What's the difference between the reaction wheel, and the SAS unit?

[Endersmens]

I've checked all the specs and stuff and they seem exactly the same. Except that the SAS unit weighs more. What's the point in using the extra mass with the SAS unit instead of just using the reaction wheel?

Edited March 25, 2014 by Endersmens

[Kasuha]

Technically:

Reaction wheel is unit which provides torque force

SAS unit is a control unit which employs available means (reaction wheels, engine gimbal etc) to keep the ship in required heading

In KSP:

Parts called "SAS" and "Advanced Stabilizer" are just reaction wheels. SAS functionality is built into all control units like probe cores or command pods.

In previous versions it was not this way, command pods and probe cores did not have SAS function and SAS and IAS were just functional parts without reaction wheel. That's also why the SAS part is mostly empty, it was designed as just containing a computer.

Edited March 25, 2014 by Kasuha

[Endersmens]

I've been playing for almost a year. This has just bothered me cause when i look at the tooltips the only difference is mass. So basically with the .21 (i think?) update the SAS unit became useless, and i should just stick with the reaction wheel instead?

Edited March 25, 2014 by Endersmens

[Kasuha]

They're all reaction wheels now. So I would recommend to stick with whichever suits your needs. The large one is actually lightest.

IAS is the only "duplicite" as it is 1.25 m exactly like the reaction wheel, but it is heavier. But some consider it prettier.

[Endersmens]

ok thank you

[Endersmens]

Actaully another quick question...how do i change "unanswered" to "answered"?

[Red Iron Crown]

Edit your original post, it's an option at the top left, I think.

[Wahgineer]

The reaction wheels used to be called SAS, while the SAS now was called ASAS. The difference is that the ASAS/SAS can use all forms of control: engine gimbal, fins, reaction wheels, rcs, etc. The SAS/RW just uses reaction wheels.

[Red Iron Crown]

The reaction wheels used to be called SAS, while the SAS now was called ASAS. The difference is that the ASAS/SAS can use all forms of control: engine gimbal, fins, reaction wheels, rcs, etc. The SAS/RW just uses reaction wheels.

That's how it used to work, but since 0.21 ASAS control functions have moved to the command pod and the ASAS unit is now just another reaction wheel. It really is a vestigial part that serves no purpose now.

[Endersmens]

found it..you have to go advanced. thanks for the info though