Time for a good ol’ “is Sci-Fi right?” post. We’ve been talking a lot about AI lately with a touch on paleontology, so let’s jump back to the couch and turn on some good space nonsense. The term nonsense in this article just covers everything in Sci-Fi, accurate or not. For this, we’re going to focus on two distinct Science Fiction shows, Star Trek, and the book soon to be movie staring Ryan Gosling, Andy Weir’s fantastic novel Project Hail Mary.
Some of the tools I used to get this data:
- https://www.omnicalculator.com/physics/space-travel
- Many Wikipedia articles, linked individually below.
In Star Trek, they use an anti-matter / matter fusion drive, to collapse (or create, depending on whom you ask) a bubble of spacetime around the ship, allowing it to travel faster than light speed. This is similar to a wormhole creation, in that they are curving the spacetime around the ship in such a way that time is decelerated during their travel, thanks to Einstein’s Theory of Relativity, and the old “send one twin to orbit a black hole, how old are they” science question. Quick Answer: the twin on Earth is much older, or long dead. Because they are curving it, when they rebound or stop, time snaps back to the point in which they departed, with the length of travel time being what they experienced. To someone else in the universe, they would forever appear younger, however they never touch on that. If they do, my fellow Trekkies, I am sure you’ll be vocal in the comments.
This is pure fiction and we don’t have this technology currently. We’ll skip over this tech.
The way we get to other planets right now is by using something called a Hohmann Transfer Window/Orbit, depending on the agency, NASA or ESA. The way these work are very inefficient, however they are currently the best we have. Once you get off the planet, you shed some weight, and thrust a 2nd time to get into a stable orbit. Microgravity is where everyone is at at this point, still with 99%+ the pull of Earth’s Gravity. Our crew are falling to Earth at terminal velocity if it weren’t for our pesky sideways motion causing them to miss the surface 100% of the time. If you were a satellite or wanting to hitch up to the International Space Station, you’re done. Some corrective burns to keep you up is all you need.
However, if you keep thrusting at this point, your orbit around Earth increases. This is how we deploy satellites in higher orbits, called the K bands. For the most common communication satellites out there, they operate in the Ku band, or “closest to Earth” band. The next area called generically just the K band, is generally where you’ll find Radar, Astronomical and other Scientific studies. The final is called the Ka band, and is designed for data transmission satellites, Star Link for example. Surely naming something with three K’s isn’t going to cause issues, right science community? hello? this thing on?
As you burn, you will eventually leave Earth’s orbit on an ever increasing circle. If you burn your rocket for a small amount of time, you can enter into an orbit around the moon, or Mars, or farther. The problem you see here is that you don’t have infinite fuel, so you can re-fuel in space (Sci-Fi, see Armageddon), collect new fuel along the way (also Sci-Fi, but farming gas in space is becoming real), or figure out how to beat physics and chemically lift all the fuel you’d need (magic). Here’s a good video explaining Homman Transfers.
In Project Hail Mary, a more efficient approach to long distance travel is presented: use a straight line. We can’t do that currently because if we do, the planet won’t be where we are when we get there, because they, the spacecraft and the starting point, are all on the move. Even if we calculated where the planet would be in our straight to the point trajectory, it would require tremendous amounts of fuel to get there, and slow down. Not efficient. Here’s what is efficient: Ion Propulsion. Slow and steady wins the race.
The Dawn Spacecraft uses this type of thruster, and thus proved it was a viable thing to continue research on, with Space-X and other private firms announcing their research wing is looking into it. Ion drives produce a tiny amount of thrust, usually only a few kilograms of force, but they never turn off. They are always producing that thrust, and in space, thrust is movement. If something is forever accelerating, it is gaining speed and reducing the travel time distance. Since Chemical rockets run out of heavy fuel, our journey is long, 75,000 years give or take.
With a gradual acceleration, things inside the ship, squishy things like humans and plants survive because inertia being in their favor. We measure this force in “g”, where 1 g is what we all experience on Earth at sea level. Humans can stand additional force, as we know with things like being on an airplane and it taking off, or a fighter pilot inside a jet taking off and doing loops – they can generally stand between 6-10 gee’s before passing out. Astronauts can experience more during take off, however with what we learned about Hommann Transfer windows, the launch curvatures around Earth, it evens it out for them.
Let’s take a movie trailer break and see what that dreamy Ryan Gosling is up too as Ryland Grace.
Sadly, a Hommann Transfer orbit insertion to Proxima Centauri (b) isn’t a feasible way to travel between intergalactic locations, and our best chemical rockets would take about 75,000 years to get there. So, back to the drawing board, right? No, not that fun one with the colors.. the math one in monotone grey we all love 🙂
With constant acceleration, a ship would need to turn around 180 degrees, so that the ion thruster can then work on decelerating the spacecraft. It would need to occur at around the halfway mark in order to slow us down enough so that our math works out, or else we would zoom past our destination at a speed that would not be controllable, if we physically made it that is. We call this a Brachistochrone Trajectory. Our friends watching The Expanse will know it by a “less fortunate” name in today’s news cycle (The Epstein Engine).
Doing some math with our calculator above, if we apply a 5kg thrust to a 10,400kg spacecraft, the current weight of the Artemis 2 crewed space capsule, our travel time to Proxima Centauri b, the closest exoplanet to our solar system, with a straight trajectory using our above described methods.
- Astronaut/Ship Aged: 1,308.5 days
- Earth Aged: 2,192.5 days
- Fuel Required: 450,000 kg
- (L AR40, can be stored in a ~9m diameter sphere)
- (Jeff added some redundant fuel)
- Astronauts/Ship Max Speed: 0.9516556237 the speed of light.
- 1,027,077,043 km/h
- 638,196,087 mp/h
Our fuel, Liquid Argon, would take up no more space than a normal 18 wheeler truck on a normal highway. It can be prepped in space by mining or even sucking it right out of the atmosphere, as Liquid AR40, is one of the most common elements outside of Hydrogen and Helium, found in the interstellar medium. This means we don’t need to calculate this additional nearly 500tns of fuel to carry up from Earth. We also calculated it so our math includes this fuel in our mass calculations during the journey, with it taking into effect it lightens as it’s used**, don’t worry 🙂
Maybe getting there fast is what’s not working out NASA. I for one would like a slow steady walk to another planet over a body-squishing 4 years at light speed.
** This additional realistic calculation for the fuel tank slowly depleting, was so complicated and applied almost no changes to my numbers at these distances.