Tensegrity Heat Shield for Atmospheric Entry through Celestial Bodies

Heat shields play a vital role in protecting space vehicles during the atmosphere reentry. Therefore, they are essential for space vehicles, and better designed heat shields will vastly improve the ability both of robots and humans to explore extraterrestrial destinations. The main goal of the current paper is to investigate the feasibility of designing, building and deploying a tensegrity-based heat shield, which would withstand the atmospheric reentry of a low gravity and dense atmosphere celestial body (such as Titan), where the reentry accelerations and therefore, drag forces, will be lower than in the case of a high gravity planet (e.g., Earth or Mars). The paper is a preliminary study, which investigates the parameters that would be helpful in designing tensegrity-based heat shields. We explore the dynamics of entry and how the atmospheric forces interact with the heat shield. Tensegrity structures consist of tension elements used in conjunction with rigid rods which are actuated by changing the lengths of the tension elements. The advantage of the proposed approach versus the traditional one (rigid heat shields) is that tensegrity structures are flexible structures able to adapt the shape to obtain an optimal reentry configuration. The proposed heat shield will be able to fold in a small space during transport (e.g., to the target celestial body), unfold when the target is reached and provide additional mobility for an optimal reentry pattern. However, to achieve a deployable configuration, the tensegrity structure must withstand significant dynamics and thermal loads. We will use NASA Tensegrity Robotics Toolkit (NTRT) to simulate the structural designs of the heat shield as well as for designing the controllers. Introduction Tensegrity systems are hybrid soft-rigid systems that are very flexible and can perform unique maneuvers because of the tension element based structure. These robots are more dynamic than conventional rigid robots but more agile and sturdy than soft robots [1]. Other characteristics of tensegrity robots are that they are highly compliant structures that have the ability to fold. Due to the compliance, these robots can withstand high impact forces. This design allows tensegrity robots to be more maneuverable and for them to exhibit a complex range of movement 1 Copyright c © 2016 by ASME as determined by the design of the robot. Tensegrity robots are built using tensile and compression elements [2]. Commonly, these would be high tension cables and rigid rods that form the structure of the robot. The design and arrangement of the rods are based on desired properties and structural capabilities of the robot. Different actuator types can be used to actuate these robots however there is one commonality to all actuation solutions, i.e. the actuator elements change the length of tensile elements in order to make the robot change its structure which consequentially controls the dynamic tensegrity structure. As spacecrafts enter atmosphere of celestial bodies at very high speeds, it causes the spacecrafts to heat up to very high temperatures. Heat shields are essential to protect spacecrafts from exposure to such high temperatures. The temperatures are enough to vaporize the spacecraft and if the vehicle does not have an effective heatshield, it can catch fire, scientific payload can potentially get damaged or other systems in the vehicle can malfunction causing it to lose stability. Tensegrity based heat shields offer a revolutionary way of designing heat shields. It is possible to mount protection material on a tensegrity robot for the purposes of thermal protection when entering the atmosphere of a celestial body. A few determining factors for atmospheric entry are deceleration rates, entry angles, types of entry methods, thermal protection systems and structural compliance.