TORONTO — Orbital Sciences Corp. will make a decision on replacing the engine used in the first stage of its Antares rocket before submitting a proposal to NASA in November for a follow-on international space station cargo contract, a company official said Sept. 30.

In a presentation at the 65th International Astronautical Congress here, Orbital Executive Vice President Frank Culbertson said the engine decision is linked to the company’s proposal for NASA’s Commercial Resupply Services (CRS)2 competition. NASA issued the request for proposals for CRS2 on Sept. 26, with responses due Nov. 14.

“We’ll make sure we’ll have a decision on that before we submit the proposal,” Culbertson said when asked about the status of the engine decision.

Orbital has been weighing for several months a replacement for the AJ-26 engines that Antares currently uses. Those engines, provided by Aerojet Rocketdyne, are refurbished versions of Soviet-era NK-33 engines originally designed for the N-1 lunar rocket developed in the 1960s.

Culbertson said Orbital had been in discussion with “several companies” on a new engine, but did not name them. One option reportedly under consideration is to replace the current Antares first stage with a solid-rocket motor from ATK, with whom Orbital is in the process of merging. ATK currently provides the solid motor used in the Antares second stage.

There are enough AJ-26 engines in stock, Culbertson said, for Orbital to perform the remaining six missions in its current CRS contract with NASA, as well as some additional launches. The existing cargo contract could be extended as a bridge until the CRS2 contracts begin. “We’ll sign it as soon as NASA offers it,” he said of a potential CRS contract extension.

An investigation into an AJ-26 engine that failed during a May test firing at NASA’s Stennis Space Center in Mississippi, is also wrapping up, Culbertson said. “We have come up with probably two potential root causes, both of which we can screen for,” he said. Engine firings on the repaired test stand there will resume in October.

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