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

Chapter 4.0 Entomopter Flight Operations
4.2 Rover-centric Entomopter Navigation
constant the perceived global image velocity. In doing so, bees landing on a horizontal surface
hold constant the image velocity of the surface as they approach it, thus automatically ensuring
that flight speed is close to zero at touchdown. This passive close-in navigation technique can be
exploited for use in the Entomopter during landing.
The philosophy of minimizing energy expenditures by the Entomopters must be maintained. If
there is a function that can be performed by the rover on behalf of the Entomopter, it should be.
In doing so, the Entomopter will reap the benefit in either increased endurance, or increased science
payload.
4.2.2 Navigation Under the Baseline Mars Scenario
The baseline Mars survey flight scenario has the Entomopter-based Mars surveyors flying in the
following way relative to the refueling rover:
1. Entomopter launches from refueling rover and proceeds at an angle of between 80 o and
90 o from the rover's direction of travel. Launch is to the right side of the rover.
2. The flight path will go out to nearly 200m in a straight line, and then a circular 180 o turn
to the left will be initiated. At no time will the Entomopter be at a range of greater than
200 m from the rover.
3. The Entomopter will then fly in a straight line back to the rover, which will have progressed
along its initial path at an assumed rate of 1 m/s. The diameter of the 180 o turn
will roughly equal the distance traveled by the rover during the entire flight out and back.
4. The rover launch platform is assumed to be 1m above the surface, and the Entomopter
flight altitude is 5m above ground level (AGL).
Under the conditions of this minimal baseline, the maximum rover navigation radar range would
be 200 m. A monopulse Doppler radar could identify each Entomopter and track it in range, azimuth,
and elevation. A switched scanning array could provide 360° track-while-scan coverage
with scan rates of 30 Hz. Each scan would provide not only range, azimuth, and elevation for
each of the Entomopters, but also a polar map of obstacles.
The high speed of the Entomopter wing flapping coupled with any radial component of flight
will be easily detectable as a Doppler shift in the return signal. The speed of the refueling rover
can be easily filtered to remove rover platform motion from the radar data. Ground odometry
from the rover will allow a notch filter to be adaptively placed directly over the platform-generated
Doppler background impressed on all targets. The Doppler return from the Entomopter, due
to its forward flight speed, could fall in the same range as that of the rover, depending on the
radial angle of flight relative to the rover's radar and could therefore be filtered out. However, in
practice, the low speed of the rover compared to the Entomopter wingbeat frequency will always
make discrimination easy, even apart from the Entomopter's fuselage skin return.
Because the atmosphere is rarefied and humidity is low on Mars, high frequency monopulse
Doppler radar emissions can be employed. Doppler shift is represented by
ƒ d = 2ν ÷ λ
Equation 4-1
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