Download FLIGHT International, 7 March 1963 347 satellite camera are stored

FLIGHT International, 7 March 1963
347
satellite camera are stored on a special-purpose transparent
polystyrene layer within the vidicon camera tube. In effect the tube
exposes and electronically develops each photograph, and stores it
for the transmission period of approximately three minutes. The
pictures taken by the camera's wide-angle lens are immediately sent
to Earth by an FM transmitter.
In the Nimbus system the cloud-cover photographs will show an
area about 1,000 miles square, including an overlap of some 300
miles between adjacent pictures, in the vicinity of the receiving
station. In the flight tests aboard Tiros, the cameras are expected
to show a smaller area.
NASA's Goddard Space Flight Center has management responsibility for the APT subsystem. RCA is the contractor for the
flight hardware, with Fairchild-Stratos as contractor for experimental ground equipment.
RRE
SATELLITE
CAMERAS
The Royal Radar Establishment, Ministry of Aviation, has
designed and constructed two 24in focus f 1 Schmidt cameras for
tracking Earth satellites. The mountings and shutter mechanisms
were made at the RRE, and the optical system was designed and
manufactured by Grubb Parsons Ltd, Newcastle-on-Tyne. These
cameras are the most powerful tracking cameras in England, and
are also thought to be the largest f 1 Schmidts in existence.
The optical system consists of a 32in-diam spherical mirror with
a simple Schmidt plate of approximately 25£in diam. There is also
a three-element lens, situated approximately 0.5in in front of the
photographic plate. This brings the image into a flat field, instead
of the spherical field normally associated with a Schmidt System,
and thereby simplifies the measurement of the plate. The optical
system has a field of 10° and is achromatized between wave-lengths
4,800 and 6,000A. This band was chosen because, when photographed, the satellite is illuminated by the Sun and the reflected
light would have an orange-to-red hue. The diameter of a
star image at the centre of the field is approximately 30 microns.
A single-blade shutter is mounted near the field lens, moving
in the gap between the field lens and the photographic plate. The
blade subtends an angle of 20° and can be made to rotate at any
speed up to 5 revs/sec. An instant on the satellite track is marked
by the shutter blade, which makes a break in the trail of the satellite
on the photographic plate. The time of the break is obtained by
means of a phototransitor mounted close to the field lens, the time
being recorded on a quartz clock to 0.0001 sec.
The camera is fixed in bearing and elevation during the recording
of a satellite, so that the stars produce trails across the plate. A
large five-bladed shutter is mounted in front of, and close to, the
Schmidt corrector plate. By rapidly opening and closing this shutter,
As described in an accompanying news-item, this field-flattened Schmidt
satellite camera has been installed at the Royal Radar Establishment,
Malvern, Worcs. It weighs 8j long tons, and can track orbiting vehicles
with an accuracy of one second of arc
These new artist's conceptions clearly illustrate the major changes and
refinement in the design of the NASA Orbiting Geophysical Observatory
since the device was featured in this journal thirteen months ago. The
1,0001b 0C0 is scheduled to be launched into eccentric orbit from the
Cape this year; later a "POGO" will be launched into Polar orbit from
Point Arguello
the stars are exposed for about 0.25sec and appear as dots. The
shutter has an aperture of 26inand is completely isolated from the
optical system by mounting the shutter on a separate turntable,
thus preventing any vibration being transmitted to the optical system.
The shutter is operated through an electromagnetic clutch and brake
and will open or close in 0.09sec. The time of operation is recorded
on a quartz clock and, from this time and the position of the stars
on the plate, the precise direction of the camera axis can be obtained.
With this camera, it is possible to measure satellite positions to an
accuracy of lsec of arc (equivalent to about 1ft in 40 miles). To
obtain this precision, the plates must remain flat both during
exposure and measurement. The photographic emulsion is, therefore coated on high-quality plate glass 0.25in thick, and the plates
measure 8Jin by 5£in.
Most Earth satellites move very rapidly across the sky, and are
so dim that they cannot be seen by the naked eye. Even with a
camera aperature of 24in, very fast emulsions must be used to
record them. Ilford H.P.S. emulsion is being used, and tests have
shown that satellites 400 miles distant and + 9 magnitude (650 times
less bright than the Pole Star or 15 times less bright than the
dimmest star that can be seen with the naked eye) can be recorded.
FRENCH
SPACE
RESEARCH
France is engaged in both national and international programmes
of space research which, in toto, surpass those of all other countries
except for the USA and Soviet Union. Accounts of the "threepronged" approach—purely national programmes, FrancoAmerican programmes and participation in various European
organizations—have appeared in several past issues of this journal,
especially those of June 28, July 5 and July 12, 1962. What follows
is an overall guide to French space research, prepared by the
Union Syndicale des Industries Aeronautiques et Spatiales.
(Continued overleaf)