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From: Dani Eder <>
Subject: Re: Onboard Non-Computer
Date: Wed, 5 Nov 1997 22:36:36 GMT

Autospammer wrote:

> Albert Passy wrote:
> >
> > The US side of ISS uses (no snickers, please) 386SX-20's with 387
> Hoot ! Hoot  !  It's got a 5 1/4 inch floppy RIGHT !?!
> How about the monitor: Is it still Hercules ,
> or did they manage to upgrade to EGA yet ?
> I'm in stitches, listen everybody, NASA needs a computer
> maybe your old 486 or low-end Pentium could

When you are done laughing, I'd like to point out a few things.  First of
all, there are 44 computers in the US portion of the Station.  This
counts redundant units, but not the Russian, European, and Japanese
computers, or the laptops the astronauts use for entering commands and
viewing displays.  One reason for having a lot of computers is if one
breaks, you don't lose the whole station.  With so many units, they don't
have to be very powerful individually.

Second, the laptops will be Pentium-based, and upgradeable.  They will be
your monitors and keyboards.  The 386's will be doing jobs like
controlling the fans that circulate air, sensing valve positions, etc.,
for which they are perfectly adequate.

Third, the Station passes through the South Atlantic Anomaly, a part of
the radiation belt that is particularly low in altitude.  The more modern
the chip, the smaller the transistors are, and the more sensitive they
are to radiation.  So an older chip with bigger components is better.

Fourth, some of the computers have 8 meg RAM, and some of the lower level
ones (that control equipment directly) have only 2 meg RAM.  All the
software is stored on EEPROM chips, which can and will be re-loaded with
updated software from time to time.  Only the top level command computer
and the payload controller have hard disks (300 meg and 2 Gig
respectively), and the laptops will have whatever they can put in them.

Fifth, the laptops are essentially off the shelf units of current vintage
(i.e. they are buying them about now). The 386s are custom units designed
to be water cooled.  This is so the waste heat can get transported to the
radiators and disposed of into space, and so the computers can work in a
vacuum.  Some are mounted outside and work in a vacuum all the time.  The
indoor ones are designed to continue operating even if you lose pressure
in a module.

Sixth, there is an operating system called "MDM Utilities Extension"
which handles low level things like communicating with other computers.
This is common across the computers.  In addition there is applications
software that depends on what that computer is in charge of.

Since I am writing the operating procedures for part of the computer
system, if you have any other questions, fire away.

Dani Eder

From: Dani Eder <>
Subject: Re: Onboard Computer
Date: Thu, 6 Nov 1997 18:55:45 GMT

Bill Bonde wrote:

>  This is all fun and everything, but I do hope that they are putting in
> network cables and the ability to put in real work computers other than
> just laptops in the ISS.

I'm not sure I understand what you mean by 'real work' computers.  If you
mean doing compute-intensive tasks like ray-tracing or aerodynamics
simulations, then no, the station is not set up for this.  The purpose of
the laptops is to give the crew a way to key in commands and display the
status of the on-board systems.  Most of the equipment on the Station
does not have a physical on-off switch that the crew can operate.  They
are remote controlled solid state switches controlled by the computers.
This way the ground controllers can operate the station as well as the
crew onboard, or even from the Shuttle Orbiter.

The control network is via MIL STD 1553B data busses, which nominally are
1 MHz busses.  They have very low bit error rates, which is important
when you are commanding the station to do things, and collecting data on
the status of the Station.  There are on the order of 30 busses,
typically with about 10-15 boxes on each bus.  Again, large numbers of
busses and large numbers of computers means that if something breaks (a
computer dies or a meteoroid takes out a data line (some of them are
outside the pressure shells)) you have enough capability left to keep
operating.  Also, a software bug or something that locks up a data bus
will only affect a small portion of the Station.

There is a separate network for science experiment racks.  It has a much
higher capacity (up to 50Mbps, shared with digitized video), but not as
good a error rate.  Experiments can incorporate as powerful a computer as
they want into their experiment racks, with their own displays and

In any case, current laptops are almost as capable as a desktop PC, and
they can be upgraded over time (they plug in to the Station through data

Dani Eder

From: Dani Eder <>
Subject: Re: Onboard Non-Computer
Date: Fri, 7 Nov 1997 18:36:42 GMT

Oleg Zabluda wrote:

> Dani Eder <> wrote:
> : Since I am writing the operating procedures for part of the computer
> : system, if
> : you have any other questions, fire away.
> Are you the one to blame for all the software problems Bit Flip told us
> about? Are you getting the $8000 bonus? If you do, tell them to make
> it $20,000.

In effect I'm writing the user's manual, not the actual code.  In this
case the users are the console operators at the Mission Control Center in
Houston, and the astronauts.  I'm did not see the previous message on
software problems, but one of them is that the sofware development is
behind schedule due to shortage of programmers.  As far as I know I am
not getting any bonus.

Dani Eder

From: Dani Eder <>
Subject: Re: Onboard Non-Computer
Date: Fri, 7 Nov 1997 19:28:55 GMT

Brian P. McCarty wrote:

> Are they actual 386-20's, or are they the microcontrollers with the
> 386 core?
> I would think an embedded controller would be better for this sort of
> thing than a generic CPU.

As far as I know they are actual 386's.  Different units have a card slot
for the processor, and a variable number of I/O slots to talk to other
boxes on the data busses, and sometimes discrete sensor lines.

Dani Eder

From: Josh Hopkins <>
Subject: Re: Onboard Computer
Date: Sat, 01 Nov 1997 09:40:01 -0800

Oleg Zabluda wrote:

> Albert Passy <> wrote:
> : The US side of ISS uses (no snickers, please) 386SX-20's with 387
> : co-processors, that are space rated and rad hardened.
> Which OS do you run on it?

Many years ago, back when the space station was still "Freedom," and
the Federal Systems division writing the software was part of IBM,
not Loral, or now Lockheed Martin, I did a summer internship at IBM
Federal Systems working on the OS for the space station.  I probably
remember just enough to make a fool out of myself, but here goes.

The computer system was called, at that time, the Data Management
System.  So the OS was called the Data Management System Operating
System.  (Really creative, right?)  The DMSOS was a heavily modified
version of a COTS (Commerical Off The Shelf) UNIX system called Lynx,
as I recall.  So, you don't have to worry about all of those jokes
about MS Windows on the Space Station, at least for the primary
computer system.  Now, I can't say for sure how much of this
information is still accurate.  My impression has been that the
plans haven't changed much, but I haven't followed the computer
system on ISS all that closely.

Incidently, back when I did my internship, the 386 was still a
reasonably modern chip.  However, it was obvious even at the time
that it was  going to be obselete before it flew, so I recall
discussing this issue with my manager.  He, like many people on
that particular project, had experience developing the shuttle
computer software.  He made an interesting point that really, the
386 was already a more powerful computer than was really needed.
The station computer, after all, has a much simpler job than that
of the shuttle computers.  There's no liftoff and no landing, and
coasting around in orbit doesn't involve anything really
computationally intensive.  There were apparently plans to make
the system upgradable, to handle faster future chips, but there
wasn't much concern that the old chips would be a problem.  After
all, much of what our fancy Pentium chips are doing are silly tasks
like running those little animated icons on the Netscape and Internet
Explorer windows, which as far as I can tell are solely intended to
show you that your computer hasn't locked up yet.  The Astronauts
won't be able to play Doom, though (except on their laptops.)

On another note, it should really be no surprise to anyone that
the space station uses outdated computer technology.  Very little
about the station is high tech.  That's one of the standard problems
with the old style "slower, expensive, worse," style of programs.
They take too long from program start to launch to be high-tech when
they finally fly.  And they cost too much to accept
the cost and risk of using anything that was high tech even at
the beginning of the program.  The space station program long ago
considered - and abandoned - high-tech systems for primary solar
power, propulsion, space suits, and many other things.

Josh Hopkins

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