New Mars Forums

"Senator, what about reports that you are unpatriotic?"
"What do you mean unpatriotic?  I have my pin right here!"

Oh I think eventually some private companies may finally get there acts together enough to compete with the likes of Boeing, Lockmart, or Rockedyne in the rocket industry.  But realistically they stand little chance of beating out NASA in the near future (like say by 2012 or so when Ares I becomes operational).  And even less chance of beating Ares V to the punch.

You have to compare what are talking about here.  Virgin Galactic has launched a very small sub-orbital space craft and has plans for a marginally large sub-orbital craft.  Mr. Bigelow has some great orbital structures but no private launch vehicle. And SpaceX (the closest to achieving anything) have launched a very small payload to LEO.  With plans for some larger craft some time in the future.  No one else has done anything of note as far as I'm aware.

None of these are at all comparable in capabilities to the Ares I (25MT), much less the Ares V (100+MT), or heck even the Delta II (6MT).  The harshness of the rocket equation dictates that as your scale up in payload the rocket scales up in size much faster.  The cost and complexity scale up likewise.  In short its going to be a lot more difficult to for the Altspace guys to put a payload the size of the Ares I into space.  Indeed the Chinese are the only ones who stand even a moderate chance of putting something the size of the Ares I into space ahead of the Ares I.

If that wasn't bad enough putting people on top of rockets increases the complexity immensely.  Now you have to design a vehicle that they can survive in and a way for it to safely re-enter.  Much more difficult than a simple satellite launch.

The second cold reality is that space-flight is not going to be profitable any time soon.  SpaceX may be able to fight its way into the launch market, but the market for vehicles as big as the Ares I is pretty much limited to government contracts (which are the majority of contracts anyways).

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But you love to throw around all kinds of wild predictions.  Frankly it appears to be a scatter shot approach at being correct (throw enough stuff out there SOME of it is bound to be right), but I'll give you the benefit of the doubt.  How about we make a wager about one of them?  You state that the 'Ares-I could NEVER fly once!'  How about if it does you buy me a six-pack of my favorite beer, and if it doesn't I'll get you one?  Game?

I'll just point out that while the decomposition of Hydrazine in theory just gives you H2 and N2, in practice that turns out not to be entirely the case.  The reaction happens VERY fast and (depending upon the conditions) you may end up with a significant percentage of Ammonia (NH4) in your exhaust as well.

What GCRN says is right as well.  A similar concept applies to the reason you don't add LOX to a NTR rocket burning LH2, as this similarly only decreases the ISP of your engine.  Though it might be useful in situations where you were already burning that fuel and need some additional thrust (assuming it could be added cheaply and easily).

While I don't know of any specific law against building a large rocket in your backyard, their are MANY regulations involved.  There are regulation about storing and handling large quantities of jet/rocket fuel, liquid hydrogen, and liquid oxygen.  In fact handling the fuel inside the SRB is probably downright illegal without the proper licenses.  Your county/city may want to speak to you about building codes/permits and the like as well.

When it comes to launching the rocket the FAA is definitely involved.  Launching any decent sized rocket requires their approval of both the launch and the design.  Launching the rocket is both incredibly loud and dangerous so the local authorities would have to sign off as well.

For better or worse building a large rocket in your backyard is not practical.

Hydrofluoric acid is simple Hydrogen Fluoride in an aqueous (water) solution.   Hopefully no chemistry teacher in his/her right mind will allow a highschool student to play around with HF.  Heck, hopefully most highschool chem labs don't even stock the stuff!  As GCRN HF is a particularly nasty substance in acid or (god help you) pure form.

However measuring the enthalpy of a acid-base reaction is really simple test that can easily be done in a high-school lab (heck you could do it in your kitchen if you had the right stuff).  A decent calorimeter can be made out of a couple nested Styrofoam cups.  And a good high school lab should have HCl, in both strong and probably already diluted to easy to handle concentrations.  Likewise it should be well stocked with a strong base (likely NaOH, lye), but you can easily get your hands on one of these if you like.  It really is a simple experiment, you can find a ready made procedure for it probably in a good chem 101 (possibly even high-school) text book/lab book, or on the net if that fails.  A great learning opportunity any teacher would jump on!

Actually this may not be true.  Hydrogen and Oxygen have the highest specific impulse (change in momentum per unit of fuel), but do not necessarily produce the largest amount of thrust.  In fact in general thrust is often hindered by high ISP as the more entergetic propellants need a higher flow-rate to achive the same amount of thrust in the same amount of time.  The SSME are probably pretty close the the limit here.  This is why the Space Shuttle has the two large SRB which have teriffic thrust but terrible ISP.

In most cases the product of a neutralization reaction is plain old water with some ions in it.  While Acid-Base reactions may seem dramatic, energy wise they are pretty pathetic compared to rocket fuels.  And its unlikely that any hydrogen would be formed in this case (though it can happen in some reactions).  Think about it rationaly, do you real think house-hold chemicals, indeed things you can eat are entergetic enough to make an effective rocket propellent?  Of course not.

Rocket propellents are highly entergetic, reactive substances.  Even the most mild of them will burn/melt the flesh right off your bones.  You of course cannot eat them.

Actually analysing a potential rocket propellant is not that difficult. 
Step #1, determine the energy of the reaction or its enthalpy.  Obviously the higher this is per gram the better.
Step #2, figure out if the products would make make good exhaust.  For this you idealy need a light gas.

Give people a chance to reply!  Its pretty easy to judge that most neutralisation reactions are not going to be entergetic enough for rocket propellant.  In would be a good experiment for you, measuring the enthalpy of a neutrilaztion reaction is classic chem 101 stuff.

Though more generaly speaking any acid-base reaction is a redox (oxidation reduction) reaction, which is the same kind of reaction that all chemical rocket fuels I am aware of rely upon.

There is no free lunch in chemistry, if you some how get the H back out of HF, you have to use as much energy as you got putting it there.  Besides the fact that this reaction won't work, there are a couple other fundamental issues.  How would you recapture your (highly entergetic) exhaust?  And caring oxygen to react again with your hydrogen only lowers your ISP.

Hmm, I never realy thought about the point you address.  When we think of NTR we do tend to think of the NERVA stuff from the 70's and assume that it is the limit for these types of engines.  Probably because conventional chemical engines pretty much have reached the limits of performance.

But as the author points out this may not be the case for NTR.  There is probably a good bit of additional preformance that can be wrung out of NTRs beyond what the NERVA guys achived.  Especially in the area of specific power increases.  The improvements he mentions for a 4th generation NTR rocket seem very reasonable to me, and would make the already good NTR even better.

As for using a NTR as an upper stage, its a marginal proposition I think.  Even the improved 4th generation NTR rockets are only marginal in this role.  Even at twice the power density they are still only okay.  Another problem is that an upper stage engine would have to be much larger, in some cases as powerful as a ground based nuclear reactor (2GW or more).  Which has obvious implications both in terms of shielding and safety.

I'm also not to sure that abort to orbit is a viable alternative.  Mainly because implementing a seperate assent system for the reactor would be expensive and complicated, and the system would ultimatly not be very reliable.  There are a large number of possible malfunctions (any of a destructive sort) in which that sort of abort system would probably be useless.  I might be willing to slide on enviromental consiquences of a largish NTR disaster, but realisticly that won't be an option.

Here's the deal.  While the amount of thrust you get per unit of fuel (specific impulse/ISP) is of critical importance to interplanetary travel, the rate at which that power can be safely released, and the amount of mass it takes to generate that rate (specific power/thrust) are very important during lift-off as well.

While most sorts of nuclear engines (be they NTR, GCNR, VASMIR, Fusion, whatever) may have superb ISP, their specific power/thrust is poor to downright terrible.  Whats more, there is a limit to the rate at which most of these engines can safely release their energy due either to heat dissipation (VASMIR and others) or radiation (anything involving Fission).

Thats why none of these is suitable for a first or second stage engine for an Earth-side lift-off.  Chemical or air-breathing really are the only options, (with chemical being the best in my book).  I wouldn't be so quick to count out other chemical fuels though.  H2OH, CH4, C2H6, and Keresone all have lower impulse than the LOX+LOH combo use in the shuttle, but they all are denser which can give you an advantage in tankage size (which is critical for SSTO).

Here's the thing though.  These men didn't die on an Apollo type mission to the moon, or a Columbuian expedition, or a Magellan trip around the world.  The died during a test fire.  This is unacceptable.  People shouldn't being dieing during tests fires!

I can accept that space travel is a dangerous business and that every now and then an astronaut or cosmonaut is going to get killed in the process.  Just like I can accept the occasional test pilot dieing on a test flight, or a test driver dieing in test drive.  But this is none of those things.  This is the equivelent of an engineer dieing during a plane runway test, or a engineer dieing during a car crash test.  Completely unacceptable.

Engines blow up on the test stand, this is a fact of rocketry.  But these sorts of occurances should be safely planned around so that such incidents don't cost human lives.  Failure to do so is completely unacceptable, and Scaled Composites is lucky to get off with a moderately small fine.

I'm all for OSHA and other safety agencies, they are one of the big forces preventing our employers from putting us in harms way for marginaly more economic gain.

The problem with para-terraforming Mercury is that the amount of solar energy it receives is massive.  It would be hard to create a structure that could survive the intense thermal roasting it receives during its long day (hot enough to melt lead) and then the shock of cold during its night.  While possibly not impossible to achive, almost all plans I have seen seek to avoid being roasted in the sun somehow.  The same issue exists for an orbital shield of some sort as well.  That close in to the sun it become difficult to deal with all the radiation (thermal and otherwise).

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Which is why I do think mega-excavation is an excellent idea.  While it is doubtful that you could dig to the point where Mercuries gravity equals 1G (if such a point actually exits), you could dig some very deep pits at the poles to provide yourself with a secure shelter from the sun.

Such a 'hole' might not actually be that difficult to create.  As I pointed out before the sun emits massive quantities of energy when you are as close as Mercury is.  A few mirrors held in place by Mercuries gravity and solar pressure at the poles could be used to melt and vaporize huge quantities of Mercuries surface, digging the whole for you.

To me the big question is why.  Mercury's core probably contains good quantities of useful metals, but that is hardly unique in our solar system.  It would be a good place to observe the sun, but that is probably better done unmanned.  Maybe it would serve as a decent staging platform for efforts to terraform Venus, or a manufacturing plant for anti-matter or possibly solar sails.

While I'm not completely certain that you could not burn silver with H2O2 under the right conditions, I am sure that it is not used as a fuel in jet packs.  Silver is heavy, not very reactive, and would probably for some sort of solid after reacting with H2O2.  Oh, and it would probably be deadly toxic (breathing heavy metals in is bad).  Most likely what is happening is that silver is being used as a catalysts to decompose the hydrogen peroxide.  I know platinum can be used, so I would not be totally surprised if silver (which has some similar properties) could be used as well.  Or possibly the source just has it wrong and platinum is in fact being used as the catalysts.

It does, most any oxidizer (such as CO2) will burn with hydrogen, which is a very strong reducing agent.  The problem with this reaction is that it is not especially powerful (you lose a great deal of energy converting CO2 to CO and burning that) and that it tends to produce carbon dust which hurts your performance ever more.

I believe that if you are going to go to the trouble of using liquid H2 (a very demanding cryogenic) that you might as well use a more powerful cryogenic oxidiser such as LO2.

Silane also suffers from much the same performance problems that CO2-H does, but does have the advantage of being dense and storeable.

Blegh, CO2 would be a pretty terrible propellant.  For a NTR molecular weight is THE key to performance.  So CO2 (molecular weight 44) performs pretty terribly.

Better choices for a NTR are Hydrogen (obviously), Ammonia (NH4 atmoic weight 18) which breaks down readily to Nitrogen and Hydrogen which improves your average to 8.  Or even water (18) or oxygen (32).  CO2 is about the worst you could get.

As I recall most serious plans involving use this shuttles main tank in orbit also include some other means of adding the extra bit of thrust necessary to get the tank fully into orbit on its own.  It really is carried very nearly all the way to orbit with the Shuttle OMS system firing only a minor burn after the ET in jettisoned and the main engines are shut down.  The loss in cargo space in the shuttle truly isn't that great (even negligible depending on the orbit the shuttle is shooting for).  And could be made up for with a slightly larger or lighter tank, or a small additional booster stage.

I used to be quite skeptical towards the idea of using the ET for anything in space, but the idea does have some merit.  As I said before the ET is carried very nearly into orbit, so you wouldn't have to loose that much to get it there.  If you COULD use the tank it would provide an incredible amount of additional space.  The ET is huge, probably bigger in usable space then the entire ISS.

Additionally the tanks are relatively strong, insulated, and air-tight.  Recall that the ET has to support several hundred metric tons of propellant, as well as structurally supporting the orbiter while the SRBs are providing thrust during lift-off.  Its certainly as light as they can safely make it, but it is not a particularly flimsy structure by any means.  While it may lack a dedicated micro-meteorite shield and radiation shielding its not clear that such things are absolutely necessary or that they could not be retrofitted fairly cheaply into the station.  Certainly its relatively hardy construction should provide some protection.

Recall as well that Skylab was essentially an upper stage for the Saturn V rocket modified into a space-station.  So I believe, in theory, that not only the idea could work, but could work very well.

Alas, in practice I believe there are some significant difficulties.

#1.  Spent fuel.  Actually this isn't a problem, but I though I'd point out that it isn't anyways.  LOX and LH2 (especially) will quickly dry up and evaporate away if exposed to vacuum, which should be easy to do in space.  Just leave the lines from the SSME open.  Their might be slight possibility of explosion, but that seems unlikely to me.  LOX and LH2 aren't hypergolic so their fumes are unlikely to spontaneously ignite.

#2.  Access.  While there ARE access hatches in the LOX and LH2 tanks they are relatively small and not suitable for use in space (I think they get welded shut as well).  In order to gain access to the LOX and LH2 in space they would have to be re-engineered for bigger access ways.  Its not clear to me to what extent this is possible/practical.

#3.  Assembly. The biggie.  Assembly in space has proven to be difficult and time consuming.  This is doubly true if EVA is required (which seems likely).  Loiter time is limited in space (for the shuttle at least) so this labor and time is doubly expensive.  I can think of no cleaver means of reducing this obsticle.

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In any case while I don't think we are likely to see the ET used in any fashion in the immediate future, I think the idea DOES have some merit.  At least enough that it should be at least examined, not rejected out of hand.