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Looking for specific data about thrust, hydrogen, and celestial bodies

  1. Jul 13, 2011 #1
    first off, thx to any that respond w useful info :)

    the end answer i need to find on the first topic is how many atoms of hydrogen are required to propel a mass of "x" at an acceleration of 1g in space (assuming no gravitic influence) but i would settle for how to figure out what the fuel energy of liquid H2 is and how that is converted into thrust, including at what efficiency the energy would be converted...

    a/o im looking for specific dimensions and quantities of the composition of solar bodies. eg. i have found that the moons core is 350km in radius and the density is 5g/cm^3 and that 6% is sulfur. therefore the moons core has roughly 59 million million tons of sulfur. info on ceres, vesta, any TNO's (pluto, makemake, eris, etal.), SDO's, OCO's, planets and moons would b a hugely ginormous help :)

    thx again
  2. jcsd
  3. Jul 13, 2011 #2


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    That entirely depends on how you generate the thrust. The answer is different for a chemical rocket engine, a nuclear thermal rocket engine, an ion engine. It also depends on (obviously) the mass of the object being propelled.

    What is the application or reasoning behind this? That could help narrow down what methods are reasonable.
  4. Jul 13, 2011 #3
    the method of thrust would be combustion as of now. still havent determined which method would b best. i was thinking 2H2(l) + O2(g) = 2H2O(g). the eventual mass of the object being accelerated by the burning hydrogen would need to include the added mass of the fuel needed to propel it and i havent wrkd out the details of that yet either. lol just thinking of the engines. the chemical energy available w/i the H2 is static irrespective of the mass of which it is applied to though. looked on internet for a several hrs now looking for this one elusive datum. must not b using the right terminology :) researching many different reactor types but i have pretty much settled on H2. it packs the most punch in the smallest package.

    the idea is an interplanetary vehicle which is cheap, efficient, low maintainance etc. however in different conditions the vehicle might need different methods of thrust to make the trip economic and fast.

    open outer space consists of about 1H / 16cm^3. @ a fast enough speed, a very VERY large retractable "funnel" might b able to b deployed from the nose of the craft to draw in additional fuel. obviously the speed of the craft will be dependent on the mass of the craft to make this a viable option but i think it will help to know the available energy of H2. @ this stage of its journey, in between gravitic slingshots around the gas giants, it may be able to aquire a significant additional thrust to cut down the length of the journey considerably, but perhaps not.

    thx for your time in responding :)
  5. Jul 14, 2011 #4


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    Well, for a chemical rocket engine, the best you can get out of hydrogen and oxygen is about 450 seconds specific impulse. What this means is that one pound of propellant will be enough to provide one pound of thrust for 450 seconds (or 450 pounds for one second, or any other combination that works out to 450 pound-seconds of total impulse).

    Honestly, though, I don't think that'll be nearly enough for what you're looking for, and you'll need to carry a tremendous amount of oxygen with you (since by mass, you'll need about 8 times more oxygen than hydrogen).
  6. Jul 15, 2011 #5
    is the oxidizer included in the propellant or would i need another 8x that mass to get the 450 impulse?

    only thing i can think of bigger than that would b like a nuclear reactor but that primarily generates heat and thru e=mc^2 it would take a really much bigger amount of mass to generate enough to provide adequate impulse. not to mention the fuel is quite massive as well. the other technologies that i have seen either dont exist ,arent feasible, or are entirely fantastic (fusion, anti-grav welling, inertial stasis). a large solar sail might be able to provide a significant thrust at the beginning of the journey and to save on mass it migh be able to be refit to the front for the funnel or the ship could oscillate 180 degrees or something..

    idk. its just kind of a thought experiment i guess. last summer i figured out that if we went to the nearest neutron star and mined off the iron from the outermost layer it could supply about 22 trillion I-beams if sufficient alloy material were also available. that was mostly just calculations though. theres a whole lot of data that seems to be hard to ascertain on this one :( but i did finally find that the specific energy of a 2H2/O2 reaction is 572 kJ.
  7. Jul 15, 2011 #6
    ah nm. i found that it includes the oxidizer as well.
  8. Jul 15, 2011 #7
    wow. finding what im looking for for a change :)

    ok so i dont understand exactly how it wrks but nuclear has a higher energy density. and while there are many conceptual methods developed it appears that a nuclear thermal rocket would be the method that could be developed the fastest. the idea of a "medusa" is interesting if used in combination but it would have to provide an even higher advantage of capturing the "loose exhaust" (w/e that means lol) than the added weight, however minimal, to provide increased thrust, and to justify the expense.

    liking the idea of solar sails more and more but they dont provide very much thrust unless w/i about .5 AU of star. but could indeed provide substantial thrust in a slingshot around sun. AND if this were used as a "funnel" theyre would be no need to carry oxygen for an oxidizer in a nuclear thermal rocket. except the funnel wouldnt wrk w a "medusa" very well lol.
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