Why can't I get this probe back to life?

[technion]

Hi,

I've been experimenting with fuel cell powered ion probes.

This one ran out of electricity and the probe shut down.

As you can see, there are solar panels on this unit that are getting light. It's not enough to run the ion engine, but I was expecting I could restart the fuel cell when these kicked in. Instead, the probe remains uncontrollable, electricity never comes in.

Edited October 15, 2015 by technion

[The_Rocketeer]

Your problem will be that the current draw is higher than what those solar panels are giving you. Kinda like a car that won't start because it needs u to pump the gas pedal.

You could try sending a Kerb to it and seeing if you can turning anything on/off by right clicking during an EVA. Alternatively, install KAS and bolt an extra battery or solar array to it, or a docking port so you can 'jump start' it.

[technion]

I would have thought the draw of one probe core was a lot less than four panels

[DeMatt]

Yeah, have to agree that even with the engine off, between the sensors and the probe core, you're still drawing more electricity than the solar panels give.

Make sure the reaction wheel is disabled, the engine is off (toggle the xenon tank if you need to), everything but the probe core itself. You can always resort to save-file editing to give yourself some electric charge if you have to.

I would have thought the draw of one probe core was a lot less than four panels

Except it's not four panels. It's two. And then you've got the reaction wheel, the sensors, the antenna...

[The_Rocketeer]

I would have thought the draw of one probe core was a lot less than four panels

Hmm... I agree there - tho yeh, it is 2, not 4.

I don't recognise some of the parts I see in the screen (could just be a bad angle). Can u post another of the whole craft?

SAS and throttle settings (for ions) can guzzle up electricity, as well as activated antennas and roverwheels. The throttle setting and antennas would be my next guesses, tho the pic shows the throttle off (or very nearly off) and the one antenna I see closed. Are there any dish antennas? Are they active?

[technion]

Make sure the reaction wheel is disabled, the engine is off (toggle the xenon tank if you need to), everything but the probe core itself. You can always resort to save-file editing to give yourself some electric charge if you have to.

Thanks. The antenna is doing anything, the sensors aren't deployed. The wheel and tank don't give me the option to disable. Don't I need a running core to do so?

[The_Rocketeer]

Don't I need a running core to do so?

Yup. You'll need an EVA nearby or an active core.

Edit: duh! Kerb on EVA can just start up your fuel cells for you!

[FancyMouse]

where is your probe core?

[DeMatt]

Thanks. The antenna is doing anything, the sensors aren't deployed. The wheel and tank don't give me the option to disable. Don't I need a running core to do so?

For the reaction wheel, yes, I forgot. The xenon tank should let you just toggle off fuel flow from it - the little blue triangle beside the fuel gauge.

'Cuz your engine is apparently still (trying to) run - the resource panel shows it drawing xenon.

[Goomblah]

The problem is that your ion engine is stuck on. The engine depleted your electricity, and when you throttled down, it didn't actually shut down the engine because the engine drains the electric charge before the probe core gets it. Note how your Xenon is still being consumed - the engine is consuming all the electric charge coming from the panels, and he probe core doesn't get any, so it can't shut down the engine. The only way to stop it is by sending a kerbal to shut down the engine on EVA. However, you probably won't be able to switch vehicles because the probe may be still accelerating from the ion thrust.

Edit: Or, you could disable the Xenon tank, if possible. Looks like I got ninja'd, haha.

Edited October 15, 2015 by Goomblah

[technion]

Thanks everyone. To answer all the questions..

It looks like you're correct that the engine is still running. It feels absurd to me that it would shutdown a probe core and keep an engine running, but that's it. I can't kill it in any way without a running core, which also seems silly. The core is definitely there, the advise to shutdown the tank does actually seem correct. It just seemed very glitched because I tried it a dozen times before it worked.

Thanks all! I've got a mission report coming on this.

[Streetwind]

The core is definitely there, the advise to shutdown the tank does actually seem correct. It just seemed very glitched because I tried it a dozen times before it worked.

Why you had to try a dozen times:

The engine is throttled to 100% and thus requests fuel from the tank as suitable for its 100% operation. However, it runs at much less than 100% because there's not enough charge for full power operation. So the fuel doesn't get consumed instantly. But the engine still requests the full amount again in the next physics step. And so on and so forth - there's always a 'buffer' of unconsumed fuel in the engine. When you turn off the tank, that buffer needs to be consumed first. By repeatedly toggling it on and off, you only allowed it to be replenished.

Basically: turn it off, then wait until the engine flames out. It may take a few moments, especially if you get very little Ec/s.

[DancesWithSquirrels]

Right click and disable the Xenon tank, right click and turn on the fuel cell (it's off, or you would see consumption of fuel as well as xenon). As soon as you get probe power, shut down the engine.

You should, when recovered, disable the (now full) probe core battery as a backup in case something like this happens again - the battery should be enough for a quick engine stop and a recovery.