Article
Guidance, Navigation and Control of Unmanned
Airships under Time-Varying Wind for
Extended Surveillance
Ghassan Atmeh and Kamesh Subbarao *
Department of Mechanical and Aerospace Engineering, University of Texas at Arlington, 211 Woolf Hall,
Box 19018, 500 W. First St., Arlington, TX 76010, USA; ghassan.atmeh@mavs.uta.edu
* Correspondence: subbarao@uta.edu; Tel.: +1-817-272-7467
Academic Editor: Javaan Chahl
Received: 21 December 2015; Accepted: 10 February 2016; Published: 17 February 2016
Abstract: This paper deals with the control of lighter-than-air vehicles, more specifically the design
of an integrated guidance, navigation and control (GNC) scheme that is capable of navigating
an airship through a series of constant-altitude, planar waypoints. Two guidance schemes are
introduced, a track-specific guidance law and a proportional navigation guidance law, that provide
the required signals to the corresponding controllers based on the airship position relative to
a target waypoint. A novel implementation of the extended Kalman filter, namely the scheduled
extended Kalman filter, estimates the required states and wind speed to enhance the performance
of the track-specific guidance law in the presence of time-varying wind. The performance of the
GNC system is tested using a high fidelity nonlinear dynamic simulation for a variety of flying
conditions. Representative results illustrate the performance of the integrated system for chosen
flight conditions.
Keywords: unmanned airship; waypoint navigation; proportional navigation guidance; wind
estimation
1. Introduction
The dream of controlled flight was first realized by the invention of the airship, where it
is claimed that Jean-Baptiste Meusnier designed the first airship in 1748 [1]; it however, lacked
a lightweight, powerful engine. Henri Giffard was the first person to equip an airship with
steam-engine technology successfully. He flew his airship 17 miles in 1852, with a single propeller
driven by a three-horsepower engine [2]. The airship’s golden age was launched by the German
Luftschiff Zeppelin in 1900, which was utilized in commercial and military applications. That
golden age tragically ended in the Hindenburg disaster in 1937. In the past couple of decades,
however, interest in airships arose due to the advancement of technology in many engineering fields.
New demands, which cannot be satisfied by conventional fixed-wing aircraft, have also enthused
interest in airships [3]. Therefore, analyzing the dynamics of airships and implementing control
structures that guarantee high performance and safety are necessary for the continued advancement
of aerospace technology.
An airship’s main source of lift is buoyancy, or static lift. This is based on Archimedes’ principle:
if a body is immersed in a fluid (air), it experiences a force proportional to the volume of the displaced
fluid in the opposite direction of its weight. When the density of the body (airship) is less than that
of the fluid (air), that force is substantial. Due to this, the dynamics of an airship are different from
that of a conventional aircraft, with significant effects from added mass and added inertia and a
much higher sensitivity to wind [4]. Added mass and inertia effects are changes in the dynamics
Aerospace 2016, 3, 8; doi:10.3390/aerospace3010008 www.mdpi.com/journal/aerospace
