EOEP Science Review Meeting 14 and 15 June 2005

GOCE

Rune Floberghagen ESA/ESTEC

Mission Performance

www.esa.int/livingplanet/goce

Outline

ü role of simulations in GOCEü system performance (Level 1b)

o gravity gradients

o GPS observablesü mission performance (Level 2)

o geoid heights

o gravity anomalieso error structure

ü role of launch date

ü role of solar cycle

System and Mission Simulations

ü Gradiometer instrument does not work under “1g”;

restrictions also on GPS receiver

ü Despite a very extensive test campaign (accelerometers,

electronics and gradiometer) the performance can only be

demonstrated to a very limited degree on ground

ü GOCE accelerometers are extremely sensitive (about 100x

the sensitivity of GRACE accelerometers); opens a new range

of effects to consider

ü Calibration is paramount (!)

ü Instrument performance depends on the performance of the

satellite and vice versa

ü Our basic tool: Complex End-to-End System Simulator, up to

Level 1b. Error propagation tools and HPF processing for Level 2

Gravity Gradient Measurement Errors

Semi-analytical prediction

MBW

End-to-End Simulation

MBW

End-to-End Simulation

MBW

SSTI Measurement Errors

SSTI Measurement Errors

0.28 m (CH06)

0.76 m (CH06)

0.19 m (CH06)

1.05 m (CH06)

0.09 m (CH06)

1.34 mm (CH06)

0.77 mm (CH06)

0.5 m0.28 m (CH03)L1 CA

1.5 m0.76 m (CH03)L2 P/Y (AS

ON)

0.25 m0.19 m (CH03)L2 P/Y (AS

OFF)

1.5 m0.99 m (CH03)L1 P/Y (AS

ON)

0.25 m0.08 m (CH03)L1 P/Y (AS

OFF)

4.9 mm1.35 mm (CH03)L2 P/Y (AS

ON)

1 mm0.75 mm (CH03)L1 C/A

RequirementMeasured

ü Based on FlightModel tests

ü Valid for 15°

elevation (not passRMS)

ü L2 tracking downto ~10° elevation

ü No cycle slipsover 100 hrs

Mission Performance

ü 6 months (1 MOP)

ü MOP1 at 250 km mean altitude

ü Gradiometer error PSD from E2E simulator; SSTI orbit error 2cm in each direction (1D, 1!)

ü Based on covariance propagation analysis techniques

Cumulative errors

HPF: Geoid Differences w.r.t. EGM96

EGM_DIR EGM_SPW

EGM_TIM

Unit: [m]

Launch in September 2007

• MOP1 at an altitude of 250 km and MOP2 at an altitude 260 km

Mission performance: Geoid accuracy of up to 1.5 cm and gravity

anomaly below 1 mGal

Launch in January 2008

• MOP1 at an altitude of 255 km and MOP2 at an altitude 265 km

Mission performance: Geoid accuracy of up to 2 cm and gravity anomaly1 mGal

Consequence of Launch Delay

**Performance indicated at degree 200 (100km spatial resolution)

Performance vs. Mission Requirements

<1 mGal @ 100 km

2 cm @ 100 km

1 cm @ 115 km

Our friend the solar cycle...

The current prediction of the next Solar Minimum is Jan 2007

As solar activity and consequently atmospheric drag increase altitude adjustments become necessary

Conclusions

ü Well-established tools and models in place for system and

mission performance assessment

ü Overall mission performance at spatial scales down to 100

km expected to be at or below 2 cm in terms of geoid heights

and below 1 mGal in terms of gravity anomalies

Getting ready for flight...