Flashback: Virgin Galactic Announces Switch From Rubber to Nylon Engine

RocketMotorTwo firing. (Credit: Virgin Galactic)
RocketMotorTwo firing. (Credit: Virgin Galactic)

Parabolic Arc Flashback: One year ago, Virgin Galactic announced it changing SpaceShipTwo’s propulsion system from a rubber hybrid to a nylon hybrid engine due to demonstrated better performance. The news was announced on a Friday at the start of long holiday weekends in the U.S. and Britain, a perfect time to dump news when neither reporters nor the public are paying much attention. Sierra Nevada, by the way, was blindsided that their rubber engine was being dropped and their lucrative agreement was going away.

Today, the nylon engine decision is being re-evaluated due to performance. The company recently revealed it is testing both hybid engines again, and it might go back to using the rubber one. That means the company still doesn’t know how its going to power its spacecraft despite being nearly 11 years into the SpaceShipTwo program. That explains why it is taking as long as it is.

MOJAVE, Calif., May 23, 2014 (Virgin Galactic PR) – Virgin Galactic, the world’s first commercial spaceline which is owned by Sir Richard Branson’s Virgin Group and Abu Dhabi’s aabar Investments PJS, has selected a polyamide-based fuel grain to power its hybrid rocket motor for the remainder of the test flight program and start of commercial operations. This decision follows numerous ground test firings and is supported by data collected over an extensive development program.

In 2008, Scaled Composites, Virgin Galactic’s primary contractor, appointed rocket propulsion specialist, Sierra Nevada Corporation (SNC) to develop the basic hybrid rocket motor design for SpaceShipTwo. As a part of the program, Virgin Galactic has been developing two variants of this motor using two types of solid fuel grain: HTPB, a type of rubber (the fuel used in the SpaceShipOne rocket motor) and polyamide, a category of benign thermoplastic using Scaled engineering. Both fuel grains were designed to be interchangeable with the hybrid motor, and both have been tested extensively.

Virgin Galactic has now determined it will use the polyamide version for its space flights. Both industrial partners will continue to support the motor program as the company progresses toward commercial service.

“Of the numerous challenges Virgin Galactic has faced and overcome in our unprecedented mission to create the world’s first spaceline, the greatest engineering challenge has been to develop the world’s largest operational hybrid rocket motor to power SpaceShipTwo and its occupants safely, regularly and efficiently to space,” said Virgin Galactic CEO George Whitesides. “It is a great credit to the work of our partners Scaled and SNC that we have completed this important milestone.”

To view a ground-firing of the polyamide-fueled hybrid rocket motor, CLICK HERE

  • GreenWyvern

    “That means the company still doesn’t know how its going to power its spacecraft despite being nearly 11 years into the SpaceShipTwo program.”

    It’s being powered by a system personally developed by Richard Branson. This is the first hot air powered spacecraft.

  • Hemingway

    It is my opinion the hybrid engine is not the right rocket motor.

  • Enrique Moreno

    Why not to use an “hybrid-hybrid” engine, I mean a nylon engine with holes in which to put rubber… the best of both… ;-D

  • Valerij Gilinskij

    I do not know how to build a hybrid engine. But I am sure that in Russia there are many engineers capable of a maximum of three to four years to create a rocket engine using liquid methane and liquid oxygen as fuel, has required parameters, reliable and suitable for reuse.

  • Snofru Chufu

    There are even Russian engineers with experiences in quite large hybrid rocket propulsion.


  • BeanCounterFromDownUnder

    I wonder how many customers have had their deposits returned?

  • Valerij Gilinskij

    I am, to put it mildly, is not sure that the hybrid rocket engines the right choice. So it might have seemed ten years ago. Now it is evident that it was necessary to use rocket engines with methane as a fuel.

  • Snofru Chufu

    I think it this case is methane not a good choice. I would prefer a liquid fuel with a high flash point, for safety reasons.

  • Hemingway
  • Valerij Gilinskij

    Methane is less dangerous than kerosene and hydrogen.

  • Snofru Chufu

    No. (BTW, I did not talk about hydrogen, that is your introduction). I talked about a liquid fuel (for example bio-biesel or some kind of advanced liquid synthetic hydrocarbon as RJ-4 for example). Such type of liquid fuel will not easily vaporize (to form an explosive or flammable mixture with air and oxidizer vapors) as cryogenic methane.

  • Christopher James Huff

    Methane is piped and trucked around on a massive scale, run into people’s homes, and there’s thousands of vehicles on the road that use it…even using the cryogenic liquid form. If you don’t think it’s safe enough for a rocket plane, you might want to just stay inside…as long as you don’t have a gas stove, furnace, or water heater, anyway.

  • Valerij Gilinskij

    Methane does not require extreme cryogenics, it has a temperature around such as liquid oxygen used as the oxidant. In the case of methane leakage evaporates and disperses outdoors without forming an explosive mixture.

  • voronwae

    This is known as “doing the thing to do the thing”, and sometimes in doing the first thing one loses track of the original goal.

    The original goal was to stand up a suborbital tourism business. That goal has been swallowed by the goal of designing a working, reliable, small hybrid engine. At some point, if it’s not too late, Virgin needs to take a step back and remember what it was they set out to do. What a nightmare.

  • Snofru Chufu

    Nobody talked about extreme or not extreme cryogenics, why do you mention it.

    BTW, oh my god, you found a new physics. Methane disperses (in what? in vacuum?) and went outdoors without mixing with air. Fine!

  • Snofru Chufu

    The most hazardous stuff is trucked around on a mssive scale. Millions of tons of nitric acid, N2O and many other dangerous stuff. That is no argument. May be we shall review accidents that happens, esp. that at home.

    I would select always the safest fuel, if no other requirements are more important.

  • Snofru Chufu

    Here is the story of the world’s first LOX-methane rockets (1931) build by Johannes Winkler. One version – HW-2 was destroyed due to the formation of an explosive mixture.