ABSTRACT 1 INTRODUCTION 2 MARS ROVER "ROCKY IV" 2 ROVER DESIGN 3 PROPOSED ROVER SCHEMATIC 3 STRUCTURE/MATERIAL 4 INITIAL FRAME CONCEPT 4 DRIVE/STEERING 5 THERMAL SYSTEM DESIGN 6 THERMAL DESIGN DIAGRAM 6 COMMUNICATIONS/SENSOR DESIGN 8 COMM AND SENSOR BLOCK DIAGRAM 8 COLOR VIDEO CAMERA 9 AUTOMATIC CONTROL SYSTEM 9 IR VIDEO CAMERA 10 POWER SYSTEM 11 POWER SYSTEM BLOCK DIAGRAM 11 POWER DISTRIBUTION AND CONVERTION 12 PHOTOVOLTAIC ARRAY 12 PATHFINDER ROVER PHOTOVOLTAIC ARRAY 12 BATTERIES 13 MICROCONTROLLER 13 SMARTCORE MICROPROCESSOR 13 CONCLUSION 14 REFERENCES 15 APPENDIX 16 LUNAR FACTS & FIGURES 16
The Texas Space Grant Consortium (TSGC) consists of teams of students and faculty from various academic institutions.3 These teams will develop a preliminary design for a small lander to perform oxygen production as well as various other experiments. In order to perform the oxygen production, lunar soil must be gathered and transported from remote areas to the lander. Therefore, a small rover will be designed to perform such a task.
The rover will be fitted with a device capable of collecting up to 1kg of lunar soil and rocks from remote areas away from the contamination region created by the landerŐs rocket thrusters. The rover will be controlled by an Earth-based station, but due to time delays, the rover will have some autonomous control to prevent damage to the rover.1 The rover will also have the ability to inspect the lander and the surrounding area with a video camera. Other scientific equipment will be considered in order to increase the usefulness of the rover and the overall effectiveness of the mission. Figure 1 shows an example of the rover designed for the Mars mission scheduled for 1997.
The rover must be able to withstand the thermal conditions of the moon. The temperatures vary from -175oC to 115oC.3 Heating and cooling systems are a major concern in order to ensure proper operation and prevent thermal damage to all equipment.3 The rover will be able to control its own temperature and the temperature of the equipment that it is carrying.
The rover will be controlled from an Earth station. This control signal will be relayed through the lander to the rover. The rover will send video images and sensor data to the lunar relay. The rover will be somewhat autonomous due to the transmission delay to and from Earth. This autonomy will prevent damage due to steering blindly.
The frame will be divided into three equal sections. This will help in distributing the mass evenly throughout the rover. Torsional springs will be used at the hinges as the main damping system. Each section will also have an independent suspension attaching it to the main body of the rover as a supplemental damping system. This independent suspension will also act as a mechanism to compact the rover for storage on the lander.
Although this design was one of the most flexible, there are several constraints. The main body of the rover will have to be anchored from the center section of the frame to allow for the outer sections to flex. Also, the dimensions of the main body will have to be smaller than the inside dimensions of the frame to allow for the required freedom of movement. An additional constraint has been placed on the design in the allocated storage space of approximately 508 mm x 305 mm x 254 mm for the rover on the lander. This space is significantly smaller than any micro-rover design we have encountered so far. Whether or not this size constraint poses a problem has yet to be determined.
The main body of the rover will be completely sealed from the elements. This will allow for total protection from lunar dust and aid in the storage of heat during the lunar night. This design will also protect the rover from any free moving parts on the lander that may damage itsŐ sensitive components. The main drawback to total isolation is the difficulty in cooling the internal components during the day. Due to this drawback, a cooling system will be implemented to "channel" the heat away from the sensitive elements. This cooling system is discussed in more detail in the thermal section of the report.
Variable speed motors will be used so that they may assist in the steering of the rover. Steering mechanisms will also be placed on the front and rear sections to work in conjunction with the variable speed motors. To further conserve mass, the wheels will be constructed of a ridged metal strip attached to the hub by eight thin spokes. This design should adequately support the rover and its cargo while maintaining traction and conserving mass. The wheels are rigidly attached to the individual sections of the frame to constantly maintain seven centimeters of ground clearance. The frame sections will be attached to the main body of the rover by a damping system to prevent damage to the internal components due to rough terrain.
Heat conduction to the moon through the wheels is minimal compared to the heat that will be absorbed from the Sun. The rover will be mirrored on the exterior in order to reflect radiant energy away. This highly reflective coating will keep the rover from rapidly overheating, preventing permanent damage to the sensitive electronic equipment. Some energy will be absorbed by the mirror, and therefore an insulation barrier made up of Aerogel will be placed between the outside and inside shells.
Aerogel has been developed since the 1930s. It cannot be frozen or destroyed by temperatures under 2000oC. This solid made of silica dioxide has a density less than that or air and is impervious to ultraviolet light.
The inside shell will contain a mirrored surface in order to maintain the internal temperature of the rover during a lunar night. The excess heat created by the electrical components, along with a backup heater will maintain the temperature of the rover during the night. A backup refrigeration unit will prevent rapid heating during the lunar day. This will be done using black-body radiation along with a Peltier device which is very rugged, and reliable. A heat conducting material may be used to surround all components in order to control the temperature efficiently.
A Peltier device is a reliable way to heat or cool the rover. There are no moving parts and it is extremely lightweight compared to other refrigeration systems. A thermoelectric refrigerator is made up of two dissimilar metals forming a junction. As current passes through the junction, the device heats up on one side, and cools on the other. Simply by reversing the polarity, the device can be easily changed from a refrigerator to a heater. Efficient Peltier devices are made of semiconductor materials.
All equipment will be insulated from the chassis. The solar array will also be insulated from the chassis. The Peltier device will have a mirrored shutter in order to help retain or disperse heat through the underside of the rover.
Communication is an important aspect of the lunar rover. The rover can be controlled from an Earth station. There is a delay of 3-5 seconds when communicating with the rover. This means that the rover will need to be partially autonomous in order to prevent collision resulting in severe damage. The Earth station will be able to control camera switching, motor direction and speed, full arm movement, and steering. A small forward looking microwave radar system will be used to prevent the rover from colliding into rock, etc.
A 3-dimensional color camera system will be implemented on the rover. This will be accomplished by multiplexing two color cameras. A 3D effect is created by spacing two 1:1 cameras within the distance of the average spacing of the human eyes (2.5"). Each camera generates 30 frames per second, but when multiplexed, the result is 15 frames per second per eye. A 3D visor can be worn by the Earth station controller in order to put the view in perspective, enabling easier control. This stereo effect will be especially helpful when operating the collection arm, as well as increasing PR. Each color camera is approximately 1.625 in3, 2.5 oz, and has 450 lines of resolution. As a comparison, SVHS and Hi-8 video have 400 lines of resolution.
An Alpha Proton X-Ray Spectrometer (APXS) will be located on the rover in order to analyze the lunar soil. This equipment can send its results back to Earth through the data link. Also, an infrared camera with IR LED illuminator array will be able to see in "darkness".
An automatic control system is available for the color camera. The color camera in Figure 6 easily fits inside the ACS. The dimension of the ACS is 2 in3. It performs many basic picture adjustments. These adjustments include: auto gain control, auto white balance, auto black balance, electronic auto shutter (1/60-1/100,000 second), automatic color processor compensates for various lighting conditions, medium wide angle lens 6" to infinity, 2 lux.
An infrared camera is an ideal choice for a third camera. It can function at night with or without its illuminator. It has a flexible design that can be easily placed in any position. The range, in total darkness, with the illuminator, is 8-12 feet.
Conversion and regulation of the power provided by the sources is needed not only because each subsystem has different requirements but to provide clean power. The design of this system will require specific data on each subsystems power requirements.