Harmonic Drive gears to touch down on Mars

Edited by the Engineeringtalk editorial team Mar 2, 2001

Astrium selected Harmonic Drive gears, from Heason Technologies Group, for five axes of motion control on the instrument arm of the Beagle 2 Mars lander, which is scheduled to touchdown in 2003

Payload, determined by weight and size, is a defining consideration when designing items destined for outer-space travel.

It was for this reason Astrium Ltd, Stevenage, selected Harmonic Drive gears, from Heason Technologies Group, for five axes of motion control on the instrument arm of the Beagle 2 Mars lander, which is scheduled to touchdown on Mars in 2003 after a seven month journey.

Packed inside its 30kg clam-like structure, Beagle 2 has an articulating arm at the end of which is a scientific analysis package that will search for signs of life (past and present) and the presence of water.

This array of instruments and data gathering devices is referred to as the PAW.

Originally, each device was going to be a separate item, being interchanged for the different experiments.

However this was considered to be too complex, creating too many opportunities for malfunction and placing heavy demands on the power supply.

The arm is used to deploy the PAW anywhere within its 700mm reach with the 'wrist' joint permitting flexible orientation of the PAW, maximising options for sample gathering and observation.

The Harmonic Drive gears used are three HFUC 11 and two HFUC 8, specially engineered in space rated stainless steel with titanium housings.

The reasons given by Nigel Phillips, robot design engineer with Astrium, for selecting these gears are their high ratio and high torque (100:1) in a small mass, low weight package.

He added that in reality that the HFUCs were the only solution, other alternatives being too bulky and heavy, whilst not offering the same degree of precision.

Their low weight enabled the total arm to weigh-in at 0.5kg below the budgeted 2.7kg.

Helping to reduce the space requirement of the gears is their shortened Flexspline and a high-stiffness, cross roller bearing which simplifies mounting to the load whilst eliminating the need for additional bearings.

In addition to meeting the performance/mass criteria, Astrium could take further confidence in the Harmonic Drive gears as they have already established credibility in the US space industry where applications include solar array drive systems.

Devices comprising the PAW array are: a stereo camera (arm navigation and mineralogy), X-ray spectrometer (dating rocks), Mossbauer (rock mineralogy and petrology), barrel grinder (rock preparation for examination by XRS and Mossbauer), microscope (optical examination of samples), corer (gathering samples for Gas Analysis Package in the lander) and mole (gathering below the surface rock samples for the GAP).

A sixth HFUC from Heason is also employed for the hinge of the 'clam' lid of Beagle 2, again for reasons of weight saving and reliability.

Beagle 2 will be carried by the European Space Agency's Mars Express spacecraft, which will be launched from Baikonur in Kazakhstan on a Soyuz/Fregat launcher.

For more information on Beagle 2 please visit http://www.beagle2.com.