by Kaye Dee

November has been a busy month in space exploration with two new missions in NASA’s ongoing series of Explorer scientific satellites, and two spacecraft bound for Venus, launched by the Soviet Union. Let's get stuck right in and see why 1965 continues to be an amazing year for the space race.

GEOS is Go!

NASA’s Explorer series keeps on producing fascinating new scientific missions that help us discover as much about the Earth as they do about space. November’s first Explorer satellite, designated Explorer 29, also goes by the name of Geodetic Earth Orbiting Satellite (GEOS)-1 or GEOS-A. It is the first successful active spacecraft in the United States’ National Geodetic Satellite Program, and more are expected to follow.

NASA illustration of GEOS-1/Explorer-29 in orbit

Geodesy is the science of accurately measuring and understanding Earth's geometric shape, its orientation in space and the shape and characteristics of its gravitational field. You could say that passive satellite geodesy began with Vanguard-1, back in 1958, when scientists used the perturbations in its orbit to determine that the Earth is actually slightly pear-shaped, not quite that round ball we see in science fiction movies (though you'd have to have really sharp eyes to notice the difference!)

Satellite geodesy has come a long way in seven years and GOES-1 is carrying a suite of instruments that are designed to operate simultaneously, so that the data from each can be combined to give a highly accurate location for a point on the surface of the Earth. These instruments include four optical beacons, laser reflectors, Doppler beacons, and a range and range rate transponder. GEOS-1 also carries a SECOR transponder, the same type as used by satellites in the US Army’s satellite geodesy program, so that it can also contribute to that program’s research.

This US Army SECOR satellite bears an interesting resemblance to the Naval Research Laboratory's SOLRAD-8, as well as sharing a transponder type with GEOS-1

The objective is to use the data from all of Explorer-29’s instruments to precisely locate a series of observation points (or geodetic control stations) in a three dimensional “Earth centre-of-mass” coordinate system within 10 m of accuracy. These precision locations will help to improve the accuracy of cartography, surveying, and satellite navigation using the TRANSIT satellites.

GEOS-1’s instruments will also help in defining the structure of the earth's irregular gravitational field and refining the locations and magnitudes of the large gravity anomalies that have so far been detected. The various instrument systems will be compared with each other to determine which is the most accurate and reliable.

Explorer-29/GEOS-1 was launched from Cape Canaveral on 6 November (US time), on the first flight of the new Delta E launcher. Powered by solar cells, GEOS-1 uses gravity-gradient stabilisation, a relatively new technique that was first successfully tested on satellite 1963-22A, launched in June 1963. GEOS-1’s range and range rate transponder is tracked by NASA’s STADAN (Space Tracking and Data Acquisition Network) stations, including Carnarvon in Western Australia and the newly-operational station (just last month) at Orroral Valley, near Australia’s capital, Canberra.

NASA's new STADAN tracking station near Canberra tracks scientific satellites including the Explorer series – whatever alternate names they are known by

Satellite for a Quiet Sun

Explorer-29 was followed just two weeks later by Explorer-30, which also goes by the names of SOLRAD-8 and Solar Explorer-A (SE-A). The SOLRAD (short for Solar Radiation) program began in 1960, with the aim of providing continuous coverage of the wavelengths of solar radiation that can't be observed from Earth's surface. SOLRAD is a project of the Naval Research Laboratory and grew out of its earlier Vanguard program. Most of the earlier SOLRAD satellites have been launched piggy-back with other satellites (which, rumour has it, were of a classified nature), but SOLRAD-8 is the first to be launched as part of NASA’s Explorer program.

SOLRAD-8 is part of International Quiet Sun Year program, which is studying the upper atmosphere and the space environment during the Solar minimum, the least energetic time in the Sun's 11 year activity cycle. The data gathered during this period can then be compared with information obtained during the International Geophysical Year, when the Sun was at its most active.

The Naval Research Laboratory's SOLRAD-8 will help us to better understand the differences in the space environment between periods of maximum and minimum solar activity

Launched on November 19 by a Scout X-4 rocket from NASA’s Wallops Island facility, SOLRAD-8 is composed of two 24-inch aluminium hemispheres, with an equatorial ‘belt’ carrying 14 X-ray and Ultra-violet photometers. The satellite weighs 125 pounds and is powered by six solar panels. SOLRAD-8 is the first satellite to use a new type of miniature gas thruster, firing ammonia, to stabilise itself with its spin axis perpendicular to the Sun. It transmits data back to Earth in real time, using a FM/AM telemetry system that is recorded at NASA’s STADAN network stations.

Will we Lift the Veil of Venus This Time?

Venus has proved to be a difficult planet to explore. Only one space probe so far, NASA’s Mariner-2 in 1962, arrived safely at the planet and returned data which indicated that Venus was molten hot, shattering all those tales of a ‘jungle Venus’ or a planet of island dotted oceans, like ERB’s Amtor. But this month, the Soviet Union is making another attempt to visit our mysterious ‘sister’ planet and pierce its veil of clouds.

Official pictures released by the Soviet Union showing Venera-2 (top) and Venera-3 (below). The slight difference between the design of the two space probes is a hint that they might have different missions when they arrive at Venus

Not one, but two spacecraft are on their way to Venus: Venera-2, launched 12 November, was quickly – and much to the West’s surprise – followed only four days later by Venera-3. Both spacecraft were launched from the USSR’s Baikonur Cosmodrome and seem to be safely on their way. It is assumed that the Soviet Union has launched a pair of space probes so that, as with NASA’s Mariner-3 and 4, if one fails the other might still succeed in sending back data to Earth. However, TASS has said that the two probes have slightly different equipment, so some of my colleagues at the WRE have suggested that perhaps the Russians are trying something bolder with this twin mission: maybe one probe will perform a flyby past Venus and the other will either try to go into orbit – or maybe even impact on the planet’s surface. That would be a really exciting achievement: I can’t wait to learn what exciting information these spacecraft will send back to earth in a few months’ time!

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