WASHINGTON — As it prepares for its first official resupply mission to the international space station, Space Exploration Technologies Corp. (SpaceX) is also testing cornerstone technology for a future fly-back booster system that could allow the Hawthorne, Calif., company to reuse the first stage of its Falcon 9 rocket.

On Sept. 21 at its rocket test facility in McGregor, Texas, SpaceX engineers conducted the first flight of the company’s experimental Grasshopper vehicle — a vertical takeoff, vertical landing rocket that is essentially a Falcon 9 first stage mounted on landing legs and powered by a single Merlin 1D engine. In its debut flight, Grasshopper rose 1.8 meters off the ground, then descended back to the pad.

“The Grasshopper test rig is mostly about characterizing new electronics and control software, figuring out remote and rapid flight operations, plus fine-tuning engine throttle,” SpaceX spokeswoman Katherine Nelson said in a Sept. 27 email. “The Sept. 21 test was to assess remote operation of the test rig vehicle and verify the landing legs were able to handle a drop of approximately [1.8 meters]. It did that.”

The next Grasshopper flight, in which the craft will boost to an altitude of about 30.5 meters and briefly hover, is slated for sometime in the next several months, Nelson said.

SpaceX is also planning a second evolution of the Grasshopper vehicle. The next iteration of the test platform, being developed now, will have “lighter legs that fold up on the side of the rocket, a different engine bay and be about 50% longer” than the current Grasshopper, Nelson said. She did not say when the updated Grasshopper might fly.

Grasshopper is intended to pave the way for a reusable Falcon 9 rocket, a medium-lift rocket the company built to launch its Dragon cargo capsule and a growing backlog of government and commercial satellites.

Elon Musk, SpaceX’s founder and chief executive, has said a fly-back Falcon 9 first stage would have to be capable of aerodynamic maneuvering, withstanding the heat of atmospheric re-entry, and landing propulsively on deployable legs.

A former employee of Masten Space Systems, a company whose experimental vertical takeoff, vertical landing rockets Xaero and Xombie have logged a combined 270 test flights since 2009, said the most difficult part of SpaceX’s reusable rocket proposition is steering the first stage back toward the launch pad after engine cutoff and stage separation at altitude.

“Ultimately, in order to really prove this out, the big question mark is going to be the aerodynamic control and then the engine relight when you’ve had the engine off for several minutes, because it absolutely has to light,” Jonathan Goff, former lead propulsion engineer at Masten, said in a Sept. 24 phone interview. Goff left Masten in 2010 and is now president and chief executive of his own company, Altius Space Machines.

Such a test of SpaceX hardware is probably years off, Goff speculated. As with any flight test regime involving reusable vehicles, “you want to be able to get the vehicle back after almost every test, so you want to minimize the number of crashes and you end up expending the envelope gradually,” Goff said.

SpaceX, in a document published last year by the Federal Aviation Administration as part of the regulatory agency’s due diligence for licensing Grasshopper flights at McGregor, said the Grasshopper test program could last up to three years. At the time, SpaceX said that Grasshopper might fly as many as 70 suborbital flights a year.

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.