cooperation between lunar scientists and astronomers: proposing lunar science missions to enable...

Cooperation Between Lunar Scientists and Astronomers:

Proposing Lunar Science Missions to Enable

Astronomy from the Moon

Yuki D. Takahashi

University of California, Berkeley

2002 / 9

Why Astronomy from the Moon?Some observations are feasible only by using the Moon...

• as a Shield (against Sun / Earth)– Permanent darkness– Radio quietness

• as a Platform (stable & large area)– Interferometry w/ long baselines

• for Access– Serviceability, Expandability– Human access from a lunar base– Much lower risk

Examples: Very-low-frequency (VLF) radio array Infrared telescope(s) for ES planets

[http://optics.nasa.gov/concept/llt.html]

Why Very-Low-Frequency astronomy?

Discover the New Universe (< 30 MHz)– The only unexplored part of the

electromagnetic spectrum in astronomyRevolution in human view of the

Universe through unexpected discoveries

• Relies on the Moon:– Interference shielding crucial (see ->)

– Stable platform for many array elements

– Urgent! (before Moon is contaminated)» [Desch 1990]

Vis

wavelength (m) 10-1510-1410-1310-1210-1110-10 10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 1 10 102 103 104

frequency (Hz) 1023 1022 1021 1020 1019 1018 1017 1016 1015 1014 1013 1012 1011 1010 109 108 107 106 105 104

observatory HST

Viewof theUniverse

UVX

CGRO ROSAT

VLF

Moon-based array?

?Let's find out!

EUVE IRAS COBE Earth-based

IR MW RADIO

[pictures from gsfc.nasa.gov]

25 cm

2 m

Lunar Far Side VLF Array• Site: a large far side crater (Tsiolkovsky ~100km)

• Array of many short crossed dipole antennas

• All-sky aperture synthesis mapping

• Relay sat. at L2

Require:– Far side access– Funding > $1BPhase III (~2030)

[ESA]

Current Status• Technically feasible w/ current technology.• Over 40 articles/papers since the 1960s.• At least 3 major published design studies:

– 1992 Hughes Aircraft Company.

– 1993 International Space University design project.

– 1997 ESA design study.

• No funding/plan.

Must publicize the significant discovery potentials of very-low-frequency astronomy.

Must begin with a cheap mission for an initial survey.

New Realistic Proposal• To save cost: Piggyback on a lunar lander mission.

– Antennas themselves are very light-weight.

– Share power/communication systems w/ the main mission.

– Antennas deposited by existing rovers. An ideal technology demonstration task? Inexpensive addition to any mission’s scientific potential.

• Next landers: Lunar South Polar region.– Water ice, Lunar base

– Malapert Mountain (communication, power)

• Initial survey of the unknown sky:– To discover new objects / phenomena at very low frequencies.

Lunar South Polar Site• Malapert Mountain (5 km high)

– could shield terrestrial interference for an observatory situated on the opposite side of it from Earth.

• Linear array will work– Rotation synthesis Simple deployment

• Sky coverage– limited, but sufficient

for an initial survey.

• Accessibility– From the lunar base

for future expansion.[Margot et al. 1999]

To Make It Happen

I. Reconfirm the need for the lunar environment.

II. Identify an ideal site near the lunar south pole.

III. Propose an affordable piggyback mission.

We need:

- Confirming measurements on the Moon.

- Detailed survey of the candidate sites.

* Lunar “Ionosphere”? Sets the lowest observable frequency.

(10~30 MHz on Earth)

• Available:– Only day-time measurements from the 1970s (Apollo CPLEE / SIDE, Luna 22)

• Need:– Cut-off frequency at the polar region.– Variations (day/night/transitions)[Dual-frequency phase-lag measurements.]

[Benson et al. 1975]

* Radio Quietness Reconfirm the lunar advantage. Sets the sensitivity.

• Available:– RAE-2 demoof terrestrial noise at the Moon ->

• Need:– Interference level

in the polar regions.– Shielding by a mountain (Malapert).[Low frequency receivers on site: 50 kHz – 30 MHz]

[Alexander et al. 1975]

* Terrain/Topography Find an ideal site (flat, smooth, large)

– Transportation, deployment, line-of-sight communication

• Available (Clementine):– Camera: x = 30 m– Altimeter: z = 40 m

• Need:– High-resolutiontopography of thesouth polar regions(especially dark areas)z = ½ m, x = 10 m

[Clementine (NASA)]

* Subsurface Ensure no disturbing reflections of radio waves off of

subsurface structures. Site selection.

• Available:– Apollo Lunar

Sounder Exp.

• Need:– Radar sounding

at 50 kHz - 30 MHz.

– To ~10 km depth.[Lunar Sourcebook 1991]

Other measurements

• Magnetic field at candidate sites (confirm low)

• Thermal environment

• Accessibility (deployability)

• Malapert Mountain utility

• Seismicity

Upcoming Missions

• LunarSat / SMART-1– Images of the south polar region.

• SELENE (2006)– Lunar Radar Sounder (4-6 MHz)

• Subsurface reflections down to ~ 5 km (z=100m)

• Radio interference from Earth / Sun.

– Terrain Camera & Laser Altimeter (x=10m, z=5m)– Radio Science (lunar “ionosphere”)– Lunar Magnetometer

Remaining Measurements

The most crucial measurements to be planned:

• Topography at vertical resolution z = ½ m, with spot size x = 10 m.

• In-situ measurements with dipole receivers:– Plasma cut-off frequency– Interference levels– Observation test

Summary• The unique lunar environment enable astronomical

observations that would otherwise be impractical from Earth or free space. The unknown, very-low-frequency window is especially promising for significant discoveries.

• VLF interferometer could be deployed very inexpensively as a piggyback project on a larger lunar lander mission.

• To propose such a mission, we need a more detailed in-situ survey of the conditions at the candidate sites.

• We should keep these interests in mind as we plan lunar science missions to make the most out of them. Thanks!

Acknowledgements:– I’d like to thank the individuals of NASA's Human Exploration and Development in

Space (HEDS) Enterprise for supporting and inspiring students like me.

Aim• Who: NASA, lunar/planetary scientists,

SELENE, SMART-1, Mike, Bernard

• Get them interested in astronomy from the Moon.– Motivation– Inexpensive mission proposal

• Ensure they know what measurements are demanded and why important.– Existing data– Required measurements