All of those you said are very true. It's also worth mentioning that that very 'safe' engine has already killed three people, and injured three others during a cold-flow test. Very tragic.

see for details: http://www.knightsarrow.com/rockets/scaled-composites-accide...

or the "Test program accident" at the wiki: http://en.wikipedia.org/wiki/RocketMotorTwo

How do you even manage to kill not one but three people with shrapnel during a pressure test? Proper safety procedure demands that anything potentially shrapnel-producing is contained within an enclosure and that engineers are outside the area while testing takes place.

The whole incident indicates a lax safety culture.

Precisely. An absence of proper safety procedures is how.

You are right. Hybrid engines are not looking like the safe & reliable middle-ground between solid & liquid engines that they were made out to be.

"The best of both worlds" has an often overlooked twin sibling.. "The worst of both worlds"

Or as it's sometimes formulated, "the sports car-slash-dump truck problem."

In other words, you can build a great sports car, or a great dump truck. But there's no way to build a great sports car that is also a great dump truck.

Maybe not, but you can always pivot[1]!

http://spectrum.ieee.org/view-from-the-valley/transportation...

"The only thing in the middle of the road is yellow lines and dead armadillos."

all the performance of solids with all the complexities of liquids!

Yeah, "rocket" + "safe enough to carry tourists regularly" just seems like a difficult combination.

Many years ago, trying to combine "flying in the air" with "safe enough to carry tourists regularly" would be seen in a similar light.

It took 54 years to go from the Wright Brothers first flight to the Boeing 707.

It took 53 years to go from Yuri Gagarin's first flight (one orbit) to this suborbital flight test.

It only took 8 / 9 years between Gagarin's flight and landing men on the Moon. That's remarkable.

It's depressing to think how much closer we'd be to humans on Mars if we had focussed all the Afghan and Iraq war money on space research.

It only took 8 / 9 years between Gagarin's flight and landing test pilots on the Moon. Which is still remarkable.

Since this sub-thread has invoked tourists and the implied safety and convenience of a commercial operation that carries passengers and other payload. Tourists are payload, test pilots are ... test pilots.

Or simply to reduce the national debt.

Fair point, but the failure modes of flying seem to be more addressable than those of rockets. Like if the airplane engine is essential, add enough that you can tolerate a failure. If control surfaces are essential, add redundant systems. Whereas the failure mode of rockets tends to be exploding, and that's pretty hard to mitigate.

The failure modes of rocket engines could be explosions but nobody says you can't have multiple redundant engines on a single rocket. In fact, in 2012 Falcon 9 demonstrated exactly that: one of their 9 Merlin engines blew up but the rest redistributed the load and the rocket successfully delivered the payload to the ISS[1].

[1] http://blogs.discovermagazine.com/badastronomy/2012/10/08/sp...

According to the article you are quoting the engine didn't explode; it's just failed. I'd be very impressed if a rocket survived an explosion of one of its engines (they are much closer together than jet engines on a passenger plane and even i such planes an explosion of one engines can damage others due to shrapnel).

The engine has been the bane of SS2. The original rubber/N2O design was problematic enough that Virgin switched from rubber to a plastic. Apparently this was the first powered flight to use the new fuel.

While the design lacks complicated turbopumps and cryogenic fuels, it does have one drawback: the N2O is contained in a pressure vessel. If that tank is damaged while still full (or close to), bad things can happen.

Looking more into their design turns up all sorts of issues with nitrous oxide as a propellant. It's used all the time in dentist offices, so it's easy to misunderstand as an innocuous gas. At higher pressures and relatively normal temperatures it can go supercritical and become very, very volatile. At that point it's an even better solvent than supercritical CO2, and still a very strong oxidizer:

http://www.knightsarrow.com/rockets/scaled-composites-accide...

http://www.dtic.mil/dtic/tr/fulltext/u2/a489459.pdf

(In that Air Force research lab report there's mention of supercritical N20 causing a spontaneous explosion with coffee grounds.)

Well, you want it to be a strong oxidizer, that's its purpose in the rocket.

Strong oxidizers are almost universally hard to handle. About the nicest ones around are Lox, Nox and hydrogen peroxide.

Agreed.

Don't forget that this is not the first fatality associated with this engine. In 2007, 3 people were killed in an explosion during a static test at Mohave Air & Space port.

So they traded sometimes dangerous moving parts that could lead to a mission fail to a rarely dangerous pressurized vessel that would lead to casualties?

Is this a case of not seeing safety's big picture? Cutting accidents in half (or by whatever) is great, but not if that means the remaining accidents are fatal. A more frequent controlled failure is a much better scenario, but I imagine hurts the bottom line too much.

I'm wary that for-profit companies aren't going to invest enough in private manned spaceflight's safety when there's a profit incentive at work dictating otherwise. At least without a fair bit of regulation.

I think it's very hard to make that determination. In spaceflight, all accidents are likely to be fatal. Also, I have no problem with a profit-motive; killing your passengers is very bad for business.

Yes in this market, the invisible hand will tend to ensure the success of companies that don't blow up their passengers.

They just switched to a new liquid powered engine because their hybrid engine was not powerful enough. This was the first powered test flight with their new engine, and given the information so far it sounds like it exploded in-flight. Very, very, tragic.

edit: I'm wrong. They simply switched to a new type of fuel for their hybrid engine.

I hadn't heard about that, thanks for the info.

I dug up this article:

http://www.parabolicarc.com/2014/10/08/work-continues-hybrid...

Interesting. I might actually be wrong about the details then. Maybe the new engines they were using is actually a new type of hybrid (nylon)? I know for a fact that they are working on their own liquid engine, but perhaps it wasn't involved in this crash.

Well Soyuz still flies and has exceptionally low human fatality rates in the last decades. So if safetey realiability is desired it could be just "buy a ride on a Souyz" for now.

I think it won't be that dire. People who sign up to fly into space on a new design would probably be aware of the risks involved.

Many people still climb Everest, dive into caves, and jump from clifs with wingsuits. I think there won't be a shortage and the future is bright and exciting.

AFAIR there is an order of magnitude of two between the prospected prices of virgin galactic and a soyuz trip.

A ride on Virgin Galactic is $250,000 a ride to the ISS on a soyuz is $70,000,000.

There is also at least an order of magnitude between their maximum altitudes.

The altitude is not important.

https://what-if.xkcd.com/58/

SpaceShipTwo is meant to get to zero velocity at ~105km up. Soyuz gets to 17,450 mph at 200km up (and then catches up to the station at 400km up). Only the speed sideways is important, and there is more than one order of magnitude difference.

> SpaceshipTwo is considered the 'simplest' and 'safest' of all the upcoming manned commercial vehicle.

XCOR's culture of safety is pretty good, though it's the school of thought quite close to Virgin Galactic . At least rocket engines in XCOR are designed with the highest standards of safety.

It's been reported that it "exploded in mid-air", and two parachutes were deployed, so the cause probably was not the wing-feathering system.

Yes, looking at the twitter feed, multiple sources state that it blew up. This means that either the tank (which takes up the whole rear half of the vehicle) failed catastrophically (unlikely; CF-wrapped tanks tend to develop hairline cracks which slowly leak out) OR the engine exploded.

What's interesting is that the SS2 engine fuel was swapped out very recently for a new thermoplastic polyamide solid fuel for better performace. Maybe this new fuel was not tested as well as it should have been?

static wick failure, minor fuel leak, big bang.

That said, I really have no clue about how these things work. That's just one scenario I could see leading to a midair explosion.

An oxidizer leak isn't going to explode.

(And it's pretty hard for a leak of anything to explode much when there's nowhere for it to build up. Limited internal space, wind rushing by...)

My bet is a hard start.

sad. also manned flight to mars to colonize it like Musk says seems impossible for at least a couple decades.

The accidents this week seem to have no bearing on that.

It may or may not be true, but it's the same thing it was last week.