Where to set up observers on Kerbin for a close encounter?

[maddog59]

I found a Class C asteroid that was going to impact Kerbin, and I managed to intercept it far enough out and moved it to a close encounter - 1400 m (not Km, not Mm) from Kerbin. I've got one brave Kerbal who's going to be riding along in the shadow, and I expect Hammer I to put on a pretty show as it passes by, so I'd like to figure out where to set up  one or more ground observers. Any suggestions? 

[AHHans]

Not an answer but another question - or a remark if you want, -  if you have a vessel that is not connected (e.g. via a Klaw) to the asteroid but following that asteroid (in its "wind shadow") while it enters the atmosphere: will it actually be shielded from atmospheric effects? The way I understand KSPs physics engine, if you are separate vessels then you experience the full atmospheric effects, no matter where you are in relation to that big asteroid.

[king of nowhere]

i would suggest to save the game, fast forward until the close pass (by the way, the asteroid will probably hit kerbin anyway, air drag will slow it down), and see on the map where it impacted. record the position, kerbin has some nice continents you can use as landmarks. then reload, and send observers to that position

[jimmymcgoochie]

Kerbin rotates once every 6 hours (one degree per minute) so you can calculate a likely impact site by the asteroid’s time to Kerbin periapsis, specifically the hours/minutes/seconds: for every hour away from a whole day the periapsis is, the impact point will be 60 degrees west of where it appears on Kerbin now; for every minute, one degree west. Example- Kerbin periapsis is right on the KSC but in 5d 2h 17m, you’d need to put your observer (60*2)+(1*17)=137 degrees west of the KSC.

You’ll also need to compensate for orbital inclination by changing your latitude to match the periapsis’ position, and remember that once the asteroid hits the atmosphere it’ll slow down due to drag so will almost certainly drop short of the projected periapsis if said periapsis is deep in the atmosphere; the Trajectories mod might help with this especially for inclined orbits. It’s also possible that your ground observers won’t be within active physics range of the asteroid as it flies into the atmosphere so they might not see anything, or the asteroid might get deleted when it drops below the minimum altitude in atmosphere (I believe it’s 25km on Kerbin) so you might want to use Physics Range Extender to prevent this.

[maddog59]

3 hours ago, AHHans said:

<snip> if you have a vessel that is not connected (e.g. via a Klaw) to the asteroid but following that asteroid (in its "wind shadow") while it enters the atmosphere: will it actually be shielded from atmospheric effects? The way I understand KSPs physics engine, if you are separate vessels then you experience the full atmospheric effects, no matter where you are in relation to that big asteroid.

That's what I figured, so I have Asteroid Intercept II attached to Hammer I by a klaw, and using it to make small adjustments (and yes, I suffer from a deficit of imagination). 

@jimmymcgoochieyou give my math skills WAY to much credit!  I think I'm going to have to use @king of nowhere's suggestion and do it through the magic of time travel. One thing I found is that the path is highly inclined so it's going to pass over the Southern Ice Cap, with closest approach being somewhere just off shore (I hope). So I'm hoping to put up a couple of Ice Stations to get different angles.

I didn't know that asteroids get deleted once they get too close to Kerbin ... I'm hoping that won't be the case since there's a ship attached.  Thanks for reminding me of the atmo drag effects ... I'm sure I'll have to play with the approach to get it right. 

If I get some decent videos I'll try to edit them together into a nice montage and post it. Thanks to all of you.