History Analysis / GravitySucks

The statite example in a science-fiction context provides an explanation for Gravity Sucking. If a ship, let's call it the ''[[StarTrek Enterprise]]'', was in a ''powered'' orbit, losing power could cause it to come crashing down. For instance, if it was holding position over one spot on the Earth's equator, but was at the orbit of the International Space Station (orbital period 92 minutes) instead of geostationary orbit (orbital period 24 hours), its orbital velocity would be nowhere near sufficient to maintain that orbit if the power goes out, causing it to be pulled down.

The statite example in a science-fiction context provides an explanation for Gravity Sucking. If a ship, let's call it the [[StarTrek Enterprise]]'', was in a ''powered'' orbit, losing power could cause it to come crashing down. For instance, if it was holding position over one spot on the Earth's equator, but was at the orbit of the International Space Station (orbital period 92 minutes) instead of geostationary orbit (orbital period 24 hours), its orbital velocity would be nowhere near sufficient to maintain that orbit if the power goes out, causing it to be pulled down.

The only two situation in which this trope might be justified is invove a satellite passing through the atmosphere and the theorectical example of a statite. If a satellite is currently in an orbit that would take it within the atmosphere of a planet and it lacked the means to sufficiently change its orbit such that the path no longer intersects the atmosphere. In this case, the orbit would decay, getting smaller with each time around the planet until it eventually crashes. What causes this is not the gravity, but rather the friction of the satellite passing the atmosphere slowing it down and reducing its angular momentum. This is how aerobreaking works, but is only usually attempted when the means of altering the orbit (aside from the atmospheric friction) is possible.

The only situation in which this trope might be justified is if a satellite is currently in an orbit that would take it within the atmosphere of a planet and it lacked the means to sufficiently change its orbit such that the path no longer intersects the atmosphere. In this case, the orbit would decay, getting smaller with each time around the planet until it eventually crashes. What causes this is not the gravity, but rather the friction of the satellite passing the atmosphere slowing it down and reducing its angular momentum. This is how aerobreaking works, but is only usually attempted when the means of altering the orbit (aside from the atmospheric friction) is possible.

If the ship is moving at any significant speed relative to the planet, in a direction other than straight up or straight down, its momentum will carry it past and create a centrifugal motion that balances against gravity. This is an application of Newton's First Law of Motion (Inertia): an object will not move unless a force acts upon it, but also an object will keep moving unless a force acts to counter it. The spaceship will continue to revolve around a planet as long as it never stops revolving. If it stops, then this trope applies. This is why the moon doesn't crash into the earth, because of such centripetal forces balancing the pull of gravity - as ''Franchise/TheHitchhikersGuideToTheGalaxy'' tells us, flying is simply the art of throwing oneself at the ground and missing...

A related subtrope involves a spaceship trying to escape a Black Hole or other gravitational BigBad by pointing the ship straight upwards, with the implication that it will fall back and be destroyed if the fuel runs out or [[PhlebotinumBreakdown something breaks]]. A more sensible approach would often be to thrust laterally, setting up a stable orbit and buying the Good Guys time to fix things. But that's not as dramatic, is it? [[note]] Not a good idea if inside 3x the critical radius of a black hole, however, as thrusting laterally will have a 50:50 chance of pulling the ship even closer to the event horizon if you thrust the right way, that is, in the same direction as your rotation. Thrust the wrong way and you wind up plummeting toward the event horizon, crossing it in a matter of seconds or less. Inside 1.5x the critical radius, ANY horizontal thrust will cause you to be pulled toward the horizon because gravity will increase by a factor greater than your rotation can resist.[[/note]]

Despite this, fictional spacecraft have the nasty habit of [SpaceIsAir plummeting from the sky like bricks]] the moment their engines go off-line.

Despite this, fictional spacecraft have the nasty habit of plummeting from the sky like bricks the moment their engines go off-line.

A related subtrope involves a spaceship trying to escape a Black Hole or other gravitational BigBad by pointing the ship straight upwards, with the implication that it will fall back and be destroyed if the fuel runs out or [[PhlebotinumBreakdown something breaks]]. A more sensible approach would often be to thrust laterally, setting up a stable orbit and buying the Good Guys time to fix things. But that's not as dramatic, is it? [[hottip:*: Not a good idea if inside 3x the critical radius of a black hole, however, as thrusting laterally will have a 50:50 chance of pulling the ship even closer to the event horizon if you thrust the right way, that is, in the same direction as your rotation. Thrust the wrong way and you wind up plummeting toward the event horizon, crossing it in a matter of seconds or less. Inside 1.5x the critical radius, ANY horizontal thrust will cause you to be pulled toward the horizon because gravity will increase by a factor greater than your rotation can resist.]]

If the ship is moving at any significant speed relative to the planet, in a direction other than straight up or straight down, its momentum will carry it past and it won't actually hit. This is an application of Newton's First Law of Motion (Inertia): an object will not move unless a force acts upon it, but also an object will keep moving unless a force acts to counter it. The spaceship will continue to revolve around a planet as long as it never stops. If it stops, then this trope applies. This is why the moon doesn't crash into the earth, because of such centripetal forces balancing the pull of gravity - as ''Franchise/TheHitchhikersGuideToTheGalaxy'' tells us, flying is simply the art of throwing oneself at the ground and missing...

Few people seem to understand that this trope only applies when you're actually in the event horizon, the actual black hole where light cannot escape. Keeping a large distance away from the black hole's centre can, in fact, sustain orbit, as long as the orbiting body does not stop orbiting and continues to generate centrifugal force. Once the orbit stops, the the gravity will suck.

Few people seem to understand that this trope only applies when you're actually in the event horizon, the actual black hole where light cannot escape. Keeping a large distance away from the black hole's centre can, in fact, sustain orbit.

The trope stems from a naive Aristotelian view of gravity, coupled with SpaceFriction. After all, a baseball falls to the ground, so do asteroids; why shouldn't a spaceship? If the ship is moving at any significant speed relative to the planet, in a direction other than straight up or straight down, its momentum will carry it past and it won't actually hit. This is an application of Newton's First Law of Motion (Inertia): an object will not move unless a force acts upon it, but also an object will keep moving unless a force acts to counter it. Unless something like a gas cloud acts on the ship to counter this inertia and slow it down (friction), it will continue to miss the planet until slight variations in the path happen to bring it into the planet itself, which can take quite a long time. This is why the moon doesn't crash into the earth, because of such centripetal forces balancing the pull of gravity - as ''Franchise/TheHitchhikersGuideToTheGalaxy'' tells us, flying is simply the art of throwing oneself at the ground and missing...