  Gauging the benefits of hypothetical gravity control propulsion is difficult,
but addressable. The major challenge is that such breakthroughs are still only
notional concepts rather than being specific methods from which performance can
be rigorously quantified. A recent assessment by Tajmar and Bertolami used the
rocket equation to correct naive misconceptions, but a more fundamental
analysis requires the use of energy as the basis for comparison. The energy of
a rocket is compared to an idealized space drive for the following cases:
Earth-to-orbit, interstellar transit, and levitation. The space drive uses 3.6
times less energy for Earth to orbit. For deep space travel, space drive energy
scales as the square of delta-v, while rocket energy scales exponentially. This
has the effect of rendering a space drive 150-orders-of-magnitude better than a
17,000-sec Specific Impulse rocket for sending a modest 5000 kg probe to
traverse 5 light-years in 50 years. Indefinite levitation, which is impossible
for a rocket, could conceivably require 62 MJ/kg for a space drive. Assumption
sensitivities and further analysis options are listed to guide further
inquires.
