Maneuvering in orbit

[GungaDin]

OK comrades - the next step for me is to dock.  I've got this baby into a nice flat 280K orbit now.  The orange tanks are pretty much spent but I have 2 stages of liquid fuel left plus 90 mono propellant for close control.   here are my questions:

1 - Before I even turn on my RCS system I am able to control my attitude using the swivel of my main thruster.  It's awkward and slow but it works...sort of.  Some engines seem to be able to turn slowly even when they are not engaged and some do not.  Why is that?  For instance the last two stages here use the swivel engine and sometimes, again even with zero thrust, the ship seems to respond to my maneuvers and sometimes it does not.  Any idea why that would be true?

2 - I'll study up on RCS but the first thing I noticed is that even when I just turn on the RCS system they start to fire and maneuver and use up my mono propellant... why is that?

3 - Finally how did we get suck with these hard to spell French space words like "maneuver" and "rendezvous"?

 

[Superfluous J]

2 minutes ago, GungaDin said:

1 - Before I even turn on my RCS system I am able to control my attitude using the swivel of my main thruster.  It's awkward and slow but it works...sort of.  Some engines seem to be able to turn slowly even when they are not engaged and some do not.  Why is that?  For instance the last two stages here use the swivel engine and sometimes, again even with zero thrust, the ship seems to respond to my maneuvers and sometimes it does not.  Any idea why that would be true?

The engines aren't turning you, your command pod is. It has reaction wheels that can rotate your craft at the cost of electricity.

As to why it doesn't work sometimes, my only guess is sometimes you're out of power

2 minutes ago, GungaDin said:

2 - I'll study up on RCS but the first thing I noticed is that even when I just turn on the RCS system they start to fire and maneuver and use up my mono propellant... why is that?

Because they're trying to hold your command pod exactly in line, and like to overshoot and then shoot back. It's best to only use RCS when SAS is off, or for smaller ships that won't flex as much in reaction to them firing.

2 minutes ago, GungaDin said:

3 - Finally how did we get suck with these hard to spell French space words like "maneuver" and "rendezvous"?

I don't know, but they're very nouveau.

[Linkageless]

6 hours ago, GungaDin said:

OK comrades - the next step for me is to dock.  I've got this baby into a nice flat 280K orbit now.  The orange tanks are pretty much spent but I have 2 stages of liquid fuel left plus 90 mono propellant for close control.   here are my questions:

1 - Before I even turn on my RCS system I am able to control my attitude using the swivel of my main thruster.  It's awkward and slow but it works...sort of.  Some engines seem to be able to turn slowly even when they are not engaged and some do not.  Why is that?  For instance the last two stages here use the swivel engine and sometimes, again even with zero thrust, the ship seems to respond to my maneuvers and sometimes it does not.  Any idea why that would be true?

The majority of your attitude control is definitely coming from your pod reaction wheel and the Advanced Inline Stabiliser below it.  While thrusting, the swivel will provide a little bit of attitude control, but nowhere near what the (supernaturally effective) reaction wheels do while they have electricity.

Ignore this... [For future construction, I'd suggest placing any Stabilisers closer to the middle of the stages you wish to control.  Ideally they should be at the centre of mass of those stages.  The slow, awkward response you've experienced is due to lack of leverage, a bit like trying to lift a ladder from one end, rather than from the middle.] Actually this is irrelevant as long as the vessel is rigid.

Edited October 29, 2019 by Linkageless
Correction of thinko.

[Superfluous J]

25 minutes ago, Linkageless said:

or future construction, I'd suggest placing any Stabilisers closer to the middle of the stages you wish to control.  Ideally they should be at the centre of mass of those stages.  The slow, awkward response you've experienced is due to lack of leverage, a bit like trying to lift a ladder from one end, rather than from the middle.

This is actually untrue in space. The problem with lifting a ladder is you're fighting gravity.

In a 0-g environment the reaction wheels will turn the ship around the center of gravity in exactly the same way (barring minor mathematical differences due to the simulation being on a computer) no matter where it's placed.

[Foxster]

All you really need on that craft is some power generation (say 3 or 4 little solar panels) and then all your attitude adjustments can be made with the reaction wheels.

Save your RCS for only translation adjustment when docking. If I am not planning to dock a craft (99% of craft) I never add RCS thrusters.

Click on each of your RCS thrusters and click Show Actuation Toggles then disable Yaw, Pitch and Roll - these you can do with reaction wheels and so no needs to waste mono on this too. 

Oh and dump the heavy spent stage to reduce mass and allow for faster attitude adjustment.  

[VoidSquid]

Привет товарищ!

5 hours ago, GungaDin said:

2 - I'll study up on RCS but the first thing I noticed is that even when I just turn on the RCS system they start to fire and maneuver and use up my mono propellant... why is that?

You remember my post from yesterday?

16 hours ago, VoidSquid said:

I also recommend, if you're using reaction wheels, to disable the rotational components (yaw/pitch/roll) of the RCS thrusters, would be not only a waste of monoprop, but that way you can control rotation by WASDQE, translation by HNIJKL, without one control set affecting the other, much easier and cleaner steering.

This is exactly what I meant.  

[Linkageless]

1 hour ago, 5thHorseman said:

In a 0-g environment the reaction wheels will turn the ship around the center of gravity in exactly the same way (barring minor mathematical differences due to the simulation being on a computer) no matter where it's placed.

Thanks, @5thHorseman . I am pretty sure you're right, and I stand corrected that for a rigid object it makes no difference. Having thought about it I think I established the practice of putting reaction wheels in CoM before finding autostrut.

Absolutely with @Foxster

on saving the RCS, those are excellent tips for economising on monopropellant. I tend to only turn on RCS (if I have it) once I'm pretty much stationary and lined up with the target maybe 100m away, but disabling attitude adjustments as he describes is undoubtably more efficient.

Targeting the docking port on the other vessel is the next useful thing to do once you have come within 100m or so (double click, or right click on it). Switch your navball mode from 'orbit' to 'target' if it hasn't automatically, and select the target SAS mode, if you have it. To give yourself time at that point, ideally you should be as close to stationary as possible compared to the target (0.0m/s). At this point excess weight (like spent tanks as Foxster suggests) should have been shed or you'll be having to manage their momentum also.

If you can turn the target so it points to your Docking port in the same way, that often helps ('control from here' on the port's right click menu will be necessary if you have it anywhere other than on the nose). Be sure to select a docking port of equal size, I once spent an age trying to use the inflatable Docking port from making history not realising it was 'Jr' sized.

After this, quicksave, and approach very slowly, perhaps only 0.1m/s for the final few meters. Tiny bursts from your RCS translation controls while keeping the prograde circle and target in the centre of your navball. Actually killing all speed when ~0.2m away is possible, at which point if you're perfectly lined up the two ports will magnetically attract each other.  With luck, they will be docked now, but if they are just gently touching at a slight angle, you can turn off SAS to see if the magnets pull you together. If you bounce off, you've come in at too much of an angle or two fast, try again more slowly. Don't be afraid to abort by backing away if you're not satisfied it's perfectly in line.

Good luck, it's very satisfying when it all comes together!

 

 

 

 

 

50 minutes ago, VoidSquid said:

You remember my post from yesterday?

This is exactly what I meant.  

Clearly and succinctly put, @VoidSquid I missed that! I think in future I may set this up on new craft in the VAB as the only things I want RCS attitude on are captured asteroids. It plays havoc with sensitive orbital rendezvous too!

[VoidSquid]

11 minutes ago, Linkageless said:

Clearly and succinctly put, @VoidSquid I missed that!

You're welcome, and it took me only a year until I got that idea  

[Linkageless]

On my part, I'd been too lazy/preoccupied to investigate. I didn't start using RCS translation until I was regularly docking large vessels at which point I realised I was putting myself through hell for no reason. In the real world, my astronauts would be frozen corpses heading for an eventual reentry viking funeral!

[GungaDin]

OK guys thanks much.  Just one more question then - I think you've outlined 3 different ways to control my ship's movements in orbit :

1- the rear engine on a swivel using mixed fuels

2 - the rcs thrusters using mono propellant

3 - the reaction wheel using electricity

My final question is this.  With SOME ships I have been able to slowly turn and maneuver (Fr) using only my rear engine while the engine is not firing!  Am I hallucinating or is this possible in KSP?

[VoidSquid]

1. Yes

2. Yes

3. Yes

5 minutes ago, GungaDin said:

With SOME ships I have been able to slowly turn and maneuver (Fr) using only my rear engine while the engine is not firing!  Am I hallucinating or is this possible in KSP?

Reaction wheels  

[Linkageless]

38 minutes ago, VoidSquid said:

Reaction wheels  

The little ones built into your command pod or some probe cores. They still use electricity.

Some other ways:

4. Vernor RCS thrusters (using LF+Ox)

5. Additional engines mounted in different directions, perhaps controlled through action groups.

6. Jeb getting out to push. (Yes, it can work!)

[GungaDin]

You guys are great.  I hope that SQUAD understands that there is no way this simulation would be popular without an active community to learn, teach and mod.

[Zhetaan]

14 hours ago, GungaDin said:

1 - Before I even turn on my RCS system I am able to control my attitude using the swivel of my main thruster.  It's awkward and slow but it works...sort of.  Some engines seem to be able to turn slowly even when they are not engaged and some do not.  Why is that?  For instance the last two stages here use the swivel engine and sometimes, again even with zero thrust, the ship seems to respond to my maneuvers and sometimes it does not.  Any idea why that would be true?

2 - I'll study up on RCS but the first thing I noticed is that even when I just turn on the RCS system they start to fire and maneuver and use up my mono propellant... why is that?

Others have answered these two well enough; I have nothing to add.

14 hours ago, GungaDin said:

3 - Finally how did we get suck with these hard to spell French space words like "maneuver" and "rendezvous"?

They come from the military tradition; modern rocketry has its origins in weapons development.  The military, in turn, gets these words from its centuries-old tradition that the nobility and aristocracy would constitute the officer corps, which lent its vocabulary to the planning process.  The vocabulary, but not the nobility, were retained by the American military when they won independence from the British.  You may be inclined to think that the British would rather prefer English words, but no.  Because of the Norman conquest, French was the language of the upper class (even though the British were often at war with the French), which of course included officers in the military, and in fact, the concept of 'the King's English' was a complete paradox for more than three hundred years, the amount of time after the conquest that it took for a king who spoke English as a first language to accede to the throne.

Even after this, the social elite continued to use French as a second language, alongside the merchants, educators, lawyers, and others who may not have been noble but nevertheless came into contact with French-speaking officials and thus needed to know the language.  The lingering effects of French on official titles and the like are seen in a few other places, such as the inversion of noun-adjective order in high offices like attorney general and tribunals such as court martial.  The lingering effects on the rest of the vocabulary are seen in words that relate (or once related) to high-class activities.  For example, many words naming livestock, such as cow and sheep, are English (technically Germanic) in origin, but the words for the meats prepared from these animals, beef and mutton, are French-derived, because raising these animals on a farm was a peasant activity, but having them prepared by a chef (that's a French word) who was trained in cuisine (also a French word) was a higher-class indulgence.  (Incidentally, the other lingering effect of French on English is to provide a ready source of euphemisms.  To return again to the barnyard example, the only functional difference between using the words dung and manure is how polite the speaker wishes to sound.  There is a similar euphemistic shield between the word derriere and butt.)

In similar fashion, manoeuvre (to move--though it comes from a word meaning manual labour) and rendezvous (to meet) are not, in themselves, high-class activities, but as military activities, they were planned by high-class officers who originally predominantly spoke French.  Many other military terms, such as the words ordnance, bombard, sergeant, enfilade, captain, fort, and munition, are similarly derived.

Edited October 29, 2019 by Zhetaan

[VoidSquid]

Robot - работать

Mammoth - мамонт

Troika - тройка

[Fierce Wolf]

10 hours ago, Linkageless said:

I tend to only turn on RCS (if I have it) once I'm pretty much stationary and lined up with the target maybe 100m away,

I sorta rediscovered monoprop while exploring Jool. Since very minute changes in orbit produce huge differences in flight paths I started using short monopropellant bursts to get it *just right*.

 

This resulted in a lot more monoprop in every ship, and eventualy in a new docking approach

[Linkageless]

Absolutely!  RCS is marvellously convenient for tweaks to eventual intercepts, etc.  I'm preferring vernors for larger vessels so there's no need to carry that mono.  A good tip above is to disable the Pitch, Yaw & Roll attitude control on the thrusters in the VAB so it doesn't mess with your periapsis by attempting to stabilise the vessel.