Here is a data dashboard from the telemetry collected via SatNOGS stations tracking LightSail2
https://dashboard.satnogs.org/d/CBwYeHSZk/lightsail-2?orgId=...
LightSail 2 Spacecraft Successfully Demonstrates Flight by Light
61–70 of 150 posts
Re: LightSail 2 Spacecraft Successfully Demonstrates Flight by Light
#62If a photon hits the sail and is reflected, it must transfer two photon momentums to the sail. The energy should be less than before it the sail. Is it redshifted?
Yes, but by a tiny amount. This reddit comment [1] explains in better detail than I can.
[1] https://www.reddit.com/r/askscience/comments/4anry6/does_lig...
Re: LightSail 2 Spacecraft Successfully Demonstrates Flight by Light
#63If a photon hits the sail and is reflected, it must transfer two photon momentums to the sail. The energy should be less than before it the sail. Is it redshifted?
Correct. Consider an initially stationary sail. Even though this isn't physically what is happening, you can imagine the reflection from the point of view of the sail as a photon getting absorbed and a photon of exactly the same frequency being emitted immediately after in the opposite direction. Now, to a stationary observer, the sail will have started moving after the absorption, so the emmitted photon will be redshifted due to the Doppler effect.
It's only be a very tiny amount of course at normal velocities, probably smaller than the energy wasted due to a mirror not being 100% efficient. To extract all the kinetic energy of a bundle of light, you'd have to bounce it between two mirrors many times. Maybe that's a possibility for shorter distances, perhaps during take off?
Re: LightSail 2 Spacecraft Successfully Demonstrates Flight by Light
#64Not really relevant but, if we we had an arbitrarily super fast spacecraft, how would we prevent it from hitting a small rock and exploding?
Maybe they we will be able to detect a marble from hundreds of thousands of miles in the empty space with new radar/lidar tech.
Re: LightSail 2 Spacecraft Successfully Demonstrates Flight by Light
#65Earlier quoted context omitted.
An electric fan on a derby car works the same way a propeller does though right? You don’t need the sail at all. It works by pushing against the surrounding medium. This seems different than a laser in a vacuum.
I'm saying the electric fan is pointed so that it is blowing air in the forward direction. A sail at the front of the car will catch said air and propel the car forward. I'm sure it would work in a vacuum too if you had a CO2 canister mounted to the car blowing forward into the sail.
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Re: LightSail 2 Spacecraft Successfully Demonstrates Flight by Light
#66Earlier quoted context omitted.
So you are saying if I put the car in a vacuum chamber and mounted a CO2 cartridge instead, it wouldn't work?
Of course it would, but what wouldn't work is bouncing that CO2 off of some sail.
I would think a sail, or rudder, could redirect the force from the CO2 canister.
Re: LightSail 2 Spacecraft Successfully Demonstrates Flight by Light
#67Ugh this title. Flight by light? A solar sail is not flying. An airfoil generating lift is flying.
Re: LightSail 2 Spacecraft Successfully Demonstrates Flight by Light
#68Not really relevant but, if we we had an arbitrarily super fast spacecraft, how would we prevent it from hitting a small rock and exploding?
Why would it explode?
More likely, the small rock would put a hole into the spaceship. This isn't a disaster. The spaceship residents would notice a gradually decreasing amount of pressure, assess where the leak is, and put a piece of duct tape over the hole.
Remember kids, real life isn't like the movies.
Re: LightSail 2 Spacecraft Successfully Demonstrates Flight by Light
#69My 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. As the perigee comes lower, it spends less time in that end of the orbit, where it's gaining velocity, and when it's apogee is high it spends more time in that end of the orbit, where it's losing velocity. It's not a winning strategy I'm afraid.
But imagine! Imagine if we had a slightly different solar sail. One that could retract and expand at will, via solar powered electric motors. Then we could have it open it's sails when the "wind" is favorable, then close them when it's not. It could slowly but surely escape earth's gravity well, and gracefully travel around the solar system. A big enough one might even be able to accelerate right out of the solar system.
Re: LightSail 2 Spacecraft Successfully Demonstrates Flight by Light
#70Ugh this title. Flight by light? A solar sail is not flying. An airfoil generating lift is flying.
Balloons, rockets and cannonballs all fly. And the last two do not require an atmosphere to fly in.