
Voyager 2 to Switch to Backup Thruster Set - J3L2404
http://www.nasa.gov/mission_pages/voyager/voyager20111105.html
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ender7
From my wikipedia dive: the Voyager spacecraft are powered by "radioisotope
thermoelectric generators", each of which is essentially a barrel full of
plutonium spheres. As the plutonium decays, it generates heat. The resulting
heat differential (one area is now hot, some other part of the craft remains
cold) is then used to generate electricity via the Seebeck effect.

<http://en.wikipedia.org/wiki/Voyager_2#Power>

[http://en.wikipedia.org/wiki/Radioisotope_thermoelectric_gen...](http://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator)

Also known as "things we really hope the press never hears about".

~~~
retube
RTGs have been powering deep space probes since the beginning of our travels
into space. It's really the only technology that will keep a craft powered for
many years/decades. Without them you simply can't do these kinds of missions.

And they're not that scary. There's no fission (or fusion) happening here.
It's just a radioactive sample that heats a surrounding material by it's
natural radioactive decay.

~~~
windsurfer
When isotopes decay, the process is known as fission, so there is certainly
fission going on.

~~~
burgerbrain
He means there is no sustained chain reaction going on. It's neither critical
nor supercritical. I have a chunk of uranium ore on my bookshelf doing it
right now.

~~~
tobylane
Where from, what cost, any requirements for potential owners?

~~~
burgerbrain
I got it from a geologist buddy of mine a few years ago, I think he said he
found it lying around in Arizona. It's fairly harmless, just looks like a rock
really (unless you have a gieger counter).

As far as I know, there are no restrictions on such things. You can pick up
pieces of uranium glass and old fiestaware on ebay for a couple of bucks (both
about as radioactive as my rock :)

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ericgearhart
What's the information security posture on these things like?

What I mean is, what was considered "secure" in 1977 (DES based encryption was
state of the art back then, right?) would be considered laughable today... I
wonder what precautions are taken by NASA to prevent someone from intercepting
and decoding NASA's commands to the probe and then beaming their own commands
to Voyager 2.

~~~
conover
From what I've read, the signals from these probes are so weak that you need
large receivers coupled with extremely low temperature electronics to detect
them. That puts it out of the reach of everyone except the extremely well
funded. In the end, it would be a short list of suspects.

~~~
mturmon
Yes, you quite literally need one of these to communicate with Voyager:

<http://www2.jpl.nasa.gov/files/images/browse/jpl9020ac.gif>

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jtchang
Does it blow anyone else's mind that we have a piece of technology 9 billion
miles away and we are actually talking to it?!

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MartinMond
Does anyone know any details on what kind of software runs on Voyager 2 and
how they program it from Earth?

Is there just a list of predefined commands (activate this, deactivate that,
send images) or do they overwrite the 'firmware' with each upload or ...

~~~
kmm
It surprises me how little information about the Voyagers is on the internet.
I'd love to know everything about what makes them tick.

~~~
js2
Try exploring <http://www.nasa.gov/mission_pages/voyager/index.html> and
<http://voyager.jpl.nasa.gov/>

The later has weekly mission reports all the way back to 1995. I also just
submitted information about its onboard computers:

<http://news.ycombinator.com/item?id=3204224>

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hammock
Really cool to think we sent this guy out there which is now 9 billion miles
away, and we are still in contact/command with it.

~~~
ImprovedSilence
Yeah, and the fact that it takes DAYS for a command to reach it.

~~~
dalke
13.4 hours
[http://www.google.com/search?q=9+billion+miles+/+speed+of+li...](http://www.google.com/search?q=9+billion+miles+/+speed+of+light)

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dquigley
That these things still work is an amazing feat of engineering.

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ajasmin
The computer on that thing probably has the longest uptime in the solar
system.

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iwwr
What are they using the thrusters for at this time? Just attitude adjustment
to get the antenna pointed at the Earth?

~~~
InclinedPlane
The Voyagers are 3-axis stabilized (vs spin stabilized) and they use the
thrusters for attitude control. Without the thrusters the antenna would drift
away from being pointed at Earth and we'd lose contact.

More modern spacecraft use non-propulsive systems such as momentum wheels and
gyrodines to maintain 3-axis attitude control and use thrusters to reset only
when those systems become saturated.

~~~
adrianwaj
Do the thrusters use the same power source as the instruments?

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dalke
No. The thrusters are chemically powered. The instruments are powered by
radio-thermal generators.

~~~
adrianwaj
"Voyager 1 changed to the backup for this same component after _353,000_
pulses in 2004."

Impressive.

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thebigshane
"Slow to impulse, standard orbit, Mr. (Crusher|Sulu)"

