ILRS 2005; N. Zelensky

GEOSAT Follow-On

(GFO)Radar

Altimeter Satellite

Satellite Laser Ranging (SLR)Tracking and Analysis Overview

GSFC Report

ILRS Fall 2005 WorkshopSeptember 2005; Eastbourne, England

ILRS 2005, N. Zelensky

GFO

Altimeter Error Budget

ILRS 2005, N. Zelensky

GFOSLR Tracking History: Jan 2004 - Sep 2005

0

5

10

15

20

25

30

35

40

0 100 200 300 400 500 600

Day of year from January 1, 2004

pa

ss

es

/ d

ay

totalNASA sitesGFO safeholdlinear fit (total)

average 12 passes/day

ILRS 2005, N. Zelensky

GFOSLR Station Tracking: Jan 2004 - Sep 2005

0

200

400

600

800

1000

1200

CO

NC

7405

CR

L_7308

AJA

C7848

TA

NG

7358

BR

ST

7604

PO

TS

7836

SF

ER

7823

WU

HA

723

HE

LW

7831

LV

IV1831

UR

UL

7355

KA

TS

1893

ME

TF

7806

SIM

E1873

HO

LL

7210

MA

ID1864

KIE

V1824

TA

HI7

124

BO

RO

7811

SH

AH

7837

GR

AS

7835

MA

TE

7941

RIG

A1884

MC

DO

708

BE

IJ7249

SA

NF

7824

SH

O_7838

PO

T37841

GR

F17105

ST

L37825

HA

RT

7501

CH

AC

7237

RIY

A7832

MN

PE

7110

RG

O_7840

WE

TZ

8834

ZIM

M7810

GR

AZ

7839

YA

RA

7090

passes

Stations (39 total) percent passes

Yarragadee (YARA) 16 %

NASA (MNPE, GRF1, MCDO, HOLL) 14 %

Other 70 %

ILRS 2005, N. Zelensky

GFOTracking Data Residuals

0

2

4

6

8

10

12

52900 53000 53100 53200 53300 53400 53500 53600 53700

MJD arc epoch

Re

sid

ua

ls/a

rc (

cm

)

SLR

Crossovers

111 arcs spanning Jan 2004 – Sep 2005

large residuals reflect periods of high solar activity

ILRS 2005, N. Zelensky

GFOGFO-1 Orbit Products

NASA GSFC computes two sets of orbits for GFO-1: (1) daily Medium precision orbits (MOE’s), exported daily to NOAA and NAVO (usually by COB local time, or ~21:00 to 22:00 UT).

(2) precise orbits (POE’s) are exported to NOAA with a latency of a few weeks, and are available via anonymous ftp.

All orbits rely on SLR, Doppler data, and altimeter crossovers. POE’s have more crossover data due to altimeter data (IGDR) latency issues, and perhaps slightly more SLR data since they rely on a later import.

Orbits are available from dirac.gsfc.nasa.gov anonymous ftp: cd pub/earth/gfo/moe/ & cd pub/earth/gfo/poe/ (TOPEX POE format).

SLR predicts are sent to stations daily based on the MOE orbits. Special predicts are sent around spacecraft maneuvers, although sometimes we receive very late notification from the GFO Operations Team.

During approach of Hurricane Rita to Texas, MOE orbits were computed and sent to NOAA twice daily (morning and afternoon).

ILRS 2005, N. Zelensky

GFOOrbit quality improves with increased SLR coverage

6

6.2

6.4

6.6

6.8

7

7.2

7.4

0 50 100 150 200 250 300 350 400 450 500

SLR coverage density (points/day)

res

idu

als

/arc

(c

m) Crossovers

linear fit

ILRS 2005, N. Zelensky

GFO

GFO POD GSFC Points of Contact

Frank Lemoine Frank.Lemoine@gsfc.nasa.gov

Nikita Zelensky nzelensky@sgt-inc.com