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132 votes
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How is stacking oranges in 24 dimensions related to receiving and decoding signals from the Voyagers?

All the different data words a transmitter can send and a receiver can detect can be imagined as dots arranged in a large space. Selecting a data encoding for error detection and correction is about ...
asdfex's user avatar
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58 votes
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Why is the James Webb Space Telescope's data storage space so small?

Best Technology Available By late 2002, SSDs had just reached ~80 GB capacities. Of course, JWST is not going to take a product which has never seen enterprise deployment, and plonk it into \$2 ...
Lawnmower Man's user avatar
55 votes

Why does there appear to be a 180-degree stereo microphone array outside the ISS?

That is a UHF antenna. It was well placed on the Lab to get in the way of robotics ops during space station assembly. This is a picture of a different UHF antenna unit (this one is on the P1 truss ...
Organic Marble's user avatar
40 votes
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Does the International Space Station get TV?

More or less. While the ISS is below the satellites use for TV transmissions, it is passing by so fast that the coverage will be highly intermittent, meaning that you would be able to watch a ...
Antzi's user avatar
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37 votes
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What exactly turned on the light indicating Apollo 8 was starting to fall towards the Moon?

The Apollo Guidance Computer used a state vector either centered at the Earth or the Moon. The switchover point is the the lunar sphere of influence, defined in the AGC as 64,373,760 meters (https://...
indy91's user avatar
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33 votes

Why is the James Webb Space Telescope's data storage space so small?

Space hardware almost always is pretty archaic technology. The problem is the long lead time coupled with the need to certify it for flight. It wasn't archaic when it was engineered. The JWT was ...
Loren Pechtel's user avatar
30 votes
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Why not a "live" visual connection with Curiosity on Mars all the time?

Why not? Because we can't. We don't have full-time communication with Curiosity: Curiosity sends data to the Mars Reconnaisance Orbiter and Mars Odyssey. These are overhead twice a day at 12-hour ...
Hobbes's user avatar
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27 votes
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What is carrier lock and bit lock?

First you lock on to energy at (or near) the expected frequency. That’s carrier lock. Then you start to look for patterns in how the phase changes. The transmitter is coding groups of bits as phase-...
Bob Jacobsen's user avatar
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22 votes
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Current maximum bandwidth between Mars and Earth?

There are 8 active Mars missions at the time of writing (11/14/17) Mars Odyssey Design Downlink Requirement: 3.6 kb/s minium On-Orbit Downlink Performance: up to 110,600 b/s for 34-m DSN passes ...
Mark Omo's user avatar
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21 votes

Will there be live HD television from Mars with the Mars 2020 mission?

Hobbes' answer explains why live broadcast is currently not feasible from the Mars side. I'd like to complement it with why this is currently not feasible from the Earth side. Mars power budgets are ...
Bear's user avatar
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19 votes
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How to calculate data rate of Voyager 1?

OK let's first understand units. The decibel (dB) is a base-10 log scale without units and dBm is a similar decibel scale for power referenced to 1 milliwatt. They also include a factor of 10, so for ...
uhoh's user avatar
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17 votes

Why is there never enough room on satellites to hold all the equipment needed?

Why is there never enough room on satellites to hold all the equipment needed? Welcome to Space Exploration SE! Because of the time involved from planning until completion of goals at the end of the ...
uhoh's user avatar
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16 votes
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Were the Apollo broadcasts recorded locally on the LM?

The live broadcasts from the Moon were not recorded on the LEM/CM. Video tape recorders were too large at the time to make this practical. They usually came in the shape of an open-reel tape recorder ...
Hobbes's user avatar
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16 votes

Why is there never enough room on satellites to hold all the equipment needed?

Perhaps there is an assumption that new photos of Earth taken from space would be inspiring, enlightening, and meaningful in some way. That was certainly true of the first photos that were taken, but ...
Steve Pemberton's user avatar
15 votes

Does the International Space Station get TV?

@Antzi's answer is right, but I'll add some context as a supplement. While Doppler (mentioned there) might or might not be an issue for an off-the-shelf commercial satellite TV box (I don't know) it ...
uhoh's user avatar
  • 149k
15 votes

What Voyager spacecraft hardware performed transmitted data coding in such a complicated way? Did ground decoding use “a big monster filling a rack”?

Though what's in the Voyager remains to be seen, the Performance Study of Viterbi Decoding as Related to Space Communications1 gives a description of such a system implemented on Earth for the ground ...
Uwe's user avatar
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14 votes

Why is there never enough room on satellites to hold all the equipment needed?

You seem to have overlooked DSCOVR, which pretty much just stares at our planet. https://epic.gsfc.nasa.gov/
Organic Marble's user avatar
13 votes

Why is there never enough room on satellites to hold all the equipment needed?

We have a large number of sources taking photos of our planet. This includes: low-altitude Earth observation satellites (Landsat, SPOT, Maxar). These take high-resolution photos of a small area at a ...
Hobbes's user avatar
  • 128k
12 votes
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Why was Kepler's orbit chosen to continue to drift away from Earth?

Initially, Kepler was slated to go to L2. However, when preparing Spitzer, NASA found that a heliocentric, Earth-trailing orbit takes less propellant to reach than L2. For Spitzer, this enabled the ...
Hobbes's user avatar
  • 128k
12 votes

Will there be live HD television from Mars with the Mars 2020 mission?

The JPL Mars Helicopter Scout transmitter can send data at up to 250 kb/s, an order of magnitude short for HD video. Communications with the rover are through a radio link called Zig-Bee, a ...
Hobbes's user avatar
  • 128k
12 votes

Hijacked space data, notable instances of recovering images or other goodies from someone else's space mission?

Two items of note: Luna 9's initially released pictures came from scientists at Jodrell Bank Observatory in England, which could be received because they were in a standard format. This came ahead of ...
PearsonArtPhoto's user avatar
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12 votes
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Opportunity's last tau was 10.8; what does that mean and how is tau defined and measured?

Vacuum would have a $\tau$ of zero. An opacity of $\tau$ means that the atmosphere is reducing the direct intensity of light from the Sun, if it were directly overhead, by a factor of $e^{-\tau}$. It ...
Mark Adler's user avatar
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12 votes
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Do the Voyager probes transmit analogue or digital data?

All communications between spacecraft and Earth will be in digital form. Voyager Press Kit p.24
Organic Marble's user avatar
11 votes

Hijacked space data, notable instances of recovering images or other goodies from someone else's space mission?

note: Here are two examples of "hijacked signals" that include "public release of the images or data that included the admission that it is 'stolen' or 'hijacked'." I am sure there are a few more. One ...
uhoh's user avatar
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10 votes
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Why is New Horizons' data transmission speed so slow compared to Voyager?

The phrase "limited by ability to capture 1.4 kbit/s data using a 70 m/34 m antenna array" indicates they used 2 large dishes to receive Voyager's signal, which takes up a lot of DSN resources (only a ...
Hobbes's user avatar
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10 votes
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What are the data storage capabilities onboard the James Webb Telescope?

This user guide seems to be reasonably recent (2017) and answers your question. The solid state recorder (SSR) onboard JWST can hold at least 58.8 Gbytes of recorded science data. JWST ...
Steve Linton's user avatar
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10 votes

To what extent could JWST continue to be useful after the propellant runs out?

Could JWST be moved to an Earth-trailing orbit (or other useful orbit) without sacrificing too much precious remaining propellent? The JWST will be moved to an Earth-trailing heliocentric orbit as an ...
David Hammen's user avatar
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9 votes
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Do you need a "wire" on a Europa submarine to phone home?

A wire would be needed to get any real amount of data out. Wikipedia has the state of the art communication with submarines. There are basically 2 ways to communicate with them. Using sound waves ...
PearsonArtPhoto's user avatar
  • 121k
9 votes
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Why are there times when the ISS can transmit audio, but not video?

Edit after being pointed in the right direction by @Organic Marble: Video goes out over the Ku-band link (which uses a very directional dish antenna), audio goes over a separate S-band link (which ...
Hobbes's user avatar
  • 128k
9 votes

Is it possible to extend high speed data transmission with lasers to the distance Earth to Mars?

No, you don't need "at least some photons per data bit". 13 bits per photon has been demonstrated with laser communications. You calculate the data rate capability the same way you do with any other ...
Mark Adler's user avatar
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