Space Ship Two - General Thread

[QuantumG]

Pressure suits are a hack for people who can't build a cabin that pressurizes properly. Anything that breaks a properly designed cabin at altitude is likely to kill you even if you're wearing a pressure suit. There's a reason why we don't walk around with belt and suspenders on.

[Borklund]

The crew of Soyuz 11 would beg to differ, if they weren't dead. There's a difference between walking around town in a plastic wrapped EOD suit and reasonably exercising caution.

[QuantumG]

The crew of Soyuz 11 would beg to differ, if they weren't dead. There's a difference between walking around town in a plastic wrapped EOD suit and reasonably exercising caution.

Not at all. Pressure suits are a hack for people who can't build a cabin that pressurizes properly. I dunno how I can make that more clear. The solution to the Soyuz 11 incident was to fix the ventilation valve. Making everyone wear pressure suits was unnecessary, as evidenced by the fact that they've never averted a disaster, ever. Pressure suits in a correctly pressurized cabin are worse than useless.

[RonM]

The crew of Soyuz 11 would beg to differ, if they weren't dead. There's a difference between walking around town in a plastic wrapped EOD suit and reasonably exercising caution.

Not at all. Pressure suits are a hack for people who can't build a cabin that pressurizes properly. I dunno how I can make that more clear. The solution to the Soyuz 11 incident was to fix the ventilation valve. Making everyone wear pressure suits was unnecessary, as evidenced by the fact that they've never averted a disaster, ever. Pressure suits in a correctly pressurized cabin are worse than useless.

How do you know if your cabin is a "correctly pressurized cabin" or not? Just saying it is doesn't make it so. After extensive ground testing and several test flights, then you might have the confidence to not use pressure suits. Using pressure suits, at least during testing, is not a hack.

As to pressure suits having never averted a disaster, if they had them on Soyuz 11, the crew would have survived.

Modern airliners are "correctly pressurized cabins" and as Borklund wrote, airliners carry oxygen masks.

In the case of Space Ship Two, I'm sure the Virgin Galactic team has studied their design to great detail and considered the risks.

[QuantumG]

How do you know if your cabin is a "correctly pressurized cabin" or not? Just saying it is doesn't make it so. After extensive ground testing and several test flights, then you might have the confidence to not use pressure suits. Using pressure suits, at least during testing, is not a hack.

Yes.

As to pressure suits having never averted a disaster, if they had them on Soyuz 11, the crew would have survived.

Says you. In all the history of human spaceflight, this is the only example you can come up with? A maybe?

Modern airliners are "correctly pressurized cabins" and as Borklund wrote, airliners carry oxygen masks.

.. and? Aircraft have completely different failure modes to spacecraft.

In the case of Space Ship Two, I'm sure the Virgin Galactic team has studied their design to great detail and considered the risks.

Borklund clearly thinks otherwise!

[sdsds]

Pressure suits are a hack for people who can't build a cabin that pressurizes properly.

Dissimilar redundancy is a tried and true technique for reducing overall risk of system failure in the face of both foreseen and unforeseen challenges.

Is there a way that can be expressed any more clearly?

[QuantumG]

Pressure suits are a hack for people who can't build a cabin that pressurizes properly.

Dissimilar redundancy is a tried and true technique for reducing overall risk of system failure in the face of both foreseen and unforeseen challenges.

Adding more complexity when there's no benefit to doing so doesn't reduce risk, it increases it.

There's no evidence to support the argument that pressure suits reduce risk. It's really not unreasonable to expect some incident to have occurred on all the human spaceflights throughout the last 50 years where a pressure suit actually saved a life, is it? That is the purpose of a pressure suit. It hasn't happened. It's clearly just a feel good measure, and criticizing someone for flying people without them is unjustified.

[RonM]

How do you know if your cabin is a "correctly pressurized cabin" or not? Just saying it is doesn't make it so. After extensive ground testing and several test flights, then you might have the confidence to not use pressure suits. Using pressure suits, at least during testing, is not a hack.

Yes.

As to pressure suits having never averted a disaster, if they had them on Soyuz 11, the crew would have survived.

Says you. In all the history of human spaceflight, this is the only example you can come up with? A maybe?

Modern airliners are "correctly pressurized cabins" and as Borklund wrote, airliners carry oxygen masks.

.. and? Aircraft have completely different failure modes to spacecraft.

In the case of Space Ship Two, I'm sure the Virgin Galactic team has studied their design to great detail and considered the risks.

Borklund clearly thinks otherwise!

Fortunately, Soyuz 11 is the only example. You're dismissal of pressure suits just because there hasn't been another Soyuz 11 style accident is illogical. It could happen on the next flight. I think the Russians know what they are doing and they still have their crews wear suits.

While there are major differences between aircraft and spacecraft, the pressurized cabins are very similar.

Borklund, you, and me are allowed to have our opinions. Remember that they are just opinions.

[QuantumG]

Fortunately, Soyuz 11 is the only example. You're dismissal of pressure suits just because there hasn't been another Soyuz 11 style accident is illogical.

That's not what I said. What I said is that there's never been an incident where a pressure suit on a spacecraft has saved a life. It wouldn't matter if there had been hundreds of cases where people had died in Soyuz 11 style accidents, implementing pressure suits would still be the wrong reaction if they're completely ineffective, which clearly they are.

While there are major differences between aircraft and spacecraft, the pressurized cabins are very similar.

No they're not! They're not even similar.

[Herb Schaltegger]

It wouldn't matter if there had been hundreds of cases where people had died in Soyuz 11 style accidents, implementing pressure suits would still be the wrong reaction if they're completely ineffective, which clearly they are.

Explain to me how pressure suits are "completely ineffective" in preventing loss of life in a loss-of-pressure situation?
Bear in mind I used to be a life support systems engineer so don't hand-wave and just keep insisting the same things over and over again to shout down the discussion.

[sdsds]

Bill Weaver, on January 25, 1966, while piloting an SR-71 that disintegrated around him at Mach 3.2/78,800 ft, was wearing a pressure suit which saved his life.

[QuantumG]

Explain to me how pressure suits are "completely ineffective" in preventing loss of life in a loss-of-pressure situation?
Bear in mind I used to be a life support systems engineer so don't hand-wave and just keep insisting the same things over and over again to shout down the discussion.

I've already explained it. What do you find incorrect about the assessment?

It's pretty clear that wearing a gas mask would save drivers from passing out should a design flaw result in carbon monoxide being pumped through the vents, but we don't require people to wear them either. Why? Don't we care about their safety? Suppose there was a single incident in 1971 by a Russian car manufacturer and, despite the best precautions being taken by car manufacturers, everyone started wearing gas masks. Wouldn't it be reasonable, 40 years later, to ask for a few examples of people being saved as a result of wearing their gas masks? If there was none, wouldn't you start to think that maybe people are being just a tad overcautious? If someone started driving without their gas mask, would you be justified in calling them reckless?

Common sense, it's not too much to ask is it?

[QuantumG]

Bill Weaver, on January 25, 1966, while piloting an SR-71 that disintegrated around him at Mach 3.2/78,800 ft, was wearing a pressure suit which saved his life.

If he hadn't been wearing a pressure suit, he'd be dead before he even got there. That's why he was wearing a pressure suit. The vehicle was designed to require one.

[RonM]

Explain to me how pressure suits are "completely ineffective" in preventing loss of life in a loss-of-pressure situation?
Bear in mind I used to be a life support systems engineer so don't hand-wave and just keep insisting the same things over and over again to shout down the discussion.

I've already explained it. What do you find incorrect about the assessment?

It's pretty clear that wearing a gas mask would save drivers from passing out should a design flaw result in carbon monoxide being pumped through the vents, but we don't require people to wear them either. Why? Don't we care about their safety? Suppose there was a single incident in 1971 by a Russian car manufacturer and, despite the best precautions being taken by car manufacturers, everyone started wearing gas masks. Wouldn't it be reasonable, 40 years later, to ask for a few examples of people being saved as a result of wearing their gas masks? If there was none, wouldn't you start to think that maybe people are being just a tad overcautious? If someone started driving without their gas mask, would you be justified in calling them reckless?

Common sense, it's not too much to ask is it?

There has only been about 300 manned spaceflights, so comparing it to cars is ridiculous.

[RonM]

Bill Weaver, on January 25, 1966, while piloting an SR-71 that disintegrated around him at Mach 3.2/78,800 ft, was wearing a pressure suit which saved his life.

If he hadn't been wearing a pressure suit, he'd be dead before he even got there. That's why he was wearing a pressure suit. The vehicle was designed to require one.

The SR-71 cockpit was pressurized. You wouldn't be dead without a pressure suit, but since the chance of failure was high, you would wear one.

[QuantumG]

There has only been about 300 manned spaceflights, so comparing it to cars is ridiculous.

I wasn't. I was just trying to make my argument in a way that people could understand, as it appears you still don't.

[QuantumG]

The SR-71 cockpit was pressurized. You wouldn't be dead without a pressure suit, but since the chance of failure was high, you would wear one.

Actually, no. You couldn't fly the SR-71 in shirtsleeves. Not even just with a g-suit and oxygen.

I appreciate the effort to actually address the issue - there's no empirical evidence that pressure suits have actually made spaceflight safer. Pressure suits are not the only example either. If you haven't heard the laundry list of things that Richard Garriott had to go through before he could fly, including prophylactic surgery (that actually put his life at risk) then you should. People have and will continue to decry Virgin Galactic for being irresponsible to dare fly people with less absurd safety precautions than the national space agencies. It's pretty much the only reason why I get disheartened when they start talking about the absurd safety precautions they are talking about doing.

[RonM]

There has only been about 300 manned spaceflights, so comparing it to cars is ridiculous.

I wasn't. I was just trying to make my argument in a way that people could understand, as it appears you still don't.

I understand your argument, I just don't agree with it.

[Lar]

I think the pressure in here is rising and people are starting to explode a bit... so no more about pressure suits unless you are actually adding some facts or at least something new. If you think I might possibly be talking to you, I am. Thankyouverymuch.

[MoeMelek]

You've got some good points, but there is some hyperbole in your statement.
Yes, the new engine is riskier in some areas (more complicated), but it's safer in others (less stress-inducing vibration).
Yes, SS1 had shuttlecock problems.  But it was an experimental testbed, not a commercial airframe.  One presumes they took a harder look at this known potential failure point when designing SS2.
Yes, SS1 had chunks of rubber flying out the back.  It was expected even if it was a bit loud.

Personally, I think the pre-flight fuel handling and potential helium handling problems are going to add some logistics and schedule adherence headaches versus plugging in a solid fuel module prior to each flight, but they've obviously calculated that it's an expense they can and have to absorb, or they wouldn't have chosen this route.

I agree with your point that the helium and menthane will hopefully reduce vibrations and increase saftey, but compared to the simple engine it was announced as they might have a more unsafe one now. The original idea was that in the event of engine problems the nitrous oxide could just be turned off, and the engine would stop. You would have an aborted launch but you'd be safe. Apparently, the vibrations in the rubber/nitrous oxide version was so bad it could rip the ship apart (I do however not know regarding the nylon one) If there is a problem with the methane or helium feeding system, there is a risk that the engine vibrations could harm the vehicle before the crew has a chance to turn off the engine. Leaking methane could cause explosions. I understand that this is speculation on my part and I do not have all the details, but in the end the engine is nevertheless not as simple as initially announced, and it has more failure modes.

Yes hopefully the shuttle cock will be more reliable in SS2, as it's survival critical.