It requires the cooperation of the NASA DSN (Deep Space Network).
The DSN, at least based on the information that one can obtain from 
websites -- probably is the most paranoid and desiring change of all of the 
parts of NASA.
When it comes to disclosing telemetry information to the general public, the 
DSN at best could get an F (1.0/4.0).

Voyager programme telemetry: available but delayed by up to 2 months.
Mars Explorer (name?): available, but tucked away in an obscure location.

All other missions (excluding Earth Missions): no telemetry [that I have 
been able to find].

I have already faxed the DC contact number, but I suspect that fax number is 
a black hole for most good ideas...
If I were related to some US Senator that had control over some of NASA's 
budget -- yes, my idea may be paid attention to.

What are the internal fax contact numbers for the NASA Pluto and Voyager 
Missions? I need to pass on a technical proposal...

=========================================

Having been on the inside of the gov (Navy not NASA) on the R&D funding 
side and receiving proposals do not waste your time. It was a while ago, 
before fax. But if you can't even call for an appointment who are you? A 
great idea but no way to implement it ... do you think I would run with 
it? Why?
-=-=-
Worse than that, an idea is no more than an idea. Show that it works and 
you have my attention. A fax does not show me that it works. And if you do 
not know all the background on the idea better than I do not bother.
-=-=
But this is just the funding side. If you contact a researcher you better 
speak his language. As a manager it was one of languages I spoke as a job 
skill but shall we say the people I was funding did not hold me to a high 
standard of correctness whereas any outside contact will be held to a high 
standard.

Enough discouragement. What you want to do is get hired by an existing 
contractor on the basis if developing your idea. If it is a good idea you 
have a good chance of getting the job and a modest budget and the support 
to help you package it into a saleable product.