The paper presents ReachBot, a robot designed to navigate and manipulate in challenging terrains such as caves and lava tubes on the Moon and Mars. ReachBot uses extendable booms equipped with microspine grippers to manipulate itself against irregular rock surfaces, enabling it to access and explore enclosed spaces. The booms terminate in grippers that can achieve force closure in confined areas, and the robot's motion is controlled using a contact-before-motion planner that utilizes internal force control similar to a multi-fingered hand. The paper details the design and implementation of the gripper, including a Monte Carlo simulation to predict grasp strength and variability, and a two-step perception system to identify potential grasp sites. Field tests conducted in a lava tube in the Mojave Desert confirmed the robot's ability to find and grasp targets, demonstrating the feasibility of ReachBot for exploring planetary caves and lava tubes. The results highlight the potential of ReachBot for scientific exploration and the challenges that need to be addressed for future missions.The paper presents ReachBot, a robot designed to navigate and manipulate in challenging terrains such as caves and lava tubes on the Moon and Mars. ReachBot uses extendable booms equipped with microspine grippers to manipulate itself against irregular rock surfaces, enabling it to access and explore enclosed spaces. The booms terminate in grippers that can achieve force closure in confined areas, and the robot's motion is controlled using a contact-before-motion planner that utilizes internal force control similar to a multi-fingered hand. The paper details the design and implementation of the gripper, including a Monte Carlo simulation to predict grasp strength and variability, and a two-step perception system to identify potential grasp sites. Field tests conducted in a lava tube in the Mojave Desert confirmed the robot's ability to find and grasp targets, demonstrating the feasibility of ReachBot for exploring planetary caves and lava tubes. The results highlight the potential of ReachBot for scientific exploration and the challenges that need to be addressed for future missions.