NetNews Usenet Archive 1992 #31/NN_1992_31.iso/spool/sci/astro/13588

Internet Message Format | 1993-01-02 | 3.5 KB

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From: [e-mail] (Chris Jones)
Newsgroups: sci.astro
Subject: Re: Galileo coverup
Message-ID: <[e-mail]>
Date: 2 Jan 93 15:07:25 EST
References: <[e-mail]>
Sender: [e-mail]
Reply-To: [e-mail] (Chris Jones)
Distribution: usa
Organization: Kendall Square Research Corp
Lines: 58
In-reply-to: [e-mail] (James Howard)

In article <[e-mail]>, steelie@csa (James Howard) writes:
>
> Ok, so the title is a bit misleading.  But it doesnt seem far from
>the truth, according to what you read in the press.   To my eyes,
>there is absolutely NO WAY to get 70% of the original mission data
>through the backup antenna.    What was the data rate 4 or 5 months
>ago.. 40bps?
>
>I dont care how much they throw around terms like "compression" , it
>doesnt fool me.   Anyone who has ever used a computer knows that
>a 300bps modem is barely in the same species as a 19.2k.  (for analogy's sake)
>
>When will NASA come out and admit that it's busted, and the original mission
>is practically dead?
>
>  James
>
>P.S.  I think NASA has great press control.. If I hadn't been reading
>this group I would never have know anything substantial was wrong with
>Galileo.

You are reaching conclusions from incomplete information.  NASA has said they
can improve the transmission rate using the low gain antenna by a factor of 100
using compression as only one component of a four-pronged strategy.  Immodestly
quoting myself from last June:

"[F]our techniques will be used to improve the effective data
rate: By reprogramming two of the spacecraft's computers to do data
compression, they can reduce by a factor of 10-20 the number of bits needed to
transmit an image (and get a factor of 1.5 to 2 for lossless compression,
which would be used for other science data).  By using more powerful error
correcting codes, data transmitted from Galileo will have fewer errors
(meaning, I assume, fewer retransmissions will be desired) and a 50% higher
data rate.  By using arrays of antennas (both DSN and borrowed), more of the
signal which gets to earth can be captured.  By increasing the sensitivity of
the Australian antenna (Galileo appears in the southern hemisphere during its
entire mission), the data rate can be doubled."

NASA has hardly hidden the problems they have been having with Galileo.  They
are posting nearly daily press reports on Galileo's status (see sci.space.news
or sci.space).  While the antenna problems aren't covered in every report, if
you read them for a week or two you'll likely see reference to it.  The lack of
coverage you see comes, in my opinion, from editorial decisions made by you in
what sources to consult and editorial decisions made by the sources you do
consult.  AW&ST, Science News, the New York Times, and the Boston Globe, to
name four off the top of my head, have covered Galileo's problems in the last
year.  I think NASA is guilty of being overly optimistic on their chances of
freeing the high gain antenna, but I won't be very surprised if they do free
the HGA, and I think their scheme for achieving 70% of the science objectives
(NOT, as you say, and I said before I was corrected, returning 70% of the
science data) is highly likely to succeed.

If you're interested in seeing a transcript of the NASA press conference at
which they detailed their plans (written last June by Jon Leech), email me and
I'll send you all 23K+ of it.

--
Chris Jones    [e-mail]