The history of ASCs at MIT was recently summarized in The Evolution of the Autonomous Surface Craft AutoCat, presented at Oceans 2000 in Providence, Rhode Island. For details on the references please contact Justin Manley the lead author.

ASCs at MIT Sea Grant

A. The ASC ARTEMIS

The first ASC produced at MIT Sea Grant was named ARTEMIS. This vessel is a 1/17 scale replica of a fishing trawler (with a total length of 137 cm) that was originally used for model basin testing. Installation of an electric motor and a servo actuated rudder made the basic model into a platform capable of testing the navigation and control systems required by an ASC.

Initial work focused on the development of control systems for the ASC. A microprocessor and digital compass were installed to provide rudimentary navigation and control functions. This configuration used a proportional-plus-derivative (PD) control system to implement simple heading control. These first steps yielded an ASC with limited autonomy but provided a valuable proof of concept [1].

Follow on work added a Differential GPS (DGPS) receiver to enhance the navigation system of ARTEMIS. This facilitated the development of a heading constrained waypoint following controller based on Fuzzy Logic. A depth sounder was added and ARTEMIS executed waypoint-defined surveys to generate bathymetric maps of the Charles River in Cambridge, MA. The addition of a radio modem allowed these bathymetric maps to be generated in real time and provided human supervisory control of the ASC [2]. Upon completion of these experiments ARTEMIS was retired from active use.

B. The Autonomous Kayak

One of the primary shortcomings of the ASC ARTEMIS was its small size. This limited its endurance and seakeeping. The field operations of ARTEMIS were limited to the Charles River, a region of limited scientific interest. To produce an ASC with more useful capabilities a kayak platform was examined [3]. Upon completion of design studies a 3 m long kayak hull was obtained and converted into an ASC. A new propulsion system and actuator were installed, as were electronics similar to those used in ARTEMIS. This new vehicle underwent a series of trials on the Charles River. It was then fitted with acoustic tracking systems and used to follow a tagged fish [4]. Upon conclusion of these experiments this ASC was turned over to the MIT Ocean Engineering Teaching Lab for use in student research and education projects.

C. The ASC ACES

To continue the automated bathymetry experiments begun with ARTEMIS, a new ASC was developed. The specifications of the next ASC were based on a desire to create a system as versatile and useful as a small manned vessel while maintaining a small size to allow for easy deployment and survey operations. As ARETMIS was slow, unstable, had poor endurance and a small payload the next ASC represented a significant improvement in platform capabilities.

The new ASC ACES (for Autonomous Coastal Exploration System) was developed during 1996 and 1997 [5]. The mechanical design will be discussed further below. The electronics suite and control software were directly ported from the ASC ARTEMIS and incrementally improved over the development of the system. The completed ASC underwent field tests off Gloucester, MA during the summer of 1997. Upon completion of these trials it was outfitted with sensors suitable for hydrographic survey and successfully completed such a survey in Boston Harbor in December 1997 [6].

Beginning in January 1998 the ASC ACES was returned to the lab for a significant upgrade of its electronic systems and software. This effort was not completed due to a change in the software strategy at the MIT AUV Lab. It was decided to postpone improvements to the ACES electronics and software until a new AUV design was completed and tested. This work was recently completed and the software and computer systems standard developed for the new AUV will be modified and applied to the ASC in the near future.

Between September 1998 and June 2000, while the AUV systems were developed, the mechanical systems of the ASC were heavily modified. During the extensive field-testing of ACES several potential improvements in the basic platform design were identified as desirable. These improvements have been made and are the subject of the remainder of this paper.