From: jim bell <jimbell@pacifier.com>
Date: Wed, 28 Aug 1996 04:23:54 +0800
To: Bill Stewart <stewarts@ix.netcom.com>
Subject: Re:Edited Edupage, 18 Aug 1996 [SATELLITES]
Message-ID: <199608271609.JAA12761@mail.pacifier.com>
MIME-Version: 1.0
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At 11:24 PM 8/26/96 -0700, Bill Stewart wrote:
>At 12:35 AM 8/21/96 -0800, mccoy@communities.com (Jim McCoy) wrote:
>>You want to avoid moving parts like the plague in orbit.  They eventually
>>wear out or fail and once that happens you have a very expensive piece of
>>junk in orbit.  Solid-state storage is the _only_ way to go if you want to
>>avoid things like neding to pressurize the drive (eliminating any cost
>>advantage over solid-state.) 
>
>Why do you need to pressurize the drive?  Most hard disk drives
>for the last N years have been airtight sealed containers,
>haven't they?  (Removables are different, of course.)

While I haven't looked at the more recent ones closely, most hard drives have an ultra-fine (<0.1 um particles?) filter element separating "inside" from "outside."  It allows air to pass to equalize pressure and humidity, while keeping out the dust.  (it is probably made of the same kind of material that is used, internally, as a filter for the airflow within the drive.)

Even if they didn't, there is a big difference between an enclosure that's good enough to hold a hard disk on earth, and one which can spend N-years in a high vacuum yet maintain enough air to run a hard drive.

>
>I'd worry far more about the stresses of launch bothering
>the drives.

That's not a problem at all.  Most modern drives are rated for 10's of G's, non-operating.  Satellite launches are probably a breeze compared to this.


Jim Bell
jimbell@pacifier.com