ation 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 levels of sensors are used for redundancy. During optimum operating conditions, several components of each level of redundancy will be used. The primary, secondary, and emergency sensor arrays rely on a radar imaging/altimeter system, several sets of accelerometers and gyros, a transponder system, a close proximity altitude detection device, and the communications system. The communications system is only used as a sensor for emergency situations.
The onboard navigation computer will be a fault tolerant advanced computer that will be capable of out-performing today's most advanced Cray computer. The rapid pace of computer and software development has shown that a system of this type will not only be possible, but will have little mass and power consumption. The navigation computer will be responsible for monitoring the output and status of each sensor, monitoring the status of and providing input for each of the control devices, and providing an interface between the two.
The lander will utilize three control techniques: momentum exchange devices, small directional thrusters, and gimbaled/throttled main engines. While some redundancy exists using all three systems, the optimum operating conditions will use each technique where best suited.
The control of the unloader will be primarily automated with a remote control system as a backup. The unloader will have optical sensors which will inform the unloader's onboard computer of obstacles. The computer will then instruct the wheel motors to make the required adjustments. The unloader will be in constant communication with the lander, in case it becomes necessary to employ the back up remote control system.
The communications systems provide three basic functions: telemetry, command, and tracking. There are three areas of communications that will be performed by the lunar lander system: Lander/Earth, Lander/OTV, and Lander/Unloader.
S-band (2.3 GHz) will be used for direct communications between the lander and earth. The antenna on the lander will be a parabolic dish wi