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.<p>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.<p>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.
Can someone more familiar with orbital mechanics help me understand why it looks like the perigree is coming down in opposite to the apogee?<p>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 apogee and the perigee, but the apogee coming up way faster?
What about <a href="https://en.wikipedia.org/wiki/IKAROS" rel="nofollow">https://en.wikipedia.org/wiki/IKAROS</a>? The only new part, is that Lightsail is a cubesat, right? (IKAROUS was 315 kg.)<p>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."
> 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.<p>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).<p>For the lightsail 2 it uses magnetic torque rods, which from <a href="https://en.m.wikipedia.org/wiki/Magnetorquer" rel="nofollow">https://en.m.wikipedia.org/wiki/Magnetorquer</a> are electromagnets so the energy comes from turning them on for a while.<p>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?
If 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?
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 .
What I'm curious about is how fast a solar sailing craft could go before the thrust of the photons is balanced out by the drag of the interplanetary medium. Five particles per cubic centimeter isn't much but I suspect it wouldn't be irrelevant for a square mile sail moving at 400km/s.
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.
Slightly unrelated, but I did a project this past semester in Grad School looking at the economics of a solar sail de-orbiting mechanism to attach to satellites. Seeing the successful demonstration here just gives me the slightest sense of pride and vindication toward the people in the class who said there's no practical use for something like that.<p>That being said, the project itself was a disaster and I'm glad to have escaped the class with a decent grade despite it.
Here is a data dashboard from the telemetry collected via SatNOGS stations tracking LightSail2
<a href="https://dashboard.satnogs.org/d/CBwYeHSZk/lightsail-2?orgId=1&refresh=5m&from=now-30d&to=now" rel="nofollow">https://dashboard.satnogs.org/d/CBwYeHSZk/lightsail-2?orgId=...</a>
I'm glad they raised the orbit, it's just that it's not enough for me (in the northeast US) to be in the radio footprint of the satellite. It was launched into equatorial orbit with a fair amount of inclination, but elevation angles from my location never exceed 11 degrees making reception difficult.<p>I was hoping to receive the satellite's Morse code beacon and/or telemetry stream [1]. BTW: Does anyone know the downlink frequency for the photos?<p>[1] <a href="http://www.planetary.org/blogs/jason-davis/2016/20160609-lightsail-2-morse-code.html" rel="nofollow">http://www.planetary.org/blogs/jason-davis/2016/20160609-lig...</a>
Can you "tack" a solar sail?<p>Niven/Pournelle had a cool idea in <i>The Mote in God's Eye</i> of charging your craft when traversing a magnetic field to change direction (not specific to sails, but another passive technique).
Would be really interesting now to see a successful experiment with an electric solar sail to get some idea of how the technologies compare in practice - <a href="https://en.wikipedia.org/wiki/Electric_sail" rel="nofollow">https://en.wikipedia.org/wiki/Electric_sail</a>
We need more of this, and more spending and results in space research. Not only because we are destroying our own planet, but also because we as a species have been stagnating for quite some time.