Re: Newbie with questions

[P3D John W Roberts <roberts@xxxxxxxxxxxxxxxxx>]

>Date: Tue, 11 Mar 1997 12:53:44 -0600
>From: P3D Paul Albers <PAlbers@xxxxxxxxxxx>
>Subject: Re: Newbie with questions

>P3D John W Roberts' wrote:'
>> Not so fast! You could have the rocket eject two 2D cameras, which hang
>> down from their own parachutes (thus pointing straight down), take circular
>> photos, and are timed to photograph a certain time after going to zero-G
>> (for instance). You could put a spring in to push the cameras apart, or
>> just rely on turbulence of the air to get the proper separation on some
>> of the launches.

>If the cameras are not rigidly held in place to point the same way, it
>is *very* unlikely that it will happen at all, too much chaos in this
>universe.  

Unless you have a really long focal length, the criterion for "down" isn't
very stringent. A few degrees off would just mean you'd have to trim the
photos a little. I specified circular images (what camera lenses produce
anyway) so that "rolling" of the two cameras about the axis of the downward
trajectory would not matter. The only thing that matters is spacing, and
you basically rely on "chaos" to provide suitable spacing once every few 
launches. (BTW, I find the "1 in 30" rule to be much less important for
long-distance shots. 1 in 50 to 1 in 100 often produces better results.
For terrain mapping, much larger interoculars are often used.

>The idea of some kind of expanding platform sounds rather
>James Bondish, I like it, but doubt it could be done without becoming
>too heavy for a modle rocket.

I didn't have anything like that in mind - maybe a small spring under
compression to help push the cameras out of the rocket and/or give the
two cameras a slight nudge away from each other after the ejection charge
fires. It's probably not even necessary - you could have a cord attached to
the nose cone pull the cameras out.

Estes / Centuri has (or had) a model suitable for inclusion of a small
camera - I think the camera enclosure is actually an extension of the
nose cone, and the picture is taken through the side of the plastic tube.
I'm not sure whether anyone actually sold a camera to go in there.

Regarding maximum separation on a single rocket, Estes had a 6-foot long 
single-stage model, powered by a D engine. I actually built one, but I gave it
away as a gift and never tried to fly it - I don't remember how the ejection
charge worked (which would be of concern for the rearward camera).

John R


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