Work at WPI

I arrived at the Worcester Polytechnic Institute in 1981 after graduating from Colegio Arubano, my High School in Aruba.  WPI has an unusual graduation system, called "The Plan".  One requirement of this system is a project/thesis in my college major of Electrical Engineering.  This project is called the MQP (Major Qualifying Project).  

Logo for the MITRE WPI Project.

I heard of a project to build and fly hardware on the Space Shuttle and was excited to learn I was accepted to participate.  This flight opportunity was through the NASA Goddard Space Flight Center in Greenbelt Maryland.  A program to fly small payloads was based there called the "Get Away Special", or GASCAN.  For about $10k, MITRE corporation sponsored WPI to build and fly several experiments packaged into a canister on the Shuttle sidewall.  The opportunity to work with NASA was very exciting.

Logo of the GASCAN project.

Development of the hardware would proceed with three teams working one year each.  These students would all be doing their MQPs and would thus all be seniors during their participation year.  The first team would build the initial prototype and test to see if the concept worked.  The second team would build the flight unit, and the third would make any final modifications to prepare for flight.  There were about a dozen experiments.  I formed part of the second year team of three people for a Fiber Optic Rotation Sensor.  The members of the first year team were Robert Lokuta and Teresa Moruzzi.  Our advisor was Professor Wolaver, and my team members were David Moriarty and Aram Falsafi.  I would become the team lead due to my experience in electronics.

Bedford periodical
Presenting our rotation sensor in a meeting at MITRE in 1984.

The rotation sensor relies on the Sagnac effect to sense rotation.  One thing I learned during this development was that there is such a thing as absolute rotation rate.  Compare this to linear translation rate, which is context and frame dependent.  For example, you may be travelling hundreds of miles an hour in linear translation, but not know it when you are in an airplane.  However, it is possible to sense the absolute rotation rate.  

The design of the sensor by the first year team required a brief output pulse of the fiber optic laser in the form of a square wave.  The electronics would then excite a piezo delay crystal in a square wave manner to cause one pulse to see a different delay than the other (see page 16 of Part 1 of the thesis report below).  This was very difficult and required precise timing.  An innovation I provided was to operate the laser in continuous mode, and then excite the piezo crystal sinusoidally (page 18, Part 1).  We could then detect the rotation by synchronous demodulation of the light using the sine waveform of the piezo crystal (page 39 of Part 1).  In addition, with an engraver, I found a way to 'cut' the piezo crystal to cause it to oscillate in resonance (page 45 of Part 1).  This greatly reduced our power requirement and simplified the drive circuit considerably.

piezo crystal
The piezo delay crystal used in the FORS.  Optical fiber is
 wrapped around it to cause a variable fiber optic delay.

Fiber Optic Rotation Sensor board
Photo of one of the board stackups with the delay crystal mounted on the right.

We completed the sensor and demonstrated it working in 1985, and I earned a "Distinction", the highest grade possible on the MQP.  Unfortunately, due to the fragile nature of the fiber and perhaps due to us not having a mechanical engineer on the project, our rotation sensor was not selected to fly on the GASCAN.  Nevertheless, the project was very rewarding, and I will always consider to have taken part on this project.

Our final thesis write-up is here. Part 1 and Part 2.

Lab and Test Reports:
Preliminary Report from our rookie year
Laser diode with integral thermo-electric cooler
Analog front end and synchronous detector
Piezo phase modulator/delay crystal
Hand-drawn schematics and diagram of prototype

The GASCAN flew as G-408, and flew on STS-40 on the back wall of Columbia in 1991.  The press-kit describes our payload as follows:
G-408) Five Microgravity Experiments

Five student experiments from the Worcester Polytechnic
Institute are included in one GAS can. One will attempt to grow
large zeolite crystals. Another will study the behavior of fluids
in microgravity. A third, the Environmental Data Acquisition
System, will record information about sound, light, temperature
and pressure within the GAS can. The fourth will measure the
acceleration of the Shuttle along three axes with a high degree of
precision. A fifth experiment will study the fogging of film in

The experimental packages are sponsored by the MITRE Corp.
Bedford, Mass. The NTM is Don Carson.
Payload bay of STS-40
All the GASCANs were on the bridge in the aft of the Cargo Bay.

A photo from 2011, with Christopher next to the as-flown hardware of GASCAN G-408.  The hardware now sits in the lobby of Atwater Kent, which is the Electrical Engineering building at WPI.

Report by Looft and Durgin on the flight results.

WPI award
In 2011, I had the privilege of receiving WPI's Robert Goddard Award.  
I am thankful for the education I received at WPI.  
It made my rewarding career at NASA possible.

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