Optimal phase angle for LKO intercept

[tent405]

I haven't been able to find an answer to this question, at least not one pertinent to 1.0+

Suppose I have a target object in circular LKO at 70km. What is the optimal phase angle to target to launch at? I know it depends on the vessel TWR and turn profile, but figure loosely, what would be a good range to try?

I guess I'll keep experimenting and post my results if nobody has this knowledge already.

°

Edited May 14, 2015 by tent405

[DDay2021]

70km seems a little low to do an intercept on, there is no room for a lower orbit so you can catch up. I think the best bet would be to get about 5-10k above the target and let it catch up to you. My guess would be to launch between 10-15 degrees in front of the target, get into orbit around 80km and then maneuver down onto the target.

[Mr Shifty]

Generally, if you're trying to launch straight to rendezvous, with the new aero and flatter sub-orbital profile, I'd launch when the target is 60-45° west of your launch location. (45° is about 4 minutes at LKO.)

[Snark]

I do this all the time (I'm a glutton for Kerbin rescue contracts).

I generally do this by flipping to map view and rotating so that it's looking due north (gives a nice side view). The ideal target position for launch is generally when it has climbed about 5 degrees or so above KSC's western horizon.

I find that my craft's TWR doesn't make much difference here, since the lion's share of time from launch to intercept is either climbing through the first 20 km (where speed is limited by atmosphere) or coasting after the initial burn.

All of the above applies to vertical rocket launches only; spaceplanes have a much more gradual ascent profile and would need a bigger phase angle. I can't offer any advice there, I'm not a spaceplane guy and never fly 'em.

[tent405]

Sweet, thanks for the hints. I was experimenting with 340-350° phase angles. A lot of it depends on your maneuvering style, but with some aggressive maneuvers starting from 345° I was able to get within 3km of my target and kill velocity. That was lucky. I am also flying a clunky 4-mission-in-one ship, something more agile would be easier.