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#61
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Operating systems used in spacecraft?
In article ,
rk wrote: Anyways, whether it's called COTS or modified COTS it is inexpensive and more or less available to anyone at a commercial fab. It's COTS if I can order it from Digi-Key and have it arrive on my desk the next morning. :-) Actually, you can take the ":-)" off that. One of the Secret Wisdoms :-) of the cheap-spacecraft mafia is that prototyping early and often, which is really good for effective debugging and thus for system reliability, is just a Whole Lot Easier if you stick to parts that *don't* have six-month delivery times and a requirement for ITAR paperwork. (Not to say that these necessarily do; haven't tried them.) Being able to implement your design change tomorrow, so you can start testing it the day after, does wonders for cost-effective engineering. -- MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer pointing, 10 Sept; first science, early Oct; all well. | |
#62
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Operating systems used in spacecraft?
(Henry Spencer) wrote:
Being able to implement your design change tomorrow, so you can start testing it the day after, does wonders for cost-effective engineering. That sounds suspiciously circular; "the secret to building stuff cheaply is to buy stuff cheaply". (Setting aside the fact that cost-effectiveness and total cost are only loosely coupled.) D. -- The STS-107 Columbia Loss FAQ can be found at the following URLs: Text-Only Version: http://www.io.com/~o_m/columbia_loss_faq.html Enhanced HTML Version: http://www.io.com/~o_m/columbia_loss_faq_x.html Corrections, comments, and additions should be e-mailed to , as well as posted to sci.space.history and sci.space.shuttle for discussion. |
#63
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Operating systems used in spacecraft?
(Henry Spencer) wrote:
Being able to implement your design change tomorrow, so you can start testing it the day after, does wonders for cost-effective engineering. That sounds suspiciously circular; "the secret to building stuff cheaply is to buy stuff cheaply". (Setting aside the fact that cost-effectiveness and total cost are only loosely coupled.) D. -- The STS-107 Columbia Loss FAQ can be found at the following URLs: Text-Only Version: http://www.io.com/~o_m/columbia_loss_faq.html Enhanced HTML Version: http://www.io.com/~o_m/columbia_loss_faq_x.html Corrections, comments, and additions should be e-mailed to , as well as posted to sci.space.history and sci.space.shuttle for discussion. |
#64
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Operating systems used in spacecraft?
In article ,
Derek Lyons wrote: Being able to implement your design change tomorrow, so you can start testing it the day after, does wonders for cost-effective engineering. That sounds suspiciously circular; "the secret to building stuff cheaply is to buy stuff cheaply". (Setting aside the fact that cost-effectiveness and total cost are only loosely coupled.) It's not so much whether the parts are *cheap* -- although that helps -- but whether you can get them quickly. It's a question of the speed of design iterations, and the ease of building multiple copies early so you can get them into testing early and make bench-test hardware widely available. When parts availability is a major bottleneck, the engineering process is much less flexible. You have to make commitments far in advance, and a lot of man-hours get spent inefficiently on reviews and double-checking because design mistakes cost a lot of time. There is great pressure to sign off on poor designs, even if they're likely to cause problems later, because there is too much invested in them and no time for more design iterations. Testing has to be delayed until near the end, and if it finds problems -- which it almost always does -- you may be in deep trouble. Related development tasks (e.g. software) have to start long before real hardware is available, so a lot of effort gets put into simulators and fake testbed hardware, which may or may not be representative. Access to real hardware is limited, and you have to be careful with it because it's not easily replaced if you break it, and that too limits testing. "Real hardware" problems like incompatible materials or fabrication problems may not be found until very late. There is pressure to cut corners when another design rev is really needed but there isn't quite time. -- MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer pointing, 10 Sept; first science, early Oct; all well. | |
#65
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Operating systems used in spacecraft?
In article ,
Derek Lyons wrote: Being able to implement your design change tomorrow, so you can start testing it the day after, does wonders for cost-effective engineering. That sounds suspiciously circular; "the secret to building stuff cheaply is to buy stuff cheaply". (Setting aside the fact that cost-effectiveness and total cost are only loosely coupled.) It's not so much whether the parts are *cheap* -- although that helps -- but whether you can get them quickly. It's a question of the speed of design iterations, and the ease of building multiple copies early so you can get them into testing early and make bench-test hardware widely available. When parts availability is a major bottleneck, the engineering process is much less flexible. You have to make commitments far in advance, and a lot of man-hours get spent inefficiently on reviews and double-checking because design mistakes cost a lot of time. There is great pressure to sign off on poor designs, even if they're likely to cause problems later, because there is too much invested in them and no time for more design iterations. Testing has to be delayed until near the end, and if it finds problems -- which it almost always does -- you may be in deep trouble. Related development tasks (e.g. software) have to start long before real hardware is available, so a lot of effort gets put into simulators and fake testbed hardware, which may or may not be representative. Access to real hardware is limited, and you have to be careful with it because it's not easily replaced if you break it, and that too limits testing. "Real hardware" problems like incompatible materials or fabrication problems may not be found until very late. There is pressure to cut corners when another design rev is really needed but there isn't quite time. -- MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer pointing, 10 Sept; first science, early Oct; all well. | |
#66
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Operating systems used in spacecraft?
snip excellent responses by rk and Henry
I bet people think I make these bonehead posts on accident. D. -- The STS-107 Columbia Loss FAQ can be found at the following URLs: Text-Only Version: http://www.io.com/~o_m/columbia_loss_faq.html Enhanced HTML Version: http://www.io.com/~o_m/columbia_loss_faq_x.html Corrections, comments, and additions should be e-mailed to , as well as posted to sci.space.history and sci.space.shuttle for discussion. |
#67
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Operating systems used in spacecraft?
snip excellent responses by rk and Henry
I bet people think I make these bonehead posts on accident. D. -- The STS-107 Columbia Loss FAQ can be found at the following URLs: Text-Only Version: http://www.io.com/~o_m/columbia_loss_faq.html Enhanced HTML Version: http://www.io.com/~o_m/columbia_loss_faq_x.html Corrections, comments, and additions should be e-mailed to , as well as posted to sci.space.history and sci.space.shuttle for discussion. |
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