1999 MI/WI Rockets for Schools Launch

1999 Loki Telemetry Payload Components

Telemetry Payload

Dimensions: The main body of the payload is cylindrical with an outside diameter of 1.735" and a length of 11.25". This is very close to the dimensions of a standard paper towel roller. The payload weight is about 11 oz. The entire payload compartment is filled with hardened foam ("Great Stuff" (tm)).

Casing: the payload is encased in a fiberglass cylinder custom made and donated by Osceola Fiberglass, Osceola, MI. Two layers of fiberglass mesh were used. The main body of the payload was painted orange to aid in visibility in the event the payload ends up on land.

Microcontroller: A PIC16C71/04I 18 pin microcontroller circuit was developed and the microcontroller programmed specifically for the payload. The microcontroller provides the audio telemetry signal. Audio is generated through a program loop which toggles one of the output pins high and low at about a 1 kHz rate. The audio frequency is somewhat voltage and temperature dependent. In addition, the PIC16C71 includes a 4 channel, 8 bit, analog to digital (A/D) converter. The A/D channels are used to send telemetry information. The entire circuit, excluding the telemetry sensors, is on one etched copper disk, 1.65" in diameter and it draws less than 10 mA. A piezo-electric beeper on a separate disk provides an audible signal when the payload is energized.

Telemetry Sensors: The battery voltage and payload temperatures are measured using a resistive divider. Two fixed 10 kiloohm resistors are used for the battery voltage and the temperature is measured using fixed 10 kiloohm resistors connected to a voltage reference in series with a thermistor. The thermistor has a resistance of 10 kiloohms at room temperature. The thermister is mounted on the microcontroller board. The third A/D monitors a pressure sensor (a Motorola MPX5100A) which will indicate altitudes below about 35,000 ft. The fourth A/D is not connected.

Transmitter: A small home-built VHF narrow band FM transmitter with an nominal output frequency of 147.51 MHz and output power of about 80mW was designed and constructed for this payload.

Antenna: The antenna is a 19" length of wire between the payload and the Starute. Hence the rf is expected to be vertically polarized.

Batteries: Four 2/3A Li cells will be used to provide power of about 8 to 10V under load (approx 110 mA). The batteries can be expected to last several hours if they don't get too cold.

payload innards

Comments or Questions? Send e-mail to suits@mtu.edu.

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