Realistic Space Battles (Long)

[Valamir]

I second the recommendation to check out Attack Vector in detail.

Any effort to make a vector movement space combat game based on "realistic" space movement assumptions that does not use this game as reference source material is a serious mistake IMO.

[acehunter]

Hi, I'm new to the Forge, but I've been active on some other gaming forums / lists, most notably http://games.groups.yahoo.com/group/sfconsim-l">sfconsim-l

The sfconsim list has debated most of the aspects of "realistic" space combat a number of times over, and I highly recommend it to those wishing to develop that type of setting.  Attack Vector: Tactical was in part developed on that list, and Ken Burnside, the principal creator of the game is active on the list.  I also would like to recommend AV:T as an excellent "realistic" space wargame.

I'd like to respond to a few remarks made in this thread, so here goes:

Re: jdagna

Why do you assume short burns and long coasting? A 2 G acceleration requires 4 times the energy of a 1 G burn for the same unit of time. If you burn at 1 G for twice as long, you've used half the energy, for the same final speed. If you burn at .01 G, you've used 1/40,000th the energy in the same time, and only need to burn for 200 times as long (thus, your total energy usage to match speed is 1/200th). This is why NASA is so interested in engines that burn at only 1-2% of G for long-distance travel.

A 2g burn for a given Delta-V requires exactly the same energy as a 1g burn, not 4 times as much.  Inefficiencies can occur if you put too much fuel into the burn for a given nozzle expansion coefficient, but if your thrust is proper for the nozzle used, the energy is exactly the same regardless of whether you burn at 1g for 2 hours or 2g for 1 hour.  In both cases your final velocity (or Delta-V) is 35,300 m/s.

Why so much fuel? if you could do a perfect energy-to-movement conversion, a ship like you're talking about could get by on a few thousand tons of liquid hydrogen which would be well under 1% of the ship size.

Hydrogen is a lousy fuel or reaction mass in terms of storage.  The density of liquid hydrogen is 0.07 tons per cubic meter.  A few thousand tons of H2 (say, 5,000 tons) takes up 71,400 cubic meters of space, which has to be contained and thermally insulated.  By contrast, water as ReMass would take up 5,000 cubic meters, or 1/14th the volume.  Granted, H2O has other problems as reaction mass, my point is that there are denser materials out there that require much less storage volume.  "Slush" hydrogen is also an option, but with its own technical issues.


Re: Rob Carriere

everything that happens has be explainable with present-day science as constrained by the notions of present-day technology. This is, of course, completely unrealistic. By the time technology has advanced enough to do this sort of thing, the technological perspective will certainly have changed and the science quite probably.

Despite advances in science during the last 400 years, one thing that has not been overthrown is the Second Law of Thermodynamics.  The second law creates most of the restrictions that Kedamono describes.  Various consequences of the Second Law can be found in the message archive on sfconsim-l.  "Realistic" space travel is a lot more restrictive than most people think.


Re: Omen

The shuttle and the ISS do not have these problems because the structure loses more heat then is generated. Heaters must be used to keep the crew in comfort.

Not true.  The electronics on board generate more heat than either craft needs.  Both the shuttle and ISS use radiators to remove excess heat and cannot operate properly for more than about 30 minutes without the radiators functioning. (The shuttle must abort after 30 minutes if the cargo bay doors are unable to open)  The shuttle (and presumably ISS) DO have electric heaters, because areas of both craft would freeze when the craft is in Earth's shadow.  They also use heat exchangers to even out the temperature of the craft (200 degrees on the sunlit side and -200 on the shadowed side) and flash evaporators / ammonia boilers to remove excess heat in addition to the radiators. (or in the case of the shuttle, when the doors are closed during reentry)

In Attack Vector: Tactical, ships have retractable radiators similar to those you describe in the rest of your post, plus heat sinks of liquid sodium or liquid lithium to remove the massive amounts of heat from the engines and the lasers. (Modern lasers are horribly inefficient - 30% of the input power becomes the beam and 70% of the power is lost as heat)


Re: Kedamono

A ship with an active drive would not be a problem, right?  Maybe.  And maybe not. If you hold a dime out at arms length against the night sky, the area it is blocking off is several times larger than the area this IR telescope can see in high detail. And this high detail is created by scanning that portion of the sky over and over and over, building up layers of detail that a snapshot cannot attain.

A ship with a fusion drive (like you describe) would have power in the terrawatt range, and in addition to neutrons would emit X-Rays.  If it were facing you, it would be like a miniature sun.  No matter which way it was pointing, it would be detectable for several dozen light-seconds as a minimum (several million km) and possibly detectable at multiple AU.  See the sfconsim-l archives for details.  Bruce Macintosh, a regular poster on sfconsim-l has discussed this subject at length, and has even written variant sensor rules for Traveller.  He is an infrared sensor specialist who does work for NASA.


Miscellaneous notes:

The two primary factors in "realistic" space combat are Heat and Fuel.

Heat: Lasers are 30% efficient.  Current DOD lasers in the various anti-missile programs are approaching 1-2MW in output power.  That means 2-4MW of heat for each of these lasers.  Worse yet, your fusion drive is outputting say, 5 Terrawatts.  If your ship's structure is 99.999% insulated from the heat of the drive, then the structure has to eliminate 50MW of heat from the drive.  Radiators are flimsy structures, and cannot be deployed if your ship wants to perform combat manuevers.  In Attack Vector, this is the purpose of heat sinks - store the heat until you can open the distance and deploy radiators.

Fuel: In any realistic spacecraft, fuel is a severe limitation, even with fusion power.  In all likelihood, a spacecraft's total Delta-V will be less than 100kps (km per second). (Probably less than 50kps, but we'll use 100 as a maximum)  Escape velocity from Earth's surface is 11.2kps.  Escape velocity from Sol at Earth's orbit is, IIRC about 30kps.  If we want a fast trip from Earth to Jupiter and back, we might spend 20kps on our initial burn, 20kps (actually a little more) braking into Jupiter orbit, and the same amount coming back.  That's 80kps of our total 100kps.  This restricts our combat delta-V to 20 kps.  If we spend more than that, we're taking a lower energy trip back to Earth. (at a lesser velocity)  We can make a trip back at a mere 4-5kps, but that would likely be a Hohmann trajectory (minimum delta-V) and would take us 2.7 years to get home (not counting the possible year to wait for our launch window, the synodic period of an Earth-Jupiter trip happens once every 1.09 years)

Kedamono, hope this helps, and I look forward to seeing what product Tri-Tac comes out with.  I own and have played Fringeworthy a number of times, and used to have Staking the Night Fantastic (Bureau 13), Incursion and FTL:2448.  Nice to see Richard Tucholka still at it after all these years!

-Matt P.

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[Kedamono]

Kedamono, hope this helps, and I look forward to seeing what product Tri-Tac comes out with.  I own and have played Fringeworthy a number of times, and used to have Staking the Night Fantastic (Bureau 13), Incursion and FTL:2448.  Nice to see Richard Tucholka still at it after all these years!

-Matt P.

Thanks Matt! This does help.

Richard is still going strong, and that's why we're working on new versions of the games. I'm not worried too much about Incursion, as it is space opera, it's FTL:2448 that is going to be the hard one to work with. Based on calculations I've made, ships in FTL:2448 move at about .14 Light. That's awful fast, and they do so with very little reaction mass. We're going to get a decent breeze from all the handwaving we're going to have to do to justify this. And to do so, we're probably going to make space combat just about impossible... Maybe. FTL:2448 has about 4 to 5 unique methods of FTL travel, a couple that could be deal breakers in combat. Imagine being able to appear in the middle of fleet and wreak havoc and then vanish before any one could respond, heck before your image appears in their sensors...

[acehunter]

Yeah, that does make combat tricky.  I highly recommend taking a look around on sfconsim-l, maybe posting a couple questions on there.  The readership on that list spans the whole list of wargamers, specialists in highly technical fields, and just plain smart individuals.  Also, you may want to contact the list admin, Chris Weuve.  He and Arius have been working on Exordium Tactical, a space wargame in the Exordium universe.  (Exordium is a set of 5 SF books written by Sherwood Smith and Dave Trowbridge)  In the Exordium universe, there is tactical FTL, so a single ship can attack another ship at the same time from multiple directions by jumping in to 10 light-seconds, firing, then to 7 light-seconds from another direction, firing again 3 seconds after the first time, then to 4 light-seconds and firing again 3 seconds later (6 seconds after the first time).  All 3 shots arrive simultaneously from 3 different directions.  Great in fiction, confusing as heck in gaming.  Chris and Arius have had some success, so they may be a good resource.  Google "Chris Weuve" and you'll find both his page for Exordium and for sfconsim-l.

-Matt P.

[Rob Carriere]

Despite advances in science during the last 400 years, one thing that has not been overthrown is the Second Law of Thermodynamics.  The second law creates most of the restrictions that Kedamono describes.  Various consequences of the Second Law can be found in the message archive on sfconsim-l.  "Realistic" space travel is a lot more restrictive than most people think.

Errrr...that would probably be for the reason that the Second Law of Thermodynamics is one of the overthrowers. Thermodynamics is less than 200 years old and was quite the upset in its day.

More to the point, Kedamo's descriptions derive from the interaction of present-day thinking with present-day physics. Even if we hold the physics constant (and YOU are the one who's gonna explain the logic of that to Marie Curie and the people of Hiroshima!) that still leaves the early-twenty-first-century expectations of How Things Are Done. It's like asking Admiral Nelson to speculate on how the Japanese fleet might attack Pearl Harbor in WW2. He might come up with all sorts of absolutely brilliant stuff, but I kind of doubt he'd foresee the aircraft carrier.

Great fun, and I did a lot of it back when I was an engineering student, but I never had the illusion that it had anything to do with realism. I have read far too much hard SF from the Golden Age period (heck, some of it from the 70s) that is now completely dated from a science/engineering point of view. To give just one example, even a very smart guy like Asimov, who did foresee the possibility of miniaturization (his `molecular valves') completely missed the fact that miniaturized computers open the way to having many small machines rather than a single central facility and all the implications of that change. Back then, Multivac was a reasonable idea. Today, it is thoroughly preposterous--and we still haven't even reached the time period where most of the Multivac stories are set.

SR
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[Kedamono]

http://www.projectrho.com/rocketstub.html

This is probably the best source of information on space travel and war
in space that I have ever seen. A must for those folks that want to do
realistic SFRPGs.

[Rob Carriere]

Neat site. Thanks!
SR
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[Jules Morley]

While I can't add much to the hard science wonkage, I'm surprised no-one has mentioned Niven & Pournelle's "Mote in Gods Eye / Gripping Hand" books - the second in particular has several large fleet actions of hard science-based non-relativistic combat.  Their one handwaving concession is the Anderson Drive and Shield (their FTL system) which itself allows for a pretty nifty take on an interstellar civilisation.

My guess is that, given the fragile nature of us squishies, space combat will be fought primarily by proxy - automated kill vehicles with sophisticated, shielded sensor packages. You save a heck of a lot of mass if you don't need life support and radiation shielding, and you gain acceleration. Unless, of course, your background includes some kind of gravity damping technology. :)