Brad Pitt Spacewalks Through the Rings of Neptune in 'Ad Astra.' Is That Even Possible? (2024)

No one comes to a space movie looking for scientific accuracy. If they do, they certainly won't find much of it, rife as these films often are with mutated monsters and physically impossible feats (Ripley avoiding getting sucked into space with her sheer finger strength, anyone?). In any case, picking apart where these films succeed and where they stumble is always an enjoyable exercise. Ad Astra is the latest film to enter into this crowded field, and much like its peers, it has a tendency to stretch the truth. Dr. Nicolas Lee, a research engineer in Stanford University's department of aeronautics and astronautics, was kind enough to fill us in on what's scientifically plausible about Ad Astra—and what's definitely not.

In one early scene, Brad Pitt and his Space Command colleagues are riding across the moon in a rover, only for space pirates to chase them in another rover. The two groups fire at one another with guns. Can you really fire a gun in space?

Nicolas Lee: Yes. The basic idea is that you need something to ignite the charge, which means you need oxygen in order to sustain the combustion. It’s sort of the same thing as certain rocket engines. Often when you fire up thrusters in space, they use chemicals that self-react, or they use cold gas thrusters that shoot out a puff of air. You could ignite a solid motor in space if you had the oxidizer built into your propellant. From what I understand, guns, in their cartridge, do have an oxidizer.

What sound would it make when you fire a gun in space?

NL: If you're holding the gun, the sound it makes could travel through your body and cause you to hear it that way. But if you were standing off to the side watching someone fire a gun on the moon, you wouldn't hear anything, because there's no medium to carry the sound. If you were the person firing the gun, I think it would sound different from on Earth, because on Earth, you've got air carrying the sound to you. In space, the sound would have to go through your spacesuit and through your body. It’s the same as when you listen to a recording of yourself—it sounds different from when you're actually speaking because you're hearing the sound through the air instead of transmitted through your skull.

Elsewhere in the movie, we follow Brad Pitt onto a spacecraft full of primates who are research subjects. Can a primate be engineered to survive in space?

NL: We’ve sent primates into space for short duration missions. At the very start of the space program, they were talking about sending chimpanzees up in small contained capsules, where they were trained to press buttons and do simple tasks. I know that the Space Station has had human-tended animals. The Russians have sent up un-crewed capsules with animal experiments. You might have seen the news about the space geckos. In terms of whether they could survive in space, I think it depends on whether or not they have the necessities of life. Are there automated machines that recycle the air? Are there machines that provide food for them? If that's the case, I don't see why they wouldn't be able to survive indefinitely.

What we know about long duration human survival in space is that one of the big things is radiation. When you’re in space, especially in deep space, you're outside of the Earth's magnetic field, so you're more exposed to solar cosmic rays and galactic cosmic rays, which can cause mutations and possibly result in higher cancer rates. That can shorten your lifetime. Radiation shielding on a spacecraft is a critical design element that engineers are working on. The other thing is, a lot of the astronauts that have spent months on the Space Station have experienced degraded vision. That’s a big concern that we don't fully understand. Someone could go into space with perfect vision and, within the span a couple of months, come back nearsighted or farsighted. Because there's no gravity, there's nothing pulling everything down within your body, so the fluids build up in your brain, including in the cavity around the optic nerve. There’s some increased ocular pressure just from the lack of gravity, but also it seems like there might be some inflammatory response that goes on with the optic nerves there. You might have very nearsighted monkeys if you've had them up there for years, and they might be dying of cancer.

Brad Pitt travels from Mars to Neptune, which takes approximately 80 days in the world of the movie. He plugs a feeding tube into his abdomen and uses some sort of electric muscle stimulator. Would a feeding tube and electric muscle stimulation really carry you through the trip from Mars to Neptune?

NL: One of the things I think is really cool about space is how far away everything is. You always see diagrams of the solar system with eight or nine planets, depending on when you grew up, and in order to show the planets, they're scaled up really, really big relative to the actual distance apart that they are. If they can get from Mars to Neptune in 80 days, that's already saying they have some sort of advanced propulsion system that we currently don't have—something that can constantly accelerate towards Neptune for half the trip, then decelerate for the other half just to get them there in that amount of time.

In terms of actual survival during that period, that’s two and a half months essentially bedridden, but vibrating. What I know is that there are studies looking at the effects of long-term bedrest. NASA was looking for volunteers to stay confined in bed to assess the effects on their body. Of course, they don't have this fancy machine that's keeping their muscles active. I’m working from a 2019 level of technology, so I don't know what else they've invented on the biological side. These days we have machines like the TENS machines, or electromagnetic stimulation machines. You can strap electrodes to yourself, which send electric currents through muscles to force them to contract and release. These machines are used for pain therapy and conditioning. I think there's some merit to expanding that technology to allow a body to avoid becoming extremely unfit or unhealthy while remaining immobile.

The moon has been colonized, and multiple governments are at war over the valuable minerals there. Marauding space pirates are also circulating, looking to steal resources and kill anyone who crosses their path. What minerals does the moon contain that would cause such strife?

NL: The big thing people have been interested in on the moon is helium-3. It's not so much a mineral as it is a particular isotope of helium, which seems to show promise in fusion technologies. If there's an energy crisis on Earth and we make some breakthrough that allows fusion to be economical, going to the moon or to asteroids to mine helium-3, which is more abundant in those places than on Earth, could be a big factor.

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Brad Pitt has to travel to Mars to send a transmission to his father, who’s orbiting Neptune. Apparently you can’t transmit to Neptune from Earth—you have to go to Mars. Is that at all sensible?

NL: I don't see why that would be the case unless Earth was, for example, in line with Neptune and the sun, and we couldn't transmit through it. If we're sending a radio signal, the problem with transmitting towards or away from the sun is that the sun itself emits a lot of radio energy, so there are times when you might not be able to communicate with something diametrically opposite. That happens with the Mars Rovers, for example, where, depending on the orbit plane alignment, there are times when you might seem diametrically opposite if you look at the solar system top down on a 2D plane, but all of these orbits are in 3D. It’s like how we don't get an eclipse every time there's a full moon, because the orbit planes are slightly off, so the chances of everything lining up, both in terms of the planes as well as the position along the orbit, is rather low.

If there's a reason that Earth cannot communicate directly with Neptune, I'm surprised that he would have to travel to Mars—that there isn't something automatically relaying. These days, NASA operates tracking and data relay satellites, which were launched in the eighties. It's basically three geosynchronous satellites. Geosynchronous means that they're placed high enough in orbit that the orbital period matches the rotation of the Earth, so they're essentially immobile, if you look at it from the surface. We have communications satellites up there so that wherever the shuttle was in its orbit, when it was flying, it would be able to transmit to mission control through these space relays. In terms of communicating with deep space missions, NASA operates stations in California, Spain, and Australia so that we have full outward coverage from the Earth's surface, no matter which way the Earth is pointing. There’s no good reason why society a hundred years from now wouldn't have set up relay communications networks so that we could transmit to Mars and relay the transmission in a different direction. I don't see why he would have to go there. That seems like a story contrivance to get him to Mars, which is still cool, because I like seeing people on Mars in movies.

There’s a moment when someone’s spacesuit is punctured, so Brad uses duct tape to make the suit airtight again. Can you really fix a hole in a spacesuit with duct tape?

NL: I think that's plausible, yes. When you're operating in space, at least these days, you're not actually operating at full Earth atmosphere. The Space Station itself is at reduced atmospheric pressure relative to the Earth. But when you go into space on a spacewalk, you pressurize even more. What they end up doing in order to save time is camp out in the airlock overnight to gradually lower the pressure. It’s like the reverse of a diver coming up slowly to avoid getting the bends. They have to do it first to lower the pressure on the way out. The pressure inside a spacesuit is actually not that extreme compared to if you were evacuating full Earth pressure on a balloon.

The concern I have is that you're putting the tape over the top of the hole, which means the pressure pushing out is going to try to de-laminate the tape. If you had an option, if you could tape the inside so that the pressure trying to escape is actually pushing your tape onto the surface, I think that would be more secure. But I do think duct tape would be viable, especially if they've got fancier space tape.

At the film’s climax, Brad Pitt is stuck on one spaceship, and he needs to get back to a different spaceship on the opposite side of Neptune's rings. He wrenches a metal panel from the spaceship's exterior and uses it as a shield to safely spacewalk through the rings of Neptune. Would a piece of sheet metal really protect you in that scenario?

NL: We’re not sure how dense the rings actually are when you're sitting inside them. In science fiction depictions of asteroid belts, you often see a spaceship dodging and weaving through them. Whereas, if you look at the solar system's asteroid belt, we've got millions of parts of asteroids in there, but it's trillions of trillions of cubic miles of space. So if you're standing on the surface of an asteroid, you probably don't see many asteroids around you. Rings and belts typically aren’t that dense, so I'm not sure how much there is to actually dodge.

One of the things I'm thinking about is Cassini. When Cassini ended its mission a couple of years ago, one of the things they did was they become more aggressive in passing the spacecraft through the ring plane of Saturn. The first time they sent it through the rings, they pointed the spacecraft so that its large antenna dish was at the front of the spacecraft. There definitely were particles of the ring that hit the spacecraft and created signals that the spacecraft could hear. These were micron-sized particles. A lot of impacts in space, just because of how orbital mechanics works, will be on the order of kilometers per second. Most likely, you’re impacting faster than a rifle bullet, which typically go about a kilometer per second. Impacts of debris on Earth tend to be on the order of seven to ten kilometers per second. Meteorite impacts from outside the Earth's system will hit us at a rate as fast as 70 kilometers per second. These things are really fast, so what that means is that really small particles can still punch through a material. If Brad had something like a sixteenth-inch sheet of metal—that's about one and a half millimeters—he could probably get hit by a half millimeter particle and it would punch through.

On the Space Station, what they have are meteoroid Whipple shields. The trick to surviving these types of impacts is to have multiple levels of shields. These days, on the Space Station, what they have is an outer layer of metal, an inner layer of metal, and layers of Kevlar in between. It really slows down and spreads the energy of the impact. The shields on the Space Station are designed to survive meteoroid impacts up to a centimeter. That’s not expected to happen very often. In terms of particle distribution, you get hit a lot more often by small particles than large particles.

The moon has a Nathan’s Hot Dog stand. Would a hot dog taste the same on the moon as it does on Earth?

NL: Where was the hot dog manufactured? Are they taking Earth cattle, creating the hot dog, and shipping it to the moon? Or are they manufacturing it out of some synthetic meat? They're getting pretty good at making synthetic meat that tastes real, which is made of plants, so you can easily grow them in some hydroponics section of your lunar base.

In terms of what an astronaut would taste, let's say you take a real hot dog, ship it to the moon, and prepare just like Nathan’s does, so the hot dog is essentially the same. I think there would be some difference. Astronauts have reported that their taste buds don't respond as strongly in space, so they like spicier things. That comes from how much of what you taste has to do with the fact that you can smell your food. Food will taste different when you have a cold because your nose is stuffed up, so you can't smell the food. In space, because of the way air circulates in your pressurized vessel, there’s a similar aspect that affects your ability to smell the food the same way.