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2020 Drop Tower Challenge

Paddle Wheel in Microgravity

The Challenge

What is the Challenge?

Teams of grade 9-12 students are challenged to design and build an experiment related to water motion that will be tested in a NASA microgravity research facility.

What forms do I need to apply?

Challenge Overview


Future Long-duration space missions will require a better understanding of fluid behavior in microgravity. Surface geometry and thin films or coatings can impact how liquids behave on surfaces by either repelling or attracting the fluid. In some cases, the right design can lead to objects that move on their own when placed in microgravity! A simple way to demonstrate this is with a paddle wheel that is attracts water on the front, while repels water on the rear of each fin blade. “Superhydrophobic” (water-fearing) and “superhydrophilic” (water-loving) surfaces or coatings can be used to achieve a self-propelled paddle wheel.


Teams of grade 9-12 students are challenged to design and build objects focused on generating mechanical motion utilizing only fluid forces. In theory, the paddle wheel, or spinner, that the students will be designing should rotate on its own during free fall while sitting on a body of water. Objects from the selected teams will experience microgravity in NASA’s 2.2 Second Drop Tower. NASA will then invite the top-performing teams to present their results in a student poster session at the 2020 meeting of the American Society for Gravitational and Space Research (ASGSR) for which the location has yet to be announced.


The design challenge is for students in grades 9-12, where teams will be favored over individuals in selection. The program is limited to students from the United States and citizenship is not required. It is open to students in the fifty states, the District of Columbia, Puerto Rico, American Samoa, Guam, the Northern Mariana Islands, the U.S. Virgin Islands, and (for the children of U.S. military personnel) all DODEA schools. Students are free to get help from adults, for example, in building their test objects. An organization (e.g., school, science center, 4-H club, or Scout troop) may submit no more than four proposals, where it is envisioned that no more than two teams will be selected from a single organization. A student may only be a member of one team.


After proposal evaluation, NASA anticipates selecting up to 20 teams to build objects to be tested in the 2.2 Second Drop Tower at the NASA Glenn Research Center in Cleveland, Ohio. Some preference will be given to teams local to the fall 2020 ASGSR conference site (e.g., within 150 miles), although its location has yet to be announced. Only a small number of top-performing teams will be invited to participate in the conference.

A. Things to Know

Key Rules

• Proposals: No more than 4 proposals will be accepted per organization (e.g., school, science center, 4-H club, or Scout troop). No more than one proposal. will be accepted from one team.

• Selection: It is envisioned that no more than two proposals will be selected from a single organization.”

• Team: Teams can be of any size, but each student can only be on one team. Each team is required to have an adult advisor, who may advise multiple teams.

• Number: Each team may include up to 4 objects in their proposal and if selected for testing may submit up to 4 objects for that purpose. Note that each drop tower operation will include two of the team’s objects, each in an independent container.

• Size: The size of a team’s object must be within a 75 mm diameter cylinder that is no more than 80 mm wide and is centered on the NASA-provided axle.

• Prohibited materials: fragile materials (e.g., glass), hazardous materials (e.g., that are corrosive, toxic, and/or radioactive), materials or coatings that dissolve in or react with water, small creatures (whether dead or alive), most biological materials


Conduct your own microgravity trials: Consider putting trial objects with water in a plastic jar mounted in a box with a video camera and dropping the box to get a glimpse of what happens in microgravity. Just a 4-foot fall provides a half second of microgravity, which can provide a hint of what will happen in the 79-foot fall in NASA’s 2.2 Second Drop Tower. For inspiration on conducting your own drop research, check out the Fire in Free Fall video by Physics Girl Dianna Cowern. Control and Variables: You should ideally have two or three different objects for testing so that you can compare the performance of each object in your report – and poster too if you are selected for ASGSR meeting participation. An added benefit is the increased probability of success with the challenge.


While coatings may specify that they are hydrophilic or hydrophobic, it doesn’t guarantee that they will bond/adhere to their object. Therefore, make sure the coating is compatible with the material of your objects. Some coatings have other requirements for adhesion, namely minimum cure times and cure temperatures. Be sure read the directions.

Timing is important

Late submissions to NASA of the test objects will disqualify teams from the competition. Late final reports will disqualify teams from being selected to participate in the ASGSR conference, so don’t wait until the deadlines to complete tasks.

Selection Criteria for ASGSR Meeting Participation

Teams will be graded for each object dropped based on the following:

1. Performance during testing in the 2.2 Second Drop Tower
2. Team’s Analysis
3. Team’s Final report

Failure to submit a final report by the deadline will disqualify a team from being selected to go to ASGSR.

B. What To Do

There are four phases to participating in the challenge

1. Prepare your proposal – open to all eligible students

2. Develop & self-test your test object(s) – if the team’s proposed project is selected for testing

3. Analyze & document the results – generally after the NASA microgravity testing and can include the self-test results

4. Prepare and present a poster at the 2020 ASGSR conference – if invited to participate based on the challenge performance and submitted report

Each phase is separated by a submission to NASA and subsequent phases rely on the earlier ones for continued participation. The proposal is used to determine whether a team will continue to phase 2, and the objects must be submitted for testing to enable phase 3. Finally, the test performance and written report will both be used to determine which teams are invited to present their results in the student poster session at the ASGSR conference (phase 4).

1. Prepare your proposal

1.1 Understand the challenge

The goal for Paddle Wheel in Microgravity is to design and build objects focused on generating mechanical motion resulting only from fluid forces In theory, the paddle wheel, or spinner, that the students will be designing should rotate, on its own during free fall while sitting on a body of water. Therefore, the surfaces on your paddle wheel or spinner may play a role in its behavior. Think about how a hydrophobic or hydrophilic (i.e. “water fearing” or “water loving”) surface can affect your object. For example, during free fall, objects with “water fearing” surfaces can be pushed from the water. That was the goal of the previous Drop Tower challenge
called Microgravity Expulsion from Water where students were asked to use hydrophobic properties to push objects out of the water under microgravity conditions.

When an object is floating on water in normal gravity, an upward force is exerted by water that opposes the weight of the less dense object. However, in microgravity, there is effectively no “weight” and the interaction between the object and the water is governed by the contact angle or wettability of the object by the water.

Provided axle: For this challenge, teams selected to participate will be provided an axle to use as a guide for their paddle wheel or spinner. This axle is a plastic rod with an “X” cross-section that is 4 mm x 4 mm. The axle is also 90 mm long. The paddle wheel or spinner must be designed to accommodate this axle as the axle will be used to position the teams’ paddle wheel or spinner in the drop tower container.

Scoring: An object’s score will be based on the number of degrees the paddle wheel or spinner rotates about the axle during the 2.2 seconds of microgravity during the drop operations.

1.2 Watch videos of hydrophobic and hydrophilic objects

The expulsion of an object floating in microgravity can be seen in a video at The video is courtesy of researchers at Oregon’s Portland State University (PSU). As can be seen, the ball ‘jumps’ out of the water in microgravity. Please know that the challenge staff will not share the hydrophobic treatment of the ball in this video. We are looking for participating teams to research and find their own approaches to the challenge rather than copy what was done in the video.

The video at Ping Pong Ball On Water shows the response of a floating hydrophilic object to free fall, where it can be seen to dive into the water. It was from an experiment created by a middle school team for a previous drop tower competition.

1.3 Develop your test object(s)

Design – Based on your research, design your test object(s) using the guidelines below to achieve the highest score as described in the previous section. Note that NASA will provide the rest of the experiment hardware including the water, the water containers in which your objects will be tested (with one object per container), the video camera, and lighting.

Number – Each selected team can submit up to four different objects for testing. This allows a team to compare test results, e.g., in the required report and – if invited – at the ASGSR conference. Of course, at least one test object must be proposed and, assuming selection, built and shipped to NASA for testing.

Materials – The objects must be fabricated from material such as plastic, 3D printed materials, etc. Glass and similarly frangible materials are unacceptable. Water-soluble materials and coatings are prohibited, as are materials and coatings which chemically react with water. For safety reasons, corrosive, toxic, and radioactive materials are prohibited. Other hazards such as sharp edges, compressed gases, batteries, and lasers are not allowed. Small creatures (such as insects), are not allowed, whether they are dead or alive. Other biological samples, such as foods, are generally not allowed. Common organic materials such as wood, cork, cotton, wool, and leather are allowed exceptions.

Containers – Each of the team’s objects will be tested in its own container of water. The vessel’s interior is a rectangular prism which is 220 mm (8.5 in) long, 90 mm (3.5 in) wide, and 90 mm (3.5 in) tall (i.e., where the cross-section is square). Each of the team’s objects will be placed alone inside a container with the center of the axle at a height of 40 mm (1.6 in) above the container floor. The team must specify the level of water for each object. This may be done by stating (a) the depth of water to be put in the container or (b) where on their object the water surface should be located.

Please note that that some jostling will occur as the drop package is transported to the top of the drop tower, so this should be considered in the design of your objects.

Size – As shown in the figure, the size of each of the team’s objects must fit within a cylinder centered on the NASA-provided axle with a diameter of no more than 75 mm and a width no more than 80 mm.

No external force – During the microgravity period, only the motion of the water and the effect of any coating can move the team’s object in the water. No external devices can be used to artificially move the object.

1.4 Prepare and submit your proposal

Prepare your proposal using the entry form in Appendix A or from the Paddle Wheel in Microgravity website. The proposal shall include information about your team plus descriptions and depictions of your test object(s). Each proposal shall consist of a single file, in either DOC or PDF formats, into which all figures must be included. The file must be less than 10 MB in size or it will not be received by the challenge staff. The proposal should be sent via e-mail to Ed- so it arrives no later than the deadline listed in the Calendar. The proposals will be reviewed and selections will be announced via email to all proposers by mid-December. Teams who have been selected for testing will continue to the next phase.

2. Build your test object(s)

Assuming that your team’s proposal is selected, design and build your test object(s) following the rules in the development section (1.3) of this guide. Also review the key rules and hints as you design your test object. It is acceptable to change your design(s), e.g., based on research conducted after your proposal submission. But you are strongly encouraged to check with to ensure that the new design(s) are acceptable. Note that you may want to make extra copies of your test objects to keep because the objects sent to NASA will not be returned.

It is highly recommended that you conduct your own microgravity trials. Consider putting trial objects with water in a plastic jar or container and dropping the jar and a video camera in a box to get a glimpse of what happens in microgravity. Just a 4-foot fall provides 0.5 seconds of microgravity, which can provide a hint of what will happen in the 79-foot fall in NASA’s 2.2 Second Drop Tower. For inspiration on conducting your own drop research, check out the Fire in Free Fall video by Physics Girl Dianna Cowern.

Once your object(s) are ready, ship your test object(s), with appropriate care in packing, to the following address. The object(s) must arrive at NASA no later than the deadline in the Calendar.

Paddle Wheel c/o Nancy R. Hall
NASA Glenn Research Center
21000 Brookpark Road, MS 77-7
Cleveland, OH 44135

Late objects will be disqualified from the competition!

3. Analyze & document the results

3.1 Draft written report

Report writing can and ideally should begin after your team’s proposal has been selected for testing. Even before your test object(s) are completed and the microgravity test conducted, your team can begin writing an introduction based on nwhat you’ve learned in preparing your proposal and from any preliminary tests performed by your team. References can also be documented. You can also draft the section describing your experiment once the design of your test object(s) has been finalized. But of course, you’ll need to wait until the tests have been conducted to write the results, discussion, and conclusions. Furthermore, the abstract should be the last section of your paper to be written.

There is no required format for the written report, but it is suggested that teams generally follow the guidance found in “A Guide to Writing a Scientific Paper: A Focus on High School Through Graduate Level Student Research” by Renee A. Hesselbach et al.

3.2 Analyze results

NASA’s goal is to electronically provide the test data to each team within two weeks of their tests and by at least March 15. The objects will be tested in the order they are received at NASA. For each test, the data will consist of a video filmed at 30 frames per second showing the objects’ motion during the drop tests and still images taken during processing of the team’s objects.

One option for analyzing the video results is through NASA’s Spotlight software. For Macintosh computers, use Spotlight-8. For Windows computers, use Spotlight-16. Many NASA researchers are now instead using ImageJ, which is freely available from the National Institute of Health (NIH). Meanwhile, the free Tracker software is shared by Open Source Physics as a tool for “physics teaching and student activities.” The Tracker software has notably been used by some participants in past drop tower challenges.

Position measurements can also be made with simple graphic software that continually reveals the position of the cursor. Simply load an image, move the cursor to each desired position and write down their values (i.e., by hand). Repeat with successive video frames to track positions as a function of time. Microsoft Paint is an example of such software, where it reveals the position of the cross-hairs in the nbottom left of the window (in pixels and relative to the image).

Measurements can also be made manually by taping a transparent overlay to your computer monitor and marking the positions using a permanent marker. You can make measurements for multiple images (i.e., times) using the same transparency, where it may be helpful to mark each position with the image number (or time). Please understand that these are just suggestions and are not meant to indicate endorsements by NASA or the federal government.

3.3 Complete and submit written report

Using the results from the testing and your analyses, complete your written report (e.g., as described in section 3.1) and e-mail it to by the deadline listed in the Calendar.

4.0 Presentation at ASGSR Conference

4.1 present at the 2020 ASGSR conference

Based on their scores and written reports, some teams will be invited in mid-May to present their results in a student session at this annual meeting. All participating teams will be contacted by e-mail about the selections.

The meeting dates and location have not yet been announced, but it is expected that the conference will be held in October or November with the student day on a Saturday. Admission will be free on that day for a limited number of students who present their posters at the conference, as well as accompanying advisors and chaperones. The free admission does not include meals or participation in the evening banquet, although tickets may be purchased for the latter.

It is tentatively expected that financial support will be made available to help invited non-local teams travel to the conference for this purpose. That anticipated travel support is unlikely to cover the full cost of the trip, so teams will need to take action to address the likely shortfall. The travel support will likely be up to $500 per student presenting at the conference.

Awards will be presented to teams on the student day based on their posters and success with the challenge. The conference will also include opportunities for students to tour the exhibit hall, attend research presentations, and interact with microgravity researchers and other students.

FAQs – Frequently Asked Questions

Q: How are microgravity conditions created?
A: During its fall in NASA’s 2.2 Second Drop Tower, each object behaves as if there is no gravity, just as if it were in orbit on the International Space Station (ISS). Our sensation of gravity and weight comes from a resistance to its pull, for example because of the floor preventing us from falling. If we are freely falling (e.g., after jumping off a diving board), we feel weightless and free fall is the basis for many amusement park rides. This occurs because all objects fall at the same acceleration unless acted upon by another force. As one result, the astronauts and the ISS fall together (around the Earth) such that the astronauts float within the space station. This happens even though the space station is so close to the Earth that the gravity is only about 10% less than that at the Earth’s surface.

Q: Can home schools participate?
A: Yes, where teams don’t need to be affiliated with a school at all and can be formed from any group of youth in grades 9-12 including siblings, neighbors, and friends as a few examples. But note that preference in proposal selection will be given to teams over individual participants.

Q: Does the number of objects proposed affect the odds of selection?
A: Preference will be given to plans with two or more objects because their results can be compared. Keep in mind that each team is limited to a maximum of four test objects.

Q: Where do we get the entry form?
A: An entry form can be found in Appendix or on the Paddle Wheel in Microgravity website

Q: What file formats are acceptable for the proposals?
A: The proposals must be submitted as either DOC or PDF files. Teams submitting their proposals in other file formats risk rejection.

Q: Are drawings required for the proposals?
A: Yes; each proposal must include both descriptions and drawing(s) of each test object(s). The drawing(s) must be included in the proposal, so the proposal will consist of a single file.

Q: What is the maximum file size for the proposals?
A: Each proposal’s file must be less than 10 MB or it will not be deliverable to the challenge staff.

Q: Can we build test object(s) using a 3-D printer?
A: Yes.

Q: Can we simply buy test object(s)?
A: Yes.

Q: Do we get our test object(s) back?
A: No

Q: Is the water used in the drop tests distilled, de-ionized, etc.?
A: It is simply tap water at room temperature

Q: Can a team submit more than one proposal?
A: No, because a student cannot be part of more than one team. However, your organization (e.g., school, Scout troop, club, etc.) can submit up to four proposals.


If you can’t find the information you need at the challenge website, or, then e-mail

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