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

Chapter 4.0 Entomopter Flight Operations
4.3 Entomopter-borne Active Emitters for Navigation and Communication
1. Detecting objects in the Entomopter’s flight path for collision avoidance. Obstacle detection
will be performed in 3D (azimuth, elevation, and range). In this manner, obstacles
are detected in front, to the side, as well as up and down so that Entomopter flight is designated
by the accurate detection of obstacles instead of trial-and-error flight patterns.
2. Altimetry for the Entomopter must have precise range for detecting the location of the
ground for landing and collision avoidance.
3. Communicating between Entomopters and the rover, with spherical coverage around the
Entomopter, so that it can communicate with the rover or other Entomopters in any
direction.
4. Positioning of the Entomopter in 3D relative to the rover.
Since the Entomopter will typically fly at low altitudes (and hence low angles relative to the
rover or other Entomopters), communications will mainly be horizontal. If the Entomopter were
flying at its maximum altitude of 10 m and maximum range of 200 m from the rover, this
implies an angle of 2.9 o with respect to the horizontal. Entomopters communicating with Entomopters
overhead will have to look upward, but if the maximum altitude of operation is only 10
m, the antenna gain can be less in the vertical dimension. However, this antenna gain must
account for the pitch and roll of the Entomopter during flight or while on an uneven surface.
(Assuming an omnidirectional antenna pattern, the design will not have to account for yaw.)
4.3.4.1 The Challenge of Antenna Pointing
Antenna pointing alternatives fall into the following categories: gimbaled, phased arrays, and
electronically switched. The main problem with all of these techniques (beyond weight and
power) is the necessity to track the aim point to which the energy is to be emitted. For a vehicle
flying straight and level, this is less of an issue as transmission angles change slowly, but if the
vehicle is changing attitude rapidly, or if the vehicle is interacting with more than one aim point
(other Entomopters and the rover), then the onboard inertial system must not only keep track of
the aim points based on some external GPS-like reference, but it must factor in its own gyrations
as the Entomopter changes altitude.
Gimbaled antennas are too heavy relative to the function that they provide, and based on flight
vehicle dynamics, are often too slow in slewing to new positions. When multiple recipients exist
(other Entomopters and the rover), the idea of a gimbal is even less attractive.
On the other hand, phased arrays can be much lighter and can redirect multiple simultaneous
beams independently, but they can be bulky if both azimuth and elevation beam positioning is
required, and the power necessary to run the multiple elements necessary to “bend” the beam is
not energy efficient.
Multiple electronically switched antennas (unlike a phased array) orient individual antennas at
all angles of interest and emit energy in the desired direction from single or multiple (simultaneous)
emitter antennas. Although not phased, and therefore not needing to be contained in an
array, electronically switched antennas suffer from the same weight penalty due to the redundant
nature of their hardware. The fact that they are discrete directed emitters means that they will be
more efficient than a phased array, but will not have the nearly infinite angular coverage of the
phased array. As the beamwidth of each switched emitter is decreased to increase gain and direc-
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