Best Way Of Setting Astroid Capture Node?

[Clipperride]

I seem to have a few questions since I actually got into playing Career Mode

I've just done my very first astroid redirect contract (a little class A number) but found setting up the maneuvere node to reach the astroid a little tricky.  Basically I just played with the node handles until the one I was tweaking stopped reducing the distance and then moved on to the next.

What's the best way to set a maneuvere node from LKO to intercept an astroid in Kerbins SOI?

[Gordon Fecyk]

Ho boy... I've only done this a couple of times myself. The last time I tried catching a rock within Kerbin SOI, I looked at the needed delta-v and went, "screw this,' and planned to intercept it while still outside of Kerbin SOI. That rock will be travelling at interplanetary speed when it crosses Kerbin SOI, and quite likely on some bizarre plane compared to your standard orbit.

What I do know, is intercepting a rock around the sun is similar to intercepting a smaller object in low Kerbin orbit, just on a much larger scale. But to use the technique you just described, you'd have to have your target's ascending or descending node match your intersect, and then fiddle with the radial and prograde directions. Then you find the AN or DN moves too far away from the intersect, and you have to repeat that.

If that sounded too complicated, I feel your pain. It's still complicated for me, too.

It may be a lot simpler to get out of Kerbin SOI and match orbital planes first, so you then only have two dimensions to worry about, at least at first. You can also place multiple manoeuvres; place one at the AN or DN and fix the plane, then place another one on the new predicted orbit to do the intercept.

If you're planning the whole course from low Kerbin orbit, you can do your escape node out to the AN or DN first, then add a plane change node there, and finally add a third node somewhere past the plane change one to intercept it. Yes that's very wasteful in delta-v at first, but you can learn to combine manoeuvres later.

If it helps any, adding Kerbal Alarm Clock will show approximately where the AN and DN are on your current orbit if they are close, by putting "Warp to X" buttons on your orbit. Then you can combine your escape and plane change nodes at least.

(I might try making a tutorial video later. But I'm sure there are folks who've done that.)

--

[Snark]

14 hours ago, Clipperride said:

What's the best way to set a maneuvere node from LKO to intercept an astroid in Kerbins SOI?

It's a little different from launching a ship to collect a kerbal in Kerbin orbit... but not that different.

1. Launch into circular LKO, in the correct plane (not equatorial), well in advance.
   • When the asteroid crosses Kerbin's SoI, it'll be at some oddball plane, generally not equatorial.
   • So, launch directly into that plane, not equatorial.  Reason #1:  it'll save you scads of dV.  Reason #2: it'll make setting up the intercept much more straightforward.
   • To do this, just wait until Kerbin has rotated to the point that KSC is located directly underneath the future track of the asteroid, and then launch in the appropriate direction.
   • Once you're in LKO, you'll probably be a degree or two off the exact plane, unless you're really good.  So do a small burn at the AN or DN to get this nicely lined up, so you're perfectly in the plane that the asteroid's going to be.
2. Do a burn to raise your Ap up to the asteroid's projected Pe.
   • Drop a maneuver node at the point of your circular orbit that is exactly 180 degrees opposite where the asteroid's projected Pe is.
   • Drag prograde on the node until it raises your Ap up to where it just "kisses" the asteroid's path, and then just a tiny smidgeon beyond (so the single intercept marker splits into two markers, but they're still really close together).
3. Leave your ship parked there until the asteroid arrives at Kerbin's SoI.
4. Set up the rendezvous.
   • This is now simple and low-dV to do, because of the setup you've already done.
   • Just drop a maneuver node right at your Ap (which is the asteroid's Pe).  Note that there will be a marker showing the asteroid's projected position at your next intercept after the maneuver node.
   • Click the "+" button on the maneuver node-- note that the asteroid's projected position gets closer.  Do that a few more times until the asteroid's projected position gets fairly close.  If it goes past your projected intercept, you clicked "+" one time too many-- in that case, click "-" to back up, then stop.
   • Now drag the prograde handle on your maneuver node, and watch your projected orbit start to get bigger.  As it does this, the projected intercept point will slide closer and closer, and your distance-at-closest-approach will become smaller and smaller.  Carefully adjust until you've gotten that intercept distance down to zero, or close to it.
   • Do the burn when it's time.
5. Wait for the asteroid to come to you.
6. Match velocities at closest approach.
7. Profit!

[Clipperride]

Thank you both for your answers.  I thought my method was a little on the rubbish side - lots of ∆v and roughly 1½ episodes of Red Dwarf to get the pesky node to give me an encounter within 1km.  It was lucky I tested the waters with a Class A astroid. At least it didn't take much of a burn to put it into Kerbin orbit!

[Enceos]

There's also a more advanced technique of asteroid rendezvous in case your grabbing vessel is in an equatorial orbit:

1. Make a maneuver node to intersect the asteroid's orbit.

2. Place a second maneuver node some distance away from the intersection and the game will draw position markers.

3. Add more orbits to the first node to get the maximum possible approach of the position markers.

4. Adjust the second node to get the encounter.

[Tyko]

If you're open to mods - Precise Maneuver or Precise Node allow you to tweak your maneuver by as little as .01 DV. I've found this to be invaluable when you're plotting intercepts millions of kilometers away.