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#1 2017-09-11 09:27:10

louis
Member
From: UK
Registered: 2008-03-24
Posts: 2,340

EM Drive - Interesting development

http://www.dailymail.co.uk/sciencetech/ … ngine.html

Looks like EM Drive might well be a feasible means of propulsion.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#2 2017-09-11 16:20:36

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 10,262

Re: EM Drive - Interesting development

We have these existing topics of discusion to which we really should try to find them when putting forward a new topic.

The EM-Drive Starship

The Impossible Propulsion Drive Is Heading to Space

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#3 2017-09-12 14:18:19

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 2,581
Website

Re: EM Drive - Interesting development

If the thrust is real (and we still don't know that),  the levels seem to be millinewtons.  The hardware to produce it is more than a kilogram,  not counting where the electricity actually comes from.

Assuming the device can be made much more efficient,  thrust levels might be 0.1 to 1 newton,  according to the article,  for those same kilograms of equipment,  plus more kilograms for the source of the electricity. 

You put a few newtons of thrust on multiple tons of vehicle,  and you get no sensible gees of acceleration.  I'm sorry,  but the notion of sending anything to Mars in 10 days (or 30 days,  or 100 days) with this thing,  much less humans with all that life support,  is still utter bullshit.

F = m a

GW

Last edited by GW Johnson (2017-09-12 14:19:42)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#4 2017-09-13 04:49:52

Oldfart1939
Member
Registered: 2016-11-26
Posts: 866

Re: EM Drive - Interesting development

Anything that appears to violate the Laws of Thermodynamics and cannot be fully explained is probably, as GW stated, utter bullshit. This is sort of like many of the supposed perpetual motion machines from years past, and will become another cobweb of history.

To paraphrase the 1st Law of Thermodynamics: You can't get sumthin' fer nuthin'.

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#5 2017-09-13 08:36:18

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 2,581
Website

Re: EM Drive - Interesting development

Well, I find the concept interesting from the standpoint of unexplained results.  There seems to be more than one group working on this,  so there's more reproducibility here than there ever has been with cold fusion.  It certainly deserves further experimentation,  because as history shows,  theories can be modified or replaced with better theories. 

But,  I am healthily skeptical of things that seem to violate the ones we have. And rightly so.  We all should be.

My objection is to the wild claims like "xx days to Mars".  This thing is a thruster.  It produces micro-thrust.  You apply that to a finite mass,  and you get micro-acceleration,  by F = ma,  and there's no need to bring relativity in here as a "better theory", because the speeds are inherently much slower than light speed. 

Like all the other electric/ion propulsion things,  which are also micro-thrusters as we currently know them,  there is no fast trip potential there,  excepting only a little speed-up on the trajectory between escape and capture maneuvers.  Otherwise,  what would be a 6-8 month trip to Mars becomes a 1-1.5 year trip due to spiralling slowly out and spiralling slowly in. 

And THAT is why there is more to deep space propulsion than just Isp!  Raw thrust/weight plays a very important role as well.

GW

Last edited by GW Johnson (2017-09-13 08:39:49)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#6 2017-09-13 12:24:11

elderflower
Member
Registered: 2016-06-19
Posts: 434

Re: EM Drive - Interesting development

Where do we propose to get it's power from? It takes kilowatts to produce microNewtons of thrust (reportedly).  If we use even thin film solar panels it will take years to get one moving due to the self weight of the drive system. Other sources of significant electric power are much heavier.

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#7 2017-09-13 16:22:12

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 10,262

Re: EM Drive - Interesting development

Since the very large solar panels would point perpendicular to the sun we can get the solar wind to push it a bit just as a solar sail would....

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#8 2017-09-15 09:25:46

Antius
Member
From: UK
Registered: 2007-05-22
Posts: 870

Re: EM Drive - Interesting development

The boiling potassium reactor, equipped with MHD generator was estimated to able to achieve P/W of 1kW/kg.  But it wouldn't be an easy technology to develop.

The low thrust of the EM drive might not be such a problem for some mission scenarios.  If we ever do get round to establishing space manufacturing in High Earth orbit, it would be very useful to have a tug that can ferry bulk materials like methane, food, water and heavy equipment from LEO to L5.  If the EM drive can achieve a round trip time of a few weeks, it would be perfectly acceptable, especially if the drive system was essentially maintenance free and could operate for decades with no requirement for intervention.

Another application is interstellar flight.  If it is going to take a century of more to get to the nearest star anyway, then the low acceleration of the vehicle is not an issue, especially if some other means can be used to boost it to solar system escape.  At a constant acceleration of 0.01m/s2, a vehicle could reach a-centauri in about sixty years.  That's as good as any theorised fusion drive.

I still can't get my head around a device that would seem to be a perpetual motion machine.  As velocity increases, the kinetic energy of the vehicle would exceed the total energy expended to accelerate it, assuming thrust remains constant.  That would seem to violate the most basic law of physics.  The other explanations are: (1) It doesn't work; (2) Acceleration declines as speed increases, maintaining conservation of energy; (3) Energy is being drawn from a source that we do not yet understand, i.e. the quantum vacuum.

Last edited by Antius (2017-09-15 09:31:36)

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#9 2017-09-16 06:00:34

elderflower
Member
Registered: 2016-06-19
Posts: 434

Re: EM Drive - Interesting development

I don't think the problem is one of energy balance. There just doesn't seem to be conservation of momentum.

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