Operation and Performance of the Mars Exploration Rover Imaging System on the Martian Surface Justin N. Maki Jet Propulsion Laboratory California Institute of Technology Pasadena, CA USA [email protected] Todd Litwin, Mark Schwochert Jet Propulsion Laboratory California Institute of Technology Pasadena, CA USA Ken Herkenhoff United States Geological Survey Flagstaff, AZ USA Abstract - The Imaging System on the Mars Exploration Rovers has successfully operated on the surface of Mars for over one Earth year. The acquisition of hundreds of panoramas and tens of thousands of stereo pairs has enabled the rovers to explore Mars at a level of detail unprecedented in the history of space exploration. In addition to providing scientific value, the images also play a key role in the daily tactical operation of the rovers. The mobile nature of the MER surface mission requires extensive use of the imaging system for traverse planning, rover localization, remote sensing instrument targeting, and robotic arm placement. Each of these activity types requires a different set of data compression rates, surface Figure 1. The Mars Exploration Spirit Rover, as viewed by coverage, and image acquisition strategies. An overview the Navcam shortly after lander egress early in the mission. of the surface imaging activities is provided, along with a presents an overview of the operation and performance of summary of the image data acquired to date. the MER Imaging System. Keywords: Imaging system, cameras, rovers, Mars, 1.2 Imaging System Design operations. The MER cameras are classified into five types: Descent cameras, Navigation cameras (Navcam), Hazard Avoidance 1 Introduction cameras (Hazcam), Panoramic cameras (Pancam), and Microscopic Imager (MI) cameras. The Descent camera, 1.1 Mission attached to the landing system, acquired 3 images during In January 2004, the Mars Exploration Rover Project the Entry, Descent, and Landing (EDL) phase of the (MER) landed a pair of Rovers onto the surface of Mars mission and was subsequently abandoned as the rover [1]. Each rover (see figure 1) carried a set of 10 cameras drove onto the surface. The other nine cameras are [2]. Upon landing, the cameras immediately began attached to the rover - the Navcam and Pancam cameras are acquiring images of the Martian terrain and returned over mounted at the top of a pan/tilt mast and the Hazcams are 70,000 individual images in the first Earth year of hard-mounted directly to the rover body. All 9 cameras operation. The cameras have made significant have been extensively used during the surface operations contributions to the mission, including the acquisition of phase of the mission. images that show evidence of past liquid water on the Navigation planning and Rover localization are Martian surface [3]. This paper performed primarily with Navcam panoramas and single frame images, although in the cases where long-distance Authorized licensed use limited to: CALIFORNIA INSTITUTE OF TECHNOLOGY. Downloaded on April 16,2010 at 22:54:53 UTC from IEEE Xplore. Restrictions apply. traverse designation is desired, the higher-resolution Cameras MER Engineering Camera Description Pancam cameras [4] are used. Operation of the rover’s and Objectives robotic arm, also called the Instrument Deployment Device Descent Acquire 3 images of the Martian surface (IDD) [5], is done with Front Hazcam imagery. Auto- Camera between altitudes of 2000 m and 1200 navigation is performed with either Navcam or Hazcam meters during descent. Field of view: 45 imagery. In addition to the engineering functions described degrees, 3-meter/pixel spatial resolution. above, all of the cameras are used for purposes of scientific Broadband, visible filter. investigation, with the Pancam [4] and Microscopic Imager [6] acquiring the majority of scientific image data. Navcams Provide terrain context for traverse Because of their operational uses, the cameras are planning and Pancam, Mini-TES grouped into two types: “engineering” cameras and pointing. 360-degree field of regard at <1 “science” cameras. All of the MER cameras share the same mrad/pixel angular resolution. Stereo electronics design [2] and differ only in their optical ranging out to 100 meters (30 cm stereo properties (with the exception of the descent imager, which baseline). Broadband, visible filter. has a slightly different video gain). Tables 1 and 2 show the operational descriptions of the engineering and science Hazcams Provide image data for the onboard cameras, respectively. detection of navigation hazards during a 1.3 Hardware traverse. Provide terrain context immediately forward and aft of the rover All of the MER Cameras were built at the Jet Propulsion (in particular the area not viewable by the Laboratory (JPL) in Pasadena, CA, under a fast-paced 32- Navcams) for traverse planning. Support month development schedule. The camera designs were Instrument Deployment Device (IDD) developed as a collaborative effort between members of the operations. Support Rover fine MER team at JPL and MER science team members at positioning near IDD targets. Wide field Cornell University in Ithaca, NY and the United States of view (120 degrees), 2 mrad/pixel Geological Survey (USGS) in Flagstaff, AZ. For details angular resolution. Stereo ranging about the camera hardware, see [2]. immediately in front of the rover (10 cm 1.4 Flight Software stereo baseline) to an accuracy of +/- 5 The MER onboard flight imaging software is described in mm. Broadband, visible filter. detail in [7]. The onboard image processing capabilities of Table 1. A description of the MER Engineering Cameras, the flight system are extensive and include: autoexposure, from [2]. image subframe extraction, image spatial downsampling, and image compression. The system also includes the Cameras MER Science Camera Description and capability to point the mast-mounted cameras in a number Objectives of surface-based coordinate frames and at selected Pancam [4] Obtain monoscopic and stereoscopic astronomical targets such as the sun and the Martian image mosaics. Obtain multispectral moons. visible to short-wave near-IR images For every image acquired by the rover, the MER Imaging over a range of viewing geometries. Services flight software generates a small (64 x 64 pixel) Obtain images of the Sun and Martian “thumbnail image”. These thumbnail images are sent back sky. Serve as the primary Sun-finding to Earth at a relatively high priority and are usually camera for rover navigation. Resolve downlinked the same day. The thumbnail images allow objects on the scale of the rover wheels ground operators to preview an image before the full image to distances of ~100 m. Support is downlinked. This opens the possibility for the operators acquisition and release of exciting E/PO to verify the success of certain imaging acquisitions and products. confirm to the rest of the operations team that the rover can move to the next target before the full images are received Microscopi Image fine-scale morphology of natural (receipt of the full images often happens several days later). c Imager [6] surfaces. Image fine-scale texture and The thumbnails are also sometimes used to reprioritize reflectance of abraded surfaces. Aid in image data for higher (or lower) downlink transmission. the interpretation of data gathered by 1.5 Ground Software other instruments by imaging areas examined by them at high resolution. Aspects of the MER ground image processing software are described in detail in [2], [8] and [9]. The ground Table 2. A description of the MER Science Cameras image processing software decompresses the image data, (Pancam [4] and Microscopic Imager [6]). assembles ancillary information into the image header, and writes the image to an Experiment Data Record (EDR) file Authorized licensed use limited to: CALIFORNIA INSTITUTE OF TECHNOLOGY. Downloaded on April 16,2010 at 22:54:53 UTC from IEEE Xplore. Restrictions apply. in PDS (Planetary Data System) format. The raw EDR 2.1.1 Uplink Process and Sol Types files are processed further into Reduced Data Record Camera commands are generated on Earth and sent to the (RDR) files. The RDR file types are numerous and include Rovers on Mars as part of the MER 10-hour daily uplink stereo correlation maps, mosaics, and 3-dimensional terrain process. Each rover has a dedicated uplink team per sol, meshes. and the two teams operate independently of one another on any given sol. The uplink process begins upon examination 2 MER Surface Imaging Operations of the most recent image data from the rovers, typically performed within hours (sometimes minutes) of data receipt The MER cameras have returned over 73,000 images as on Earth. During the MER primary mission (Sols 1 of 13 March 2005 (table 3). The camera hardware (and through 90) the generation of the camera commands associated software) has functioned nominally since (approximately 150 per sol, per rover) required 3 landing. The cameras and flight software have been operations personnel per sol, per rover. The introduction of utilized as expected, and the ground software has efficiencies and software automation has reduced the performed extremely well – over 750,000 derived image number of camera sequencing personnel to 2 operations products have been generated on the ground [8]. personnel per day, per rover. We have considered the The majority of the images acquired during a typical sol possibility of utilizing 1 operations personnel per day per on Mars are scientific in purpose. This paper discusses the