The Science in Your Science Fiction: Conventional Space Travel

by Melanie Marttila
published in Writing

If you’re writing near-future science fiction involving space travel, along the lines of Andy Weir’s The Martian, or alternate history science fiction, like Mary Robinette Kowal’s The Calculating Stars, you’re going to find your space travel limited to what we can currently achieve.

When NASA, or a similar space organization, launches a rocket loaded with fuel, supplies, and astronauts, it may take hours (if your characters are traveling to the moon), days, months, or even years (if they’re going to Mars, or another destination in our solar system) to get to their destination.

Back in 2016, I attended a presentation at WorldCon by astronaut Stan Love on “why Mars is so hard.” It was a fascinating and, frankly, startling look at what it really takes to travel in space with our current level of technology.

Because he understood that he was addressing an audience of science fiction fans and authors, Love stayed away from the specific calculations, as will I. Though research will always be necessary, it’s not as necessary to put formulae and technical detail into your fiction. You need enough to make your story believable, and you must be certain that the science you choose to include is accurate, but you want to avoid the dreaded infodump.

Love illustrated the difficulties of space travel with a trip that NASA astronauts have accomplished six times: the moon landing.

But first — a few things to know before we leave the ground.

The largest part of any rocket’s payload is always fuel. It takes a lot of fuel to escape gravity, less to manoeuvre, another large amount to decelerate and land, more to leave the moon–despite its lower gravity–and another small amount to manoeuvre the craft to re-enter the atmosphere at the proper angle. The moon missions to date have landed back on Earth in an uncontrolled fashion, decelerating using parachutes, and touching down in a body of water, which, while softer than the ground, is still quite an impact.

Rockets also have to carry the oxygen the astronauts breathe, food and water, and any equipment they might need to conduct the mission’s experiments. And then there’s the weight of the astronauts themselves.

Calculating the right amount of fuel to get all this cargo to the moon and back, plus a little extra for emergencies, is a complex and critically important process. The sections of every rocket that break away as it ascends are fuel containers. As they empty, they are ejected. This changes the overall weight of the vehicle and, once the rocket leaves the atmosphere and the largest part of the gravity pull of Earth, less fuel is needed. The calculations must be adjusted every time weight or the force of gravity change.

The trajectory of the rocket/landing module must also be precisely calculated. Earth rotates on its axis, so what looks like a straight rocket shot is actually a curve. The gravity well of the planet must be escaped at an angle to conserve as much fuel as possible. Usually a rocket enters an orbit around Earth until it can line up with the moon, leaves that orbit, again at an angle, and makes another curving approach to the moon to accomplish its lunar landing.

Imagine the calculations that had to be done to accomplish the very first moon mission. They had little hard data to work with. Everything was theoretical. Hidden Figures, I’m looking at you brilliant women. If you need a moment to boggle, I’ll wait 🙂

Now, onto the moon!

Nine problems a character may encounter on a voyage to the moon

1) Launch

Though gravity is the weakest of the four forces we currently know about (electromagnetism, the strong and weak nuclear forces, and gravity), it still takes a huge amount of force to break away from it. It’s not just the amount of fuel, but also the integrity of the rocket. If there’s a leak, or a crack, or a structural weakness, it could mean trouble.

Possible negative outcomes can include (but aren’t limited to): explosion at ignition, failure to ignite, launch followed by explosion.

2) Reaching escape velocity

Escape velocity is the speed at which the rocket with its payload escapes Earth’s gravity well.

Negative outcome: fuel miscalculation or non-catastrophic leak could mean escape velocity isn’t reached, gravity pulls the rocket back down, and it crashes.

3) Stage separation

The various stages of the rocket separate at different points along its journey, so this is a recurrent problem to contend with. If the stage does not detach, or does so imperfectly, there’s no longer enough fuel to get the rocket where it needs to go because of the added weight. Depending on where that happens, it could result in different challenges.

Negative outcomes: if before the rocket escapes the gravity well, gravity pulls the rocket back down, and it crashes; if after, the rocket may be stuck in orbit with insufficient fuel to re-enter the atmosphere safely with the extra weight, resulting in the aforementioned crash, or potential starvation or suffocation before a rescue can be mounted; the non-ejected fuel tank may change the pull and trajectory of the rocket, again causing it to crash or be stranded in orbit; if it is only the final separation that fails, the landing module may crash on the moon, or may be unable to safely return to Earth (crash, or starvation or suffocation).

4) Achieving orbit

The rocket slips into orbit at an angle. If this doesn’t happen at the right time and position, the rocket may not achieve orbit.

Negative outcomes: possible crash, or rocket overshoots and continues on its trajectory, missing the moon and possibly being stranded in space.

5) Lunar approach

The rocket stays in orbit, circling the planet until the proper exit point is reached, slips out of orbit and approaches the moon on a curving path until there is sufficient lunar gravity to assist in the module’s landing.

Negative outcomes: orbital escape is not precise and the rocket isn’t on the correct trajectory, misses the moon, and is stranded in space; approach is mistimed, module misses the moon and is similarly stranded.

6) Lunar landing

Though the module will use the moon’s gravity to assist in the landing, there’s still some manoeuvring to line the module up with the proper landing area. Also, thrusters have to be fired to slow the module on its way down.

Negative outcome: the module crashes into the moon.

7) Lunar escape

As with the launch, the module’s departure from the moon had to be calculated exactly. It has to be on the right path to pass through orbit and the atmosphere, and safely land.

Negative outcomes: module fails to leave the moon resulting in starvation or suffocation of the astronauts; module leaves at the incorrect time, or thrusters misfire causing the module to bounce off the atmosphere and get stranded in space, enter the atmosphere at the wrong angle, or re-enter at the wrong place, missing the landing zone.

8) Re-entry

The module must eject its final fuel tank and thrusters, becoming a pod, and re-enter the atmosphere at the right angle. The tiles that protect the pod against the stresses of re-entry are only on the part of the pod that takes the brunt of atmospheric friction. The point at which the pod re-enters the atmosphere is also critical to reaching the proper landing zone.

Negative outcomes: friction bounces the pod back out of the atmosphere and it is stranded; the pod catches fire or burns up in the atmosphere; the pod misses the landing zone.

9) Splashdown

Once the pod is clear of the worst of the atmospheric friction, giant parachutes are deployed to slow descent. When the pod lands in the water, flotation devices inflate to keep it afloat until the astronauts can be extracted.

Negative outcomes: Chutes fail to deploy, are tangled, or are damaged resulting in crash; flotation devices fail to inflate and the pod sinks.

Stan Love emphasized each stage and issue in the mission with these words: … and then you die. By the end of his presentation, the audience was saying it along with him.

I have to point out that nearly every disaster has been considered, contingency plans for each potential problem have been devised, and the astronauts trained to anticipate and resolve them. For example, if the first stage fails to separate, there may be time to manually eject the pod and deploy the parachutes before the pod crashes. It depends on when it happens and how much time the astronauts have before impact.

But considering the danger and difficulty of a moon landing, think of how much more complex a mission to Mars would be. Because the length of the journey would be approximately 300 days, the better part of a year, conflicts between the astronauts would also have to be taken into consideration.

If you employ conventional space travel in your novel, the potential problems I’ve listed above can afford all kinds of juicy conflict for your characters to encounter. As ever, I’ll recommend research and possibly expert review. Andy Weir consulted experts to fact-check his science in The Martian and Mary Robinette Kowal attended a NASA launch as part of her extensive research for The Calculating Stars. Here are a couple of places to start: NASA’s Space website and the Jet Propulsion Laboratory website.

I hope you have fun writing your space travel adventure!

Melanie Marttila creates worlds from whole cloth. She’s a dreamsinger, an ink alchemist, and an unabashed learning mutt. Her speculative short fiction has appeared in Bastion Science Fiction Magazine, On Spec Magazine, and Sudbury Ink. She lives and writes in Sudbury, Ontario, Canada, where she spends her days working as a corporate trainer. She blogs at and you can find her on Facebook and Twitter.

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