Space exploration Mission
Based on an initial analysis of scientifically relevant and technically challenging mission scenarios performed in the first iteration of WP10, the CoRob-X consortium selected the Lunar lava tubes exploration mission outlined in this section. The mission is subdivided into four phases, each of which is performed by all or a sub-set of the ADRES components. The preliminary Test and Demonstration Plan foresees that all four mission phases are performed in sequence. However, each mission phase comprises an independent stand-alone activity.
As an initial condition, the mission phases assume that all REUs have successfully landed in a lander spacecraft and have been successfully deployed on the planetary surface near the Skylight of the lava tube to be explored.
The rock-outcrops exposed by the collapse of the lava tube ceiling during the formation of a “Skylight” provides a unique opportunity to explore the geological strata normally hidden under the lunar dust. The lava tube itself may provide protection from radiation and meteorites and have a stable temperature range compared to surface conditions. These characteristics allow building safe, yet economical habitats in lava tubes. Prior to establishing a habitat, such a lava tube needs to be explored and categorized for assessment of stability and safety and for the existence of frozen water. Thus, the exploration of the geological strata in the Skylight and of the lava tube itself (both from the inside of the tube and from the lunar surface) are the key scientific objectives of the CoRob-X Space exploration mission.
Mission Phase 1 – Cooperative Exploration and Mapping
Based on remote sensing data created by an orbiter, the area in the vicinity of the Skylight is divided into segments. This division considers the different locomotion capabilities of the REUs and merges their individual traversability maps. Each segment is explored by the REU capable to access it. REU-1 and REU-2 will demonstrate their flexible locomotion capabilities to traverse this terrain. Each REU uses a customized version of the I3DS sensor module to create a detailed Digital Elevation Map and a 3-D environment map
During the whole operation, the robots communicate with each other and exchange the map data. Thus, a joint map is built simultaneously in all three systems.
Mission Phase 1 also includes the mapping of the roof of the lava tube with the GPR sensor on board of REU-2. The joint environment map will thus include an indication of the location and depth of the lava tube.
Mission Phase 2 – Skylight Exploration with Payload Cube
Once the surroundings of the lava tube entry hole are mapped, a convenient approach to the skylight is planned and all systems move towards the rim of the skylight. REU-3 is equipped with a deployable ballistic Payload Cube. The cube is deployed into the skylight by a mechanical deployment device (“propeller”). On the Moon, due to the low lunar gravity, the cube will drop at a relatively low speed and will be able to log data for a high-resolution image of the walls and the skylight floor with its on-board cameras and an integrated lighting device. In the analogue mission, the drop will be faster and thus the data recovered somewhat less detailed.
Before the deployment, the three REUs position themselves around the rim of the skylight and track the Payload Cube in-flight using their on-board sensors and the markers and light source of the Payload Cube. The sensor data are merged on REU-1 and used to create a precise trajectory analysis of the cube’s flight. The ADRES uses this data together with the data collected by the Payload Cube itself to compute a preliminary 3-D representation of the skylight. This representation is transmitted to the RMS.
Mission Phase 3 – Skylight Exploration with Rapelling Robot Team
The ADRES is able to select a feasible starting point for the exploration, and REU-1 and REU-2 move into position. REU-3 takes a position at the opposite side of the skylight. Its task is to monitor the descend of REU-2 in support of the coordination of the actions of REU-1 and REU-2.
REU-1 uses its manipulator arm to guide the tether and enable REU-2 to connect via the HOTDOCK interface to the Tether Management and Docking System (TMDS). The active suspension system of REU-1 can be used to lower the body of REU-1 to the ground if stable anchoring is required. Alternatively, the mobility of REU-1 can be used to establish a mobile anchor for improved mobility of REU-2.
Once REU-2 is connected, REU-1 uses its arm to guide the tether in the Rapelling of REU-2 down the cliff into the skylight.The current concept for the tether/lander management foresees that the tether is stored on the lander side, i.e. on REU-2. This way, the tether can be spooled from REU-2 and tangling or rupture of the tether (when gliding over rocks) can be avoided.
On its way down, REU-2 uses its on-board illumination device to illuminate the scene and its sensors, including the GPR, to create a vertical visual profile of the cliffs, as well as a 3D reconstruction of the area it traverses.
Mission Phase 4 – Lava Tube Exploration with Scout Rover
For the exploration of the lava tube REU-2 disconnects from the tether and moves into the lava tube. REU-2 uses the GPR and the time-of-flight cameras on board to a.) create a 3-D model of the lava tube and b.) explore the consistency, porosity, and thickness of the lava tube walls. The latter is valuable information to answer the question of whether the lava tube can be sealed off and filled with an atmosphere at a later stage. In addition, if some water in the form of an ice crust is present, this will be detected.
The data from REU-2 are sent via the tether module and/or Payload Cube – which now acts as a relay beacon – to REU-1 and to the RMS. This allows to implement a redundant communication link.
After the mission in the lava tube is finished, REU-2 moves back to the tether and re-docks to the tether/lander unit. As energy can be sent from REU-1 through the cable, REU-2 may re-charge and thus effectively stay in the lava tube as a “resident rover” able to explore for an extended period of time. Alternatively, it may be lifted out of the lava tube with the help of REU-1. In the analogue mission, the latter will be demonstrated (3 times).
In this project, we will develop the concept of a re-docking interface based on HOTDOCK that is integrated into a lander/tether management unit and rappelled down into the Skylight with REU-2. In a real lunar (or even Martian) mission, the weight of this unit plus REU-2 would be manageable by REU-1 without a problem as a result of the lower gravity. In the analogue mission, we will apply extreme light-weight construction so that it can be handled by REU-1 (SherpaTT). With the exploration of a lava tube described above, the CoRob-X mission tackles one of the most difficult and complex, yet scientifically most rewarding challenges for robotic exploration. The mission scenario in CoRob-X is targeted for lunar exploration, but it is – with slightly altered system parameters due to the different gravity and atmospheric conditions – in principle also valid for the exploration of lava tubes or cliffs/canyons on Mars. In addition, if the ADRES can handle the entry of a rover into a lava tube via the skylight, it can also handle the descend into any lunar or Martian crater.