Light-induced propulsion of graphene-on-grid sails in microgravity | Hacker News Reader

Light-induced propulsion of graphene-on-grid sails in microgravity

sciencedirect.com

38 pointsbookofjoe13 comments

>Light sailing is the only existing in-space propulsion technology that could allow us to visit other star systems in a human lifespan.

as this article shows the light sailing requires unobtanium to make the real light sail. Whereis nuclear explosion propulsion - project Orion - can me made with existing materials. Of course bringing into orbit the required several millions tons of cargo to build the ship from, majority of it being the tens of thousands of nukes, seems to be an endeavor behind our current capabilities.

This research pertains only to the question of how we propel an object in a way that enables interstellar travel with a duration of fewer than ~100 years.

There's a whole other question, which must be answered separately, about how to keep that object from being destroyed during its travels.

The effectively 2D graphene material might be the right material from a propulsion perspective, but it may be totally unsuitable in terms of making sure the object gets to another star system in one piece.

The most interesting piece of the link isn't the sail application, it's the theoretical implication. More thrust was experienced than expected from photon pressure alone. A lot more.

How why? New physics?

All good questions.

> The measured thrust is one order of magnitude larger than the theoretical calculations for radiation pressure alone.

Nice!

>> 2D sails pave the way for reaching other star systems in a human lifespan.

Pave the way? Explain to me how the laser is going to work? There are some fundimental size/optics restrictions here that keep the sail very much a seconday concern in terms of interstellar travel.

What are the size/optics restrictions?

For a given distance to the target, there is a minimum required lens size to focus the laser so (most of) it hits the target. The required size is proportional to the target distance.

When the distance to the target is interstellar-scale, the required lens gets pretty big.

You have to focus the outgoing light, the laser energy, just as a telescope does inbound light. To hit a small target (say a 1x1km light sail with a 4x4km beam) at interstellar ranges would require laser emitting equipment many kilometers in size repeated across multiple locations.

How large of a telescope is needed to focus the image of a 4km feature on Pluto? Then multiply that by a few orders of magnitude. Then plug in a laser powerful enough to vaporize a small town. Those are the real problems, not the mass of the sail.

IIRC the breakthrough starshot project is proposing accelerating a small probe (cubesat sized) to relativistic speed in a very short timespan.

The old Starwisp (I think) proposal involved accelerating a lens as well, keeping it positioned between the laser and the payload sail, to refocus the beam. (A 2D diffractive lens, of course, not a giant piece of glass.)

Love seeing when science fiction starts to turn into reality!

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