Interplanetary Lasers

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Interplanetary Lasers
Free space optical communications
Joss Hawthorn,Jeremy Bailey,Andrew
McGrath Anglo-Australian Observatory
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This Presentation

• Illustrating the current communications problem
• Cost advantages of optical solution
• Reasons for an Australian involvement

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Exploration of Mars

• Highlights the communications problem
• Long term and substantial past and continuing
  international investment

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Exploration of Mars

• 1960 Two Soviet flyby attempts
• 1962 Two more Soviet flyby attempts,Mars 1
• 1964 Mariner 3, Zond 2
• 1965 Mariner 4 (first flyby images)
• 1969 Mariners 6 and 7
• 1971 Mariners 8 and 9
• 1971 Kosmos 419, Mars 2 3
• 1973 Mars 4, 5, 6 7 (first landers)
• 1975 Viking 1, 1976 Viking 2

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Exploration of Mars

• 1988 Phobos 1 and 2
• 1992 Mars Observer
• 1996 Mars 96
• 1997 Mars Pathfinder, Mars Global Surveyor
• 1998 Nozomi
• 1999 Climate Orbiter, Polar Lander and Deep Space
  2
• 2001 Mars Odyssey

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Planned Mars Exploration

• 2003 Mars Express
• 2004 Mars Exploration Rovers
• 2005 Mars Reconnaissance Orbiter
• 2007 Scout Missions 2007
• 2009 Smart Lander, Long Range Rover
• 2014 Sample Return

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Interplanetary Communication

• Radio (microwave) links, spacecraft to Earth
• Newer philosophy - communications relay (Mars
  Odyssey, MGS)
• Sensible network topology
• 25-W X-band (Ka-band experimental)downlink

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Communications Bottleneck

• Current missions capable of collecting much more
  data than downlink capabilities (2000!)
• Currently planned missions make the problem 10x
  worse
• Future missions likely to collect ever-greater
  volumes of data

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Communications Bottleneck

• Increasing downlink rates critical to continued
  investment in planetary exploration

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Communications Bottleneck

• NASA presently upgrading DSN
• NASA's perception of the problem is such that
  they are considering an array of 3600
  twelve-metre dishes to accommodate currently
  foreseen communications needs for Mars alone

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Communications Energy Budget

• Consider cost of communications reduced to
  transmitted energy per bit of information
  received

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Communications Energy Budget

• Assumptions

• information proportional to number of photons
  (say, 10 photons per bit)
• diffraction-limited transmission so energy
  density at receiver proportional to (?R/DT)-2
• received power proportional to DR2
• photon energy hc / ?
• So Cost proportional to R2? / (DT2DR2)

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Communications Energy Budget
Cost proportional to R2? / (DT2DR2) X-band
transmitter ? 40 mm Laser transmitter ?
0.5-1.5 ?m Assuming similar aperture sizes and
efficiencies, optical wins over microwave by 3
orders of magnitude
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Long-term Solution

• Optical communications networks

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Long-term Solution

• Optical communications networks

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Long-term Solution

• Optical communications networks
• Advantages over radio
• Higher modulation rates
• More directed energy
• Analagous to fibre optics vs. copper cables

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Lasers in Space

• Laser transmitter in Martian orbit with large
  aperture telescope

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Lasers in Space

• Laser transmitter in Martian orbit with large
  aperture telescope

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Lasers in Space

• Laser transmitter in Martian orbit with large
  aperture telescope
• Receiving telescope on or near Earth
• Preliminary investigations suggest 100Mbps
  achievable on 10 to 20 year timescale
• Enabling technologies require accelerated
  development

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Key Technologies

• Suitable lasers
• Telescope tracking and guiding
• Optical detectors
• Cost-effective large-aperture telescopes
• Atmospheric properties
• Space-borne telescopes

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Optical spacecraft comms

• ESA have already run intersatellite test
• NASA/JPL and Japan presently researching the
  concept and expect space-ground communications
  tests in the near future

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An Australian Role

• Australian organisations have unique capabilities
  in the key technologies required for deep space
  optical communications links
• Existing DSN involvement
• High-power, high beam quality lasers
• Holographic correction of large telescopes
• Telescope-based instrumentation
• Telescope tracking and guiding

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The University of Adelaide

• Optics Group, Department of Physics and
  Mathematical Physics
• High power, high beam quality, scalable laser
  transmitter technology
• Holographic mirror correction
• Presently developing high power lasers and
  techniques for high optical power interferometry
  for the US Advanced LIGO detectors

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Anglo-Australian Observatory

• Telescope technology
• Pointing and tracking systems
• Atmospheric transmission (seeing, refraction)
• Cryogenic and low noise detectors
• Narrowband filter technology

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Australian Centre for Space Photonics

• Manage a portfolio of research projects in the
  key technologies for an interplanetary optical
  communications link
• Work in close collaboration with overseas
  organizations such as NASA and JPL

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Australian Centre for Space Photonics

• Take advantage of unique Australian capabilities
• Australian technology critical to deep space
  missions
• Continued important role in space

FOR MORE INFO...
http//www.aao.gov.au/lasers