The upper limit for the *mass* of a NASA sponsored robots is set at 80 kilograms.
The numerical value of the "weight" (in newtons) of the robots is never an important consideration. To weigh (a verb form) is "to balance forces, almost always to measure the *mass* of an object." The forces in balance (on the surface of the earth) are the gravitational force acting on a "mass standard" (perhaps a cylinder of metal) or the elongation force of a spring or compression force of a "load cell" (both calibrated in units of *mass*; grams or kilograms), in equilibrium with the gravitational force acting on the object in question. The *mass* of the object being examined is measured in grams or kilograms! The "weight" of the object (in newtons) is usually of no interest. In "free fall" (e.g. *inside* the International Space Station) gravitational forces arising from the distant presence of the earth are not sufficient for measuring the masses of objects. Instad, some kind of inertial device is required, perhaps a rotating balance responding to centrifugal forces. Eugene Mechtly ________________________________ From: [email protected] [[email protected]] on behalf of John M. Steele [[email protected]] Sent: Thursday, June 06, 2013 6:27 AM To: U.S. Metric Association Subject: [USMA:52885] Fetch! Robot retrievers compete in $1.5 million NASA contest http://news.yahoo.com/fetch-robot-retrievers-compete-1-5-million-nasa-184103001.html Reuters reports all units dual. Note (near end of article) that the weight and size limits set by NASA are metric and Reuters reports them as metric primary.
