Whitesides Responds to Bower’s Allegation About SpaceShipTwo’s Engine

branson_behind_the_maskVirgin Galactic CEO George Whitesides has responded to Tom Bower’s new book, “Branson: Behind the Mask.” The author makes a series of claims about the performance and safety of the nitrous oxide-rubber engine that is scheduled to send SpaceShipTwo on a suborbital flight later this year.

Whitesides wrote a letter to The Sunday Times, which began serializing the biography a week ago. The response, published on Feb. 2, is reproduced below:

Dear Sir:

Tom Bower’s claims in extracts from his new book on Richard Branson that Virgin Galactic has “no licence” and “no rocket” to go to space (“Lost in space” and “The sun lizard fading into exile”, News Review, last week) misrepresent the facts and use old information to create a story. Indeed the recent progress of the Galactic programme, including the latest rocket powered flight, renders Bower’s main claims false.

The company’s rocket motor has burned for the full duration and thrust multiple times, and the company released video footage of one such test in December. Bower also fails to note that the team has an experimental permit from the Federal Aviation Administration for the test flight programme phase.

The company applied for a commercial licence in 2013 as planned and to coincide with the latter stages of the test flight programme. It expects to receive that licence well in advance of commercial service later in 2014.

Most seriously, Bower attempts to cast doubt on Virgin Galactic’s absolute commitment to safety, particularly by suggesting that any potential lessons that could have been learnt by the tragic 2007 industrial accident at Scaled Composites were somehow brushed under the carpet. The opposite is true. The company supported the full independent enquiry and accepted all the resulting recommendations in terms of system re-design along with their costs and time implications. The end result is a system that will be significantly safer.

Bower also claims that Richard no longer owns any of the principal Virgin businesses and that the company has ceased to innovate. Among others, Virgin Galactic is majority owned by Richard Branson and it certainly innovates. Richard’s empire has not shrunk and his work, through his foundation and companies, is creating a real impact.

Yours sincerely

George Whitesides
CEO, Virgin Galactic

Let’s look at the response more closely.

Engine Claims

Bower’s claim is specific: he says that Virgin Galactic lacks an engine powerful enough to get SpaceShipTwo with two pilots and six passengers above the 100 km (62.1 mile) boundary of space (aka, the Karman Line). This is what the company has been promising to ticket holders for the past nine years.

Whitesides’ response doesn’t specifically address that claim. It references  several developments that show significant progress in the air and on the ground. However, the letter doesn’t say, ‘SpaceShipTwo can reach 100 km with a full load of crew and passengers with the RocketMotorTwo engine we have. Bower’s claim is false.’

The letter points to the recent third powered test of SpaceShipTwo, which fired its engine for 20 seconds, reached Mach 1.4, and flew to a new record altitude of 71,000 feet.  The test was similar to one performed in September, although the ship went 2,000 feet higher.

My sources tell me that they have gone as far as they can with that version of the hybrid nitrous oxide-rubber engine. It has serious vibration and oscillation problems that engineers have been attempting to solve.

The letter references a video of a 55-second hot fire of RocketMotorTwo. The test looked good, but Virgin Galactic has  released no details about it, including thrust, when it was conducted, or whether this is the final version of what will fly on SpaceShipTwo. Without those specifics, it’s impossible to evaluate whether the engine is powerful enough to lift SpaceShipTwo to 100 km and thus disprove Bower’s claim.

Assuming the test was conducted recently, then it would have been part of an ongoing series of ground hot fires that Virgin Galactic Vice President Will Pomerantz told NBC News Science Editor Alan Boyle about recently.

“We and our contractors at Scaled Composites and Sierra Nevada are continuing to develop ways to improve the motor design by making them easier to manufacture and install, or by further improving their handling characteristics and performance,” Pomerantz wrote in an email to Boyle.

The goal of that hot fire might well have been to test a method to dampen out the oscillations in the nitrous oxide-rubber hybrid. Did the engineers achieve this goal? What modifications did they make to do so? And what impact, if any, would those modifications have on the ability to SpaceShipTwo to reach 100 km?

The letter provides no answers. In sharp contrast with Virgin Galactic’s chattiness about the Newton engines it is developing for LauncherOne, the company has been extremely reluctant to release details about RocketMotorTwo.

The engine hot fire test logs on partner Scaled Composites’ website are so lacking in specifics that it’s very difficult to glean very much useful information from them. The entries tell you when a test took place, what parameters were tested, and that all results were inevitably achieved. Beyond that, there’s not much there.

It’s not even possible to tell what type of engine they tested on any given day. Scaled conducted a hot fire test of an alternative engine design that uses nylon and nitrous oxide on Jan. 16. The hot fire, which sources say is part of a series of engine tests using nylon, ended up on the Scaled’s log page along with entries about rubber hybrid tests.

It has long been public knowledge that SpaceShipTwo might go through flight tests with a nitrous oxide-nylon engine instead of one that burns rubber. This was clearly indicated in the FAA’s Final Environmental Assessment for the Launch and Reentry of SpaceShipTwo Reusable Suborbital Rockets at the Mojave Air and Space Port  published in May 2012.

The assessment, which was required for the experimental flight test permit that Whiteside mentioned in his letter, includes emissions calculations for both nitrous oxide-rubber and nitrous oxide-nylon engines.

The evidence shows that even as Virgin Galactic is promising to start commercial service this year, engineers are still working on perfecting the engine it will use to do so. The company has provided no evidence to specifically knock down Bower’s claim about SpaceShipTwo’s performance issues, i.e., can the ship reach 100 km with a full load of crew and passengers.

Commercial License

Whitesides is likely correct in saying Virgin Galactic will receive a commercial license to fly passengers well in advance of doing so. There has been some confusion on this issue, which I inadvertently contributed to with some recent ill-informed speculation about the FAA’s licensing process.

I had earlier believed that the FAA would need to see some evidence that SpaceShipTwo was capable of performing its principle mission — flying into space — before it issued a license. Jeff Foust and others say that I’m wrong, and I believe they are correct in their judgment.

In commercial aviation, it’s up to an aircraft’s builder to prove to the FAA that the vehicle is safe to fly passengers under a strict certification regime. That system has worked well in producing reliable aircraft, although the problems Boeing experienced with the 787’s batteries show it’s not perfect.

With suborbital commercial spaceflight, the company must only prove to itself that the vehicle is safe enough to fly passengers. There is no certification regime and no requirements for extensive flights tests prior to the granting of a license.

Virgin Galactic and other spaceflight companies are operating under an informed consent regime. As long as customers are informed that the activity is dangerous and they could die, and they sign a waiver acknowledging these realities, they can fly on these vehicles.

The FAA’s main concern is the safety of the uninvolved public.  The agency uses a similar standard in licensing commercial satellite launches. The FAA doesn’t care if a Falcon 9 launch vehicle fails, it just doesn’t want the rocket killing anyone at Cape Canaveral or crashing into Cocoa Beach.

Safety of Hybrids

Whitesides says that the hybrid motor will be “significantly safer” as a result of what engineers learned from that tragic accident that killed three engineers in Mojave nearly seven years ago. That is almost certainly true.

Bower’s book raises more specific questions. One is the issue of whether nitrous oxide is safe enough to use in human spaceflight. There are engineers who have worked with nitrous oxide who are quite passionate in saying that it is not safe enough to use.

The second issue Bower raises is the accuracy of Virgin Galactic’s claims about the safe, benign nature of its hybrid rocket system and nitrous oxide. The company makes very strong claims on the safety page of its website, including the assertion that hybrids are superior to both liquid and solid-fuel engines.

“However, there is a third type of rocket propulsion known as a hybrid motor. Here the fuel is in solid form and the oxidizer is a liquid. The passage of the oxidizer over the fuel is controlled by a valve which allows the motor to be throttled or shut down as required.

“Hybrid motors offer both simplicity and safety. This is the type of motor that SpaceShipTwo will employ and that was used by SpaceShipOne. It means that the pilots will be able to shut down the SpaceShipTwo rocket motor at any time during its operation and glide safely back to the runway. The oxidizer is Nitrous Oxide and the fuel a rubber compound; both benign, stable as well as containing none of the toxins found in solid rocket motors.”

Again, there are very strong counter opinions about just how safe hybrids are, and whether they offer any real advantages over liquid and solid-fuel systems. That’s an engineering debate I’m not going to wade into.


The letter addresses more general concerns than the specific ones that Bower has raised in his book. Something more specific will need to be released to put the concerns about performance. Even then, only test flights above 100 km will finally put the issue to rest.

As for safety, that question can only be resolved after SpaceShipTwo flies many times using the nitrous engine. It’s the only way to prove the reliability of any rocket engine.