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Long cables to power arcjet rockets to orbit?

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Robert Clark

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Mar 20, 2006, 11:23:18 PM3/20/06
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In this post I suggested delivering electrical power to "lifter" craft
using long cables:

From: Robert Clark - view profile
Date: Tues, May 17 2005 2:53 pm
Email: "Robert Clark" <rgregorycl...@yahoo.com>
Groups: sci.astro, sci.space.policy, sci.physics,
sci.electronics.design, sci.electronics.misc
Subject: Long cables to power "ioncraft" to orbit?
http://groups.google.com/group/sci.astro/msg/d33c11b037e41226

However, these lifter devices have only been demonstrated in test
vehicles at grams of thrust. It is also a big question how well they
will work at high velocities.
However, arcjet rockets are a well demonstrated techonology that are
already used on satellites for maintaining their orbits under drag.
I've seen two actually different explanations for their operation. One
is that the high temperatures produced by the electric arc is able to
generate high exhaust velocities. This is true for any propellant used.

However, another explanation I've seen is in regard to when the fuel
is hydrogen. In this case I've seen it explained that the electrical
charge itself at sufficient power causes the bonds in H2 to dissociate.
Then it is known that single H atoms when recombining to H2 release the
highest known chemical reaction energy to weight.
This is known as atomic hydrogen or monatomic (or monoatomic) hydrogen
fuel. It isn't a type of nuclear engine. The terminology just means the
hydrogen occurs as single atoms rather than the usual H2 seen in
hydrogen gas. The specific impulse (ISP) of this fuel could be as high
as 1500 s. The big problem with this fuel is keeping it stable against
it's recombining into H2 when stored in its monatomic form. This still
hasn't been solved:

Use of Atomic Fuels for Rocket-Powered Launch Vehicles Analyzed.
http://www.grc.nasa.gov/WWW/RT1998/5000/5830palaszewski.html

However, you can store the hydrogen in the normal H2 form and use
arcjets to dissociate the hydrogen into its monatomic form. This has
been demonstrated to produce ISP's in the range of 1200 s.
Note that the space shuttle engines have an ISP of about 430 s. Having
an ISP 3 times as high would result in tremendous saving in fuel
required since the mass ratio is an exponential function of 1/ISP.
Question: how much electrical power would be required to produce say
1000 lbs of thrust?


Bob Clark

Damon Hill

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Mar 21, 2006, 12:09:08 AM3/21/06
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"Robert Clark" <rgrego...@yahoo.com> wrote in
news:1142914997.9...@t31g2000cwb.googlegroups.com:

The weight of the cables would be self-defeating, even
if carbon nano-tubes were used.

--Damon

John Schilling

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Mar 21, 2006, 11:28:39 AM3/21/06
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In article <Xns978CD72E4CBAB...@216.196.97.131>, Damon Hill says...

The weight of the arcjets would be self-defeating, even if a
Mr. Fusion(tm) Home Energy Center were used.


--
*John Schilling * "Anything worth doing, *
*Member:AIAA,NRA,ACLU,SAS,LP * is worth doing for money" *
*Chief Scientist & General Partner * -13th Rule of Acquisition *
*White Elephant Research, LLC * "There is no substitute *
*schi...@spock.usc.edu * for success" *
*661-951-9107 or 661-275-6795 * -58th Rule of Acquisition *


--
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tj Frazir

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Mar 21, 2006, 12:45:58 PM3/21/06
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HA HE HA ...dumbest thing you ever said

William Mook

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Mar 21, 2006, 12:57:47 PM3/21/06
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This is an interesting idea. Wire guided munitions certainly show you
can deploy wire fast enough, and light weight wires can stay attached
over kilometers of distance;

http://www.pakdef.info/pakmilitary/army/atgm/redarrow.html

Which is all you need - especially if you use high gees. Let's say you
use an arcjet type rocket to achieve 1/3 orbital speed - that's in
round numbers 2.5 km/sec - with gravity losses, you need say 3 km/sec.
With a 4 gee acceleration you have

D = V^2 / 2a = 3,000^2 / (2*4*9.82) = 114.6 km. - which is 30 times
longer than the 3 km in the red arrow missile for example. Which means
its 30 times the weight. The red arrow by the way masses about 11 kg
at launch, and if we assume 1/4 of the weight is wire - that's only 3
kg of wire for 3 km. So, 114.6 km of this type wire would mass 114.6
kg of mass.

Of course the red arrow just sends guidance signals through the wire,
not power. So, that's an issue. Wire weight goes up with power
capacity. But, I am not aware of any power scaling studies that have
been done. And, there may well be innovative approaches that radically
decrease wire weight - that is, the wire may guide a microwave or laser
beam by ionizing the air for example - and creating a larger conduit
than its mass would suggest! lol.

If we had a 150,000 lb thrust launcher - thats about 75,000 kg or
736,000 N of force you'd need to transmit about 1,400 MW of electrical
energy if your arcjet worked at 850 seconds Isp. If it worked at 1,900
sec Isp, you'd need to transmit energy at a rate of 2,800 MW of
electricity! The size of a power generator needed for a city of 4
million! But only for minutes at a time! lol

Okay, so one can imagine a nuclear thermal rocket on the second
stage...

to get a sizeable fraction of the lift-off mass to orbit.

pete

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Mar 21, 2006, 7:44:21 PM3/21/06
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In sci.space.policy, on 21 Mar 2006 09:57:47 -0800, William Mook
<willia...@mokindustries.com> sez:

` This is an interesting idea.

Continuing in the same spirit of extracting an interesting concept
from your post...

` Of course the red arrow just sends guidance signals through the wire,


` not power. So, that's an issue. Wire weight goes up with power
` capacity. But, I am not aware of any power scaling studies that have
` been done. And, there may well be innovative approaches that radically
` decrease wire weight - that is, the wire may guide a microwave or laser
` beam by ionizing the air for example - and creating a larger conduit
` than its mass would suggest! lol.

I was going to say, nope, nothing like that currently possible, but
what you've got here is reminding me of the lightning studies, where
they call down lightning on demand using a wire guided rocket to
provide a conductive path for the bolt. The wire gets vapourized,
but by that time you've got an ionized current path for the bolt.

So, you launch your rocket in a thunderstorm, while ensuring that
you have insulation to ground so the bolt goes the other way :)

No, but you have a ground based generator that puts out a current
like a lightning bolt, to use the same concept. The problems are 1)
you need a current sink at the other end, even if you're dealing
with AC - the earth works well for lightning bolts, but how do you
convince a bolt to ground itself in the upper atmosphere - (at the
voltages needed you're not going to be able to run two conductors
up the same path!) and 2) you need a thrust device on your rocket
that can make use of such power, not just fuse into a blob, or
acquire a vapourizing ion path across it. This could be a great way
of delivering a lot of power to a rocket, if you could just figure
out a way to handle the form in which it arrives...

` If we had a 150,000 lb thrust launcher - thats about 75,000 kg or


` 736,000 N of force you'd need to transmit about 1,400 MW of electrical
` energy if your arcjet worked at 850 seconds Isp. If it worked at 1,900
` sec Isp, you'd need to transmit energy at a rate of 2,800 MW of
` electricity! The size of a power generator needed for a city of 4
` million! But only for minutes at a time! lol

` Okay, so one can imagine a nuclear thermal rocket on the second
` stage...

` to get a sizeable fraction of the lift-off mass to orbit.


--
==========================================================================
vincent@triumf[munge].ca Pete Vincent
Disclaimer: all I know I learned from reading Usenet.

Jim Logajan

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Mar 22, 2006, 1:17:53 AM3/22/06
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"William Mook" <willia...@mokindustries.com> wrote:
> Wire weight goes up with power capacity.

That is an over simplification. First determine what is considered
acceptable loss - either a certain percentage of the power delivered to the
vehicle (e.g. less than 10% impedance loss) or as much as the wire can take
before melting during the few minutes of boost. Take your pick - depending
on whether you consider your ground station power cheap.

Then determine how much voltage you can apply without arcing taking place
between the supply and return lines. I believe atmospheric breakdown
voltage drops with pressure, so spacers will need to be several meters long
for the portion of the wire reaching the upper atmosphere if the line
voltage is in megavolt range.

> If we had a 150,000 lb thrust launcher - thats about 75,000 kg or
> 736,000 N of force you'd need to transmit about 1,400 MW of electrical
> energy if your arcjet worked at 850 seconds Isp. If it worked at 1,900
> sec Isp, you'd need to transmit energy at a rate of 2,800 MW of
> electricity! The size of a power generator needed for a city of 4
> million! But only for minutes at a time! lol

Fast discharge lead-acid batteries can be purchased retail for for an
effective cost of ~US$0.05/W. Those batteries can discharge at max current
and voltage rates for ~5 minutes - more than sufficient. A 2,800 MW
"powerplant" comprised only of lead-acid batteries would have the
relatively low cost of ~$140M. Then use a ~$1000 generator to recharge them
after each launch, if you really want to save a few bucks and don't mind
waiting a bit between launches.

The thing is, cabled launchers can be scaled down sufficient for
experimentation on small budgets.

tj Frazir

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Mar 22, 2006, 1:19:30 AM3/22/06
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The list of stupidity would be too great to list.
test the cable for us ..please.
Yet here on the ground people ae still stupid.
I cant look at the subject and get past stupid.

William Mook

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Mar 22, 2006, 4:23:31 AM3/22/06
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lol. Why skimp on your generator when you've already spent
$140,000,000 on batteries?

A 50 MW generator could recharge the battery pack in about 19 hours.
And it would cost around $60 million - and you'd burn around 70,000
gallons of fuel to operate it. Batteries last about 3,000
charge/discharge cycles at best. So, you're talking about $47,000 per
launch for battery replacement costs, and another $200,000 per launch
for fuel and maintenance. Say $250,000 per launch.

You could put 9,888 lbs into LEO with a 100,000 lb launch weight using
this approach versus a 100,000 lb conventional rocket which could only
put up 1,671 lbs into the same orbit.

My figures are reproduced below.

A 150 lb rocket would require a system 1/1000th the size and 1/1000th
the cost - but the wire weight goes up as a proportion of the total...

WIRE/NUC TSTO-RLV
1900 Isp
9.82 g0
18658 Ve
3000 Vf
0.1607 Vratio
1.1744 exp(Vratio)
0.1485 u
2970.5 lbs Structure
100000 lbs Total
14853 lbs Propellant
253 lbs Wire
7500 lbs Engine

25576 Stage 1

850 Isp
9.82 g0
8347 Ve
6000 Vf
0.7188 Vratio
2.0520 exp(Vratio)
0.5126 u
7631.0 lbs Structure
74424 lbs Total
38155 lbs Propellant
0 lbs Wire
18750 lbs Engine

64536 Stage 2

9888 lbs Payload
=============================
LOX/RP1 - LOX/LH TSTO-RLV
290 Isp
9.82 g0
2847.8 Ve
3000 Vf
1.0534 Vratio
2.8675 exp(Vratio)
0.6512 u
13025.3 lbs Structure
100000 lbs Total
65127 lbs Propellant
0 lbs Wire
2142.8 lbs Engine

80295 Stage 1

440 Isp
9.82 g0
4320.8 Ve
6000 Vf
1.3886 Vratio
4.0093 exp(Vratio)
0.7505 u
2958.0 lbs Structure
19705 lbs Total
14790 lbs Propellant
0 lbs Wire
285.71 lbs Engine

18034 Stage 2

1671 lbs Payload

Willia...@gmail.com

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Mar 22, 2006, 9:53:46 AM3/22/06
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I was wondering if you could use this approach on a smaller scale to
power torpedoes (as well as guide them)??? Salt water certainly has a
higher capacity to absorb unipolar DC power. Power requirements would
be far lower for this sort of thing than for a rocket, but this might
have the capacity to increase range and speed while reducing torpedo
mass for the same payload on target. So, you could have morer rounds.

This approach might be used to power supersonic torpedoes and make good
use of the supercavitation wake! Of course here, your power discharge
rate would be so high, I would suspect you'd launch the whole system
out of a torpedo tube and fire it conventionally before setting it off
- for safety's sake. lol. Here I'd use super-capacitors that are kept
charged by the nuclear sub's reactor until it was needed. lol The
supersonic round would be only a small part of the entire torpedo mass
in this case. The stationary component might even be outfitted with a
communications link back to the sub for guidance as well.

Firing it conventionally and getting some sort of stand off distance
would also allow the sub to remain more stealthy when the supersonic
round did go off.

ianpa...@gmail.com

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Mar 22, 2006, 9:56:27 AM3/22/06
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There is another alternative and that is to focus lasers onto the
rocket exhaust. I have a feeling that that has actually been tried. It
is in principle quite feasible.

Suppose to want to focus on a 10cm area, and your wavelength is 1
micron. At a distance of 500km. we have 0.2 microradian. At
1.22lambda/d this implies 6m aperture. Not impossible. The Moura Kea AO
system has a diameter of some 10m and 20m is planned.

Jim Logajan

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Mar 22, 2006, 4:49:03 PM3/22/06
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Willia...@gmail.com wrote:
> I was wondering if you could use this approach on a smaller scale to
> power torpedoes (as well as guide them)???

"John Ericsson invented [in] 1873 a torpedo that was cable-powered by an
external source, as electric batteries of that time didn't offer enough
capacity for useful range and speed figures." From:

http://en.wikipedia.org/wiki/Torpedo

Likewise, power was supplied to the Brennan Torpedo through wires - not by
electricity but by the mechanical action of pulling the wires off rotating
drums inside the torpedo! More here:

http://en.wikipedia.org/wiki/Brennan_Torpedo

rgrego...@yahoo.com

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Mar 23, 2006, 11:26:07 AM3/23/06
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Where are you getting a 1900 s number for the ISP? The highest I've
seen was by using hydrogen propellant and that was at 1500 s. Do arcjet
thrusters with 1900 s ISP exist?
Also I thought an arcjet engine would be a trivially simple construct:
basically just two graphite electrodes connected to the wires with high
amp electricity flowing through. Why are you getting high numbers for
the weight of the engines.


- Bob Clark

Robert Clark

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Mar 23, 2006, 9:26:10 PM3/23/06
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This page gives the bond energy of N2 the usual gaseous form of
nitrogen as 946 kJ/mol, 226 kcal/mol:

The Chemistry of Nitrogen and Phosphorous.
http://dwb.unl.edu/Teacher/NSF/C14/C14Links/chemed.chem.purdue.edu/genchem/topicreview/bp/ch10/group5.html

This is higher than the hydrogen amount per mol, but would not be as
efficient on a per gram basis as nitrogen is heavier. But an advantage
is that the nitrogen comes for free in the air; you would not have to
carry a propellant.
Does monoatomic nitrogen release the same energy as the bond energy
when recombining into N2 as is the case for hydrogen?
The page also says lithium reacts with nitrogen N2 in air:

"The strength of the nitrogen-nitrogen triple bond makes the N2
molecule very unreactive. N2 is so inert that lithium is one of the few
elements with which it reacts at room temperature.

6 Li(s) + N2(g) <---> 2 Li3N(s)"

Anyone know what the bond energy of Li3N is? If it is lower than the
bond energy of N2 this might provide a lower energy method of creating
the monoatomic nitrogen, though you would have to carry the lithium on
board.


- Bob Clark

Robert Clark

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Mar 24, 2006, 6:40:05 AM3/24/06
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>
> This page gives the bond energy of N2 the usual gaseous form of
> nitrogen as 946 kJ/mol, 226 kcal/mol:
>
> The Chemistry of Nitrogen and Phosphorous.
> http://dwb.unl.edu/Teacher/NSF/C14/C14Links/chemed.chem.purdue.edu/genchem/topicreview/bp/ch10/group5.html
>
> This is higher than the hydrogen amount per mol, but would not be as
> efficient on a per gram basis as nitrogen is heavier. But an advantage
> is that the nitrogen comes for free in the air; you would not have to
> carry a propellant.
> Does monoatomic nitrogen release the same energy as the bond energy
> when recombining into N2 as is the case for hydrogen?
> The page also says lithium reacts with nitrogen N2 in air:
>
> "The strength of the nitrogen-nitrogen triple bond makes the N2
> molecule very unreactive. N2 is so inert that lithium is one of the few
> elements with which it reacts at room temperature.
>
> 6 Li(s) + N2(g) <---> 2 Li3N(s)"
>
> Anyone know what the bond energy of Li3N is? If it is lower than the
> bond energy of N2 this might provide a lower energy method of creating
> the monoatomic nitrogen, though you would have to carry the lithium on
> board.
>
>
> - Bob Clark

Li3N, lithium nitride, can also be used to store hydrogen:

Lithium Nitride
http://en.wikipedia.org/wiki/Lithium_nitride

This proceeds by reacting Li3N with H2 resulting in LiH. This page
gives the bond energy of of LiH as 238 kJ/mol, 57 kcal/mol:

Chemistry : Periodic Table : lithium : bond enthalpy data
http://www.webelements.com/webelements/elements/text/Li/enth.html?vo=1

However, this states this is for the gaseous form, but using this
number and a molecular weight of 8 for LiH, it would take about 30 kJ
or 7.1 kcal per gram to dissociate it. This compares to the 104/2 = 52
kcal per gram needed to dissociate H2. So it's lower by a factor of 7.
The LiH would be heavier to carry as fuel per the energy produced in
the H + H ---> H2 combining but in regards to the amount of electrical
power that must be delivered to the arcjet this may be more efficient.


Bob Clark

Robert Clark

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Mar 24, 2006, 1:26:26 PM3/24/06
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That was not a good way a measuring its efficiency. The lithium is
essentially just part of the container to hold the monoatomic hydrogen,
so you should not rate it highly because the container weight is
higher. Better is to measure the hydrogen contained to the energy
required to break the bonds. By this measure for LiH, it takes 57 kcal
per 1 mol or 1 gram of hydrogen whereas H2 itself takes 104 kcal per 2
mols or 2 grams of hydrogen. So H2 is more efficient (requiring less
electrical power to run) as the ratio is 52 kcal per gram.
However, we still might be able to get more out of LiH. This page says
it forms from lithium and H2:

Lithium hydride.
"It is produced by reacting lithium metal directly with hydrogen gas to
form lithium hydride:
2Li + H2 ---> 2LiH"
http://en.wikipedia.org/wiki/Lithium_hydride

So after the LiH dissociates to Li and H, we allow the H + H ----> H2
reaction to occur then perhaps following that we could get a 2Li + H2
---> 2LiH reaction.
Question: would the energy we get out of 2Li + H2 ---> 2LiH be the
same as the energy to dissociate the LiH?


Bob Clark

Madalch

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Mar 24, 2006, 2:45:46 PM3/24/06
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> Question: would the energy we get out of 2Li + H2 ---> 2LiH be the
> same as the energy to dissociate the LiH?

If you read up on Hess's Law, you should be able to get the answers to
your questions.

Message has been deleted

William Mook

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Mar 27, 2006, 9:53:14 PM3/27/06
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Where did I get my Isp figure? Well I gave a range of 850 to 1900 - I
used the highest number of which I was aware.

Your figure of 1500 falls near the upper end of that range.

Your question is pointlessly argumentative in my view. You ask a
question and expect me to answer it though its not well formed since
you didn't provide details around your 1500 sec figure.

So, what's your point? To create more argument? I'm not up for it.

The only thing I will say is that your lower figure might not reflect
everything that can be done with an external power source to boost Isp.
But that's pretty obvious.

For example, if you ower the mass flow rate at a given power level
below a certain threshold you can create monoatomic hydrogen with your
arc - and then if your work your details right, cause the hydrogen to
recombine efficiently in the engine, boosting your performance -
keeping a portion of the monatomic hydrogen frozen in the resulting
super-heated stream - recombining only a portion of it - this will
lower your molecular weight along with increased temperature, and get
you specific impulse figures higher than 1900 seconds even.

You can also do other things as well with the current to boost things -
so, I thought the 1900 figures was a reasonable upper end..

I also disagree that these engines are trivially simple. Nothing that
operates at the power levels, the temperatures and the pressures of the
proposed engine is trivial. If its trivial I challenge you to make
one! lol.

As to the engine weight - why are you being so cranky? You pitch a fit
about the weight I assume for the engine without giving any rationale
or proposed weight except make a general statement about how simple the
engine is How much do you think the engine should weigh? lol.

As for me, I assumed a 150,000 kg thrust and a 7,500 kg engine.
That's a thrust to weight of 20:1

http://en.wikipedia.org/wiki/Thrust-to-weight_ratio

T/W of 70:1 is typical of engines like the RD180.

So, I'm assuming the thrust to weight is 1/3 that of a typical rocket
engine. I think this is rational. Two reasons, the first, is the mass
flow rate,is lower with pure hydrogen which lowers thrust for a given
weight. Second, you said it yourself - arcjets have electrodes! How
thick is your graphite? Is your engine reusable? How much graphite do
you carry?

I think a conservative estimate would be engine weight double due to
the extra graphite you're carrying around. And, then a thrust 54% that
of an equivalent engine burning LOX/RP1.due to lower mass flow rates
achievable with pure hydrogen.

Robert Clark

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Mar 28, 2006, 2:29:36 PM3/28/06
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I wasn't being cranky, just impatient for affordable space access.
Robert Zubring in his book "Entering Space: Creating a Spacefaring
Civilization", published 1999 notes that current launch prices on
expendable rockets are in the $10,000/kg range, but the actual energy
cost for sending body to space is quite small:

"The energy required to place a kilogram in orbit around Earth is 32
million Joules, or 9 kilowatt-hours. At current U.S. electricity
prices, this much energy could be bought off the grid for 45 cents -
which would indicate that our 100-kg passenger should be launchable for
about $45!"
Entering Space, p.22.

He notes though the cost itself should be higher than this because
there is the energy cost of bringing the vehicle to orbit and the cost
of fuel as well. He gives an estimate of $100/kg as a reasonable cost
for sending mass to orbit, or $10,000 for a 100-kg passenger.
However, let's go back to the pure energy cost. If there were a simple
way of transmitting the energy the required distance and of converting
the energy to propulsive thrust, this would result in dramatic
reduction in lost cost.
That's why I'm suggesting transmitting the required energy as
electrical power over power lines, something already well established
even over tens to hundreds of kilometer distances.

Bob Clark

William Mook

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Mar 28, 2006, 5:36:52 PM3/28/06
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I see,

Well perhaps I was being cranky. lol.

Beamed energy is an interesting concept. Laser energy is one
possibility. Laser energy can be used directly to produce the needed
thrust, as in laser sustained detonation, or laser thermal propulsion.

http://en.wikipedia.org/wiki/Laser_propulsion

The problem with this is the cost of laser photons. Even so, lasers
can be 60% or more efficient.

http://compoundsemiconductor.net/articles/news/8/6/14

And beam steering isn't really an issue with conjugate optics;

http://en.wikipedia.org/wiki/Nonlinear_optics
http://www.physics.montana.edu/students/thiel/docs/FWMixing.pdf#
http://www.wiley.com/WileyCDA/WileyTitle/productCd-0471439576.html

Which can use a weak pilot beam originating from the target to inform a
much more powerful power beam originating from the laser source.

A payload must be travelling at 7 km/sec to attain orbit. But,due to
air drag and gravity losses (lifting against gravity) rockets typically
must attain 9 km/sec ideal final speed. Converting this to energy is;

E = 1/2 * m * V^2 = 0.5 * 1 * 9,000^2 = 40.5 MJ per kg

With 60% conversion efficiency, and another 50% loss due to
transmission and reflectance losses, we have a 30% efficiency overall.
Conversion from thermal to electrical power is 40% efficient - and this
is 12% overall..

Oil costing $61 per barrel, has 6,100 MJ - so, this is 100 MJ per
dollar. So, the energy costs alone will be 12 MJ per dollar. That's
$3.38 per kg to orbit.

Capital costs are around $1.50 per watt for the generator, and $10 per
watt for laser, and $8.50 per watt for the beam steering apparatus.
That's a total of $20 per watt. Cost of this is around $2 per year -
and if its used more than 100x per year - that's $0.02 per watt per
launch. Add another $0.01 per watt per launch for maintenance - a total
of $0.03 per watt per launch.

Worst case the 40.5 MJ per kg will translate to 486 MJ per kg. If the
acceleration cycle is 10 minutes, that's 600 seconds, so, we're talking
810,000 watts per kg. At $0.03 per watt - that's $24,300 per kg per
launch for capital expense. So, this is the killer.

A more careful analysis,using more optimistic numbers, the result of a
development effort,we'd have;

Capital cost is 10% per year of capital expense, and we use it 100x per
year,so capital cost per launch is 1/1000th the capital cost total -
then figure how much energy must be processed per launch, divide by the
number of seconds per launch, and get the power rating.

ENERGY COSTS: $3.38 per kg

CAPITAL COSTS (advanced): $849 per kg - 100x per year

$0.60 per watt for generator at 486 MJ per kg - 810 kW - $486 per kg
$1.00 per watt for laser at 194.4 MJ per kg - 324 kW - $324 per kg
$0.20 per watt for beamsteering 116.6 MJ per kg - 195 kW - $39 per kg


Since there are 526 ten minute periods between launches here, we can
see that it is possible to reduce costs by this factor if we use the
laser launcher continuously.

CAPITAL COSTS (advanced/high volume) $1.62 - 52,600x per year

Each kg of payload or vehicle in a space vehicle costs about $1,000 pr
kg. If the same vehicle is used, 100x per year, we can say this adds $1
per kg to the launch cost.

VEHICLE COSTS: $1.00 per kg

So, we have $6.00 per kg - with advanced high volume launcher. If
vehicles can launch 1,000 kg into LEO at a time, with 52,600 launches
per year, that's 52,600,000 kg into LEO a year - to achieve these
costs. At 300 kg (including support equipment) per person, this is 3
people per flight and 157,800 people - each paying $1,800 per
passenger.

With a launch rate 1/12th this rate, once every two hours - we have
$23.82 per kg and $7,146 per person and around 1,100 people per month
launched to orbit.

http://www-phys.llnl.gov/clementine/ATP/Lsrprp1.gif

Unless there are economies of scale,this system favors smaller vehicles
that are launched more often rather than larger vehicles launched less
often.

William Mook

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Mar 29, 2006, 11:12:56 AM3/29/06
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We can also see how cheaply we must make things in order for ballistic
transport to be as inexpensive as automotive transport .

We get down to $100 per kg for the vehicle - a factor of 10, and we get
down to about 1% of the cost of the advanced lasers and so forth we
described earlier.

I believe the vehicle costs can be achieved through automation and mass
production techniques. I believe the costs of the laser energy as well
as the laser itself can be reduced through adoption of orbiting solar
pumped lasers - operating continuously to provide energy to everyone on
Earth in an optical power net.

While we are several decades away from this visionary system, I do
believe there are not technical roadblocks to its ultimate achievement.
In the end, we'll have tens of thousands of orbiting thin film
mirrors, each two kilometers or more in diameter. These mirrors will
concentrate light onto solar pumped laser systems, each mirror
simultaneously direct beams of laser energy to hundreds of thousands of
targets in its field of view using nonlinear optical systems - at a
cost of pennies per kg moved. So, we can fly to orbit for $18 instead
of $1800 - and fly anywhere on Earth for about the cost of what it
takes to drive across town a half hour away.

This technology, when combined with wireless global broadband from
space, and wireless navigation from space - will make of the Earth -
truly - a global village. And, space homes in Earth orbit, will be the
preferred mode of living- and orbiting factories orbiting farms and
orbiting forests fed by captured asteroids become the preferred mode of
industry. The Earth's surface will become a vast residential nature
preserve without roads or large cities - except for historically
important ones.

Just as the automobile created the suburbs, and spelled the end to
downtowns, the personal ballistic flier, if it ever comes about, will
spell the end to cities and nations altogether.

Beyond Earth, expansion of efficient means to capture sunlight can
expand our reach across the cosmos by lowering cost of energy another
factor of 3.

Cellular automata - small optical cells automatically mass produced in
deep space from asteroidal materials throughout the solar system - will
use sunlight to navigate into a tight orbit inside the orbit of
Mercury. Trillions and ultimately quadirllions of cells will form a
thick haze that intercepts all available sunlight and converts it to a
broad range of laser frequencies. The haze will have the capacity to
operate as a single optical device for billions of receivers throughout
the solar system. Sunlight to each of the planets and other smaller
bodies in the solar system - down to individuals floating between
planets - can easily be regenerated and maintained for all objects the
system detects. But, more importantly, ultimately, the entire output
of the sun can be captured and put to industrial use. These uses
include moving space homes - the size of small colonies in current
design literature - privately owned - throughout the solar system and
beyond, using laser rockets as well as laser light sails.

In this way people will come to travel throughout the solar system as
easily as we now travel around the US - and we will send
self-reproducing industrial seeds to nearby stars to engulf them in a
similar system of energy capture, and use, and use that energy to
remake portions of those distant star systems into habitats, spare
parts, and supplies for arriving tourists (who return home), settlers
(who stay) and explorers (who move on).

Again, while the details of this grand vision may take a century or
more to work out cost effectively, there is not technically infeasible
aspect to it.

When many star systems have been settled with human inhabitants, each
with its own power source and industrial system fed by local planetary
and asteroidal resources found around those stars - star systems may
decide to cooperate in a large experiment. The making and shaping of
large pieces of Iron-56 - locally - and dispatching them to a point in
space at a time so that a dozen or so pieces totally thousands of tons
in mass, collide perfectly at 1/3 light speed or more. Creating a
massive implosion of mass. Ultimately creating an engineered black
hole, or through patterning the pieces and timing their arrival and
varying their arrival vectors, creating an engineeered black hole dust
consisting of tens perhaps thousands perhaps more black holes each with
its own engineered property each interacting with the others in
controlled ways.

What could humanity do with such an engineered product?

Its hard to tell.

But we might speculate.

We might create time machines, faster than light travel, or time
telephones, or faster than light communications, and computing systems
based to time circuits - which others have worked out in more detail,
and perhaps if we're very lucky, we'll find ways to tap into the zero
point energy with these products in a way so that these products can
self reproduce using no more than the vacuum itself to do so..

This will take several centuries to work out and make real - but at the
end of that period - a period of time nearer to us than William the
Conquerer is to us today - we may have some very capable devices to not
only explore the galaxy, but to explore ALL of space and time.

Some have even speculated that robotics and computer science may reach
a point where we will 'upload' our personalities into a machine system
so as to become essentially immortal. Computers built around
collections of engineered black holes, powered by quantum fluctuations
occuring in the vacuum, may be the ultimate expression of this idea of
immortality - which would allow those inhabiting this virtual world to
communicate effectively with any point of space and time at essentially
zero cost - throughout the multi-verse (the many universal histories
that the big bang gave rise to, whether they have decohered or not into
separate time lines)

This I think is the ultimate promise of technology to humanity, and
perhaps humanity's ultimate gift to the universe.

Another answer to Fermi's Paradox - Where are they? They're waiting
for us! lol.

Cheers

Robert Clark

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Mar 31, 2006, 1:05:07 PM3/31/06
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rgrego...@yahoo.com wrote:
> William Mook wrote:
> > ...
> > WIRE/NUC TSTO-RLV
> > 1900 Isp
> > 9.82 g0
> > 18658 Ve
> > 3000 Vf
> > ...

>
> Where are you getting a 1900 s number for the ISP? The highest I've
> seen was by using hydrogen propellant and that was at 1500 s. Do arcjet
> thrusters with 1900 s ISP exist?
> Also I thought an arcjet engine would be a trivially simple construct:
> basically just two graphite electrodes connected to the wires with high
> amp electricity flowing through. Why are you getting high numbers for
> the weight of the engines.
>
>
> - Bob Clark

If the monatomic hydrogen gives an ISP of 1500 and the usual H2 +
oxygen propellant gives an ISP of 430, could you combust the H2 formed
after the recombination of the monatomic hydrogen with oxygen to get an
ISP of 1930?
Even better, after the monatomic hydrogen recombines to H2 could we
apply electrical power again to it to get more thrust?
The question is would the thrusts be additive in these cases? For in
both cases the H2 is exiting as exhaust, so how could its reuse add
additional thrust to the rocket? Why would it be pushing against the
rocket on its reuse?
The question is similar to what happens with afterburners. In jet
exhaust, some oxygen remains uncombusted in the exhaust stream. Then
afterburners inject some fuel in the exhaust stream creating greater
thrust. Presumably there is some portion of the jet engine that this
further combustion product can expand against to provide the additional
thrust.
So the idea in our case is that the extra combustion could still
expand against some part of the rocket so it indeed would form
additional thrust.
In the case of the H2 dissociating and recombining repeatedly, we
would probably have to design the combustion chamber and nozzle so we
could do the process repeatedly while the fuel remained within the
confines of the rocket.



Bob Clark

Robert Clark

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Apr 1, 2006, 10:27:19 AM4/1/06
to
Robert Clark wrote:
> ...

>
> This page gives the bond energy of N2 the usual gaseous form of
> nitrogen as 946 kJ/mol, 226 kcal/mol:
>
> The Chemistry of Nitrogen and Phosphorous.
> http://dwb.unl.edu/Teacher/NSF/C14/C14Links/chemed.chem.purdue.edu/genchem/topicreview/bp/ch10/group5.html
>
> This is higher than the hydrogen amount per mol, but would not be as
> efficient on a per gram basis as nitrogen is heavier. But an advantage
> is that the nitrogen comes for free in the air; you would not have to
> carry a propellant.
> Does monoatomic nitrogen release the same energy as the bond energy
> when recombining into N2 as is the case for hydrogen?
> ...
> Bob Clark

This page appears to suggest it would:

Plasma Flame Theory.
"Plasma flames for thermal spraying can produce temperatures around
7,000 to 20,000K far above the melting temperature (and vapour
temperature) of any known material. The extreme temperature of the
plasma is not the only reason for the effective heating properties. If
for example helium gas is heated to around 13,000K without a plasma
forming, it would have insufficient energy for normal plasma spraying.
Nitrogen on the other hand heated to 10,000K going through dissociation
and ionisation forming a plasma is an effective heating media for
thermal spraying, being able to supply about six times more energy than
an equal volume of helium at 13,000K. The plasma is able to supply
large amounts of energy due to the energy changes associated with
dissociating molecular gases to atomic gases and ionisation which occur
with little change in temperature.

N2 + E = 2N
Diatomic molecule of nitrogen + energy gives 2 free atoms of nitrogen
2N + E = 2N+ + 2e-
2 free atoms of nitrogen + energy gives 2 nitrogen ions and 2 electrons

The reverse process provides most of the energy for heating the spray
material without a dramatic drop in temperature:

2N+ + 2e- = 2N + E
2N = N2 + E
Nitrogen and hydrogen are diatomic gases (two atoms to every molecule).
These plasmas have higher energy contents for a given temperature than
the atomic gases of argon and helium because of the energy associated
with dissociation of molecules."
http://www.gordonengland.co.uk/pft.htm


Bob Clark

William Mook

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Apr 1, 2006, 3:17:38 PM4/1/06
to


Your question and observation tells me that your understanding does not
seem to derive from a fundamental appreciation of the physics involved.


Its all a matter of temperature and molecular weight. Temperature is a
function of how much energy you can put into a given mass of
propellant.

Yes, if you limit your temperature to the energy you can put into the
mono-molecular hydrogen through recombination you are limited to 1500
sec Isp or thereabouts (depending on details) But, if you exhaust
superheated mono-molecular hydrogen - you can have any exhaust speed
really - depending on how much energy you kick it with.

The other question can you do this efficiently? Well, if you get some
of the gas, it doesn't have to be total - if you can get some of the
gas into a conductive state, you can kick it with magnetic fields, and
since you've got a helluva lot of current flowing through the gas
anyway, it makes sense to shape your electrodes to take advantage of
this if you can.

Lots of numbers are quoted in the literature, understanding where those
numbers come from is more important than what they are. Some have
proposed electrical systems with Isp up to 30,000 sec! But what are we
proposing here?

I believe 1900 is achieveable with arcjets - and in fact you'll get the
best engine weight for Earth launch using this number, assuming zero
weight power plant (because its on the ground!)

You can find all sorts of numbers quoted based on what sort of analysis
the engineers or scientists have gone through.

http://www.nuclearspace.com/A_HEADNA.HTM

Here's a URL that talks about thermo/electric propulsion achieving
3,000 sec Isp.

Which number is right? Well, that depends on the details, and the
number you actually get will depend on precisely how you've elected to
build your rocket.

http://en.wikipedia.org/wiki/Rocket_engine

The idea of removing the power source from the rocket allows us to
consider arcjet rockets in applications they otherwise would not be
suited for. In this regard, they are more like nuclear rockets, with
the mass of the electrodes and power coupling replacing the mass of the
nuclear reactor;

http://en.wikipedia.org/wiki/Nuclear_thermal_rocket

Here, temperatures are limited by the materials used to heat the
propellant, again, similar to a nuclear thermal rocket.

http://www.pma.caltech.edu/~chirata/deltav.html

This is one of the coolest URLs around. It shows our relationship in
terms of delta-vee to the rest of the solar system. All you have to do
is put in thrust requirements per kg and you'll get a true picture in
terms of momentum! lol.

http://trajectory.grc.nasa.gov/aboutus/papers/STAIF-2003-177.pdf

This URL is a pretty complete analysis of current thinking on what you
can do with electric propulsion. Here you're carrying the nuclear
power source around with you, so your power to weight sucks, which
means that your thrust to weight sucks - so your application is
limited.

But if you can change the power/weight ratio by beaming or some other
way keeping your power plant stationary and off the vehicle, then you
can use any of these techniques in higher thrust applications than
discussed here - since power determines thrust, and high power with low
weight means you have higher thrust to weight ratios and high thrust
to weight is essential to operation off of planetary surfaces like
Earth.

If you've got God's own current available at zero weight you can use
any of these techniques in this paper to produce thrust. The highest
specific impulse quoted here is 8,000 seconds, over 4x what I quoted -
and much closer to the 1500 sec you seem bent on defending (because you
read it somewhere and don't really understand how its arrived at?) lol.

The question is why I chose 1900 sec Isp and not a higher Isp! lol.

The answer is thrust to weight of an arcjet rocket - and how it scales
with increasing Isp. 1900 sec is about the best you can do if you want
high thrust to weight and your power plant is zero weight (since its
not carried along with you)

To understand this you've got to go back to the fundamentals;

http://www.qrg.northwestern.edu/projects/vss/docs/Propulsion/3-how-you-calculate-specific-impulse.html

Which are given pretty much at the URL above.

This can be approximated by;

(Ve)^2 = Rgas * T

Where; Ve= Exhaust velocity
Rgas = constant for gas
T = temperature (in Kelvins)

http://www.qrg.northwestern.edu/projects/vss/docs/Propulsion/3-how-you-calculate-specific-impulse.html

And specific impulse is

Ve = Isp / g0

Where g0 = 9.82 m/sec/sec

Rocket science isn't this easy, and this is merely handwaving - that's
why I find this discussion unsatisfying because it doesn't get down to
the basic physics of what's going on. And what goes on depends
strongly on a lot of details.

Okay, so, breaking this down to just one of the details, by fixing it,
if you are are using a delaval type nozzle in your arcjet engine, when
you change the temperature and pressure in the throat of the engine
you're changing the sound speed, and when you expand that to a vacuum,
or to atmospheric pressure, you get an exhaust speed that's three to
five times sound speed in the throat

http://en.wikipedia.org/wiki/Speed_of_sound

In an ideal gas sound speed is given by;


c^2 = k * R * T / M

Where

c = sound speed
k = adiabatic index
R = gas constant (again)
T = absolute temp (Kelvins)
M = molar mass of gas

So, you see that when you put together all this gobbledy gook when you
exhaust mono-atomic hydrogen with molar mass of 1, you increase the
sound speed by 40.4% from normal old hydrogen whose molar mass is 2 -
so the impact of your temperature rise, which is produced by the arc
you're creating, is increased by that amount.

Now, there is a cost in making the H2 molecules into H atoms - that's
the energy per mole to separate things out. This energy doesn't
increase the temperature, so you've got to choose a temperature where
the advantage due to lower molecular weight outweighs this loss in
energy due to phase change. And this happens around 1900 sec irc. Any
increase in Isp beyond this causes large increases in power (in a
constant thrust system, increasing Isp increases power demand by the
square of the Isp increase) which means big increases in engine weight,
and lowered thrust to weight - which is a no no for high thrust launch
from planetary surfaces. lol.

Is this detailed enough for ya? lol. These were just my thoughts on
the subject as I posted.

I also pulled up some other useful stuff relating to high Isp and large
electric power sources;

http://pdf.aiaa.org/jaPreview/JPP/2006/PVJA15337.pdf
http://www.answers.com/topic/variable-specific-impulse-magnetoplasma-rocket

The vasimir concept can use magnetic plasma techniques to raise Isp of
hydrogen ions to the 30,000 sec range. The cool thing about this is
that you can vary Isp, sort of like varying gear ratios in a mechanical
system - and you can adapt the engine for a variety of applications! A
constant power source can give high to low thrust depending on how you
set the engine up.

But these are very low thrust systems due to the large weight for a
given power output. But this can be improved by operating reactors in
unusual ways;

http://en.wikipedia.org/wiki/Gas_core_reactor_rocket

Its all a matter of temperature. But its easy to see its all a matter
of temperature.

This is why I like the simplicity and ease of anti-proton triggered
fusion reactions that produce alpha particles. Boron-hydride for
example, in tiny nuclear pulse rockets. Here Isp in the 100,000 sec
range is possible and at high thrust - essentially solving the problem
of practical spaceflight.

Of course, if succesful, this raises the issue of practical
thermonuclear hand-grenades! lol. Which I think is one of the reasons
we don't do this sort of thing.

I vote for doing it anyway and solve the thermonuclear hand-grenade
problem directly and not limit space faring technology because of this.

Robert Clark

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Apr 1, 2006, 5:22:56 PM4/1/06
to

There appear to be two different mechanisms discussed for the
operation of the arcjets and I was conflating the two. If you consider
purely the *chemical* energy produced by using monoatomic hydrogen then
you get an ISP of 1500 s. ONE way of creating the monoatomic hydrogen
is by using an electric arc to split the H2 bond. In this case, you are
only concerned with supplying sufficient energy to split the bond,
whether that energy is in thermal or electrical form.
However, the way the arcjets are actually operating in practice is
that the arcjets are being used to heat the propellant whatever it is
to high plasma temperatures. In this case you can get very high ISP by
supplying sufficient energy to get the temperatures you want. The high
temperatures do cause the fuel to dissociate but it's the high
temperature itself that is the origin of the high thrust.

The method of combusting the H2 with oxygen after it had recombined
from monoatomic H wouldn't work to produce a greater ISP. The thrust
would be higher, but the ISP's wouldn't be simply additive because you
are also increasing the propellant flow rate with the oxygen. The new
ISP would be some number between the two ISP's.
However, I believe the method of repeatedly recombining and
dissociating the hydrogen itself would work to create a higher ISP. In
this case you are not using additional propellant but are using the
same propellant over and over again. At each stage you are supplying
additional energy to the fuel which would account for its increased
velocity.
However, it may be that it would be more efficient to supply the same
total energy to the hydrogen initially.


Bob Clark

William Mook

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Apr 1, 2006, 7:17:58 PM4/1/06
to

Okay.

>. If you consider
> purely the *chemical* energy produced by using monoatomic hydrogen then
> you get an ISP of 1500 s.

Correct. There's only so many joules per kg of material and that
limits the speed of the molecules.

> ONE way of creating the monoatomic hydrogen
> is by using an electric arc to split the H2 bond. In this case, you are
> only concerned with supplying sufficient energy to split the bond,
> whether that energy is in thermal or electrical form.

Yes, if you supply just enough,and then get it back out. You can do
this too with a nuclear power source too.


> However, the way the arcjets are actually operating in practice is
> that the arcjets are being used to heat the propellant whatever it is
> to high plasma temperatures.

Yes, and since plasma is conductive, you can actually use the current
flow itselt to help speed up the flow too!

> In this case you can get very high ISP by
> supplying sufficient energy to get the temperatures you want.

Yes. And the materials you make your electrodes out of and the other
materials, can limit the temperatures available to you.

> The high
> temperatures do cause the fuel to dissociate but it's the high
> temperature itself that is the origin of the high thrust.

The temperature is a measure of the amount of energy in the system.
Exhaust speed is proportional to the square root of the temperature.
So, to double the exhaust speed you must quadruple the temperature!

Thrust is the product of mass flow rate and exhaust speed.

Power is equal to one half the mass flow rate times the exhaust speed
squared.

Exhaust speed is specific impulse times earth's surface gravity (9.82
m/s/s)

If you know Isp and thrust of an engine, you can calculate the mass
flow rate by rearranging the first relation for the engine and
substitute that mass flow rate in the second relation to figure out the
power of the engine.

> The method of combusting the H2 with oxygen after it had recombined
> from monoatomic H wouldn't work to produce a greater ISP.

It would add directly as you implied in one of your posts. If you
added the energies - and there were no losses - then you take the
square root of the energies to get the added exhaust speeds.

As ratios lets say that recombination energy is 1 and the energy added
by adding Oxygen adds 0.4 - so the energy of the combined jet is 1.4
taken together. The rise in exhaust speed, with all things being
equal, is 1.183 - the square root of 1.4 - ALL THINGS BEING EQUAL - but
of course they aren't equal because each gram of hydrogen in the first
mass flow stream would be combined with 6 grams of oxygen in the second
mass flow stream, which means that 1.4x energy would be divided by 7x
the mass flow rate, which REDUCES exhaust speed to about 44% of the
monoatomic hydrogen stream alone - square root of 0.2.

> The thrust
> would be higher, but the ISP's wouldn't be simply additive because you
> are also increasing the propellant flow rate with the oxygen.

Yes. E = 1/2 * m * Ve^2 - of course, if your m becomes dm/dt (aka
mdot) then E becomes dE/dT or Power (P) -

But normalize everything as a steady state - over one second say - and
then you can see that you can increase exhaust speeds if you increase
the amount of energy per unit mass - and adding oxygen at an optimal
ratio - 6:1 Oxygen:Hydrogen - then, you've increased mass flow 7x even
if you increase the energy of the jet, which lowers the jet speed. Jet
being the exhaust jet out of the engine.

> The new
> ISP would be some number between the two ISP's.

No, it would actually be lower. - but higher than the Hydrogen and
Oxygen by itself. Check it out,

Mono-atomic hydrogen jet: 1 energy unit, 1 mass flow unit 1
exhasut speed unit
Hydrogen oxygen jet 0.4 energy unit 7 mass flow unit
0.25 exhaust speed
Mono + Oxygen 1.4 energy unit 7 mass flow unit
0.44 exhaust speed

So, if you have a convenient way to 'freeze' in the monoatomic hydrogen
you can increase Isp over hydrogen and oxygen alone, but hydrogen all
by itself can really kick ass!

> However, I believe the method of repeatedly recombining and
> dissociating the hydrogen itself would work to create a higher ISP.

This is akin to a phase change - and it happens at a particular energy
- an is a way of wasting energy. Its not a way of increasing
temperarture of the gas any more than repeatedly freezing and thawing
ice, or boiling and recondensing steam increases the temperature of the
water involved.

You pump in a lot of energy into the exhaust jet as efficiently as you
can, and when you reach the point where hydrogen disassociates, you
have a kink in the specific impulse curve, - but to get it to go
higher,you just keep adding energy - not by cycling around the phase
change where the kink occured, but by dumping in more energy - with
more current, or whatever it is you're using for energy.

> In
> this case you are not using additional propellant but are using the
> same propellant over and over again.

Going from mono-atomic to di-atomic form is akin to a phase change.
It occurs at certain conditions and absorbs lots of energy - which show
up as frozen flow losses - the only way to overcome this loss is to
stop adding energy when you get there, and let the material recombine -
which limits you to 1,500 sec as you pointed out. Or, take advantage of
the lower molecular weight of the mono-atomic hydrogen to make good use
of the heat energy you add, to get even higher temps.

> At each stage you are supplying
> additional energy

Which comes back out when it recombines - and you pump back in.
Remember, you want to change the stagnation temperature of the exhaust
jet. You're not doing that by cycling the phase diagram around a single
point. You have to deal with this phase change, sure, but the only way
to get more performance is to keep pumping energy in by adding more
current or whatever - if your electrodes can take it.

> to the fuel which would account for its increased
> velocity.

Temperature is proportional to velocity squared. The phase change you
are talking about occurs at a specific temperature - so, cycling
through that point guarantees you won't heat the system.


> However, it may be that it would be more efficient to supply the same
> total energy to the hydrogen initially.

I don't know what you mean by this. You add energy to the propellant
any way you can - in the case of an arc jet, that's by passing huge
quantities of current through the gas as it enters the 'combustion'
chamber - and is compressed to sonic conditions at the throat. Then,
you expand it, to get a lot of that heat out - and turn it into exhaust
speed. You increase voltage, or current, or both, to put more power
into your propellant flow - that's all you really need do. When you do
this, you'll find that your electrodes want to melt,and your throat
wants to melt, and the propellant wants to eat away at the rocket
engine, and all sorts of things and well, you're limited by the
materials you've got to work with.

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