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Compass

On board the Space Shuttle by Len:
On your Grid Compass website, some of your viewers listed that the Grid Compass computer was used on board the early Space Shuttle Flights. That is correct because in 1986, when I was in Washington, DC; the National Air and Space Museum on the Mall had a Grid Compass computer in a display case that stated that it was used on board the Space Shuttle to determine the location of the Shuttle for the Astronauts. The Grid Compass computer showed a world map with the shuttle location on the map with coordinate date displayed on the computer at the upper and lower display margins.

In 1992, at San Antonio, I attended a local ham radio fest. One of the vendors was selling NASA surplus, mostly old telemetry receivers. One of the items for sale was an old Grid Compass II computer, Model 1139. This Grid Compass computer was their most expensive computer with a cost of over $10,000. The reason that it was so expensive was because of the large electroluminescent display that it used (the display screen was larger than the other Grid Compass II, Model 1129 which used a smaller electroluminescent screen). I brought it for $100 with a companion Grid Hard and Floppy Disk Drive unit.

When I took it home, I turned it on and nothing happened. I then took apart the computer, noticing that nothing appeared to be missing. It had two ROM chips plugged into the front panel ROM sockets. One ROM chip was labeled SPoC SITEMGR and the other ROM chip was labeled SPoC CGMGR. I then noticed that this computer did not have a Grid Operating System ROM. I had a GridCase computer with a Grid Operating System ROM. I took this Grid Operating System ROM and placed it into one of the empty ROM sockets on the Compass II computer. When I powered on the computer, a world map appeared.

The SPOC SITEMGR ROM chip software is the one that is used to display to the astronauts when they came into range of ground based communication sites during their orbits. The circles on the World Map indicated the coverage area for the ground base communication stations that NASA used for the Space Shuttle. You had the option on the display screen to add and subtract from these communications stations. The other SPOC CGMGR ROM software is used to provide information to the astronauts on fuel usage with the Cargo that they carried in their Space Shuttle bay. I did take the two SPoC ROM chips out of this Grid Compass II Computer and placed them in a Grid Compass II, Model 1129 that I have. The SPoC ROMs would not work with the Model 1129. There must be something in the BIOS of this Grid Computer that is necessary to use those SPoC ROM chips. The boot up screen for this Compass II computer is very different than the standard Grid boot up screen for other Grid Compass computers. NASA and Grid most likely changed the BIOS on this computer so that someone could not burn other SPoC ROM chips and use the software on other Grid Compass Computers.

Also, when you get to the World Display Screen, the Mission Elapsed Time does not advance on this computer. I suspect that this Compass computer was connected to the Master Clock on board the Space Shuttle using the HP-IB bus on the back of the computer since the timing chip inside the Compass would not be accurate enough to determine the exact location of the shuttle over a prolonged period of time. I suspect that this particular Grid Compass II computer was used in training astronauts since it has a standard 110 VAC 3-prong computer connector on the back of it. NASA would have used a more secure power connector for the computer if it was used on board one of the Space Shuttles.