Jenny Win­der

Sky at Night Magazine - - CONTENTS -

Space writer As­tro­nauts usu­ally hog the lime­light, but Jenny checks out a book in which NASA’s ground con­trol crew are the he­roes.

Jack Cle­mons be­gan work as part of the en­gi­neer­ing team that sup­ported NASA space mis­sions in 1968, three days af­ter the launch of Apollo 8, the first manned space­craft to or­bit the Moon. He was tasked with de­vel­op­ing, writ­ing and test­ing com­puter soft­ware to con­trol the Com­mand Mod­ules’ re-en­try through Earth’s at­mos­phere. At the time, this was done us­ing a slide-rule, as the first hand-held cal­cu­la­tor wasn’t avail­able un­til 1972 and cost the best part of £2,000. Com­puter pro­grams were hand­writ­ten in the com­puter lan­guage FORTRAN and typed onto cards in a punch card ma­chine (one line of pro­gram per card).

Cle­mons’ mem­oir fol­lows the ground teams through all the sub­se­quent Apollo mis­sions, in­clud­ing a de­tailed ac­count of the Apollo 13 res­cue, as well as the Sky­lab and Space Shut­tle mis­sions, up to the mid-1980s, and from the ridicu­lously prim­i­tive Dis­play and Key­board (DSKY) de­vice on the Apollo Com­mand Mod­ules to the five flight com­put­ers aboard the Space Shut­tle.

The team needed to an­tic­i­pate every even­tu­al­ity, cal­cu­lat­ing all the vari­ables such as changes in geo­graphic lo­ca­tion and an­gle of re-en­try. Even the time of year and the weather had to be taken into ac­count, with al­ter­na­tive back-up plans in place.

The mar­gins for er­ror were tiny. In com­puter pro­gram­ming, the in­dus­try av­er­age is 10-12 er­rors for every 1,000 lines of code. Over the 30-year Space Shut­tle pro­gramme, the er­ror rate for com­puter code de­vel­oped by IBM for the On­board Flight Soft­ware went from 0.8 er­rors per 1,000 down to less than 1 er­ror per 5,000 lines of code. That is closer to er­ror free than any large com­plex soft­ware sys­tem be­fore or since. The book has a very nice ap­pendix cov­er­ing fre­quently asked ques­tions about Apollo and the Space Shut­tle, which in­cludes some in­ter­est­ing as­sess­ments of both the Space Shut­tle Chal­lenger and Space Shut­tle Columbia dis­as­ters. This book is not just for com­puter geeks. If you have seen (and loved as much as I did) Ron Howard’s 1995 film Apollo 13, then you will love this insider’s tale of hu­man space ex­plo­ration from the point of view of the team back on planet Earth. Why should the as­tro­nauts get all the glory?

JENNY WIN­DER is a free­lance sci­ence writer, astronomer and broad­caster

Tense times at mis­sion con­trol dur­ing the ill-fated Apollo 13 mis­sion

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