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DEMOSAT MISSION TEAM LITTLE STAR

Tully Baetz

Raymond Dao

Caleb Ogg

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Mission StatementThe DemoSat Project shall test several components of

the ALL-STAR mission in order to reduce risks in those areas.

Mission Objectives

• Compare the performance of epoxied and traditionally soldered solar cells by measuring output current and voltage.

• To test the ALL-STAR Star Tracker.

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Mission Success Criteria• Solar Cells

• Success is defined as measuring identical IV curves for both strings in identical pairs. That is, the epoxied solar cell measurements are in agreement and likewise for the soldered cells.

• Star Tracker• Success is defined as detection of multiple stars in a single image.

This is required if Star Tracker is to have a chance of identifying star arrangements.

• Success is also dependent on functionality and undamaged condition of Star Tracker after payload is recovered.

• Payload Recovery• Payload must be recovered for data analysis

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Structure Overview• Foam Core Exterior• 1 cm thick on each wall• 1/8 in thick acrylic skeleton plates in interior

• Helps component interface and mounting• Mounting points and holes for components/stand-offs

• Aids structural integrity • Provides strength for flight tube assembly

• Flight String Assembly• ¼ in inner diameter tube for flight string• Washers and Metal Clips used for security of assembly

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Final Acrylic Frame• One edge panel removed

• Ease of access• Mass constraints

• Attachment of components interface• Holes added for stand-offs• Baffle Created and interfaced

• Tooth and Grove design• Added Structural Integrity

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Assembled View (Labeled)

Photodiode 1Photodiode 2

Photodiode 6

Solar Cells

MOSFET PCB

Star Tracker Camera/baffleFlight String

DE2 PCB

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Baffle

Payload Attachment• Washers will be used as the

anti-abrasion brushings• Washers will be attached to

the acrylic frame.• The flight string will pass

through a ¼ inch plastic tube• Metal wire will be run

through the tube to limit rotation of the satellite.

• Metal wiring will also help prevent flight string line from slipping through payload.

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Overview of Electrical System• Arduino based system

• 2 types of solar panels• PCB• Photodiode array• Star Tracker

• Star Tracker• FPGA• Camera and baffle

• Heating System

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Solar Panels• Two strings, one soldered and one epoxied• Data read and converted by PCB• 10V, 40mA max output

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PCB and Arduino• PCB of own design, based off of DANDE’s solar circuit• Arduino Uno, with microSD shield for storage

• Provides us with all the analog and digital pins needed to control the whole system

• Each component powered by one 9V battery

Data Flow Structure

PCB

Data Storage• We calculated the data storage needed for the IV curves

to be . .4644 GB or 464.4 MB We will use a microSD card attached to the Arduino to store all our data.

• All temperature and relativity humidity data will be Stored on the HOBO Data logger

• Current mission ops require flying an additional temperature sensor to determine altitude for the star tracker. However the reordered data for this sensor will not be logged since it is redundant.

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Photodiode Array

• 6 Photodiodes• Attached to analog in• 3.3V power• Data stored as a 6 bit

integer to display position of sun

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Star Tracker• Consists of DE2-115 FPGA and camera board

• Star tracking software provided by ALLSTAR loaded on DE2• Camera board connected to and powered by DE2• 12V power provided to DE2

• Receives one line from Arduino to allow control of when pictures are taken• Will start taking photos at 1 hour after launch

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Star Tracker Positioning• The Star Tracker must be positioned to maximize star

viewing potential• Must not be obscured by balloon or pointed at Earth.• Calculated ideal Star Tracker tilt based on balloon

dimensions and Star Tracker’s field of view.• Maximum Balloon Diameter: 90 ft• Distance Between Balloon and Payload: 50 ft • Star Tracker’s Max Field of View: 25°

• Star Tracker will be tilted at a 37-41° angle above the horizontal.

• This provides a 10-15° “buffer” on the balloon side for the minor variations in payload tilt.

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Heating• Circuit consisting of 6 batteries and 6 heating resistors• Placed centrally to evenly distribute heat

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Software Overview• The software has four main functions.

• It reads the data from the analog ambient light sensors• It reads the data from the ADC while varying the value of the DAC• It stores all read data on the microSD card for processing later • At a predetermined altitude the software turns on the star tracker

camera for picture taking

• Since speed is of the essence for generating a lot of IV curves during flight the software has been designed and built to take a data point once every 2 milliseconds.

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Quality Assurance• During development, we put the payload through a series of tests

to better prepare for conditions that will be encountered on launch day.

• Drop Test – Structural test simulating landing• Whip Test - Structural test for strength flight string

attachment• Flat Sat Testing – Electronics test for individual component

functionality.

• Day in the Life Test – Electronics test for long term success of all component functionality

• Cold Test – Systems test simulating cold environment

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Quality Standards• Quality Standards

• Secure Flight String Assembly(Whip Test)• Structural Integrity(Drop Test)

• No damage to inner components

• Thermal Heating(Cold Test)• Maintain temperature above 0˚C

• Component Functionality and Interface (Flat Sat Testing)• Everything works

• Day in The Life Testing• Electronics work for estimated duration of flight

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Flight and After Recovery• Payload rose to altitude of 89,000 feet.• Program crashed ~30 seconds into flight.

• Faulty and Loose wiring caused the crash

• Recovery• Structure performed extremely well

• No Cracks discovered in plastic skeleton• Only a few exterior abrasions and cuts from landing

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Organizational ChartEmily Proano

Project Manager

Sean RiveraLead Systems Engineer

Tully BaetzStructures Lead

Caleb OggSystems Lead

Raymond DaoStructures

Vignesh Muralidharan

Electrical Lead

Edward LoweElectrical

Eric JacobsonStructures

William WhiteneckSystems

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Appendix• Slides Included

• Testing Details• Whip Test• Drop Test• Star Tracker Test• Photo Diode Test• Solar Cell Test• Flat Sat Testing• Day in the Life Testing• Cold Test

• Trigonometric Analysis• Memory Calculation

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Whip TestTopic Details

PurposeDetermines whether or not the current structure can hold on to the flight string and not detach from it. The flight string was attached using knots, ¼ inch diameter tube, and pins.

Test DetailsSpin structure (by flight string) at high speeds to simulate forces during flight

Limitations Components were simulated with masses and locations

ResultsFlight String Assembly held on for the duration of the test. Test showed that the assembly was strong enough to hold the weight.

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Drop Test Topic Details

Purpose Determines whether or not the current structural design can withstand impact with ground while keeping components functional and undamaged.

Test Details Drop payload from 6 meters onto concrete surface to simulate worst case landing.

Limitations Payload landed on bottom, which is not guaranteed during real landing.

Mock Ups were used for the components

Results Foam core and insulation remained intact. Acrylic frame was shattered into only a few places

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Drop Test Pictures

Exterior after Drop Test Interior After Drop Test

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Star Tracker Testing• Not tested with DE2 because ALLSTAR is still working on

star tracker• Arduino system emits +5volt at 1 hour after launch on the

attached pin to tell DE2 to start taking photos• Tested with multi-meter

• This means our project has been tested to meet ALLSTAR’s requirements

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Photodiode Test• Photodiodes were taken into direct sunlight• Slowly moved from direct sunlight to only receiving

ambient light• Once in ambient light the distinguishing constant was

changed accordingly• A baffle and grate will still be needed to limit exposure to

direct sunlight

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Solar Panel Test• Solar Panels emit voltage + current when hit with sunlight• Tested using multi-meter• Already tested previously to be operational by ALLSTAR

team• Load is varied by the Arduino and works

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Flat Sat Testing• Flat Sat Testing has found the photodiodes to work

• Photodiodes have been calibrated to detect sunlight no longer detect ambient light

• Flat Sat Testing has gotten the PCB to output the correct voltage and current• 30 minute data trial test showed all systems to be operational and

the data was checked to be correct

• Flat Sat Testing has shown the microSD card can store data• All data was stored correctly and did not exceed memory limits

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Flat Sat Test• Sample data is shown below showing data is recorded for

3.3 hours, until which the old battery died. • This was replaced by new batteries

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Flat Sat Testing Details• Flat Sat testing included all components required for

measuring solar cells:• PCB Board + Arduino + Internal Power Source + SD Card shield.

Flat Sat testing did NOT include any components related to Star Tracker. DEMOSAT has tested that we can provide the Star Tracker with a +5 volt signal and power it with our linear regulator. We were not provided with the Star Tracker in time to incorporate it into flat sat testing.

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Day in the Life Testing• Flat Sat was operated for 4 hours to make sure the

program didn’t crash or components didn’t fail after being continuously operated.

• Day in the life Test passed while powered externally.• Day in the life failed while powered internally.

• Corrected, was due to insufficient power.

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Cold TestTopic Details

PurposeTo simulate the low temperature conditions the payload will experience during flight.

Test Details-20 lbs. of dry ice placed in a 6 ft2 thermally isolated box.-Climate will be simulated to -65˚ C

Success Criteria

The inside of the payload must stay above 0 MC.

Limitations Components were simulated with masses and locations

Results Results will be shown after cold test

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Specifications for Cold Test• All relevant electrical components functioning and placed

inside payload for Cold Test• Baffle Hole and Baffle were cut and created.• Foam Insulation was cut precisely to seal vertices. • Flight String Assembly accounted for

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Cold Test Minimum Interior Temperature reached: -45 MC

Total Time Elapsed: 5 hours

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Results of Cold Test • Temperature was at zero only after three hours

• Expected flight time in high altitude is far below 3 hr.• Showed that enough heat was on board

• The external temperature sensor was placed at the very top of the box, thus having a lower than actual reading• Internal Temperature drops below External Temperature• External Temperature Readings were only at -5 MC

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Trigonometric Analysis

13.72 m

13.72 m

15.24 m

Arc of View:

25°

Horizon

64°

10-15°

24-29°

Memory Calculation • Each port on the ADC has 12 bit accuracy in the returned

data. • 12 bit data, if converted to an integer, can give numbers

up to 4 digits large. • Each digit will the be converted into a char to be saved by

the program in a text file. • Therefore, every millisecond we will receive at most 32

different chars since there are 8 ports with a possibility of 4 digit numbers from all of them.

Memory Calculation• The photodiodes output will be taken as at most a 2 digit

number since there are only 6 of them and they are treated as single bits• (ie. return 1 if facing the sun, otherwise return 0)

• Therefore the maximum amount of digits created in a millisecond is 34

• Each data point shall be broke up with a comma, and a millisecond will be broken up with apostrophe

• With identifiers, which allow for easier data processing, the total comes to 43 digits created every millisecond

• Therefore there are 43000 digits of data created every second

Memory Calculation

43000 digits/second = 154800000 digits/hour.

154800000 digits/hour = 464400000 digits over the course of the flight.

• Each digit of data is a byte in size • Therefore, we generate 464400000 bytes of data or .4644

GB of data total.