The Economist - UK (2022-02-19)

72 Science & technology TheEconomistFebruary19th 2022

with thousands of public comments. Offi cials have promised a decision within weeks. But broader environmental issues could yet force the firm to suspend work at Boca Chica entirely. An internal memo leaked last year revealed serious problems with the Raptor engines intended to power Starship. In his press conference, Mr Musk left himself a fair amount of wriggle room. An orbital flight, he said, might come in “a couple of months”—though it could also slip to the end of the year.

Zero gravitas Something like Starship has been in devel opment at SpaceX for over a decade, under names such as mct(Mars Colonial Trans porter), its(Interplanetary Transport Sys tem), and bfr(Big Fucking Rocket). Earlier versions were huger still: the itshad a 300 tonne payload at one point. But all ver sions had one thing in common: they are designed to be entirely reusable. SpaceX already flies partially reusable rockets: the first stages of its Falcon 9 ma chines fly back to Earth under their own power. Once refurbished and refuelled, they can fly again, spreading their con struction cost over many launches. But their second stages, which end up much higher and moving at orbital speeds, re main expendable. With Starship, SpaceX plans to recover both parts. Its Super Heavy first stage, like the Falcon 9’s, is designed to fly back to the ground shortly after launch. SpaceX plans to catch it in midair with a pair of robotic “chopsticks” attached to the launch tower from which it took off. Recovering the upper stage requires more drama. Starship will fall bellyfirst from space, relying on atmospheric drag to shed most of its speed. It will use its stubby fins for control, “rather like how skydivers use their hands and feet”, says Scott Man ley, a physicist and programmer who runs a popular rocketryfocused YouTube chan nel. When it is within a few hundred me tres of the ground it will flip itself upright, relight some of its engines and make a rocketpowered landing of its own. Several test flights have practised this flipping manoeuvre already, though not after a descent from orbit. Mr Musk (whose bold visions sometimes work, and some times do not) hopes that each Super Heavy booster could be ready to fly again within an hour. Since the rocket’s upper stages would have to complete at least one orbit before returning to Earth, he hopes they might one day manage three flights a day. (The minimum reuse time for a Falcon first stage is about a month.) Starship’s Raptor engines are also de signed with reusability in mind, says Mr Manley. They use a sophisticated, highly efficient design pioneered—but never flown—in the Soviet Union in the 1960s.

Somewhatunusually,theyrunonmeth ane rather than kerosene,a morecom monlyusedrocketfuel.Methaneproduces verylittlesoot,whichhelpskeeptheen gine’sinternals clean—anotherboonfor anengineintendedtoflyagainandagain. Andbothmethaneandtheoxygenneces sarytoburnitcanbemadefromMars’s thincarbondioxideatmospherewiththe help of some straightforward industrial chemistry. SpaceXhopesthatcould,one day,allowMarsboundStarshipstorefuel fora returntriptoEarth. Buthighleveldesigndecisionsarenot theonlyreasonStarshipischeap.SpaceX has an iterative, rapidfire, startupstyle culture verydifferentfromthatofolder aerospacefirms(henceallthecrashland ingsandexplosions).MrMusk’sdevelop mentphilosophyisthat“ifthingsarenot failing,youaren’tinnovatingenough.”Ina speechinNovembertoAmerica’sNational Academies ofSciences,Engineering and Medicinehespokeofrunninga dozentest flightsin2022.Thefirmmixeshightech, bespokedesigninsomeareas(suchasthe Raptor engines) with a makedoand mendattitudeelsewhere(someSuperHea vyprototypeshavefinscontrolledbyelec tricmotorstakenfromcarsmadebyTesla, anotherofMrMusk’sbusinesses). Onegoodexampleistherocket’sstain lesssteelconstruction.Starshipwasorigi nallygoingtobebuiltfromhightechcar bonfibrecomposites,whicharebothvery strongandverylight.Butin2019,despite havingproducedseveralbigcomponents, SpaceX wentbackto thedrawing board. Carboncomposites,itturnsout,havesev

eraldisadvantages.Theyareporous,fiddly toworkwith,andneedtobecuredinan autoclave—noteasywhenmakingrocket bodysegmentsthatareninemetresacross. And,ataround$130perkilogram,compos itesareexpensive. Stainlesssteel,bycontrast,isstrongbut heavyandthereforenotanobviouschoice for rocketbuilding. Some steel alloys, though,getsignificantlystrongerasthey cooldown,meaninglessisrequiredfora given strength. And since Starshipuses cryogenicpropellant,coolingisinabun dantsupply.Steelistougher,too,which cansaveweightelsewhere.SpaceXhopes togetawaywithapplyinga heatshieldto onlythewindwardpartoftheupperstage, whichfeelsthefullforceofreentryheat ing,leavingtheleewardsideasbaremetal andsavingmass.Stainlesssteeldoesnot needpainting,whichreducesweight.Itis mucheasiertoworkwith,andcostsmere dollarsperkilogram.Fora companythat intendsto massproduceitsrocket,says SimonPotteratBryceTech,a firmofspace industryanalysts,thatmatters. Thatmaysoundlikea riskyapproach whenitcomestosomethingasunforgiv ingas rocket science. Butit hasserved SpaceXwellsofar.Ithaspulledoff 111 Fal con 9 launchesinarowwithoutfailure, makingitoneofthemostreliablerockets everflown.SomeFalcon9 firststageshave alreadybeenlaunchedtentimes. A cheap,big,reusablerockethasbeena dreamofspacecadetsfordecades.Onpa per,atleast,Starshipfulfilsit.“Youalmost gettoa pointwherelaunchcostswouldgo awayentirelyasa consideration,”saysMr

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Metres

Boeing 747-400

Delta IV Heavy

Ariane Energia 5

Soyuz 2.1a

New Shepard na

*AtFeb2022,yettofly

SLS Block 1* Saturn V Starship*

Payloadtolow-earthorbit,tonnes

Long March 5

Space Shuttle 720 29 25100 29 95 10 Up to 150

Person

So much for subtlety Selected carrier rockets (past and present)

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The Economist - UK (2022-02-19)

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