Film cooling of rocket motors is to be demonstrated in the next quarter in long-duration tests of a prototype flight-weight engine built under a US Defense Advanced Research Projects Agency and US Air Force contract to develop technology for operationally responsive space vehicles.

California-based Rocket Propulsion Engineering was awarded the contract in late 2005 to develop cooling mechanisms for engines of different sizes. Film cooling uses fuel flow along the interior wall of the combustion chamber to protect the engine. A research target was to develop an engine that would have a six-week delivery lead time and require only a $30,000 deposit.

The company's film cooling demonstrator is a 4,500lb-thrust (20kN) liquid oxygen/kerosene upper-stage engine designed for its planned C-50 rocket, intended to carry 180kg (400lb) to low-Earth orbit. The third hot-fire test at the company's Mojave, California test site lasted 3.7s. In firings the coolant fuel can be seen as a glowing ring surrounding the core cone of propellant flame.

"For the final design of a flight unit we will use various cooling technologies for its lighter structure," says Rocket Propulsion president Jim Grote. The company declines to give details of the other cooling techniques, but it will also use what it calls liquid cooling, which the company says is a combination of film and convection cooling.

Rocket Propulsion started working with DARPA and USAF in 2000, and developed its own two-stage small launch vehicle concept that would use multiple cooling technologies in a pressure-fed engine design with a thrust-to-weight ratio of greater than 130:1. The vehicle was designed to be stockpiled easily, readied for flight quickly and able to place up to 730kg into LEO.

Source: Flight International