BUZZSAT CONTROL SYSTEM

Control System Architecture

Microcontroller Options -UT80CRH196KDS Rad-Hard -Microchip 18F452

UT80CRH196KDS Advantages: Radiation Hardened. Radiation Hardened.Disadvantages: No internal PROM No internal PROM Fewer built in features than the Microchip Fewer built in features than the Microchip No previous Instruction Set Experience No previous Instruction Set Experience Would have to find a hardware programmer Would have to find a hardware programmer The devices are still on backorder The devices are still on backorder

Advantages: Many built-in features like I 2 C Many built-in features like I 2 C Simple to program using Prof. Peatman’s “QuikBug” Simple to program using Prof. Peatman’s “QuikBug” Instruction Set Experience (ECE 4175) Instruction Set Experience (ECE 4175)Disadvantages Not radiation hardened. Not radiation hardened. Microchip 18F452

Which one? Simple wiring interface, so why not just make either one work. Work on the PIC with experience we already have and simple programming, and get rad-hard processor to work when we actually get a flight slot.

IR Sensors  Introduction General information General information Approach Approach  Proposed functionality and design  Challenges and constraints  Concluding remark Decision on this plan Decision on this plan Other option Other option

IR Sensors--Introduction Taking into account the Inverse Square Law, at 400km from earth, IR sensors will distinguish the sun from the earth using their different wavelength region of maximum intensity. Spectrum of the earth. The earth emits most of its radiation in a wavelength band between 0.5 and 30.0 micrometers (µm). Spectrum of the sun. The sun emits most of its radiation in a wavelength band between 0.1 and 4.0 micrometers (µm).

IR Sensors--Functionality & Design Using IR sensors that will check for radiation at ~10 micron, the electromagnetic torque device will rotate the satellite so that the transmission link will be pointed towards earth. IR ( ) km 6371 km 43.3°

Wavelength IR detectors that detect at 10 microns are extremely rare. IR detectors that detect at 10 microns are extremely rare. MgCdTe (Mercury CadiumTelluride) A very fragile and difficult to process material, yet the only one to meet the wavelength requirement. A very fragile and difficult to process material, yet the only one to meet the wavelength requirement. RAD hard Usually used in military applications. Usually used in military applications.Price Ranging in the thousands Ranging in the thousands IR Sensors--Challenges & Complications

IR Sensors--Concluding Remarks Contacts GTRI for regular IR sensors. GTRI for regular IR sensors. Judson Technologies for “special” IR sensors. Judson Technologies for “special” IR sensors.Decision The cost of IR sensors is beyond the current budget. The cost of IR sensors is beyond the current budget. Other option Permanent magnetic coils provided that satellite travels in inclined orbit, and not a polar orbit. Permanent magnetic coils provided that satellite travels in inclined orbit, and not a polar orbit.

Direction Control by Electromagnets Deviations from rotational orientation: Atmospheric drag (dominant for LEO) Atmospheric drag (dominant for LEO) Solar pressure on antennas Solar pressure on antennas Spacecraft body Spacecraft body Reason for direction control: Antennas need to point correctly at earth Antennas need to point correctly at earth

Direction Control by Electromagnets

Magnetic moment = NiA N=# of turns N=# of turns i = current i = current A=cross-sectional area A=cross-sectional area Torque = (mag. moment) X (external field)

Direction Control by Electromagnets Things to consider: Material for coil Material for coil Variation of earth’s mag. field vs position Variation of earth’s mag. field vs position Magnetometer Magnetometer

Shielding Options Radiation- Radiation is a real concern for Buzzsat electronics in space. It can cause irreversible damage to the spacecraft electronics without shielding. It can cause irreversible damage to the spacecraft electronics without shielding. It can cause sudden latch up in digital circuits, that can cause improper logical operation. It can cause sudden latch up in digital circuits, that can cause improper logical operation. Shielding Materials Using a “sandwiching” technique where the circuits are covered on both sides with a shielding material. Using a “sandwiching” technique where the circuits are covered on both sides with a shielding material. Lead is a possibility, and was proven to work with PCSAT. Lead is a possibility, and was proven to work with PCSAT. With a little bit of an investment, Rich Katz at NASA Goddard recommends that we use a Tungsten/Copper alloy. With a little bit of an investment, Rich Katz at NASA Goddard recommends that we use a Tungsten/Copper alloy. This shield is highly effective. This shield is highly effective.

Shielding Options

Schedule

Material/Facility Needs Circuit Components These should be readily available from the Van Leer supply room. These should be readily available from the Van Leer supply room. Clean Room While not necessarily needed right now, some of our more specialized components require a Class 10,000 to 100,000 humidity controlled clean room. While not necessarily needed right now, some of our more specialized components require a Class 10,000 to 100,000 humidity controlled clean room. PCB fabrication Although there are facilities at the ECE building, it may be better to use a commercial option, being that the turnaround time is just a couple days. Although there are facilities at the ECE building, it may be better to use a commercial option, being that the turnaround time is just a couple days.

Budgetary Breakdown Microcontroller- We have samples of both the PIC and the UTMC microcontroller. Printed Circuit Board- this is from $50 to $100. ACS- If we are not using $2000 IR detectors, then the most of the materials should be free. Transmitter- The power switching device should be free radiation hardened or not. Receiver- Most of these devices can be sampled for free. System Integration and Test- There is really no cost here other then time. Shielding- Rich Katz at NASA Goddard recommends using a Tungsten/Copper Alloy. This may cost around $100 dollars as well.

References