Colder Wars

MAD will not work in outer space; pre-emptive strikes are nigh-guaranteed.
transhumanism, politics, SF
2009-06-072013-06-22 finished certainty: unlikely importance: 10

SF novel is famous, and its end­ing well-known: the pro­tag­o­nist is tricked into com­mand­ing a pre-emp­tive inva­sion fleet which destroys all the fleets, their home­plan­et, and by a quirk of their biol­o­gy, the entire alien race. The rea­son­ing given is that they could­n’t risk wait­ing for a (third) inva­sion fleet.


This is rea­son­ing, of course; ver­sion 1.0. The strat­egy is sim­i­lar to early Cold War views, such as those who advo­cated that the USA strike Rus­sia first, before it had devel­oped A-bombs/lots-of-bombs/H-bombs.

In ret­ro­spect, such advo­cacy seems fool­ish to us who sur­vived the Cold War; we are not quite so impressed by the argu­ment that Com­mu­nism is inim­itable to the and that it is bound by its inter­nal logic to sub­ju­gate the world and war on us. It did insti­gate var­i­ous wars, prop us var­i­ous regimes, and so on; but the USA has done quite as much of that in its his­tory (and often for rea­sons only osten­si­bly related to ideals such as coun­ter­ing com­mu­nis­m). Nor are we impressed by the argu­ments that such and such a achieve­ment must be pre­vented by all-out war; the world did not end because Rus­sia devel­oped an atomic bomb, nor when it had con­structed use­ful quan­ti­ties of them, nor when it cracked the H-bomb.

Why strike first?

The cru­cial char­ac­ter­is­tics of the early Cold War, that made a first strike so com­pelling, is that:

  1. attacks can be launched simul­ta­ne­ously on all fronts from mul­ti­ple loca­tions
  2. each attack is utterly dev­as­tat­ing
  3. the attacks can­not be guarded against (one thinks of the quip that base was obso­lete the day it was built.)
  4. the attacks are not pre­dictable or observ­able suffi­ciently in advance to take action like retal­i­a­tion

If a fleet of s have anchored off one’s cap­i­tal, the attack can begin and end within half an hour, and the mis­siles—which boomers carry in sub­stan­tial quan­ti­ties—­can tar­get any­where in the nation. There is no prac­ti­cal more than half a cen­tury after nuclear war­fare became pos­si­ble, and lit­tle prospect of one that could with­stand any more than a few mis­siles. Sur­viv­ing nuclear explo­sions is an extremely diffi­cult task, and can­not be guar­an­teed. A gov­ern­ment attacked would crum­ble instant­ly, yield­ing imme­di­ate vic­tory to the foe. Such s are strate­gi­cally attrac­tive.

In each respect, nuclear war­fare differs from con­ven­tional war­fare.

  1. It is diffi­cult in con­ven­tional war­fare to have troops on mul­ti­ple fron­tiers pre­pared for an inva­sion. Planes do not much affect the lin­ear move­ments of mech­a­nized troops, as they must pro­vide air cover and can­not range freely over enemy ter­ri­tory (due to anti-air­craft defenses and the enemy air force); even were total air dom­i­nance achieved, the Air Force could not para­chute large for­ma­tions and their equip­ment wher­ever they pleased.
  2. Con­ven­tional wars using small arms and low-yield explo­sives rarely utterly destroy a city or oppos­ing forces; deci­sive clashes are rar­i­ties, and not nearly as deci­sive as a mush­room cloud.
  3. For­ti­fi­ca­tions and nor­mal mil­i­tary forces can put up a stal­wart resis­tance to an inva­sion. In some peri­ods, defense was even stronger than the offense—­for exam­ple, in World War I. With nuclear bombs, the only defense is to dig deep into the earth as pos­si­ble, and then even deeper than that. From the defen­sive per­spec­tive, this is infe­rior in every way to the bal­ance of power in WWI.
  4. Mass mobi­liza­tions can be observed for weeks or months in advance; with mod­ern telecom­mu­ni­ca­tions, the mes­sage of inva­sion can work its way up the chain of com­mand in mere hours. (This is quite fast com­pared to his­tor­i­cal empires, which might not know that they’ve been invaded for weeks or months, but still not fast enough to cope with s, much like s.)

A con­ven­tional war is intrin­si­cally lim­ited. A coun­try can be invaded and lose ter­ri­tory with­out too much con­cern. Even the tini­est coun­tries like Israel have space to fall back and regroup. The action hap­pens on a human time-s­cale, with human lev­els of casu­al­ties. There can be ebb and flow; strikes can be prob­ing, smal­l­-s­cale.

If one wanted an anal­o­gy, con­ven­tional war­fare is like mar­tial arts spar­ring: mul­ti­ple moves, each strike hurt­ing but not fatal, with a back­-and-forth, and wind­ing up after a while; while nuclear war­fare is like duel­ing with s. And a cur­tain between the duelists.

Fun space warfare

Sci­ence fic­tion often deals with space war­fare, but usu­ally in an extremely unsci­en­tific or roman­ti­cized way.

Even when the author throws many details into it, with hard num­bers and equa­tions and rules he must fol­low, the over­all pic­ture is some­times still absurd. ( warns us to be wary of being seduced by Near/Far think­ing: it is not true that the more detail a pro­jec­tion or fic­tion has, the more true or likely it is!1)

We can eas­ily crit­i­cize the real­ism of Bat­tlestar Galac­tica (both of them) or that of Star Wars (“prob­a­bly the worst”), but even the ones praised for their care­ful thought are vul­ner­a­ble.

Con­sider the of . His ships are described in lov­ing detail; one can’t go a bat­tle with­out fig­ures like ‘10,000 KPS’ being thrown out; the his­tory is described in tremen­dous detail in appen­dixes and sec­ondary works; the plan­ets num­ber in the hun­dreds, and the com­plex­i­ties of their inter­ac­tions feel authen­tic. Plot events often hinge on accel­er­a­tions and vec­tors; books are pow­ered by tech­ni­cal inno­va­tions. It feels awfully real­is­tic.

But is it real­ly? The Hon­or­verse is a naked retelling of the old naval genre like , right down to the names of the wicked French antag­o­nists (eg. ). The ship designs and the uni­verse is con­structed to make ‘’, ambush­es, etc. plau­si­ble in outer space.

It may be fun to read about “War­shawski sails” or “alpha and beta nodes”, or “wedges” and “side­walls”; but these are all ad hoc bits of tech­nol­ogy and arbi­trary, most obvi­ously in the case of the “wedges”2. The mass of details may over­load our crit­i­cal think­ing & fool us, but they ought to make us sus­pi­cious—in the real world, the prin­ci­ples are sim­ple & ele­gant but the appli­ca­tions com­plex; both prin­ci­ples and appli­ca­tions should­n’t be com­plex and detailed. We enjoy only by sus­pend­ing a great deal of dis­be­lief.

Grim space warfare

“A reac­tion dri­ve’s effi­ciency as a weapon is in direct pro­por­tion to its effi­ciency as a dri­ve.”

, “The Kzinti Les­son” (“The War­riors”, 1966)

After all, the hum­drum alter­na­tive is some­thing like uni­verse, where travel between the stars takes years or mil­len­nia3, where s and s are the best (and also non­fic­tion­al) meth­ods of trav­el, where works its ter­ri­ble mag­ic, where trips are one-way and solar sys­tems do not see incom­ing ves­sels (trav­el­ing at frac­tional ) until it is too late.

A more fac­t-based view of space war­fare would look some­thing like this analy­sis by the char­ac­ter Bean from Card’s (a com­pan­ion novel to Ender’s Game), Chap­ter 12:

“Let me read you some­thing,” said Dimak. “’There are no for­ti­fi­ca­tions, no mag­a­zi­nes, no strong points … In the enemy solar sys­tem, there can be no liv­ing off the land, since access to hab­it­able plan­ets will be pos­si­ble only after com­plete vic­tory … Sup­ply lines are not a prob­lem, since there are none to pro­tect, but the cost of that is that all sup­plies and ord­nance must be car­ried with the invad­ing fleet … In effect, all inter­stel­lar inva­sion fleets are sui­cide attacks, because time dila­tion means that even if a fleet returns intact, almost no one they knew will still be alive. They can never return, and so must be sure that their force is suffi­cient to be deci­sive and there­fore is worth the sac­ri­fice…. Mixed-sex forces allow the pos­si­bil­ity of the army becom­ing a per­ma­nent colony and/or occu­py­ing force on the cap­tured enemy plan­et.”

This is a sum­mary of a length­ier analy­sis in Chap­ter 8:

“Well of course for­ti­fi­ca­tions are impos­si­ble in space,” said Bean. “In the tra­di­tional sense, that is. But there are things you can do. Like his mini-fortress­es, where you leave a sal­ly­ing force out­side the main for­ti­fi­ca­tion. You can sta­tion squads of ships to inter­cept raiders. And there are bar­ri­ers you can put up. Mines. Fields of flot­sam to cause col­li­sions with fast-mov­ing ships, hol­ing them. That sort of thing.”

Dimak nod­ded, but said noth­ing.

Bean was begin­ning to warm to the dis­cus­sion. “The real prob­lem is that unlike , we have only one strong point worth defend­ing – Earth. And the enemy is not lim­ited to a pri­mary direc­tion of approach. He could come from any­where. From any­where all at once. So we run into the clas­sic prob­lem of defense, cubed. The far­ther out you deploy your defens­es, the more of them you have to have, and if your resources are lim­it­ed, you soon have more for­ti­fi­ca­tions than you can man. What good are bases on moons on Jupiter or Sat­urn or Nep­tune, when the enemy does­n’t even have to come in on the ? He can bypass all our for­ti­fi­ca­tions. The way and used two-di­men­sional against the of the Japan­ese in World War II. Only our enemy can work in three dimen­sions. There­fore we can­not pos­si­bly main­tain defense in depth. Our only defense is early detec­tion and a sin­gle massed force.”

Dimak nod­ded slow­ly. His face showed no expres­sion. “Go on.”

Go on? That was­n’t enough to explain two hours of read­ing? “Well, so I thought that even that was a recipe for dis­as­ter, because the enemy is free to divide his forces. So even if we inter­cept and defeat nine­ty-nine of a hun­dred attack­ing squadrons, he only has to get one squadron through to cause ter­ri­ble dev­as­ta­tion on Earth. We saw how much ter­ri­tory a sin­gle ship could scour when they first showed up and started burn­ing over Chi­na. Get ten ships to Earth for a sin­gle day – and if they spread us out enough, they’d have a lot more than a day! – and they could wipe out most of our main pop­u­la­tion cen­ters. All our eggs are in that one bas­ket.”

“And all this you got from Vauban,” said Dimak.

Final­ly. That was appar­ently enough to sat­isfy him. “From think­ing about Vauban, and how much harder our defen­sive prob­lem is.”

“So,” said Dimak, “what’s your solu­tion?”

Solu­tion? What did Dimak think Bean was? I’m think­ing about how to get con­trol of the sit­u­a­tion here in Bat­tle School, not how to save the world! “I don’t think there is a solu­tion,” said Bean, buy­ing time again. But then, hav­ing said it, he began to believe it. “There’s no point in try­ing to defend Earth at all. In fact, unless they have some defen­sive device we don’t know about, like some way of putting an invis­i­ble shield around a planet or some­thing, the enemy is just as vul­ner­a­ble. So the only strat­egy that makes any sense at all is an all-out attack. To send our fleet against their home world and destroy it.”

“What if our fleets pass in the night?” asked Dimak. “We destroy each oth­er’s worlds and all we have left are ships?”

“No,” said Bean, his mind rac­ing. “Not if we sent out a fleet imme­di­ately after the Sec­ond Bug­ger War. After Mazer Rack­ham’s strike force defeated them, it would take time for word of their defeat to come back to them. So we build a fleet as quickly as pos­si­ble and launch it against their home world imme­di­ate­ly. That way the news of their defeat reaches them at the same time as our dev­as­tat­ing coun­ter­at­tack.”

Easy warfare

Card’s analy­sis, while good as far as it goes, does­n’t go far enough. The sit­u­a­tion is actu­ally more unbal­anced in favor of the attack­er. Card seems to assume that com­bat will be con­ducted with ships, and that these ships while appro­pri­ately dev­as­tat­ing are nev­er­the­less rather short­-ranged and must get close to a planet to attack.

But ships on a scale com­pa­ra­ble to exist­ing naval ships or space­ships have tremen­dous prob­lems in plau­si­ble space war­fare. (Space fight­ers anal­o­gous to air­planes have even more prob­lems.) They can be seen com­ing from very far away (al­ready pri­vate ama­teurs rou­tinely spot spy satel­lites; aca­d­e­mic tele­scopes can spot some­thing like the Space Shut­tle doing a lit­tle bit of maneu­ver­ing as far away as the aster­oid belt, and spot its launch from past Plu­to’s orbit—and the tele­scopes will only get bet­ter4); they can’t carry very much shield­ing5 and metal shield­ing can be an out­right lia­bil­ity as far as defense goes6; being in a vac­u­um, they have great diffi­culty dump­ing heat gen­er­ated by lasers; and require implau­si­bly effi­cient engines just to carry any weapons at all! Nor do the SF sto­ries we all think of when we think about space com­bat do jus­tice to just how effec­tive plan­e­tary defenses can be against any sort of space fleet. (The fleet can’t hide, can’t see its tar­gets very well, can’t carry an occu­pa­tion force, and the planet can build much big­ger and longer-ranged weapon­s.)

What would one do if one wanted to destroy an oppos­ing world’s civil­ian pop­u­la­tion, on the cheap, and also with great secre­cy? One could send a fleet of pow­ered war­ships straight in to smash the other fleet and then scour the world. If one can even do that, a premise I hope I cast a great deal of doubt upon with the pre­ced­ing para­graph.

But there are many bet­ter alter­na­tives. Geol­ogy teaches us that the 2 most dev­as­tat­ing & life-de­stroy­ing events are erup­tions, and . Super­vol­canos are rather hard to trig­ger, but aster­oids? (And mass and veloc­ity are inter­change­able; an aster­oid is heavy and slow, a light and fast. The power demands are extreme in either case, rul­ing out known fea­si­ble design­s—we can’t build a rocket which would kill a plan­et.)

If one is a inter­stel­lar pow­er, aster­oids are quite easy to come by. One could stealth­ily creep into the vast or and send rocks fly­ing into the inner sys­tem. The Kuiper and Oort are com­posed largely of light­weight bod­ies (com­posed of things like water or methane), but they are pretty siz­able objects— is a typ­i­cal Kuiper Belt inhab­i­tant, and masses 2 to kg. That could still hurt, to put it light­ly. Nep­tune’s moon, which weighs a meaty kg, is a for­mer Kuiper Belt object.

And such an attack would be impos­si­ble to pre­vent. The Kuiper Belt alone is a shell around the Solar Sys­tem from 30 to 55 AU; or an area of ~1.9530 kilo­me­ters7. This is a large vol­ume of space to patrol. More fea­si­ble would be mon­i­tor­ing each and every body: after all, there are only ~70,000 bod­ies. Over 100 kilo­me­ters in diam­e­ter. Esti­mat­ed.

And let’s not even talk about the Oort Cloud (5-50,000 AU)!

If that’s not bad enough, one could envi­sion fling­ing appro­pri­ate small moons or large aster­oids from other solar sys­tems. Why not? Boost­ing a large body to frac­tional c veloc­i­ties and aim­ing it at a far away planet isn’t inher­ently any more absurd than build­ing a ship and boost­ing it to frac­tional c. The motion of stel­lar bod­ies is famously pre­dictable out for many cen­turies. The body could guide itself: add some small motors, and it could even cor­rect for small errors in pre­dic­tion. It would be the ulti­mate fire-and-for­get weapon of mass destruc­tion.


Stop it? How could one stop a small moon? If it is trav­el­ing at a good frac­tion of light­speed, then its kinetic energy will have reached gar­gan­tuan pro­por­tions: no fran­tic last minute attacks will alter its path very much. Sup­pose one did shat­ter it with explo­sives; con­ser­va­tion of energy and mass will still apply—if a bil­lion tons of ice are fly­ing towards New York at 0.5 c, and a bomb shat­ters it, what’s fly­ing towards New York at 0.5 c? A bil­lion tons of ice.

And remem­ber the early points about the vast­ness of space and how ene­mies can attack from any degree—not just along the eclip­tic. (At­tack­ing from a Kuiper Belt, trav­el­ing through or just above or below the eclip­tic may well be the most effi­cient path. But from another solar sys­tem located at some odd angle?) For every mea­sure the defend­ers take, like exten­sive tele­scope arrays look­ing for fast-mov­ing bod­ies, there are coun­ter­mea­sures like reduc­ing to pitch-black­ness by apply­ing soot.

Counter-point: nowhere to hide

There is one advan­tage a defender may or may not have in space war­fare. We already dis­cussed, in pass­ing, some of the dis­ad­van­tages of attack­ing space­ships, which must obvi­ously be advan­tages for defend­ers:

  1. If attack­ers can be seen com­ing from very far away, then that implies defend­ers can attack them since any­thing you can see, you can tar­get with lasers
  2. If attack­ers have diffi­culty car­ry­ing shield­ing because they are attack­ing, defend­ers can have arbi­trary amounts of armor if they are, say, on a planet and can dig hun­dreds of meters deep under­ground
  3. If attack­ers have diffi­culty dump­ing heat gen­er­ated by lasers into empty space, then defend­ers have heat sinks handy (eg. oceans)
  4. If use­ful attack­ers are diffi­cult to engi­neer, then any break­throughs for them may just increase the advan­tage for defend­ers who have fewer trade­offs to deal with

The linked Project Rho pages inves­ti­gated these fac­tors in more numer­i­cal detail and, I think, demon­strated con­vinc­ingly that a net­work of sur­veil­lance tele­scopes linked to a mas­sive laser is supe­rior to any even half-plau­si­ble attack­ing space fleet. But do those con­sid­er­a­tions apply to a large guided aster­oid or other such body?

Laser abla­tion is one of the stan­dard pro­posed , but that and other all seem to fail if there is any active intel­li­gent resis­tance. It does no good to shoot some rock from the Moon at an incom­ing aster­oid if there is a laser on the aster­oid ablat­ing the Moon rock itself!

Which brings up the obvi­ous point: the enu­mer­ated advan­tages for a plan­e­tary defender also apply to an aster­oid! A aster­oid laser can be dug into the aster­oid to some degree, can use the aster­oid for cool­ing to some degree, can see the plan­e­tary defend­ers (and their pro­jec­tiles or laser defens­es) from far away to some degree, etc. The aster­oid defenses would be lim­ited in armor or size by the smaller size of the aster­oid com­pared to the plan­et, yes, but the defenses can be on the los­ing side of each exchange as long as the aster­oid sur­vives to impact! The plan­e­tary defend­ers need to win and neu­tral­ize the aster­oid entire­ly, while the aster­oid defenses just need to delay the war of attri­tion suffi­cient­ly.

Which has the rel­a­tive advan­tage? This is not clear. It may be that the plan­e­tary defend­ers still have an advan­tage and all attack­ers, both space­ships and asteroids/comets, are doomed. Per­haps they are doomed but one can over­come local defenses by going past aster­oids to small moons, but moons are still ineffec­tive because to accel­er­ate a moon is so ener­get­i­cally diffi­cult that it can be observed from the tar­get sys­tem and appro­pri­ate defenses set in motion to neu­tral­ize the moon; and know­ing this, no one will bother with moon-strikes. I am not opti­mistic about either sce­nar­io, so let us con­tinue to assume that things will not work out as one would hope (in favor of defend­er­s).

Nuclear & space first-strikes

To return to our 4-point nuclear war­fare list.

  1. Space is vast & 3D8. Attacks can be begun from any axis. There are no space equiv­a­lents of moun­tain passes or val­leys. So this point holds: nuclear war­fare can attack from any­where on the globe to any­where on the globe, and space war­fare is even more free in its approach.
  2. Each attack could be even more dev­as­tat­ing than nuclear attacks9. Even small comets or aster­oids exceed nor­mal atomic bombs, and it’s about as easy to go for large bod­ies as small.
  3. Nuclear attacks have no defenses besides being buried deep. They can­not be shot down or inter­cept­ed. This is true of moons or aster­oids as well. Remem­ber the ulti­mate sce­nar­io: a moon at near-light­speed. Such an impact is best described as ‘world-shat­ter­ing’. There’s an old mil­i­tary joke: the best way to sur­vive a nuclear attack is to not be there.
  4. A SLBM attack is first observ­able when the mis­siles break the water’s sur­face. An aster­oid gone bal­lis­tic is rather diffi­cult to spot at any point on its jour­ney. In the night­mare sce­nar­io, even if the moon is observed imme­di­ately & reported on, the alert will reach its des­ti­na­tion only shortly before the moon does!

In every point, space war­fare is even more favor­able to the attack­er. There is no per­cent­age in try­ing to defend.


Of course, every­one knows that the first strike doc­trines even­tu­ally yielded to ‘’ doc­tri­nes: . If point #2 is weak­ened to being dev­as­tat­ing to only the nation and con­ven­tional mil­i­tary, spar­ing the nuclear ele­ments, then retal­i­a­tion is pos­si­ble. There is no point in strik­ing first if it will only pro­voke a retal­ia­tory strike that does you as much dam­age as their first strike would have.

Can we hope for MAD? Per­haps. It’s clear enough that there are all sorts of tech­niques: each star sys­tem could have a fleet qui­es­cent in deep space lis­ten­ing to omni­di­rec­tional broad­casts. The heart­beat stops, the fleet sets off for revenge. (They would be space sub­marines in effect; this would also be an exam­ple of “”.) Or a sys­tem could be con­stantly accel­er­at­ing bod­ies at a rival sys­tem, but off-course; then on an attack, the bod­ies could be re-aimed at their tar­get. And so on.


There is one prob­lem with MAD as applied to space. Nuclear attacks in the real world inher­ently involve account­abil­i­ty. If an ICBM lands in New York City, the satel­lites track­ing it from launch will tell us exactly what coun­try it came from. If a nuke is qui­etly shipped into San Fran­cisco & explodes, the fall­out will be imme­di­ately sam­pled and traced back to its man­u­fac­tur­ing coun­try. Within days or weeks, the USA and the world will know if it was an Amer­i­can nuke, or Rus­sian, or North Korean etc.

The vary sub­tly, and the USA has for decades col­lected fall­out from tests by the nuclear pow­ers to deter­mine the char­ac­ter­is­tic iso­tope ratios of those nations’ ura­nium and plu­to­ni­um. Fun­da­men­tal­ly, there’s no way to nuke a nation with­out being blamed for it. Even if Pak­istan gave Al-Qaeda a bomb and they used it in a way that was not trace­able to Pak­istan, the iso­topes would still fin­ger Pak­istan as the cul­prit and fire would rain down upon their head by the aggrieved par­ty. Every nuclear power knows this: they will be held respon­si­ble for any use of their weapons, autho­rized or unau­tho­rized—pe­ri­od.

Deceiving MAD

The MAD equi­lib­rium depends on always hav­ing some­one to blame and attack. But this is not nec­es­sar­ily true of bal­lis­tic war­fare. Sup­pose the attacked solar sys­tem is attacked from its own Kuiper Belt? What other sys­tem does it blame? Short of cap­tur­ing the crew or dis­cov­er­ing incrim­i­nat­ing foren­sic evi­dence on a body, there’s no way of fig­ur­ing out who the attacker is. They can analyse the body all they want; all they’ll find out is the obvi­ous fact that its from their own sys­tem.

Or more sin­is­ter, what if the attack­ers are steal­ing a body? That is, ships from sys­tem A steal a Kuiper object from sys­tem B and accel­er­ate it to sys­tem C? It’s a poor MAD indeed whose sec­ond-strike attacks the wrong par­ty!


A Cold War replayed on an inter­stel­lar scale is a fright­en­ing prospect. One could only hope for as child­ish a real­ity as the Hon­or­verse, but the sober real­ity seems to be a chill­ing esca­la­tion of the risks of the Cold War. Outer space is cold indeed.

  1. Han­son, “Near Far In Sci­ence Fic­tion”:

    Like many oth­ers I enjoyed the new movie, even if I don’t espe­cially respect myself for that, and recently just rewatched Star Wars . And the most com­pelling visu­als and scenes in those movies were sim­i­lar, in that they com­bined famil­iar and emo­tion­al­ly-true fore­grounds with dra­matic sym­bol­i­cal­ly-mean­ing­ful back­grounds which often made lit­tle sense if you thought much about them. For exam­ple, in Star Trek iso­lated crowded ship­yards are shown scat­tered in sim­ple farm­land, wildly vio­lat­ing economies of agglom­er­a­tion… This all sup­ports my detached detail warn­ing: don’t assume that because the char­ac­ter lives described are com­pelling, the his­tor­i­cal arcs are as plau­si­ble.

  2. After all, how plau­si­ble is it, real­ly, that the wedge would pro­vide per­fect pro­tec­tion in 2 direc­tions but not the other 4, and that no bet­ter sub­sti­tute than side­walls would have been devised?↩︎

  3. In many of his bet­ter short sto­ries, at least; the nov­els are usu­ally far enough in the future that mul­ti­ple FTL dri­ves are avail­able.↩︎

  4. Another com­par­i­son I’ve seen; from “City Lights Could Reveal Civil­i­sa­tions On Other Plan­ets” and respec­tive­ly:

    “There is another search that could be done closer to home. With the help of some back­-of-the-en­ve­lope cal­cu­la­tions, Loeb and Turner say that today’s best tele­scopes ought to be able to see the light gen­er­ated by a Toky­o-sized metrop­o­lis at a dis­tance of about 50 AU [Pluto is 30-49 AU], that’s roughly the dis­tance to the .”

    “This implies that an f⊕-il­lu­mi­nated sur­face would pro­vide the same observed flux F as a sun­light-il­lu­mi­nated object at that dis­tance, if it is ∼√3.6×102 = 19 times smaller in size. In other words, an f⊕-il­lu­mi­nated sur­face of size 53 km (com­pa­ra­ble to the scale of a major city) would appear as bright as a 103 km object which reflects sun­light with A = 7%. Since ∼103 km objects were already found at dis­tances beyond ∼50 AU, we con­clude that exist­ing tele­scopes and sur­veys could detect the arti­fi­cial light from a rea­son­ably brightly illu­mi­nated region, roughly the size of a ter­res­trial city, located on a KBO [Kuiper Belt Objec­t].”

  5. Shield­ing against what? Slugs of met­al? Every pos­si­ble fre­quency of laser? Beams of plasma or charged par­ti­cles? Nukes and their x-rays?↩︎

  6. An ene­my’s laser can melt through metal like any­thing else, and if the laser is pow­er­ful, the metal might just evaporate/explode—which isn’t very help­ful at all.↩︎

  7. The area of a sphere is given by the equa­tion:
    1 AU = kilo­me­ters
    30 AU = , or km
    55 AU = , or km
    So the shell is the vol­ume of the outer sphere minus the inner sphere:
    , or .↩︎

  8. In the same way con­ven­tional war­fare is 2D; nuclear war­fare is mod­estly 3D.↩︎

  9. While in the­ory H-bombs can be scaled to indefi­nitely large giga­ton­nage, this is exceed­ingly imprac­ti­cal and large bombs are waste­ful.

    As the bomb becomes larg­er, ever more of the explo­sion’s energy is dis­si­pated away by the atmos­phere or space, and less is directed down­ward into the earth. The rea­son the Rus­sians went as large as the was that they needed overkill to com­pen­sate for poor tar­get­ing—the US with more trust in its accu­racy pre­ferred putting mul­ti­ple smaller bombs onto a tar­get.↩︎