Lasers and Rules of the Road for Responsible Space-Faring Nations
On 12:30pm on Thursday, February 12, 2009, the Stimson center hosted a discussionofthe multiple uses of lasers for outer space activities and how rules of the roadmight help clarify their responsible and irresponsible uses. Dr. Michael Pearlman discussed his work as Director of the International Laser Ranging Service (ILRS), and Dr. Yousaf Butt discussed his research into a specific case involving lasing of U.S. intelligence satellites.
Dr. Pearlman summarized his presentation as follows:
Satellite Laser Ranging (SLR) uses short pulse lasers to measure the distance from ground stations to Earth orbiting satellites with passive (no power required) retroreflector arrays to support program in earth science and space applications. SLR provides precision orbit determination on satellites and a time history of ground station positions, which are developed into data products to support the terrestrial reference frame, measurements of plate tectonics and crustal motion, gravity field, Earth orientation, ocean and ice surface topography, relativity, and spacecraft dynamics. The technique is known for centimeter quality orbits and long period, stable time series of geodetic parameters. The technique originated at NASA in 1964. Presently a consortium of 33 SLR station around the world routinely track 25 – 30 satellites and provide their data to international data centers for access by a community of 20 analysis centers that furnish data products for scientific applications. Targets tracked range from low earth orbiting satellites with active payloads such as altimeters, synthetic aperture radars, satellite to satellite tracking for gravity field mapping, and atmospheric monitoring devices to navigation satellites such as GPS and Galileo. SLR also tracks a complex of heavy passive spherical satellites, uniformly covered with retroreflectors to help maintain the terrestrial reference frame that permits us to measure terrestrial change (earth, oceans, ice, etc) over thousands of kilometers of distance, decades in time, and evolving technology. Satellite being tracked have been built in the US, Europe, Russia, Japan, China, and Korea. Organizations in 35 countries participate in the ILRS.
The International Laser Ranging Service (ILRS), established by the International Association of Geodesy, coordinates these activities, develops the standards and specifications necessary for product consistency, and sets the priorities and tracking strategies for the network. The Service organizes and overseas the data cycle through to the issue of data products for the scientific community. It also works with space agencies on the design of retroreflectors arrays for future satellites.
New satellites are added to the ILRS tracking roster through an application and vetting process. Satellites are deleted as projects are completed.
The laser ranging technique advances with new technologies. Current developments that are appearing in the network include kilohertz ranging operations, low-power eye-safe laser transmitters, automated tracking, faster rise time electronics and web-based remote systems to protect satellite missions that for some periods of time may have optical detectors in vulnerable configurations. Also being developed are optical transponders to extend laser ranging operations to interplanetary distances.
Dr. Pearlman's presentation is available here.
Dr. Butt made the following points:
Satellite Laser Ranging (SLR) is a widely used technique for determining the orbits of objects in space with high accuracy. There are seven known SLR stations in China, two of which are mobile. These stations are part of a scientific collaboration called the International Laser Ranging Service (ILRS) based at the Goddard Space Flight Center in Greenbelt, Maryland. The typical average laser power used in the Chinese SLR stations is below about 1 Watt (W), although experimental systems of roughly 40W have also been used to characterize objects such as space debris. Most of the ranging takes place at night although some capability for more technically challenging daytime SLR reportedly exists at two of the fixed stations.
Consider laser ranging to an earth-observing imaging satellite and what effect that might have on the satellite. Under a broad set of conditions such ranging would not adversely affect the satellite’s sensitive detector, but cases exist in which the effects can be significant, although the probability of damaging the detector is extremely low. This is because considerable energy may be concentrated in a single pulse of a pulsed laser used in SLR operations. Therefore, SLR cannot be considered an anti-satellite (ASAT) weapon and, in fact, would be ineffective in this role. Nonetheless, the possibility of laser ranging to ground-imaging satellites without authorization, resulting in unexpected detector performance, is motivation for converging on a set of international rules governing it use. As a concrete case, the Fall 2006 allegations of Chinese lasing of US Spy (i.e. National Reconnaissance Office) Satellites and offer one possible explanation in terms of SLR.
Dr. Butt's presentation is available here.
An audio recording of the event will be available shortly.
When: Thursday, February 12, 2009
