Writing SciFi is a lot of fun. As writers, we can make up anything we need for a story. In this post, I’m going to talk about traveling between the stars. Also known as Interstellar Travel.
I read a book some years ago called Centauri Dreams. It’s a technical, “what if” type of book that explains what it would take to build a ship and travel to the nearest start, known as Alpha Centauri using currently known technology. Alpha Centauri is a triple star system that is the closest neighbor to our solar system. It’s about 4.2 light-years away, which doesn’t sound very far until you get your head wrapped around the distance light travels in a year.
According to the book Centauri Dreams, humans would need to solve several “miracles” in order to reach Alpha Centauri. The book talks about a modest plan to fly to the nearest neighbor at one-tenth the speed of light. That’s 67,100,000 miles per hour. A ship moving at 1/10 the speed of light (or 0.1c) would arrive at Alpha Centauri in about 42 years. The fastest object that humans have created is the Voyager I spacecraft. It’s currently flying at approximately 39,057 miles per hour. Obviously the first problem is how to make a spacecraft move at a speed that could get us there.
The book covers the problems with various propulsion systems. Chemical rockets need so much fuel that it would take more mass than the entire known universe to power a craft to Alpha Centauri. Therefore, burning hydrogen with oxygen is not going to cut it. There are various proposals for harnessing fission and fusion. One method would use nuclear bombs that would be ejected out the back and detonated at a distance from a pusher plate. A fission reactor can be used to run powerful magnets to accelerate Xenon particles. There are solar sails and laser driven spacecraft. Each of these propulsion systems are doable and they all have their own issues. Building such a propulsion system would be a major undertaking.
The second problem is the 42-year time span. I doubt if anyone can pack that much food in a storage module. A manned ship would need to recycle and grow its own food, which would make the ship the size of a city. Then there is the reliability problem. How do you build a complex spacecraft that can survive 42 years? The Voyager crafts have both been in space for 42 years now (Voyager Mission Status). However, both spacecraft are seriously degraded.
Centauri Dreams talks about sending a robotic probe. This eliminates the food problem, but the probe will need to be intelligent or have robots that can think and repair the ship along the way. The intelligence will also be needed to steer the ship and react to unexpected challenges (like avoiding a collision with an unknown object). The distances are so great that it can take years for a signal to reach the craft. Direct control of the ship from Earth is impossible.
Next up is the problem of cosmic dust. These are tiny particles of matter that exist between the stars. The density is very low (only a few particles per square mile), but a ship traveling at 0.1c will collide with the particles at a speed that will do damage. The ship will need some type of thick shield that can survive the expected number of impacts that will occur during the long trip.
Finally, communication will be a problem. A radio signal degrades at a rate of the square of the distance. In other words, a space probe that is 10 times more distant than the Voyager probes will have a radio signal that is 100 times weaker. Centauri Dreams quotes a number that a probe at Alpha Centauri would be 1/81,000,000 the strength of the Voyager spacecraft from Neptune. As the signal gets weaker the data rate must be reduced. To keep the data rate the same as a probe transmitting from Mars using a 100-watt radio signal would require a tera-watt transmitter (one trillion watts) from Alpha Centauri.
Now you know why SciFi story writers ignore much of the science behind traveling between the stars. There is an assumption that technology will be invented that will make it all possible. The formulas for a warp drive system have been worked out by Miguel Alcubierre. How a device will be built that can exploit these formulas is beyond our current knowledge. The concept behind warp drive is that a device can warp space so the ship can skip over a large distance without breaking the speed of light. I’m keeping my fingers crossed that someone figures out how to build a device to do this. I suspect it won’t happen in my lifetime.
Some SciFi stories skip over the actual technology used and just call it an FTL or Faster Than Light drive. Sometimes they’ll call it a jump drive, or hyper-drive. We, the readers, don’t really care about the technology behind the drive system as long as it sounds plausible. The Expanse did a good job of using reactors or nuclear drives. These were not interstellar ships and they still had an episode that explained a technology that some “loner” scientist/engineer came up with to make the acceleration possible with little fuel.