Perfect auto-orbit. How low can you go without controls?

[Pds314]

The aim of this mission is to put satellite into orbit without touching the controls once you're off the pad/runway.

The scoring is fairly simple. Have the lowest possible Apoapsis with a Periapsis of at least 70,000 meters. Any orbit below that is considered disqualifying. The payload satellite should decouple from the launcher unless you're not using KAL.

Don't alt-F12 cheat or use over/underclocking or mods that give an advantage.

Edited June 30, 2022 by Pds314

[QF9E]

Fun little challenge! My best result so far:

[Pds314]

5 hours ago, QF9E said:

Fun little challenge! My best result so far:

Wow nice. Under 76 km is impressive.

[QF9E]

Just now, Pds314 said:

Wow nice. Under 76 km is impressive.

Thanks! Some more testing indicates that this is at the limit of KSPs accuracy, at least with my current craft. I did do a run with slightly different timings which ended up in a 72 x 74 km orbit, but I did not get a screen capture. And when I did a re-run to capture video, my craft did not make it to orbit.

[Pds314]

12 hours ago, QF9E said:

Thanks! Some more testing indicates that this is at the limit of KSPs accuracy, at least with my current craft. I did do a run with slightly different timings which ended up in a 72 x 74 km orbit, but I did not get a screen capture. And when I did a re-run to capture video, my craft did not make it to orbit.

It probably depends a lot on launch profile. Minimizing entropy and the butterfly effect essentially.

Edited July 1, 2022 by Pds314

[QF9E]

3 hours ago, Pds314 said:

It probably depends a lot on launch profile. Minimizing entropy and the butterfly effect essentially.

I've been relying on fins to keep my craft oriented in the Surface Prograde direction, and I tipped over my rocket slightly on the launchpad to initiate the gravity turn. I think the biggest errors in the flightpath arise from that. So far I haven't used the KAL to control my trajectory, I've only used it as a timer to start and stop the engines and initiate the stage separation.

I've got an idea to use a docking port on a hinge to let the KAL steer my trajectory, but I'll have to get some good values for the hinge angles. I might even write a kOS script to record those angles from a manually controlled flight and see if the KAL is able to reliably and accurately replicate that flight.

[QF9E]

With my new KAL-controlled trajectory I've been able to improve on my previous result. I also ditched the two-stage design I used earlier for a single stage rocket, as staging events are bound to add uncertainty.

With the new steering mechanism the gravity turn is now very stable, reaching the same AP plus or minus about 100 meters every time. Unfortunately I haven't been able to lower AP below 72 km without PE going below 70: I'm hitting the limit of timing accuracy, as the difference between 72 x 70 km and 71 x 69 km orbits is a single KSP clock tick or 1/50th of a second. Perhaps this can be overcome by lowering the engine thrust for the circularization burn, but for now this will have to do. The good news is that it is repeatable:

Second run with the exact same KAL program.

Edited July 2, 2022 by QF9E

[QF9E]

Further improvement:

The way I got this one is by carefully timing the circularization burn (it's 0.2 seconds earlier than in last night's attempt) so that the end of the burn coincides with the craft hitting AP, and by carefully throttling back the engine by a couple of percent near the end of the burn, in order to be able to control the amount of dv better than with timings alone. Now KSP inaccuracies are taking over again, and a second run produced worse results:

In the second run the gravity turn resulted in a slightly higher AP (69927.0 meters compared to 69863.5 meters for the previous run) and I doubt that can be fixed. Fine-tuning the gravity turn to remove small kinks from the launch profile might help but would also be very time-consuming.

Here's a video of a third launch with the exact same KAL program:

I've tried to capture a video with the KAL editor window open, but it turns out that having the KAL editor window open in flight  influences the result, so a screenshot from the VAB will have to do.

 

Edited July 2, 2022 by QF9E