Reply To: Richard Branson – Virgin Pledge

[Aeronaut]

Duke, I’ve had the distinct impression that nobody’s reading Eric’s slide, just responding. It clearly states 2 tons of mass. I wish Jimmy hadn’t linked to the slug- its purpose has something to do with continuity between units in the English system. Not needing the slug is another powerful reason for using Metric, in addition to round number gravity and continuity of units.

Here’s 2 familiar formulae that demonstrate mass as I understand it- Weight =mass * gravity, and Momentum=mass * velocity. Weight is not a constant, but mass is. That’s why Eric gave the “weight” in terms of mass. Aboard a spaceship, nothing would have any weight, but try to compute length of burn to achieve specified delta-vee without knowing the mass of everything from the contents of your propellant tanks on down to what’s in the galley and holding tank.

If that doesn’t make it clear, we had best agree to disagree, and simply move on, in my opinion.