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Observation Challenges & Strategies for the LCROSS Impact

Observation Challenges & Strategies for the LCROSS Impact. Diane H. Wooden (NASA Ames). Challenges due to Impact Physics. Ejecta curtain evolves quickly (20 sec to 5 min) Ejecta curtain spreads sideways (3” at peak brightness at ~20-40 sec, to 15” wide at 5 min)

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Observation Challenges & Strategies for the LCROSS Impact

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  1. Observation Challenges & Strategies for the LCROSS Impact Diane H. Wooden (NASA Ames)

  2. Challenges due to Impact Physics • Ejecta curtain evolves quickly (20 sec to 5 min) • Ejecta curtain spreads sideways (3” at peak brightness at ~20-40 sec, to 15” wide at 5 min) • Most of mass is below height of Rim+2.5 km (1.25” above crater Rim) • Expecting large particles (30 micron), so scattering properties/IR brightness not as great as for small particles (~0.5–1 micron)

  3. Challenges due to South Pole • illumination: pointing in the dark • crowded region • Rim not a limb • distance from Rim to limb changing from month to month due to libration • Virtual Atlas of Moon (freeware) is a possible aid ... Caution: I did not find the position of terminator accurate enough for real-time pointing checks as of 9/2/2006

  4. Challenges of observing the Moon • pointing: can use JPL Horizon Ephemerides generator to get RA,DEC (Tony Colaprete says impact site will be known to 0.5 km or 0.25 arcsec) EXAMPLE Cabeaus: Moon [Luna][g:324.5,-84.9,0@301] [g: long, lat, height@luna] • guiding: fast and quickly changing tracking rates • impact timing: over HI, but CA,AZ,TX possible • instrument ‘campaigns’ on telescopes <-?-> impact date, lunar phase • scattered light from lit areas of Moon entering instrument • seeing variations (post data may need blink comparison to select best) • guide cameras may be too sensitive, or too low spatial resolution to discern terrain; • Moon moves too fast for Adaptive Optics (AO) guide stars • Develop DATA REDUCTION PIPELINES: calibration of measurements of diffuse/extended plume using point sources that fill instrument profiles differently than extended sources • Can focal planes be maximized (fiber-fed spectrographs)?

  5. Cabeaus: Moon [Luna] [g:324.5,-84.9,0@301] ****************************************************************************************************** Date__(UT)__HR:MN R.A._(ICRF/J2000.0)_DEC dRA*cosD d(DEC)/dt Azi_(a-appr)_Elev a-mass Illu% ****************************************************************************************************** 2009-Feb-05 05:28 Am N- 04 58 50.93 +26 46 17.9 1323.68 197.35 56.9989 76.3251 1.029 74.961 2009-Feb-05 05:32 m N- 04 58 57.51 +26 46 30.9 1320.56 190.13 55.1488 77.0848 1.026 74.977 2009-Feb-05 05:36 m N- 04 59 04.08 +26 46 43.5 1317.69 182.88 53.0477 77.8264 1.023 74.994 2009-Feb-05 05:40 m N- 04 59 10.63 +26 46 55.5 1315.08 175.60 50.6549 78.5464 1.020 75.010 2009-Feb-05 05:44 m N- 04 59 17.17 +26 47 07.0 1312.71 168.30 47.9232 79.2403 1.018 75.027 2009-Feb-05 05:48 m N- 04 59 23.70 +26 47 18.1 1310.60 160.98 44.7996 79.9028 1.015 75.043 2009-Feb-05 05:52 m N- 04 59 30.22 +26 47 28.7 1308.74 153.64 41.2263 80.5272 1.013 75.059 2009-Feb-05 05:56 m N- 04 59 36.73 +26 47 38.8 1307.14 146.28 37.1444 81.1054 1.012 75.075 2009-Feb-05 06:00 m N- 04 59 43.23 +26 47 48.4 1305.79 138.90 32.5007 81.6279 1.010 75.091 2009-Feb-05 06:04 m N- 04 59 49.73 +26 47 57.5 1304.69 131.52 27.2591 82.0835 1.009 75.108 2009-Feb-05 06:08 m N- 04 59 56.23 +26 48 06.1 1303.86 124.12 21.4169 82.4602 1.008 75.124 2009-Feb-05 06:12 m N- 05 00 02.72 +26 48 14.2 1303.27 116.71 15.0226 82.7456 1.008 75.140 2009-Feb-05 06:16 m N- 05 00 09.21 +26 48 21.8 1302.95 109.30 8.1909 82.9286 1.007 75.156 2009-Feb-05 06:20 m NL 05 00 15.69 +26 48 28.9 1302.88 101.88 1.1019 83.0011 1.007 75.172 2009-Feb-05 06:24 t NL 05 00 22.18 +26 48 35.6 1303.06 94.46 353.9805 82.9598 1.007 75.188 2009-Feb-05 06:28 m NL 05 00 28.67 +26 48 41.7 1303.51 87.04 347.0578 82.8067 1.008 75.204 2009-Feb-05 06:32 m NL 05 00 35.16 +26 48 47.3 1304.20 79.63 340.5291 82.5486 1.008 75.220 2009-Feb-05 06:36 m NL 05 00 41.66 +26 48 52.5 1305.16 72.21 334.5278 82.1959 1.009 75.236 2009-Feb-05 06:40 m NL 05 00 48.16 +26 48 57.2 1306.37 64.81 329.1197 81.7609 1.010 75.253 2009-Feb-05 06:44 m NL 05 00 54.67 +26 49 01.3 1307.84 57.41 324.3144 81.2558 1.011 75.269 2009-Feb-05 06:48 m NL 05 01 01.19 +26 49 05.0 1309.56 50.02 320.0831 80.6921 1.013 75.285 2009-Feb-05 06:52 m NL 05 01 07.71 +26 49 08.2 1311.54 42.64 316.3760 80.0798 1.015 75.301 2009-Feb-05 06:56 m NL 05 01 14.25 +26 49 10.8 1313.77 35.28 313.1349 79.4273 1.017 75.317 2009-Feb-05 07:00 m NL 05 01 20.80 +26 49 13.0 1316.25 27.94 310.3013 78.7417 1.019 75.333 The first symbol indicates if the target surface location is on the side of the target facing the observer: 'N' Surface location on the target body is on the near-side, facing TOWARD the observer. Visible, however, ONLY when target location is also above the horizon at the observing site. '-' Surface location on the target body is on the far-side, facing AWAY FROM the observer. NOT visible. The second symbol indicates if the target surface location is illuminated by any portion of the Sun's extended disk: 'L' Surface location on target body faces Sun (is lit) '-' Surface location on target body does NOT face Sun (is NOT lit) N Near-side – NOT Lit L Lit

  6. 2009 Mar 03, 04, 05, 06, 07 UT (6:30-7:10 UT) Ephem. Calc. for Cabeaus Mar03 ‘sets’=2 AirMass@8:40UT in HI; Mar05 good, Mar07 great HI-CA-AZ-TX Moon moves 1˚/4 min = point separation; betw. Astronomical Twilights or ≤2 Air Masses circles show Air Mass on Mar05 6:30UT in HI, CA, AZ, TX as indicated on right of plot

  7. Predicting the Ejecta Curtain Brightness 0.1 km Ejecta cloud optical depth modeled with a truncated conical section, the “upside-down lampshade” model. Conical section grows at a rate which follows the maximum cloud density contour. t+2 Solar Scatter for LCROSS Shepherd SpaceCraft t+1 t Projected column annulus at time, t Solar Scatter for Earth Observing

  8. PLUME EVOLUTION (`LONG’ TIME...) OH Exosphere Lunar Prospector Predictions A,C = 90 minutes B,D = 190 minutes 0.308 µm OH- (different sticking coefficients) Goldstein et al. 2001 JGR 106, 32841

  9. Mass(kg) at 2–5 km (D. Wooden’s analysis of D. Korycansky model 1/17/08)

  10. [R(t, 0 km)] = [2R(t)-5 km/tan(45˚)] s=5 km/sin(45˚) 0.1 km 5 km R(t) s 2.5 km 45˚

  11. R(t)=6 km height=width=5km t=45 sec (MAX MASS) 5 km

  12. R(t)=15 km height=width=5km t=90 sec (1/2 MAX MASS) c

  13. R(t)=30 km height=width=5km t=150 sec (1/5 MAX MASS) c 30 km

  14. Calculate Area of ‘filled cone’ by using vertical slices and integrating from front to back

  15. Area = AreaΩ- AreaØ = Ø/2 R2– 1/2 RcosØ RsinØ– Ω/2 R2 + 1/2 RcosΩ RsinΩ Ø Ω ∂x AreaØ= Ø/2 R2– 1/2 RcosØ RsinØ RcosØ = R – ∂x cosØ = 1 – ∂x/R Ø = cos–1(1–∂x/R) AreaΩ= Ω/2 R2– 1/2 RcosΩ RsinΩ cosΩ = 1 – 2∂x /R sin Ω = √(1 – cos2 Ω) Ω = cos–1(1– 2∂x/R) ß Area = Areaß– AreaΩ– AreaØ = ß/2 R2– 1/2 Rcosß Rsinß – [Ω/2 R2– 1/2 RcosØ RsinØ] – [Ω/2 R2– 1/2 RcosΩ RsinΩ] cosß = 1 – 3∂x/R cosΩ = 1 – 2∂x/R cosØ = 1 – ∂x/R

  16. Calculate Area of ‘hollow cone’ by subtracting two ‘filled cones’

  17. Multiply surface area bins by dm/dA and divide by mass per grain to get Number of Grains (1E10) 100um grain radius πa2 Q=3E-8 (~2) m2 so marg. optically thin R(t)=6 km height=width=5km t=45 sec (MAX MASS)

  18. Temporal Evolution of Surface Brightness as measured in Ngrains (100um radius) • With TIME Ejecta Plume expands in Radius (but does not change much in height) • Surface brightness declines slowly because surface area of plume that is sampled (per square arcsec) increases with time • Surface brightness 50% higher at 80 sec (follows total mass, which in this model is larger at 80 sec at at 2–5 km -- next slide)

  19. Mass(kg) at 2–5 km (D. Wooden’s analysis of D. Korycansky model 1/17/08)

  20. Qscat, Qabs computed with Mie scattering for solid spheres of glassy (Mg,Fe)SiO3 Flux_scat = Ngrains * πa2 Qscat *E_lambda [W m-2 um-1] dmoon2 Flux_emission = Ngrains * 4πa2 Qabs *πB(Tgrains) dmoon2

  21. Scattered and Emitted Light from 30um radii grains plotted above water ice % Absorbance (T. Colaprete)

  22. Mass(kg) at 2–5 km (D. Wooden’s analysis of D. Korycansky model 1/17/08)

  23. Instruments will be challenged • Spectroscopy: slit parallel to Rim? • Multi-fiber spectrographs can ‘pack’ focal plane with slits? • Imaging in multi-colors at same time, even at lower spatial resolution, will aid in calibrating data sets at discrete wavelengths • Larger aperture telescopes gain in spatial resolution • Want to achieve broad wavelength coverage but also some overlap to help with cross-calibration between ground-based telescopes+instruments. • How long (>>5 min=300 sec) should plume be followed? • Integrate longer to improve S/N but ‘smear’ plume? • How stringent is the Full Moon avoidance (±2.5 days)?

  24. Wavelength & Method/Telescope A: VIS Imaging (Flash?) B: VIS Spectra (OH-) C: NIR Imaging (mass distribution, height) D: NIR Spectra (water! ice!) E: MID-IR (heat) F: radio? G: UV-HST Lunar Specialists to help with science justifications Lunar Specialists to help w/pointing Scattering/Emission properties of grains Signal-to-Noise: what is possible Can instruments read out fast enough? (10-30 sec?) Let’s Team Up for the LCROSS Challenge

  25. Collect into Teams... brainstorm and then report back to the workshop members

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