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Who Let the Gas Out? NASA Tank Venting Challenge

$30,000 USD
Entries Received:
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Participants need to fill out the Challenge Registration form before submitting the solution. Please refer to the Guidelines tab for more information.


As space travel extends to greater duration and distance, missions may require a propellant refill in space. To achieve this, spacecraft may require larger tanks and efficient refueling along with tanks that have the capability of isolating propellant from ullage fluid (a gas and vapor mixture) during a vent. The goal of this Challenge is to develop a novel solution for the venting of ullage contents from a partially full propellant tank, in microgravity, with minimal loss of propellant. This ullage venting solution would help allow the adjustment of pressure in the receiving tank prior to, during, and/or after the liquid propellant transfer.  
This Challenge is seeking solutions to propellant tank venting in micro-gravity with minimal loss of propellant. Although all concepts will be considered, solutions that are external to the propellant tank are preferred as they could use existing (heritage) propellant tanks and avoid development costs related to designing and qualifying a new (or modified) tank.  

If you can solve this Challenge, submit a complete concept design of your tank venting solution and you could win your share of the $80,000 (USD) purse. 


On Earth, liquid propellant tanks typically (and easily with the assistance of gravity) allow receiver tank venting. To enable a high mass fill fraction and a timely liquid fluid transfer in space, there must be a way to vent residual gas from the receiver tank in microgravity with a minimal loss of liquid propellant in the process. Fluid surface tension properties will dominate in large vessels/tanks when a fluid transfer is performed in low or zero gravity, resulting in somewhat unpredictable fluid (particularly liquid) distribution within the tank; therefore, it may be difficult to separate liquid from gas. Additionally, direct venting to space could alter the velocity of the spacecraft or generate undesirable stress on or contamination of components. Controlled propellant tank venting in space is historically rare but may be required for future missions where an in-space propellant transfer is needed. These future examples may include long duration missions to the Moon, Mars, and beyond, or operations to repurpose or extend the mission life of satellites or observatories.  
At present, there is no viable, efficient, multi-use, reasonably sized solution for venting propellant tanks that are non-bladder or diaphragm type. As some of the fluids (such as nitrogen tetroxide) being transferred are extremely corrosive and damaging, there does not exist an elastomeric material approved for long term life cycle use. Moreover, a metal bellows type tank solution is not a viable option because of quantity transfer limits, reusability (material fatigue), and tank sizing design challenges. A recent NASA project opted to perform mission operations for refueling without venting, relying instead on a larger tank volume and a lower propellant fill fraction. A negative consequence of this design is a progressive decline in thruster performance as the propellant tanks are drained and depressurized with propellant consumption through the thrusters. Also, the non-optimal refill Concept of Operations (ConOps) leads to a higher technical risk to the hardware since the tank would be compressed as it is filled, thus potentially heating the ullage pneumatic gas to near the system upper thermal limits. To address this, the project team developed a refueling ConOps solution that required multiple heating and cool down cycles to transfer propellant. This was not an optimal solution, due to its inherent complexity, fueling duration, and, as mentioned above, gradually decreasing efficiency of thruster performance, but it did allow the design of the system to meet the mission schedule and budget constraints. Future missions with larger tanks and/or more rapid transfer timelines will need a better solution. NASA anticipates that the winning Challenge solutions will include a gas venting capability that avoids loss of liquid and does not require any major increase in spacecraft mass, size, or performance. Moreover, they will not introduce greater technical risk of possibly exceeding current propellant tank thermal qualification limits. 
Developing an effective venting solution could result in higher propellant transfer efficiency, improve safety, reduce task duration, increase mission life cycle usage durations, and decrease operational and system complexity. This capability will increase the operational capabilities of  NASA, DoD, and commercial spacecraft allowing mission operators to complete long distance, duration, or unplanned repurposing of missions with increased confidence. Winning solutions may be considered for continued support to advance the concepts using existing NASA programs such as The Space Technology Research Grants (STRG) Program. 


In an ideal space fluid transfer system, the primary goal would be to transfer liquid propellant from one tank to another using a motive force (e.g. pump or other similar process) and achieve the maximum propellant fill level of approximately ​​​​95% by volume with the lowest risk and in the shortest time. The transfer would be performed with the two tanks connected to each other (ullage and propellant) as shown in the image attached (in Files tab). Pressure levels would be regulated to desired flowrate parameters between the tanks via this receiver vent while the liquid propellant flows from one to the other over an approximate period of hours to days depending on mission requirements and volumes being transferred. A vent would also be required in other (non-ideal) scenarios in which the receiving propellant tank is depressurized (vented to space) prior to (or after) the propellant refill. 
Important project assumptions and items to note:
The tanks do not store cryogenic fluids. The fluids of interest are in a liquid phase, maintained while in storage with spacecraft thermal control at approximately room temperature (20° +/- 5° C). Examples include hydrazine, monomethyl-hydrazine, nitrogen tetroxide, anhydrous ammonia, ASCENT, and water. These fluids are currently the most commonly used for space propulsion and thermal control. Future space missions may include cryogenic propulsion systems, but those fluids should not be considered for this study.
The tanks are in a micro-gravity environment. Spinning spacecraft ConOps and active spacecraft thrust vector control of the fluid within tanks in preparation for and during transfer should not be considered for this study.
No outside forces or moments may be imparted on the spacecraft or on the tanks to force the fluid in one direction; however, a localized (smaller scale) force/acceleration using a component external to the tank may be considered. The spacecraft or propellant tank cannot be accelerated. Typically, propellant transfers in space require that the spacecraft is not rotating so that it can remain in a thermally stable configuration.
The tanks have direct interaction between the ullage gas and the liquid and do not include an internal bellows or diaphragm. Tank venting from bellows or diaphragm style tanks has already been solved. Not all highly corrosive commodities such as nitrogen tetroxide oxidizer (NTO) have flexible long term reusable elastomeric materials available, and a bellows system has limitations on percentage capability of transfer and life-cycle reusability. See:
Less than 5% liquid ingestion by volume into the gas/vapor stream being expelled from a tank while venting is allowed. Ideally, 0% ingestion is preferred, but it is understood that some residual liquid amounts entering the vent may be inevitable depending on the solution design.
An example of 5% liquid ingestion to vent space: Suppose that, prior to venting, a tank holds 100 gallons of liquid. After venting, 5 gallons of liquid or less are “lost” to the vent resulting in a remaining amount of 95 to 100 gallons of liquid in the tank.

Solution Requirements

meet or exceed the threshold requirements for the key performance parameters (KPPs). Note: if the threshold of a KPP cannot be achieved, you must provide an explanation or rationale for any minor deviations and any potential solutions or enhancements. You will receive 0 points for that KPP and your solution may be considered for judging (% of points allocated) at the Judges’ discretion based on your explanation / rationale and suggested solutions or enhancements.
be able to withstand the very harsh corrosive environment of exposure to NTO, monomethyl hydrazine (MMH), hydrazine, or anhydrous ammonia throughout a long mission life (defined here as 15+ years).
not impose safety risks such as potential electrical sparks (if the device is electronic in nature) that could ignite a fuel such as hydrazine or MMH.
be able to withstand the harsh environment (radiation, vacuum, thermal, etc.) of space.
be able to withstand the vibration environment of a launch.
should not be something that has already been​​ tried such as European patent No. EP3296216 from 2016. However, a proposed solution could be an improvement, variation of, or enhancement of any alternative type of prior efforts that are formally cited / referenced.

Challenge Schedule

Challenge Launch
October 11, 2023
Challenge Close
February 22, 2024, 5:00 PM Eastern Time (EST)
April 9, 2024

Other supporting documents 

Q&A Tracker - link

Webinar recording


Please submit your questions in the challenge Clarification Board or via email at:
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Skills Required

Aeronautical Engineering
Aerospace Engineering
Aircraft Performance
Aircraft Propulsion
Aircraft Structures
Aircraft Systems
Computational Fluid Dynamics
Control System Design
Materials Engineering
Materials Science
Mechanical Engineering

Accepted File Formats


Clarification Board
No spam, self-promotion or advertisement is permitted.

User Avatar
Dennis David S.
1 month ago
Congratulations to the winners! Sure I’m a little bummed that my PorousCentrifuge Gas Separator was not a winner but thanks to NASA and Freelancer for the AWESOME contest!
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Georgios P.
3 months ago
I want to submit my idea half an hour ago how can I?
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Ross Daryl P.
3 months ago
Hi, can I get a quick clarification if whether Ukrainians are under the OFAC Sanctions? My team representative is a Ukrainian would he be allowed as the Team Lead?
3 months ago
Hello, My friend is trying to register us a team. He is a citizen from an eligible country and resides in a non-eligible country . The system wont let him register. How would he go about registering?
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Khadija Tul Z.
3 months ago
Hi If Pakistan available for the contest?
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Tutkucan A.
3 months ago
Hi is Türkiye eligible for the contest?
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Jeffrey M.
3 months ago
Can team submit more than one entry?
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Nattakit J.
4 months ago
Hi is Thailand eligible for the contest?
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Yamnat I.
4 months ago
Dear contest holder, I've a concrete idea for the project but I find it impossible to draw the required pictures like drawings, diagrams, etc. This is because I've never drawn anything. If in my submission I submit only descriptions of the drawings and diagrams, will my submission be considered??? PLEASE REPLY
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Manish S.
4 months ago
Hi is Singapore / Australia eligible for this contest ?

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