MEMS - based Inertial Navigation Systems onboard Balloons

Giovanni B. Palmerini - Emanuele Medaglia Maria Cristina Oliva - Paolo Montefusco

1st Workshop on Science and Technology through Long Duration Balloons, INAF-Rome, June 3-4, 2008

• Rexus - Bexus is a bilateral German-Swedish cooperation to offer students experiment opportunities using sounding rocket and stratospheric balloon flights from Esrange in Northern Sweden.

• Each flight will carry a payload consisting solely of student experiment.

• An announcement of opportunity was made in November 2007 for flight campaigns in 2008 and 2009.

- Esrange Space Center is located in northern Sweden, 45 km from the town of Kiruna at 67oN, 21oE- Esrange has been the site of many campaigns, involving different types of balloons (more than 500 launches)

BEXUS experiments are lifted to an altitude of 20-35 km for a flight duration of 2-5 hours, depending on total experiment mass (40-100 kg). The balloon has a volume of 12000 m3, and an inflated diameter of 14m

• Flight durationFlight duration: 2-5 hours

• AltitudeAltitude: 25-35 Km

• AccelerationAcceleration: -10g vertically and ±5g horizontally

• Landing velocityLanding velocity: 8 m/s (approx.)

• Thermal environmentThermal environment: down to -90 °C

Our entry for BEXUS payload selection is LOWCOINS, for LOW COst Inertial Navigation System,

an experiment based on the recently available MEMS (Micro Electro Mechanical Systems) technology

GyrosGyros

AccelerometersAccelerometersResolution of

measurementsResolution of

measurementsDouble

integrationDouble

integration

G-loopG-loop

Attitude determination

Attitude determination

State:• Position• Velocity

State:• Position• Velocity

The advantages of MEMS sensors:– Lightweight – Volume and Power minimal requirements– Low cost – Availability– Ruggedness – Reliability

• To learn

• To investigate the feasibility of a MEMS-based INS in a slow dynamic environment

• To estimate errors derived by using COTS components

• To compare results with more precise navigation system (GPS) provided by Bexus (EBASS bay)

• To provide attitude data for the gondola

• To verify the possibility to offer an inexpensive backup in case of main system unavailability

• LOWCOINS experiment is an INS based on a strapdown design

• Inertial measurements are gained by MEMS-based motion sensing devices

• A Microchip PIC processor will collect measurements, compute an approximate solution, provide data to balloon housekeeping for downlinking to ground and store data into a flash memory

• Different sensors (pressure, magnetic) will be added to improve the inertial solution

Magnetic Field Sensor

Pressure Sensor

Attitude Determination

Measurements Reduction

Navigation ComputerDouble integration

Position & Velocity

Temperature Sensor

Gyros

Accelerometers

Magnetic Field Sensor

Pressure Sensor

Attitude Determination

Measurements Reduction

Navigation ComputerDouble integration

Position & Velocity

Temperature Sensor

Gyros

Accelerometers

Gyros

Accelerometers

Magnetic Field Sensor

Pressure Sensor

Attitude Determination

Measurements Reduction

Navigation ComputerDouble integration

Position & Velocity

Temperature Sensor

• Comparison between on-board data (computed with limited resources, i.e. at a limited data rate) and exhaustive on ground processing (complete data set + calibration for on-the-run drift)

• Test of the solution validity with re-alignment (from “official” data performed at various times and mission phases)

• Behavior of the error equation for the INS obtained considering the “official” telemetry data – GPS benchmark - as the true solution and linearizing about (i.e. check the performances of MEMS sensors on different time-scales)

• Acquisition of hands-on experience on sensors’ errors and calibration

Analog Devices Analog Devices ADIS16355ADIS16355

• High precision three-axes inertial sensor• ± 10 g , ± 300 °/s range• 14 bit resolution• Factory calibrated sensitivity, bias and alignement

-40 °C to +85 °C• SPI compatible serial interface

Speake & Co LlanfapleySpeake & Co LlanfapleyFGM-2 FGM-1FGM-2 FGM-1

• High sensitivity 2-axis and 1-axis magnetic field sensors• +5 volt operations• The output is a robust 5 volt rectangular pulse whose period is directly

proportional to the field strength

HoneywellHoneywellASDX015A24RASDX015A24R

• Pressure ranges from 0 to 15 psi • 5.0 Vdc supply• High level output (4.0 Vdc span) • Quantization step of 3 mV • Wide compensated temperature range 0 °C to 85 °C

Microcontroller specification:

Microchip PIC 18F2620Microchip PIC 18F2620• 28 pin microcontroller• Up to 40 MHz clock• SPI & I2C interface• 10 channel 10 bit ADC• 64 Kb program flash memory

Flash memory specification:

ATMEL ATMEL AT45DB161D AT45DB161D • 8 pin SOIC serial flash memory• 16 Mbit• 3 wires SPI interface

ANALOG DEVICES ADIS16355 IMU

FGM-2FGM-1

Magnetic Field Sensors

PICmicrocontroller

RS 232 interface

To PC(Service Mode)

E-LINKTM/TC interface

Voltage RegulatorPressure Sensor

battery pack

Flash Memory 1

SPI bus

Flash Memory 2

Flash Memory 3

Flash Memory 4

3.3 V & 5 V

To components

HEATER

Temperature Sensor

Measurement Resolution (bit)

Memory occupation (bytes per sample)

Sampling Frequency

(Hz)

3 accelerations 14 2 20

3 angular rates 14 2 20

3 magnetic field components 16 2 20

1 temperature 12 2 1

1 pressure 10 2 1

TOTAL 364 bytes/s2912 bps

• 64 Mbit memory allows for up to 6.4 hours of data recording

G. Palmerini, E.Medaglia, P.Montefusco, M.C.Oliva

“MEMS-based Inertial Navigation Systems onboard Balloons”

1st Workshop on Science and Technology through Long Duration Balloons, Rome, June 3-4, 2008

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G. Palmerini, E.Medaglia, P.Montefusco, M.C.Oliva

“MEMS-based Inertial Navigation Systems onboard Balloons”

1st Workshop on Science and Technology through Long Duration Balloons, Rome, June 3-4, 2008

LOWCOINS board

Power and heating portion layout

May 2008

Past BEXUS flights indicate possible problems for COTS components

The combination of undetermined temperature range and flight duration led to consider conservative solutions

Requirement: Electronics should be kept above ~ 0 °C

Step 1 - Theory

• Hypotheses– Worst case external temperature: -90 °C– Isothermal conditions inside the box – Heat transfer by conduction through housing walls – Insulation panels: foam 3 cm thickness with k=0.03 Wm-2K-1

• Findings– 10 W are required to keep a temperature difference of ~ 100 °C

• Experiment insulation box:– 20x20x15 cm

• Foam panels with aluminium skins: – 3 cm thickness– 30 Kg/m3 density

The microprocessor switches the heater on whenever the temperature T0 (middle of the component side) falls below 15°C and turns it off above 20°C.

Test conduced in presence of free convection!

Test in thermal-vacuum chamber needed to define thermal control power requirements

(mA) @ 5V

Analog Devices ADIS16355 57

Pressure sensor - ASDX015A24R 6

Magnetometers - FGM 1 + FGM 2 24

PIC 18F2620 2

ATMEL AT45DB161D 12

ICL 232 10

Contingency 50

TOTAL 150

• Even with a really conservative contingency the power requested by sensors and data processing is limited

• Thermal conditioning will be the driver

• 10 W for thermal control– 1.5 W experiment self heat– 8.5 heater

• 3 LSH20 battery (10.8 V)– @ 1 A discharge current – Effective capacity: 7 Ah– Allows for 7 hours of

operation (heater always on!)

– Reliable (ESA suggested part)

Mass (grams)

Analog Devices ADIS16355 16

Pressure sensor - ASDX015A24R 2

Magnetometers - FGM 1 + FGM 2 5

PIC 18F2620 6

ATMEL AT45DB161D 1

LSH 20 battery pack (3 cell) 300

Housing (aluminium)

2000(20x20x15 cm - 0.2 cm thickness)

Contingency 200

TOTAL 2500

Constrained by the uncertainties on the actual take-off time and on the flight duration:

• Experiment powers up plugging a connector with shorted pins which acts as an outside-located switch

• The unit goes in sleep mode during launch preparation phase

• The unit wakes up and starts recording upon telecommand reception

• The unit goes in sleep mode when memory is full

Northrop Grumman Italia (NGI) kindly agreed to support LOWCOINS activities, providing help in different fields

The company, in a cooperation scheme which allowed for the students to have their stage at NGI, granted:

• Support for mechanical and thermal interface design and manufacture• Advice for electrical & software design• Facilities for experiment hardware building & testing

o Soldering for SMT componentso Thermal chambero Vacuum & thermal-vacuum chambero Vibe testso Static calibrationo Dynamic test campaign

PaoloPaolo: Electronic designOnboard software developmentPower InterfaceMechanical interface Post-processing software for attitude and position determination

Maria CristinaMaria Cristina: Ground station software developer for TM/TC handlingReal-time computationMechanical design CAD design WebmasterPost-processing software for attitude and position determination

EmanueleEmanuele::Thermal interface Thermal and Structural analysis Onboard computationPost-processing software for attitude and position determination

16 Nov 2007 - Announcement of opportunity for BEXUS 7 experiments 7 Jan 2008 - Deadline for applications 28 Jan 2008 - Announcement of short-listed proposals and invitations to workshop 5-6 Mar 2008 - Workshop at ESA-ESTEC in Noordwijk, The Netherlands 15 Mar 2008 - Announcement of final selection of the experiments for BEXUS 6 & 7 flight 21-25 Apr 2008 - Student Training Week and Preliminary Design Review (PDR) at Esrange

in Kiruna, Sweden

• 20 June 2008 - Critical Design Review (CDR) • end Aug 2008 - Delivery of experiments to Esrange for Experiment Acceptance Review

(EAR) • tbd Oct 2008 - BEXUS 7 Launch Campaign at Esrange • 15 Jan 2009 - Submission of Experiment Reports to ESA