Attenborough’s Email to Virgin Galactic’s Ticket Holders Explaining Engine Change

Nitrous nylon engine test on Jan. 16, 2014. (Credit: Ken Brown)

From: Future Astronauts
Date: May 23, 2014
Cc: Future Astronauts
Subject: Rocket Motor Milestone News

Dear all,

We have said on previous occasions that of the numerous challenges Virgin Galactic has faced and overcome in our unprecedented mission to create the world’s first spaceline, the greatest has been that of creating and perfecting the world’s largest operational hybrid rocket motor to power SpaceShipTwo and its occupants safely, regularly and efficiently to space. This has also been, of late, the area of greatest external speculation.

While we have tried to provide regular updates, commercial and regulatory restrictions have at times prevented us from disclosing every twist and turn in the propulsion system development program. We are therefore happy today to be able to share the completion of another milestone in this area.

In 2008, Scaled Composites, our primary contractor, appointed rocket propulsion specialist Sierra Nevada (SNC) to develop the basic hybrid rocket motor design for SpaceShipTwo. As a part of that development program, we decided to develop two variants of this motor design using two types of benign solid fuel: HTPB, a type of rubber (the fuel used in the SpaceShipOne rocket motor and for the first three powered flights of SpaceShipTwo) and polyamide, a type of plastic. Both fuels were designed to be interchangeable with the hybrid motor, with only minor plumbing modifications, meaning that we have been able to remain objective and unbiased in our assessment of the alternative fuel choices. Both have also been tested extensively.

As we have entered the qualification phase of the commercial hybrid motor in preparation for the final series of powered test flights, it has been critical to finalize the fuel that we’ll use for this and into the start of commercial operations. We have now determined we will utilize the plastic-based option, which has demonstrated more promising performance characteristics in burn duration, stability and predicted altitude. Both Scaled and SNC will continue to support the motor program as the company progresses toward commercial service.

Having made this decision, we will now be working hard to make the minor modifications to the spaceship systems in order to continue powered flights with the chosen fuel type as soon as safely possible. The benefit of having pursued the parallel development paths is that the modifications required are minimal, and we continue to be on schedule to resume powered test flights with SpaceshipTwo later this summer.

We are excited to have completed this milestone and hope the clarification around our propulsion system development work will put to rest some of the questions and concerns in this area. As always, thank you for your continued support and don’t hesitate to get in touch with Clare, Gemma or me if you have any questions.

Best wishes for the weekend,

Stephen Attenborough
Commercial Director

Editor’s Note: The rubber-nitous engine really doesn’t work very well. It would have torn SpaceShipTwo apart with oscillations and vibrations before it got anywhere near space. They way they have been portraying this change — as a choice between a good, safe engine and a better engine — is not accurate.

Oh, I also got some news on the WhiteKnightTwo carrier aircraft today. A directive has gone out from Virgin Galactic CEO George Whitesides demanding that engineers stop using the word “cracks’ to describe the cracks in WhiteKnightTwo’s wings. They must now refer to them as “adhesive imperfections.”