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2021 Drop Tower Challenge

Droplet Ejection


Teams of grade 9-12 students are challenged to design and build simple devices using capillary flow (only) to eject water droplets as far as possible while the devices fall down NASA’s 2.2 Second Drop Tower.

Teams are only responsible for their capillary devices. NASA will provide the rest of the experimental hardware. After developing their concept(s), the youth prepare their proposal, consisting of conceptual drawing(s) and a short entry form, which is then e-mailed to  Note that this is different from a past challenge that used silicone oil as the test fluid.

If selected, the team prepares their capillary devices based on information provided on the challenge website.  The devices are then sent to NASA where they will fall 24 meters (79 feet) and experience 2.2 seconds of apparent near weightlessness, i.e., microgravity.  Video results will then be provided for student analysis and reporting.

What forms do I need to apply?

Challenge Overview


The odds are very high that your team will be selected for testing.  Thus far, 100% of the proposing teams have been selected for participation in this series of problem-based drop tower challenges.  Participation in a nation-wide NASA challenge might be a good addition to college applications.


This design challenge is for students in grades 9-12 from U.S. schools, including the fifty states, District of Columbia, Puerto Rico, American Samoa, Guam, the Northern Mariana Islands, the U.S. Virgin Islands, and all DODEA schools (which are for children of U.S. military personnel).  With the exception of the DODEA schools, it is not open to participants outside of the United States regardless of citizenship.  Teams, which can be of any size, will be favored over individuals in selection.  Students may get help from adults, for example in building their experiment hardware.

An organization (e.g., school, science center, 4H club, Scout troop) may submit no more than four proposals, where it is envisioned that no more than two will be selected from a single organization.  Each student may belong to only one team, which may submit only one proposal.


asgsr logoNASA anticipates selecting up to 20 teams to build objects to be tested at the Glenn Research Center in Cleveland, Ohio. After evaluation of the experimental results and teams’ reports, a small number of top-performing teams will be invited to present their results in a student poster session at the 2021 meeting of the American Society for Gravitational and Space Research (ASGSR).


2.2 Second Drop TowerChallenge participation is remote and participants do not travel to NASA for the testing.  But top-performing teams will be invited to present their results at the 2021 ASGSR meeting, which is to be held in Baltimore, Maryland.


There is no cost to participate in the challenge other than for the (1) preparation of the test objects, (2) shipment of the test objects to NASA, and (3) travel costs for those invited to present their results at the ASGSR meeting.  Regarding the latter, the ASGSR has often provided travel support of $500 each for invited non-local students who present their results at the conference.

Things to Know


Now                          open for proposals

Nov. 10, 2020         deadline for e-mail submission of proposals to NASA

Mid-December       teams selected for testing announced by NASA

Dec.-February       preparation of test objects

Feb. 15, 2021         deadline for objects to arrive at NASA

Feb.-March             objects tested in NASA’s 2.2 Second Drop Tower

May 1, 2021            written report due to NASA

Mid-May                   teams selected for ASGSR participation announced by NASA

Fall 2021                 annual ASGSR meeting (presumably in Oct. or Nov.)

It is possible that the COVID-19 pandemic may delay testing and subsequent activities, where the challenge staff will notify selected teams of any schedule changes.

Key Rules

Selection Criteria for ASGRS Conference

Teams will be evaluated 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 for ASGSR participation regardless of their test performance!

What To Do

There are four phases to participating in the challenge:

      1. prepare your proposal – open to all eligible
      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, but some draft text can be written during the second phase
      4. present at the 2021 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 in order to have results to analyze and write about in 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 2021 ASGSR conference (phase 4).

1. Prepare your proposal

1.1  Understand the challenge

The goal is to design and build an object which will cause water droplets, to be spontaneously ejected upward as far as possible due to capillary forces (only) when they enter microgravity conditions.

Scoring: An object’s score will be calculated based on the vertical distance travelled by the ejected droplet(s).  If water is not ejected from the nozzle, the vertical distance travelled inside the nozzle will be used (although there will be a point penalty for no ejection).  For this reason, we recommend making your nozzles out of a clear or translucent material so that the water rise can be observed.  If your nozzle is opaque, you won’t earn any points if the water isn’t ejected.  In case of a tie, the winner will be  the team with the largest droplet ejected.  If there is still a tie, the team with the most droplets ejected will be the winner.

Capillary action occurs when the attraction between the liquid and the surface (adhesion) is stronger than the the liquid’s attraction to itself (cohesion).  The adhesion/cohesion balance affects how liquids interact with a surface and can cause the liquid to move, for example when the force of gravity seems to disappear.  [Recall, that motion (or a change in motion) occurs when forces are not balanced.]  The geometry of the surface, including both the shape and dimensions, can influence the resulting motion.

A surface’s properties can also affect liquid interactions, where their influence can be particularly strong in microgravity.  Surfaces can be either hydrophobic or hydrophilic, that is ‘water fearing’ or ‘water loving.’  As an extreme example, the leaves of the Lotus flower have a superhydrophobic surface where researchers are working to mimic the Lotus effect.

1.2  Watch video of droplet ejection

Droplet ejection in microgravity can be seen in the video clip at Please know that the challenge staff will not share additional details of how the spontaneous capillarity-driven droplet ejection was achieved, as 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. Note that the referenced video used silicone oil, while this challenge uses water. These fluids have different properties that determine how each rises up a nozzle.

1.3  Develop your test object concepts

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 (which will tentatively be colored), the three 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 three different objects for testing. Using multiple objects allows a team to compare test results, for example in the required report and – if invited – at the 2021 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 should be fabricated from transparent material such as plastic or you risk a scoring loss as discussed in section 1.1.  Glass and similarly fragile materials are acceptable with proper packaging.  Coatings, if any, must also be transparent or you similarly risk a scoring loss.  Water-soluble materials and coatings are prohibited, as are materials and coatings which chemically react with water.  For safety, 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, but materials such as wood, cork, cotton, wool, and leather are allowed exceptions.

Droplet Ejection ContainersContainers – 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 210 mm (8.25 in) tall and 63 mm (2.4 in) across from left to right and front to back (i.e., where the cross-section is square).  Each of the team’s objects will be placed alone inside a container which will then be filled with water to a height of 100 mm (4.0 in).  The team may specify if a certain orientation is required for their object, e.g., in a drawing.  Three objects, each in a separate container, are typically tested during a single drop operation.

Size – The longest dimension of each object shall be no more than 60 mm (2.36 in) and no less than 40 mm (0.241.575 in).

Water Rise – In microgravity conditions, the water must rise because of the object’s capillary action associated with the objects’ shape and surface properties and must not rise because of other reasons, for example, mechanical pumps initiated during free fall.

1.4  Prepare and submit your proposal

Prepare your proposal using the entry form, shown in Appendix B which will be available online as a stand-alone document.  The proposal shall include information about your team plus descriptions and depictions of your test object(s).  It must be written in English and consist of a single file, in either doc or pdf formats, into which all figures must be ‘pasted.’ The file must be less than 10 MB in size or it will not be received by the challenge staff.  E-mail the proposal to by no later than Nov. 10, 2020.  More precisely, your proposal must be e-mailed to NASA by no later than midnight in your local time zone.  The proposals will be reviewed and selections will be announced via e-mail to all proposers by at least mid-December. Teams who’ve been selected for testing may continue to the next phase.

2.  Build your test object(s)

Assuming that your team is selected for participation in the testing, build your test object(s) following the rules in the design section (1.3) of this guide.  Make sure to review the key rules and hints as you design your test object.  It is acceptable to change your designs, e.g., based on research conducted after your proposal submission.  However you are strongly encouraged to check with to ensure that any new designs are acceptable.  Note that you may want to make extra copies of your test objects to keep because the objects sent to NASA won’t be returned.  For example, you could display them at your school or perhaps even the ASGSR conference.

It is highly recommended that you conduct your own microgravity trials: Consider putting trial objects with water in a plastic jar and dropping the jar in front of a video camera 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 objects are ready, package them to prevent breakage during shipping and injury to challenge staff.  Although a team’s objects should be shipped together in one box, each object should be packaged individually.  An object’s indivdual package can be as simple as a resealable plastic bag, but the package must be labeled (e.g., with a permanent marker) with the organization name, team or experiment name, and the nozzle number or other identifier.  An advisor with multiple teams may ship their objects together to NASA, making such labeling even more important.  But note that the shipment of more than three objects by a team is unacceptable even if more than three different nozzles were built.  Three is the ‘magic’ number and each team must chose no more than three objects to ship to NASA.

Ship the objects to the following address, where they must arrive at NASA by no later than February 15, 2021.

Droplet Ejection 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 and document your 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 what 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 (i.e., attempt at the challenge), 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.

While student names should not be included in your proposal, they should be included in your written report and on the poster as well if your team is invited to present at the ASGSR meeting.  Similary, identify your organization and where it is located, but just the city and state (for example) and not a full address.  This is where you should be recognized for your work!

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 April 1, with objects tested in the order received at NASA. However, please recognize that it is possible that testing and subsequent activities could be delayed as a result of the COVID-19 pandemic.  The challenge team will contact participating teams if this happens.

For each test, the data will consist of a video filmed at 30 frames per second showing the water motion during the drop tests, tentatively supplemented by still images taken from the video.

Tracker, which is shared by Open Source Physics as a tool for “physics teaching and student activities,” is a suggested way to make measurements of the droplet motion.   The Tracker software has notably been used by some participants in past drop tower challenges.  As an alternate, many of NASA’s microgravity researchers use ImageJ (from the National Institute of Health) or its ‘batteries included’ version called Fiji, which are both freely available for making such measurments.

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 bottom 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, complete your written report (e.g., as described in section 3.1) and e-mail it to by no later than May 1 2021, more specifically by midnight in your time zone.  Note that the report must be written in English.

4.  Present at the 2021 ASGSR Conference

Based on their performance in the drop testing and written reports, some teams will be invited in mid-May to present their results in a student poster 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. It is expected that 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 student-day 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 invited student presenting at the conference.

Additional awards will be presented to teams on the student day based on their poster presentation. 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; 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: Can teams from countries other than the United States participate?

A: No, unless your team is from a DODEA school for the children of U.S. military personnel.  Students from other schools outside of the USA are not eligible, even if they are U.S. citizens.

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 three test objects.

Q: Where do we get the entry form?


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: Can proposals or reports be submitted in a language other than English?

A: No.

Q: Are drawings required for the proposals?

A: Yes; your proposal must include descriptions and drawing(s) of each test object(s). The drawing(s) must be ‘pasted’ into the proposal, so that the proposal consists 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: Will 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 that will tentatively be dyed with food coloring to allow us to better see the fluid behavior.

Q: Can a team submit more than one proposal?

A: No, and a student can only be a member of one team so a student cannot be part of more than one proposal. However, your organization (e.g.,  school, Scout troop, club, etc.) can have as many as 5 teams submit proposals.


Answers can be found at  If that doesn’t suffice, email the challenge staff at

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