Speed keeps increasing?

[spaceisnothing]

I am trying to dock a landing module and a rover in space to take to Mun and land. The problem is when I try docking using the landing module my orbital speed and my target speed keeps increasing by 0.1 m/s every second. I have no idea what might be causing this because even wit the throttle all the way down and the RCS off it still keeps increasing.

[KerbMav]

To start out silly: Is your orbit still stable?

But: Your orbital will change if you are not on a -perfect- circle - it will always be somewhat elliptic.

Also no two orbits will be the same - at least not if the orbiting crafts are getting closer to each other.

Although my spaceplane drifted quite a lot yesterday while my kerbonaut EVAed to get the fuel line from the station ...

[blizzy78]

If you're confused about orbital velocity changing - that is normal. It's quite hard to actually achieve a perfectly circular orbit, so a common orbit will always be elliptical. This in turn means that you will be going faster when nearer to the body, and slower when further away. This is usually not a problem for docking, though, since it's the relative velocity between vessels that matters.

If the confusion is about relative velocity increasing and most possibly preventing you from docking successfully - that's a whole different can. To come down to a relative velocity of zero between two vessels, switch your nav ball into "Target" mode, then burn (or RCS thrust) towards the "retrograde" marker, which in nav ball "Target" mode changes its meaning to "decrease relative velocity between vessels here."

Edited August 30, 2013 by blizzy78

[daffy]

Best way is to continue 'closing' the target, and then matching target speed by burning retrograde until the two bodies are pretty well synced at a few hundred meters. I've learned that if you simply burn at the target and close the distance, and then fail to burn off the speed retrograde, it's like chasing a mouse on a bungee cord. You'll never match up. The steps have to be done repeatedly until orbits are synced well enough to maintain a stationary distance before you begin the actual docking phase.

Also, once you have the target set and are fairly relative, you can work the pro grade aim point into the targets node. When you have that lined up correct, then you can just RCS thrust in reverse to control the closing velocity. Now, as I'm writing this, I'm thinking to myself that...ok, so that makes sense to ME! But, I could be sending you on a goose chase! Please jump in and tell me to stop at anytime! lol ;p