Novel space probe warming role tests resistor reliability

The THEMIS heliophysics constellation of satellites was commissioned by NASA to investigate what causes auroras in the Earth's atmosphere to dramatically change from slowly shimmering waves of light to wildly shifting streaks of colour. The aim is to provide scientists with information on how the planet's magnetosphere and all-important Sun-Earth connection work. Now in its sixth year in space, THEMIS is helping to show how even small variations in the magnetosphere can sometimes cause extreme space weather.

The THEMIS satellites have proven to be so reliable that NASA has been able to repurpose two already in-orbit spacecraft to extend their useful science mission in a new project known as ARTEMIS (Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon’s Interaction with the Sun). This additional use has removed the need to build and launch new spacecraft, saving NASA tens of millions of dollars.

Arcol was commissioned to provide a highly reliable heat source to protect the sensitive data gathering and processing electronics. The company proposed its HS range of high-power resistors, the design of which goes back to 2007 when a number of the products were tested for out-gassing under conditions of high vacuum.

SSL Berkeley undertook the design confirmation process to ensure that the resistors provided the appropriate thermal range under worst case conditions. From those tested, the Arcol parts were found to have the lowest out-gassing characteristic, thanks to a novel moulding process that ensures the case is completely filled, minimising voids and imperfections.

Further, there was the requirement to withstand rigorous preparation processes, from mechanical and electrical characteristics modelling to ultrasonic cleaning with Isopropyl alcohol for installation in the module.  It was through this process that the HS type device was tested and selected by the Space Sciences Laboratory at Berkeley for inclusion in the THEMIS module.

ARCOL's HS Series is a range of high quality, high stability high power wire-wound resistors, packaged in a compact and robust aluminium casing designed for direct heat-sink mounting or panel attachment using a thermal compound. Ten standard power ratings are offered, from 10 to 600W, with liquid-cooled versions extending the range to 900W. Ohmic resistance values are available over the range R005 to 100K, depending on wattage. Some seven different termination options are also available.

ARCOL’s HS series power resistors are optimised for stability, linearity and reliability, making them suitable for many renewable energy, power supply, traction and industrial applications including; inverter/converter, snubber, braking resistor, inrush limiter, balancing resistor, voltage divider, capacitor discharge , cross over, shunt and power supplies.