Current Trends in Satellite Laser Ranging(2012.5.23转载)

 

中的文字部分大约2000个单词,涉及到一些专业

术语,尝试对以下文字进行翻译(摘要部分400词略去):

1   The Laser Ranging Technique and Science/Applications of SLR

 

The laser ranging technique consists of a precise range measurement between an SLR ground

station and a retroreflector-equipped satellite using ultrashort laser pulses corrected for refraction,

satellite center of mass, and the internal delay of the ranging machine. The global network

of SLR stations has supported more than sixty space missions supported since 1970; five of

these missions have been rescued in the last decade by laser ranging measurements.

1.1 Concept: 概念

• Simple measurement of range from accurate time interval

counters

• Space segment is passive

• Accurate atmospheric delay correction (independent of

water vapor)

• Night/Day Operation

• Near real-time global data availability

• Satellite altitudes from below 300 km to synchronous

satellites, and the Moon

• Unambiguous centimeter accuracy orbits

• Long-term stable time series of positions, low degree

spherical harmonics, orbital elements, and others

1.2  Measurements:测量

• Precision Orbit Determination (POD)

• Time history of station positions and motions

• Low degree gravitational harmonics and GM

• Tidal harmonics, planetary Love numbers, etc.

1.3 产品

SLR/LLR products contributing to:

• Terrestrial reference frame (Center of mass and scale)

• Plate tectonics and crustal deformation

• Static and time-varying gravity field

• Earth orientation and rotation (polar motion, length of day)

• Orbits and calibration of altimetry missions (oceans, ice)

• Total Earth mass distribution

• Space science (tether dynamics, etc.)

• Relativity measurements and lunar science

1.4 SLR和地球参考框架

SLR and the Terrestrial Reference Frame

• SLR is one of the key space technologies that contribute to the development

of the ITRF:

- An accurate, stable set of station positions and velocities.

• The unique contribution of SLR to ITRF is the link of its origin to the

center of mass of the Earth system

• SLR contributes also in maintaining a stable scale for the ITRF, in equal

parts with VLBI

• The ITRF Requirements of GGOS are:

- <1 mm reference frame accuracy

- < 0.1 mm/yr stability

• The primary science driver is the

measurement of sea level change

• The GGOS goal requires a factor of

10-20 improvement over current ITRF

performance demonstrated below for

ITRF2008

1.5

Need for SLR measurements on the GNSS Constellations

Geoscience

• Improve the Terrestrial Reference Frame (co-location of techniques

in space)

• Improve LEO POD based on GNSS tracking of SLR-calibrated GNSS

orbits

GNSS World

• Provide independent quality assurance:

- GNSS orbit accuracy cannot be directly validated from the GNSS

data itself

• Assure interoperability amongst GPS, GLONASS, Galileo, COMPASS,

QZSS, etc.

• Ensure realization of constellation-dependent reference frames

(WGS84 , GTRF, etc.) are consistent with ITRF

 

2

The International Laser Ranging Service and its Support of Missions through Laser Ranging

2.1

The International Laser Ranging Service (ILRS), founded by the International Association of Geodesy (IAG) in 1998, organizes and coordinates Satellite Laser Ranging (SLR) and Lunar Laser Ranging (LLR) to support programs in geodetic, geophysical, and lunar research and provides the International Earth Rotation and Reference Frame Service (IERS) with products important to the maintenance of an accurate International Terrestrial Reference Frame(ITRF).

The ILRS produces quality-assured scientific results from the SLR and LLR data including:

• Satellite ephemerides

• Earth orientation parameters

• Position and velocity of the ILRS tracking

stations

• Time-varying geocenter coordinates

• Static and time-varying coefficients of the Earth's gravity field

• Fundamental physical constants

• Lunar ephemerides and librations

• Lunar orientation parameters

The ILRS accomplishes  its mission through the  following components:

• Tracking Stations and Subnetworks — range to the approved

constellation of artificial satellites  and the moon

• Operations Centers

— collect, QC, merge  data from tracking sites and transmit todata centers

• Data Centers — archive laser ranging data and products

• Analysis and Associate Analysis Centers — produce official ILRS products(station coordinates and EOP) as well as special products

• Working Groups — provide expertise to make technical decisions and planprogrammatic courses of action

• Central Bureau — coordination and management of ILRS activities

• Governing Board — responsible for general direction of service and defines official ILRS policy

3  Current SLR/LLR Network(图,略)

4  New Technology and Developments

• The Russian Blits satellite with a novel Luneberg Lens, a single corner

cube reflector whose center of mass correction can be very accurately

computed independent of aspect angle resulting in very precise

ranging measurements.

• Stations with kHz repetition laser systems provide ranging measurements

that show details of retroreflector geometry and can measure

spin rate on spherical geodetic satellites. At this time, four stations

in the ILRS network operate at kHz rates.

• NASA supports the development of the Next Generation SLR (NGSLR)

system, a prototype automated SLR system for replication and deployment

as part of the future GGOS network.

• New French MEO system at Grasse built for both satellite and lunar

ranging. The MLRO system in Matera Italy has recently revived its

lunar capabilities.

• New high performance Apache Point Observatory Lunar Laser-ranging

Operation (APOLLO) measures the round-trip travel time of laser

pulses to the lunar retroreflectors to a precision of a few picoseconds,

corresponding to about one mm of precision in range to the

Moon. These data will be used to gauge the relative acceleration of

the Earth and Moon toward the sun in order to ascertain the free-fall

properties of Earth's gravitational self-energy.

 

4.1  Test Facility for Laser Retroreflector Arrays

Schematic of facility developed at the Laboratori

Nazionali di Frascati to test, characterize

and validate the performance of laser retroreflector

arrays (S. Dell’Agnello et al.). The array

allows performance testing under space simulated

vacuum and thermal conditions.

4.2  LRO Laser Ranging (LRO-LR)

One-way Laser Ranging data from the international SLR network is being used to determine LRO

spacecraft clock drift and to “transfer” time and will also be used to improve orbit determination

in support of gravity modeling and precise positioning.

Approximately 450 hours of successful LRO Laser Ranging data has been collected since launch in

both synchronous (28 Hz) and asynchronous modes by stations in the ILRS network.

4.3

The T2L2 experiment on Jason-2 uses an event timer, photo detection modules, and ultra-stable

quartz oscillator and a laser retroreflector array to implement a two way time transfer system to

synchronize clocks on the ground and on the satellite. It is anticipated that time transfer among

participating SLR ground stations will reach the 100 ps level once the current modeling activities

are completed.

4.4  Spin Rate Measurements

 

Graz kHz SLR station measures the spin

period of Ajisai with accuracy of 80μs. Chart

A shows the spin period measurements of

Ajisai (years 2003.8-2009). Chart B shows

the spin period change during arbitrary selected

163 days. Chart C shows spin period

residuals to the spin period trend function

for the selected data set. The distribution of

the residuals is correlated with the percentage

of the Ajisai orbit illuminated by the

Sun. The spin period is increasing faster

when the full orbit is exposed to the solar

irradiation. The minimum percentage of Ajisai orbit in the Sun is about 75% - this corresponds

to the minimum value of the spin period residuals (chart C). The average slowing

down rate is 29.7 ms/year.

SLR allows for spin period determination of

the passive satellites LAGEOS-1 and

LAGEOS-2. The chart presents spin period

values obtained from all available laser

measurements of all SLR stations: 10 years

for LAGEOS-1 (10426 values) and 15 years

for LAGEOS-2 (15580 values). Due to the increasing

spin period of LAGEOS-2, only Graz

2 kHz SLR system – with its high repetition

rate and 10 ps pulse width – permitted measurement

of the spin period after year 2003;

the kHz data also yields an order of magnitude

higher accuracy

 

4.5  NASA’s Next Generation SLR (NGSLR)

系统能力

System Capabilities

• Centimeter ranging accuracy

• Two-way ranging to satellites up to

22,000 km altitude

• Automated

• No ocular, chemical, or electrical hazards

(system with microJoule laser is

eye-safe)

• Small, compact, low maintenance

• Lower replication/operating costs

System Characteristics:

• Telescope: 40 cm off-axis parabola

• Mount: Arc-second precision tracking

• Detector: MCP PMT 4-quadrant

• Laser: < 100 microJoules per pulse at

2 KHz

• Outgoing beam divergence: ~ 4

arcsec FWHM

• Pointing accuracy: 2-3 arcseconds

 

 美国航空航天局的新一代SLR

(来自:

NASA’s Next Generation

Space Geodesy Project

A Core Contribution to the

Global Geodetic Observing System

Submitted by

NASA Goddard Space Flight Center

Jet Propulsion Laboratory

December 16, 2011

)

 

Next Generation SLR (NGSLR)

NASA undertook the development of a Next Generation SLR (NGSLR) because it recognized

the older systems were literally "falling apart' and that the older technologies were not capable of

satisfying projected performance requirements. The NGSLR is being built to demonstrate that a

system using existing commercial off-the-shelf technology can satisfy the performance

requirements as an autonomous, photon-counting SLR station with normal point precision at the  mm level. The system is intended to provide continuous 24 hour tracking coverage of artificial

satellites up to GNSS altitudes. NGSLR has already demonstrated much of its new technology  and performance capability. Some developmental work remains to be completed to fully

demonstrate the technologies can be integrated into a realizable system that meets the required

performance criteria. Based on this experience, specifications then need to be written for a

production system that can be built by industry.

The NGSLR system is now operating at GGAO near MOBLAS-7, one of the early NASA

systems still in operation after nearly 30 years. Over the past year, NGSLR has taken over 250

passes of data, over the full range of capability for engineering, diagnostic, and operational

testing, during both nighttime and daylight conditions. Over the next two years, NASA will

complete the NGSLR prototype and make it part of the prototype GGOS station at GGAO.