40 Dives in 2.5 Hours on a Parabolic Flight, or Just Another Thursday at Interlune

Photo, from left to right: Me, Martin Johnson (intern), Lexi Humann (senior mechanical engineer), and Gary Lai (co-founder and CTO)

Gravity on the Moon is one-sixth as strong as on Earth. As a result, most people could dunk a basketball from the 3-point line in a lunar pickup game. If you fell off a ladder hanging Christmas lights on your Moon house, you wouldn’t be opening gifts with one arm in a cast. 

Machines work differently on the Moon as well, which is why Interlune has an extensive program to test its hardware and technology in simulated lunar gravity. One of the only ways to do this is by operating our systems onboard a plane flying a series of steep dives and climbs, or parabolas. Interlune has conducted four such tests to date with leading parabolic flight provider Zero-G.

What we’re testing

The Interlune harvesting system comprises four steps: excavation, sorting, extraction, and separation. In February and October 2024, we tested our proprietary extraction technology, a low-power, highly efficient way of releasing gasses from lunar soil or regolith. We analyzed trade-offs in size, weight, and power required for different performance levels, which will inform our plan for scaling the technology to handle multiple tons of regolith. This testing is partly funded by a NASA TechFlights grant. 

In August, we tested our size sorting device, which uses centrifugal force to rapidly spin and sort through large volumes of regolith using fewer moving parts. Interlune received a National Science Foundation (NSF) Small Business Innovation Research (SBIR) Phase I award to operationalize this technology.

With a mix of government grants and its own capital, Interlune will continue its rigorous testing program for all technology and hardware designed to operate on the Moon, with parabolic flights as a key component.

Preparing for a flight 

About 60 days before the flight, we submit details to Zero-G so they can ensure the experiment will be safe for passengers and the other experiments around it, even in an emergency. Zero-G tells us the exact amount of space we will have on the plane for our equipment, tools, and bodies, and then we recreate that situation in our lab on the ground. 

At Interlune HQ, we tape out a shape on the ground the same size as we'll have on the plane and gather all the necessary tools and materials. We make our ground tests as similar to the plane as possible, choreographing every movement and gathering data to measure how the device functions in Earth's gravity for comparison to its performance during the flight test.

The parabolas

Zero-G uses a Boeing 727 cargo plane retrofitted with padding on the floor, ceiling, and walls, with only a few seats in the back. There's an enormous cargo door where forklifts are used to get the equipment up and into the plane.

Takeoff feels like a normal flight, and once we reach cruising altitude, the pilot gives us permission to walk around the plane and set up our equipment. 

About 35 minutes in, when all experiments are ready, the pilot tells everyone to lie down, and the plane starts its steep climb. We experience hypergravity for about 20 seconds, which feels like being under a weighted blanket. Objects on Earth fall at 9.8 meters per second squared (9.8 m/s²), referred to as one g (gee). One g is the reference point for comparing gravity in other places and situations. During the flight pullup, gravity (or hypergravity) is about 1.8 g. 

When the plane is about to enter the parabola, as it reaches its peak and begins to dive, it feels like being at the top of a massive roller coaster. For the next 20 to 30 seconds, everything in the plane experiences one-sixth gravity. And that’s when we get to work. It’s sobering because months of work and preparation led to this moment. Crunch time. 

Keep in mind we have less than 30 seconds to test the equipment in reduced gravity before the plane comes out of the parabola and we’re in hypergravity again. At that point, we lie down again for the pull-out. And we repeat the process for 40 parabolas. During some of these parabolas we experience one-sixth gravity, while some of the parabolas are steeper and we experience zero gravity.

What about motion sickness?

Consider the nervous energy and excitement of doing a microgravity experiment combined with the pressure of getting the job done. And that’s all happening before we even take off.

Our first priority is always to get good data in the test, but the second is to not throw up. So far, no one from Interlune has thrown up during a test campaign, which is something we’re all proud of. But of course, there’s still time.

We get prescriptions for small medicated patches that go behind the ear and vibrating wristbands with an electric pulse that helps to distract your brain as well. But nothing fully compensates for the fact that we’re climbing and diving thousands of feet repeatedly for a couple of hours in a large, empty aircraft with no windows.

It feels like a dream

It all happens so quickly with these unbelievably intense feelings. Over the course of the flight, we go from lunar gravity to hypergravity and back to lunar or zero gravity up to 40 times. Then it’s all over, and we’re back on the ground where we started. 

I remind myself that getting to conduct experiments on a zero-gravity flight with equipment my team has designed and built is on a lifetime bucket list for so many people. But at Interlune, it’s just our Thursday.

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