NASA Grounds Space Shuttle Fleet 34
Rytsarsky writes "This story (Reuters) at MSNBC explains why NASA has grounded the fleet. They have been grounded 'indefinitely after finding small cracks in propellant lines on the main engines of two shuttles.' This will 'delay the scheduled July 19 launch of shuttle Columbia.' Good thing this was caught before something catastrophic happened."
Aging shuttles may be retired. (Score:2, Insightful)
Re:Aging shuttles may be retired. (Score:1)
It's time for a two-stage, reusable except for fuel, airplane based system, which is what they should have used all along.
"Science ain't an exact science with these bozos..." -- mysterious disembodied voice, 12 Monkeys
Alternate link to Reuters (Score:2, Informative)
Endeavour (Score:2, Interesting)
Might as well inspect it, all the others are undergoing the same process. It's sufficiently old to warrant it, and fresh off a two-week mission, no time is like the present.
Why they wouldn't do it would boggle me, considering the possible consequences.
Time to move on (Score:3, Interesting)
NASA has been crippled by budget cuts and the deadweight of maintaining technology that was designed 25 years ago (remember, the Enterprise test flights were in and around 1980, and by then the design was mainly done). Perhaps it's time for us to revisit Chuck Yeager's opinion that we should not use deadlift rockets but should instead fly into space. I've heard that the shuttle uses up more fuel to go the first 100 feet than a packed 747 uses for its entire flight. Now, if we could use a graceful system like horizontal launch to first break the inertia, then a rocket boost up in the 10K-30K feet range (3KM-10KM roughly) would be much more efficient and allow heavier cargo and more people in the same space as our current shuttles.
The rumor is that Chuck Yeager was struck down in the first place because of the political reality that rockets were more impressive and seemed a radical break with past technology, not because of superior lifting ability. I don't know that to be true however...
Re:Time to move on (Score:2)
Granted rockets have *lots* of drawbacks for space flight, but are the delivery method of choice for nuclear weapons. They are quick, don't require runways, cheap and their altitude makes them harder to shoot down.
Re:Time to move on (Score:3, Informative)
It's actually remarkably difficult to get from the surface (or subsurface) of the Earth into space. There's a reason that they compare the difficulty of things to "rocket science". The payload is typically less than 10% of the weight lofted, with the rest being fuel/oxidizer (for simplicity, henceforth "fuel") and structure. And of that, most of the weight is oxidizer. The more you want to lift, the more fuel you need. But adding fuel adds the weight of both fuel and the structure to contain it. This means that you need more fuel to lift it. Eventually, you find a nice place where you can lift the appropriate payload and fuel and structure. If, that is, you can build something that big - depends on the payload size and orbit (which together determine the amount of energy needed to loft the payload), launch pads, assembly buildings and so forth. It's difficult and it's expensive.
Are there other ways to do this than big chemical rockets? You bet. You can use nuclear rockets, like the NERVA program. You can build a rocketplane (hybrid rocket/jet). There are other options (lifting under a balloon, for example), but they are not very attractive, for a variety of reasons.
Nuclear rockets are great from a technical standpoint. If you used minimal shielding (to minimize the weight while still protecting the cargo) and didn't care about radioactive exhaust, you could theoretically launch more for less, given the high specific impulse of the engines and the lack of oxidizer, which together make up for the weight of the reactor vs. a traditional rocket. Practically, this won't happen for political reasons, though nuclear rockets may some day be lifted into space as payload, then used to move things around.
Pathfinder takes a nice approach: put both jets and rockets onto the ship, and take off without oxidizer. The ship would use the jets to fly up to a tanker, which would provide the oxidizer. The ship would then separate from the tanker, point up and light the rockets. Since no oxidizer is carried to get through the majority of the atmosphere, the total weight of the ship is much less (it needs less structure to hold oxidizer, because it uses less oxidizer). The oxidizer is carried up by a tanker, which is airbreathing, and the net effect is to be much more efficient. You could argue whether or not to carry the rockets and jets both, or just to carry rockets, and enough oxidizer to get up to tanking altitude. There are advantages and disadvantages to either.
The other nice thing about this approach is that you have built an airplane. It can be tested incrementally, and can be fully reusable with minimal refurbishment between flights. It can self-ferry to whatever airport is appropriate for whatever mission it is going to fly, and could land at any large airport that can provide the fuel of your choice (probably kerosene). The problem with this approach is that it's never been done, and there is no real constituency to do it. Unless a private company like Pioneer Rocketplane manages to get the necessary funding, or a government suddenly decides to anger its current spaceflight constituency in order to boost a doubtful new spaceflight constituency, the concept won't get tested.
The end result of all of this is that it is unlikely that the current situation will change, and it is unlikely that a shuttle-like system will ever be built to replace the shuttle. We'll continue to use disposable rockets for most things, with huge failure rates, and refurbish the shuttles until we decide that manned spaceflight is too hard for us to do, the precedents of history notwithstanding.
Re:Time to move on (Score:2)
The problem with this is that your speed when fueling from the tanker will be slow enough that you'll get questionable gains from this system. The tanker will, at best, be travelling around 1 km/sec (and that's in the Mach 2-3 range). Your shuttle needs to get to 8 km/sec. Burn time is directly proportional to delta-V, so you save very little even with a very fast tanker.
I also question how much of a problem the atmosphere is. For small craft, it's a very big deal, but for craft large enough that their cross-sectional weight is much, much greater than that of the air column they plow through, atmospheric drag isn't a concern. This is especially true given that most of the boosting happens at great altitude (less atmosphere to worry about).
The big advantage to an air-breathing rocket is a huge specific impulse boost (as your rocket fuel needs no oxidizer). However, getting rockets to work at extremely-hypersonic speeds is an unsolved problem, and if your jets can only be used at (relatively) low speeds, you again don't get much benefit (and have to drag the extra weight of the jet engines along).
Getting from ground to orbit is an interesting problem with no easy solutions visible in the near future.
Re:Time to move on (Score:2)
It's not so much the speed, it's the altitude and the fact that your takeoff weight is reduced. If the tanker and craft separate at 100 km, it's much easier for a small craft to make orbit.
Your shuttle needs to get to 8 km/sec. Burn time is directly proportional to delta-V, so you save very little even with a very fast tanker.
The small craft needs less undercarriage because it doesn't take off with any weight, and has less structure because you only have to worry about fuel in it when you are flying- the lift of the wings holds the fuel from snapping the wings.
I also question how much of a problem the atmosphere is. For small craft, it's a very big deal, but for craft large enough that their cross-sectional weight is much, much greater than that of the air column they plow through, atmospheric drag isn't a concern.
Yes.
This is especially true given that most of the boosting happens at great altitude (less atmosphere to worry about).
The idea is that the dry mass ends up less, also, because you can fly around you can take off nearer the equator, and there significant range control issues that go away.
The big advantage to an air-breathing rocket is a huge specific impulse boost (as your rocket fuel needs no oxidizer).
Only whilst its in the atmosphere. But staying in the atmosphere costs fuel and it quickly becomes uneconomic, except at low speeds. Rockets deliberately leave the atmosphere as quickly as possible for a reason.
However, getting rockets to work at extremely-hypersonic speeds is an unsolved problem, and if your jets can only be used at (relatively) low speeds, you again don't get much benefit (and have to drag the extra weight of the jet engines along).
Re:Time to move on (Score:2)
For a small craft, yes (this is the idea behind the Pegasus, among other things).
However, anything that has to lift substantial amounts of payload will be large enough for the atmosphere to be mostly irrelevant (the benefit only comes when your rocket is small enough for its cross-sectional mass *not* to be greater than the atmosphere's at low altitudes).
The small craft needs less undercarriage because it doesn't take off with any weight, and has less structure because you only have to worry about fuel in it when you are flying- the lift of the wings holds the fuel from snapping the wings.
When you're boosting, both gravity and airfoils are irrelevant - the dominant force by far is the several gravities of thrust being supplied by your engines. The thrust-induced stresses are the same whether you're on the launchpad or flying free, or in the atmosphere or out of it (aside from exhaust expansion in the rocket nozzle). So no matter what you do your rocket has to be braced enough to take a very heavy axial load.
So, I'm having trouble seeing how launching dry would reduce your structural requirements. As soon as you fuel up, you'll have all of the stresses you would on take-off (because you need as much fuel as you would have on take-off, assuming a rocket large enough for atmospheric effects to be negligeable).
Only whilst its in the atmosphere. But staying in the atmosphere costs fuel and it quickly becomes uneconomic, except at low speeds. Rockets deliberately leave the atmosphere as quickly as possible for a reason.
Assuming a magical scramjet that could work at very high speeds in very thin air, it would be more efficient to stay within the atmosphere for most of your boost. The problem is that we don't have this ultra-scramjet yet. I agree that during rocket-based boosting leaving the atmosphere provides an advantage.
Even with the magic scramjet, it might or might not be possible to boost enough in the atmosphere to make it worth carrying the jet. Beyond a certain point friction heating will be bad enough that no heat shielding material can take it in steady-state conditions. Things are *almost* this bad on re-entry as it is (the calculations are a fun exercise, and nicely explain why the shuttle's underside is graphite coated with tungsten carbide).
An interesting thought experiment, whatever the result ends up being.
Re:Time to move on (Score:2)
Atmosphere isn't really the main problem; it's gravity. It is far more efficient to climb up the gravity well on wings than it is to blast up it on a rocket.
But you do have to lift a weight into orbit, of which most is not the payload but the vehicle. Reducing the weight of vehicle to be lifted increases the payload for the same amount of thrust. The structure has to withstand the same loads during boost, but the takeoff and landing loads are much smaller, and thus the undercarriage and body structure both get lighter. This reduces the mass fraction occupied by structure. In addition, using less energetic fuels (kerosene/LOX) makes it easier to abort if needed, and reduces costs/complexities in ferrying, over a hydrogen engine. But you pretty much need hydrogen if you're going to lift straight up, which eliminates any benefits to cheaper/safer fuels. Also note that you don't need as much oxidizer, because the oxygen required to lift the craft to fuelling height was not carried onboard, but rather came from the air. This accounts, by the way, for much of the oxidizer burned in a conventional rocket - just getting through the part of the air which has useful amounts of oxygen in it.
I'd rather not assume any technology that doesn't yet exist. I'd be willing to bet that the technology for getting SSTO using this method is available now, with perhaps some development needed on a wider high-altitude nozzle for the rockets. (Since they don't have to consider the boost phase with thick atmosphere, the nozzles could be wider, and thus give higher specific impulse for the fuel used, since the range of pressures they would have to operate in would be smaller.)
Most of the literature I've seen discussing this kind of technique assumes subsonic climb to altitude, subsonic fuelling (at maybe Mach 0.8) and a subsonic ferry mode - in other words, the jets wouldn't be powerful enough to reach supersonic speeds. Thus, the only time the aircraft would experience significant atmospheric friction would be for a short period during the boost phase and during reentry.
Re:Time to move on (Score:2)
Yes, but "climbing" is a negligeable part of the thrusting you need to do. Most of your thrusting is tangential thrusting to get to orbital speed - and you need 8 km/sec whether you're orbiting at 300 km or a foot above the surface of the Earth. Getting to 300 km altitude takes almost no energy by comparison (3 MJ/kg versus about 30 MJ/kg for orbit). Getting to 100 km "for free" saves even less (1 MJ/kg).
Flying on wings does nothing to help you gain tangential velocity.
But you do have to lift a weight into orbit, of which most is not the payload but the vehicle. Reducing the weight of vehicle to be lifted increases the payload for the same amount of thrust.
The weight you have to lift is mostly _fuel_. The amount of fuel you have to carry is the same whether you're starting from the ground or starting from 100 km up. Starting from 100 km up does not reduce the weight of your rocket, and so does not reduce the stresses your rocket must withstand when boosting to gain tangential velocity.
How are you proposing to reduce the craft stresses, given this? If you have the same weight, and the same amount of thrust... you have the same stresses.
Most of the literature I've seen discussing this kind of technique assumes subsonic climb to altitude, subsonic fuelling (at maybe Mach 0.8) and a subsonic ferry mode - in other words, the jets wouldn't be powerful enough to reach supersonic speeds. Thus, the only time the aircraft would experience significant atmospheric friction would be for a short period during the boost phase and during reentry.
This is not proposed because launching from high altitude is magically more efficient for all rockets - it's proposed because the SSTO designs being considered are all much smaller than the space shuttle, and so have non-negligeable atmospheric effects, making it *only* possible to launch them from high altitude.
As strength to weight ratios get better for smaller craft, this lets less of the non-fuel mass be structure and more of the non-fuel mass be cargo. The fuel to non-fuel mass ratio is pretty much the same as for large rockets (or worse, if you're burning kerosene instead of hydrogen).
Re:Time to move on (Score:2)
But then: That's not to say that I have a replacement or that I'm smug enough to believe I know better than the rocket scientists though...
So who are you to say what's unnecessary exactly?
Perhaps it's time for us to revisit Chuck Yeager's opinion that we should not use deadlift rockets but should instead fly into space.
Maybe, but I've seen no evidence that flying in space is a good idea, and a rocket needs 93% of its velocity going sideways very fast if it is to make orbit. Going fast within the atmosphere- well mach-3 would be doing well, about mach 25 is orbital velocity; that's a massive difference.
I've heard that the shuttle uses up more fuel to go the first 100 feet than a packed 747 uses for its entire flight.
Then again when it gets to orbit it needs essentially no fuel at all, for weeks. Try doing that in a 747. The point is really that a rocket burns its fuel all at once early on, so it looks impressive; if a 747 burnt all its fuel at takeoff you'd be moaning about how inefficient they are. In actual fact rocket engines are 'heat engines' and more efficient than jet engines and routinely achieve 80% efficiency. Consider this: water vapour in some rocket exhausts has been known to condense out, because the rocket nozzle has extracted so much heat. Now that's impressive.
Now, if we could use a graceful system like horizontal launch to first break the inertia, then a rocket boost up in the 10K-30K feet range (3KM-10KM roughly) would be much more efficient and allow heavier cargo and more people in the same space as our current shuttles.
Huge IF . The problem is you need a lot of fuel to reach orbit. Jet engines for example can barely lift their own weight in most cases, although some can lift a light aeroplane, straight up, for a shortwhile. A rocket engine can lift 70-130 times its own weight, and even then reaching orbit isn't all that easy in fact, some rockets barely make it off the launchpad due to the fuel load necessary to make orbit.
Undercarriage costs weight too. The typical problem found is you end up carrying so much equipment and spend so long messing about in the drag of the atmosphere that you use more fuel, not less.
Re:Time to move on (Score:1)
I think not. A rocket engine is not a heat engine. And the maximum efficiency of a heat engine is 27% [bgsu.edu].
Undercarriage costs weight too.
The shuttle already has an undercarriage, as is evidenced by this picture [nasa.gov] on this site [nasa.gov]
Re:Time to move on (Score:2)
I think not.
Yes, I haven't noticed you doing any thinking either.
A rocket engine is not a heat engine.
You seem to have put the word 'not' in that sentence. Take it out and you form a true statement. It turns heat energy into fast movement of the exhaust. And it does so with extremely high efficiency.
And the maximum efficiency of a heat engine is 27% [bgsu.edu].
True. 'a' heat engine does have 25% percent efficiency. Heat engine's efficiencies depend on the temperatures involved. All rocket engines I am familiar with don't run at 100C however, they run at ~3000C, and if you do the maths (you can do maths can you?) you should notice a quite startling increase in efficiency. Yes it does go up to around 80%. Have a nice day.
Re:Time to move on (Score:2)
Go learn some thermodynamics. The maximum efficiency of a heat engine is not 27%. It may be for a heat engine operating between a temperature difference of 100 Kelvin degrees, but the theoretical Carnot efficiency varies depending on the temperature difference between the hot and cold reservoirs. For example, an ideal heat engine drawing from a hot reservoir of 300 degrees Celsius and depositing into the cold reservoir at 120 degrees Celsius would yield a theoretical 31.4% Carnot efficiency.
(Hot Temp - Cool Temp) / (Hot Temp) = Efficiency
(573.15 - 393.15) / 573.15 = 0.314
Re:Time to move on (Score:2)
The shuttle already has an undercarriage, as is evidenced by this picture [nasa.gov] on this site [nasa.gov]
Really? Gasp! And where's the picture with it using it to take off? Hint: there isn't one, because it can't take the weight.
Re:Time to move on (Score:2)
Re:Time to move on (Score:2)
Re:Time to move on (Score:1, Insightful)
This is nearly what happened to Concorde.
Problem is that if the Shuttle or Concorde is grounded there isn't a hope in hell of having anything equivalent up and running within a decade, even if the money is available, which it isn't.
The US is paying the price for putting all its eggs in the one basket (Shuttle). The Shuttle should have been built as a one-off test vehicle with the continued production and use of expendable launchers, NOT pushed straight in as the base launch vehicle.
Ironic, innit, that it's only the Russians who can reach the ISS following the grounding? All those who wish the Russians had never come on board (yes, that's you NASAWatch) should be eating their words.
If it had been all-US, there would have been a single point of failure for resupply of ISS - BAD!!! Remember what happened to Skylab (which was supposed to be boosted to a safe altitude by an early Shuttle flight...).
Re:Time to move on (Score:1, Funny)
I have always maintained that the reason we use rockets is because they are the most phallic-looking means. "Our dick is bigger than the Russians'!"
Holy Crap! (Score:1)
Re:Holy Crap! (Score:2)
Rigorous inspection of all of those parts. Have you ever looked at the price of rebuilding a shuttle between launches?
Re:Holy Crap! (Score:1)
NASA Contractor Economics (Score:2, Informative)
This is just another example of the dying gasps of the entire space-industry in the United States, and certainly another nail in the coffin of the many contractors who are having to tighten their belts and lay off a few more employees while praying for a flight, and sympathetic Washington headcount. Priorities and agendas sure need to be re-evaluated by this nation's leaders. Without an ample budget, I fully expect this to just be the first of many such show-stopping problems that will begin to plague the program as the orbiters age. NASA has begun looking to privatize and sell off the shuttle program, to solely act as a management group. I expect to see the shuttle bought out by a consortium of aerospace leaders like United Space Alliance, Boeing, Lockheed-Martin, or others. Pop-stars in space is a symptom (yes, I know, that was the Russians) of an increasing problem of budgetary cut after cut. Let's hope that people start to look at the stars again soon, before we lose a once-proud testament of engineering.
So the Shuttle's down?... (Score:1)
Then we cancel the project to build a seven-seater lifeboat for it, so we use a Russian Soyuz instead and limit the crew to three, the same as Mir always had.
Then we ground the Space Shuttle, meaning that the only spacecraft taking people to orbit in the first place is the good old three-seater Soyuz.
Nice one NASA.