SAS, ASAS and turning

[grom]

I built a satelite using:

• ISA MapSat Satelite
  
• Stayputnik Mk2
  
• Communotron 16
  
• Communotron 88-88
  
• 3 x Z-500 Rechargable Battery Bank
  
• 4 x Illuminator mk1
  
• 2 x OX-4B Photovoltaic Panels
  
• FL-R25 RCS Fuel Tank
  
• Rockomax Brand Adapter
  
• Hull-mounted Clamp-o-tron
  
• 4 x RV-105 RCS Thruster Block
  
• FL-T800 Fuel Tank
  
• LV-N Atomic Rocket Engine
  

And the problem I had was it was very slow to turn. What options would there be to improve turning speeds?

Do SAS modules help with turning when SAS is not on?

Do SAS modules work with ASAS? Or do they work against it and are conflicting?

[Pyotor Gagarin]

ASAS will use every relevant part of the ship to STOP rotation whenever it is turned on.

SAS is a set of reaction wheels that enable turning without using RCS propellant. Capsules and probe-cores come with their own reaction wheels, but generally the ones in the SAS module are more powerful.

So if you want to rotate your ship you'll want to disengage the ASAS temporarily by hitting "T", or holding down "F", and then turn it back on when you're finished to hold the ship in its new direction. I don't know whether turning off ASAS turns off SAS with it or not; in my experience, it doesn't seem to.

hope that helps

[Eric S]

[*]Stayputnik Mk2

Here's your problem (or at least one of them).

Assuming you have your RCS turned off (it's off by default), your engines aren't firing, and you're out of the atmosphere, your only ability to turn comes from the reaction wheels of the command pods. Having ASAS turned on while you do this is bad as mentioned above, but if that's not the problem, it's probably that you don't have enough torque from reaction wheels.

The thing is, the stat you're looking for doesn't appear in the VAB. Command Pods have two stats, rotPower and linPower. I think it's the former that you're concerned with here, but it doesn't really matter since almost every pod I've ever seen has the same values for both stats. This stat reflects how much torque the command pod can subject the craft to.

Most of the manned command pods have a rotPower in the range of 5 to 20. Most unmanned command pods have a rotPower of 0.5.

The Stayputnik, however, is the exception to that second part. It has a rotPower of 0.3, meaning it will only turn a ship 60% as fast as the other command pods.

Now, that's plenty of rotPower, possibly even too much, for a very light satellite. But between the FL-T800 and the LV-N, you're definitely not a light satellite. If you're trying to turn with those still attached, the Stayputnik will have a hard time.

So, the first step is to use one of the other probe command pods, ANY of them would be an improvement. They might weigh a little bit more, but the weight of the probe pod is insignificant compared to all the other stuff.

At best, that's going to have you turning about 66% faster. If that's still not enough then you either need to add more pods (the rotPower is basically additive), or turn your RCS on. You could even stick a Mk1 pod under a probe pod just for it's greater rotPower, flying a potentially kerbal'ed ship unkerbal'ed.

[Jason Patterson]

As Eric S said, it's rotPower that is involved in controlled turning of a vehicle. SAS only stops rotation, it does not (and cannot) help start rotation. Your probe module is the reason your turning is slow.

You can increase turning power by adding additional probe modules (or an empty crew module) to the vessel, or use physics warp (alt-.) or wait patiently for the existing setup to do its job. It really shouldn't be terribly slow, even with the kind of mass you've got.

SAS - When activated it works to stop rotation by applying a countertorque to the ship.

ASAS - Uses any and all ship's systems (vectored engines, control surfaces, command module torque) to maintain a fixed attitude. It will return the ship to that attitude if the ship turns away. If it is used on a vessel without any system capable of causing a torque (don't know how that would be possible, but let's pretend) then it will do absolutely nothing.

Avionics - Identical to ASAS except that instead of a fixed attitude, avionics works to maintain the vessel's current attitude. If it is perturbed from that to a new orientation, avionics will maintain the new orientation.