Orbital rendezvous in RSS/RO

[TheMoltenJack]

I've installed RSS and RO alongside with RN Soviet Spacecraft and Rockets mods. What I'm trying to do is to recreate the Soyuz 4-Soyuz 5 mission and dock two Soyuz spacecrafts. The launch site is Baikonur while the orbit's inclination is 51.7°.

To achieve orbit I'm using MechJeb2 with Powered Explicit Guidance. When trying to launch the second spacecraft to the same plane as the first one I can get at minimum a 0.77° of difference between the two, difference that requires to much delta-v to take care of (105m/s, the Soyuz only has 172m/s). What can I do to perform a precise rendezvous? I'd prefer to not have to fly by hand as it seems extremely difficult. What about kOS?

[Ultimate Steve]

So, MechJeb can only do as good as 0.77 degrees... I can get 0.1 degrees on occasion if I'm lucky, but I usually do better than 0.7 (although the orbit's inclination is 27 instead of 51, so you have it harder). I'd suggest (against your wishes, unfortunately) to try manually flying it at least once, it's just like a normal KSP rendezvous, but a bit bigger (and you don't usually do inclined rendezvous in normal KSP). If you have a tool (MJ, KER) that tells you your angle to the ascending or descending nodes, launch when it is at about 1-0.5 or so (right before it) and make corrections during ascent to make the nodes get as close to zero. That's the method I use, at least.

However, there is another way. In vanilla KSP, we're a bit spoiled, being able to have huge margins because of the small planet size. As a result, we fly with a certain degree of inaccuracy knowing we'll have fuel to fix it. In IRL this isn't really the case, most spacecraft margins are very low. So, in your case, if you really don't want to fly it manually, I'd suggest clipping an extra fuel tank into the Soyuz spacecraft. It doesn't have to be huge, even a smallish tank could double your Delta-V. Although in RO I usually give my service modules at least 400m/s because I'm a bad precision pilot.

There's also a third solution. Split the plane change burn between both spacecraft so it's only 52m/s per spacecraft. That will leave 120m/s for rendezvous and return.

Also, welcome to the forum! I hope you enjoy your stay!

[Laie]

I'm not too fond of MJ full-on autopiloting, hence have zero experience with how it behaves in recent versions. However, I have learned to make ascents "manually" by dialling numbers into the SmartASS thingy, and can regularly launch to within 0.1 degrees of my target inclination.

I'd recommend this as the fastest route to solve your problem. It might take a few attempts to get it right, but that's only an hour or two of exercise. Programming your own autopilot will definitely take longer than that.

[Pand5461]

Looks like MechJeb's PEG is in essence the Apollo-level version, which can do only coarse plane matching.

There's a thread on Space Shuttle PEG implementation in kOS here on forums:

You can find download links there and give it a try with your rocket.