New Mars Forums

There's been some discussion about the difficulty of using lunar aluminum as a fuel. 

:idea: Why couldn't a lunar rocket use liquid aluminum, mined from the moon?

Load aluminum in powdered form into a thin steel fuel tank, possibly surrounded by a light-weight insulative blanket - but unlike on Earth, the native vacuum could be the main insulator.   Use electric heaters to raise the aluminum to abut 665 degrees C - just above it's melting point - typically using power supplied from solar electric collectors.   Probably have some pressure relief valves, in case contaminants create too much pressure in the tank. 

(Alternatively, you could have equipment to store and handle liquid aluminum, but that would be more dangerous for human operators, and requires more complex infrastructure.  Loading powdered aluminum into a tank might not take much more than a shovel and a storage bin to keep the aluminum pure.)

The liquid Aluminum  would be pushed or drawn through steel flow control valves (gas pressure or simply gravity/acceleration), into a lower chamber, where it would be blown under high pressure into a fine mist (likely by a small hydrogen-oxygen rocket) into a reaction chamber.  LOX would be pre-warmed to its boiling point, then sprayed under high pressure into the reaction chamber to ignite the aluminum, generating the rocket exhaust.

I'm sure it'd end up being more complex than that, but that'd be the basic scheme.   It could serve as a cheap first stage for launching to lunar orbit or directly into Earth return. 

Are there fundamental flaws in the basic scheme?

Major complications that'll need to be overcome to make it work?

The advantages seem pretty obvious, in terms of reduced Earth launch costs.  Especially if you manage to make a re-usable lunar launcher/lander using liquid aluminum fuel.

Main "driving" industries will include lunar residence (hotel, scientists), some support of Mars missions, and transport/maintenance/salvage of Earth satellites and other near-Earth traffic.  Support industries would include mining and purification of O2, aluminum, titanium, silicon, maybe water;  shipping O2 for use in space; cryotank production, wire extrusion and other simple metal forming; glass (sapphire?) production; solar collector and concentrating mirror production;  life support - air and food production and recycling; solar power collection and night-time power storage/production; repair and low-volume custom equipment production in support of other activities. 

Note that I'm *not* saying these will all spring up right away.  I'd guess it'll go slowly, and only really take off once we start heading to Mars, as government budgets for the moon are cut, and those who still want to go there look for ways to cut costs or bring in income to pay their way.

Yes, we ship them all over the world for pennies a pound - and that's why it's relevant to a context where it'll cost high hundreds of dollars a pound to ship products that cost only pennies a pound to make on Earth.  Even if the product costs 10x or 100x more to make on the moon, it'll be cheaper to make it on the moon.

First, I didn't say "lots", I said "some".  And given the costs and risks of transport to/from Earth - even with "cheap" launch, anyone going to the moon is going to stay quite a while, no matter that it's a relatively short trip.

  A better analogy would be to Gold-rush days, when one had to pay a lot to get there, and everything cost far more than back home because it had to be shipped in from the East coast.  In such a case, some will realize they can get rich providing goods and services to those who come there for other reasons.  And the cost differential for the moon will be many times that of the California Gold Rush.

  And of course, I said nothing about "complicated' equipment.  The most sensible approach for lunar industries is to focus on making stuff that is needed locally, and masses quite a bit or is inherently bulky, but which is easy to produce.  I've already addressed why it'll make economic sense to things on the moon - even stuff that costs pennies a pound on earth.

  If cheap isn't $10/pound (and it won't be),  there'll be huge incentives to make things out of local materials.

GNC: 
While it's true for the short term that the moon isn't a likely source of complex manufactured goods, in the longer term it should get some industry. 

After all, we don't only make cars or ships or semiconductors in one country, and ship them all over the world.   And even if we get down to $100/pound to LEO, that's a heck of a lot more than it costs to ship stuff across an ocean.   

Once enough people live in a place, they inevitably build up some degree of local economy using local resources.  So we'll probably mine the moon for O2 and probablly use aluminum to build cryo-tanks to deliver the O2.  But we'll need machine shops to repair equipment.  And that'll let us modify equipment, and build custom equipment to improve mining and launch capabilities.  It'll make sense to build stuff with local materials (mostly aluminum and maybe sapphire glass) and only ship the minimum mass of components up from Earth.   So that'll bootstrap a tiny local industrial system.

When we have lunar O2 and Al mining, local machine shops will be needed to fix and modify equipment.  Inevitably they'll invent new equipment customized for the lunar environment, and it'll be cheaper to make the bulk of it from local materials and only ship in the stuff that can't be made locally.

Still, other than better solar energy density and purer vacuum, the moon doesn't appear to offer many advantages that'd make it likely to sell many finished products to Mars.

Private access to space is currently very far from a reality.   However, getting to LEO is far more than "half the way to anywhere", in terms of the cost. 

Some have suggested privatizing space by letting commercial operations do launches for the government, e.g. for NASA - thinking that eventually commercial launchers would get the cost of launch down. 

But what if we reversed that?  Let the government provide heavy lifting services, heavily subsidized, for private commercial space projects.

After all, NASA is developing a heavy lift capability, and has lots of experience at launching large payloads.  It's politically difficult to down-size NASA, so we're going to be paying for it anyhow.   If they launched more often, their fixed costs would be spread over many more launches - an instant reduction in cost per launch.

Any US company could propose a mission.  If they can convince the government that they're competent to pull it off, they'll be allowed to buy a launch ticket - maybe even for the mythical "$100 per pound" at first, though eventually the price would probably be set via bidding.  Got an idea for an automated lunar mining mission?  Want to launch a space elevator?  Think you can make a profit providing taxi service from LEO to GEO?   Great!  Go for it!  Your Government is Here to Help!

To keep this going in the long term, launch costs have to come down.  So have the government offer $5 for every $1 in yearly launch cost savings.  If a manufacturer can sell NASA rockets for $1M less, and NASA is launching 2 of them a year, that manufacturer gets a bonus of $10M.  If a corporation takes over some aspect of ground control for $10M less a year than NASA is spending, that corporation gets a $50M bonus (once they've demonstrated they can do the job).

It's a bit like the Louisiana Purchase - pay a big price up front, to create huge new (taxable) value years down the line.

Well, "Streakie", if the moon could be made profitable for Earth, it'd be an answer.  I find that very doubtful, so we need a different motivation.

We can at best hope to make exploitation of the moon *locally* profitable - profitable if you're already living off Earth.  E.g. making air on the Moon so you don't have to pay to have it brought from Earth.   The ultimate sign that you have a truly profitable colony would then be that it becomes self-sustaining and able to grow on its own - but we could also consider every step in that direction to be "profit".

Once we take that attitude, does it still make sense to build a moonbase?   Except for the difficulty of getting humans there, Mars seems like a better long term choice for true human colonization.

Why not focus on :
-  Testing concepts for an Earth to Mars craft - tethers for artifiical gravity, producing food in space, etc.  Maybe get some value out of ISS by using it as a base where we can do those experiments for extended periods of time.
- Testing prototype equipment on Mars, before humans have to rely on it?  Aero-braking, ISRU, Habs, etc.  How about using aerobraking to deliver an ISRU unit that will provide fuel to a robotic "rocket hopper" to undertake multiple long range missions to evaluate possible colony sites?

I can see how you would take my post to mean that, but to get an accurate picture of what I was proposing, you need to take the "bacteria and fungi" post in the context of my previous post.  I.e. the bacteria would be the fast-reproducing base of a short food chain, providing protein and other essentials to the humans at the top, but having other animals in between.  Shellfish, worms, snails, protozoa, etc could eat bacteria as well as sugar/starch.  Probably there'd be another layer of animals that eat those - and humans could graze on any of them that can be made palatable.

No doubt the first colonists would not want ONLY locally produced foods - so they could bring a reasonable supply of food from Earth - but the idea would be to stretch that supply as far as possible, and not rely on it if that supply should fail, e.g. due to loss of a supply ship.

One goal would probably be to establish an automated bio-reactor prior to colonists arriving, analogous to the proposal to produce fuel for return rockets prior to arrival of explorers. 

And yes, eventually the colonists would want greenhouses - though I suspect it doesn't make sense to have clear domed greenhouses as some have mentined, when you're probably going to want to concentrate sunlight anyhow to achieve good growing conditions.  You may as well concentrate the sunlight with a mirror into light pipes leading through portholes into buried greenhouses, making it easier to retain heat, especially at night.

Maybe it's a mistake to try to base a Mars colony's food production on plants and greenhouses, at least to start.   

In essence you need a means to convert energy to edible food.  So it might make more sense to chemically produce simple sugars and starchs.   Feed those to fish, chickens, rabbits - and of course humans.   

I won't try to guess whether this is more energy efficient - but it's likely to be more reliable and easy to repair than any plant-based conversion system.

As far as recycling - I'd think recycling the water might make sense, if you're not located close to an abundant source - relatively easy to accomplish.

Virtual reality ought to be awfully good by 2025 or when ever we manage to do a manned mission to Mars, especially if you can easily afford to spend $1M per person.   

Given a choice between providing really adequate space to move around and not get cabin fever, or providing an expensive full-body VR suit, I think they'll end up going for the latter, with just enough room for one crew person at a time to get out of their suit to clean up once a day.   

You'd still want to spin the capsule on a tether to simulate gravity.

And unless AI has come along a lot faster than I'm expecting, VR won't do much to alleviate loneliness - the crew will have to be mostly loners - needing minimal social contact to be satisfied.

If the objective is "cheaper spaceflight", engine/fuel efficiency is the least concern.   

The shuttle requires an expensive standing army of technicians to refurbish and inspect it before each flight, and of course to monitor it continuously on orbit.  That army has to go, or at least be spread over far more launches.  I doubt we're likely to see the latter any time soon.  Even if we get a moon base, I'd expect no more than 2-3 launches a year - and even that rate would be hard to sustain if we don't get per-launch costs WAY down.

1) Solid boosters only for the first stage.  No expensive super-efficient rockets for the heavy lifting first phase.   Too difficult to recover and refurbish to make it worth going to re-useable engines, too expensive to throw them away.  Maybe add one or two small liquid fueled rockets to the stack to give some dynamic control and guidance.   

2)  Eliminate the naval operation used to recover the shuttle's SRBs before they're ruined by salt water.  Don't bother recovering the boosters for refurbishing - just pay a nominal amount to have them salvaged by independent operators, so they don't pollute the ocean too much.

3) Build the boosters close to the launch site - maybe build them on a barge, on canals leading out to the launch sites.  Float them out, stand them up, load the last stage/payload, and fire them.  No multiple stages of production, transport, assembly, etc.

4)  The last stage should be designed for minimum maintenance costs compatible with safety - whether that means "simpler and more durable" or "smaller, redundant plug-in components".   If it can't be designed in a way that total refurbishing costs are substantially less than the cost of a non-reusable upper stage, go with a non-reuseable upper stage, and work to get manufacturing costs down.   

5) The last stage should probably strap on beside the first stage.  That allows a single method for bundling a variable number of stages, with no separate design for interfacing upper and lower stages.   If multiple stages are needed, use more solid boosters.  Drop spent boosters before lighting off the next stage's boosters. 

6) For larger cargo launches, perhaps such as a moon base hab, use more boosters and a specially designed non-reuseable "on top" stage.   Make it efficient enough to be reliable, but otherwise focus on net system and operating costs.

7) The last stage goes only to LEO.  Crews and cargo for the moon or Mars or a more permanent orbit should be transferred in a capsule to a true spacecraft that never has to re-enter atmosphere.  So there must be a separable and separately re-entering capsule "stage", but it doesn't need any engines of its own. 

This won't get costs down to "cheap" - that'll probably take something far more exotic.  But it seems achievable, and isn't too far off from the current NASA plan.  $1000/kg of useful payload to LEO seems a reasonable goal, and far better than the shuttle.

I thought the message was to only hire blue-eyed brunettes to help build the ship and maybe crew it, because blue-steel is toxic to everyone else?

Though I'm not so sure of the practicality of this - sure it kills the aliens, but if only blue-eyed brunettes can fly in the ship, it's not all that practical - they're fairly rare after all.

A Mars colony is going to need energy and lots of it - not just to survive, but to establish a manufacturing base for producing at least glass and metals and fuel - likely a much wider range of materials - in order to grow.

Nuclear power is pretty much required to bootstrap a Mars colony - but how about the longer term?  Building a new nuclear reactor may be a bit beyond the capabilities of a small but growing colony - high pressure steam pipes, high temperature/pressure turbines, electronics for monitoring and controlling the reactor, and of course processing fuel and spent fuel (Earth is unlikely to be willing to keep launching radioactive fuel).

Most likely there are no fossil fuels (though we could be surprised).   Solar electric collectors have dust issues on top of the questions of manufacturing them and the lower solar intensity.   

Very large solar concentrating mirrors might work acceptably, and not be too difficult to produce locally.   So assume you've got a concentrated heat source - how do you use it for processing and manufacturing?   You'd need to think low tech and crude. 

E.g. dig a conical pit in the rock, dump in metal ore, and direct the mirror's hot point onto that, scrape off the dross to leave the molten metal.   Tap that off to a deeper pit to fill molds.  (Rather than waste the heat to simple cooling, maybe use that heat to run chemical processs, or at least to heat the habs.)

GNC - you can get as insulting as you want, but you can't change the rocket equation.   You referenced it, but did you bother trying to apply it?

Losses to atmospheric drag and fighting gravity (i.e. vertical thrust to stay aloft while building up horizontal velocity) seem relatively small - but once you plug the small losses into the the rocket equation as required additional delta-V, they turn out to be not quite so small in terms of payload to orbit.

Suppose you have a rocket that needs 7500m/s net delta-V for orbit (assuming final orbital velocity of ~7900m/s, and a gain of around 400m/s from earth's rotation).  But due to atmospheric drag and the need to launch vertically, assume it needs to be built as if it needs 500m/s more delta-V - 8000m/s.  Assume average rocket exhaust velocity of ~3600m/s (LOX-hydrogen).  The theoretical mass ratio for that is 9.23 : 1. 

Then suppose I can shave off just 300m/s by getting above most of the atmosphere and launching more nearly horizontally - call it a net 7700m/s required. That requires a mass ratio of 8.49 : 1. 

Hardly looks worth bothering with, doesn't it? 

But suppose the original rocket weighs 200000kg fueled and 21670kg dry - 178330kg of fuel, 19670kg rocket, and 2000kg payload.   Using the same fuel and rocket, but the 8.49 mass ratio and a bit of algebra, I get 4140kg of payload - well over twice as much!

But I suppose doubling the payload of a rocket is trivial and useless - after all, all you need to do is more than double the mass of the rocket and you can get the same effect.

Sorry, I don't have any cute cartoons to help explain it to you better.  :-D