SpaceX will get an early opportunity to show what it can do to help scientists and engineers use the International Space Station by flying a powerful thruster testbed up in the unpressurized section of its Dragon cargo capsule.

That capability to fly large unpressurized cargo, and to bring samples back from space to a splashdown recovery off the California coast, will ease a couple of transportation bottlenecks as NASA shifts gears from building the space station to using it.

Last week the agency cleared Innovative Space Propulsion Systems (ISPS), a Houston-based partnership developing green rocket engines that use its patented non-toxic monopropellant, to fly a thruster testbed on the space station. The experimental package, which will ride in the unpressurized section of a Dragon set for launch next year, is exactly the type of work the station was built to accomplish.

“We want to do the hard things, if they're of benefit to society,” says Mike Suffredini, NASA's ISS program manager. “So a high specific impulse, relatively non-toxic engine that uses green storable propellant has a lot of interest to a lot of folks.”

The “NOFBX” engine that ISPS has been developing for the past eight years has attracted “very broad interest from spacecraft and system integrators, as well as propulsion suppliers,” says Max Vozoff, the company's vice president of business development. The work has generated more than 30 patents for the propellant—a proprietary blend of nitrous oxide and other ingredients—and for the engine technology developed to burn it, Vozoff says.

In ground tests, the engines have demonstrated they can be started with a spark igniter, are self-pressurizing and will fire if the propellant is in the liquid or gas states, he says. The company has patented four different propellant mixtures, which deliver specific impulses ranging up to 325 sec., comparable to standard hypergolic propellants.

But unlike hypergols, the monopropellant is non-toxic, Vozoff says, and can be loaded without protective gear or the need for technicians trained to work with hazardous materials. That saves money, as do a number of engine features—low-cost materials throughout, low operating temperatures inside the regeneratively cooled engine jackets, and etching-based production processes borrowed from the microchip industry.

Before joining ISPS, Vozoff spent five years at Space Exploration Technologies Inc.—the formal name for SpaceX. Among his duties was drafting the company's proposal for NASA's Commercial Orbital Transportation Services (COTS) seed-money effort. SpaceX was set to close out its COTS milestones this week, launch conditions permitting, with the first docking of a commercial vehicle at the ISS set for May 22.

Aside from Dragon, the only other vehicle that can deliver unpressurized cargo to the ISS is Japan's H-II Transfer Vehicle. Tentatively set for the Dragon's third commercial flight, the 430-lb. NOFBX Green Propellant Demonstration will ride in the unpressurized bay so the station robotic arm can grapple it.

The demonstration package will be mounted on a Columbus External Payload Adapter, the European version of NASA's Flight Releasable Attach Mechanism (FRAM) pallet, and installed on the outside of the European Space Agency's Columbus laboratory module. The 46 X 34 X 26-in. testbed will include 8 liters of the non-toxic monopropellant, a 100-lb.-thrust engine, and associated valves, tanks and other hardware.

During a year-long test period, the engine will go through a series of hot-fire tests, including steady-state burns, pulses, deep throttling, and restart after long-term storage. Because of the risk associated with firing a rocket attached to the station, the clearance process was rigorous.

“When a new rocket engine, this NOFBX rocket test, wants to go on station, that's a big deal,” says Suffredini. “It fits on a FRAM interface, but ultimately it wants to fire its rocket at different levels, at different times, and the whole station is affected by that.”

Just as NASA took pains to ensure the rocket tests will be safe, the agency's station program office undertook elaborate software checks before certifying that the Dragon will be able to berth at the station safely (AW&ST Feb. 13, p. 27).

The caution exercised in granting clearance to berth does not reflect the level of anticipation among agency scientists awaiting the capability the Dragon can offer. In addition to the external-cargo capability ISPS will use, which can be applied to telescopes and other exposed sensors, the company has procedures to accommodate last-minute stowage in both directions.

“SpaceX becomes really key for our biotechnology development on the NASA lab side, as well as [NASA-funded] life sciences and human research,” says Julie Robinson, the agency's ISS chief scientist. “You have to be able to put those samples in right before you launch, not load them too early . . . and you sometimes need to take them off the space station right before you undock and get them home quickly. SpaceX is going to have the best capability for both those launch and return issues.”