NEW HORIZONS — Gold in the heavens

Whether in steady orbit around the earth or on a long journey to a distant planet, satellites and the success of their missions depend on gold.

Handheld Global Positioning Satellite (GPS) units are being used by backpackers, installed in dashboard locators in cars, in homing devices to locate lost children or stolen cars and in field instruments for geologists mapping mineral deposits observed by satellite imagery.

The GPS system relies on a network of 24 satellites in orbit around the earth, and gold plays a crucial role in keeping those machines aloft.

Keeping the satellites properly oriented and stable requires a system of on-board gas thrusters, which are powered by hydrazine, a highly volatile liquid. This on-board system automatically compensates for any misalignment in the satellite’s orientation with a blast of hydrazine.

The tanks in which the hydrazine is stored, however, are susceptible to the sun’s heat, which can prematurely expand the liquid, thereby placing pressure on the system and exhausting the gas. The liquid is protected from the effect of this solar heating by a thin coating of gold that covers the storage tanks.

The satellites are also vulnerable to heat shock, a phenomenon they experience each time they emerge into the sun after a 6-hour period in the earth’s shadow. Heat shock can severely damage a satellite’s internal components and affect its performance. The delicate electronic components within the thruster system rely on gold’s properties to shield solar heat and cosmic radiation.

In order to protect both the hydrazine in the tanks and the alignment system’s electronic components, a layer of gold is plated on a plastic-like sheet which covers exposed areas. A thin coating of the yellow metal is enough to provide maximum deflection of the sun’s heat.

The Mars Global Surveyor, which was launched in November, is the first in a series of orbiters and landers designed to map and explore the red planet over the next 10 years.

The Surveyor is designed to orbit Mars and provide global maps of surface topography, distribution of minerals and monitor the planet’s weather. Among the spacecraft’s payloads is the Mars Orbiter Laser Altimeter (MOLA), which will produce detailed topographic maps of the entire Martian surface.

A gold-coated mirror on the telescope is used by the MOLA to capture the reflections of a laser beam that is transmitted to the surface 10 times per second. Working on the same principal as police radar, the altimeter calculates how long it takes for the laser to hit the surface and reflect back to the spacecraft. That calculation is translated into tiny variations from which the Surveyor can determine the height and shape of plains, valleys, craters and mountains.

As a result of gold’s high-quality reflectivity of infrared radiation, the gold coating provides optimum sensitivity for detecting the returned laser.

The MOLA is not the only device on the Surveyor whose operation relies on gold. On-board transmitters, for example, are exposed to a steady barrage of solar radiation that produces not only heat, but electromagnetic radiation which can cause radio interference. A thin coating of gold around these components guards against such interference and reflects the sun’s damaging heat rays.

Gold has been used in spacecraft since first appearing in the Galileo probe, which was launched in the early 1990s. The computers and transmitters aboard the craft, which reached Jupiter in 1995, were covered by a thin shield of gold to prevent radio interference and deflect heavy ion bombardment as the probe approached the planet.

— From “Gold News,” the publication of Washington, D.C.-based The Gold Institute.