Lightsail 2

[Catastrophe]

After reading an article in All About Space Issue 125 "Lightsail 2 Solar Sail is still soaring above Earth more than two years after launch", I searched "Lightsail2" only to find about 40 hits such as:

"LightSail 2 Healthy as Mission Team Continues… | The Planetary Society"

which really told me nothing. OK, so it may be my ignorance, for which I apologise.

From AAS 125, I read "The spacecraft is . . . . . . about the size of a loaf of bread, fitted with a sail about the size of a boxing ring, or about 32 sq metres (433 sq ft)".

I can find wonderful detail, like its orbit has increased by 2 metres, but I can't find what use it is going to be?
Doubtless this is all down to my ignorance. Mea culpa.

I thought we had dismissed light sails as being totally impractical. What am I missing?

Cat

 

[Dratonia]

I thought we had dismissed light sails as being totally impractical. What am I missing?

This is true, however it is still valuable to have smaller experiments with it, as you may still learn things that relate to other things, as well as technologies changing to the point where they become more valuable.

 

[suneritz]

Have the large scale idea been rejected too? Thanks

http://www.niac.usra.edu/files/studies/final_report/320Zubrin.pdf

 

[Catastrophe]

"A loop of superconducting cable perhaps tens of kilometers in diameter is stored on a drum attached to a payload spacecraft "

That's a good start!

Cat

 

[Pogo]

Cat, I agree, didn’t get much out the article, got way more from the Lightsail Wiki article.
The concept appears to be OK for free energy minor orbit adjustments, but as a space travel means, not so much, especially beyond Earth or Mars orbits.

 

[Catastrophe]

Pogo, this is from a former LS topic::

Probably the most practical and informative approach you can find is in the book "Extraterrestrial" by Avi Loeb, John Murray (Publishers), 2021. Author is Chair of Harvard's Astronomy Department, and all the rest - one of the world's top astrophysicists.

He was approached by a billionaire (as happens a lot at the moment) over a special project. This guy wanted to fund a mission to the Centauri system, to arrive there during his lifetime - unmanned of course. Conventional chemical propulsion would require over 100,000 years. Avi came up with the idea of using a light sail. However, this is totally impracticable for anything over a few grams. They only wanted to take pictures and similar as they passed by. Obviously it would take too long to stop.

The system uses a 100 gigawatt laser beam. It is stated that everything they propose be within existing technological bounds. This is no joke. It is a serious mission. To avoid burning the sails, they had to absorb less than 1/ 100,000 of the (laser) light striking them.

There is an article published in Astrophysical Journal, October 2015, by Avi and James Guillochon on lightsails. It was decided to announce the Starshot Initiative, as they call it, on April 12 2016, On the stage were included Stephen Hawking, Freeman Dyson and Yuri Milner.

I hope this will help, but if you are thinking about manned trips using lightsails - forget it - unless you want to completely ignore the science.


Cat

 

[Pogo]

Yes, I remember that. I don’t the laser idea will go anywhere, either.

 

[suneritz]

Why not combine these approaches. You can easily fit 10km of wire into shoebox size, charge it in orbit with extreme currents and you have a Webb size mag sail. You can then use it to propel itself out of our solar system and accelerate to relativistic speeds with lasers. When it arrives to Proxima use it to slow down with Centauri’s solar wind/plasma, then you can travel at a rocket speed around that system photographing with long exposure. Questions remain since you have to fly directly into the neighboring star. Can the mag shield help with heat, will it offer enough drag to overpower star’s gravity pull and it’s own forward momentum. What are the main goals of the mission (per trillioner), such as can any kind of (microbial) life be found through this type of explanation.

 

[Helio]

Why not combine these approaches. You can easily fit 10km of wire into shoebox size, charge it in orbit with extreme currents and you have a Webb size mag sail. You can then use it to propel itself out of our solar system and accelerate to relativistic speeds with lasers. When it arrives to Proxima use it to slow down with Centauri’s solar wind/plasma, then you can travel at a rocket speed around that system photographing with long exposure. Questions remain since you have to fly directly into the neighboring star. Can the mag shield help with heat, will it offer enough drag to overpower star’s gravity pull and it’s own forward momentum. What are the main goals of the mission (per trillioner), such as can any kind of (microbial) life be found through this type of explanation.

What are the engineering details to this cool idea? How do you run lots of amps through a very tiny diameter wire?

What if something similar could be done by dropping the probe closer to the Sun and put it in orbit until a CME or flare occurs and in the direction of alpha Cen? This more concentrated field strength might make a big difference in acceleration, even if given extra shielding. I don't know, just wondering if this makes sense.

 

[Catastrophe]

6 miles of wire in a shoe box? As Helio correctly suggests - pretty thin wire.

Cat

 

[suneritz]

Engineering wise, on page 15 of this document a somewhat similar cable (1mm thick by 4mm wide) is represented and will be used for Artemis mission.

Your idea of waiting for the flare in a specific direction sounds cool. The sail would be switched off until there is a flare. Cat I hope I am not deferring too much from your initial post. As Sail 2.0 it could be viewed in a variety of ways.

https://bigidea.nianet.org/wp-content/uploads/2020-BIG-Idea-Technical-Paper_MTU.pdf

 

[Dratonia]

Engineering wise, on page 15 of this document a somewhat similar cable (1mm thick by 4mm wide) is represented and will be used for Artemis mission.

Your idea of waiting for the flare in a specific direction sounds cool. The sail would be switched off until there is a flare. Cat I hope I am not deferring too much from your initial post. As Sail 2.0 it could be viewed in a variety of ways.

https://bigidea.nianet.org/wp-content/uploads/2020-BIG-Idea-Technical-Paper_MTU.pdf

I think that in order for anything like this to be possible within out lifetimes, we will need to learn to exploit natural occurances, instead of purely rockets.

 

[Catastrophe]

suneritz, no problem.. I cannot see any practical use whatsoever for lightsails of any size - especially large ones. Just look at area/weight/flimsiness of sail. Smaller sails might have some use (photography) but then the small sails would be hard to keep on beam. Whatever the size, you have the inverse square law. I'd rather put my money on the lottery, so to speak.

Cat

 

[Helio]

suneritz, no problem.. I cannot see any practical use whatsoever for lightsails of any size - especially large ones. Just look at area/weight/flimsiness of sail. Smaller sails might have some use (photography) but then the small sails would be hard to keep on beam. Whatever the size, you have the inverse square law. I'd rather put my money on the lottery, so to speak.

I think the huge wattage in laser power is to cause huge acceleration over a short distance because of the inverse square law.

I stumbled across an article about using a very large lens to focus extremely powerful lasers to not only accelerate but decelerate objects, including in one design, a 70 ton spacecraft. A giant ring would move with the space craft that would unfurl ahead of the spacecraft and the laser would cause deceleration. A pipe dream but interesting.

 

[Catastrophe]

Helio, one of the many problems with larger sails, is the integrity of the sail, especially its resistance to heat.

Cat

 

[Helio]

Helio, one of the many problems with larger sails, is the integrity of the sail, especially its resistance to heat.

Goof point. A closer solar orbiting craft could have a pilot craft shielding it until whatever needs unfurling, Fast radial acceleration using coils to exploit the mag. field could likely also have some temporary lightweight shielding, perhaps.

 

[Catastrophe]

Trouble is . . . . . . . . . shielding is proportional to weight.

Lightweight shielding . . . lightweight protection.

Cat

 

[Helio]

Trouble is . . . . . . . . . shielding is proportional to weight.

Lightweight shielding . . . lightweight protection.

Cat

Yes, normally. There may be things like asbestos or other lighter material that would serve for the more temporary use during departure from the protective pilot craft.

I haven't really thought of much of the details. Can we even exploit the monster magnetic field from a flare or CME? The force from a mag. field imparted on the wire with current isn't radial with the flare's direction, I assume, so there are challenges to consider. This is likely serious surfing!

There are far fewer ways a surfer can catch a wave than not.

 

[Catastrophe]

Here are the two methods compared:

https://imgur.com/3mkkIHz

View: https://imgur.com/3mkkIHz


CMB on left, Cepheids on right, turquoise strips.
The Hubble "Constants" are the 65 70 etc along the x axis.

Cat

 

[Catastrophe]

Lead is really excellent.

Cat

 

[Helio]

Here are the two methods compared:

https://imgur.com/3mkkIHz

View: https://imgur.com/3mkkIHz


CMB on left, Cepheids on right, turquoise strips.
The Hubble "Constants" are the 65 70 etc along the x axis.

Nice display! Thanks.

It will be interesting if the differences can get explained in the near future. Gravity waves were mentioned as being the up-comming and superior method since scattering of the wave, etc., isn't an issue.

 

[Catastrophe]

Why should different methods have to be explained. The problem is expecting different methods to give the same answer.

If you are caught speeding, does it matter if radar says 70.1 mph and a cop with a stopwatch says 71.7?

Cat

 

[Helio]

Why should different methods have to be explained. The problem is expecting different methods to give the same answer.

If you are caught speeding, does it matter if radar says 70.1 mph and a cop with a stopwatch says 71.7?

Yes, but this margin of error is too little of a comparison. If it were only 1% or 2% then there'd be no real issue; the H-L constant would become another piece of concrete in the halls of science. But the difference, using your chart, is about 8%.

So, to use your apt analogy, if you have multiple radar units of both great precision and from different makers give a result of 70.1 mph, but multiple precision stop watches give you a 75.8 mph consistent result, then some sort of investigation is needed. This, I think, is the case explaining why it's called the Hubble Tension.

 

[Catastrophe]

Helio, as you know, I bow to your great expertise, and happily gather the crumbs from your table.
I don't think that we disagree here. The HT or HC is really not that important, imho.

I am not even that sure whether 'the' universe (small u) is expanding, or whether our rulers vary with distance. (OK CMB blah blah blah).

Cat

 

[Helio]

Helio, as you know, I bow to your great expertise, and happily gather the crumbs from your table.

Hey, those are the same crumbs that feed me. I'm just an amateur.

I don't think that we disagree here. The HT or HC is really not that important, imho.

It is, however, integral to a unified theory. The original calculation showed that the universe was younger than stars. That was no small hint something was amiss.

I am not even that sure whether 'the' universe (small u) is expanding, or whether our rulers vary with distance. (OK CMB blah blah blah).

The evidence greatly favors expansion, though De Sitter's first solution to GR had redshift without expansion (but no matter in the universe). I think this influenced Hubble and kept him from declaring the universe is expanding, which is why I prefer the H-L term to give credit to the one who first both predicted it and calculated it, though it was wrong given the erroneous distances he had to work with.