Mars Science Laboratory: Robotics

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Mars Science Laboratory: Robotics

Overall Question: How do they communicate and maneuver a rover on Mars?(Note: Sources are at bottom of notepads)Using the Deep Space Network and the orbiter relay system, the Curiosity rover can communicate with Earth. The rover can either send data directly to Earth or relay the data through the satellites. It maneuvers itself by using Autonomous Planetary Mobility, which means that the rover can drive itself for a certain distance without human assistance.

Mars Science Laboratory: Robotics

Figure 1. Communications from Curiosity to Earth.

Figure 2. Demonstration of Autonomous Planetary Mobility. This is from the rover Opportunity near Victoria Crater. Red areas are "keep out" zones (the crater wall). This area was established by human operators. White shows unknown areas. Green shows where it is safe to travel. The moving purple rhombus shows the rover Opportunity, while the blue line is the best path to the destination.

Deep Space NetworkThe Deep Space Network is used to provide communications for missions far into space. It also provides backup to the Near Earth Network and the Space network. The DSN is NASA's array of radio antennas that supports interplanetary missions and some that orbit Earth. The stations are 120 degrees apart on the Earth so that a satellite will always be in contact with one station, and located far enough from cities that external radio signals won't interfere. The sites are located at Goldstone, near Barstow, California; near Madrid, Spain, and near Canberra, Australia.Sources:

Orbiter Relay SystemMars Surveillance Orbiter and Odyssey use two different radio waves. X-band is the current standard in communications. When amplified, the orbiter can send data to Earth more than 10 times faster than previous missions. Ka-band is a previously untested radio frequency. It is four times higher than X-band, which means scientists can bring back data faster.Sources:

Video 1. Animation of how controllers will communicate with curiosity during landing. Video not working? Use this link.

Rover AntennaeThe rover has three antennas: the low gain antenna, the high gain antenna, and the ultra-high frequency (UHF) antenna. The low and high gain antennae are similar to satellite television dishes, but they transmit signals at higher frequencies. These are called X-band frequencies. The higher frequencies transmit more data in the same amount of time using smaller wavelengths, but they must be narrower and more focused to be received. They have a much higher range than the rover's UHF antenna. The low gain antenna transmits less focused signals. They are the rover's main link to Earth for the first several Martian days after landing. The signals spread out, so the signal will reach Earth no matter how the rover is facing. After controllers have figured out the rover's location and attitude (direction the rover is facing) communications switch to the high gain antenna. It sends a more efficient signal aimed at Earth. These signals are detected by the Deep Space Network. There is also a third antenna, called the ultra-high frequency (UHF) antenna. The UHF antenna is a short-range antenna and is used for communication with the orbiters. This is how the rover will communicate most of the time.

Quantity and Speed of DataThe data from Curiosity to Earth can vary from 500 bits per second to 32,000 bits per second (roughly half as fast as a standard home modem). The data rate from the Mars Reconnaissance Orbiter is selected during communications and can be as high as 2 million bits per second. The data rate to the other orbiter, Odyssey, is selectable. It can be either 128,000 or 256,000 bits per second (4-8 times the speed of a home modem). An orbiter can only communicate with the rover for about eight minutes at a time, per Mars day (sol). During that time, between 100 and 250 megabits of data can be transferred to an orbiter. That same data would then take up to 20 hours to get to Earth if the rover were communicating directly with Earth. When night falls on the part of Mars that the rover is on, the rover cannot communicate directly with Earth. The orbiters can see Earth for about 16 hours per day. They can send more data directly to Earth than the rover because they have more power and bigger antennas than the rover. They can also see Earth for longer.Sources:

Autonomous Planetary MobilityAutonomous Planetary Mobility allows rovers to find the best path and avoid dangerous areas without human involvement. Curiosity has inherited some technology from previous rovers, such as a six-wheel drive, a rocker-bogie suspension system, scene-scanning instruments that help select exploration targets and routes, and autonomous navigation software that allows the rover to move without human help. The MSL also inherits technology tested on the Mars Exploration Rovers, such as global path planning and visual target tracking. Rovers can now plan a path to somewhere 50 meters away, as opposed to just a few steps. The MSL's size is another advantage. Its ground clearance is more than 60 centimeters, which means that it can climb over larger rocks than any previous mission. The capability is aided even further by the suspension system that keeps the rover balanced. The rover can withstand a 45 degree tilt in any direction, but is not allowed to tilt past 30 degrees by the fault protection system.Sources:

Figure 3. A 70 meter Deep Space Network antenna at the Goldstone complex.

Main Points:- The Deep Space Network is the network of radio antennas that connect Earth to the two Mars orbiters and the rovers. They are placed so that satellites will always be able to communicate with at least one antenna.- The Orbiter Relay system is the system that the Mars rovers use to forward a message to Earth. It uses two radio waves, X-band and Ka-band, to provide the fastest transfer speeds possible.- Curiosity has 3 antennas to communicate with Earth. One is an Ultra-high Frequency (UHF) antenna, one is a low-gain antenna, and the other is a high-gain antenna. The low and high gain antennas can send a message further, but the UHF antenna is used for communication with the orbiters.- Curiosity can send data back at speeds of 500 bits per second to 32,000 bits per second if it communicates directly to Earth, up to 2 million bits per second if it communicates using the Mars Reconnaissance Orbiter, and either 128,000 or 256,000 bits per second if communicating through the Odyssey.-Autonomous Planetary Mobility is how the rover finds its own way around. Old rovers could only plan a couple of steps ahead, but today's technology allows for the rover to select and go to a destination up to 50 meters away.

For more information, read the notepads.


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