Speed of Sound

Team BalloonWorks

Table of Contents

• Mission Goal and Objectives• Science and Technical Backgrounds• Mission Requirements• Payload Design• Payload Development Plan• Project Management• Master Schedule• Risk Management and Contingency

Mission Goal

To measure the speed of sound in Earth’s atmosphere in order to establish a relationship between speed of sound and altitude up to an altitude of 30,480 meters and to consider the effects of atmospheric properties on the speed of sound.

Science Objectives

• Determine the profile of the speed of sound with altitude.• Determine the general profile of temperature

with altitude.• Determine the relationship between

temperature and speed of sound.• Determine the effects of humidity on the speed

of sound.

Technical Objectives

• Obtain accurate and precise measurements for speed of sound.• Obtain accurate and precise measurements for

temperature, pressure, and humidity.• Operate in expected atmospheric conditions.• Obtain data post-flight and be able to analyze

the data retrieved.• Complete all required flight documents such as

the PDR, CDR, and FRR.

Science Background

Earth’s Atmosphere

• Troposphere• Surface to ≈ 12 km• Temperature decreases

• Stratosphere• ≈ 20 to 50 km• Temperature increases

• Mesosphere• Thermosphere• Exosphere

Expected Outcomes

• Speed of sound is primarily dependent on temperature.• Speed of sound will decrease until the balloon

reaches the tropopause.• Speed of sound remain constant in the

tropopause.• Speed of sound will increase in the stratosphere.• Humidity is expected to play a minor role in

determining the speed of sound when compared to temperature changes.

Technical Background

Temperature Sensor

• Required Range: -70 ˚C to 38 ˚C• BalloonSat’s AD780 (U5)• -55 ˚C to 120 ˚C

• Resistive Temperature Detector (RTD)• -200 ˚C to 650 ˚C

• Thermocouples• -270 ˚C to 2000 ˚C

• Thermistor• -80 ˚C to 120 ˚C

Pressure and RH Sensors

• Required Range: 10 hPa to 1020 hPa• ICS1210 Model• Sensor interfacing exercise• Has already been tested• Piezoresistive-type sensor

• Required Range: 0 %RH to 100%RH• Resistive RH Sensor• -40 °C to 100 °C• 0 %RH to 100 %RH

• Capacitive RH Sensor• -80 °C to 150 °C• 0 %RH to 100 %RH

Speed of Sound Apparatus

• 20 to 30 measurements on the ascent will be necessary to reproduce profile• If 25 measurements are taken

during ascent:• 4 min between each

measurement• Based on a 305 meters/min

ascent rate and a 100 min ascent time

• Payload will still continue to take measurements during descent

Mission Requirements

• Team BalloonWorks and the payload shall comply with all LaACES requirements.• The payload shall measure the speed of sound in

ambient atmospheric conditions in order to construct a profile of the speed of sound versus altitude.• The payload shall measure temperature,

pressure and humidity to verify the data gathered on the speed of sound.• Team BalloonWorks shall retrieve and analyze

data post flight.

Payload Design

Principle of Operation

• The main objective of the payload will be to measure the speed of sound during the flight. • In order to obtain an accurate speed of sound

profile with respect to altitude, temperature, pressure, and relative humidity sensors will operate in the same environment as the speed of sound apparatus.

System Design

Sensors• Temperature: 44000 Series Thermistor

• -80 °C to 120 °C• ± 0.2 °C

• Pressure: ICS1210

• 0 hPa to 6900 hPa• -40 °C to 125 °C• ± 1.0 %

• RH: P-14 Rapid Capacitive RH Sensor

• 0 %RH to 100 %RH• -80 °C to 150 °C• ± 1.5 %

• Measurement Specialties, Inc. (2003). IC Sensors Product Databook, p. 18. Retrieved from http://nees.berkeley.edu/Facilities/pdf/Instrumentation/ic_sensors_catalog.pdf

Sensor Interfacing• Temperature Sensor:

• Pressure Sensor:

Sensor Interfacing• RH Sensor:

Control Electronics

Power Supply

Power Budget

Component Voltage (V)Current (mA)

Power (mW)

Charge (mA-hours)

Energy (mW-hours)

RH Sensor 12 ≈2.0 ≈24 ≈8 ≈96

Thermistor 12 0.015 0.18 0.06 0.72

Pressure Sensor

12 2.0 24 896

Speaker 1.5 35 52.5 140 210

Field Recorder

3 ≈100 ≈300 ≈400≈1200

BalloonSat 12 ≈80 ≈960 ≈320 ≈3840

Total Needed

12 219.015 1360.68 876.065442.72

Power Budget

Software Design• Data Format and Storage• BASIC Stamp Editor Version 2.5 • RTC• Time interval between measurements• Time stamp is formatted as a hexadecimal number • Digital Sensor Data• Counter• Data Point requires 1 byte per unit data: Temperature, Pressure,

RH, Hour, Minute, Second• On Board storage must be greater than 540 bytes• Speed of Sound Apparatus

Initialize all hardware pins and declare all

variables

Initiate EEPROM address to 0

Write to EEPROM in increments of EEPROM

Address

Write to EEPROM in increments of EEPROM

Address

End Program

Get RTC hour, minute, second values

Get ADC channel 0, 1, and 2 values

Is EEPOM ADDR>=max

EEPROM Address

Thermal Design

• -70 °C to 38 °C• Box built from LaACES foam material• Should keep closed compartment at T > -10 °C• Heat by electronics will help

• Open compartment will remain at ambient conditions

Mechanical Design

• External Design• Rectangular: 25 cm by 10 cm by 10 cm• 0.636 cm thick• 17 cm separation for strings• Plastic mesh covering 20% of bottom face area to

allow open compartment

Mechanical Design

• Internal Design• Open Compartment• T, RH, Speaker, Recorder• Reflecting Arc

• Closed Compartment• Pressure Sensor• Sensors’ Conditioning Circuitry• BalloonSat• Power Supply

Weight Budget

Component Weight Budget Estimate (g)

Box 100

BalloonSat 65

Sensors, Speaker and Conditioning Circuitry

≈40

Recorder 180

Power Supply 115

Total 500

Payload Development Plan

• Electrical Design Development • Software Design Development• Mechanical Design Development• Mission Development

Project Management

Team Responsibility and contact information

• Team Contract• Configuration Management Plan • Interface Control

WBS

Project Timeline and Milestones

Risk ManagementRisk Event Likelihood Impact Detection

DifficultyWhen

Loss of payload 3 5 5 Post-Flight

Component Failure 4 4 2 During Flight/Testing

Incorrect code 2 4 1 CalibrationPart unavailability 3 3 2 Pre-Flight

Internal deadlines not met

4 4 3 Pre-Flight

Team member refusing to cooperate

2 4 1 Pre-Flight

Team member quits

1 4 1 Pre-Flight

Unmet external deadlines

2 5 3 Pre-Flight

Over budget 2 2 4 Pre-FlightIncrease in price of components

2 2 3 Pre-Flight

Risk ManagementProgram coding loss

1 4 2 Calibration

Memory deficiency

4 4 3 Flight

Unexpected environmental conditions

2 3 1 Flight

Battery malfunction

4 4 2 Flight

Payload breaks during construction

3 4 3 Pre-Flight

Data storage exceeds maximum memory space

4 4 3 Flight

Payload walls fall off during flight

1 5 4 Flight