NASA's new rocket nozzle passes transonic acceleration test with high overall efficiency, according to initial results

A NASA-led team has completed the first flight tests of a solid-fuelled aerospike rocket that appears to deliver better than expected performance through the critical transonic acceleration phase.

The tests took place at the Pecos County flight test range at Fort Stockton, Texas in conjunction with NASA Dryden Flight Research Center, the US Air Force Flight Test Center and model rocket specialist Blacksky. The rocket reached an altitude of 29,000ft (8,850m) and a speed of Mach 1.5.

An aerospike nozzle depends on atmospheric and airstream pressure to shape the optimum plume as the rocket climbs, whereas conventional "bellmouth" rocket nozzles are efficient at only one point in the trajectory.

The heavily-instrumented 3m (10ft) rocket was fitted with a NASA-developed flush air-data system to capture detailed information about the performance of the nozzle. "One of our original objectives was to try to measure the aerospike nozzle performance through, or just at, transonic conditions," says NASA's principal project investigator Trong Bui. "Initial data shows somewhat of a drop in nozzle efficiency at Mach 1 but, even with the drop, the overallefficiency stays high throughout the trajectory so we are pretty excited," he says.

Future plans include tests in 2005 with a longer-firing rocket motor with a burn out altitude from 15,000-20,000ft rather than the 6,000-7,000ft of the recent tests.

The team also plans to test a "truncated" nozzle version, if further funds are allocated. "At the moment we have the perfect shape right now which is a sharp spike at the end of the nozzle. We would like to investigate the effects of chopping this off. We think we can get more or less the same efficiencies even with it pretty severely truncated. This offers weight and cost savings," says Bui. The aerospike nozzle and motor was developed by Cesaroni Technology of Canada.

The NASA solid-fuelled aerospike tests follow the launch last September of a liquid-propellant aerospike engine on the California State University/Garvey Spacecraft-developed, 4m-long Prospector 2 research vehicle. The liquid oxygen/ethanol fuelled engine achieved an altitude of around 4,000ft on a flight from the Mojave Test Area but went out of control and crashed following the failure of the combustion chamber seal.



Source: Flight International