performances, lifetime data and giove-b related

1www.spectratime.com ®SpectraTime

Space Passive Hydrogen Maser

Performances, lifetime data and GIOVE-B related telemetries

IGNSS 2009

Daniel Boving, Fabien Droz, Pierre Mosset, Qinghua Wang,

Pascal Rochat

SpectraTime

Neuchâtel, Switerland

Marco Belloni, Marina Gioia

Selex Galileo

Milan, Italy

Alberto Resti, Pierre Waller

European Space Agency

Nordwijk, Netherlands


Presentation Outline

• Introduction• Development & Qualification Activities of PHM• PHM Activities for the In Orbit Validation• Lifetime Facilities• Correlation between Ground and Orbit Data• Lifetime Ground Data• Conclusions

3

Introduction 1Introduction 1

• Global Navigation Satellite System Jointed by EC & ESA• Constellation

– 30 satellites – 3 circular MEOs– Altitude 23’222km– Inclination 56o

• Mission life time of 12 years• Clock model update < 10’000 sec.• Metric/sub-metric navigation accuracy

www.spectratime.com ®SpectraTime

Galileo program description

4


• Two baseline clock technologies– Rubidium Atomic Frequency Standard (RAFS)– Passive Hydrogen Maser (PHM)


Present Onboard Clocks for Galileo

5


• Two experimental satellites flying– GIOVE-A Two RAFS unit (Dec. ’05)– GIOVE-B One PHM (PFM) unit and two RAFS units (April ’08)

• Main targets of the satellites– Frequency Filling– Test of critical technologies (like clocks)– Experimentation on Galileo Signals– Characterisation of MEO environment

• Mission lifetime of 3 years


In-progress GIOVE-A and -B

6



Why use PHM for navigation?• 1ns equals 30cm of precision• Minimum 8hrs of operation without relying on ground station

How many seconds the clock keeps 1ns

0.1

1

10

100

100 1'000 10'000 100'000 1'000'000

seconds

Mas

s of

the

cloc

k in

kg

USO

RAFS

Mini PHM

PHM

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Development & Qualification Activities of PHM 1

• First development activity tailored to navigation applications kicked off in 2000– Predevelopment led by Observatory of Neuchatel with Selex Galileo as subco for EP– Development achieved in 2003 with a prototype ready for testing

• Industrialisation development kicked off in January 2003– Industrial Consortium led by Selex Galileo in charge of the instrument integration and EP

design – SpectraTime responsible for redesign and manufacturing the PP

• Overall structure and design reviewedto increase compactness / robustness

• Manufacturing and qualification of 4 QMs, two of them are under test for lifetime estimation


PHM Development Milestones and Industrialisation

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Development & Qualification Activities of PHM 2

• Exemple of sub-assembly characterisation (Microwave Cavity sub-assembly) with SpectraTime specific measurement system

At nominal operational condition,– Gain: 3.6 dB– Line width: 2Hz @ 1.420GHz


PHM Characterisation

Cavity Response

0.75

0.85

0.95

1.05

1.15

744 746 748 750 752 754 756 758

Frequency 1'420'405 kHz + …Hz

Am

plitu

de [

V]

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PHM Activities for the In Orbit Validation

• Performances improvement:– Better control on processes and adjustments led to better stability


The first 4 IOV satellites vs. GIOVE

Allan Deviation in GSTB-V2 Production

1.E-15

1.E-14

1.E-13

1.E-12

10.00 100.00 1'000.00 10'000.00

Averanging Time in seconds

EQM

PFM

FS

Allan Deviation in IOV-Production

1.E-15

1.E-14

1.E-13

1.E-12

10 100 1'000 10'000 100'000Averanging Time in seconds

EQM

PFM

FM2

FM3

FM4

FM5

FM6

FM7

FM8

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Lifetime facilities 1


Lifetime facilities

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• The two identical units consist of:– the vacuum chamber with pumping system and gauge– the base-plate connected with cooling system– the frequency stability measurement system (2 Picotime)– the data acquisition system for additional TM (temperatures, pressure, …) – the PC with automatic control and acquisition system– the power supply and UPS

• The common elements are:– the QM lifetime EGSE, i.e. the man-machine-interface support including serial

telecommand (TC) generation and main serial TM recording for both units– the reference frequency system; H-Maser (EFOS C) with GPS monitoring and the

frequency distribution unit (common for all the SpT facilities)


Lifetime facilities

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Lifetime facilitiesIn addition to frequency stability performances, more than 20 parameters are

measured. The most relevant are:

– Atomic signal amplitude

– Cavity Varactor voltage

– Hydrogen supply pressure and temperature as H2 consumption indicator

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0 500 1000 1500 2000 2500 3000 3500 4000 4500-10

0

10

20

30

40

50

60

70

Days

Cav

ity F

requ

ency

Shift

(kHz)

QM1 extrapolationQM2 extrapolationGiove-B extrapolation

Correlation between Ground and Orbit Data 1


Lifetime preliminary measurementsMicrowave Cavity Ageing extrapolation– Image of the microwave magnetron frequency stabilization over time – Relevant due to the Automatic Cavity Tuning (ACT) function

14

0 500 1000 1500 2000 2500 3000 3500 4000

35

40

45

50

Days

Hyd

roge

n Storage

Tan

k Te

mpe

rature (°

C)

QM1 extrapolationQM2 extrapolationGiove-B extrapolation



Lifetime preliminary measurementsHydrogen Supply Tank Temperature extrapolation– Use of hydride for small tank volume and low pressure operation (<3 bar) – Temperature is relevant of the Hydrogen consumption– Beginning at QM2 all PHM are equipped with new Hydride

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Lifetime preliminary measurementsExtrapolation over 12 years for most critical parameters (QM2):

Both parameters stay within expected limits with limited margins as first conclusion. Nevertheless:

– Margin for the tank are restored within IOV design by a change of the hydride (lower operational temperature). About 10°C margin.

– Cavity frequency shift is <<150kHz which is the worst case value that can recovered acting on the cavity temperature (20kHz per °C) and ACT.

< 150kHzCavity Frequency Change

~40°CHydrogen Supply Temperature

Extrapolation in 12 yearsTelemetry

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0 100 200 300 400 500 6004.6

4.8

5

5.2

5.4

5.6

5.8

6

6.2

6.4

Days

ATO

M te

lem

etry

(V)

PHM on Giove-B



Lifetime preliminary measurementsAtomic Signal Amplitude– The most relevant parameter for ageing of the PHM (Teflon coating,

dissociation efficiency, microwave cavity quality factor, high vacuum level, pollution, …)

150 200 250 300 350 400 450 500 5506

6.5

7

7.5

8

8.5

9

Days

ATO

M te

lem

etry

(V)

PHM-QM2

0 50 100 150 200 250 300 3505

5.5

6

6.5

7

7.5

Days

ATO

M te

lem

etry

(V)

PHM-QM1

17

Lifetime Ground Data 1


Lifetime preliminary measurementsFrequency Stability Performances (QM1 Lifetime):

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Lifetime preliminary measurementsFrequency Stability Performances (QM1 Lifetime):

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Lifetime preliminary measurementsTypical Frequency Stability Performances:

18kgMass

<3*10-13 / GaussMagnetic Sensitivity

< 2*10-14 / °CThermal Sensitivity

<1*10-15 / dayDrift

<3*10-15Flicker Floor

<7*10-15 @ 10‘000secFrequency Stability

MeasurementParameter

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Conclusions


Lifetime preliminary measurementsThe lifetime program has been providing useful results and demonstrating the capability of the PHM to operate for 12 years under vacuum without significant degradation.

The ageing trend observed is in line with prediction of the lifetime program results and is compatible with Galileo 12 years mission.

The performances achieved provide sufficient margins for sub-metric navigation system with long autonomy (up to several days).

The ageing trend observed on ground and the GIOVE-B data confirm that the PHM fully complies with the Galileo mission requirements.


Thank you very much Thank you very much for your attention for your attention

Daniel Daniel BovingBoving

SpectraTimeSpectraTime, Switzerland, Switzerlandbovingboving@@spectratimespectratime.com.com

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