Ten ton craft work time is the hours of labor required to build a stage of the spacecraft with an empty mass of ten tons ( ten thousand kilograms ). With a typical mass ratio of eight to one, this corresponds to a gross liftoff mass, including fuel of about eighty tons.

Building commercial aircraft is a routine job, five thousand hours for a ten ton craft. Building a well designed rocket is doable, twenty thousand hours for a ten ton craft. Building an impractical craft, for instance one with a combination of solid and liquid propellants, is considered to be almost impossible, eighty thousand hours for a ten ton craft. Ten ton craft work is used along with the empty mass and labor scale factor to calculate the initial hours required to build the craft .

initial hours = pow( ( empty mass / 10,000 ), labor scale factor ) * ten ton craft work
 

This is used in rocket cost and spacecraft cost.
 

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