Solar Sail using Solar Panel Gamedata

[slate reef]

I was wondering if it would be possible to create a defacto solar sail part using the existing solar panel module, by making it generate a thrust value instead of a value for EC generation.

Solar Sails are relatively simple:

1. open the sail.
2. thrust will be applied to the craft in the radial out direction, depending on the area of the sail exposed to the star, and the intensity of the sunlight hitting it.
   https://en.wikipedia.org/wiki/Solar_sail

i may be wrong, but isnt this basically what solar panels are already doing to calculate EC generation? They use distance from the closest star to determine sunlight intensity, and the angle between the surface normal and radial direction to calculate exposed area. could one take those values, but make them produce thrust rather than EC?

i imagine the equation would look something like this:
Thrust_radial_out = base value * %area_exposed * intensity_modifier

i'd love to hear your thoughts about this! :)

[onyx brook]

I suspect this is more complex than you may be anticipating. You would need basically a whole new engine module (which is a KSP2 component all current engines use), as that module is looking for your throttle setting and max thrust to compute thrust, and applying that in the direction of the thrustTransform vector (which is typically either in a fixed orientation to the craft's body, or is a child of the gimbal vector). With a solar sail one can't simple throttle up or down except by changing the orientation or size of the sail. I suspect sails are not ridged, so making an orientation change is not something you would do with the craft's ordinary attitude control system. And are solar sails deployable and retractable? How would that work? While the math is not terribly complex, the game play and underlying mechanics may not be simple to develop.

Also, this would be hard to work into the game from another aspect. Currently in the game electric engines are rediculously OP. They typically have thrust that's higher than anything realistic by about a factor of 1000x. Their Isp isn't necessarily unrealistic, and so the fuel consumption for thrust is not wacky, but the thrust is very very high realtive to anything realistic. The stock Dawn engine produces 0.2 kN of thrust. Typical real ion engines produce thrust measured in mN, not kN. This is done specifically to foster player enjoyment. Most players would never have the patience to sit through days of thrust to accomplish a single maneuver. So, with realistic Isp and insane thrust electric engines are quite a lot of run in the game - they feel more responsive than they really would.

How would this work with solar sails? Should we just give them similarly ludicrous thrust in the interest of being playable? Then what happens once the craft is up to speed? We stow the sail until it's needed again? It could work that way, but it's very unrealistic.

[slate reef]

you're right, i failed to consider how difficult it would be to get the thrust vector always lined up to radial out regardless of the orientation of the craft.. disregarding that for a moment; for the throttle/deploy aspect, i think that could be solved relatively simply by either limiting the sail to a deployed and a retracted state, having it act like an SRB, where thrust is non-throttleable but with the difference of it being able to be turned off by retracting it, or have it behave like a throttleable engine where throttle would be correspond to how 'deployed' the sail is (as an animation, not an input slider). The first option sounds simpler on paper, but i assume it would still not be that straightfoward since an engine like that doesnt currently exist. the alternative would be to not have it be retractable, essentially making it behave like a true SRB with infinite runtime

[slate reef]

yeah, sacrifices will have to be made on that front to make a sail thats actually usable for players. you could probably get away with having it provide less thrust than an ion engine, since accelerate under timewarp can compensate for that somewhat. the main difficulty would be to use it to actually get somewhere, as you cant exactly change anything about the thrust vector once its deployed. for that reason i think giving it unrealisticly high thrust wont hurt too much

[onyx brook]

I've really not been following solar sail technology. Is there a presumption that real use of these would require they have a furled and unfurled state?

[onyx brook]

People keep talking about accelerate under time warp, but the thing is we have no way to control attitide under time warp. Yes, you can turn the engine on and warp. No you can't change your pointing vector while warping, and so you can't steer.

As far as I'm concerned the current game's ability to accelerate under time warp is far to gimped to be actually usable in any sense.

[cedar portal]

Well it's mostly meant for interstellar travel

And for that you don't really need to change your vector

[onyx brook]

When we can also change attitude under warp then that may be an interesting thing

[slate reef]

it depends. in most (interstellar) probe concepts they are non-retractable, since that would add undesired extra mass. in other media like For All Mankind they are retractable, because they're fitted onto a much larger vessel there with the purpose of interplanetary travel

https://youtu.be/uTzTH4lPSZI?t=360

[onyx brook]

When you consider a brachistochrone trajectory (flip-n-burn) like in The Expanse, you do need to control orientation, or at the least you need to be able to stop the time warp and control orientation, but I think for the fine tuneing that would be needed on an interplanetary trip you'd really need to be able to control orientation. For any sort of even emi-realistic low thrust (ion or solar sail) you most defintiely need to control orientation for interplanetary.

[onyx brook]

Great scene in a great show!

[slate reef]

the fun thing about solar sails is that you really cant control their thrust vector in any way; they'll always provide thrust pointing straight away from the radiation source (a star in this case). changing the orientation of the sail only changes thrust based on exposed area, not the direction of that thrust. that in and off itself would make it very difficult to use them in the game. so they would likely have to be able to be restracted for the sake of gameplay

[slate reef]

if IG ever adds a solar sail in stock, they better have an easter egg where deploying it has a small chance of playing a sea shanty😛

[onyx brook]

There is this idea. Go back to comm nets. You build a gigantic space laser... No! Stop laughing, I'm serious! And then you launch your ship and direct the photons from the laser to hit the sail.

Now this would be a mod!

There would need to be all sorts of space laser parts, and this would give a whole new purpose to TNO...

[slate reef]

people have unironically suggested this on the Intercept server hahah

[keen ingot]

I should watch for all mankind

[onyx brook]

This has also been proposed as a way to make nuclear powered ion craft a bit mroe possible

[onyx brook]

Yes! You should! It's really very good.

[slate reef]

heck, you could even have them be colony modules! now that would be an incredible mod: build lasers on colonies, use them to blast your laser sail probes all over the system basically for free. Only drawback is that it would need a crazy amount of EC, which is something TNO is already headed toward anyway👀

[slate reef]

absolutely!

[cedar portal]

I've seen the first few episodes, I don't even know why I didn't continue

[onyx brook]

If you approached it like this, where there would need to be a code (DLL) part of the mod to check to see that there is in fact a working laser and what the distance and power are...

[slate reef]

how hard would that be to code you think?

[keen ingot]

Honestly if we can figure out sound, that would be great for a mod

[onyx brook]

I like this!

[slate reef]

Hasnt Lux already managed to add sounds to his SORRY engines?

[onyx brook]

He has, that bastard...

[keen ingot]

And managed to completely forget to document it?

[onyx brook]

As I said...

[slate reef]

oh no🤣

[onyx brook]

Yes, Sea Chanty must have a probability of playing when the sails are deployed. Perhaps the probability is scaled by the size of the sails?

I really do like the way they looked on Sojourner in FAMK. That deployment retraction system was sick. The size/power isn't terribly realistic, but whatever.

[slate reef]

we can ignore reality for a bit if it means scoring more Cool Points™️

[keen ingot]

Honestly, inline solar panels at the size of the rover cockpit would be cool

That cockpit is great for cool looking interplanetary vessels

[slate reef]

agreed

[keen ingot]

Case in point

[onyx brook]

I've made rovers before with built in engines so the whole craft flies to Duna, descends, lands (vertically using legs), then flips over on it's belly and drives away

[slate reef]

(its also incredible for stations)

[keen ingot]

Holy shit

[onyx brook]

How do you get that into space? Even with Lazy Orbit?

[keen ingot]

Those could be hotel rooms

[onyx brook]

It would collapse under it's own weight on the pad

[slate reef]

with a lot of boosters and even more struts

[keen ingot]

What kinda computer have you

[slate reef]

i did use lazy orbit tho, performance was absolutely non-existent trying to launch it. its over 1K parts

[onyx brook]

What kind of frame rate have you got?

[slate reef]

oh boy

a laptop

[onyx brook]

LOL!

[keen ingot]

Same

[cedar portal]

now THAT should be used for benchmarking

lmao

[onyx brook]

So it's in seconds / frame, not frames / sec?

[slate reef]

i dont even meet min spec😅 🤣

[slate reef]

about 0.1

[keen ingot]

Ahh mine does meet min spec

A laptop with I forget the processor, a mobile 3080, and 64 gigabytes of ram

[slate reef]

if you ever want to enjoy the experience of launching a ridicously large craft at a comfortable 10spf, be my guest ;)

[slate reef]

Intel Core i7-1065G7
NVIDIA GeForce MX350
8GB

quite the step up from what i have

[onyx brook]

My laptop is a MBP with Apple silicon... I've not yet even tried to run the game on that.

[cedar portal]

omg, 20MB craft file

[slate reef]

if i had a better system i could probably go (a lot) larger👀

[cedar portal]

Well... Trying to launch that almost crashed my game

On a high end desktop

Lmao

And the whole thing completely fell apart

Nice fireworks though

[slate reef]

it remains one of the only 2 craft that has ever brought Anths system to its knees lol

[keen ingot]

What was the other

[slate reef]

it used to stay in one piece when i last tested it in 0.1.3, but it might not work anymore in the current one😢 here's a save of it in orbit if you want to look at it (hopefully) in one piece

[slate reef]

this duna base

we've gone a bit off topic so back to the solar sail idea for a bit:
so the main dificullty in actually pulling this off would basically be finding a way to write the solar panel module into an engine module, and then figuring out how to stick a thrust vector on the radial axis regardless of craft orientation?

[cedar portal]

it depends on how realistic you want the solar sail

if you were ok with it not pushing you in just one direction, then that would be really easy, like you said, with a simple solar panel module

it could be set up so that it's not tracking the sun, and it would give you proportionately as much power as there is sun coverage

and then an engine module that would just run on EC

and the EC storage would be very little, like 1 unit

and the engine module set up so that it couldn't drain EC from other parts

(not sure how doable that part is)

then you'd have a sail that definitely wouldn't work in the opposite direction

but it would kinda work sideways, just less efficiently

[onyx brook]

I can tell you right now this isn't going to work - or at least not quite like that. With the SPARK ion engines, if your craft is underpowered (which is the state 99.99999% of the time with this arrangement - since when are you perfectly aligned?) then what happens is the engine gobbles up 100% of the available EC leaving nothing for control and you can't do anything, not even adjust throttle. The only remedy I've found is to go in to the parts manager and deactivate the engine, then set the throttle lower, and reactivate if you like.

I think what you need instead is a new module in place of Engine Module that will do what you want without this sort of kluge and the associated mayhem

This is what I was alluding to in my first post #1168822510918324234 message

This hypotetical new module would be some hybrid of the solar panel and engine modules so that it calculates the available thrust based on sun incident angle and the current deployed area of the sail, then applies it as thrust along the radial out vector.

No need for power shenanigans.

You may find you need a very unrealisticly high amount of thrust to get it to be playable.

[slate reef]

you're right, ive had that exact same issue of not having control because the engines eating up all EC with the stock ions too

i just thought of another issue: staying in the radial out direction wile timewarping isnt possible :/

[onyx brook]

Keeping your craft pointed that way isn't possible, but computing the angles, resulting thrust and so forth may be.

So, once again, for interplanetary you do need attitude control under time warp - which we don't have. Now that would be a mod!

[slate reef]

whoever makes that will be considered a KSP2 hero

[onyx brook]

And for interstellar you might need to position along the vector you want, then deploy and wait... and wait... and wait...

[slate reef]

and maybe turn on a sea shanty or 2😛

[keen ingot]

I cant imagine plotting a maneuver node that always faces radial out and has to deal with decreasing thrust from going further and further from the sun

That sounds like calculus hell

[cedar portal]

isn't there a way to set flow modes so that the solar sail part would be basically isolated from the rest of the craft? only draining EC from its own modules?

what would NO_FLOW do?

Basically like how solid boosters work, those also can't drain solid fuel from any other resource containers than their own

I'm sure there has to be a way

Although, maybe not

That stuff is defined per resource type, not per resource container, right

[onyx brook]

I'm not sure. That wasn't really an option for my ion engines, but it might be one for this.

[cedar portal]

Now I really want to go and write a Module_SolarSail lol!

So much to do, so little time

[onyx brook]

I want to look into a time warp autopilot. Possibly a harmony patch to SAS, or possibly it's own thing like SmartASS.

[slate reef]

if someone wants to try...it'd make a lot of people really happy. solar sails are quite popular, apparently :p

[storm fern]

Solar sails require a completely different set of maneuvering and control abstractions, I fail to see how they can have any practical use without those...

[storm fern]

AFAIK that's not true at all, you can directly control the thrust vector by controlling the sail surface orientation relative to the sun. It's the light reflection that imparts a force, and that force is perpendicular to the reflective surface.

The whole concept would be totally useless otherwise...

(well, even more useless :P)

[keen ingot]

Hmm, I think it might be an average of the incoming and outgoing momentum vector angles for the angle that the force would come from ... so a right angle to the sail

As you said

But not all photons get reflected

Some get absorbed ... and im not sure if that has an affect on the momentum

And if it does, it would drive the force vector more towards the incoming rays direction

[slate reef]

huh, you're completely correct. i have no idea how i got that so wrong...

great, so my idea is even more difficult to put into practice

[cedar portal]

well, not really, technically that should make it easier, if anything

since it follows the heading of the vessel

[slate reef]

hey yeah

[cedar portal]

well, that is if the sail surface is pointing in the prograde-retrograde vector

[keen ingot]

So its exactly how i described

[cedar portal]

yep

[slate reef]

apologies for getting it so wrong haha

i have no idea where i got the idea that thrust is always in the direction of the incoming light from. that doesnt make much sense, thinking about it now

https://www.planetary.org/articles/what-is-solar-sailing#:~:text=Solar sailing is a revolutionary,to push the spacecraft forward. this seems like a good article to read up on the basics, if anyone's interested

[stray sun]

you can say that again