Project STERN Information
Introduction
The Skylon spaceplane - image courtesy of Reaction
Engines Limited / Adrian Mann
The STERN project (Static Test Expansion deflection Rocket Nozzle) was formed by a consortium of Reaction Engines Limited, University of Bristol and Airborne Engineering Limited, to construct rocket engine hardware to investigate the performance of an Expansion Deflection (ED) design, evaluate its potential for use on the propulsion system for the Skylon Single Stage To Orbit spaceplane, and to produce the first published results from a live firing of an ED design, with the intention of determining the evidence for the wake evacuation effect. The ED nozzle will then continue to be evaluated in free flight conditions, through its use on the Canary sounding rocket.
The STERN engine is the first ED nozzle rocket engine to be tested in the UK.
On the Skylon spaceplane, the altitude compensation of ED nozzles offers the promise of further improvements to the Skylon propulsion system, the SABRE (Synergetic Air Breathing Rocket Engine). This is why a hydrogen / air combination was chosen for the hot fire run tests of the STERN engine.
Expansion Deflection (ED) Nozzles
Expansion Deflection nozzles have long been considered for use in trans-atmospheric vehicles due to the potential increments in performance offered through altitude compensation. However, there are several difficulties associated with the type, primarily a more complex combustion chamber and throat design, and the importance non-isentropic flow phenomena such as viscosity and shock waves on flow field composition. This means that the flow solution techniques required for the design process are more complex than conventional nozzle analysis, until relatively recently (the last decade or two) beyond the capabilities of standard aerodynamic tools in widespread use. Furthermore the greater complexity results in a broader design space, increasing the length of the design process as a greater number of issues must be investigated.
The STERN rocket engine with RZ-20 based ignition system,
injector manifold, and sensors
Ignition System
The STERN engine ignition system, built by Reaction Engines Limited, builds upon the ignition system used for the Rolls Royce RZ-20 Liquid Hydrogen / Liquid Oxygen upper stage rocket engine, which was developed and tested as part of the long term development of the Blue Streak rocket programme.
The STERN ignition system is in fact, the same ignition system as that to be used in the SABRE engine on the Skylon spaceplane, thus the successful ignition and combustion tests of the STERN engine validate this aspect of the SABRE engine design.
Prior to integration into the STERN engine, the hydrogen / oxygen based ignition system was hot fire tested on many test runs at the Reaction Engines test facilities. This was followed by hot fire tests at the static test facility.
The STERN engine during
static testing
Test Programme
The initial test programme consisted of 2 hydrogen / air rocket engines designed by Alan Bond and Richard Varvill of Reaction Engines Limited. One rocket engine is used as a calibration rocket engine, and the other rocket engine incorporates the ED nozzle designed by Dr Neil Taylor of University of Bristol.
For the test programme, Airborne Engineering constructed a fully instrumented static test rig for vertical firings of the rocket engines. A comprehensive, networked sensor system feeds all the test data back to rack mounted Linux servers in a secure control bunker facility, from where all firing control operations are conducted remotely, with viewing via several high resolution CCD cameras mounted around the static test stand.
Following a comprehensive set of tests of the ignition system, hydrostatic testing of the static test rig and the rocket engines, and cold flow hydrogen and air tests of the static test rig and engines, the test data was carefully analysed before proceding to the hot fire tests. The Airborne Engineering test facility enables data analysis to be performed on site, enabling rapid turnaround for any configuration changes.
The Project STERN calibration rocket
engine undergoing static testing
The first tests of the STERN engine with an ED nozzle took place on Wednesday 19 March 2008. This was the first UK firing of a rocket engine with an ED nozzle and the first ever test of an ED nozzle with air-hydrogen propellants. It also demonstrates that it is still possible for a small team on a low budget to take a rocket engine from concept to live testing in less than a year.
| Type of Test | Number of Tests |
|---|---|
| Cold Flow Tests | 15 |
| Hot Firings | 20 |
| Type of Test | Number of Tests |
|---|---|
| Cold Flow Tests | 8 |
| Hot Firings | 7 |
History
- March 2006 - First discussions at BROHP 2006 Conference
- March 2007 - Formal project start meeting of Project STERN Consortium at BROHP 2007 Conference
- September 2007 - First hydrogen / oxygen igniter hot fire static tests
- October 2007 - Project STERN ED Nozzled engine completed ready for test firing
- November 2007 - The first ED nozzled engine under Project STERN was publically displayed at the BIS symposium in Glasgow's SEC
- February 2008 - Static test cell construction completed
- March 2008 - Calibration rocket engine hot fire static tests
- March 2008 - Start of first phase of ED nozzle hot fire static tests
- August 2008 - Final first phase ED nozzle hot fire static tests
- September 2008 - Start of second phase of ED nozzle hot fire static tests
- December 2008 - Start of third phase of ED nozzle hot fire static tests
- February 2009 - Continuation of third phase of ED nozzle hot fire static tests
- February 2009 - Transition to Project STRICT rocket engine development
