The incredible and underestimated achievement that is the international space station is not one to be pushed around lightly. "Lightly" of course takes on loose meaning once up in the peanut gallery of this planet's gravity well; forever in free fall Alpha suffers rare encumbrance with her ethereal orbit and obeys only the incessant and unavoidable siren call of a homeworld eager to pull anything to a fiery embrace. To compensate for orbital drag we (that is to say, the Russians, acknowledging the work they do with inadequate salutes for the trouble) use temporarily docked rocket-thrusters (conveniently filled with food and spare parts). The Progress supply ships have become a lifeline until next year's Automated Transfer Vehicle and potential shuttle launches step in to help shoulder the load.

Expedition 9 has been a rousing success, and God willing it remains that way. Spacewalks have accomplished necessary mission goals including the recent jettison of Progress 14 and subsequent attachment of Progress 15, docked at the station only a few days ago (the third such supply ship this year). Filled with trash and brought home on special trajectory, Progress 14 burned up carrying a little more of the inaccuracy with it. We can avoid some things but their consequences continue to press us. As these ships have been coming and going, some loss of detail has occurred to the point that frankly, no one's quite sure how much ISS weighs right now.

In a way it's human to see the project so large that they've lost contact with some of the basic facts underlying the effort, like how much has actually been sent up there! As it stands reliable estimates are hard to come by- duh- but the best I've seen was slightly upwards of 180 metric tons. As noted earlier that puts the station and the shuttle on comparable grounds size-wise, a value that places it about one thousand times smaller than Kirk's Enterprise. But first year physics provides the answer.

The pre-launch weight of the latest Progress and calculated rate of fuel consumption for its eight engines come to bear as the component mass of thruster plus station which is to be pushed. (My understanding is that it took an extra day in transit and this permits more precision in the answer.) The acceleration can be determined by sensors aboard the station; total resolution of the final figure is computed to be within two percent. I hope somebody makes sure the crew holds fast to something immovable during the experiment!


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