Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!ut-emx!nowhere!sking From: sking@nowhere.uucp (Steven King) Newsgroups: sci.space.shuttle Subject: Re: New Shuttle Computers Message-ID: <1991Mar10.210059.26743@nowhere.uucp> Date: 10 Mar 91 21:00:59 GMT References: <1991Mar9.044834.27802@cimage.com> <1991Mar10.164459.5216@rodan.acs.syr.edu> Organization: American Anarchist Union Lines: 42 In article <1991Mar10.164459.5216@rodan.acs.syr.edu> amichiel@rodan.acs.syr.edu (Allen J Michielsen) writes: >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....) > This is precisely what the AP101B required. Again quoting from the article in the E E Times; "we've always underestimated memory requirements in the shuttle program" Littleton [ manager at JSC Orbiter Avionics Systems office ] said. "We had a concern for transition from orbiter ascent-type software to re-entry software in the case we might need a transatlantic abort". As a result of the new computer-data organization, NASA will use the extra memory to place in SRAM many of the flight routines that previously were off-line -- resident on tape drives that required them to be loaded into system memory on demand. Now these commands could be at the ready in battery backed SRAM, boosting the flexibility of the shuttle mission. It would be interesting to see some of this software. Some early 70's fortran code no doubt... -- Look Ma! No .sig! ..!cs.utexas.edu!ut-emx!nowhere!sking