Reach For the Moon

Mission outline

The spacecraft will be launched into Geostationary Transfer Orbit (GTO) on the 29th of July of the year 2012, using the Indian Polar Satellite Launch Vehicle. A direct transfer from GTO to the Moon will inject the spacecraft into a circular Low Lunar Orbit (LLO) with 100 km altitude, where the lower stage is seperated to reduce landing mass. From the LLO the spacecraft is injected into an Intermediate Lunar Orbit (100 km x 18.5 km). From the ILO the spacecraft will initialize the descent phase. The last 500 m of the descent will be performed vertically. At 15 m altitude the engines are shut down and the spacecraft finally lands on pressurized cushions. The whole landing process is filmed by a fixed horizon looking high definition (HD) camera, as required by the X-Prize Foundation. As a landing site, ‘Sinus Medii’ with coordinates 0.0 N and 1.0 E is selected. The total mission duration will be approximately 10 days.

Immediately after landing,the high gain communication dish is pointed towards Earth to re-establish communications and send the near real-time video of the landing. After this the surface vehicles are deployed. The data of these secondary vehicles is relayed to Earth by the lunar lander throughout the whole mission duration. Possibly also the condition of the vehicles is monitored by the horizontally place camera, if the condition of the lunar surface allows this, making images of the vehicles as they distance themselves from the lander.

The lander vehicle

The spacecraft consists of two stages: a lower stage and a lander stage, as shown in figure 1. The lower stage consists of a cylindrical structure above the engine, with a total length of 1.9 m. Figure 2 shows the backbone structure of the lander stage. The lander stage consists of a base plate of 2.2 diameter with conic structure of 1.1 m high (excluding antennas) placed on top. The rovers are placed inside the cone. Body mounted solar panels have been chosen to protect the instruments and rovers. On the bottom side of the base plate eight inflatable cushions are mounted around the three bipropellant rocket engines.

In the thermal design three radiative surfaces with a total area of 1.4 m2 are used to dissipate the heat generated by the subsystems. By use of a mathematical model the spacecrafts thermal extremes have been defined and calculated. The only system that shows a significant deviation from the allowed temperature is the battery, which will need additional thermal control. The spacecraft will use two stages for propulsion, both of which use a MMH/NTO bipropellant liquid system. The lower stage brings the craft into LLO, whereas the lander stage provides the delta-V for landing. The lower stage uses an R40B engine, providing 4000 N of vacuum thrust. The lander stage uses three S400-12 engines for a combined maximum vacuum thrust of 1350 N. For attitude control a total of sixteen S4 thrusters are used, each delivering 4 N of thrust. Helium pressurant is used for controlled propellant expulsion.

The communication subsystem will contain five antennas: one high gain dish and one low gain dish on the top of the spacecraft, two small omni-directional antennas attached to the side of the spacecraft base plate disc and finally an additional omni-directional antennas for the WiMax system. The X-band frequency will be used for communication between the primary spacecraft and the Earth, whereas WiMax will be used for communication between the lander and the rovers. Only the descent video will be recorded by the lander, all other videos will be recorded by the rovers. To record the descent video a JAI CV-A80 Color HDTV CMOS camera will be installed above the rover bay. An additional camera will be used for obstacle detection during the landing, installed in the bottom of the base plate of the lander stage. For the Command & Data Handling subsystem, it is decided to use a Commercial Off The Shelf (COTS) system. Two COTS Texas Instruments Digital Media Processors will form the core of the central computer. Furthermore, two times 128 MB of DDR2 memory and 2 GB of solid state memory are used. The C&DH system is sensitive to hazards from the space environment, therefore several protection and error detection methods will be used.

For the Guidance Navigation and Control (GNC) system sixteen thrusters will be placed on the spacecraft: twelve on the lander stage and four on the lower stage. Three reaction wheels, one star sensor and one IMU will be used. Additionally, to ensure a safe landing, the obstacle avoidance system will use a camera and a RADAR or LIDAR.

Properties:

Lander power system:

During the mission to Moon, the lander requires power for keeping the subsystems active. The electronic power system of the lander consists of solar panels (Galium arsenide) with an effective area of 1.9 m2, and batteries. Primary battery is used to satisfy the launch power needs and secondary batteries provide space for the storage of energy recieved from the solar panels as well as providing power for eclipse conditions. Furthermore, power management and distribusion is done with several components such as power converts to keep the voltage within the needs, power regulator to regulate the bus voltage and prevent the batteries from overcharging, powe control unit and finally power distribution unit. The total mass and power of the electical power system are estimated to be 33 kg and 300,000 $ respectivly.

More information:

During the Design Synthesis excersise the group has made several reports. A summary of the project is given in the Executive summary.

Also several presentation were given during the project. The final review has been recorded and can be viewed here: Final review -GLXP - 'Getting There'.

Images

Figure 1: Render of the total spacecraft as inserted into GTO by the PSLV launcher. The lower stage will be decoupled in LLO.

Figure 2: Backbone structure of the lander stage. The base plate has a diameter of 2.2 m and the cylindrical core has a diameter of 1 m. The total height of the lander stage, from the base plate to the top of the antennas, is approximately 1.3 m.

Figure 3: Bottom view of the lander stage with the eigth landing cushions inflated. As can be seen, the lander will have three engines.

Figure 4: Lander vehicle with the two rover bay doors opening. The gray spheres are the fuel and pressurant tanks and the two gray panels sticking out of the top are radiators.