Engine exhaust a moving asteroids

[Phos]

I'm building an asteroid tractor, and I'm not sure how picky KSP is about an engine's thrust having a clear path away for the vessels.  Does it not care if I'm "blowing into my own sail"?  Does KSP even pay attention to this?

Are tractor style asteroid movers better at avoiding floppiness?  My pusher designs so far have had a hard time with the class E asteroids, it wouldn't be as bad if there were a way to avoid autopilot induced oscillations, but here we are.

[bewing]

Yes, KSP does model "blowing into your own sail". We call it "exhaust obstruction". The game checks for a medium distance to see if any part of your craft is directly behind the exhaust plume. An asteroid counts as being part of your craft. If it finds something there, then 100% of your thrust gets cancelled.

If you want to use a pulling-tug, then you will need to do some tests on the ground before you launch your craft to find the obstruction distance. It's long enough to be a nuisance, but not so long as to be insurmountable.

 

[peteletroll]

You can stop the wobble in a pusher by autostrutting the engines to the heaviest part, that it's the asteroid itself.

[AHHans]

What also should work is angling the engines to point outwards so that the exhaust doesn't hit the asteroid. You'll loose some thrust because the engines are not all pushing in the same direction, but if the setup is symetrical then it should work fine.

My "Class E Tug" is a pusher design. It has five Klaws (one in the center and four in a square around it) on the front that are mounted on robotic pistons (from the BG DLC). That allows me to have all five Klaws connected to the asteroid while still pointing towards the center of mass.

[Phos]

9 hours ago, AHHans said:

What also should work is angling the engines to point outwards so that the exhaust doesn't hit the asteroid. You'll loose some thrust because the engines are not all pushing in the same direction, but if the setup is symetrical then it should work fine.

My "Class E Tug" is a pusher design. It has five Klaws (one in the center and four in a square around it) on the front that are mounted on robotic pistons (from the BG DLC). That allows me to have all five Klaws connected to the asteroid while still pointing towards the center of mass.

Ah the pistons, I forgot about those, I guess I haven't really used them so I'm not sure how strong they really are.

15 hours ago, peteletroll said:

You can stop the wobble in a pusher by autostrutting the engines to the heaviest part, that it's the asteroid itself.

Thanks, a good temporary solution so I don't have to keep launching these things.

16 hours ago, bewing said:

Yes, KSP does model "blowing into your own sail". We call it "exhaust obstruction". The game checks for a medium distance to see if any part of your craft is directly behind the exhaust plume. An asteroid counts as being part of your craft. If it finds something there, then 100% of your thrust gets cancelled.

If you want to use a pulling-tug, then you will need to do some tests on the ground before you launch your craft to find the obstruction distance. It's long enough to be a nuisance, but not so long as to be insurmountable.

 

I found some mention of obstruction but it was mostly in the context of spaceplanes so I thought that might be referring to something's collider clipping into the engine bell.  Thanks for the info.

[AHHans]

3 hours ago, Phos said:

Ah the pistons, I forgot about those, I guess I haven't really used them so I'm not sure how strong they really are.

Well, especially with lateral forces they aren't all that strong. But in this instance I only apply longitudinal compression forces, they can handle those well enough. And I lock them before I start accelerating which also helps.

3 hours ago, Phos said:

I found some mention of obstruction but it was mostly in the context of spaceplanes so I thought that might be referring to something's collider clipping into the engine bell.

Ah, no. My recent encounter of exhaust obstruction was in a plane but with no clipping: I had the horizontal stabilizer on the tailplane in the path on the jet engines, i.e. the engines blew onto the leading edge of the horizontal stabilizer. In KSP this doesn't mean that I get good pitch authority because I effectively have thrust vectoring, but that I don't have thrust at all...