Defining the problem :
Mars Direct vs. Earth orbit
The problem must first be defined in order to start analyzing different
alternatives for the propulsive system. We know for sure that we want to
get from Earth to Mars, land there and come back to our home planet. But
where will be launch from?
The two alternatives have been extensively studied. Advocates of the
Mars Direct and Semi Direct,
led by Dr. Robert Zubrin call for a giant booster in stages to propel the
spacecraft directly from the Earth's surface onto Mars.
The more traditional approach considers an excursion vehicle launching
from Earth orbit and possibly assembled in the Space Station, thus requiring
less thrust in terms of propulsion. The Mars
Direct plan does without the Space Station, partly through skepticism
on its operability that would retard the development of a Mars mission
by many years.
At this point, it would be very difficult to select an approach that
would be technically justified as superior to the other, for it would involve
economic and cost related considerations that are beyond the goals of our
However, both approaches share common features. Even in the Mars
Direct plan, or any plans that involve a direct trip from Earth surface
to Mars, the mission would be staged and probably stay in Earth orbit for
a while in order to check all systems. The final Mars insertion burn will
have to be accomplished by a stage of the initial giant rocket or by the
excursion vehicles engines themselves, similarly to launching that excursion
vehicle from the Space Station.
So in fact, our task would consist in designing an excursion vehicle
(last stage of the Mars Direct plan or unique spacecraft to be launched
from the Space Station) that would take off from LEO to Mars. If it is
finally decided to adopt a direct approach, then the spacecraft will be
integrated into the giant booster. Placing a payload in Earth orbit is
not a technological problem, and the excessive weight problem could be
solved by Earth orbit rendezvous of the different parts.