Phase II Final Report - NASA's Institute for Advanced Concepts

Chapter 5.0 Potential Payload Functions Using a Communication/
Control Subsystem
power and flight hardware. Prior knowledge of the exploration terrain could obviate the need for
constant radar readings for collision avoidance and provide an optimum flight pattern.
A single Entomopter could be tasked with this digital terrain mapping of a designated area using
ISAR as described above. Upon its return to the refueling rover, the digital map could be
uploaded to the rover and this information transferred to the other Entomopters. Once the terrain
map has been uploaded, it could then be used by the Entomopters to calculate optimum flight
patterns. Accurate knowledge of aircraft position relative to the terrain and the terrain ahead will
lead to a flight pattern based on the required clearance height and collision avoidance. This terrain-following
feature would avoid energy-consuming maneuvers to avoid obstacles and allow
the Entomopter to fly at the minimum required clearance height. The reduction in required mass
and power on the other Entomopters would allow additional payload functions to be accomplished.
This procedure could be repeated for each exploration area. Alternatively, the Entomopters
could have modular payload, where the payload is switched for the desired exploratory
function. In this manner, each Entomopter would create a digital map of the terrain for a designated
area. Upon completion, it would return to the refueling rover and shed its mapping gear to
be replaced by additional payload, such as video equipment. The first method seems to be a
more realistic alternative. Switching complex payload equipment might sacrifice reliability.
The key capability of a DTS is terrain-referenced navigation. A combination of the stored digital
map of terrain elevation and real-time measurements of the aircraft height above the ground
allows highly accurate navigation referenced to the terrain without external signals. Typically,
this terrain-referenced navigation includes processing and combining data from a dead reckoning
system, radar altimetry to give the height above ground, and the digital terrain elevation data
map. Generally, there are two modes of operation: Acquisition mode, where the system is initialized
by identifying the initial position of the aircraft, and Track mode, where navigation data is
provided at a rate of about 2 Hz to 4 Hz. Acquisition mode involves processing a number of
altimetry readings to identify aircraft position relative to the terrain map database. This approach
relies on the uniqueness of ground profiles within the map. The Acquisition mode will likely be
unnecessary for the Entomopter mission, because its initial position relative to the refueling
rover will always be known. Thus, the Track mode can immediately be executed.
In Track mode, the aircraft has an estimated position at some point in time (update N). Based on
the aircraft dynamics, a Kalman filter is used to propagate ahead (Update N+1) to provide a prediction
of the height above ground level from the map database. To account for uncertainties in
position, a batch of altimetry measurements can be processed to calculate the location of the aircraft
within the map database. The difference between the actual position and the predicted position
can be used to correct the Kalman filter estimates. Again, the operation relies upon the
uniqueness of the terrain to identify the unique position in the map database. If the Mars terrain
is relatively flat, performance will be degraded.
Whether a DTS would be used for the proposed Entomopter mission would be highly dependent
on the specific mission goals. Perhaps a terrain map could be uploaded to the rover and transmitted
to Earth for review. Based on that information, an Earth-bound mission planner could communicate
back to the rover that the Entomopters should explore certain areas.
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