
Update on Voyager 2 status - zargon
http://www.planetary.org/blog/article/00002485/
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westbywest
It's interesting to note that although the Voyager probes are sometimes
depicted as small (compared to satellites like the Hubble, where images of it
next to shuttle astronauts are common place), they're not. The diameter of the
main dish, 3.7m, is nearly twice the height of an average adult, and height of
the magnometer boom is comparable to that of a 3-storey house.

Even despite this size, the article mentions the current transmission rate, a
measly 1.2kbs, despite what is probably the most ideal antenna size &
placement feasible, both on Earth and on the probe. Doesn't this suggest there
are pragmatic limits to the operational range of 2-way radio transmission
throughout the solar system?

I am curious if future such deep-space science missions would be more
effective if they instead launched swarms of micro-probes, where the probes
arranged themselves radially around a center-point to effect a very large
antenna, possibly up to 1km in diameter.

Also, having so many micro-satellite could allow for a substantial degree of
redundancy to tolerate more rad damage, and ideally have less of the mission
control acrobatics described in this article. (Which is not to discount the
scientists' effort in any way, for it is amazing.)

~~~
InclinedPlane
Voyager 2 uses X-band radio for communications, more modern systems use Ka-
band radio, so with the same size antenna that would increase received power
by about a factor of 10. Also, more modern communications technologies such as
turbo-codes, which are significantly more efficient than the Reed-Solomon
codes used by Voyager 2, further increase throughput for modern systems.

Overall though, yes, there are some pretty harsh limits to radio communication
across the outer solar system (Voyager 2 is nearly 3 times as far away as
Neptune, and well over twice as far away as Pluto's maximum distance from us).
But this is fairly easily remedied by switching to yet higher frequencies or
using optical communication.

~~~
eru
> But this is fairly easily remedied by switching to yet higher frequencies or
> using optical communication.

Isn't this the same?

~~~
InclinedPlane
Yes and now. Switching to higher radio frequencies uses a lot of the same
systems, switching to optical communication would use entirely different
systems (some of which have not even been built yet).

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mturmon
Some other relevant details from
[http://voyager.jpl.nasa.gov/Proposal-2008/Voyager_SR_2008.pd...](http://voyager.jpl.nasa.gov/Proposal-2008/Voyager_SR_2008.pdf):

"Voyager 1 is escaping the solar system at a speed of about 3.6 AU/year while
Voyager 2 is leaving at about 3.3 AU/year. Power is the limiting lifetime
consumable. The two spacecraft have power to continue returning science data
beyond the year 2020. It is likely that at least one of the spacecraft could
enter interstellar space while adequate power is still available. All other
consumables are adequate for continued operations well past 2020."

"Electrical power is supplied by three Radioisotope Thermoelectric Generators
(RTGs) which are performing nominally. The current power levels are about 286
watts, with power margins of about 34 watts and an average degradation rate of
about 4.3 watts per year."

"Real-time telemetry data capture is accomplished using 34- and 70-meter
tracking antennas of the DSN. Capture of the recorded high rate plasma wave
data from Voyager 1 requires the use of an array of 70- and 34-meter
antennas."

"Uplink communication is via S-band (16-bits/sec command rate) while an X-band
transmitter provides downlink telemetry at 160 bits/sec normally and 1.4 kbps
for playback of high-rate plasma wave data."

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nkassis
Just wondering, is voyager going at the maximum speed we could we
realistically go today or would a newer craft be able to exit the solar system
faster? would that even be useful to science?

~~~
hugh3
Well, rocket technology hasn't really advanced all that much since Voyager was
launched. We could certainly send a faster probe out by spending more money to
build a bigger rocket. On the other hand, they could have done so back then,
as well.

On the other hand, Voyager picked up an awful lot of its speed not from its
initial launch but from slingshotting around the various planets it visited --
essentially picking up some free energy at the cost of infinitesimally
perturbing the planet's orbit. If our goal was to send a probe out of the
solar system as quickly as possible, we might be able to do a better slingshot
than was done back then.

On a third hand, Voyager 2 benefited from a rather fortuitous arrangement of
planets which enabled it to visit all four giant planets and presumably pick
up some momentum from each. This kind of configuration only comes around once
every few centuries so if we launched it now then it would have to miss some
planets. I don't know how much of an effect this would have; did the
Uranus/Neptune visits "pay for themselves" momentum-wise? (Edit: I looked it
up and apparently not, because Voyager 1 which skipped the last two planets is
further out and travelling faster than Voyager 2).

One thing we can do now which we couldn't do back then is build a good ion
drive. A probe with an ion drive and a nuclear fuel cell could keep
accelerating for many years, so it would probably be able to outpace Voyager
eventually.

So in conclusion, if we wanted to build something faster than Voyager I think
we probably could. But in answer to your second question, no, I don't think it
would be very useful to do so. There's not much that's particularly
interesting beyond the solar system. We're still keeping Voyager alive because
we might as well, but sending another probe out there with it would be a
fairly low priority for missions.

~~~
bkudria
With your three hands you clearly support the "Aliens messed with it" theory.

~~~
rbanffy
That will be Voyager 6, after it falls into a black hole and ends up being
rescued by machines.

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bprater
Doesn't it seem like, as part of the engineering part of this project, that
they would have a system in place that would sweep through and do a comparison
for "flipped bits" and, if found, would keep a clone of what the memory should
look like and reset those bad bits? What happens when the flipped bit causes
the machine to rotate out of communications view? You would basically be dead
in the water without a failsafe system like this. What am I missing?

~~~
bkudria
What if the system to guard against this itself got a flipped bit? What if the
malfunction caused it to think bits in "normal" memory were flipped when they
weren't, really?

~~~
mturmon
Quite true. One standard solution is TMR:

<http://en.wikipedia.org/wiki/Triple_modular_redundancy>

I doubt that Voyager used TMR, they probably used the best rad-hardened
hardware they could build at the time (within power and weight constraints).

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tylerritchie
"Ed told me that that software dump has been completed, and it's 'just a
matter of time to determine which bit is flipped.'"

Can they not just diff it?

~~~
mturmon
They've got to be simplifying this a lot for the sake of making a press report
understandable. They don't even know there's only one bit flipped. If there is
one, they will have to do some analysis to figure out that it would really
cause the problem.

~~~
jared314
I wonder if they have a Voyager VM.

~~~
InclinedPlane
Even if they did, it might prove challenging to feed it exactly the same input
as Voyager 2 itself in order to ensure it's in the same state.

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headShrinker
Does somebody know how long it takes to send a message to Voyager 2? I
calculated roughly 12 hours...

~~~
wglb
From <http://en.wikipedia.org/wiki/Voyager_2>, _There are regularly posts of
the current distance of Voyager 2 to earth in light-travel time to twitter_.
And _Information on the current location of Voyager 2 can be found at
HeavensAbove._ at <http://www.heavens-above.com/solar-escape.asp> which looks
like a seriously interesting page in its own right.

