PARIS — Mobile satellite services provider Inmarsat on Nov. 3 said launch-service provider SpaceX has identified the root cause of the Sept. 1 explosion of its Falcon 9 rocket during a launch-pad test and likely will return to flight in December.

“SpaceX has obviously spent some time investigating the reasons behind their recent launch failure,” Inmarsat Chief Executive Rupert Pearce said in a conference call with investors. “We believe they now have found a root cause that is fixable quite easily and quite quickly. So they should be able to return to flight in December.”

London-based Inmarsat is one of the world’s biggest commercial satellite fleet operators. It is one of the few that have maintained an in-house technical staff capable of going beyond satellite manufacturer and launch-service provider assurances to make its own engineering evaluations.

Inmarsat is also one of the many customers of Hawthorne, California-based SpaceX that are pacing the corridors awaiting SpaceX’s announcement of a return-to-flight date.

SpaceX on Oct. 28 issued a statement that suggested — but did not declare outright — that the Sept. 1 explosion during propellant filling in preparation for a test ignition of the rocket was likely due to some combination of the way the rocket’s second-stage cryogenic liquid oxygen propellant and helium pressurant tanks were filled.

The helium tank is immersed in the oxygen reservoir, inside a composite overwrapped pressure vessel. Outside observers have speculated that the composite structure gave way because of the thermal gradient produced when the cryogenic oxygen came in contact with the helium vessel.

SpaceX said it was able to reproduce the failure by using different filling procedures or sequences, but it did not say it reproduced the failure with the same filling procedure used on Sept. 1, nor did it say it had identified a root cause of the incident.

SpaceX on Nov. 3 issued a brief statement reiterating that it was continuing to work to return to flight safely and reliably and a the earliest possible date, without specifying a date. “Inmarsat is a long-time partner, and we remain committed to working with them to meet the needs of their business and customers,” the statement said.

Inmarsat’s three SpaceX contracts

Inmarsat has three launch contracts with SpaceX. Up to now, it had planned to launch its Inmarsat 5-F4 Ka-band broadband mobile communications satellite on a Falcon 9 in late 2016; an S-band aeronautical-connectivity satellite on a new Falcon Heavy rocket in early 2017; and the first of the Inmarsat-6 satellites after that.

Inmarsat’s S-band payload is on a satellite co-owned by fleet operator Arabsat of Saudi Arabia. It had been scheduled for a late-2016 launch on a Falcon Heavy rocket. Falcon Heavy’s debut has slipped to 2017.

Inmarsat’s portion of the satellite is an S-band payload to provide broadband connectivity to airline passengers over Europe alongside a network of terrestrial signal repeaters whose installation has already begun.

Inmarsat’s S-band European Aviation Network (EAN) is operating under a license from the 28-nation European Union, which had set a launch deadline of December 2016.

Because of the possibility of further SpaceX delays, and because finding a geostationary-orbit launch slot is no easy task given the manifests of the main launch-service providers, Inmarsat has decided to stick with SpaceX for the 5-F4 satellite, but to seek alternatives for the mid-2017 S-band satellite launch.

“It’s largely a function of where you are in the manifest,” Pearce said of Inmarsat’s launch reasoning. “With Inmarsat 5 F4, we’re well up in the queue — I think we are number five or six. We have confidence that it will be a modest delay, and a high degree of confidence that we’ll have 5-F4 up quite quickly in the new year.

“So we’re going to stick with SpaceX. We have confidence… in the Falcon launch vehicle and we don’t think there is anything systemic here that would reduce our confidence in a successful launch of 5-F4.”

With the S-band EAN satellite, he said, the reasoning is different.

“We are further [back in] the queue and therefore there’s a risk of further delays because SpaceX not only has to get back to flight but to demonstrate that it can maintain a very good launch schedule. So you could presumably have a day-to-day delay.

European Commission deadline

“For the S-band there are two reasons. One is a regulatory reason: We want to minimize any delays beyond the December date we had initially committed to. And of course to have a service to launch as well at about the middle of next year — which is dependent on a successful satellite launch, or may be dependent. All things being equal we are actively looking at the ability to maintain schedule.”

Pearce said it remain possible that SpaceX will be able to confirm a May or June launch, but that would be difficult to achieve in the deadline Inmarsat has to find an alternative rocket. Pearce said Inmarsat has more than one launch option in addition to SpaceX.

“It’s probably more likely we would look to exercise one of the options we have been quietly cultivating behind the scenes,” Pearce said. “We’ve talked about one of them, which is the [International Launch Services] Proton launch that we have up our sleeve anyway. But we do have other options as well, which we will look to execute on in the next few weeks. If we need to do so, the May-June time frame is where we are comfortable currently.”