Moon Observation by means of Microwave Instruments on board of Small Lunar Orbiter. A preliminary Study

Transcription

1 Moon Observation by means of Microwave Instruments on board of Small Lunar Orbiter. A preliminary Study Gemma Manoni (1), Marco D Errico (2), Maria Rosaria Santovito (3), Luigi Colangeli (4), Claudio Scarchilli (1), Alfredo Renga (5), Salvatore Dinardo (3), Goro Komatsu (6), Elena Razzano (2), Sergio Losito (7) Template reference : K-EN 1 Thales Alenia Space, 2 Dept. of Aerospace and Mechanical Engineering, Second University of Naples, 3 CORISTA, Napoli, 4 INAF - Osservatorio Astronomico di Capodimonte, 5 Dept. of Aerospace Engineering, University of Naples Federico II, 6 Int. Research School of Planetary Sciences - Università d'annunzio Pescara, 7 Italian Space Agency All rights reserved Corista

2 MicroMoon ASI Study Page 2 The paper summarizes the results of a study financed by the Italian Space Agency which has been aimed at: Identification of scientific goals, Preliminary assessment of payload characteristics, Preliminary assessment of bus design for a small mission exploiting Moon Observation in the microwave spectrum.

3 Observation from the Moon Page 3 Universe Observation LORA P/L for Radio Astronomy and Cosmology at low frequency MIRA P/L for Radio Astronomy and Cosmology at millimeter wavelength Earth Observation MIMO P/L MIcrowave Moon-based Observatory VEDORA P/L VEry Different ORbital Altitude

4 Observation of the Moon Page 4 Initial Study of all imaginable radar MW instruments from Moon orbiter ( radar altimeter, radiometer, SAR, sounder, INSAR, Bistatic SAR) with following general goals: Surface Mapping & Processes Geomorphology and Crater counting Stratigraphy Direct water ice detection

5 Chosen Lunar MW P/L Page 5 CONCEIVABLE MW P/L MINIATURIZED SAR OBJECTIVES Water-Ice Deposits Detection Lunar Global Imaging Surface Roughness Mapping and Crater Counting RADAR SOUNDER Global Subsurface Sounding (e.g. lava tubes) Surface Profiling OBJECTIVES Ionospheric and Noise Characterization

6 Page 6 LUNAR MINISAR

7 SAR Design Strategy ICE DETECTION Page 7 INCOHERENT Shadowing and Layovering SWATH= S => Antenna HEIGHT BROADSIDE ANGLE SELECTION 38 POLARIMETRIC PRF SELECTION 3 KHZ Gain 27 db => Antenna LENGTH CARRIER FREQUENCY SELECTION 3 GHZ COHERENT Low Penetration Scattering Maximization Antenna Dimensions GOAL: SNR 10 db PEAK POWER 20 W MAX BW 1.5 MHZ Expected Scattering - 20 db

8 Instrument Performance Page 8 MicroStrip Antenna Transmitting circular polarization wave Receiving coherently two orthogonal components High Performance over a narrow bandwidth 0.5 m RESOLUTIONS AND SENSITIVITY 150 m Ground Range Resolution 100 Across Track Resolution (Looks 128) Sigma Noise Equivalent -30 db (weakest expected signal -28 db) Radiometric Resolutions 0.5 db Data Rate 13 Mbps 1.5 m Antenna efficiency 0.5 Assessment of physical features ITEM UNITS VALUE GAIN 27 db SWATH=32 Km Low Ambiguity Level ( ASR<-25 db) Low Cross Polarizations Level (<-25 db) mass Kg 10 size dm 3 < 10 power W 50

9 Page 9 LUNAR SOUNDER

10 Sounder Design Strategy Lava Tubes LUNAR SUBSURFACE TARGETS Middle Depth Ice/Rocks Page 10 Rocks/Permafrost Shallow Depth Far Depth Penetration Depth Regolith Thickness Carrier Selection MHz Buried Craters σ 0 BW d PRF SELECTION 700 Hz PRF > 2f dmax at 30 db SNR SCR

11 Instrument Performance Page 11 HIGHLIGHTS Multifrequency Simultaneous Operations in HF and VHF High SNR ( up to 70 db) High Fractional Bandwiths RESOLUTIONS REQUIREMENTS Depth Res. 70 (HF1) 30 (HF2) 5 (VHF) m Max Penetration Depth 3 (HF1) 2 (HF2) 0.3 (VHF) Km DETRIMENTS Two Dipole Antennas, one for HF1 and HF2 and one for VHF Switching Circuitry HF-VHF Low Distortions Signal High Data Rate ( > 33 Mbits) Assesment of physical features ITEM UNITS VALUE mass Kg <20 size dm 3 <40 power W 70

12 Page 12 ORBIT AND ORBITER

13 Preliminary Orbit Overview Page 13 Ramanan and Adimurthy (2005) used most recent Lunar gravity field from Lunar Prospector: orbit lifetime optimized by inclination and ascending node selection for Lunar circular orbit at initial altitude of 100km Folta and Quinn (2006) showed that near-frozen orbits exist at i=90 and initial periselenium altitude of 100km with low eccentricity values (<0.05). Payload requirements do not lead to very low orbit. Thus, nominal Lunar Prospector orbit can be used to fly microwave payloads: Periselenium altitude (km) 100 Orbit inclination ( ) 90 Eccentricity Perilune anomaly 270

14 Preliminary Orbiter Sizing Page 14 Bus to payload mass ratio assumed at 25% (typical value for small satellites) Propellant mass: perilune decay of an initially polar, low (100km) circular orbit in 144days (Meyer et al. 1994) for a mean rate of km/day V=112.6m/s per year for eccentricity control Payload duty cycle per orbit is envisaged at 6% per payload (global coverage in 311 orbits) average power of 4.2W for RS and 4.8W for Mini SAR, 9W overall. Average power ratio (payload to bus) of 25% (Larson and Wertz, 1992)

15 Conclusions Page 15 In the frame of Italian Vision for Moon Exploration Program, founded by Italian Space Agency, an evaluation of Radar Sounder and MiniSAR on a lunar orbiter mission has been performed. An assesment of preliminary Payloads parameters and possible Istruments architecture has been carried out. A small Lunar orbiter, embarking a MiniSAR and Radar Sounder, can be based on existing or easily derivable technologies, with obvious advantages in economical and programmatic terms.