TransLunar Transportation System
Section 4.2.1.
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Hazards from the LTV Thruster Exhaust Plume

We have some concerns about the Lunar Transfer Vehicle's RCS thrusters contaminating the LTV itself as well as its payload, the Descent Stack. Exhuast from the LTV's hypergolic thrusters deposit poisons on the outside of the spacecraft, which in turn could be imported to the pressurized environment on space suits.

For the case of the Space Shuttle, it sounds like NASA is not too worried about the level of contamination we'll see from the Orbiter pluming the International Space Station. The primary difference is that the Orbiter will be arriving at the space station only once every few months, and its thrusters are aligned to avoid pluming the vehicle it is approaching.

The Orbiter's -Z thrusters in the nose and tail are canted at an angle. The X vectors cancel each other out giving you a net thrust in the +Z direction.

The Space Station external contamination team has been, is, and will be assessing all aspects of external contamination induced on-orbit on both the Internataionl Space Station and the Space Shuttle Orbiter. Included in these assessments is the effect of Orbiter plume-induced contamination. Monomethyl hydrazine-nitrate was identified as the principal contaminant in the Orbiter exhaust. The assessments to date indicate contamination to be minimal and of no identifiable concern. These assessments incorporate the latest experimental results obtained on a recent Shuttle-Mir flight.

So whether this is applicable to the concern about the LTV pluming itself is still an open question. The LTV still has the risk of pluming itself and its payload (the landing stack) every time it fires its thrusters. If the LTV is to spend a long time in orbit and make multiple sorties to the moon, then we will need assess plume contamination after each flight and consider methods for keeping the thruster exhaust away from the spacecraft in the design during the initial design of the vehicle.

TransLunar Transportation System

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