Harness ICD

Overview

This section details the LIBus harness interface control information. Refer to the main harness ICD for more.

Electrical Interfaces

This section details the electrical interfaces of the harness subsystem.

Phase A: Preliminary Intermodular Connector Pin Assignments

At this time, since LIBus structure layout was only preliminary concept design, the overall harnessing layout and connector design corresponds to general harness ICD.

Phase B: Updated Intermodular Connector Pin Assignments

In Phase B, the power distribution system and intermodular connectors were changed. This required a new pinout assignment. The new pin naming convention is shown below on a diagram of each type of intermodular connector. These connectors are keyed, meaning they are unique to its connector pair. 

With the power distribution design, the power contacts P1 (V+) and P2 (V-) are used to provide power to all other subsystems. The pin assignments for the signal contacts vary with location in the satellite. The bus location of each pair of connectors is shown below. Outside bus pin outs include signals such as RS485, RS232 and RF coaxial. More information on their connections here. 

Current Power and Data Layouts 

The two diagrams show the current power and data layouts of harnessing. Below is a schematic at a conceptual level, which is intentionally not drawn to scale.

Umbilical Connectors 

There will be three umbilical connectors located in the satellite that allow for external connections to be made from the exterior. Below is diagrams showcasing the allocated pinouts for each connector: 

Phase C: Assembly Plan and CAD 

Currently, the Engineering Model for LIBus harnessing is underway. The EM consists of measuring and testing out wire lengths to make sure to ensure slack and bend radius of the wire is considered. The minimum bending radius of the wires are considered for both minimum and optimal design radii. 

Bending Radius Consideration and Calculations

The bend radius was considered for both the power wires and the data wires that will be used on the satellite. The following adheres to Table 7.1 of NASA-STD-8739.4A:

Power Wires (Primary Conductors, untwisted wire): 

• 18 AWG

• Outer Diameter (finished wire) is 0.070 in or 1.778 mm.

• Link 

Data Wires (Primary Conductors, untwisted wire): 

• 26 AWG 

• Outer Diameter (finished wire) is 0.040 in or 1.016 mm. 

• Link

These wires fall under the row "Overall harness (with AWG size 10 or smaller without coaxial cable)." on the table in the standard. 

Therefore:

Power Wires

Optimum Bend Radius: 10 x OD = 1.778 * 10 = 17.78 mm

Minimum Bend Radius: 3 x OD = 1.778 * 3 = 5.334 mm

Data Wires:

Optimum Bend Radius: 10 x OD = 1.016 * 10 = 10.16 mm

Minimum Bend Radius:  3 x OD = 1.016 * 3 = 3.048 mm

The following is the CAD model of one of the data wires and showcasing the measured bending radius: 

Slack Considerations

The amount of slack chosen was based on two main considerations: 

1. That there is enough slack to ensure that wires will not damaged or pulled out of the connection due to the allowed amount. 

2. That the slack amount isn't too large and interferes with overall harness of the system and causes wire buildup and force on components.

Referring to NASA MSFC-SPEC-494, it states "slack shall be provided between clamps to avoid stress on harness but it shall not be greater than 1/2 inch between support points." for wires that are not 0-4 AWG. Clamp consideration will be for the use of the Kapton taped down wires that will be on the satellite. 

Slack of the wire was also inspected and tested within assembly of the harnessing build models.

Harness Tie Considerations

For the harnessing ties of the connector assembly, the use of the lockstitch lace tie is implemented. Based on NASA-STD-8739.4A, consideration of Table 9.1 which deals with the harness diameter of the wire bundle to the maximum distance each of the ties can be made. 

Another consideration is of Table 9.2 will be made while making ties, which deals with the distance that the tie should be from the connector based on the harness bundle diameter. 

More information on assembly of these connectors are found here.

Harnessing Pathways in Structure Design

The structure shells are created with harnessing cutouts which are pathways for harnessing on each of the four sides of the shells. This ensures that wires can go from each module of the satellite efficiently. The harnessing will also flow through the middle rails of the 6U satellite if needed.

The following picture is from structure design details showcasing the four cutouts on the shells: 

Figure 9 and 10: Structure shells with four harnessing cutouts. 

Shrouding/Shielding Considerations

The current considerations for the harnessing are to twist all of the data and power harnesses to avoid electromagnetic interference (EMI), instead of using shielding. This approach has been successfully implemented in our previous CubeSat, IRIS, where twisting the wires yielded excellent results in reducing EMI. For the upcoming EM and FM models, the same approach of twisting the wires to prevent EMI will be used. To further mitigate any potential noise transfer between the power and data wires, we’ve separated the power connectors from the data connectors, which helps reduce interference. 

EM Assembly

So far, the main points of assembly have been the following connections: 

• ADCS board to CDH board. 

• ADCS board to the power board (neglecting the communications board for now due to manufacturing of it still underway). 

Each harness wiring length was designed and assembled to allow for slack of the wires to avoid pulling or damage of the wire. 

ADCS to CDH board: 

This connection deals with being able to fit the wire, with following the standards mentioned earlier, between a 20 mm standoff gap. 

• The following is a CAD view of the connection:

The exact measurement within the CAD was 73.984592 mm or 7.3984592 cm.

• The physical assembly built within the lab: 

The exact measurement within the assembly was found to be 14 cm +/- 0.5 cm based on visual inspection. 

1. The wire bundle connected between the two boards laying flat. A piece of Kapton tape to secure the wires in place on the board. 

2. The CDH board was then placed into the EM shell. 

3. Stand-offs are added to the top of the board. 

4. ADCS board is placed on top of the CDH board, being mindful of the wire bundle underneath. 

Figure 16 and 17: View of the ADCS board placed on the stand-offs ontop of CDH board with the wire harness. 

5. Screws on all four corners are added and fastened.

Figure 18, 19 and 20: Showcase the fastening of the corner screws to the stand-offs.

ADCS Board to Power Board: 

This connection is the connection from ADCS board to the power board through the bottom of the satellite (beside the star tracker and GNSS antenna).

• The following is a CAD view of the connection (blue wire):

The exact measurement of the wire within CAD:  28.722925 cm. 

• The physical assembly built within the lab: 

The exact measurement of the full wire for physically assembly was 29 cm +/- 1cm of slack room.

1.  Connecting the connector to the fastened ADCS board and placing the other side of the harnessing bundle through one of the cutouts in the upper 1/2 of the structure shell. 

2. Next closing the 1/2 shell on to the other 1/2 shell with wire placed inside while carefully minding the bending of the wires. 

3. Insert the harness bundle into the 1/2 shell of the power module. 

4. Place it aside and secure power module on lower half of its shell. Connect the connector from the ADCS board to power board. 

Figure 25 and 26: Top view of connected ADCS to power module. 

5. The final assembly of the wiring with shells closed. It was observed that the measured value of 28.7 cm (with a given with a +1 mm) from the CAD model was a bit too long for assembly as there was too much slack on the top of the shells. This length will be changed and adjusted as more tests and practice assemblies take place. 

Electrical Properties

The electrical properties of relevant components are summarized below.

Intermodular Connector Headers:

Maximum working voltage (V): 800

Maximum current (A): 20 (power), 2.2 (signal)

Maximum contact resistance (mΩ): 6 (power), 25 (signal)

Minimum insulation resistance (MΩ): 100

Intermodular Connector Receptacles:

Maximum working voltage (V): 800

Maximum current (A): 20 (power), 2.2 (signal)

Maximum contact resistance (mΩ): 6 (power), 25 (signal)

Minimum insulation resistance (MΩ): 100

Power wires:

Maximum working voltage (V): 600

Maximum current (A): 14

Unit length resistance (Ω/m): 0.0059

Intermodular signal wires:

Maximum working voltage (V): 600

Maximum current (A): 0.361

Unit length resistance (Ω/m): 0.125

Intramodular signal wires:

Maximum working voltage (V): 600

Maximum current (A): 0.361

Unit length resistance (Ω/m): 0.125

Data Interfaces

The harnessing system has no direct data interfaces with other subsystems.

Mechanical Interfaces

The components that have mechanical interfaces with the structure subsystem are:

Component Connected parts Fastening

Intermodular connector headers All circuit boards Soldering

Intermodular connector receptacles Intermodular connector headers M2 jackscrews, Loctite

Power wires Receptacles, all boards, structure shells Soldering, cable ties

Intermodular signal wires Receptacles, all boards, structure shells Soldering, cable ties

Intramodular signal wires Receptacles, all boards, structure shells Soldering, cable ties

Cable ties Structure shells Tying

The mechanical properties of each component are summarized below.

Intermodular Connector Headers:  12 signal (2 power)

Mass (g): ~1.6 (~1.2)

Height (mm): 5.6

Length (mm): 30 (20)

Width (mm): 5.55

Outgassing concerns: None

Intermodular Connector Receptacles: 12 signal (2 signal)

Mass (g): ~1.6 (~1.2)

Height (mm): 12.7

Length (mm): 30 (20)

Width (mm): 5.55

Outgassing concerns: None

Power wires:

Linear density (g/cm): 0.35

OD (mm): 1.778 

Length (mm): variable, see TBD LINK

Outgassing concerns: None

Intermodular signal wires (26 AWG):

Linear density (g/cm): 0.24

OD (mm): 1.016 

Length (mm): variable, see TBD LINK

Outgassing concerns: None

Thermal Interfaces

Intermodular connectors:

Operating/survival temperature range: -55 - 125 C

All wires:

Operating/survival temperature range: -55 - 200 C

Cable ties:

Connector Assembly Plan 

Introduction

The Connector Assembly Plan is a step-by-step plan for setting up the connectors used in LIBus. 

Equipment 

The equipment needed for this assembly: 

• 26 AWG Wire 

• 18 AWG Wire

• Wire Strippers

• Soldering Iron 

• Solder (Contains Lead) 

• Flat edge screwdriver

The final assembled connector consists of two female connectors, 12 data wires, and 2 power wires that are twisted. 

The final product that we are expect is displayed below: 

Procedure

1. Cut wires you would like the use:

• You will need a total of 12 data wires (6 pairs). 26 AWG was used for the example connector. 

• For this connector, a length of 25 cm was cut for each wire, but the length is dependent on the specific length you need. 

2. Strip off 1-2 mm off each data wire. 

3. Clamp core into helping and place wire into the core. The wire should be fully submerged in there with no exposed stands.

**Note: make sure the end of the core with the tiny hole on the side is where the wire goes in. This tiny hole is to help solder be displaced in the core easily.

Figure 29 and 30: Visual of what should be observed when deciding the right wire strip length.

4. Using lead solder, start by heating up the core with a solder pen and lightly add solder into the entrance of the core. Once enough solder, place wire in and continue to heat and add solder if needed. 

5. After the joint cools down, you will be able to lightly tug on the connection and the wire should not come loose. The final look below:

6. Continue 3-5 for each 12 of the data wires. 

7. Now on the other side of each of the 12 wires, proceed with step 2-5. You should now have a core on each end of the wire. Below is what you should have:

8. Cut the wire to the same length you made the data wires. These will be your power wires. One will be power and one will be ground. The wires used were sized 18 AWG. 

9. Strip 1-2 mm off the wires, both ends. 

10. The core you will be using for the power wires are the larger cores in the set. 

Placing the stripped wire into the end of the core with the hole, be sure to check again for an exposed wire coming out of the core. 

11. Clamp the core and wire secured into it, heat it up, and add solder to the hole on the side of the core. This will allow the solder to coat the connection inside the core. Once the hole and wire are coated with solder, let it cool down and proceed with a pull test. The finished product should look like below: 

12. Decide what the wire will be used for (ground or power, red or black) and add heat shrink onto the core just below the spikes of the exterior of the core. 

13. Repeat 10-12 for the other side of the wire, and you should have something as the following below:

14. Repeat 8-13 for the second power wire and it ,should look something like this: 

15. Place the black connector part into the blue holding jig. This jig allows the black connector not to move around when inserting the cores. 

16. Adding the wires on by one starting with the data wires and then the power ones. You want to be sure to insert the cores without damaging the wires. The flat head screwdriver may be useful but be certain you are only applying pressure at the top of the core and not on the wire or the connection. You should hear a click when the core is in. 

17. Repeat 15 and 16 on the other side of the wires. You should have something that looks like the below picture, with power wires twisted together. 

18. To organize the wiring and make things a bit more tied down. Apply NASA-STD-8739.4A cable harnessing ties and standard for tie distances. The one used for this example is a lockstitch lace tie. 

Updated EM Model and FM Model

While working on the updated EM model and FM model, we realized we needed to update the harnessing plan. First, we separated the power connectors from the data connectors to reduce electromagnetic interference (EMI) and twisted the wires to help with that as well. We also found a shortage of pins, so we had to switch to a larger connector. This led to changes in the intermodular connectors and a new pinout assignment. The updated pin naming convention is shown in the diagram below for data intermodular connectors. These connectors are keyed, ensuring each one is uniquely matched to its corresponding pair. 

The new intermodular connector system consists of a 2-pin power connector that supplies the main power bus and a 34-pin data connector that routes all data lines to their respective subsystems. The pin assignments ensure proper connectivity and signal integrity across the system.

The detailed pin assignments for data intermodular connectors are shown in Table 9-17.

Updated Intermodular Data Connector Specifications

Mechanical Interfaces (for both receptacles and headers):

• Number of Positions: 34

• Number of Rows: 2

• Pitch (Mating): 2.00mm (0.079”)

• Row Spacing (Mating): 2.00mm (0.079”)

• Mated Stacking Heights: 7.3mm, 7.7mm, 9.75mm, 10.75mm, 13.35mm, 14.75mm

• Durability: 500 operations

Electrical Interfaces (for both receptacles and headers):

• Current Rating at 25◦C : 3.0A Max

• Current Rating at 85◦C : 2.2A Max

• Voltage Rating: For Receptacles (120V) - For Headers (800V)

• Contact Resistance: <25mΩ

• Insulation Resistance: >100MΩ

• Operating Temperature: -55◦C to +125◦C

Dimensional Specifications

Data Intermodular Connectors (Receptacles):

Maximum Insulation Height: 5.55mm

• Recommended Wire Type:

– 24–28 AWG PTFE Insulated

– Ø 1.0mm Strip Wire, 7.00mm

• Tolerance:

– X, X.X = ±1.0mm

– X.XX = ±0.50mm

– X.XXX = ±0.10mm

– Angles = ±1°

Data Intermodular Connectors (Headers):

Insulation Height: 5.60 (0.220)

Recommended PCB Hole Size: 0.70 ± 0.05

Tolerance:

• X, X.X = ±1.0

• X.XX = ±0.50

• X.XXX = ±0.10

• Angles = ±1

Contact and Material Specifications

Data Intermodular Connectors (Receptacles):

• Contact Clip Material: Beryllium Copper

• Contact Shell Material: Copper Alloy

• Jackscrew & Circlip Material: Stainless Steel

• Finish (All Over Nickel):

• – 05 – 0.3μ Gold Clip, 0.25–0.3μ Gold Shell

• – 42 – 0.3μ Gold Clip, 3.5–0.0μ 100% Tin Shell

• Insulation Material: Glass-Filled PPS (Polyphenylene Sulfide)

• Insulation Color: Black

• Material Flammability Rating: UL94 V-0

Data Intermodular Connectors (Headers):

• Contact Material: Phosphor Bronze

• Contact Shape: Circular

• Contact Length (Post): 3.25 (0.128inch)

• Contact Finish (Mating): Gold (0.75 / 29.5 inch)

• Contact Finish (Post): Tin (3.00 / 118.1 inch)

• Insulation Material: Polyphenylene Sulfide (PPS), Glass-Filled

• Insulation Color: Black

• Material Flammability Rating: UL94 V-0

Updated Data Intermodular Connectors Purchasing links: 

Intermodular Power Connectors

In the power distribution design, the power contacts P1 (V⁺) and P2 (V⁻) supply power to all subsystems. The naming convention for power intermodular connector is based on Figure 43.

Updated Intermodular Power Connector Specifications

Mechanical Interfaces (for power receptacles): 

• Contact Type: Female Socket, Power

• Number of Positions: 2

• Pitch: 0.157" (4.00mm)

• Number of Rows: 1

• Mounting Type: Free Hanging (In-Line)

• Wire Type: Discrete

• Wire Gauge: 12 AWG

• Durability: 500 operations

Mechanical Interfaces (for power headers): 

• Contact Type: Male Pin, Power

• Pitch (Mating): 0.157" (4.00mm)

• Number of Positions: 2

• Number of Rows: 1

• Style: Board to Cable/Wire

• Shrouding: Shrouded - 4 Wall

• Mounting Type: Through Hole

• Fastening Type: Threaded

• Contact Length (Post): 0.138" (3.50mm)

• Insulation Height: 0.220" (5.60mm)

• Contact Shape: Circular

• Contact Finish Thickness (Mating): 10.0µin (0.25µm)

• Mated Stacking Heights: 7.3mm, 9.75mm

• Durability: 500 operations

Electrical Interfaces (for power headers):

• Current Rating: 20A

• Voltage Rating: 800V

• Contact Resistance: <6mΩ

• Insulation Resistance: >100MΩ

• Operating Voltage: 180V AC at 500mA

• Contact Material: Copper Alloy 

• Contact Finish (Mating): Gold 

• Termination: Solder

• Operating Temperature Range: -55°C to 125°C

Electrical Interfaces (for power receptacles):

• Contact Resistance: <6mΩ

• Insulation Resistance: >100MΩ

• Operating Voltage: 180V AC at 500mA

• Wire Gauge: 12 AWG 

• Cable Termination: Solder 

• Wire Type: Discrete

• Contact Finish: Gold 

• Fastening Type: Screw Lock 

• Operating Temperature Range: -55°C to 125°C

Updated Power Intermodular Connectors Purchasing links: 

LISSA-SWIR Payload Harness Interface ICD

Based on our evaluation (detailed here: Test Information) the following is required to harness the SWIR Payload to LISSA. 

• The payload's power harness connecting to the LISSA bus shall have 24 cm of slack sticking outside the payload.  

• The payload's data harness connecting to the LISSA bus shall have 12 cm of slack sticking outside of the payload.

• The payload shall have space internally to house any excess harnessing slack during mechanical integration. If required, the harness length should be shortened if there is not enough space inside of the payload to store the excess slack.

• As per the figure below, female connectors from the SWIR payload shall directly harness to the male connectors located on the Power and Regulator CCAs. 

  • The SWIR payload data harness connector interfacing with the bus shall be M80-4613405.

  • The SWIR payload power harness connector interfacing with the bus  shall be M80-4000000F1-02-325-00-000.