Wobbly Asteroids

[Caelib]

Can anyone with experience provide some best practices for controlling a burn on a Class E asteroid? I've got one captured and i'm trying to circularize its orbit around Kerbin but for the life of me I cannot do any burn with stability.

First and foremost, I have targeted the center of mass on the asteroid and docked there. In addition, I have freed the pivot once docked and made a fine-tune of the center of mass. I suspect the problem is related to the fact that my ship is not PERFECTLY perpendicular to the center of mass, but I have no way to determining that.

The burns get so unstable that the asteroid starts spinning.

Anyone who has solved this problem, please post your solution!

[vger]

As far as the current mission, I'm not sure, but with a modified ship, load up some extra reaction wheels? Remember, once you grab an asteroid, you're wielding way more mass than your rocket even had at liftoff. Controlling it is going to be a Kitch.

[RocketPilot573]

I found a way to control it: Use the engines to turn. Basically give your ship a cluster of engines and toggle them on/off to keep it under control, this works, but only barely... Or you can set up a ship that pulls instead of pushing.

[Caelib]

I found a way to control it: Use the engines to turn. Basically give your ship a cluster of engines and toggle them on/off to keep it under control, this works, but only barely... Or you can set up a ship that pulls instead of pushing.

I had not considered this option, but it sounds like it will work ... thanks!

[Caelib]

Ok, I have tried the "tug" approach, and given a sizable extension in front of it to prevent the thrust from blocking or interfering with the asteroid -- but alas, the asteroid REFUSES to anything but spin uncontrollably.

I am fairly certain at this point that the center of mass indication has problems ... in addition, I have noticed that the Class E asteroids have minds of their own when it comes to rotation. I have had a ship with SAS & RCS off coming straight out of the Space Center and it starts to tumble all on its own. There's issues here that need to be addressed.

[RocketPilot573]

Ok, I have tried the "tug" approach, and given a sizable extension in front of it to prevent the thrust from blocking or interfering with the asteroid -- but alas, the asteroid REFUSES to anything but spin uncontrollably.

I am fairly certain at this point that the center of mass indication has problems ... in addition, I have noticed that the Class E asteroids have minds of their own when it comes to rotation. I have had a ship with SAS & RCS off coming straight out of the Space Center and it starts to tumble all on its own. There's issues here that need to be addressed.

How far do the engines have to be away from the asteroid to produce thrust? Because I want to land a E on Minmus.

[ScottyDoesKnow]

Ok, I have tried the "tug" approach, and given a sizable extension in front of it to prevent the thrust from blocking or interfering with the asteroid -- but alas, the asteroid REFUSES to anything but spin uncontrollably.

I am fairly certain at this point that the center of mass indication has problems ... in addition, I have noticed that the Class E asteroids have minds of their own when it comes to rotation. I have had a ship with SAS & RCS off coming straight out of the Space Center and it starts to tumble all on its own. There's issues here that need to be addressed.

How far do the engines have to be away from the asteroid to produce thrust? Because I want to land a E on Minmus.

From a screenshot I just saw, you only seem to need about an orange tank distance between the back of the engine and the asteroid.

For pushing a class E, locking the pivot will never work. What I had to do was free pivot, zoom in on the navball in IVA view and "herd" the center of mass marker around. Burning slightly to one side to make it move the other way and always keeping it under control. It's somewhat painful.

[Caelib]

For pushing a class E, locking the pivot will never work. What I had to do was free pivot, zoom in on the navball in IVA view and "herd" the center of mass marker around. Burning slightly to one side to make it move the other way and always keeping it under control. It's somewhat painful.

Yeah, that has been my experience ... center of mass on Class E is wonky. Well, it was good practice ... time to capture a Class D for my space station core I guess

[RocketPilot573]

Ok, so I just tested it. To pull asteroids you only need the engine's flame to not be touching anything, and pulling it was WAAAAAY easier than pushing. I felt like I could actually control it. When you push it, the claw is too wobbly (even with multiple) to keep the CoT in line with the CoM, so that will never work. But when pulling it, the Asteroid automatically "wobbles" into place (due to your ship's thrust) so that it won't spin. So I just had to dock my ship "close enough" to the asteroids CoM.

My E class is now in a low Minmus orbit, I just need to land it at my base now.

[kiwiak]

Well thats just my idea i just had, but how about adding rcs ports to asteroids using KAS?

Im not sure if asteroids allow fuel crossfeed, so maybe each rcs port woudl have its own tank.

[Caelib]

Well thats just my idea i just had, but how about adding rcs ports to asteroids using KAS?

Im not sure if asteroids allow fuel crossfeed, so maybe each rcs port woudl have its own tank.

They do allow cross-feed.

[edemlama]

@Caelib

Are you using MechJeb to keep the asteroid pointed in a specific direction or to execute a burn? if you do it could be MechJeb's attitude control system freaking out, I use to have the same problem, even with small asteroids.

You have to open attitude adjustment from the MJ side panel and select use stock SAS, it doesn't completely solve the issue but it helps a lot (now I can throttle up to 60% without loosing control before I had to stop at 25%)

[Caelib]

@Caelib

Are you using MechJeb to keep the asteroid pointed in a specific direction or to execute a burn? if you do it could be MechJeb's attitude control system freaking out, I use to have the same problem, even with small asteroids.

You have to open attitude adjustment from the MJ side panel and select use stock SAS, it doesn't completely solve the issue but it helps a lot (now I can throttle up to 60% without loosing control before I had to stop at 25%)

I don't use mods.

[Kasuha]

My experience is: torque. LOTS of torque. Make several torque probes - probe core, a bit of RCS, a claw and 3-4 SAS wheels each and attach them to the asteroid from all sides. Use only limited torque on the ship itself. Then you will be able to push the asteroid with limited thrust without much wobbling.

[cantab]

My experience is: torque. LOTS of torque. Make several torque probes - probe core, a bit of RCS, a claw and 3-4 SAS wheels each and attach them to the asteroid from all sides. Use only limited torque on the ship itself. Then you will be able to push the asteroid with limited thrust without much wobbling.

This seems like a popular approach, and it's what I've done for my asteroid tug. I only expect that one to push around C's and maybe small D's, but better safe than sorry.

[Technical Ben]

I was able to uses "move freely" then "target COM" then line up the asteroid for near zero "wobble". Small RCS and 1 SAS was enough for a rock about 10 times the size of the craft. Possibly more RCS/SAS for much larger rocks.

[Caelib]

I have moved a class C into an equatorial, circular obit around Kerbin without much problems, but the class E just spins like crazy. I've also noticed that time acceleration + Class E asteroid can be a bad combination if there was any rotation when starting the time acceleration ... I've had my ship break into a dozen pieces when coming out of time acceleration because of this (bug?).

[edemlama]

I have moved a class C into an equatorial, circular obit around Kerbin without much problems, but the class E just spins like crazy. I've also noticed that time acceleration + Class E asteroid can be a bad combination if there was any rotation when starting the time acceleration ... I've had my ship break into a dozen pieces when coming out of time acceleration because of this (bug?).

had the same issue with time warp with a class C

[RedPine]

I have this problem for all asteroid sizes. Pulling instead of pushing, and loads of RCS/Torque are the only fixes I've heard of. Hopefully the asteroid COM indicator and claw physics will be improved to make pushing more practical... or at least possible.

[MysticPing]

I did so i docked a cluster of mini drones with rcs ports on it to be able to steer it better, almost worked well!