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SPIDAR: �VLF Astronomy on the Moon

Jodi Y. Enomoto

University of Southern California

ASTE 527: Space Exploration Architectures Concept Synthesis Studio

December 15, 2008

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Contents

  • Context and Rational
  • VLF Astronomy
    • A New View of the Universe
    • Why do we need the Moon?
  • South Pole Observatories
    • SPIDAR (South Pole Isolated Dipole ARray)
    • Optical Interferometer
    • Heliograph
    • Infrared Interferometer
  • Further Studies & Future Missions

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Context

  • Mission Statement:
    • Return humans to the Moon for reliably advancing and honing Mars Forward technologies and experience.
    • In the process, establish “permanent science assets” with ASAP returns for all of humanity.
  • This presentation mainly focuses on the 2nd priority.
    • Astronomers are a large and active Origins and “lunar science from the Moon” community.
    • How to deploy, calibrate and commission a variety of science payloads, using crew, as well as their preferred locations spread out globally.

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Rationale

  • “Astronomy may not be the reason to go to the Moon, but it is definitely something we can do that would be beneficial to the scientific community and humanity as a whole.”

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VLF Astronomy: �A New View of the Universe

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  • What will we find?
    • New phenomenon, objects…
    • Low frequency SETI?

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VLF Astronomy:�Why do we need the Moon?

  • Used as a shield
    • The Sun – Solar Wind, Solar Flares, Coronal Mass Ejections

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  • Large stable platform
    • Interferometers with very long baselines
    • No propellants or thrusters necessary for positioning or formation flying

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Observatory Locations�

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Mid Latitude Observatory:

Grimaldi Basin

(East Side, View from Earth)

Far Side Observatory: Daedalus or Tsiolkovsky Crater

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South Pole Observatories:

Mons Malapert, Shackleton Crater, Schrodinger Basin

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= Observatory

North Pole Observatory:

Peary Crater

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Future Missions

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South Pole Observatories

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Mons Malapert

Shackleton

Schrodinger

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Schrodinger Basin:�SPIDAR Observatory

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5km Diameter

Length = 50 x

Communication & Power

Dipoles

“Anchors”

Rover + Crossbow

Supporting Cables

SPIDAR South Pole Isolated Dipole ARray

Transmit to Lunar Base Station

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SPIDAR Observatory �A Curved (Hanging Parabola) Geometry

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50km Diameter

Length = 500 x

Communication & Power

Rover + ABE’s

Allowing some slack the lines would make it more feasible to achieve an array with a MUCH longer baseline

“ABE” = Artillery Based Explorer

SPIDAR South Pole Isolated Dipole ARray

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Schrodinger Basin:�SPIDAR Observatory

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5km Diameter

Length = 50 x

Communication & Power

Dipoles

“Anchors”

Rover + Crossbow

Supporting Cables

SPIDAR System Parameters

Site

Schrodinger Basin

Frequency

1MHz

Wavelength

λ = 300m

Dipole Spacing

λ/2 = 150m

Number of Elements

500

Aperture

5km

Bandwidth

~100kHz

Resolution

TBD

Lifetime

20+ years

Weight (Earth value)

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Array

< 1000kg

Anchors

< 50kg

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Possible Location for SPIDAR:�Schrodinger Lava Tube

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High Resolution

http://www.lpi.usra.edu/publications/slidesets/clem2nd/slide_4.html

Dark-Halo Crater on the Floor of Schrödinger Basin

Located at 76°S, 139°E

5 kilometers across is a volcanic vent that erupted ash during the period of mare volcanism on the Moon, more than 3.5 billion years ago.

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5km

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Assumptions

  • 14 Lunar surface days.
  • Astronauts will assist emplacement of the array on the lunar surface.
    • Rovers, Tele-Operations, etc.
  • Power and communication infrastructure is established prior to the observatory
  • Lunar libration is accurately accounted for with software algorithms.
  • Diurnal temperature variation considerations.

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Emplacement of the Array

    • Raytheon TOW (Tube-launched, Optically-tracked, Wire-guided) Weapon System Technology
    • Simple, straight forward approach: Shoot a line across the crater, secure it, and pull the array across.
    • Pneumatics and (reusable) spring launchers with crossbows.
    • Fine adjustments: Use a laser (pointing) system to indicate desired emplacement points for the array.
      • After the lines are shot across the distance of the crater, astronauts can make fine adjustments to the final placement.

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Calibration of the Array

  • Inertial Measurement Units and Star Trackers (with accurate star maps) to accurately estimate the position (orientation and curvature) of the array
    • Curve fitting of each line array
    • Interpolate / Extrapolate each element position
  • Using laser range finders to get several accurate measurements along each line

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Calibration

    • Inertial Measurement Units and Star Trackers (with accurate star maps) to accurately estimate the position (orientation and curvature) of the array
      • Curve fitting of each line array
      • Interpolate / Extrapolate each element position
    • Using laser range finders to get several accurate measurements along each line.

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Mons Malapert:�Optical Interferometer

  • Meets the objectives and requirements of the 2005 ESAS report.
    • Location: Longitude 0 degrees, latitude 86 degrees S
    • Continuous LOS to Earth for communications link capability
    • Summit is a large, relatively flat landing area
      • 50km in its east-west dimension
  • Optical Interferometer placed on Mons Malapert
    • 3 or more observatories placed 1km or more apart
    • Resolution of milli-arc-seconds to micro-arc-seconds

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Mons Malapert:�Optical Interferometer

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http://www.sciencecodex.com/graphics/Altair_Comp.jpg

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Space Interferometry Mission:

Search for Extrasolar Planets

http://en.wikipedia.org/wiki/Space_Interferometry_Mission

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Shackleton Crater: �Heliograph & Infrared Interferometer

  • Peak of eternal light 🡪 Heliograph, Solar Observation
  • Crater of eternal darkness and extremely low temperatures 🡪 Infrared Interferometer
  • ILOA (International Lunar Observatory Association): Planning 3 missions to the Moon
    • ILO-X (Precursor)
    • ILO-1 (Polar Mission)
    • ILOA’s Human Service Mission
    • Mons Malapert and Shackleton Crater

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Future Studies…

  • SPIDAR baseline aperture
    • Increased for higher resolution capability
  • Artillery Based Explorers (ABE’s) for array emplacement (towed lines)
    • Up to 10km (accurate) range
  • Calibration of the array
    • Accuracy requirements
  • Timeline
    • Latest ESAS document specifies 14-day missions
    • Limits the amount of time on the lunar surface to ~4 days

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Future Missions…�A Phased Approach

  • Early Missions:
    • Seismic activity study
    • UV, Visible and Infra-red (IR)

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  • Future Missions with a Permanent Lunar Base:
    • Observation extra-solar planets, environment, surface
    • Very long wavelength radio astronomy
      • Giant radio telescopes “carved” out of existing craters on the Moon.
    • Optical Interferometer
      • 3 or more observatories spaced 1km apart.
    • ISRU and Giant Liquid Mirror Telescopes (50m)
      • Spinning lunar regolith in a circular dish to create large parabolic surface.
      • Impossible without gravity. However, the Moon’s lower gravity provides the opportunity to achieve extremely large scopes.

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References

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  • Jodi Y. Enomoto, has 5 years of experience in Governmental and Aerospace engineering programs, whose interests include attitude determination and control systems, digital signal processing, and signal processing algorithms for airborne radar systems. She has a B.S. degree in EE with an emphasis on Control Systems from the University of Hawaii, Manoa, and is currently pursuing an M.S. degree in EE with an emphasis on DSP and Communications at the University of Southern California. Her experience related to the contents within this document are almost entirely limited to the research performed while creating this concept in order to fulfill the course requirements of ASTE 527 during the Fall 2008 semester at USC .

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Reference:

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BACK-UP SLIDES

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  • VLF Astronomy:
    • http://www.ugcs.caltech.edu/~yukimoon/RALF/
    • We, humans on Earth, have essentially never observed the universe at any wavelengths greater than 20m (frequencies below 15MHz) because of absorption and scattering by the Earth’s ionosphere.Even at 30MHz (10m), ionospheric phase effects limit the interferometry baseline to only 5km, corresponding to only about 10 arcmin resolution.Observing through this new spectral range will lead to discoveries of new phenomena and new classes of objects.

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Abstract Picture

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Rover + Crossbow

SPIDAR South Pole Isolated Dipole ARray

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Schrodinger Basin

  • Low Frequency SETI and Radio Astronomy
  • SPIDAR (South Pole Isolated Dipole ARray) Observatory
    • Frequencies < 20 MHz 🡪 Wavelengths > 15m
    • High resolution requires huge antenna aperture
  • ILOM (In-situ Lunar Orientation Measurements) and LLFAST (Lunar Low Frequency Astronomical Observatory) are proposed as plans of astronomical observations on the Moon which should be realized in a future lunar mission. ILOM is a selenodetic mission to study lunar rotational dynamics by direct observations of the lunar physical libration and the free librations from the lunar surface with an accuracy of 1 millisecond of arc in the post-SELENE project. Year-long trajectories of the stars provide information on various components of the physical librations and we will also try to detect the lunar free librations in order to investigate the lunar mantle and the liquid core. The PZT on the moon is similar to that used for the international latitude observations of the Earth is applied. The measurement of the rotation of the Moon is one of the essential technique to obtain the information of the internal structure. The highly accurate observation in the very low frequency band below about 10 MHz is yet to be realized, so that this range is remarkable as one of the last frontiers for astronomy. This is mainly because that the terrestrial ionosphere prevents us from observing the radio waves below the ionospheric cutoff frequency on the ground. It is, moreover, difficult to observe the faint radio waves from planets and celestial objects even on the earth's orbit because of the interference caused by the solar burst, artificial noises and terrestrial aurora emissions. The lunar far-side is a suitable site for the low frequency astronomical observations, because noises from the Earth can always avoided and radio waves from the Sun can be shielded during the lunar night.

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Scientific Experiments

  • Early Missions:
    • Seismic activity study
    • UV, Visible and Infra-red (IR)

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  • Future Missions:
    • Observation of extra-solar planets
    • Very long wavelength radio astronomy
      • Giant radio telescopes “carved” out of existing craters on the Moon.
    • Optical Interferometer
      • 3 or more observatories spaced 1km apart.
    • ISRU and Giant Liquid Mirror Telescopes (50m)
      • Spinning lunar regolith in a circular dish to create large parabolic surface.
      • Impossible without gravity. However, the Moon’s lower gravity provides the opportunity to achieve extremely large scopes.

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Limitations / Showstoppers

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  • Moon-quakes
    • Highly debated. Seismic disturbances were measured over the course of 8 years by the Apollo missions, showing at most 1 disturbance in a given area per year.
  • Lunar dust

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Effective Aperture Study

  • Effective aperture of a large pseudorandom low-frequency dipole array�Ellingson, S.W.�Antennas and Propagation Society International Symposium, 2007 IEEE�Volume , Issue , 9-15 June 2007 Page(s):1501 - 1504�Digital Object Identifier   10.1109/APS.2007.4395791�Summary:The long wavelength array (LWA) is a new aperture synthesis radio telescope, now in the design phase, that will operate at frequencies from about 20 MHz to about 80 MHz.This paper describes some preliminary estimates of Ae for such an array. This is a non-trivial problem because the antennas are strongly coupled and interact strongly with the ground. To bound the scope of this preliminary investigation, the antennas are modeled as thin straight half-wave (nearly resonant) dipoles, and we restrict our attention to the co-polarized fields in the principal planes. First, we consider results for a single element in isolation. Next, we consider the results for the entire array, which are compared to the results for the single element and also to the physical aperture of the station.�

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History: VLF Array Design Studies

1990’s

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LOFAR;�Operational Since 2006

(LOFAR) Low Frequency Array: 10-240MHz

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http://images.google.com/imgres?imgurl=http://web.mit.edu/annualreports/pres02/images/03.05_fig2.jpg&imgrefurl=http://web.mit.edu/annualreports/pres02/03.05.html&usg=__b5RH0Z3amUyVzN_Gk58a7JjoGHg=&h=354&w=500&sz=59&hl=en&start=72&um=1&tbnid=2detmLAniIBN6M:&tbnh=92&tbnw=130&prev=/images%3Fq%3DLOFAR%26start%3D54%26ndsp%3D18%26um%3D1%26hl%3Den%26sa%3DN

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