Science: Spacecraft: Propulsion
Moon Raft Transport   (-5)  [vote for, against]
Novel solution for a sample test

This invention is my wife's as she was given this test for one of the graduate classes she was taking. It is a standardized test and I have found several references to it on the internet.

The test is as follows:

Your spaceship has just crash landed on the moon. You were scheduled to rendezvous with a mother ship 200 miles away on the lighted surface of the moon, but the rough landing has ruined your ship and destroyed all the equipment on board, except for the 15 items below. Your crew's survival depends on reaching the mother ship, so you must choose the most critical items available for the 200-mile trip. Your task is to rank the 15 items in terms of their importance for survival (on the moon). Place number 1 by the most important item, number 2 by the 2nd most important, and so on to 15, the least important.

The items:

A box of matches. Food concentrate. Fifty feet of nylon rope. Parachute silk. Solar-powered portable heating unit. Two .45-caliber pistols. Once case of dehydrated milk. Three 100-pound takes of oxygen. Stellar map (of the moon's constellations). Self-inflating life raft. Magnetic compass. Five gallons of water. Signal flares. First aid kit containing injection needles. Solar-powered FM receiver-transmitter.

Her invention was to inflate the life raft and strap the O2 tanks to it and fly/sled it back to the mother ship using the gas as a rocket.

I was originally annoyed with the test because the survivors were so obviously doomed, and this just seemed like rearranging the deck chairs, but her solution may be the one way to cheat death.
-- MisterQED, Feb 14 2008

Same test, with """NASA's""" answers http://bbs.tastytro...y%20Brain%20Teaser/
Dumb, dumb, dumb. [MaxwellBuchanan, Feb 14 2008]

Well, half of that stuff is just crazy. Matches on the airless moon? Solar-powered HEATER in the hot sun? Magnetic compass on the no-magnetic-field moon? Map of the same-as-the-Earth's MOON's constellations?

Her solution is pretty good. The raft might make an "air-cushion" vehicle with the gas bottles--maybe. The silk could help that, and the rest of the stuff, including the pistols, could serve as and/or propel reaction mass.

Otherwise, I'd use the pistols to shoot the guy who wrote the test.
-- baconbrain, Feb 14 2008

Unless one of those items is a space suit, a rocket sled isn't going to do you much good.
-- 2 fries shy of a happy meal, Feb 14 2008

Need more information on their situation - do they have enought air, suits, etc. Can they navigate to the mother ship? DOes the compass give any response (is it necessary)? Is anyone hurt? Can the mother ship mount a rescue mission (ie sit tight and wait for the cavalry - this is a purely survival scenario, as opposed to a "move 200miles and survive" one).

Would water vaporise or freeze on the moon surface? If it vaporises, it might be a useful energy source. There's a good chance the flares won't do jack, or at least not be very visible as there's no oxygen to burn the illuminating components. I was toying with the idea of a powderised milk/oxygen explosive/rocket fuel, but there doesn't seem to be anything you could use as a nozzle.

May I ask - what sort of graduate course is this??
-- Custardguts, Feb 14 2008

Which moon are we talking about? Endor? Yaavin 4? Are the survivors droids or human? Are they being pursued by bounty hunters? Does the mother ship have a tractor beam?
-- jaksplat, Feb 14 2008

//May I ask - what sort of graduate course is this?// It sounds like the sort of stuff they do in courses on "Human resource management" and the like. I believe the expression is "ninny-pinny dopey stuff."
-- MaxwellBuchanan, Feb 14 2008

It's a graduate teaching course. And yes we do need to hunt down the guy who wrote the test. I assume that it was a shipwreck scenario that someone rewrote for the moon by adding the oxygen and then blaming it on NASA.
-- MisterQED, Feb 14 2008

The crashed ship still has air and presure or we would be dead. We make a bubble of the silk on top of the raft. We sit on raft inside bubble with some air to breathe. we leave water and food behind. We shoot holes in crashed ship. The air that comes out sets us on our sliding way in the direction we judged with the charts. We use some oxygen and the powdered milk as a rocket propellant type thingy. Start with matches. We slide home. We radio ahead to look out for us.

I'm going to loose much sleep over this.
-- zeno, Feb 15 2008

How the heck do you get a life-raft to slide on the moon? (Other than [baconbrain]s air-cusion concept.)
As for a "stellar map (of the moon's constellations)", it would be easier just to use the Earth as a "pointer", because it never moves!
-- neutrinos_shadow, Feb 15 2008

I think 800 kg of oxygen tanks is going to be a bit much.
-- lurch, Feb 15 2008

This question completely ignores the fact that those screwed people in space. Who the shit uses matches in space. You gonna start a fire on the moon? Does this life raft have an air tight bubble to hide in? or do you simply get out of your trashed space craft and ride an air mattress to safety.

A graduate teaching course for retards?
-- Antegrity, Feb 15 2008

//A gun does not work on the moon (see needing oxygen to burn the propellant// Hmm.
Remind me again how the oxygen gets into the sealed brass case?
-- coprocephalous, Feb 15 2008

ok, so you make a balloon with the silk containig air and powdered milk. Use needle to make hole, light match in airstream to ignite. Tie yourself to it, use co2 tank from liferaft, guns and flares to change course.
-- zeno, Feb 15 2008

A gun doesn't need oxygen; the oxidizer is part of the gunpowder. However, the finger of your space-suit glove wouldn't fit through the trigger guard.

Match heads, likewise, contain their own oxidizer; however, there's no oxygen to burn the stick. Just flare and go out.

Nylon rope would only last a matter of hours exposed to direct sunlight. (Molecular breakdown by ultraviolet light, no atmospheric protection.) Apparently (and I was quite surprised by this) the sik parachute material would fare even worse.

The flares, depending on the design, might work in vacuum. (If not, somebody bought the wrong ones.) If they're Very pistol flares, you could shoot them up to gain signaling distance. They'll fly higher in lunar gravity, but not high enough: on the moon, the horizon is much closer to the observer than on earth because of the small diameter. To be viewed from 200 miles, the flare would have to reach 100,000 feet altitude. Same problem for the radio - it's line of sight.

Insufficient info on the raft - I would guess it would quickly fall victim to sunlight.

Five gallons of water - probably would be sufficient to drive you insane. It's in a container; if you open it, it'll boil off. Leave it closed and it'll explode. You get thirsty, and want the water. Perhaps you could just take the syringes and inject it into yourself.

I agree with [MisterQED] - this was a terrestrial scenario converted without adequate know-how.
-- lurch, Feb 15 2008

..Can I ask why the water tank would explode? Vapour pressure wouldn't be all that high... Unless you mean it'll freeze and expand - in which case have the bottles 2/3 full. I mean at room temperature water vapour pressure <1 bar, so unless the lunar surface is really hot, you'll have <1 bar overpressure in your water bottle. Hell, a glass bottle can take that, easily.

For the record, I imagine a .45 auto would work exceptionally well in space. If it's gas-operated the slide might be a bit more energetic (extra 1 bar acting on piston), but that's about all.
-- Custardguts, Feb 15 2008

//Why water tank would explode// Day side lunar temps 100 to 125 Celsius. So, as you suggest, it would be very dependent on the type of container - strength & insulation.
-- lurch, Feb 15 2008

//Three 100-pound takes of oxygen.//

Mass measured where?
-- Ling, Feb 15 2008

Doesn't matter where mass is measured. Mass is mass.
[EDIT] Proviso: velocity not approaching c.
-- coprocephalous, Feb 15 2008

100 lbs of oxygen is the mass of the O2 not the tank, so in this specific instance mass is not mass, per say, the mass of the tanks aren't counted in the number. My question is that I don't think 300lbs. of LOX is enough to keep even one person breathing long enough to walk/hop 200 miles on the moon. But would it's thrust be enough to propel one person 200 miles? Friction would be less, due to 1/3 gravity. Air resistance isn't an issue at all. The whole reason I like the raft is that it seems slightly more survivable in a man-meets-mountain incident. Otherwise I guess you could just strap them on like rocket packs and fly back.
-- MisterQED, Feb 15 2008

Lbs is weight, not mass. If it's 100 lbs weight on the moon, that, as I said before, is about 800 kilos. 100 lbs earth weight is closer to 130 kg mass. Nowhere does it say what fraction is 02 and what's tankage.
-- lurch, Feb 15 2008

lbs force is weight, lbs is mass.
kgf is weight, kg is mass.
-- AbsintheWithoutLeave, Feb 15 2008

Why not sit tight and wait for the better-equipped rescue party to find us?
-- AbsintheWithoutLeave, Feb 15 2008

// My question is that I don't think 300lbs. of LOX is enough to keep even one person breathing long enough to walk/hop 200 miles on the moon.// A human being uses about 300kg (600lb) of oxygen **per year** with typical levels of activity. One of those tanks is going to last the whole crew for as long as they'll need it.
-- MaxwellBuchanan, Feb 15 2008

//Her invention was to inflate the life raft and strap the O2 tanks to it and fly/sled it back to the mother ship using the gas as a rocket.//
And seconds later you'd lose control, smash into a rock, puncturing both the raft and your spacesuit. The remaining crew are now kicking themselves for letting her run off with the oxygen tanks, which are now bouncing across the landscape.
The better solution is to first try the flares. If that doesn't get the attention of the mother ship, you shoot the other members of the crew, extending your survival time to the maximum. This doesn't work any better for the crew, of course, but at least they're not kicking themselves.
-- ldischler, Feb 15 2008

The oxygen tank is worthless unless you have some N2 to blend with it to make it breathable. One without the other can only be used for propulsion, or for making light by combining with the other flamable crap. Its really hard to control the output of a cylinder to make a propulsion system but i think i would try if my death was inevitable otherwise. I imagine power hopping by harnessing myself to the cylinder would work better than trying to use the raft as a raft.
-- WcW, Feb 16 2008

Nobody likes to walk anymore . With rebreathing your body supplies the mixing co2 .
-- wjt, Feb 16 2008

A CO2/O2 blend would also be fatal. I hated this project because it suggested that an inept boyscout troup was teleported to the moon and that you were to blame for this inept boyscout SNAFU.
-- WcW, Feb 16 2008

I love this place.
-- methinksnot, Feb 16 2008

[AWOL] - you don't commonly hear of it, but the unit of mass is the "slug". It is the amount of mass which one lb of force will accelerate at a rate of 1 ft/sec^2. Hence, in 1 g conditions, a slug weighs in at 32.16 lbs. If you go using the lb as a unit of mass, your dimensions get all goofed up when you throw them into an equation. For example, measuring power in foot-lbs/second.

Maybe instead of having a scenario that makes it look like John Young and Gus Grissom hijacked a welder's DC-3 to the moon, we ought to come up with our own set of items that might
a) be possible for use on the moon, and
b) be something actually found / used on a spacecraft.
-- lurch, Feb 16 2008

You don't need N2 to breathe O2. If you did, Gus Grissom might be alive today.
-- AbsintheWithoutLeave, Feb 16 2008

You need somthing and that somthing is not CO2 unless my understanding of lung function and blood pH is totally incorrect.
-- WcW, Feb 16 2008

//The oxygen tank is worthless//
Of course, I should've realized. With their mothership and all, these could only be ammonia breathing Arcturians.
-- ldischler, Feb 16 2008

//Stellar map (of the moon's constellations)//

Surely the moon isn't so far away that the constellations are different? If that small distance was enough to change the constellations, imagine the changes as the earth travels from one side of our solar orbit to the other side! Maybe [jaksplat] has it right; we've crashed on Endor. (Which would make our task easier: atmosphere, food, abandoned Imperial speeders...)
-- gardnertoo, Feb 16 2008

Look, if they need those O2 tanks back on the ship they better rescue our asses because there is no way I am going to lug them back 200 miles as an act of charity.
-- WcW, Feb 16 2008

Why is there a mix of metric and english measurments in this question? Was this some sort of international Co-Op?
-- WcW, Feb 16 2008

[WcW] You *really* don't need anything other than pure O2, albeit at less than normal atmospheric pressure, so yes, your understanding of blood chemistry and lung function probably is incorrect.
Pure O2 at only about 1.6 ata is potentially dangerous, but at the nominal operating pressure of, say, Apollo 1 of about 6 psi, pure oxygen can be breathed for extended periods without harm.
-- AbsintheWithoutLeave, Feb 16 2008

Ok that makes sense. You couldn't hewever just blend up an atmosphere of 92% CO2, 8% 02, at 1atm and breathe it as seemed to be suggested. I was sure that they used an atmospheric blend in the space station. What about fires and such?
-- WcW, Feb 16 2008

As I recall it, the early Apollos used pure oxygen at low pressure, once in space, as was said by [AbsintheWithoutLeave]. I think it was 1/5 atmosphere pressure, so there was about as much oxygen as in normal air, which is 20 percent oxygen.

The fire that killed Grissom and the others happened when a capsule leak test was conducted. The pressure inside the capsule was run up to one-and-a-fifth, to duplicate flight differences. The problem was that pure oxygen was used, possibly to more accurately duplicate flight conditions. Turns out that pure oxygen under pressure will allow just about anything to burn.

That may not be the facts, there. I was about seven years old when it happened, and don't remember where I read about all that.
-- baconbrain, Feb 16 2008

Neat! I learned somthing new. I am in your debt.
-- WcW, Feb 16 2008

Cannibalize the solar-heater, pistols and injectors to make a powdered-milk/oxygen(dustbomb) rocket; attach the FM-transmitter as payload and send it up... duh.
-- FlyingToaster, Feb 18 2008

1. Inject a bit of the morphine to calm you down. (What? There's no morphine?) 2. Eat a bit of the food concentrate to give you the blood sugar to get bouncing. 3. Take a take of oxygen and if you don't make the 200 miles, well, there's always the .45's.
-- gabrielsnew, Feb 18 2008

I was set this test in primary school many years ago. I didn't do very well.
-- david_scothern, Feb 18 2008

I'm working on a new solution.

Inflate the raft carefully (normal inflation would explode it in vacuum) and seal the parachute over the top to make a tent for the rest of the crew with tape from first aid kit. Bleed O2 from two tanks into the tent to supply air and 5psi air pressure in tent.

Use rope to strap the last tank on to one man. Scavenge tubular ladder from crashed ship. Cut/bend ladder into a T shape (including serifs, the ends of the top T facing down). Tie a length of rope under the astronaut’s armpit and to the top end of the T bar for support. Convert the firing mechanism from the flare gun into a pin valve to vary thrust. Use hose from raft inflater to connect the tank to the gun/valve and the gun/valve to the base of the T. Attach second scavenged piece of tubing to T bar for a control arm.

Assuming a 200 lb. man in a 100 lb. space suit straps a 30 lb O2 tank with 100lbs of O2 to his back. Throw in another 20lbs for the rigging the jet pack and you have 450 lbs to lift. On the moon this will feel like 75lbs on Earth since the Moon only has 1/6th gravity. This should MacGyver you back to the main ship like a jet pack.
-- MisterQED, Feb 18 2008

random, halfbakery