This section details the LIBus harness interface control information. Refer to the main harness ICD for more.
This section details the electrical interfaces of the harness subsystem.
At this time, since LIBus structure layout was only preliminary concept design, the overall harnessing layout and connector design corresponds to general harness ICD.
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.
Figure 2: Signal pin naming convention for intermodular connector receptacle.
Figure 3: Signal pin naming convention for intermodular connector header.
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.
Figure 4: Location of intermodular connectors in satellite.
Tables 9-16: Intermodular connector signal pin assignments.
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.
Figure 5: Current Power Wiring Diagram
Figure 6: Current Data Wiring Diagram
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:
Figure 7: Diagrams of umbilical cord connectors.
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.
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.
Data Wires (Primary Conductors, untwisted wire):
26 AWG
Outer Diameter (finished wire) is 0.040 in or 1.016 mm.
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:
Figure 8: CAD sketch of data wire.
The amount of slack chosen was based on two main considerations:
That there is enough slack to ensure that wires will not damaged or pulled out of the connection due to the allowed amount.
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.
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.
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.
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.
Figure 11: Twisted data and power harnesses.
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:
Figure 12: CAD model of the wiring from ADCS to CDH boards.
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.
The wire bundle connected between the two boards laying flat. A piece of Kapton tape to secure the wires in place on the board.
Figure 13: ADCS and CDH board side by side with the connector.
2. The CDH board was then placed into the EM shell.
Figure 14: CDH board within the first half shell.
3. Stand-offs are added to the top of the board.
Figure 15: Insertion of the stand-offs between the two boards.
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):
Figure 21: CAD model of the ADCS board to power board wiring location and routing.
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.
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.
Figure 22: Wire harness being inserted in harness cutoff of a 1/2 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.
Figure 23: Top view of the shell with harnessing cable inside.
3. Insert the harness bundle into the 1/2 shell of the power module.
Figure 24: Harnessing bundle being inserted into one of the shell's harnessing cut-outs.
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.
Figure 27: Final assembly view of the ADCS to Power module.
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
The harnessing system has no direct data interfaces with other subsystems.
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
Intermodular connectors:
Operating/survival temperature range: -55 - 125 C
All wires:
Operating/survival temperature range: -55 - 200 C
Cable ties:
The Connector Assembly Plan is a step-by-step plan for setting up the connectors used in LIBus.
Female Connector M80-4C11205F1-02-325-00-000
Male Connector M80-5T11205M1-02-331-00-000
https://www.digikey.ca/en/products/detail/harwin-inc/M80-5T11205M1-02-331-00-000/2264240
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:
Figure 28: Final assembly of wire harness with the two connectors.
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:
Figure 31: Completed one side of the data wire with soldered core.
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:
Figure 32: Completed wire with both soldered on cores.
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.
Figure 33: Measuring the power wire using the length of the data wire.
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.
Figure 34: Visual aid of what the power cores look like.
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:
Figure 35: Soldered power wire to its core.
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:
Figure 36: Final assembly of the power wires with black heat shrink applied to the the soldered ends.
**Note: don't forget to place heat shrink before you place the second core on wire or you won't be able to get heat shrink over core.
14. Repeat 8-13 for the second power wire and it ,should look something like this:
Figure 37: Final assembly of a power wire with red heat shrink applied to soldered ends.
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.
Figure 38: Jig created within the lab to help with the insertion of the wires into the connector.
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.
Figure 39: The inserted wires into the connectors.
The cores should be fully submerged in the black holder, you can also double check by looking at the bottom of the holder.
Figure 40: Visual inspection of the back of the connector with the wires inserted.
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.
Figure 41: The final assembly of the cable harness without harnessing lace.
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.
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.
Figure 42: Signal pin naming convention for data intermodular connector Header.
Table 9-17: pin assignments for data intermodular connectors
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.
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
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
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°
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 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
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
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.
Figure 43: Pin naming convention for power intermodular connector receptacle.
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
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
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
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
Receptacle (Female Connector): M80-4000000F1-02-325-00-000
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.
Figure 44: Interface of the LISSA bus with the SWIR payload