@S1-A.ARPA,@MIT-MC.ARPA:amon@cmu-ri-fas.arpa (06/25/85)
From: Dale.Amon@CMU-RI-FAS Actually, the hydraulic voting is an elegant solution to the need for redundancy and the avoidance of common mode failures. Each computer independantly controls actuators. If one computer screws up, the other four actuators present enough pressure to overcome. If two go one way, and 3 the other, controls are mushy, but still function. I do find the 120 pounds of computer a bit silly. I can only figure they were used for DOD reasons. A commercial operation would NEVER have used such aging hunks of antidilivian technology. For the weight cost of those things, they could have 20 real computers. To put things in perspective, a few years ago the astronauts took a Grid Compass PC on board. The carry on machine was the most powerful computer on board, and it fits into a brief case and only takes half the depth. I'd say (in 1985 off the shelf technology) each shuttle main computer represents about one PC board of computer power, and probably less. It's getting to the point where you can walk into a Computerland and buy peripherals that are nearly as powerful as the shuttle computers. (Like the new Hayes modem). Even the requirement for core can be nicely handled by battery back up or by EPROM. (Although I'd personally recommend they buy Japaneses: the US EPROMS I've worked with in a commercial environment had a serious bit dropping rate. By that I mean that if you have 50 of them running for a month, you'd probably have one or two that have leaky bits. I NEVER had a drop out from the equivalent Japanese product. Of course that was five years ago, so maybe the US manufacturers have learned how to make a decent PROM by now...)