GRAVITAS: A novel fuel-cell-based technology for efficient, clean, reusable near-space transport
By Milo Eirew
Senior Category (Grades 11-12)
Innovation | Energy and Natural Resources, Engineering and Computer Science, Environment, Physics
As humanity shifts to repeated high-altitude and eventually extraterrestrial endeavours, clean, reusable near-space transport for aerospace pursuits will be vital. GRAVITAS aims to offer this by harnessing the gravitational potential energy generated when oxygen and lighter-than-air hydrogen are converted into heavier-than-air water at a height through emissions-free fuel cells, creating a balloon that can efficiently bring itself and a payload a quarter of the way to space and back.
The hydrogen balloon lifts itself, a proton exchange membrane fuel cell (which converts hydrogen and oxygen gas into water and electricity), and an electrolyzer (which does the reverse, splitting hydrogen and oxygen into water and electricity) into the atmosphere. By converting back and forth between hydrogen and oxygen and water and electricity, GRAVITAS can alter its own buoyancy, enabling it to travel up to 25,000m in the atmosphere without any emissions. The hydrogen reservoir in the balloon acts as both a buoyancy source, and an energy reserve for the fuel cell.
By creating heavier-than-air water from our reaction, we generate additional gravitational potential energy, which adds to the fuel cell’s theoretical efficiency. We modelled this using gravitational potential energy, the definite integral of the gravitational potential energy from 0 to height h, as well as Gibbs free energy, the thermodynamically adjusted amount of energy gained from a reaction, all over the net bond energy of the fuel cell reaction. I graphed efficiency gain versus height, which yielded a graph with an approximate asymptote of 500%. However, the increase in efficiency is small enough that when viewing at atmospheric heights, the graph appears linear, with an efficiency increase of around 1.7% at 25 kilometers, the range of GRAVITAS. I simulated the balloon path in MATLAB.
In the GRAVITAS prototype, an Arduino Uno-housed microcontroller makes decisions based on information fed to it from pressure, temperature and acceleration sensors onboard the balloon. The relay allows the microcontroller to interface with the fuel cell, turning it on and off. Hydrogen molecules enter on one side of the fuel cell, then contact the central membrane. This splits the H2 molecules into two H+ ions, and 2 electrons. Protons freely pass through the membrane, but electrons have to take an alternate path to reunite with the hydrogen ions and oxygen molecules to create water. This alternate flow of electrons provides our electric current. However, if our electronic relay opens the circuit, cutting off the flow of electrons so that the reaction cannot proceed, the hydrogen keeps its original state, and its buoyancy. This buoyancy modulation allows GRAVITAS to travel throughout the atmosphere.
This work is developed from years of modelling and improving the theoretical efficiency of fuel cells. Harnessing the buoyancy change from Hydrogen and Oxygen to Water offers an aerospace transport that is more efficient than alternatives, offering a “free ride” a quarter of the way to space. This has ramifications for repeated trips to space heading for the extraterrestrial barrier, since at the apex of its journey, there is negligible air resistance for a rocket to contend with. Other high altitude aerospace technologies do not offer carbon dioxide free impact nor the immediate reusability.
I consulted with National Research Council Drs Fuller & Girard regarding prototype launch and safety. The risks are notable, and can be avoided through distancing the electronics from the balloon and surrounding it with inert gas. When weighed alongside the rewards of such a system, GRAVITAS’ potential is very positive: capable of travelling a quarter of the way to space, with high efficiency, creating a profound positive impact on the energy input and carbon dioxide output of our increasingly spacefaring civilization.
