Orbital Sciences Corp. engineers already are looking for another rocket engine to power the Antares medium-lift launch vehicle, after closing out the week demonstrating that the new commercial cargo carrier can safely approach the International Space Station (ISS).

The supply of surplus Soviet-era Nk-33 kerosene-fueled engines extends beyond the 20 Orbital will need to fly out more than $2 billion in NASA work through 2015. Another two of those engines, which Aerojet has modified and labeled as the AJ-26, lifted the first Cygnus cargo capsule to orbit last week.

Assuming all goes well in the next month or so, that mission to the ISS will close out the company's $288 million Commercial Orbital Transportation Services (COTS) Space Act agreement with NASA. After that, the next 16 are destined for the eight ISS resupply missions under Orbital's $1.9 billion Commercial Resupply Services (CRS) contract.

SpaceX as a commercial resupply vendor. (Credit: Mobile Aerospace Reconnaissance System www.marsscientific.com)">

But NASA will continue to need station resupply from Orbital and fellow COTS/CRS contractor SpaceX, and Orbital wants to expand its market beyond the ISS in any event.

The company has indefinite delivery/indefinite quantity contracts with NASA and the Air Force for other medium-lift launch services. While no payloads have surfaced yet, the company is courting the private sector as well.

“We have a lot of interest from people who are waiting to see if we succeed with this before they place a firm order,” said Frank Culbertson, Orbital executive vice president, before last week's launch.

Liftoff of the 13-story Antares/Cygnus stack from the new state-owned spaceport pad on Wallops Island, Va., occurred at 10:58 a.m. EDT Sept. 18. The apparently flawless ascent marked the beginning of 10 safety-of-spaceflight demonstrations over four days, capped by berthing and about a month of operations at the ISS, to complete Orbital's COTS milestones.

A longtime sounding-rocket facility run by NASA's Goddard Space Flight Center, Wallops is a barrier island on Virginia's Eastern Shore that lies near small communities, working farms and other settlements on the mainland. That proximity led NASA officials to check at least four residences shortly before liftoff when range-safety officials raised concerns that a temperature inversion could focus enough overpressure on them in an explosion on ascent to cause windows to blow in. The condition lifted before launch.

The Cygnus vehicle carried about 700 kg (1,543 lb.) of supplies on the demonstration mission, but on early CRS flights it will be able to handle as much as 2,000 kg of pressurized cargo; an enhanced Cygnus would have a 2,700-kg capability. The Cygnus—a pressurized aluminum cylinder made by Thales Alenia Space with heritage in the ISS modules the company built in Turin, Italy—maneuvers using an Orbital Sciences service module based on the company's geostationary-satellite bus technology.

Orbital controllers in Dulles, Va., were maneuvering the Cygnus toward the ISS last week, in preparation for a final set of demonstration maneuvers on Sept. 29—the nominal berthing day. At least two of three orbit-changing burns were completed on Sept. 19 to set up eight planned maneuvers leading to rendezvous, grapple with the station's robotic arm and berthing to the nadir port on the station's Node 2.

Among capabilities to be demonstrated were relative GPS navigation, autonomous maneuvering, lidar navigation using a reflector on the station as a tracking target, and hold-and-retreat maneuvers. The station crew was ready to grapple Cygnus from the robotic control station in the cupola on the nadir side of Node 2, move it to its assigned common berthing mechanism and open the hatch to begin unloading the cargo. Once the vehicle is empty, station crewmembers will begin loading it with trash, discarded gear and other extraneous material for a destructive reentry over the South Pacific east of New Zealand by mid-October, which will mark the mission's end.

Even before the Cygnus started chasing the station, the successful Antares launch encouraged market analysts on Orbital's prospects. “With the end of the development of Antares and Cygnus approaching, and the first CRS missions planned for December, Orbital is on the cusp of improved profitability and an upturn in free cash flow,” wrote Jefferies LLC analyst Howard Rubel.

Culbertson says Orbital plans to find a replacement for the rapidly dwindling store of Russian engines to enable it to continue flying Antares.

“We are looking at what the options are, who has engines that might be compatible and available and how long would it take to develop and/or order them,” he says. “We know that sometime after 2016 we need to start looking at other alternatives, so we've got a very active effort going on with everybody who says they make an engine.”