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General Description:

Horizon Crossing Indicators (HCI) are normally used on

spin stabilized spacecraft to provide both attitude control

and timing information for spin control or to trigger

onboard experiments.

The Model RH 310 HCI is a radiation hardened device

designed to accurately determine the transition from space

to the Earth’s horizon and back to space by using a small

field of view (FOV) optical system. The sensor operates by

detecting the Earth atmosphere’s carbon dioxide emissions in the 14 to 16 micron band. The

standard system consists of a separate sensor head and an electronics package. The electronics

package can accommodate both single and dual sensor heads and is fully redundant. The standard

system is designed for spin rates between 3 and 10 rpm, however other spin rates can be

accommodated with minor modifications to the design. The sensor produces two separate output

pulses, each 80ms long with amplitude of +5V. There are two separate outputs, one from an Earth -

space crossing and one from a space -Earth crossing. The leading edge of these pulses indicates a

horizon crossing. The system is powered from 28V input with 1W maximum power consumption.

The unit is designed to withstand radiation dose of 100krads (total dose) within the sensor head

and 20krads at the electronics box.

An optional sun gate and moon pulse width discriminator circuit can be used to inhibit crossing

pulses from these sources.  The picture below shows the two RHCIs mounted on the STRV1d

satellite prior to environmental testing.

 

Specifications:

Sensor

IR Detector Proprietary LTO

Pyroelectric

Optical Bandwidth 14-16 microns (CO2

Absorption)

Optical System Diamond Turned

Germanium Lens (f1) ARC @ 15

microns

Optical Field of View 1.5 deg. Diamond

Shaped

Alignment Uncertainty 0.015 deg.

Radiation Dose 100 Krad

Mass 500 gr (each head)

Operating Temperature Range -20° C. to

+60° C

Processor/Power Supply

Spinrate 3 to 10 RPM Std. (Can be adjusted for

other spin rates .5 to 50 RPM)

Noise Equivalent Angle: 0.05 deg.

Output "A" +5 volt x 80 msec. for Space–Earth

CrossingOutput "B" +5 volt x 80 msec. for

Earth–Space CrossingOptional Output Sun/Moon

gate

Operating Voltage 28 VDC (+7-6)

Operating Power 1 Watt

Radiation Dose 20 Krad (normally placed in a

shielded section of the spacecraft)

Mass 1000 gr.

Operating Temperature Range -20° C. to +60° C