The Mars Exploration Rover mission, also known as MERS, is the second mission sent to Mars that involved rovers. MERS aims to study Mars surface looking for clues about the past water activity on Mars. This information is vital to accomplish one of the goals of the mission: to find out whether life ever existed in Mars.
To do so, twin rovers, Opportunity and Spirit, were sent to different locations on opposite sides on Mars that were apparently affected by liquid water in the past, the Gusev Crater and Meridiani Planum.
Spirit was launched on June 10, 2003 and arrived to Mars on January 4, 2004, and Opportunity was launched on July 7, 2003 and arrived on January 25, 2004.
 |
| Spirit and Opportunity Instruments |
 |
| Rover's wheels |
Rovers have both a low-gain and high-gain antenna used to communicate with Earth. The low-gain antenna is omni directional, and it's used to communicate with the Deep Space Network (DSN). High-gain antenna can send information in a specific direction and is steerable allowing the rovers to communicate with earth without changing its position. Moreover, rovers can also communicate with the 2001 Mars Odyssey and Mars Global Surveyor orbiters which can pass along data from the rovers to Earth or viceversa.
Due to delay in communications, rovers can't be driven in real time. So, they receive commands from earth through their high-gain antenna at the beginning of the day. An improved version of Sojourner's auto navigation-driving software helps rovers to drive safely avoiding any hazard. The rover has been programmed to drive for roughly 10 seconds, then stop for 20 seconds and using the stereo camera pairs (body-mounted on spirit and mast-mounted on Opportunity) to take pictures and generate 3D maps. These maps are used to get a list of possible paths. Rover chooses the best one and continues driving for another 10 seconds until it has reach its goal. Furthermore, odometry software has been added to help tracking the distance traveled by the rover. This is done by by comparing pictures taken before and after a short drive.
At the end of the Martian day the communication between Earth and the rover is reversed. Data that have been gathered are transferred through the high-gain antenna.
The rover CPU is a 20MHz IBM RAD6000 with 128 MB of DRAM, 3MB of EEPROM, and 256 MB of Flash memory, and it's inside the Rover Electronics Module (REM) which is located in the Warm Electronics Box (WEB), also known as rover body. Also, batteries and electronics are located in the WEB. To prevent components being damaged by extreme temperatures, heaters have been placed inside the WEB helping to keep the internal temperature warm during the night, and radiators are used to release the excess heat. Besides, rover body's has gold-painted insulate wall which keeps the internal heat.
To achieve the scientific goals rovers are equipped with a series of instruments which are used to perform experiments and acquire data about Mars surface. These instruments are cameras, miniature Thermal Emission Spectrometer (Mini-TES), Mossbauer Spectrometer (MB), Alpha Particle X-Ray Spectrometer (APXS), Rock Abrasion Tool (RAT), and Magnet Array.
According with their function, cameras are divided in two groups: navigation and science. Both rovers have in total nine cameras. Two black-and-white cameras, called Navigation Cameras or Navcams, are used for navigation purposes and hazard detection. These cameras are mounted on the rovers’ neck, or Pancam Mast Assembly (PMA), and use visible light to gather panoramic three-dimensional (3D) images. Cameras also work together with the four Hazard Avoidance Cameras or Hazcams for safely driving the rover. Hazcams are mounted in the lower portion of the front and rear of the rover. Like Pancams, cameras are black-and-white and provide 3D images. Each camera has a field of view of 120°, and the rover uses these cameras to map out the shape of the terrain as far as 3 m (9.8ft) in front of it. Two CCD and high-resolution color panoramic Cameras or Pancams have double porpuse support science experiments and creating maps of the area where the rover lands. Pancams are mounted in the rover's PMA at 1.5m (5ft) high and provide 360° of stereoscopic, humanlike views of the terrain. They can generate image mosaics as large as 4,000px high and 24,000px around. The PMA allows the cameras to rotate a full 360° to obtain a panoramic view of the Martian landscape. The camera bar itself can swing up or down through 180° of elevation.
 | |||
| Cameras location |
 | ||
| Nacam and Pamcam |
 |
| Microscope Imager Camera |
Rovers' arm not only carries the MI but also the other science instruments like the Mossbauer Spectrometer, APXA and RAT. The rover arm or Instrument Deployment Device (IDD) has three joints: shoulder elbow and wrist, and instruments are located at the end of the arm. The arm can place instruments directly up against rock or soil targets of interest. After completing the experimentation phase and before moving to another place the arm stows itself underneath the front area of the rover body.
 |
| Robotic Arm Diagram |
 |
| Robotic Arm's Instruments |
 |
| Simulated View of the Rover's Arm |
Miniature Thermal Emission Spectrometer or Mini-TES is an infrared spectrometer used to identify the mineral composition of rocks and soils by detecting their patterns of thermal radiation. Mini-TES is located at the bottom of the PMA. Two mirrors are placed under the Pancams in the PMA getting a better view of the terrain and serving as a periscope which sends the light down to the instrument.
Mossbauer Spectrometer (MB) is an instrument specially designed to study iron-bearing minerals. Measuments are taken by placing the instrument's sensor head directly against a rock or soil sample. And, one measument can take about 12 hours.
 |
| Image Taken by The Rover of the Mossbauer Spectrometer |
Alpha Particle X-Ray Spectrometer (APXS) is used to determine the elemental composition of rocks and soil. The APXS is placed against the rock or soil to perform a test. Measurements are usually taken at night and require at least 10 hours to be completed.
 | ||
| Image Taken by the Rover of the APXS |
 |
| APXS parts |
Rock Abrasion Tool or RAT is a powerful grinder able to create a hole 45mm about 2in in diameter and 5mm (0.2in) deep into a rock on the Martian surface. It's located on the arm of the rover and weighs less than 720grm (2lb). It uses three electric motors to drive rotating grinding teeth in the surface of a rock, and its able to grind through hard volcanic rock in about two hours. Once fresh surface is exposed, other science instruments perform analysis on the composition. This is done to determine differences between surface and core of rocks useful to know about how the rock was formed and the environmental conditions in which it resided. In addition, the forearm holds a small brush so that the Rock Abrasion Tool can spin against it to "brush its teeth" and rid the grinding tool of any leftover pieces of rock before its next test.
 |
| Rock Abrasion Tool |
Initially, rovers were designed to last for 90 soles (Martian day). But so far, both rovers have exceeded that goal with more than 2000 soles of mission. Unfortunately, communications with Spirits has been lost since March 22, 2010 (sol 2210), and after a lot of effort trying to recover the rover the mission concluded on May 25, 2011. While Opportunity is still up and working, it continues exploring the red Planet.
Sources:
Sources:
Additional Resources:
*Images property of Nasa and Cornell University
No comments:
Post a Comment