T he U.S. Air Force is making the correct call in sticking with the Space Exploration Technologies Corp. (SpaceX) Falcon 1 rocket to launch its TacSat-1 satellite this September in spite of the vehicle’s failure to reach orbit in its only two flights to date.

Is there risk involved? Certainly, but TacSat-1, as a relatively low-cost demonstration, is the type of payload for which a higher level of risk is generally acceptable. Moreover, TacSat-1 already is well behind schedule and has been leapfrogged into space by a follow-on satellite, TacSat-2. The longer TacSat-1 sits on the ground, the less relevant the experiment becomes.

To be sure, SpaceX has some work to do, notwithstanding the company’s victory declarations even after it became clear that the Falcon 1 did not achieve orbital velocity during its March 20 demonstration. The fact that the vehicle, technically speaking, made it into space would have been of no consequence had there been an actual satellite on board . The happy talk, while perhaps understandable given that the rocket did much better than during its first time out, when its main engine failed, might irritate nervous satellite owners.

But it is undeniable that SpaceX learned a lot from this second launch: The vehicle was well into its second-stage burn when it was done in by a roll control issue at an altitude of about 300 kilometers. If SpaceX founder and Chief Executive Elon Musk overreached in saying the company had retired nearly all of the risk associated with the Falcon 1, so did his critics in scoffing at his characterization of the mission as a near success.

The notion that there is no such thing as a partial success in the launch business is itself only partially correct. This was, after all, a demonstration: The data collected during the flight has value, and this value was not negated by the loss of a payload.

It is not unusual to encounter trouble in the first few launches of new rockets — just ask the designers of Orbital Sciences Corp.’s Pegasus or Boeing Co.’s Delta 3, the latter of which never made it as an operational launcher.

It is to Mr. Musk’s credit that he intends to continue his quest for space access at a reasonable cost. That the Air Force is giving SpaceX the benefit of the doubt by entrusting Falcon 1 with TacSat-1 is to the service’s credit as well as in its own best interest.