I. P. 6th SW Maj. Michael L. Manning Maj. John R. Davis Capt. Jonathan K. Seckman On 28 January 1986 , at 11:39am EDT the Space Shuttle Challenger explodes 73 seconds after liftoff during mission STS-51-L. On 26 April 1986 , reactor number four at the  Chernobyl  nuclear powerplant,  near the town of Pripyat in