Self-Unloading, Unmanned, Reusable Lunar Lander Project - Abstract
Self-Unloading, Unmanned, Reusable Lunar Lander Project
Kevin Cowan, et. all
May 5, 1991
The future of the U.S. space program outlined by President Bush calls for a permanently manned lunar base. A payload delivery system will be required to support the buildup and operation of that lunar base. In response to this goal, RS Landers has developed a conceptual design of a self-unloading, unmanned, reusable lunar lander. The lander will deliver a 7000 kg payload, with the same dimensions as a space station logistics module, from low lunar orbit (LLO) to any location on the surface of the moon.
This executive summary briefly introduces the technical aspects of the design as well as the management structure and project cost.
This concept is a product of rigorous brainstorming followed by meticulous inspection of the resulting ideas. The payload delivery system consists of a lander, unloader, and payload.
As the figure shows, the payload and the unloader are loaded in an inverted position on top of the lander. After post-landing stabilization on the lunar surface, the entire structure will rotate 180ˇ with respect to the legs. This rotation will take at least thirty minutes.
When the rotation is complete, the unloader will be lowered to the surface. The unloader will then drive out between the legs and deliver the payload to its desired location. The unloader has a range of 5 km when loaded with the payload. The 5 km range was needed because it was determined that the lander should land at least 1-2 km away from the lunar base. This is necessary in order to avoid excessive plume damage. Once the payload has been delivered, the unloader can return to low lunar orbit (LLO) with the lander, or it can remain on the surface to await the lander's return.
Solid core nuclear motors were chosen for use on the lunar lander. These motors have an optimistically projected specific impulse of 1200 sec. and thrust to weight ratio of 11.3. The maximum required thrust occurs during the descent phase of the mission, and it is 22,584 lbf.
It is not currently known whether a three motor configuration or a single motor configuration would be superior for use on the lander. For conventional motors, the three motor configuration is recommended for situations of engine out. There are studies being done to determine the effect of clustering nuclear motors. It may be necessary to use one nuclear motor with redundant turbopumps. All lander drawings in this document, however, show the three motor configuration.
The detailed design of the mechanical components of the various payload unloading mechanisms is beyond the scope of this study, however, there are a few points that should be considered in their design. The areas that were considered are the types of electric motors, bearings, and drive train or gear reduction system that should be used.
The motors that are most promising for the RS Landers La Rotisserie concept use direct current, deliver moderate torque, medium rotation rates (around 1000 rpm), and are of a brushless design.
Coated bearings are suggested for use on the lunar lander. Lubricants will prove to be ineffective in the harsh lunar environment. They will either become filled with dust, freeze up, or boil off. Possible bearing coatings include Teflon¨, Nomex¨, and diamond. Diamond coatings can be applied using Chemical Vapor Deposition.
A harmonic drive system is recommended for use on the lunar lander. Harmonic drives have fewer moving parts than the conventional gear box. They are therefore less massive. Harmonic drive systems use flexible splines that wear faster than conventional gear box components, but with the advent of advanced materials, the harmonic drive can be designed to more than meet the lander's requirements.
The lander trajectories have been designed and optimized using a computer program called Lander. Program Lander was developed by Eagle Engineering in Houston, TX to simulate the ascent and descent phases of a lunar landing mission.
The landing site loc