IEEE - Aerospace and Electronic Systems - July 2022 - 3

In This Issue -Technically
I AM NOT AFRAID OF THE GPS JAMMER: RESILIENT NAVIGATION VIA SIGNALS OF OPPORTUNITY
IN GPS-DENIED ENVIRONMENTS
I am not afraid of the GPS jammer, as long as there are ambient signals of opportunity (SOPs) to exploit in the
environment. In environments where GPS signals are challenged (e.g., indoors and deep urban canyons) or denied
(e.g., under jamming and spoofing attacks), SOPs could serve as an alternative positioning, navigation, and timing
(PNT) source to GPS, and more generally, to global navigation satellite systems (GNSS). This article presents a
radio simultaneous localization and mapping (radio SLAM) approach that enables the exploitation of SOPs for
resilient and accurate PNT. Radio SLAM estimates the states of the navigator-mounted receiver simultaneously
with the SOPs' states. Radio SLAM could produce an SOP-derived navigation solution in a standalone fashion or
by fusing SOPs with sensors [e.g., inertial measurement unit (IMU), lidar, etc.], digital maps, and/or other signals
(e.g., GNSS). This article presents the first published experimental results evaluating the efficacy of radio SLAM
in a real GPS-denied environment. These experiments took place at Edwards Air Force Base, California, USA,
during which GPS was intentionally jammed with jamming-to-signal ratio as high as 90 dB. This article evaluates
the timing of two cellular long-term evolution (LTE) SOPs located in the jammed environment, showing timing
stability over 95 min ofGPS jamming. Moreover, the article presents navigation results showcasing a ground vehicle
traversing a trajectory of about 5 km in 180 s in the GPS-jammed environment. The vehicle's GPS-IMU system
drifted from the vehicle's ground truth trajectory, resulting in a position root mean-squared error (RMSE) of
238 m. In contrast, the radio SLAM approach with a single cellular LTE SOP whose position was poorly known
(an initial uncertainty on the order of several kilometers) achieved a position RMSE of32 m.
DEVELOPMENT AND VALIDATION OF A CANFIELD JOINT AS A PRECISION-POINTING SYSTEM
FORDEEPSPACEINSTRUMENTATION
A mission plan for an integrated radio and optical communications payload, based on the Mars Reconnaissance
Orbiter, is presented with emphasis on the derivation of precision pointing requirements. The Canfield joint, a parallel
robotic linkage capable of hemispherical pointing, is discussed as a platform for optical communication and
other deep space instrumentation. The capabilities ofa prototype are compared to those ofcurrently available gimbals
qualified for deep space, and the advantages of the Canfield joint, including size, weight, and power savings,
cable handling, and mechanical redundancy, are discussed. Validation procedures and results for the space hardware
prototype are presented. This work was undertaken through the Integrated Radio and Optical Communication
Project at NASA Glenn Research Center.
A VISION-BASED GUIDANCE ALGORITHM FOR ENTERING BUILDINGS THROUGH WINDOWS
FOR DELIVERY DRONES
This article introduces a novel vision-based guidance algorithm to make a camera-equipped drone capable of collision-free
entrance to a building through its windows. To eliminate the reliance on any extra sensor (ultrasonic
range finders, lidars, depth sensors, stereo cameras, etc.), which are frequently used in the literature, we introduce
an image-based optimization scheme to detect the exact boundaries of a window portal section. The optimization
is based on a common facade segmentation technique, referred to as projected profiles, and relies on the assumption
that the window portal is one of the least light-reflective segments in a facade structure. In combination with
a visual tracking algorithm, our method elevates the tracking performance to avoid any guidance failures due to
tracking drifts. As a result, the drone gets a rich extent of navigation data during the flight enabling it to reliably
enter through the window. The window portal detection is evaluated using two online facade datasets, suggesting
a 75% success rate in finding the correct entrance passage. Also, it is shown that the visual tracking performance
is improved up to 58% in the specific case of tracking an entrance portal. The efficacy and real-time capability of
the overall vehicle guidance are experimentally demonstrated using a rotorcraft micro aerial vehicle.
JULY 2022
IEEE A&E SYSTEMS MAGAZINE
3

IEEE - Aerospace and Electronic Systems - July 2022

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