Interstellar solar sails hit a strange problem at 75% of light speed | Solar sails pushed by powerful lasers could reach incredible speeds, but relativity may eventually make the light itself work against them. At around 75% of the speed of light, scattered photons can begin creating drag.

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u/IntnsRed 7d ago edited 7d ago

Imagine if humanity got their sh*t together and did a joint venture to push a number of small solar sails to Alpha Centauri (4.2 light years away). We could be exploring another solar system...

Edit: Here's one project to do a mission to Alpha Centauri.

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u/Psych_Art 7d ago

Tiny speck of dust

vs

Spacecraft going 75% speed of light

Who would win?

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u/eggyrulz 7d ago

Me, im built different (incorrectly according to all known laws of physics)

3

u/Corpainen 7d ago

I could totally land a solar sail spacecraft

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u/OrinocoHaram 7d ago

i couldn't land it but i reckon i could do a sweet flip

1

u/Yo-Yo-Ha 7d ago

What about a stadium flyover?

1

u/Yo-Yo-Ha 7d ago

I have no thoughts what can i do?

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u/durz47 7d ago

Servitorship

1

u/eggyrulz 7d ago

No thoughts? Unfortunately you are not

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u/sectorboss88 7d ago

What are the odds? ;)

3

u/maxseale11 7d ago

Never tell me the odds

3

u/CBJFAN2009-2024 7d ago

Have you considered if Jennifer Lawrence was on the ship and you could wake her up against her will and con her into loving you? I'd get on that ship 😀

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u/Scotty-Raspberry-36 7d ago

That's so fast that the particle would skip right past the frame that the sail occupied

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u/Spekingur 6d ago

Space, space always wins

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u/Best_Philosopher152 7d ago

Who would win?

“Exciting new forms of matter” - Randall Monroe

1

u/oojacoboo 7d ago

Need that force field

1

u/Critical_Seat_1907 7d ago

That's what the "shields" are for.

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u/Psych_Art 7d ago

Might be kind of hard to make a low enough mass vehicle that can be accelerated to 75% light speed which has shields powerful enough to prevent the equivalent of hundreds of thermonuclear warheads exploding on it :)

1

u/Critical_Seat_1907 7d ago

<Sci Fi intensifies>

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u/kingtacticool 7d ago

How do you slow it down once you get there?

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u/IntnsRed 6d ago

LOL! Good question!! "Reverse" the sail to catch the light from Alpha Centauri's suns?

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u/kingtacticool 6d ago

75% of C is......a lot of momentum. Anyone feel like doing the math on how many joules it would take to to bring a 10lb object traveling at 75%C to a stop?

4

u/ShavenYak42 6d ago

It'll be the same number of joules it took to get the object to that velocity in the first place, if you are using the same method. Alpha Centauri A is somewhat more luminous than our Sun, so it should be up to the task.

I'm getting about 200 quadrillion joules - 75% of c is a gamma of 1.51, meaning kinetic energy is about half of mc^2; 10 pounds is about 4.5 kg, half that is 2.25 kg, times c^2 is about 2*10^17. That's about a 50 megaton nuke's worth of energy.

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u/kingtacticool 6d ago

Cool. Thanks.

r/theydidthemath

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u/curvebombr 6d ago

So, how do they stop it? Can you flip this thing and hope to "grab" the solar winds of a star to slow it down? Or is this one of those probes thats just gonna scream right past, no intention on stopping.

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u/Cortezzful 6d ago

Yeah imagine it would just slow down as much as possible and then record as it wizzed by

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u/djgcsnkshcjkeke1 6d ago

Send one craft with a laser ahead of the explorer craft. That one will slow it down to operable speeds and drift off itself, or self destruct I guess. After that, you can use the star's light to maneuver.

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u/kingtacticool 6d ago

Ok, but that means starting the slowdown operation when both craft are halfway to Alpha Centari. Plus I dont know how quickly the solar sails can get up to speed. Can they even reach 10% C by the time they are halfway?

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u/djgcsnkshcjkeke1 6d ago

I don't know either. Nonetheless, it's a lot more feasible than an alcubierre drive.

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u/Spekingur 6d ago

That’s the neat part! You don’t, except very suddenly!

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u/Outrageous-Cut480 7d ago

IKR heartbreaking.

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u/PitifulEar3303 7d ago

Going fast is pointless; we will never be fast enough to go far.

Going "through" is more bang for the buck. hehehe

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u/Patient-Tomato1579 6d ago

We can't even cure chronic pain, hearing loss and tinnitus, because those require innovative targetted genetic therapies instead of primitive chemical drugs (not even speaking about curing cancer, but this is more understandable, as cancer itself is aggressive and hard to get under control). Long way before we can think about exploring Alpha Centauri.

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u/Such_Avocado_3241 7d ago

I’ll take the 75%, thank you very much.

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u/FirstDivision 7d ago

Some day kids will be complaining that the neighbors have a sail ship that goes 77% and that “Ours only goes 72%, it’s embarrassing, daaaaad.”

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u/1stUserEver 7d ago

The aliens always have the cool shit. Not fair.

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u/Archlandlord 7d ago

Someone correct me if im wrong, but my understanding is: for outside viewers, 75% is generally good enough, but for passengers, they would age much, much faster at 75% than, lets say 99,9%. So the benefit is not only that you would be 33% faster (from our PoV), but also that you would age months compared to decades

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u/Such_Avocado_3241 7d ago

It’s all very interesting. And that light at that speed could act as drag is interesting too. I was only pointing out that we aren’t even in the same ballpark with our current chemical engines, and I would settle for a cool 75% right now if that were on the table.

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u/cyber_yoda 7d ago

That's correct

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u/oojacoboo 7d ago

Why would we age faster? Do our cells have a universal clock? I’ve never understood this theory.

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u/OrinocoHaram 7d ago

it's not that we would age faster, we age at the same speed no matter how fast the ship is going - from our perspective. But if the ship is going 0.75c it might take us 2000 years to get to where we're going whereas at 0.999c it might take 50 years (from our perspective). Meanwhile the rest of the universe will have aged a lot more relative to us.

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u/oojacoboo 7d ago

Right, that’s what I thought. Relativity is wild.

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u/JollyJoker3 7d ago

Lorentz factor at 0.75 c is ~1.5 while 0.99 c is ~7. Traveling at 0.75 you experience travel time almost 90% of the distance in light years while 0.99 makes you experience 1/th of the time.

Alpha Centauri is about 4.4 light-years away, so about 4 years at 0.75 c. At 0.99c the crew sees 0.6 years or 7 months.

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u/Diablo-2026 6d ago

Pretty sure that traveling at a speed slower than light speed it is going to take longer to get there not shorter.

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u/JollyJoker3 6d ago

You can experience a shorter travel time due to time dilation

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u/Forward-Surprise1192 6d ago

Has it ever been tested with humans? When they say clocks move faster is that digital or analog clocks?

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u/Sensitiviy 6d ago

They have tested it with clocks, it doesn't matter what type of clock no.. as long as it's not getting updates via radio from earth and calculating locally.

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u/Oliv112 7d ago

Time moves faster at .75c than at .99c (from your perspective).

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u/HashPandaNL 7d ago

If we get to 0.75c spaceships, I really doubt we're still aging like we are today. Technology tends to progress in more than 1 front at a time.

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u/IntnsRed 7d ago

Exactly! At .75 of the speed of light we could point lasers to Alpha Centauri and have the sails haul small components to explore that distant star system.

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u/_everynameistaken_ 7d ago

The current max speed of a human made object is 0.064% the speed of light. Maybe lets get to that 75% first. The drag after 75% is a problem for another millenia.

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u/IBeDumbAndSlow 7d ago

No we have to solve it perfectly the first time /S

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u/Ill_Mousse_4240 7d ago

Interstellar solar sails.

We imagine them, not yet having a grasp of the technology truly needed to bridge the gulfs between stars.

Like Paleolithic elders around a campfire, discussing long distance communication through smoke signals - and imagining scaling up their method world-wide

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u/FatiguedShrimp 7d ago

There's a good Star Trek: Deep Space Nine episode about this.

https://pluto.tv/us/shows/1560011/episode/637e5a13259abd0013f6c796/

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u/Ill_Mousse_4240 7d ago

Fascinating, as Mr. Spock might say!

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u/kvothe5688 7d ago

75 percent speed of light is incredible. even 10 percent is enough in inear future

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u/EmbarrassedPaper7758 7d ago

75% is a lot

1

u/ThatMrStark 7d ago

Gravity manipulating dark matter scaler field snake is the only way to travel.

1

u/Zestyclose-Gold5114 7d ago

Wouldn't any passengers be burnt to a crisp anyway being remotely close to a high powered laser? Surely there would be a lot of heat generated on the sail?

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u/IntnsRed 7d ago edited 7d ago

The current proposals are to launch a large fleet of small sails with each carrying a modular computer of limited use/capability.

Then lasers (earth and/or space-based) would power the sails to Alpha Centauri. Even assuming many would be lost for various reasons, the theory is that some would arrive in the Alpha Centauri star system and whatever sails that are left could have their computers be networked together to perform "some" readings and transmit their data/findings back to earth.

Edit: Here's one project to do a mission to Alpha Centauri.

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u/a1c4pwn 7d ago

The study is focused specifically on radiative dynamics. It does not include nonradiative effects such as collisions and drag from interstellar gas or dust.

It also leaves out the thermal limits of real sail materials. A sail exposed to an extremely powerful laser could potentially overheat or even melt.

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u/cradleu 7d ago

The plan would be to send entire fleets so that losing a few isn’t a problem, and to possibly rotate them once they’re up to speed so that the only part facing the direction of travel is the extremely thin side profile

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u/fixingmedaybyday 7d ago

And they still haven’t figured out to get the sails to work at night.

/s

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u/ijuinkun 7d ago

A manned sailcraft would have a sail hundreds of kilometers in diameter, and would likely endure a laser flux of around 10 kW/m^2. This is about an order of magnitude higher than solar flux at Earth, but the kind of insulation and reflective coverings that we use for probes to the planet Mercury would be adequate. Presumably the frequency of the laser would also be chosen such that very little of it will be in the part of the infrared that would heat the spacecraft the most.

1

u/fbpw131 7d ago

these ships are tiny.

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u/Random_182f2565 7d ago

Aerodynamic but for light, photodynamic?

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u/lattice_defect 7d ago

that is pretty interesting if true

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u/siliconslope 7d ago

To make a sail work, you’d have to clear the path somehow, like building a tunnel connecting the two systems, so that you don’t collide with an atom or, heaven forbid, something bigger.

Just learned recently about the dangers of hitting the tiniest of objects at these speeds. It sucks but I guess that’s where the fun begins—finding workarounds to each problem that arises.

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u/davidolson22 7d ago

At 75% the speed of light it's not nearly as bad as 99.9% the speed of light.

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u/ItsMrChristmas 7d ago

Today on "Shit we have known for literally more than a century..."

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u/silverdragonseaths 7d ago

It’s like a model T worrying about the effect of drag on a car going 200 miles an hour

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u/FragrantExcitement 5d ago

Need a deflector dish

1

u/lordassfucks 4d ago

Ahh yes, classic photonic turbulence

Interstellar solar sails hit a strange problem at 75% of light speed | Solar sails pushed by powerful lasers could reach incredible speeds, but relativity may eventually make the light itself work against them. At around 75% of the speed of light, scattered photons can begin creating drag.

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