The scientific expedition has a problem. Their experiment, which is supposed to help them better understand gravitational effects is stuck on the surface of the strange planet Mesklin, where the surface gravity is so powerful humans cannot go down and fix the craft. On the bright side, there is an intelligent race of centipede-like creatures inhabiting the world, and the captain of a seagoing vessel has agreed to embark on a journey to locate the device.
And so our adventure begins.
Barlennan, captain of the sailing ship Bree, and his crew embark on an adventure from the equator of their plate-shaped planet (where the gravity is three times Earth's), to the pole (where gravity is several hundred times Earth's). On the way they will encounter storms, strange creatures, unexpected geography, strange countries and barbarians.
Mission of Gravity provides examples of:
- Alien Non-Interference Clause: Played with. The human crew attempt to minimize the impact they have on the natives of Mesklin. They're even loathe to share anything more than they have to with Barlennan, and their audio-visual communication abilities are treated as magical by natives. Despite this they still are forced to depend on Barlennan's help and collaborate with him the entire way. In the end, Barlennan forces their hand by proving a shrewd businessman (businessbug?) and renegotiate the precious probe data in exchange for their knowledge. Although at this point, he perfectly understands that the technological advance of the humans is considerable, and that his people can only dream of catching up within many generations. But the Mesklinites are still happy with learning everything they can from the scientists.
- All Planets Are Earthlike: Extremely averted. Mesklin is not only extremely cold, but its day is less than 20 minutes, so it's lens-shaped rather than spherical. The equator is only barely reasonable for humans to visit with assistance.
- All There in the Manual: Clement published an essay titled Whirligig World along with the novel when it was serialized in the magazine Analog, detailing the planet Mesklin and his process for designing it — including a couple of points where he admitted to not following physics for the sake of the story.
- Black Box: The probe, to the Mesklinites. They hope to use it as a bargaining chip.
- Bold Explorer: Barlennan and his crew travel into the unknown, for their planet. But they hope to make a profit, eventually.
- Double-Meaning Title: The mission involves a probe which studies gravity, and it is a mission of importance.
- Fantasy World Map: Inverted. Clement created a globe of the planet Mesklin and wrote the story around it, but the book didn't include a map.
- The Federation: The mention of humans having other races along for the expedition is made, but not dwelt upon.
- Heavy Worlder: The inhabitants of planet Mesklin (which not only has high gravity, but extremely fast rotation) are adjusted to this by looking somewhat like flat centipedes. The Mesklinites are the main characters of the story.
- Higher-Tech Species: The humans are this to the Mesklinites.
- Hollow World: Due to a combination of its gravitic and atmospheric oddities, Mesklin was thought by its inhabitants to be bowl-shaped. They were incorrect.
- Humans Through Alien Eyes: This book gives us a view of humanity from an alien centipede who is terrified of heights greater than a few centimeters. The humans' insistence on standing upright seems dangerously insane.
- Inflation Negation: A great deal is made about how the probe at the pole cost TWO BILLION dollars, and indeed in 1954, $2 billion was a lot of money. Factoring inflation, $2 billion in 1954 dollars is about $17 billion in 2015 dollars. Of course, having actually seen space projects that have cost far more than that (The International Space Station alone has cost $150 billion so far), how much could those humans be costing their superiors to spend their time hanging around Mesklin waiting for Barlennan?
- In Medias Res: When we first meet Barlennan, he's already met the humans and agreed to take the journey.
- Moving the Goalposts: Barlennan stops just short of the goal to renegotiate.
- No Plans, No Prototype, No Backup: The probe on the planet is the only one the humans have. There is no backup plan for if it doesn't launch... and it didn't.
- Primal Fear: Mesklinites have extreme and justified fears of heights and falling objects. In the polar regions of Mesklin, falling even a very short distance is fatal and chunks of ice falling off the tops of what short cliffs there are hit the ground at the speed of sound.
- Weather Report Opening: The book opens with the description of a storm hitting the Bree.
- World Shapes: Due to the planet's intense gravity, the density of Mesklin's atmosphere varies so strongly with altitude that refraction makes it look bowl-shaped. The Mesklinites can see that the world curves up around them, so they believe that they live in a giant bowl. They are skilled sailors and map-makers and should know better, however when you are measuring distances on a curved surface, there are two different shapes that will make all the math work out (convex and concave). The Mesklinites — at least those who usually live far from the equator — chose the wrong one for their maps and never noticed. The result is perfectly accurate and usable maps based on a fundamentally flawed premise.
- The World Is Not Ready: The justification the humans use for why they're so cagey about sharing any information with Barlennan. Eventually he gets fed up and demands more information before he'll complete his mission.
