WASHINGTON — The explosion Sept. 1 that destroyed a SpaceX Falcon 9 rocket and its satellite payload took place not during a launch attempt but instead in a pre-launch test that is all but unique to SpaceX.

The explosion at Space Launch Complex 40 at Cape Canaveral Air Force Station occurred while the Falcon 9 was being filled with liquid oxygen and kerosene in preparation for a static-fire test, where the rocket’s nine first stage engines are briefly ignited on the pad a few days before the scheduled launch.

The static-fire tests have been a standard part of pre-launch preparations for Falcon 9 launches throughout the vehicle’s history. They are intended to serve as full dress rehearsals for launches and also verify the performance of the first stage engine.

They are, however, not used by other launch providers. While vehicle providers may perform acceptance testing of engines during development, they typically do not fire the engines once the vehicle is on the pad being prepared for launch. Moreover, such tests are impractical for solid-fueled vehicles, whose motors cannot be turned off once ignited.

Orbital ATK has done static fire tests of its Antares launch vehicle at Virginia’s Mid-Atlantic Regional Spaceport, both before the inaugural launch of the vehicle in 2013 and again May 31, prior to the first launch of a new version of the rocket that has different first stage engines. However, those tests took place well in advance of the scheduled launches, and in the case of the May 31 test involved a different first stage from the one the company planned to use on its next launch, now planned for no earlier than the second half of September.

Other companies will do various types of dress rehearsals of launches, but even those can be limited. Several years ago, United Launch Alliance discontinued a pre-launch test known as a wet dress rehearsal for all Atlas 5 launches. In that test, the launch vehicle is fueled during a practice countdown, but the main engines are not ignited.

There are cases where ULA does perform a wet dress rehearsal, primarily for Atlas missions that have short launch windows, such as NASA planetary missions. ULA did a wet dress rehearsal last month in advance of the scheduled Sept. 8 launch of NASA’s OSIRIS-REx asteroid sample return mission.

Part of the reason for ending the practice of wet dress rehearsals for all Atlas missions was to save time and money. In 2012, when ULA stopped doing those rehearsals for all Atlas launches, the Aerospace Corporation found that skipping the rehearsal would save five days and about $500,000 during a launch campaign.

An effort to save time may have also contributed to the loss of the payload on this Falcon 9, the Amos-6 communications satellite. Falcon 9 static fire tests in the past have not always included the satellite payload, waiting instead to install the satellite after the test, but now payloads are more commonly installed on the rocket prior to the test. Doing so, industry sources say, cuts a day from launch processing schedules.

The pad explosion also raises questions of what constitutes a “launch failure.” While both the rocket and payload were lost in the accident, the explosion took place during preparations for a test, rather than the launch itself, and before the main engines ignited. In a non-scientific poll of SpaceNews readers, nearly 55 percent believed the incident should be classified as a launch failure as of late Sept. 2.

That definition is more than just an intellectual curiosity. Because the explosion took place before the “intentional ignition” of the Falcon 9, the loss of the satellite is not covered by launch insurance. Spacecom, the satellite’s owner, did have a separate insurance policy on the satellite to cover pre-launch activities.

Losses of launch vehicles in pre-launch activities are rare, but not unprecedented. In August 2003, a Brazilian VLS small launch vehicle exploded during pre-launch preparations at the Alcântara launch site when one of the rocket’s solid-fuel motors inadvertently ignited. The explosion destroyed the launch pad and killed 21 workers there.