104 research outputs found
Survey of capabilities and applications of accurate clocks: directions for planetary science
No full textFor planetary science, accurate clocks are mainly used as part of an onboard radioscience
transponder. In the case of two-way radio data, the dominating data type for planetary
radioscience, an accurate spacecraft clock is not necessary since the measurements can
be calibrated using high-precision clocks on Earth. In the case of one-way radio data, however,
an accurate clock can make the precision of one-way radio data be comparable to the
two-way data, and possibly better since only one leg of radio path would be affected by the
media. This article addresses several ways to improve observations for planetary science, either
by improving the onboard clock or by using further variants of the classical radioscience
methods, e.g., Same Beam Interferometry (SBI). For a clock to be useful for planetary science,
we conclude that it must have at least a short-time stability (< 1,000 s) better than
10^−13 and its size be substantially miniaturized. A special case of using laser ranging to the
Moon and the implication of having an accurate clock is shown as an example
Drag-Free Satellite Control
No full textScientific satellite missions trying to investigate questions regarding geodesy and fundamental physics have become increasingly dependent on ultra low disturbance environments. The precision demanded by the experiments has risen continuously as experimenters strive to deepen their understanding. Standard attitude and orbital control systems are not capable of providing such an ultra low disturbance environment which lead to the introduction of so called drag-free control systems.
Drag-free control is an enabling technology with the capability to provide these ultra low disturbance environments. The application of drag-free control systems is of course not limited to geodesy and fundamental physics. It is a useful technology for every mission that requires a low disturbance free-fall environment.
Drag-free control has come a long way since the introduction of the original drag-free concept by Benjamin Lange in 1964. The aim of this paper is to give an introduction and overview about the drag-free technology and its implications for scientific satellite missions. In addition to the original drag-free concept and its advancements the paper introduces key technologies in sensors and
actuators whose development was fueled by the application of the
drag-free concept in scientific satellite missions. Moreover problems and challenges connected to drag-free satellite control and the technologies involved are discussed and current drag-free missions like LISA and its technology demonstrator LISA Pathfinder, MICROSCOPE, STEP or GOCE are presented
International Workshop on From Quantum to Cosmos : Fundamental Physics Research in Space
No full text
Gravitational lensing for interstellar power transmission
No full textWe investigate light propagation in the gravitational field of multiple
gravitational lenses. Assuming these lenses are sufficiently spaced to prevent
interaction, we consider a linear alignment for the transmitter, lenses, and
receiver. Remarkably, in this axially-symmetric configuration, we can solve the
relevant diffraction integrals -- result that offers valuable analytical
insights. We show that the point-spread function (PSF) is affected by the
number of lenses in the system. Even a single lens is useful for transmission
either it is used as a part of the transmitter or it acts on the receiver's
side. We show that power transmission via a pair of lenses benefits from light
amplification on both ends of the link. The second lens plays an important role
by focusing the signal to a much tighter spot; but in practical lensing
scenarios, that lens changes the structure of the PSF on scales much smaller
than the telescope, so that additional gain due to the presence of the second
lens is independent of its properties and is govern solely by the transmission
geometry. While evaluating the signal-to-noise ratio (SNR) in various
transmitting scenarios, we see that a single-lens transmission performs on par
with a pair of lenses. The fact that the second lens amplifies the brightness
of the first one, creates a challenging background for signal reception.
Nevertheless, in all the cases considered here, we have found
practically-relevant SNR values. As a result, we were able to demonstrate the
feasibility of establishing interstellar power transmission links relying on
gravitational lensing - a finding with profound implications for applications
targeting interstellar power transmission.Comment: 20 pages, 4 figure
SIM PlanetQuest: Science with the Space Interferometry Mission
No full textSIM - the Space Interferometry Mission - will perform precision optical astrometry on objects as faint as R magnitude 20. It will be the first space-based astrometric interferometer, operating in the optical band with a 10-m baseline. The Project is managed by the Jet Propulsion Laboratory, California Institute of Technology, in close collaboration with two industry partners, Lockheed Martin Missiles and Space, and TRW Inc., Space and Electronics Group. Launch of SIM is currently planned for 2009. In its wide-angle astrometric mode, SIM will yield 4 microarcsecond absolute position and parallax measurements. Astrometric planet searches will be done in a narrow-angle mode, with an accuracy of 4 microarcseconds or better in a single measurement. As a pointed rather than a survey instrument, SIM will maintain.its astrometric accuracy down to the faintest, magnitudes, opening up the opportunity for astrometry of active galactic nuclei to better than 10 pas. SIM will define a new astrometric reference frame, using a grid of approximately 1500 stars with positions accurate to 4 microarcseconds. The SIM Science Team comprises the Principal Investigators of ten Key Projects, and five Mission Scientists contributing their expertise to specific areas of the mission. Their science programs cover a wide range of topics in Galactic and extragalactic astronomy. They include: searches for low-mass planets - including analogs to our own solar system - tlie formation and dynamics of our Galaxy, calibration of the cosmic distance scale, and fundamental stellar astrophysics. All of the science observing on SIM is competitively awarded; the Science Team programs total about 40% of the total available, and the remainder will be assigned via future NASA competitions. This report is a compilation of science summaries by members of the Science Team, and it illustrates the wealth of scientific problems that microarcsecond-precision astrometry can contribute to. More information on SIM, including copies of this report, may be obtained from the project web site, at http://sim. jpl.nasa.gov
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