Slingshot around gravitational bodies

[aman]

I am trying to understand the theory behind "slingshotting" around planets or suns. I can see the benefit of aiming towards Jupiter and missing it to reach Saturn. Let the gravitational pull of Jupiter add to your acceleration and detract a bit once you are past it so you wind up with a net profit in avg. velocity. Is there a circumstance where it will actually give you a net increase in end velocity.

Just aman

[Kedas]

The law of containment of energy is in effect so no you don't gain energy from it but depending where your satelite is (in reference to gravitational pulls) you could have a bigger/lower velocity.

 

BTW what do you mean with 'end velocity'?

[YT2095]

I`m not 100% sure, but I think it`s more akin to using gravity as a Steering Mechanism rather that to gain Net momentum, it kinda saves having to use side thrusters

[aman]

By end velocity I meant at the point equidistant from the start so the gravitational pull had the same distance coming and going. I guess it works out to net zero but adds a plus in avg velocity over the entire path. Also now I see it does save a lot of fuel in making major course corrections. Thanks

Just aman

[alt_f13]

Whaaaa?

 

You accellerate until you reach escape velocity (not necessarily, but that is an extreme example), at which point the gravitational pull is not sufficient enough to pull you back in.

 

The total energy used going to and from a point in an orbit would be equal and opposite, but seeing as the object reaches escape velocity (or whatever velocity it needs to reach its final destination) before it has a chance to lose kinetic energy to gravitational energy, we do not observe the total conversion of energy.

 

And when accellerating, you might just accellerate past escape velocity all together.

[alt_f13]

Whoops most of that was just repeating what y'all just said, I think.

[swansont]

You can add to your KE if you do it right. The symmetry of losing as much energy as you gained is true for a stationary planet, but if you approach in the direction of the orbit, you can gain extra energy (the planet keeps moving away, so you spend more time/travel a longer distance accelerating toward it). The trick is that it is asymmetrical in our frame, so the energy lost is smaller than the energy gained. Here is amore complete explanation.

[Jenab]

I saw slingshot events happen during some of my celestial mechanics simulations. I was trying to determine how far apart a binary planet could be and stay bound. Beyond that point, the star's tides would unbind the pair, and each planet would thereafter pursue a separate orbit around the star.

 

I also modeled the orbits of planets in binary star systems, where the planet was initially loosely held by one star and strongly perturbed by the other. some very weird orbits can result. The planet can start out orbiting its primary star in a fairly well-behaved way, but before long it's sort of wandering around loose between and beyond the orbit of the two stars.

 

Sooner or later, this planet takes a prograde dive down close to one star or the other, and ZINNGGG... it's gone! As though the star kicked it like a football.

 

Jerry Abbott

[z9999GhZbRaiNzZ89]

that is sort of a large sling shot huh

 

 

[Joatmon]

You can add to your KE if you do it right. The symmetry of losing as much energy as you gained is true for a stationary planet, but if you approach in the direction of the orbit, you can gain extra energy (the planet keeps moving away, so you spend more time/travel a longer distance accelerating toward it). The trick is that it is asymmetrical in our frame, so the energy lost is smaller than the energy gained. Here is amore complete explanation.

 

Does the extra energy gained come from a minute slowing down of the planet? ( the link "here" isn't available so perhaps it covers my question)

Edited April 19, 2012 by Joatmon

[Janus]

Does the extra energy gained come from a minute slowing down of the planet? ( the link "here" isn't available so perhaps it covers my question)

 

Yes it does.

[Airbrush]

A good example of sling shotting is the Cassini mission to Saturn. It went towards the Sun first and gained speed from the inner planets a couple of times before heading outwards. Then it got another boost from Jupiter.

 

It was a once in a lifetime opportunity, since the planets would not be aligned that way for a long time.

 

"The Cassini space probe performed two gravitational-assist fly-bys of Venus on April 26, 1998, and June 24, 1999. These fly-bys provided the space probe with enough momentum to travel all the way out to the asteroid belt. At that point, the Sun's gravity pulled the space probe back into the inner Solar System, where it made a gravitational-assist fly-by of the Earth.

 

On August 18, 1999, at 03:28 UTC, the Cassini craft made a gravitational-assist flyby of the Earth."

 

 

http://en.wikipedia.org/wiki/Cassini_mission

Edited April 19, 2012 by Airbrush

[pantheory]

I am trying to understand the theory behind "slingshotting" around planets or suns. I can see the benefit of aiming towards Jupiter and missing it to reach Saturn. Let the gravitational pull of Jupiter add to your acceleration and detract a bit once you are past it so you wind up with a net profit in avg. velocity. Is there a circumstance where it will actually give you a net increase in end velocity.

Just aman

I have had at-length discussions on this subject with the mathematician and physicist Michael Minovich some 30 years ago or longer and more recently. He is the person who developed the original gravitational whip concept and calculations for NASA, which we have used ever since. You are correct in that by entering a gravitational field an object accelerates, and by leaving the system it loses this gained speed, with no net gain. The whip advantage instead comes from planetary momentum so a craft would enter the gravitational field in the direction of its planetary velocity around the sun and could leave the system in a hyperbolic passing with a net gain in velocity. The best planets for this procedure are Venus and our own planet because of both their mass and planetary velocity/ momentum. Mercury is distant and relatively small although its momentum is faster. Mars is both smaller and slower than Earth or Venus. And the outer planets although bigger, move much slower in their orbits providing a lesser gravitational assist than Venus or Earth could. For the larger planets the direction of their rotational velocity and the distance of approach is another consideration concerning a better whip or braking.

 

As far as an assist from the sun, when our spacecraft fly inward toward the sun they will accelerate. As they get a gravity assist from an inner planet they increase their speed again by this whip, but when flying away from the sun they lose this first advantage of accelerating inward. So the sun does not help or hurt. Gravity assists are also used for braking. When flying to the planet Mercury both Venus and the Earth can be used for braking when doing its flyby in the opposite direction of the planetary momentum. This braking system could have been used concerning Neptune, for a small fuel saving braking maneuver when settling into orbit around its moon Titan.

 

I have read some online explanations of these procedures that seem authoritative but are completely wrong concerning their explanations

 

http://en.wikipedia....chael_Minovitch

 

http://www.gravityassist.com/

Edited April 20, 2012 by pantheory