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Gamma-Rays and Cell Phones
Gamma Rays in Space

Source: Article by Melissa Gibby, Jacobs ESTS Group and GBM Operations Scientist, Science and Mission Systems Office

How are the most energetic explosions in the universe and an ordinary cell phone connected within MSFC's operations center for Fermi, NASA's newest gamma-ray observatory? When the Gamma-ray Burst Monitor (GBM) onboard Fermi detects an explosion, ground systems are alerted, data is sent to the Fermi Mission Operations Center at Goddard Space Flight Center, and a cell phone text message is sent to the scientist on duty, either at MSFC or at the Max Planck Institute in Germany, so he or she can start analyzing the newest data. Although the cell phone is a very low-tech solution, it allows the scientist on duty to have the freedom to venture away from his or her office. It is also very cool when you receive such a notice to be able to tell those around you that you are one of the few people in the world who know about a huge explosion that happened millions of years ago.

The real-time system for the Fermi mission is an interconnected series of computers and processes that receive, process, and notify scientists worldwide when the detectors on-board Fermi locate a gamma-ray burst. There is a requirement that states that the time from the detection of a burst to the receipt of the notice by the scientists should be no longer than seven seconds.

The main reason for such a short latency requirement is so that the worldwide ground based telescopes can retrain their telescopes to the reported location in hopes of catching a glimpse of the optical afterglows from the stellar explosion. The code for much of the real-time system uses TCP/IP sockets, sending data directly from a process on one computer to a process waiting for the data on another.

Since the real-time system for Fermi is required to be functional at all times, the system is duplicated, one at MSFC and the other at GSFC. A keep-alive signal between the two systems controls which one of them functions in the primary mode and which functions as a secondary system. If the primary system has a failure in a code segment, the other system will take over as the primary system. When the original primary system is healthy again, it regains control as the primary machine and the other becomes secondary again. Each real-time system sends state-of-health data to a third system that alerts the GBM operations manager—by cell phone, of course—when either system has an element that is not functioning for some reason. The statusing system also sends an alert to the operations manager when the system is healthy again.

The real-time system also refines the localization for the gamma-ray burst. Since the on-ground computed localization does not have to meet the seven-second latency requirement of the on-board localizations and we have more computing resources on ground, the refined locations should be more accurate than those obtained on-board. These refined coordinates for the burst are then sent to the Gamma-Ray Coordinates Network for transmittal to the scientists worldwide.

The GBM operations center also has a statusing Web site used for monitoring the real-time system. This includes the list of the gamma-ray triggers that have been received in the last two weeks along with information about those triggers. Included in that information is the summary of the notices sent out to the world via the Gamma-ray Coordinates Network at GSFC, the times that each of the packets was received (both on the primary and secondary systems), and a report of the missing packets received both in real time and in the data received later from the regular data downlinks.

Although the use of cell phones in a real-time system is not unique to Fermi, it has given the Fermi scientists reasons to look forward to hearing their cell phones ring. They always hope that the next time their phone rings it is one of the largest explosions ever detected texting them.