In truth, it wouldn’t have made a difference if he had considered it. The crucial decision had been made and executed weeks ago by Sean Probst, when he had laid in a course at L1 and executed the burn that had placed Ymir on its current trajectory. This was an ellipse with a very low perigee. That was a sound idea from an orbital mechanics point of view in that the steam engine would have maximum leverage at that point—it was the natural place to make a burn and effect a transition to a low circular orbit matching Izzy’s. But, sick and exhausted from his two-year odyssey, isolated from the latest scientific discourse by radio failure, Sean might have overlooked the expansion of the atmosphere when making his calculations.