Fwd: sci-fi ftl drives

JUst a bit of info for the list, sent to me by a freind. Thought it
might come
in handy with the Campaign topic.

Randy
http://www.clark.net/pub/nyrath/stardrv.txt

--------------------
STAR DRIVES IN SCIENCE FICTION: A Catalog
by Geoffrey A. Landis  <geoffrey.landis@lerc.nasa.gov>
Originally appeared in the Usenet newsgroup rec.arts.sf.science.

(Mr. Landis makes reference to the EMF classification created by
Erik Max Francis <max@alcyone.com>,
this appears in the appendix. -WC)

Four fundamental separate categories of starflight:
   STL: Slower than light drive travel
   Lightspeed: Travel *at* the speed of light
   FTL: Faster than light travel
   Otherspace: Travel to other dimensions, universes, parallels, etc.  

The meaning of STL is obvious, and it is the basis for all
spaceflight in reality so far.

Lightspeed is not used very much in fiction.  If you could travel at
exactly the speed of light, time would stop for you.  Occasionally
this appears in SF.  Williamson recently has been writing short
stories featuring a "quantum drive" that operates at exactly the
speed of light; from the point of view of the riders, it is
instantaneous.	Also, many teleport systems are assumed to transport
at the speed of light (cf. Niven)

FTL is, of course, faster than light.  This is used so much in SF
that there's little need to define it.

Otherspace is a category I include for completeness.  Note that going
to a different universe can get you starflight, if there are stars in
the other universe, without the FTL paradoxes.	Several books have
*implied* such a system in throw-away lines, but it hasn't been
discussed very much in any detail.  [and most "alternate history"
travel sf assumes that travel takes you from the surface of the Earth
to the surface of the Earth.  What a helpful coincidence!]

OK.  Here I will try to classify *only* FTL; this is the one that's
got the paradoxes.  The classifications are completely on how they
appear; not on the actually physics of operation.

[1.0] Discontinuous Drives ("teleport-like").
    [1.1] Flash gates.
	[1.1.1] Transmitter to receiver.
	[1.1.2] Transmitter to anywhere.
	    [1.1.2.1] Transmitter to anywhere /variant.
	[1.1.3] Anywhere to receiver.
	[1.1.4] Distant transmitter.
    [1.2] "Door" gates.  
	[1.2.1] Portal to portal. 
	[1.2.2] Portal to anywhere.
	[1.2.3] Anywhere to portal.
	[1.2.4] Distant portal.
    [1.3] "Permanent" gates (Wormholes).  
    [1.4] Teleportation (aka "jump")
	[1.4.1] Single jump.
	    [1.4.1.1] Single jump/variant.
	[1.4.2] Multiple-connection.
	[1.4.3] Multi-jump (Stutter).
	[1.4.4] Hopscotch drive.
	[1.4.5] FTL by time travel.
    [1.5] "Fold" drive ( Telportation/variant ).
[2.0] Continuous Drives.
    [2.1] "Railroad" drives
	[2.1.1] Fixed trail
	[2.1.2] Consumable trail
    [2.2] "Non-railroad" drives.
	[2.2.1] Real space drives.
	    [2.2.1.1] Newtonian space drives.
	    [2.2.1.2] Post-relativistic space drives.
	    [2.2.1.3] Tachyonic travel.
	    [2.2.1.4] Modified local speed of light.
	    [2.2.1.5] Modified regional speed of light.
	    [2.2.1.6] Modified universal speed of light.
	    [2.2.1.7] Tachyonic teleportation. 
	    [2.2.1.8] Other real drives.
	    [2.2.1.9] "Bubble" drives.
	[2.2.2] Alternative space (non-real space drives)
	    [2.2.2.1] Alternative space with fixed nodes.
		[2.2.2.1.1] Hyperspace with transmitter and receiver.
		[2.2.2.1.2] Hyperspace with transmitter.
		[2.2.2.1.3] Hyperspace with receiver.
		[2.2.2.1.4] Hyperspace with distant transmitter.
	    [2.2.2.2] Alternative space without fixed nodes.
		[2.2.2.2.1] "Jump" hyperspace. 
		[2.2.2.2.2] Direction hyperspace.
		[2.2.2.2.3] Navigable hyperspace.
[3.0 Modifying the Universe
    [3.1] Modify distance in space.
    [3.2] Modify the speed of light.
    [3.3] Universal parameter change. 

FTL travel breaks down into two main categories:

[1.0] DISCONTINUOUS DRIVES ("Teleport-like")
	 Discontinuous drives are ones in which the traveler does not
traverse the space between origin and destination.  

[2.0] CONTINUOUS DRIVES ("Ship-like")
	Continuous drives, on the other hand, are ones in which the
traveler does traverse the space between start and finish. A ship
gets from point X to point Y by traveling rather than by an instant
"jump", although the travel is not necessarily in "real" space.
	The word "ship-like is a little fuzzy, since many SF writers use
'ships' to accomplish what is actually teleportation- like travel.
This is, I think, because ships are such a great story device

[3.0] MODIFYING THE UNIVERSE
	A final category of FTL, not precisely fitting in elsewhere,
requires modifying the universe.  Some items in this category also
could be made to fit other categories.

Subcategories:

[1.0] DISCONTINUOUS DRIVES ("Teleport-like")

[1.1] FLASH GATES
Devices in which the object transported disappears from point X and
reappears at point Y.
[1.1.1] TRANSMITTER TO RECEIVER
Teleport in which a discrete transmitter and a receiver are needed.
May require a ship, or may not.
[1.1.2] TRANSMITTER TO ANYWHERE
Teleport in which a transmitter is needed, but a receiver is not;
the transporter can select the target location ("Beam me down" is
the most well-known example)
[1.1.2.1] TRANSMITTER TO ANYWHERE/ VARIANT
Transmitter can be transported with the teleportation.
See also [1.4.1.1] "Single jump/variant".
[1.1.3] ANYWHERE TO RECEIVER
Teleport in which a receiving unit is needed, but a transmitter is
not. ("Beam me up" is an example of this.)
[1.1.4] DISTANT TRANSMITTER
A teleport system in which a fixed unit is needed, but this unit can
teleport you from a place to another place. (The "point to point" use
of the transporter in Trek is an example.)

[1.2] "DOOR" GATES
Gates in which an opening is made between point X and point Y which
exists for some finite time; the object transported then moves though
the gate. 
[1.2.1] PORTAL TO PORTAL
A transmitting device to act as the "out" door and a receiving device
to act as the "in" door are both required. (e.g., Poul Anderson,
_The Enemy Stars_.) 
[1.2.2] PORTAL TO ANYWHERE
Here the transmitting door opens a receiving door without
requirement for any device at the receiving end.  ('Tak Halus'
(pseud. of Steven Robinette) did a series of stories in _Analog_in
early 70s with this premise)
[1.2.3] ANYWHERE TO PORTAL
The same as [1.2.2] "Portal to anywhere", but traveling in the
opposite direction.
[1.2.4] DISTANT PORTAL
Anywhere to anywhere, device located elsewhere. Here "door" opens
from X to Y by use of a device at a third location C. The 'door'
equivalent of [1.1.4] "Distant transmitter".

[1.3] "PERMANENT" GATES (Wormholes).  
"Permanent" here means that these stay open without the requirement
of a device, that is, they are a path from X to Y without being
energized. There are a wide variety of subsets of this. 
Recently the most talked-about are Lorentzian wormholes, which are
apparently allowed by the general theory of relativity if the
presence of negative matter is permitted. General relativity
variants include Morris-Thorne spherical wormholes, Visser portals,
Kerr ring-wormholes, Einstein-Rosen bridges (nb: which actually
collapse before allowing you to traverse them), Tippler rotating
cylinders (nb: which don't actually serve as bridges, but at least
one SF writer, Poul Anderson, wrote a book which assumed that they
did).  A non-relativity version is the "mirrors" used in Wolfe's
_New Sun_series of books.
 
[1.4] TELEPORTATION (aka "jump")
Here I use "teleportation" to imply something that can transport
itself without a fixed transmitter or receiver.  Reference to quantum
"tunneling" is often made. Some books imply that humans can do this
unassisted (_Tyger, Tyger_/_The Stars My Destination_).
Many more use ships which can 'jump" with some device.	Here I use
'jump' or 'teleportation' only for the case that physical travel is
not required in some alternate version of space, in distinction to
some SF writers who use the term or a variant for cases where a ship
'jumps' to some 'hyperspace' (jumpspace, subspace, etc) where it can
travel FTL.
[1.4.1] SINGLE JUMP
A ship (or person) who can jump from place to destination in a single
step, and can select the target.
[1.4.1.1] SINGLE JUMP/ VARIANT
In the variant, this only works at selected places, and takes you
only to selected spaces (_The Mote in God's Eye_).  This type of
variant in general can be considered a
version of the [1.1] "Flash-gate" discussed above.
[1.4.2] MULTIPLE-CONNECTION
The ship can engage a "jump" drive, which will connect your location
in space-time with another location in space-time that is fixed by
the universe.  [may depend on your state of motion in some variants].
The connection will vary from place to place, so to go to a given
destination you need a "map" of where to go in space to find the
place that jumps to the right spot.  The analogy is of the universe
to a crumpled sheet of paper.  An ant can cross from one place on the
paper to another where the paper touches itself.  (Heinlein).  For
some locations, a long trip moving from one place to another to take
multiple jumps may be necessary.
[1.4.3] MULTI-JUMP (Stutter)
A ship can jump from place to place, but not far enough to travel in
a single jump.	Thus, the ship travels by a series of short jumps.
In the limit of very short jumps, the ship "appears" to be traveling
through space at a "pseudo" velocity without actually having any
momentum. (This shades into [1.4.1] "Single jump" as the length of
jump gets longer).
[1.4.4] HOPSCOTCH DRIVE
Use of any version of a gate or portal to accomplish self-motivated
teleportation by having a transmitter transmit a transmitter, so that
a ship "bootstraps" across space by continuously beaming itself
incremental distances.	(Such a drive is somewhere in the fuzzy
region between a [2.0] "Continuous" and a [1.0] "Discontinuous drive").
[1.4.5] FTL BY TIME TRAVEL
In FTL by time travel, faster than light travel is achieved by traveling
to
the destination at ordinary slower-than-light speed, then teleporting
backward in time to arrive at the same time you started

[1.5] TELEPORTATION/ VARIANT  ("Fold" drive)
A "fold" drive appeals to the "folded space" concept of [1.4.2]
"Multiple-connection", but now assumes that the ship can intentionally
"fold" space to produce the direct connection between point X and
point Y required.  Since this categorization is by how the drive
appears, and not how it functions, "fold" variants are identical to
actual teleport (or "portal") variants, cf. [1.2] "Door gates")

[2.0] CONTINUOUS DRIVES ("Ship-like")

[2.1] "RAILROAD" DRIVES
[2.1.1] FIXED TRAIL
A "railroad" drive is one in which it is assumed that some physical
structure connects two points, and that FTL travel is possible, but
only traveling along this structure (as railroad travel is only
possible along a railroad).  One might appeal to the concept of a
cosmic string, or some other astrophysical object.  The railroad is
in some ways a conceptual link between wormhole-like drives and
ship-like drives.  If the travel is actually instantaneous, with an
object leaving one end appearing at the same time at the other end,
the railroad drive becomes a variant of [1.3] "Permanent gate".
[2.1.2] CONSUMABLE TRAIL
In a consumable trail, some structure must be put in place between a
and b, and the drive consumes this material as it travels in order
to produce FTL.  Some versions of the Alcubierre drive, for example,
require that a structure of negative energy be put in place along the
path from x to y, and the ship can then travel between the two points,
but destroys the structure as it travels.

I don't recall having seen either type of railroad drive proposed
in SF. (Note from Winchell Chung: I seem to recall a railroad style
drive 
in Glen Cook's THE DRAGON NEVER SLEEPS. There is also
something like it in Kim Stanley Robinson's THE MEMORY OF WHITENESS) 

[2.2] NON-RAILROAD DRIVES
This section covers continuous drives (that is, drives where the ship
traverses space to get to the place desired) which do not require a
structure in place in space.  EMF categorizes these as realdrive,
hyperdrive, warpdrive, and fakedrive depending on the operating
principle used to go faster than light.  I will instead categorize
them in to main categories, depending on whether the ship remains in
the "real" universe or leaves it, however, since my categories are
similar to EMF's, I quote him where appropriate
[2.2.1] REAL SPACE DRIVES
Real space drives assume that faster than light travel is possible in
physical space.  In terms of appearance, all of these drives
apparently operate the same way (you go faster than light), and so if
I were to keep to my strict classification, these would all be in the
same category.	The main difference between the drives is how they
talk around relativity.  
[2.2.1.1] NEWTONIAN SPACE DRIVES
This version of a FTL drive simply ignores relativity.	The ship goes
faster than light merely by speeding up to a velocity which is faster
than light.
[2.2.1.2] POST-RELATIVISTIC SPACE DRIVES
This is a minor variant [2.2.1.1] "Newtonian space drive"; the
drive assumes that there is some (yet unknown) "correction" to
relativity such that the speed of light is not, in fact, a barrier.
Often this correction will be some added term which applies only very
close to the speed of light.
	  [2.2.1.1] and [2.2.1.2] are both "fakedrives" in the
classification by EMF.
[2.2.1.3] TACHYONIC TRAVEL
Tachyonic travel notes that faster than light speeds are in fact
permitted by relativity for bodies of imaginary rest mass, and
assumes that there is some way to reach the faster than light state
(often invoking "tunneling") from slower than light states without
leaving "real" spacetime.  (nb: tachyonic FTL travel still has
causality paradoxes in special relativity).
[2.2.1.4] MODIFIED LOCAL SPEED OF LIGHT
Drive assumes that the speed of light in the vicinity of the ship can
be modified by the drive system in some way, so that although the
ship does not exceed the speed of light, it nevertheless can travel
faster than 300,000 kilometers per second.
[2.2.1.5] MODIFIED REGIONAL SPEED OF LIGHT
Assumes that the speed of light is greater than 300,000 kilometers
per second in some places in the universe.  Faster speeds can be
achieved in other places in the universe .
[2.2.1.6] MODIFIED UNIVERSAL SPEED OF LIGHT
A scientist discovers a way to change the speed of light in the
entire universe, and does so.  Now any ship can go faster than
(what used to be) the speed of light.
[2.2.1.7] TACHYONIC TELEPORTATION
The ship and/or person is converted into a stream of tachyons and
beamed across space, then reconstituted at the receiver.  Actually a
variant of [2.2.1.2] "Tachyonic travel" and/or [2.2.2.1.1]
"Hyperspace with transmitter and receiver"; listed separately
because it is significant that the ship does not travel as a cohesive
unit.  Other variant names can be used for the particles, which can
travel either through real space or some alternative space. 
[2.2.1.8] OTHER REAL DRIVES
This covers other ways of dealing with relativity problems without
leaving real space.  (Usually this involves employing doubletalk
and bafflegab.)
[2.2.1.9] "BUBBLE" DRIVES (EMF classification: warpdrive)
"A bubble of different space is projected around the ship so that
the ship can travel faster-than-light while still in realspace."
This is listed last, since it is an intermediate step between
"real space" drives and alternative space drives, with some nature of
both.  (This seems to be the FTL system used on Star Trek.)

[2.2.2] ALTERNATIVE SPACE DRIVES (non-real space drives)
In SF parlance, often called hyperspace, hyper, jumpspace, FTL space,
and other such words. EMF classification: "Type I; hyperdrive:	The
ships enters some different space during the trip, whether or not
time passes for the crew while in this space."

[2.2.2.1] HYPERSPACE WITH FIXED NODES
Like teleport systems, a alternative space drive may require a fixed
station.
[2.2.2.1.1] HYPERSPACE WITH TRANSMITTER AND RECEIVER
A fixed station boosts the ship into hyperspace; another station is
needed to retrieve the ship out of hyperspace.	In some variants,
only specific locations are nodes which can be used to access
hyperspace.
[2.2.2.1.2] HYPERSPACE WITH TRANSMITTER
A fixed station boosts the ship into hyperspace.  (Babylon-5)
[2.2.2.1.3] HYPERSPACE WITH RECEIVER
A ship can enter hyperspace on its own, but needs a receiver to get
back into real space.  Another one I've never seen in SF.
[2.2.2.1.4] HYPERSPACE WITH DISTANT TRANSMITTER
In this variant, a fixed machine is needed to access hyperspace, but
the machine need not be at either the original location or the
destination.  I've never seen this in SF; included for completeness.

[2.2.2.2] ALTERNATIVE SPACE WITHOUT FIXED NODES
These are the variants of the classic SF hyperdrive.  There are
probably more examples of this in SF than all other of the drive
types combined, and hence it is possible to make very fine divisions
within the type.
EMF classification:
"Type I; hyperdrive:  The ships enters some different space during
the trip, whether or not time passes for the crew while in this space."
The space is often explained away as being a dimension different from
the four dimensions we currently can perceive (this explanation
typically advanced by people who seem to have only a foggy idea what
a "dimension" is).  There are many variants based on the supposed
"theory" of how the drive works, including entering a space where the
speed of light is faster, entering a space which maps onto real space
with a mapping such that points far apart in real space are closer in
the alternative space, entering a space where the ship expands and
then contracts to a different place, entering a space where everything
moves at the same FTL speed, etc.  Likewise, there are a long list of
"conditions" which hyperspace drives are imagined to require.  A
common one is that the FTL space cannot be entered when "in the
gravitational well of a massive body," (Niven, _Ringworld_ series) or
that your ship must have a high velocity in real space before you can
enter FTL space (Niven, _World of Ptavvs_, O'Donnell,
_Fire on the Border_)  These two are convenient for sf writers,
because they explain why spaceships are required.
Important questions for hyperspace concepts are whether ships can see
and/or dock with each other in hyperspace, whether all ships travel
the same speed, and whether a ship can navigate while in hyperspace.
These questions can also be asked of [2.2.2.1] "Hyperspace with fixed
nodes".  I will take this last to be the question used for subdivisions.
[2.2.2.2.1] "JUMP" HYPERSPACE
The destination is fixed when the ship enters the alternative space,
either as a function of its position and velocity entering, or else
by some settings in the drive.	After a ship enters the alternative
space, there is no way for it to change the destination.
[2.2.2.2.2] DIRECTIONAL HYPERSPACE 
A ship's direction is fixed when the ship enters hyperspace (often,
but not always, fixed by the direction the ship was traveling when
it entered).  How far it travels, however, is a variable that can be
changed.  Usually the distance is proportional to time spent in
hyperspace, but may be a more complicated function.  The ship may or
may not be able to calculate its position in real space while
in hyperspace.
[2.2.2.2.3] NAVIGABLE HYPERSPACE
The ship is able to completely navigate in hyperspace.	It may or may
not be able to calculate its position in real space while in
hyperspace.  Sometimes the hyperspace may have geography or dangers
which must be navigated around.

[3.0] MODIFYING THE UNIVERSE
[3.1] MODIFY DISTANCE IN SPACE
Remove or shrink the space between two points.
[3.2] MODIFY THE SPEED OF LIGHT
Change the value of the speed of light in the region where travel is
desired (see [2.2.1.6] "Modified universal speed of light")
[3.3] UNIVERSAL PARAMETER CHANGE
Gain access to the parameters that describe the universe, possibly by
hacking into the operating system that the universe runs.  Find the
parameters which describe your location. Rewrite these parameters to
put you in the place you want to be.  (Greg Bear, _Moving Mars_)

____________________________________________
Geoffrey A. Landis,
Ohio Aerospace Institute at NASA Lewis Research Center
physicist and part-time science fiction writer
____________________________________________

APPENDIX: The EMF classification
Erik Max Francis <max@alcyone.com>

Type 0; realdrive:  A drive which uses tricks of spacetime geometry
(a la general relativity) to travel faster than light.

Type I; hyperdrive:  The ships enters some different space during the
trip, whether or not time passes for the crew while in this space.

Type II; warpdrive:  A bubble of different space is projected around
the ship so that the ship can travel faster-than-light while still in
realspace.

Type III; jumpdrive:  The ship travels from one point to another,
possibly in multiple jumps, without occupying the intervening space
and without the use of a different space to assist the travel.

Type X; fakedrive:  Assume that special relativity or general
relativity are incorrect in part or in whole, or just ignore them.
Now you can just accelerate at constant gravity until you go faster
than light.