The orbits of the Earth and Mars allow us to launch about every 26 months. The NASA Reference Mission begins with a launch of crew support equipment. Conventional chemical rockets, such as those used on the space shuttle, will probably be used to launch the Mars rocket into low-Earth orbit. Propulsion systems being considered for the Mars transit vehicles include nuclear thermal propulsion engines, ion engines, and variable speed impulse magneto-plasma rocket engines. An international effort could pool the resources of these countries and others including the European Space Agency members, India, Brazil, and other countries entering the aerospace business.

Once at Mars, cargo and crew ships will be captured by the Martian atmosphere using an aeroscapture maneuver. 

Aerobraking, parachutes, and thrusters are used to get the spacecraft safely on the surface. The astronauts will arrive in a crew module that will house them for the trip and while on the surface. Previously sent cargo ships will provide power, return propellant production, and surface life support.

Using an aerobraking technique, one of the two 
lander transport vehicles slows down and glides into 
Mars's orbit.

The amount of mass that must be lifted from Earth for human missions to Mars can be reduced by as much as 50 percent if a structure called an aerobrake is employed. The Mars landing vehicle depicted here uses a "molly bolt" design that allows the aerobrake to be deployed in a flat shape for atmospheric entry and landing, and then retracted to form a smooth conical shape for ascent.

In the 1997, NASA Mars Exploration Scenario, a launch vehicle using propulsion systems with space shuttle heritage, boosts one stage of a Mars spacecraft into Earth orbit. Two such launches put a complete Mars-bound vehicle in Earth orbit. A fully assembled Mars spacecraft is made ready for its voyage to the red planet. 

 With all engines running, the crew and their spacecraft leave Earth orbit and begin their six-month voyage to the red planet.  Prior to their takeoff, the first cargo ship has arrived and put into production the propellant factory that will produce fuel for the crew's return trip. The cargo ship has also brought additional supplies for the crewed mission.
 

After a 125 million mile journey the ship reaches Mars. The lander uses atmospheric breaking to decelerate prior to landing. After landing on the Martian surface, the crew uses an unpressurized rover to unload cargo and supplies.

The crew attaches an inflatable laboratory to their lander to increase the pressurized volume of their Martian home. The completed outpost includes the two-story lander habitat, an inflatable laboratory, and the unpressurized rover. After the habitats are joined, the crew has multiple pressurized volumes available for conducting greenhouse experiments, biological research, and geochemical analysis of samples and for general crew accommodations. The crew's ascent vehicle and propellant production facility are located near the completed outpost.
 

After spending nearly 500 days on Mars, the crew begins their 180-day voyage back to Earth by ascending into orbit to rendezvous with their Earth-return vehicle. Subsequent human missions have the option of returning to the site established by the first crew or placing additional footholds on the surface of Mars. The Earth return vehicle has awaited the crew's arrival in Mars orbit for nearly three years.  After checking out the ERV's systems, the crew takes off on their journey in the now-familiar Mars habitat. This familiarity will pay off in terms of increased crew safety and reduced program costs.

Questions to think about:

• Which systems would need to be checked out on Mars from the unmanned cargo ship before sending the crew ships?

• How would you go about checking these systems from Earth?

• What would happen if there was a failure of one of these systems before the human crew arrived?

Next... Propulsion Systems (pg. 14 of 17)