6 BA TTIN

ha ppen ed. Du ring t hat time a 2 47- seco nd bur n to ok p lac e und er the

co ntro l o f th e MIT gu id anc e s yste m a nd A p oll o 8 was i n lu na r or bit.

The a stro nau ts an nou nce d thei r orb ital para meter s pro vide d by th e

AGC when vo ice c ont act was re sume d. T h e Mis sion Con tro l folk s

were o bvio usly d isc onc erte d:

“How d o they kn ow? W e h aven’ t had time t o tra ck the m

yet . ”

They were not y et exp eri ence d with self -con tain ed i nert ial sy ste ms.

At 8:4 0 p m Ch ristma s Eve, 1 968 , the Apo llo 8 a stro nau ts we re

on te levisi on bro adc astin g from lu nar orb it. “For all the p eop le

on Ea rth, ” s aid Bi ll Ande rs, “ th e c rew of Ap ollo 8 has a me ssag e

we wou ld l ike to sen d y ou. ” He p aus ed a momen t a nd then b egan

rea din g:

“In th e b e g inni ng God c r e ated th e He ave n a nd the Ear th

: : :

and Go d sa w t hat it was g ood . ”

The co mmand er Fr an k Borma n add ed:

“And f rom t he c rew o f Apoll o 8, we cl ose wit h go od ni ght,

goo d l uck, a Me rry Chr istma s, a nd Go d bl ess a ll o f you —

all of y ou on t he go od Ea rth. ”

Day s lat er , in t he W as hin gton Post , t here a ppe are d an e dito rial :

“At some p oint i n th e h isto ry of the wo rld s omeo ne may

hav e read th e  rst ten ve rses o f the

Book o f Gen esis

und er c ond itio ns t hat g ave th e m greate r mea nin g t han

they h ad o n Chr istma s Ev e. Bu t it seems unl ikely

: : :

This

Chri stmas wil l a lway s be r e membe r ed as th e lun ar o ne. ”

In Retrospec t

The eu pho ria fol lowing t he su cce ss o f Ap ollo 8 was quic kly over-

sha dowed by th e de part ure of mo s t of ou r top s oftwar e tale nt. One

of th e ma ny “sp inoffs ” o f th e I nstr umen tati on Lab was h app enin g

aga in. Like s o many o ther s befo re th em, t hey were sta rtin g th eir

own c ompa ny . It was a h ard blow in de ed.

But we di d su rvive. By th at time we ha d ve ry s tron g te am memb ers

an d they wer e read y fo r the p romot ion s t o fo llow .

Apollo 11 was a mag n i  ce nt t riumph! Bu t th e ac tual l and ing was

more ex citin g th an we h ad c oun ted o n. Ju st befo re tou ch down th e

Apo llo Guid ance Comp ute r a lmo st c aus ed a ne ar p ani c b y d ispl ay-

ing a larms . The NAS A  ig ht c ontr olle rs re main ed co ol and d id not

ord er an a bort .

Durin g the sho rt st ay o f Nei l Ar mstro ng and Bu zz Ald rin o n

the lun ar su rfac e, every one who c ould p ossi bly co ntri bute to a n

un ders tan ding of th e pr obl em was ha rd a t w o rk . The re was c onc ern

ab out the up comi ng l ifto f f and r end ezvou s in jus t a few h our s.

The c ulpr it was a n er ron eou s mod e s ettin g— th e re nde zvou s rad ar

was tran smitt ing pu lses to th e co mput er at maxi mum r ate. Dur ing

lan din g, t he c ompu ter h as p len ty o f work to do. The ad ditio nal t ask

of co unt ing all thos e extra neo us p uls es was j ust to o much .

There a re s till a lo t of peo ple, wh o s hou ld k now be tt er, wh o

de scrib e th at even t a s a co mpu ter ma lfun ctio n. Not hin g c oul d b e

fart her from th e trut h. It was , in fa ct, a t riump h o f s oftwa re d esig n.

When th e c ompu ter was op era ting ne ar ca pac ity a nd sen sed an

over load c ond itio n, i t wa s p rog ramme d to sto p everyt hin g, c lear

the t able , an d re star t on ly the to p pr iori ty j obs. The d isp lay of the

ala rm was to tell t he as tro naut s a nd g rou nd co ntr olle rs j ust wh at was

ha ppen ing .

The s oftwar e d esig ner s had th e for esig ht to a ntic ipat e suc h a

po ssib ility a nd the sk ill to co pe wi th it sh oul d i t ever ha ppe n. No

on e e ve r th oug ht i t wo uld ha ppe n— ex cep t Mu rph y , of c our se.

Neil Ar mstro ng reme mber ed t he Ap ollo c ompu ter when h e was

lat er ass ign ed to N ASA hea dqu arte rs to head the re sear ch an d

devel opme nt p rog rams. One suc h pro gram in vo lved a n F8 a irpl ane

to be u sed for a  y-b y-wir e ex per imen t. N ASA n eed ed a re liab le

co mpute r to  y th at a irpl ane . A c ompu ter fa ilur e w o uld mea n th e

los s of the p lan e.

Neil s ugg este d th e Ap ollo Gu idan ce Comp ute r:

“It’ s th e mos t re liab le c ompu ter I kn ow . It go t me s afe ly

to t he moo n and b ack . ”

And th at is exact ly th e co mp uter th at was us ed. Ph il Fellem an, a n

ou tstan din g le ade r an d s yst ems e ngin eer a t t he Dra per Lab , was

given the jo b to do . And he d id it we ll.

The Apo llo Guid anc e Co mput er never fa iled in any  ig ht. Th ere

was co nce rn when lig htn ing str uck Apo llo 12 du ring la unc h. It

wipe d out the era sab le memo ry l oad and ini tiat ed a co mpute r

res tart . Bu t t he me mory w a s relo ade d i n eart h o rbi t a nd a ll went

well .

The qu ality -co ntro l peo ple c oul dn’ t calc ula te the “me an- time-

bet ween -fail ures ” si nce it wou ld have req uire d divi din g by ze ro.

Gener ally, en g inee rs st are in d isbe lief whe n tol d tha t the Apo llo

com pute r h ad ab sol utel y n o buil t-in red und ancy. There wer e many

po ssib iliti es of sin gle- poin t fai lure s wh ich wou ld h a ve dis able d th e

com pute r . Bu t no ne o f th em hap pen ed.

Even the co mput er it self was not redu nd ant. In th e Spa ce S hu ttle

tod ay th ere a re  ve gui dan ce co mput ers but th ere was o nly o ne

eac h in the Co mmand Modu le a nd th e Lun ar Mo dule .

(

There was

a b ack -up c ompu ter of li mited ca pab ility in th e LM fo r emerge ncy

use , desi gne d an d built by TR W , but it was never n eed ed.

)

It wasn ’ t a matte r of lu ck eit her. Rel iabi lity con side rati ons wer e

up permo st in th e desi gn rig ht fro m t he sta rt.

For exa mple, onl y o ne typ e of in tegra ted lo gic circ uit , a t hree -

inp ut NOR ga te, was us ed. This mea nt th at Eldo n Hall an d Rayth eon ,

the co mput er ma nufa ctu rer, cou ld co ncen tra te on qu ality con trol of

a s ingl e ci rcui t ra ther tha n seve ral. A wid er va riet y of c ircu its wo uld

have re duc ed t he n umbe r o f co mpon ent s pe r co mput er bu t r el iabi lity

woul d have bee n a dvers ely affec ted.

In the wa k e o f the Ap o llo 1 1  ight, Dave Hoag , th e MIT Pro gram

Man age r for Apol lo, an d I were invite d to Russ ia a s gu est s of the

USSR Acad emy o f Scie nce s. W e to ok with us t he NASA  l m of the

lun ar lan din g.

It wa s a n imme diat e s ucc ess. No mat ter wh ere we we nt, ever yon e

wante d to se e th e  lm . If ther e w a s n o scre en, they wo uld ha ng u p

a be d sh eet. W hen the lig hts wen t o ut, c lea ning la dies , jani tors , a nd

oth er ext rane ous fo lk wo uld squ eez e in to th e r oom. It w a s sh own s o

many t imes on so m any s tran ge pro ject ors th at th e sp roc ket ho les

were d amag ed bey ond rep air .

Durin g th e q uest ion a nd a nswe r pe riod followi ng t he s how , th ere

was a lw a ys the qu esti on:

“Whe n will the Amer ican s go to th e moon a gain ?”

Fortu nate ly , we k new t he pla nne d da te of Apol lo 12 a nd t old the m.

They were inc redu lou s. No on e ever a nno unc ed l aun che s a hea d o f

time .

As it h app ene d, we wer e d ead righ t. Ap ollo 12 did  y on sc hed ule

Novemb er 1 4, 19 69 . That mus t have d one a lo t f or o ur cr edi bilit y

bac k in th e USSR.

The Sov iet pe n c hant for s ecrec y ha s alwa ys b af ed me . Ju st b efor e

we  ew to Ru ssia , th e S o yu z 6 wit h two cos mona uts abo ard w a s

lau nch ed on Octo ber 1 1, 19 69. Whe n we c han ged p lan es in Lon don ,

we le arne d of th e l aun ch of Soyuz 7 o n Oct obe r 12. “W ond erfu l, ”

we th o ugh t. “W e will be ther e in p erso n an d lear n all abo ut t his  rst

han d.”

As we dr ove towar d Mos cow fr om th e airp ort wit h ou r ho st,

I a sked ab out t he pu rpo se of t he do ubl e lau nch . T h e r eply was

an irr elevant c ommen t a bou t s ome h ous ing pro ject we ha d ju st

pas sed .

The n ext d ay , Oct obe r 13 , Soyu z 8 lif ted o f f to j o in t he o ther t w o .

Now th ere we re t hre e sp a cecr aft a nd si x c osmo nau ts i n o rbit — a rea l

spe cta cula r! W e kn ew o f th is o n ly f rom pict ures in

Pravd a

. Non e

of us re ad Rus sian so we we re at t he mercy o f our Rus sian ho st fo r

det ails . Bu t, to our dis may , we a gain l earn ed noth ing . Any que stio n

was c oun tere d b y a qu ick cha nge o f th e su bjec t.