University students testing space technologies on ZERO-G aircraft
ORLANDO, Fla. — Students from three U.S. universities (the University of Florida, Carthage College, and the University of Maryland) have been using Zero Gravity Corporation’s microgravity Boeing 727-200 aircraft, dubbed “G-FORCE ONE”, to test useful space technologies. The testing work evaluated propellant management, chill-down, and thermal management hardware in microgravity.
Testing in microgravity on Earth
Zero Gravity Corporation (ZERO-G) has been providing commercial microgravity flights since 2004. While most of those flights have been flown to give private citizens the opportunity to experience microgravity through a series of 15 parabolic arcs, the company has also been making its aircraft available as an alternative to sending experiments into space.
Science flights on ZERO-G go through 25 reduced-gravity cycles, where the plane ascends from 24,000 to 32,000 feet (7,315 to 9,754 meters), then pushes over, dropping through the sky and giving the people and hardware aboard the sensation of reduced gravity. Imagine doing a science experiment aboard jet-powered roller coaster as it drops from its first big hill.
By testing aboard the aircraft, experimenters can run science experiments or hardware and be there to observe the results in real time. They also have the advantage of being able to get hands-on with their hardware in flight and get it back once the aircraft lands.
In the near future, companies like Virgin Galactic and Blue Origin also expect to conduct similar low-gravity science flights aboard the SpaceShipTwo and New Shepard rockets. Also, while ZERO-G doesn’t fly to the border of space, their modified Boeing 727-200 can provide longer periods of low-g: 20 to 30 seconds compared to approximately 4 minutes for the suborbital rockets.
Student-driven space engineering
Chilling out in space
The lack of gravity in space makes activities that we take for granted on Earth’s surface much more difficult. For example, cryogenic liquids, such as liquid hydrogen and liquid oxygen, don’t automatically flow “down” and must be pumped to move from propellant tanks to a rocket engine. To fire a rocket engine in space, a portion of a rocket’s cryogenic fuel must first be pumped through the lines and vented into space. On long-distance missions, such as to asteroids or Mars, this chill-down must be done with a minimal amount of propellant.
A team of nine undergraduate and four graduate students led by Professor Jacob Chung tested a special coating on the inside of a propellant transfer pipe to provide a faster cooling process and minimize cryogen loss. The team’s system could handle extreme temperature changes and maintain integrity in microgravity and high g-forces during their flight. Their transfer pipe coating reduced the chill-down time and fuel consumption by as much as 50 to 70 percent – an impressive figure. The Florida team will continue to perfect their technology.
Checking the gas gauge
Another microgravity challenge with liquid propellants is that they slosh around and stick to the sides of the propellant tank through surface tension. This makes it difficult to estimate the amount of propellant on board. Current systems for determining the amount of fuel on a rocket in zero-g can be off by as much as ten percent.
To address this challenge, a team of students from Carthage College and their professor Kevin Crosby have developed the Modal Propellant Gauging (MPG) Project. MPG analyzes sound waves produced by vibrations applied to the tank. This experiment also shows promise, as the Carthage team’s experiment demonstrated a margin of error less than two percent over a range of propellant volumes. If put into production, this increase in accuracy would amount to annual industry-wide savings of tens of millions of dollars.
Keeping cool – Content needs technical sanity check
Ever have your laptop overheat in zero gravity? The third challenge for spacecraft operating in zero-g is thermal management; that is, the removal of excess heat from the system. On Earth, heat is removed by contact with moving air (fans) and by hot air rising and cool air sinking (convection). Neither of those options is available in zero gravity and vacuum.
Currently, spacecraft use heat pipes containing a liquid coolant to capture heat from inside the spacecraft and circulate it to radiators on the outside, where it can be radiated into space. In the future, such single-phase (as in the phase of matter) systems will be replaced by two-phase thermal systems that include both liquid active cooling and a solid heat sink.
Single-phase thermal subsystems are used on spacecraft due to the lack of reliable models for predicting the performance of two-phase systems in various types of gravity. To design efficient heat removal equipment for spacecraft, engineers need a heat transfer database and dependable models.
Researchers at University of Maryland’s Department of Mechanical Engineering designed an experiment to collect the data and develop the necessary models. The team tried something new in the field and obtained local measurements using temperature-sensitive paints. Data from their experiment on ZERO-G will be analyzed in Martian gravity, lunar gravity, and low-G to determine how cooling, temperature changes within a coolant system, and heat flow rates are affected by various gravity environments.
“G-FORCE ONE is the perfect test bed for space-bound technology and is one of the last steps before sending experiments into orbit,” said ZERO-G’s CEO Terese Brewster. “The data collected from these universities and future groups who do research with us is vital for the future of space exploration.”
Bart Leahy is a freelance technical writer living in Orlando, Florida. Leahy's diverse career has included work for The Walt Disney Company, NASA, the Department of Defense, Nissan, a number of commercial space companies, small businesses, nonprofits, as well as the Science Cheerleaders.