WASHINGTON — A Space Exploration Technologies Corp. Dragon spacecraft arrived at the international space station April 20, delivering nearly 2,100 kilograms of cargo to the orbital outpost. Dragon’s arrival followed an April 18 launch aboard a SpaceX Falcon 9 launcher that pulled double-duty as an experiment in rocket reusability. The goal was to do a simulated “landing” at sea of Falcon 9’s first stage, which was equipped with four landing legs for the experiment.

After separating from the upper stage that sent Dragon to orbit, Falcon 9’s first stage fired back up, steered itself back down to sea level, extended its landing legs, and turned itself vertical more or less as it would for touchdown on solid ground. SpaceX says the stage hit the water at near-zero velocity.

“I’m happy to confirm that we were able to do a soft-landing of the Falcon 9 boost stage in the Atlantic, and all the data that we received back shows that it did a soft landing and was in a healthy condition after that,” SpaceX founder and Chief Executive Elon Musk said during an April 25 press conference here.

The stage was not recovered intact because of rough seas, Musk said. SpaceX did get bits and pieces of the stage back, including one of the stage’s four landing legs.

Dragon, meanwhile, is slated to bring back some 1,600 kilograms of cargo, including scientific experiments and medical samples, when it splashes down May 18. Dragon’s launch was delayed several times, most recently April 14, when a faulty helium valve on Falcon 9’s first stage prompted the company to abort liftoff and swap out the balky hardware.

On April 23, with Dragon still berthed with station, astronauts completed a spacewalk to replace an external computer that failed April 11.

Now that Dragon has arrived, NASA’s other contract cargo hauler, Orbital Sciences Corp. of Dulles, Va., is set to launch its next cargo delivery mission in early June.

SpaceX, Hawthorne, Calif., and Orbital are delivering cargo to the ISS under Commercial Resupply Services (CRS) contracts signed in 2008. SpaceX’s $1.6 billion deal calls for delivering at least 20 tons of cargo spread over 12 flights. Orbital, which has flown one delivery mission so far, has an eight-flight, $1.9 billion contract.


Reduce, Reuse, Refly

SpaceX’s latest ISS cargo run, its third CRS flight to date, marked the second time the company has conducted launch-day experiments with rocket reusability.

Looking ahead, a landing attempt on terra firma might yet happen this year, and SpaceX might fly a recovered booster as early as 2015, Musk said during the press conference. Besides experiments conducted after launches for customers — the first took place after Falcon 9 launched Canada’s Cassiope space-weather satellite in September — SpaceX has been testing components of its reusable booster system on test bed vehicles known as Grasshopper and F9R.

The single-engine Grasshopper, now retired, started flying in 2011 from SpaceX’s test facility in McGregor, Texas. F9R, a three-engine variant that logged its first flight April 14 in McGregor, will eventually transition to New Mexico’s Spaceport America for suborbital flights.

The company’s goal is to land a used booster stage on the ground, retrieve it, reintegrate it with another payload, refuel it and relaunch it, engines and all. Musk used the phrase “fully, and rapidly reusable.” After a dry landing, it might take as little as one day to refuel and reuse a recovered booster, Musk speculated at the April 25 press conference.

NASA, meanwhile, was interested in the April 18 experiment because of its applicability to landing large payloads on Mars. However, the agency was not able to get the data it wanted because the Lockheed Martin P-3 aircraft that was supposed to be dispatched from the Langley Research Center in Hampton, Va., to track the descending stage was not able to get off the ground “because of icy conditions,” according William Gerstenmaier, NASA’s associate administrator for human exploration and operations.

“What we were doing is looking at how [rocket] thrusters work supersonically for braking into the thinner martian atmosphere instead of using parachutes,” Gerstenmaier told SpaceNews at the Humans to Mars summit here April 22. “We needed external photographic evidence, external thermal imaging.

An aircraft that tracked the first stage’s entry, descent and splashdown for SpaceX did not produce the sort of data NASA wanted, Gerstenmaier said.

Dan Leone is a SpaceNews staff writer, covering NASA, NOAA and a growing number of entrepreneurial space companies. He earned a bachelor’s degree in public communications from the American University in Washington.