Harness ICD

Overview

This contains information on the mechanical, electrical, data, and thermal interfaces for the harness subsystem of the ArcticSat project. For more harness interfacing, see the general page.

Electrical Interfaces

This section details the electrical interfaces of the harness subsystem.

Phase A: Preliminary Intermodular Connector Pin Assignments

The modular layout of ArcticSat, including the intermodular connector locations and naming scheme, is shown below. Currently, the relative location of each module is not yet known. However, there will likely be a need for 3 intermodular connection points as shown.

As the structural layout of ArcticSat is not yet completely known, a pin assignment for the intermodular connectors has been created for each of the structural layout concepts. These are shown in the tables below. The pin names are chosen as detailed in the general harness ICD. Note that an asterisk beside the pin name is used to indicate that the pin assignment in question may not be necessary, depending on the structural shell orientation.

The assigned power pins include power for Comms, CDH, ADCS, and Payload, for eight total. There are six more pins put aside to actuate each of the deployable components, two each of which are for solar panels (1), communications antenna (2), and payload antenna (3).

There are 4 data pins assigned for SPI communication with ADCS, another 2 for CAN communication with CDH, and 4 more for JTAG debugging.

This concept was used in the Iris mission and will only be used in this mission if updated intermodular connectors do not work. 

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.

With the new 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 locations of each pair of headers and receptacles are shown below, and the corresponding pin assignments follow.

Preliminary Power and Data Layouts 

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

Updated Power and Data Layouts 

The two diagrams showcase the updated 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:

The umbilical connectors we plan to use are DB15 Micro-D receptacle connectors with 15 female socket positions. Below, you can find the ICD for these connectors.

Umbilical Connector Specification:

Connector Name: Micro-D Receptacle (DB15) 

Mechanical Specifications

• Connector Style: D-Type, Micro-D

• Connector Type: Receptacle, Female Sockets

• Number of Positions: 15

• Number of Rows: 2

• Contact Pitch: 0.050” (1.27 mm)

• Row Spacing: 0.043” (1.09 mm)

• Mounting Type: Panel Mount

• Termination Type: Solder Cup

• Shell Material and Finish: Aluminum Alloy, Nickel Plated (Electroless)

• Contact Material: Copper Alloy

• Contact Finish: Gold

• Contact Finish Thickness: 50.0 µin (1.27 µm)

• Features: Shielded

Electrical Specifications

• Current Rating: 3 A

Environmental Specifications

• Operating Temperature: -55°C to +135°C

• Material Flammability Rating: UL94 V-0

Compliance & Classification

• RoHS Status: RoHS3 Compliant

• Moisture Sensitivity Level (MSL): 1 (Unlimited)

Connector Saver Adapter Specification

Connector Name: DB15 Connector Saver Adapter 

Mechanical Specifications

• Connector Style: Connector Saver

• Convert From: D-Sub, 15 Pin Male

• Convert To: D-Sub, 15 Pin Female

• Number of Rows: 2

• Mounting Type: Free Hanging (In-Line)

• Shell Material and Finish: Aluminum Alloy, Yellow Chromate Plated

• Contact Finish: Gold

• Contact Finish Thickness: 50.0 µin (1.27 µm)

• Shielding: Unshielded
  
  

Electrical Specifications

• Current Rating: 3 A

Environmental Specifications

• Operating Temperature: -55°C to +135°C

• Material Flammability Rating: UL94 V-0
  
  

Compliance & Classification

• RoHS Status: Not listed (assume compliant unless specified)

• Moisture Sensitivity Level (MSL): 1 (Unlimited)

Design Evolution and Connector Strategy for ArcticSat EM and FM Models 

Our design plan for the ArcticSat Engineering Model (EM) and Flight Model (FM) changed, and as a result, our testing approach for FM and breadboard setup for EM also differ between the two.

For example, in the EM testing and breadboard model, we used an intermodular connector with 12 data pins and 2 power pins combined in a single connector. Also, the umbilical connectors we initially intended to use were DB9 connectors with 9 pins.

However, for the FM model, we are switching to a 34-pin intermodular connector for data and a separate 2-pin connector for power. We also plan to use a 15-pin umbilical connector (DB15) instead of the original DB9.

These changes were made to ensure compatibility with other CubeSat projects we are currently developing. This unified design helps save time and effort by allowing us to reuse the same boards across multiple CubeSat projects without needing to redesign them for each project. Additionally, the increased number of pins gives us flexibility for future development, and separating power and data connections helps reduce electromagnetic interference (EMI).

Phase C: Assembly Plan and CAD 

Currently, the Engineering Model for ArcticSat harnessing is done. The EM consists of measuring and testing out wire lengths to make sure to ensure that slack and bend radius of the wire are 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. There is enough slack to ensure that wires will not be damaged or pulled out of the connection due to the allowed amount. 

2. That the slack amount isn't too large and interferes with the 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 following picture is from EM structure design details, showcasing the four cutouts on the shells: 

HRS Figure 13 - 14: Structure shells with four harnessing cutouts. 

It’s worth mentioning that our initial intermodular connector in the EM model was smaller, with limited pin count (12 pins for data and 2 pins for power), which required relatively small cutouts. However, for the FM model, we are using a 34-pin intermodular connector for data and a separate 2-pin connector for power. This configuration requires larger cable pathways, and therefore, the corresponding cutouts are also larger.

In the figure below, you can see the enlarged cutouts on a shell designed specifically for the FM model.

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 Using Initial Intermodular Data and Power Connectors 

So far, the main assembly work has focused on making the key connections between modules. Each harness was built with enough slack to make sure there's no tension on the wires, helping avoid any damage during handling or operation.

One of the important connections involves fitting a wire through a 20 mm standoff gap. This had to be done while following our earlier wiring standards, so things like connector orientation and wire bend radius had to be carefully considered.

The CAD view below shows how that connection looks in the design:

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 first board was then placed into the EM shell. 

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

4. The second board is placed on top of the first board, being mindful of the wire bundle underneath. 

HRS Figure 21-22: View of the second board placed on the stand-offs on top of the first board with the wire harness. 

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

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.

Initial (EM) 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

Initial (EM) 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

• Male Connector M80-5T11205M1-02-331-00-000

https://www.digikey.ca/en/products/detail/harwin-inc/M80-5T11205M1-02-331-00-000/2264240

Connector Assembly Plan

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

Coaxial RF Cable Interface for Payload Integration 

To connect the payload (passive radiometer antenna) to its board, we will use a coaxial RF cable. A visual of this connection is shown in the figure below. 

Other Connections Beyond the Intermodular Connectors

In addition to the main intermodular connectors, the harnessing plan includes other critical connections to various subsystems.

For the sun sensor connection, we use a 10-position right-angle surface-mount header from Hirose:

• Manufacturer: Hirose Electric Co. Ltd

• Part Number: DF13-10P-1.25H(21)

• Pitch: 1.25 mm

• Type: Surface Mount, Right Angle

• Digi-Key Part Numbers:

  • H125973TR-ND (Tape & Reel)

  • H125973CT-ND (Cut Tape)

  • H125973DKR-ND (Digi-Reel)

• Description: 10-position SMD header, 0.049" (1.25 mm) pitch

Below you can see a photo of these connectors:

Purchasing Link: https://www.digikey.ca/en/products/detail/hirose-electric-co-ltd/DF13-10P-1-25H-21/3977731?s=N4IgTCBcDaIBIEYwFYCcB2AzAYQCoFoA5AERAF0BfIA 

For the harnessing of the reaction wheel, we use a 7-position connector system from Molex:

Purchasing Link Connector Header: 

https://www.digikey.ca/en/products/detail/molex/0532610971/699101 

Purchasing Link for Receptacle: 

https://www.digikey.ca/en/products/detail/molex/2181120904/14309241 

For the harnessing of GNSS and s-band transceiver via interface boards, we use a 7-position connector system from Molex:

• Header Connector:

  • Manufacturer: Molex

  • Part Number: 0532610771

  • Pitch: 1.25 mm

  • Type: Surface Mount, Right Angle

  • Digi-Key Part Numbers:

    • WM7625TR-ND (Tape & Reel)

    • WM7625CT-ND (Cut Tape)

    • WM7625DKR-ND (Digi-Reel)

  • Description: 7-position SMD header, 0.049" (1.25 mm) pitch

Below you can see a photo of these connectors:

Purchasing Link: https://www.digikey.ca/en/products/detail/molex/0532610771/699099?s=N4IgTCBcDaIOoFkDsA2MBWAKgJQLQDkAREAXQF8g 

Mating Cable Assembly:

• • Manufacturer: Molex

  • Part Number: 0151340703

  • Digi-Key Part Number: WM15271-ND

  • Description: 7-position PicoBlade cable assembly, socket-to-socket, 300 mm (11.81") length

Below you can see a photo of these cables:

Purchasing Link: https://www.digikey.ca/en/products/detail/molex/0151340703/6198161?s=N4IgTCBcDaIOoFkCMBWMB2JBaAcgERAF0BfIA 

These connections are essential for interfacing smaller subsystems while maintaining mechanical reliability and signal integrity throughout the harness.

Harnessing GNSS and S-Band Transceiver via Interface Boards:

During the development of our EM boards, we realized that some components—specifically the GNSS receiver and the S-band transceiver—require dedicated interface boards. These interface boards are needed to provide properly regulated power to these components. As a result, we designed and added specific interface connectors to harness these components. The highlighted areas in the figures below show the connectors used for the GNSS and COMS radio on the regulator board. 

In Figure X below, you can see the GNSS interface board and the S-band transceiver interface board. 

However, for the FM model, the final assembled connector will consist of two female connectors with 32 twisted data wires, along with a separate connector for the 2 twisted power wires.

Procedure

1. Cut the wires you would like the use:

• You will need a total of 34 data wires (68 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 the core into the holder and place the 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.

HRS Figure 35-36: 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 is below:

6. Continue 3-5 for each 34 of the data wires. 

7. Now on the other side of each of the 34 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. 

While updating the EM model, we realized that the harnessing plan also needed modification. To reduce electromagnetic interference (EMI), we separated the power and data connectors and implemented twisted wire pairs. Additionally, we opted to switch to a larger connector to allow for potential future expansion and additional pin requirements.

These changes resulted in an updated set of intermodular connectors and a revised pinout assignment. The new naming convention for data intermodular connectors is shown in the diagram below. Each connector is keyed to ensure it is uniquely mated with 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: