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Operating systems used in spacecraft?



 
 
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  #61  
Old December 2nd 03, 10:38 PM
Henry Spencer
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Default 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. |
  #64  
Old December 6th 03, 06:50 AM
Henry Spencer
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Posts: n/a
Default 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  
Old December 6th 03, 06:50 AM
Henry Spencer
external usenet poster
 
Posts: n/a
Default 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  
Old December 9th 03, 02:10 AM
Derek Lyons
external usenet poster
 
Posts: n/a
Default 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  
Old December 9th 03, 02:10 AM
Derek Lyons
external usenet poster
 
Posts: n/a
Default 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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