# Tag Info

52

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 segment) but it's clearly the same device. Fortunately this is from a credible source, NASA's ISS Flight Systems brochure (warning, pdf). I can't quite figure ...

41

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 channel for only a couple of minutes, have black outs over the oceans, and repeat. Other notable differences would be: Normal satellites receiver are "fixed": The ...

36

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://www.ibiblio.org/apollo/NARA-SW/R-577-sec5-rev4-5.6-end.pdf PDF page 127). When in the idle program P00 the AGC will periodically check if it needs to update the ...

29

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 intervals. MRO and MO are in sun-synchronous orbits, so the planet rotates underneath the orbiter and they cover the entire planet in 1 day. Both are in orbits ...

26

Spacecraft that take pictures take them similar to a digital camera. However, the camera is very far away. Similar to downloading a movie off of a website so you can watch it on your local device, it takes time to transmit those images. However, because the distance is so far away, it can take a lot of time to download the images. The images reside on a ...

25

Organic Marble is correct in the comment, New Horizons is now busy with Departure Phase (DP2 from Aug 5-Oct 22) science and transmitting plasma and dust data, and no additional images will be transmitted until September 14 when Science Data Playback phase starts. All images from New Horizons Press Conferences Materials: Image sources: (1): Alan Stern, New ...

25

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-change “symbols”, and you want to find the time-pattern of those: symbol lock. But those are not yet bits because the coding works in blocks of bits. Once you ...

24

Look up the inverse square law. With the same power available at the spacecraft, the signal strength received at Earth diminishes as the square of the distance. If the vehicle is solar powered, then it is possible that it will also reduce the transmitted power as it goes farther from the Sun. However it is more likely to reduce the transmission duration ...

21

New Horizons also uses very strong error correction coding. Specifically, rate 1/6 turbo coding and BPSK (binary phase shift keying). This expands the signal bandwidth by a factor of six, but it still reduces the required energy per user data bit. This allows a higher data rate for a given transmitter power. The minimum Eb/N0 for this code is about 0 ...

21

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 not generous, so by the time spacecraft transmissions get back to Earth they are incredibly faint. The only equipment used to reliably receive these signals is ...

19

(10 year old version) The pictures are sent by radio, and the radio signals travel at the speed of light. Although the speed of light is very fast, it is not unlimited, and space probes can be very far away. So the time that elapses is simply the time it takes for the radio waves to travel at the speed of light over the very long distances between the ...

17

TL;DR: Data rate is directly related to effective noise floor, which is related to bandwidth and received power (and lack of interference). Lower received power means increasing transmit power or reducing bandwidth (speed). APL had to choose the latter due to constraints. Read on for a much more detailed and long-winded explanation (sorry if too long ...

16

Yes, they can and do watch TV shows on the ISS. From an interview with Scott Kelly aboard the ISS: Apart from posting pictures to Twitter and Instagram, Kelly also said he spends some of his limited downtime watching television. What exactly does a highly trained astronaut watch while orbiting the planet and contemplating the mysteries of life? ...

16

@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 could probably be fixed with a mod that NASA could easily manage. Several answers to Do astronauts get Netflix on ISS? indicate that there is access to "new ...

16

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 with 2" wide tape. This is the Ampex VR-660, a "portable" VTR that weighed 50 kg: NASA used the VR-660 at ground stations to store slow-scan video. The ...

15

There are 8 active Mars missions at the time of writing (11/14/17) Mars Odyssey Design Downlink Requirment: 3.6 kb/s minium On-Orbit Downlink Performance: up to 110,600 b/s for 34-m DSN passes Source: DESCANSO Design and Performance Summary Series, Article 6, Odyssey Telecommunications Mars Express Mars Reconnaissance Orbiter Design Downlink Requirement: ...

14

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 example 10 dB is a ratio of 10^1, 20 dB is a ratio of 10^2, etc, while 10 and 20 dBm would be 10 mW and 100 mW. But in the block quote, they use dBW instead of ...

12

Satellites are nowadays definitely not bandwidth starved, considering we've just had a few launches in the past month orbiting satellites capable of relaying live telecasts even in quad HD resolution. But the problem with tracking someone on the ground in real-time is more one of radial resolution, than the communications capabilities of satellites. You see,...

12

I didn't work on the server end of things, but I recall hearing at work that normal Internet streaming doesn't work because the general assumptions made about connections are violated. The latency is long, and connection pathways change often and by extreme amounts. A normal web-app will detect a problem and reset the connection. The software I worked on ...

12

Radio waves are such an abstract concept that it might be useful to explain to a child using an analogy of concrete objects. In a real way, picture information contained in a radio transmission could just as well be a string of baseballs thrown at high velocity, where the patterns or aiming of the throws enable reconstructing the picture at the other end. If ...

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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 standard 900 MHz chipset that will be mounted in both the rover and helicopter.[10] The communication system is designed to relay data at 250 kb/s over distances of ...

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A correct analogy would be: There is an image at some location. Someone is here and talks to someone else at a distance. The first person announces the color of each pixel, one by one. The second person, who hears the first one, draws each pixel according to the announcements. The sound of the voice takes time to travel, the further, the longer (this can be ...

11

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 switch to a smaller launcher. This finding also applies to Kepler.

10

I really can't add much to the already excellent answers but as seen as this is for a 10 year old the following picture from wikipedia may help explain the concept. It shows a pulse of light travelling at the finite speed mentioned in the other answers.

9

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 could work for short period distance, and that might be possible to use from a surface component to the underwater submarine. Very low frequency (3-30 kHz) can ...

9

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 looks to be less directional, so less likely to go down).

9

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 few large antennas are available, and they must divide their time between more missions than there are antennas). New Horizons used one dish instead, so the ...

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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 the official release of the first photographs from the surface of the Moon. Apollo 11 signals were received and decoded by Amateur Radio operators. Many ...

9

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 was measured by the rovers every sol by pointing the PanCam at the Sun, or where the Sun is supposed to be, measuring the intensity, correcting for the slant ...

9

"We should wait for all the problems on earth to be solved before going into space". I've seen this sentiment multiple times, and I disagree vehemently. 1. There are other much more worthy targets of this kind of argument Whenever a space mission has cost overruns in the billions, I convert the dollar amount into B-2 bomber equivalents. That is, 2 billion ...

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