Question Private Companies will build spacecrafts, is it new?

[T.Neo]

You appear to believe that NASA engineers just wrote off the idea for no good reason. Back in the real world there are many problems with the ET space station idea, including at least the following:

NASA studied this idea quite seriously; I believe there are several papers on NTRS. It just made little sense once they started doing the detailed engineering work.

Thanks for listing all the problems, that I already knew about... :shifty:

1. The fuel tanks have a fairly low sectional density so they're not easy to keep in orbit.

You can point the tank prograde to minimise air drag. Ok, so that doesn't remove the problem at all... but it makes it a bit better.

And you just reboost it. The ISS also needs to be reboosted, though obviously these are two different scenarios with two different objects.

Another alternative would be to launch the tank into a high orbit to minimise air drag, but this would impact Shuttle payload capability.

And of course, as you filled the tank with hardware, sectional density would improve.

2. You can't get enough tanks in one place to build a large space station unless you have a lot of shuttles going to the same orbit... which you probably won't have until you've already build a large space station.

You only need a single tank for a large space station- with roughly twice the internal volume of the ISS. One of the problems with the whole concept is finding a reason for all that space...

3. The ET's insulation pops off when exposed to strong UV, which not only causes problems with thermal control, but would also create large clouds of space debris. Fortunately it's light enough that it should reenter fairly quickly, but it could easily wipe out a few satellites in the process.

I believe one of the plans was to have the ET in a low orbit and let the SOFI crumble off. It'd create a cloud of debris, but it would soon deorbit- I'm not sure if there are any satellites at that low altitude.

Of course, doing so would increase air drag on the tank as well.

Another proposal was to 'wrap' the insulation in plastic once reaching orbit, I think. Would probably have been a more complex (and dangerous) operation.

Also, a double-skinned tank, or placement of foam on the inside of the tank would eliminate foam-strikes during ascent, and would presumably solve this problem as well... but was never adopted in practice due to concerns over impacting payload performance.

4. NASA has no experience with reusing 'wet' fuel tanks in orbit. It was considered for Skylab, but they decided the risks were high enough that the 'dry' SIVB Skylab was the better choice.

Er...

The Skylab wet workshop was derived when there were no Saturn V boosters available to launch a dry S-IVb into orbit (which was, AFAIK, von Braun's original idea). The wet workshop concept came about because there were surplus S-Ib launchers (left over from cancelled test-phase flights), but these had to have a working S-IVB stage to reach orbit. Once the later Apollo missions were cancelled, surplus Saturn V launchers became available. Since work was already done on the wet workshop concept, it made sense to convert the S-IVb into a 'dry workshop' (since it wouldn't need to be propulsive to reach orbit) instead of building a whole new spacecraft to launch on the Saturn V.

Also: how do you expect to have any experience, if you don't try to learn?

5. In order to get into the tanks you need to add extra access panels to allow astronauts to enter them in orbit. Who wants to be the first to fly on an ET with holes cut in the tanks which are designed to be easily opened in orbit? Who wants to take responsibility if it blows up?

The ET already has holes cut into it, to allow inspection on the ground. I'm not sure if it would have been possible to enter the tanks effectively on-orbit through these manholes, but I think it was researched to some extent.

If you need a larger opening in the tank, you can always try to cut one into the tank on orbit, which probably isn't impossible- but it would be more complex, and more dangerous..

6. You also need to add extra structure inside the tanks (e.g floors and attachment points for hardware). Again, who wants to risk flying on the first ET with those modifications?

Drain-through floors for a wet-workshop actually flew on Skylab- they're clearly visible. That said, you might not need to actually pre-install such structures in the tank- though attachment points, internally, would be nice. That said, what is really so dangerous about such modifications? That they are an unknown, yes.

Who wants to risk flying on the first STS mission of all time? Apparently Young and Crippen were... er, crazy enough to do it. But seriously, making a vehicle with an intrinsic manned interface is nice. Making it impossible to fly without a human crew, is just stupid.

In that case, perhaps some sort of unmanned mission would be a best bet, though it would require all sorts of other hardware as well. Needless to say, that might be worth it.

NASA studied this idea quite seriously; I believe there are several papers on NTRS. It just made little sense once they started doing the detailed engineering work.

I think it depends on how much effort you're willing to put into advancing things. If you don't want to risk, or bother, or whatever, with pushing the boundaries, then why start a Space Shuttle program at all? Why make a space station? Why even fly in space?

 

[movieman]

All ETs have access hatches to both tanks. Take a look at the bottom of any ET and you'll see the circular "manhole" access hatch.

And none of them are designed to be opened in orbit by an astronaut in a space suit with a spanner.

---------- Post added at 12:57 PM ---------- Previous post was at 12:49 PM ----------

You can point the tank prograde to minimise air drag.

You can't, because it's not stable in that orientation. You'll be continually burning fuel to keep it that way.

Another alternative would be to launch the tank into a high orbit to minimise air drag, but this would impact Shuttle payload capability.

ISS is about as high as you can go before radiation starts to become a serious problem.

Also: how do you expect to have any experience, if you don't try to learn?

Who's going to take the responsibility of 'learning' when you're putting the lives of seven astronauts and an irreplaceable multi-billion dollar space shuttle at risk to do so?

Drain-through floors for a wet-workshop actually flew on Skylab- they're clearly visible. That said, you might not need to actually pre-install such structures in the tank- though attachment points, internally, would be nice.

Skylab was not a wet workshop. NASA has never flown one. NASA has never flown a fuel tank with floors inside it. NASA has certainly never flown a shuttle tank with floors inside lt.

That said, what is really so dangerous about such modifications? That they are an unknown, yes.

They significantly change the fuel flow in the tanks and put seven lives and an irreplaceable multi-billion dollar spacecraft at risk. Who's going to sign off on that?

Who wants to risk flying on the first STS mission of all time? Apparently Young and Crippen were... er, crazy enough to do it.

Young also said that if he'd know what happened during the launch he would have pulled the ejection handle and let Columbia crash into the sea. They were test pilots, not fools.

 

[T.Neo]

And none of them are designed to be opened in orbit by an astronaut in a space suit with a spanner.

Can you provide a source that describes how these access hatches are opened?

I've read somewhere that they did tests in the NBL of an astronaut in an EMU moving through that aperture, I'm not sure if they tested opening it in simulated conditions.

You can't, because it's not stable in that orientation. You'll be continually burning fuel to keep it that way.

And? How much propellant are you going to burn to keep it at an ideal attitude? Do you have any calculations or research papers done on the matter, that decisively say that controlling an ET in such a manner on-orbit is impossible?

ISS is about as high as you can go before radiation starts to become a serious problem.

Radiation never proved troublesome on Hubble missions. I'd imagine that you might want to launch the tank into a high orbit at first, and then lower it down to a safer altitude once it enough mass had been added to it.

Who's going to take the responsibility of 'learning' when you're putting the lives of seven astronauts and an irreplaceable multi-billion dollar space shuttle at risk to do so?

Who's going to take the responsibility of putting the lives of astronauts and your multi-billion asset at risk on any flight?

The space shuttle was an entirely experimental program, and was terribly botched by the fact that someone decided to declare it "operational", when it should really have been regarded as a test program...

Skylab was not a wet workshop. NASA has never flown one. NASA has never flown a fuel tank with floors inside it. NASA has certainly never flown a shuttle tank with floors inside lt.

Except that the Skylab design started out as a wet workshop. I never said it was a wet workshop. That design existed, and obviously quite a few people had enough faith in it to believe that it would work. When Saturn Vs became available, they took the wet workshop design, and turned it into a 'dry workshop'.

They significantly change the fuel flow in the tanks and put seven lives and an irreplaceable multi-billion dollar spacecraft at risk. Who's going to sign off on that?

Who says you are even flying seven people on the vehicle anyway? I think that is a pretty interesting assumption. :dry:

Does changing the fuel flow make doing things impossible? No. Do they make the spacecraft (any more than it already is) a deathtrap? I certainly wouldn't say that, without further research. Of course you would put a lot of research into such a system, before you actually started playing around with it.

Young also said that if he'd know what happened during the launch he would have pulled the ejection handle and let Columbia crash into the sea. They were test pilots, not fools.

Yes, and he would have ejected into a nice white hot plume of SRB exhaust. :shifty:

They were no fools, sure. But the guys who actually planned the mission? Who didn't intend to test the vehicle unmanned first? I think that is a pretty bad decision. It would have been entirely possible to have a LOCV on STS-1, and if you look at all the things that occured during the mission, it is pretty scary. The ejection comment by Young is about the body flap, and even though the vehicle landed safely, he obviously would have thought at the time that what occured would have had lethal results.

And of course your new manned vehicle failing on the first flight and killing two people would be very bad PR indeed.

 

[n0mad23]

Dave Hunt's page, "The Only Throwaway Component on the Space Shuttle: The External Fuel Tank" addresses most of what's being discussed here. I'm posting the link as the bibliography is worth sharing. http://aeromaster.tripod.com/paper1.htm

From Permanent.com - "What does NASA have to say about this ?"

NASA operates the Shuttle, so NASA is the authority/boss. Prodded by outside inquiries, NASA eventually supported a study into retaining the tank in orbit, and the result was more positive than expected at first.

However, NASA has taken on a policy of relying on business to take the initiative in this area instead of government, which most of us will probably agree with. (NASA is not much of a leadership agency anymore.) Indeed, an external tanks space station would be a direct competitor to the NASA space station Alpha and the joint US-Russian space station effort that has gained so much political support and money for NASA.

NASA doesn't want to spend its limited budget on the infrastructure required to bring these tanks to orbit and handle them. NASA has offered to deliver the tank to orbit for free, but at the same time has pointed out a number of complications and costs involved to the Shuttle program and established understandable conditions for delivery, mainly for a third party to be waiting to collect it for at least safety reasons.

There is no system in orbit to collect these tanks, and NASA can't be expected to modify its clients' launch schedules and orbits to accommodate putting all the tanks in close orbits to each other.

Nonetheless, NASA has stated what is needed to utilize the tanks, e.g., a system to collect the tanks and control them so that they don't become a hazard, a way to pump the residual fuel out of the tanks, a way to outfit the tanks with the desired contents (by teleoperated robots or human extravehicular activity), and various infrastructure. NASA is not willing to launch the material to be moved inside the tank, but is willing only to give an empty tank which anyone can dock with later, on their own. NASA is not willing to devote much shuttle astronaut time or resources on behalf of the tank client, and any client requests to the manufacturer of the tank to redesign the tank must not entail any risk to the mission at all, i.e., probably no significant redesigns of the tank will be acceptable.

Fair enough. NASA has done its part; now it's up to business to come up with a best scheme to capitalize upon such an opportunity, without using U.S. taxpayers' dollars and without interfering too much with the Space Shuttle's agenda.

I seem to remember (thought I can't seem to find a better source than Permanent) NASA semi-publicly making this offer in the early `80's.

Here's a link to the 1983 California Space Institutes conference paper titled, "Report on the Utilization of the External Tanks of the Space Transportation Network." - http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19940004970_1994004970.pdf

And here's a pdf published in 2006 titled, "Evaluation of Aerodynamic Drag and Torque for External Tanks in Low Earth Orbit." - http://www.fire.nist.gov/bfrlpubs/build06/PDF/b06026.pdf

It really looks like a lot of people were interested in this right up until the end of the program, and even continue after the fact. NASA administrator Michael Griffin said publicly in 2008 that NASA is prepared to hand over the Aries ETs for LEO to any company stepping forward with a viable plan. - http://www.flightglobal.com/articles/2008/07/30/226272/oshkosh-2008-nasas-constellation-rockets-could-be-used.html