Asteroid intercept and circularization - estimating DV requirements

[Tyko]

How would I build an estimate for the DV cost of intercepting and then slowing an asteroid down to a Kerbin orbit. There are two numbers that I'd need and I'm not sure how to get either 1) the asteroid's speed at PE over Kerbin and 2) the asteroid's mass.

So far I've thought that I could rendezvous a small tracking probe first. If it could Claw onto the asteroid I think that KER would give me the total mass of probe + asteroid.

[Plusck]

1 hour ago, tjt said:

How would I build an estimate for the DV cost of intercepting and then slowing an asteroid down to a Kerbin orbit. There are two numbers that I'd need and I'm not sure how to get either 1) the asteroid's speed at PE over Kerbin and 2) the asteroid's mass.

So far I've thought that I could rendezvous a small tracking probe first. If it could Claw onto the asteroid I think that KER would give me the total mass of probe + asteroid.

Asteroids are generally within a fairly narrow range of orbits around Kerbin (I haven't seen a real fast-moving one yet, put it that way).

That means they basically all hit Kerbin's SOI with very little speed. That means they're passing Kerbin at the sort of speed you'd be going if you wanted to go to Duna or Eve, to within 100m/s or so...

Another way of looking at it is just to select it as target. You'll see when it enters the SOI and when it leaves. If that's a 25-day difference, you'd only have to breathe on it to capture.

[Aegolius13]

You can cheat and look at the asteroid stats in the save file

Or you're right, you can send a little probe.  In addition to mass, you can plot a maneuver node and see what it will cost to move it where you want.  Recall that delta v for a maneuver is independent of mass, so that part will be right even with a different ship.  But you'll need to include that mass when figuring out your ship's delta v capacity. 

If you plan to mine the asteroid with the larger ISRU, most of the asteroid mass is effectively wet mass.  Which makes things much easier.

[WanderingKid]

I'm sorry, I can't answer your questions directly, but I can try to help with what you're aiming for:

Rough Guide for weights (best to worst case) when you're in the hangar:

A Class (2.1-9.5 tons): FL-T400 to a RockoMax X200

B Class (9.5 - 42.5): X200  to a Kerbo S3-7200

C Class (42.5 - 190): Kerbodyne S3-7200 to 2xS3-14400

D Class (190 - 854): 2xS3-14400 to Kerbin-Eve Round Trip direct flight ship.

E Class (854 - 3828): Bring mining equipment and prepare for very slow adjustments.

Interception of the Asteroid isn't usually too bad.  From LKO (Low Kerbal Orbit) for a deep space rondevous (my preferred method) you'll typically spend 1000 or so d/v to get out of Kerbal SOI, another 500 or so in adjustments for the rendezvous, and between 2000-3500 on the intercept.  You can save some d/v if you can launch on the right plane for reversing the intercept to approach it in deep space. 

Once you've got the asteroid, it's a matter of where do you want to put the asteroid?  Adjusting the asteroid's course for Kerbal intercept isn't usually too bad.  Anywhere from 50-300 d/v in my experience, depending on how outrageously you're changing it.  Obviously you can get excessive but I usually just pick a different asteroid if that's the case.  From there, if you're trying for LKO in the 75k range, I recommend you build with the idea of your ship hiding behind the asteroid for an aerobrake. If you're just needing to get it into any orbit aim for the outer edge of SOI and brake way out there, it'll save you a ton and you won't care if you're pro or retrograde or even on an equatorial orbit.  It all depends on where you want it when you're done.

Edited October 27, 2016 by WanderingKid