A return to the moon isn’t just about who will be next to step onto the lunar surface. To address the complex issues that a return entails, it requires problem-solving and innovative thinking. Purdue alumni were the first and most recent to step foot on the surface 50 and nearly 47 years ago, and alumni have played key behind-the-scenes roles, too.
Within NASA are alumni William Gerstenmaier, Julie Kramer White and Mark Geyer. Dan Dumbacher, former NASA deputy associate administrator in the Exploration Systems Development Division for the Human Exploration and Operations Mission Directorate, is currently the American Institute of Aeronautics and Astronautics executive director.
Kathleen Howell, the Hsu Lo Distinguished Professor of Aeronautics and Astronautics, and her team have been instrumental in identifying pathways for a proposed Lunar Orbital Platform-Gateway facility by using nontraditional orbits called near-rectilinear halo orbits (NRHO). Howell also was part of a team that identified lava tubes on the moon, which could allow habitation for more extended stays. No one has been able to last longer than three days on the moon because of its harsh conditions, varying from extreme heat to extreme cold.
Every potential challenge to a return — and a sustained stay, either on the Gateway or the moon itself — is being evaluated and explored.
“I’ve always been motivated by an assessment that says, ‘It can’t be done,’” Howell says. “I typically tell my graduate students, ‘You don’t ever say you can’t do something. It only depends upon how it can be accomplished.’ And maybe it takes a new propulsion system or something like that. It’s not that it can’t be done. But it’s how to accomplish it that maybe drives the research, not only in our field but in the neighboring directions as well. And it’s complementary. The guys at Zucrow, including Tim Pourpoint, will say to me, ‘If I gave you this, what could you do with it?’ Then we see what we can do with it, and we go to the scientists and say, ‘You could do this cool stuff.’ It goes two ways.”
Howell and her team certainly are doing their part. Bloomberg Businessweek featured the longtime Purdue professor in the summer of 2018, highlighting her expertise on NRHOs, which aren’t traditional orbit ellipses around the Earth or the moon. They’re “exotic,” in part because they’re leveraging multiple gravity fields. NASA wants to use those orbits in the Lagrange Point 2 region for the Gateway because, once positioned, the orbit can be maintained and serve as a hub for various activities. NASA is planning to build the Gateway in the 2020s, and Vice President Mike Pence said in 2018 he expects to have an American crew aboard the Gateway before the end of 2024.
But NASA has to be able to calculate the orbits. That’s where Howell and her team come in.
Howell started studying NRHOs as a graduate student, and she has shared her knowledge with her students at Purdue. The paper that spurred Bloomberg’s interest, Howell says, was written by Howell, one of her current graduate students and a then-Ph.D. student who now works at NASA JSC.
One of the reasons NASA prefers the NRHOs, Howell says, is because they can keep a spacecraft out of shadows. That’s important because spacecraft may need the sun as an energy source via solar panels, and there’s a maximum amount of time that a spacecraft could be in shadow and still be able to recover. Batteries only last so long, Howell says.
“So part of my job, when I look at trajectories, is to figure out what trajectories might meet that power requirement,” she says. “That’s another reason why it may not be quite as straightforward. Propellant is not effective without the capability to fire the thrusters. Also, without power, communications may be restricted. Thus, this particular type of orbit can be leveraged to avoid Earth and moon shadows.”
Two Lagrange points already have been leveraged, in a Genesis mission in 2001 and Artemis in 2010. The first was Sun-Earth system and the latter the Earth-Moon, which a lot of critics said could never be done, Howell says. “But here we are,” she says. “With the success of Artemis, the Earth-Moon region is now available, and non-Keplerian orbits can be successfully used in this region.
“Folks hear that orbits are chaotic, an unfortunate word choice. Some folks may interpret ‘chaotic’ as unpredictable. But that is not necessarily true,” Howell says. “We can also consider flipping the concept. As an orbit designer, it can also be useful. If one small disturbance can cause the vehicle to shift away, it also means that a very small amount of propellant can maintain the vehicle on orbit. So, deterministic chaos reflects an environment that is complex. It means that if we understand it, we can work with it.”
There are advantages and disadvantages to both ways of thinking, Howell says. “But when we have a human vehicle that we can control, it’s something that we can actually work with.”
In October 2017, Howell teamed with a group on a published study that confirmed the existence of a large open lava tube on the moon that could be used to protect astronauts from hazardous conditions on the surface. That’s not only important for understanding the moon’s internal structure but also, if it is studied close to home, could be something that exists on Mars, which is a considerably longer journey.
There continue to be revelations about Earth’s moon, seemingly validating why it’s so important to return. “I personally have always been an advocate of not bypassing the moon. Because although Mars is great, asteroids are great, I don’t think of these just as destinations we visit,” Howell says. “I see less long-term value in simply passing by, say the moon or Mars, and returning to Earth. I would like to see a more complete expansion into space. Part of a natural expansion is an extension throughout your own neighborhood first. So the current thinking is, let’s expand in our own, what’s now called the Earth-Moon neighborhood, and build up our infrastructure, build up our capabilities and use the moon to help us plan to go to these other destinations as part of a natural evolution of exploration and expansion.”