Inclined Retrograde Orbit: Easiest Optimized Rendezvous?

[Xavven]

On 10/22/2016 at 2:49 PM, Diche Bach said:

I'll have to try that.

So I've established, it is exactly a 137-degree inclination, which seems weird somehow.

From KSC:

directly east (azimuth 090) = 000.0 - degree inclination

directly north (azimuth 000) = +090 inclination

directly west (azimuth 270) = 180 degree inclination, no?

So why is "southwest" from KSC not > 180 inclination?

 

He had to launch southwest because he was on the other side of the orbit. If he waited exactly half a day, he would have to launch northwest.

Think of it this way -- if you launched into a perfectly polar orbit (exactly north) then you'll be going directly south on the other side of the planet. Depending on when you launch you might have to go south or north to match orbits. It's the same with this slightly inclined retrograde orbit.

[moronwrocket]

You'll have to head slightly west of what you calculate, because of the "free" rotational velocity provided by the equatorial launch site.  Once you get to 35km altitude or so, switch to Map mode, and wobble around the prograde marker, watching the effect on your AN/DN numbers.  Figure out which direction you need to tweak to get the numbers as low as possible.  Once you get there, start heading prograde again and get into orbit.  From there, follow normal rendezvous techniques to get to the 'roid.

The key thing though is trying to launch when the AN/DN passes directly over KSC. Mk 1 eyeball FTW!

[Leafbaron]

If you get Kerbal Alarm Clock you can set a reminder for ascending and descending nodes. Target asteroid from Launchpad and set a reminder for earlist AS/DS node. Then launch with the appropriate heading. 

[monstah]

On 22/10/2016 at 5:00 PM, Diche Bach said:

Actually, it seems to be SOUTHwest.

 

On 22/10/2016 at 5:39 PM, EpicSpaceTroll139 said:

Oops, yes that's right. Derp.

Launch half a day later, and it'll be northwest again  

[Diche Bach]

On 10/24/2016 at 1:09 PM, moronwrocket said:

You'll have to head slightly west of what you calculate, because of the "free" rotational velocity provided by the equatorial launch site.  Once you get to 35km altitude or so, switch to Map mode, and wobble around the prograde marker, watching the effect on your AN/DN numbers.  Figure out which direction you need to tweak to get the numbers as low as possible.  Once you get there, start heading prograde again and get into orbit.  From there, follow normal rendezvous techniques to get to the 'roid.

The key thing though is trying to launch when the AN/DN passes directly over KSC. Mk 1 eyeball FTW!

Yep I watched a video of 5th Horseman doing this and that "switch to map mode" part was a huge step.

The problem now though: I am having a HELLUVA time getting a rendezvous now that I got my orbit way out there, and that is even WITH precise maneuver, and KER.

Not sure if I just 'forgot' how to rendezvous or if this one is a bit unusual because of the size/eccentricity plus the tiny SOI of the target?

[Sandworm]

On 10/23/2016 at 8:00 PM, Lelitu said:

This only works for intercepts in very high orbits.

By definition a rendesvous requires matching planes(and all other orbital parameters). Otherwise you're not in the same orbit, and will fly past at speed.

So you're making a large plane change, but at a high enough altitude (and thus low velocity) that's not too painful.

You don't need to match planes as a separate maneuver.  The system I described allows the planes to be aligned at the interception, rather than waste fuel doing a separate change.  As a general rule, combining maneuvers is more efficient.  If you have followed the system, you aren't talking a 5*+ alignment.  With practice anyone should be able to eyeball a launch to within a degree or two.

[Lelitu]

2 minutes ago, Sandworm said:

You don't need to match planes as a separate maneuver.  The system I described allows the planes to be aligned at the interception, rather than waste fuel doing a separate change.  As a general rule, combining maneuvers is more efficient.  If you have followed the system, you aren't talking a 5*+ alignment.  With practice anyone should be able to eyeball a launch to within a degree or two.

Combining the maneuvers only makes much savings if the alignment change is small, and doesn't skip aligning planes at all.

The method you outlined will work well as long as step 1 goes off well.

get a poor plane match (and don't/can't revert) and you're talking a *very* expensive burn to match orbits at intercept. often enough that it's cheaper to raise the apoapsis high, and planechange there as a seperate maneuver.

I usually play career with no quicksave and no revert, because they make it way too easy. 

[Diche Bach]

On 10/23/2016 at 3:15 PM, Sandworm said:

There is a simple procedure, even in stock.  You don't even need to use maneuver nodes.

 

(1) Launch, as best you can, into the plane of the target but in a much lower orbit, the lower the better.

 

(2) You now have ascending/descending nodes.  Pick the one on the dark side.  At that node, burn prograde.  The opposite node will lift.  Burn until the opposite node crosses the path of the target.  Do not attempt to match planes.

 

(3) The opposite node is where you will meet the target.  The only issue is time.  You should see one of the white tick marks at the node and the other somewhere else.  Warp to the node, to just after the intercept marker. Then burn prograde.  The other marker should rotate around the target's path.  Burn until the two markers match each other.  You now have an intercept.  Do not attempt to match planes.

 

(4) Warp to the intercept then burn to equalize speed with the target.

 

Done.  No fiddling.  No maneuver nodes.  No plane matching.  This system isn't perfect, but it is very efficient even in stock.

Ah I'll have to come back and re-read this when I have the game running and try this. It sounds simple!

[MitchS]

(I can't quote you guys on my work computer, sorry, but you mentioned earlier) "but it's still nothing compared to how much plane changes cost in delta-v in real life"...

I read from a technical write-up on the Space Shuttle a couple years ago that with every drop of OMS fuel on board burned toward the radial at AN/DN, it can manage only 2.3 degrees of inclination change before it's dry. 2.3 degrees! Time to learn how to launch straight into inclined orbits. Hahaha.

Edited December 12, 2016 by MitchS
edit: readability

[Sharpy]

On 22.10.2016 at 7:10 PM, Diche Bach said:

So what is the actual method to determine the launch time and inclination for this sort of rendezvous? What tools does the game provide to allow the user to determine where the nodal line is, what the actual inclination of the target is, etc.?

 

One stock method: Launch a tiny probe with a plenty of delta-V (Okto2 + ant + 2x Oscar B) into LKO of similar inclination (eyeball it). Adjust it to precise inclination by setting the asteroid as target, then burning normal/antinormal at AN/DN. Bring it into as low LKO as allowable (70-71km).

During proper launch, set the satellite as target. Go to map mode, turn into orbital plane of the satellite (so that the orbit becomes a single line). Wait until KSC is under that line, and the satellite has passed over it. Set it as target, navball mode to orbit, launch into such inclination that your prograde marker is in line with the target marker. You may even set SAS to Target, and it will be doing your gravity turn for you

You won't land into the *exact* orbit because Kerbin rotation will throw you out of sync and the moment won't be precise, but still you should be less than 100m/s away from the asteroid.

Also remember plane change maneuvers are way cheaper "way out". Way cheaper to perform first the transfer burn, then plane change halfway there.

 

Or just hunt for encounter at AN/DN without ever doing any plane change. You can do it even from equatorial prograde LKO. True your flyby will last a fraction of second... but hey, cash is cash.