Neutron Slingshot: new interstellar propulsion method

[Martin]

Unless I am mistaken, a new method of interstellar propulsion has been invented here at SFN, and blike may wish to apply for a patent so that everyone can share in the royalties

 

the method is based on the fact that

http://www.scienceforums.net/forums/showthread.php?p=208256#post208256

our galaxy is full of neutron stars whizzing around at speeds up to 1000 kilometers a second.

 

Here is a map that shows over 200 of them with arrows to show the speed and direction----look at Figure 1 on page 2 of:

http://arxiv.org/abs/astro-ph/0504584

 

so the method is TO HOOK A RIDE by means of GRAVITY SLINGSHOT.

 

It takes neglible propulsion compared with what you get, but the tradeoff is you have to be patient and wait until conditions are right. You wait until one of these suckers passes by here within a couple of LY of the sun and you get out there and wait in its path (somehow, a slow spacecraft can do it if you know well enough in advance)

 

And it comes along at 1000 km/s

 

and you hang a tight orbit around it which results that you are now going in the same direction as it but almost TWICE AS FAST

 

so you are now going almost 2000 km/s

 

that is easily enough to escape from this galaxy

 

from the neutron star point of view, you come in towards it at 1000, and whip around like a comet, and go back out at 1000 towards where you came from

 

but from your point of view you just picked up a speed of 2000 km/s

 

IT WOULDNT DO FOR PEOPLE though, because conditions near a neutron star are apt to be a bit rough on living organisms (maybe someone who knows more about neutron stars can make this precise). So this is really more for robot spacecraft.

 

Basically this is just the same gravity assist maneuver that several spaceprobes have used with Jupiter (and other planets) where you get out to Jupiter's orbit and wait there with neglible velocity and Jupiter comes by and you fall in towards and whip around it and come out with Jupiter orbit speed plus whatever your approach speed was. the limit being how close to center of mass you can approach----Jupiter is not perfect for this because it is fat, but a neutron star would be ideal because all that mass concentrated in small radius.

[ydoaPs]

so, gravity assist with a star that is quickly moving relative to you?

[Martin]

so, gravity assist with a star that is quickly moving relative to you?

 

that is right, maybe like pinball you could zigzag among stars and pick up some speed in several successive encounters

 

 

neutron stars are good because they have very high speeds (some of them, like 1000 km/s) and because you can come in very close to the center of mass

 

 

the closer you come to the center of mass the more efficient it is. I forget the details. maybe you or somebody else can help out.

 

actually I need to brush up on gravity assist, not sure what is possible with a fast neutron star, anybody up on this?

[[Tycho?]]

I'm not sure if I'd call this a new form of propulsion, its just gravity slingshot using a particular case which will probably never come up. Neat idea however.

[Martin]

'']I'm not sure if I'd call this a new form of propulsion, its just gravity slingshot using a particular case which will probably never come up. Neat idea however.

 

you are right Tycho

 

it is not really a new form of propulsion, and not really practical either

 

but the idea intrigues me anyway. those neutron star speeds are impressive

 

right now it is bugging me that I can't recall the formula for the slingshot angle

it is trigonometrical and it depends on the ratio of the speed you come in with to the ESCAPE VELOCITY at however close in you get.

conceptually I am relying on the escape velocity from the neutron star being very high because you can, in principle, get very close, and this making the gravitational assist very efficient, but i can't remember the formula

 

EDIT, some online stuff:

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

http://www.mathpages.com/home/kmath114.htm

http://www.go.ednet.ns.ca/~larry/orbits/gravasst/gravasst.html

 

LATER EDIT: Ahhhh! found it.

It gives a formula for the turn angle. For maximum efficiency you want the turn angle to be 180 degrees------the hairpin

 

[math]2\arcsin \frac{1}{1+rv_{\infty}^2/GM}[/math]

 

this is the turn angle flying by a body with gravitational parameter GM where r is the closest approach to center. Here v-infinity is the speed of approach at infinity. This can be rewritten in terms of v-infinity and v-circ, the circular orbit speed at the distance r of closest approach:

 

[math]2\arcsin \frac{1}{1+v_{\infty}^2/v_{circ}^2}[/math]

 

the good thing about neutron stars is you can get in very close and make v_circ very large compared with your v_infinity, so you are basically taking the arcsine of ONE which is 90 degrees and twice that is 180 degrees.

So you can do a hairpin around a neutron star, even if you are approaching it at 1000 km/s. Reassuring what?