Mysterious power drain, 0.01 units per second?

[PnDB]

Greetings fellow Kerbonauts!

Jeb was on his way to Minmus today to collect some ground samples and see once and for all if that little moon was in fact made of mint ice cream. Near the end of his transfer orbit, Jeb noticed that he has less electric power than he expected, and it was draining at a rate of less than 0.01 units per second. Seeing as the wonderful engineers back in the VAB saw fit not to include any solar panels on his craft ("we couldn't include any more parts!" they claimed), Jeb grumbled and continued with his mission, fully expecting to spend a little longer than planned on the surface of Minmus. After a significanly abbreviated visit to the surface, Jeb packed up his ground samples, stowed his EVA reports, and blasted back into space, hoping he could get home. Power continued to drain at an gradually increasing rate, now slightly more than 0.01 units per second. Burning to escape Minmus' SOI, Jeb realized he woud not have any power left for his next maneuver to return to Kerbin. As soon as his escape burn was completed, Jeb used what little power remained to aim himself in what he thought would be roughly retrograde once he left Minmus' SOI, and hoped the engines would still fire when he needed them. By a stroke of luck, he was pointed in nearly the right direction, completed a hard retrograde burn which would bring him into Kerbin's atmosphere on his return orbit. Jeb decided there would be a few... discussions... between him, Gene, and the engineers about this rocket design.

So folks, I have no idea what would cause a 0.01 unit per second drain on power. I was not using SAS, the reaction wheels were idle. There was no power drain early in the mission unless I was making a maneuver. Any ideas as to what might be the culprit?

The transfer rocket was very simple:

• Chute
  
• Command pod
  
• Decoupler
  
• FL-T800 tank
  
• LV-909 engine
  
• 2Hot thermometer
  
• Presmat barometer
  
• Kerbal Engineer Redux parts
  

Do the science instruments drain continuous power, even if they are not being used? Jeb didn't get a chance to use either one on his quick trip to the surface. I don't recall seeing any power requirements for the science instruments or the KER parts. Thoughts?

Edited January 27, 2015 by PnDB

[Kelderek]

I would assume it was the command pod based on the list you gave. Hard to tell for sure though.

One thing you can always do is disable the flow of electric charge for anything you want to remain "powered down". The same buttons that you use for stopping flow for other fuels like liquid fuel and oxidizer are there to use for electric charge too. So if you know you're going to drift through space for a while, then you can manually shut everything down and guarantee no drain at all. I've used this before on batteries when I knew I would pass through the dark side of a planet and lose solar power.

[tsotha]

I don't see anything there that would drain power unless you left the SAS on.

[AlexinTokyo]

Science instruments don't drain power to do experiments, but they do drain power when used as monitoring devices.

Is it possible you hit 'Toggle Display' (I think that's the label) on the thermometer or barometer? If so, they will drain power until you toggle them off again.

[PnDB]

Keldrek, I don't think the command pod by itself uses power. When I checked the various components on the craft by right clicking on them, nothing appeared powered up.

Tsotha, I am certain that the SAS was off. I rarely use SAS unless I am landing or doing some other type of complex maneuver. Otherwise, I just let things drift.

Alex, you might be on to something. What would it look like if I toggled the display of, say, the thermometer? Would there be some HUD that pops up, similar to how ScanSat shows the mini-map? I can't say I saw a display, though if it were small and off in a corner of the screen, then I suppose I could have missed it.

[AlexinTokyo]

The display toggles on the right-click menu itself.

This screenshot is from an older version ('cause I'm not on my KSP machine right now), but it was the best I could find in a hurry

[Steelsunoa]

I think AlexinTokyo is right. I had a power drain from my barometer from accidentally toggling the display, which basically was only telling me that we were in a vacuum...duh!

[Zargg]

Not sure but it might also be the Kerbal Engineer part that is draining it. I use Mechjeb and had this issue on my latest rocket (I don't think it was always like this?), but just did a test of removing the Mechjeb module and the drain didn't occur. It even happens on launchpad before lift-off.

[AlexinTokyo]

I can say for certain that the KER parts do not drain power (unless you've added that config yourself or using MM).

Hmm, it actually might be a nice restriction if they did... must go off and think about that.

AFAIK (I've never used it), MechJeb does drain power, for at least some of its modules.

[PnDB]

AlexinTokyo, Steelsunoa, I think that's probably what happened. I did check the 2Hot thermometer at one point, and it must have been constantly displaying the temperature for the rest of the flight. I'm going to mark this one as Answered. Thanks guys.

[RocketScientistsSon]

Well now I need to know. Did you have enough power to deploy the chutes and get Jeb safely back to Kerbin to enjoy his *ahem* mint ice cream?

[PnDB]

Strangely enough, deploying the chutes requires zero power. Also, the stack decoupler worked fine. We were completely out of power well before we crossed Mun's orbit, so I'm sure there was nothing left.

I have visions of Jeb in the command pod with a hammer, hitting those explosive decoupling bolts and then reaching for the "Pull to Release" handle for the chutes.