NASA’s Poo-Powered Rocket Will Go Where No One Has Gone Before
It sounds like fodder for late-night comedians or a humorous science fiction novel: Scientists have developed a way to convert human waste into rocket fuel.
The process was described in a recent study published in the journal Advances in Space Research.
“The idea was to see whether we could make enough fuel to launch rockets and not carry all the fuel and its weight from Earth for the return journey,” Pratap Pullammanappallil, a University of Florida associate professor of agricultural and biological engineering and the study’s lead author, said in a statement.
“Methane can be used to fuel the rockets,” he added. “Enough methane can be produced to come back from the moon.”
Pullammanappallil, who conducted the research with graduate student Abhishek Dhoble (now a doctoral student at the University of Illinois), ran tests to determine how much methane could be produced from the waste.
Their work resulted in the creation of a space-based anaerobic digester that kills pathogens and produces biogas—a mixture of methane and carbon dioxide.
The study was conducted at the behest of NASA, which is working with a private American company to develop a permanent base on the moon and is planning a mission to Mars with the Orion rocket project.
“NASA had recently developed rocket propulsion using methane as fuel,” Pullammanappallil wrote in an email. “So on one hand we have the means to make methane, and on the other hand NASA had developed the technology to use the methane. The next step was to identify the feedstocks from which to make methane on a lunar base.”
The space agency was seeking ways to lighten the weight of spacecraft leaving Earth by generating fuel during the mission for the trip home. Until now, astronauts have put space-generated waste in containers that are loaded into cargo vehicles that incinerate during reentry.
But long-term missions will generate too much waste to send back to Earth—and it cannot be left behind.
“There are international conventions that prohibit disposal of biological materials on planetary and lunar surfaces,” said Pullammanappallil.
That’s where poo power comes in.
In reality, the methane-generating waste does not just consist of human fecal material; it also includes food waste, food packaging, towels, and clothing. Each crew member generates approximately two pounds of total waste per day.
“This much waste would produce 290 liters [about 76 gallons] of methane,” Pullammanappallil said.
The process would also yield about 200 gallons of nonpotable water, which can be split through electrolysis into hydrogen and oxygen—which astronauts could use as a backup system for breathing.
The hydrogen, meanwhile, can be combined with carbon dioxide exhaled by the crew and converted in the digester into even more methane, Pullammanappallil said.
Human-waste fuel is being contemplated for the Orion mission to Mars.
“We wouldn’t be able to make enough propellants to bring the astronauts home,” Rob Mueller, a senior technologist in NASA’s Surface Systems Office, wrote in an email. “We would use the propellants for other purposes.”
As for fuel to return home, it would be made from Mars’ own atmosphere, Mueller said, along with “hydrogen feedstock that we would have to get from the water in the soil, or bring it with us.”
NASA will test this process on its unmanned Mars rover mission in 2020.
This is the first time that a waste-to-methane application has been developed for space, though converting waste from humans, cows, and even dogs into methane is not new on Earth.
“Anaerobic digestion is an economical technology compared to producing biofuels like ethanol or butanol,” Pullammanappallil said. “Methane from digesters can be used for transportation in the form of compressed natural gas or for electricity generation or for heating. It displaces natural gas.”
In other words, humans who consume fossil fuels can also produce alternatives to fracking and other polluting extraction technologies.