Rendevous with asteroids

[tomf]

What is the best way to set up a rendevous with an asteroid?

I have a target asteroid in mind that will enter Kerbin's SOI in a few hundred days on an inclined hyperbolic orbit. The asteroing is a D class and its eventual target is Gilly so I would like to capture it before intercept and use Kerbin for some slingshot. I am capable of setting up a burn from Kerbin's orbit that will get me to within a few hundred kilometer of an intercept, and then fine tune to much closer. However when I get close I require a massive burn to match speed with the target.

Can anyone describe, from launch to capture, an optimal (in delta-v) strategy for lassoing asteroids?

[TheXRuler]

Sadly I don't have a lot of time on my hands atm, however I will just quote myself

ARM missions can be hard...

As Randazzo says, the best way is get your relative velocity at closest approach to a minimum.

Eg you could get a kerbin escape, then adjust your solar orbit to intersect the asteroids orbit before it enters Kerbins SOI. This should significantly reduce the dV costs, as only a small velocity change is required to alter the ateroids course when you are further away from Kerbin.

If however the asteroid is inside kerbins SOI your best option might be to launch to an orbit wich is going the same way as the ateroid will when it passes Kerbin, taking account of the inclination, as launching to an inclined orbit is cheaper than making an inclination change burn while in LKO. Once in LKO you could raise your ap and then try getting a close approach to the asteroid as far from Kerbin as possible.

and link you to [thread=114501]this Thread[/thread].

The biggest problem with D-Class Potatoes is that they are very heavy, meaning they will reduce a ship with say 4000 m/s dV to a few hundred at best.

[AlexinTokyo]

I heartily recommend Claw's excellent tutorial: link

[tomf]

Ok, that was what I was doing before. I was hoping that there was a method that would avoid the 700-1700 m/s of Claw's step 5.

[Superfluous J]

Ok, that was what I was doing before. I was hoping that there was a method that would avoid the 700-1700 m/s of Claw's step 5.

Sadly, no. You can't rendezvous with something going X m/s faster/slower/different than you, without making a burn going X m/s.

[Mister Dilsby]

Best practice to rendezvous with anything is to reduce relative velocity to zero as you reduce distance to zero. On the navball, you will "push" the retrogade marker towards target heading as you approach, thus reducing velocity and correcting heading at the same time. If approaching at ~1km/s I like to decelerate to ~100m/s within 20km, and steadily decrease until I am closing at ~10m/s with 2km to go and ~1m/s within 100m.

[thadisjones]

Best practice to rendezvous with anything is to reduce relative velocity to zero as you reduce distance to zero.

This is more than a best practice, it's pretty essential. Generally it's important to make sure your time-to-target is always greater than the minimum time at max thrust you'd need to align and cancel your relative velocity. For example, if you're closing on an asteroid 200m away, and your relative velocity is 20 m/s, you have 10 seconds to counterthrust. Otherwise you hit the target, or go flying past it and then waste more fuel trying to reverse relative course and catch up.

<plows SSTO full of fuel through space station at 50 m/s>

Edited April 13, 2015 by thadisjones

[Superfluous J]

This is more than a best practice, it's pretty essential. Generally it's important to make sure your time-to-target is always greater than the minimum time at max thrust you'd need to align and cancel your relative velocity. For example, if you're closing on an asteroid 200m away, and your relative velocity is 20 m/s, you have 10 seconds to counterthrust. Otherwise you hit the target, or go flying past it and then waste more fuel trying to reverse relative course and catch up.

While this is true if you're not thrusting, it's not true when slowing down. If you can thrust at 20 m/s (2 gees, not that hard to do really) then you should wait until you are 1 second away to thrust.

It also helps to not aim directly at the thing, so if you mistime it you pass a little, not crash