The
primary motivation for probe missions to the outer planets derives from the
need to constrain models of solar system formation and the origin and evolution
of atmospheres, to provide a basis for comparative studies of the gas and ice
giants, and to provide a valuable link to extra solar planetary systems. The gas
and ice giants offer a laboratory for studying the atmospheric chemistries,
dynamics, and interiors of all the planets, including Earth, for it is within
the deep, well-mixed atmospheres and interiors of the planets that pristine
material from the epoch of solar system formation can be found, providing clues
to the local chemical and physical conditions existing at the time and location
at which each planet formed.
Although
planetary entry probes sample only a small portion of a planet’s atmosphere,
probes provide data on critical properties of atmospheres that cannot be
obtained by remote sensing, such as measurements of constituents that are
spectrally inactive, constituents found primarily below the visible clouds, and
chemical, physical, and dynamical properties at much higher vertical
resolutions than can be obtained remotely. The Curiosity probe, for instance,
returned compositional data at Mars that has challenged existing models of
Mars’s formation. To provide for comparative studies of the Mars environment,
additional probe missions are essential.
One
of the most important aspects of preliminary interplanetary mission planning
entails designing a trajectory that delivers a spacecraft to the required
destinations and accomplishes all the objectives. The design tool allows an
investigator to explore various interplanetary trajectories quickly and easily.
The
design tool employs the patched conic method to determine heliocentric and
planetocentric trajectory information. An existing Patch Conic Targeting
routine and other common algorithms are utilized in conjunction with the design
tool’s specialized code to formulate an entire trajectory from Earth departure
to arrival at the destination. The STK-AGI & GMAT tools includes many options for the
investigator to accurately configure the desired trajectory, including
planetary gravity assists, deep space maneuvers, and various departure and
arrival conditions. The trajectory design tool is coded in STK-AGI & GMAT, which
provides access to three dimensional plotting options and user adaptability.
The design tool also incorporates powerful STK-AGI & GMAT optimization functions that
adjust trajectory characteristics to find a configuration that yields the
minimum spacecraft propellant in the form of ∆V.
Designing
a preliminary trajectory is an important step in the mission design process,
because of the impact it plays upon the useful spacecraft mass. The mission
requirements and objectives help to identify key trajectory features that must
be implemented, including launch trajectory constraints, entry or parking
orbits about other celestial bodies, etc. These important features and
constraints are combined with efficient trajectory configurations, such as deep
space maneuvers and planetary gravity assists, to create an initial
interplanetary trajectory configuration. Once an initial configuration is
chosen, the trajectory information can be used in an array of available
computer programs to generate more accurate solutions.
The accuracy of a trajectory design is determined by
comparing the assumptions and forces accounted for in the design to the true
trajectory. The more realistic and complex force environments used in the
design tool reflect a more accurate trajectory design. The choice of design
tool is dependent on the maturity and complexity of the trajectory design as
well as the accuracy desired. The current available trajectory design programs
require substantial time for learning how to use the tool correctly, usually
scaling with how much accuracy and capability is needed in designing the
trajectory.
Figure 1: Illustration of
MAVEN scenario in GMAT, likely to be: 23/Sep/2014.
Figure 2: Illustration of
MAVEN scenario in STK-AGI
Figure 3: Illustration of
MOM/Mangalyaan in STK-AGI
