What can I do with spacecraft attitude?

[NFunky]

Hey guys, I've recently been having a LOT of fun playing KSP without reaction-wheels.  It adds a whole new depth to the game.  Whereas before, the only thing I ever had to think about was whether I had decent electric charge, I now have to think about where/when to use the RCS (and most importantly when to save it), aerodynamic surfaces, and engine gimbaling.  Seriously, it's like I've installed some crazy new mod pack or something, but it's all stock.

Becausse monopropellant is limited, not using it whenever possible is obviously very important for a satellite/spacecraft.  So I've been playing around with spin-stabilization, and it does in fact work.  The only requirement is that you MUST have at least two non-physicless parts attached radially.  The physics engine will model angular momentum if there are actual masses whizzing around in circles.  A big bonus (to me) is that spacecraft and satellites look more realistic, and very cool, while spinning in orbit.  I may even install PersistentRotation so they keep spinning in time warp.

Anyway, I have started wondering if there's anything besides main engine orientation that depends on attitude in KSP.  Are there any tasks I can do with spin-stabilized spacecraft?  Are there any mods that would add extra reasons for attitude control, like antenna/sensor aiming?

Thanks!

[SickSix]

How do you dock? You are far braver than I.

[cdm86]

RemoteTech has some dish type antennas which have to be oriented.

linky linky

Normally though you orient them by telling them where to point.

I do not know if it would work by "manually" adjusting the orientation of the craft they are on.

The relevant part of the description on its github reads as such:

Quote

Useful for long range communications, dishes are directional or beam antennas that must be instructed what direction to point at. They do not need to be physically rotated; you need merely select a target from a list of comsats. These dishes come with a cone of vision (which becomes narrower for a longer range). If the dish is pointed at a planet or moon, anything inside this cone can achieve a connection with the dish.

Now "not need to be physically rotated" does not necessarily mean "physical rotation would also work".

If I were to code such a mod, I would probably simply have dishes set to pretend to be pointing at a target and then calculate the FoV and distance from the craft to the target for connection logic. This would also get around certain limitations of the game such as physics and thus current rotation not being calculated for far away craft. Maybe you are already aware of this because you noticed that f.e. solar panels sometimes magically work while the craft they are on are on the night side of a body because the last time physics was calculated for them was when the craft was on the day side, at least I believe this to currently be the case.

But how it actually works I do not know.

[NFunky]

4 hours ago, SickSix said:

How do you dock? You are far braver than I.

Honestly, docking isn't really any harder than it was before.  As long as I've balanced the RCS well enough, the minor rotational and translational tweaks don't affect each other too badly.  I do tend to start lining up for docking pretty far out though, like 150-200m, and orient both vessels if at all possible.

[Ten Key]

6 hours ago, NFunky said:

Anyway, I have started wondering if there's anything besides main engine orientation that depends on attitude in KSP.

Solar panels.

6 hours ago, NFunky said:

Hey guys, I've recently been having a LOT of fun playing KSP without reaction-wheels.  It adds a whole new depth to the game.

Agreed. I dumped reaction wheels a while ago and have never looked back.

[DrLicor]

Playing RSS/RO you you have to use the RCS because the reaction wheel are way under powered, just as in real life. 

Most of the time when I turn a spacecrafts, I disable the SAS so that I only have to tick the control key I need, watch how the crafts slowly turns and give it some retro fire with the RCS. 
Same for docking, etc. Also, because you have limited engine ignitions in RO, I do small manouvre nodes on the RCS instead of wasting a ignition.

You can try a full munmus landing with only RCS, no engines  

But indeed, it has it's limits and that's why in real life, some probes use reaction wheels instead of RSC. Even the ISS keeps its orientation by reaction wheels. 

 

[Snark]

1 hour ago, cdm86 said:

RemoteTech has some dish type antennas which have to be oriented.

Targeted.  Not "oriented".  Doesn't matter where they physically point, it's just whatever you select in the targeting menu for the antenna.

1 hour ago, cdm86 said:

I do not know if it would work by "manually" adjusting the orientation of the craft they are on.

It wouldn't.

1 hour ago, cdm86 said:

Now "not need to be physically rotated" does not necessarily mean "physical rotation would also work".

Matters of phraseology aside, that is, in fact, the case.  Physical rotation's irrelevant for RemoteTech.

 

1 hour ago, Ten Key said:

Agreed. I dumped reaction wheels a while ago and have never looked back.

Except that reaction wheels are, in fact, an IRL thing, and real-world spacecraft do, in fact, have them.

Of course, they don't work the way that KSP reaction wheels work, since KSP reaction wheels are magical sources of endless torque that violate conservation of angular momentum all to heck.  (It's not just that they're "overpowered".  It's that they're wrong, they violate fundamental physical law.  Scaling their torque levels down by a factor of 100 or even 1000 wouldn't fix the problem.  They'd still be violating conservation of angular momentum, just more quietly.)

I've occasionally thought it would be cool to have a mod that tweaks reaction wheels so that they work the way that they really do in real life, i.e. so that you can use them for adjusting your angular position, but not your rotation.

[bewing]

43 minutes ago, Snark said:

I've occasionally thought it would be cool to have a mod that tweaks reaction wheels so that they work the way that they really do in real life, i.e. so that you can use them for adjusting your angular position, but not your rotation.

I partially agree and partially disagree with snark on this one. Reaction wheels do work IRL. They do make 1 ton industrial versions of them called "kinetic energy storage systems". The ones on satellites are indeed quite weak, but that is not an inherent problem with the tech -- it's just that the technology is not being taken anywhere near its limits. They do work by causing a temporary rotation of the attached ship -- but the current ones reach their limits very quickly and need to be stopped and "desaturated". Which is another process that could be done much more efficiently than is currently the case.

So IRL, with a better reaction wheel technology than we have now, some amount of angular momentum can be stored, can be transferred into a different dimension of the craft, and can be bled off slowly using one of several other physical mechanisms to desaturate the reaction wheels.

Limiting KSP to 1970's tech levels does indeed show how hard it is to fly spaceships around with 1970's technology. But reaction wheels are going to be improving significantly over the next 50 years, and I see no real problem with having some tech in the game that's not completely outdated.

 

 

Edited March 2, 2017 by bewing

[Snark]

 

28 minutes ago, bewing said:

They do work by causing a temporary rotation of the attached ship -- but the current ones reach their limits very quickly and need to be stopped and "desaturated".

This is how all reaction wheels work.  It's how they work now, and it is how they always will work, forever and ever, because that's what conservation of angular momentum is.  They're just storage batteries for angular momentum.  You can put it in, and you can take it out.  But you can't create or destroy it (like KSP reaction wheels do), because that would violate conservation of angular momentum.

28 minutes ago, bewing said:

Which is another process that could be done much more efficiently than is currently the case.

If you mean "could operate on less electricity", or "can store more angular momentum", or something like that, fine.  Certainly, that aspect of technology can be improved.  But that's irrelevant to what I said in my post.  Violating conservation of angular momentum is physically impossible, and future technology won't change that.  My comment was simply "wouldn't it be interesting to have KSP reaction wheels that don't violate conservation of angular momentum."

28 minutes ago, bewing said:

So IRL, with a better reaction wheel technology than we have now, some amount of angular momentum can be stored

Yes, just the way they already do.  Maybe store a larger amount of it, but it's still just storing and later releasing.

28 minutes ago, bewing said:

can be transferred into a different dimension of the craft

I have no idea what this statement means.  What's this "different dimension"?

28 minutes ago, bewing said:

can be bled off slowly using one of several other physical mechanisms to desaturate the reaction wheels.

Kinda lost me on this one.  The way you desaturate the reaction wheels is to stop them.  Which you do with a high-tech device called a "brake".  That's true now, and I expect will be true in the future.  They're saturated because you put angular momentum into them.  The only way to desaturate them is to take angular momentum out again, which restores that momentum back into the ship, which undoes the effect of the wheels.

The momentum can't go anywhere because the ship is a closed system as far as angular momentum is concerned.  Unless, of course, you either expend reaction mass (e.g. via RCS), or interact with some external force (electromagnetic or whatever)... but if you do that, that has nothing to do with the reaction wheels themselves, it's a different function of the spacecraft.

28 minutes ago, bewing said:

I see no real problem with having some tech in the game that's not completely outdated.

There's a difference between "outdated" and "physically impossible because it violates the laws of physics."

 

To be clear, I don't really have a problem with the fact that KSP reaction wheels do the impossible.  I use them myself all the time, and have no desire to stop using them any time soon.  I think it's a reasonable compromise for the sake of playability.

Just sayin' that I think it could be interesting to make them behave as real-life reaction wheels do, as a thing to play around with in a mod.

[bewing]

24 minutes ago, Snark said:

 

This is how all reaction wheels work.  It's how they work now, and it is how they always will work, forever and ever, because that's what conservation of angular momentum is.  They're just storage batteries for angular momentum.  You can put it in, and you can take it out.  But you can't create or destroy it (like KSP reaction wheels do), because that would violate conservation of angular momentum.

I disagree with this. You add and subtract angular momentum to/from a craft by applying a torque. Once you have some angular momentum, you aren't stuck with it forever. There are ways to cancel it out again.

In space, you can create a torque with a nozzle, with magnetic field interactions, with solar wind interactions, by shooting a laser out one corner of your ship, etc. Applying a brake to your wheel isn't the only way.

 

Quote

I have no idea what this statement means.  What's this "different dimension"?

A single reaction wheel operates in one dimension only (usually roll). With a clutch and another reaction wheel, you can acquire some roll angular momentum, declutch, rotate the ship 90 degrees around the reaction wheel (with the other reaction wheel), activate the clutch, and then brake the first wheel. This can turn angular momentum in the roll axis into angular momentum in the pitch axis (for example).

In fact, you can use this method to cancel out angular momentum between two wheels.

Quote

The momentum can't go anywhere because the ship is a closed system as far as angular momentum is concerned.  Unless, of course, you either expend reaction mass (e.g. via RCS), or interact with some external force (electromagnetic or whatever)... but if you do that, that has nothing to do with the reaction wheels themselves, it's a different function of the spacecraft.

Exactly. No, it's not a closed system at all. The easiest way is to interact with the magnetic fields that permeate our solar system. It's not a "different function of the spacecraft" if the entire purpose of that function is to desaturate your reaction wheels. You just have to broaden your definition of the "reaction wheel system" of the craft to include the extra bits that desaturate the wheels using another physical mechanism.

 

Edited March 2, 2017 by bewing

[NFunky]

So... These are the attitude dependent things in KSP I know of so far.  Main engine orientation, docking port alignment, solar panel efficiency, aerodynamics, and heat occlusion.  I was wondering if anyone knows if the sun produces heat radiation in KSP, and if so, if a vessel would be protected by using a heatshield between itself and the sun?

[c4ooo]

@Snark I don't quite understand, how do KSP reaction wheels break real world physics? And what is the difference between rotation and angular position?

 

@NFunky The sun does indeed produce heat radiation and can blow up your craft if you get too close. Therefore you should only approached the sun at night.

Edited March 2, 2017 by c4ooo

[Snark]

10 minutes ago, bewing said:

In space, you can create a torque with a nozzle, with magnetic field interactions, with solar wind interactions, by shooting a laser out one corner of your ship, etc.

Sure, that's what I said.

34 minutes ago, Snark said:

Unless, of course, you either expend reaction mass (e.g. via RCS), or interact with some external force (electromagnetic or whatever)

That has nothing to do with the wheel.  And it doesn't require advanced technology that we don't have.  Ships already have RCS.  Pretty sure they've already done some stuff with magnetic fields.  I think I may have even heard about someone who came up with a really cheap way to (very very gradually) spin a satellite, propellant-free, by painting some vanes black on one side and white on the other so that they reflect sunlight differently.

When it comes to rotating a spaceship, there are, broadly speaking, two ways to do it:

1. Store it somewhere internal (where it has to be un-stored, at some point)
2. Dump it somewhere external (by interacting with the outside world).

Reaction wheels are #1.  RCS is #2.  There are other techniques (which you and I have both listed) which fall into category #2, too.  In general, these other techniques that do #2 without expending reaction mass tend to be very, very weak ones that only exert very microscopic torques over very long periods of time.

If you want something that works fairly quickly (i.e. on a time scale where a game is playable, not hours or days), AFAIK you've basically only got reaction wheels and RCS to work with.  So everything that I said, still stands.

17 minutes ago, bewing said:

A single reaction wheel operates in one dimension only (usually roll). With a clutch and another reaction wheel, you can acquire some roll angular momentum, declutch, rotate the ship 90 degrees around the reaction wheel (with the other reaction wheel), activate the clutch, and then brake the first wheel. This can turn angular momentum in the roll axis into angular momentum in the pitch axis (for example).

Sorry, I'm confused, I think we're talking at cross-purposes here.  Ships can do that today. 

1 hour ago, bewing said:

So IRL, with a better reaction wheel technology than we have now, some amount of angular momentum can be stored, can be transferred into a different dimension of the craft

^ That doesn't take better reaction wheel technology than today.  They do that now.  As long as you have a minimum of three wheels (or, often, four wheels arranged tetrahedrally, so it can still maintain control if one wheel fails), they can rotate the craft freely about any axis they want.  Subject, of course, to saturation, due to conservation of angular momentum.  So?

23 minutes ago, bewing said:

This can turn angular momentum in the roll axis into angular momentum in the pitch axis (for example).

Well, yes, though I feel that stating it that way has the potential to be a bit misleading.  It hasn't "turned" the angular momentum anywhere; the angular momentum would still be pointing in the same direction it always was.  It's the ship that's rotated.

30 minutes ago, bewing said:

You just have to broaden your definition of the "reaction wheel system" of the craft to include the extra bits that desaturate the wheels using another physical mechanism.

To be explicit:  suppose that the ship's longitudinal axis is originally pointing in, say, the +X direction.  And on board, there's reaction wheel A, whose axis is mounted longitudinally on the ship (i.e.. parallel to the X axis), and another reaction wheel, B, that's at right angles-- say, parallel to the Y axis.  Yes, it's possible through a combination of wheel operations to re-orient the ship, so that it ends up with its longitudinal axis pointing +Y instead of +X, and reaction wheel A ends up dead still, and now reaction wheel B is spinning instead... except that reaction wheel B is now aligned on the X axis and therefore the original angular momentum is still pointing +X and there's no way to change that (or get rid of it) without interacting with something external to the ship.

20 minutes ago, bewing said:

In fact, you can use this method to cancel out angular momentum between two wheels.

You've lost me again.  How so?  The only way two wheels can "cancel each other out" is if they have equal angular momentum in opposite directions, but I can't imagine why a ship would ever have wheels in that configuration, since it would mean they never stored any net angular momentum in the first place and therefore are just useless dead weight.

If you've got a reaction wheel-- or any assembly of any number of reaction wheels, arranged in any fashion-- and they have a net angular momentum, there's no way to cancel that out without either expending reaction mass or interacting with forces external to the craft, i.e. via mechanisms outside the reaction wheels.

30 minutes ago, bewing said:

You just have to broaden your definition of the "reaction wheel system" of the craft to include the extra bits that desaturate the wheels using another physical mechanism.

Well, sure, you can do that if you want, but then you have to call the RCS a "reaction wheel system", too, which seems a bit odd.

And there's still going to be the distinction between internal-storage mechanisms (i.e. reaction wheels), which can act quickly but have a finite storage capacity, and external-interaction systems (other than RCS), which have infinite capacity but are generally (other than RCS) very weak and slow-acting.

All I was saying, in my original post, is that the idea is kind of interesting to model a reaction wheel, i.e. a system that's fast-acting but finite storage capacity.

[Snark]

23 minutes ago, c4ooo said:

@Snark I don't quite understand, how do KSP reaction wheels break real world physics? And what is the difference between rotation and angular position?

Sorry, I didn't really speak very precisely.  What I mean by "rotation" is angular velocity (well, really, momentum, but that goes hand-in-hand with velocity, for a rigid object rotating about a particular axis).

Angular momentum is conserved.  Angular position is not.

Put me in a spacesuit, and let me float in a vacuum in zero gee, motionless (i.e. no net rotation, no angular momentum).  Suppose I'm facing in the +X direction, and I want to do an about-face so that I'm facing in the -X direction.  I can do that without expending any reaction mass whatsoever.  I can just make some swimmy motions with my arms and get myself turned around to face the other way-- or, indeed, in any direction I like.  But what I cannot do, without expending reaction mass or interacting with an external force, is to give myself a net rotation, i.e. arrange matters so that when I stop wiggling my arms and just relax, I'm rotating instead of being stock-still, as I was when I started.

A detailed explanation of how KSP reaction wheels violate the heck out of real world physics, is here:

...the TL;DR being that they're an infinite source of free torque, rather than behaving as storage batteries for angular momentum.

Note that this explanation assumes "no interactions with external forces".  As the above lively discussion with bewing points out, there are other physical methods to interact with the environment that can impart a net torque to the ship, but that's not what I'm talking about here.

[bewing]

2 hours ago, Snark said:

To be explicit:  suppose that the ship's longitudinal axis is originally pointing in, say, the +X direction.  And on board, there's reaction wheel A, whose axis is mounted longitudinally on the ship (i.e.. parallel to the X axis), and another reaction wheel, B, that's at right angles-- say, parallel to the Y axis.  Yes, it's possible through a combination of wheel operations to re-orient the ship, so that it ends up with its longitudinal axis pointing +Y instead of +X, and reaction wheel A ends up dead still, and now reaction wheel B is spinning instead... except that reaction wheel B is now aligned on the X axis and therefore the original angular momentum is still pointing +X and there's no way to change that (or get rid of it) without interacting with something external to the ship.

You're not taking into account several effects. https://en.wikipedia.org/wiki/Tennis_racket_theorem

You can couple angular momentum out of one axis into another. It's only the total that's conserved. Not the individual axes.

 

[Snark]

9 hours ago, bewing said:

You're not taking into account several effects. https://en.wikipedia.org/wiki/Tennis_racket_theorem

You can couple angular momentum out of one axis into another. It's only the total that's conserved. Not the individual axes.

Not relevant.  You can change the orientation of the ship, no problem.  But if a system has a net angular momentum pointing in one direction, the direction and magnitude of that net angular momentum cannot change unless the system interacts with something external.

https://en.wikipedia.org/wiki/Angular_momentum#Conservation_of_angular_momentum

Remember that angular momentum is a vector quantity.  It has a magnitude and a direction.  The individual axes are conserved... if you're talking about the coordinates in the inertial, non-rotating reference frame (which is what I've been talking about all along, since that's the only frame in which "angular momentum" is a meaningful concept).

Certainly the individual axes of the object don't "conserve their momentum" (if that's what you're saying, here), since that's not even a thing (nor have I ever claimed that it was); the object can change to different orientations.

[Ten Key]

15 hours ago, NFunky said:

I was wondering if anyone knows if the sun produces heat radiation in KSP, and if so, if a vessel would be protected by using a heatshield between itself and the sun?

Yes to the first question, and "kind of" to the second. I've never actually tried this myself, but I did a little bit of reading and it looks like you can create a thermal shadow with a heat shield in KSP. The problem is that the heat shields are ablative and will eventually start to cook off as they heat up, just like they do on reentry. It looks like people have managed it, but it takes a bit of fiddling.

This thread is a year and a half old, but AFAIK the heat management system in stock KSP should be similar to the current version of the game. Some of the screenshots show the radiation flux on the shield parts, and at least one person managed to protect a probe with a depleted heat shield. 

[Spricigo]

KSP's reaction wheel work accordingly to physics of Roadrunner

Exactly the same principle. No reaction,  opposite in direction and equal in intensity, in the fan or in the reaction wheel, just the action in the vehicle  and nothing else.

[NFunky]

Hey all, sorry to resurrect this post, but I had another related question, and I didn't want to open a whole new thread for it.

 

Does anyone know if the Asteroid Day sensors need to be aimed a certain way?  I mean, they're telescopes, so I would hope they would.

 

Also, does anyone know if there is a way to write a contract (for Contract Configurator) that requires a certain attitude?  I'm not what command would check for that, but I'd really like to write my own contract pack for more interesting satellite/science contracts.

[fourfa]

Too bad this thread turned into the inevitable arguing about reaction wheel physics, which seem irrelevant to the OP's questions...  

Back to playing the game - I built some Apollo replica missions with zero reaction wheels (just deactivate torque in stock) and MAN O MAN is it different.  Everything you need to do is 100% achievable with RCS, but you will have to up your game.  Most of it happens in the VAB/SPH balancing your CoM and RCS vectors.  Docking becomes a very slow, methodical process a little more like real life.  The downsides are carrying a lot more parts and mass in thrusters and monoprop which (compared to vanilla) impose a dV and part count penalty, and the usual aesthetic challenges given the limited stock parts.

If you've tried playing the game on Hard mode and are looking for an additional challenge, give zero reaction wheel a go.  I've added it to my list of minor stock-ish realism tweaks (like electric lights and EVA suits drawing electric charge, EVA fuel draws from monoprop stores, etc)

[NFunky]

Really hate to do this, and I'm really sorry for bringing this thread back up again.  I just never really got much in the way of answers to my original question (except for the reminder about solar panels).

 

I'd really appreciate anyone who could suggest other attitude specific tasks/mission elements are in KSP.  Can anyone help lay some more of these out for me?  Also, does anyone know of any mods that require attitude alignment?

 

Thank you!

[Spricigo]

 

I suspect that you already get your answer, while its not what you was hopping for.

Basically, in real life spacecraft attitude is important for 3 things: propulsion, communications, sensors, KSP being simpler don’t account for communications and sensor orientation/occlusion.

I know there mods for space telescopes, maybe some of those cares about attitude. However  I wont hold my breath or neither I have a specific one to suggest.

[fourfa]

Agreed, I think it's going to be up to the OP to roleplay this the way he wants to, or write his own mod to do what's he's looking for.