Mini-RF: An Imaging Radar for the Moon. Ben Bussey The Johns Hopkins University Applied Physics Laboratory

Transcription

1 Mini-RF: An Imaging Radar for the Moon Ben Bussey The Johns Hopkins University Applied Physics Laboratory Paul D. Spudis President s Commission on Implementation of United States Space Exploration Policy and The Johns Hopkins University Applied Physics Laboratory

2 Contents The Value of the Moon The Lunar Poles: An ideal base site? Illumination Conditions Resources Mini-RF Answering the Ice question Technical details Expected results

3 Why is the Moon part of the Vision? Moon is close, easily accessible, and of great scientific and utilitarian interest Use the Moon to create new spacefaring capability Obtain experience and practice at planetary exploration in both techniques and equipment Understand the difficulties, advantages, and tradeoffs of Using lunar materials Building and operating complex structures Exploring a planet with people and robots working together

4 The Value of the Moon Science A natural laboratory for planetary science A platform to observe the universe Inspiration A nearby world to explore and use Resources Materials and energy for cislunar space

5 The Poles of the Moon North pole South pole

6 Unique Environment of the Poles Interesting for both operational and scientific reasons Spin axis 1.5 from the perpendicular to the ecliptic plane results in special illumination conditions Permanently shadowed regions are cold traps (< 120 K) and are possible locations of ice deposits Poles offer abundant solar power and relatively benign operational environment (220 K)

7 Permanent sunlight? South Pole No areas were constantly illuminated at the scale of the Clementine data (500 m/pix) Three areas identified with sunlight for more than 75% of lunar winter day Lit areas in close proximity to permanent darkness (e.g. interior of Shackleton) Data obtained during southern winter (maximum darkness)

8 Permanent sunlight? North Pole Three main areas on the rim of Peary crater were constantly illuminated for the entire summer day. Can not definitively claim that these are permanently illuminated but they represent the best candidate sites on the Moon. Lit areas in close proximity to permanent darkness (e.g. Peary B & W) Data obtained during northern summer (maximum sunlight)

9 Abundant Permanent Shadow 1000 s km 2 of permanent shadow in simple craters at both poles Permanent shadow exists in simple craters at long distances from the pole Represent possible locations of volatile deposits

10 The Importance of Ice The existence of ice is not a REQUIREMENT in order to make the poles an excellent lunar outpost site. However, ice deposits would represent a significant resource that would likely yield significant benefits Therefore the existence of ice deposits has the capability to shape the lunar exploration architecture. It is therefore vital that the Ice question: Is it there? If so, how much, where and it what form be definitively answered as quickly as possible Mini-RF on Chandrayaan-1 and Lunar Reconnaissance Orbiter will answer those questions.

11 Clementine Bistatic Radar Experiment Use RF transmitter of s/c as source of RCP CW radio; stare at pole continuously Listen to echoes on DSN in RCP and LCP Observe reflection behavior through phase angle Get control from sun-illuminated groundtracks to compare with polar dark groundtracks

12 Lunar Prospector Results Neutron Spectrometer detected significant H 2 concentrations near both poles Highest resolution data correlates with permanent shadow, as mapped on Clementine mosaics and modeled for small craters Fast neutron data show no significant H 2 content; implies that ice is not present at surface, but may occur at depths below a few cm

13 Earth-based Radar Goldstone-Arecibo bistatic image shows enhanced same sense polarization (box) Clementine orbit 234 groundtrack (blue) passes directly through this anomaly Radar anomaly (red) occurs in sunlight dark region (gold) of crater Shackleton Possible patch of water ice

14 Lunar Polar Deposits Current Knowledge Clementine found evidence for ice in permanently shadowed regions Lunar Prospector showed enhanced H 2 concentrations, correlated with permanently dark regions of lunar poles Earth-based radar shows small patches of high backscatter (consistent with ice); origin uncertain None of these results was definitive for the presence of ice, but collectively they merit further investigation

15 Mapping Ice from Orbit Mini-RF on Chandrayaan 1 & LRO will image polar deposits and morphology of shadowed areas Mapping polar deposits with bistatic imaging using 2 instruments simultaneously removes ambiguity from interpretation of ice

16 Water-Ice Radar Signatures Unique microwave properties of radar backscatter from very cold & massive ice deposits Enhanced total reflected power Large reflected power in the unexpected polarization Proven measurement methodology (Earth-based and spacecraft) Transmit circular polarization (e.g. right-circular polarization RCP) Receive same-sense (RCP) and opposite-sense (LCP) polarizations Measure albedo (total reflected power): σ 0 RCP + σ 0 LCP Measure circular polarization ratio (CPR): σ 0 RCP / σ 0 LCP

17 Mini-RF on Chandrayaan-1 Objectives Differentiate potential water-ice from lunar regolith Transmit circular polarization, receive same-sense and opposite-sense polarizations Nominal incidence 45 o to preserve responsiveness to various ice-regolith ratios Minimize false indications of anomalous reflectivity Map water-ice deposits Radar image maps (from 80 o poleward), N & S Resolution (pixel): 150 m (75 m), range and azimuth ref: NASA LRO ORDT (2004) recommendation Drives geolocation accuracy; Multi-look imagery Left-looking and right-looking aspect, N & S Full coverage: Terrain & altitude height tolerance Nadir-viewing radar (scatterometer)

18 Mapping Strategy - SAR

19 Mapping Strategy - Scatterometry

20 Operational Strategy

21 Mini-RF Physical Characteristics

22 Summary Mini-RF will map the polar deposits of the Moon and allow us to determine their composition and purity We will also map the morphology of the dark regions near the poles Data will include SAR image mosaics in both polarizations and both left- and right-looking as well as scatterometry maps of both poles The flight of this instrument on both upcoming lunar missions, Chandrayaan-1 & LRO, will permit bistatic imaging of the lunar poles, definitively resolving the question of lunar polar water-ice.

23 The Poles of the Moon From the radar mapping, we will locate probable deposits of water ice and estimate their extent We then need to land on these deposits to characterize the chemical and physical state of the ice The lunar poles offer areas of terrain that are illuminated for extended periods and possess a benign thermal environment They also offer permanently dark regions that contain trapped volatiles, which can be mined to support a lunar base Thus, the poles of the Moon are the most valuable pieces of real estate in the Solar System