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LightSail 2 Spacecraft Successfully Demonstrates Flight by Light

planetary.org

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Re: LightSail 2 Spacecraft Successfully Demonstrates Flight by Light

#131

Post by 8456523 »

wiredfool wrote: post #130
Skunkleton wrote: post #57

Earlier quoted context omitted.

This is just a complicated way of saying the same thing. Of course a jet engine is not just a really fast propeller. And if you hooked a "bag of air" to a propeller, that would also work in space. Either way, an LED is not generating any meaningful thrust, and pointing that thrust at a sail adds no benefit.

No, it's not. A propeller makes thrust like a paddle, by pushing off of something. A jet/rocket engine makes thrust by recoil, using conservation of momentum.

Almost all modern jet engines have (ducted) fans. In planes that never go supersonic, e.g., all current commercial airliners, the fan provides most, but not all, the propulsion. And the only difference between a fan an a propeller is how many blades it has. (The presence of a duct around the fan does not change anything basic.)

But even if they did not have fans, there is no fundamental difference between using a propeller or fan to speed up the flow of air and heating the air inside a chamber to speed up the flow of air. (The fan is used because at subsonic speeds it can be made more efficient.)

In other words, all 3 means of propulsion work by conservation of momentum.

Re: LightSail 2 Spacecraft Successfully Demonstrates Flight by Light

#132

Post by fluffysandwich »

parsimo2010 wrote: post #114
gibolt wrote: post #108

Earlier quoted context omitted.

Hypermiling in space is an awesome concept. Would be so cool to have the solar race competition evolve from cars to spacecraft.

I have to admit, I got the idea from the beginning of the book Abaddon’s Gate . Solar sails might not be required but I think there’s a future in people plotting slingshot trajectories and sending packages around the solar system as fast and as cheap as possible. One day it will be manned missions, the space equivalent of people that fly hot air balloons around the world.

And a couple years after that, Amazon Prime parcels...

Re: LightSail 2 Spacecraft Successfully Demonstrates Flight by Light

#133

Post by toong »

abecedarius wrote: post #115
mabbo wrote: post #69

My understanding of what's going on here is that the light sail isn't aiming or changing at all. It's just a big sail, in orbit. When it's moving away from the sun, the sail is being pushed "forward", which adds to it's velocity- this increases the apogee on the opposite side of the orbit. When it's moving towards the sun, the sail is being pushed "backwards", lowering it's current velocity and reducing the perigee.…

You can try tilting a sail in 2-d simulation: http://wry.me/t/gravity/gravity.html (I don't promise I got the light-pressure math right, but it least this shows maneuvering without needing to extend and retract it.)

Nice simulation. I think I managed to reach escape velocity :-)

Re: LightSail 2 Spacecraft Successfully Demonstrates Flight by Light

#134

Post by mkl »

umvi wrote: post #26
bmdavi3 wrote: post #18

Earlier quoted context omitted.

I don't know if the strength of an LED is enough to move the craft significantly, but if it is you'd need to point it at anything _but_ the ship itself, otherwise the two forces would cancel out. Just shine it in the opposite direction of where you want to go.

No, the two forces don't cancel out, I can't remember exactly why but elastic collisions don't work like that. That's why you can point a fan into your sailboat's sail and it will still go forward, mythbusters proved it.

Mythbusters demonstrated something different, and something much less efficient than simply pointing the fan backwards like a normal fan boat (no sail required). Here: https://mythresults.com/blow-your-own-sail

Re: LightSail 2 Spacecraft Successfully Demonstrates Flight by Light

#135

Post by mkl »

walrus01 wrote: post #52
umvi wrote: post #2

Very cool! I know nothing about solar sails, but I wonder if the craft could have LEDs mounted to it so it could bombard different regions of the sail with photons to make it turn appropriately.

https://en.m.wikipedia.org/wiki/Photon_rocket It's a real idea, but you would need a truly ridiculous amount of electricity available on a spacecraft. Only possible by a huge nuclear reactor. Doesn't violate any laws of physics.

There are key differences with that: either the photons are shot backwards (like a rocket), or the source of the photons is not on the ship itself. ("The limitations posed by the rocket equation can be overcome, as long as the reaction mass is not carried by the spacecraft.")

Re: LightSail 2 Spacecraft Successfully Demonstrates Flight by Light

#137

Post by mkl »

ben-schaaf wrote: post #110
cptaj wrote: post #20

Earlier quoted context omitted.

They are in a low earth orbit and there is still considerable atmospheric drag in the region. This causes the satellite to deorbit. This was a technology demonstrator and it has completed its mission successfully. It simply wasn't launched to an orbit where it can do more (Cubesats hitch rides on rockets launching larger, expensive payloads) NASA does have a mission intended to navigate quite a bit more using a solar…

As long as the trust produced by the solar sail is more than atmospheric drag it technically has enough Δv to go anywhere.

Solar sail thrust isn't like rocket thrust; you can't just point it wherever you like, or turn it on and off as effectively, and there isn't nearly as much thrust available either. This craft can't leave low Earth orbit.

Re: LightSail 2 Spacecraft Successfully Demonstrates Flight by Light

#138

Post by Tepix »

mabbo wrote: post #69

My understanding of what's going on here is that the light sail isn't aiming or changing at all. It's just a big sail, in orbit. When it's moving away from the sun, the sail is being pushed "forward", which adds to it's velocity- this increases the apogee on the opposite side of the orbit. When it's moving towards the sun, the sail is being pushed "backwards", lowering it's current velocity and reducing the perigee.…

They have 3 perpendicular coils that can orient the spacecraft relative to Earth's magnetic field. The reaction wheels are for fine tuning the attitude.

Re: LightSail 2 Spacecraft Successfully Demonstrates Flight by Light

#139

Post by Tepix »

zeroping wrote: post #118

What about https://en.wikipedia.org/wiki/IKAROS ? The only new part, is that Lightsail is a cubesat, right? (IKAROUS was 315 kg.) From article: "Our criteria was to demonstrate controlled solar sailing in a CubeSat by changing the spacecraft’s orbit using only the light pressure of the Sun, something that’s never been done before. I'm enormously proud of this team. It's been a long road and we did it."

Yes, they demonstrated putting a light sail in a tiny cheap satellite and controlling it

Re: LightSail 2 Spacecraft Successfully Demonstrates Flight by Light

#140

Post by initium »

parsimo2010 wrote: post #114
gibolt wrote: post #108

Earlier quoted context omitted.

Hypermiling in space is an awesome concept. Would be so cool to have the solar race competition evolve from cars to spacecraft.

I have to admit, I got the idea from the beginning of the book Abaddon’s Gate . Solar sails might not be required but I think there’s a future in people plotting slingshot trajectories and sending packages around the solar system as fast and as cheap as possible. One day it will be manned missions, the space equivalent of people that fly hot air balloons around the world.

The novels of the James S. A. Corey authors are very inspiring given our recent space achievements. A highly recommended sci-fi series.
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