How the Internet Changes Data Acquisition

You don’t have to be a rocket scientist or a fan of Sesame Street to know what the word of the ‘90s is. Can you spell Internet? Or World Wide Web?

Recently I witnessed first hand the effects of the Internet. What I experienced showed me that the whole concept of data acquisition has changed.

I was part of the team providing ground support for an experiment on the Space Shuttle Endeavour (STS-77, May 16-29, 1996). If you were lucky enough to see data from that experiment “live” on the Web—and half a million people did, then you saw the future of data acquisition. You still can see the data replayed at http://www.ni.com/shuttle.

The data was sent from Endeavour to the Payload Operations Control Center, part of Mission Control at NASA’s Johnson Space Center (JSC) in Houston, then to the Jet Propulsion Laboratory’s (JPL) Measurement Technology Center. From JPL it was sent to National Instruments (NI) in Austin, then out on the Web. Most times it was on the Web 10 seconds after we saw it in Houston (Figure 1).

The Internet has revolutionized data acquisition. Not so long ago, data acquisition was a local event. A computer was connected to sensors to provide direct data acquisition. Networking was usually rare, and “sneaker net” was often used to take data from the lab to the office for analysis.

Data acquisition, analysis, display and monitoring are now global events. Information can be parceled out and delivered in custom formats to scientists, engineers, managers and the public—in real time.

Previously, only small teams of scientists or engineers had access to the data, with the public seeing it six months to one year later. The Web provides everyone potential access to the data. And after all, because the public is paying for it, shouldn’t the public see it?

Put It on the Web

This experiment also provides an example of a “seamless transition” from ground support to flight. The same ground-support equipment tested and characterized the flight hardware for more than a year prior to the launch. It was then disconnected from the flight hardware and reconnected to Mission Control and used during the flight. The advantages include robust software, real-time data reduction and display evaluated during ground usage, and savings in time and cost.

To show the data on the Web was an afterthought—a bonus, if you will. We had planned to send the data back to JPL for analysis by members of the science team who could not be at Mission Control. When we realized that we could get it to JPL, we decided to also put it on the Web.

Because the system we developed used LabVIEW from NI and operated on a Macintosh, I asked NI and Apple if they would like to host a Web site. Both eagerly agreed. In fact, Apple was about to kick off a new science and technology home page http://www.technical.apple.com/.

The Experiment

The Brilliant Eyes Ten-Kelvin Sorption Cryocooler Experiment (BETSCE) is a space-shuttle technology demonstration experiment designed to show that cryocoolers of this type, called “sorption coolers,” can operate in the weightless, vacuum environment of space. 1 Essentially, sorption coolers do not vibrate, require very low input power in this extremely cold temperature range, and operate reliably for more than 10 years. This was the first space flight of chemisorption cryocooler technology.

BETSCE measured and validated critical microgravity performance characteristics of a hydride sorption cryocooler designed to cool long-wavelength infrared and submillimeter-wavelength detectors to 10 K and below. With the flight-validation data provided by BETSCE, this refrigeration technology can be used in many future precision-pointing astronomy, earth-observation and surveillance space-satellite applications (Figure 2).

BETSCE successfully validated sorption-cooler operation in a microgravity environment. It produced solid hydrogen at 10 K in its first attempt on-orbit, cooling down from 70 K to 10 K in less than two minutes. It sustained a 100-mW at load for 10 minutes to meet the primary system performance objectives. Eight quick-cool-down liquid hydrogen cycles were completed, achieving a minimum temperature of 18.4 K and a maximum cooling duration of 32 minutes.

Total cycle times ranged from eight to 11 hours, depending on the shuttle orbiter attitude. Flight data obtained for 18 compressor cycles demonstrated the capability to consistently recompress the hydrogen refrigerant fluid and to archive the same high pressures as obtained in ground testing.

The Data Acquisition System

Figure 3 shows the system layout. Two Macintosh computers were used. One was the primary computer for telemetry down from and commands up to the shuttle. The other computer provided data display, analysis and Ethernet to JPL and the World Wide Web. Additional computer stations (Analyst and CSR) were used for data analysis and display.

Only when we could demonstrate that the system using the Ethernet was physically uncoupled from sending commands were we allowed to use it. There is always the security risk that someone from the outside will try to hack into what must be hacker’s nirvana—NASA’s Shuttle Mission Operations.

That leads into another aspect of the Internet and World Wide Web—responsibility. Simply because you can put information on the Web does not mean you should. Even though the Cold War is over, the United States is in a ‘war’ to remain competitive with the rest of the world.

Information that can give another country an unfair advantage hardly belongs on the Web. There is a difference between showing data and showing enabling technology. You can show that something was done without giving away how it was done.

The system was originally developed five years ago as a ground-based data acquisition system. It was developed to acquire data for the ground system (Proof-of-Principle). The system interfaced and archived 64 channels of temperature, pressure and flow data with direct connections through an interface board, external multiplexer and signal conditioners. Utilities provided post-processing analysis. There were no control outputs although the manual controls were monitored as inputs.

The ground-based data acquisition system transitioned to a system to test and characterize the flight experiment using the RS-232 port as the connection to the up/downlink. This system provided the only user interface for the principal investigators to the flight experiment. This was accomplished by uplinking immediate commands or command sequences to be operated on later, and recording and displaying all the downlinked data from the experiment.

The system also provided utilities for calibration, converting spreadsheet command sequences to machine code for uplinking and post-processing of recorded data. It was then moved to Mission Control where it provided exactly the same functions, the only difference being the length of the RS-232 cable (in effect, going to the orbiting shuttle).

One more function was added transparently which echoed the downlinked data to a similar system at JPL. With this function, a “shadow site” could operate without impacting the critical operations of the principal investigators.

An additional display, the Payload Monitor, was a result of a safety meeting—certain channels of the telemetry had to be monitored by the support people at JSC and their system was not flexible enough to make modifications close to launch time. We provided an additional LabVIEW screen detailing certain channels of our telemetry using Ethernet. It was an excellent example of the flexibility that graphical programming provides when compared to text-based programming. The additional system was modified and delivered in about one day.

Figure 4 is an example of the LabVIEW user-interface screen displayed to the science team. It shows valves opening and closing and the locations, type and value for the approximately 100 sensors used in the experiment. It also shows graphs for three sensors. The identical data was sent to JPL for display. From JPL, a subset of data was sent to the NI Web site.

Conclusion

BETSCE successfully achieved its primary objectives:

Proved a thorough end-to-end characterization and performance validation of a hydride sorption cryocooler in the 10 to 30 K temperature range.

Acquired the microgravity data base needed to provide confident engineering design, scaling and optimization.

Identified and resolved interface and integration issues.

Provided hardware qualification and safety-verification heritage.

The ground support achieved its objectives of flexibility in configuration and modification, reduced software and system development cost and schedule by a factor of from 4 to 10, and reduced system development, configuration, documentation, training and operating costs.

BETSCE also provided an excellent example of how fast and easy information can be made available to the public. It demonstrated the new world of instant-global data acquisition. And tools such as the Internet and World Wide Web need to be considered as part of any current data acquisition system.

References

1. Bard, S., Karlmann, P., Rodriguez, J., Wu, J., Wade, L., Cowgill, P. and Russ, K.M., “Flight Demonstration of a 10 K Sorption Cryocooler,” Ninth International Cryocooler Conference, Waterville Valley, NH, June 1996.

Disclaimer

This article was written by the author as a private individual and not in conjunction with JPL.

Acknowledgments

The author thanks George Wells and the members of the BETSCE science team, especially Dr. Steven Bard and Larry Wade, for their contributions in writing this article.

About the Author

Edmund C. Baroth, Ph.D., conceived, developed and is the Technical Manager of the Measurement Technology Center, part of the Measurement, Test and Engineering Support Section of the Jet Propulsion Laboratory. He holds a bachelor’s degree in mechanical engineering from City College of New York, and master’s and doctorate degrees in mechanical engineering from the University of California, Berkeley. Dr. Baroth has received five NASA Certificates of Recognition and a NASA Group Achievement Award, has produced two patents and has one pending, and has been a faculty member at California State University. Jet Propulsion Laboratory, 4800 Oak Grove Dr., Mail Stop 125-177, Pasadena, CA 91109, (818) 354-8339. e-mail: [email protected]

Copyright 1997 Nelson Publishing Inc.

February 1997


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