What is some scientific evidence used in "The Cold Equations", by Tom Godwin?

The EDS has been fuelled only sufficiently to deliver the ship and its contents to the surface of the planet, with no margin for errror. It only has to follow the pre-programmed flight plan to get safely down to the surface, where the pilot will have to remain until the next scheduled contact. If a stowaway is not discovered, or allowed to remain on board, the pre-calculated fuel burn rate will not decelerate the ship sufficiently, and it will impact on the surface at high velocity, or, if the burn rate is increased to allow for the added mass of the stowaway, the ship will run out of fuel at some point above the surface, and it will crash, both scenario's spelling death for the pilot, the stowaway, and the colonists. The mass/energy equations admit no other outcome, and the stowaway must be jettisoned.