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Speculations on spaceship (esp. Rider) drive and fuel



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>From: Onno Meyer <Onno.Meyer@arbi.informatik.uni-oldenburg.de>
>Subject: cherryhlist
>Date: Fri, 21 May 1993 10:38:29 +0200 (MET DST)
(...)
> 	Yes. She states somewhere in _DS_ that a carrier can hit up
> to 10G, with the synced rotational crew-cylinder. If you do the calculations
> though, the Norway breaks dock at Pell at XX:00, and at YY:00 it is
> going .75C. Plugging the numbers into your standard newtonain acceleration
> you get the Norway accelereating at 43G!
But todays rockets spent a huge percentage of their mass to operate for shorter periods of time with less acceleration. What kind of exhaust velocity would be required for the carriers? (...)
Onno
(...)

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>From: Jo Jaquinta <jaymin@maths.tcd.ie>
>Subject: Re: C. J. Cherryh List
>Date: Mon, 24 May 93 14:02:00 BST
> But todays rockets spent a huge percentage of their mass to operate
> for shorter periods of time with less acceleration. What kind of 
> exhaust velocity would be required for the carriers?
I don't think the carriers (or any of their ships) use an inertial based system. Their fuel, for all intents and purposes, appears to be water. This looks like they have hydrogen-fusion based power-plants. They never take on propellant which makes me argue for a inertialess (i.e. magic) drive.
				Jo


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>From: Onno Meyer <Onno.Meyer@arbi.informatik.uni-oldenburg.de>
>Subject: cherryhlist
>Date: Fri, 28 May 1993 17:18:52 +0200 (MET DST)
> >Date: Mon, 24 May 93 11:52:59 +0200
> >From: mst@vexpert.dbai.tuwien.ac.at (Markus Stumptner)
> >Subject: Cherryhlist
> 
> Even if both types of ships use the same type of drive, this does
> not mean that all drives are powerful enough for FTL capability.
> The dfrives in the riders could still be much smaller and more
> efficient at sublight speeds if they are designed not to got to
> FTL.  Given that we know next to nothing about how the FTL drives 
> are supposed to work, this is as valid a reason as any. Do riders 
> have vanes, btw?   
Do you think FTL- and STL-engines are the same hardware operating in different modes, or what does that mean? I always assumed that carriers have rocket-engines and jump-engines, while the riders have only rocket-engines.

(...)
> 	I don't think the carriers (or any of their ships) use an
> inertial based system. Their fuel, for all intents and purposes, appears
> to be water. This looks like they have hydrogen-fusion based power-plants.
> They never take on propellant which makes me argue for a inertialess
> (i.e. magic) drive.
I don't agree with this. - Water makes a nice starship fuel, if it is broken down into hydrogen and oxygen. In _Rimrunner_, the Station was unable to aquire and _process_ enough water in time (That's from memory, I might be wrong).

- "Raw" water can be heated (for example, by a fusion plant) and then ejected as water vapor: a simple but efficient rocket engine.

- In _Hellburner_, the craft lost an significant part of it's mass in an instant because it fired and moved. The powerplant would consume it's fuel in a more steady manner.

- In one of the Chanur books (I boldly assume it's the same technology) a docking port is hit and someone said that if the "ugly" pipes hadn't been outside, they would all be dead. this _might_ have been fuel.
Further more, the _Legacy_ aquired speed in a gentle _burn_ due to it's passenger, and that sounds like a "conventional" rocket.

- If the engines were hydrogen-consuming plants, why haul all the unnecessary oxygen that is contained in the water.

- Why introduce another "magic" technology without compelling reason? Jumpdrive was necessary to mace interstellar stories possible, and tape-teaching was necessary to colonize Cyteen. All the plots work with "conventional" rockets.

(...)
            Onno


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>From: Jo Jaquinta <jaymin@maths.tcd.ie>
>Subject: CherryhList -- M-drive
>Date: Mon, 31 May 93 9:55:33 BST
> > 	I don't think the carriers (or any of their ships) use an
> > inertial based system.
> I don't agree with this.
> - Water makes a nice starship fuel, if it is broken down into hydrogen
>   and oxygen. In _Rimrunner_, the Station was unable to aquire and
>   _process_ enough water in time (That's from memory, I might be wrong).
Oh, I agree that water is the *fuel*.
> - "Raw" water can be heated (for example, by a fusion plant) and then
>   ejected as water vapor: a simple but efficient rocket engine.
It doesn't corespond to what we see in the books. Assuming the exhaust velocity of a ship's propellant was lightspeed the ship would have to eject twice its own mass in propellant to boost it up to lightspeed, under simple newtonian mechanics. Thus to carry out the maneuvers in the books the ship would have to have started off with about 98% of its mass as fuel. This doesn't match the picture of the Norway on "The Company War" (I have this in a GIF on FTP if anyone wants it) let alone descriptions of the ships.
> - In _Hellburner_, the craft lost an significant part of it's mass
>   in an instant because it fired and moved. The powerplant would 
>   consume it's fuel in a more steady manner.
I'd say that was more the weight of the armament. Taking the analogy of modern fighter/bombers their payload is a significant proportion of their mass. Thus when they exhaust their arms they become much more maneuverable.
> - In one of the Chanur books (I boldly assume it's the same technology)
>   a docking port is hit and someone said that if the "ugly" pipes
>   hadn't been outside, they would all be dead. this _might_ have been
>   fuel.
This can be answered along with:
> - If the engines were hydrogen-consuming plants, why haul all the
>   unnecessary oxygen that is contained in the water.
There was a long discussion on the Traveller Mailing List about how the fuel for the hydrogen-burning powerplants of Traveller was stored. It was always assumed to be liquid hydrogen (H2). All the physists came out of the closet, though, and pointed out that water (H2O) was nearly as efficient a way of storing hydrogen as in its liquified form. It also doesn't need special storage. Methane (CH4) apparently wasn't that great but ammonia (NH3) was better than water. Perhaps some of the Compact ships (more technologically advanced) burn Ammonia rather than Water, assuming fusion plants.
Of course in Traveller only the *volume* of the ship is considered when computing drive speed rather than *mass*. There is a much lower %weight of hydrogen in water/methane/ammonia than pure hydrogen.
>   Further more, the _Legacy_ aquired speed in a gentle _burn_ due to
>   it's passenger, and that sounds like a "conventional" rocket.
I'd propose it is more a case of Conventional Terminology being applied to advances. (Like I "knit" chainmail or ask friends if they want to "go down" a MegaTraveller "dungeon" :-)
> - Why introduce another "magic" technology without compelling reason?
Well I hope my arguments for them not having a inertia based system are convincing. All the "magic" required is some device that converts heat energy (created by a conventially plausable fusion plant) into inertial energy. A common device in SF.
				Jo


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>Date: Tue, 1 Jun 93 11:50:35 +0200
>From: mst@vexpert.dbai.tuwien.ac.at (Markus Stumptner)
>Subject: Cherryhlist
(...)
>I always assumed that carriers have rocket-engines and jump-engines,
>while the riders have only rocket-engines.
Whatever they're using, it's certainly not rocket engines. You need huge amounts of reaction mass to maneuver at high g's with rocket engines. This would either make the riders the size of a Saturn V or it would make them sitting ducks, in terms of the accelerations carriers (and therefore any weapon intended for attacking carriers) can tolerate. Therefore, since they need a "magic" drive as badly as the carriers, it could well be a minor version of that used by the carriers.

I also recall several instances of riders being described as guarding the outskirts of a system, which again implies accelerations unachievable with rocket drives unless you have access to significant amounts of reaction mass. Otherwise it would have taken them months to get there.
>- In _Hellburner_, the craft lost an significant part of it's mass
>  in an instant because it fired and moved. The powerplant would 
>  consume it's fuel in a more steady manner.
I haven't read "Hellburner", but does "craft" refer to a rider ship here, or to another vessel? The non-military ships in "Heavy Time" all use conventional rocket engines (and note that they also get a large part of their acceleration from the stations' beams).
>  Further more, the _Legacy_ aquired speed in a gentle _burn_ due to
>  it's passenger, and that sounds like a "conventional" rocket.
I would rate that as a colloquialism.
>- Why introduce another "magic" technology without compelling reason?
I did not introduce any, I used the one already in place. The compelling reason, unfortunately, *is* there, given the performance of the ships that Cherryh describes.
>  Jumpdrive was necessary to mace interstellar stories possible, and
>  tape-teaching was necessary to colonize Cyteen. All the plots work
>  with "conventional" rockets.
The plots would, in general, but not the descriptions given of insystem maneuvering.
>A carrier may "shed its riders, which will travel at that speed". 
>I read from this that a ridership is not capable of the major
>speed/vector changes done with the FTL-engines.
>Of course, this interpretation is not supported by the remainder of
>the text (the notes about rider movement).
Exactly. In such a case I would prefer to dismiss that single line of the text (which I suppose is taken from the game supplement), especially since it would severely limit the utility of riders in combat (see above comments).
	Markus


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>From: Onno Meyer <Onno.Meyer@arbi.informatik.uni-oldenburg.de>
>Subject: cherryhlist
>Date: Wed, 2 Jun 1993 10:51:49 +0200 (MET DST)
> > - "Raw" water can be heated (for example, by a fusion plant) and then
> >   ejected as water vapor: a simple but efficient rocket engine.
> 	It doesn't corespond to what we see in the books. Assuming the
> exhaust velocity of a ship's propellant was lightspeed the ship would
> have to eject twice its own mass in propellant to boost it up to
> lightspeed, under simple newtonian mechanics. Thus to carry out the
> maneuvers in the books the ship would have to have started off with
> about 98% of its mass as fuel. This doesn't match the picture of the
> Norway on "The Company War" (I have this in a GIF on FTP if anyone wants
> it) let alone descriptions of the ships.
This is a point in favour of a magic engine, but I'm still not convinced, see my reasons below.
Is this the same picture that appears in the front of _DS_? (There is a picture of Pell station, too.) If not, where do I get this GIF?
> > - In _Hellburner_, the craft lost an significant part of it's mass
> >   in an instant because it fired and moved. The powerplant would 
> >   consume it's fuel in a more steady manner.
> 	I'd say that was more the weight of the armament. Taking the
> analogy of modern fighter/bombers their payload is a significant
> proportion of their mass. Thus when they exhaust their arms they
> become much more maneuverable.
That's possible. (...)
> (...)
> 	There was a long discussion on the Traveller Mailing List about
> how the fuel for the hydrogen-burning powerplants of Traveller was stored.
> It was always assumed to be liquid hydrogen (H2). All the physists came out of
> the closet, though, and pointed out that water (H2O) was nearly as efficient
> a way of storing hydrogen as in its liquified form. It also doesn't need
> special storage. Methane (CH4) apparently wasn't that great but ammonia
> (NH3) was better than water. Perhaps some of the Compact ships (more
> technologically advanced) burn Ammonia rather than Water, assuming
> fusion plants.
> 	Of course in Traveller only the *volume* of the ship is considered
> when computing drive speed rather than *mass*. There is a much lower
> %weight of hydrogen in water/methane/ammonia than pure hydrogen.
But we know that both sublight acceleration and jumpspeed depend on the ratio of ships mass and engine power. This Idea of a volume/speed relation is convenient for a game ("With 200 tons of cargo and 70% fuel we have an acceleration of, err, ... ,just a moment, ...") but it violates both physics as we know it and physics as described in the books.

And, if the fuel was needed for an fusion plant, the plant would have to be really big to use a significant quantity of fuel. I've found a physics book that said if the Tokamak(?) design should work, a 30.000 MW plant would use 10kg of fuel every day. With such a plant no starship should have to rely on station power, but the compact ships routinely hook up to station power lines.

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>From: Onno Meyer <Onno.Meyer@arbi.informatik.uni-oldenburg.de>
>Subject: cherryhlist
>Date: Wed, 2 Jun 1993 16:29:45 +0200 (MET DST)
> Whatever they're using, it's certainly not rocket engines.   You need
> huge amounts of reaction mass to maneuver at high g's with rocket
> engines.  This would either make the riders the size of a Saturn V
> or it would make them sitting ducks, in terms of the accelerations
> carriers (and therefore any weapon intended for attacking carriers)
> can tolerate.  Therefore, since they need a "magic" drive as badly 
> as the carriers, it could well be a minor version of that used by 
> the carriers. 
I agree that the riders do need the inertialess(?)/reactionless(?) engine badly, but you don't always get what you need.

_HB_ p.52
The carrier dropped into a star-system and launched the riders- trusting that realspace ships, launched like missiles, with more firepower than ability to maneuver at v, could do their job...

_HB_ p.325
Pulse of the main engines. ... Second pulse, high-g RO, intermittent accel and ...

The second quote comes from the only description of an ridership flight I've ever read (are there others???). The rider is boosted up to .3 c by it's carrier, released, drifts for a while, followed by a rapid sequence of engine bursts up to 10.5 g and missile salvos. After the mission completed signal from the carrier the rider docks again.

This first operational ridership shows nothing of the maneuver abilities and endurance the riders in _DS_ demonstrate.

Perhaps the riders of the 2350s were improved over the riders of the 2320s.

> I also recall several instances of riders being described as guarding
> the outskirts of a system, which again implies accelerations unachievable
> with rocket drives unless you have access to significant amounts of reaction
> mass.  Otherwise it would have taken them months to get there.
If you're talking about _DS_, the riders went out there with carrier support. Not all the carriers, but always one or two.
> (...)
> 
> I haven't read "Hellburner", but does "craft" refer to a rider ship here,
> or to another vessel?  The non-military ships in "Heavy Time" all use 
> conventional rocket engines (and note that they also get a large part
> of their acceleration from the stations' beams).
I was describing the first rider prototype (that is, the third, but the first one that was declared ready for operations).
> >- Why introduce another "magic" technology without compelling reason?
> 
> I did not introduce any, I used the one already in place.  The compelling
> reason, unfortunately, *is* there, given the performance of the ships
> that Cherryh describes.
Are you sure? Someone found a quote in _Legacy_ that might indicate instant acceleration with the jump-engine the same way it can brake. Civilian insystem-ships are described as very slow, and I can't recall any story where a rider goes to c-fractional speed with his own engines.

Of course you may be right, it would be an easy explanation of the ship movements, but I'm not sure it's the only explanation.
 Onno


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>Date: Thu, 3 Jun 93 11:56:22 +0200
>From: mst@vexpert.dbai.tuwien.ac.at (Markus Stumptner)
>Subject: cherryhlist
From Onno Meyer: 
>Are you sure? Someone found a quote in _Legacy_ that might indicate
>instant acceleration with the jump-engine the same way it can brake.
Exactly, so the technology is already there. Now all that's necessary is that the application of jump engines to braking be a minor effort compared to an actual jump, which is clearly the case (since they don't need to go outsystem, take drugs, and all that stuff).
>Civilian insystem-ships are described as very slow, and I can't recall
>any story where a rider goes to c-fractional speed with his own engines.
I wasn't talking about the insystem freighters, of course (I was talking about them in the context of Heavy Time, where I mentioned they had rocket drives only). The citations you list would indeed tend to support your view. However, in DS, a battle at Pell has the carriers Tibet and North Pole with deployed riders trying to break through the Union fleet to rejoin the rest of the Company fleet. Such a maneuver would be completely impossible if the riders were limited to, say, 1/1000 the acceleration of a carrier, since the Union carriers (of which about a dozen were available) could run rings around them. In effect, deployed riders would make *any* battle a deathtrap for an outnumbered carrier. Also, since they lack the acceleration to try and evade missiles, they would certainly be the first casualties in any kind of combat, contradicting the fact that all Company fleet carriers still have their original riders. Probably she just didn't think too closely about these points when she designed the riders.
	Markus


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>From: Jo Jaquinta <jaymin@maths.tcd.ie>
>Subject: CherryhList-- Norway GIF/Reactionless/Inertialess
>Date: Thu, 3 Jun 93 13:10:20 BST
(...)
Since you have _HB_ to hand can you see if they give a time check on the rider run? They start at the Lagrange point and end up in Lunar orbit. I can work that distance out. If you can find the time out we can get an estimate of it's average acceleration.
					Jo


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>From: Onno Meyer <Onno.Meyer@arbi.informatik.uni-oldenburg.de>
>Subject: cherryhlist
>Date: Fri, 4 Jun 1993 09:06:20 +0200 (MET DST)
One more addition to the ridership/engines discussion, I've just found the following quote:

_The Pride of Chanur_, p.30
The _Pride_ leapt forward by her generation pulses, borrowed velocity at the interface, several wrenching flickers, whipped into the between.

I think this shows clearly that the compact ships use their jump-engines to change their realspace-speed. If the human ships use the same technology, I see three possibilities:

- Riderships are unable to perform major vector changes without their carriers, they have to get hauled up to speed and get collected by the carriers at nearly the same speed.

- The speed change is done by a part of the FTL-engines that is installed on the riders.

- Riderships use a third, entirely different engine-type for their realspace-operations.

I can't believe the second explanation, since the pulses are usually generated by the vanes and a rider has no jump-vanes. The third explanation seems unlikely since it is unnecessaryly(sp?) complicated and I can think of no quote that directly supports it.
The only evidence for inertialess/reactionless engines on the riders is their guard duty in the outskirts of a system.

Any comments? (Or reasons why I totally screwed up? :-)
Onno


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>From: David Zink <zink@Panix.Com>
>Subject: cherryhlist
>Date: Fri, 4 Jun 1993 09:25:04 -0400 (EDT)
> (...)
> Such a maneuver would be completely impossible if the 
> riders were limited to, say, 1/1000 the acceleration of a carrier, since the 
> Union carriers (of which about a dozen were available) could run rings around 
> them.  In effect, deployed riders would make *any* battle a deathtrap for an 
> outnumbered carrier.  Also, since they lack the acceleration to try and
> evade missiles, they would certainly be the first casualties in any kind
> of combat, contradicting the fact that all Company fleet carriers still
> have their original riders.  Probably she just didn't think too closely
> about these points when she designed the riders.
My impression is that riders are capable of great accelerations (10.5 g is mentioned in one place), however they lack the fuel to do it for the extended periods needed to attain high speeds. I would be surprised if something as large as a carrier could attain 10.5 without artificial gravity systems to lessen the load. Unless the entire crew is embedded in gel you aren't even going to get that high, and I'd be surprised if even gel would give the necessary support to human internal structures to allow such high acceleration for any period. 10.5 newtonian still takes a while to attain light speed.
	-- David


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>From: Onno Meyer <Onno.Meyer@arbi.informatik.uni-oldenburg.de>
>Subject: cherryhlist
>Date: Sat, 5 Jun 1993 13:21:59 +0200 (MET DST)
(...)
> 	Since you have _HB_ to hand can you see if they give a time
> check on the rider run? They start at the Lagrange point and
> end up in Lunar orbit. I can work that distance out. If you can
> find the time out we can get an estimate of it's average acceleration.
That is pretty useless since the Hellburner flight was launched from a carrier, and while the speed at the separation point was given (some .3 times lightspeed), we don't know what the carrier did in the 40 minutes it took to plot and confirm (number from memory).
	Onno


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>Date: Tue, 8 Jun 93 13:16 PDT
>Subject: cherryhlist
>From: Nick_Janow@mindlink.bc.ca (Nick Janow)
> This is a point in favour of a magic engine, but I'm still not convinced,
> see my reasons below.
I thought the high velocities were gained by pulsing the jump drives. I noticed that in HB, and somewhere else too.

(...)
> And, if the fuel was needed for an fusion plant, the plant would have to be
> really big to use a significant quantity of fuel. I've found a physics book
> that said if the Tokamak(?) design should work, a 30.000 MW plant would use
> 10kg of fuel every day.
A fusion reactor doesn't need much fuel to generate energy, but a fusion drive also needs reaction mass (hydrogen is good) to generate thrust from that energy. With such a plant no starship should have to rely on station power, but the compact ships routinely hook up to station power lines.

Sure, to cut down on maintenance charges. If parts of the reactors "wear out" quickly, you'll want to minimize its operation time.

It also sounds good in a story. :)
Nick_Janow@mindlink.bc.ca


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>From: Onno Meyer <Onno.Meyer@arbi.informatik.uni-oldenburg.de>
>Subject: cherryhlist
>Date: Fri, 11 Jun 1993 14:46:31 +0200 (MET DST)
> I thought the high velocities were gained by pulsing the jump drives.  I
> noticed that in HB, and somewhere else too.
There are quotes that show that speed can be gained with jumpdrive pulses, but while the braking pulses are almost allways mentioned, acceleration pulses are seldom described. This could be because

- Arrivals are more interesting than departures, and get longer descriptions

- The minimum speed to enter jump (if there is such a minimum) is much lower than the speed when exiting hyperspace

- There is another drive to accelerate in realspace

I think the first two explanations are the most likely, but I can't be sure.

(...)
> A fusion reactor doesn't need much fuel to generate energy, but a fusion
> drive also needs reaction mass (hydrogen is good) to generate thrust from
> that energy.  With such a plant no starship should have to rely on station
> power, but the compact ships routinely hook up to station power lines.
But that would be a drive that used reactionmass to accelerate. Somebody said he assumed there had to be a fusion reactor plus an inertialess drive to get the realpace agility described in the books. If the ships ejects some heated exhaust to accelerate, a good chemical engine would do the job, since some other kind of vector change would be necessary anyway.
Is there any data how long a carrier can accelerate at 10+ g?

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>Date: Mon, 14 Jun 93 15:12:40 +0200
>From: mst@vexpert.dbai.tuwien.ac.at (Markus Stumptner)
>Subject: cherryhlist
>There are quotes that show that speed can be gained with jumpdrive pulses, >but while the braking pulses are almost allways mentioned, acceleration >pulses are seldom described. This could be because > (...) I agree (note that no separate realspace drive is ever mentioned), and would tend to favor the first explanation. In Heavy Time, reference is made to the carrier's extremely high acceleration upon *starting* the chase of the Shepherd ship (obviously signifying use of the jump drive), which would contradict the second explanation.
	Markus

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