Key advance in solar sails for the search of extraterrestrial life.

[Exoscientist]

1 hour ago, darthgently said:

I’m not seeing how the forces on both sails don’t cancel out in deceleration mode.  What am I missing?

 

 A good question. His idea needs to be tested in the lab. If I’m to make a guess, the side of the smaller sail facing the Sun is non-mirrored so has low light pressure pushing it away from the Sun, but the side facing the larger main sail is mirrored. And more importantly that larger main sail focuses all it’s light onto the smaller sail in concentrated fashion. 

  Bob Clark

[JoeSchmuckatelli]

1 hour ago, darthgently said:

I’m not seeing how the forces on both sails don’t cancel out in deceleration mode.  What am I missing?

Just from the diagram it looks like the 'rendezvous stage' becomes a reflector for the return stage and is renamed to ' accelerator stage' - and it goes away but reflects enough light to push the return back?? 

I'm just... This all looks like a thought experiment rather than anything practical.  1000 km 'paralens'?  That has to be continuously illuminated by (presumably) a massive laser array? For YEARS!?! 

Just trying to imagine the orbital mechanics of the 1000km paralens - an object 1/12 the diameter of the Earth - and how to keep that both fed by the lasers and oriented on the target during just a single year seems unlikely.  

Put at L4 / L5, it will need to be on a 1 Rev per year rotation to stay oriented to the target - which means that for significant portions of the year it will be effectively edge on towards the Earth.  During other times it will have to be a reflector and others a classic lens. 

This is an impractical idea at best 

She's dead, Jim. 

[Superfluous J]

1 hour ago, darthgently said:

I’m not seeing how the forces on both sails don’t cancel out in deceleration mode.  What am I missing?

You drop the first reflector

[AckSed]

1 hour ago, darthgently said:

I’m not seeing how the forces on both sails don’t cancel out in deceleration mode.  What am I missing?

The actual proposal: http://www.geoffreylandis.com/lightsail/Lightsail89.html

The force on the deceleration stage would feel the incident pressure, but would not cancel out, as the light-collecting area of the first stage is greater, and all of that would (somehow) be focused on the deceleration stage... aaand it's been answered. :-)

Dealing with the energy focused on this smaller sail would be another problem. The proposal was to use dielectric mirrors made of refractory substances that reflects 99.5% of the energy with minimal absorption, and can take extreme temperatures.

Personally, if you have these fancy focusing arrays on the sail, I think you could leverage Y. K. Bae's photonic thrusters by coating the back of the deceleration sail with a thin-film laser gain medium. That way, you have a laser cavity that bounces the light back and forth, recuperating the energy and increasing the thrust with less thermal load.

1 minute ago, JoeSchmuckatelli said:

Just trying to imagine the orbital mechanics of the 1000km paralens - an object 1/12 the diameter of the Earth - and how to keep that both fed by the lasers and oriented on the target during just a single year seems unlikely.  

They do say that a staged array of a hundred 500km lenses would be more achievable.

[magnemoe]

2 hours ago, darthgently said:

I’m not seeing how the forces on both sails don’t cancel out in deceleration mode.  What am I missing?

I assume the dropped stage is heavier, diameter is larger and it need to focus the incoming light on target so its more than basic structure. 
You might also use other ways to slow down like an magsail interacting with galactic and solar wind who works better who faster your moving.

You could also anchor the second stage to an asteroid, more realistically you send an one way mission first. 
It has an secondary mission to anchor its second stage sail to an asteroid to work as an braking sail for next mission.
You launch the second mission then first mission rover has an first contact. 
 
 

[JoeSchmuckatelli]

1 hour ago, AckSed said:

They do say that a staged array of a hundred 500km lenses would be more achievable

Grin!

 

1.  World spanning laser array dumping power into outer space.  - World spanning because of the rotation.   Feasible because who doesn't have extra power to beam into space? 

2. Torturously complex system of mirrors, prisms and lenses.  - Complex because it has to dominate a Lagrange Point and at different times during the year, the light must be focused going straight out from the Earth or reflected back past the Earth, or continuously refracted through every degree from 180 to zero between the two extremes 

3.  Star Trek seems more plausible 

Edited January 3 by JoeSchmuckatelli

[darthgently]

1 hour ago, Superfluous J said:

You drop the first reflector

That makes more sense.  From the diagram I thought it was all one big perpetual motion machine

47 minutes ago, magnemoe said:

I assume the dropped stage is heavier, diameter is larger and it need to focus the incoming light on target so its more than basic structure. 
You might also use other ways to slow down like an magsail interacting with galactic and solar wind who works better who faster your moving.

You could also anchor the second stage to an asteroid, more realistically you send an one way mission first. 
It has an secondary mission to anchor its second stage sail to an asteroid to work as an braking sail for next mission.
You launch the second mission then first mission rover has an first contact. 
 
 

Yes, “dropped stage” was pivotal to my understanding. I thought it remained one assembly

[Exoscientist]

7 hours ago, JoeSchmuckatelli said:

Just from the diagram it looks like the 'rendezvous stage' becomes a reflector for the return stage and is renamed to ' accelerator stage' - and it goes away but reflects enough light to push the return back?? 

I'm just... This all looks like a thought experiment rather than anything practical.  1000 km 'paralens'?  That has to be continuously illuminated by (presumably) a massive laser array? For YEARS!?! 

Just trying to imagine the orbital mechanics of the 1000km paralens - an object 1/12 the diameter of the Earth - and how to keep that both fed by the lasers and oriented on the target during just a single year seems unlikely.  

Put at L4 / L5, it will need to be on a 1 Rev per year rotation to stay oriented to the target - which means that for significant portions of the year it will be effectively edge on towards the Earth.  During other times it will have to be a reflector and others a classic lens. 

This is an impractical idea at best 

She's dead, Jim. 

That was for a crewed mission to another star system, tens of trillions of kilometers away. But the primary focus of this new research is for missions still in the Solar System, 1/10,000th the distance, with cubesat-like probes.

 Here’s the published report by Rene Heller et.al.:

Low-cost precursor of an interstellar mission.
René Heller1,2, Guillem Anglada-Escudé3,4, Michael Hippke5,6, and Pierre Kervella7
ABSTRACT
The solar photon pressure provides a viable source of thrust for spacecraft in the solar system. Theoretically it could also enable inter- stellar missions, but an extremely small mass per cross section area is required to overcome the solar gravity. We identify aerographite, a synthetic carbon-based foam with a density of 0.18 kg m−3 (15 000 times more lightweight than aluminum) as a versatile material for highly efficient propulsion with sunlight. A hollow aerographite sphere with a shell thickness εshl = 1 mm could go interstellar upon submission to solar radiation in interplanetary space. Upon launch at 1 AU from the Sun, an aerographite shell with εshl = 0.5 mm arrives at the orbit of Mars in 60 d and at Pluto’s orbit in 4.3 yr. Release of an aerographite hollow sphere, whose shell is 1 μm thick, at 0.04 AU (the closest approach of the Parker Solar Probe) results in an escape speed of nearly 6900 km s−1 and 185 yr of travel to the distance of our nearest star, Proxima Centauri. The infrared signature of a meter-sized aerographite sail could be observed with JWST up to 2 AU from the Sun, beyond the orbit of Mars. An aerographite hollow sphere, whose shell is 100 μm thick, of 1 m (5 m) radius weighs 230 mg (5.7 g) and has a 2.2 g (55 g) mass margin to allow interstellar escape. The payload margin is ten times the mass of the spacecraft, whereas the payload on chemical interstellar rockets is typically a thousandth of the weight of the rocket. Using 1 g (10 g) of this margin (e.g., for miniature communication technology with Earth), it would reach the orbit of Pluto 4.7 yr (2.8 yr) after interplanetary launch at 1 AU. Simplistic communication would enable studies of the interplanetary medium and a search for the suspected Planet Nine, and would serve as a precursor mission to α Centauri. We estimate prototype developments costs of 1 million USD, a price of 1000 USD per sail, and a total of <10 million USD including launch for a piggyback concept with an interplanetary mission.
https://www.aanda.org/articles/aa/pdf/2020/09/aa38687-20.pdf

 From the scaling indicated there, it appears the mass scales by the areal size of the sail, i.e., by the square of the diameter. So a 100 meter wide sail, would have a sail mass of 2.3 kg and a payload mass of 22 kg.

  Bob Clark