At 300 meters, and a dry mass of around 80,000 tons, this is a respectable sized vessel, the size of modern day nuclear powered aircraft carrier or unladen oil tanker.
But when you take away all the space dedicated to reactionless drive, reactor, thermal radiators, FTL zone-transit, manoeuvering rockets, fuel, container haulage, hanger, storage, water and volatiles, biospherics, defensive lasers, radiation and armour shielding, etc etc, there isn’t much space left.
Which of course makes for fun writing. I want to keep the sense of claustrophobia. Space may be vast, infinite even, but the ships that traverse it aren’t necessarily large. Sure, some can be, like the classic starliners and kilometers long corporate bulk and container haulers and giant mining vessels, the huge worldships and hab ships and the dreadnoughts and carriers. But I expect most ships would be small and cramped, the equivalent of a WW II sub. Add jerry-rigged construction and a mishmash of parts and modules from other ships, or matter printed on the fly, and the FHSS Alcione may not be the shiniest ship in the spacedock. But she’s still home for those who sail her across the infinite ocean of space.
The only two really spectacular piece of tech on this vessel is the reactionless drive, with negmass stored in hyperspace and constantly transferred back and forth to balance the changing positive mass of the ship (as the two have to be equal at all times, though I suppose there would be some margin of error or the system would probably be unworkable), and the ortho-rotational FTL unit which enables the ship to shift from real space to superluminal zones and back.
From whence comes such miraculous pieces of clarketech (technology so advanced as to be indistinguishable from magic)? Luckily, being a scifi writer I can cheat (if I was rigorously hard science I probably couldn’t!) and say they were gifted to humanity and other lesser races by technologically more advanced aliens (and more than one race. The race that has the reactionless drive isn’t the same as the FTL race).
This is actually an old trope. Arkady and Boris Strugatsky’s Roadside Picnic has hyper-advanced aliens visiting Earth, and leaving extraordinary tech with their refuse, after they depart. Alastair Reynolds Revelation Space universe uses the classic &gifting& trope, but replaces aliens with a posthuman clade called &conjoiners&. It really doesn’t matter what literary or worldbuilding device you use. Aliens, posthumans, and the gods of mythology are all equally symbols and metaphors of the transcendent.
But why would these aliens do this, if being so advanced they could take whatever they want by force?
Well, any number of reasons. They may need humans as cannon fodder to fight their futile and monstrous wars. They may be scavengers who stole it from some other race, and in turn trade it for whatever (but whatever they trade it for, the price is horrendous). They may be engaged in some vast strategic game of which we cannot even glimpse (and if we do, any glimpse we have is totally wrong). Or they may just be nice and generous people.
The freehaulers who just break even keeping their horrendously expensive ships running on whatever profits they make from cargo haulage to grey market profiteering to honest freight transport to on the side smuggling, don’t really care. They love their austere lifestyle and libertarian-anarchist freedoms and wanderlust, travelling from world to world and space station to space station, beholden to no-one but themselves and their fellow merchanteers and freehaulers.
And like everyone else, they never stop to think of the terrible cost humankind paid (or didn’t pay, does anyone really know or care?) for the stardrive. They just want to keep doing what they’re doing.
My original intention for the Freehauler Alcione ‘Verse (created universe) was to combine realistic science (say 8 on the Mohs Scale of scifi hardness) with esotericism, new weird, and similar crazy things that would rank at say 3 on that same scale (like Warhammer 40,000). I didn’t want to write a pure hard science story, but an imaginative and imaginal crossover.
Anyway, since space opera always will be central, I figured it’s important to get the spaceships right. Sure I have hyperspace FTL, a classic trope which ranks at say 5 or 6 on the scientific realism scale, but for the rest I wanted everything to be kosher. I consulted the excellent atomic rockets site, to get all the stats on a realistic high performance spaceships. Only the ship kept getting bigger as I added more modules, until by no stretch of the imagination could it be a privately owned (freehauler) tramp spacer! It was megacorp fleet hauler size.
Another problem is such ships have to be insanely powerful (just check out the figures required on the Atomic Rockets torchships page, this for a tiny ship of a mere one thousand tons!). Assuming classic newtonian rocket science only, if you have a million ton ship you need about half a hiroshoma bomb / second of output for even milligees or tens of milligees of acceleration. I mean, talk about a Weapon of Mass Destruction drive! Also, how to stop the engine, and for that matter the rest of the ship, vaporising, even with magnetic plasma handwavium containment and exhaust focussing.
Then the other day I came across a brief essay on negative mass at Science News Org. Apparently, physics says you can have mass with a negative value . Not antimatter, but a sort of counter matter, that is identical except opposite in effects. So if you push it, instead of moving away, it moves towards you. Like charges attract. Gravity is repulsive.
What really got my attention, negative mass falls towards positive mass. But positive mass is repelled by negative mass. Put a bit of negative mass near an equal amount of positive mass in a zero gee environment, and they two will fly off, the former chasing the latter, forever. Moreover, this doesn’t contradict the laws of physics, because the net kinetic energy and momentum is always zero (the negative mass has negative kinetic energy, the positive mass positive.
Wow. A space drive.
Actually this was originally shown by the physicist and science fiction writer Robert Forward in a paper some years ago . There’s a neat drawing, which appeared on Atomic Rockets, that I have reposted here.
This made me think, if you have a ship that weighs N tons, and you have a dense plate of negative mass of weight N tons at the back, you have reactionless, inertialess drive.
Most importantly, you can go up to relativistic speeds, but net kinetic energy always remains zero. So no planet busters. (Unlike the conventional scifi reactionless drive, in which anyone can make a bathtub into a planet cracker, but for some strange reason no one does. This is how you do it. Stick your handy Acme Agrav Acceleration Unit on the back of any small object, say, a fridge, or a bathroom sink. Accelerate it to high relativistic velocity, and aim it a planet. Boom, no planet).
Like the Alcubierre drive it doesn’t contradict the laws of physics. It’s just, unobtanium. But unlike the Alcubierre drive, you don’t have to worry about being fried by hawking radiation, or frying whatever your destination is with the same (note, this only happens with afaster than light Alcubierre drive ). But if you have this amazing unobtanium stuff, you can just stick it on the back of your ship, and off you go.
Or, according to John Cramer Anti-Gravity and Anti-Mass Alternate View Column AV-14, you don’t. Because by tethering the positive ship to the negative mass, the two forces cancel each out. It seems this only works if the two are not physically tethered.
So the only way around this (other than having the negative mass as a sort of big floating ball following the ship) is to add still more handwavium, and say hey no worries we have a special hyperspace thingie in which the joint momentum isn’t cancelled out! (science fiction is good because whenever you are in a whole, you can always cheat). Alternatively, use the Alcubierre metric but only go slower than light  (will save this for the next blog post).
There are still a few questions that need answering.
Given equivalence of normal matter and negative mass (say 10,000 tons and -10,000 tons), how fast would the ship accelerate? Or is acceleration determined by how close the two are?
Is it necessary to have equivalence. If you have a 10,000 ton ship, and you add (subtract, whatever) 5000 tons of negative mass, will it still be a reactionless drive, but only accelerate half as fast? Because the negative mass would contribute less momentum? Or would it accelerate twice as fast, because negative mass attracted to positive moves faster the smaller it is?
Also minor technical questions. How do you steer? How do you switch it off? I guess if you can couple and decouple the negative and positive mass with some special gizmo, you can switch it off, or tilt it like sails on a sailboat. Or whatever.
Incidentally, one thing negative mass won’t do. As the Science News Org essay points out, it won’t float just above the ground. You can’t have ships hovering on a planet, or a cool hover bike like Rey’s on The Force Awakens. When it comes to a planetary gravity well, negative mass behaves exactly the same way positive mass does. No negmass newtonian apples falling upwards. 
So, just like an atomic rocket, a negmass ship can only be used in deep space. No standard space opera trope of rusty tramp freighters or sleek warships effortlessly climbing up and down the gravity well, a la StarWars or Firefly. Just as well, because it means I can keep space habitats, not as peripherals, but as central to the entire setting as the ships are.
There’s something to be said for being not too imitative of standard tropes.
 Bondi, H. “Negative Mass in General Relativity,” Reviews of Modern Physics, Vol. 29, No.3, July 1957, pp. 423-428.
 Forward, R. L. “Negative Matter Propulsion”, Journal of Propulsion and Power (AIAA), Vol. 6, No. 1, Jan.-Feb. 1990, pp. 28-37. See also Winterberg, F. “On Negative Mass Propulsion,” International Astronautical Federation, Paper 89-668, 40th Congress of the International Astronautical Federation, Malaga, Spain, Oct., 1989.
Just as there’s a Mohs Scale of Hardness in mineralogy, so there’s a metaphorical Scale of hardness in Science Fiction, where “hardness” refers to Hard Science Fiction (Hard SF for short), the genre that has the greatest technological plausibility and scientific realism. (Hard SF on its own also tends to dryness and socio-cultural and character shallowness, but that’s another story)
Regarding the following, four things should be pointed out.
First, the opposite of Hard SF is not Soft SF. Soft Science Fiction refers to science fiction that explores themes and possibilities based on the social or “soft” sciences such as psychology, anthropology and sociology. This is a perfectly respectable field of science fiction, and indeed Hard SF stores may be decidedly lacking in the social realism stakes, just as social science fiction may be lacking in the astronomy and rocket science stakes.
Second, even when science marches on, a work still remains hard science. To quote Wikipedia: “Later discoveries do not necessarily invalidate the label of hard SF… Arthur C. Clarke’s 1961 novel A Fall of Moondust (is still) hard SF,…even though a crucial plot element, the existence of deep pockets of ‘moondust’ in lunar craters, is now known to be incorrect.” HG Wells War of the Worlds for example was hard science by the standards of its day. Nevertheless, the future never turns out as we imagine or predict it, so “Future Rust” is common in older books, and even more recent technothrillers.
And third, no story or worldbuilding is uniform in its realism or lack thereof. A scenario may include ultra hard SF (9 out of 10) ships for interplanetary travel but give them hyperjump capability for FTL (6 out of 10).
And finally, all science fiction is still fiction. The science in science fiction enhances the fiction, but generally less so the reverse, although there are exceptions, e.g. many scientists and astronauts who work at NASA grew up watching Star Trek. But for a writer it is less what is absolutely, objectively, real, and more what serves the story.
Here then is my current provisional list, from most to least realistic, where 10 is the real world, and 0 is total cartoon nonsense, with especially emphasis on spaceships and space opera:
(Update: have included decimal-tenths just for the heck of it. So n.6 is more speculative and n.5. more realistic)
10. The real world. Science is explained, no handwavium. Also, Non-Fiction. As TV Tropes puts it: “The Apollo Program, World War II, and Woodstock fall in this class.”
9.6. to 9.9 Technothrillers and Futurology. Technothrillers take place only a few years in the future, with only a few plausible near future tech projections. This category overlaps with Futurology which includes, as explained in TV Tropes “stories which function almost like a prediction of the future, extrapolating from current technology but do not assume or invent any important new technologies or discoveries.” Quite likely some of the more rigorously and scientifically realistic of the ultra hard space exploration categories of the following category actually go here.
8.6.to 9.5 Ultra Hard Science – only extrapolation from known laws of physics. In TV Tropes this is called Speculative Science. In contrast to the previous categories, the science is “genuine speculative science or engineering, and the goal of the author to make as few errors with respect to known fact as possible.” Interplanetary vessels have milligee thrust. Rockets have to choose between high thrust low isp, or high isp low thrust, you can’t have both. Adherence to thermodynamics, real science. No torchships. Preferably no aliens, if there are, they are limited to the same physics we are, and also must justify in terms of Great Silence (Fermi Paradox). Greg Egan, Kim Stanly Robinson Mars Trilogy, Arthur C Clarke 2001, Asimov The Gods Themselves, GURPS Transhuman Space, Andy Weir’s The Martian, the first two books in Robert L. Forward’s Rocheworld series and Robert A. Heinlein’s The Moon Is a Harsh Mistress fall in this class. 9.5 is the most realistic, with only plausible near future tech projections. For some excellent examples on Ultra Hard SF ships in fact and fiction, with authentic rocket science, see Winchell Chung’s Atomic Rockets website, a resource that I simply cannot recommend highly enough. For tabletop spaceship combat game, see Ken Burnside’s Attack Vector: Tactical (although this also has less realistic FTL as a background explanation for why the battles are not in our solar system). John Lumpkin’s Human Reach series features similarily authentic spaceships, although the setting includes wormholes which pertain to one or two realism grades down.
7.6.to 8.5. Very Hard Science – extrapolation from laws of physics, with minimum handwavium for story purposes. Basic torchships (high thrust high isp), interplanetary vessels average around 0.3 gee thrust or less. Adherence as much as possible to thermodynamics and real science. Interstellar, non-relativistic travel. In TV Tropes this is called “One Small Fib”, “stories that include only a single counterfactual device (often FTL Travel), but for which the device is not a major element of the plot.” Some alien or posthuman handwavium / unobtanium allowed. Big Dumb Object without handwavium. Preferably have an explanation for Great Silence (Fermi Paradox). Arthur C Clarke Rama novels, Gregory Benford, Bruce Stirling Schizmatrix, Stephen Baxter. Many Hal Clement novels (e.g. Mission Of Gravity, Close to Critical) and Freefall belong here.
6.6 to 7.5. Hard Science – extrapolition from laws of physics, plus some handwavium for storytelling purposes. In TV Tropes this is called “One Big Lie”. “Authors invent one, or, at most, a very few, counterfactual physical laws and writes a story that explores the implications of these principles.” Tech otherwise consistent and explained. Interplanetary vessels average around 1 gee. Relativistic travel. May have reactionless drive but must be realistic, say exotic matter or singularity or other unusual tech. FTL only if plausibly explained, otherwise relativistic travel. Includes thermodynamics, rocket science, etc. Aliens with realistic-seeming biology, non-humanoid only. Token explanation of Great Silence (Fermi Paradox). Most works in Alan Dean Foster’s Humanx Commonwealth series, the Ad Astra board games and Robert A. Heinlein’s Farnham’s Freehold fall in this category, as do many of Vernor Vinge’s books. Also Haldeman Forever War, Niven Mote in God’s Eye, Greg Bear various stories, Alastair Reynolds Revelation Space/Galactic North Universe, Posthuman Studios Eclipse Phase (everything else very hard, say 9 out of 10, but “sleeving” consciousness with its associated cartesian ghost in the machine implications, also alien wormholes that are pure unexplainedium). John C. Wright’s The Golden Age probably would go here as well (say 6.7)
5.6.to 6.5. Firm Science – with handwavium and unobtanium, but these reasonably explained in the context of the setting. Torchships rather than reactionless drive, but absurd acceleration given energy allowance (fudging the figures). Token thermodynamics only. FTL with reasonably plausible explanation. Ignores Fermi Paradox. Niven’s Known Universe, Peter Hamilton, James Corey’s The Expanse, a lot of space opera in general.
4.6.to 5.5 Physics Plus (to use the TV Tropes moniker). “Stories in this class once again have multiple forms of Applied Phlebotinum, but in contrast to the prior class, the author aims to justify these creations with real and invented natural laws — and these creations and others from the same laws will turn up again and again in new contexts.” Some Science. Reactionless drive ships easily pull dozens or hundreds of gees. Doesn’t explain why relativistic reactionless drive ships aren’t used as doomsday devices to annihilate whole planets, or as perpetual motion free energy devices. Differs from Token Science in that there is still some rocket science. Heinlein Citizen of the Galaxy, Starship Troopers, Brin Uplift universe, Iain M Banks Cultureverse, Schlock Mercenary, David Weber’s Honor Harrington series, David Brin’s Uplift series, and Battlestar Galactica (2003) fall in this class.
3.6.to 4.5 Token Science. Some real science, but only because this is “science fiction”; the science is there only for storytelling purposes rather than realism. For the most part handwavium and unobtanium with little or no explanation. Ignores thermodynamics (no radiator fins). Reactionless drive, agrav, forcefields, tractor beams, stealth, some aliens look like humans, others very different. FTL with arbitrary explanation. Consistency in worldbuilding, in contrast to the Pure Technobabble category. Frank Herbert’s Dune, Dan Simmons Hyperion Cantos, Firefly/Serenity, maybe Eve on line. Babylon 5 may belong here, although humanoid aliens belong to the next category down, and conversely fighters use vector thrust and larger ships generate artificial gravity by centrifugal spin, which put them in at least the 6 or 7 out of 10 category.
2.6 to 3.5. Technobabble and Handwavium. Differs from Science Fiction In Name Only in that at least there is some attempt, no matter how poor, at a rational explanation. Or in otherwords, to quote TV Tropes: “Phlebotinum is dealt with in a fairly consistent fashion despite its lack of correspondence with reality and, in-world, is considered to lie within the realm of scientific inquiry.” So for example the Enterprise cannot land on a planet, showing that large ships are outer space only. Even so, this is still full of sillytech and inconsistent worldbuilding. Because of handwavium and phlebotinum, anything can be explained. You can have ST style matter transportation because it is assumed all the technical problems were solved, most aliens are humanoid, many identical in appearance to H. sapiens, human and aliens can interbreed, and humans live in similar environments can eat same food etc, because it is assumed there were humanoid progenitors. At the same time, there is serious worldbuilding incompatabilities e.g. if you have ST matter teleportation otherwise you could easily drop a nuke in an enemies lap, have immortality, limitless clones, etc. But it is never explained why this never happens. Star Trek is the classic example, but also included here is E. E. “Doc” Smith’s Lensman series, Neon Genesis Evangelion, Warhammer 40k, the Star Wars Expanded Universe novels (now called “legends” and considered non-canon) which at least make some attempt at explanation over the totally unrealistic canonical movies, Cowboy Bebop, and StarCraft.
1.6 to 2.5 Artistic License. Although unambiguously considered to be “Science Fiction”, there is no actual science to be found. Rather, the story follows what looks good artistically from our contemporary early 21st century perspective. Ships wheel and bank in a vacuum, blaster bolts move slower than tracer rounds. Battles directly mapped from WW II naval engagements. Lantern-jawed heroes and busty maidens, or scary monsters, or both. More realistic than comic book superheros only in that it’s assumed you need a spaceship to travel through space, and there is an attempt at a consistent plot. Star Wars, Guardians of the Galaxy, Dr Who, Red Dwarf, Farscape, Space Battleship Yamoto. Some Star Trek movies, e.g. Star Trek out of Darkness has worldbuilding inconsistencies that are if anything even worse, e.g. Transwarp allows teleporting across interstellar distances, but it is never explained why people still use spaceships
0.1. to 1.5 Comic books. Only token attempts at explanations – Marvel and DC superheros, e.g. superpowers because from a planet with a red sun, Genetic mutation, or Peter Parker bitten by a radioactive spider. Sometimes not only that, so that, to quote TV Tropes: “Green Rocks gain New Powers as the Plot Demands”. The DC and Marvel superhero universes belong here, along with Futurama, manga and anime like Dragonball Z and Tengen Toppa Gurren Lagann, and humorous aspects of The Hitchhiker’s Guide to the Galaxy.
0. Cartoons that are not meant to make sense, e.g. Marvin the Martian
In writing space opera there’s two ways you can go.
The most difficult is hard science, or rather diamond hard science, where you try to get all the rocket science exactly right, according to the current laws of physics. An excellent site in this regard is Winchell Chung’s Atomic Rockets, which I cannot recommend too highly. Especially with ships there are nuclear powered torchships, which output literally terawatts of power.
I mean, you are basically sitting on a series of mini nuclear bombs, or riding a continuous nuclear torch. Forget the pissy ships of tv and movie sci-fi, they barely glow.
The problem, I found, is if I wanted a freighter of, say, 30,000 tonnes and even moderate 0.03 g acceleration (as fast as a freight train accelerating, almost nothing) it would require about a third of a Hiroshima bomb’s worth of energy a second. Every second for as long as the ship gets to speed, say 2 weeks. No engine could handle that without vaporising. In fact even if it didn’t, the whole outside of the ship would glow and be almost incandescent.
So goodbye hard science…
The alternative is handwavium, which is a fancy nerd word for “making things up”. This means you assume some amazing magical breakthrough in science that’ll let you get around all these sticky problems of real universe energy requirements.
So you can have the pissy little puny rocket exhaust of pop sci-fi after all! Because at some point in the future some Plott-DeVice Drive is invented which lets you have something for nothing. And then you can whizz around the universe and still call it science
By the way, I was later pointed at a space opera setting that does use torchships, John Lumpkin’s Human Reach, though they are smaller than my freighter and accelerate more slowly at cruising speed, they can also put on bursts of high G acceleration (though that’d wreck their delta v (range) something chronic)