New Mars Forums

Seems to me that throwing away 300 KW as waste heat is squandering a lot of energy. Couldn't this heat be utilized in some useful manner? Maybe not initially, but later after we get men there who need heat?

We're seeing increased sophistication of all the hardware through the private companies--not NASA. Going to the Moon again with an upgraded capability will translate to Mars in just a few more years. It's no longer the option game of "The Moon OR Mars," but the Moon "On the way to Mars."

I agree that having a 1 MWe  unit "would be nice," but we should fly something immediately available and not wait around for the "perfect unit," that simply delays implementation of any realistic program. My first mission would be a lot like the Zubrin Mars direct model. It would include a working COTS Nuclear reactor, of any power output beyond the minimum of the SAFE-400; a reasonable scale MOXIE unit, as well as a Sabatier reactor. Both reactors should include a scaled down cryo-liquifaction system and associated storage tanks. This demonstrates the feasibility of fuel/oxidizer ISPP.  This is a lot more than some of the other landers have accomplished, since it will not get bogged down in a sand drift.

I did some checking on prices for some of these other fuels, such as Aerozine-50, and the stuff isn't cheap. Of course the cost isn't based on the chemicals but the handling and transportation under EPA rules. Roughly $135 per kg is pretty stiff. Even worse for NTO, though. It's certainly NOT the production costs, but the regulatory burden is certainly oppressive. Fueling a Delta II second stage would cost roughly $800,000, at this rate. I'm sure the Russians are having none of these environmental impediments to interfere with their launches. Looking at the Aerojet-Rocketdyne engine, it's rated for up to 7 restarts, and is non-regeneratively cooled, using instead an ablative lining for the combustion chamber. This puts it in the "use and throw away" category of equipment.

GW-

Maybe SpaceX should consider a redesigned second stage using MMH or Aerozine 50 as a fuel and NTO as oxidizer? This is what initially attracted my attention to the Russian built Proton M third stage. Just design/build a new deep space  stage fueled with the most stable and reliable fuels. Could also serve as a Trans Mars stage and maybe even a descent stage? Of course, my chemist prejudice is showing in these decisions! This has been the "missing link" for most of the brainstorming efforts on this website aimed towards an improved Mars Mission architecture--and now the redux of both Apollo 8 and Apollo 11. We've gotta' stop thinking small; think big and achieve great things!

Rather than focusing on Isp; the use of Id is a far better number to look at for mass control of a spacecraft. The Id for a combination of LF2 with Hydrazine is nearly 3x that of LF2/LH2: 432 kg-sec/l. Another potential exotic oxidizer is FLOX, a 50-50 mixture of LOX and LF2; when used in combination with Aerozine 50, it yields Id of 403, and with UH 25 (25% UDMH/N2H4), it goes up to 411. These are all significantly better than RP-1 using FLOX, at 386 kg-sec/l. When we subsequently look at using Dinitrogen Tetroxide, the use of Aerozine 50 jumps off the page w/r to safety in handling over that of N2H4, but with a significant performance edge at 326 kg-sec/l.

Note: all values are at sea level, so vacuum performance should be significantly higher.

These exotic propellant schemes are pretty impressive on paper, but they aren't going to be allowed at Cape Canaveral if they produce oceans of hydrogen fluoride as exhaust products. For upper stages, on the Moon in vacuo--go for it.

Looking at the possible fuels in more detail this afternoon; hydrazine is maybe too unstable for use as a fuel, but MMH and UDMH are a lot better; the blend of UDMH with hydrazine called Aerozine 50 looks very useable, as does MMH.

This will probably come down to an "OldSpace" versus "NewSpace" bidding; if I were running things there would be a budget established for a Lunar landing by 2019 of $3 to $5 Billion, with the competition open to all bidders. The goal: more than an Apollo 11 Redux, but also land a base module for long-term habitation and begin establishment of a permanent presence on Luna.

I see that GW's and my figures in my post # 96 are in pretty good agreement.

I personally like GW's idea of horizontal cylinders laid in trenches and covered by regolith. Reminds me of the 1950s backyard bomb shelters constructed to survive the blast and radiation from nuclear bombs. Structurally very strong, easy to manufacture, and could be transported by a Falcon Heavy.

SpaceNut-

Great tables in the first article; took some time to dig out the appropriate numbers, but seems that Hydrazine comes out second only to LH2 w/r Isp, and much better Id, when combined with LOX. Better than LCH4, and when density is considered, may be the best overall non-cryogenic fuel/oxidizer combination. UDMH isn't too shabby, either.

I haven't seen any data regarding any Isp data for the couples of MMH/LOX or ADMH/Lox. It seems that there isn't too much of a problem at deep space temperatures for keeping LOX around; both of these hydrazines have pretty low freezing points, so less supplementary heat would need be applied their tankage for keeping them available in the liquid form. All the gaseous combustion products would be low molecular weight compounds which allow for higher exhaust velocities which relate back to higher Isp values.

The problem with GW's "dirty gas," is it's really no longer a gas and isn't calculable by the gas equations based on the "perfect gas laws." Which--it ain't. This is where theory fades and empiricism prevails. Another perfect example of how "theory guides---but experiment decides."