Masataka Okutsu

Mars free returns via gravity assist from Venus

The safety of the crew is the top priority for human exploration of Mars. If an unexpected emergency occurs, a free-return trajectory can bring the spacecraft back to the Earth without a large trajectory correction maneuver. Such mission-abort scenarios are analyzed by searching for various Mars free-return trajectories, including gravity assist from Venus en route. Thorough investigations of Earth-Mars-Earth, Earth-Mars-Venus-Earth, and Earth-Venus-Mars-Earth sequences are made for the 15-year launch window beginning in 2010. Out of this study, a Mars-Venus free-return abort option, which satisfies the energy and time-of-flight constraints of NASAs Design Reference Mission in January 2014, is discovered. If aerogravity assist (consistent with the capability of the Design Reference Mission vehicle) is employed at Mars, the abort option can be improved over pure gravity assist at Mars in terms of more launch opportunities and lower time of flight. The planned mission date in January 2014 is remarkably fortuitous because the Mars-Venus abort trajectory only repeats every 32 years.

A LOW-THRUST VERSION OF THE ALDRIN CYCLER

§In this paper we seek a low-thrust version of a cycler orbit between Earth and Mars known as the Aldrin cycler. The principal goal is to design trajectories that have low flyby V at both planets while minimizing the total propellant cost. Our research is aided by several powerful software tools, including a recently developed low-thrust optimizer. With these tools, we are able to produce several promising low-thrust versions of Aldrin cyclers. Our analysis shows that such cyclers can significantly reduce the total propellant cost.

Low-Thrust Trajectories to Jupiter via Gravity Assists from Venus, Earth, and Mars

We design low-thrust gravity-assist trajectories to Jupiter via gravity assists from Venus, Earth, and Mars. Trades between time of flight, mass, and hardware specifications are examined for various flyby bodies such as Mars, Earth, Venus-Earth, and Venus-Venus. We find (locally) propellant-optimal trajectories for ranges of specific impulse and specific mass that represent present-day technologies (such as an ion thruster with a radioisotope power source) and future technologies (such as a nuclear-powered magnetoplasmadynamic thruster which may be available in 10 to 15 years). We consider the 35-year launch period from January 2010 to December 2044.

PRELIMINARY ANALYSIS AND DESIGN OF POWERED EARTH - MARS CYCLING TRAJECTORIES

We discuss preliminary results on constructing a powered cycler from semi-cycler trajectories. We present a powered cycler with reasonable transfer times and low encounter velocities. In addition, we develop a metric for evaluating cycler designs in comparison to other mission-to-Mars scenarios. The metric suggests that as vehicle mass (with respect to propellant mass) increases, the most advantageous system progresses from a “Design Reference Mission” scenario to Semi-Cyclers to Cyclers, which is highly indicative of how a human Mars transportation system might evolve.