Stuck on an 'easy' satellite contract

[Hordern]

Hi all

Sooo, I had what looked a pretty easy first satellite orbit contract, just had to take a thermometer on a powered satellite to a polar orbit with an Ap of 5,602,500 and a Pe of 3,878,404. Well, I got pretty well aligned but it just didn't seem to want to complete, so tweaked here and there and I've managed to get myself within 296m of the Pe and 1,750m of the Ap (I was pretty smug about the Pe...). Still no luck. I read up on things a bit and double and triple checked and now I want to cry. I'm flying the wrong way around Kerbin >.<

What's the best way to reverse my orbit, or should I just scrap my satellite (or perhaps save it for a 'move to orbit' contract in the future) and just launch a new one?

I'd best go and check my other satellite now that's heading for a much more distant orbit and see if it's going to go the right way *sigh* (Edit: I've checked and thankfully that one's going the right way already though I could probably have adjusted that one OK).

Edited May 14, 2017 by Hordern

[Alshain]

The best way to reverse your orbit is a pure retrograde burn (unless you can get a Mun encounter) Go sub orbital and back again.  You might as well try, if you have enough fuel.  If you don't, you haven't lost much in trying.

Edited May 14, 2017 by Alshain

[Cpt Kerbalkrunch]

29 minutes ago, Alshain said:

The best way to reverse your orbit is a pure retrograde burn

I'd counter by saying the very best way is "revert flight". 

[bewing]

Welcome to the forums -- too bad it's under these conditions.

Reverting the flight is a really good answer if available.

Second best answer depends a little on how high your orbit is. If it's pretty high, and your orbital velocity is low enough, you can do as Alshain said -- set to retrograde to get pointed in the right direction, set to Stability mode to hold that direction, and burn until you are going the other way. If your orbit is rather low, you can burn to raise the Ap really high, and then reverse your orbit at the Ap, and then lower it back down again. It won't cost as much fuel that way.

Third, the game has a cheat tool called the Debug Menu. If you do all the work of creating the right orbit, only to find that you made an innocent mistake that's going to cost you a lot of pain -- hit Alt-F12. Go to Contracts. Select the Active tab. Find the specific satellite contract and click the "Complete" button. And then promise yourself not to do it again.

 

[Alshain]

1 hour ago, Cpt Kerbalkrunch said:

I'd counter by saying the very best way is "revert flight". 

Except he said he switch craft to check his other satellite.  No reverts available

[Spricigo]

Notice you can save quite a lot of deltaV if you raise your apoapsis to the edge of SoI,  reverse the orbit there and circularize back in the desired orbit. 

[Capt. Hunt]

Generally speaking, as I understand it, completely reversing an established orbit's inclination is going to cost double the orbital velocity, you can remedy this by taking the Apokerb out to a point where the orbital velocity is much lower, but added Delta-V to do that may offset the saved delta-v.  Your best bet is probably to write it off and launch another.  Just make sure that you dispose of the first satellite beforehand, or else you'll end up smashing the two together at twice orbital velocity.

[Hordern]

Thanks very much everyone

While it's not a low, low orbit, it is reasonably fast and i didn't set out with tons of fuel, I took 'plenty' to get me to the orbit, but I don't expect I have the Delta V to just turn around and go the other way. Thanks for the tricks on other ways to reduce the delta V requirement, useful info for the future, and as for reverting to launch... yeah... I've done a good 8 or so other contracts and gained a bunch of science since I launched that satellite (though it would mean I wouldn't have yet launched Jeb's ill fated attempt to land on the moon but forgetting to take any solar panels because I thought all engines produce electricity... Rather than lose him stuck in a Muner orbit I just let him hit the SOI and then come back with some high Mun science).

I think I shall probably use belwing's third suggestion of the de-bug menu this once as it was a genuine 'I thought I was going the right way' sort of thing because I thought I had to be going up to the Apo on the side where the Ascending node was, and towards the Per on the Descending node. It seems that these are associated with your own orbit rather than the required orbit >.<  I do however now know for future so if I mess up again it's absolutely my fault and I shall either have to revert, turn around, or just send up another.

Having said that, sending up a new one and seeing if I can get such a spot on orbit that I can collide them would be quite fun

[Cpt Kerbalkrunch]

14 hours ago, Alshain said:

Except he said he switch craft to check his other satellite.  No reverts available

Yeah, I saw it in the OP. Was just being a Smart S. 

[swjr-swis]

18 hours ago, bewing said:

Third, the game has a cheat tool called the Debug Menu. If you do all the work of creating the right orbit, only to find that you made an innocent mistake that's going to cost you a lot of pain -- hit Alt-F12. Go to Contracts. Select the Active tab. Find the specific satellite contract and click the "Complete" button. And then promise yourself not to do it again.

An alternative to this, if you are already considering using the Alt-F12 option: 'Set Orbit'. Fill in the parameters as required and place it in the correct orbit. The contract should get completed when you focus on the sat, and as a bonus, you also get to have the sat where it was intended to be.

[Loren Pechtel]

On 5/13/2017 at 8:58 PM, Alshain said:

The best way to reverse your orbit is a pure retrograde burn (unless you can get a Mun encounter) Go sub orbital and back again.  You might as well try, if you have enough fuel.  If you don't, you haven't lost much in trying.

Disagree.  The cheapest way to reverse is to raise your apoapsis to the SOI and do your reverse burn out there.  If you have an atmosphere do the reversing burn so as to leave your periapsis high in the atmosphere and let the atmosphere bring your apoapsis down, finally burning to circularize when it's low enough.  (Note that this will take a while!!)

[Alshain]

8 hours ago, Loren Pechtel said:

Disagree.  The cheapest way to reverse is to raise your apoapsis to the SOI and do your reverse burn out there.  If you have an atmosphere do the reversing burn so as to leave your periapsis high in the atmosphere and let the atmosphere bring your apoapsis down, finally burning to circularize when it's low enough.  (Note that this will take a while!!)

You disagree with what?  I never said anything about the cheapest way.

[Kryxal]

If you want to get really complicated, just set up a gravity assist with the Mun ... if the sat's a writeoff anyway, messing up won't cost anything.

[The Kracken]

The best way of reversing is to get to a high orbit and then burn retrograde until you are going the right way. It works for me! 

 

 

Edited May 30, 2017 by The Kracken

[weissel]

(SmartAssMode->on) The best way of reversing ones' orbit is to go the right way the first time. (SmartAssMode->off)

[Spricigo]

2 hours ago, weissel said:

(SmartAssMode->on) The best way of reversing ones' orbit is to go the right way the first time. (SmartAssMode->off) 

Incorrect,  same effort to reverse a orbit going the left way or rigth way.  (dumbass off) 

[genericeventhandler]

On 5/14/2017 at 3:35 AM, Hordern said:

Hi all

Sooo, I had what looked a pretty easy first satellite orbit contract, just had to take a thermometer on a powered satellite to a polar orbit with an Ap of 5,602,500 and a Pe of 3,878,404. Well, I got pretty well aligned but it just didn't seem to want to complete, so tweaked here and there and I've managed to get myself within 296m of the Pe and 1,750m of the Ap (I was pretty smug about the Pe...). Still no luck. I read up on things a bit and double and triple checked and now I want to cry. I'm flying the wrong way around Kerbin >.<

What's the best way to reverse my orbit, or should I just scrap my satellite (or perhaps save it for a 'move to orbit' contract in the future) and just launch a new one?

I'd best go and check my other satellite now that's heading for a much more distant orbit and see if it's going to go the right way *sigh* (Edit: I've checked and thankfully that one's going the right way already though I could probably have adjusted that one OK).

Low periapse, very high appo,  reverse at Ap   How much DV would the reversal at AP be and how much do you have left?

[weissel]

5 hours ago, Spricigo said:

Incorrect,  same effort to reverse a orbit going the left way or rigth way.  (dumbass off) 

(SmartAss->on) If you go the left way at start and then reverse your orbit you could have gone the right way and not need to reverse your orbit.  Which is obviously less effort! (SmartAss->off)

But that falls squarely into the category "Why do you not start searching where you found $ITEM, instead of looking there last?".

[Spricigo]

4 minutes ago, weissel said:

(SmartAss->on) If you go the left way at start and then reverse your orbit you could have gone the right way and not need to reverse your orbit.  Which is obviously less effort! (SmartAss->off)

the same way that if go right way at start and then reverse your orbit, you could have gone the left way and not need to reverse your orbit...unless you need to go both ways.

BTW: while I see your point about where to look for $ITEM first, I'm curious what its your idea about a more appropriated place to look last than where I found the $ITEM.

 

[weissel]

Just now, Spricigo said:

the same way that if go right way at start and then reverse your orbit, you could have gone the left way and not need to reverse your orbit...unless you need to go both ways.

BTW: while I see your point about where to look for $ITEM first, I'm curious what its your idea about a more appropriated place to look last than where I found the $ITEM.

But you should try to go the correct way, not the sinister one.  :-P

My appropriate place: last place to look == first place to look.

[Hordern]

On 6/3/2017 at 3:32 AM, genericeventhandler said:

Low periapse, very high appo,  reverse at Ap   How much DV would the reversal at AP be and how much do you have left?

Surely the DV to lower my Pe (or raise the Ap), then reverse the orbit and bring the Pe back up (or Ap back down) would equal the same as just reversing the orbit at the AP in the first place?

Even if not, it's safe to say I would never have had enough DV to complete an orbit reversal.

[weissel]

Orbital mechanics are counterintuitive.  You slow down to catch up with a vessel in front of you!? Madness!

But this is KSP. You can try it out. (And yes, speeding up to be able to slow come to a stop for less dV overall is just as crazy as slowing down to catch up.)

Just place a manoeuvre node at AP and see how much dV you need to reverse the orbit. Note that down. Then do the same for a "raise Ap to border of SOI", "reverse direction" and "lower Ap again" (same as raising it). Add the numbers (you might need a mod to read out the node values, or simply check your speed at Ap and multiply it by to to get the numbers).

You can save the game and cheat infinite fuel to try it out, then reverse to the save game (and turn the cheat back off).  Or use a different game - a sandbox, likely. 

[Spricigo]

22 hours ago, Hordern said:

Surely the DV to lower my Pe (or raise the Ap), then reverse the orbit and bring the Pe back up (or Ap back down) would equal the same as just reversing the orbit at the AP in the first place?

Even if not, it's safe to say I would never have had enough DV to complete an orbit reversal.

Maybe not much of a difference in OP's situation but the ideas here are:

1.since orbital velocity is lower at higher altitudes and orbit reversal cost twice your speed it will cost less in higher orbits. 

2.your orbital heigh depends on your orbital energy. Since the energy change ,  for a given change in velocity,  will be proportional to the velocity at the time of the maneuver (that is,  the Oberth effect),  you gain(/reduce) more energy,  and thus raise(/lower) your orbit more,  with a maneuver at lower altitude. 

The question is if that differences are big enough to pay for the manuever necessary to put your craft in those situations.