Interplanetary travel issues - has this happened to anyone?

[AndrewBCrisp]

So in my current Career Mode save, I recently launched a probe to perform an Eve flyby. I used the KSP launch window planner to launch it on Day 147 of year 1, and for the first ten days of its trajectory everything seemed to be fine. I was on course to an 81,000 km close approach with Eve on day 198, and after an inclination burn and second correction burn, I thought I'd shaved that close approach down to 670 km. The orbit looked good - almost textbook Hohmann, I would say.

Satisfied, I went off to do other things - launching a probe to Moho (failed - the orbital trajectory went wide and I lacked the fuel to correct), and sending a Kerbal into orbit around the Mun and bringing him back. It should be noted I'd closed KSP and opened it again for each of these missions, taking a nice, casual approach. I then decided to check in on my probe and make sure it was still on track.

It wasn't. Without any prompting on my part, the orbit had changed to a highly elliptical orbit coming in very close to the sun and going out almost to Duna orbit. I was able to salvage the mission with some additional burns, using up the last of my fuel and getting to within 28,000 km of Eve.

I'm at a loss on this one. There were no close approaches to other planets until the probe reached Eve. I'd left the engine off when I finished my last burn while it was on its proper course. Any ideas on why the orbit changed so dramatically?

[FenrirWolf]

Could it have hit the encounter while you were busy and thrown off on a new path?

[AndrewBCrisp]

I can't see how. The projected date of arrival was on 198 (which I confirmed by hovering my mouse over the Eve Periapsis marker, noting the time, and doing a little arithmetic) and I discovered it was on its new orbit on day 181. My inclination and secondary correction burns (bringing it to the projected 670 km periapsis) occured on Day 166 (T+19 days according to my records).

Between the second burns on 166 and my discovery of the new orbit on 181 I'd launched two seperate missions. Venturer 2 to Moho lifted off on 169. I sent it on its way, exited KSP. Then this Saturday I cycled the clock forward (done by focussing on a flag I planted near the KSC on Day 1 for just this purpose) to Day 181 and launched my Kerbal 5 mission to orbit the Mun and return. Mission completed, I shut the game down again. Then I thought "well, why not bring Venturer 1 to its conclusion", rebooted KSC, went to Venturer 1 and did a spittake when I saw the orbit.

The probe itself is very simple - a Stayputnik core with 2 Z200 batteries, 6 OX-STAT panels, an OSCAR-B fuel tank and an LV-1 engine. No science gain, just a "let's practice interplanetary travel and get neat pictures" mission. I've noticed the Stayputnik is very odd on turning without any extra reaction wheels to aid it, but if that was going to throw off my trajectory on the previous burns, it should have shown up when I finished said burns, not two loadings of the game later.

EDIT: I forgot to mention, my version of KSP is vanilla, no mods.

Edited November 17, 2013 by AndrewBCrisp

[bsalis]

Could it have hit the encounter while you were busy and thrown off on a new path?

That's all I can think of too. But could be some other random persist bug... Some people have lost whole crafts.

Always be there for SOI transitions.

[Awaras]

Always be there for SOI transitions.

This.

Did you perform your burn while still in Kerbin's SOI? Did you wait until your craft left Kerbin's SOI or did you switch away to another craft before that? There is a known bug when SOI changes happen under warp that causes large changes in velocity.

[SRV Ron]

"I can't see how. The projected date of arrival was on 198"

The Add Maneuver Mode can get the wrong orbital encounters if it thinks that you are doing a complete solar orbit before the encounter. Eve doesn't take that long to encounter once you have committed to the intercept. No doubt, you ended up with an encounter slingshot while doing other things. Any aerobraking to slow down for a capture will not take place when you are off elsewhere or time accelerating.

[Awaras]

"I can't see how. The projected date of arrival was on 198"

The Add Maneuver Mode can get the wrong orbital encounters if it thinks that you are doing a complete solar orbit before the encounter. Eve doesn't take that long to encounter once you have committed to the intercept. No doubt, you ended up with an encounter slingshot while doing other things. Any aerobraking to slow down for a capture will not take place when you are off elsewhere or time accelerating.

He launched on day 147 and got an encounter prediction for day 198. 51 days sounds about right to me for a Hohmann transfer to Eve...

Edited November 17, 2013 by Awaras

[Jason Patterson]

It's possible that you've come across a new bug, but it's very unlikely. If you launch another mission in the same way does it recur? A close pass by another body is by far the more likely scenario.

Were you completely out of Kerbin's SOI when you left your craft? An unexpected pass by the Mun or Minmus can completely change your orbit, and sometimes the game doesn't track those encounters very well. My only other thought is that perhaps there was some simple recording or arithmetic problem.

[AndrewBCrisp]

Re: SOI transitions. Not sure about this one, though it's a possibility. I do know that after I finished the ejection burn and closed the game I was still in Kerbin's SOI, and that I was out of Kerbin's SOI (but still - mostly - on course) for the inclination and correction burns on Day 166 (this might account for the fact that I needed to perform a correction burn then, however). Since my mission was intended only to be a flyby of Eve, I made no provisions for aerobraking - and I never got close enough to a planet to do so anyway.

The only other thing I can think of was that I'd launched a second interplanetary mission on Day 169 and I followed the same procedure there - i.e. it was still in Kerbin's SOI when I left the game. The two probes were carbon copies of each other, so perhaps when the second probe made its SOI change the game somehow affected the first probe? Now that I think about it, the orbits of the two probes did look as if they'd been swapped...

I have another launch window for Eve opening up around Day 314, and no other interplanetary missions planned before then - all Mun / Minmus missions. If my mission schedule and tech allows for it, I'll be attempting an Eve orbital mission then, and I'll see if the problem recurs. For now, it might be prudent to have only 1 interplanetary mission at a time.

[Awaras]

Nah, if you were more or less on course when you did your correction burn than SOI change is not the cause of your problem.

Could a mod be causing issues? Do you use any mods?

[Rusty6899]

The closest thing I have had to this is when I had a probe in an elliptical orbit around Jool that passed within 500km of the surface. I left it there and went to do other things and the next time I checked I was near my apoapsis on a collision course with the planet.

Normally I only carry out one interplanetary mission at a time, but I doubt that would affect your trajectory. Other than that, when you exit a SOI at a high time warp it tends to change your trajectory, but it is normally very slight.

[TheGeoninja]

You could have been thrown off course somehow with a Mun or Minmus encounter but I doubt it.

[FlamedSteak]

SOI intercepts are buggy as hell if you're not paying attention to them. I've had interception altitudes change from 15,000m to 2,000,000m simply by time warping. F5 is your friend when intercepting planets.