From all indications, the launch, satellite deployment, upper stage restart and booster re-entry and landing milestones appeared to come off without a hitch for a picture-perfect mission.
“The satellites were deployed right on target and the Falcon 9 booster came back and landed, it looks like, almost dead center in the landing pad,” said SpaceX founder and CEO Elon Musk. “And then the upper stage did a coast and then restarted to prove out the coast and restart capability.”
“There are just so many things that have to go right, and it’s an incredibly complex set of maneuvers that the booster has to make,”
After a few days of delays due to weather and to provide the highest probability of a successful first stage lanidng, the Falcon 9 blasted off at 8:29 pm EST and rapidly arced to the northeast on a trajectory matching the orbital inclincation of the Orbcomm spacecraft.
Two and a half minutes after launch, the upper stage separated from the first stage aidied by a new push mechanism that ensured the two sections of rocket would not re-contact. The Merlin engine on the upper stage then ignited to continue the job of delivering Orcbomm’s eleven new machine-to-machine communications satellites to their proper orbits.
After coasting a short period, the first stage, following its own programming, turned around to point back to Cape Canaveral and then restarted 3 of its main engines for what SpaceX calls a “boostback burn” that slowed the rocket’s forward momentum and accelerated it on a reverse path back to Florida.
The engines then shut down to complete the first of three burns required for landing. A few minutes later, the engines restarted again for a “re-entry burn” to manage the rocket’s velocity as it fell faster and faster under the force of gravity and entered the thicker region of Earth’s atmosphere. High above the coast of Florida, the brilliant flame from the rocket startled observers, many of whome remarked it looked like the rocket was heading straight toward them.
However, Falcon was flying a perfect trajectory and once again the engines shut down. Ffor the next few minutes the Falcon stage quided itself toward Landing Zone 1 using four symmetrical grid fins that kept it stable while maintaining a precise trajectory back to Cape Canaveral.
Then, seemingly out of nowhere, the center Merlin engine roared to life just a few miles above the landing pad, lighting up the surrounding area like an eerie launch playing out in reverse to the cheers and awe of the multitude of public spectators up and down the coast.
Flying true as an arrow and without and last-minute hover, the rocket lowered itself on the center of the large SpaceX “X” at Landing Zone 1 (formerly Atlas Launch Complex 13), then shut down its engine and opened vents to relieve pressure in the fuel tanks. Landing occurred at 8:38 pm EST.
“The Falcon has landed,” radioed a SpaceX engineer from launch control while employees at Cape Canaveral and company headquarters in Hawthorne, CA erupted in cheers, tears and backslapping knowing they had just made history.
“[I]t’s a revolutionary moment,” Musk said. “No one has ever brought a booster, an orbital-class booster, back intact. This is something that was actually a useful mission. It delivered eleven satellites to orbit, and then came back and landed. I think that’s perhaps the thing that’s really significant. We achieved the recovery of the rocket in a mission that actually deployed eleven satellites. This is a fundamental step change in technology compared to any other rocket that has ever flown.”
Seconds after Falcon touched down and its engine went dark, two sonic booms rattled over the landscape – one boom from the nose and one from the tail, just like the shuttle. To spectators, and even Elon Musk, who were either not expecting sonic booms or expected them to be heard before landing, the sound caused quite a start before they realized that the sound was the sound of something new and normal for Cape Canaveral.
“The sonic boom reached me about the same time as the rocket touched down, so I actually thought at first that it had exploded. But it turned out just that the sonic boom almost exactly coincided with the touchdown point so the sound reached me several seconds later,” Musk recalled during a postflight media teleconference. “I thought, ‘Well, at least we got close,’ but I went back into launch control, and there was this amazing view of the rocket still standing there on the landing zone. I can’t quite believe it.”
Shortly after landing, Musk tweeted, “Welcome back, baby”. Even SpaceX’s public affair officials could barely contain themselves as the media gathering at Port Canaveral’s Exploration Tower also erupted with cheers and a few wet eyes. SpaceX rented Exploration Tower for the launch since no media or unnecessary personnel were permitted on Cape Canaveral AFS this time.
The sonic booms were followed by the roar of the Merlin engine as it guided the rocket to the ground, making the event seem like a complete reverse-replay of launch.
Meanwhile, high in space, The Falcon upper stage had commenced the deployment sequence for the 11 OG2 satellites, which will complete Orbcomm’s constellation that includes 34 satellites already in orbit.
An amibitious 2015 was interrupted by a disappointing failure when the rocket’s second stage liquid oxygen tank failed a minute and a half after launch. The mishap was traced to an internal strut in the tank that failed below its certified limit, causing the tank to rupture and destruction of the rocket and Dragon spacecraft loaded with supplies for the International Space Station.
SpaceX clearly needed a successful return to flight and wanted it to take place before the end of the year, leading some critics to wonder if they were rushing to return to launches. However, considering the number of “firsts” on the flight – not to mention the landing – one should probably give greater credit to a “can do” attitude coupled with a methodical engineering process to “find it, fix it, fly it”, paraphrasing NASA’s mantra after the Columbia accident.
“Today clearly placed the exclamation mark on 2015, by closing out another successful year for the Eastern Range in historic fashion,” said Brig. Gen. Wayne Monteith, 45th Space Wing commander and launch decision authority. “This launch and flyback speaks volumes to the hard work this team puts in every single day driving innovation and success. This was a first for us at Cape Canaveral Air Force Station, and I can’t even begin to describe the excitement the team feels right now having been a part of this historic first-stage rocket landing.”