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Space Shuttle MKII (Design Discussion)

  1. Jul 22, 2011 #1
    This is more an applied physics question, but I was wondering what the space shuttle would look like if we designed it today. I've got some project goals in mind:
    -Minimize design and construction costs
    ----design should use existing and developed technologies to minimize cost
    ----design should efficiently utilize existing resources
    ----stay within the NASA budget, or close
    ----design cost must be less than that of the shuttle(adjusted for inflation)
    -operation should be as safe and inexpensive as possible
    ----maximize flights per year
    ----minimize turn around time between flights
    ----minimize launch costs
    ----maximize redundancy

    Current day launch costs for the shuttle is between $100M and $1B depending on how you calculate it. The yearly budget we have to work with is $4.3B. Lets see what we can do!
     
    Last edited: Jul 22, 2011
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  3. Jul 22, 2011 #2

    Drakkith

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    That is a pretty complicated question.
     
  4. Jul 23, 2011 #3
    It is indeed a very complex questing, but I figure challenge is good. Personally, I picture an integrated solution to the problem of supplying the ISS, getting back to the moon, getting to Mars, and launching and servicing various satellites.

    My solution involves a mother-ship which takes off conventionally carrying the shuttle beneath, and a larger shuttle, nuclear powered and using a combination of ramjet, rocket, and ion drive propulsion to achieve the desired orbit. Funding could be augmented by reselling launch services to the defense and private sectors.

    I picture the mother-ship as a large flying wing with no power of it's own. It would have batteries or another storage technology for power, and be propelled by large electric fans operating off of the shuttle's nuclear reactor. It should be able to take the shuttle to between 10km and 20km (10km/30000ft is where commercial plane operate). It would take off conventionally from an existing airfield in the US (NASA has several), then fly to its peak altitude, release the shuttle, and return to base under glide and battery power.

    The shuttle would be powered by a nuclear reactor from the same contractors that currently supply the US navy's nuclear submarines. This reactor combined with the mother-ship's fans would carry the shuttle to at least 10km, at which point the shuttle would detach and enter free fall. After falling 1-2km, and attaining enough speed, ramjets would activate, and carry the shuttle to approximately mach 6, or roughly 2km/s (higher speeds may be possible depending on design). Once at the maximum speed and service ceiling for the ramjets, ion drive propulsion will augment and then take over accelerating the space craft. The inclusion of a nuclear reactor in this design makes the ion drive even more efficient, and, depending on fuel included, could easily take the shuttle to the moon, or provide plenty of maneuvering fuel while in orbit. Liquid nitrogen heated directly by the reactor would augment thrust for maneuvering burns.

    The nuclear reactor on the design would be the same one as used on either the Ohio class ballistic missile submarine, or on the Virginia class nuclear fast attack subs. Assuming we use the one from the Ohio we have 33.6MW of power to work with, at a cost around $1-10M. Safety would be provided by the excellent safety record of our nuclear submarine force, in addition to multiple redundancies that will prevent destruction of the reactor even in the event of a catastrophic failure(see safety section)

    Engines would consist of (both craft):
    -8-16 large electric fans(ground - mach .8 / 20km): each theoretically being able to produce 1.5 - 4 MW worth of thrust (your average home fan runs on 80W)! Because they're electric running on a nuclear reactor, no fuel is needed. Also means that the shuttle gets to 20km with effectively no increase in mass.
    -Free-fall: convert gravitational potential energy to velocity sufficient to start ramjets
    -2-4 Ramjet engines(free fall - mach 6): Running on your average jet fuel, these would be part of the shuttle itself. They'd activate following a short free-fall after release. Ramjets need initial speed to activate, so the shuttle would need to fall to about 2km to generate that. After this point they activate taking the shuttle to mach 6 or 2km/s.
    -(optional) Scram-jet: a scram jet (supersonic combustion ramjet) could add another 3 to 18 to the above mach number, allowing the spacecraft to (almost) reach the required altitude
    -Ion propulsion(mach 6 - orbit): At this point, ion drives take over as the primary means of propulsion. Because the craft is supersonic, air begins dissociating and ionizing in the shock-wave. According to my research, it just so happens to be enough that, by extending a negatively charged probe into the shock-wave, and applying a large positive potential to the back side of the wing, ions will accelerate through the electric field created by the potentials, accelerating the craft. Even with ionization around 1%, the force of the ions on the rest of the air makes it even more efficient. This piece will require the most R&D on the craft.

    Safety:
    Already, by replacing conventional rockets we've taken care of a major safety issue: Rockets explode, jet engines don't. Because there is no conventional rocketry involved, there is no risk of a challenger-like incident. Redundancy is provided during any engine failure by having multiple engines. If for any reason an abort is needed during launch, one simply needs to turn around, slow down, and land again. The glider nature of the space shuttle also means that it could land on only 1 engine, maybe even without depending on trajectory. An additional layer of heat shielding around the reactor could allow it to survive reentry, even in the case of a Columbia like breakup of the shuttle. Further, the shorter turnaround time of these shuttles should allow prompt rescue missions should something go wrong in orbit. In the event of failure in orbit, the reactor core could be jettisoned and recovered by another shuttle with special equipment.

    I'll add to this once I've finished crunching more numbers.
     
  5. Jul 23, 2011 #4

    Ryan_m_b

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    With any luck this.
     
  6. Jul 25, 2011 #5

    enigma

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    Supplying the ISS, going to the moon, and going to Mars are all vastly different missions which have different requirements. If you want inexpensive, you don't want a craft able to do all of them.

    No congress is going to approve the launching of a nuclear power plant, even if it wasn't so heavy to preclude being launched. We've lost two shuttles already. Can you imagine the fallout (pun intended) if a nuclear plant blew up like challenger or Colombia?

    Fans aren't going to get you any higher than commercial airplanes will.
     
  7. Jul 26, 2011 #6
    I was actually thinking of a modular system to address that. There are two tasks common to every mission, and that is getting to orbit, and getting back to earth. Anything beyond that falls under the category of "Payload". If you don't need to get very far (Say, just to the ISS and back), then you can carry all supplies and modules for the station. If you need to go farther, you fill some of the modular cargo area with fuel, as needed.
    You are certainly right that the greatest opposition to any worthwhile program would be the nuclear aspect. I have to say that I personally feel that if a reactor is safe enough to power the boats carrying %50 of the US nuclear arsenal, then it's good enough for a spacecraft. Further, without any conventional rockets, a challenger type explosion is impossible. Also since the craft is powered, reentry can be conducted such that debris would land in the pacific ocean(since 70% of the planet is ocean, it shouldn't be hard to avoid population), where there are minimal consequences from an accident; on successful reentry, the ramjets would activate and carry the craft past the location of splashdown for a conventional landing. There are dozens of precautions that could be taken to conduct missions safely even with a reactor on-board, and dozens more that would reduce the collateral damage of catastrophic failure to effectively nothing.

    They don't need to. The service ceiling for a jet aircraft is around 60000ft/18km(and I'm talking about fans as powerful as jet engines). Assuming a velocity of 300m/s(mach .87 at sea level). If the shuttle enters free-fall at 18km, and we need to get to Mach 1.5 for the ramjets to become effective(514m/s), a little math gives:
    VT= (VX2+ 2g[itex]\Delta[/itex]h)1/2
    (VT2-VX2)/(2g)=[itex]\Delta[/itex]h
    [itex]\Delta[/itex]h=8735m
    In other words, it might not be much compared to getting to orbit, but it's more than enough to get ramjets started.
     
  8. Jul 26, 2011 #7

    enigma

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    I suggest you run some ideal rocket equations for fuel use. Needing three different motors to get to orbit, even if you could get enough thrust out of the ion engine (which you cant), will mean that the craft would have to be absolutely gargantuan.

    We don't use multistage rockets to get to orbit because we lack vision. We use them because they're the moat effective way to do so.
     
  9. Jul 26, 2011 #8
    [itex]\downarrow[/itex]
    ==
    [itex]\downarrow[/itex]
    I hate to be too rude, but that particular statement is BS(See my math further down). Even a cursory understanding or jet propulsion will tell you that rockets are the least efficient type of jet engine.. This is because in an air-breathing jet engine there is an additional source of mass: the incoming air; oxidizer doesn't need to be carried with the craft. Because of this, the total mass is less, a given expenditure of energy will cause a grater change in momentum, since the energy that must be expended to achieve a given exhaust velocity increases by the square of velocity, where change in momentum is linear with respect to velocity. Just because it's the easy way doesn't mean it's the safest or most efficient.
    Further, the space shuttle is an SSTO craft; it does not implement staging; this is unlike rockets such as the Saturn V. Are you implying that the Saturn V is an efficient design?
    Nowhere in my design is there a conventional rocket. Ramjets are air breathing engines, meaning that the conventional equation for rocket propulsion is inaccurate; regardless, we can still come up with some equations:
    To make an extremely conservative fuel estimate, assume 2% efficiency in conversion of fuel energy to altitude. Further ignore the fact that we don't have to carry the weight of spent fuel.
    e = efficiency
    Energy requirement E=mTg[itex]\Delta[/itex]h/e
    E=(mShip+mPayload+mFuel)g[itex]\Delta[/itex]h/e
    kh2 is a constant representing the energy released when 1kg of fuel combines with oxygen. Dimensions J/kg
    E=MFuelKH2
    system of linear eqs
    ( mShip + mFuel )( g [itex]\Delta[/itex]h / e + V2/(2e) - V02 / 2e) = MFuel KH2
    MFuel=MShip(g [itex]\Delta[/itex]h + V2/2 - V02 / 2)/( Kh2 e - V2/2 + V02 / 2 - g[itex]\Delta[/itex]h)
    Plugging in absurdly conservative numbers:
    e = 2%
    MShip (mass of everything except fuel) = 500000kg
    V0=mach 1.5
    V=mach 6
    [itex]\Delta[/itex]h = 100000m
    KH2=247000000J/kg
    MShip=500000kg
    MFuel=1305000kg of LH2 fuel
    Giving a fuel to payload ratio of .383
    The actual ratio using a less conservative equation should give a ratio closer to 1
    Compare to 109000kg/(2*590000kg+760000kg)=.0561 for the space shuttle orbiter
    Jet engines weigh next to nothing in comparison to the fuel they need. 4 ramjet engines would actually be fairly light, figure 20000kg for all four.http://www.grc.nasa.gov/WWW/BGH/ramjet.html" [Broken] (A Boeing 747 jet engine weighs about 5000kg, ramjets are lighter than turbofans). The type of ion drive I'm picturing would come in at less than 1000kg. Most of the weight will be in the enormous reactor powering the thing. Further, the fans are part of a carrier craft, which doesn't have to be carried into orbit.
    I'll do the math on this as well, but I believe the kind of ion drive I'm thinking of would generate sufficient thrust. It isn't a conventional ion drive, but rather an atmospheric one; because air ionizes to some extent when contacting a hypersonic body, a simple electrostatic drive outside the spacecraft could accelerate the protons towards the back of the ship, while pushing electrons forward. The same work would be done on both sets of particles, but the protons would have a greater change in momentum, thus the ship accelerates forward. MythBusters built one out of a kit in an afternoon, and it levitated; can't be that hard to do, Ja?

    I'm starting to think I should just move bits and pieces of my design to their own threads. I'll start a new one for the ion drive, because that's a discussion of it's own.

    I'd like to hear some other possible designs other people have found/come up with; I didn't want this thread to be just for my own design.
     
    Last edited by a moderator: May 5, 2017
  10. Jul 26, 2011 #9

    D H

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    You can't do that. Sorry. These are inherently conflicting goals.

    Whoa there! Everything you said in this post directly contradicts what you said in post #1.

    You need to go back to step 0, or before.
     
  11. Jul 26, 2011 #10

    enigma

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    Being in orbit does not mean being in space.

    Being in orbit means going ~7.75 km/sec and being in space.

    Do you really think you're not only going to have something going that fast in atmosphere, but you're going to have it pulling enough oxygen from the surrounding plasma field to speed it up without melting the craft that's pushing it?

    You want to do this within NASA's current budget how?
     
  12. Jul 27, 2011 #11
    I'm still waiting for a TTO vehicle.*


    *Trebuchet to Orbit
     
  13. Jul 27, 2011 #12
    SpaceX corporation using 800 million dollars developed two rockets and launched them multiple times. They also developed a human rated space capsule (Dragon) and orbited it and returned it to a safe splashdown. Their launch cost is $1000 per pound. This is 10 to 20 times cheaper than the space shuttle. The problem you propose has already been solved.

    They will be docking the Dragon Capsule with the space station before the end of the year. The Dragon Capsule has rockets around the perimeter that can be used to soft land on land on Earth or Mars. They can also serve as an escape system during launch.

    I believe NASA after having spent four billion dollars on Ares was able to build an ullage motor.
     
    Last edited: Jul 27, 2011
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