Yuki D. Takahashi University of California, Berkeley 2002 / 9 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? [pictures from gsfc.nasa.gov] Discover the New Universe (< 30 MHz) The only unexplored part of the electromagnetic spectrum in astronomy Revolution 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]

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 > $1B Phase III (~2030) [ESA] 25 cm 2 m

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 Reconfirm the need for the lunar environment. Identify an ideal site near the lunar south pole. 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. Available: (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 demo of 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: Dx = 30 m Altimeter: Dz = 40 m Need: High-resolution topography of the south polar regions (especially dark areas) Dz = ½ m, Dx = 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 SELENE (2006) Images of the south polar region. SELENE (2006) Lunar Radar Sounder (4-6 MHz) Subsurface reflections down to ~ 5 km (Dz=100m) Radio interference from Earth / Sun. Terrain Camera & Laser Altimeter (Dx=10m, Dz=5m) Radio Science (lunar “ionosphere”) Lunar Magnetometer

Remaining Measurements The most crucial measurements to be planned: Topography at vertical resolution Dz = ½ m, with spot size Dx = 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