Earth Sensor Keeps Satellite on Track

Aaron J. Hand

Researchers from 15 countries have gained new insight into ozone, thanks to the continuation of a series of joint missions by NASA and Germany's space agency DARA. The German-built Crista-Spas II was sent on an 11-day mission in August to study small-scale tracer filaments (long, thin regions of differing atmospheric composition) in the stratosphere. By studying atmospheric flow patterns, researchers hope to better understand how filaments contribute to the transport of ozone and the chemical compounds that affect the distribution of ozone.

Servo's Mini-Dual Earth Sensor provides attitude control for the Crista-Spas II mission.

The latest mission was accomplished with the help of Servo Corporation of America's Mini-Dual Earth Sensor. Through a Small Business Innovation Research grant from NASA's Goddard Space Flight Center in Greenbelt, Md., Servo built this sensor to provide attitude control for Earth-orbiting unmanned satellites.

The Mini-Dual Earth Sensor gathers data with two pairs of lithium tantalate pyroelectric arrays that are positioned 90° apart in the imaging plane. Each 16-element array is spatially separated into two eight-element staggered columns to provide sun/moon rejection and radiance compensation. Covering a range of 11°, the pixels detect the temperature difference among the reference chopper, Earth and space. An algorithm calculates the position of the horizon based on the voltages obtained from the pixels that subtend the horizon gradient and the pixels that look at space and Earth.

Servo has an ongoing relationship with NASA and has produced other types of Earth sensors for various missions. In fact, the Mini-Dual Earth Sensor is a high-accuracy sensor that could be used for attitude determination in future space missions. It is an example of a successful project coming out of the Small Business Innovation Research project, according to Servo's Dick Burton.

The Mini-Dual Earth Sensor also will be found in commercial applications. Servo has built a version for Surrey Satellite Technology Ltd. of the UK that will be incorporated into the UoSAT-12 mission scheduled for launch later this year. The experimental mini-satellite will carry high-resolution and multispectral remote sensing payloads to demonstrate imaging not feasible on existing micro-satellites.