To analyze the composition and properties of soil with BEAR, a mechanism is necessary that can penetrate the ground to a certain depth and transports soil samples to the rover. Additionally, it must be possible to analyze the soil samples on board of the rover. To solve these tasks, a sample retrieval device (SRD) is designed, that can collect soil samples from a depth of 15cm and analyzes them inside the rover (see figure 1).
Figure 1: SRD in raised and lowered position
The SRD consists of a lowerable drilling platform on which a mini laboratory is located (see figure 2). The soil samples are extracted with an earth drill and transported inside the rover through a pipe (see figure 3). At the upper end of the pipe the soil is ejected directly into the minilab. The circular laboratory consists of four chambers where the soil samples can be analyzed. One of the chambers has no ground, so that the earth that is collected while the drill lowers down to the desired depth falls directly back down to the ground.
Figure 2: drilling platform with minilab
Figure 3: view into the inside of the extraction pipe
To determine the actual drilling depth, an ultrasonic sensor is used to measure the height of the drilling platform above the ground. When the desired drilling depth is reached, the laboratory is rotated and the soil sample falls inside a chamber where it will be analyzed. The analysis is done by a camera that investigates the soil sample in the visual and ultra violet wave length. With this data it is possible to generate absorption profiles of the soil sample to get information about the physical and chemical composition of the ground. The complete data processing and control of the drill and analysis process is done on the drilling platform. The processed data, as well as the housekeeping data of the drill and analyze instruments are transmitted to the on board computer (OBC) of BEAR via Bluetooth. The complete power supply of the drilling platform is also done independent from the rest of the rover. That avoids a complex cable routing from the moving platform to the OBC and the electrical power system (EPS) of BEAR. The analysis of the soil samples happens completely autonomous and can be done without the need of the functions of other subsystems of the rover. With the SRD a total of three soil samples can be extracted and analyzed. The EPS of BEAR is only used to raise and lower the drilling platform. The raising and lowering process is realized with a stepper motor that is connected to a gear transmission (see figure 4). A fail safe brake prevents the drilling platform from falling down in case of a lack of energy supply. The raising mechanism allows the platform to be raised to a height where an unimpeded driving of the Rover is possible. So it is safe that obstacles that get between the wheels of BEAR while it is driving cannot collide with the drilling platform.
Figure 4: raising mechanism
To finish the SRD, the control of the several components, as well as the processing algorithm to analyze the collected data must be realized. Setup and test of the SRD are other activities that have to be done before the use of the SRD on BEAR.