Pre-launch conditions Space Shuttle Challenger disaster

1 pre-launch conditions

1.1 delays
1.2 thiokol–nasa conference call
1.3 ice

pre-launch conditions
delays

challenger set launch ksc in florida @ 14:42 eastern standard time (est) on january 22, 1986. delays in previous mission, sts-61-c, caused launch date moved january 23 , january 24. launch rescheduled january 25 due bad weather @ transoceanic abort landing (tal) site in dakar, senegal. nasa decided use casablanca tal site, because not equipped night landings, launch had moved morning (florida time). predictions of unacceptable weather @ ksc on january 26, caused launch rescheduled 09:37 est on january 27.

the launch delayed next day, due problems exterior access hatch. first, 1 of micro-switch indicators, used verify hatch safely locked, malfunctioned. then, stripped bolt prevented closeout crew removing closing fixture orbiter s hatch. time repair personnel had sawed fixture off, crosswinds @ shuttle landing facility exceeded limits return launch site (rtls) abort. while crew waited winds die down, launch window expired, forcing yet scrub.

thiokol–nasa conference call

forecasts january 28 predicted unusually cold morning, temperatures close −1 °c (30 °f), minimum temperature permitted launch. shuttle never certified operate in temperatures low. o-rings, many other critical components, had no test data support expectation of successful launch in such conditions.

by mid-1985 thiokol engineers worried others did not share concerns low temperatures effects on boosters. bob ebeling in october 1985 wrote memo—titled help! others read it—of concerns regarding low temperatures , o-rings. after weather forecast, nasa personnel remembered thiokol s warnings , contacted company. when thiokol manager asked ebeling possibility of launch @ 18 degrees, answered [w]e re qualified 40 degrees ... business have thinking 18 degrees, re in no-man s land. after team agreed launch risked disaster, thiokol called nasa recommending postponement until temperatures rose in afternoon. nasa manager jud lovingood responded thiokol not make recommendation without providing safe temperature. company prepared teleconference 2 hours later during have justify no-launch recommendation.

at teleconference on evening of january 27, thiokol engineers , managers discussed weather conditions nasa managers kennedy space center , marshall space flight center. several engineers (most notably ebeling , roger boisjoly) reiterated concerns effect of low temperatures on resilience of rubber o-rings sealed joints of srbs, , recommended launch postponement. argued did not have enough data determine whether joints seal if o-rings colder 12 °c (54 °f). important consideration, since srb o-rings had been designated criticality 1 component, meaning there no backup if both primary , secondary o-rings failed, , failure destroy orbiter , kill crew.

thiokol management supported engineers recommendation postpone launch, nasa staff opposed delay. during conference call, hardy told thiokol, appalled. appalled recommendation. mulloy said, god, thiokol, when want me launch — next april? nasa believed thiokol s hastily prepared presentation s quality poor support such statement on flight safety. 1 argument nasa personnel contesting thiokol s concerns if primary o-ring failed, secondary o-ring still seal. unproven, , in case argument did not apply criticality 1 component. astronaut sally ride stated when questioning nasa managers before rogers commission, forbidden rely on backup criticality 1 component.

nasa claimed did not know of thiokol s earlier concerns effects of cold on o-rings, , did not understand rockwell international, shuttle s prime contractor, viewed large amount of ice present on pad constraint launch. reasons unclear, thiokol management reversed , recommended launch proceed scheduled; nasa did not ask why. ebeling told wife night challenger blow up.

ken iliff, former nasa chief scientist had worked on space shuttle program since first mission (and x-15 program before that) stated in 2004, violating couple of mission rules primary cause of challenger accident.

ice

ice on launch tower hours before challenger launch

the thiokol engineers had argued low overnight temperatures (−8 °c (18 °f) evening prior launch) result in srb temperatures below redline of 4 °c (39 °f). ice had accumulated on launch pad, raising concerns ice damage shuttle upon lift-off. kennedy ice team inadvertently pointed infrared camera @ aft field joint of right srb , found temperature −13 °c (9 °f). believed result of supercooled air blowing on joint liquid oxygen tank vent. lower air temperature , far below design specifications o-rings. low reading later determined erroneous, error caused not following temperature probe manufacturer s instructions. tests , adjusted calculations later confirmed temperature of joint not substantially different ambient temperature.

the temperature on day of launch far lower had been case previous launches: below freezing @ −2.2 −1.7 °c (28.0 28.9 °f); previously, coldest launch had been @ 12 °c (54 °f). although ice team had worked through night removing ice, engineers @ rockwell still expressed concern. rockwell engineers watching pad headquarters in downey, california, horrified when saw amount of ice. feared during launch, ice might shaken loose , strike shuttle s thermal protection tiles, possibly due aspiration induced jet of exhaust gas srbs. rocco petrone, head of rockwell s space transportation division, , colleagues viewed situation launch constraint, , told rockwell s managers @ cape rockwell not support launch. rockwell s managers @ cape voiced concerns in manner led houston-based mission manager arnold aldrich go ahead launch. aldrich decided postpone shuttle launch hour give ice team time perform inspection. after last inspection, during ice appeared melting, challenger cleared launch @ 11:38 am est.