LightSail's solar sails look good in latest deployment

June 9, 2015 by Nancy Owano, Phys.org weblog
LightSail captured this image of its deployed solar sails in Earth orbit on June 8, 2015. Credit: The Planetary Society

The Planetary Society solar sail exploration called LightSail is looking good. The concept—a spacecraft designed to propel through space on beams of sunlight— pushed through by nothing but the pressure of sunlight—is making news this week with reports of a successful solar sail deployment. This is a test mission serving as a precursor to the 2016 mission. In measuring mission success, observers were looking to the deployment of LightSail's Mylar solar sails.

Jason Davis, Planetary Society, wrote on Monday: "It's official: The sails are out. This afternoon, LightSail controllers downlinked a partial image of the spacecraft's solar sails in space."

An image of LightSail's deployed solar sails was captured by one of the spacecraft's onboard cameras on Monday.

NASA has its eyes set on the deployment too. Davis said that NASA and The Planetary Society are sharing data on the LightSail mission through a Space Act Agreement. In 2018, the space agency is preparing to launch two -powered CubeSats: Lunar Flashlight and NEA Scout. A team at NASA's Marshall Space Flight Center in Huntsville, Alabama, captured a video of LightSail "soaring across the sky with its solar sails deployed."

Jacob Aron in New Scientist walked readers through the events: Over the weekend, he said, mission managers made contact with the craft and unfurled its 32-square-meter sail. "On Saturday the Planetary Society made contact with LightSail again, and issued the command to unfurl the sail. On Sunday the craft sent back data confirming the sail deployed successfully."

Aron described the craft as "designed to test technology that derives thrust from sunlight." He said solar sails offer "a potentially cheap way of exploring the solar system, but few have been tested in orbit. They work by reflecting photons from the sun, providing a small thrust in the opposite direction. The force from each reflected photon is tiny, but a large enough sail can build up significant momentum."

What will the present deployment achieve? New Scientist said "This version of LightSail can't gain enough thrust from the sun to overcome the drag of the atmosphere at its current altitude, so it will fall back to Earth in the next few days. But the technical difficulties it encountered will inform the launch of a second version of the spacecraft, bound for a higher orbit next year."

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Abhay
3 / 5 (3) Jun 10, 2015
It's fine that such sails would get momentum after they are impacted by Photons from star like sun. But I fail to understand that any such sail starts its journey through the space with the aim of crossing our solar system, there might be possibilities that some light (photons) from opposite direction might impact the sail too. This will act as a "break" to the speed of the sail if the intensity of the light is greater than sun. How do we tackle this problem or I am stupid here.
antialias_physorg
5 / 5 (8) Jun 10, 2015
there might be possibilities that some light (photons) from opposite direction might impact the sail too.

There will. There are stars in basically all directions. However, you can calculate the amount of impulse the photons of each star impart to the sail each second.

This is dependent on:
- The temperature of the star (higher frequency photons impart more momentum...with the qualifier that the sail is not refelctive to all photons. E.g. gamma rays will go right through for the most part).
- the size of the star
- the orientation of the sail to the star
- divided by the distance of the star from the sail squared.

The last one is the killer argument why the sun will always WAY outweigh any other source (or combination of sources) when it comes to the imparted photon momentum as long as we're talking propulsion within our solar system. Under those conditions all other sources are negligible.
Abhay
5 / 5 (2) Jun 10, 2015
Thanks antialias_phyorg !

I have a weird idea which just flashed my mind. If the there is light from opposite direction which is acting as a break, there should be some mechanism in the sail which will deploy a structure shaped similar to character "C". This optical fibre should guard the sail from the light from front and redirect it in the back (through optical fibres) to the back of the sail !!!
This should continue the photons hitting the sail from behind !!!
Please dont laugh !

Cheers !
antialias_physorg
5 / 5 (5) Jun 10, 2015
I have a weird idea which just flashed my mind. If the there is light from opposite direction which is acting as a break

Setting the sun aside: If you posit that stars are equally distributed over the entire sky* then you will have as many sending photons that hit your sail from the front as they do from the back no matter which way you point it. So the cumulative effect will be zero.

Optical fibers work both ways. You'd also be letting photons from the back through to the front (and those from the back are the MANY photons coming fron the sun that you want to use). It'd lower efficiency of the sail a lot.

* Not entirely true, but good for a first knee-jerk answer. Along the plane of the milky way you have significantly more stars.

Please dont laugh

Why should I laugh? I frequent this comment section exactly for these exchanges. Just because an idea may not be workeable doesn't mean it's bad to throw it out there. Only that way can it be discussed.
antialias_physorg
5 / 5 (2) Jun 10, 2015
try to steer the sail to reflect sunlight to the earth, it would be a great show, especially with sails much bigger.

Conflicts a bit with the test. They are trying to see whether they can get the craft to speed up. Science before show.

How about sending in independent orbit around the sun a host of large sails and try to send messages of light to the entire universe?

Unless you mean solar sails that are the size of Earth or thereabouts (and who's gonna pay for that? That'd be a quite significant mass you would have to lift into a quite a bit higher orbit first)
In any case it would be pretty pointless. If they can pick up that kind of signals they already know we're here by just looking at Earth.

antialias_physorg
5 / 5 (2) Jun 10, 2015
LightSail is a kickstarter project. In this case show would cost funds (because you'de have to start another mission to do the science).
I agree that if it costs nothing then there is no drawback to a little show. But putting stuff in space never costs nothing.
Osiris1
not rated yet Jun 10, 2015
It is already proven. Japanese Aerospace Agency JAXA did it and so can we. They actually sent Ikaros I to a flyby of Venus not long ago. It got there incredibly fast. Heaven only knows where it is now. We learn to tack and sail in space with this and our system is ours, period. A new age of sailing......like Heinlein's: "To Sail Beyond The Sunset"!

How about we build a BIG one and put some control mechanisms in it to do space 'tacking' just like sailing ships in two dimensions, only we in space will use three dimensions. No such thing as capsizing, but uncontrolled spins could be damaging. So we need to learn.
Osiris1
not rated yet Jun 10, 2015
Build a dyson sphere around the sun to harvest its entire energy....LOL. And send it all to some fictional super power accumulator to build up a charge large enough and finely focused enough to create a stable wormhole to another place that we can send ships through..LOL again... Awww Stephen Hawking thought of this first. We first need to perfect very large current carriers akin maybe to Star Trek plasma conduits. Course the trick is to confine these enormous energies to the conduit till it gets to its destination be it laser or be it a magnetohydroelectrodynamic generator.
retrosurf
not rated yet Jun 13, 2015
Osiris 1, you can't tack with a photon sail.
There's no way to provide a keel in space, and tacking requires a keel.

You could, however, use a vectored solar sail to kill your Terra-inherited orbital velocity to proceed inward toward Venus, or you could use a solar powered reaction drive of some sort.

Why visit Venus or Mercury? They're both awful.
Our future lies here on our earth,
on orbit and at L1 and L2; in the asteroid belt,
on Mars and the Jovian moons,
and in Saturn's rings.
Osiris1
not rated yet Jun 14, 2015
Retro, I see your point as the sail provides the 'tack' but the keel provides the 'track'. However the medium, water , in which the keel lives and tracks, is fluid so the 'track' can move as well. Perhaps a second system of solar electric propulsion or a solar/shawyer drive in a set of two for moment couple to provide lower power 'track' in each of the 'other' two dimensions for a total of four Shawyer drives for 'sail-boat' stability to 3D 'tack' in space. Another problem I can think of is 'slip' related to the water sailboat's being in a liquid medium that will 'slip' in directions vectorially 'off normal' to main sail force result; only in space that slip will not only be in X-Y but X-Z. Analysis will I feel get into multivariable partial differential equations. Thanks for your input, Retro. We will skull it out yet.
robweeve
not rated yet Jun 14, 2015
How fast would the craft travel?

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