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  • 1
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    Sedimentological Evidence for Pronounced Glacial‐Interglacial Climate Fluctuations in NE Tibet in the Latest Pliocene to Early Pleistocene (2021)
    Details
    Publication Date: 2021-07-04
    Description: The intensification of Northern Hemisphere glaciation (iNHG) and uplift of the Tibetan Plateau have been argued to be among the main drivers of climate change in midlatitude Central Asia during the Pliocene/Pleistocene. While most proxy records that support this hypothesis are from regions outside the Tibetan Plateau (such as from the Chinese Loess Plateau), detailed paleoclimatic information for the plateau itself during that time has yet remained elusive. Here we present a temporally highly resolved (~500 years) sedimentological record from the Qaidam Basin situated on the northeastern Tibetan Plateau that shows pronounced glacial‐interglacial climate variability during the interval from 2.7 to 2.1 Ma. Glacial (interglacial) intervals are generally characterized by coarser (finer) grain size, minima (maxima) in organic matter content, and maxima (minima) in carbonate content. Comparison of our results with Earth's orbital parameters and proxy records from the Chinese Loess Plateau suggests that the observed climate fluctuations were mainly driven by changes in the Siberian High/East Asian winter monsoon system as a response to the iNHG. They are further proposed to be enhanced by the topography of the Tibetan Plateau and its impact on the position and intensity of the westerlies.
    Description: Key Points: Pronounced glacial‐interglacial climate fluctuations on the NE Tibetan Plateau during the latest Pliocene and early Pleistocene. Changes in East Asian Winter Monsoon and the position of the westerlies influenced sediment transport on the NE Tibetan Plateau. Intensification of Northern Hemisphere glaciation amplified climate fluctuations on the NE Tibetan Plateau.
    Description: German Research Foundation (DFG
    Keywords: 551.7 ; loss on ignition ; EMMA ; SEM ; dust ; Asian monsoon ; Westerlies
    Type: article
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    CITATION GEO-LEO
  • 2
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    Suborbital Intercept and Fragmentation of an Asteroid with Very Short Warning Time Scenario (2015)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Small near-Earth objects (NEOs) is approx. 50-150 m in size are far more numerous (hundreds of thousands to millions yet to be discovered) than larger NEOs. Small NEOs, which are mostly asteroids rather than comets, are very faint in the night sky due to their small sizes, and are, therefore, difficult to discover far in advance of Earth impact. Furthermore, even small NEOs are capable of creating explosions with energies on the order of tens or hundreds of megatons (Mt). We are, therefore, motivated to prepare to respond effectively to short warning time, small NEO impact scenarios. In this paper we explore the lower bound on actionable warning time by investigating the performance of notional upgraded Intercontinental Ballistic Missiles (ICBMs) to carry Nuclear Explosive Device (NED) payloads to intercept and disrupt a hypothetical incoming NEO at high altitudes (generally at least 2500 km above Earth). We conduct this investigation by developing optimal NEO intercept trajectories for a range of cases and comparing their performances. Our results show that suborbital NEO intercepts using Minuteman III or SM-3 IIA launch vehicles could achieve NEO intercept a few minutes prior to when the NEO would strike Earth. We also find that more powerful versions of the launch vehicles (e.g., total deltaV is approx. 9.5-11 km/s) could intercept incoming NEOs several hours prior to when the NEO would strike Earth, if launched at least several days prior to the time of intercept. Finally, we discuss a number of limiting factors and practicalities that affect whether the notional systems we describe could become feasible.
    Keywords: Astronomy; Space Sciences (General)
    Type: IAA-PDC-15-03-09 , GSFC-E-DAA-TN22381 , IAA Planetary Defense Conference; Apr 13, 2015 - Apr 17, 2015; Frascati, Roma; Italy
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Mission Design and Analysis for Suborbital Intercept and Fragmentation of an Asteroid with Very Short Warning Time (2014)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Small near-Earth objects (NEOs) approximately 50-150 m in size are far more numerous (hundreds of thousands to millions yet to be discovered) than larger NEOs. Small NEOs, which are mostly asteroids rather than comets, are very faint in the night sky due to their small sizes, and are, therefore, difficult to discover far in advance of Earth impact. Furthermore, even small NEOs are capable of creating explosions with energies on the order of tens or hundreds of megatons (Mt). We are, therefore, motivated to prepare to respond effectively to short warning time, small NEO impact scenarios. In this paper we explore the lower bound on actionable warning time by investigating the performance of notional upgraded Intercontinental Ballistic Missiles (ICBMs) to carry Nuclear Explosive Device (NED) payloads to intercept and disrupt a hypothetical incoming NEO at high altitudes (generally at least 2500 km above Earth). We conduct this investigation by developing optimal NEO intercept trajectories for a range of cases and comparing their performances. Our results show that suborbital NEO intercepts using Minuteman III or SM-3 IIA launch vehicles could achieve NEO intercept a few minutes prior to when the NEO would strike Earth. We also find that more powerful versions of the launch vehicles (e.g., total delta V of approximately 9.5-11 km/s) could intercept incoming NEOs several hours prior to when the NEO would strike Earth, if launched at least several days prior to the time of intercept. Finally, we discuss a number of limiting factors and practicalities that affect whether the notional systems we describe could become feasible.
    Keywords: Astronautics (General)
    Type: GSFC-E-DAA-TN15869 , AIAA/AAS Astrodynamics Specialist Conference; Aug 04, 2014 - Aug 07, 2014; San Diego, CA; United States|AIAA SPACE 2014 Conference and Exposition; Aug 04, 2014 - Aug 07, 2014; San Diego, CA; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    Microhard MHX 2420 Orbital Performance Evaluation Using RT Logic T400CS (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A major upfront cost of building low cost Nanosatellites is the communications sub-system. Most radios built for space missions cost over $4,000 per unit. This exceeds many budgets. One possible cost effective solution is the Microhard MHX2420, a commercial off-the-shelf transceiver with a unit cost under $1000. This paper aims to support the Nanosatellite community seeking an inexpensive radio by characterizing Microhard's performance envelope. Though not intended for space operations, the ability to test edge cases and increase average data transfer speeds through optimization positions this radio as a solution for Nanosatellite communications by expanding usage to include more missions. The second objective of this paper is to test and verify the optimal radio settings for the most common cases to improve downlinking. All tests were conducted with the aid of the RT Logic T400CS, a hardware-in-the-loop channel simulator designed to emulate real-world radio frequency (RF) link effects. This study provides recommended settings to optimize the downlink speed as well as the environmental parameters that cause the link to fail.
    Keywords: Communications and Radar
    Type: ARC-E-DAA-TN5503 , Annual AIAA/USU Conference on Small Satellites; Aug 13, 2012 - Aug 16, 2012; Logan, UT; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 5
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    Suborbital Asteroid Intercept and Fragmentation for Very Short Warning Time Scenarios (2015)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Small near-Earth objects (NEOs) 50150 m in size are far more numerous (hundreds of thousands to millions yet to be discovered) than larger NEOs. Small NEOs, which are mostly asteroids rather than comets, are very faint in the night sky due to their small sizes, and are, therefore, difficult to discover far in advance of Earth impact. However, even small NEOs are capable of creating explosions with energies on the order of tens or hundreds of megatons (Mt).We are, therefore, motivated to prepare to respond effectively to short warning time, small NEO impact scenarios. In this paper we explore the lower bound on actionable warning time by investigating the performance of notional upgraded Intercontinental Ballistic Missiles (ICBMs) to carry Nuclear Explosive Device (NED) payloads to intercept and disrupt a fictitious incoming NEO at high altitudes (generally, at least 2500 km above Earth). We conduct this investigation by developing optimal NEO intercept trajectories for a range of cases and comparing their performances.Our results show that suborbital NEO intercepts using Minuteman III or SM-3 IIA launch vehicles could achieve NEO intercept a few minutes prior to when the NEOwould strike Earth. We also find that more powerful versions of the launch vehicles (e.g., total V 9.511 kms) could intercept incoming NEOs over a day prior to when the NEO would strike Earth, if launched at least several days prior to the time of NEO intercept. Finally, we discuss a number of limiting factors and practicalities that affect whether the notional systems we describe could become feasible.
    Keywords: Lunar and Planetary Science and Exploration; Launch Vehicles and Launch Operations
    Type: GSFC-E-DAA-TN22238 , IAA Planetary Defense Conference; Apr 13, 2015 - Apr 17, 2015; Frascati; Italy
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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