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Tohoku University ARLISS 2003 Project (A Rocket Launch for International Student Satellites) |
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ARLISS (A Rocket Launch for International Student Satellites) is a project for students to learn a whole process of a space mission from design to launch of their own payload. The payload is launched into the sky at 4,000m (about 12,000ft) altitude by a solid rocket provided by an American amateur rocket group. This project is held at Black Rock desert, Nevada, U.S.A. since 1999. As a part of this activity, " Come Back Competition " has been organized since 2001, in which each payload is autonomously maneuvered to reach a goal. Some payloads try aerodynamic maneuver during the parachute-descent phase using a controllable parafoil. But, we have challenged to navigate a payload that has self-mobility over the surface of the desert. Such a demonstration is called " Run-back approach ".
We have taken part of the Run-Back approach since 2002, reflecting our background technology of the lunar/planetary exploration rovers. One of the advantages of the Run-back is that the rover can use unlimited time to navigate itself towards the goal without any disturbances such as wind. The Run-Back approach consists of the following sequence:
We have mainly considered how to enhance an effective locomotion of the rover and how to pack it in the limited allowed volume. In general, the larger the rover's wheels become, the more effective its locomotive performance will be. The obtained solution is a Dual-Wheel system. Each wheel is independently driven by a DC motor. The configurations of our rover are shown in Fig.1 and Fig.2. The main body of the rover is made of aluminum and is wedged between the two wheels. In order to avoid the main body from flipping over, a stabilizer which is a tiny aluminum plate is attached on the main body. The rover can steer by differentiating the velocity of two wheels. The maximum size of the rover is ƒÓ146 mm in diameter and 220 mm in length.
On the main body, the control system for autonomous navigation is mounted, which includes PIC16F877 as MPU, a GPS receiver, and an EEPROM to store the navigation data. A communication system is also mounted for the telemetry to monitor the status and position of the rover. A commercial lithium ion battery is mounted as a power source. The schematic diagram and specifications of the rover are here.
ARLISS 2003 was held on Sep. 25th-27th. The launch was beautiful and then, at the apogee, the ejectment of the rover was fine. A few seconds later, the parachute was opened. After about 15 minute-descent by the parachute, the rover was able to land softly at a distance of approximately 2 km from the prescribed target. But, the rover didn't move at all and the telemetry data wasn't sent to the ground station either. A reason of this trouble was that the GPS receiver absorbed a very big part of the launching acceleration (about 6.5G) so that the sequence was stopped temporarily. Then, at the moment of restarting the GPS receiver, the MPU detected the landing of the rover based on altitude data and the parachute separation system started to work automatically. Soon after that, the autonomous navigation was started. The rover conducted a successful navigation and a precisely arrival at the goal. The motion trace of the rover is shown in Fig.3. The navigation trace was pulled away from the straight path to the goal. This is considered due to the wheel slip on natural terrain. Even though such motion drift, the rover successfully came to the goal by virtue of the GPS based navigation. The total traveling distance was approximately 3 kilometers, and the rover took 3 hours to continuously complete this navigation. Average traveling velocity was 1 km/h. 
Figure 3 : Navigation trace of the Rover
We have developed a self-contained, autonomous rover and successfully demonstrated a long-range navigation over a natural desert for the continuous distance of 3 kilometers. This Run-back is a very significant demonstration of the rover we've developed, which can withstand the launch and the landing impact, then navigate itself towards the target using GPS. Furthermore, it is a meaningful result to achieve the long range navigation.
Click at the following figures to watch its video clip.
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