THE ARTEMIS PROJECT
PRIVATE ENTERPRISE ON THE MOON
Ascent and Rendezvous
Section 4.1.1.5.
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Reusing Descent Stage Engines for the Ascent Stage

Lunar exploration base Lunar landing stack. Ascent stage is on the left.
Artwork by Vik Olliver.

In the original reference mission, we had the ascent stage sandwiched into the lunar landing stack between the descent stage and the exploration base. The crew rode down to the moon inside the habitat module.

When we decided on using different fuel for the ascent engines, the advantage of this configuration disappeared. We modified the configuration, putting the ascent stage alongside the descent stage as show in the illustration. Now, the crew rides down to the lunar surface in the ascent stage. Should a problem arise during descent to the mon, they can separate from the landing stack at any time, abandoning the landing stack to its fate.

The essay below describes the original design, where the ascent stage was between the descent stage and the habitat.

Original Design of the Lunar Landing Stack

We based weight estimates on reusing one of the descent stage engines for the ascent vehicle. The descent propulsion package has five small rockets for redundancy. The center of these is attached to the ascent vehicle. When the lunar base module lands and is rotated out of the way, the descent propulsion package becomes the launch platform for the ascent vehicle.

The ascent vehicle has its own fuel tanks, so that the descent tanks can be left behind. The crew will have to disconnect the engines from the tanks before they level the module. This saves weight on ascent, and we're hoping we can use the descent tanks to store gasses at the base. They carry extra oxygen for the first flight, to be used to replenish the atmosphere during the stay on the lunar surface.

This scenario adds some risk to the project. Unlike Apollo, we do not have an emergency abort scenario during descent. The five descent engines provide some redundancy, but if we lose more than a couple of them, the crew is going to have a very bad day. Once the stack lands, they still have to reconfigure the fuel plumbing and move the module out of the way before they have an escape vehicle. This is among the major issues in the conceptual design for the reference mission. The probability of failure in this part of the flight is very small, but the consequences of failure are critical.

We don't know if we'll be able to use cryogenic hydrogen and oxygen yet. The specific impulse of H2-O2 engines is great, but we have to get the cryo fuel there, and somehow we have to provide the reliability and simplicity of hypergolics. There is currently a study being conducted to determine if the additional complexity and risk is warranted.

Ascent and Rendezvous

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