Comment by Gravityloss | Hacker News Reader

Comment by Gravityloss | Hacker News Reader

They sure write a lot but for someone more technologically oriented, the water plasma engine or CAT is most interesting.

http://pepl.engin.umich.edu/thrusters/CAT.html

"First, from a propellant tank, our fuel propellant will be injected from its storage tank into the plasma liner, a quartz chamber that distributes the gas and contains the plasma. The gas is turned into a plasma by a radio frequency antenna that surrounds the liner and launches a plasma wave known as a "helicon." Then the plasma is launched out of the liner with magnetic fields from extremely powerful permanent magnets, pushing the satellite in the opposite direction. Unlike conventional rockets, almost any gas can be used as propellant for the CAT - even water vapor! "

Some ion engines use electrostatics (charged grids) for accelerating the ions. Maybe here it's just their random movement?

Here's the noble gas helicon double layer thruster, I don't know how related the CAT is related to this: http://physics.anu.edu.au/prl/sp3/hdlt/how_does_it_work.php

So basically the water is reaction mass, and it's actually powered by solar cells?

They should write that WAY more prominently on the kickstarter page, as is it feels like a scam.

In the second sentence of the kickstarter page it says "a new rocket propulsion system powered by the Sun and propelled by water". I think that is pretty clear.

Clear for people in the know, I guess.

But suppose I had a Kickstarter for a car on the same premises: "A revolutionary car powered by sunlight and water - fill up with water every now and then, and it will run forever". No further details. Would you buy?

I think it's a very small percentage of the world that would know off the bat why "sun and water" could work for a spacecraft, but not for a car.

I think some more detail on the physics behind it, aimed slightly below say Physics 101 level, would help to convince more people to contribute. It makes it simpler to distinguish this from "crystals can change your life" or "lose X pounds of weight in Y days" style marketing, which promise the moon but don't explain how their miracle is supposed to work.

They do give an explanation in their link[0], but I think having a summarized version on the Kickstarter page itself would help donations. (To be clear, this is a comment on the marketing, not on the physics or feasability.)

[0] http://pepl.engin.umich.edu/thrusters/CAT.html

They could do a little comparison of existing technologies:

Chemical rockets - put fuel and oxidizer together, burn them, resulting gas is shoved out the back and pushes the rocket forward.

NERVA - reaction mass is heated by a nuclear heat source, resulting gas is shoved out the back and pushes the rocket forward.

Ion thruster: reaction mass (such as xenon) is charged electrically using a grid and the resulting ions are shoved out the back and pushes the rocket forward.

CAT: reaction mass (such as water) is charged electrically using a glass bottle thingy and the resulting plasma is shoved out the back and pushes the rocket forward.

Shove that in an infographic and you can get the basic concept across to someone who knows high-school physics and sound convincing to people that don't even have that level of background knowledge.

http://en.wikipedia.org/wiki/NERVA http://en.wikipedia.org/wiki/Ion_thruster

Upon reading the entire page, it looks legit. But when the page first loaded, I read "propelled by water" and immediately thought "Uh... aren't normal rockets also propelled by water?" I just think the kickstarter page could have been a little more upfront about the plasma part.

I felt that way a little bit, but since I already knew the physics (and heard of a similar system that uses a microprinted array of spikes (conductive spikes naturally create a charge separation when pumped to a voltage) I wasn't put off by it.

They're going to reach their goal, so it might be a moot point

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