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Noise Characterization Using Transfer Functions: Examples from Spacecraft Doppler Tracking

This workshop presentation discusses the application of the Doppler technique and transfer functions for noise characterization in spacecraft tracking, particularly in the context of the Cassini mission. It delves into identifying mechanical and phase noise, signal transfer functions, and the impact of irregular media. Detailed examples showcase how transfer functions can isolate noise from proof masses and improve our understanding of instrument performance and data sensitivity. Insights from the workshop are valuable for future missions like LISA.

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Noise Characterization Using Transfer Functions: Examples from Spacecraft Doppler Tracking

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  1. Noise Characterization Using Transfer Functions: Examples from Spacecraft Doppler Tracking John Armstrong for the Cassini Radio Science GW Group* * R. Ambrosini, J.W. Armstrong, B. Bertotti, L. Iess, P. Tortora, H.D. Wahlquist AMIGOS workshop, October 15 2005

  2. Noise Characterization Using Transfer Functions • The Doppler technique & its signal and noise transfer functions • Examples of noise identification using transfer functions • Frequency & timing system • Antenna mechanical noises • Phase noise due to propagation through irregular media • Model example for LISA: identifying proof mass noises AMIGOS workshop, October 15 2005

  3. DSS25 and Cassini AMIGOS workshop, October 15 2005

  4. Cassini Radio System AMIGOS workshop, October 15 2005

  5. Three-Pulse GW Response AMIGOS workshop, October 15 2005

  6. AMIGOS workshop, October 15 2005

  7. Frequency/Timing Glitch AMIGOS workshop, October 15 2005

  8. Antenna Mechanical Event AMIGOS workshop, October 15 2005

  9. Plasma Events AMIGOS workshop, October 15 2005

  10. AMIGOS workshop, October 15 2005

  11. Isolating Proof-Mass Noises with Transfer Functions • LISA unequal-arm geometry • Nomenclature for proof mass disturbances vi and vi* • Idea: isolate which proof mass glitched (Braginsky, ≈2001) -- or which proof mass is noisier -- through their transfer functions AMIGOS workshop, October 15 2005

  12. Isolating Proof-Mass Noises with Transfer Functions • Temporal transfer fucntion of 6 PM’s to the three unequal-arm Michelson combinations (X, Y, Z) + symmetrical Sagnac (z) • First generation TDI AMIGOS workshop, October 15 2005

  13. GW Transfer Function to TDI “X” • Source/detector geometry dependent • “8-pulse” response in general for first-gen TDI [equal arm lengths assumed in this example so it degenerates to 7-pulse response; ApJ 527, 814 (1999)] • Will not be confused with PM glitches AMIGOS workshop, October 15 2005

  14. Isolating Proof-Mass Noises with Transfer Functions (Statistically) • Noise-only spectra of first-generation TDI combinations X and Z (expressed here as spectra of fractional Doppler fluctuations, vs. phase) • Proof mass 1 assumed 10X noisier than nominal • PM1 does not enter in Z, so it is OK -- spectrum of X affected, however CQG, 20, S283 (2003) AMIGOS workshop, October 15 2005

  15. Concluding Comments • In spacecraft Doppler tracking, at least, the data themselves are much more sensitive than any of the engineering housekeeping channels which monitor experiment health -- so you have to use the data themselves, in general, to understand the noises • I would expect this to be true for LISA, too • Transfer functions of the signal and noises to the TDI combinations offer a way to use the “science” data to understand the noises and instrument performance AMIGOS workshop, October 15 2005

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