New Horizon Cameras Options

[Guest_vjkane2000_*]

I've been wondering what the focal lengths are for the two New Horizon cameras (Ralph and Lorri). Curious to know how much Alan et al. were able to squeeze into their weight budget.

[edstrick]

Bob Shaw: "... but it doesn't change the fact that nowadays the problems are known yet dumb mistakes keep getting made. "

AMEN.

I think it was a BAD mistake not to have a coarse focus adjustment on the deep impact camera.

A big "Uh... I thought we knew about this..." problem... Stardust had a massive problem with condensate from outgassed crud fogging the optics. The earth-flyby image of the moon was 90% fog and 10% image.... massively blurred. Repeated heating of the camera to degass the optics got most of it, but I'm not at all sure they ever did get all of it and the Wildt comet flyby pics I think are somewhat degraded by it. NEAR's optics were significantly fogged by hydrazine byproducts during the loss-of-control event at the first arrival burn attempt that nearly lost the mission (not the camera's fault), and Cassini has had significant fogging problems between Jupiter and Saturn that I think still has some residual that makes it impossible to search for low brightness outgassing plumes at Enceladus.

Fogged optics seem to be the other problem-of-the-decade, besides out of focus cameras.

[mcaplinger]

Bob Shaw:  "... but it doesn't change the fact that nowadays the problems are known yet dumb mistakes keep getting made. "

AMEN.

I think it was a BAD mistake not to have a coarse focus adjustment on the deep impact camera.

I don't know all the details of the DI story, but I don't think you guys are being completely fair here.
You might recall that in the "old days" cameras had all-metal structures and masses of over 50 kg. For example, the Cassini ISS mass is about 58 kg, fully 4x heavier than the MOC on MGS with its graphite-epoxy optical structure. But for that mass savings, you have to work with a much trickier material. To say that all of the problems are known at this point is not really accurate.

You can usually assume that with optics, even mistakes that seem dumb with 20:20 hindsight are fairly subtle and hard to avoid once you appreciate all the details.

As for focus adjustment; it may be nice to have, but it's heavy and complex and if it fails, you can easily be worse off than before. We studied this trade very carefully for MRO CTX and ended up with no focus adjustment, and we intend to do the same for our LRO instruments. The MOC has focus control heaters, by necessity, but they have only a fairly limited adjustment range. See Ravine, M. A., et al., Graphite-epoxy optical systems: lessons learned on the way to Mars, Proceedings of the SPIE, 5179, 311-322, 2003.