Thermal ICD

Introduction

This page describes the mechanical, electrical, thermal, and data interfaces to all components of the spacecraft thermal management subsystem. It also describes any constraints or limitations on these interfaces, including when and how data may be transferred. The interfaces that are described are the direct interfaces to the components, not the interfaces found through the CDH or PCU.

Part Mount Thermistor Interface

The thermistor selected for direct mounting on components is TE GA10K4A1A . The drawing below shows the physical dimensions and materials of the thermistors, including lead wire gauge.

Mechanical Interface

The approximate mass of each thermistor is 0.041 g, not including the additional epoxy used for mounting or additional wire length necessary for reaching connection locations. Physical dimension of the thermistor head is approximately 2.4 mm diameter. No shock or vibration testing known of, but not expected to be susceptible (no moving parts). Epoxy for coating and mounting is low outgassing; alloy material used for leads is not in NASA outgassing database so exposed leads will be conformal coated or shrink wrapped. Thermistors will be mounted in place using Stycast 2850 thermal epoxy. General mounting locations of thermistors are in the table below. The only part mount thermistor present in the design will be mounted on the payload sample plate. Exact location is the back side of the plate (not sun/space facing) in the centre.

Software Interface

There is no software or commands that are defined by the thermistors themselves. The electrical interface to the thermistors will supply a known voltage and measure the output voltage from the voltage divider.

Board Mount Thermistor

The thermistors selected for mounting on boards are TDK NTCG163JX103DTDS . The drawing below shows the physical dimensions and materials of the thermistors.

Mechanical Interface

The approximate mass of each thermistor is 0.05 g, not including the additional solder used for mounting . The thermistor chip has a footprint of approximately 1.6 mm by 0.8 mm, with a height of 0.8 mm. No shock or vibration testing known of, but not expected to be susceptible (no moving parts). Thermistors will be soldered directly to boards; beads of Stycast 2850 thermal epoxy may be used to increase thermal conductivity if necessary. General mounting locations of thermistors are in the table below. Specific mounting locations on boards are dependent on the results of board layout decision.

Software Interface

There is no software or commands that are defined by the thermistors themselves. The electrical interface to the thermistors will supply a known voltage and measure the output The software will then calculate the resistance of the thermistor.

Thermostats

The thermostats selected are Honeywell Precision Thermostat 3100U 00031434. The mechanical drawing of this component is shown below.

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Electrical Interface

Thermostat is rated to 30 V AC/DC. Terminals are nickel/iron alloy, 3.96 mm wide and 0.41 mm thick with 1.98 mm diameter holes. The thermostat will be connected in series with the power lines to the redundant battery heater. The thermostat will open and cut the power to the heaters when the temperature goes above 21.1C, and will close and allow power to flow again at 10C.

Thermal Interface

Operating temperature range is -28.89C to +260C , survival temperature range is -62C to 288C.

Software Interface

No commands, entirely mechanical operation.

Mechanical Interface

Dimensions are as seen in the drawing which will fit within the current battery pack design footprint and go between PCB and battery saddle. The location of some of the fastener holes has changed since the manufacturing of the prototype, this is reflected in the updated CAD model. The thickness of the heater is less than 0.5 mm. The heater substrate is aluminum. Heater will be mounted with Stycast 2850 thermal epoxy. Not expected to be shock or vibration sensitive as it is a single solid part.

Electrical Interface

Rated to 240 V AC/DC. No connector, comes with leads to be directly soldered in to circuit.

Thermal Interface

Maximum allowable temperature is +240C. Minimum temperature tbd.

Software Interface

No commands or software on the heaters. PCU controls the voltage supply to the heaters based on battery temperature readings. The heater control algorithm is shown in the following flow chart.

Important things to note:

If both battery thermistors are operating, the average temperature of the thermistors is used to control the primary heater.

If it is clear that one of the thermistors has failed, the data from the failed thermistor will be neglected and only one thermistor will be used for the primary heater control.

In the case where the primary heater has failed, determined by telemetry, the switch to the primary heater will be turned off permanently and the redundant heater with the thermostat control will be relied on.

Redundant Heaters

The redundant heater selected is Minco polyimide thermofoil heater part HK6900. This heater will only be used if the primary heater fails. The Minco HK6900 heater is given below. The location of the redundant heater can be seen in the close up of the power module shown under the thermostat section.

Mechanical Interface

Mounting location is directly on the battery saddle. Maximum mass is approximately 5 g. The heater dimensions are 0.5 in in width and 1 in in length. Many models with different lengths are available off the shelf. The heaters come with Minco pressure sensitive adhesive #19 (3M 966 adhesive) for installation (NASA low outgassing approved). Stycast 2850 thermal epoxy will be used for additional security in mounting. Considerable space flight heritage, not expected to be shock or vibration sensitive.

Electrical Interface

Lead wires are AWG #24-26, model dependent. Rated to 28 V. No connectors.

Thermal Interface

Identical operating and survival temperature ranges of -32C to +100C.

Software Interface

No commands or software on the heaters. PCU controls the voltage supply to the heaters based on battery temperature readings.