December 21, 2015

— SpaceX achieved two returns on Monday night (Dec. 21): returning its Falcon 9 rocket to flight after a failure last June and returning the booster's first stage to a historic landing on land.

The spaceflight company launched its upgraded Falcon 9 rocket from Complex 40 at the Cape Canaveral Air Force Station in Florida at 8:29 p.m. EST (0129 GMT Dec. 22) on a mission to put 11 Orbcomm commercial communications satellites into Earth orbit.

About four minutes into the flight, as the Falcon's second stage was boosting the satellites into space, the rocket's spent first stage re-ignited its engines to propel itself back toward the launch site. Decelerating while descending, the 156-foot-tall (47.5 m) first stage generated a sonic boom, the first heard across Florida's Space Coast since the final space shuttle landing in 2011.

Deploying four legs, the Falcon first stage then descended upright onto a former launch pad, Complex 13, now known as "Landing Zone 1," located 5.6 miles (9 km) from where it launched.

The controlled touchdown marked the first time in history that a rocket used to put a payload into orbit then flew itself back to the ground, making its reuse a possibility.

ORBCOMM-2 launch. Click to enlarge and view video in a new pop-up window. (SpaceX)

"I think this is quite significant," said Elon Musk, SpaceX's billionaire CEO and chief technology officer, in a post-flight briefing with reporters. "It is difficult to say exactly where it ranks but I do think it is a revolutionary moment."

"No one has ever brought an orbital class booster back, intact," he continued. "This is something that was actually, it was a useful mission, delivered 11 satellites to orbit, and then came back and landed. That's perhaps the thing that is really significant — that we achieved the recovery of the rocket on a mission that actually deployed 11 satellites."

"I think this is a fundamental step change in technology, compared to any other rockets that have ever flown," Musk remarked.

SpaceX has attempted twice before to recover its Falcon's first stage using an ocean-going platform, the company's Autonomous Spaceport Drone Ships, but both tries ended with the loss of the rocket in the final moments. Monday's landing was SpaceX's first success at landing the stage.

Musk said that reusability is key to substantially reducing the cost of space access.

"The Falcon 9 rocket costs about $60 million to build. It is kind of like a big jet. But the cost of the propellant, which is mostly oxygen and a gas, is only about $200,000," Musk stated. "That means the potential cost reduction long term is probably in excess of a factor of a hundred."

Monday's launch was SpaceX's first flight since a Falcon 9 suffered an in-flight breakup on June 28 while attempting to loft a Dragon cargo capsule to the International Space Station for NASA. An investigation by the company found that a faulty strut inside the Falcon 9's second stage had caused a helium tank to come free, which resulted in an over-pressurization and the loss of the vehicle.

In addition to implementing a new inspection process for the struts and other vehicle hardware, SpaceX also used Monday's Orbcomm launch to also introduce the use of its upgraded Falcon 9. The new generation Falcon 9 features nine first stage Merlin 1D engines rated for higher thrust.

The older Falcon 9 rockets that flew 19 times since 2010 had first stage engines that had a maximum power level of 147,000 pounds of thrust, or 1.3 million force-pounds when firing together. The Merlin 1D engines generate 170,000 pounds of thrust at sea level, collectively producing more than 1.5 million pounds of thrust.

The upgrades to the Falcon 9 also incorporate a modified interstage to accommodate a second stage Merlin engine with a lengthened nozzle and extended tanks, as well as condensed, super-chilled propellant, allowing extra fuel to be loaded into the rocket. The Falcon flies on liquid oxygen and RP-1, a refined form of kerosene similar to jet fuel.

"There are a number of other improvements in the [Falcon 9's] electronics," Musk said last Tuesday (Dec. 15) during his remarks at an American Geophysical Union meeting in San Francisco. "It is, I think, a significantly improved rocket from the last one."

The upgraded Falcon can now lift communication satellites into geostationary transfer orbits and still have enough fuel to attempt landing the first stage.

The satellites launched Monday will complete Orbcomm's next generation (OG2) network, providing faster message delivery and larger message sizes for their customers.

According to NASA, the recovered Falcon 9 first stage will next be used by SpaceX as a test article for qualifying the modifications to the agency's Launch Pad 39A. SpaceX is leasing the pad from NASA to support crewed launches to the International Space Station and for its planned Falcon Heavy rockets.

"The plan is to take the booster over to Launch Complex 39A, the Apollo 11 launch site we lease from NASA, and do a static fire at the launch pad there, to confirm that all systems are good and that we are able to do a full thrust hold-down firing of the rocket," Musk told reporters. "And then I think we'll probably keep this one on the ground just because it is kind of unique. It is the first one we brought back."

"So I think we'll keep this one on the ground for tests that prove it could fly again and then put it somewhere — just because it is quite unique," he said.