Not sure I'm correctly using RCS

[Guest Jack6251]

Hi guys ,

I've done a wee search but not really found anything to answer my query relating to RCS usage.

I place the tanks on and the outlet engine parts but not really at all sure I'm using them to aid manouvres or rotations as I can't easily spot any vapour graphic to indicate they're firing (no smoke trail).

Turning the rocket with main rockets off seems as sluggish as normal even when RCS is mounted.

So for example, I have a simple rocket to get to the Mun, how should I best fit RCS parts on (stages, connectors etc)?

Also, how's best to use RCS with Mechjeb mod?

Thanks

Edited July 11, 2015 by Jack6251
solved

[Tex_NL]

A picture is worth a thousand words.

Please post some pictures of your craft and how you're using it. With those people can much easier see what you are or aren't doing wrong.

[Chaos_Klaus]

You need to press R to actually activate RCS. To use the translation capabilities, use the keymapping: IKJL and HN.

[Mic_n]

Just to make sure - you do have the RCS system activated? IE press "R", you should see the RCS indicator around your navball light up. You can turn the whole thing on and off so that you don't waste monoprop when you don't need it.

[Cairol]

Press "R" to activate RCS.

wasdqe is for rotation, ijklhn is for lateral movements.

For placement:

For smaller ships you can place the thrusters near the center of mass.

For larger vessels or if you can't place them near the CoM, place multiple RCS clusters farther away from the CoM, but always equidistant from it.

Good Examples:

Bad example (not equidistant from CoM):

If you do not place your RCS thrusters equidistant form CoM, your ship will swing back and forth after each RCS burst,

which makes it much more difficult to steer and for example can make docking a pain.

[Weywot8]

Some pics of your problem would assist anyone trying to help.

Edit: Ninja'd by everyone else.

In general though, try to place the RCS ports symmetrically (4X typically) and as far away from the centre of mass to get the maximum benefit after they've been activated.

[Foxster]

Unless planning to do some docking I simply never use RCS.

[Red Iron Crown]

Unless planning to do some docking I simply never use RCS.

In addition to docking I find it is sometimes useful for fine-tuning an orbit or transfer.

[Foxster]

In addition to docking I find it is sometimes useful for fine-tuning an orbit or transfer.

Umm, maybe. On balance I don't find it worth the extra mass, the RCS tanks/ports, the drag or heating. At best, if really stuck, then I might throw on a few vernors but I can't remember the last time I did that.

[Sharpy]

Lots of Vernors on the nose is useful in balancing off-balance payloads - say, wheeled vehicles attached vertically, like fuel trucks.

They are indispensable for rescue missions that require more than picking up the Kerbal. (although I just did away with crew cabins and simply deorbit whatever the kerbal is in).

In very lightweight crafts I do away with any "main engines" and just give them RCS thrusters.

...and I hardly ever use monopropellant anymore. No need for extra tanks, Vernors all the way.

Oh, and ladning and start in vacuum, of vehicles that normally land or start horizontally.

Edited July 11, 2015 by Sharpy

[Evanitis]

Also, how's best to use RCS with Mechjeb mod?

Everything but this seems to be answered. MJ doesn't activate RCS when doing manuvers, but it rapidly consumes it's fuel if you allow it. In my experience, if I need 100 units for a docking, 'jeb will use like 6-800. You can help it conserve the fuel for simpler manuvers by manually turning it on and off. So if I instruct MJ to turn a bulky rocket 180 degrees, I switch it on only at the start and the end of the turn. Otherwise it just burns during the whole turn.

[Red Iron Crown]

There's also an option in MJ to use RCS for translation only, not for rotation. It's in the RCS Balancer screen IIRC.

[Guest Jack6251]

No pics needed chaps, thanks for everything!

Simply put, I haven't even activated by using R, assumed MJ did something on auto for some reason.

Thanks for your time, solved

[Snark]

If you do not place your RCS thrusters equidistant form CoM, your ship will swing back and forth after each RCS burst,

which makes it much more difficult to steer and for example can make docking a pain.

This is true... however, you can adjust for that by turning on "fine control" mode (caps lock is the default key for this).

When fine control is enabled, RCS does something very nice: it causes the individual ports to auto-adjust their thrust proportionally, to keep the center of thrust lined up with the center of mass.

Thus, for example, in your last "bad" example ("not equidistant from CoM"): if you pilot that ship with RCS when in fine control mode, the thrusters farther away from the CoM will fire at lower thrust levels, with the result that you get smooth, torque-free lateral thrust.

A really nifty feature that is often overlooked.

[moogoob]

This is true... however, you can adjust for that by turning on "fine control" mode (caps lock is the default key for this).

When fine control is enabled, RCS does something very nice: it causes the individual ports to auto-adjust their thrust proportionally, to keep the center of thrust lined up with the center of mass.

Thus, for example, in your last "bad" example ("not equidistant from CoM"): if you pilot that ship with RCS when in fine control mode, the thrusters farther away from the CoM will fire at lower thrust levels, with the result that you get smooth, torque-free lateral thrust.

A really nifty feature that is often overlooked.

I did not know this. Have some rep!

[Tatonf]

I only use them for 2 things :

- Docking, since the "Thruster Block" is the only multidirectional "engine" with it's 4 ways thrusters

- Stabilization/Rotation of big rockets when reaction wheels are not enough

Monopropellant is completly useless for everything else. There's always a better solution.

You want a low thrust engine ? Go with the ant/spider engines. They have better ISP.

You want a fine tuning for your interplanetary travel but it isn't worth adding spiders ? Right click on your main engine and lower the max thrust to 5.5. Therefore, an engine with 250 kN would go at 13.75 kN at max thrust, and should you put your thrust at 10% you would get 1.375 kN thrust, which is quite small.

Actually if anyone could show me a situation when the use of a monopropellant engine ("O-10 Puff" or "Vernor") is the best option, I would be quite happy, because for the moment I just think they're useless parts.

Edited July 12, 2015 by Tatonf

[Wallygator]

IRL RCS engines ARE used for minor course corrections. In the instance of Apollo, if a course correction was required which was less than (I think) approx 20m/s then RCS was used in favour of the Service Engine.

Having RCS on any vessel is generally a good idea. Having way too much RCS propellent is usually not a good idea. New players typically carry too much propellent as insurance. I did early on. With experience, you can gradually get off the sauce and only take what you need for the mission.

[Tatonf]

Probably because IRL the engines can only go full thrust (or at least a good percentage of it), resulting in overshooting if you attempt to use them, while you can seriously lower the thrust in KSP.

I also experimented the "too much" monopropellant as a noob, because I had no idea how the game (and rocket science in general) works, and someone was saying to always put a tank of it in a tutorial, so I was just blindly adding them to every single rockets without noticing how hungry those things were in terms of delta-V. Plus, I was only using them with the RCS button and I didn't know you could use them for propulsion purpose.

But as soon as I installed mechjeb and noticed that I got rid of them.

[moogoob]

I only use them for 2 things :

- Docking, since the "Thruster Block" is the only multidirectional "engine" with it's 4 ways thrusters

- Stabilization/Rotation of big rockets when reaction wheels are not enough

Monopropellant is completly useless for everything else. There's always a better solution.

You want a low thrust engine ? Go with the ant/spider engines. They have better ISP.

You want a fine tuning for your interplanetary travel but it isn't worth adding spiders ? Right click on your main engine and lower the max thrust to 5.5. Therefore, an engine with 250 kN would go at 13.75 kN at max thrust, and should you put your thrust at 10% you would get 1.375 kN thrust, which is quite small.

Actually if anyone could show me a situation when the use of a monopropellant engine ("O-10 Puff" or "Vernor") is the best option, I would be quite happy, because for the moment I just think they're useless parts.

The only situation I can think of is simplicity - only using a single propellant. I haven't found an opportunity, however, which maybe proves your point.

[moronwrocket]

By the way, Caps Lock allows for precise maneuvers with RCS, and supposedly fires them such that they are balanced with your COM. Not sure how it will work with one ring completely offset from the CoM, maybe the game calculates how much torque your SAS modules can provide.

I use the RCS build aid mod, totally worth it.

I also use it to tune rendezvous the last few m/s for my encounter burn, gets me down to 500 or less half an orbit away.

[Cairol]

This is true... however, you can adjust for that by turning on "fine control" mode (caps lock is the default key for this).

When fine control is enabled, RCS does something very nice: it causes the individual ports to auto-adjust their thrust proportionally, to keep the center of thrust lined up with the center of mass.

Yeah, but you die from old age when using RCS precision mode for docking. XD

You are right. I didn't know that precision mode does this auto-adjust thing. But I normally use this mode only for fine-tuning an orbit anyway.

I always try to place my RCS thrusters to get the least possible veering from excentric placement.

Of course with decreasing fuel, the CoM changes and it will never be perfectly aligned. But if not planning it at all, it can become really bad.

[Wemb]

Actually if anyone could show me a situation when the use of a monopropellant engine ("O-10 Puff" or "Vernor") is the best option, I would be quite happy, because for the moment I just think they're useless parts.

Possibly my 'Grasshopper' lander which collects science from the surface of Minmus and returns it to the orbital lab? It needs to have RCS to dock anyway (well, I do) - so I ditched the rocket fuels tanks and engine. Landing is fine - returning is more difficult due to the low thrust - but doable.

Wemb

[Tatonf]

The trick is that actually only one of the two ships needs RCS for docking, the other one stay passive. And while it can seems illogical to do it, it's better to have the RCS on the mothership instead of the lander.

Why ? Because adding monopropellant to your lander meen you add mass, and therefore you'll have to add more fuel/engines to get it doing what you want.

This is especially true if you go only with monopropellant, since they have bad ISP.

So what I do is positionning my lander as best as I can in front of the mothership and finish the work with the last one.

I'm going to show you two of my scientific mirco-lander that would clearly not be feasible with monopropellant.

They use the dirty external seat that nobody likes on this forum, so prepare your physiological serum.

First the Mun lander. You can't see them very well but there's an ant engine and two spiders. It's designed for an Apollo-style refueling after each landing.

This one is for Minmus. It's ion-powered and can get all the science of Minmus without refueling.

They both have the mystery goo at the opposit side of the external seat.

Edited July 13, 2015 by Tatonf