STK provides angular data for each face of the cubic satellite
Angular data are converted to power W/m2
Power data are converted to energy data J/m2
10 Data from STK 11 Data from STK The Zenith Nadir Leading and Trailing faces have approximately the same exposure to the sun. The antenna will be located on the Nadir face so it reasonably follows that the solar panels be placed on the Zenith face directly opposite the antenna. A circular orbit with an altitude of 500 km and inclination of 45 was chosen because with the options available this orbit allows the solar panels to receive the most sunlight. 12 Thermal Management 13 Thermal Management
To perform thermal analysis of the satellite and ensure a suitable operating environment for the payload.
Thermal Desktop software
Low earth orbit environment
Temperature requirements for internal components
14 External Environment
In LEO the satellite will be heated by
Earths IR emittance
The total heat absorbed by the satellite will not remain
constant. Fluctuations occur due to
Entering/exiting Earths shadow
Varying surface conditions on Earth
15 Satellite Interior
The interior environment of the satellite must be kept at
a proper temperature range. Most electronic equipment
onboard must operate in a surrounding temperature
range of 0 to 50 degrees Celsius.
Factors to consider for the internal energy balance
Fluctuating external heat rates
Heat released by electronic equipment
-Low level baseline operation
-High level during periodic transmission
Thermophysical properties of structural material
16 Cooling/Heating Methods
Radiators Do not require energy. Release heat without re-entry (thermal diode)
Thermoelectric Coolers/Heaters Require energy. Can absorb/emit heat by reversing polarity
Mechanical cooling Expander compressor or heat exchanger. Takes up space and weight.
Resistive Heating Requires energy but elements are compact in size.
Heat Pipes Passive
17 Thermal Desktop
Develop a model for the satellite module.
Use the orbital information from STK to determine thermal environment of the satellite.
In process of creating models.
18 Thermal Desktop Continued Example of absorbed flux from sun earths albedo and IR emittance. 19 Materials and Structures 20 Structural Requirements
The satellite must have ability to
Withstand launch loads
Provide desired rigidity
Protect sensitive payload components from extreme temperatures.
21 Material Selection Currently evaluating two different materials
Ti6Al4V Titanium alloy VS. Aluminum Alloy( 7075-T651)
Although Titanium is 60 heavier than Aluminum it is over twice as strong.
Possibility of having titanium based honey comb exterior joined by a smaller portion of aluminum interior.
22 Weight Comparison 23 Honeycomb Layer
Planned use of Honeycomb design
Uses the least amount of material to create a lattice of cells within a given volume
24 Preliminary Sandwich Structure Layered design that takes advantage of each materials different thermal properties. 25 Energy System 26 Goal Requirements
Collect Solar Energy and store it to power the RF amplifiers
Collect power from 1m2 solar panel.
Store energy in a medium that can withstand high drain current.
Energy storage mediums must have a wide operating temperature range.
27 DC to RF Converter Options
Tube magnetron _at_ 5.8 GHz
Can output 650W with 65 efficiency
Heavier than solid state options
(1.1kg vs .6g)
Produces more heat than solid state converters
Requires a high voltage power supply
to excite the electrons.
GaN HEMT solid state converters _at_ 5.8 GHz
Fujitsu converter can output 320W theoretically
Cree converter can output 35W commercially
Lightweight (.6 g) and extremely small size
relative to the magnetron.
28 Energy Storage Li-ion
For storing energy from the photovoltaic cells Li-ion and Li-S batteries are being considered.
Li-ion batteries have an energy density of 110 Wh/kg.
Saft MPS space series batteries that are already thermally insulated and autonomously heated.
Have a wide operating temperature range ( -5o F to 140o F for charging and -40o F to 140o F in operation)
Built in over current and charging circuits into the module.
17 Ah capacity per battery _at_ 28V.
29 Energy Storage - Continued
Lithium sulphur batteries are being considered for their higher energy density (350 Wh/kg vs the 110Wh/kg for Li-Ion)
Experimental expensive technology.
No history of satellite use.
High energy density capacitor used for powering the Solid state microwave converters when transmitting a signal.
Ultracapacitors can handle 20A continuous current.
Will be used in conjunction with the Li-ion batteries to power the GaN HEMT amplifiers at their maximum capacity
30 Current Concept
Maximum Power Point Tracker monitors the voltage and current of the Solar Panel and tracks the peak point on the power curve.
Battery Management System tracks the charge rate voltage and current.
31 Antenna and Retrodirective Control 32 Retrodirective Beam Control
The implementation of retrodirective beam control is critical to accurate beam pointing as well as the overall safety of the system.
The key objective is to have the power beam of the solar power satellites transmitter pointed only in the direction of a received pilot beam which provides a phase reference
Retrodirective beam control ensures that microwave power transmission is both safe and insusceptible to accidental misalignment.
33 Proposed Retrodirectivity Method
The 2.9 GHz incoming pilot signal is received at a Frequency of 1 and Phase f1
To conjugate the received signal is next mixed with a reference source of Frequency 21 and Phase fref
The conjugated signal is then mixed itself to produce a signal with Frequency 21 and Phase -2f1
After conjugated and doubled the signal is transmitted from a different transmitting subarray
The complete phased array transmits a 5.8GHz beam in the direction of the incoming pilot signal
34 Proposed Phased Array Antenna Concept
Linear Microstrip Patch Phased Array Antenna
The Microstrip Patch Antenna will operate at a Frequency of 5.8 GHz and will have an Input Impedance of 50
The Antennas design features a 4x4 Phased Array consisting of 15 Transmitting Elements and 1 nested Receiving Element each spaced 0.5 apart
The 4 subarrays are expected to be at different phases prior to power transmission
5.8 GHz 4x4 Linear Microstrip Patch Phased Array with nested 2.9 GHz Receiving Element 35 Antenna and Transmitter Interface
Facilitates electronic beam steering
Power amplifier and phase shifter are placed behind each transmitting element
Microwave filters are required to countervail amplifier-spawned noise
RF power is split to feed fed to each antenna subarray
Negligible power loss may occur during energy feed
Loss expected from phase shifter
36 Advantages of Proposals
Microstrip Patch Antenna
Low cost to manufacture
Light weight and low profile
Supports both Linear and Circular Polarization
Conjugates pilot signal directly at RF
Reduction in the number of electronics per antenna subarray
Less power consumption
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