Atlas V performed flawlessly earlier today to place Cygnus “Deke Slayton II” into orbit. (“Deke Slayton I” was the vehicle lost in the Antares launch explosion.) The 16,517 pound vehicle was the heaviest payload ever lifted by Atlas V — yet it only required the lightest configuration of the rocket. This counter-intuitive detail is because Cygnus only must climb as high as the ISS; most of Atlas’ customers are launched to much higher orbits, requiring much more energy. Cygnus thus breaks the record previously held by the MUOS military commsats, which are over 15,000 lbs but are lifted by the 551 configuration Atlas V (the largest configuration yet flown — 5 meter payload fairing and 5 strap-on boosters) to place them into geosynchronous transfer orbit, so require much more energy than this launch required.