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Archive for the ‘ISRU’ Category

Rand Simberg talks about impedance matching. So I’d like to make a post of my comment there (I’ve always wondered why this obvious alternative gets mentioned so little…)

What to do when you arrive at Mars or Earth with your solar electric propelled vessel?

So, the problem with most low fuel demand velocity change schemes is that they only give slow accelerations. Low fuel high velocity change means solar or nuclear electric propulsion and aerocapture mainly.

High delta vee aerobraking is hard to do in one pass – it gets dangerous because of atmospheric variability and potentially other reasons.

Simple: detach a small capsule with the humans that goes directly to the surface (with only days of life support) and leave the untended craft to do multi-pass aerobraking. Hitting van Allen belts a few more times or taking a long time doesn’t matter that much with no humans onboard.

You could also potentially ultimately leave the long distance craft at some Lagrange point instead of LEO. (Cue some clever and complex maneuvers to save fuel – maneuvers that take long.)

Something similar could also be done when a long distance stack is assembled in LEO: send the humans there only after it’s through the belts. They can go with a smallish capsule again. Potentially at some Lagrange point, or in space without any fixed reference, just along the way. It could be dangerous though if the capsule doesn’t have much life support.

Many of these things have potential delta vee penalties as well as timing inflexibilities, but they could have enough other benefits that they should be considered.

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He who controls the [Earth-Moon Lagrange points/Phobos/Deimos/Lunar North Pole], controls the solar system.

Why?

Because in space, it is not the tyranny of distance that sets the rules – it’s delta vee instead.

Since there’s no resistance, traveling large distances just takes longer, but doesn’t necessarily require more propellant. Unmanned craft can take this long trip time just fine. This is completely different from the implicit mental models of everyday life or historical exploration, travels and colonization. Even places that are far away in distance can be close in delta vee, and vice versa.

The Earth-Moon Lagrange (EML) points have really low energy trajectories to all the other places, including low Earth orbit (or Earth re-entry). They’re the crossroads. They’re probably not controllable though, like you can’t control low Earth orbit either, it’s just a figure of speech* to stress their significance.

For example, Phobos and Deimos have really low delta vee needs from EML2. And they have really low gravity. This means that it’s cheap to send stuff to them, but perhaps more importantly, it’s cheap to bring stuff from them. Since a lot of space faring is limited by mass that can be brought to locations, a low energy source of material is a real paradigm changer.

The Lunar north pole’s peaks of eternal light are much closer to Earth, but the Moon is so heavy that it takes quite a lot of propellant to descend to and ascend from the surface. The good constant sunlight is an asset though. The area is limited so this is the best incentive so far for a “race”, though I’m skeptical of that.

This post was written partly inspired by Paul Spudis’ and Clark Lindsey’s talking about the importance of the Moon as an enabler for other stuff – I am somewhat less certain. (On VASIMR and JIMO I can refer to Kirk Sorensen who has good reasons for skepticality – the power to mass ratio needed is huge and that’s the really hard part, yet it’s rarely talked about. Space reactors are much harder than Earth ones because of the cooling problem.)

We must dismiss analogies that do not work, since space is a different medium. We must use completely different planning than for exploration on land or the seas, because of the completely different role distance plays. And we must also plan on advancing from exploration ultimately to infrastructure, colonization and self sufficiency.

*: From Frank Herbert’s Dune of course.

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Or what you are going to call it, an unrealized proposal from Aerojet around 1984. PDF Found on NTRS.

The idea was to have two turbopumps (like on SSME), but instead operate on the expander cycle. Two heat exchangers, two turbines, two pumps. One for each propellant.

 

aerojet_cycle

Both propellants go through a heat exchanger and an expander driving a pump

 

This is a LOX-hydrogen engine. Also this means that since there is the same propellant on both sides of the axle, in the turbine and in the pump, no elaborate seals are needed. Original intent for these engines was for in-space reusable stuff, that needs to be operated many times and for a long time without maintenance. Size was in the RL10 class, about 70 kN. (RL10 has grown though.)

aerojet_margin
Simplicity and margin were claimed

Think for example if you let a fired turbopump sit in space for a long time. Will some fuel leak to the oxidizer side through the seals? This could avoid that. (You can use helium purges too though but then you’ve got one more fluids you need to tank.)

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Jeff Greason is a rational person who simply gets it. It is mind boggling how completely opposite from someone like Mike Griffin he is.

See Jeff’s presentation with the Augustine Panel.

Paraphrasing, “we could go to Mars with Ares V but we shouldn’t – cause we couldn’t stay anyway”. Exactly. That’s the problem with NASA. (or the major one)

I bet he will be ignored completely.

Also, I would like to work for that guy. Too bad because of ITAR I couldn’t work in the USA.

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There are a lot of implicit assumptions that heavy lifters of this or that throw weight must be used for future exploration beyond low Earth orbit.

These “needs” have never been logically derived from anything.

Yet space policy and exploration architectures must be based on rationality above all. There is no excuse whatsoever to do things on a whim. Hundreds of billions of dollars, and the future of humanity’s spacefaring are at stake.

There is no foreseeable need to launch over 25 tonne monolithic payloads to low Earth orbit in lunar exploration, and probably even that number could be seriously diminished with some more thorough planning. Orion, EDS, LSAM, all are below that weight, if they are refueled using a depot in space.

If the huge development and operational estimated costs for a heavy lifter rocket go away, then that money is freed for real exploration work. In-space hardware development, more launches, more missions and operations.

Flight rate is _the_ most important way of reducing launch costs, the single largest impediment for advancement of spacefaring, and the propellant depot enables a higher launch rate. Multi-launch scenarios with a propellant depot also enable competition, redundancy and flexibility, all very good things, ensuring safety, robustness and progress.

I repeat as a summary how

1) Solutions for space exploration, like any large endeavour, must be rationally justified. No baseless assumptions should remain.

2) The need of heavy lift is a baseless assumption. It can be one of the alternative ways of execution, but it can not be a starting point or an axiom.

3) The current architecture is heavily based on the implicit assumption of heavy lift. Hence a rational space exploration architecture would examine things from the ground up. It could end up with some radically different conclusions.

4) Propellant depots is one alternative way of executing space exploration beyond LEO, and it does not need heavy lift.

5) Propellant depots can, if executed correctly, increase launch rates many fold, and thus enable lower costs, progress, reliability, redundancy, robustness – all the things that the space shuttle promised but failed to do because it was a sole solution that could not sustain a high enough launch rate and was too costly.

6) NASA at the same time should keep on working with fundamental research, to enable continuous progress trends in space technology.

7) Space exploration should look as different from Apollo as possible – there should continuity and continuous improvement possibilities, robustness and progress. The architecture should be affordable as well.

8) New space technology, like cheaper launchers, should be demonstrated at a smaller, humble scale first. That way many things can be tried and progress is faster, for the same price and effort. One failure also will not be as critical.

9) There seem to be impediments for information flow inside NASA, and many professionally acknowledged things like propellant depots, EML2 rendezvous or space tethers are never even mentioned in NASA high level planning. This is not rational.

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Concept art of lunar bases tends to show spherical or cylindrical structures, but they suffer from one problem: radiation. (Both of the gamma / particle and heat kinds). The lunar environment has lots of solar and cosmic radiation. Nights also last for two weeks, during which a badly insulated thing will freeze.

If you bury your moon base under a layer of regolith, you can avoid both of these problems. You don’t have to bring heavy shielded modules from earth, or heat during the night with nuclear batteries. Regolith is thermally well insulating.

NASA seems to catch onto this a little in some clearly low budget “alternative configuration” posted at Nasawatch, but it only goes halfway, putting some shallow “berms” around cylindrical structures, for shielding.

In reality, lunar bases (if crews are to spend many lunar nights there) would probably be completely buried.

Burying might actually be easy: a small automated/remotely controlled snow blower style rover vehicle might be able to do it slowly with the help of just solar power. Since there is no air, tiny amounts of regolith can be thrown large distances. A thin wheel with whiskers spinning rapidly would throw the sand to the wanted direction. A lunar day is 336 Earth hours. Even if the “regolith lobber” robot can not survive the night and is expendable, it could manage to move significant amounts of regolith. A sub-MER size rover with large solar cells could throw perhaps 20 grams of regolith per second, or 72 kg in an hour. That’s 7 tons if there is 100 hours of efficient sand throwing time.

Say, landing at 50 hours from dawn, setting up 50 hours (survey area, lower rover from lander, unfold solar cells etc), operating for 150 hours (which includes maneuvering 50 hours and sand lobbing 100 hours), and finally stopping at a low sun angle 50 hours before dusk.

Such concepts are probably unlikely to work in an atmosphere, though I would be happy if proved wrong. The 2009 lunar regolith excavation challenge is coming up, after all…

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And partly what this blog is about (I realized in the middle that I’m typing like in a slide show, so I changed it into bullet points, as it’s an overview and not a deep text). I present my vision that should be aimed for:

What should NASA do?

  • In the near term, NASA should change to EELV:s (Atlas V, Delta 4) and COTS (Falcon 9, Taurus 2) as launchers for the ISS and lunar programs.
  • At the same time, NASA should do basic research and cheap small tech demonstrators for space technologies that give more for less.
  • This should move humanity closer towards spacefaring.

Spacefaring? Spacefaring is making space operations routine.

  • Space faring requires that space access is cheap, reliable and hassle free.
  • Launch is only part of the spacefaring,
  • But only from that point on can the better in-space technologies (tethers, ballutes, sails, ISRU, slings, whatnot) be developed.
  • Hence launch improvements are absolutely crucial for spacefaring

How can cheap and reliable space access be reached? There must be:

  • Many independent providers of space access.
  • It is done largely with well reusable vehicles.
  • The architecture – more of a market – is multi-faceted and the launchers can be improved, new ones can enter the market and old ones can be scrapped

This coal can be reached, in the next few decades.

Things to avoid:

Technically unrealistic choices at the highest level:

  • In the NASP program, the early performance numbers were fudged and there were unacceptable internal politics meaning no real independent technical criticism would be heard at the top
  • In the “Safe Simple Soon” Ares rockets vs the already flown EELV:s debacle, OMB has lacked the expertise to keep NASA on a leash so they are a “loose cannon” controlled too much by the whims of a leadership that fires all who disagree
  • Countless other examples…

Program mentality:

  • Apollo was ended since it was just a short unsustainable program with a specific stunt style goal, not fitting in any overarching smart picture as a sustained capability
  • STS has been an unimprovable yet critical massive monolith, barely sustainable, for various reasons
  • Danger of having yet another single solution launcher (or two) just for a definite program

Lack of motivation:

  • Has NASA become too big and corrupt by internal politics to really do technical or economic choices? Has it just become pure politics and internal struggles for personal or group benefits? (ESMD) There are great and talented people working there, but does it make a difference?
  • What does the whole agency exist for anymore anyway? Or its current lunar program? Is it just a relic from Apollo?
  • How much actually flying a few people to space every year conflicts and directs efforts away from the goal of reaching real spacefaring?

Summarized, NASA’s goal should be a spacefaring humanity in the future, not having a narrow minded program after another.

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