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