Wreckage of the Virgin Galatic SpaceShipTwo

Analysis: What was behind the SpaceShipTwo crash?

Virgin Galactic has been synonymous with space tourism since the start of its partnership with California-based Scaled Composites, the company that won the Ansari X-Prize in 2004 after its SpaceShipOne became the first private spacecraft to reach the edge of space.

Virgin Galactic has been synonymous with space tourism since the start of its partnership with California-based Scaled Composites, the company that won the Ansari X-Prize in 2004 after its SpaceShipOne became the first private spacecraft to reach the edge of space.

Thanks to the media influence of the company's CEO, British billionaire Sir Richard Branson, the public was led to believe that Virgin was the undisputed frontrunner in the space tourism race that will open space to masses (or at least to those who can afford the '150,000 ticket).

However, after the catastrophic crash of its SpaceShipTwo in late October, some industry insiders stepped forward disputing Virgin Galactic's choice of technology and safety engineering practices.

Although investigators of the US National Transportation Safety Board concluded that the ill-fated spacecraft was likely torn apart by aerodynamic forces after its braking mechanism deployed prematurely at supersonic speed, the engineers remained adamant that the space-plane's hybrid rocket engine is of the gravest concern.

"What happened to Virgin Galactic is very sad, it's terrible," said Jose Mariano Lopez Urdiales, an MIT-educated aerospace engineer who trained at the European Space Agency and spent some time working for aerospace giant Boeing.

"Regardless of what happened, their choice of engine has been very problematic since the beginning. It may have been the right choice of engine to win the XPrize but it was not the right choice of engine to develop a commercial business. And that's not just my opinion. Anybody who knows anything about rocket propulsion would say the same."

SpaceShipTwo was powered by a hybrid rocket engine using solid fuel burning in liquid oxidiser - nitrous oxide. This chemical compound, also known as laughing gas, is known for its tendency to spontaneous decomposition, which can lead to deadly explosions - as Virgin Galactic learned first-hand after a tank filled with the gas exploded during a ground test in 2007 killing three Scaled Composites engineers.

This tendency to explosions led to the original suspicions that SpaceShipTwo may have exploded in flight, killing co-pilot Michael Alsbury and injuring pilot Peter Siebold. But the fact that the tanks and engine were found intact, ruling out the explosion, did not ease concerns from the space community.

"The problem with the engine is not only that it can blow up, [but] also the vibrations that it induces on the rest of the airframe," said Lopez Urdiales. "And when you have very strong vibrations, you can expect to have subsystems or some mechanisms failing."

Hybrid rockets are simpler than their more commonly used liquid propellant counterparts. This simplicity, allowing the designers to work with only one set of tanks, was likely the main motivation of Burt Rutan, the Scaled Composites' founder, to choose this type of engine for his SpaceShipOne.

However, what worked well for the slender SpaceShipOne was likely causing difficulties in the case of bulkier SpaceShipTwo, designed to carry two pilots and six paying passengers above the Karman line.

"What we see with these engines is that you can't scale them up. It works for certain sizes but not for bigger sizes," Lopez Urdiales said. "This was known from the time when hybrid engines were looked at as potential systems for missiles and considered unstable. So when they were considered unstable for missiles, how could they be OK for manned rockets?"

Virgin Galactic's competitor XCOR, for example, is using a liquid rocket engine burning liquefied natural gas (LNG) in liquid oxygen.

"That's a very clean propellant, there is a lot of data about it, it's well understood," Lopez Urdiales said. "LNG or methane, those are the cleanest, least expensive and best understood fuels. These fuels are cheap, clean and they don't produce the huge vibrations in combustion that you get with hybrids of certain sizes."

Lopez Urdiales, CEO of a Barcelona-based space start-up Zero2Infinity, can't hide his disappointment with Virgin Galactic. In fact, he has a very personal interest in its success and is concerned about the impact the tragedy will have on the fledgling industry including, of course, his own company.

"Five years ago, Virgin Galactic got a cheque from Sheikh Mansour for about $390m. Had they followed the advice from all these people, including myself, today they would be giving a bigger cheque back to the Sheikh, possibly $1bn maybe via an IPO," Lopez Urdiales said.

"This would mean that capital would flow into new space ventures, which is exactly what is needed. It would be much easier for companies like mine or XCOR to raise the capital to complete their systems. The limiting factor now is not market or technology but capital."

But despite the media hype and frequent announcements of upcoming commercial operations, Lopez Urdiales admitted he never considered Virgin Galactic the likeliest winner in the space tourism race.

"The way I look at these things is about safety performance and I don't see this thinking in Virgin Galactic, I don't see the company being run with an engineering mind," he said. "I believe that Blue Origin, XCor or SpaceX are all more likely to fly a customer before Virgin Galactic does."

The fact that multiple high-ranked engineers, including the vice-president for propulsion Thomas Markusic, have left the company adds gravity to Lopez Urdiales's words. But it's not only the space start-up community who is critical of Virgin Galactic.

Tommaso Sgobba, former head of safety at the European Space Agency and president of the International Association for the Advancement of Space Safety, said Virgin Galactic is not employing modern hazard mitigation engineering practices and is instead using a trial and error approach.

"In the early days of aviation, the designers were using an approach known as fly-fix-fly," Sgobba said. "You build a machine, you fly it, you get a problem, perhaps an accident, you fix it, you fly it again, until your performance is OK. But at about the time when nuclear ballistic missiles were being developed, this approach had to be abandoned because you couldn't afford having a nuclear disaster in order to learn from mistakes."

Instead, a technique known as hazard analysis, mandated in all Nasa projects today, was developed. It expects all possible risks and their severity to be determined ahead of the construction of a spacecraft with solutions mitigating or minimising all possible hazards integrated into the design.

“If Virgin Galactic had performed an engineering hazard analysis, they would have considered the possibility of a human error or an inadvertent release of its feathering mechanism and they would have designed a solution to mitigate this hazard,” Sgobba said. “Had they done that, there would have likely been no accident and no fatality.”

Unlike Virgin Galactic, private space companies such as SpaceX or Orbital Sciences, working for Nasa, are obliged to carry out hazard analysis as a standard requirement.

Virgin Galactic declined to comment on its technology choices and design practices until the NTBS investigation is completed. However, this may take up to a year. The latest findings suggest the co-pilot prematurely pre-activated the space-plane’s moveable tail section for reasons unknown. The mechanism, designed to slow down the plane for atmospheric re-entry, subsequently deployed without an actual command being issued.

Recent articles

Info Message

Our sites use cookies to support some functionality, and to collect anonymous user data.

Learn more about IET cookies and how to control them