Modified architecture for AIV measurements at Cannes .

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Development phases for T2L2 on the Jason 2 satellite

The T2L2 concept and feasibility on Jason 2 had been validated in May 2005. This study included also some minor changes to the initial T2L2 architecture, notably the use of an external retroreflector instead of the mono corner cube developed previously. The second point was of course the use of the DORIS oscillator as the clock.
The phase B preliminary development phase of the space instrument was initiated not earlier than September 2005, with a projected launch in June 2008. This tight schedule left not very much room for misconceptions. Advantageously, due to the different conducted previous studies and some successful ground based prototype testing in 2004 [21], the concept was rather mature at that time. The preliminary definition of the instrument architecture and composition, conducted by OCA and the chosen industry partners, EREMS, subcontracting SESO for the optical part, was already finished in December 2005, with the PDR (Preliminary Design Review). It dates also in this time when it was decided by E. Samain and the author to reorient the mainpart of the present thesis from the formerly principal topic ILIADE (see Part II of this document) to the characterization of the T2L2 instrument. An immediate work was then the characterization of the chosen non-linear detector. The second, somewhat more substantial agreed topic was the definition, integration and operation of a test bed for the detailed characterization of the T2L2J2 instrument engineering and flight model (MI and MV).
After a detailed study of the requirements on the test bed, based on the needed tests to be performed [22], the basic architecture and components (as laser, pulse picker, energy bench etc.) were determined and presented at the PDR of T2L2J2 on December 21, 2005. The studies around the test bed were continued and refined and led to its detailed definition that was presented at the respective key point on April 13, 2006 and the CDR (Critical Design Review) on May 13, 2006 [23]. For the T2L2J2 instrument, following model philosophy had been chosen: For the electronics part, the French space electronics manufacturer EREMS would produce prototypes, an engineering model and a flight model. For the optical part, to be supplied by SESO, it was opted to go for a proto-flight model without any prototype or engineering model. The electronics prototypes were evaluated and troubleshooted from January to April 2006, then, after the conclusion of the C-phase (detailed definition) mid-May 2006 with the CDR, the construction of the engineering model was begun. After its detailed design, the integration of the optical subsystem (SSO) started already in February 2006; after some tests during the summer 2006, including the mechanical verification tests, the optical subsystem was ready in autumn.
End of July, beginning August 2006 we performed a detailed evaluation of the engineering model of the electronics subsystem (SSE); this aimed at the detailed definition of some parameters as well as the comply to specifications in terms of metrology.
After this preliminary test campaign, carried out with a partial implementation of the test bed, the construction of the flight model (MV) was started. With some small delay, the instrument (SSE and SSO) was delivered to CNES by end of February 2007 (end of production phase D). The Qualification Review (QR) was held mid March 2007. At that time, the integration and test of the associated test bed had also been concluded and the flight instrument could be subjected to a detailed characterization campaign aiming at the calibration and the determination of the final performances of the instrument. These tests, including their preparation, are the main part of the present work and are presented in Chapter 3.

The goals of T2L2 on the Jason 2 satellite

The objectives of the T2L2 experiment on Jason-2 may be classified in three groups, concerning the functional validation of the T2L2 scheme and its performances, scientific objectives based on the performed time transfer and complementary objectives in conjunction with the Jason 2 mission.

Validation of T2L2 scheme and its derivatives

Apart from the validation of the time transfer scheme by T2L2, there are two further concepts that may be proven by the mission. Functional validation of T2L2: The T2L2 experiment on Jason 2 will allow for the validation of optical time transfer in terms of time stability and accuracy. A reference value is represented by the LASSO results, obtained in 1992 that should be ameliorated by two orders of magnitude in terms of time stability and one order in terms of accuracy. The metrological specifications on the T2L2 instrument are given in Section 2.3.2. Validation of one-way laser ranging: The concept of one-way laser ranging is based on only the start date and the arrival time on a satellite. Differential distance measurements may be deduced from the clock readings at ground and aboard. This scheme is proposed (see TIPO [24]) for long-haul distance measurements (on solar system scale) where no return signal may be expected; the scheme evidently needs an extremely stable clock, but the concept may be analytically emulated with T2L2 by comparison of the different ranging methods.
More precise satellite laser ranging: The quality of the T2L2 ground segment, represented by a set of ameliorated laser ranging stations, allows for a gain in exactitude of classical two-way satellite laser ranging data. Further, the determination of the laser pulse energy in orbit in conjunction with its energy on ground (return pulse) will permit to ameliorate current atmospheric models.

Constraints and implications by the Jason 2 mission

As mentioned above, since T2L2 was accepted as a passenger instrument, its design had to subordinate the overall layout of the Jason 2 mission. This concerned not only mass or power constraints but in particular two vital subsystems of the original T2L2 proposal. As the Jason 2 primary mission, ocean altimetry, relies primordially on very precise orbit determination, it is equipped with several such systems, namely, DORIS, GPS and SLR. Since the new type of mono-corner-cube retroreflector (of the initial T2L2 proposal) would represent a too risky undertaking for the whole mission, it was decided that in turn T2L2J2 would use the retroreflector of the Jason 2 mission. A second issue was the clock: Since both time and financial budget were too small for the development of a dedicated clock for the T2L2 experiment, the T2L2J2 version has to content with the local oscillator of the DORIS positioning system as a frequency reference. After giving some insight in the Jason 2 mission in general, these two mission-originated quasi-subsystems will be outlined in the following sections.

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The Jason 2 ocean altimetry mission

The Jason 2 satellite mission is a joint undertaking of CNES, NASA, EUMETSAT and NOAA and is intended to replace the Jason 1 satellite that, on its turn replaced the TOPEX/Poseidon (and actually has been flying some time in tandem with it). Together with SEASAT (1978), GEOSAT (1985), ERS-1 (1991), ERS-2 (1995) and ENVISAT (2002), these missions cover a wide field of oceanographic applications mainly through ocean topography. Ocean scientists use the ocean altimetry data for the establishment of sea surface current charts, the study of their intra-seasonal to seasonal variations and the observation of climatic anomalies through the understanding of oceanic signatures [26].

Table of contents :

I. The Time Transfer by Laser Link experiment 
1. Time transfer 
1.1. What is time transfer?
1.1.1. What is time in the first place?
1.1.2. The measurement of time
1.1.3. Clocks and time scales
1.1.4. Comparison of clocks and time scales: Time transfer
1.2. Actual time transfer systems
1.2.1. Time dissemination with GNSS
1.2.1.1. Principle of GPS
1.2.1.2. Time transfer with GPS
1.2.2. Two-way system for time and frequency transfer (TWSTFT)
1.2.3. MWL of the ACES mission on the International Space Station
1.2.4. Other systems
1.2.5. Limitations of radio frequency systems
1.2.6. The optical world
1.3. The T2L2 scheme
1.3.1. T2L2 time transfer
1.3.2. Advantages of the optical scheme with T2L2
2. The Time Transfer by Laser Link project on the Jason 2 satellite 
2.1. The development of T2L2J2
2.1.1. Heritage of LASSO
2.1.2. T2L2 feasibility studies
2.1.3. Development phases for T2L2 on the Jason 2 satellite
2.2. The goals of T2L2 on the Jason 2 satellite
2.2.1. Validation of T2L2 scheme and its derivatives
2.2.2. Scientific objectives
2.2.3. Jason 2 mission related objectives
2.3. The design of T2L2J2
2.3.1. Constraints and implications by the Jason 2 mission
2.3.1.1. The Jason 2 ocean altimetry mission
2.3.1.2. Laser Retro-Reflector Array
2.3.1.3. DORIS space oscillator
2.3.2. Specifications on the T2L2 instrument
2.3.3. T2L2 on Jason 2 instrument synopsis
2.3.4. The optical architecture of T2L2J2
2.3.4.1. Linear detection channel
2.3.4.2. The non-linear detection channel
2.3.5. Electronics architecture
2.3.5.1. Signal forming and management: Detection board
2.3.5.2. Event timer
2.3.5.3. Other electronics
2.3.6. T2L2 on Jason 2 budgets
3. Characterization of the T2L2J2 instrument 
3.1. A metrological test bed for T2L2J2
3.1.1. Scope and demands on the test facility
3.1.2. Design and composition of the test bed
3.1.2.1. Test bed optics: Laser and optical architecture
3.1.2.2. Reference energy measurement
3.1.2.3. Sun noise generation
3.1.2.4. Reference timing and reference signals
3.1.2.5. Data acquisition and control of the test bed
3.1.2.6. General architecture
3.1.2.7. Test bed implementation at CNES
3.1.2.8. Modified architecture for AIV measurements at Cannes .
3.1.2.9. The evaluation of the LRA
3.1.3. Performance of the test bed
3.1.3.1. Laser system
3.1.3.2. Timing precision and stability
3.1.4. Conclusion test bed development
3.1.4.1. From development to operation
3.1.4.2. Performance
3.2. Performance of the T2L2J2 instrument flight model
3.2.1. The T2L2J2 event timer
3.2.1.1. Frequency synthesis
3.2.1.2. Timing
3.2.1.3. Internal calibration signals
3.2.2. The T2L2J2 optical subsystem
3.2.2.1. Precision of non-linear photodetection
3.2.2.2. Long term stability of the non-linear detection
3.2.2.3. Influence of laser repetition rate
3.2.2.4. Coupling efficiency of the optics
3.2.3. Time stability of the DORIS USO
3.2.4. Conclusion T2L2J2 final performance
3.2.5. Lessons learned
3.3. Calibration of instrumental parameters of T2L2J2
3.3.1. Event timer: Vernier calibration
3.3.2. Optical subsystem
3.3.2.1. Time-walk and pulse measurement linearity
3.3.2.2. Optics calibration for incidence angle
3.3.2.3. Influence of polarization and incidence angle
3.3.2.4. Effect of wide-field albedo irradiation
3.3.3. Conclusion of calibration measurements
4. The T2L2 ground segment: Laser station 
4.1. Three examples of laser stations
4.1.1. MéO on the Plateau de Calern
4.1.1.1. The laser(s)
4.1.1.2. The MéO telescope and detection device on Nasmyth table .
4.1.1.3. Timing, time base and operation
4.1.2. The French mobile station FTLRS
4.1.3. Wettzell laser ranging station
4.2. Calibration of a laser station
4.3. Calibration of time/frequency system vs. laser station
4.3.1. Time/frequency laboratory
4.3.2. Calibration equipment
4.3.2.1. Passive calibration method
4.3.2.2. Active calibration method
4.3.2.3. Status
5. T2L2J2 error budget 
5.1. Contribution of the T2L2J2 instrumentation and mission
5.1.1. Event timer
5.1.2. Photodetection
5.1.2.1. Precision and stability of optical timing
5.1.2.2. Uncertainty of the time-walk correction
5.1.2.3. Summary T2L2J2 photodetection
5.1.3. The DORIS oscillator
5.1.4. Geometry of the T2L2J2 instrument and LRA retroreflector
5.1.4.1. Attitude and mechanics
5.1.4.2. Retroreflector response with respect to attitude
5.1.5. Atmosphere
5.1.6. Relativity
5.2. Contribution of the laser ranging station
5.2.1. Start date
5.2.2. Return date
5.2.3. Event timer
5.2.4. SLR system internal calibration
5.2.5. Calibration between time/frequency and SLR systems
5.3. Summary I: Clock to clock time transfer stability
5.3.1. Time stability budget for common view time transfer
5.3.1.1. Ground to space time transfer
5.3.1.2. Operational aspects of the common view time transfer
5.3.1.3. Time transfer in common view
5.3.2. Time stability budget for non-common view time transfer
5.3.2.1. Operational aspects of the non-common view time transfer .
5.3.2.2. Time transfer in non-common view
5.4. Summary II: Clock to clock time transfer uncertainty
5.5. Conclusion
6. T2L2: Conclusion and future 
6.1. Conclusion of the described activities for T2L2 on Jason 2
6.2. Actual status
6.3. Outlook: Future of T2L2
II. ILIADE – Towards distance measurement on wavelength scale 
7. Measuring distances in space 
7.1. Scientific applications dealing with distance measurement in space
7.1.1. Distance measurement for metrology
7.1.2. Distance as central observable
7.2. Technologies addressing the problem
7.2.1. Interferometry on the optical carrier
7.2.1.1. Classical single-wavelength interferometry
7.2.1.2. Multiple-wavelength interferometry
7.2.1.3. Frequency-sweeping interferometry
7.2.1.4. Dispersive or white-light interferometry
7.2.2. Modulation of the optical carrier
7.2.2.1. Time-of-flight measurement
7.2.2.2. Sinusoidal carrier amplitude modulation
7.2.3. Combining carrier and modulation measurements
7.2.3.1. Excursus: The frequency comb
7.2.3.2. The scheme proposed by Ye
8. The project ILIADE at OCA 
8.1. Combining interferometry and chronometry
8.1.1. The ILIADE baseline experiment
8.1.2. Design issues
8.1.3. The ICB source
8.1.4. ILIADE development
8.2. Phase measurement
8.3. Timing experiments
8.3.1. Optical timing in laser cavity clock mode
8.3.2. Optical timing with electronic pulse picking
8.4. Discussion
Conclusion and outlook
Appendix
Bibliography 

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