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 MARS Dead or Alive Classroom Activity

Objective
To investigate three variables affecting a parachute's rate of descent and then design a parachute that will descend as slowly as possible.

• copy of the "Slowing Things Down" student handout (PDF or HTML)
• copy of the "Engineering Team Directives" student handout (PDF or HTML)
• copy of the "Testing Your Parachute" student handout (PDF or HTML)
• 113-L (30-gallon) large plastic trash bag (0.9-1.1 mL thick)
• three 2.6-cm metal washers
• kite twine—Variable A teams: 12 m; B teams: 15 m; C teams: 10 m
• 25-cm compass—Variable A teams only
• tissue paper—Variable B teams only
• plastic grocery bag—Variable B teams only
• meter stick
• scissors
• clear tape
• fine-point marker
• 8-m measuring tape
• stopwatch
• calculator

1. Discuss with students some uses for parachutes (to slow down human descent, to drop supplies and other materials into war zones, to slow down vehicles such as the space shuttle and the rovers). Ask students what variables affect a parachute's rate of descent (e.g., canopy surface area, canopy material, length of suspension lines, number of suspension lines, shape, payload weight, vent diameter, and wind). Write their answers on the board.

2. Tell students they have been hired to design, construct, and test a parachute that will bring a payload down to the ground as slowly as possible. In this activity, students will test three of the variables that affect descent rate.

3. Organize students into enough teams so that each variable outlined in the "Engineering Team Directives" student handout is tested by at least two teams.

4. Distribute the materials and student handouts to each team. Have each team make and record a hypothesis about how its variable will affect the descent rate of its parachute. Ask students to explain their reasoning.

5. Emphasize the importance of constructing the parachutes as closely as possible to the specifications provided. This is important to ensure the consistency of results among both the parachutes tested within each team and the parachutes tested among teams.

6. After students have constructed their parachutes, locate a safe and suitable place to drop the parachutes, such as from a balcony, theater stage, gym bleachers, or window. Make sure the drop height is at least 4-5 meters and that there are as few drafts as possible. Emphasize to students the importance of conducting each trial the same way—dropping the parachute in a consistent manner and accurately timing the drop is critical to this activity.

7. Have each team report its results. Create a data table on the board for each variable listing the average descent rates. What contributed to slower descent rates for each variable tested? Once students have shared their findings, present students with another challenge: Based on the results of previous trials, design and construct a parachute that will have the slowest average rate of descent while carrying a 2.6-cm metal washer payload. You may want to give students the option of changing untested variables, such as number of suspension lines or canopy shape. Provide students with any additional materials they may need.

8. Have each team drop its parachute five times and determine the average rate of descent for the five trials. Once all teams have finished, compare the parachute with the slowest descent rate to the others. What about it might have contributed to its longest descent time? To conclude, discuss with students whether the slowest parachute would be the best parachute. What other considerations might affect parachute design?

9. As an extension, have students research different kinds of parachutes and their uses.

A parachute helps reduce the speed of a falling object by providing air resistance, or drag. The upward force of the air on the parachute opposes the downward force of gravity on the payload. In addition, drag is produced when air moves through the small holes in porous canopy material, across the surface of the chute, or along the suspension lines. Parachutes that create more drag have a slower descent rate, while parachutes that create less drag have a faster descent rate.

A parachute with the slowest descent rate might not necessarily be the best parachute for any given task. Engineers also need to consider other aspects of parachute design, such as stability, weight, and materials cost.

Students tested the following:

Canopy Size: In general, parachutes with a larger surface area produce more drag, and therefore descend more slowly. There is a point where a larger canopy size yields no more added benefit.

Canopy Material: In general, lighter and/or less porous materials create more drag than heavier and/or more porous materials.

Suspension Line Length: Longer suspension lines allow the canopy to inflate fully and thus create more drag, slower descent rates, and more stability. They also add more weight. Shorter suspension lines create less drag, faster descent rates, and less stability. However, suspension lines that are too long may become tangled, while suspension lines that are too short may prevent the parachute canopy from fully inflating.

There are myriad additional variables that contribute to parachute descent rate, including number of suspension lines, payload weight, number and size of vent holes, number of canopy layers, and canopy shape. How these are combined, and the ratios of the materials used, all contribute to how slowly a parachute descends.

In addition to these and other design factors, parachutes are affected by outside forces such as wind and atmospheric pressure. Because the atmospheric density of Mars is less than 1 percent of Earth's, a parachute alone cannot slow down the Mars Exploration Rover enough to ensure a safe, slow landing speed. Therefore, the MER parachute system includes rockets to help slow the descent of the lander and to help counteract the effect of strong Martian winds.

To help the rover land safely, the NASA team designed several systems, including an aeroshell to protect the lander carrying the rover from heat and forces during atmospheric entry, a parachute to slow the lander's speed prior to impact, and airbags to soften the landing. The Martian lander requires a parachute system that will slow the lander enough to prevent it from crashing into the surface, and stable enough to prevent the lander from striking the surface at an angle.

Sample Results

Variable A: Surface Area
Parachute 1: 18 cm canopy

 Height(m) Time(s) Rate(m/s) Drop 1 4.5 m 2.14 2.10 Drop 2 4.5 m 2.23 2.02 Drop 3 4.5 m 2.23 2.02 Drop 4 4.5 m 2.28 1.97 Drop 5 4.5 m 2.04 2.21

18 cm:
average descent rate: 2.06 m/s

27 cm
average descent rate: 1.25 m/s

36 cm
average descent rate: 1.04 m/s

Variable B: Canopy Material
Parachute 1: trash bag

 Height(m) Time (s) Rate (m/s) Drop 1 4.5 m 4.09 1.10 Drop 2 4.5 m 4.20 1.07 Drop 3 4.5 m 4.48 1.00 Drop 4 4.5 m 4.56 .99 Drop 5 4.5 m 4.67 .96

trash bag
average descent rate: 1.02 m/s

grocery bag
average descent rate: .87 m/s

tissue paper
average descent rate: .96 m/s

Variable C: Suspension Line Length
Parachute 1: 15 cm line

 Height(m) Time (s) Rate (m/s) Drop 1 4.5 m 2.05 2.20 Drop 2 4.5 m 2.65 1.70 Drop 3 4.5 m 2.05 2.20 Drop 4 4.5 m 2.20 2.05 Drop 5 4.5 m 2.15 2.09

15 cm
average descent rate: 2.05 m/s

25 cm
average descent rate: 1.31 m/s

50 cm
average descent rate: .96 m/s

Web Sites

NOVA's Web Site—MARS Dead or Alive
www.pbs.org/nova/mars/
In this companion Web site for the NOVA program, watch the program online, learn why water is necessary for life, investigate the rover's parts, explore Mars' landscape, and design your own parachute.

Mars Academy
www.marsacademy.com/
Features an international online collaborative project to find real-life solutions to problems involved with designing a manned mission to Mars, including landing site selection, trajectory calculations, rocket design, crew selection, and life support system plans.

Mars Daily
www.marsdaily.com/
Contains a collection of articles related to Mars exploration.

Mars Exploration Rover Mission
mars.jpl.nasa.gov/mer/
Includes short biographies of the scientists who worked on designing the rovers and background information about the mission.

Mars Exploration Rovers
athena.cornell.edu/
Provides information about the scientific instruments on board the rovers, the flight plan, and video simulations of the rovers landing on Mars.

Martian Invasion: Probing Lively Puzzles on the Red Planet
www.sciencenews.org/20031108/bob10.asp
Outlines the objectives of the European Space Agency's and NASA's near-simultaneous missions to Mars.

NASA Center for Mars Exploration
cmex-www.arc.nasa.gov/CMEX/index.html
Presents hundreds of concept maps of Mars-related information, digital atlases of the Red Planet, a menu of human and robotic missions to Mars, educator resources, and more.

NASA Spacelink: Mars
spacelink.nasa.gov/Instructional.Materials/Curriculum.Support
/Space.Science/Our.Solar.System/Mars/.index.html

Provides image libraries, resource guides, investigations, and more.

NSTA Web News Analysis: Mars Journeys
www.nsta.org/main/news/stories/nsta_story.php?news_story_ID=48395
Offers a digest of online news articles focusing on Mars journeys.

Slowest Model Parachute Challenge
www.cc.gatech.edu/projects/DITC/designTasks/parachute/index.html
Provides an in-depth investigation for a coffee filter parachute challenge, complete with video clips from three classrooms that completed the unit.

Books

Boyce, Joseph M. The Smithsonian Book of Mars. Washington: Smithsonian Institution Press, 2003.
Provides a firsthand account of the history of the planet's exploration by one of NASA's Mars program scientists. Includes explanations of Mars's atmosphere, climate, surface, and interior derived from NASA mission findings.

Croswell, Ken. Magnificent Mars. New York: Free Press, 2003.
Discusses what is known about Mars and what is still to be discovered.

Hartmann, William K. A Traveler's Guide to Mars: The Mysterious Landscapes of the Red Planet. New York: Workman Publishing Company, 2003.
Discusses the three major eras of Mars's 4.5-billion-year history and compares the geologic time processes on the Red Planet with those on Earth. Includes many photographs.

Morton, Oliver. Mapping Mars: Science, Imagination, and the Birth of a World. London: Fourth Estate, 2002.
Examines scientists' efforts to map Mars and profiles researchers and science fiction writers who have contributed to how Mars has been viewed.

Raeburn, Paul. Mars: Uncovering the Secrets of the Red Planet. Washington: National Geographic, 1998.
Chronicles the history of human exploration of Mars, describing each Mars mission and its key players. Includes a pair of 3-D glasses to view a foldout landscape of Mars.

The "Slowing Things Down" activity aligns with the following National Science Education Standards.

Grades 5-8

 Science Standard B:Physical Science

Motions and Forces:

• If more than one force acts upon an object along a straight line, then the forces will reinforce or cancel one another, depending on their direction and magnitude. Unbalanced forces will cause changes in the speed or direction of an object's motion.

 Science Standard E: Science and Technology

Understandings about science and technology:

• Perfectly designed solutions do not exist. All technological solutions have trade-offs, such as safety, cost, efficiency, and appearance.

• Technological designs have constraints.

 Mathematics Standard 13: Measurement

Grades 9-12

 Science Standard B:Physical Science

Motions and Forces:

• Gravitation is a universal force that each mass exerts on any other mass. The strength of the gravitational attractive force between two masses is proportional to the masses and inversely proportional to the square of the distance between them.

 Science Standard E: Science and Technology

Understandings about science and technology:

• Creativity, imagination, and a good knowledge base are all required in the work of science and engineering.

 Mathematics Standard 13: Measurement

Classroom Activity Author

Margy Kuntz has written and edited educational materials for 20 years. She has authored numerous educational supplements, basal text materials, and trade books in science, math, and computers.

 MARS Dead or Alive Original broadcast:January 4, 2004

 Mars Dead or Alive: A Hostile Environment Learn in this Teachers' Domain video segment (5m 17s) about the Mars mission and why scientists are so interested in exploring the red planet.
 Major funding for NOVA is provided by the Park Foundation, Sprint, and Microsoft. Additional funding is provided by the Corporation for Public Broadcasting and public television viewers.

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