# ADCS: magnetorquer design/sun sensor design and build 23ss
> Referenced from old work, and come up with some discussion points
> Written by: Jui-Wen, Yeh

## Introduction
Since the last balloon launch after ADCS lost the sun sensor, we are trying to rebuild the capacity and the modules for the team. Currently, there are 2 modules that have a higher building priority:

* sun sensor
* magnetorquer

Originally ADCS team was trying to either negotiate or develop the modules, but we were having some troubles regarding not having the ability to design PCB, having concerns about the stability...etc. However, my target is to restore the ADCS team to the status of MOVEII. This means the ADCS team needs to have at least the following modules integrated and implemented onto the satellite:

1. IMU
2. Magnetorquer
3. Sun sensor

The reason why we are building these modules is because these are the easier ones. However, before building the modules, I talked to Jona about this part and we decided to form a tiger team to build the module.

Need to be noticed that the requirements are not fully set. So we will focus on references from commercial sun sensors and magnetometers to set up the precise requirements.

## Target of the project
* ADC-implementation on SSB to test 1D sun-sensor prototype (mainly software, but also electrical)
* ADC selection and PCB design of a new ADCS Protoboard (Electrical)
* Magnetorquer design, build, placement and cabling (Electrical and Mechanical). We need to define this task more clearly
* Sun-sensor design/development, choosing technology, etc (Design task, in combination with electrical)
* Test design of sun sensors (Electrical, software, mechanical)
* Sun sensor placement + cabling (Design, Mechanical)

## Requirement set up
### reference from Design Day
During the design day, we came up with the full requirement. The following is the result.


However, this is just the rough requirement. We have to define it more precisely.

To be more precise, the following are the options that we will explore/build:

#### Sun sensor:
1. Coarse Sun Sensor
The one that we should be able to build easily. It's basically a 1D photodiode with ADC actually. Last year we bought some photodiode (BPW34, [datasheet](https://www.vishay.com/docs/81521/bpw34.pdf)). But there's some problem with the connection as we don't have ADC.


2. Fine Sun sensor


There are 2 methods for creating a fine sun sensor. Either using a 2D photodiode or CCD to detect the orientation of the sun.

The problem that we might encounter is the reliability of the sun sensor. For example, originally the plan is to build a fine sun sensor with [2D photodiode](https://www.hamamatsu.com/us/en/product/optical-sensors/photodiodes/si-photodiode-array/segmented-type-si-photodiode/S5980.html). But the manufacturer asked for a disclaimer for acknowledging it might not work. We still got the quote under this condition.

#### Magnetorquer
For magnetorquer, we are building it on our own. The current status can be found [here](https://gitlab.lrz.de/move/design/adcs/-/tree/main/Magnetorquer)

As for the draft, the current design is to build an aircoil magnetorquer. The original design is discussing choosing between 3 aircoils or 6 aircoils. However, 3 aircoil option was chosen.

The following is the advantage and disadvantage of the current design:
##### Advantage
1. low space consumption for single coil with high-external torque
2. Cheaper and easy to build. More Inspiring

##### Disadvantage
1. 3 aircoils require 3 separate PCBs, which means it will increase the mass of it.
2. not space-proven.


### Reference from commercial models
#### Sun sensor
The current doable plan at this moment with the modules we had will be building a coarse sun sensor. The reference Coarse Sun Sensor
https://www.cubesatshop.com/product/tensor-tech-css-10-coarse-sun-sensor/
##### properties for CSS-10:
* 1-axis analog coarse sun sensor
* <5 deg (1-sigma) of sun determination accuracy is achievable following the user manual’s calibration instructions
* Hardware protection for short-circuit-caused system failure prevention
* Six coarse sun sensors can provide a full sky (4π) FOV coverage (± 60 deg for each sensor)
* An analog-to-digital converter should be installed to extract information.
* Three pins including Vcc, GND, and output line.
* Field of view: ± 60 deg
##### Power and mechanical properties
* Power consumption: < 0.1 mA
* Mechanical: 20.00 × 10.00 × 5.70 mm (< 0.5 g)
* Radiation tolerance: > 10 krad

#### magnetorquer
As for a more similar product, [this](https://satsearch.co/products/exa-mt01-compact-magnetorquer) magnetorquer is the reference/expected result we might have. The following are the rough properties of the commercial module:

| name | properties |
| -------- | -------- |
| mass | 7.5 g |
|length| 50 mm|
|width|50 mm|
|power: normal mode |250 to 1750 mW|
|power: Saturation | 250 to 1750 mW|
| voltage| 1.25 to 7.5 V|
|operating temperature|-55 to 85 C|
|torque|5.36 µN m|
|magnetic moment: normal mode|> 0.19 A m^2|
|magnetic moment: saturation magnetic moment| >0.85 Am2 (saturation magnetic moment)|

Although we already have a design, since we are starting the move-beyond, the required torque calculation(or estimation) might need to be done again. Including estimating the worst possibilities for the payload.

## Precise requirement
### Sun sensor
Best option is of course design and integrate a 2D photodiode. But as things are not fixed yet I am concerning about touching the budget. So we will start with building a low-pointing requirement CSS to practice and prepare for the potential of designing a FSS.

The following are the requirements that I would like to have for the design of the sun-sensor (negotiable):

| name | properties |
|----|----|
|field of view | 60deg |
| accuracy | 3 deg|
| independent ADC | yes |
|power source | 5V |
| sampling rate | 10Hz |
| data rate | 50Hz |
| environment: temperature | -50deg ~ 100 deg with 5deg accuracy |
|environment: radiation tolerance| >10 Krad |

The requirement is just a rough draft. It still negotiable

### Magnetorquer
The requirements are not fixed yet, but currently for development, I would like to have the same specification as the MOVEIII magnetorquer at this moment. The following are the specifications:

| name | properties |
| -------- | -------- |
| Size | 75𝑚𝑚 𝑥 75𝑚𝑚 𝑥 10𝑚𝑚 |
|Number of windings|500
Max power (per aircoil)|131𝑚𝑊
Voltage|5𝑉
Max Torque (@ detumbling)|1,2992 ∙ 10−6𝑁𝑚

The specification is not fixed as the design team needs to re-calculate to see if it's reasonable or not.

## Integration with the mechanical team and software team

As we are forming a tiger team, it's not just about ADCS and Electrical. The software for the sensor/actuator and the mechanical implementation still need to be considered. I will ask Phillip and Benedikt about this part to see how to cooperate.

For personal expectation, we will need a person to write the software for the sun sensor, and a person to write the software for the magnetorquer (or the same person?); we also need a person to do mechanical design to make sure the size (PCB size and the air coil size) of the sun sensor and magnetorquer fits the satellite.

## other reference
1. Sensor fusion to improve accuracy: https://ieeexplore.ieee.org/document/9430484