Bring a Newly Discovered Class A Asteroid Into An Orbit Around Kerbin

[genekrantz]

Contract: Bring a Newly Discovered Class A Asteroid Into An Orbit Around Kerbin

I have spent the better part of the day going through a few video tutorials on intercepting asteroids including this nice tutorial . For a Class A asteroid that is on a collision trajectory with Kerbin, I have been unsuccessful in intercepting the asteroid and a lot of the information out there seems tailored around capturing asteroids that will not impact or get very close to Kerbin.

My current procedure is the following:

1. I have built a big rocket

2. I launch matching the inclination of the target asteroid

3. I circularize my orbit

*4. Create a new maneuver node and attempt to line up intercept points on target asteroid. <-- This fails I seem to not be able to get intercept points to closely match up.

Question

1. What is the best way to setup an intercept for an Asteroid of this type, where the target will impact or get very close to Kerbin?

2. How close should the intercept be?

I have performed rescue missions and rendezvous docking without much trouble, my main problem with this contract is being able to get an intercept that is close enough. Thanks in advance for any help you can provide.

[Claw]

You'll want to set up your maneuver at the asteroids lowest point of the pass (PE) even if it's going to impact. If you put it in another spot, your craft's orbit will be misaligned with the asteroids inbound leg (resulting in no rendezvous).

As you saw in my tutorial, I prefer to meet with the asteroid further out. When you do that, you can just sort of initially eyeball getting the orbits to intersect. This gives a lot more time to adjust things but takes longer for it all to happen. Some people prefer waiting until it reaches the SOI but I found that to be a lot more effort with timing and getting things all lined up.

The path of the asteroid in that picture does look a bit unusual, but it's hard to tell from that picture. Is the asteroid just glancing off the side of Kerbin's SOI? It should still have a low point. If you can't get perfectly lined up, you should parallel the asteroid's direction and plane, and matching approximate PE location. You will likely have to zoom out and around a lot to get the axes to all line up. Once you get away from Kerbin, you'll have to do some midcourse corrections. My emphasis should be on getting a lose to parallel departure orbit setup. You don't want to angle your PE toward the asteroids PE as that will send you the wrong way. Parallel is better, erroring on the PEs slightly away from each other.

Not sure if that will help...

Welcome to the forums!

Cheers,

~Claw

Edited January 19, 2015 by Claw

[FlyingPete]

You're basically doing the same thing as an orbital rendezvous, though obviously you only have one orbit to do it in, and the target has a rather odd trajectory. First get the inclinations matched, either by launching into that plane or doing a plane change in LKO. Then it's a case of tweaking your maneuver node until you get a close approach. You can always do a course correction later.

If you can get the asteroid far enough out, it shouldn't take much delta-V to nudge it into an aerocapture trajectory instead on an impact.

[LethalDose]

*4. Create a new maneuver node and attempt to line up intercept points on target asteroid. <-- This fails I seem to not be able to get intercept points to closely match up.

The intercept nodes for asteroids, uhm... what is the word...

oh right.

Suck. They suck.

You only get an intercept node if you're going in roughly the same direction as your target (as best as I can tell from the problems I've had in the exact same situation), and the absence of intercept markers don't necessarily indicate the absence of a close encounter. Sometimes you gotta eyeball the intercept.

Edit: I just got the picture link to work. That orbit "looks odd" because the asteroid had a very slow encounter from a high inclination. But that's a good one!

Yeah, you want to launch into a co-planar polar(ish) orbit going the opposite direction as the asteroid, and the burn so your outward path is as on top of the asteroid as possible. aim for just above escape velocity. You probably won't get intercept nodes, but remember, that's a filthy, filthy LIE!

When you get close, burn retro to your target, and intercept as you normally would for a rendezvous. You just gotta watch your distance instead of counting on the marker.

Edited January 19, 2015 by LethalDose

[capi3101]

Going to point you to '>this tutorial; the guidelines in it worked well for me when I did the exact same thing for the exact same reason...

You can get more delta-V and more thrust out of the probe that Claw (his tutorial) proposed if you use an LV-N instead of an LV-909 despite the increase in mass. You might give some consideration to adding rudimentary RCS capabilities but it isn't necessary, strictly speaking.

Mass of a class A rock will be somewhere between 1.11-2.50 tonnes.

[wibou]

Intercept nodes usually stop working when you get close to the asteroid... it's kind of dumb really.

A step by step guide would look like:

1. While orbiting kerbin, use the intercept node to get relatively close (<100km, ideally <20km) from your target. As long you are still orbiting kerbin, you SHOULD be able to use the intercept nodes.
   
2. Once you are almost at intercept point, switch the navball into "target" mode and burn retrograde to cancel your velocity relative to the target... it's usually the point where you will lose the intercept nodes.
   
3. At that point (assuming your velocity relative to the target is ~0m/s), find the "target prograde" node on your navball and burn that way. If you are far away (>50km) you probably want to give yourself a hell of a push, up to 100m/s. Below 50km, anything between 25m/s and 50m/s is probably fine. Less if you are even closer (lucky guy!).
   
4. If you use your map at that point, it should give you the distance between you and the target but (oddly enough??), you won't see intercept node. Spot that distance... if it start INCREASING instead of DECREASING, then burn "retrograde" to cancel your velocity and do a burn "target prograde" again (step 3).
   
5. Eventually, you WILL get an intercept with your target... You probably want to do the last 3km very slowly (<2m/s) to make sure you don't overshoot.
   
6. The last 75m should be done using RCS for maximum precision; click on the target and select "target center of mass" to make sure you don't end up with a disbalanced charge. If you grab too far from this point, the ship composed of your rocket and the asteroid will be very hard to control (although a "A" type asteroid is light enough it wouldn't matter).
   
7. Once you have it, it's all orbital mecanic baby: switch back the navball to "orbit" and burn retrograde to get back into kerbin orbit.
   
8. There, your very own asteroid!
   

Some people might point out this is ZERO fuel efficient and that be true. But around Kerbin, fuel is rarely an issue and it is way easier to execute (and to explain) that way