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Power/Solar%20Cells

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Solar arrays are the primary source of power for the satellite. ... Subsystem Power Interface - The solar arrays will need to transfer power from ... – PowerPoint PPT presentation

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Title: Power/Solar%20Cells


1
Power/Solar Cells
  • Brian Shepard
  • Aerospace and Ocean Engineering
  • Virginia Tech
  • brshepa2_at_vt.edu
  • http//www.aoe.vt.edu/hokiesat
  • Voice (540) 2961-1483

2
  • Rate of Pressure Change - All
    components must be capable of surviving a
    pressure change of 2068 Pa/sec (0.0204 atm/s).

3
  • Magnetic Fields - All components
    shall be capable of surviving exposure to
    magnetic field strengths of up to 34 Gauss.

4
  • Construction Materials - All
    materials used in the construction of any
    spacecraft component must be listed on the NASA
    approved materials list (http//map1.msfc.nasa.gov
    /WWW_Root/html/page7.html).

5
  • Fasteners - All fasteners (nuts,
    bolts, rivets, inserts, etc.) on the spacecraft
    must be listed on the NASA approved fasteners
    list (http//lmd.gsfc.nasa.gov/fasteners/), and
    obtained through NASA sources. Nuts and bolts
    must be torqued to specified values and provide
    back out protection.

6
  • Wiring, Cables and Connectors - All
    ground paths in the spacecraft shall be
    consolidated to a single grounding tree (no
    ground loops). Cabling must be securely fastened
    by use of adhesive or approved material (high
    temperature rated) cable ties. TECSTAR
    recommended the use of 24-gauge wire for the
    solar cells. The military specification for this
    wire is the following MIL-W-22759/44. This wire
    is fluoropolymer-insulated with cross-linked
    Ethylene-tetrafluoroethylene copolymer (ETFE).
    The wire is silver coated copper.

7
  • Out-gassing and Venting - In
    space, all materials emit gases that reduce the
    vacuum in closed volumes, coat nearby surfaces
    with condensable material, and increase the
    likelihood of an electrical arc. Plastics,
    polymers, potting compounds, and coatings are
    particularly common sources of out-gassing.
    Out-gassing may be diminished by cyclical
    exposure to heat in a vacuum. Where components
    are positioned within an enclosure, sufficient
    vent openings must be present.

8
Schematic
9
System Parameters
  • Detailed list of specific parameters describing
    the subsystem
  • This might include pressure, voltage, current,
    temperature range etc., but not mass, power or
    volume as these are called out specifically in
    later slides

10
Mass and Volume
  • Subsystem Mass - A solar array
    consist of a Solar Cell (CIC), Silicone, Kapton,
    wiring, and connectors hooked together in a
    series on a given side of the satellite. The
    masses are as follows 1) Solar Cell
    (CIC)- 250 grams 2) Silicone-
    110 grams 3) Kapton-
    25 grams 4) Wiring- 100
    grams 5) Connectors- 50
    grams This gives a combined mass of
    500 grams

11
Mass Volume
12
Subsystem Overview
  • Subsystem requirements
  • Safety requirements
  • Schematic
  • Operations summary
  • Subsystem parameters
  • Mass volume
  • Power
  • Interfaces
  • On-Orbit Operations
  • Ground Operations Summary
  • Analysis
  • Hardware
  • Subsystem Fabrication and Assembly
  • Integration test
  • Remaining work
  • Concerns

13
Subsystem Objective
  • Solar arrays are the primary source of power for
    the satellite. These arrays of solar cells will
    convert radiation from the sun into usable power
    through the photovoltaic process. This subsystem
    is designed to generate power as an entity of the
    power system, which will regulate and control the
    distribution of power to the other systems of the
    satellite.

14
Subsystem Requirements
  • Subsystem Mass - A solar array
    consist of a Solar Cell (CIC), Silicone, Kapton,
    wiring, and connectors hooked together in a
    series on a given side of the satellite. The
    masses are approximately as follows
    1) Solar Cell (CIC)- 250 grams 2)
    Silicone- 110 grams 3)
    Kapton- 25 grams 4)
    Wiring- 100 grams 5)
    Connectors- 50 grams This
    gives a combined mass of 500 grams.

15
  • Subsystem Power Interface - The
    solar arrays will need to transfer power from the
    individual cells of the subsystem to the current
    and voltage regulation circuitry controlling the
    distribution of power to the secondary power
    source (batteries) and the power consuming
    devices throughout the satellite. Wiring will
    facilitate this transfer of power. Each string
    of solar cells will have two wires that will go
    to the power board (V, and GND), which will
    make 26 wires total unless the grounds are tied
    together at the panel connectors rather than all
    being tied inside of the electronics box.

16
  • Subsystem Data Interface - The
    flight computer will monitor the current coming
    off of each of the arrays of solar cells. This
    current reading will be generated by a set of 7
    current sensors that will read the current from
    each of the arrays. This is the only piece of
    data that needs to be transferred to the rest of
    the satellite. There is no data that will be
    read into the subsystem.

17
  • Subsystem Power Consumption - This
    system provides power to the rest of the
    satellite. The solar cells that make up the
    arrays are designed to convert 23 of the suns
    radiation to usable power. The power exiting the
    current sensors going into the rest of the power
    system should be around 94 of the power that
    will be generated by the solar cells. This loss
    of power is due to the voltage drop across the
    reverse current protection diode that is located
    on each line coming to the power regulation
    system from the solar array.

18
  • Component Lifetime - The
    operational lifetime of all components shall be
    no less than four months. The non-operational
    storage lifetime of all components shall be no
    less than 24 months (two years).

19
  • Subsystem Survival and Operational Temperature
    Range - Component Survival
    Temperature(?C) Operating Temperature(?C)
    Kapton -250 to 400
    -250 to 400 Solar Cells -100
    to 150 -40 to 150
    Silicone -115 to 260
    -115 to 260 Connectors -40 to
    80 -40 to 80

20
  • Static Structure Loads - No
    individual component or its structural interface
    shall experience yielding or buckling at 13.5 gs
    in all axes simultaneously. This corresponds to
    a safety factor of FS gt 1.2.

21
  • Dynamic Structure Loads - All
    components and its structural interface must be
    capable of withstanding 40 g shock loads in all
    axes, and 9.1 g RMS random vibration at the
    spectrum shown

22
Power
  • Voc 2.4 V
  • Isc .35 A
  • Diode loss 6.6 V
  • Total Voc 22.2V

23
Interfaces
  • Structural
  • Cells are bonded to substrate using the epoxy CV
    2568.
  • Power
  • 24 gauge wire will be used in string to string
    connection. An Sn-62 (62.5 tin, 36.1 lead,
    1.4 silver) will be soldered to end terminations
    of strings.

24
On-orbit Operations Summary
  • Solar Cells will be taking the sunlight and
    converting it to usable power when the satellite
    is in orbit.

25
Ground Operations Summary
  • Procedures for ground operations
  • When solar cells are hooked to the satellite
    testing is recommended outside in natural
    sunlight between the hours of 11 a.m. and 1 p.m.

26
Analyses
  • Detailed list of the analyses and tools that have
    been used to support the design
  • Solar cells to be set up at USU.
  • Facilities should provide accurate measuring
    devices and assembly tools.

27
Hardware Item 1, etc
  • Description GaInP2/GaAs/Ge high efficiency
    (22.6) cascade solar cell. Included is an
    antireflective coverglass, interconnects for
    connecting cell to cell, and terminations.
  • Heritage Widely used in the Aerospace field.
  • Manufacturer Techstar
  • Part number
  • Properties
  • Mass 3.07 grams
  • Status Available at USU for panel setup and
    layout.

28
Subsystem Fabrication and Assembly
  • Describe how the subsystem is put together,
  • VT, USU, and UW will be assembling solar cell
    strings at USU at a later date.
  • Cells are placed on a specially designed aluminum
    block. This block keeps any stresses off of the
    fragile interconnects and allows for precise
    soldering of cells, interconnects, and
    terminations.
  • Groups of two or three are working together in
    order to assure soldering is satisfactory.
  • The stings of cells are attached to the surface
    skin of the panels using an epoxy that has been
    carefully created while soldering and cleaning
    the cells.

29
Integration Test
  • Initial test can be performed at USU to see if
    the cells are producing the desired current.
  • The solar cells will be powering the satellite
    and therefor will need the other components of
    the satellite to test upon.

30
Remaining Work
  • Sheets of Mylar with printed cell locations and
    70 area for the epoxy will need to be made.
    These are a necessity when assembling the solar
    arrays.
  • 5 days will need to be set aside so that two
    representatives from Virginia Tech can visit USU
    and assemble the individual strings of cells.
  • Once panels have solar cells placed in there
    respective locations they will need to be
    transported back to Virginia Tech.

31
Unresolved Issues
  • The solar cells are extremely delicate and
    expensive. Laying them out onto the panels
    should not be a problem with the expertise
    supervision at USU, but transporting them back
    here may cause cracking in the cells.
  • Once the cells are on the panels if there is any
    more work that needs to be done in or around the
    panels it could potentially harm the cells.
  • If a cell should crack, does VT have the
    facilities to fix or replace a solar cell?
  • Time is running short and there is a lot of work
    to do.
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