
Crowdfunded spacecraft LightSail 2 prepares to go sailing on sunlight - kouh
https://techcrunch.com/2019/06/21/crowdfunded-spacecraft-lightsail-2-prepares-to-go-sailing-on-sunlight/
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umeshunni
Note that this is an orbital test and not the actual 'launch' to alpha
centauri.

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dghughes
Several small spacecraft with solar sails project Breakthrough Starshot. Some
solar energy will provide a push on the sails but the main push is from
powerful ground-based lasers since solar energy alone isn't enough energy.

At 20% speed of light (c) or about 60,000 kilometres per second it will take
20 years to get there. Then 4 years for the radio signals to get back.

I may see some pictures of Alpha Centauri in my lifetime if they get this
project going soon.

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sandworm101
Will this thing actually accelerate?

The last project was in such a low orbit that acceleration was never possible.
At best it could have managed a measurable decrease in the rate of orbital
decay. The light pressure was less than the atmospheric drag. As drag is
directly related to sail area, and is constant whereas sunlight isn't, is
acceleration possible even in a 700+km orbit?

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greglindahl
Drag is not constant, it depends on which way the sail is pointing. One of the
things they're testing is constantly swiveling the thing to maximize thrust
and minimize drag.

The ISS maneuvers constantly to reduce drag.

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ExodusOrbitals1
Crowdfunded spacecraft are definitely a cool addition to our space exploration
program.

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JoeDaDude
Thought it would be fun to receive the downlinks from Lightsail 2 with an SDR.
Does anyone have any info on frequencies/modulation modes being used, above
and beyond the Morse code beacon [1] at UHF?

[1] [http://www.planetary.org/blogs/jason-
davis/2016/20160609-lig...](http://www.planetary.org/blogs/jason-
davis/2016/20160609-lightsail-2-morse-code.html)

~~~
kawfey
The FCC license registration [0] contains some interesting information.

\- Experimental radio service call sign WM9XPA

\- Using an Icom IC-821C Transceiver [1], a twenty-something year old VHF/UHF
ham radio...wow for a $7M project couldn't they have spent more on a radio?
Well, maybe not, I'll get to that in a minute.

\- Ground station is in the middle of nowhere? I think something with the Lat-
Lon might be off if they mention West Lafayette, IN as the city (Purdue is
located here).

\- The satellite's datalink is FSK on 437.025 MHz, designation 15K0F1D, which
is a standard 15kHz wide FM modulated FSK signal. The signal's parameters are
not known from the registration but I googled some more and found their FAQ
which links to their protocol description [2]. In a nutshell it's run-of-the-
mill AX.25 at 9600baud using a simple encoding for various parameters. You
could decode this easily with an SDR and Direwolf [3] or GNURadio. This is why
they can use the low-cost ham radio. I'm also willing to bet they'll be
leveraging submissions from amateur radio operators and the automated SATNOGS
network [4] to harvest more data.

[0] [https://fcc.report/ELS/The-Planetary-Society/1029-EX-
ST-2019](https://fcc.report/ELS/The-Planetary-Society/1029-EX-ST-2019)

[1]
[http://www.rigpix.com/icom/ic821h.htm](http://www.rigpix.com/icom/ic821h.htm)

[2]
[https://planetary.s3.amazonaws.com/projects/lightsail/manual...](https://planetary.s3.amazonaws.com/projects/lightsail/manuals/ls2-beacon-
info-v01.txt)

[3]
[https://github.com/wb2osz/direwolf/blob/dev/doc/README.md](https://github.com/wb2osz/direwolf/blob/dev/doc/README.md)

[4] [https://satnogs.org/](https://satnogs.org/)

~~~
JoeDaDude
Great info, thank you! I'll see if I can rig some of this up in GNU Radio.
Thanks again!

PS: Casual trivia. I used to own that Icom model radio ages ago, gave it to my
father who used it for SWL.

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Roritharr
I'd love to play around with the math, but am extremely ill-equipped to answer
my XKCD What If?-Style Question, so I'll just ask it here.

If i'd ignore the time necessary to accomplish my goal, could I use such a
craft to steer an asteroid to earth?

I'm imagining to balance the minuscule gravity a craft like the LightSail 2
would effect on an asteroid with the propelling force of the lightsail over a
few centuries to slowly but steadily tug the asteroid on a collision course.

When looking at the cost of the LightSail 2 I'd imagine this to be the most
cost effective method of putting a deadline on humanity for the enterprising
villain on the lookout for a bargain.

~~~
kadoban
If your math is good enough, could you just "paint" the surface of a suitable
object enough to steer it via differences of light pressure?

~~~
sandworm101
Not really. The differences in pressure would create spin, not push the craft
in a different direction. You would need something else to push against, to
"tack" against the solar wind, like how a sailboat's keel pushed against the
water. Magnetic fields are an option, but those get less and less as you move
away from the sun.

There are some complicated options involving mirrors that could move a craft
in other directions, but they are radically difficult to manage. You send five
mirrors with the craft as a formation, one on each side and one _ahead_. Then
you can bounce the lasers off these mirrors to steer the ship. At the
destination, the ahead mirror is used to slow the craft. All these mirrors
would essentially be separate craft that would need to be themselves
accelerated and managed.

~~~
hughes
If you use a material on the back of the asteroid that had a higher albedo at
more oblique angles, you could have a form of feedback.

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booleandilemma
So we’re living at the beginning of the second Age of Sail?

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max_
Would like to learn more about "Age of Sail"

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yial
I would believe it's a tie to exploration.

Quite literally "Age of Sail"

[https://en.wikipedia.org/wiki/Age_of_Sail](https://en.wikipedia.org/wiki/Age_of_Sail)

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StreamBright
Can you rely on sunlight between star systems?

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abdullahkhalids
No. In fact, the solar irradiance gets fairly low even by the time you reach
Saturn, because the power propogates via an inverse square law. Near Earth,
which is 1 Astronomical Unit (AU) away from the Sun, you get about 1000W/m^2.
Around Saturn, which is about 10 AU away, irradiance will be down to 1000/10^2
= 10W/m^2. So 1% of what you get near Earth.

