GRACE USO

Short and Long-term Stability of the GRACE Ultra-Stable Oscillator (USO)

How stable are the GRACE Ultra Stable Oscillators (USO)'s? Do they behave consistently with respect to each other? How are they impacted by temperature, radiation, and acceleration? How does the accuracy of the USO affect GRACE data products?

How stable is the time and frequency behavior of the transfer system, i.e. the GPS system itself? Which parts of the GPS system have the greatest influence and how can they be improved for future NASA missions (e.g. GRACE Follow-On and PARCS)?

NEW

orbital elements
Once/rev power: difference in uncorrected values for GRACE A and B are consistent with the difference in the eccentricities of the two satellites.
Twice/rev power: note change in y-axis
comparing one day - note that indeed the once per rev is larger amplitude for GRACE A than GRACE B

GRACE antenna temperatures
Temperature files: GRACE A, GRACE B.
Mean eccentricity, from Srinivas Updated mean eccentricity, from Srinivas

ECI GRACE POSITIONS AND VELOCITIES (m and m/s) from Texas (John Ries)

Grace A ECI position and velocity 2004 April 1 Grace B ECI position and velocity 2004 April 1
Grace A ECI position and velocity 2004 May 2 Grace B ECI position and velocity 2004 May 2
Grace A ECI position and velocity 2004 May 24 Grace B ECI position and velocity 2004 May 24
GRACE B ECEF pos/vel - from JPL 2004 April 1 GRACE B ECI pos/vel - from JPL 2004 April 1

GRACE Eccentricity Plot

2004-05-02 GRACE A clock estimates GRACE B clock estimates
The units are tricky. The first column is seconds past J2000, but in GPS time. To help you convert, 136717500 seconds is 2004 5 1 21 5 0 0 GPS time. This would be 2004 5 1 21 4 47 in UTC (I think!). The solutions all start ~ 3 hours before midnite and end 3 hours after midnite. The second column is the clock estimates, which are in km.

NEW-All for GRACE B - no shifting

2003-10-01, poly removed 2003-11-01, poly removed
2003-12-01, poly removed 2004-01-01, poly removed
2004-02-01, poly removed 2004-03-01, poly removed
2004-04-01, poly removed 2004-05-01, poly removed

Other timing work at CU

comparison of GRACE A and 2RdotV/c/c term (these have been shifted in time to agree)

FFT of GRACE A

FFT of RdotV for GRACE A (2days)

2004-May-02 comparison of GRACE A and relativity term calculated from John Ries' orbits

2004-May-02 GRACE B with John Ries' orbits, after shifting

04may01 04may02 04may03 04may04 04may05 04may06 04may07 04may08 04may09 04may10 04may11 04may12 04may13 04may14 04may15 04may16 04may17 04may18 04may19

Plots of the exact (via numerical integration) and approximate (-2RdotV/c^2) relativity corrections for GRACE,
plus the difference in the corrections:

GRACE B, 2004 Apr 01
GRACE A, 2004 May 02
GRACE A, 2004 May 24

10 day Topex orbit (2.7 Mbytes)

Official GRACE website

My internal GRACE website

Neil's latest pdf
Neil's first notestex, pdf. Kouba's paper*