A rover is a vehicle designed to move across the surface of a celestial body. For the US Apollo program to the Moon the rover was the Apollo Lunar Rover which was added to the program for Apollo 15, 16, and 17. For the USSR N1/L3 program to the Moon the rover was the Lunokhod which was sent to the Moon separately from the planned N1/L3 program and driven remotely.
All of these rovers used electric motors to drive their wheels, but they didn't use the same drivetrains or batteries. The Apollo Lunar Rovers had four wheels similar to a car. The Lunokhod rovers had eight wheels.
Autonomous rovers have also been operated on Mars. These include Sojourner, the MERs Spirit and Opportunity, and Curiosity. These rovers also used electric motors. However, Sojourner and subsequent US Mars rovers have used six wheels in a rocker-bogie suspension arrangement.
|Rover||mission type||country of development||mass (kg)||drivetrain||electricity storage||control system technology|
|Luna 17, 21 / Lunokhod 1, 2||Lunar Rover||USSR||756||8 wheel||remote control (R/C) by humans|
|Apollo 15, 16, 17 Lunar Roving Vehicle||Lunar Rover||USA||210||4 wheel||silver oxide zinc batteries||local control by humans (astronauts)|
|Mars Pathfinder / Sojourner||Mars Rover||USA||11.5||6 wheel||lithium thionyl chloride (LiSOCL2) batteries||Intel 80C85 (8080 architecture) on Sojourner rover|
|MER-A, B / Spirit, Opportunity||Mars Rover||USA||185||6 wheel||lithium ion batteries||IBM RAD6000 (POWER architecture)|
|MSL Curiosity||Mars Rover||USA||899||6 wheel||lithium ion batteries and radioisotope thermoelectric generator||RAD750 (POWER architecture)|
|Chang'e 3, 4 / Yutu-1, 2||Lunar Rover||China||140||6 wheel|
It's important that drivetrains be designed so that the rover won't get stuck. There are no roads on the Moon or Mars so rovers are like off road vehicles. There's also nobody to call to pull them out if they do get stuck.
Most rovers have used electric batteries, or batteries partnered with solar panels. The Apollo Lunar Rover used silver oxide zinc batteries. Sojourner used 9 lithium thionyl chloride (LiSOCL2) D-cell sized batteries. It also had 13 strings of 18, 5.5 mil GaAs solar cells each, for a total of 0.22 square meters. This combined batteries/solar panels provided Sojourner 30W of peak power (mid-sol) which included 16W peak solar panel production. The the MERs (Spirit and Opportunity) used lithium ion batteries similar to what is used today in most smartphones and laptop computers. The Curiosity rover also used lithium ion batteries along with a radioisotope thermoelectric generator.
It's important that batteries are light weight, can hold a charge, and if partnered with solar panels can be charged efficiently.
The Apollo Lunar Rovers had a simple navigation system to help the astronauts know how far and in what direction the Lunar Module was. The Lunokhod rovers were operated by remote control from Earth. More recently, the Sojourner rover used an 8085 processor to aid navigation guidance and control, and the MERs Spirit and Opportunity, and the Curiosity rover have all used Power processors for this purpose.
While Mars is farther from the Sun than the Earth and the Moon and thus colder on average, the 14 days of sunlight followed by 14 days of night on the Moon causes much larger termperature variations than on Mars or Earth. Further the effects of the atmosphere and oceans of the Earth, aren't available to transfer heat from places in sunlight to places in shadow on the Moon. The Apollo Lunar Rovers only had to work on the Moon during the duration of the manned mission which was only a couple of days during Lunar morning. However, even though they only had to work for a couple of days, the Apollo Lunar Rovers were never parked in the shade of the Apollo Lunar Module because they would get too cold there. The rovers used tanks filled with paraffin wax to store excess heat from electronics while driving. The heat would melt the paraffin wax. This heat would then be released through mirrored radiators when the rover was parked causing the paraffin wax to solidify. Unlike Apollo, the Lunokhod rovers survived from 4 to 10 months on the Moon. The Lunokhods had solar panels mounted on the underside of a lid. During the Lunar days, the lid was open and the solar panels were exposed to the Sun to generate electricity. During the Lunar nights, the lid was closed to allow a polonium-210 heat source to keep components at operating temperature. The Yutu rover went to sleep during lunar nights. Similar to the Lunokhods, it used radioisotope heater units which used plutonium-238 and two-phase fluid loops. Mars rovers have also used radioisotope heater units along with electrical heaters; however, they haven't had to deal with significantly higher day time temperatures than night time temperatures as found on the Moon. Finally, the private company LunaCorp, which had plans for a Lunar rover, had plans at one point that called for continuously driving the rover in the direction of the Sun at a high latitude, to keep the rovers solar panels always in sunlight and to keep the temperature relatively consistent.
Sojourner: An Insider's View of the Mars Pathfinder Mission by Andrew Mishkin (2003-12-02)
Roving Mars: Spirit, Opportunity, and the Exploration of the Red Planet
Mars Rover Curiosity: An Inside Account from Curiosity's Chief Engineer
For students who want to do experiments related to landing systems, here are some ideas for science experiment ideas related to power supplies and mobility.
|Question||What is Tested?||What Stays the Same?||Data Collected|
|Does the size of a lemon affect a lemon battery?||Size of lemon, distance between placement of anode and cathode||Metals used for anode and cathode, temperature of lemon battery||Voltage between anode and cathode|
|Does the type of citrus fruit affect a citrus fruit battery?||Type of citrus fruit used to make a battery such as lemon, lime, orange||Size of fruit, metals used for anode and cathode, temperature of battery||Voltage between anode and cathode|
|What materials are best for conducting electricity?||Materials||Battery, circuit arrangement||Ability of light bulb to light up|
|How does temperature affect a magnet's strength?||Temperature of magnet||Type, shape, and size of magnet, type of thermometer, placement of thermometer on the magnet||Magnet's ability to hold an object|
|How do different surfaces affect friction?||Different surfaces||Slope of ramp, mass/shape/material of object slid down ramp||Time it takes object to slide down the ramp|
|How doies the size of a wheel affect how big of a bump it can roll over?||Wheeled toys with different size wheels||Slope of ramp, mass/shape/material of object rolled down ramp||Size of bump on ramp that the wheeled toy will make it over|
For students who want to experiment with a working example of an autonomous rover, in addition to the Moon or Mars, rovers can operate on Earth. Before building anything it's a good idea to know what you're trying to accomplish. For example, if you want to build an autonomous rover, are you building it to take photos, make scientific measurements, dig a hole, or setup a terrarium or greenhouse? That will tell you something about what sensors and actuators your rover will need in addition to its drive mechanism. If you want to build your own autonomous rover, you could start from scratch, or you might be able to leverage components that already exist.
Thus, the three general options to consider if you want to build a simple rover are:
There are many robotics kits and construction sets available commercially that you can use to build a rover. These can be powered by batteries similar to what was used in Lunar or Mars rovers, and they quite often have a control system based on a processor that is similar to those used on Mars rovers. While robotics kits can be easy to build and inexpensive, they don't allow from easy modification from what they were designed to do. On the other hand, robotics construction sets allow for a lot of customization, but tend to be more expensive. Some common robotics construction sets include:
There are many toy remote control (R/C) cars and trucks available commercially that you can use to build a rover. The key difference between an R/C vehicle and a rover is that an R/C vehicle typically doesn't have a control system or processor, but rather constantly relies on a human to guide it. To turn an R/C vehicle into a rover you would need to add a control system and the necessary electronics to control the motors with it and the necessary software to provide some automated operation. You will also probably want to have some navigatational input sensors to guide a steering mechanism, and maybe some environment sensors and environment manipulators. Here are some exaples of autonomous rovers built from R/C vehicles.
For this you will need:
Again, you will also probably want to have a steering mechanism, navigatational input sensors, and maybe some environment sensors and environment manipulators.
Some retailers for electronics and other parts are:
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