Mission Options
Section 5.
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Why We Won't Fly a Space Shuttle to the Moon

One idea that keeps coming up is to use a Space Shuttle Orbiter as a Lunar Transfer Vehicle. We'd fly it to lunar orbit, drop off our goodies, and fly it home.

It's an intriguing idea. The Shuttle Orbiter has all the habitability equipment we need, all nicely designed, debugged, and demonstrated; and the payload bay with its robot arm and payload retention latches has everything we need to deploy the moon lander.

However . . .

Vehicle Mass

Dry weight of Shuttle Orbiter is about 250,000 lbs, compared to the space-only LTV's weight of perhaps 7500 lbs. We'd be accelerating a lot of mass that we don't really need in lunar orbit.

Refueling the Orbiter

Since the Shuttle Orbiter gets to LEO with near-zero extra fuel, we'd have to use other launches to get the fuel up there. You can work out the math. Use Isp=460 sec, delta-V=Isp*g*ln(Mo/Mf). The delta-V requirements are in the Mission Timeline. It's a lot of launches.

The Orbiter isn't designed to be refueled in orbit. We could conceivably build a fixture that would enable us to attach an External Tank or two, and use the famous scenario of carrying ETs all the way to orbit. But we'd still have to get that fuel up there somehow, and we'd have to launch some sort of servicing fixture. (That sounds like a really complex space facility; not quite like the International Space Station, but close.)

Heat Shield

The Orbiter's heat shield is designed for entry from low Earth orbit, about 25,000 ft/sec. Coming home from the moon, we'd hit the atmosphere at about 36,000 ft/sec. Whether the Shuttle could take that increase in kinetic energy is an unknown.

Atmospheric Entry Loads

The Orbiter is designed for 3 g's max operational load. Assuming we didn't use rockets to decelerate while coming home from the moon, we'd hit up to 6 g's; even up to 12 if the piloting is just a bit off.

We could use the rocket-braking scenario -- that's the way we put the Artemis Project reference mission together -- but the fuel required to decelerate a 250,000-lb Orbiter is bodaciously more than what we need for that little LTV.

Radiation, Vehicle Reliability, Operational Flexibility

Shuttle wins all those issues. It has a proven track record. If we got to LEO and the Orbiter was fully operational (fuel cells and auxiliary power units all in the green), it would probably be as reliable for the rest of the mission as anything else we could design.

There's also a huge inventory of cool stuff already on the shelf that would enhance this mission: surface-mapping cameras, payload-bay laboratories, EVA equipment, payload deployment mechanisms.

Long-Range Concepts

OK, so this isn't a viable first-mission scenario. However, add some more ingredients and stir well, and you have a scenario very similar to the argument for a translunar SSTO: one vehicle all the way to the moon.

The ingredients to add are lunar oxygen to refuel the Shuttle, and a servicing facility launched from the moon. The key to those is an electromagnetic launcher on the moon to keep the launch costs down. The fuel tank could be designed to interface directly with the Shuttle's attachments for the ET.

While we're fantasizing, add in a situation where NASA approves the original SPACEHAB scenario. SPACEHAB was orginally designed to be a passenger compartment for commercial Shuttle flights. Put a couple of SPACEHAB modules full of happy passengers in the payload bay, and we're running tourist flights to lunar orbit!

It would be very difficult to modify the Shuttle Orbiter system so that we could actually land it on the moon. The landing gear is in the wrong place, with a big fuel tank in the way. So we'd need another vehicle, perhaps a carrier for those SPACEHAB passenger compartments, to get between lunar orbit and the lobby of the Luna City Hotel.

Since the Shuttle's design is so specific to its original mission, my guess is that we'd be way ahead with a new design; but this is certainly a mind-expanding scenario. It's certainly an interesting mental image of a space shuttle in orbit around the moon!

Mission Options

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