Gravity, G-Forces, and Galactic Travel: The Sci-Fi Science of Constant Acceleration

Building on last Sunday's post about the speed of gravity being equal to the speed of light, let's delve further into the subject of gravity.

Hollywood's Take on Gravity

Sci-fi films and series tackle the concept of gravity on spaceships in various ways. Some use spin drives to create gravity, as seen in "The Martian" and "2001: A Space Odyssey." Others, like "Star Wars," "Star Trek," and "Firefly," rely on what some of them call gravity plating, essentially just asking the audience to "go with it."

The Expanse's Ingenious Solution: 1g Burn

Another intriguing perspective comes from the series "The Expanse." It introduces the concept of constant acceleration, or a "1g-Burn." In this setup, the ship continuously accelerates at a rate of 9.81 m/s2, equivalent to Earth's gravity. So, instead of everyone walking around on the spacecraft horizontally, as if they were on the deck of a boat crossing the ocean, the entire ship is constructed vertically! Meaning your head is pointing towards the nose of the ship/direction of travel and the decks are constructed perpendicular to the fuselage, so that the force from the acceleration is pushing everything down onto them, thereby recreating the feeling of gravity!

The Speed Conundrum

If you were wondering about the speed of the ship when it does finally arrive at its destination if it's constantly accelerating at that rate, then you would be correct. Supposing we were traveling to Jupiter's largest moon, Ganymede, from our own moon. By about mid-journey and having been accelerating at a rate of 9.81 m/s^2 for the entire trip, we would reach a speed of approximately 1,890 km/s!! For comparison: a rocket leaving Earth's atmosphere [escape velocity] only needs to reach speeds of 11 km/s, while the ISS is currently orbiting or 'falling to' the Earth at a speed of 7.78 km/s.)

How are we ever going to be able to stop by the time it reaches Ganymede without turning the passengers into a puddle of goo?

The Flip: A Solution to Deceleration

The answer is ingenious: By performing a mid-journey "flip."

That's right, about halfway through the journey, the engines or 'thrust' get cut off, everything goes weightless, and the ship flips 180 degrees and lights up the engines again, reciprocating the same speed as before, but now it's DE-celerating at a rate that is still consistent to 1g! It will continue to do so until it either changes course or arrives at its destination, at which time it will slow down to a gentle stop and enter a state of weightlessness until the ship either lands or docks with a space station that is probably spinning. Pretty cool, huh?

Challenges and Implications

Now, this is of course not without its own set of implications and challenges, but the other sci-fi series will have these on top of their gravity issue, too. The first and probably most obvious is the fuel issue. For this, we need to imagine that we do finally come up with a fusion reactor that is capable of much much more output than we ever even dreamed of, even for a fusion reactor (the constant 1g burn requires A LOT of energy)

Then there are also the issues that arise when traveling at the speeds that would be achieved during these types of journeys, such as the very real dangers of encountering space debris. Despite the vastness of space, micro-meteoroids, cometary debris, and mini-asteroids are very much present out between the planets and other celestial bodies & they do pose a significant risk. At such high speeds, new science altogether would be needed in order to mitigate these risks, whether through advanced collision avoidance systems or protective "shielding" like electrostatic or laser ablation. Nothing currently in development would even remotely be able to survive an impact with any object when traveling at speeds that high. The ISS would be shredded and it is "only" traveling at 7.78 km/s!

What are your thoughts on the subject? Are there any other dangers associated that I left out?

The suspense continues!!