Peer Review DINO July 9, 2003
Overview ADCS C&DH COMM PWR Science Software Structures Thermal Systems CM Actions and Review Summary Agenda
Overview • Purpose: For everyone to understand the satellite at a systems level, help other subsystems with their current design, and to determine that interfaces between subsystems are correct. • Action Item forms
ADCS Peer Review Jeff Parker Stephen Stankevich
Requirements • Maintain attitude knowledge to within 2°. • Control s/c in 60° cone for boom deployment. • Maintain control in roll/pitch axis to +/- 10°. • Maintain yaw control per science requirements ~ +/- 10°.
Requirements • System use of less than 2kg and 4W • Weight • Actuators < 1.5kg • Sensors < 1.5kg • More weight allotment possible • Power • Acuators @5V and < 2.5W • Sensors < 1W
Possible Hardware • Sensors • Magnetometer • Sun Sensor • Earth Sensor • Rate Gyro • GPS • Actuator • Torque Rod/Coil • Reaction Wheel
Sensor Trade Studies • Magnetometer • Low cost, low weight, low power • Effective measurement of field to compare with model. • Sun Sensor • Accurate measurement of s/c - sun direction vector in 2 axis. • Earth Sensor • Medium weight and power draw • Very accurate measurement of earth horizon (Yaw Axis). • Rate Gyro • Large weight and expense • Excellent measure of s/c rotation rates.
Sensors • Magnetometer • Honeywell HMC2003 • 100g • 20mA @ 12V • 40μGauss Resolution with +/- 2 Gauss Range • $200 • Sun Sensor • Possible donation from Ithaco Space Systems
Torque Rods • Less complex and lighter than reaction wheels. • Commonly made of cylindrical iron core wrapped with copper wire. • The output is a magnetic dipole moment based on the current passed through the wire, # of turns of wire, and area of the rod. (M=INA) • Dipole moment interacts with Earth’s magnetic field to create the desired torque. (T = MxB) • Need to actuate torque rods as multiple current levels.
Torquer Sizing • Power • I = 150 mA • V = 5V • P = 0.75 W • Length = 0.75” • Diameter = 1.8” • Moment = 1 A*m2 • Mass < 0.3 kg • Power Dissipation < 0.02 W • # Turns ~ 40
Slew Times • Torque Rods will not allow for immediate slew maneuvers of the s/c • The larger the torque rods the quicker the slew times.
Converters • A/D Converters will be needed for the magnetometer and sun sensors • Intersil HI7188 for magnetometer • 8 Channel, 16 Bit • .1mA @ 5V • D/A converter may be necessary for torque rods
C&DH Peer Review
Why RPX_LITE? • Processor: MPC823E • Software compatibility • Supports necessary interfaces • Lightweight, low power
Requirements Imposed by EPS: • 1 RS-232 serial port for subsystems control • Current Sensor readings? • General purpose I/O Lines?
Requirements Imposed by COMM • 1 dedicated RS-232 serial port to TNC • 1 RS-232 serial port to radios
Requirements Imposed by Science • Multiple USB ports for cameras. • I think Science should be responsible for USB hub • Control lines?
Requirements Imposed by ADCS • 16 bit ADC with 4 channels (minimum)
Requirements Imposed by Tip-Mass • 802.11b link between main satellite and tip-mass
Other Requirements? • Structures • -? • Thermal • -?
Interface Board FLIGHT COMPUTER General Purpose I/O Pins USB RESET SMC1 SMC2 I2C PCMCIA TIP-MASS SCIENCE USB HUB RS232 DRIVER RS232 Serial 802.11b MULTIPLEXER CPLD CPLD ADC INTERFACEBOARD ADCS TNC RADIO EPS Multiple Wires COMM Wireless
Power Needs FLIGHT COMPUTER (5V, 1A) General Purpose I/O Pins USB RESET SMC1 SMC2 I2C PCMCIA TIP-MASS RS232 Serial RS232 DRIVER (5V, 7mA) SCIENCE USB HUB (5V min) 802.11b (5V, 1A) MULTIPLEXER (5V) CPLD CPLD (5V, 150mA) ADC INTERFACEBOARD ADCS TNC RADIO EPS Multiple Wires COMM Wireless
Communication System DINO Peer Review July 9, 2003
Power Requirements • Daytime Operation • Receiver: 0.54 W (6 V, 90 mA) always. • TNC: 5.52 W (13.8 V, 400 mA) always. • Transmitter: 8.4 W (6 V, 1.4 A) for approx. 2 minutes, otherwise same as Receiver (0.54 W).
Power Requirements • Nighttime Operation • Receiver: 0.54 W (6 V, 90 mA) always. • TNC: 5.52 W (13.8 V, 400 mA) always. • Transmitter: 8.4 W (6 V, 1.4 A) for approx. 4 seconds, otherwise same as Receiver (0.54 W). • Safe Mode • Same as nighttime.
Calculating Transmission Time • Time needed to send one packet: • 10 bits/byte * 256 bytes/packet 9600 bits/sec = 0.267 sec/packet • Total transmission time (assuming 50 kB per pass during daytime): • 0.267 sec/packet * 50 kB/pass 256 bytes/packet = 52 sec/pass
Transceiver Trade Study: Four Choices • ICOM IC-ID1 1.2 GHz digital • Pros • Allows for small antenna • Built-in TNC with 64-128 kbps baud rate • USB interface • Cons • Expensive • Only one frequency band: need half-duplex comm. • Newly released, untested, unlicensed by FCC • Needs new ground equipment
Transceiver Trade Study • Kenwood TH-D7 dual band 70 cm/ 2 m • Pros • Operates in 2 frequency bands • One third of the cost of the ICOM radio • Compatible ground equipment already set up • Previous experience from other missions • Cons • Max. baud rate of 9.6 kbps. • Requires larger antenna than ICOM • Uses RS-232 interface
Transceiver Trade Study • TEKK SD-5200 synthesized radio and TEKK KS-960 crystal radio • Pros • Can be set to one frequency by the manufacturer: no actual programming required (unlike Kenwood) • Currently being proven in space flight on Stanford’s Quakesat mission • Significantly cheaper than the Kenwood radios • Cons • Only UHF version available: so we would need a different radio for VHF (no longer advantageous)
Design Decision • Two Kenwood TH-D7 radios: one for uplink, the other for downlink. • Reasons • Only choice that allows two distinct channels for uplink and downlink, respectively. • Much better to use same model for both channels • 9.6 kbps should be a sufficient baud rate for the purposes of this mission • No idea when the ICOM 1.2 GHz radio will ever be available for our use.
Antenna Trade Study • Monopole • Pros • Simple design • Does not take up space on the satellite’s surface • Cons • Deployable • Could be very long (~50 cm)
Antenna Trade Study • Patch • Pros • Preferable gain pattern • Non-deployable • Cons • Could occupy a lot of space on nadir surface • More complicated design process • More expensive
Power DINO Peer Review
ADCS COMM Science Structures 12 Volt Line 5 Volt Line 28 Volt Line EPS System C&DH Inhibits Side Panel and Aero Fins FITS Solar Array Batteries
EPS System Voltage Bus Switches Sensors Batteries Charge Controller Microprocessor C&DH
The Ball Systems vs. CU System • The drop dead decision date is tomorrow • Ball: Complicated, Clean, Expensive • CU: Simple, Cheap, Not as good • Ball will advise regardless
Power Distribution and Monitoring • Must distribute and regulate power to all subsystems • +24V (regulated) • +15V (unregulated) • +12V (regulated) • +5V (regulated) • Must be commandable by C&DH • Communication will be through a RS-232 port • The PWR team must provide a commands list to C&DH and Software
Power Distribution and Monitoring • Monitoring • 4 internal temperature monitors for each battery cell • Voltage Monitoring • Battery Stack Voltage • All major voltage buses • Each solar panel • The current draws from each subsystem must be monitored
Power Distribution and Monitoring • The temperature should nominal be 20ºC and can fluctuate ±20ºC. • The latest sample from the monitoring must be able to be stored in memory. • All subsystems must be able to turn on/off.
Structural Concerns • The power system shall weight less than 2.25 kg • The system will use only required components • The system will use the lightest components possible • The power system shall be structurally supported • The batteries will be in a contained box with potting material • The EPS will be in box mounted to a side panel of the satellite • The structure ground will be separate from the electrical ground • The structure will have less than an 1 ohms resistance • The boxes of the structure will be anodize to prevent electrical shorts
Power Safety • Meeting all safety concerns Following NASA’s guidelines for safety The proper connections will be made between systems The system will be properly grounded and tested Inhibits will be used to ensure systems are NOT powered 4 inhibits will be used to separate the power sources switches will be used to turn on and off devices Ball Aerospace will assist us in testing Selection of batteries will be supervised Charge control system will be test with Ball Engineers
Switch Relays • Pros Manages large amounts of power. Used on previous mission. Resets to a open state. Simple circuit design Widely available costing about $2-5 • Cons Has a bulky size, about 2-3 cm tall. Will require a driver to trigger. Slow reaction time, the time is based how fast the coils will charge. A switch can do most of the same functions • Pros Simple setup, Is either on or off. Low power usage, using less than a Mw. Controlled by high and low signals. The cost of switches will between $1-3. • Cons There is no fail safe. May not be able to handle the power going through it.
Lithium Batteries 4 Cell Stack ~3.7V/Cell, 14.8V Stack At least 4 A-hr capacity Cells must be structurally contained Cells from Valence Tech.
Why Lithium-Polymer? • High capacity, small physical size and weight make an unbeatable combination • No liquid electrolyte reduces risk of fire/short • Support from Ball Aerospace • 3.7 V/Cell • Nickel-based cells are too heavy and lack enough capacity
What’s the catch? • Cell stack will need careful charging to make it last for entire mission • Charge controllers will need to have different, optimal charge profiles • Each cell in the stack will need temperature monitoring and shunt diodes • Cells have no integral structure and must be completely supported • No Space Shuttle flight heritage • Battery system must be two-fault tolerant
Science Jessica Pipis