Suggestions on getting a close intercept in heliocentric orbit?

[Soda Popinski]

I've been playing for a couple of weeks now (started playing in career mode), and my first attempt at a Mun landing ended with Jeb's ship being ejected out of Kerbin's SOI, and in heliocentric orbit. Jeb is long out of fuel and electricity...and has been floating out there for about 2 years while I've been continuing the space program and honing my skills at rescuing stranded kerbals (about 2/3 of my missions are rescue missions on previous fiascos).

I've since built a probe ship with a rudimentary grapple / catcher's mitt (using landing legs attached to girders) that I know I can use to capture the small capsules. I even added an empty capsule if I have to resort to EVA, but I'd rather bring back the original capsule. It's currently in heliocentric orbit ahead of Jeb (with a higher apoaps to let Jeb catch up).

So here's my problem, it's really really hard to figure out how to get the best intercept. I don't want to time warp 10000x the whole time to keep waiting to get back to apoapsis over and over to adjust the intercept point (closest intercept near periaps). The reason I'd rather not, is because I'm in career mode with multiple missions going on that I'm switching between.

So far, using the maneuver nodes, I can get as close as about 300 km, which is tiny compared to the Kerbol system, but a bit far for a rendevous. I try to adjust the maneuver nodes, and zoom in as best as I can to see how closely the orbital paths come, but it's really hard to do when the node is on the other side of the star system.

I'm not using any mods besides the docking cross-hairs thingy.

Edited November 13, 2013 by Soda Popinski

[Rosco P. Coltrane]

EDIT: Never mind, I misread. Yeah, what you're doing is pretty much what I'd do.

[Franklin]

I wish I could help, but I'd love to see photos of this 'catcher's mitt' in action

[Taki117]

Make sure you are aligning planes. If he's on any kind of other plane it's going to be hell trying to catch him. Your best option is to fiddle with maneuver nodes for the best approach, and pack lots of DVD. You could also get MechJeb to assist with maneuver planning.

[Collin Dow]

I too would be curious to see the catcher's mitt as well.

[maltesh]

If you can get within 300km, that's more than close enough on a solar orbit. Remember that you can flick the navball over to target-relative velocity at any time by clicking on it as long as you have a target selected; you don't have to wait for it to autoswitch.

From there, it's a matter of using your main engine to push the relative velocity indicator onto the target-direction indicator, with adjustments to keep it there until you finally close the distance.

That said, bringing back a capsule using grappling legs from solar orbit is going to be pretty difficult. Since you won't be docked to your target, it will be considered a separate vessel, and every time you use time acceleration or switch to a distant vessel, the game will recalculate its position based on its then-current velocity converted to Keplerian elements, which will result in it escaping from your cage and moving significant distances away from your spacecraft.

Unless you're willing to spend time re-rendezvousing with your rescued pod on the way back, (or worse, do the entire trip in Physwarp) you should probably either look into using Kerbal Attachment System to dock and tow back your pod, or settle for just rescuing the Kerbals.

[Kasuha]

Change your orbit so it touches the target orbit in one point. If your orbital planes are not perfectly aligned, it helps greatly if you move DN or AN to that point, too. That will show you indicators of closest approach. Then you can enlarge/shrink your orbit by burning at that point to get close encounter as soon as possible. It may still take a few orbits.

After you get a close encounter (mind you: 2000 km is a close encounter in sun orbit) switch to target mode on navball and perform standard approach using navball indicators like in Kerbin orbit. Just the distance and speeds may get higher. Until you get under 100 km, you'll need to use Map view to see the distance. Make sure your relative speed does not exceed 1-5% of your distance.

I don't recommend you to use that "mitt" you designed. If your two ships are not docked together, you cannot time warp without them going their own ways and if you stop warping when they overlap - even a little - they will explode. You can use that "mitt" to give the ship an impulse you need but definitely don't try to hold it there. Move to safe distance before each warp instead. Or rather just transfer Jeb using EVA and leave the ship where it is.

Edited November 13, 2013 by Kasuha

[Sirrobert]

I'd ditch the idea of catching the a stranded craft, and just send up a rocket with a free seat in the cockpit. Leave the craft, just EVA the stranded Kerbal the last bit and than fly home without extra weight

[Smidge204]

I have tried exactly what you're talking about: Behold, the ship I have dubbed "Basket Case"

Now, from the benefit of experience I can offer you the following advice: Forget it.

You will not be able to use time acceleration at all. If you have not docked, so that your ships are considered one collection of parts (or use a mod - Kerbal Attachment System's electromagnet perhaps?) any attempt to use time acceleration will lead to disaster sooner or later... or sooner or immediately.

Physical time warp isn't so bad, except for being limited to 4x. As long as you maintain a SMALL amount of thrust to maintain a pushing contact between the two you're fine. Using Time Warp will disable physics - including collision detection - and they will drift right through each other... so all turns had to be done while thrusting at least some amount to keep the capsule pinned to the bottom of the "net."

Turning that thing was a hassle, too. The capsule likes to clip itself through the girders which resulted in a few quickloads. Turn the ship and see the capsule floating off on its own.

Just do the EVA :/

=Smidge=

[Soda Popinski]

Thanks for all the help. I'll ditch the idea of bringing it back in the mitt. EVA it is. The mitt worked on a Kerbin orbit rescue, but all I did was push the capsule enough so it's periaps intersected the atmosphere. I may try to do this to see if I can get the capsule back into Kerbin's SOI.

Maltesh, any suggestion on when I should start trying to match relative velocities? When I get to that 300 km mark? How fast should I close at that speed? 100 m/s would be about an hour, which I can time warp.

By the way, Smidge, your mitt wins. My basket was much smaller, just 8 girders, and the first time I used it, I forgot I had goo pods on attached to the exterior of the capsule, so it wouldn't fit in the basket. When I tried to "close the trap" with landing legs, it just pushed the capsule away. So I went with the push instead. It was easy that time, as the capsule still had power, so I could face it for a retrograde "dock." No such luck this time. At least it's not spinning...yet.

[Sirrobert]

Thanks for all the help. I'll ditch the idea of bringing it back in the mitt. EVA it is. The mitt worked on a Kerbin orbit rescue, but all I did was push the capsule enough so it's periaps intersected the atmosphere. I may try to do this to see if I can get the capsule back into Kerbin's SOI.

Maltesh, any suggestion on when I should start trying to match relative velocities? When I get to that 300 km mark? How fast should I close at that speed? 100 m/s would be about an hour, which I can time warp.

By the way, Smidge, your mitt wins. My basket was much smaller, just 8 girders, and the first time I used it, I forgot I had goo pods on attached to the exterior of the capsule, so it wouldn't fit in the basket. When I tried to "close the trap" with landing legs, it just pushed the capsule away. So I went with the push instead. It was easy that time, as the capsule still had power, so I could face it for a retrograde "dock." No such luck this time. At least it's not spinning...yet.

First match orbits, don't bother with a randevous. Next, push the orbit of the resque craft out (or in. Depending on if it's infront or behind the stranded one) so the 2 crafts get closer tougether. Now make a node that intersects the 2 orbits, and drag the node around your orbit until you get a decent randevous. Once you are relativly close tougether, switch to target mode and match velocity. Now burn towards the target.

[Kasuha]

Maltesh, any suggestion on when I should start trying to match relative velocities? When I get to that 300 km mark? How fast should I close at that speed? 100 m/s would be about an hour, which I can time warp.

When you get your orbits intersect or touch and the closest approach indicator shows you're getting sufficiently near (2000 km is near enough, you don't have to try for 300), put a maneuver to that point and do what's needed to have the after-maneuver orbit match the target orbit as close as possible. You will NOT execute that maneuver, but it will tell you how long before the closest approach you need to care and what the orientation of your ship at that time should be.

When you're the burn time before the maneuver, switch the navball to target mode and start burning. Then delete the maneuver and start watching just the to/from target indicator, relative speed indicators (you need to push your relative retrograde over the "from target" indicator), and distance (you need to check it in the map until you get below 100 km distance). Keep your speed about 1% of the distance, i.e. when you're 100 km far, your relative speed can still be 1000 m/s but you need to decrease it as you get closer.

You can use time warp during approach, but don't be surprised if the target suddenly "jumps" somewhere else as soon as you enter it. It's caused by numerical inaccuracies in representing the orbit. So far I always only had one such "jump", subsequent time warps were ok. But you may feel better executing the maneuver using just x1 time warp or physical time warps. Even physical time warp might be accompanied by some strange shifts of the target along its orbit, though. It's nothing that can't be handled if you know it may come.

Edited November 14, 2013 by Kasuha

[Soda Popinski]

Quick update. Looks like Jeb is on his way home. It was a bit hairy, and I did end up having to do a push.

Basically, I launched the rescue craft early in the career, and I didn't know crap about delta-V yet and didn't have the atomic rocket. Once I got the intercept, I plotted a course to get Jeb to Kerbin capture, but when I did the delta-V calculations I needed about 1000 m/s. My relatively large rescue craft only had 400 m/s or so by the time I got there, but luckally Jeb's original craft had about 800 m/s. Neither had enough to get home.

So I ended up pushing Jeb's craft with my rescue probe for several minutes until my rocket fuel ran out, then switched to RCS for about almost two large tanks worth (physics warp + jammed the "H" key down using a pen. The rest I did with Jeb's remaining fuel.

[Rosco P. Coltrane]

jammed the "H" key down using a pen

hahahaha, with all the automation mods you have for KSP, you had to use an external aid.

[Soda Popinski]

hahahaha, with all the automation mods you have for KSP, you had to use an external aid.

Avoiding MechJeb. Pens jammed into keyboards are good enough for me.

Update: Jeb made it back with 66 m/s of delta-V to spare! He's a National hero with 853 days in space (he's a little funny in the head now).