• Analysis of Communication Rates in the Proximity of Near-Earth Asteroids

      Nelson, Evan; Creusere, Charles D.; Critz, Thomas; Butcher, Eric; New Mexico State University (International Foundation for Telemetering, 2013-10)
      In this paper we analyze fundamental local-area communication issues related to proximity operations around near-earth asteroids. We are motivated by NASA's plan to send robotic spacecraft to numerous such asteroids in the coming years in preparation for an eventual manned mission. We consider here the case where multiple probes are deposited on the surface of an asteroid and must communicate the data they collect to each other and to earth by using the orbiting `mothership' as a relay. With respect to this scenario, we statistically analyze the ability of surface probes in various locations to communicate with the mothership as well as their abilities to network with one another. For the purposes of this analysis, we assume the simplest possible communications scenario: a surface probe can communicate with the mothership only when it has an unobstructed line of sight. At the frequencies of interest here, line of sight is a necessary condition but it is obviously not sufficient - the end-to-end link margins of our communications system must be high enough to support the desired/required data rates. The work presented in this paper extends our previous research in which we only analyzed the visibility of the locations on the surface of the asteroid. Here, we consider how visibility affects the required communications bandwidth and buffer sizes for both surface-to-spacecraft and surface-to-surface scenarios.
    • Full-Waveform LIDAR Recovery at Sub-Nyquist Rates

      Creusere, Charles D.; Castorena, Juan; New Mexico State University (International Foundation for Telemetering, 2013-10)
      Third generation LIDAR full-waveform (FW) based systems collect 1D FW signals of the echoes generated by laser pulses of wide bandwidth reflected at the intercepted objects to construct depth profiles along each pulse path. By emitting a series of pulses towards a scene using a predefined scanning patter, a 3D image containing spatial-depth information can be constructed. Unfortunately, acquisition of a high number of wide bandwidth pulses is necessary to achieve high depth and spatial resolutions of the scene. This implies the collection of massive amounts of data which generate problems for the storage, processing and transmission of the FW signal set. In this research, we explore the recovery of individual continuous-time FW signals at sub-Nyquist rates. The key step to achieve this is to exploit the sparsity in FW signals. Doing this allows one to sub-sample and recover FW signals at rates much lower than that implied by Shannon's theorem. Here, we describe the theoretical framework supporting recovery and present the reader with examples using real LIDAR data.