LIST OF ABSTRACTS

Session 12: "Operational Issues and New Missions"

Applications of the Precision Expandable Radar Calibration Target (PERCS)

Paul A. Bernhardt
Naval Research Laboratory, USA,
E-mail: bern@ppd.nrl.navy.mil

A large (10 m) diameter sphere, with conducting edges composed of open-faced polygons, is being planed for launch in low earth orbit. The primary purpose of the Precision Expandable Radar Calibration Target (PERCS) is calibration of high frequency (3 to 30 MHz) backscatter radars used for geophysical studies of the upper atmosphere. The PERCS sphere with 180 vertices and 360 edges provides about 200 square-meters radar cross section at HF frequencies [Bernhardt et al., 2008]. Measurements of radar backscatter from a sphere with known radar cross section will calibrate ground-based HF radars to permit absolute measurements of the strength of meteor trail echoes and scatter from auroral disturbances in the ionosphere.
The addition of corner cube retro-reflectors at the 180 vertices enhances the use of PERCS by permitting (1) high accuracy measurements of the target position, (2) determination of its orientation, and (3) estimation of the PERCS rotation rate. With these measurements using laser backscatter from the retro-reflectors permits studies of the electrodynamic drag of the conducting wire-frame sphere moving in low-earth-orbit (LEO) across magnetic field lines. Currents induced in the gold-plated conducting struts of PERCS will interact with Earth's geomagnetic field yielding forces that affect both the orbit and the rotation of the sphere. A mechanical model for deployment of the 10 meter diameter sphere from a 1-meter stowed configuration has been developed at NRL and Hoberman Associates. The model also includes corner reflectors at vertices of polyhedral wire frame with design considerations of the diffraction pattern of the reflected laser signals as well as the effects of the velocity aberration from the orbiting sphere. Some vertices will be vacant of reflectors at selected wavelengths so that the unique orientation of the PERCS can be determined from ground laser observations. The PERCS sphere is being considered for launch in the 2011 to 2012 time period.

Reference: Paul A. Bernhardt, et al., The Design and Applications of a Versatile HF Radar Calibration Target in Low Earth Orbit, Radio Science VOL. 43, RS1010, doi:10.1029/2007RS003692, 2008

SLR Return Analysis for SOHLA-1

Takahiro Inoue, Shinichi Nakamura, Ryo Nakamura, Keisuke Yoshihara (JAXA), Hiroo Kunimori (NICT), and Toshimichi Otsubo (Hitotsubashi University)
E-mail: inoue.takahiro@jaxa.jp

SOHLA-1, which is planned to be launched in 2009, is a 50kg-class spin stabilized satellite. One of the missions of SOHLA-1 is the tech-demo of the low-cost, micro-GPS receiver developed by JAXA based on COTS automobile technology. SLR is needed for the calibration of GPS based satellite positioning. The SLR data are intermittently observed because of the satellite's spin. To evaluate the impact of spin on return availability, the patterns of observation data are simulated.

SLR Return Analysis for Astro-G

Takahiro Inoue, Shinichi Nakamura, Ryo Nakamura, Keisuke Yoshihara, and Hiroshi Takeuchi (JAXA),Hiroo Kunimori (NICT), and Toshimichi Otsubo (Hitotsubashi University)
E-mail: inoue.takahiro@jaxa.jp

Astro-G, which is planned to be launched in 2012, is a next-generation space radio telescope which is designed to reveal fascinating phenomena such as the relativistic phenomena in the space around super-massive black holes at the centers of galaxies. For the space Very Long Baseline Interferometry(VLBI) mission, this satellite requires an orbit determination accuracy higher than 10 cm at the apogee, and therefore will carry a GPS receiver and a LRA. The SLR data are expected to fluctuate because of the phase referencing observations. The expected returns from Astro-G are simulated and proper bin sizes and editing methods for making QLNPs are studied.

Upcoming missions from Asian region

Hiroo Kunimori and WPLTN contributors
NICT, Japan
E-mail: kuni@nict.go.jp

The paper is summary report of new mission which carries laser retroreflector array in Asian countries, namely China, India, Japan and Korea who have been planned including information not only already formally submitted to ILRS but also that of new and updated. It is summarized regarding mission objectives, orbit, retroreflector design and launch schedule. Those missions are featured the following types:

1. Regional Navigation :

Mission Name	Orbit	Time frame	Nation
COMPASS series	GEO/MEO	~2011 or earlier	China
(12 satellites constellation) and pre-test satellite was launched in 2007.
QZS-1	IGSO	2009	Japan
IRNSS	GEO/IGSO	2009-2012	India
(7 satellites constellation)

2. Science

Astro-G SVLBI	MEO	2011 or later	Japan
HY-2 Oceanography	LEO	2010	China
STSAT-2 Atmosphere and Earth radiation	LEO	2009	Korea
KOMPSAT-5 A-Occultation	LEO	2010

3. Engineering and test

SOHLA National Made-GPSR	LEO	2009	Japan
(OICETS) Laser-COM	LEO	Re-activation 2008	Japan

All orbit is circular except Astro-G and STSAT2.
Although detailed presentation should be in a separate paper in workshop and/or ILRS WEB sites, how variety missions emerging from Asian region should be noted. It is intersting in comparing array design of high satellites and in discussion on role of SLR depending on required accuracy, and on primary/secondary importance for science and to understand ground network resources and strategy needed in each country, regional and global level.
LEO: Low Earth Orbit
MEO: Medium Earth Orbit
GEO: Geostationary Earth Orbit
IGSO : Inclined Geostationary Earth Orbit

Aircraft Avoidance Technologies

T. W. Murphy, E. G. Adelberger, J. B. R. Battat, W. Coles, C. D. Hoyle, K. Kassabian, R. J.  McMillan, J. Melser, E. L. Michelsen, C. W. Stubbs, H. E. Swanson, J. Tu, A. White
University of California, San Diego, USA,
E-mail: tmurphy@physics.ucsd.edu

Propagating a non-eyesafe laser beam through the atmosphere requires a scheme for aircraft avoidance. In the U.S., the Federal Aviation Administration (FAA) requires two human spotters with laser kill-switches to maintain vigilant watch on the sky during operations. A technological solution to this problem is far preferable. The APOLLO lunar ranging operation has installed an infrared camera on the telescope frame coupled with software that looks for motion of a thermal source across the sky, shutting the laser off when an airplane is visible in the 5x7 degree field of view. Also, an aircraft transponder detector senses the presence of aircraft within 15 degrees of the telescope boresight. The transponder detector consists of a phased array of patch antennas in conjunction with an omni-directional patch, together alerting the system to an airplane within the directional beam, independent of distance or transponder power. The array spans about 0.5 m, and can sit on the sky-side of the secondary mirror on large telescopes. Processing of the signals can produce a log of coded aircraft identities and altitudes. The two systems complement eath other, with the IR system good for close, high-angular-velocity airplanes, and the transponder system appropriate for distant high-altitude commercial traffic.

Satellite Laser Ranging Tracking through the Years

Carey Noll
NASA GSFC
E-mail : Carey.Noll@nasa.gov
Presenter: Maurice Dube

Poster:
Satellites equipped with retroreflectors have been tracked by laser systems since 1965. Satellite laser ranging supports a variety of geodetic, earth sensing, navigation, and space science applications. This poster will show the history of satellite laser ranging from the late 1960's through the present and will include retro-equipped satellites on the horizon.

ILRS Web Site Update

C. Noll (1), M. Torrence (2)
(1) NASA GSFC E-mail : Carey.Noll@nasa.gov
(2) SGT, E-mail: mark.h.torrence.1@gsfc.nasa.gov

Poster:
The ILRS Web site, http://ilrs.gsfc.nasa.gov, is the central source of information for all aspects of the service. The Web site provides information on the organization and operation of ILRS and descriptions of ILRS components, data, and products. Furthermore, the Web site and provides an entry point to the archive of these data and products available through the data centers. Links are provided to extensive information on the ILRS network stations including performance assessments and data quality evaluations. Descriptions of supported satellite missions (current, future, and past) are provided to aid in station acquisition and data analysis. This poster will detail recent improvements made in several areas of the ILRS Web site including specific examples of key sections and webpages.

An overview of ESA's upcoming missions equipped with SLR

M. Otten, T.A. Springer, Daniel Navarro-Reyes, Pierre Femenias, Pierrik Vuilleumier, Rune Floberhagen, Mark Drinkwater, Roger Haagmans, Berthyl Duesmann, J. Dow
ESA/ESOC, Germany
E-mail: michiel.otten@esa.int

In this presentation we will give an overview of ESA's upcoming missions equipped with Satellite Laser Ranging reflectors. This overview will include the ESA Earth Observation missions: GOCE (2008), Proba-2 (2009), CryoSat-2 (2009), Swarm (2010), Sentenil-3A (2012), Proba-V (2012) and Sentenil-3B (2014). Besides these Earth Observation missions ESA's Galileo spacecrafts will be equipped with a satellite laser reflector. We will also give a short status on the future of Envisat and ERS-2.
In each of the overviews we will specifically focus on the mission characteristics that are important to the Satellite Laser Ranging community.

Implementing the Consolidated laser Ranging Data (CRD) Format throughout the ILRS Network

Randall Ricklefs(1), Carey Noll(2), Julie Horvath(3), Oscar Brogdon(3), Erricos Pavlis(4
(1) The University of Texas at Austin, Center for Space Research
(2) NASA Goddard Space Flight Center
(3) HTSI
(4) University of Maryland Baltimore County, Joint Center for Earth Systems Technology
E-mail: ricklefs@csr.utexas.edu

Due to technological changes and new missions such as LRO and T2L2 that require higher precision laser ranging data and additional data fields, a new laser data format was required. After several years of development, the Consolidated laser Ranging Data (CRD) format, which combines full-rate, sampled engineering, and normal point data in an expanded, flexible format, is ready to be implemented throughout the ILRS network. The first step in implementation requires the Operations Centers (OCs) and Data Centers (DCs) to be able to accept and distributed data in the CRD format. Next, a number of analysis centers (ACs) must be able to ingest data in the new format for testing. Finally, the stations need to produce the CRD format. Owing to the changes in precision and total restructuring of the data format, it has been decided to require validation of each station's normal points in the new format prior to their being made generally available. The timetable, details, and status of the implementation will be presented.

Considerations for an Optical Link for the ACES Mission

Ulrich Schreiber, Ivan Prochazka
TUM - FESG, Germany
Email: schreiber@fs.wettzell.de

Satellite Laser Ranging (SLR) provides a technology, which is most suitable for time transfer. While other optical timescale adjustment approaches usually perform frequency comparisons and make use of data averaging, SLR directly links the epochs of the respective timescales with high accuracy on a shot by shot basis. However technologically one has to overcome a few obstacles, because the timing of optical laser pulses still requires the transition from the optical regime into the electronic regime. Systematic effects in the signal conversion cause extra time delays and this may result in an unwanted timescale offset if not properly accounted for. Additional difficulties are coming from the measurement requirement of a very wide receiver field of view (1 rad or more) and the corresponding high level of background light. Therefore the proper choice of the applied optical detector in the most stable operation regime makes up an important part of the proposed laser ranging clock comparison on the ACES mission. The K14 Single Photon Avalanche Diode (SPAD) fulfills these requirements. Operated in the coherent Geiger mode the calculations show, that a sufficient signal to noise ratio can be achieved even when the entire receiver footprint on the Earth is illuminated by the sun.

Moblas 8 Return to Operations

Scott Wetzel, Howard Donovan, Julie Horvath, Dennis McCollums, Thomas Oldham, Alice Nelson, Don Patterson, Mike Henick
NASA SLR / HTSI, USA
E-mail: scott.wetzel@honeywell.com

The MOBLAS 8 station located on the island of Tahiti has been operational at that location since 1997. Recently, in 2007, the station suffered from multiple failures of components and subsystems. Due to the changeover of station personnel and the removal of HTSI from the island to help with the operations and maintenance in 2004, the multiple failures of the system caused the MOBLAS 8 system to be inoperable in March 2007. Working closely with NASA, CNES, and UFP, HTSI developed a training plan for the station manager from the Moblas 8 site as well as the TLRS-3 station manager from Arequipa, Peru. Following the training back at NASA's Goddard Space Flight Center (GSFC) in Greenbelt, Maryland, the MOBLAS 8 Station Manager worked with HTSI personnel to repair subsystems and components at GSFC. Later, two HTSI engineers traveled to the MOBLAS 8 station to work with the Station Manager and the UFP and CNES crew to complete the system and site repairs, resulting in the restart of operations at this critical site in the South Pacific. This paper chronicles the work that was planned and executed along with the benefits to the NASA, UFP, CNES and the ILRS with the repairs and efforts to return the station to operations.

Planetary Laser Ranging and Altimetry Missions and Studies at NASA/GSFC and MIT

David E. Smith, Maria T. Zuber
NASA-GSFC, USA
E-mail: David.E.Smith@nasa,gov

Several planetary missions are being contemplated that will utilize laser ranging for tracking or landing while others will be used to demonstrate laser ranging capabilities over AU distances. MGS has already been used to demonstrate 1 way tracking to Mars at 80M km, and MESSENGER has been used to demonstrate 2-way ranging at 24M km and experiments will be attempted when the spacecraft is in orbit at Mercury. LRO will carry a one-way laser ranging system for precision (10cm) tracking in lunar orbit and also a small laser array for 2-way ranging for the most capable of stations. The LADEE mission to the Moon will carry a laser com system but at present will not do laser ranging. The two GRAIL spacecraft will probably carry small micro-arrays for possible detection of the spacecraft after impact. All the above missions are in flight or are approved to fly in the next few years.
In addition, several concepts are understudy as planetary missions that use lasers for geodetic measurements or instruments that we expect to use on future missions. In the majority of cases these concepts are for actual science measurements or investigations and not primarily demonstrations; thus they are not pushing the technology but pushing the application. These include a Europa altimeter mission with a one-way ranging system that will operate in Europa orbit at Jupiter for precision orbit determination, a solar system dynamics mission that would use laser ranging between 2 spacecraft over interplanetary distances, a mission that would place laser reflectors on an asteroid in an orbit that comes close to Earth, and a mission that would map and track an asteroid for measuring the Yarkovsky effect on planetary bodies and detect the gravitational flattening of the sun.