SEDSAT-2 ADCS
From SEDSWiki
This is the page for the SEDSAT-2 Attitude Determination and Control team.
Contents |
News
Latest updates on the progres of the ADCS team:
April 2008
Current state of subsystem
Development of a prototype coil system is currently underway . Currently the team is working on the reqierments for the coils themself, and the magnetometers used to sense the magnetic field around the earth. Amodell of the magnetic field is also under investigation.
Progress since Design Review I
- New team. more regular meeting activity
- access to equipment to make prototype coils have been gained.
- new major design choises made.
Timeframe for completion
We are currently hoping for a functional prototype of the main ADCS systems to be completed by IAC2008.
Design Choices Made
- Using a active magnetic system with 3 magnetic coils controlled by a MCU that gets input form a 3axis magnetometer and a modell of the earths magnetic field.
- magnetic field modell will be stored in a dedicated NV Flash Memory device. Flash memory is cheap, small in size and robust and is ideal for this type of application. Substantial storage capacity can be easily implemented and data storage should not be an issue.
- The coils will be made from Printed Cuircut Board (PCB) material, this is easy to make, easy to test/prototype and easy to install behind the solarpannels.
- ADCS will send attitude data to CDH via the onboard I²C bus. CDH will send the data back to earth as part of a houskeeping packet. ADCS will also be able to recive simple commands from CDH, like start and stop.
Preliminary Figures
- Mass: ~ 170 to 200g
- Dimensions: mainboard: 100cm^3 (10x10x1cm) coils: (10x10x0.1cm) X3coils
- Operating Voltage: 5VDC or 3.3VDC
- Control/Data Interface: Philips I²C
- Power Consumption: 200mW (avrage, more on startup, less after stabilisation)
Discussion
- the prossesing power needs for the system is a bit unsure, hopefully we will be ok with an 8-bit MCU, worst case we have to move the prossesing down to earth
- what kind of secondery sensing sysstem will be used? sun, earth, moon trackers?
March 2008
We are working heavily on the Coils. Hoping to have a working prototype for testing within a couple of weeks. First step is calculating all the variables, like the number of turns, thiknes of wire, material etc. The design of the prototype will be traces printed on a PCB in a rounded square pattern. The idea is that the coils will be fastend directly behind the solarpannels on 3 of the sides. The PCB will be aprox. 0.5 mm thick. The image is just to show the consept, on the real coils there would be more traces and they woul be closer together.
February 2008
Just making the Wiki site ready for more active use, also updated the "system diagram":
January 2008
Thw ADCS team have decided on what system type we are going to go with. It is going to be an activ magnetic system for attitude controll, and an magnetometer system for determination. More info will come when I get the time.
Interface Tables
Inputs edit inputs
- To: Attitude Control - Structure - 3 Magnetic torkers - Mass: ~13g (each, estimation)
- To: Attitude Control - Structure - 3 Magnetic torkers - Mass: unknown
- To: Attitude Control - Power - 3 Magnetic torkers - Power: unknown
- To: Attitude Control - Structure - 3-axis magnetometer - Volume: ~ 10 X 10 X 0.3cm (each, estimation)
- To: Attitude Control - Structure - 3-axis magnetometer - Mass: unknown
- To: Attitude Control - Power - 3-axis magnetometer - Power: unknown
- To: Attitude Control - CDH - Starting command
Outputs edit outputs
- From: Attitude Control - CDH - System status
- From: Attitude Control - CDH - Attitude information
Environments edit environments
- On: Attitude Control - test output - test output description
Team Members
- Sigve Haugsnes (Leader) (Norway) - sigve@hotmail.com
- Xiaowen Shi (China,UK) - physicshome@gmail.com
- Tiffany Frierson (USA)
- David Krejci (Austria) - dakrejci@gmx.at
- Lawrence Tinsley (England, UK)
Older Links
SWOT analysis of uppt vrs magnetics
SEDSAT-2 ADCS Design Notes 20071017
Passive Systems
Passive Magnetic
-Permanent Magnet and hysterisis rods
Gravity gradient boom
-Gravity gradient boom (this is a partial control system, and needs a determination system)
Provides gravity gradient stabilization on small spacecraft
- Accurate to within ±5 deg of nadir
- Used for “short” deployments (< 6m)
- High stiffness compared to tethers
- Bigger and heavier than a tether
There are 5 main boom types to consider:
- STEM Boom
- Elastic Memory Composite (EMC) Boom
- STACER Boom (SSTL)
- Coilable Booms
- Inflatable Boom
questions:
The accuracy seems to me quite high, do you happen to know about the timeframe such accuracy will be achieved? looks like there has a lot of time to pass to achieve that.....?
About the initial orientation, how do you get the boom to start prezising in the right direction? (towars or away from nadir)
Active Systems
Reaction Wheels
Momentum Wheels
Active Magnetic System
Determination: Magnetometers
Control: Magnetic Coils
Detailed documentation: http://www.cubesat.auc.dk/, http://www.ncube.no/
SWOT Analysis
| Strenghts | Weaknesses |
|---|---|
| > Often used by other CubeSats (well tested) > cheap > no moving parts | > interaction with magnetometers > not innovative > not free |
| Opportunities | Threats |
| > None | > None |
Micro propulsion system
see http://en.wikipedia.org/wiki/Pulsed_plasma_thruster for general information
Design Goals for µPPT by ARC Seibersdorf (we would get fly-ready prototypes for SEDSat):
- Impulse bit: 10-20µNs, which would guarantee a pointing accuracy of <1 degree - Spec. impulse: 500-1000 s - Power: 0,5-1,5 W - Weight: < 30g
SWOT Analysis
| Strenghts | Weaknesses |
|---|---|
| > Innovative (I think the first use with CubSat) > Very Accurate (<1°) > Electr. Prop: Can almost never run out of propellant > non-toxic propellant (Teflon) > professional manufactured devices > free | > High electr. Power Consumption (maybe up to 1,5 W per Thruster) > relatively heavy (<30g) -> only 6 thruster configuration to use |
| Opportunities | Threats |
| > Could also be used for Orbit Changes (in limits), with additional thruster(s) > PR for using an innovative new technology for CubeSat | > Not available before Fall 2008 > New Technology (first ones to test) |
Attitude determination systems
magnetometers
accelerometers
Gyroscopes
Sun sensors
Horizon sensors
Documentation: Image:OM6802WCW5R2 071204.pdf
SWOT Analysis
| Strenghts | Weaknesses | |
|---|---|---|
| > Innovative (I think the first use with CubSat) > Accurate > professional manufactured devices > free > light weight, small volume | > Possibly High electr. Power Consumption depending on use > Have not determined precisely how they would be used | > Complicated |
| Opportunities | Threats | |
| > PR for using an innovative new technology for CubeSat | > New Technology (first ones to test in space) >need to test them to determine how we will use them > need to negotiate in order to obtain them without committing to using them. company representative currently out of office |
ADCS design notes are filed in Category:SEDSAT-2 ADCS.
Create new design note: SEDSAT-2 ADCS Design Notes 20080725
