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Science with a Rover-based Low-frequency Dipole Array

Science with a Rover-based Low-frequency Dipole Array . A multi-configuration rover-borne dipole array for Low-frequency RadioAstronomy from the Moon. Ettore Carretti INAF-IRA Bologna On behalf of the Radio WP group in collaboration with CIRANO (PoliMi).

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Science with a Rover-based Low-frequency Dipole Array

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  1. Science with a Rover-based Low-frequency Dipole Array A multi-configuration rover-borne dipole array for Low-frequency RadioAstronomy from the Moon Ettore Carretti INAF-IRA Bologna On behalf of the Radio WP group in collaboration with CIRANO (PoliMi) E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007

  2. Why n=3-30 MHz astrophysics? • Almost unexplored frequency band • next years (2009+) the ground-based array LOFAR will explore the 30-80 and 120-240 MHz bands; • < 30 MHz almost impossible from ground (ionosphere) • Only strongest sources and very large scales maps (HPMW = 2°-10°) TO OPEN A NEW ASTROPHYSICS WINDOW ! E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007

  3. Extragalactic astrophysics • Cosmology • Physics of Acceleration of high energy particles in the Universe • Origin and amplification of magnetic fields in the Universe • Physics of Black Holes and Duty cycles • Most distant and oldest radio emitting plasma in the Universe • New Physics … (coherent emission, serendipity) E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007

  4. Galactic astrophysics • Diffuse Emission from the Galaxy • Magnetic field in the Galaxy • Acceleration and diffusion of high energy particles in the Galaxy • Mapping HII in the Galaxy • Supernova Remnants in the Galaxy • Physics of Micro-Quasars • New Physics … (coherent emission, serendipity) E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007

  5. 2.1 MHz 3.7 MHz Ellis 1982 Ellis 1982 8.3 MHz 22 MHz Roger et al. 1999 Ellis 1982 Dq = 2°-3° What is possible from ground? Roger et al. 1999 LOW RESOLUTION ! E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007

  6. 2.1 MHz Ellis 1982 Haslam et al. 1982 Resolution improvement by >10X... Roger et al. 1999 subdegree resolution (at least) down to 3 MHz E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007

  7. 408 MHz 22 MHz 2.1 MHz Dq = 2°-3° Haslam et al. 1982 Roger et al. 1999 Ellis 1982 Low frequency: strong signal • Low frequencies dominated by synchrotron • Synch spectrum: negative slope => strong signal at low frequency • Galactic diffuse emission >10000s K (30MHz) even at high lat. • > 1 MK (2-3MHz) • It is not required a huge collecting area to map the sky. E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007

  8. Instrument • Need for high resolution => large telescope aperture • No need for high sensitivity (strong signal and first survey experiment) • => interferometric small antenna array • many separated antenna, whose signals are 2-by-2 correlated • N antennas => N(N-1)/2 independent pairs • resolution Dq = l /Dmax (Dmax = maximum baseline – pair distance) • 10 Km equivalent aperture: n [MHz] l [m] Dq [arcmin] ---------------------------------------------------- 100 3.3 1.0 30 10 3.5 10 33 10 3 100 35 E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007

  9. Array • each antenna pair is sensitive to the angular scale q l/D • several baselines D are necessary to cover from largest to smallest angular scales • D from “a few”-m to 10 Km (even 3 Km would be OK) • Array “shape” E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007

  10. Antennas • Which antenna? • Mirrors not suitable: • need D >> l • 3 MHz => l = 100m • it’d be D = HUGE !?! • Dipole antenna: “Natural” choice for a low frequency antenna • .l/2 electric dipoles not suitable because of lengths and very narrow frequency band • magnetic dipoles: using coils, much higher efficiency with same length • length: 10s-cm • double dipoles: both polarizations • Large F.o.V.: 90° => optimal for surveys, i.e. full sky mapping • lightweight: just wire E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007

  11. Antenna (2) • Receiver: simple and well developed technology • Dipole antennas • Receiver: sky signal dominated conditions (10-kK to 1-MK) • amplifier sensitivity is not an issue (state-of-the-art technology not necessary); • commercial components can be used; • standard Medium/Short-Wave telecommunication components (well tested in space-enviroment and space-qualified); • standard electronics • No “critical” technology to be developed E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007

  12. Experiment LIGHTWEIGHT!!! • Main requirement: • Mass < 60-70 Kg • 10-15 antennas: not enough to realize all the baselines from 3-5m throughout 10km • solution: reconfigurable array • => Rover-Borne antennas (new approach w.r.t. ESA or EADS studies) PROs: • it allows to deploy antennas from the lander to the wanted position with the wanted attitude. • flexibility • it allows to re-deploy the antennas in different configurations of larger and larger size E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007

  13. Rover-Borne Stations • Station = telescope (dipole + electronics) + rover • Mass station: 5-6 kg • 10 stations stay within mass requirements E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007

  14. A “walking” experiment • reconfigurable array: • first the 10 antennas realize the most compact core and observe the sky with this configuration; • ... and so on for a number of steps until the 10km baselines are set so to realize the full array • 6 steps: Dmax = 30m, 100m, 300m, 1km, 3km, 10km • then: antennas are moved to longer distances to realize a larger configuration and observe the sky; E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007

  15. Where • Far side of the Moon: Earth is shielded => RFI fully mitigated • Lunar latitude: within the range 30°- 60° E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007

  16. Operations • observing frequencies: • 3, 6, 12, 25, 50, 100 MHz • 3, 4.5, 7, 10, 15, 22, 30 MHz • lunar night observations – Sun is too strong ! • observations all lunar night long, for optimal angular frequency space coverage • 1 array configuration a lunar night • 1 lunar day (= 1 month) observing cycle: • 6 months to realize Dmax = 30m, 100m, 300m, 1km, 3km, 10km E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007

  17. Operations (2) • Station data must be correlated for each station pair • Data must be collected by one processing station. Two possible solutions: • one master station (central one); • orbiter. • Communications to Earth: only once a month (simple and cheap mission control) E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007

  18. Science with WARP • Walking Array Radio Pathfinder (WARP): • subdegree Galactic diffuse emission • relativistic electron age, confinement and diffusion processes, magnetic field • New SNR: oldest visible at low freq only (high res to separate them from diffuse em.) • Micro quasars (e.g. SS433): no lobes. Why? old, or p+? • Extragalactic sources: all 3C catalogue: • spectrum, lowest energy e-, evolution history; • free-free absorption: W-IGM • synchrotron self-absorption: direct measurement of B, ne • galaxy-cluster halos and relics ... but ... most important.... it is an unexplored window: hunt for new sources and astrophysical (and physical) processes fully unknown so far. E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007

  19. Conclusions • To open a NEW window in astrophysics. • High interest of the scientific community (e.g. ESA and EADS studies for experiments in this frequency band). • Instrument: a simple, easy, well developed technology: No “critical” developments required • New approach based on a Rover-borne experiment: FLEXIBILITY • Safe against failure of one/more stations • Many-stations array realized with “few” stations • Lightweight payload. E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007

  20. Conclusions (2) • ESA studies for a lunar experiment in such band • WARP: unique opportunity for the italian community (astrophysics + space engineering) to earn experience and be candidate to lead the European mission. • A rover colony getting around on the lunar surface: high impact for the Italian System • italian space industry; • italian engineer research; • italian astrophysics research; • visibility; • italian space technology capabilities. E. Carretti, Observation of the Universe from the Moon, Frascati, 07 May 2007

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