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This page provides the detailed harnessing plan for every subsystem. Information of harnessing part selection and datasheets will be included here. The mechanical interfaces focus on the assembling process of each component, and the electrical interfaces illustrate the signals flow in each connector.
Introduction
Introduction
The Harness subsystem focuses on how to physically connect hardware using wires and connectors. All off-from-board components connections and inter-modular connections will be taken into consideration. Harness subsystem ensures the safety and reliability of power/data interactions between subsystems. The selections of harnessing components (wires, connectors, and etc.) will conform to NASA standard EEE-INST-002.
Mechanical interfaces
Mechanical interfaces
Inter-modular connectors
Inter-modular connectors
A 15-pin Micro-D connector has been selected as inter-modular connector, the part number is DCCM15SSBN (female connector) and DCCM15PSBN (male connector), the current rating is 3A, a data and power cable will be distributed to two individual connectors in order to minimize the noise in data wires induced by high-current power wires. For consistency in assembling, all upper shells will be mounted with female connectors and the male connectors are all on the lower shell of each module. The mechanical drawing of the connectors is shown below.
The inter-modular connector's shell is made of aluminum alloy with electroless nickel plated, the dielectric material is Diallyl Phthalate (DAP) with glass filled. The contact material is copper alloy. All materials conform with EEE-INST-002.
There will be 2 connector holes on every shell as the wires for power supply and data transmission are running on separate connectors. The data and power connector locations are on the same side of the shell. The locations of these two connector holes are as shown in the picture:
The process of mounting inter-modular connectors to shell should follow the steps:
Firstly put the connectors into their corresponding holes on the shell.
Then insert the bolts UMS-0208 to the module shell, make sure the bolt head is at the outside of the upper shell.
On the -z surface (inner side) of the upper shell, put 2 washers UMS-0210 to each of the bolt (so 4 washers in total for every connector), then insert the connector (2a and 5a are identical UMS-0206) .
Put nuts UMS-0209 to the rest of bolts (inside of the module) and tighten it.
Note that before putting on the screws, make sure the longer edge of the connector plug is always on the side (that is closer to the center of the shell).
If assemble correctly, the connector assembly should look like:
Wire selection
Wire selection
The wire selection is based on the maximum current rate for every subsystems. Based on the results of power analysis, the maximum current rate among all subsystems is 1.8A, which is the power supply of solar/antenna deployments. According to NASA standard EEE-INST-002 [2], the 24 AWG wire is selected, which has the maximum current capacity of 2A.
The insulation material also conform to EEE-INST-002, PTFE (Polytetrafluoroethylene) is selected for wire insulation because of its good out-gassing characteristics and ease of availability. One of the possible suppliers is Ryan Electronics Corporation, part number: M22759/11-24. Consist of 1 twisted pair of wires.
Connector lock mechanism
Connector lock mechanism
The inter-modular connectors are panel-mount type, usually mounted to a panel. However, for Iris, ADCS module and CDH & COMS module have no lower shell, the inter-modular connectors are free-hang in the module, which could be easily unplugged by vibrations. Therefore, a connector lock mechanism is developed for connectors that have no place to be mounted to.
There are 4 connectors that need to be fixed by the connector lock: connector 6b, 3b, 4b, 1b. (The corresponding locations can be found in section 'Electrical interfaces')
The assembly of the connector lock is shown in the picture below, the prong-fork structure is used to hold the free-hang connector once it is plugged.
The connector lock assembly is mounted to the shell where the connector's mated-pair is on. For example, the connector in the figure is the inter-modular power connector between CDH and Payload, in which case the CDH module has no lower shell for the inter-modular connectors and the connector lock is mounted to the payload module upper shell.
Umbilical connector
Umbilical connector
The umbilical connector provides connections to outside devices (i.e. computers), the functions of the umbilical connector are: re-charging the batteries (2 wires), CAN BUS (2 wires) and debug/reprogramming the software (4 wires) that is also used for monitoring subsystems' status during the ground test.
The 9-pin female Micro-D connector (Digi-key part number: DCCM9SSBN) has been selected as the umbilical connector. The 9-pin umbilical connector uses the same shell material and dielectric material as the 15-pin inter-modular connector, therefore the security of materials are guaranteed.
The umbilical is designated to be located beside the RBF pin on the -x surface, because that is the only accessible surface once the satellite is placed in the deployer. The location of the umbilical connector is as indicated in the picture on the right-hand side of this page.
The process of mounting the umbilical connector to the shell should follow the steps:
1. Firstly, put the umbilical connector into the corresponding reserved hole on the lower power shell.
2. Then insert the bolts UMS-0208 into the module shell, make sure the bolt head is on the outside of the shell.
3. Put nuts UMS-0209 to the rest of the bolts (on the inside of the module) and tighten it.
The electrical interfaces of the umbilical connector are included in the following sections.
Electrical interfaces
Electrical interfaces
Inter-modular connector pin-signal correspondence table
Inter-modular connector pin-signal correspondence table
The following figure outlined all inter-modular connectors and corresponding gender of each connector:
In order to keep the consistence of the wires, each pin/socket on the male/female connector has been labeled:
The signal on each pin for inter-modular connectors are listed in the tables below, note that there are some signal names are subject to change according to their specific PCB schematics: UMS_CDH_X, Payload solar panel_POS/NEG.
Umbilical connector pin-signal correspondence table
Umbilical connector pin-signal correspondence table
There will be 8 wires connect to the umbilical connector: 2 for charging the batteries, 2 for CAN BUS and 4 from CDH for debugging/reprogramming.
Similarly, the pins on umbilical connector are firstly assigned with index, and the signals on those pins are listed in the table below. Note the signal names are subject to change to ensure its consistency with power control board schematics.
Parts list
Parts list
Here are all required parts from harnessing, include wires, connectors and accessories.
Bill of Materials
Bill of Materials
The outgassing properties of those materials are secure and can be found from NASA database "Outgassing Data for Selecting Spacecraft Materials "[1]
BoM.xlsxGSE List
GSE List
GSE list.docxSubsystems' Harness Assembly Plan
Subsystems' Harness Assembly Plan
PLD assembly plan.docxADCS assembly plan.docxCDH&COMS assembly plan.docxPower assembly plan.docxReferences
References
[1] “Outgassing Data for Selecting Spacecraft Materials System,” 08-Jan-2008. [Online]. Available: https://outgassing.nasa.gov/. [Accessed: 27-Oct-2020].
[2] K. Sahu, "EEE-INST-002: Instructions for EEE Parts Selection, Screening, Qualification, and Derating," https://nepp.nasa.gov/DocUploads/FFB52B88-36AE-4378- A05B2C084B5EE2CC/EEE-INST-002_add1.pdf
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