Re: Noise in space research


John (Liberty) Bell wrote:
In the Pioneer 10 mission, the ability to maintain communication was
extended to larger distances post launch, by the substitution of a
lower noise preamplifier in the pedestal unit. Despite this, it looks
like noise was still the reason why communication was eventually lost.

Does anybody know whether such remaining noise was still predominantly
electronic noise generated in the improved preamp, or external noise
picked up by the dish?

I hope that the reason for asking this question is obvious. If the
answer is still preamp noise, then space missions could be taken to
still greater distances, and for longer durations, simply by further
improvements in preamplifier design.

John Bell
http://accelerators.co.uk
(Change John to Liberty to respond by email)

As you alluded to above, there exists some distance over which the
received signal will be indistinguishable from the noise-floor of the
receiver-chain. Through the evolution of technology, this maximum
distance has increased over time.

So given that the last clean signal was received in April of 2002 when
Pioneer 10 was ~80AU from Earth
(http://en.wikipedia.org/wiki/Pioneer_10), this puts a *lower* bound
on the maximum distance over which we can receive a signal with current
technology. In other words, there could be other reasons why we lost
touch with Pioneer 10, but the ground-based preamp allowed us to
successfully receive a signal up until at least the ~80AU mark using
Pioneer 10's 1972 on-board equipment. Unfortunately, I do not know
what the *upper* bound on the maximum distance is assuming noise is the
only limiting factor.

Another related question I don't have an answer to is 'How close are we
to making a low-noise amplifier with the lowest possible noise figure'?
All I can tell you is that LNA's already exist with noise figures less
than 1dB and we know "zero-noise" systems are not possible.

Sorry I didn't answer your questions directly, but I hope this helped
nonetheless.

Regards

.

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