In article ,
"JasiekS" writes:

Uzytkownik "Peter Stickney" napisal w wiadomosci
...
[snip...]

Yes. Luna, in 1947. (Naval Observatory-Pearl Harbor.
Luna was also the first U.S. Elint Satellite, used in the mid 1950s
to map the Soviet's network of Tall King search radars.
(Nobody said that the satellite had to be _artificial_, did they?)

Sorry for one ignorant question. Do you mean Luna=the Moon, Earth's natural
satellite?

Yes, I do. The first signals bounced from the Moon and received on
Earth were in 1946, by an U.S. Army Signal Corps Lieutenant waiting to
be mustered out. He used a UHF Air Search Radar with a 3 KW
transmitter. The Navy, needing a reliable method of communicating
with remote bases, (Please remember that the Immediate Warning Message
to Pearl Harbor from the cryptanalysts in Washington D.C. couldn't be
broadcast (Normal Ionosphere skip) due to atmospherics, and had to be
sent via commercial cable.) Their solution was to use the Moon as a
passive reflector. By the early 1960s, Moonbounce was used by Navy
Command Ships at sea, as well as fixed bases.
These days, there's a fairly active segment of Amateur Radio Operators
who build and operate Moonbounce systems. By picking the proper
frequencies, and using CW or digital signals, rather than voice, you
can get by on surprisingly little power. A Google Search on
"Moonbounce" gives a lot of hits.


If YES, then how it could help in mapping anybody's radar network? I assume
that US didn't have any sensors placed there these days. If they used
reflection of radio waves - how they differentiate between radars of
interest and others?

Well, it wasn't easy, as I understand it. (A bit before my time), but
it wasn't impossible. Radars of the same type, especially if located
within line of sight of each other, do not operate on exactly the same
frequency. This is to avoid the problem of one radar picking up
another radar's signals and generating false targets.
The Soviets, not being fools, were very careful not to operate their
network when Western "Elint" - Electronic Intelligence or, more
commonly, Ferret, aircraft were offshore. So, we had to find some
other means of characterizing and locating their radars. The
frequencies that work best for Air Search Radars, and the high power
required for such a radar, made it possible to receive their signals
as the pulses continued into space and reflected from the Moon.
Locating the radars was an exercise in geometry, and precise
measurement, complicated by the fact that the Moon's not a perfectly
spherical reflector.

Electronic Intelligence gathering at that time was a fascinating game
played by master chess players. We were clever in some area, the
Soviets were clever in others. An example would be the Soviet
invention of the Resonant Cavity Microphone. It's simple, sensitive,
and requires no connection to external power, or signal transmission
lines. Just take a small tube, suitable to use as a section of
waveguide, and put a flexible diaphragm on the back, with a half-wave
antenna. It does nothing, until you beam the appropriate microwave
signal at it. At that point, it will resonate like a flute,
re-radiating through the small antenna. The flexible diaphragm will
modulate the signal, allowing the voice information to be extracted.
We were finding them for years without figuring out what they were.


If NOT, then do you suggest, that in 1947 anybody (including US) had rockets
capable of lifting a satellite to orbit?

In 1947, certainly not. In 1956, it was just barely possible. (The
rocket system that the U.S. used for its first Artifical Satellite,
Explorer 1, was the Jupiter C reentry vehicle test rocket built at the
Redstone Arsenal in Huntsville, Alabama, for testing the newly
developed ablative reentry vehicle for Ballistic Missiles. The only
difference between a reentry test Jupiter C, and the Explorer 1 shot
was the trajectory - it was set up for orbital insertion, rather than
the maximum aerodynamic heating, and the satellite/instrument package
atop the 4th stage. The Huntsville team had been warned off from
putting up a satellite in 1956 by the President's Office. By that
point, the Naval Research Lab Vanguard satellite, and its rocket
booster, had been selected as the main thrust of the U.S. satellite
effort. The success of Sputnik in late 1957, and the failure of the
first Vanguard shot in early 1958, got the Army effort de-mothballed,
as it were, and rushed into place to launch Explorer.
A 1956 launch wouldn't have accomplished much except that launching a
satellite could be done - neither the instrumentation, or the tracking
network needed to properly observe and monitor the satellite existed
before mid 1957.

--
Pete Stickney
A strong conviction that something must be done is the parent of many
bad measures. -- Daniel Webster