New Horizons at Pluto

Corsair 115 said:
Why would God need a starship?
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Hey! Gawd wants one!
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NASA has announced the selection of New Horizon's follow-on target as 2014 MU69.

“2014 MU69 is a great choice because it is just the kind of ancient KBO, formed where it orbits now, that the Decadal Survey desired us to fly by,” said New Horizons Principal Investigator Alan Stern, of the Southwest Research Institute (SwRI) in Boulder, Colorado. “Moreover, this KBO costs less fuel to reach [than other candidate targets], leaving more fuel for the flyby, for ancillary science, and greater fuel reserves to protect against the unforeseen.”

New Horizons was originally designed to fly beyond the Pluto system and explore additional Kuiper Belt objects. The spacecraft carries extra hydrazine fuel for a KBO flyby; its communications system is designed to work from far beyond Pluto; its power system is designed to operate for many more years; and its scientific instruments were designed to operate in light levels much lower than it will experience during the 2014 MU69 flyby.”

The 2003 National Academy of Sciences’ Planetary Decadal Survey (“New Frontiers in the Solar System”) strongly recommended that the first mission to the Kuiper Belt include flybys of Pluto and small KBOs, in order to sample the diversity of objects in that previously unexplored region of the solar system. The identification of PT1, which is in a completely different class of KBO than Pluto, potentially allows New Horizons to satisfy those goals.
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Skeptic Ginger said:
:eye-poppi

Wow, either it's a very slow connection or that's a hell of a lot of data (or both ;) ).
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We've been here before. In 1964, Mariner 4 made the first fly-by of Mars and saved a handful of pictures on tape. These were transmitted back to Earth at either eight and a third or 33 and a third bits per second. Considering that Pluto is some 60 times further away, a data rate of 1000 bits per second represents a huge advance in radio technology.
 
I wish they'd release the unprocessed images as they get them, to be honest. Things like GalaxyZoo have demonstrated that getting the general public involved is a fantastic way to advance science, and "Let's try to figure out these pictures" seems to be the best kind of study for current citizen-science protocols.
 
The data rate is only about 1 Kbps. I recall reading somewhere that it can go down to 100 bps under certain conditions and up to 3 Kbps. From an article by Emily Lakdawalla of the Planetary Society.

The short answer to that question is: Pluto is far away -- very far away, more than 30 times Earth's distance from the Sun -- so New Horizons' radio signal is weak. Weak signal means low data rates: at the moment, New Horizons can transmit at most 1 kilobit per second. (Note that spacecraft communications are typically measured in bits, not bytes; 1 kilobit is only 125 bytes.) Even at these low data rates, only the Deep Space Network's very largest, 70-meter dishes can detect New Horizons' faint signal.
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...[images] can be zipped up to about 2.5 Megabits without any loss of detail. They can be made even smaller with lossy JPEG compression, but for optical navigation, precision counts; the pictures have to be returned losslessly.

So, do the math. 2.5 Megabits, at 1 kilobit per second: it takes 42 minutes to return one LORRI photo to Earth. Most communications sessions last about eight hours. That's eleven images per communications session. And that assumes that New Horizons is transmitting only LORRI data, which it's not; there are other science instruments and spacecraft housekeeping data, too.
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As for the question of "Why does data rate transmission/reception decrease with distance?", I found this to be the best answer of all on this site linked, taking for granted of course that signal strength decreases with the square of the distance.

The probability of correct detection of a data bit is a function of the energy (not the power) in the received pulse. When the received power diminishes due to increasing distance, we can still meet the required energy by making the bit last longer (E = P x T). Longer pulses mean reduced data rate.
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Though it seemed at first counter intuitive to me as an amateur radio operator, as one narrows the bandwidth of a communications receiver to avoid adjacent channel interference and increase signal to noise, high speed code (CW), teletype (RTTY) or voice (AM/SSB), reception begins at some point to become muddled. Unless the sending rate is decreased, reception tends to become a meaningless blur.
 
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