Session 11 : 3060Time-transfer Experiments between Satellite Laser

Ranging Stations via One-way Laser Ranging to the Lunar Reconnaissance Orbiter

Dandan Mao1 (dandan.mao@nasa.gov), Xiaoli Sun2, David Skillman2, Jan McGarry2, Evan Hoffman3,4, Gregory Neumann2, Mark Torrence5, David Smith6, Maria Zuber6

(1Sigma Space Corporation, Lanham, MD 20706, USA; 2Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA ; 3GFZ German Research Center for Geoscience, Germany; 4Honeywell Technology Solutions, Inc. (HTSI), Columbia, MD 21046, USA; 5Stinger Ghaffarian

Technologies, Greenbelt, MD 20770, USA; 6Department of Earth, Atmospheric and Planetary Sciences, MIT, Cambridge, MA 02129, USA)

•Monitoring the station time to sub-nanosecond at the Next Generation Satellite Laser Ranging (NGSLR) at NASA GSFC with an absolute accuracy of ~1ns and a stability mainly governed by the station clock, 4e-15 for the hydrogen maser and 1e-13 for the cesium clock source.

•NGSLR station H-Maser time referenced to USNO master clock via All-View GPS receivers

•~1 ns precision and accuracy since Jan 2013.•Similar method is used to reference the clock at the McDonald Laser Ranging Station (MLRS) in Ft. Davis, Texas.

…

Pier_C Test 1, 2011-11-30:M7-Invariant Point to NGSLR event timer = 513.27 nsTest 2: 2012-12-18:M7-Invariant Point to NGSLR event timer = 513.00 ns

Pier_BTest 1, 2012-12-18M7-Invariant Point to NGSLR event timer = 513.296 ns

45.6 45.8 46 46.2 46.4 46.6 46.8 47−5

−4

−3

−2

−1

0

1

2

3

4

5

day of year 2013

time

diffe

renc

e be

twee

n N

GSL

R a

nd M

OB7

(ns)

226.8 226.85 226.9 226.95 227 227.05 227.1 227.15 227.2−5

−4

−3

−2

−1

0

1

2

3

4

5

day of year 2013

time

diffe

renc

e be

twee

n N

GSL

R a

nd M

OB7

(ns)

262 264 266 268 270 272 274−5

−4

−3

−2

−1

0

1

2

3

4

5

day of year 2014

time

diffe

renc

e be

twee

n N

GSL

R a

nd M

OB7

(ns)

Feb 4-5, 2013 Aug 14-15, 2013 … Sep 19-30, 2014

Results of time transfer via LRO between NGSLR and MOBLAS-7 at NASA GSFC

Work in Progress:•Time transfer tests between NGSLR in Greenbelt, Maryland to the McDonald Laser Ranging Station (MLRS) in Ft. Davis, Texas, have been conducted. Test data are under analysis.

Three tests performed:2011-11-30, Pier C, 10 minutes 2012-12-18, Pier C, 1 hour2012-12-18, Pier B, 1 hour

The Technique:•Two or more ground stations perform simultaneous one-way laser ranging to LRO, LRO time-tags all received laser pulses to the on-board clock•Each ground station time-tags its laser emission times to its own time base•Radio frequency (RF) tracking provides the spacecraft ephemeris•A hydrogen maser or a cesium clock provides a stable time base for each of the ground stations•An All-View GPS receiver compares the primary ground station clock to the near-by USNO master clock via the GPS satellites with most of the common view atmosphere effects canceling out•Solve for the difference between two ground station epoch times and hence transfer the time from the primary station to the remote station(s)

Transferring time between two SLR stations to within ~1ns and repeated after 6 months, then 13 months.

Verification and Validation with Ground Targets:Three tests performed with two ground targets in an LRO like configuration from two ground stations, NGSLR and MOBLAS-7, both at NASA GSFC, and the results agreed to within 0.3 ns.

−300 −200 −100 0 100 200−8

−6

−4

x 104

day of year 2014NGSL

R Hm

aser

− U

SNO

(ns)

−300 −200 −100 0 100 200−1000

−500

0

500

day of year 2014

Line

ar R

esid

uals(

ns)

−300 −200 −100 0 100 200

−5

0

5

10

day of year 2014

Resid

uals

(ns)

Gaussian smoothing (green) over residuals of 6th order polynomial fit to NGSLR Hmaser and USNO GPS in ns (blue)

Monitoring the Station Time with an All-View GPS Receiver

Friday, October 24, 14