PC Gamer - UK (2021-12)

youmoveaway,thenshallowsout.Understandingthis

formulaiskeytoplayingKerbalSpaceProgram,inwhich

yousendlittlegreenmentovisitotherplanetsina

kookyyetunforgivingapproximationofoursolar

system.“It’sthethingthatmakesorbitswork,”Falanghe

says.“Ifyoudon’taddthatorbitswilllooklike...well,

theywon’tlooklikecircles.”Indeed,mostKerbal

spaceflightslooklikecraters.

IfKerbalstickstothetextbooksonthiscount,it

‘cheats’onotherfronts.Inparticular,itsidestepsthe

so-called’n-body’problem,wherebyeveryplanetarymass

inagroupexertsagravitationalpulloneveryotherbody

simultaneously.“KSPdoessomethingthatisnotentirely

realisticwhichissometimescalledpatchedconic

approximation,whichisjustafancywayofsayingthatwe

switchgravitysourceswheneveryougetcloseenoughto

anotherone.Whenyoucrossintothe‘sphereofinfluence’

ofthemoon,thesourcesswitch,andnowyou’reonly

affected by gravity from the moon.”

Treating gravity as a strictly two-way affair makes for a

more stable and predictable simulation, which is vital

given that missions in Kerbal can take several in-game

years. It means that the simulation doesn’t have to

recalculate gravity ‘step by step’; indeed, the game can

switch mid-spaceflight to a “deterministic” means of

calculating movement without causing discrepancies. “We

used to call it the rails system because the spacecraft was

on rails, and it basically meant that we could freeze all

physics, and just carry things through space.” The

horizon,youhavetofigureoutwhereyouareinrelation

totheplanetandapplyforcetowardsthecentre.”

Astohowmuchforceyoushouldapply,most

developersandastrophysicistsfollowIsaacNewton’s

inversesquarelawofgravity,whichdictatesthatan

object’sgravityisstrongupcloseanddropsoffrapidlyas

andgravitybecomesevenmoreofa

riddle.“The

definitionofdownisn’tdownanymore,”

saysFelipe

Falanghe,creatorofKerbalSpaceProgram

move .“Youcan’tjust

thingstowardsthebottomofthescreen

orthe

SQUARINGTHECIRCLE

Expandtheplayablespace

toencompassanactualplanet,

specificmovementtrajectory.

pillars,he’llhave

clones.”Assuch,

switchesoffgravity FryingJellysometimes

entirelywhenit

wantstoadda

longlegs,he’ll

beagrasshopper

jumpingonto

broken

mechanic

thatthe

playeruses

• he’ll be a cart, he’ll have

Pachniewski. “And each time, there’s a different

grotesque ways,” says Frying Jelly’s founder Pawel

nightmare, where he’s transforming in weird and

thosethatadheresternlytothesciencestruggleto

portraytheideasputforwardinAlbertEinstein’s

theoryofgeneralrelativity.

UPWARDLYMOBILE

BeforewegettoEinstein,however,let’stalkMario.

Workingouthowtomakeacharacterfallinaplatformer

isoneofgamedevelopment’sbread-and-butter

challenges.Itsoundssimpleenough:yousubtracta

certainverticaldistancefromthecharactereveryframe

unlessthere’ssomethingintheway.Butgettingaleaping

characterto‘feel’rightcantakemonthsofwork,because

everydaygravityisgenerallymoreinconvenientthan

enjoyable.Tomakeitsingina

videogame,youhavetofigureout

howandwhentobreaktherules.

“Ifyouapplygravityontopofa

normaljump,you’regoingtoget

thisparabolashape,”explains

FryingJelly’sEricStryczek,oneof

themindsbehindthedreamyyet

ferocious 99 Fails.“It’sperfect.

[But]itactuallyfeelsreallyterrible

asajump.SowhatMariodidallthe

waybackontheNintendo

EntertainmentSystemwashave

thissortofextrabehaviour–when

you’refalling,velocitygetsexponential.Soyousortof

goup,stayintheairforawhile,andthenyouget

suckedrightbackdownreallyquickly.”

TheequationforhowfastobjectsfallonEarthis

minus9.81metrespersecondsquared–manythird-party

gameengineslikeUnitytreatthisastheroughdefaultfor

theirphysicssystems.ButasStryczekgoeson,“Itfeels

reallyfloatytohaveavaluelikethat.Becausein

platformers,wetendtojumpreallyhigh.Whatalotof

beginnersgetwrongisthattheydon’tmesswiththis

value–you really need to have that snappy feeling.”

In 99 Fails, things are complicated by the protagonist

Zeebo’s habit of changing shape. “Zeebo has this recurring

withrealityoutofnecessityorsimply

inthenameoffun.

Theyaretheirownlittlebespokeuniverses

• and even

need a PhD to understand, but most games compromise

visualising equations and

phenomena

you’dotherwise

space

sims. These games can be a useful means of

theJenga-esque launch vehicle physics of full-blown 3D

medium’s birth, from the geometric landslides of

Tetris to

Videogames have been wrestling with gravity since the

Gravity

FEATURE

YOU HAVE

TO FIGURE OUT

HOW AND WHEN

TO BREAK

THE RULES