Micro-Imager Dust Cover, Micro-Imager Contact Sensor, and Mössbauer Spectrometer Contact Sensor mechanisms for the Mars Exploration Rovers

Abstract

This paper discusses three mechanisms developed for the Mars Exploration Rover (MER) program which will land two rovers on the Martian surface in January 2004: the Microscopic-Imager Dust Cover, the Microscopic-Imager Contact Sensor and the Mossbauer Spectrometer Contact Sensor. These mechanisms enhance the capabilities of the rovers and their in situ science instruments, specifically the Microscopic-Imager (MI) and Mossbauer Spectrometer (MB), located on the end of the rover’s robotic arm. The MI Dust Cover mechanism covers the lens of the Microscopic-Imager protecting it from dust and incidental contact while the instrument is not in use. The cover opens when the MI is positioned over a target and closes after a series of images has been taken. The MI and MB contact sensors, as their name implies, sense contact with the Martian surface, indicating that the instrument is positioned at the proper distance from the target and can begin taking measurements. While the functions these mechanisms perform are fundamentally simple, the implementation of the mechanisms under typical constraints (mass, schedule, budget, science requirements, etc...) provides an excellent illustration of the subtleties involved in designing a mechanism for use on Mars, interfacing to existing hardware, and working to conflicting requirements. Very few mechanisms have been designed to sense contact with an extraterrestrial surface (or to protect an instrument from the Martian environment), and fewer yet have successfully touched the surface of Mars. As we continue to expand our reach beyond Earth, these mechanisms will become more prevalent and increasingly important. For this reason, a discussion of how these mechanisms are implemented, what issues are important to the scientists, what the relevant trades and requirements are, and what work has been done before (and lessons learned from that work) is essential. This paper presents, in detail, precisely those topics. Introduction and Background MER Mission and Science Objectives The Mars Exploration Rover (MER) program began to take shape in the summer of 2000 with the goal of landing two rovers on Mars in January of 2004. MER (illustrated in Figure 1) is part of NASA’s continuing effort to explore Mars and, like previous Mars missions, primary responsibility for its development was given to the Jet Propulsion Laboratory (JPL). Figure 1. MER on the surface of Mars [1] The decision was made to launch two rovers to reduce risk and increase science return. Instead of a lander with a separate, small rover like the Mars Pathfinder mission, the entire MER lander is, itself, a rover. The rovers are much bigger than the Sojourner rover of the Pathfinder mission and can rove much greater distances (up to 100m each day). The science package for MER is known as the Athena payload. The Athena payload consists of six primary instruments [2]. Two of these, the Pancam camera and the Mini-TES spectrometer are mounted to the body of the rover. The other four instruments are located on the end of a robotic arm referred to as the Instrument Deployment Device, or IDD (Figure 2). The IDD along with the associated electronics and software algorithms required to position each instrument at its target constitutes the complete Instrument Positioning System (IPS). The four instruments residing on the end of the IDD are: the Microscopic Imager (MI), the