New Mars Forums

I used "SSTO" mainly to specify how I did the rocket calculations.  If you want to count jets and parawing as a "stage", feel free.  I don't much care how you define it, or whether you use one rocket stage or two, as long as it can make it to orbit.  

There's no reason to make the rocket weigh millions of pounds.  Project Mercury made it to orbit without millions of pounds - and there are jets that can carry as much weight as the total Mercury mission.

Right - which is why I was writing in the context of air-breathing jets that carry rockets to the edge of space before the rocket kicks in.   The para-wing would likely be released a few miles up.  It's just for getting off the ground.

Thinking about the various "jet plane carries rocket to edge of space" schemes - how about using a giant jet-powered hang-glider to get the rocket off the ground?

Big wings are needed to get off the ground - but once you get up to reasonable velocity, a lifting body and small wings should be adequate.

So use an air-filled para-wing to get off the ground.   Once you get high and fast enough, drop the parachute-wing.   Accelerate under jet power to fly on up to the edge of space - kick on the rocket, dump the jets and small wings and let them parachute down for recovery.   

Any winged carrier approach limits the size of the rocket - but it should be a higher limit than for a fixed wing carrier craft.

Manned vs un-manned:  I can understand how people who dream of going into space could be irritated with those who advocate dropping all manned-space efforts in favor of un-manned (which just happens to favor those people's pet projects).   

What I have a hard time understanding is any human exploration advocate who rejects using robots in every way possible, to bootstrap humans into space as cheaply as possible.  Get enough robots up there working under remote human guidance (not direct control), and eventually it'll pay to have humans on site to eliminate the feedback delay and handle tasks that the robots have a hard time doing. 

If we *don't* use robots as much as possible to get the costs of human missions way down, so humans can get out there within a reasonable period, robots are just going to keep getting better and smarter and eating away at the domain of tasks that "need a human being on site".  At the pace human space flight is now scheduled to move - forget about the inevitable delays - we may get near-human AI before we get a decent moonbase, let alone move on to Mars.

Yeah, we could dump many billions into going directly to Mars - but that'd end up as little better than a flags, footprints and rocks mission, as cost over-runs and budget cuts erode mission plans.  Probably to be followed by another 30+ years in which we don't expand on that success.  Of course, having watched NASA waste ~30 years in which we could have been building on the moon and getting ready for Mars, maybe I should just take the attitude "screw you younger guys - I want to see someone on Mars in my lifetime, and who cares what happens after that?"

I'd disagree about not needing tons of platinum - on a global scale we will be wanting tons of it.  We're producing 133 tons a year on Earth.  If the moon is to be a significant source worth investing billions to exploit, I think we're talking maybe 100 tons a year - a couple billion dollars worth.  Even if a RLV could handle a ton of it, that's 100 flights a year - eating up any profits.

And I don't think you can project from metal heat shields for dense re-entry vehicles to the bubble concept - a bubble will have much less kinetic energy to convert to heat, and will shed most of that energy high in the atmosphere, after which it will fall at terminal velocities too low for significant heating.   Taking an extreme example, would you expect an inflated toy balloon to burn up on re-entry?   A bubble will need to be more like that balloon, than a typical re-entry vehicle.

I won't pretend to have worked out the technology needed to make metal bubbles - but if the metal cools faster than is desired, keep heating it until it's inflated as much as you want.  Otherwise, fast cooling is a major benefit for reliable bubble production.

By using a few crude lunar fabricated parts, I'd guess each bubble might get by with as little as 2kg of Earth-launched components, and return maybe 10kg of platinum.  Even if it's 10kg of Earth components, each bubble might cost $50k to launch parts.  No need for expensive attitude control, btw - the mass of the rocket and the platinum, fixed to one side of the bubble, will keep the rocket oriented forward.

I know this isn't original, but maybe someone can tell me why we couldn't deliver metals to Earth's surface by making big, low density "bubbles" by carefully inflating molten metal in LEO?   If it's light enough, it seems like it shouldn't melt or burn up, and stay intact enough to float when it splashes down in the Pacific. 

Platinum, being hard to melt, might have to be delivered in small quantities inside a bubble of other metal.

Turn the ISS into a bubble factory - get some use out of it.

The problem I'd have with investing in Falcon is that it creates yet another way to get into space, without creating any added economic purpose for going, and without vastly reducing launch costs so that a whole new spectrum of applications become possible.

I don't expect that one could do anything, with a mere billion dollars, that could export anything of value back to Earth.   

But perhaps one could establish some infrastructure in space that would reduce the costs of going into space?  The O2 and H2O mining on the moon is a good example of this - though even that might be beyond a billion dollars?   

Perhaps something like a solar powered ion engine "tug" for moving cargos between Earth and Lunar orbit?  Since it wouldn't need to land in a gravity well, it seems likely to be less expensive to develop, more affordable to make it last longer.    Just an example - not saying it'd be the best investment.

Suppose Bill Gates has a bout of temporary insanity, and offers me a billion dollars to accelerate human expansion into space.  A billion dollars isn't a lot for space - but it isn't pocket change either...

Suggestions?  Just in case Bill calls?

Speaking of re-useablility - how much of the lunar descent components could be re-used locally, and how?

Offhand :
- the fuel tanks could be used for storage tanks in a prototype O2 production facility.  Longer term, maybe re-use locally filled tanks directly, attaching them to ascent stages.

- since you'd want to land with some excess fuel (a safety margin), left-over methane could be used to provide H2 for O2 extraction.

- Landing struts might be designed to form the frame of a shelter - drape it with a "tent" and bury it with lunar soil.  Line up several to make a larger shelter.  Ideally figure out a way to do that with the lander you came down on - but that means figuring out how to safely remove them and still be able to launch the ascent stage.  If we can't get that clever, use the struts from a previous lander.

- Struts might also be used as supports for a drill.

- foil shielding could be used in a solar concentrator, to double or triple solar collector energy production.

Suppose you've got the center of your rotating skyhook at just 220km, and you want to meet it at 20km - a 200km radius rotating arm.  Assume you can meet the tether moving at 300m/sec (~1000km/hr), and that the center of the tether is moving at 8km/sec - so the outer end of the tether has to be counter-rotating at 7.7km/sec.

Let's suppose you don't have to grab exactly the end of the tether - let's say you position yourself 1km above the lowest point the tether will go, so you've got the time for the tether to move 1km down and 1km back up past you.  How long is that?

You've got twice the time it takes for the tether to rotate R radians, where 200km(1-cos(R))=1km.  200-200cosR = 1, 200cosR = 199, cosR = 199/200 = 0.995, R = 0.1 out of 2pi = 6.283, so ~1/63 of the rotational period. 

Rotating at 7.7km/sec around a circumference of 1257km, the rotational period is 163 seconds.  So 163 / 63 = 2.6 seconds.  Double that time is about 5 seconds.

Five seconds to grab 1km of tether moving vertically at an average of about 400m/sec.  And that's ignoring any horizontal relative motions of the cable.  Challenging indeed.

Hmm - what if the bottom of the tether were a loop, held open by small remote-controlled wings around the circumference?   The jet could tow a hook on a tether, with the hook also being a remote-controlled wing or kite.  As the loop passes, have your hook flying off to the side, so your towed tether crosses the loop-tether, and the hook is dragged by it's tether to catch on the loop.   I can see some problems with that - e.g. one of the tethers might be cut - but at least it has some chance of catching... 

Of course, your jet is then instantly jerked upward at 400m/sec, and thereafter subjected to a continuous 30 G's.  That could be moderated by using a longer tether arm - at 1000km radius, it'd be down to 6 G's, and since the center of mass would be much higher, you could make the tether system have mass equal to your jet, which would cut the acceleration down to 3 G's as you drag the tether into a lower orbit and it drags you up.

We all know the problems with getting radioactive materials launched for space reactors.   I suspect that problem will continue indefinitely.  Eventually we'll have to solve it by finding, mining and refining radioactive materials in space.

In the meantime, the moon really doesn't lack for energy - just conversion of solar energy and storage for 2 week periods. 

Fly wheel storage might be practical.  You'd need a long beam with big tubs to mount at the ends and fill with lunar soil.   Spin it up with power from solar panels during the day, generate power at night.   Even using local mass that way, this probably requires the most total mass from Earth.

Another approach might be to pump heat deep into the ground during the day, and tap that at night for power using a stirling engine.   That would take deep drilling  but we'll probably be doing that anyhow.    It'd also take a lot of plumbing, which might be difficult to install in a hole.

A cruder approach - but easier to construct - would be to bulldoze lunar soil into a big pile over tubing, and pump heat into that during the day from tubes exposed to the sun.   This might be kept simple enough to set up via remote-control robots.

While some might prefer we abandon ISS and shuttle, it's pretty clear that we ARE going to "fix" shuttle and "finish" ISS - if only for political reasons.

From what I can see, the shuttle has only one problem that must be resolved to consider it "fixed and fly-able" from a political perspective (the only perspective that counts in this case, I'm afraid) - the foam.  We need an "good and affordable" fix - akin to the re-engineering done for the O rings. 

But NASA has looked at the foam problem and apparently can't figure out any way to keep it from falling off.  They've considered in-space tile repair, but that appears to be an unacceptably risky approach for several reasons.

If we can't keep foam from coming off, and can't safely fix tile damage in space, why not just keep falling foam from damaging the shuttle?   That does appear to be a solvable problem.  A very small area of the shuttle is actually at risk - foam can't get very far from the tank before falling below the shuttle. 

Sacrifice a small amount of payload capacity by adding strategically placed "shields" to intercept the foam - either to directly protect at-risk areas of the shuttle, or maybe to re-direct airflow near the shuttle so that falling foam is pushed away from the shuttle.

Even if the solution was estimated to only have a 90% success rate, that'd be adequate to consider the shuttle fixed, so long as it won't be flying much longer.

**Get a shuttle fix "done" so we can get on with getting beyond LEO.**