Keeping a steady launch vector

[WatchDragon]

Is there a more automated way to keep a rocket on a launch path?

[Kryten]

That\'s pretty much what the SAS and ASAS are for.

[Richy teh space man]

You mean like asas?

Theres mechjeb under plugins if you want to try that..

[WatchDragon]

Ohh, lol, then i have no idea how to use them, Do i need to attach them to a specific place on the rocket?

[Anomalous_Matter]

Put them anywhere and press 'T'. They\'ll hold you steady where you were pointing when you pressed it. However, if you decouple the SAS it\'ll stop working, so I recommend placing it near the top.

[Richy teh space man]

Asas you only need one of, somewhere near the top of the rocket, before you blast off turn it on with T and it\'ll try and keep your craft pointed in that direction

[WatchDragon]

Very nice, thank you. I was driving myself up the wall manually controlling the rocket and not really getting to see any of the flight itself.

[Foamy]

Also you need to put some RCS/stabilizers on the rocket for it to use. The best approach is to put a set of 4 controllable fins at the bottom and another 4 at the top, that was the ASAS gets the maximum force possible in all directions.

[vexx32]

ASAS and *perhaps* one set of fins will be sufficient, so long as you put an extra standard SAS module or two every stage. More will only be beneficial, so even 3 can be used per stage. Just remember that they do weigh a fair bit, so don\'t go overboard or you aren\'t going anywhere. With this, you\'ll only really need RCS for turning the rocket manually, and to stop it turning after a manual turn. That way, you can minimise the amount of RCS fuel tanks you have to slap on the rocket.

[Temstar]

SAS is really only useful for large spacecrafts that need attitude control while thrusters are off. They\'re quite heavy and impose a noticable performance penalty on your boosters. You\'re much better off using that gimballed LV-T45 engine for attitude control on 2nd stage. Strategy I used to use is:

(Assuming stage 1 means <20000m, where air is dense enough for fins to work)

Stage 1 attitude control - fins attached to stage 1

Stage 2 attitude control - LV-T45 gimballed engines

Spacecraft attitude control - Command pod reaction wheel + SAS (if large ship) + RCS (if huge ship and I have RCS fuel to spare for the mission).

Nowadays I fire my stage 1 and 2 together in parallel with fuel crossfeed from stage 1 to stage 2, as a result I don\'t even need fins anymore on stage 1 since stage 2\'s gimballed engine will provide enough attitude control for the whole stack before stage 1 separation.

You wouldn\'t want to use purely LV-T45 for first stage though because it has poor thrust to weight ratio, LV-T30 or Aerospike with fins is fine but a mixture of LV-T45 with non-gimballed engines with no fins or SAS at take off results in the most efficient rockets.

[Millst0ne MK II]

How about a picture of your rocket. I\'m sure some of the pros here could give you a hand in figuring it out, and optimizing it all!

[xclusiv8]

I\'ve always wondered what it is that makes my rocket turn in space if I only have a basic sas or the advanced one. I mean how they make the ship change direction without any thrusters?????

[Temstar]

I\'ve always wondered what it is that makes my rocket turn in space if I only have a basic sas or the advanced one. I mean how they make the ship change direction without any thrusters?????

Magical reaction wheels that never need to cancel stored up momentum.

http://en.wikipedia.org/wiki/Reaction_wheel

[what-the]

I\'ve always wondered what it is that makes my rocket turn in space if I only have a basic sas or the advanced one. I mean how they make the ship change direction without any thrusters?????

Easy. You can do it yourself. Sit on a 360 chair (office chair) with a heavy book. Hold book out and move the book left or right. You can keep spinning around by bringing the book to the centre of gravity after you can\'t reach any further and then extending to the side you started from. By using weights you could turn the ship too.

[vexx32]

Aye, as what-the says, it employs a device using an electrical motor (as described briefly by Temstar) to alter the craft\'s rotational momentum by an application of the conservation of angular momentum. It\'s used to keep satellites and telescopes in particular orientations as well as slowly turning them.

And while 'magical' is an apt description, it\'s just basic physics that can be demonstrated as what-the outlined. In the absence of a swivelling chair, you\'ll see similar effects on anything that spins -- for example, ice-skaters can control the speed of a spin by bringing their arms in close or flinging them out wide as they spin. And no, air resistance will not account for all that, before you ask.

[xclusiv8]

Super cool :-)

[Nibb31]

There are two elements required:

- a control computer (ASAS) and

- some sort of physical system to control the rocket\'s attitude: either RCS, SAS, or winglets.

ASAS on its own is just a computer. If you don\'t attach an RCS, SAS, or winglets, it won\'t do anything. In the absence of an ASAS, the RCS, SAS, and winglets also react to manual controls.

SAS works like a gyroscope. This is how you can control a spacecraft without RCS, even large ones. The ISS uses multiple gyros to maintain its orientation, not RCS thrusters. SAS does not control anything by itself. They really should have called it a gyro, so as to reduce confusion, because that is how it works.

[Zephram Kerman]

Yah, what they all said above. To put it in a more organized way:

add just one of either of these for autopilot:

ASAS

MechJeb

add as much of any of these for control authority:

SAS

RCS

fins

gimballed engines

Each one works in its own way, with advantages and costs. That\'s where it gets more complicated, and you make engineering decisions.