Starship design revamping

Sorry, but GURPS is wrong, and Traveller is much closer to being correct.
For the drives alone it can easily be shown that the "thousand miles to
the gallon" is correct.

First of all, there was a paragraph buried in the original rules that
gave fuel consumption as an option. I worked it out and it gave an Isp
of 600,000 for the drive. (which incidentally matches the figure given
for a "fusion drive" on a chart that NASA seems to have put in 90% of the
secondary school classrooms in the US during the 60's) Isp relates thrust
and fuel consumption as follows: Isp =thrust(in pounds)/fuel consumption
(in pounds per second). Astute readers will notice slight problems with
dimensionality in this calculation. More astute readers will realize
that this is expected when one uses the same unit for mass and force.
Anyway, to get 6 million pounds opf thrust with such a drive (same as a
Saturn V) you need 10 pound per second of fuel. This is enough to move
a 3000 ton ship at 1g. So much for 200 years of fuel...

If you want to figure it yourself, the standard rule of thumb is that a
fusion reaction converts .1% (.001) of the reaction mass into energy. So
you can figure from that how much fuel in needed to get how much energy.
This gives an lower limit for fuel consumption. It'll likely take more as
the equipment isn't going to be 100% efficient at turning the energy released
by the reaction into power or thrust, or whatever.

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[email removed] writes:
> Sorry, but GURPS is wrong, and Traveller is much closer to being correct.
> For the drives alone it can easily be shown that the "thousand miles to
> the gallon" is correct.
>
> First of all, there was a paragraph buried in the original rules that
> gave fuel consumption as an option. I worked it out and it gave an Isp
> of 600,000 for the drive. (which incidentally matches the figure given
> for a "fusion drive" on a chart that NASA seems to have put in 90% of the
> secondary school classrooms in the US during the 60's) Isp relates thrust
> and fuel consumption as follows: Isp =thrust(in pounds)/fuel consumption
> (in pounds per second). Astute readers will notice slight problems with
> dimensionality in this calculation. More astute readers will realize
> that this is expected when one uses the same unit for mass and force.
> Anyway, to get 6 million pounds opf thrust with such a drive (same as a
> Saturn V) you need 10 pound per second of fuel. This is enough to move
> a 3000 ton ship at 1g. So much for 200 years of fuel...

I'm not sure that the Isp is usable for reactionless thrusterplates...
This "fusion drive" is probably more similar to the "fusion rocket"
in the COACC.

I looked fusion up in a physics textbook and it states that for standard
deuterium fusion with all its secondary stages. (First deuterium fuse
with deuterium to produce various hydrogen and helium isotopes and free
neutrons and assorted other radiation. Then some of these products fuse
to make some more energy.)
The book gives the energy gained from fusion of one atom of deuterium
(including all byproducts etc) to 13E-13 Joules.
The occurance of deuterium in hydrogene it states as 15 to 100,000.
(Deuterium is a hydrogene isotope).
One gram (1E-3 kilos, 1E-6 tons) of hydrogene contains 6.023E23 hydrogene
atoms, and will thus yield 11E9 Jouls.
One ton of Tech15 plant uses 0.009 tons of H2 per hour.
This translates to about 99E12 MWatts per per kl of plant per hour or, in
other words, 99,000,000 MW per kl of plant...

(I hope I havn't done any errors too big to explain away:-)
- -bertil-
- --
Bertil K K Jonell @ Chalmers University of Technology, Gothenburg
NET: [email removed]
VOICE: [phone removed] / +46 300 61004     "Don't worry,I've got Pilot-7"
[address removed]                             (Famous last words)
"GOOD DEEL ON SLIGHTLY USED CRANE" Orson Scott Card 'The Abyss'

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[email removed] writes:

>Sorry, but GURPS is wrong, and Traveller is much closer to being correct.
>For the drives alone it can easily be shown that the "thousand miles to
>the gallon" is correct.

No, it isn't. I did similar calculations for High Guard back in the bad
old days
and came to the same conclusion: the power plant/manuver drive did not use
enough fuel to account for the kinetic energy of the ship after
accellerating at
say, 1G for a month.
	The problem is that the MT manuver drives are not rockets! The fact
that they are reactionless has a fundamental effect on how much energy can be
given to the ship in the form of velocity. See below.

 [email removed] writes:

>I looked fusion up in a physics textbook and...

[lots of calculations deleted]

>This translates to about 99E12 MWatts per per kl of plant per hour or, in
>other words, 99,000,000 MW per kl of plant...

Your physics looks fine to me. The way the rules stand, fusion powerplants
are hideously inefficient. It is even worse than your calculations show,
because
you assume the hydrogen has not been enriched in deuterium in any way --
meaning that more than 99.9% of the fuel is just thrown away, or vented for
cooling, or whatever.
	The problem with the Mega-Traveller power plants and manuver
drives is very subtle. The inefficiency of the power plant is masked by the
remarkable (read: physically impossible) efficiency of the manuver drive.
Having a reactionless manuver drive not only lets you violate Newton's
3rd law (reaction for action), but conservation of energy as well! As far as I
can tell, it is impossible to have a reactionless drive without this property.

Example: Take a standard scoutship, which masses 916 tons full, has drives
that require 350 Mw to accellerate it at 2G's, and has enough fuel for a month.
Suppose it accellerates for a month in one direction. At the end of the
month, it
is travelling at 5.08E8 meters per second, giving it a kinetic energy of
1.182E23 Joules.  During that month, the drives have used 3.5E8 * 3600 * 24
* 30 = 9.072E14 Joules, giving an effective efficiency of 1,303,000,000%
(I want a drive like that for my car...)
	The energy to power the drive doesn't have to come from a fusion
plant. It could just as easily come from batteries, or lots of people
riding bicycle
generators. The fact that it usually comes from fusion plants just helps
to hide
their extravagant fuel use.
	The fundamental problem is that the manuver drive uses energy
at a constant rate, but gives the ship kinetic energy that goes up as
the square
of the time, assuming constant accelleration. This means there is NO fixed
number for drive power consumption that won't eventually start giving you
free energy, after going in one direction for long enough.  Sooooo.... if you
want your system to be consistent, you have to give up either reactionless
drives or conservation of energy. I personally favor keeping the drives,
because
they work in game terms, which is really the important part.
	The powerplant problem is more serious, because fusion plants are
used for things other than powering ship drives.  The MT fusion plant outputs
and fuel usage are lifted directly, unchanged, from Striker. This bothers me,
since it makes fusion plants not much better than fuel cells in terms of fuel
use per unit of output. Since they just took the numbers from Striker, and
made them apply to starships as well, I would prefer to go back to the
numbers from High Guard, which worked better (1 kl of fuel to power 1 kl
of plant per month at TL15, instead of 6.48 kl fuel per kl of plant as
it is now.)
If you think things are bad for starships, try designing a robot with a fusion
power source....

	Anyway, I thought people might be interested in the results I got.
Comments and error corrections welcome.

					W. Dow Rieder
				alias Capt. Kagariilian Grant

All opinions and material above is the responsibility of the originator.
Submissions: [email removed], or [email removed]
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[This came to [email removed], looks like it was
meant for [email removed].  Watch those automatic reply
headers! -- James]

W. Dow Rieder writes:

>  [email removed] writes:
>
> >I looked fusion up in a physics textbook and...
>
> [lots of calculations deleted]
>
> >This translates to about 99E12 MWatts per per kl of plant per hour or, in
                                  ^^^^^^
> >other words, 99,000,000 MW per kl of plant...

Oops, I seems to have made a fumble mishap. Well, that's what happens when
one uses a book to gain a temporary skilllevel :-)

The MWatt should have been Joules. This changes the final figure to
27500 MW per kl. Coming from a lump of machinery 1m x 1m x 1m this sounds
somewhat large (to say the least) , so the best solution might be to reduce the
fuelconsumption.
On the other hand, TL15 can be used to justify almost anything :-) so a simple
solution is to increase the fusion pp outputs with a factor 1000.
That way on kl of TL15 plant will produce 6 * 1000 MW, and if it was
part of a 14+ kl plant 6 * 1000 * 3 MW (18,000 MW) which is resonably close
to 27,000 MW.

> 	The problem with the Mega-Traveller power plants and manuver
> drives is very subtle. The inefficiency of the power plant is masked by the
> remarkable (read: physically impossible) efficiency of the manuver drive.

A suggestion, why not correct both things and with the same amount? If both
energy production and energy consumption is increased, lets say, 1000 times
(volume etc left untouched) the net change would be zero (Aside from a
net gain in space available, because the volume of the part of the power-
plant thats dedicated to supply the non-drive components is reduced by a
factor 1000.
Of course, the definition of agility would have to be changed, or else every
tom, dick and harry would have a ship with Agility 6.
As a definition of agility I would like to suggest the enery required to
make the ship rotate along its long axis with a certain speed.
This way, agility would be dependent on the mass of the ship *and* it's
configuration. (A ship with lots of stuff sticking out here and there is
harder to turn than a ship shaped as a sphere.)
Presumably, ships with AirFrame config should also get a agility bonus when
manuvering in atmosphere,because they can use aerodynamics to make faster turns.

- -bertil-
- --
Bertil K K Jonell @ Chalmers University of Technology, Gothenburg
NET: [email removed]
VOICE: [phone removed] / +46 300 61004     "Don't worry,I've got Pilot-7"
[address removed]                             (Famous last words)
"There's a sucker born every month, except february, which have 28!" Alf Tanner

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I suggest that you recheck your figures. You have that starship traveling at
5.0e8 meters/second. But lightspeed is only 3e8 m/s!! And at 1 g, ignoring
relativistic effects, it'll take nearly a year to reach lightspeed.

A month at 1 g gives a velocity of 2.5e7 m/s. This is 1/12th lightspeed and
close enough that you'd have to worry about relativistic effects a bit.
(tau=.997)

The figures *I* mentioned came from the original 3 books. And there was
nothing in there about the drive being reactionless. That's an *assumption*
that was made by so many people that it became official.

A "reactionless" drive can be handled by assuming that it "pushes" on the
rest of the universe. This would give (in effect) double the efficiency
of a reaction drive. Gravitic effects work that way, but then you'd have to
explain why the people inside the ship experience *any* acceleration.

BTW, nobody ever asks what happens to all the helium (and unfused hydrogen)
with reaction drive, no problem. It's the exhaust. But on a ship with a
reactionless drive, you either store it, or dump it. Both require changes
in the way things work.

Dumping it means you leave this nice trail of helium for the sensors to
pick up. Storing it, means that the tanks aren't empty (and leads to
other problems as well).

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[suggestion for defining agility as the amount of energy required to rotate
the ship about its axis at a certain rate]

Sorry, but rotating the ship, and changing course have nothing to do with
each other. Check the rules on plotting space combat in the old rules or grab a copy of MAYDAY. Both use correct physic in showing the result of course changes

If you are going "north" at 5 km/s, and you use the engines to give yourself
5 km/s of "east" velocity, you are now going "northeast" at 7.07 km/s! You have
to kill the "north" velocity and then add the "east" velocity if you want to
go "east". This could be done with one "burn", I *think* it would be a 7.07 km/s
burn applied in the "southeast" direction!!

Ain't physics fun?

ps. don't evenn *think* about arguing that the drives can get around this via
"magic" physics. This stuff is taking place in an area of physics where we
know what the loopholes are. (If you want "inertialess" drives, that's a
different matter, but don't forget to watch you intrinsic velocity!! :-)

All opinions and material above is the responsibility of the originator.
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[email removed] writes:

>I suggest that you recheck your figures. You have that starship traveling at
>5.0e8 meters/second. But lightspeed is only 3e8 m/s!! And at 1 g, ignoring
>relativistic effects, it'll take nearly a year to reach lightspeed.

Dropped a decimal -- should be 5.08e7... thanks for catching that. That
means the drive will only be 13,000,000% efficient. Oh well.

>The figures *I* mentioned came from the original 3 books. And there was
>nothing in there about the drive being reactionless. That's an *assumption*
>that was made by so many people that it became official.

from my post:
>The problem is that the MT manuver drives are not rockets!

I was referring to Megatraveller. Check the Ref's Manual p.56:

"This new, artificially generated force pushes against a vessel's
`thrust plates' themselves, which make true reactionless thrusters
a reality for starship-sized vessels."

Not until MT was the power consumption of the manuver drive given
(High Guard had power plant energy point figures, but that was in
addition to powering the drives.)  There was never anything in the
old set that said the manuver drives were rockets, either. Everyone
I ever discussed it with assumed they were rockets, as did I, since
that was the obvious explanation for the high fuel consumption.  I don't
know what Marc Miller and co. intended them to be at that time. Metlay?
My guess is that they were intended to be reactionless all along, otherwise
why switch?

Bertil Jonell writes:

>A suggestion, why not correct both things and with the same amount? If both
>energy production and energy consumption is increased, lets say, 1000 times
>(volume etc left untouched) the net change would be zero (Aside from a
>net gain in space available, because the volume of the part of the power-
>plant thats dedicated to supply the non-drive components is reduced by a
>factor 1000.

This would cause BIG problems for warship design, since the limiting factor
for many designs is power for weapons, and this would make it 1000 times
easier to get.....  It would probably work better to reduce the fuel needed
for the power plant, while keeping the output the same.

					W. Dow Rieder
				alias Capt. Kagariilian Grant

All opinions and material above is the responsibility of the originator.
Submissions: [email removed], or [email removed]
Administrator: [email removed] (James Perkins)
The TML is made possible by facilities provided by Tektronix, Inc.

[This came to [email removed], looks like it was meant for
[email removed].  Watch those automatic reply headers! -- James]

To Dow, and Bertil, and the other wranglers over fusion drives:

There is no official line about the operation of maneuver drives in
Trav Classic, to the best of my knowledge. The information was codified
and made "official" by Digest Group, probably with no knowledge that
they were asking for trouble from people who could work out the math.
I'll be honest: I avoid starship combat like the plague in this game,
and when I need a starship designed, well, I, uh.... Oh, hell, I may
as well own up and be honest. I get *Dow* to do it for me. There, I've
admitted it, I'm a lazy slob who can't stand the aggravation of
haggling over tonnages when the drives can generate enough free power to
push ANYTHING. So sue me. |->

Anyway, for what it's worth (that and 50 yen gets you a video game), I have
always assumed that fusion drives were reaction based. It makes maneuvers
like the Jerusalem Shuffle take on a whole new meaning.

metlay
(still in Tennessee, argh)

Dow: Nice to see you (and Grant) on TML at last! Welcome! And pass along
my best regards to Rob (Sanchez), Paul (O'Connor), Boris (Kherkhoulloth),
and David (Jaeger). I'll be home in a couple of weeks, and we can get
the game up and running again, so I'll have more story material |-> .

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Submissions: [email removed], or [email removed]
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> [suggestion for defining agility as the amount of energy required to rotate
> the ship about its axis at a certain rate]
>
> Sorry, but rotating the ship, and changing course have nothing to do with
> each other.
> Check the rules on plotting space combat in the old rules or grab a copy of MAYDAY. Both use correct physic in showing the result of course changes
>
> If you are going "north" at 5 km/s, and you use the engines to give yourself
> 5 km/s of "east" velocity, you are now going "northeast" at 7.07 km/s! You have
> to kill the "north" velocity and then add the "east" velocity if you want to
> go "east". This could be done with one "burn", I *think* it would be a 7.07 km/s
> burn applied in the "southeast" direction!!

Imagine two ships:
The first one is a fast smuggler with Manuever 6 and Agility 0
(He trusts his engines to keep away from trouble)
The second one is some type of fighter with Manuever 6 and Agility 6

The smuggler is trying to penetrate a RedZone and the fighter is there to
stop such cases of hooliganism.

They have agreed to use the old Traveller (vector) rules :-)
(In fact, I think that the new MegaT system of Space combat movement is
quite unrealistic, To be able to stop travelling by "circling in the same
square", SHEESH!)

In the combat, both ships would move in a totally similar way, since there
is no provision for the effects of agility in movement.
(Of course, it would still affect firing (if they used higuard  or MegaT
for firing).

That a course change from "north" to "east" requires a "southeast" burn is
pure "Vectors 101", But the problem is *HOW* to *MAKE* the southeast burn.
Since the trustors works best pushing the ship forwards, a ship wanting to make
a burn in a certain direction would have to turn to that direction before making
the burn.

Agility helps to make the ship harder to hit, presumably by enabling it to make
small, rapid changes in course. This would indicate that the agility is a
measure of the ships ability to change course rapidly (It has been stated
officially that the agility is a measure of the ships ability to change course)

If the agility is a measure of the ships ability to change course, and ships
change course by first turning, then burning,and the Manueverrating is the ships
ability to make the burning, then the Agility must mean the turning.

In the example above this could be implemented by plotting which way each ship
points, and letting high agility ships change this direction faster than the
low agility ships. This would make it quite simple for the fighter to follow the
smuggler, and give agility a real impact on space combat aside from just being
the ability to "jinking" the ship to make the opponent miss.

- -bertil-
- --
Bertil K K Jonell @ Chalmers University of Technology, Gothenburg
NET: [email removed]
VOICE: [phone removed] / +46 300 61004     "Don't worry,I've got Pilot-7"
[address removed]                             (Famous last words)
"During the high point of the Downes Age, they put Ming the Merciless in charge
of designing California gas stations" W.Gibson "The Gernsback Continuum"

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Stuff about Mayday, I would have included the mail article, but we have
changed vaxes so the system is without any type of emacs support. And
I don't know vi at all.

I remember playing Mayday once. It was quite fun and very physics intensive.
Also, I remember that the game took forever. We did a space battle between
to 100 ton Scouts with triple turrets, Laser, Sand and Missile. It is
quite an interesting game.

Greg

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