IEEE - Aerospace and Electronic Systems - April 2023 - 28

Feature Article:
DOI. No. 10.1109/MAES.2023.3239342
Neural Network-Based Controller for Terminal
Guidance Applied in Short-Range Rockets
Raul de Celis and Luis Cadarso, Rey Juan Carlos University, 28933 Madrid,
Spain
INTRODUCTION
Global navigation satellite systems (GNSS) signals have traditionally
been used during the terminal phase of flight in
rockets. Regrettably, reliability declines in direct proportion
to the application necessity for which it was created. It is
worth noting that GNSS signal attenuation and loss lead to a
lower signal-to-noise ratio. Even though inertial measurement
units (IMUs) provide signals that do not depend on
external perturbations, they can present significant defects
in the measurements caused by different reasons, such as
gyro and accelerometer imperfections, inaccurate navigation
system startup, and imprecision in gravity model estimation,
that finally create time increasing errors, that can be
important, especially for long-distance flights. However,
when paired with GNSS receivers, which can reduce IMUs
mistakes, they are a valuable source of navigation information
[8]. The INS/GNSS integration is a great advantage for
many applications, such as vehicles, ships, aircraft, and
robots. In the case ofvehicles, it is very important to have a
precise location ofthe vehicles, especially when it is a vehicle
used for security and defense applications. In this case,
INS/GNSS integration can be used to determine the location
of the vehicle and reduce the errors of the INS, making the
vehicle more reliable and precise while performing its mission.
INS/GNSS integration is not only used for determining
the position and velocity of the vehicle, but also the orientation.
This information can be used to change the direction of
the vehicle to avoid obstacles. Another application for INS/
GNSS integration is atmospheric flight vehicles. In this
case, INS/GNSS integration can be used to determine the
Authors' current address: Raul de Celis and Luis
Cadarso are with the Aerospace and Transportation
Research Group, Rey Juan Carlos University, Fuenlabrada,
28933 Madrid, Spain (e-mail: raul.decelis@urjc.
es, luis.cadarso@urjc.es).
Manuscript received 25 April 2022, revised 27
September 2022; accepted 16 January 2023, and ready
for publication 23 January 2023.
Review handled by Stefan Bruggenwirth.
0885-8985/23/$26.00 ß 2023 IEEE
28
position and velocity of the aircraft and the orientation, and
adjust it and keep it to the desired direction and altitude,
even when the INS is not able to provide this information.
This can be very important when precision is required, such
as in navigation, landing, or impacting at any point [8].
Shoulder-launched rockets are mainly guided projectiles
that are meant to counter the threat posed by low-flying aircraft,
such as helicopters or ground vehicles. These rockets
can be guided using a variety of systems, including infrared
and laser. The guidance of these systems is based on an INS,
which needs to be initialized before launch. This initialization
could include the measurement ofthe location ofthe launcher
and the target, the knowledge ofthe direction to the target (for
example, as provided by a laser designator), or additional
information, such as the direction to the GNSS satellites [6].
However, the major drawback ofusing GNSS for guidance is
that the signal could be blocked by terrain features or its
acquisition characteristic time could also be longer than mission
flight time. As said before, the location of the launcher
and the target can be estimated using a GNSS receiver to
obtain a fix. In addition, a direction to the target can be
obtained using a laser pointer [6]. These systems can also be
utilized for surface-to-surface defense in situations where the
target location is known and laser or infrared guiding is not
required. In this instance, INS paired with GNSS receivers
can provide a reliable source ofdata. However, due to the low
range and flight periods ofmost man-portable air-defense systems,
successful reception of the GNSS signal might be
impossible. If no additional external sources of information
are available, accuracy must be obtained before launch utilizing
only onboard autonomous systems and loaded data.
Cost, precision, and robustness are crucial attributes
regardless of the system's architecture. However, these are
diametrically opposing objectives. Precision seeks to minimize
" collateral damage. " An all-weather and all-terrain
system, or one that does not degrade regardless ofthe working
conditions, is robust. Obtaining a system with great precision
and robustness at a low cost is always difficult.
Research into the controllability and stability of aerial
platforms has been motivated by the need for improved guidance,
navigation, and control (GNC) systems [8].Creaghand
Mee [5] proposed cooperative solutions for numerous
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