Light sail, er, sails....

[Zirconia]

http://www.planetary.org/press-room/lightsail/
http://www.planetary.org/blogs/jason-davis/lightsa...
https://www.syfy.com/syfywire/soon-we-may-be-saili...

Raising its apogee by a couple of km's.

[Beati Dogu]

It sure is pretty.

It'll be interesting to see how it gets on. They didn't have a lot of luck with the first version.

[Einion Yrth]

Problem is that at perigee it's a light sail, and at apogee it's a sea anchor; this can only end one way...

[Eric Mc]

Almost 50 years ago, I read Arthur C Clarke's short story "Sunjammer". We are finally getting there.

[Zirconia]

I believe that is expected for this test. Burn up that is. I assume so no debris added to the already accumulated crud surrounding the planet (without nations blowing them up to prove a point).

[Gojira]

Eric Mc said:

Almost 50 years ago, I read Arthur C Clarke's short story "Sunjammer". We are finally getting there.

That's exactly what I thought, when I saw this thread!

[Eric Mc]

Can't the solar sail; "tack" as a normal sail would?

[Eric Mc]

What effect would tacking have? I assume it would give you a DV plus or minus which would cause your trajectory to change - although very slowly.

How slow would these changes be compared to say, an ion drive?

[Zirconia]

I was think the hull in the water bit was the reason you can tack but there is a reaction wheel on this, rotate that another way or use two sails?

[Zirconia]

Righto.


Makes note to get back into Kerbal.

[RobM77]

ash73 said:

Eric Mc said:

Can't the solar sail; "tack" as a normal sail would?

Tacking requires you to change course; you can boost the opposite side of the orbit by accelerating, or reduce it by decelerating, or change the path of the orbit by accelerating in a perpendicular direction (e.g. to switch from an equatorial to polar orbit) but that requires a huge amount of dV.

In space everything is orbiting something (up to the scale of galaxy clusters); you can't just fly around.

Interesting question.. Tacking is only a feature of sailing craft that can sail in a different direction to the wind. Sailing boats manage this via resistance from their hull and keel - if the wind's coming from 12 o clock most sailing boats can sail in any direction from 2 o'clock round to 10 o'clock, so any direction between those, with the exception of a 'run' (6 o'clock) can be flipped - e.g. 90 degrees at 3 o'clock can be flipped to 9 o'clock, or 4 flipped to 10 etc. A solar sail powered craft in deep space would only be able to travel in the direction of a solar wind. However, gravity provides a different force on the craft, so in theory I guess, yes, depending on circumstances and proximity to gravitational fields. The presence of a solar wind does of course mean gravity as well!

[Gandahar]

Eric Mc said:

Can't the solar sail; "tack" as a normal sail would?

Only if you moved the sun is the answer,.

Elliptical orbits and light photons are not easy to compare to yachts trying to go upwind on the earth in summary.

[Eric Mc]

RobM77 said:

Interesting question.. Tacking is only a feature of sailing craft that can sail in a different direction to the wind. Sailing boats manage this via resistance from their hull and keel - if the wind's coming from 12 o clock most sailing boats can sail in any direction from 2 o'clock round to 10 o'clock, so any direction between those, with the exception of a 'run' (6 o'clock) can be flipped - e.g. 90 degrees at 3 o'clock can be flipped to 9 o'clock, or 4 flipped to 10 etc. A solar sail powered craft in deep space would only be able to travel in the direction of a solar wind. However, gravity provides a different force on the craft, so in theory I guess, yes, depending on circumstances and proximity to gravitational fields. The presence of a solar wind does of course mean gravity as well!

I reckon it could be done, but it would be a lot more complex than an earth based yacht and there would be far more forces acting on the craft.

[RizzoTheRat]

ash73 said:

I guess you could do it by boosting the orbit one way, then waiting six months and boosting the other way when the Earth is on the other side of the Sun?

Presumably it gets moved perpendicular to the angle of the sail/mirror, so you should be able to get a reasonable angle on the sun and therefore be able to it in a fair bit less than 6 months.

Zirconia said:

Righto.


Makes note to get back into Kerbal.

There's a mod for that

[kiseca]

RobM77 said:

ash73 said:

Eric Mc said:

Can't the solar sail; "tack" as a normal sail would?

Tacking requires you to change course; you can boost the opposite side of the orbit by accelerating, or reduce it by decelerating, or change the path of the orbit by accelerating in a perpendicular direction (e.g. to switch from an equatorial to polar orbit) but that requires a huge amount of dV.

In space everything is orbiting something (up to the scale of galaxy clusters); you can't just fly around.

Interesting question.. Tacking is only a feature of sailing craft that can sail in a different direction to the wind. Sailing boats manage this via resistance from their hull and keel - if the wind's coming from 12 o clock most sailing boats can sail in any direction from 2 o'clock round to 10 o'clock, so any direction between those, with the exception of a 'run' (6 o'clock) can be flipped - e.g. 90 degrees at 3 o'clock can be flipped to 9 o'clock, or 4 flipped to 10 etc. A solar sail powered craft in deep space would only be able to travel in the direction of a solar wind. However, gravity provides a different force on the craft, so in theory I guess, yes, depending on circumstances and proximity to gravitational fields. The presence of a solar wind does of course mean gravity as well!

I get that you can't tack like a yacht because you're missing a resisting medium, but is the only force available always pushing directly away from the sun? What happens if the sail is presented to the sun at a 45 degree angle? Does the propulsive force get a corresponding lateral component, or do you just end up with a reduced force directly away from the sun proportional to the reduced area presented to the sun's photons?

[Eric Mc]

What about radiation pressure coming from outside the solar system i.e. cosmic radiation. Could that provide a medium against which a keel effect could be operated against?

Or using radiation flows around planets that possess magnetic fields, such as the earth or Jupiter?

[AnotherClarkey]

Some years ago now I contributed to the crowdfunding of Lightsail 2. It was a long wait but made following the mission over the last few weeks very satisfying. Links have already been posted but here is another - the 'mission control' page updated with every pass over the control centre:

http://www.planetary.org/explore/projects/lightsai...