Designing a Star Tracker for Astronaut Don Pettit to Use on the ISS
petapixel.com
petapixel.com
"I was not a big fan of designing a
mechanical clock unless there was
another option."
I've seen some crazy/shitty rigging done, but this one gets a pass because it's in spaaaaaaaace
It also seems like it does not need to be capable of very long exposures, as also betrayed by the traces of the bright terrestrial lights in the demo photograph at the end.
To find the angle that the camera must rotate in 15 seconds: 15sec/93min * 360° ≈ 1°
How does that image betray anything you just said. In the example image, the background is clear while the earth is a motion blur. This is obvious of a long exposure image while showing the camera is moving to track the stars with the earth is in motion below it.
If you have seen any videos from LEO satellites, including the ISS, you would notice that any particular point on the ground moves very fast from the camera's point of view.
In the photo presented on the post, you can see the tracks of man made light pollution - the bright light emanating from cities being smeared across the image plane. But you can see the start and the end of those tracks, and they are small. Which means you can gauge the relative position of a single point on the ground at the beginning and at the end of the exposure.
And it hasn't moved much. Ergo, you can estimate that the exposure time is quite small.
Let me know if that wasn't clear enough, I am not used to explaining things to this level.
I don’t get it, anyone able to explain?
Edit: I think maybe Don's reputation as an in-space inventor (first patent for something invented in space) means the clock spring device got a long and contrived name for it's quite basic function.
Debbie Downer: Looks like it fairly easily could have been made with like 50% less mass.
Perhaps that wouldn't have mattered though.
I also can't imagine that the resupply flights are volume limited instead of mass.
Once it's up there, it's a negligible percent of the total spacecraft mass, and might be useful for later astronaut photographers.
the front/back plates? looks like your standard 3/8" aluminum plates. could they have used 1/4"? other materials like plastic/carbon would probably not have passed NASA requirements. plastic/carbon could chip into small pieces which is a very bad thing on the ISS. so you're left with a metal, and aluminum is pretty safe choice. it's clear there are several holes in these plates that are not tapped and are there solely as a means to reduce the weight.
moving the pieces closer for a tighter fit resulting in a overall smaller unit size? this thing is meant for ease of use. extra space affords that, and making it more compact complicates its use.