A SpaceX launch slated for 9:49 p.m. Sept. 19 at Vandenberg Air Force Base will not go ahead as scheduled.

In response to a Business Times inquiry on Sept. 8, a SpaceX spokesman said in an email “There’s no SpaceX launch scheduled for Sept. 19,” but did not elaborate further.

On Sept. 1, a SpaceX Falcon 9 rocket exploded during a static fire test prior to the planned Sept. 3 launch of the Amos-6 communications satellite on the coast of Cape Canaveral, Fla. A $200 million Facebook satellite that was destroyed would’ve brought the Internet to under-served parts of the developing world including parts of Africa.

The cause of the explosion still is not known, but this week the Air Force joined an investigation into the cause of the incident.

SpaceX said in a statement at the time that the explosion occurred while propellant was being added to a fuel tank and that the explosion was around an upper oxygen tank.

“At approximately 9:07 a.m. ET during a standard pre-launch static fire test there was an anomaly at SpaceX’s Cape Canaveral Space Launch Complex 40 resulting in the loss of the vehicle,” the statement said on Sept. 1.

The explosion was SpaceX’s second in 15 months after a June 28, 2015 explosion occurred off the coast of Cape Canaveral less than three minutes into an unmanned mission to resupply the International Space Station.

After its second failure, doubts are now being raised about SpaceX contracts with NASA worth billions. In November 2015 the agency awarded SpaceX a $2.6 billion contract to carry crew to the International Space Station in a manned version of its Dragon Capsule beginning by 2017.

In February, the agency also awarded a $700 million contract to SpaceX that builds upon a $1.6 billion contract NASA awarded the company in 2008.

The Sept. 19 launch would’ve been the first of seven to send 10 small Iridium satellites into orbit. The launch has been delayed since May because of ongoing maintenance at Vandenberg at buildings used to monitor rocket launches.

Virginia-based Iridium Communications has been hampered by SpaceX’s stalled launch schedule. Over the past two months its stock has fallen from $9.26 per share to a close of $7.24 on Sept. 7

In addition to the Sept. 19 launch, another Falcon 9 Iridium launch was tentatively scheduled for late December. After that, five remaining SpaceX launches of Iridium satellites were to happen in 60-day intervals.

Iridium customers who intend to use the satellites once in orbit and operable have also been hampered by the delays.

“Our No. 1 priority is to safely and reliably return to flight for our customers, as well as to take all the necessary steps to ensure the highest possible levels of safety for future crewed missions with the Falcon 9,” SpaceX said in a Sept. 2 statement. “We will carefully and thoroughly investigate and address this issue.”

SpaceX started conducting tests at Vandenberg in 2005 and currently leases two launch pads at Vandenberg from the Air Force.

Both pads were built in the 1960s for early Atlas rockets and modified in the 1970s for the Titan family of rockets. SpaceX demolished structures at the second pad in September 2014 to make it easier to complete landings.

A separate United Launch Alliance launch is still scheduled for about 11:30 a.m. Sept. 15 and will send the WorldView 4 observation satellite into orbit.

• Contact Philip Joens at pjoens@pacbiztimes.com.