Scale Composites’ Mojave Hot Fire Likely Didn’t Involve RocketMotorTwo

RocketMotorTwo test firing. (Courtesy Beverly S. Rother)

CORRECTION:  Virgin Galactic says this test did involve RocketMotorTwo. I regret the error.

By Douglas Messier
Parabolic Arc Managing Editor

The engine hot fire done at Scaled Composites test site at the Mojave Air and Space Port on Wednesday does not appear to have involved the RocketMotorTwo that will be used on the SpaceShipTwo suborbital tourism vehicle, a careful reading of the test summary reveals.

The summary for Hot Fire No. 12 on the Scaled Composites “RocketMotorTwo Hot-Fire Test Summaries” page says it was the “first full scale firing of a rocket motor at Scaled’s test site under full control of the spaceship’s Rocket Motor Controller (RMC).” [Emphasis mine].

Each of the previous 11 test entries on the page includes the phrase “full scale flight design RM2 hot-fire.” That phrase is absent from the summary for the brief test on Wednesday, which is reproduced below.

Fire: 12
Date: 20 June 12

Perform first full scale rocket motor hot-fire at Scaled’s test facility
Test stand evaluation
Data Acquisition system evaluation
Rocket Motor Controller performance
Pressurization System Controller performance
Rocket system performance
Valve / Injector / Igniter evaluation
Fuel formulation evaluation
CTN structural evaluation

First full scale firing of a rocket motor at Scaled’s test site under full control of the spaceship’s Rocket Motor Controller (RMC). All objectives achieved. The difference between Scaled’s site and SNC’s site at Lakeside is the focus on using SS2 flight vehicle hardware. These tests provide an end to end test of all the vehicle’s rocket motor systems and additional confidence before committing the vehicle to powered flight test.

It’s unclear precisely what was fired earlier this week. My best guess is that the test was of a smaller “starter” engine that Virgin Galactic CEO George Whitesides mentioned recently. He said the company expected to begin powered flights with the motor toward the end of the year. Depending upon how the flights go, commercial service would hopefully begin with the full motor at the end of 2013.

How realistic that scenario is has been the subject of much discussion in Mojave. It is well known that engineers have faced serious difficulties in scaling up the hybrid engine used on SpaceShipOne for its much larger successor. A major problem they have had to overcome is severe oscillations during the hot firings. Many believe the big engine remains problematic.

There are also multiple reports of a parallel liquid-fuel engine development program to replace the hybrid. Those reports have been difficult to pin down with exact certainty. What changes, if any, such a move would require in SpaceShipTwo’s design and how it would affect the test schedule are uncertain.