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

Planetary Exploration Using Biomimetics
An Entomopter for Flight on Mars
Navigation would be accomplished as follows: The refueling rover would maintain a general
awareness of its environment through various sensors, including radar. The radar, if configured
as a monopulse Doppler system, could provide range, azimuth, elevation, and relative speed of
targets within its hemisphere of influence. The rover will be able to determine these parameters
for each of the Entomopters as they are launched and fly in the rover's vicinity. This positional
information can then be impressed upon the radar signal as a modulation. When an Entomopter
is painted by the radar beam, it will receive information about its own position, that of other
Entomopters, and the refueling rover. The relative position of looming obstacles can also be
communicated.
In addition, radar will serve as a transponder to elicit responses from each Entomopter as it is
painted by the radar beam. This response will contain telemetry information identifying the specific
Entomopter, its health status, fuel remaining, above-ground-level (AGL) altitude as locally
measured by the Entomopter, as well as any other low bandwidth information of import.
One key feature of the transponder signal is that it is passive. Because the radar signal from the
rover necessarily has a return that is reflected back to the rover, the Entomopter may use techniques
to modulate the radar cross section (RCS) to impress its telemetry information onto the
radar return passively. In this way, the Entomopter need not expend any energy in transmission.
A property of an omnidirectional retroreflector made of trihedral facets is that it will redirect
incident radiation (from the rover) back along its transmission path (regardless of the retroreflector
orientation). For this reason, the orientation of the Entomopter need not be tracked or even
known. It is completely passive in this regard and even works when illuminated by multiple
sources simultaneously. It is independent of flight path and orientation.
The reflectivity of the entire retroreflector can be modulated by changing the RCS of the corner
reflector elements electronically. This involves changing the RCS, for example, by ionizing an
area that momentarily creates or destroys the corner reflector. To ionize a small region takes
high voltage, but essentially no current, so it is very low power. It is also rapid, so it can be used
to passively modulate the radar return with amplitude or phase information, or possibly polarization.
The U.S. Naval Research Lab (NRL) has demonstrated laser activated quantum well
remodulators with data rates of 4.2 Mbits per second from a hovering UAV. They expect to
achieve as much as 10 Mbits per second in the future. The power required would be what it takes
to light up a small neon bulb. The key is the placement of the remodulator. Upon sensing the signal
from the refueling rover as it passes over the Entomopter, an ID code would be impressed
upon the reflected signal that tells the rover, “This is Entomopter No. 2 and I am currently at an
altitude of four meters, and have nine minutes of fuel remaining.” This method provides widearea
coverage, avoids Entomopter-borne tracking or pointing systems, and avoids frequency
interference between Entomopters.
Position updates for the Entomopters will need to be no more than a few times per second (when
not in the landing mode), or even less. The rover is not flying the Entomopter (which is fully
autonomous) so continual position updates are not necessary. These updates let the rover know
only where the Entomopter is relative to itself and the other Entomopter(s). Similarly, health
monitoring does not need to occur more than a few times per second. If the Entomopter is self
monitoring, it will have a high internal diagnostic bandwidth, but the “I'm OK” signal back to
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Phase II Final Report