General Question Unstable Orbit

[Jason210]

Hi

After a journey to Mars and back with TransX, I found myself in retrograde orbit around Earth. I spent some time correcting this by moving the orbital plane 180 degrees, but then found that the orbit was unstable. The Periapsis and Apoapsis were constantly moving.

Can anyone tell me what is going on?

Thanks
Jason

 

[boogabooga]

Do you have non-spherical gravity sources enabled?

 

[Jason210]

Thanks for your reply :thumbup:

No, it isn't enabled.

 

[Urwumpe]

Thanks for your reply :thumbup:

No, it isn't enabled.

If your orbit is nearly circular, the effects of sun and moon alone can be enough to change your orbit a bit. And if you are nearly circular, this means that the argument of periapsis can change a lot by even small accelerations by sun or moon.

 

[boogabooga]

How high of an orbit are we talking about?

 

[Jason210]

Hi again!

I don't recall seeing this happen before as a result of the sun or moon. In real time, the periapsis is changing at approximately 100m per sec. Periapis is about 850km and the orbit is circular - or was. The inclination is 42 degrees.

I'm using the Arrow add-on with Dan's DGIV docked iniside it.

Jason

 

[DaveS]

Check that there's no thruster activity going on.

 

[Jason210]

Check that there's no thruster activity going on.

Yes. That was the problem. Although the bar graph thrust indicators were showing no thrust, there must have been a small amount being applied. I had thought of this earlier and tried CTRL NUM + and CTRL NUM - but evidently missed the 0 point.

Which brings up another question - is there a reliable way to ensure that both prograde and retro thrusts are off? Fiddling with CTRL NUM + and CTRL NUM - doesn't seem like the right way. Perhaps there is an MFD that shows thrust readouts as numbers and has a way setting it absolutely by entering a value, for example zero.

Thanks for the help!
Jason

 

[Urwumpe]

Yes. That was the problem. Although the bar graph thrust indicators were showing no thrust, there must have been a small amount being applied. I had thought of this earlier and tried CTRL NUM + and CTRL NUM - but evidently missed the 0 point.

Which brings up another question - is there a reliable way to ensure that both prograde and retro thrusts are off? Fiddling with CTRL NUM + and CTRL NUM - doesn't seem like the right way. Perhaps there is an MFD that shows thrust readouts as numbers and has a way setting it absolutely by entering a value, for example zero.

Thanks for the help!
Jason

You can cancel all thrust by pressing "*" on the numeric keyboard.

 

[DaveS]

You can cancel all thrust by pressing "*" on the numeric keyboard.

That only kills main/retro thrusters, not hover thrust. AFAIK, there's no way to instantly kill hover thrust. You have to throttle down that manually with the NumPad Del key.

 

[statickid]

Also, the thruster "bar graphs" DO have a numerical read out. It's directly below the bar.

 

[Jason210]

You're quite right to point out that the default HUD has digital readouts.

As I said, I was using Dan's addons, and these have VCs. In the VC for the Arrow, there is no digital readout on the engine gauges. I tend to only use vehicles with VCs (except for the ISS) - never occurred for me to check the default HUD. Just watching the readouts now indicated how tricky it is to cut-off thrust with CRTL + / - alone.

The best procedure to kill everything seems to be to hit NUM PAD "*", and then hit NUMPAD "DEL" for a few seconds.

 

[statickid]

For main thrusters, I just press numpad asterisk, for hover, I just hold numpad decumal for a few moments after i feel its off. Not too tricky :lol:

You can also spot a low thrusting event by watching the fuel mass readout.

 

[Cras]

A nasty thing that can happen in the Arrow, I have fallen victim to it quite often, that being accidentally leaving a bit of hover or retro thrust on and later wondering why is my orbit so borked

 

[Jason210]

For main thrusters, I just press numpad asterisk, for hover, I just hold numpad decumal for a few moments after i feel its off. Not too tricky :lol:

Yes, that's what I meant