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Photonics in Space Applications

Nov 15, 2012
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Webinar Questions and Answers from Dr. Rubenchik:

Dr. Alexander Rubenchik
Lawrence Livermore National Laboratory, Livermore, Calif.

The Promise of Pulsed Lasers in Removing Orbital Debris

38 years of poor practice in space launches, plus deliberate as well as accidental spacecraft collisions, have created several hundred thousand pieces of space debris larger than 1 cm in the 400-2000-km altitude low Earth orbit (LEO) band (At typical closing velocities, debris as small as 1 cm can punch a hole in the Space Station). This runaway collisional cascading, predicted more than 30 years ago, threatens the use of LEO space.

Dr. Rubenchik will speak on "The Promise of Pulsed Lasers in Removing Orbital Debris." He will present research from a paper he co-authored on a proposal for laser orbital debris removal, which uses a focused, pulsed ground-based laser to change the debris orbit and cause it to re-enter the atmosphere.

Alexander M. Rubenchik received his PhD in theoretical physics from the Institute of Nuclear Physics, Novosibirsk, Russia, in 1974, and the Dr. Sci. degree from the Space Research Institute, Moscow, in 1983.

Dr. Rubenchik has been a physicist at Lawrence Livermore National Laboratory since 1992. His main scientific interests are in physics of laser-matter interactions, nonlinear optics including the studies of optical damage, laser physics and plasma physics. He is the author of more than 300 publications and is a member of OSA and The Directed Energy Professional Society (DEPS).

Questions & Answers from the Webinar for Dr. Rubenchik:

Do you have any thoughts on how we might accurately find and track these objects so the laser can be aimed correctly?

Today tracking and finding have been done with radar mainly.Their resolution is not good for debries smaller then 10 cm. Laser radars greatly enhanced tracking accuracy. The ground system for debris removal can be used also for debris tracking. Details see in -C.Phipps et al Removing Orbital Debris with Lasers. Advances in Space Research 49. 1283.2012.

How does one choose the appropriate power laser?

See discussion in A.Rubenchik , A.C.Erlandson, D.Liedahl, “ Laser system for space debris cleaning”, AIP Conference Proceedings Volume: 1278 Pages: 347-53, HPLA 2012.

Is this ground-based laser using an inverse atmospheric focusing system?

Yes.The system will used adaptive optics based on beacon located out over the atmosphere.

Where can I reference mechanical coupling coefficients?

See review C.Phipps et al Removing Orbital Debris with Lasers. Advances in Space Research 49. 1283.2012 and reference therein.

What is the effect of the atmosphere on a high intensity beam. in terms of turbulance and heating?

It is a manageable problem. See review C.Phipps et al Removing Orbital Debris with Lasers. Advances in Space Research 49. 1283.2012 and reference therein.

What is the influence of atmosphere on beam quality? Are there Kerr lens effects in the atmosphere at these powers?

It is a manageable problem. See review C.Phipps et al Removing Orbital Debris with Lasers. Advances in Space Research 49. 1283.2012 and reference therein.

Is it dependent on energy rather than fluence? Rather than peak power per unit area?

Local laser matter interaction is determined by the fluence. But the spot size is larger then debries, a lot of energy is lost. So the total laser pulse energy is important.

So, are we to understand that the ablation process is independent of spot size and pulse duration?

For the nanosecond pulses, the interaction is determined by the local intensity and independent of spot size for spots larger 1 mm. Pulse duration dependence is important.

Does this assume that momentum change occurs at the center of mass? What are the challenges related to the motion of the debris (600 km at the speed of light is about 2 ms, for LEO we're around 8 km/s, so the debris has moved about 16m).

There is no simple answer to your question. The velocity change depends on debris shape.Ablation not only changes center mass velocity but can induce the rotation. See details in D.Liedahl , S.Libby, A.Rubenchik, Momentum transfer by laser ablation of irregularly shaped space debris” AIP Conference Proceedings, Volume: 1278 Pages: 772-9 HPLA 2010.2010. During the 4 nsec laser shot the target moves by 30µm only. For the next pulse the spot must be moved with debris.

Dr. Mark Clampin
Observatory Project Scientist
NASA Goddard Space Flight Center

The Optics of the James Webb Space Telescope

Dr. Clampin will address the design of the telescope optics, discuss the program to fabricate and test the optics and review on-orbit phasing and alignment.

The James Webb Space Telescope (JWST) is a large, infrared-optimized space telescope. JWST's primary science goal is to detect and characterize the first galaxies. It will also study the assembly of galaxies, star formation, and the formation of evolution of planetary systems. The observatory has a large primary mirror 6.5 meters in diameter, designed to deliver high angular resolution and a large collecting area. The telescope optics are designed and fabricated to operate at the cryogenic temperatures (~40 k) required for an IR optimized telescope.

Since the observatory dimensions exceed the Ariane 5 fairing size, the observatory has to be stowed for launch and deployed following launch, so the primary mirror has a segmented mirror architecture to facilitate deployment after launch. The observatory is designed to achieve its cryogenic operating temperature via passive cooling, facilitated by a five-layer sunshield that keeps the telescope in the sun's shadow. The observatory will be launched into an L2 orbit that provides continuous science operations and a benign thermal environment for optical stability.

Dr. Clampin is the Principal Investigator of the Extrasolar Planetary Imaging Coronagraph (EPIC) Discovery Mission Concept and of the Transit Characterization Explorer (TRACER), a SMEX mission concept. Dr Clampin was a Co-Investigator and Detector Scientist for Advanced Camera for Surveys (ACS) science team; and he is a Principal Investigator and Co-Investigator on the Hubble Space Telescope, Spitzer and ground-based investigations of debris disks.

Additional information on the James Webb Telescope is available at:
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