McMaster Experimental Reduced Gravity Team (MERGE)

About MERGE

The McMaster Experimental Reduced Gravity Team (MERGE), is a student led research group focused on studying the effects of sloshing that occurs during satellite refueling in microgravity. The team first began in 2018 and was a part of the Canadian Reduced Gravity Experiment (CAN-SBX), hosted by SEDS-Canada, the Canadian Space Agency (CSA) and the National Research Council (NRC). This past year the team was offered an individually funded flight by the CSA and NRC, to allow the team to re-fly the experiment with updates on the NRC Falcon 20 research aircraft.

About my Role

The MERGE team at our second flight campaign in January 2021

I have been the Team Lead of MERGE since April 2020. Over the past few years, I have been able to lead MERGE through a second flight campaign to test our research in reduced gravity, process the data, and communicate our results in two research papers. Through this team, I have been able to gain invaluable skills, from project management, leadership, to hands-on technical skills to develop my software and electrical knowledge.

The McMaster Experimental Reduced Gravity Team (MERGE) had the opportunity to conduct experiments in a reduced gravity environment over two different flight campaigns. The purpose of our research is to understand how fluid sloshing develops on orbit. Fluid slosh is a phenomenon in which fluid acts irregularly when pumped into an empty container. This irregularity of motion can have serious implications in a space environment, and it can occur when a satellite is being refueled on orbit.

Two analogue fluids to common spacecraft propellant were tested in a microgravity environment in our experimental test setup. The experimental test setup consisted of three analogue test chambers, two of which were fitted with custom slat screens, and one test chamber had no slat screens in order to act as a control. Under the microgravity conditions, aboard a research aircraft equipped to pull microgravity parabolas, the test chambers were pumped with the analogue fluids. The fluids movement when being pumped into the test chambers were then captured using a camera inside of the tank.

The first set of experiments tested water’s development of fluid slosh in the microgravity environment. The second set of experiments tested how FC-72 did the same. Video footage was captured for each of the flight campaigns, and required post-processing to understand the fluid sloshing results. This document will go over the challenges associated with each fluid that required design decisions when collecting data from each flight campaign, and lessons learned. It will also introduce the methods for processing each set of data.

About the Research

This is an image made to show the objects in Earth's orbit that are currently being tracked

The importance of this research is focused around the issue of space debris. Most satellites that are in orbit and run out of fuel are decommissioned despite having all onboard systems working properly. One option for decommissioning a satellite is to use the last bit of fuel to slow the satellite down and bring it back into orbit so that the satellite can burn up in the atmosphere. The other option is to push the satellite even farther away from Earth using the last of the satellite fuel. These solutions do not always solve the greater issue of technological waste, and space debris which can be hazardous to working satellites and spacecrafts.

A more favorable option would be to refuel the satellite and extend it's lifetime, to prevent unnecessary waste. Our research is focused on what occurs when a satellite is being refueled by another in a zero gravity environment. Currently there is a lack of research into the fluid mechanics of propellent transfer that occurs during in orbit refueling. This requires an understanding of how fluid slosh develops inside the fuel tanks and general guidelines for designing tanks that mitigate the sloshing effect.

Technical Development

Electrical Contributions

On the team I have been able to work on the electrical changes to the experiment from the previous campaign. The largest electrical change was the addition of accelerometers on each of the test chambers and inside of the electronics case. These were added in order to measure the acceleration of motion of the structure. I was also able to make an updated electrical schematic.

As the co-team lead, I have been responsible for the documentation for progress presentations and presenting to the CSA and NRC. It has been rewarding to receive feedback and guidance on our research design!

Electrical Schematic of the Experiment

The components I worked on were updating parts of the sensor package, particularly the load cells and flow sensors to get a better read on the forces acting on each test chamber throughout the experiment. This required me to understand the available sensors available on the market, and the best ones we could use for our research purposes that were also in our budget. The sensors we went with fit our budget and were easily integratable into our design. Unfortunately after the flight campaign we found out that the sensors were not able to read the force measurements as expected, therefore we could not garner much useful information from them. With a larger budget a more expensive sensor package can be purchased to improve upon the design and allow us to better understand the forces acting on each test chamber.

Software Contributions

The main design consideration for this project was to subject these analogue fluids to the refueling process under microgravity conditions, and then verify the results using computer vision (CV) software to understand the fluids behavior. In order to use the flight data to apply computer vision software, the fluid motion must be clearly distinguishable. Both Water and FC-72 are clear fluids however, so adjustments were needed. Furthermore, the video footage from these experiments were analyzed using Python and OpenCV, in order to track the fluid’s movement. The main analysis point I will be describing here is how the video footage was processed to get the fluid bitmask, a vital component in tracking each fluids motion in the test chambers under microgravity conditions.

Example of a test chamber with water and its corresponding bitmask

In the case of water, the easiest solution was to simply dye the water a distinguishable color. For the first flight campaign the water was dyed red and so the video footage could then be processed (as seen in Fig 2). In order to process this data, a bitmask was created which was able to identify the water in the test chamber, as it identified pixels with hues in the dye’s color range. A bitmask is typically a binary array that has the same dimensions as the image, where each element of the array corresponds to a pixel in the image. Each element of the bitmask can either be a 1 or a 0, where a 1 indicates that the corresponding pixel should be selected or identified, and a 0 indicates that the corresponding pixel should not be selected. Then the video’s color space was changed from RGD to HSV, to make the pixel detection more sensitive.

In the case of FC-72, due to the fluid’s inert properties, the simple solution of dying the fluid was not possible. Thus a more creative design decision was needed. The fluid could not just be left as is, or else it would be difficult to distinguish from the surroundings due to the lighting in the experiment’s case. The design decision made was to use a color gradient background behind the three test chambers (as seen in Fig 4). Due to the color gradient background, when FC-72 was present in the test chamber, the colored light from the gradient would be refracted from behind the test chamber, which would then change the color of a given pixel. So the footage of the test chamber with FC-72 in motion could then be compared to a reference frame, of a test chamber without any FC-72, to identify the pixels in which the fluid was present. This then allowed for the generation of the bitmasks for this fluid.

Example of a test chamber with water and its corresponding bitmask

This project required specific software design decisions to be made. Due to limitations with each of the anaologue fluids tested under microgravity conditions, clever solutions prior to the campaigns had be adopted for each flight campaign, so that data can be processed. Due to these design decisions made ahead of the time, the software processing for each flight campaign had to be different, with a similar principle to detect the pixels of fluid above specific thresholds, to indicate if the slat screens being tested actually impacted the sloshing of each analogue fluid. The statistics was primarily handled by a different group member. From viewing the statistics, we found that the bubble formation in the FC-72 data actually posed a challenge in analyzing, since it was difficult to detect and there is no explanation for this bubble formation to occur in microgravity conditions. Future work would benefit from better understanding the bubble formation for FC-72 under microgravity conditions.

Dyed water in the experimental setup under microgravity conditions, at different times in the parabola

FC-72 in front of the colored gradient background under microgravity conditions, at different times in the parabola

This is a diagram showing the experiment operation during the parabolic flight

Flight Campaigns

The previous flight campaign for the MERGE Team was in 2018 for the CAN-RGX Challenge hosted by SEDS-Canada, the CSA, and the NRC. More information about that flight campaign can be found here: MERGE 2018 Flight Campaign

The CSA and NRC have funded an individual flight for MERGE this upcoming February to fly our experiment! I have been chosen alongside MERGE's previous team-lead, Michael Stramenga, to fly the experiment on the NRC Falcon 20. To learn more about the flight campaign, read our team's feature by the Faculty of Engineering at McMaster here!

Publications

The team published our research in the conference proceedings at the International Astronautical Congress in 2021. I was able to present our work virtually alongside team member, Paula Bosca. The paper's abstract can be found here.

The team was also able to publish our research findings in the peer-reviewed Journal of Space Safety Engineering (JSSE) in July 2022, and the publication can be found here.

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