Getting to Mars: Justification
The division of the payload into three packages was determined in order to maximize time and cost efficiency
while maintaining feasibility. Since the effectiveness of the mission depends on the
health and well-being of the human crew, the focus in the spacecraft design was to minimize the
time spent in micro-gravity. In order to accomplish this task, the weight on the spacecraft with
the humans had to be minimized since less weight allows for greater velocities with less fuel. Since a
faster transfers corresponds to a high cost, only the crew and essential equipment will be sent on this
faster transfer. The other equipment, which are not affected by a prolonged transfer, will be sent to Mars
on a slower, hence more cost efficient, transfer.
Thus formed the initial plan to separate
the humans from materials that would not be essential to the interplanetary travel. The third separation
of the communication satellites came from the inconvenience of placing the communication package into
either the Ion Propulsion Package (IPP) or the Nuclear Propulsion Package (NPP). Also the confirmation
of established communication on Mars is essential to subsequent mission stages.
Establishment of these three packages was derived from research into propulsion systems.
Proton rockets were chosen to transport modules into LEO and directly to Mars for five primary reasons.
They have a relatively low cost, a higher payload capability, a higher ISP, a greater control of thrust,
and a higher reliability as compared to other well-developed technologies. The ion propulsion system
was determined to be the most efficient means of transporting equipment despite the long transit time
of a few years. Ion propulsion is low in cost and produces a constant thrust. The constant thrust allows
a spiral transfer to be used, thereby taking advantage of the characteristically low delta v (8 km/s).
The specific spiral transfer chosen for this mission involves the use of both chemical and ion propulsion
systems. To avoid the adverse effects of the Van Allen Radiation Belt on the ion engine, a chemical rocket will be used to
escape the Earth's gravity influence quickly. The IPP will consist of a number of individual ion
propulsion systems, each carrying their own payload to Mars. This avoids a problem that surfaces when
ion propulsion systems are scaled for excessively large payloads. Nuclear propulsion was chosen over
other propulsion systems for transporting humans because of the numerous advantages that lead to a
shorter transit time: Nuclear Propulsion rockets are capable of carrying 2-3 times the payload of other
rockets. In addition, the nuclear propulsion system enhances mobility in space, and provides a source of power.
It allows for more flexibility in design since the energy-supplying medium can be separate from the propellant.
In other words, the energy source may be located at the head of the spacecraft, while the propellent and nozzle
are located at the rear. Additionally, nuclear propulsion provides a greater source of thrust.
Furthermore, it is delta v efficient, meaning nuclear propulsion
uses half as much propellant for a given delta v than other propulsion systems.
On-orbit docking of the NPP modules is required because the NPP system is too large to
be launched into LEO as a whole. Automatic docking is a proven technology. Russia has used similar
technology to dock cargo ships with Space Station Mir for decades. Also, the NPP will follow a
free-return trajectory to ensure the safety of the crew. A free-return trajectory would guarantee
that in the case of propulsion system failure on the way to Mars, the crew would have a means of
returning to Earth. Mars' gravitational pull would "slingshot" the NPP back to Earth safely.