N94- 25699 271 LOW-COST UNMANNED LUNAR LANDER United States Naval Academy Aerospace Engineering Department Annapolis, Maryland Assistant Professor Walter IC Daniel Abstract and survey the lunar surface to provide information as to the possibility of future lunar missions. Two student groups designed unmanned landers to deliver 200 kilogram payloads to the lunar surface. Payloads could include astronomical telescopes, small Requirements lunar rovers, and experiments related to future human exploration. Requirements include the use of existing The requirements for Lunar Scout are as follows: hardware where possible, use of a medium-class launch • Use off-the-shelf hardware for economy. vehicle, an unobstructed view of the sky for the payload, • Provide a two-year spacecraft lifetime. and access to the lunar surface for the payload. The • Allow for systems shutdown during lunar night except projects were modeled after Artemis, a project that the for equipment to provide heat to critical components. NASA Office of Exploration is pursuing with a planned • Launch in 1996. first launch in 1996. • Make a soft landing on the lunar surface between +/- 60 degrees latitude. The Lunar Scout design (see Figures 1 and 2) uses a • Deliver 200 kg payload to lunar surface. Delta II launch vehicle with a Star 48 motor for insertion • Provide 10 Watts power during two-week lunar night into the trans-lunar trajectory. During the transfer, the to heat the spacecraft. solar panels will be folded inward and the spacecraft will • Use Delta II launch vehicle. be powered by rechargeable nickel-cadmium batteries. The lander will use a combination of a solid rocket motor and hydrazine thrusters for the descent to the lunar Orbital Dynamics and Propulsion surface. The solar arrays will be deployed after landing. The lander will provide power for operations to the A two-body problem with the Earth and moon was used payload during the lunar day; batteries will provide "stay- to do a patch conic transfer. A Delta II launch vehicle alive" power during the lunar night. A horn antenna on carries the 3775 kg spacecraft to a 1366.7 km circular the lander will provide communications between the orbit where a Star 48A lunar insertion motor kicks the payload and the Earth. Scout into the elliptical transfer orbit which passes through the center of the moon. The three-dimensional view of the problem shows the launch point at Cape Introduction Canaveral at 28.5 degrees North latitude. The launch is slated for 1996 when the moon's orbital plane will also be Project Artemis is NASA's program to put a lander on at its maximum inclination of 28.5 degrees which will the lunar surface in 1996. The lander will carry payloads provide for a minimum energy transfer. At the patch such as a lunar telescope, a possible robotic lunar rover or point at an altitude of approximately 66,300 km above the various other experiments. These payloads will be used lunar surface, the lander enters the moon's sphere of ultimately to determine the feasibility of developing a influence. At an altitude of 200 km the retrograde liquid lunar outpost for future manned missions and to rocket will fire for 135 sec to reduce the velocity to zero. demonstrate mining equipment to process hydrogen, The remaining 30 km to the lunar surface wilt be nitrogen, and helium from the moon's soil. Thus, the computer-controlled using the radar altimeter and lander project is named Lunar Scout since it will go up Proceed_gs of the _ Summer Coqferettce 272 NASA/USRA Advaxced Deslgtt Program thrusters. Table 1 shows the breakdown of the mass payloads. The available payload envelope is a cylinder of budget. 1.7 m diameter and 1.8 m height. The payloads, however, can be slightly taller if their diameter is small, e.g., a lunar Table 1 Mass Budget telescope. Component Mass (kg) Payload 200.0 Structure 45.0 LUNAR SCOUT Electronics 25.0 Communications 18.84 Batteries 8.18 Solar array 33.0 Attitude control sensors 20.06 Solid rocket motor 2547.32 Propellant 675.36 0.II.J Propulsion support hardware 108.74 Main engine 51.2 Attitude control thrusters 32.24 SIDE VIEW OF LANDER WITH PANELS UP Total 3775.0 Fig. 1 Side view of Lunar Scout with panels up There is a total mass of 3775 kg at takeoff; mass upon touchdown is approximately 530 kg. Attitude control sensors consist of a wide angle sun sensor and a star tracer. There are sixteen 2-Newton thrusters arranged in four four-engine clusters to provide for the variation of the center of mass due to the burning of the liquid propellant. There are also four 4.5-Newton vertical thrusters located around the lander body. Structure The structure will be made of 1.25-in diameter 6061-T6 aluminum tubing with a 0.125-in wall thickness. Thc propulsion subsystem consists of bipropellant tanks and a thrust nozzle located at the bottom of the lander. The three lander legs will be stowed folded up in the payload fairing and will be springloaded to lock into place when _.O _ the fairing splits away. The 0.30-m diameter landing pads will be made of aluminum flex-core to absorb the impact upon lunar touchdown. Upon landing, the spacecraft will deploy six 1.1-m 2 solar panels to provide power. The Fig. 2 Top view of Lunar Scout with solar panels folded panels will rotate down to a 45 degree angle and be out supported by the edges of the lander legs. The lander is equipped with a payload adaptor ring of 1.3-m diameter to allow for attachment of a variety of diffcrent 200 kg UniledStalesNavalAcademy 273 Power The goals of the power system are to provide 500 Watts via solar panels during the daytime and 10 Watts via batteries during the lunar night. Prior to launch, the batteries will be fully charged to provide power to systems intermittently during the trajectory to the moon. After landing, the solar panels will deploy and begin providing power. During the daytime, the solar panels will provide between 240 W and 750 W of power to the payload depending on the position of the sun relative to the spacecraft. The solar cells used are 4cm by 4 cm gallium arsenide on germanium to provide for lighter weight and smaller size arrays. In the nighttime, all systems will shut down and the batteries will provide 10 W to heat the vital systems and the payload. The battery consists of 22 seven-A*hr cells and a 28 V bus. Degradation of the battery from charge and discharge was taken into account even though the battery will only undergo 28 cycles in its two-year lifetime. Communications Communications will be made in the S band using a 2.3 gigahertz, 0.13 m wavelength signal on the Deep Space Network. The telemetry downlink will use two 0.30 m omni-directional antennas with a bit rate of 10 BPS and 5.79 W power requirement. The data downlink will use a 19.5 W feedhorn antenna with a bit rate of 1000 BPS. The feedhorn antenna will provide for a 23 degree horizontal by 21 degree vertical bandwidth. Since the Earth stays in the same position in the lunar sky relative to the lander, the angle of the feedhorn will be set prior to launch and will only need to be rotated once upon landing to be aimed at the Earth. The ground station uplink will use a 4-m dish to communicate with the lander and will require 4.5 W of power. The small 4-m dish uplink was chosen so as not to tie up one of the larger antennas for the two-year projected lifetime of the Lunar Scout.