Path: utzoo!news-server.csri.toronto.edu!rutgers!usc!rpi!uupsi!rodan.acs.syr.edu!amichiel From: amichiel@rodan.acs.syr.edu (Allen J Michielsen) Newsgroups: sci.space.shuttle Subject: Re: New Shuttle Computers Message-ID: <1991Mar10.164459.5216@rodan.acs.syr.edu> Date: 10 Mar 91 16:44:59 GMT References: <1991Mar7.010752.10632@agate.berkeley.edu> <1991Mar9.044834.27802@cimage.com> Sender: amichiel@sunrise.acs.syr.edu Organization: Syracuse University, Syracuse, NY Lines: 65 In article shafer@skipper.dfrf.nasa.gov (Mary Shafer) >In article <1991Mar9.044834.27802@cimage.com> gregc@cimage.com (Greg Cronau) >> The bottom line is that harddrives are only useful in situations where >>you will be *writing* alot of new data. The control program for the >>shuttle is only *read* during flight, never written. A read only tape drive >>can be made much more rugged than a hard drive. I don't have proof positive, but would wager sums of money that the shuttle 'system' is NOT read only, else nasa would have certainly done 'rom' work. A MAJOR defect of tape systems in interactive systems like flight controls is the search/seek/acquire time. When the shuttle is traveling mach 3 and it yaws slightly or is determined to be off course slightly, a several second delay while the appropriate correction program/data is loaded could be tragic. The same can be said about the prefromance problem if all data is out together, and miles of tape needs to be fast forwarded as the shuttle transitions between major segments of it's mission (1. ignition, 2. launch, 3. clear tower, 4. roll 5. etc....) >We were using a read-only tape drive in the F-15 HIDEC (Highly >Integrated Digital Engine Control) when we were doing one phase of a >trajectory control program. We ended up aborting a lot of trajectory >guidance flights when the miserable tape drive died as we tried to >load the trajectory guidance code and checkpoints shortly after >takeoff. We weren't doing anything like high-g maneuvering, either. >Just taxi, takeoff, and try to load on climbout. As hard drive technology improves, density increases, head size decreases, amplifier/noise improves, shock/temp stability improves, all of whiich we see every day, EVENTUALLY, they (nasa/contractors) will probably be able to make drives that have enough head fly space & 'stuff' like density, speed, etc, that will make them reliable enough for the demanding rigors of space flight or sim. I've heard it flung around about portable drives and stuff, but this is like comparing a skateboard to a porsche. Ask a few people who were using computers during the world series earthquakes. The reports I've seen put the computer damage in the millions, and that wasn't just water damage or stuff either... I have yet to see anybody using a portable that was moving in 3 axis, vibrating 'inc' at multiple frequencies and accelerating and decelerating through multiple planes simultaneously. Mary's story provides a indication just how rugged and demanding data i/o services need to be for hostile enviroments AND what happens EVEN when the hostile environment is planned for. I wish Mary was able to provide a bit more info in regards to the flight/data system. Such as how much tape storage and other data storage was required for the system described. And possibly a indication of how long a period of time during which the biggest portion of this was to be done. I suspect that even this system had to have compromises made, and experienced a forced reduction of desired data. Further that these limits efectively lengthened the total time (number of flights) required to complete everything desired. The shear amount of data for even 1 flight handled would astound most people in both volume and time. al -- Al. Michielsen, Mechanical & Aerospace Engineering, Syracuse University InterNet: amichiel@rodan.acs.syr.edu amichiel@sunrise.acs.syr.edu Bitnet: AMICHIEL@SUNRISE