Bargain Basement Lunar Rocket

Factual Questions
1

The other night, after having too much to drink, I was outside staring up at the full moon, cursing my luck at being born in a time when cheap space travel isn’t available, and doesn’t look to be available before I’m too old to go, and I got to wondering: What would be the absolute rock bottom way to send something to the Moon?

I wasn’t thinking about humans, or just some five pound payload, but a useful amount (say roughly the same as the shuttle can put into Earth orbit) of something. I wasn’t even thinking about pinpoint accuracy either, just getting it to the Moon and hopefully onto the surface intact.

Rummaging through the garbled facts in my head I came up with an idea, but I’m not certain how well it would work.

Since the Moon rounghly orbits the Earth over the tropics, it seems to me that the best place for a launch site would be around there. The rocket (parts reusable only if it was cheaper) would be a multi-stage solid fueled design with a cargo module (CM) on top. For guidance, I figured one could probably get away with some photo-eyes (the Moon being one of the brighest objects in the night sky), a radar gun (modified to show distance instead of MPH), and perhaps a PDA for computing power.

The manoeuvering thrusters would be liquid fueled. You launch the thing a few nights before the Moon is full, and it goes directly towards the Moon (i.e. doesn’t spend any time orbiting the Earth). Program the PDA (or other small computing device) so that if a photoeye goes dark it fires the thrusters to bring the ship back on course (taking into account times when the thing might get confused by something else), then when the radar gun detects that the CM is a pre-set distance from the Moon, the CM rotates 180 degrees and another solid rocket engine fires. This kills the forward motion of the CM so that it is at a dead stop, roughly 100 feet above the lunar surface, then gravity brings the CM down, with the thrusters firing at periodic intervals (assuming there’s any fuel left) to slow the descent.

The bottom of the CM is designed with “crumple zones” similar to those found on cars. This would cushion the landing and (hopefully) compensate for any boulders the thing might land on. It wouldn’t help it survive a landing on a Lunar mountain, but assuming it got lucky enough to land in a relatively flat area, might prevent the thing from cracking up completely.

Still not a cheap operation, but probably lower cost than swiping the Saturn Vs parked in front of NASA. So, could such a design work with a roughly fifty percent chance of success? (And, yes, it would have a “self-destruct” mechanism so that if it started falling out of the sky, you could blow it up and didn’t have to worry about it killing anyone on the ground.) If you launched them at twenty eight day intervals could you have a reasonable expectation that they’d land within a few hundred miles of one another?

The main thing that I think might be problematic with the design is the guidance system. I’m not sure such a system could work. Anybody have any ideas?

2

Your guidance idea might work, but I don’t think it’d be very efficient. Why make regular course adjustments over the three days or so it’d take to get there? Remember, the Moon’s moving at better than 2000 miles an hour, that adds up to a bunch of wasted fuel. Calculating where the Moon’ll be in three days and aiming to intercept it is more straight-forward.

Also, the shuttle carries 65,000 pounds to low Earth orbit. That’s double what the Apollo Lunar Lander weighed. To land that much on the moon, you would need a rocket of roughly Saturn V size.

Eric

3

I’m afraid I can see a number of problems. The guidance system is way too simplistic - you need a fairly sophisticated circuit to distinguish between the sun, earth and the moon. Even if you do that, you can’t go to the moon by pointing your rocket at the moon and firing the engines - the orbit is a bit more complex than that. The optimal angle for firing the engine may not be directly away from the moon - in fact, if you spral away slowly from the earth, part of the time your enginges will be pointed towards the moon. At the very least you need a set of optical sensors to tell you the attitude (maybe one sensor to track the sun, another to track a bright star) and a set of gyroscopes. You also need to know the position in space - it’s probably easiest to do that from the ground and send the info to the on-board system.

And that’s just the guidance system. How are you going to fabricate the enormous solid rocket? You need a certain size because there is economy of scale when it comes to pushing through the earth’s atmosphere. How will you control the flight path during ascent? How will you make sure everything works reliably in the cold and vacuum of space - especially the re-startable control thrusters and other moving parts? It’s an enormous engineering work. After you answer those questions, your design will look very similar to the lunar missions already done by the Soviets, NASA and Japan. Despite what you may believe, all engineers try to make the simplest possible design to accomplish the goal.

4

The biggest cost would be the fuel and superstructure of the thing (to withstand the forces acting upon it at launch). How much does solid hydrogen cost? How difficult is it to store it safely, and how much will this storage cost? What is the minimum - and likely - G-Forces that such a launcher would be subject to upon lift-off and acceleration? How much maneuvering fuel will it need on its way to the Moon? How much space is needed to accomodate the thrust system? How many nozzles will you need?

For that matter, how much coolant will you need when the rocket first takes off? How extensive of a launching pad would you need? How many people would you need to hire, and how much would it cost for reasonably competent employees? How much construction equipment would you need? Do you want to drink Coke or Pepsi when you’re watching your project blast off to oblivion?

Those are the questions you need to ask (and answer). Especially that last one. It’s crucial.

5

Damn, SPOOFE, you take all of the fun out of drunken dreams. :wink: (And we’ll have none of this Pepsi or Coke crap at the launch pad! It’ll be either scotch or Dr Pepper!)

Seriously, though, there have been things brought up that I didn’t think of. Forgot about the little stablizers at the bottom of the first stage. Definately need those. What I’m trying to do is strip out everything that one possibly could and yet still be sure that the rocket would work. That’s why I suggested solid fuel (Not sure what you mean by “solid hydrogen,” I was thinking along the lines of the same propellant in the shuttle’s solid rocket boosters.) because then you can dispose of the triple redundant fuel pumps, plumbing, computer controls, and electrical systems for the stages. (Of course, that means when you ignite the rocket, there’s nothing you can do to abort the launch other than blowing it up. Better make sure the flight path is clear first!)

The guidance system was what really had me, though (forgot about the gyroscopes, good thing I’m not an engineer, huh?). A timer won’t work because if you’re a second or two off in the engine firing you’ll end up thousands of miles away from the Moon by the time you cross the quarter of a million miles that seperates it from the Earth. So it has to be something that can detect where the Moon is in relation to the ship and make the necessary course corrections.

Again, I’m not trying for a pin-point landing on the Moon here. Just get it there, and hopefully intact.

6

Your navigation and control methods show a complete lack of understanding of orbital mechanics. You can’t just point and shoot and go straight from the Earth to the Moon. For instance, leaving Earth’s atmosphere (orbital zone) and aiming for the Moon, you don’t want to point straight at where the Moon is, but rather where it will be. You also need some way to tell which way your thrusters are pointed (gyroscopes, startrackers). Then the direction you fire the thrusters and point near the Earth will not be on the side nearest the Moon, but 90 deg before (or would that be 180 deg? need to figure that out).

Launching from the equator is better - less fuel to get to orbit if using the Earth’s rotation. Preferrably on a mountain peak - as high as you can get above the ground. Less air to cut through, slightly less gravity, less fuel to lift.

Also, you won’t guarantee landing anywhere near your landing zone without careful planning and fine-timed operation.

Also, aiming for a dead stop over the surface is probably a bigger waste of fuel. Rather, you enter lunar orbit (or just near the Moon), and then you slow down vectoring thrust against your motion around the moon and against your momentum toward the surface. Come in for a sliding landing, just like Apollo.

7

Solid fuel rockets are simple, but the fuel itself isn’t cheap. If you truly wanted to get something into space at the lowest possible cost, you could try the “Big Dumb Booster” approach.

Engineers have been trying to tell us for decades that our approach to rocketry is all wrong. The cheapest design for a rocket is to use cheap common fuels (kerosene and liquid oxygen), simple robust motors, and industrial-grade sheet steel for the tankage. Even though such a rocket might weigh two or three times as much gross weight for a given payload than high-tech rockets, it would more than make up for it by being much cheaper to build. And as a plus it would be more mechanically reliable too.

Design studies have estimated that such rockets could cut the cost of boosting payload into orbit to between one-tenth and one-twentieth of what we’re paying now. But neither NASA, the Pentagon, nor the aerospace contractors have any institutional interest in pursuing this strategy.

8

Is that how the Russians do it? I know that they were using kerosene (and I think some kind of paraffin compound as well) and LOX. That would work better than what I came up with, but I figured that the tanks would have to be fairly robust to contain the LOX under pressure, and that the whole thing would be so complicated as to counter any cost savings.

9

I think your plan is flawless. I only see 100% success. Failure is not an option (to coin a phrase). Go for it!