Voyager 1 and 2 still operational

[Channel Hopper]

Well, as from July

Both spacecraft, now over 10 and 6 billion (US) miles from Earth have been sent commands with confirmation from Voyager 2.

The Deep Space Network confirms the amount of propellant onboard the two craft could allow them to carry out additional tasks on a fly-by within the Kuiper belt should there be the discovery of something out of the ordinary from the new generation of ground based telescopes. Presently the only fuel being used corrects the trajectory for optimum signal path to Earth.

_http://voyager.jpl.nasa.gov/mission/weekly-reports/index.htm

As a comparison to the other news on the first Earth like planet found some 20.5 light years away, Voyager 1, the fastest man-made object, would take just under 50,000 years to reach it, at it's current speed of 38,000mph.

Whilst Voyager is not 'speeding' towards Gliese 581, it is destined to pass another red dwarf star, AC+79 3888, at a distance of some 1.6 light years, (originally thought unable to be large enough to have a planetary system) . However since the discovery of five planets around Gliese 581, including the earth like planet, Gliese 581 g, telescopes are already being trained towards this star, in the hope another planetary system is orbiting AC+79 3888.

Voyager is expected to pass by in 40,500 years time. If it was still transmitting data, it would take just under 18 years to arrive back on Earth.

_http://en.wikipedia.org/wiki/AC%2B79_3888



AC+79 3888 - Wikipedia, the free encyclopedia

 

[Huevos]

(US) miles

What is a US mile? I thought miles were statute or nautical. I've never heard of a US mile.

 

[Topper]

Correct but they like to hype up their country by making them exclusive

A certain measure of distance, being equivalent in England and the United States to 320 poles or rods, or 5,280 feet.

 

[Analoguesat]

Wow - they certainly new how to build their spacecraft in the 1970's!

Shame they lost contact with Pioneer 10 a few years ago.

 

[Channel Hopper]

What is a US mile? I thought miles were statute or nautical. I've never heard of a US mile.

The (US) relates to the 'billion', not the length of the mile. The UK also started using the 'short scale' in 1974 for some strange reason.

_http://en.wikipedia.org/wiki/Long_and_short_scales

 

[Channel Hopper]

Btw, spot the error.

[tube]efvhQ8kWIEY[/tube]

 

[Huevos]

The (US) relates to the 'billion', not the length of the mile.

Ah! That explains it. Silly me! Well at that distance, just to get the radio signal in one direction would take 8 hours, 56 minutes, and 14 hours 54 minutes respectively. I wonder what sort of EIRP would be needed for the spacecraft to be able to receive signals at that range, and what sort of gain dish back on Earth to hear the spacecraft's response.

Btw, spot the error.

A few too many zero's.

 

[Channel Hopper]

I wonder what sort of EIRP would be needed for the spacecraft to be able to receive signals at that range, and what sort of gain dish back on Earth to hear the spacecraft's response.

Well, the dishes used on the ground are between 35m and 70m in diameter

_http://deepspace.jpl.nasa.gov/dsn/features/70metermaintenance.html

and this allows a rather fine beamwidth to focus the signal.

But since there is little need of fast data, (the craft is not only travelling at a speed that couldn't be reversed/slowed or altered by the onboard motors, but the time of receiving/deciphering any message is some half a day after sending), absolute power isn't the most important.

A trade off is made between detection (transmission/reception power), and the algorithm of the data stream, which has an enormous error correction component. Basically the time base of any message is extended to allow the multiple errors of a received signal to be calculated as errors, and then eliminated. Additionally the more times the same data is sent, the probablility increases of an error free string appearing at some point.

I'll post some more technical detail of algorithms in deep space comms later, once I've found where the journals have gone (probably after the next glass of wine has disappeared ).

 

[Channel Hopper]

Well, these are for starters

_http://www.cs.man.ac.uk/~barry/mydocs/CS3282/Notes/DC06_7.pdf

_http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA515463&Location=U2&doc=GetTRDoc.pdf

_http://www.stanford.edu/class/ee379b/class_reader/jpl1.pdf

_http://www.stanford.edu/class/ee379b/class_reader/jpl4.pdf

and a historic look into the practical side of things (with some superb pictures)

_http://www.mentallandscape.com/V_Telemetry.htm