# I Does the gravity sling require rocket guidance to be non-negligible?

#### Jonathan212

Is the gravity sling possible without rocket propulsion which dynamically guides the object to the right point? Ie, if instead of using a rocket, you shoot the object with an accurately aimed cannon from the moon, will it either hit the planet or miss it but never get slung/accelerated substantially?

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#### phinds

Gold Member
Is the gravity sling possible without rocket propulsion which dynamically guides the object to the right point? Ie, if instead of using a rocket, you shoot the object with an accurately aimed cannon from the moon, will it either hit the planet or miss it but never get slung/accelerated substantially?
Slingshot depends only on the rocket having the right trajectory as it approaches the large object. If you can aim a cannon to put it there then it will get the gravity assist.

#### Jonathan212

Did the spaceships that used the slingshot make a turn with the rocket propulsion to get the right angle of approach?

#### phinds

Gold Member
Did the spaceships that used the slingshot make a turn with the rocket propulsion to get the right angle of approach?
Depends on whether or not they were already on the right trajectory.

#### jbriggs444

Homework Helper
Taking the question in a broader context, a space craft using a slingshot maneuver is an example of a three-body problem. You have the craft, the object being sling-shotted around and, presumably, a primary (e.g. the sun) about which the object is orbiting.

Except for a few special cases, the three body problem has no stable solutions. It yields a result which can depend critically on small variations on the initial position, speed and direction of the craft. A tiny margin of error can, over a sufficiently long period, make the difference between an eventual collision, a temporary capture or an eventual ejection on an escape trajectory.

#### Jonathan212

How do we define a stable solution of an N-body problem?

"Does the gravity sling require rocket guidance to be non-negligible?"

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