curs 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 location of the Apollo 15 mission was chosen for the lunar lander simulation. The resulting total delta-velocities were 1.839 km/sec for ascent and 1.92 km/sec for descent. The flight times were 50 minutes for ascent and 63.25 minutes for descent. The use of the solid core thermal nuclear propulsion system greatly increased the efficiencies of the trajectories.
Structures and Materials
The lander structure provides connectivity and integrity to all of the lander's systems. The central box of the lander structure carries all of the loads generated by the subsystems. This box is a truss structure enclosed by honeycomb core panels. The truss structure is strong enough to support the loads generated by the subsystems, and its lightweight panels protect the subsystems from solar radiation, dust, and micrometeorites.
The landing gear is composed of four struts that are lightweight planar trusses with Apollo style Lunar Module landing pads. To enable the lander to remain level on an incline of up to 8ˇ, a terrain adaptive system is incorporated into the landing gear.
Aluminum-lithium alloys were chosen as the main construction material for the lander. In addition to having the advantages of standard aluminum alloys, they can have a high tensile strength (over 100 ksi), along with increased weldability and a higher cryogenic strength.
Guidance, Navigation, & Control
The purpose of the guidance, navigation, and control (GNC) system is to determine the linear and angular position, velocity, and acceleration of the lander, to compare that data with the desired state, and to make corrections when necessary. The desired state of the lander will be provided by the predetermined trajectory analysis for each specific mission.
The GNC system is made up of three components: Sensors, Computer, and Control. The sensors provide information on the state of the lander. The computer evaluates the data from the sensors and instructs the control mechanisms. The control mechanisms then change the state of the lander by their action.
Three lev