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DaCaptain
2018-Jul-26, 04:23 PM
Hypothetically I want to make a spacecraft that uses the solar wind to maneuver. I always pictured catching the solar wind to be similar to sailing the ocean. Is being able to tack and jib possible? Or is it a one way trip? How big of a sail would I need for a small 100kg spacecraft?

selden
2018-Jul-26, 04:58 PM
It's not quite the same as what I think you're trying to describe, but here's a popularized article about solar wind sail technology: https://cosmosmagazine.com/technology/nasa-begins-testing-solar-wind-sail-technology

Here's a somewhat more technical NASA page about it: https://www.nasa.gov/feature/heliopause-electrostatic-rapid-transit-system-herts

and here's a formal paper about it: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150016542.pdf


A recent six month investigation focused on: “Determining the benefits of propelling a
scientific spacecraft by an ‘Electric Sail’ propulsion system to the edge of our solar system (the
Heliopause), a distance of 100 to 120 AU, in ten years or less” has recently been completed by
the Advance Concepts Office at NASA’s MSFC.

Ken G
2018-Jul-28, 03:33 PM
An analog of "tacking" would be possible, even if all the sail does is deflect the path of the protons. If all you do is deflect the path of particles (be they solar wind or regular wind particles), the sail itself can never produce a component of force that is "into the wind". But there are two forces on a sailboat, one from the wind on the sail and one from the water on the keel. It would therefore suffice to be able to tack even if the force of the wind on the sail was perpendicular to the sail and the force from the water was perpendicular to the keel. The keel force can cancel all forces except those toward the front of the boat, so if you put the sail between the direction of the wind and the direction of the front of the boat, you can get a force in the direction of the boat even that is into the wind. This happens even though the sail by itself never produces any force component into the direction of the wind.

For a solar sail, the force from the keel would be replaced by the Sun's gravity. This is a somewhat different situation, because the "keel force" doesn't depend on the direction the ship is pointed, it just points toward the Sun all the time. But that's even better, because now you have a constant force that points "into the wind", and the only thing keeping you from "sailing into the wind" is your orbital speed. So you use the sail to get a sideways force that reduces your orbital speed, and you use the Sun's gravity to pull you where you want to go, achieving a result that would look a bit like tacking.

profloater
2018-Jul-28, 04:41 PM
A boat with a windmill geared to a prop can sail into the wind thanks to the water force. So i guess the solar wind could be caught and redirected in any direction but it would still not make progress directly into the wind except by falling in the gravity field.

Ken G
2018-Jul-29, 02:25 PM
Exactly.

selden
2018-Jul-30, 01:17 PM
It seems to me that interacting directly with the Solar magnetic field (in addition to interacting with the flow of particles around the field lines) could be used for steering. Or am I overlooking something?

DaCaptain
2018-Jul-30, 02:21 PM
It's not quite the same as what I think you're trying to describe, but here's a popularized article about solar wind sail technology: https://cosmosmagazine.com/technology/nasa-begins-testing-solar-wind-sail-technology

Here's a somewhat more technical NASA page about it: https://www.nasa.gov/feature/heliopause-electrostatic-rapid-transit-system-herts

and here's a formal paper about it: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150016542.pdf

These three sources are great information about the subject. Still digging through the third one.

Grey
2018-Jul-30, 05:26 PM
It seems to me that interacting directly with the Solar magnetic field (in addition to interacting with the flow of particles around the field lines) could be used for steering. Or am I overlooking something?You can build a magnetic sail (https://en.wikipedia.org/wiki/Magnetic_sail#Solar_wind_example) that interacts with the charged particles of the solar wind, rather then with light. In some ways, it's very similar, but in others very different. For a given thrust, a magsail has to be larger (because the solar wind has less net momentum for a given area than sunlight), but can be a loop, rather than a sheet, so it can have a lower mass.

DaCaptain
2018-Jul-30, 08:25 PM
What about "catching" coronal mass ejections. Could the space ship could ride a wave of material ejected from the sun like a surfer rides a wave on the ocean?

Jens
2018-Jul-31, 03:52 AM
What about "catching" coronal mass ejections. Could the space ship could ride a wave of material ejected from the sun like a surfer rides a wave on the ocean?

It depends on how far you want to take the analogy. If the solar wind increases, it will increase your acceleration. But it is not really like "riding a wave." You can ride the wave because the wave is traveling horizontally and you are using gravity to slide down the front of it to stop it from overtaking it.

DaCaptain
2018-Jul-31, 03:19 PM
It depends on how far you want to take the analogy. If the solar wind increases, it will increase your acceleration. But it is not really like "riding a wave." You can ride the wave because the wave is traveling horizontally and you are using gravity to slide down the front of it to stop it from overtaking it.


Catching a wave probably wasn't the best analogy. The CME would act more like a strong gust of wind.


23473

I don't like the design of the e-sail. Although the skinny wires would work it seems like a mesh of some sort would be able to catch more of the solar wind. You'd create the mesh by using group of bots that would sinter the sail together when the ship is in space. Once the sail is deployed would it ever need to be retracted? The bots could also be used to fix the mesh if need be.

selden
2018-Aug-16, 04:52 PM
Here's info about a similar technology which uses electric fields:

popularization:
https://www.nextbigfuture.com/2018/08/propellantless-interstellar-travel-using-electric-fields-that-is-better-than-laser-driven-sails-up-to-5-of-light-speed.html#more-147881

and the abstract of its preprint:
https://arxiv.org/abs/1808.02019

SPACECRAFT WITH INTERSTELLAR MEDIUM MOMENTUM EXCHANGE REACTIONS:
THE POTENTIAL AND LIMITATIONS OF PROPELLANTLESS INTERSTELLAR TRAVEL
by Drew Brisbin



We propose a new mode of transport which relies on electric-field moderated momentum exchange with the ionized particles in the interstellar medium. While the application of this mechanism faces significant challenges requiring industrial-scale exploitation of space, the technological roadblocks are minimal, and are perhaps more easily addressed than the issues presented by light sails or particle beam powered craft.