ASI W9700492r1.0

Moon Miners' Manifesto

#99 October 1996

Section the Artemis Data Book

Coasting Earth-Moon & Moon-Mars

Peter Kokh

COASTING: Earth to Moon & Moon to Mars

Relevant Readings From MMM Back Issues:

MMM # 21 DEC '88 "Lunar Overflight Tours"
MMR # 12 JAN '93, pp 2-8 "The Frontier Builder: An Earth-Moon Hotel Cruise Ship". Definition & Design Exercise, Doug Armstrong and Peter Kokh
MMM # 80 NOV '94 "Stretching Out", P. Kokh

Relevant Readings From Other Sources:

Ad Astra July/Aug '96, pp. 24-27. "Recycling Our Space Program: No Deposit ... No Return", (Earth-Mars Cycling Ship scheme) Buzz Aldrin and Leonard David

Propulsion Questions

LANTR: (Liquid oxygen [LOX] Augmented Nuclear Thermal Rocket) - In Moon Miners' Review #18, JAN '96, Editor Mark Kaehny reprinted an article by Dr. Stan Borowski of NASA-Lewis, about a very promising new propulsion concept which could cut Earth-Moon transit time down to a day, and delivery more cargo to boot.

If total transit time is drastically cut, then the mass of ship-board facilities needed to keep passengers amused and content should be less. Less ship mass per capita [per fare] means less fuel needed per fare, or cheaper passage.
NIMF: (Nuclear rocket using Indigenous Martian Fuel) - In Moon Miners' Manifesto # 30 NOV '89, we reported on Dr. Robert Zubrin's concept for manufacturing both get-around Mars exploration fuel and return-home fuel from Mars' atmosphere, instead of bringing it along from Earth. This scenario would cut drastically the size and mass of a ship or expedition needed to put a given crew and amount of equipment on Mars.

AEROBRAKE: a ship configuration that can present a large cross-section to the atmosphere upon entry or grazing, allowing it to dump momentum without firing retrorockets. Ships returning to Earth or Earth orbit from the Moon or Mars, and ships headed for Mars or Mars orbit can benefit from aerobraking. But this is an economic plus only if any extra mass needed to provide an aero-braking profile is less than the mass of fuel that would be burned in firing retrorockets. Thus it is a nice idea that presents design challenges.

Dividing & Conquering "Delta-V": Shuttle-Ferry-Shuttle Rendezvous

At first blush, Moon Direct and Mars Direct - the idea of transferless passage from one planetary surface all the way to another - is as mentally comfortable to those of us breast-fed on science fiction as an old slipper to tired feet. But what costs is fuel spent on changing momentum, accelerating and decelerating. We need to look at the structure of a passage from one planet to another. A few minutes of acceleration - days to months of cruising - a few minutes of deceleration. From the point of view of fuel expenditures, it would be ideal for an accelerating or decelerating ship to be as lean and pared down in per capita mass as possible. From the point of view of passenger comfort, it would be ideal if the long-cruising vehicle be as spacious and full-featured as possible, implying more, not less mass per capita. Contradictory indications, it would seem.

Bear in mind that deceleration and acceleration periods are an extremely brief fraction of total time of passage. Passengers don't mind having nothing more than a seat to sit tight in for short periods. Bear also in mind, that a circuit-cruising ship that does not stop, but only makes once or twice a loop course corrections, need spend very little fuel on anything but emergency power generation.

The elegant answer then, is not Moon direct or Mars direct, but lean Earth surface to cruise ship rendezvous shuttle. comfortable circuit cruise ship s for near-Earth to near-Moon or near-Mars passage, and lean shuttles between Lunar or Martian surface and cruise ship rendezvous.

Note that all the delta V needed to go from Earth to Moon or Earth-Moon to Mars is spent on either end by briefly occupied spartan crowded shuttles. In contrast, the relatively luxurious, creature comfort bestowed cruise ships on which 99% of the passage time is spent, use hardly any fuel.

The burden of rendezvous by logic falls on the lighter vehicle. The mountain doesn't come to Mohammed. Mohammed goes to the mountain. The more massive vehicle has "the right of momentum", yes, akin to "the right of way". If the ferry has to brake into Earth or Mars orbit, making discontinuous interrupted trips to and fro, all such benefits are lost, and to be affordable, it would have to be as spartan as possible, just like a shuttle.

Another way such a scenario makes sense is that the cruise ships on which travelers spend by far the most time, can afford to be amply shielded from cosmic radiation and solar flares, whereas the darting shuttles needn't be.

Now we can hardly run our first expedition to Mars in such a manner. But the benefits are so clearly apparent, that this is mission profile we need to aim at if we are going to sustain any amount of traffic - regularly scheduled expeditions to a sequence of immigration waves to tourism. MMM

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