Lunar Launching to LEO

[Warren Platts]

This may be way off the wall, but I was thinking about future lunar economies, and what advantages the Moon might have, and an obvious one is that it has 1/6 the gravity of Earth. So a simple, and no doubt incorrect back-of-the-envelope calulation suggests that if you have a rocket that can lift 25 tons on the Earth, an identical rocket should be able lift 150 tons on the Moon. So I could see how it might actually take less rocket fuel to place a satellite into LEO when launched from the Moon than when launched from Earth, even taking into account the extra distance. (Maybe aerobraking could be used to slow down the satellites, thus reducing the need for a big orbital insertion burn.)

So I can envision a day, far in the future, when Lockheed-Martin will have facilities to build satellites and rockets on the Moon using local materials. The Moon might even become a net exporter of food to supply Earth orbiting space stations. Earth launches would mostly be relegated to moving humans into orbit and those rare supplies that can't be made on the Moon.

But I'm not much of a rocket scientist because I don't know how to figure out the delta-v's involved, so I don't know if it would in fact take more or less rocket fuel to place a satellite into LEO from the Moon as opposed to launching from Earth. Any thoughts?

[Larry Jacks]

It's a bit more complicated than that. First of all, lunar escape velocity is approximately 6,000 MPH (~10,000 KM/HR). That means something launched from the moon doesn't have to gain nearly as much velocity to send something towards the Earth than putting a payload into LEO. It's roughly 1/3rd the required velocity. The moon has no atmosphere and weak gravity, further contributing to the savings. In fact, you don't need a rocket at all if you're willing to use something like electromagnetic rail guns to launch stuff from the moon. Aerobraking could be useful to lower the velocity with thrusters (perhaps ion) to put the satellite into the final mission orbit.

The hard part of your idea is getting the necessary satellite building infrastructure built on the moon. Satellites are typically built in clean rooms using very high precision components (mission payloads such as communications transponders, structural systems, propulsion systems, attitude control systms, thermal control systems, command & control systems, etc). You'd need to be able to build a lot of stuff to make a reliable satellite. Doing that on the moon would mean you'd need to be able to create specialized metal alloys and composites, computer chips and solar cells, and a host of other stuff. That's the hard part. Not impossible, just difficult.

[Saluki]

I was thinking the same thing as Larry. Infrastructure is everything. If you can't turn raw materials already on the moon into everything you need (habitats for workers, buildings for manufacturing, launch facilities, energy production, electronics etc), you have to get it from Earth to the moon. Unless the material coming from earth was exceedingly small, you might as well do it all here.

[Larry Jacks]

To be fair, you wouldn't have to build all of the infrastructure at once. For example, the equipment needed to create computer chips would be challenging to set up on the moon. It would likely be worthwhile to create these low mass objects on the Earth and send them to the moon. You wouldn't need large amounts of metal for your satellites, so it might not be too difficult to smelt the metal on the moon. Besides, if the launch efficiencies are there, you might not be as concerned with building the lightest possible structure for your satellite. Once you can make good quality metal, them machining parts like thrusters may not be too difficult.

Back in the 1970s, the L5 Society proposed using lunar materials (maglev launched) to build huge human habitats at the L5 LaGrange point. The economic justification for the habitats was to build solar power satellites to supply power for the Earth. They proposed habitats capable of housing up to 100,000 people. Such a habitat would be more than large enough to support the infrastructure needed to build satellites.