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How the heck does it know where earth is? That's some impressive science there, not like there is a deep-space GPS. Does it look for the sun and figure out fr
by ck2 3y ago
How the heck does it know where earth is?
That's some impressive science there, not like there is a deep-space GPS.
Does it look for the sun and figure out from there?
- gregsadetsky 3y agoI assume star tracking -- wikipedia seems to confirm "... and celestial referencing instruments (Sun sensor/Canopus Star Tracker) to maintain pointing of the high-gain antenna toward Earth" https://en.wikipedia.org/wiki/Voyager_2 https://en.wikipedia.org/wiki/Voyager_2
- kyleyeats 3y agoDung beetles do this too.
- gregsadetsky 3y agothat's nuts! "- African dung beetles orient to the starry sky to move along straight paths - The beetles do not orientate to the individual stars, but to the Milky Way" https://www.cell.com/current-biology/fulltext/S0960-9822(12)01507-2 https://www.cell.com/current-biology/fulltext/S0960-9822(12)... https://www.science.org/content/article/dung-beetles-navigate-milky-way https://www.science.org/content/article/dung-beetles-navigat...
- CMCDragonkai 3y agoSo you can see astrological events do affect us.
- ozzmotik 3y agos/log/nom/
- dylan604 3y agoAs long as there's not too much light pollution. Fortunately for the dung beetles, their habitat isn't very urban. However, it's the little examples like this that make me a light pollution dork.
- gregsadetsky 3y agoSorry to self-reply, but this Q&A on "Space Overflow" about this specific star tracker is great: https://space.stackexchange.com/questions/43803/how-did-the-canopus-star-tracker-work-are-there-any-still-out-there-in-service https://space.stackexchange.com/questions/43803/how-did-the-...
- rvnx 3y agoCool finding!
- vntok 3y agoBasically the probe knows where it is because it knows where it isn't. By subtracting where it is from where it isn't, or where it isn't from where it is (whichever is greater), it obtains a difference, or deviation. The guidance subsystem uses deviations to generate corrective commands to drive the probe from a position where it is to a position where it isn't, and arriving at a position where it wasn't, it now is. Consequently, the position where it is, is now the position that it wasn't, and it follows that the position that it was, is now the position that it isn't.
- mcguire 3y agoOk, what is this quote from?
- wizofaus 3y agohttps://web.archive.org/web/20031218192524/http://w3.uwyo.edu/~jimkirk/guidance.html https://web.archive.org/web/20031218192524/http://w3.uwyo.ed...
- wholinator2 3y agoWait, i don't understand. I was under the assumption that this text was a joke, but now I'm seeing it in reference to air force training materials? Is it a joke there as well or did someone actually write this text seriously, and plan for it's use as intelligible instruction?
- wizofaus 3y agoThere's oodles of references to this online but nothing really I've found so far explaining whether it was ever intended to be taken seriously in the first place. It's hard to imagine anyone doing so.
- KptMarchewa 3y agoIt's apparently from the 50s, as seen here: https://archive.org/details/sim_electronics-now_1959-03_30_3/mode/1up https://archive.org/details/sim_electronics-now_1959-03_30_3...
- Dylan16807 3y agoSo other people talked about how it does track, but there's another thing to note here. "The high-gain antenna has a beamwidth of 0.5° for X-band, and 2.3° for S-band." At 130-150 AU, the earth is always within about 0.4° of the sun. Since commands are sent on S-band, pointing directly at the sun gets a pretty good signal.
- mcv 3y agoIs that signal not drowned out by the sun? Or are these bands where the sun doesn't do anything?
- Dylan16807 3y agoIf I can trust arbitrary estimates on stack exchange, the deep space network transmitters will be about equal brightness to the sun at frequencies near 2GHz when the 20signal is 10 Hertz wide. That would put the transmission rate in the ballpark of 10 bits per second, and the real number is 16 bits per second, so that seems to work out. Being drowned out is harder than you might think. The maximum data rate of a weak signal is 1.4 x [bandwidth] x [signal-to-noise ratio]. If you transmit across a 200MHz band, and your signal is a million times weaker than the noise, you can do hundreds of bits per second.
- detourdog 3y agoit probably has both gyroscopes and star-charts for navigation.
- dekhn 3y agoI should point at that astronomical navigation is a remarkable skill that was developed and turned into routine calculations in a relatively short period of time. The first order calculations are based on star imaging and used a Kalman filter,which had been invented just a few years before (https://en.wikipedia.org/wiki/Kalman_filter#History https://en.wikipedia.org/wiki/Kalman_filter#History) along with a star catalog (list of known star locations relative to the sun/earth) and direct observation by astronauts. I think a sextant was useful. Second order calculations use careful analysis of the signal pattern in telemetry data- IIRC you can see a slow stretch of the phase which can be used to estimate distance and velocity with high accuracy. Voyager, along with Apollo, stand as the finest examples of human engineering done yet- we got a bunch of people to the moon and back, and built a probe that still operates 50 years later... farther than anything else humans have launched... I'd be lucky if I can deploy my web app once a week.
- wkdneidbwf 3y agoyeah, it really puts my god awful pile of terraform in perspective.
- gzer0 3y agoLogged in to comment that this particular comment made me laugh. It really puts what I personally do to shame, many times over. Thanks for the laugh. Cheers.