Hot answers tagged

131

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 keeping valid code words at a certain distance from each other. As a result, a slight change ("movement") of a valid word doesn't make it look like ...


93

First, space is absolutely gigantic; the chance of either of the Voyagers, or ay other outer-planet mission, hitting an asteroid was infinitesimal. Second, the asteroid belt itself isn't really constrained to the ecliptic plane; plenty of asteroids have significant inclinations, so staying out of the ecliptic wouldn't guarantee safety. Third, incorporating a ...


59

A Keplerian trajectory in the Solar system essentially needs to be in a plane defined by three points: the location of the Sun, the location you're starting from, and the point your target will be at when your spacecraft arrives. Since planets are close to the ecliptic, this plane will usually be close to the ecliptic for an interplanetary mission. Then ...


23

On April 6, 1978, a fault-protection algorithm onboard Voyager 2 automatically switched from the prime to backup receiver. However, the backup receiver's tracking-loop capacitor3 was found to have failed sometime previously. Soon after returning to the prime receiver by ground command, that receiver failed, leaving the spacecraft uncommandable. Seven days ...


19

The asteroid belt is toroidal, the asteroids aren't confined to the ecliptic plane. This diagram from Wikipedia shows that most asteroids have orbital inclinations under 10°, but there are still significant numbers out to 20° or so. This plot of orbital inclination ($i_p$) versus eccentricity ($e_p$) for the numbered main-belt asteroids clearly shows ...


18

Voyager 1 and 2 are still in the "neighborhood" of our solar system and very close to our Sun compared to any other star. They are roughly three times farther from the Sun than Neptune and Pluto and so already past the Kuiper belt where New Horizons is currently traveling. As the diagram below shows, the Voyagers have passed the boundary where the ...


14

Wikimedia has the following graph for the heliocentric velocities of both Pioneer probes: (SVG) As far as I can tell it's accurate, since it clearly shows the velocity change of Pioneer 10 during its Jupiter flyby on new year 1974, and Pioneer 11's two flybys of Jupiter on new year 1975 and Saturn in 1979. And New Horizons: (SVG) (This answer also has one.) ...


12

The tape recorder shown in the above article (by @user6972) and the one shown within this article are each representative of both the Viking Mars Lander DTR and its look-a-like brother, the Voyager DTR. However, please note that the previous article's DTR take-up reel "flange" is notably different than that shown in the photo of the DTR presented ...


12

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 station: It is not the prototype, it is the final version. The prototype may have required about 4 to 8 times the volume. Not a real monster, but filling a ...


8

Given historical context, I can map three of the four parameters of the mystery planet on those of Pluto, given what was known about Pluto at the time of the production of the golden record in 1977. Hence, I'm reasonably certain that the mystery planet is supposed to be Pluto, although I cannot explain the fourth parameter. In summary: the late 1960s and the ...


8

A couple considerations enter here. We do not expect the alignments to occur every 175 years over the long haul. Rather, they are likely to occur in clusters internally spaced by that interval until the alignment is "permanently" lost, and takes a much longer interval to reset. The period of 175 years represents a compromise between multiple ...


7

According to this source, the quiescent Sun produces about 10-20 Watts per square meter per Hertz at 2 GHz at Earth's orbit. At a distance of 152 AU, it will be a factor of 1522 weaker or about 4 x 10-25 W/m2/Hz. Collected with a 12 foot dish (~10 square meters) gives 4 x 10-24 W/Hz for solar noise. Thermal noise in the front end is kT W/Hz. Assuming a ...


7

For free, but low-resolution: Small versions of all1 the images are included in the book Murmurs of Earth by Sagan etc. Chapter 3 "Pictures of Earth" includes a visual index and then slightly higher quality versions of each picture1. Some are even in color. Descriptive text is included for each image. You can check it out and see them at the ...


6

So, this is VERY interesting. I have a Voyager golden record vinyl set that has a reference book included. In it, it has various images included with the record, among which are the same schematics and units of measurement table (also (c) Drake). The numbers appear to be identical to the ones you posted. I did a 'mystery planet' comparison to Pluto to see ...


6

There is useful current data at Heavens Above. The relevant bit is Voyager 2 is currently (Nov 2020) 125.4 AU from the Sun travelling at 3.231 AU/year, and Pioneer 10 at 127.2 AU and 2.512 AU/yr. So we expect them to change places in the list in $$\frac{127.2-125.4}{3.231 - 2.512} = 2.50\quad\mathrm{ years}$$ so roughly May 2023.


5

It is explained in the original paper from Sagan: A Message from Earth Author(s): Carl Sagan, Linda Salzman Sagan and Frank Drake Source: Science, New Series, Vol. 175, No. 4024 (Feb. 25, 1972), pp. 881-884 I found a copy on the website of Swarthmore College: link to PDF On page 2, it is explained: Those radial lines for which the earth-pulsar distance ...


5

It would be nice to look at Voyager image data compression and block encoding by Urban, but it's paywalled. It's described in Space Data Compression Standards though, which says Robert Rice of the Jet Propulsion Laboratory devised an adaptive code for the Voyager mission,6-10 which was extremely efficient in terms of detecting changes in data entropy and ...


5

Keiper belt is 50 AU thick....correct? Not really. Objects are classified as Kuiper Belt Objects if their semi-major axis length is greater than that of Neptune and less than or equal to the semi-major axis needed for a 1:2 orbital resonance with Neptune. The latter means a semi-major axis length of about 48 AU. To be in a 1:2 resonance with Neptune, those ...


3

Question: If the Voyagers' lowest playback speed is 7200 bits per second, how does it transmit to Earth at only 160 bps? It doesn't. The 160 bps transmission is real-time data rather than playback data. The playback data is rather infrequent and was at 1400 bps. (It may be at 600 bps now.) From https://voyager.gsfc.nasa.gov/Library/DeepCommo_Chapter3--...


3

I tried to look for a publicly accessible link to the Urban (1987) paper that was referenced in @Organic Marble's answer. Fortunately, it is publicly accessible through the University of Arizona: Voyager Image Data Compression and Block Encoding From pages 5 and 6, we see that: the Image Data Compressor (IDC) is a universal noiseless coding compressor the ...


3

Partial answer, exploring some details It's clearly not an artefact of the SVG vectorised file on Wikipedia. A photograph of the Voyager Golden record (which features the same map), shows the same gap. Using this to decode the pulsar map, the distance of the most similar pulsar can be established (280 parsecs) The gap is then around ~200 parsecs. I ...


3

This answer is somewhat speculative and relies upon a generous interpretation of what "minimizes accelerations" means. I obtained a three-view drawing of the Voyager from a link in this answer What does it mean when the Voyagers "switch thrusters"? I've cropped and annotated a portion of the drawing dealing with the pitch thrusters. ...


2

The lineup occurs once every 175 years. The launch window the last time this alignment occurred was from 1976 to 1980, so the next time it would open would be 2151-2154. Source: Grand Tour program


2

On some level, it was absolutely a publicity stunt by NASA, although the word "stunt" is too disparaging. The people who put the record together (Carl Sagan, Frank Drake, and others) wrote a book about it called Murmurs of Earth. Early on, the record was just going to be a plaque, and one of their consultants is quoted in the book as saying: There ...


2

This is an interesting but challenging question. I've found the following footnote on page 39 of Voyager Telecommunications, DESCANSO Design and Performance Summary Series, Article 4 Section 7.2.6 Voyager 2 Procedures to Compensate for Voyager 2 Receiver Problem and so am posting as a partial answer for now. I will have to dig deeper and then update ...


2

Does anybody know the bandwidth of the Voyager 2 radio antenna? Well there are different bandwidths for different functions. This summary of Voyager's telecommunications systems by JPL's Deep Space Communications and Navigations Systems Center of Excellence (DESCANSO) claims Voyager has 4 main functions for communication. They are carrier tracking (Doppler),...


2

Since Urban (1987) is available, I could look for the Details of IDC and FAST implementation missing: What spatial predictor was used? Simple scanline order pixel differences, or in other words a LEFT predictor. What does "adaptive split pixel compressor" mean? "Adaptive" here means they spilt the image into blocks and use different ...


2

Question: Did the Voyager spacecraft use a Golay, a Reed-Solomon and/or a Hamming code for data transmission encoding for error correction? Yes! And there's a convolutional coder in there as well. From DESCANSO Design and Performance Summary Series, Voyager Telecommunications, (2002): The TMU [telemetry modulation unit] encodes the high rate data stream ...


2

Voyager 2 is indeed outside the usually understood limits of the Kuiper belt. (About 50 AU, but typically defined as being in resonance with Neptune). That puts it in the scattered disk, but not as far as the Oort cloud. The beginning of the Oort cloud is typically set to 2,000 AU. All these regions are sparsely populated with small icy bodies, which the ...


1

The RS encoder is similar to Golay and Hamming encoders (shift-register based). For example, this resource gives a schematic diagram. In principle, it is as "simple" as binary encoders (check bits calculated from info bits). The main difference (and complication) is that additions and multiplications now operate on bytes (check bytes calculated ...


Only top voted, non community-wiki answers of a minimum length are eligible