Virgin Galactic

[2fast748]

eharding said:

cb31 said:

Looks a lot more spacey than I imagined, very impressive. Would need to be a longer ride for me, not that I can afford it. Plus there is no way they should be called astronauts, they are passengers.

I think the definition is going to change over time as Virgin Galactic, Blue Origin and Space X change the game regarding space tourism, but what degree of participation in the conduct of the flight would you say qualified someone as an astronaut or cosmonaut?

Gagarin was, to all intents and purposes, a passenger. Such controls as there were in the capsule were deliberately locked, and everything was managed by the automatic systems. Are you going to argue he didn't in fact qualify as a cosmonaut? Or would you also qualify your categorisation based on the amount of risk and discomfort involved?

You might say the distinction revolves around the amount of training required to justify a seat on the vehicle, and whether what they are doing during the flight could be regarded as productive work rather than a leisure activity - crew rather than Self Loading Space Freight.

Gagarin wasn't a cosmonaut because he didn't land with his ship but the Ruskies kept quiet about that for a while....

It's a difficult one because although Dickie B experienced weightlessness you can also do that at far lower altitudes on the aforementioned vomit comet (or most Ryanair flights..). An arbitrary number of miles/kilometres in altitude is never going to satisfy everyone.

[Eric Mc]

You can experience Zero G on a roller coaster, or a Cessna, or driving fast over a hump back bridge.
The issue is the duration. The higher you are, the longer the experience lasts. On "vomit comet" type Zero G trainer aircraft, you will be lucky to get about 30 seconds. If you do one of these Virgin or New Shepard sub-orbital flights, you will get 2 to 5 minutes. In orbit or travelling through space, of course, you will experience Zero G pretty much indefinitely.

[bmwmike]

Would the re-entry have had flames at the front and been really bouncy, or just gently dropped back into atmosphere like that video seems to show? I dont see any sick bags either

[Einion Yrth]

bmwmike said:

Would the re-entry have had flames at the front and been really bouncy, or just gently dropped back into atmosphere like that video seems to show? I dont see any sick bags either

Max speed about mach 3 - would have got a bit warm, but not flamey stuff. I'm sure they had barf bags somewhere; vomitus in microgravity doesn't make for a pleasant trip.

[Eric Mc]

bmwmike said:

Would the re-entry have had flames at the front and been really bouncy, or just gently dropped back into atmosphere like that video seems to show? I dont see any sick bags either

Neither the New Shepard capsule nor the Virgin Spaceship 2 are travelling fast enough during re-entry to generate significant heat. Consequently, neither are fitted with a specific heatshield. They would not survive re-entry from orbit.

When a craft is coming in from orbit, it hits the upper atmosphere at 17,500 mph (Mach 22) This causes the air ahead of the craft to compress and heat up to over 3,000 degrees C in some places on certain types of spacecraft. Here is a heat distribution diagram for the Space Shuttle -





Spacecraft coming back from the moon or other parts of the solar system will impact the upper atmosphere at speeds of around 25,000 mph which generates even higher re-entry temperatures.

[bmwmike]

Einion Yrth said:

bmwmike said:

Would the re-entry have had flames at the front and been really bouncy, or just gently dropped back into atmosphere like that video seems to show? I dont see any sick bags either

Max speed about mach 3 - would have got a bit warm, but not flamey stuff. I'm sure they had barf bags somewhere; vomitus in microgravity doesn't make for a pleasant trip.

Eric Mc said:

interesting stuff

Interesting; thanks both. I honestly didn't realise that but it makes sense. Probably my next question would have been why not just slow down before hitting atmos (for the Shuttle et al) but presumably cheaper, lighter, and safer to engineer for the high speed re-entry in the first place (less fuel, less to go wrong, perhaps).

As for vomit in microgravity, again, didn't really think of that - imagine one person getting sick and it floats around, or triggers everyone else to get sick. Quite amusing thinking of the rich folk all trying desperately to "swim" away from the approaching vomit cloud.

Edited by bmwmike on Thursday 15th July 11:50

[Dr Jekyll]

It takes several kilos of fuel to get each kilo of spacecraft and payload into orbit. So it would take a good few kilos in extra fuel to get it slowed down to Mach 3 or so before entering the atmosphere, and of course all that extra fuel has to be got into orbit.

[Eric Mc]

bmwmike said:

Interesting; thanks both. I honestly didn't realise that but it makes sense. Probably my next question would have been why not just slow down before hitting atmos (for the Shuttle et al) but presumably cheaper, lighter, and safer to engineer for the high speed re-entry in the first place (less fuel, less to go wrong, perhaps).

As for vomit in microgravity, again, didn't really think of that - imagine one person getting sick and it floats around, or triggers everyone else to get sick. Quite amusing thinking of the rich folk all trying desperately to "swim" away from the approaching vomit cloud.

Edited by bmwmike on Thursday 15th July 11:50

For the Space Shuttle (or any other orbiting spacecraft) to slow down to a more reasonable speed to avoid re-entry heating, it would need to use retro rocket firings to slow down, in space, from 17,500 mph to around 3,000 mph (at least). Imagine the amount of fuel that would be needed together with the weight of that fuel and the size of the tanks to achieve that. It would be almost as much as was needed to get the spacecraft up to orbital speed in the first place.

And, on top of that, all that additional fuel and weight required for the re-entry burn would have had to be lifted into space and orbital velocity in the first place - so the initial launch vehicle would have been impossibly huge. It's much better to use a fairly small amount of re-entry fuel for a fairly small reduction in orbital velocity and use the atmosphere to do the braking for you.

[ch37]

They have (as far as I can tell) been completely quiet, and not released any interior footage of...

- the initial drop before the rocket fires up (which I imagine is the scariest part of the whole experience, that's not a natural feeling when you're essentially just up in a plane)

- the near vertical rocket launch after the drop, which looked incredible from the outside. I imagine that's a bit scary at first but awesome when you think back to it.

- Re-entry.

Considering (if I've read it correctly) each trip comes with a couple of days of training/prep, I assume it's not quite the straightforward leisure trip the carefully edited footage of this trip would have us believe.

[Eric Mc]

Spaceship 2 is completely manually flown, so it's all a bit wobbly when seen from the outside.

[JuniorD]

I’m personally more interested in and impressed by the the guy who piloted the thing and the people who designed it.

[Eric Mc]

Yes - as any aviation/space enthusiast might be. I was interested in Concorde but not terribly interested in the passengers it carried.

[annodomini2]

Eric Mc said:

bmwmike said:

Interesting; thanks both. I honestly didn't realise that but it makes sense. Probably my next question would have been why not just slow down before hitting atmos (for the Shuttle et al) but presumably cheaper, lighter, and safer to engineer for the high speed re-entry in the first place (less fuel, less to go wrong, perhaps).

As for vomit in microgravity, again, didn't really think of that - imagine one person getting sick and it floats around, or triggers everyone else to get sick. Quite amusing thinking of the rich folk all trying desperately to "swim" away from the approaching vomit cloud.

Edited by bmwmike on Thursday 15th July 11:50

For the Space Shuttle (or any other orbiting spacecraft) to slow down to a more reasonable speed to avoid re-entry heating, it would need to use retro rocket firings to slow down, in space, from 17,500 mph to around 3,000 mph (at least). Imagine the amount of fuel that would be needed together with the weight of that fuel and the size of the tanks to achieve that. It would be almost as much as was needed to get the spacecraft up to orbital speed in the first place.

And, on top of that, all that additional fuel and weight required for the re-entry burn would have had to be lifted into space and orbital velocity in the first place - so the initial launch vehicle would have been impossibly huge. It's much better to use a fairly small amount of re-entry fuel for a fairly small reduction in orbital velocity and use the atmosphere to do the braking for you.

It's not technically infeasible, but Specific Impulse would need to be somewhere between 4000-5000 secs before it could be considered practical.

Basically the engines would need to be roughly 10x more fuel efficient than the most efficient existing chemical rockets.

[Einion Yrth]

annodomini2 said:

Eric Mc said:

bmwmike said:

Interesting; thanks both. I honestly didn't realise that but it makes sense. Probably my next question would have been why not just slow down before hitting atmos (for the Shuttle et al) but presumably cheaper, lighter, and safer to engineer for the high speed re-entry in the first place (less fuel, less to go wrong, perhaps).

As for vomit in microgravity, again, didn't really think of that - imagine one person getting sick and it floats around, or triggers everyone else to get sick. Quite amusing thinking of the rich folk all trying desperately to "swim" away from the approaching vomit cloud.

Edited by bmwmike on Thursday 15th July 11:50

For the Space Shuttle (or any other orbiting spacecraft) to slow down to a more reasonable speed to avoid re-entry heating, it would need to use retro rocket firings to slow down, in space, from 17,500 mph to around 3,000 mph (at least). Imagine the amount of fuel that would be needed together with the weight of that fuel and the size of the tanks to achieve that. It would be almost as much as was needed to get the spacecraft up to orbital speed in the first place.

And, on top of that, all that additional fuel and weight required for the re-entry burn would have had to be lifted into space and orbital velocity in the first place - so the initial launch vehicle would have been impossibly huge. It's much better to use a fairly small amount of re-entry fuel for a fairly small reduction in orbital velocity and use the atmosphere to do the braking for you.

It's not technically infeasible, but Specific Impulse would need to be somewhere between 4000-5000 secs before it could be considered practical.

Basically the engines would need to be roughly 10x more fuel efficient than the most efficient existing chemical rockets.

Bob Zubrin's Nuclear Salt Water Rocket has a designed ISP of around 10,000 seconds.

'Course you probably wouldn't be wanting to use it in low earth orbit, let alone sub-orbitally.

[Dr Jekyll]

annodomini2 said:

It's not technically infeasible, but Specific Impulse would need to be somewhere between 4000-5000 secs before it could be considered practical.

Basically the engines would need to be roughly 10x more fuel efficient than the most efficient existing chemical rockets.

Endangering my geek credentials here. But what's 'specific impulse'?

[coanda]

Dr Jekyll said:

annodomini2 said:

It's not technically infeasible, but Specific Impulse would need to be somewhere between 4000-5000 secs before it could be considered practical.

Basically the engines would need to be roughly 10x more fuel efficient than the most efficient existing chemical rockets.

Endangering my geek credentials here. But what's 'specific impulse'?

It's a measure of how efficiently a reaction engine (like a rocket motor) uses its reaction mass (fuel), or put another way, creates thrust. On a like-for-like basis, higher numbers are better.

[annodomini2]

Dr Jekyll said:

annodomini2 said:

It's not technically infeasible, but Specific Impulse would need to be somewhere between 4000-5000 secs before it could be considered practical.

Basically the engines would need to be roughly 10x more fuel efficient than the most efficient existing chemical rockets.

Endangering my geek credentials here. But what's 'specific impulse'?

https://en.m.wikipedia.org/wiki/Specific_impulse

[Flooble]

coanda said:

Dr Jekyll said:

annodomini2 said:

It's not technically infeasible, but Specific Impulse would need to be somewhere between 4000-5000 secs before it could be considered practical.

Basically the engines would need to be roughly 10x more fuel efficient than the most efficient existing chemical rockets.

Endangering my geek credentials here. But what's 'specific impulse'?

It's a measure of how efficiently a reaction engine (like a rocket motor) uses its reaction mass (fuel), or put another way, creates thrust. On a like-for-like basis, higher numbers are better.

Yes, it ends up being measured in seconds because (almost) everything cancels out as you are measuring your thrust in m/s divided by acceleration from gravity in m/s/s. (If you work it backwards you are measuring how long you can thrust for a given mass of fuel at a given flow rate, so again you can see how the given mass of fuel at a given flow rate (in mass per second) ends up cancelling out to just seconds.

Most liquid rockets hover around 330-380, as noted above you need 10x that to be able to consider "stopping then landing" instead of just plunging into the atmosphere.

[Beati Dogu]

The word is that Elon Musk bought a ticket for a flight with Virgin Galactic.

They've a couple more test flight before opening it up to paying passengers though. Branson's flight was moved up to beat Bezos' of course.

Edited by Beati Dogu on Friday 16th July 20:22

[eharding]

Beati Dogu said:

The word is that Elon Musk bought a ticket for a flight with Virgin Galactic.

Also, subtly flicking two fingers at Bezos.

"Yeah, I've got an operational orbital human-rated launch system of my own, but that Virgin ride looks like a must-do absolute hoot"