Warp Drive Physics

As you might figure from the title, this is a little post detailing the nature of faster than light travel in my own little imaginary universe. When it comes to the details of how a warp drive works… well I’ve based it somewhat loosely off of the warp drive as described by Miguel Alcubierre. Other than that, the actual physics are left completely in the air except for some references to overcoming the need for exotic matter through the use of Higgs-boson-mediated zero-point energy interactions and whiffle-waffle(that’s the sound my fingers make flapping wildly as I handwave). My interest, in this case, isn’t in a detailed description of how an FTL drive would actually work. If I knew that I’d patent the bloody thing and take a vacation trip to Alpha Centauri as a billionaire… I just want to describe the capabilities and limitations of the drive for story purposes.

Capabilities & Limitations

Speed

I’ll go over the rough capabilities of the warp drive in-universe first. Speed would vary from ship to ship, but in the modern era(I’m calling it the 25th century, but the timeline is in a bit of flux) a typical freighter might make one or two lightyears a day and the fastest assault ships in the advanced military forces might make up to about five lightyears a day. The very fastest pNu racing ships might be able to make ten light years a day, but that’s where we hit the next limit that afflicts all warp ships up to the “modern” period.

Range

The maximum distance a warp ship can travel at faster than light velocity without having time to “relax” or “discharge” in  a fairly strong gravitic field is about nine light years. More exactly: Sqrt(26 * π) ~= 9.038 lightyears. Very earlier warp ships had such a limited range that flights from Sol to the Alpha Centauri System had to stop off at Proxima Centauri to make the trip. Advances quickly brought that up to the “modern” limit, where it plateaued for centuries. Even modern science as of the “25th century” doesn’t understand the reason for this limitation.

After a ship travels beyond that limit astrogation becomes increasingly difficult as the ship becomes “decoupled” from ordinary space. One problem is that the position of the ship relative to real space becomes increasingly indeterminate and the detectible indicators of that position within the warp bubble(what I’m provisionally calling, “witch light”), become increasingly indecipherable. The ship can be pretty much anywhere in the universe, and sometimes thats where they find themselves. Some researchers are excited at the possibility of a “slipspace” drive to take advantage of this phenomenon, but the problem of navigating to anywhere in particular doesn’t appear anywhere close to a solution. Several lost colonies have been discovered well beyond anywhere where settlements were expected because they had been marooned in this manner. The other problem that manifests itself when a warp drive travels too great a distance at FTL speeds is that it becomes increasingly difficult to avoid damage to the engines. Warp drives blow up when they’re ridden too far.

These problems are much greater when traveling through unknown space. It is a routine task for an astrogator to chart a safe course as far as nine light years through well-surveyed space. The task is much more difficult for a scout exploring new territories. This is why the Interstellar Survey Service has the best-skilled(and best payed)astrogators in space. Well-travelled regions will obviously have the best charts, but old charts grow stale with disuse. Information on a route that is in excess of ten years old will become somewhat unreliable and after a hundred years it will be little more than a guide for a good scoutship astrogator.

Whatever the cause of this “decoupling” it can only be alleviated by a stop within a strong gravity well. Forty-eight hours in freefall within a gravity field in excess of about one ten-thousandth of a “gee”(~0.1 cm/sec2), is a reliable rule of thumb for full “relaxation” of the warp drive. This “relaxation can be accomplished within as little as twelve hours if the warp drive is completely shut down, but restart of a cold drive requires about thirty minutes. In secure systems near Earth, full shut down is a common method to speed travel, but further out on the periphery a sensible captain would be loathe to shut down his warp drive unless he was very confident about his security situation as his ship would be left a sitting duck if pirates or other hazards were to show up.

FTL Cut-off

The first warp drive ships were completely incapable of exceeding the speed of light, no matter where they flew or how much power was poured into the engines. Newer ships, built expressly for in-system work still often forego FTL capability in exchange for faster in-system speeds from lighter, cheaper, more easily maintained and less power-hungry equipment. But even warp drives built with FTL capability are limited to STL flight within the “FTL Cut-off” radius of massive bodies. No warp ship is capable of exceeding lightspeed within a gravitational field exceeding one ten-thousandth of a gee(~0.1 cm/sec2). Within this radius, the speed capability of a drive goes down such that a ship capable of 1 lightyear/day in interstellar space is only capable of about 0.48 a.u./day. This is proportional to the FTL speed of the craft, so a ships speed will abruptly drop by a factor of 166,420 on passing the FTL Cut-off. The exact location of the FTL Cut-off is somewhat conjectural, as ships rigged for STL flight aren’t effected by it and ships rigged for FTL flight have to temporarily deactivate their drive to reset it for STL(this isn’t a full  shutdown, so a cold restart is unnecessary: a good crew can ready a ship for STL or FTL in less than a minute typically). The one ten-thousandth gee limit is a reliable rule of thumb based on experience watching ships blow their engines going FTL too deep into a gravity well. The actual value seems to vary a bit(or some engines take longer than others to fry themselves, who knows), but no one has ever slagged their warp drive by going STL in a 0.1 cm/sec2 gravity field.

Although, the warp drive is much slower in STL mode, even a slow ship goes at a pretty good clip. The first warp trip to Mars, on a primitive and feeble DR-60 took only a month to make the trip compared to the roughly five months required for a conventional rocket. If its warp drive had been capable of FTL flight it would have made only 0.2 light years per day.

Tangential Vector Translation Maneuver

Ships don’t just have to move using a warp drive, they can also use their warp drive to maintain a position. This has an interesting use and some interesting political and physical implications that haven’t all been well addressed by the “modern” part of my future. The use and, its an important one in a future that hasn’t developed reactionless thrusters or any rocket more advanced than plasma thrusters and solid-core NTR, is the Tangential Vector Translation Maneuver.

Basically, let’s say your flying well above the atmosphere, maybe you popped up there with a suborbital rocket. You want to make orbit, but you’re going too slow. Well then, just point your warp drive away from the planet and get it going just fast enough so you don’t fall. As gravity accelerates you downward, just tweak the throttle a bit to maintain your position. Even at the altitude most of the shuttles or the ISS orbit at the acceleration from gravity is most of a gee. For free. No reaction mass needed, and not really a whole hell of a lot of power. Once your ship has fallen in place long enough to reach orbital velocity(straight at the Earth, but that’s just a detail), you whiz to a location such that your current velocity vector is pointed tangentially to the Earth’s surface and shut down the drive. Did I say we didn’t have a reactionless drive? Heh! When the warp drive was first developed, physicists assumed that somehow this particular maneuver wouldn’t work. Trouble is, at least in principle, this does amount to a reactionless drive, which kind of piddled on one of Newton’s little laws. After a bit of fiddling they were able to explain that little problem away. Gravity was pulling the Earth toward the ship with the same force that it was pulling the ship toward the Earth. Equal and opposite reaction: check! Worse, though, this completely violated conservation of energy. In principle, you could put a big magnet on a ship, let it fall through a coil to generate a current, use the warp drive to move the ship back above the coil and repeat. You could draw more energy from the coil than was required to run the warp drive. This problem was not as easily solved as the previous one. A number of conjectures have been bandied about. The simplest being that the whole of thermodynamics only applies as a special case. To… pretty much the entire observable universe that isn’t currently inside a warp field! Another conjecture is that the warp drive, somehow when this is done, draws energy out of an, also conjectural, Dark Energy field that permeates the universe and drives its expansion. If this conjecture is correct, then at the rate warp drive ships are whizzing around the galaxy trying to match velocities between different stars and place themselves into stable orbits, astronomers should find a detectible slowing of universal expansion. Maybe in a million years or so… maybe a little less.

The political implications are a bit scarier, if you don’t mind too much trashing a cornerstone of physical science or two. This isn’t just a perpetual-motion engine, its a perpetual acceleration engine. A warp ship could get to a pretty fast intrinsic velocity(as opposed to its pseudovelocity, intrinsic velocity is the measure of the actual momentum vector of the ship which will be its velocity when the warp drive shuts down), potentially much faster than its STL warp capability with some smart astrogation. There’s little to prevent a vessel from reaching a high relativistic velocity and slamming into an inhabited world. Given the time it would take and planning this is unlikely to occur accidentally, but a malevolent actor could ruin a world pretty thoroughly this way. For dealing with the possibility of accidents every inhabited world of any significance at all has an extensive Space Traffic Control system and a number of fast warp interceptors of various kinds to deal with vessels that lose control or fail to follow instructions. The two most common interceptors are the DSRV-Deep Space Rescue Vessel- and shieldcraft. The DSRV is not to be mistaken for an emergency response vessel, it has no real capacity to save the crew of another vessel, nor is it manned. Its sole purpose is to intercept any body whose current intrinsic velocity vector endangers an inhabited planet, match velocites with it, extend its warp field to cover that body and move till the intrinsic velocity vector no longer intersects the surface of the planet. If there are surviving personnel on that body then a successful intercept by a DSRV, while not gentle, is far more forgiving than an encounter with the shieldcraft. Pretty much every planet inhabited by more than a million people has at least a belt or two of shield craft. Each belt consists of several dozen or hundreds of automated shieldcraft circling the planet, usually with a great deal of intrinsic velocity in a direction away from the planet’s surface. These are the last ditch against kinetic energy threats to the planet. Basically the purpose of a shieldcraft is to ram any body on a threatening trajectory. If a DSRV can’t remove the threat, shieldcraft will try to hit the offending body hard enough to move its vector away from the planet or failing that cause its pieces to spread enough to be too diffuse to do any damage.

I’m considering whether to make the higher velocities essentially impossible largely by author fiat. Trouble is matching velocity with a relativistic projectile would be a time consuming and hazardous process, and an object going that fast doesn’t give a lot of warning. Even with really long-distance detection, the light from the object wouldn’t arrive much before the object itself. With FTL delivery to cut-off radius that margin gets even thinner. With that in mind I think there could be a limit to the amount of work that can be applied to a body within a warp field before the warp drive, even on STL, begins to malfunction. Make it enough delta-V that a ship can readily match velocities between most stars(at least within a radius of about 9 lightyears), but not much over that. Honestly, the more I think about this, the more I think this is a problem that can’t be solved so much as abated to the point where only the most motivated and best equipped villain could contemplate it. Perhaps reducing it to the realm of semi-credible Bond villain threat.

Time travel

Although there has been a great deal of experimentation with trajectories that should allow for breaking of causal relationships none of these have resulted in actual time travel. There seems to be a bit of wibbly-wobbliness to the time passing aboard an FTL warp vessel, the port it departed and the port it arrives at, but no one has ever been able to chart a route that leads to returning to the port of departure before your original departure, nor has causality been violated in any detectable manner. The closest documented example was in 2408 when the M.V. Iron Lady made a round trip from Arete to Callista and back. By her own clock she spent four days in transit to Callista, nine days on Callista, and three days on the return leg. While the captain was congratulating the astrogator on such a fast transit, they received a message from Arete system STC expressing surprise at their return after only twelve hours and asking if they were in distress.

Scientists in the more developed systems near Earth are working to build an interstellar radio communication and timebase system to measure such events more closely. Although the system currently links Sol, Alpha Centauri, Bernard’s Star and Tau Ceti with work in progress on an Epsilon Indi link, no examples of causality violation have yet been documented.

History

As this post is already a bit long, I’ll keep this short and fairly simple. In my current timeline the first experimental warp drive flew(about forty feet in an evacuated tube somewhere under San Fransisco Bay) in 2048. The first actual use of warp drive in a space craft was an unmanned test of a modified Dragon Rider Model 6(referred to as a DR-10, the only DR-10 as it turned out) in 2051. The DR-40 and DR-50 were the first truly useful warp vehicles introduced in 2055. The DR-40 was an automated warp vehicle used to assist suborbital cargo into orbit using the TVT maneuver, while the DR-50 was the first manned warp drive vehicle used to ferry personnel and cargo between low Earth orbit and lunar orbit. The first manned flight to Mars was a DR-60 launched on October fourth 2057 to mark the one-hundredth anniversary of the first launch of a human-made artifact into orbit. The DR-80 which was introduced in 2064 would remain the workhorse of space exploration and exploitation until after WWIII ended in 2076 including the manned Discovery I expedition to Jupiter in 2069. The DR-100 class, whose prototype vessel completed assembly in Earth orbit by the end of 2071, was intended to be the first interstellar vessel using both the fastest STL warp drive ever developed and the new suspended animation technology to deliver a manned expedition to Alpha Centauri by 2140. The planned launch date of 2075 was set back considerably by the war and the considerable chaos which followed. It was cancelled altogether in 2087 when it was demonstrated that faster-than-light warp travel was possible. The Leif Ericson expedition of 2104 reached Alpha Centauri in only 64 days of travel not including the 12 day stop to look over the Proxima Centauri system. The nine lightyear limit was attained by the middle of the 22nd century.

In 2161 the first commercially successful fusion plant is opened on the Moon. It proved easier to reach the stars than to harness their power.

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One Response to Warp Drive Physics

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