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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

#111

Post by peanutz454 »

WalterBright wrote: post #109
parsimo2010 wrote: post #83

Earlier quoted context omitted.

I didn’t work on Lightsail, but the article implies that it does aim the sail. It isn’t expanding/contracting, but it does change orientation using the reaction wheels. Basically, they turn the sail broadside to catch the sunlight to raise the orbit, and turn it on edge when they don’t want the extra drag. This particular satellite won’t ever leave orbit because the sail can’t overcome even the tiny amount of atmosph…

> a bigger sail and a higher orbit But a bigger sail would increase the atmospheric drag!

higher orbit will reduce drag

Re: LightSail 2 Spacecraft Successfully Demonstrates Flight by Light

#112

Post by ben-schaaf »

Gustomaximus wrote: post #92
alpha_squared wrote: post #46

Earlier quoted context omitted.

Ultimately, you can't. Space is really, really, really big and empty, though. Unimaginably so, which would make an incident be some really bad luck. In something like the lightsails, you'd just launch multiple simultaneously. Space is so big and empty that even for something like the asteroid belt you could pass through any point randomly and on average be thousands of kilometers from the nearest rock. Perhaps even t…

Is it though? To try and quantify risk I looked up how many metoeites hit the earth each day and its 18,000 to 84,000 that are over 10 grams. Whiile the earth is obviously much bigger than a space craft, you would think should there be a bunch of craft flying around in the future, theres a fair odds of it happening every few years. Also for example, the ISS has already been hit a couple of times: https://www.iflscien…

Things tend to collect around large gravity wells, that's just kinda how that works. I don't think you can compare the ISS in LEO to something traveling within or without the solar system.

Re: LightSail 2 Spacecraft Successfully Demonstrates Flight by Light

#113

Post by parsimo2010 »

WalterBright wrote: post #109
parsimo2010 wrote: post #83

Earlier quoted context omitted.

I didn’t work on Lightsail, but the article implies that it does aim the sail. It isn’t expanding/contracting, but it does change orientation using the reaction wheels. Basically, they turn the sail broadside to catch the sunlight to raise the orbit, and turn it on edge when they don’t want the extra drag. This particular satellite won’t ever leave orbit because the sail can’t overcome even the tiny amount of atmosph…

> a bigger sail and a higher orbit But a bigger sail would increase the atmospheric drag!

But the higher orbit would reduce the drag. You could probably get away with the same size sail, but you’ve got to start high enough that the sail’s tiny thrust over its 50% (ish) duty cycle can overcome the drag present in 100% of the orbit. Once you’re high enough a bigger sail would mean lifting the orbit faster.

Re: LightSail 2 Spacecraft Successfully Demonstrates Flight by Light

#114

Post by parsimo2010 »

gibolt wrote: post #108
parsimo2010 wrote: post #83

Earlier quoted context omitted.

I didn’t work on Lightsail, but the article implies that it does aim the sail. It isn’t expanding/contracting, but it does change orientation using the reaction wheels. Basically, they turn the sail broadside to catch the sunlight to raise the orbit, and turn it on edge when they don’t want the extra drag. This particular satellite won’t ever leave orbit because the sail can’t overcome even the tiny amount of atmosph…

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.

Re: LightSail 2 Spacecraft Successfully Demonstrates Flight by Light

#115

Post by abecedarius »

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.)

Re: LightSail 2 Spacecraft Successfully Demonstrates Flight by Light

#117

Post by claudiawerner »

zitterbewegung wrote: post #38

In grade school they asked us to make a model spaceship. I made a light sail spaceship. It’s really neat that we have a working implementation of the technique .

When I was 16 in my physics class the light sale ship (or perhaps just the idea of it) was part of the section where the physics of photons were being investigated (along with stuff like lasers and the photoelectric effect). Fantastic stuff.

Re: LightSail 2 Spacecraft Successfully Demonstrates Flight by Light

#118

Post by zeroping »

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."

Re: LightSail 2 Spacecraft Successfully Demonstrates Flight by Light

#119

Post by hoseja »

TeMPOraL wrote: post #34
adrianpike wrote: post #27

Can someone more familiar with orbital mechanics help me understand why it looks like the perigree is coming down in opposite to the apogee? I'm but a mere KSP player, but I've always thought the perigee comes down in a fairly linear fashion based on drag, which is mostly a function of altitude - I would assume they'd be using the sail to just "burn prograde" whenever the solar angle is possible, raising both the apo…

My "mere KSP player" guess (without having access to my desktop on which I'd check that, in KSP) is that the angle at which they're reflecting the Sun amounts to burning prograde and radial-in (i.e. forward and down), which when done near perigee should both rise the apogee (the prograde component) and lower the perigee (the radial-in component).

Yes, that would be my intuition as well, they seem to be "shifting" the orbital trajectory "sideways".

Re: LightSail 2 Spacecraft Successfully Demonstrates Flight by Light

#120

Post by silasdavis »

> Most spacecraft use chemical thrusters to desaturate momentum wheels; LightSail 2 relies on electromagnetic torque rods, which orient the spacecraft by pushing against Earth's magnetic field.

I'm trying to visualise what this process might look like. Having read a bit about momentum wheels it seems like it's probably not a one way street in terms of the direction of torque so the wheel at times might speed up and other times slow down so to avoid saturation. Clearly this is not always possible so an external energy source is used to provide a balancing torque so the wheels can be slowed down without turning the craft (too much).

For the lightsail 2 it uses magnetic torque rods, which from https://en.m.wikipedia.org/wiki/Magnetorquer are electromagnets so the energy comes from turning them on for a while.

Can anyone guess a bit more or explain where in the orbit the saturation might occur and what this desatiration process would look like in terms of the motion of the craft?

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