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How do space shuttles reach escape velocity?

  1. Sep 1, 2012 #1
    How are space shuttles accelerated to escape velocity? Would it be possible to build a rocket at home that would be capable of getting into space if it were to use liquid hydrogen and oxygen as fuel?
     
  2. jcsd
  3. Sep 1, 2012 #2

    NascentOxygen

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    By hitching a ride on a powerful rocket much bigger than the shuttle.
    With no payload? Probably, depending on the size of your home. But one stray spark, and your home would be in orbit before the rocket!
     
    Last edited: Sep 1, 2012
  4. Sep 1, 2012 #3
    Home built hydrogen-oxygen rocket.
    What is your budget? I think you need more than $100 for this kind of adventure.
     
  5. Sep 1, 2012 #4
    You are probably confused about escape and orbital velocities. A spaceship can stay in orbit (and thus never fall back) upon reaching the orbital velocity, which is quite a bit less = about 8 km/s.

    However, even the orbital velocity is quite difficult to reach. First, you need to burn a lot of fuel - hundreds of tons! Second, you need a rocket engine to burn that much fuel fast, in about two minutes, without it melting down or exploding.
     
  6. Sep 1, 2012 #5

    K^2

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    First of all, Shuttles don't reach escape velocity. They never went past geostat, and most missions have been to LEO. Though, in theory, it might have been possible. (Ninja'd by voko.)

    Liquid fuel rocket engines are extremely difficult to design. Not only do you have to build a pump and a nozzle with cooling channels, but these things are susceptible to failure due to resonance. You are not going to be able to build an LH2/LOX rocket at home with anywhere near the efficiency you need to reach orbit.

    With a home-built rocket, your best bet is a hybrid. This is what many serious hobbyists and most private companies developing cheap reusable rockets are working with. But keep in mind that no home-built rocket has ever gotten anywhere even close to orbital speeds.
     
  7. Sep 1, 2012 #6

    D H

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    Not possible. While the Shuttle released spacecraft that went to geosynchronous altitude and beyond, the Shuttle itself never went beyond LEO. The highest altitude attained by the Shuttle was 600 km during STS-31.
     
  8. Sep 1, 2012 #7

    phinds

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    As has already been explained, the shuttle doesn't ever get even close to escape velocity.

    As for home rockets, no, you'll never reach escape velocity. I don't think home rockets have ever even reached orbital velocity. I do seem to remember, however, that they HAVE exited the atmosphere (if you're not too picky about defining where the atmosphere ends) before falling back, but that might have been one launched from a high-flying balloon.

    EDIT: I missed K2's statement that home rockets have never gotten close to orbital speeds. I believe it.
     
  9. Sep 1, 2012 #8

    K^2

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    Breaking atmosphere is comparatively easy. Still a challenge, but doable. LEO is about 7.8km/s. It takes about 9-9.5 km/s of specific impulse to actually establish such an orbit. The .4 km/s boost due to Earth rotation is wasted if you don't actually establish orbit, so for a small rocket, you would need a little over 2km/s of specific impulse to reach LEO altitudes. High power rocket motor can give you that with the right build.

    Here is a page dedicated to Space Shot 2004 "GoFast", which was the first amateur rocket to officially break atmosphere (100+ km).

    GoFast specs:

    Length: 21'
    Diameter: 10"
    Weight: 724lb (liftoff weight, including propellant)
    Propellant: 435lb of APCP

    The motor was classified as S-50,000. That's 328-656 kNs range with 50 kN average thrust. Flight data indicated a total delivered specific impulse of 2.1 km/s, which is consistent with analysis in opening paragraph.

    The propellant was an amonium perchlorate based composite, which points to ISP of up to about 2.5km/s. Space Shuttle Solid Rocket Booster is APCP powered with ISP of a little under 2.4km/s. The ratio of delivered specific impulse to propellant specific impulse is the natural log of ratio of liftoff weight to final weight (liftoff less the propellant). That's a factor of .91 for this rocket, meaning the ISP of propellant had to be about 2.3km/s, which is consistent with APCP.

    So that's what it takes to launch a rocket into space. A 2 story-tall rocket, a quarter ton of propellant used to launch a shuttle, a Level 3 High Powered license, and a team of professionals to put it all together. This is not a basement build.



    Note: I prefer to work with ISP in impulse per mass rather than impulse per weight. Hence all the impulses are given in km/s rather than in seconds. If you want to compare these to ISP expressed in seconds, divide these values by 9.8m/s².
     
  10. Sep 1, 2012 #9
    The first satellite launched by the US was about 14 kg. To put in orbit, the four-stage rocket Juno I was used, and that payload was its maximum. The mass of Juno I at liftoff was about 30 tons. I guess that is the closest to a "home rocket" capable of inserting something minimally useful into orbit.
     
  11. Sep 1, 2012 #10
    Maybe $1,000. I am going to build it in stages though, so it won't be all at once.
     
  12. Sep 1, 2012 #11

    russ_watters

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    Sorry, but that just isn't possible.
     
  13. Sep 1, 2012 #12

    K^2

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    Sure, and it's impossible to build an airplane in your garage that will stay in the air for more than a minute, because the Wright Flyer didn't either.

    I understand where you are coming from with your comparison, but a regular Joe today has access to composite materials, better fuels, and computational power that could not have been dreamed of in the 50s.

    We've had private rocket enthusiasts launch a rocket into outer space on a flight profile comparable to that of a V-2 rocket. Naturally, the payload is much smaller, but everything Explorer 1 could do with its 14kg can now be done with much less than 1kg. Hell, my phone has more sensors and better battery than that thing did. Perhaps, in another decade or so, a non-commercial team will manage to put a small broadcasting satellite in orbit.

    Again, we aren't talking about a garage build here. This would still be a well-funded undertaking by a group of professionals, but we'd be talking private funding by individuals who do it just because. Not the economical and intellectual power of an entire country panicking over a red threat with their Sputnik.
    For $1,000, you might be able to build a rocket that breaks sound barrier and goes up a few kilometers.

    Edit: Have you ever built a model rocket? Try making one from scratch. It might be beneficial to launch a store-bought one first, just to get an idea of what goes into it, and then try to make your own. You can buy rocket motors without any kind of license in most places. I'd start with C6 motors. A pack of 3 of these made by Estes will set you back $10 or so. Also, while there are no official regulations, semi-officially, the NAR Safety Code is fairly well recognized in US. In other countries, you'd need to look up which laws/rules apply. In either case, these are good rules of thumb for staying safe.
     
    Last edited: Sep 1, 2012
  14. Sep 1, 2012 #13
    What better fuels? We are talking about liquid oxygen and hydrogen here.

    The most important factor is the engine here, and the progress was not nearly as spectacular as in electronics. The best liquid fuel engines we have today are the ones designed in 80's in the USSR, and those engines are only marginally better than the ones designed in the 60's in the US. And those were not an order of magnitude more efficient than those used in Juno I, either.

    To launch a small satellite, you are still looking at something in the 10,000 kg 100,000 kg range, depending on what technology you can source.

    I have no doubt that this is achievable given enough money, but I find that hard to regard as a "home project".
     
  15. Sep 1, 2012 #14

    sophiecentaur

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    I think that someone hasn't done their sums about this.
    This is one of those Engineering Projects that succeed or fail on the strength of the actual numbers involved. "wouldn't it be nice' just doesn't count, I'm afraid. If it was as 'do-able' as people are implying here, then every little tin-pot state would have launched their own satellite - just because they could. (We are all very lucky that it is beyond the means of nearly everyone, aamof)
    The Wright brothers are not a comparable example. Birds have been flying in the atmosphere for millions of years; that technology is feasible at reasonable cost and technical ability. Heavier than air flight is, actually 'not rocket Science' but launching actual rockets into space is.
     
  16. Sep 1, 2012 #15

    russ_watters

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    Not for $1000 he doesn't.
     
  17. Sep 1, 2012 #16

    K^2

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    On Juno I? Are you joking? There wasn't a single engine on that rocket that exceeded 2.5km/s. LH2/LOX gives you 4km/s+. You can get 4km/s on an aerospike with LH2. Something that wasn't even an option back then. And the difference between 2.5km/s and 4km/s is enormous. On a 9km/s burn, that's a factor of 4 in fuel before I factor in the stages. There is a reason Juno I had to go with a 4 stage design. And that's where bulk of the extra weight came in. An LH2 rocket can be a two-stager easily. SSTO if you are smart about it. Venture Star was designed for a 50:1 liftoff to payload ratio. Compare it to Juno's 2,000:1.

    Of course, the bulk of these savings aren't due to fuel. You are right that there is only so much that you can do with that. But composite materials? These are a game changer. The reason Soviet-built Soyuz-U rockets are still using kerosene is because tanks for LH2 are extremely heavy, making up the bulk of the stage's mass. That tends to eat up all of the advantage of LH2. Space Shuttle's use of external tank managed to get just enough of an edge to make LH2 a better fuel for it. But for most purposes, you are stuck with much crappier fuels that are easier to store.

    Unless you use cryo-safe composite materials, of course. You do that, and you can carry a huge tank with you without making a stage too heavy. You do that, and you don't really need multiple stages. The savings are huge.

    Of course, there is more than one reason for using multiple stages. Conventional engines aren't equally efficient at all pressures. Carrying a huge nozzle for liftoff stage would make the whole thing too heavy. Plus, you actually have a drop at efficiency if pressure on the edge does not match. Space Shuttle resolves this problem, partially, by utilizing solid boosters, giving it enough of a kick on liftoff to compensate for the engines. But we have even better solution in the aerospike engine. It is lighter, more reliable, and makes it unnecessary to worry about the nozzle geometry. It's also something that they were only thinking up in the 60's. Not that they could have actually made a use of it.

    And don't even get me started on solid motors. How efficient you can make a use of these depends almost entirely on how well you can compute the pressure. These days, we can run simulation on a computer for an arbitrary starting shape. Back in the 60's they had to make a rough estimate for a circular bore of given diameter and cross fingers. Juno I's solid stages had ISP of roughly 2.1 km/s. Shuttle's are almost 2.4 km/s. Modern solid boosters can go as high as 2.8 km/s. And since these don't require a tank AND an engine, for small rockets, that actually makes them competitive with LH2. Even with composite tanks.

    So yes. Using Juno I as an example of how difficult it is to build a rocket is outdated beyond any honest use. This is not a technology standard on which someone with a limited budget is going to build a rocket this day. The technology standard is going to be something like Falcon 9, which gets 10,000 kg to LEO with a 330,000 kg rocket. That's the difference between using technology of late 1950's and technology of late 2000's.

    Now, if you can maintain that 33:1 ratio, and launch a 10kg satellite with a 330kg rocket, suddenly, it just doesn't sound all that crazy of a project. Naturally, these things don't scale quite that well, and small rockets have a bunch of challenges of their own, but give it another decade.

    And for the second time, no, we are not talking about a hobby basement build. We are talking about "amateur rocketry". Basically, anything that's not built for profit or some sort of scientific gain. Kind of like the Space Shot I mentioned earlier.

    I can buy a modern APCP model rocket engine for under $50. I can buy a carbon fiber tube to use as a body for under $20. I can buy a microcontroller with built in accelerometers and more computational power than Apollo 11 combined for $5 and use it for basic guidance. The remaining $900-something I can pocket, and I'd still have a rocket that makes use of modern fuels, materials, and electronics.

    That rocket won't be going to space, but that's not the point. The point is that this is technology that scales. This is technology which I can use to make improvements to a rocket on any budget. Whether I'm making a rocket to take some aerial photos, a rocket to break atmosphere, or a commercial rocket to deliver cargo to ISS, today I can build it orders of magnitude cheaper than I would be able to in the 50's. So you can't compare anything that anyone builds today, be it a real space rocket or a hobby rocket, to anything built in the 50's and 60's.

    I'm the only one actually quoting numbers so far.
     
  18. Sep 1, 2012 #17
    No, not on Juno. Juno did use LOX, though. LH2 was used as of the Apollo program which was not too far apart in time. And since that, there has not been much of a significant improvement in that field. And RP-1 vs LH2 is not really much different in terms of the engine technology. It is the oxidizer path that's the more difficult to get right.

    It does not take LH2 for two stages to orbit. Sputnik was launched with two stages and no LH2. Falcon 9 that you are talking about below, is also two stage, also RP-1.

    This is not a correct comparison. The vehicles are in two different ballparks.

    No, that's not the reason. The reason is that it is good enough and mass produced. Cheap and reliable. It remains to be seen whether all the extravagant stuff you are talking about will be able to compete with it. The Shuttle has tried.

    We can all see the rockets that Iran and North Korea launch today. They are pretty much the 50's technology. Why is that?

    Strangely enough, it is LOX/RP-1. Not much use of composite materials, either. The original Soyz, mostly the 50s technology, launch mass 308,000 kg, would get 6,450 kg to LEO. i.e., 48:1 ratio. I fail to see any revolutionary difference.

    If the original Soyuz had 48:1, then why wasn't this possible back then? OK, you could say that back then it would be useless. But now, as you say, we can make a useful 10 kg satellite, why isn't there anyone wishing to build 480 kg rocket with the 50's technology?

    Can you see that your assumption that you can scale a rocket from one class into another just does not work? Again you could say the new technology makes this scaling possible - but this is just unknown. No one has done it yet. It is pure speculation. Even Falcon 9, for some reason, does not much use this new technology, either. Don't you think there is a problem with your assumption?

    So far you have not convinced me that you could launch a tiny satellite without building a 10 - 100 ton rocket. Now, amateurs may have varying budgets, but 7-8 digits project costs would require some very serious amateurs.
     
  19. Sep 2, 2012 #18

    mfb

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    With big rockets, launching stuff into LEO costs something like 10,000 - 20,000 $/kg. Scaling this to a 1000$-rocket would mean ~100g of payload and (with 100:1 ratio) 10kg of total rocket mass. This will not happen.
    While payload scales with the volume of the rocket, air drag scales with the area, so it is much more important for small rockets. Some systems do not scale at all - a microprocessor for Falcon 9 needs the same weight as a microprocessor for a small rocket.

    However... why do we need an orbit?
    Fire a rocket to reach a height of ~100km, let it fall back. delta_v ~ 1.5km/s plus something for air drag + finite burning time. Should be possible with a single stage.
     
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