Background After Comparison with Apollo, Luna, · Apollo, Luna, and Surveyor landing sites.!...
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' Ryan N. Clegg 1 , Bradley L. Jolliff 1 , Aaron Boyd 2 , Mark S. Robinson 2 , and Jeffrey B. Plescia 3 1 Washington University in St. Louis and the McDonnell Center for the Space Sciences, 1 Brookings Dr., St. Louis, MO 63130, [email protected] , 2 School of Earth and Space Exploration, Arizona State University, Tempe, AZ, 3 The Johns Hopkins University, Applied Physics Laboratory, Laurel, MD. On 14 Dec. 2013, China’s Chang’e 3 soft landed at 44.12°N, 340.49°E in Mare Imbrium [1, 2]. Goals of this study: 1) Investigate the change in reflectance at the landing site related to the impingement of rocket exhaust from the lander (blast zone, “BZ”) [3,4]. 2) Use Lunar Reconnaissance Orbiter (LRO) Narrow Angle Camera (NAC) images to compare with reflectance before landing (Fig. 1) and to compare with 40-year old disturbances at the Apollo, Luna, and Surveyor landing sites. Background 50 m Before After i = 54° e = 2° g = 56° i = 58° e = 2° g = 59° Reflectance profiles - used to extract reflectance values within the BZ, and to measure spatial extent of disturbed area (Fig. 3). 1) a-a’ – across northernmost tip of BZ 2) b-b’ – across the center of BZ 3) c-c’ – N-S; crosses the lander. Also taken across the site before landing for comparison. Hapke photometric modeling - used to fit reflectance (I/F) data, which is normalized to the Lommel-Seeliger function (IoF/LS) to reduce effects of different illumination geometries [5,6]. Methods Reflectance increase (at 45° phase angle; normalized using Hapke photometric function [3,6]): Apollo: 16% Luna: 12% Surveyor: 15% Chang’e 3: 12% Blast zone elliptical area Apollo*: 23,800 m 2 Luna: 4100 m 2 Surveyor: 300 m 2 Chang’e 3: ~2100 m 2 * excluding Apollo 12 Comparison with Apollo, Luna, and Surveyor 0.04 0.05 0.06 0.07 0.08 0.09 0.1 0 20 40 60 80 100 120 140 160 180 IoF/LS Distance from Start (m) Edge of BZ Edge of BZ Crater b b’ • Reflectance increase at the Chang’e 3 landing site (Table 1) compares favorably with the average increase in reflectance for other landing sites [3]. • Variations in descent trajectory and maneuvering or different engine configuration and design likely contributed to BZ size variations between Apollo, Luna, Surveyor, and Chang’e 3 landing sites (Table 2). • Based on reflectance changes (Table 1), we infer that lunar surface features (mm – cm scale) are not significantly altered on a time scale of decades by rocket exhaust impingement. Conclusions [1] Wagner, R. et al. (2014), this Conf., Abstract #2259. [2] Robinson et al. (2014), this Conf., Abstract #1859. [3] Clegg R. N. et al. (2014), Icarus, 227, 176-194. [4] Kaydash V. et al. (2011), Icarus, 211, 89-96. [5] Hapke B. W. (2001), Icarus, 167, 523-524. [6] Hapke B. W. et al. (2012), JGR, 117. [7] National Space Science Data Center (NSSDC). [8] Harvey, B. (2007), Soviet and Russian Lunar Exploration. References Fig. 3: Reflectance profiles before and after landing; dashed yellow line outlines the BZ. NAC image M1144936321L, 59° phase angle. Profile before landing taken from image M183661683L; 56° phase angle. Solid lines in plots indicate average IoF/LS values for the BZ, dashed lines indicate average IoF/LS values for the background. • Reflectance profile shapes are consistent with trends observed at Apollo, Luna, and Surveyor landing sites [3]. • Magnitude of reflectance increase is ~12% after landing (at 45° phase angle; Table 1). • Average area of Apollo BZ is 10 times larger than average Luna BZ and 80 times larger than average Surveyor BZ [3]. • The Chang’e 3 BZ area measurement falls close to the expected value, based on the Surveyor, Luna, & Apollo correlation (Fig. 4; Table 2) and variations in descent trajectory and topography. Results 0.04 0.05 0.06 0.07 0.08 0.09 0.1 0 20 40 60 80 100 120 140 160 180 IoF/LS Distance from Start (m) Edge of BZ Edge of BZ a a’ 0.04 0.05 0.06 0.07 0.08 0.09 0.1 0 20 40 60 80 100 120 140 160 180 IoF/LS Distance from Start (m) Edge of BZ Edge of BZ Lander c c’ Fig. 4: Plot of lander mass versus blast zone elliptical area for the Apollo, Luna, Surveyor, and Chang’e 3 landing sites. Variations largely a function of descent parameters. Fig. 1: Images of the Chang’e 3 landing site, before (left; NAC image M183661683L) and after (right; NAC image M1144936321L) landing. Dashed line outlines the area of increased reflectance (blast zone); arrow points to lander. IoF/LS blast zone IoF/LS background percent increase Apollo 11 0.081 0.070 16 Apollo 12 0.098 0.085 14 Apollo 14 0.112 0.097 15 Apollo 15 0.092 0.076 21 Apollo 16 0.184 0.164 12 Apollo 17 0.083 0.072 15 average 0.108 0.094 16 Luna 16 0.071 0.064 11 Luna 17 0.077 0.065 18 Luna 20 0.137 0.127 8 Luna 23 0.088 0.080 10 Luna 24 0.089 0.078 14 average 0.092 0.083 12 Surveyor 1 0.061 0.052 17 Surveyor 5 0.075 0.061 23 Surveyor 6 0.077 0.067 15 Surveyor 7 0.163 0.155 5 average 0.094 0.084 15 Chang’e 3 0.065 0.058 12 Table 1: Average reflectance (IoF/LS) values for the BZ and background areas at the Apollo, Luna, Surveyor, and Chang’e 3 landing sites (for 45° phase angle). dry mass (kg) max thrust (kN) BZ area (m 2 ) Apollo 7440 45 23800 Luna 2070 18.9 4100 Surveyor 300 0.46 300 Chang’e 3 1320 7.5 2100 Fig 2.: Lower incidence angle image (M1147290066R), showing Yutu rover tracks. Table 2: Average mass, thrust and BZ area values for Apollo, Luna, Surveyor, and Chang’e 3 [7,8]. 50 m Yutu Rover tracks Scan to see an LROC Featured Image of the Chang’e 3 landing site! i = 45° 0.04 0.05 0.06 0.07 0.08 0.09 0.1 0 20 40 60 80 100 120 140 160 180 IoF/LS Distance from Start (m) Approximate future location of lander c c’ Before landing 0 5,000 10,000 15,000 20,000 25,000 30,000 35,000 40,000 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 BZ elliptical area (m 2 ) lander dry mass (kg) CE-3 Surveyor Luna L17 Apollo 16 17 15 11 14 R 2 = 0.90
Transcript of Background After Comparison with Apollo, Luna, · Apollo, Luna, and Surveyor landing sites.!...
'Ryan N. Clegg1, Bradley L. Jolliff1, Aaron Boyd2, Mark S. Robinson2, and Jeffrey B. Plescia3
1Washington University in St. Louis and the McDonnell Center for the Space Sciences, 1 Brookings Dr., St. Louis, MO 63130, [email protected], ���2School of Earth and Space Exploration, Arizona State University, Tempe, AZ, 3The Johns Hopkins University, Applied Physics Laboratory, Laurel, MD.
On 14 Dec. 2013, China’s Chang’e 3 soft landed at 44.12°N, 340.49°E in Mare Imbrium [1, 2]. Goals of this study: 1) Investigate the change in reflectance at the landing site related to the impingement of rocket exhaust from the lander (blast zone, “BZ”) [3,4]. 2) Use Lunar Reconnaissance Orbiter (LRO) Narrow Angle Camera (NAC) images to compare with reflectance before landing (Fig. 1) and to compare with 40-year old disturbances at the Apollo, Luna, and Surveyor landing sites.
Background
50 m
Before After
i = 54° e = 2° g = 56°
i = 58° e = 2° g = 59°
Reflectance profiles - used to extract reflectance values within the BZ, and to measure spatial extent of disturbed area (Fig. 3). 1) a-a’ – across northernmost tip of BZ 2) b-b’ – across the center of BZ 3) c-c’ – N-S; crosses the lander. Also taken across the site before landing for comparison. Hapke photometric modeling - used to fit reflectance (I/F) data, which is normalized to the Lommel-Seeliger function (IoF/LS) to reduce effects of different illumination geometries [5,6].
Methods
Reflectance increase (at 45° phase angle; normalized using Hapke photometric function [3,6]): Apollo: 16% Luna: 12% Surveyor: 15% Chang’e 3: 12% Blast zone elliptical area Apollo*: 23,800 m2
Luna: 4100 m2 Surveyor: 300 m2 Chang’e 3: ~2100 m2 *excluding Apollo 12
Comparison with Apollo, Luna, and Surveyor
0.04
0.05
0.06
0.07
0.08
0.09
0.1
0 20 40 60 80 100 120 140 160 180
IoF/
LS
Distance from Start (m)
Edge of BZ Edge of BZ
Crater
b b’
• Reflectance increase at the Chang’e 3 landing site (Table 1) compares favorably with the average increase in reflectance for other landing sites [3].
• Variations in descent trajectory and maneuvering or different engine configuration and design likely contributed to BZ size variations between Apollo, Luna, Surveyor, and Chang’e 3 landing sites (Table 2).
• Based on reflectance changes (Table 1), we infer that lunar surface features (mm – cm scale) are not significantly altered on a time scale of decades by rocket exhaust impingement.
Conclusions
[1] Wagner, R. et al. (2014), this Conf., Abstract #2259. [2] Robinson et al. (2014), this Conf., Abstract #1859. [3] Clegg R. N. et al. (2014), Icarus, 227, 176-194. [4] Kaydash V. et al. (2011), Icarus, 211, 89-96. [5] Hapke B. W. (2001), Icarus, 167, 523-524. [6] Hapke B. W. et al. (2012), JGR, 117. [7] National Space Science Data Center (NSSDC). [8] Harvey, B. (2007), Soviet and Russian Lunar Exploration.
References
Fig. 3: Reflectance profiles before and after landing; dashed yellow line outlines the BZ. NAC image M1144936321L, 59° phase angle. Profile before landing taken from image M183661683L; 56° phase angle. Solid lines in plots indicate average IoF/LS values for the BZ, dashed lines indicate average IoF/LS values for the background.
• Reflectance profile shapes are consistent with trends observed at Apollo, Luna, and Surveyor landing sites [3].
• Magnitude of reflectance increase is ~12% after landing (at 45° phase angle; Table 1).
• Average area of Apollo BZ is 10 times larger than average Luna BZ and 80 times larger than average Surveyor BZ [3].
• The Chang’e 3 BZ area measurement falls close to the expected value, based on the Surveyor, Luna, & Apollo correlation (Fig. 4; Table 2) and variations in descent trajectory and topography.
Results
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IoF/
LS
Distance from Start (m)
Edge of BZ Edge of BZ
a a’
0.04
0.05
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0 20 40 60 80 100 120 140 160 180
IoF/
LS
Distance from Start (m)
Edge of BZ Edge of BZ
Lander
c c’
Fig. 4: Plot of lander mass versus blast zone elliptical area for the Apollo, Luna, Surveyor, and Chang’e 3 landing sites. Variations largely a function of descent parameters.
Fig. 1: Images of the Chang’e 3 landing site, before (left; NAC image M183661683L) and after (right; NAC image M1144936321L) landing. Dashed line outlines the area of increased reflectance (blast zone); arrow points to lander.
IoF/LS blast zone
IoF/LS background
percent increase
Apollo 11 0.081 0.070 16 Apollo 12 0.098 0.085 14 Apollo 14 0.112 0.097 15 Apollo 15 0.092 0.076 21 Apollo 16 0.184 0.164 12 Apollo 17 0.083 0.072 15 average 0.108 0.094 16
Luna 16 0.071 0.064 11 Luna 17 0.077 0.065 18 Luna 20 0.137 0.127 8 Luna 23 0.088 0.080 10 Luna 24 0.089 0.078 14 average 0.092 0.083 12
Surveyor 1 0.061 0.052 17 Surveyor 5 0.075 0.061 23 Surveyor 6 0.077 0.067 15 Surveyor 7 0.163 0.155 5
average 0.094 0.084 15
Chang’e 3 0.065 0.058 12
Table 1: Average reflectance (IoF/LS) values for the BZ and background areas at the Apollo, Luna, Surveyor, and Chang’e 3 landing sites (for 45° phase angle).
dry mass (kg)
max thrust (kN)
BZ area (m2)
Apollo 7440 45 23800 Luna 2070 18.9 4100
Surveyor 300 0.46 300 Chang’e 3 1320 7.5 2100
Fig 2.: Lower incidence angle image (M1147290066R), showing Yutu rover tracks.
Table 2: Average mass, thrust and BZ area values for Apollo, Luna, Surveyor, and Chang’e 3 [7,8].
50 m
Yutu
Rover tracks
Scan to see an LROC Featured Image of the
Chang’e 3 landing site!
i = 45°
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0 20 40 60 80 100 120 140 160 180
IoF/
LS
Distance from Start (m)
Approximate future location
of lander
c c’
Before landing
0
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20,000
25,000
30,000
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0 1000 2000 3000 4000 5000 6000 7000 8000 9000
BZ e
llipt
ical
are
a (m
2 )
lander dry mass (kg)
CE-3 Surveyor
Luna L17
Apollo 16
17 15
11
14
R2 = 0.90
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