When the External Tank (ET) is mated to the Solid Rocket Boosters (SRB’s), it is necessary that the ET be precisely positioned. The ETCAS is a tool that assists personnel in this operation by providing an automated measurement of the distance that separates the ET from each SRB. The ETCAS also provides a laser line that assists personnel in aligning the ET such that the two SRB’s and the ET have the same centerline (see figure 1).

The current ETCAS uses two sensor units that each contain an acoustic sensor and a laser crosshair. These are connected to a central display unit by long, stiff cables that provide power to the sensors and a path for the measurement data. The sensor units are attached to the SRB by magnets. These acoustic sensors require frequent calibration and are suspect at temperature extremes.

A replacement for this system is in development. The new system uses a new commercial off-the-shelf (COTS) laser distance sensor to measure the distance between the SRB and the ET and to provide a line for the centerline adjustment. Laboratory testing will characterize the sensor’s performance over the required temperature range, and a temperature measurement will be made along with the distance measurement to compensate for environmental changes.

The new system will use wireless technology to communicate. A core wireless system has been in development for several years in the Engineering Development Laboratory (EDL). This wireless system will be integrated with the laser distance sensor, a custom control and power circuit, and a battery pack to create the sensor unit. This new sensor unit package (see figure 2) will be magnetically attached to the SRB as before.

The new user interface will have a small, color, liquid crystal display (LCD) touch-screen panel that will show the relative position of the ET to the SRB both numerically and graphically.

The new ETCAS will have a number of advantages over the current system. The laser distance sensor will provide greater accuracy and will not require calibration. The entire system will fit in a case the size of a deep briefcase. Eliminating the cables to the remote units, the wireless ETCAS will allow the operator using the interface display to direct the alignment from a safe and effective distance.

Key accomplishments:

• Characterized and tested prototype sensor.
• Developed custom interface hardware and software.
• Integrated the EDL modular wireless system with COTS technology to gain utility and save money.

Key milestones:

• Final design of sensor hardware and display.
• Testing and debugging of user interface software.
• Approval and field use of the developed hardware.

Figure 2. ETCAS User Interface Prototype

Figure 3. ETCAS Sensor Unit

Contacts: J.M. Perotti (Jose.Perotti-1@ksc.nasa.gov), YA-D2, (321) 867-6746; and Dr. R.C. Youngquist, YA-D2-C4, (321) 867-1829
Participating Organization: Dynacs Inc. (Dr. C.T. Mata, J.J. Randazzo, B.M. Burns, N.N. Blalock, J.D. Taylor, and A.J. Eckhoff)