orbital rendezvous without maneuver nodes

[Mundiver]

Hi all,

I accepted a rescue contract in my early career mode game since the money return looked great. I've not yet built up enough money to upgrade the tracking station so I don't have maneuver nodes available. While I can get quite close (~5-10 km) to the stranded kerbonaut I can't seem to quite get our velocities and positions to match up.

My approach is:

1. Launch to a circular orbit about 15 km lower or higher than the target

2. Make my inclination change so we match

3. Try like crazy to make a burn that produces an encounter that lets me rescue them.

Number 3 has been the problem step. From lower orbit I make a burn when my vector is pointing where I guessed they'd be when I hit the higher orbit, and vice versa for the case with me in the higher orbit. These produced close-ish encounters but we drifted apart again quickly.

Any advice on how to do this more reliably?

Is there a way to close and match once they are 5-10 km away? Burn toward the target marker on the navball? That didn't seem to work well but maybe I just need to try again.

Edited January 9, 2015 by Mundiver

[Rosco P. Coltrane]

Well, you shouldn't need nodes at that stage of the rendezvous anyway.

You can select it as a target right? Then match velocities by burning retrograde. Then burn towards target to get your prograde marker over it and some 10 m/s in speed. Without nodes, you don't know when the next encounter will occur, but I guess you can keep an eye on the distance in the... erm... "not-map" view, once you see it increasing again burn retro and towards again and so forth. You should sooner or later get to it.

[The Yellow Dart]

The best way to get this done is to take baby steps. Without maneuver nodes, it is very hard to go from 15km below to a close approach accurately. It is too big of a step at once, and once you get there, even if you get pretty close, the target's orbital speed will be very different from yours.

A better, safer way to rendezvous is this: Get your orbit circular and match inclination (I know you said you already did that part) then you have to gradually step your orbit closer to his. The closer your orbit is to his the closer your speed will be to his when you get your close approach. So if you start from 15 km lower than him and he is a good bit in front of you, take note how much closer you get each orbit at the Periapse or Apoapse. When he starts getting closer, step your orbit in closer to his, so you are gaining less ground on him each orbit. Keep stepping your orbit out to his until you're orbits are very close and he is very close to your craft. This method guarantees that when you get close, the difference in velocities is negligible and you can burn more or less towards your target, rather than trying to guess the right way to burn to null your velocity relative to the target. If I remember correctly, once you get quite close (<4km? <1km? not sure), it lets you double-click target him so you can accurately null velocities and get close safely.

[THX1138]

This shouldn't be too difficult once you know a few pointers.

Right click on your target and select "set as target".

You need to decide whether you're letting the target catch up with you or you're catching up with the target. Whomever has the smallest orbit will be orbiting faster and doing the catching up.

By watching you craft and target orbit in time warp, you'll get an idea of when an encounter is coming up. When an encounter is about one or two orbits away, adjust your orbit so that the difference between your orbit and the target orbit is smaller. This will reduce the rate of catch up and allow you to more finely tune the encounter.

When your target is less than 10 km away adjust your prograde marker so that it aligns with your target marker. Accomplish this by burning on the opposite side of the target marker (compared to your prograde marker).

Click on your speed indicator to change it to target speed (the speed of you relative to your target). You need to get this to zero by the time you have completed your rendezvous. If you do this too early, you'll make the whole procedure take longer than necessary. You will shed this speed by burning retrograde.

As you near your target, small deviations between your prograde and target marker will become more obvious. By the time you'll actually be more interested in your retrograde and anti-target marker. Bring your anti-target marker into alignment with your retrograde marker by burning on the opposite side of the anti-target marker (compared to the retrograde marker) - note that this is the opposite strategy to getting the prograde and target markers into alignment. Failure to get your relative speed to approx 0 m/s is why you had the target rush past you earlier.

By hovering your cursor over target, you will get an indication of the separation between you and you can use this to inform an appropriate relative speed between you and the target.

Edited January 8, 2015 by THX1138

[The Yellow Dart]

Edit: Nevermind

[Scarecrow88]

I never use manoeuvre nodes for rendezvous, so can't really appreciate the problem. Surely all you need to do if you are getting to within 5-10 kms is to use the nav ball in target mode.

[PnDB]

I inadvertantly accepted a Kerbal rescue contract while I was in the same situation as you... no maneuver nodes. Here is what I did.

The stranded Kerbal was in an orbit with Ap ~180km and Pe ~120km and slightly inclined (I missed the inclined part until mid-mission)

I built a rocket with enough delta-V to get into orbit, do a bit of maneuvering, and have enough left to de-orbit. I also made sure there was space on board for an extra Kerbal... double-stacked command pods!

1. I launched and circularized into an 85km orbit. The Kerbal was significantly ahead of me in his orbit. Since I was lower than him, I just waited a few orbits to close the distance.

2. I then brought my Ap up to nearly 180 km, leaving my Pe around 85 km. I was still behind the Kerbal, so the low Pe still allowed me to catch up, albeit somewhat more slowly.

3. When I was getting "close enough", I brought my Pe up to nearly 120 km (still less than the Kerbal's Pe, though) to creep up on him.

4. At this point, I realized that his orbit was slightly inclined to mine, which explained why he kept flying north and south of me.

5. I matched inclination and matched his Ap and Pe as best as I could, and when he got within about 10 km of me, I selected him as the target. Now the navball displayed my velocity relative to the Kerbal.

6. I burned prograde/retrograde/norma/antinormal as needed to reduce our relative velocities. When our relative velocity was only a few m/s, I aimed toward the target and burned to close at about 10-20 m/s.

7. When the Kerbal came to within 2 km of me, I turned away from him and burned to drop our relative velocity, making adjustments for any lateral motion at the same time.

8. I then switched to the Kerbal using the [ and ] keys, activated his EVA jetpack using the R key, and then thrusted toward the rescue vessel.

9. I had to go back and forth between the Kerbal and the rescue vessel a couple of times to tweak our relative velocities and positions, and I also rolled the vessel to aim the hatch in the direction of the Kerbal for an easy ladder grab.

10. Once the Kerbal was safely onboard, I just pointed retrograde and burned for re-entry.

It took about 2 hours of real time, and about 2 days of game time to complete the contract.

[EtherDragon]

Is there a way to close and match once they are 5-10 km away? Burn toward the target marker on the navball? That didn't seem to work well but maybe I just need to try again.

Yes, you are very near to having the exact right idea. Here is what I recommend - a slight adjustment to your plan:

1. Try to time your launch so that you establish a stable orbit slightly behind or ahead of your target - this is guess work and will be imperfect.

2. Position your orbit so that your perioapsis and apoapsis are both 5km below or above the target orbit.

2b. If you establish orbit behind, set your Pe and Ap lower than the target orbit. If you come in ahead, set your Pe and Ap higher than the target.

3. Manual inclination change to match - as best you can by eye-balling it.

Now, all you have to do is wait; you are guaranteed an encounter that is no more than 5km away. If you have more patience, you can set your Pe and Ap to 2km, and be guaranteed 2km of separation.

[Mundiver]

Thanks everyone, this was really helpful. I was able to use the navball to maneuver close enough to the kerbal to [] switch to him and eva over to the rescue craft. I was able to get him to grab onto the ladder but now the 'f' key is not letting him board. Is there something I'm missing here?

It's an uncrewed Mk 1 pod flown by an octo probe.

EDIT: Nevermind. He was just too far down the ladder. Thanks again for the help.

Edited January 9, 2015 by Mundiver

[bsalis]

It can be done reliably using the visual distance to target.

See http://forum.kerbalspaceprogram.com/threads/8915-Tutorial-Orbital-Rendezvous-Made-Easy