The Reaction Control System (RCS) is the shuttle's system that has primary responsibility for maneuvering the aircraft while it is in space. It consists of fuel and oxidizer tanks, valves and other plumbing needed to provide propellant to the maneuvering jets of the shuttle. It also includes electronic circuitry: both to control the valves in the fuel lines and to prepare the jets to receive firing commands.
The RCS is computer controlled during takeoff and landing. While in orbit, however, astronauts have the primary control. When an orbital maneuver is required, the astronauts must perform whatever actions are necessary to prepare the RCS. These actions generally require flipping switches. These switches are used to open or close valves or to energize the proper circuitry. In more extreme circumstances, such as a faulty switch, the astronauts communicate the problem to the ground flight controllers, who will come up with a sequence of computer commands to perform the desired task and will instruct the shuttle's computer to execute them.
During normal shuttle operations, there are pre-scripted plans that tell the astronauts what should be done to achieve certain goals. The situation changes when there are failures in the system. The number of possible sets of failures is too large to pre-plan for all of them. Continued correct operation of the RCS in such circumstances is necessary to allow for the completion of the mission and to help ensure the safety of the crew. An intelligent system to verify and generate plans would be helpful. It is within this context that this work fits.
The RCS/USA-Advisor can be viewed as a part of a decision support system for shuttle controllers. It is based on a reasoning system and a user interface. The reasoning system is capable of checking correctness of plans and finding plans for the operation of the RCS. It employs a programming methodology based on the declarative language A-Prolog, algorithms for computing answer sets of programs of A-Prolog, and programming systems implementing these algorithms. The user interface is written in Java. It allows the user to specify the reasoning task to be performed, and then assembles into a program various A-Prolog modules, chosen according the components of the RCS that are involved in the task. Finally, the interface invokes program smodels to compute the answer sets of the A-Prolog program, and presents the results to the user.

Starting with version 0.95, the RCS/USA-Advisor includes two CR-Prolog planners that improve the quality of plans. Planner "XFeed" is able to generate plans that use the crossfeed, but avoids unnecessary use of the crossfeed. Planner "XFeed_SW" is, too, able to generate plans that use the crossfeed. Moreover, XFeed_SW avoids the use of computer commands if possible, and tries not to generate unnecessary actions. In order to use the new planners, you will need to have crmodels installed in your system (and reachable from $PATH) when you install the RCS/USA-Advisor.

For more information on the RCS, refer to the Links section.


The current version of the RCS/USA-Advisor system is 0.95. The RCS/USA-Advisor Installer automatically downloads, compiles and installs the RCS/USA-Advisor program. The installer assumes that Lparse and Smodels are already present in the system, in a directory contained in the user's PATH. In order to use the new XFeed and XFeed_SW planners, you will also need to have crmodels installed.

Quick installation tips for lparse and smodels:
lparse: download lparse and unpack it in a directory of your choice. Then, move to that directory and type:
% ./configure
% make
% make install
Make sure you execute the last step as root.
smodels: download smodels and unpack it in a directory of your choice. Then, move to that directory and type:
% make
% cp smodels /usr/local/bin
% chmod a+rx /usr/local/bin/smodels
Make sure you execute the last TWO steps as root.

When you are done, make sure that /usr/local/bin is in your PATH environment variable.

Download the installer and put it in a directory of your choice. After the installation process is over, you can safely remove the installer.

Run the installer by typing:

java -jar rcs_install.jar

If another version of the RCS/USA-Advisor is already installed in the directory where you plan to install the new version, please be sure to remove the following files before you start the installation process:

The installer has been designed for Unix systems running Java 1.3. In order to check what version of Java you are running, you can type "java -version" at the command line prompt. The program has *not* been tested with Java 1.4. The installer has been tested on NetBSD and Solaris. In principle, it should run on any Unix system with Java 1.3, a standard shell (sh), and the tar and gunzip commands.

Click here to download the installer.
Click here to go to the Lparse and Smodels web page.
Click here to go to the crmodels web page.

The RCS/USA-Advisor Group

The RCS/USA-Advisor has been developed at the Knowledge Representation Lab of the Computer Science Department, Texas Tech University as part of a research project supported by United Space Alliance.

People currently working on the RCS/USA-Advisor are:

Reasoning System User Interface and Installer


Publications regarding the RCS/USA-Advisor system can be found in the Papers section of the KRLab web site.


United Space Alliance Knowledge Representation Lab Texas Tech University
United Space Alliance Knowledge Representation Lab Texas Tech University
NASA NASA Human Space Flight Space Shuttle Reference
NASA NASA Human Space Flight Space Shuttle Reference
NSTS 1988 News Reference Manual
Description of the RCS from the NSTS 1988 News Reference Manual

Author: Marcello Balduccini (marcello.balduccini@gmail.com)