JHU Applied Physics Laboratory

Laurel, MD, United States

JHU Applied Physics Laboratory

Laurel, MD, United States
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Lorenz R.D.,JHU Applied Physics Laboratory
IEEE Aerospace Conference Proceedings | Year: 2017

The Huygens probe mission is reviewed with particular attention to system and instrument behaviors that were not in accord with expectations. These include the radio system, radar altimeters, the descent spin and attitude behavior, and instrument operations. Lessons for future missions are drawn. © 2017 IEEE.

Heisler E.,JHU Applied Physics Laboratory | Abel E.,JHU Applied Physics Laboratory | Congdon E.,JHU Applied Physics Laboratory | Eby D.,JHU Applied Physics Laboratory
IEEE Aerospace Conference Proceedings | Year: 2017

Solar Probe Plus (SPP) is a NASA mission that will go within ten Solar Radii of the sun. One of the crucial technologies in this system is the Thermal Protection System (TPS), which shields the spacecraft from the sun. The TPS is made up of carbon-foam sandwiched between two carbon-carbon panels, and is approximately eight feet in diameter and 4.5 inches thick. At its closest approach, the front surface of the TPS is expected to reach 1200°C, but the foam will dissipate the heat so the back surface will only be about 300°C. Solar Probe Plus is scheduled to launch in 2018, and the program is in the beginning stages of integration and testing. As part of the testing process, SPP's cooling system and the full spacecraft will undergo thermal tests. Radiation from the back of the TPS plays a large part in both of these systems thermal environment. To get the back surface of the TPS to 300°C, large amounts of energy needs to be put into the top of the TPS. However, there are not many thermal chambers that can accommodate the amount of energy required at the vacuum environment required to simulate space. It is also extremely risky to expose the flight hardware to that much energy. Instead, a Thermal Simulator will be used that mimics the thermal and geometric footprint of the bottom of the TPS. The Thermal Simulator is designed as an oven box, similar in size and shape to the flight TPS, which uses tubular heaters to heat a 32 mil thick aluminum bottom sheet. The heaters and bottom sheet are supported by a large stainless steel structure. The sides and top of the structure are blanketed using stainless steel sheets. To verify the concept, a miniature simulator was built and tested. Despite a successful trial simulator, there were difficulties extrapolating the design into a larger size. This paper will focus on the construction and testing of the full-sized simulator. After extensive structural and thermal analysis, the full simulator was fabricated and assembled. A thermal vacuum test was done at NASA Goddard Space Flight Center in chamber 238. At high vacuum, the bottom sheet was successfully brought to 250°C, 300°C, and 350°C with gradients of +/-30°C. Each temperature point was held for at least three hours after steady state was achieved. This simulator will be used in winter 2017 for the Integrated Thermal Vacuum Test, and again in the future for the full spacecraft test. By successfully executing the thermal system testing using GSE, we will prove that a full system can be validated using piecemeal testing. © 2017 IEEE.

Lorenz R.D.,JHU Applied Physics Laboratory | Tokano T.,University of Cologne | Newman C.E.,Ashima Research
Planetary and Space Science | Year: 2012

We use two independent General Circulation Models (GCMs) to estimate surface winds at Titan's Ligeia Mare (78° N, 250° W), motivated by a proposed mission to land a floating capsule in this ∼500 km hydrocarbon sea. The models agree on the overall magnitude (∼0.51 m/s) and seasonal variation (strongest in summer) of windspeeds, but details of seasonal and diurnal variation of windspeed and direction differ somewhat, with the role of surface exchanges being more significant than that of gravitational tides in the atmosphere. We also investigate the tidal dynamics in the sea using a numerical ocean dynamics model: assuming a rigid lithosphere, the tidal amplitude is up to ∼0.8 m. Tidal currents are overall proportional to the reciprocal of depth - with an assumed central depth of 300 m, the characteristic tidal currents are ∼1 cm/s, with notable motions being a slosh between Ligeia's eastern and western lobes, and a clockwise flow pattern. We find that a capsule will drift at approximately one tenth of the windspeed, unless measures are adopted to augment the drag areas above or below the waterline. Thus motion of a floating capsule is dominated by the wind, and is likely to be several km per Earth day, a rate that will be readily measured from Earth by radio navigation methods. In some instances, the wind vector rotates diurnally such that the drift trajectory is epicyclic. © 2011 Elsevier Ltd. All rights reserved.

Troshichev O.,Arctic and Antarctic Research Institute | Stauning P.,Danish Meteorological Institute | Liou K.,JHU Applied Physics Laboratory | Reeves G.,Los Alamos National Laboratory
Advances in Space Research | Year: 2011

The relationships between the magnetic disturbance onsets, aurora dynamics and particles injections at the geostationary orbit have been analyzed in detail for 25 sawtooth substorms. It is shown that inconsistency between the above signatures of the substorms onset is typical of the powerful sawtooth substorms, unlike the isolated ("classical") magnetospheric substorms. The distinguishing feature of the aurora in case of saw-tooth substorms is permanently high level of auroral activity irrespective of the magnetic disturbance onsets and the double oval structure of the aurora display. The close relationship between the aurora behavior and the particle injections at geostationary orbit is also broken. The conclusion is made, that the classical concept of the substorm development, put forward by Akasofu (1964) for isolated substorms, is not workable in cases of the sawtooth disturbances, when the powerful solar wind energy pumping into the magnetosphere provides a permanent powerful aurora particle precipitation into the auroral zone. © 2010 COSPAR. Published by Elsevier Ltd. All rights reserved.

Savage C.J.,Brigham Young University | Radebaugh J.,Brigham Young University | Christiansen E.H.,Brigham Young University | Lorenz R.D.,JHU Applied Physics Laboratory
Icarus | Year: 2014

Analysis of large-scale morphological parameters can reveal the reaction of dunes to changes in atmospheric and sedimentary conditions. Over 7000 dune width and 7000 dune spacing measurements were obtained for linear dunes in regions across Saturn's moon Titan from images T21, T23, T28, T44 and T48 collected by the Synthetic Aperture RADAR (SAR) aboard the Cassini spacecraft in order to reconstruct the aeolian surface history of Titan. Dunes in the five study areas are all linear in form, with a mean width of 1.3. km and mean crest spacing of 2.7. km, similar to dunes in the African Saharan and Namib deserts on Earth. At the resolution of Cassini SAR, the dunes have the morphology of large linear dunes, and they lack evidence for features of compound or complex dunes. The large size, spacing and uniform morphology are all indicators that Titan's dunes are mature features, in that they have grown toward a steady state for a long period of time. Dune width decreases to the north, perhaps from increased sediment stabilization caused by a net transport of moisture from south to north, or from increased maturity in dunes to the south. Cumulative probability plots of dune parameters measured at different locations across Titan indicate there is a single population of intermediate-to-large-sized dunes on Titan. This suggests that, unlike analogous dunes in the Namib and Agneitir Sand Seas, dune-forming conditions that generated the current set of dunes were stable and active long enough to erase any evidence of past conditions. © 2013 Elsevier Inc.

Lorenz R.,JHU Applied Physics Laboratory
IEEE Aerospace Conference Proceedings | Year: 2013

Desert dust devil phenomena on Earth and Mars are reviewed, and progress in studying them with novel unattended field sensors, and with timelapse imaging, is described. These new datasets present data analysis challenges which are familiar in other tracking/target identification applications. © 2013 IEEE.

Avritzer A.,Siemens AG | Cole R.G.,JHU Applied Physics Laboratory | Weyuker E.J.,AT and T Labs Research
Journal of Systems and Software | Year: 2010

In this paper we describe several methods for detecting the need for software rejuvenation in mission critical systems that are subjected to worm infection, and introduce new software rejuvenation algorithms. We evaluate these algorithms' effectiveness using both simulation studies and analytic modeling, by assessing the probability of mission success. The system under study emulates a Mobile Ad-Hoc Network (MANET) of processing nodes. Our analysis determined that some of our rejuvenation algorithms are quite effective in maintaining a high probability of mission success while the system is under explicit attack by a worm infection. © 2009 Elsevier Inc.

Lorenz R.D.,JHU Applied Physics Laboratory
IEEE Aerospace Conference Proceedings | Year: 2010

Dust devils are dry convective vortices that loft dust into the air, often a nuisance for outdoor activities and occasionally responsible for structural damage and fatal aircraft accidents. 12They are also the most prominent dynamic phenomena observed on the surface of Mars, where they influence the climate by acting as the principal mechanism of dust-raising. Atmospheric dust, and its removal by dust devils from solar panels, can also significantly impact the operation of spacecraft on the Martian surface. However, many aspects of dust devil behavior and properties are not well-understood. Here I report progress towards obtaining robust statistics on dust devil properties, and their 2-dimensional horizontal structure, using arrays of small dataloggers and wireless motes. I additionally report some ancillary observations using a thermal camera, and timelapse optical imagery derived from inexpensive consumer digital cameras. ©2010 IEEE.

Boyd-Graber J.,University of Maryland College Park | Glasgow K.,JHU Applied Physics Laboratory | Zajac J.S.,University of Maryland College Park
Proceedings of the ASIST Annual Meeting | Year: 2013

Spoilers-critical plot information about works of fiction that "spoil" a viewer's enjoyment-have prompted elaborate conventions on social media to allow readers to insulate themselves from spoilers. However, these solutions depend on the conscientiousness and rigor of Internet posters and are thus an imperfect system. We create an automatic alternative that could alert users when a piece of text contains a spoiler. An automated spoiler detector serves not only as an additional protection against spoilers, but it also contributes to important problems in computational linguistics. We develop a new dataset of spoilers gathered from social media and create automatic classifiers using machine learning techniques. After establishing baseline performance using lexical features, we develop metadata-based features that substantially improve performance on the spoiler detection task.

Agency: Department of Defense | Branch: Navy | Program: STTR | Phase: Phase I | Award Amount: 80.00K | Year: 2015

We propose the design and development of LCS radar modeling for training a radar modeling engine that capture the effects of environment, weather, jamming/interference and operator actions on radar display. The purpose of this engine is to reduce or eli

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