The Earth Horizon Sensor is used as part of an Attitude Control System (ACS), to sense the angle of a spacecraft
relative to the Infrared Horizon. The unit measures relative radiant intensity in the CO2 (15μ) frequency band. It produces DC voltages from an infrared detector array that views the Earth, the horizon and space. The voltages are then used to determine the angle to the horizon.

The voltage from each of the detector elements is delivered to the Attitude Control Computer, where it is processed by
a simple supplied software algorithm to produce an angle to the infrared horizon. Earth and space pixels are used to
normalize the horizon data and to reduce errors caused by seasonal and orbital radiance variations.

The unit is also available with a dual array, allowing the ability to operate with the Sun in the field of view.

FUNCTIONAL CHARACTERISTICS

• Field of view: +/-5° Operational
• Accuracy: <0.2° (3σ)
• Noise Equivalent Angle (NEA): 0.05°
• Detector: Proprietary LTO
• Optical Pass Band: 14.6-15.8μ
• Output Sensitivaty: ~80 mV/° Linear
• Data acquisition rate: 20 Hz

PHYSICAL CHARACTERISTICS

• Mass: 500 grams
• Size: 61mm x 95mm x 61mm Plus Optics & Mounting Feet

ENVIRONMENTAL CHARACTERISTICS

• Random Vibration: 25g rms
• Temperature: -30 to + 55°C
• Lifetime: 7 years at 750km

INTERFACES

• Power Supply: +/- 12V DC
• Output: Analog 0-5VDC, from 3 Pixels through multiplexer
• Power: < 1.5 W

FEATURES

• Optional built in sensor redundancy
• Patented Sun-Moon rejection scheme
• Requires no temperature control, heater or
  compensation
• Proven pyroelectric detector technology

APPLICATIONS

• Sense the attitude of a spacecraft relative to the
  Earth
• Primary attitude sensor in eclipse
• Low cost, accuate nadir pointing solution