Interplanetary LasersInterplanetary Lasers

Joss Hawthorn,Jeremy Bailey,Andrew McGrath

Anglo-Australian Observatory

Free space opticalFree space optical communications communications

This PresentationThis Presentation

Illustrating the current communications problem

Cost advantages of optical solutionReasons for an Australian

involvement

Exploration of MarsExploration of Mars

Highlights the communications problem

Long term and substantial past and continuing international investment

Exploration of MarsExploration 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

Exploration of MarsExploration 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

Planned Mars ExplorationPlanned 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

Interplanetary CommunicationInterplanetary Communication

Radio (microwave) links, spacecraft to Earth

Newer philosophy - communications relay (Mars Odyssey, MGS)

Sensible network topology25-W X-band (Ka-band experimental)

<100 kbps downlink

Communications BottleneckCommunications 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

Communications BottleneckCommunications Bottleneck

Increasing downlink rates critical to continued investment in planetary exploration

Communications BottleneckCommunications Bottleneck

NASA presently upgrading DSNNASA'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

Communications Energy BudgetCommunications Energy Budget

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

Communications Energy BudgetCommunications Energy Budget

• 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 / (DT

2DR2)

Assumptions:

Communications Energy BudgetCommunications Energy Budget

Cost proportional to R2 / (DT2DR

2)

X-band transmitter ~ 40 mmLaser transmitter ~ 0.5-1.5 m

Assuming similar aperture sizes and efficiencies, optical wins over microwave by > 3 orders of magnitude

Long-term SolutionLong-term SolutionOptical communications networks

Long-term SolutionLong-term SolutionOptical communications networks

Long-term SolutionLong-term SolutionOptical communications networksAdvantages over radioHigher modulation ratesMore directed energyAnalagous to fibre optics vs. copper

cables

Lasers in SpaceLasers in SpaceLaser transmitter in Martian orbit

with large aperture telescope

Lasers in SpaceLasers in SpaceLaser transmitter in Martian orbit

with large aperture telescope

Lasers in SpaceLasers in SpaceLaser transmitter in Martian orbit with

large aperture telescopeReceiving telescope on or near EarthPreliminary investigations suggest

~100Mbps achievable on 10 to 20 year timescale

Enabling technologies require accelerated development

Key TechnologiesKey TechnologiesSuitable lasersTelescope tracking and guidingOptical detectorsCost-effective large-aperture

telescopesAtmospheric propertiesSpace-borne telescopes

Optical spacecraft commsOptical 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

An Australian RoleAn Australian RoleAustralian 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

The University of AdelaideThe University of AdelaideOptics 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

Anglo-Australian ObservatoryAnglo-Australian ObservatoryTelescope technology Pointing and tracking systems Atmospheric transmission (seeing,

refraction) Cryogenic and low noise detectors Narrowband filter technology

Australian Centre for Space PhotonicsAustralian 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

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

Australian Centre for Space PhotonicsAustralian Centre for Space Photonics