Ten seconds after the separation of the boosters, two-and-a-half minutes into the climb, the OMS engines fired in a novel engineering test. Normally only ignited in space, they were used this time while still in the 'sensible' atmosphere as part of evaluating ways to enable the vehicle to carry 230 kg of extra cargo into orbit. ''The goal'', said Altman of the so-called 'OMS Assist' exercise, which lasted 1 minute and 42 seconds, ''is to help to increase the Shuttle's performance margin, to get more mass to orbit by using some of that performance of the OMS engines.''
In total, 1,810 kg of propellant was expended. Four minutes later, as STS-87 did the previous November, Columbia's computers rolled the spacecraft 180 degrees from a 'heads-down' to a 'heads-up' orientation to improve space-to-ground communications through the TDRS network. All in all, it was an awesome ride. ''The physical sensation'', recalled Searfoss, who was doing this for the third time, ''starts out with a tremendous jolt when you first release off the pad and then there is an awful lot of vibration because as you go through the atmosphere you are affected by the upper-level winds and turbulence. Also [along] the way, the [SRBs] produce a lot of vibration. When the boosters drop off, the ride becomes very, very smooth. The last six-and-a-half minutes is a very smooth ride, but you get progressively pressed further and further into your seat as the acceleration picks up, so in the last couple of minutes you're feeling about 3 gs, so your body weighs three times its normal weight. It's not particularly uncomfortable. The seat supports you very well. You can't move around very much, but you don't want to move around anyway. You just want to enjoy the ride. When the main engines stop, and you get to zero gravity, the transition is instant. You go from 3 gs, pressed into your seat, to floating up against your straps. Various things start to float up. It's a very sudden and amazing transition to a whole different world.''
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