A final series of rocket engine test firings that could lead to low-altitude flights are being prepared by Mojave air and spaceport-based Interorbital Systems (IOS) for its SeaStar launch vehicle.

A cluster of four and then eight 3,000lb-thrust (13.5kN) engines will be fired together at the IOS Mojave engine test stand over the next couple of months.

The company's throttleable engine design use a proprietary liquid hydrocarbon-based fuel called Hydrocarbon-X and white fuming nitric acid (WFNA) as an oxidiser, which is a hypergolic combination.

The SeaStar flight-test vehicle is nearly complete and the first low-altitude launches could take place by year-end off the coast of southern California. The SeaStar is fired from a canister floating upright in the sea, eliminating the need for land-based infrastructure.

Because the hypergolic fuels are storable at room temperature, IOS expects its SeaStar to be stored fully fuelled enabling a rapid-response launch capability. IOS chief executive Randa Milliron says: "You can let it sit there for six years and it's ready to go by opening a valve."

According to the US National Institute for Occupational Safety and Health, WFNA is corrosive to metals. IOS uses composite storage tanks to cope with this. The company is working with the US Federal Aviation Administration's commercial space transport office for launch licences.

Source: Flight International