Propelling New Ventures to Mars

An online publication from Purdue University’s College of Engineering.

AAE’s Timothée Pourpoint is working on fuel candidates that could be used to launch rockets on Mars.

by Poornima Apte

NASA’s potential Mars Ascent Vehicle is a daunting endeavor that is part of a larger Mars Sample Return effort with the ultimate goal of bringing samples from Mars back to Earth. It will involve a rocket with the samples taking off from Mars into space to be captured by another spacecraft before eventually returning to Earth.

Launching a rocket from Earth is one thing; doing the same from Mars is another. The first challenge: What propellant do you use? It is this problem that Timothée Pourpoint, associate professor of aeronautics and astronautics, has been working on with NASA’s Jet Propulsion Lab. The extremely low pressures on Mars’ surface (about one-hundredth that on earth) and low temperatures (-50°C) complicate any potential fuel candidates, Pourpoint says. “Conditions of low pressure and low temperature make ignition in general harder.”

The Goldilocks propellant

To further complicate matters, the ideal propellant candidate must satisfy a number of additional parameters, Pourpoint says. It must be hypergolic, which means the fuel constituents ignite spontaneously when they come into contact with each other without the need for an external ignition source, and the fuel needs to be solid, so it can be more stable for the time period (up to a year) it is expected to be on Mars.

“We also want something that doesn’t get brittle at low temperatures, so it has to have good mechanical properties at low temperatures,” Pourpoint says. The fuel-flow rate — the rate at which it is consumed over time — has to be optimal to achieve the right rocket thrust, and the right fuel has to take payload capacity into account as well. “We want the rocket to take off from Mars under a certain flight profile and acceleration. If it goes too fast, it might run out of fuel too quickly, so that’s a factor too,” he adds.

Above all, the propellant fuel must be reliable. “We’re really looking for a means of igniting the rocket very reliably at least three times during the mission,” Pourpoint says. After years of research, he and his team have arrived at sodium amide and potassium bis(trimethylsilyl)amide as potential solid hypergolic additives that might pass these stringent parameters.

What reliable looks like

To make sure everything works as predicted on Mars, Pourpoint says the propellants must be evaluated rigorously on Earth.

“You have to test for so many variables,” he says. “What if the temperature is actually a bit lower than the temperature that’s expected to be the norm? What if the injection profile doesn’t come out as well as we want? What if we have a sticky valve and it doesn’t open as fast as we want?”

Even if all these potential scenarios can be tested on the ground, Pourpoint says, “We can’t account for every [eventuality]. At some point you take a risk. There are also challenges with respect to time and money. That is, in part, why space exploration is so exciting.”

To test for various conditions and eventualities, you need to simulate Mars-like conditions on Earth. Pourpoint plans on testing the propellant in an altitude (vacuum) chamber that can simulate the pressure conditions on Mars. “We will check that the propellant ignites quickly, that it ignites well and that the chamber pressure rises in a nice and uniform fashion,” he says. “We will check that we get the predicted thrust under those conditions and make sure to repeat tests until we’re satisfied.”

In situ resource utilization

An alternate theory is the reliance on found materials to use as fuels. Pourpoint has suggested, for example, that we use the ice on the moon and make hydrogen and oxygen for the rocket to come back to Earth. “SpaceX is suggesting we do the exact same thing on Mars except with methane, using CO₂ in the atmosphere,” he says.

Such ideas are not far fetched, Pourpoint says, and he sees the value in using locally sourced materials. “We have to learn to use the resources where we’re going to and learn to live off the land. The first explorers to America didn’t bring all their food for months; they made their food here. It’s exactly the same if we go to Mars — we need to learn how not to bring all our fuel to Mars or to the moon. We have to use the resources on the land.”

As for back on Earth and at Purdue, after racking impressive early success with the sodium amide and potassium bis(trimethylsilyl)amide combination, Pourpoint is hoping to test the candidate further and make it a contender at NASA’s JPL design review process in the fall.

“This is all one step toward a solution,” he says. “It’s getting the project one step closer toward reality.” With his research on exploring the right fuels for the right conditions, Pourpoint is paving the way for exciting explorations in new frontiers of space.

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“We can’t account for every [eventuality]. At some point you take a risk. There are also challenges with respect to time and money. That is, in part, why space exploration is so exciting.”
— Timothée Pourpoint

Step 3 – Moon to Mars

Humans have basic needs for food, water, air and shelter. Ecosystems within Earth’s biosphere provide for these needs. As we continue exploring space, and plan expeditions to other planets, NASA is developing ways to support living away from Earth for long periods of time.

Exploration of the moon and Mars is intertwined. The moon provides an opportunity to test new tools, instruments and equipment that could be used on Mars, including human habitats, life support systems and technologies, and practices that could help us build self-sustaining outposts away from Earth. Living on the Gateway for months at a time will also allow researchers to understand how the human body responds in a true deep space environment before committing to the years-long journey to Mars.

In spite of this, there are challenges facing future space pioneers.

Isolation and confinement

Behavioral issues among groups of people crammed in a small space over a long period of time, no matter how well trained they are, are inevitable. Crews will be carefully chosen, trained and supported to ensure they can work effectively as a team for months or years in space.

On Earth we have the luxury of picking up our cell phones and instantly being connected with nearly everything and everyone around us. On a trip to Mars, astronauts will be more isolated and confined than we can imagine. Sleep loss, circadian desynchronization and work overload compound this issue and may lead to performance decrements, adverse health outcomes and compromised mission objectives.

To address this hazard, methods for monitoring behavioral health and adapting or refining various tools and technologies for use in the spaceflight environment are being developed to detect and treat early risk factors. Research is also being conducted in workload and performance, light therapy for circadian alignment, phase shifting and alertness.

Distance From Earth

Perhaps the most apparent hazard is, quite simply, the distance. Mars is, on average, 140 million miles from Earth. Rather than a three-day lunar trip, astronauts would be leaving our planet for roughly three years. While International Space Station expeditions serve as a rough foundation for the expected impact on planning logistics for such a trip, the data isn’t always comparable. If a medical event or emergency happens on the station, the crew can return home within hours. Additionally, cargo vehicles continual resupply the crews with fresh food, medical equipment, and other resources. Once you burn your engines for Mars, there is no turning back and no resupply.

Planning and self-sufficiency are essential keys to a successful Martian mission. Facing a communication delay of up to 20 minutes one way and the possibility of equipment failures or a medical emergency, astronauts must be capable of confronting an array of situations without support from their team on Earth.

Long-term research outposts on the moon or Mars will require more recycling of material. It will be too expensive to resupply food and water. Growing plants for food in lunar or Martian habitats makes sense at many levels. As plants grow, they remove carbon dioxide and replenish oxygen. Decomposers in soil or hydroponics systems can recycle biological waste and provide nutrients for more plant growth. Plants do a good job of purifying water. Researchers are developing biological systems that will allow long-term human habitation in a sealed container. Researchers are also developing improved physical-chemical systems. New packaging materials are also being developed that can go into space and be recycled.

Source: NASA