FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 
New Posts RSS | Change Site Style

Microwave beam a way forward?
Goto page 1, 2  Next
 
Post new topic   Reply to topic   printer-friendly view     Hacked BY ALAMUT. Forum Index -> Related Topics
View previous topic :: View next topic  
Author Message
louis
Lime
Lime


Chapter: Yes
Joined: 06 Apr 2007
Posts: 690

PostPosted: Sun Nov 04, 2007 10:26 pm 
Post subject: Microwave beam a way forward?
Reply with quote

I see from a discussion on Mars Drive that

Microwave Electrothermal Thrusters

are being given serious consideration. Apparently these could power satellites in orbit and on interplanetary journeys. The idea is to use solar panels to generate the microwaves which heat fuels such as water - splitting them into hydrogen and oxygen and creating thrust. All this seems to be accepted as a way forward.

I wonder if that then brings us back to my hunch that we could use ground stations (or indeed orbiting stations) to generate microwave beams which then power such craft. Or is the mass of the fuel still an issue in terms of getting free of the Earth's gravitational pull?

I am hoping we can get to a situation where we could lift space craft in sections - say 300 kgs a time - using these sorts of systems.

Any thoughts?
Back to top
View user's profile Send private message
MirariNefas
Turquoise
Turquoise


Chapter: No
Joined: 12 Dec 2004
Posts: 2747
Location: LA

PostPosted: Mon Nov 05, 2007 2:15 am 
Post subject:
Reply with quote

Quote:
I wonder if that then brings us back to my hunch that we could use ground stations (or indeed orbiting stations) to generate microwave beams which then power such craft. Or is the mass of the fuel still an issue in terms of getting free of the Earth's gravitational pull?


The sort of wavelength that be useful over large stretches of atmosphere would require a prohibitively large rectenna. The wavelengths they would use in engines would end up getting dissipated in a stream of hot atmosphere within a few hundred meters.
Back to top
View user's profile Send private message
Terraformer
Red
Red


Chapter: Yes
Joined: 30 Oct 2007
Posts: 81

PostPosted: Mon Nov 05, 2007 6:42 am 
Post subject:
Reply with quote

Instead of using solar power to get electricty to split the water, just use the UV light directly.
Back to top
View user's profile Send private message
louis
Lime
Lime


Chapter: Yes
Joined: 06 Apr 2007
Posts: 690

PostPosted: Mon Nov 05, 2007 10:30 am 
Post subject:
Reply with quote

I don't think you'd get enough power that way.

Another thought...

In the tropics where there a reliable thick humid cloud cover, woudl there be anyway of a craft creating its own water source as it rose, thus again saving on mass?
Back to top
View user's profile Send private message
louis
Lime
Lime


Chapter: Yes
Joined: 06 Apr 2007
Posts: 690

PostPosted: Tue Nov 06, 2007 9:44 pm 
Post subject:
Reply with quote

OK Miraris -

Wouldn't like to rain on your fountain. So I've transferred back to this thread.

You said:

"Quote:
but I do know NASA have flown a plane with a microwave beam, so at some level it must be technically feasible.

A plane needs no propellant.

Quote:
I don't have the technical knowledge for all this but clearly ion type engines are a candidate, with the microwave beam providing the fuel.


I thought Gourdhead disabused you of that notion. Microwave beams provide power, not fuel.

In any case, this really isn't the place for these discussions. Talk about beams elsewhere."

My comments are as follows:-

1. A plane doesn't need propellant? Would you like to justify that? It certainly needs a machine driven propeller, or a jet, or a rocket to stay up there. Space planes are a recognised concept. If a microwave beam can get a plane going up and up then it could be used as part of a space plane concept.

2. Well, I may have misunderstood. I thought the lesson was that the microwave beam was the fuel not the power. In fact I am sure that is right - it is the ion flow that is the power isn't it? So the microwave beam would be the fuel for the power.

3. Fact remains: microwave propulsion is a lot more advanced than your fanciful fountain.
Back to top
View user's profile Send private message
MirariNefas
Turquoise
Turquoise


Chapter: No
Joined: 12 Dec 2004
Posts: 2747
Location: LA

PostPosted: Tue Nov 06, 2007 11:00 pm 
Post subject:
Reply with quote

Quote:
1. A plane doesn't need propellant? Would you like to justify that?


Not really, but I guess I will anyway. Planes (or at least, propeller driven craft, though jets as well to a lesser extent) use the air around them as propellant. They carry no propellant. As long as they are immersed in propellant, they need to carry none. And in space, there is no propellant for a plane to be immersed in.

Quote:
Space planes are a recognised concept.


I think you are confused. A space plane is basically a minishuttle. It uses rockets. It is nothing like an air-breathing plane.

Quote:
If a microwave beam can get a plane going up and up then it could be used as part of a space plane concept.


If you were utterly determined to do so then I suppose yes, you could lift a carrier plane like the one they used with Spaceship One, and then the actual spaceplane could fire its rockets and take off from there. But it would be pretty pointless. Flying in the atmosphere is the easy part.

Quote:
2. Well, I may have misunderstood. I thought the lesson was that the microwave beam was the fuel not the power.


Yes, you misunderstood.

Quote:
In fact I am sure that is right - it is the ion flow that is the power isn't it?


An ion flow can be used for power, fuel, or direct propulsive force (that is, it could be the propellant in a reflective system). It generally is not just used for power. Perhaps you would like to tell me exactly which ion beam propulsion system you are thinking of though.

Quote:
So the microwave beam would be the fuel for the power.


Why are you mixing microwave beams with ion beams?

Quote:
3. Fact remains: microwave propulsion is a lot more advanced than your fanciful fountain.


Nope.
Back to top
View user's profile Send private message
MirariNefas
Turquoise
Turquoise


Chapter: No
Joined: 12 Dec 2004
Posts: 2747
Location: LA

PostPosted: Tue Nov 06, 2007 11:07 pm 
Post subject:
Reply with quote

Here's a quote from a recent discussion we had on this topic.

Gourdhead wrote:
Quote:
SpaceNut - You article was v. helpful but I'm still not clear whether microwave beams could fuel a plasma engine.
Microwave beams can power plasma engines--not fuel them. You need an energy source and a propellant source and an infrastructure to maintain each supply. With an energy source of suficiently energetic gamma rays and the ability to generate pair production from them in a controlled manner, you could provide both power and propellants from a single source---very helpful for interstellar travel.
Back to top
View user's profile Send private message
freeyourmind
Yellow
Yellow


Chapter: Yes
Joined: 17 Jul 2006
Posts: 443
Location: Worcester, MA

PostPosted: Wed Nov 07, 2007 11:39 am 
Post subject:
Reply with quote

Right, this is an argument about semantics.

An ion engine turns a gas like argon or xenon into plasma, and then accelerates it through a series of meshes with electrostatic forces. Other variants may use magnetic forces.

The propellant is the gas, the argon or the xenon, while the power is the electricity needed to create those electrostatic forces. A power beam could provide the electrical power to generate the electric or magnetic fields, but you would still be limited by how much argon or xenon you could carry, and how fast you could expel it from the engine.
_________________
"It is difficult to say what is impossible, for the dream of yesterday is the hope of today and the reality of tomorrow."
-Robert H. Goddard
Back to top
View user's profile Send private message Visit poster's website AIM Address
louis
Lime
Lime


Chapter: Yes
Joined: 06 Apr 2007
Posts: 690

PostPosted: Wed Nov 07, 2007 2:41 pm 
Post subject:
Reply with quote

Thanks FYM.

As you say semantics really although if one is going to make the fuel/power distinction then I am not sure Gourdhead got it right. Seems to me the ion stream is the equivalent of steam (power) and the microwave beam is the equivalent of coal (fuel).

I am not sure how practical development of a microwave beam space craft is at present but it seems to me all the essentials are there. As I understand it plasmas can be created from various materials e.g. water. It might even be possible for a beam to create some kind of jet effect in the initial stages, drawing in water vapour from the atmosphere in some part of the world where humidity can be guaranteed to be high and superheating it. Just a guess on my part but I think it would be interesting to explore these possibilities. By getting rid of the mass of the fuel/power, if not the plasma substance, one is making progress.

More semantics...

"Most rockets use liquid or solid chemical propellants. A propellant includes fuel the part that burns and an oxidizer (like oxygen) that enables combustion. Jets use jet fuel and burn it using oxygen. In space, there is no oxygen, so rockets have to carry their own." Quote from rocket website.

Seems to me it is perfectly legitimate to call the aircraft fuel in a jet plane a "propellant". The principle is exactly the same as with a rocket except the oxygen is being drawn from the atmosphere.

I think Mirari has to accept that microwave beam powered propulsion has been demonstrated but a space fountain has not. That doesn't settle the matter as to which is best to develop but it is an indication that at least one is feasible in some form.
Back to top
View user's profile Send private message
freeyourmind
Yellow
Yellow


Chapter: Yes
Joined: 17 Jul 2006
Posts: 443
Location: Worcester, MA

PostPosted: Wed Nov 07, 2007 4:08 pm 
Post subject:
Reply with quote

Ok, ok. It is indeed a matter of semantics, but you should still get it right to enable smooth communication.

The universally accepted meaning for what a propellant does is anything (usually a gas) that is expelled from the engine to provide a reaction force (Newton's 3rd law) and "propel" the craft forward.

The power for that can come from any number of sources, including the propellant itself or electricity or microwave beams... etc.

So you see, based on that quote from Gourdhead, he did get it exactly correct.
_________________
"It is difficult to say what is impossible, for the dream of yesterday is the hope of today and the reality of tomorrow."
-Robert H. Goddard
Back to top
View user's profile Send private message Visit poster's website AIM Address
MirariNefas
Turquoise
Turquoise


Chapter: No
Joined: 12 Dec 2004
Posts: 2747
Location: LA

PostPosted: Wed Nov 07, 2007 4:38 pm 
Post subject:
Reply with quote

Quote:
I think Mirari has to accept that microwave beam powered propulsion has been demonstrated but a space fountain has not.


Microwave beam powered propulsion has been demonstrated as a means for powering craft, but not as a space launch system. The design principles of a space fountain have similarly been tested as means of producing forces in acceleration structures (particle accelerators). In terms of the physics behind the engineering principles, both are well-explored and demonstrated, and neither has been attempted on an appropriate scale for space usage.

Quote:
I am not sure how practical development of a microwave beam space craft is at present but it seems to me all the essentials are there. As I understand it plasmas can be created from various materials e.g. water. It might even be possible for a beam to create some kind of jet effect in the initial stages, drawing in water vapour from the atmosphere in some part of the world where humidity can be guaranteed to be high and superheating it.


The water would also provide an obstacle to the efficient transmission of the beam. The smaller your rectenna on the craft, the more you have to worry about things like this.

By the way, why aren't you considering laser beaming?
Back to top
View user's profile Send private message
louis
Lime
Lime


Chapter: Yes
Joined: 06 Apr 2007
Posts: 690

PostPosted: Wed Nov 07, 2007 6:42 pm 
Post subject:
Reply with quote

Nothing against laser beaming!

Bracket the two together as far as I am concerned.

It would be very interesting if we could get to a position where we could get small packages (say less than 100kgs) into space possibly for robot assembly.

Humans might then be sent up in conventional chemical rockets.

I understood microwaves could operate through clouds.
Back to top
View user's profile Send private message
MirariNefas
Turquoise
Turquoise


Chapter: No
Joined: 12 Dec 2004
Posts: 2747
Location: LA

PostPosted: Wed Nov 07, 2007 8:39 pm 
Post subject:
Reply with quote

Quote:
I understood microwaves could operate through clouds.


Boil some water in your microwave oven and tell me that again.

It depends on the wavelength. Wavelengths that can be transmitted to smaller rectenna are blocked more by water and other atmospheric constituents. The reason microwave energy from solar satellites can be transmitted so efficiently is because they would be beamed to facilities that cover more than a hundred square kilometers. You are certainly free to design a spaceship that large, but I think you'll end up bigger than my space fountain and you'll still need propulsive mass for all that.
Back to top
View user's profile Send private message
louis
Lime
Lime


Chapter: Yes
Joined: 06 Apr 2007
Posts: 690

PostPosted: Thu Nov 08, 2007 8:27 am 
Post subject:
Reply with quote

Thanks for that clarification.
Back to top
View user's profile Send private message
louis
Lime
Lime


Chapter: Yes
Joined: 06 Apr 2007
Posts: 690

PostPosted: Fri Nov 16, 2007 9:22 am 
Post subject:
Reply with quote

Don't want to see the Space Fountain Verticle Accelerator (SFVA) get too far ahead on this site! I still think microwave beams will be more efficient in the long run. Does anyone have any comments on the following link which geos into some detail about experiments:

http: pdf aiaa org preview CDReadyMJPC2003_775 PV2003_4430 pdf

One thing to bear in mind I think is that we aren't necessarily looking to a microwave system to lift huge amounts of mass. As long as you have a system that can lift say 250kg loads, then that is fine as long as the system can do multiple launches in quick succession (that is one of the issues I have with the SFVA - are we sure it can given all the safety issues?). If the system can deliver on that then the name of the game becomes robotic assembly in space of these smaller loads.
Back to top
View user's profile Send private message
Display posts from previous:      View previous topic :: View next topic  
Post new topic   Reply to topic   printer-friendly view     Hacked BY ALAMUT. Forum Index -> Related Topics All times are GMT - 4 Hours
Goto page 1, 2  Next
Page 1 of 2

 
Jump to: