TDI Ranging for the GRACE-FO Laser Ranging Interferometer

Transcription

1 TDI Ranging for the GRACE-FO Laser Ranging Interferometer Andrew Sutton Jet Propulsion Laboratory, California Institute of Technology Kirk McKenzie William Klipstien Brent Ware Robert Spero Glenn DeVine Samuel Francis Daniel Shaddock David McClelland

2 2 LEGOP Activities Funded NASA ROSES APRA (Dec. 2012) Research Opportunities in Space and Earth Sciences, Astrophysics Research and Analysis Program 11-APRA GRACE (Since 2002) GRACE-FO YEAR LISA PATHFINDER LEGOP ` (APRA grant) Flight LEGOP Experiment (Not supported by APRA proposal) Gravitational-Wave Astronomy Mission (Late 2020 s?) Develop interesting LISA technology experiments that can be demonstrated on GRACE-FO. Time Delay Interferometry with Optical Ranging, and Arm Locking. Simulate/demonstrate experiments with the GRACE-FO conditions and hardware. Utilise existing LISA Interferometry Testbed, Prototype algorithms & hardware.

3 Time Delay Interferometry TDI combinations rely upon relaying frequency noise between links. -- synthetic interferometer arms -- 3

4 4 GRACE-FO LRI Quadrant Photodiode Phasemeter To other SC Local Laser SC A ~200km SC B CM Measurement Axis Triple Mirror Assembly Steering Mirror Cavity Error Microwave Instrument Point-to-point measurements are combined to measure the round-trip displacement SC A ~200km SC B From other SC

5 Time Delay Interferometry Recover `active transponder architecture in post-processing 5

6 Time Delay Interferometry TDI is limited by delay knowledge GRACE-FO allows testing of TDI algorithms with a significant delay (~ms) & delay fluctuations (~30%) >> requirement (~ns) => LRI has NO explicit absolute ranging (GPS ) TDI Ranging (TDIR) Implicit TDI Ranging Minimise RMS over regions without range signal (laser freq. noise limited) Tone Assisted Minimise In-band frequency modulation upon noisy laser. 6

7 7 TDI in GRACE-FO GRACE Microwave ranging data (1-4 Jan. 2012) Displacement Amplitude Spectral Density (m/ Hz) Spacecraft A Cavity Stabilised GRACE-FO LRI Requirement Spacecraft B TDI (6 ns Error) Spacecraft B Free-running ~10 9 Suppression of free-running laser Microwave Thermal Noise (5 μm/ Hz) 10-8 Spacecraft A TDI Frequency (Hz)

8 GRACE-FO Simulation GRACE Range Range Spectrum (m/ Hz) Stabilised Master Laser Free-running Slave Laser Single Link Shot Noise Frequency (Hz) 8

9 GRACE-FO Simulation GRACE Range Range Spectrum (m/ Hz) Stabilised Master Laser Residual Master Laser Frequency Noise Free-running Slave Laser Δτ << 6 ns Single Link Shot Noise Frequency (Hz) 9

10 GRACE-FO Simulation GRACE Range + Simulation TDI Ranging Tone Range Spectrum (m/ Hz) Stabilised Master Laser Residual Master Laser Frequency Noise Free-running Slave Laser Single Link Shot Noise Frequency (Hz) 10

11 GRACE-FO Simulation GRACE Range + Simulation TDI Ranging Tone Range Spectrum (m/ Hz) Stabilised Master Laser GRACE-FO LRI Requirement Residual Master Laser Frequency Noise Free-running Slave Laser Single Link Shot Noise Frequency (Hz) 11

12 12 GRACE-FO Simulation Iteration: Window SC i data Nelder-Mead simplex Derivative-sensing FFT for delay error 1) Form un-interpolated combination - No orbit or GPS knowledge. 2) Displacement gives higher order delay terms - Iterate to fit delay. 3) Feed range estimate to smoothing & prediction filter 4) Generate TDI data product.

13 13 GRACE-FO Simulation SC 1 Range SC 2 Range Un-interpolated DOWR Interpolated DOWR DOWR Residual Theory Residual

14 14 GRACE-FO Simulation Residual Range - - Meets 2m requirement - -

15 15 GRACE-FO Simulation Structure in the ranging error is imposed onto the TDI tone. Range delay Changing phase delay Phase modulation Structure from orbital tone & harmonics. Broadband error from white noise + smoothing filter. Ranging Tone SC 1 Range SC 2 Range Un-interpolated DOWR Interpolated DOWR DOWR Residual Theory Residual

16 TDI Testbed Stablised Master + free-running Slave λ/2 Nd:YAG M Generate signals with real optical delay. O E λ/4 EO Nd:YAG M PBS PBS PD0a Add a displacement signal. PM PD1a Sense the delay using TDI Ranging. PD2a PM Nd:YAG Sensitive to optical pathλ/4length PBS λ/4 PD0b PM PD1b PD2b PM Nd:YAG PBS λ/4 α Zero-area Sagnac Interferometer λ/2 Fiber delay: 150 ns Dummy Spacecraft A P0 Truth frequency measurement Dummy Spacecraft B G. de Vine et al. Phys. Rev. Let. 104(21) (2010) ULE Glass Cavity Laser 1 Master Spacecraft Dual One-Way Range p12(t) + + p0(t) 0.85Hz p21(t) 30m optical fiber Truth Laser 2 Slave Spacecraft Displacement Signal 16

17 TDI Testbed LRI prototype phase measurement & locking Displacement injected via Sagnac phaselocking ULE bench. Out-of-loop measurement to subtract displacement signal. φ cw (t) φ' ccw (t)+d(t) Laser D1 ULE Glass Cavity Laser 1 Master Spacecraft p 12 (t) p 0 (t) + + φ ccw (t) φ' cw (t)+d(t) ADC 40 MHZ Phase Locker - Laser D2 0.85Hz p 21 (t) 30m optical fiber Phase Locker + + Laser 2 Slave Spacecraft Displacement Signal D(t) Displacement Signal 17

18 18 TDI Testbed: RESULTS P0 DOWR Int DOWR Int. Alpha Corrected Alpha PhaseLocking Req Master A cavity stabilized Slave A Free-running with a 0.85Hz tone. Phase noise [ cycles / Hz] Frequency [Hz]

19 19 TDI Testbed: RESULTS P0 DOWR Int DOWR Int. Alpha Corrected Alpha PhaseLocking Req TDIr Tone Master A cavity stabilized Slave A Free-running with a 0.85Hz tone. Phase noise [ cycles / Hz] Displacement Signal DOWR has a 0.18mHz tone added through Sagnac phaselock. TDIR finds Interpolated DOWR Frequency [Hz]

20 TDI Testbed: RESULTS P0 DOWR Int DOWR Int. Alpha Corrected Alpha PhaseLocking Req Master A cavity stabilized Slave A Free-running with a 0.85Hz tone. Phase noise [ cycles / Hz] DOWR has a 0.18mHz tone added through Sagnac phaselock. TDIR finds Interpolated DOWR. Delay used to Interpolate Alpha 10 Corrected Alpha is formed by subtracting the injected displacement Frequency [Hz] Δτ<6ns: Meets GRACE-FO Phaselocking Requirement 20

21 21 Conclusion develop in-flight tests of core-techniques and high-risk elements of laser interferometry for a future space-based gravitational-wave astronomy mission for deployment on the GRACE Follow-On (GRACE-FO) mission, using that mission s optical technology package as a Mission of Opportunity. Simulation Shows operation of Tone-Assisted TDI ranging for GRACE-FO. Demonstrated suppression of laser frequency noise. Experiment Demonstrated < 6ns ranging error using Tone-Assisted TDI Ranging. Displacement signal injection via Sagnac phase locking. Non-reciprocal displacement noise limited This project was funded under NASA ROSES-APRA Grant 11-APRA