Center Space Physics Research - baylor.edu

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Center for Astrophysics, Space Physics and Engineering Research 2013 Baylor University RET Program

Investigating Microgravity and the Physics of a Drop Capsule

Dr. Steve Rapp Linwood Holton Governor’s School

P.O. Box 1987 Abingdon, VA 24210 [email protected]

Abstract—the researcher experienced a combination of educational research and experimental research during this Research Experience for Teachers program. One of

the objectives was to test a drop capsule to see if a one second microgravity environment could be achieved during free fall. After several modifications of the drop capsule were made, a microgravity environment of .7 seconds was attained. This paper will also explore what microgravity is and why experimentalists are studying it, how microgravity environments are created, and present details of the microgravity experiment completed during this program

What is Microgravity? First, to understand the concept of microgravity let’s discuss gravity for a moment. Gravity is an attractive force that affects every object in the universe. The Earth’s gravity pulls us toward its center, but we also attract the Earth, even though that attraction is minute. By stepping on a bathroom scale we can see how much we weigh. So, the force of the pull of Earth’s gravity is what determines our weight. Microgravity is an environment in which the apparent weight of a system (or us) is small compared to its actual weight due to gravity. You may have heard the term “zero gravity” on newscasts or even in a book. You may have thought that this meant there is no gravity. Zero gravity does not mean there is no gravity; gravity is just less than gravity normally experienced on Earth [1]. Why do Microgravity Research? Many people assume that any research conducted in space is done mainly to benefit the space mission. However, this assumption may be incorrect. There are many industrial based researchers who find microgravity research extremely valuable in solving ground based problems. Microgravity research is proving to be beneficial to many different science areas such as materials, thermo physical properties, fluids, foams and emulsions science, thermal physics and heat transfer, cold atom technology, biotechnology, and combustion science [2]. For example, microgravity research is helping researchers find ways to improve the combustion process. On Earth, flames are driven by convection currents resulting in a familiar rising flame as found in a candle or camp fire (see image 1 below). In microgravity convection does not occur and therefore combustion can occur only as quickly as oxygen can diffuse in and the

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combustion products disseminate from the reaction environment. So, combustion in a microgravity environment is much simpler than on Earth.

Image 1: Candle on left driven by convection currents; right, combustion in microgravity

As a result of improving the combustion process in automobile engines an increase of 1% in fuel efficiency can be realized. This would be analogous to changing your gas mileage from 25 miles/gallon to 25.25 miles/gallon. That doesn’t sound like much, but that translates into a savings of about 100 million barrels of oil per year for America or about $5.5 million dollars per day [2]! Indeed, microgravity research can help solve land based problems. How is a Microgravity Environment Created? Microgravity conditions can be produced in many ways. One way is to travel away from Earth. As you may recall this is what the Apollo astronauts did when they explored the moon. Even then their weight was not zero; it was one sixth of what it was on Earth (image 2).

Image 2: Astronaut James B. Irwin, Apollo 15 lunar mission, August 1, 1971

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Another way to achieve a microgravity environment is to orbit the Earth in a spacecraft such as the International Space Station (ISS). The astronauts experience a greatly reduced gravitational force as opposed to being on the Earth and can actually float around in the spacecraft as shown in image 3.

Image 3: ISS astronauts experiencing microgravity conditions

Flying on NASA’s “Vomit Comet” produces 15‐25 second intervals of weightlessness by flying a parabolic path as illustrated in image 4. The plane (image 5) is used to introduce potential astronauts to the feeling of weightlessness. A typical flight will see two to three hours of plunging arcs, giving astronauts about 30 or 40 chances to experience weightlessness when the airplane drops to a lower altitude. Some researchers also use the flights as a chance to run experiments in weightlessness [3].

Image 4: The “Vomit Comet” dips and climbs through the air to simulate the feeling of

weightlessness

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Figure 5: The “Vomit Comet” Sounding rockets (image 6) are also used to create microgravity conditions for several minutes; they follow prescribed parabolic paths achieving an acceleration of 10‐5 g. Sounding rockets have some advantages over other forms of space‐borne experiments. First, they are more simplistic; there are fewer interfaces to deal with as well less complicated launch facilities. Second, the cost is much more reasonable than an orbital spacecraft. Lastly, payload development is quick since most payload can be developed from pre‐existing equipment [4].

Image 6: Sounding Rocket Launch

Drop towers are also prevalent in providing microgravity environment for experiments. The Zero Gravity Research Facility (ZGRF) at NASA Glenn Research Center (image 7) in Cleveland, Ohio is the largest facility of its kind in the world. Microgravity can be only achieved on Earth by putting an object in a state of free fall. In the ZGRF objects free fall 132 m and are weightless for 5.18 seconds during the fall. The objects fall through a vacuum chamber which is at a pressure of .01 torr. Acceleration is reduced to less than 10‐5 g [5].

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Image 7: Object being prepared for a drop at the Zero Gravity Research Facility

The BRIC Drop Capsule Experiment Introduction In the not so distant future the Baylor Research Innovation Collaborative (BRIC) site will have its very own 24 m drop tower predicted to be capable of producing a microgravity environment for about 2.2 seconds. With that inspiring thought in mind the researcher pondered the idea of microgravity research as an interesting topic of study. As a matter of fact, the researcher was invited by Dr. Rene Laufer to work on a microgravity research project this summer. As with all research projects, much time was spent learning more about microgravity as evidenced in the first section of this paper. Purpose The objective of this project is to determine how long a microgravity environment can exist in a drop capsule released from a height of 6 m. Calculations indicate that a 1 second microgravity environment should be possible. Method The actual experimentation began with the student construction of a drop capsule [6] as shown in image 8. The structure is basically a cylindrical structure within a larger cylindrical structure. It is .6 m high and .4 m wide. The sides of the drop capsule were covered with saran wrap to cut down on drag forces. The inner cylinder will experience free fall or microgravity conditions as the capsule is dropped from the second floor (a distance of about 6 m) of the BRIC.

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An iPhone with an accelerometer app was used to determine when microgravity conditions occurred within the inner drop capsule. The first drop happened on June 19, 2103 (image 9). Excel was used to plot the data; the plot is found in the results section. The capsule was dropped (with some modifications) on four other occasions, July 8, July 11, July 16 and July 29.

Image 8: Drop capsule used in the microgravity experiment

Image 9: Capsule was dropped initially on June 19

outer capsule inner capsule

iPhone case

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Since the free fall time for the first drop was only .4 seconds, some changes were made to the capsule before the next drop. A mirror was installed just below the video port of the iPhone; the mirror was pointed toward the calibration grid taped to the outer capsule (see images 10 &11). It was thought that the inner capsule might be hitting the outer capsule. This apparatus showed, that as suspected, there was contact between the inner capsule and outer capsule. So, the inner capsule was shortened to about one third of its original length to resolve the situation. It was also noted that the drop capsule seemed to be falling with a slight angle instead of falling straight. The cause of this problem seemed to be related to the cutting of the rope that held the capsule in position. Enough horizontal force was being applied by the scissors to cause the slight tilt. Henceforth, fishing line was substituted for the rope and a lighter was used to melt the line. This provided a much better release mechanism. Image 10: iPhone with attached mirror Image 11: calibration grid The next launch event occurred on July 11. Five drops were made but only one drop produced usable data. The plot of that data is found in the results section. Microgravity conditions were observed for only .6 seconds. Again modifications were made to the drop capsule. The flat top of the capsule may be causing drag forces. A dome top was added to reduce the drag force as the capsule moved through the air (image 12). On July 16, the modified capsule was dropped 10 times. Drops 1, 2, 3, and 4 did not have the dome top but had the shortened inner capsule. Drops 3, 4, 5, and 9 produced no data. The configuration of the capsule for drops 2, 6, 8, and 10 is given in chart 1. The domed capsule is shown in image 13. In drops 8 and 10 the inner capsule was attached to the top of the outer capsule. Since in those drops the inner capsule could not possibly hit the side of the outer capsule, a microgravity environment of more than .6 seconds should be observed.

Drop Number Configuration

2 Inner capsule free Flat upper end

6 Inner capsule free Dome upper end

8 Inner capsule fixed Flat upper end

10 Inner capsule fixed Dome upper end

Chart 1: Drop Capsule Configuration

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Image 13: Modified capsule with domed top, fixed and shortened inner capsule, and extended

calibration grid

After the July 16 drop event, a closer look at the “outer skin” (saran wrap) was taken. The saran wrap is fairly flimsy, enough so that some turbulence may occur as the capsule encounters air resistance on the way down. So, replacement of the flimsy saran wrap ensued. A heavy duty clear plastic shower curtain was cut to enclose the outer capsule. The dome was replaced with a cone (party hat) to help reduce the drag force as shown in Image 14. Perhaps this will enhance the attainment of a one second microgravity environment.

Image 14: Drop capsule with party hat

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Results Graph 1 shows a plot of the data for the initial drop of the capsule on 6/19. Notice that zero gravity conditions are present in the capsule from 93.2 s to 93.6 s.

Graph 1: Drop 1, June 19

Some modications were made after the June 19 drop to try and increase the time of microgravity conditions. Graph 2 shows that the time for microgravity conditions was extended to .6 seconds.

Graph 2: Drop 4, July 11

Once again some modifications were made to try and increase the time of the microgravity environment. Several graphs are posted on the next 3 pages to show the results of various

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1

2

3

4

92 92.5 93 93.5 94 94.5 95 95.5

z‐axis acceleration (g)

time (s)

Drop 1‐ 6/19/13

Drop 4 ‐ 7/11/13

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configurations of the capsule. The microgravity environment was increased to .7 seconds, an increase of 8%. Graph 4 shows .7 seconds of microgravity.



‐2.5

‐2

‐1.5

‐1

‐0.5

0

0.5

1

1.5

62 63 64 65 66 67 68 69

Z axis acceleration (g)

Time (s)

Drop 1 ‐ 7/16/13

‐2.5

‐2

‐1.5

‐1

‐0.5

0

0.5

1

1.5

2

2.5

62.5 63 63.5 64 64.5 65 65.5 66 66.5 67


Time (s)

Drop 2: 7/16/3

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‐2.5

‐2

‐1.5

‐1

‐0.5

0

0.5

1

1.5

2

2.5

88 89 90 91 92 93 94 95


Time (s)

Drop 8 ‐ 7/16/13

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Summary and Conclusion The initial drop of the capsule yielded microgravity conditions for .4 seconds (graph 1). After decreasing the length of the inner capsule by about a third and changing the release mechanism a microgravity environment of .6 seconds was observed (graph 2). The flat top of the capsule was thought to be causing turbulence that would affect the motion of the inner capsule. Hence the inner capsule was fixed to the outer capsule to prevent that condition from occurring in drop 8 (graph 6) and drop 10 (graph 7). Drop 6 (graph 5) and drop 10 (graph 7) had domed outer capsules. It is worthy to note that drop 6 achieved microgravity conditions for .7

‐2.5

‐2

‐1.5

‐1

‐0.5

0

0.5

1

104 105 106 107 108 109 110 111


Time (s)

Drop 10 ‐ 7/16/13

‐2.5

‐2

‐1.5

‐1

‐0.5

0

0.5

1

1.5

69 70 71 72 73 74 75 76 77


Time (s)

Drop 4 ‐ 7/29/13

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seconds, and drop 2 (graph 4) with a flat end did as well. The party hat capsule (graph 8) did not significantly improve the time of the microgravity environment. More trials definitely need to be conducted to reach a finite conclusion. With a little more time and a few more modifications and trials, the microgravity environment may be extended to 1 second. Especially For Educators

Videos of the descent of the drop capsule are available for download at: https://app.box.com/s/6rajedp39q3mizn2ayyp. Teachers you might want to use these videos with your classes for motion analysis. Have the students find acceleration, velocity, distance and time of fall using video analysis software. Excel is a good program for data analysis and for creating graphs. The drop capsule data can be found online at: https://app.box.com/s/2br4lmsk08hchmn7sleh. NASA’s Microgravity Teacher’s Guide [7] is an excellent resource with activities for grades 4‐12. Another really nice resource is The Physics Classroom at http://www.physicsclassroom.com/Class/. The site has extraordinary physics tutorials.

Useful equations Newton's Law of Universal Gravitation: F = Gm1m2/r

2 D = ½ gt2

Resources For more information about microgravity research, visit these websites:

Microgravity Research Program Office http://microgravity.nasa.gov/ Microgravity Research Division Headquarters http://microgravity.hq.nasa.gov/ Microgravity Science Division at Glenn Research Center http://microgravity.grc.nasa.gov/ The National Center for Microgravity Research on Fluids and Combustion http://www.ncmr.org/ NASA Spacelink, Education Programs http://spacelink.nasa.gov/

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Works Cited [1] Serway, R.A., Vuille, C., and Faughn, J. S. (2009). The laws of motion, College Physics, (9th edition), (pp. 89‐91). Belmont, CA: Brooks/Cole. [2] ESA Impress Education (2013, July 14), Retrieved from http://www.spaceflight.esa.int/impress/text/education/Microgravity/Why%20Do_MicrogravityResearch.html

[3] Live Science, TechMedia Network (2013, July 15). What is the vomit comet, Retrieved from http://www.livescience.com/29182‐what‐is‐the‐vomit‐comet.html [4] Microgravity.com (2013, July 15), Retrieved from http://www.microgravity.com/tutorial‐duration.html [5] NASA Zero G Research Facility (2008, January 23), Retrieved from http://facilities.grc.nasa.gov/zerog/ [6] Boehm, K. J., (2013, June 2), Analysis, concept, design and operations of a two‐second high quality micro gravity drop tower facility, (pp. 36‐38). [7] National Aeronautics and Space Administration, Microgravity, a teacher’s guide with activities, in science, mathematics, and technology, Retrieved from http://www.nasa.gov/pdf/62474main_Microgravity_Teachers_Guide.pdf

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