Tip: Click "View" at center bottom of 3D window to see list of pre-programmed viewpoint angles. Click left-arrow to scroll through viewpoints. Three series of viewpoints are provided: outside the crater at 15 kilometers; inside the crater at 7.5 kilometers and a spacecraft view positioned looking down from an impact angle of 76 degs altitude. Load time and action are slow due to the number of modeled points. A second wireframe 3D window is provided to aid the user to distinguish between lighting effects and physical particle. The auto-loading Cortona 3D plug-in viewer limited to MS-IE.
Notes: Purpose of this simulation is to explore changes in the lighted shape of the LCROSS dust ejecta curtain at various lighting angles. Illumination and viewpoints correspond to LCROSS mission constraints that exclude 30 degs lunar age within full Moon and New Moon. The curtain is simulated at T+40 secs after impact with a 5km base diameter and 10km top diameter and 100 meter thick shell in an upside down lampshade shape. The scene is tilted towards an Earth observer at 7 degs (3 degs from libration and 4 degs from latitude position.) The curtain is positioned at the center of a 10km diameter crater with a 1km high rim that masks the base of the impact curtain. The dust curtain is simulated using small reflective spheres. Changing viewpoints alters the relative Sun angle to match an Earth-based observer and an impact within LCROSS mission parameters. This is a primitive simulation that does not capture all of the known physical variables, e.g. Mie scattering. See Conclusions at bottom of this document.
Reflected light version
Wireframe version
Conclusions: The brightest portions lampshade ejecta curtain figure are principally determined by the total density of particles and the Sun-target-observer angle. The most dense portion of the figure occurs where the viewer looks through the edge of the curtain, i.e. - where there is most apparent number of particles. At high angles of solar elongation (when the scene is lit nearly at a right angle), the edge opposite the sun is brighter than the edge nearer the Sun. This is consistent with the LCROSS high-velocity gun experiment in the LCROSS "First Steps" video. The gun experiment shows at brighter far side and dimmer near side edge. In the simulation, as the light moves closer to Full Moon illumination, the ejecta curtain has a relatively more uniform brightness, although the edge effect remains. The spacecraft view simulation appears very sensistive to Sun angle changes in azimuth. Illumination at Sun at a right-angle to the spacecraft is much dimmer than illumination where the Sun is aligned behind the spacecraft viewpoint.
Prepared by: K. Fisher 3/2009 fisherka@csolutions.net