Robots on Mars: LEGO ROBOLAB Activity

Teacher Training Workshop II- April 23, 2005

Purpose-

The purpose of this activity is to recreate a Mars Rover Mission using several simple programs related to actual activities of rovers exploring the surface of Mars. In so doing we will show how science and mathematics are involved in the design and execution of a mission to Mars.

Introduction-

Last year, NASA successfully landed a pair of rovers, Spirit and Opportunity, on the surface of Mars. These rovers have far exceeded their planned mission lifetimes and are still currently in operation. They have been given the go ahead to continue their work for another 18 months. In order to control these rovers successfully from up to 250 million miles away, the vehicles have to be pre-programmed to do simple tasks on their own. Can you think of at least three basic functions that the rovers need to “know” how to do in order to function successfully on Mars?

 

 

 

 

 

 

http://mars4.jpl.nasa.gov/gallery/video/2001-2004.html has some interesting animations related to the missions to Mars both current and future.

 

We have recreated a fictitious LEGOland Mars Landing site, complete with rovers, equipment, a lander, a crater and rocks. Each rover has a set of tasks to perform that have been pre-programmed into its “brain”. Before we can release the rovers to do their mission, there needs to be some ground testing of their abilities, so that we know how they will perform on the surface of Mars and how much they can accomplish in a given period of time. You will have the opportunity to investigate how position, velocity, and acceleration are related to one another as you test the rovers.

 

Also, an additional program is needed to ensure the success of the mission. After having some time to “play” with the rovers and their existing programs, you will have a chance to “tweak” and upload another program to ensure success of the mission. You also will be able to plan for the remainder of the mission to maximize the amount of data collected by the robots.

Procedure

The mission is divided into three main components: preflight, inflight, and surface activity. For the preflight portion, the rover is tested and analyzed so as to become familiar with its capabilities. Several experimental runs will be performed to gauge how far the rover can travel in a given amount of time, and how much the rover can accelerate as it moves from one location to another.

 

Preflight: We will run tests to familiarize with the abilities of the rover to perform on Mars. We will focus on velocity and acceleration. The “manned” rover (the vehicle with the LEGO figure on it) has a pair of programs loaded in its memory. The programs run in series with a 10 second break between programs. The first program runs the rover at constant speed for a set period of time; the second increases progressively the speed of the rover. Define a starting line from where you will start the trials. Run the program and measure the time the rover takes to cover a distance d, which you also will measure. Enter these values in the first table on the Data Sheet.

 

When the vehicle pauses, place it back at the starting line. Have two people ready with stopwatches. When the program runs, one person will start his/her stopwatch and stop it when the vehicle stops. The second person will start the watch when the vehicle reaches a predetermined mark (at 200cm distance) and stop it when the vehicle stops. The corresponding distances and times will be recorded in the table below.

 

Once the two sets of distances and times are recorded, find the averages of each. Using these averages and the two formulas below, find the acceleration using two methods (Method 1 or “real” and Method 2 or “approximate”)

 

Method 1:                    Method 2:      

 

 

 

Two points summarizing the relationship between position, velocity, and acceleration:

·        As the rover moved, it changed position over a period of time. That change of position with time is the velocity, expressed in our case as meters per second.

·        In the next case, the rover will accelerate. That is, it will change its velocity over time, which is simply what acceleration is, the change of velocity in unit time squared.

 

In addition, we can work with the second vehicle (unmanned, with the flat panel that serves as a solar panel) and repeat the constant motion exercise for smooth surfaces (the bare floor) as well as not-so-smooth surfaces (the carpeted floor). What would the results from both, taken together, tell us about the rover’s performance over surfaces of different textures / roughness.

 

Inflight (Optional): Two optional exercises involve selecting a landing site on Mars as well as a simulated flight to Mars. Both of these activities, as well as others, can be found at this website:

  http://www.marsquestonline.org/investigations/01_rover.html

 

The website listed provides an opportunity to search for landing sites that are both safe and interesting. Once there, one can click on the “Explore Mars” tab for a list of activities, including the challenging and interesting applet “Fly to Mars”. For extended workshops, these activities provide invaluable lessons on how real-life Mars missions are planned and executed. We encourage you to explore these activities on your own after the Workshop and evaluate their usefulness for a summer science camp.

 

On the Surface: In real-life missions, the progress starts slow, as mission controllers assess the health of the rover just after arrival to Mars. Once the craft passes a series of tests, it is ready to explore the surface of Mars. We will reflect this progression in our activity. First we will move the rover off the lander and move it back on. Just like real missions we start slowly and build up as we gain confidence. We will eventually, after a series of exercises, have the rover roll off the lander, take data from several locations, then have the rover return to the lander.

 

With the first rover, run the program and allow it to come off the lander and come back on. Record the time it takes for the rover to completely egress (leave) the lander, and the time it takes for it to return to the lander platform. Are the two times the same? What does that tell you about the performance of the rover on inclined pieces of land?

 

The rover will come off the lander a second time and perform a series of actions before returning to the lander. What types of data do you envision this rover taking as it turns and “dances” in the four pre-determined locations? Time the length of this mission and what fraction of the time is spent taking and processing data. What fraction of the total time does it take to transmit data to the transmission station (which occurs when the rover pauses and apparently does nothing)?

 

The second rover is able to sense color differences in the terrain and can change directions based on these changes. What usefulness can you see in having this as part of the mission (think of terrain types and what different types can tell us about the geologic history of the surface)?

 

As the mission progresses, depending on the time we have to work with, we will perform some additional activities. There is provided space in the Data Sheet for you to record the outcomes of these activities.

 

Data Sheet for Mars Rover Activity

The first part deals with the ground testing or preflight portion of the mission.

 

Data table 1: Constant velocity

Trial

Distance

Time

Velocity

1

 

 

 

 

2

 

 

 

 

3

 

 

 

 

4

 

 

 

 

5

 

 

 

 

Average

 

 

 

 

What is the average velocity of the rover? _______________

 

 

Data Table 2: Acceleration

Trial

Distance (d1)

Time (t1)

Distance (d2)

Time (t2)

Total distance (d1+ d2)

Total time

(t1 + t2)

1

 

 

 

 

 

 

 

2

 

 

 

 

 

 

 

3

 

 

 

 

 

 

 

4

 

 

 

 

 

 

 

5

 

 

 

 

 

 

 

Average

 

 

 

 

 

 

 

What is the acceleration you got from Method 1? _______________

 

What was the acceleration from Method 2? __________________

 

Use the Percent Difference formula to see how close the first value is to the second.

 

Inflight: If you attempted to fly a spacecraft to Mars using the simulation, how successful were you? What made it difficult?

 

 

 

 

 

What are some considerations that went into determining a suitable landing site?

 

 

 

On the surface:

 

Height and length of Ramp:

 

Angle of Inclination: (=arcsin [height/length]):

 

Time of egress:

 

Time of Return:

 

If the two times were different, why so? Also, what useful information does this provide for the robot’s ability to drive on inclined terrain?

 

 

 

 

What types of data do you envision the rover taking as it turns and dances in the pre-determined locations?

 

 

 

 

What usefulness can you see in having the ability to discern color differences as part of the mission (think of terrain types and what different types can tell us about the geologic history of the surface)?

 

 

 

 

Extended Mission: Once we successfully go through the preliminaries, we can prepare to take the rovers for extended tours of duty. We will assume the rovers can travel 8 hours a day, given the fact that they are run by solar power and that the Sun is high enough in the sky during this time period for the rovers to get enough energy to work with.

 

From the average velocity obtained from Data Table 1, how far can the rover travel in a day?

 

 

From the measurements of the speed of the first surface rover (the one that pushed the ramp down in order to exit the lander), how far can this rover travel in a day? If it found a hillside with the same incline as the ramp, how high would it make it up the hill in one hour?

 

 

 

 

 

 

 

If eight features (craters, boulders, etc.) were strung along a line and were evenly spaced (500 meters between each feature), and it took two hours to explore each feature, given the above conditions of operability (speed, hours in the sun, etc.), how many days would it take to gather data for all of these features?

 

 

 

 

 

 

Conclusions

Some additional thoughts for consideration: