scholarly journals ASTROD AND ASTROD I — OVERVIEW AND PROGRESS

2008 ◽  
Vol 17 (07) ◽  
pp. 921-940 ◽  
Author(s):  
WEI-TOU NI
Keyword(s):  
Gravitational Field ◽  
Solar System ◽  
Gravitational Waves ◽  
Binary Stars ◽  
Precise Determination ◽  
The Sun ◽  
Free System ◽  
Dynamic Distribution ◽  
Magnitude Improvement

In this paper, we present an overview of ASTROD (Astrodynamical Space Test of Relativity using Optical Devices) and ASTROD I mission concepts and studies. The missions employ deep-space laser ranging using drag-free spacecraft to map the gravitational field in the solar-system. The solar-system gravitational field is determined by three factors: the dynamic distribution of matter in the solar system; the dynamic distribution of matter outside the solar system (galactic, cosmological, etc.) and gravitational waves propagating through the solar system. Different relativistic theories of gravity make different predictions of the solar-system gravitational field. Hence, precise measurements of the solar-system gravitational field test these relativistic theories, in addition to gravitational wave observations, determination of the matter distribution in the solar-system and determination of the observable (testable) influence of our galaxy and cosmos. The tests and observations include: (i) a precise determination of the relativistic parameters β and γ with 3–5 orders of magnitude improvement over previous measurements; (ii) a 1–2 order of magnitude improvement in the measurement of G; (iii) a precise determination of any anomalous, constant acceleration Aadirected towards the Sun; (iv) a measurement of solar angular momentum via the Lense-Thirring effect; (v) the detection of solar g-mode oscillations via their changing gravity field, thus, providing a new eye to see inside the Sun; (vi) precise determination of the planetary orbit elements and masses; (vii) better determination of the orbits and masses of major asteroids; (viii) detection and observation of gravitational waves from massive black holes and galactic binary stars in the frequency range 50 μHz to 5 mHz; and (ix) exploring background gravitational waves. The baseline scheme of ASTROD is to have two spacecraft in separate solar orbits and one spacecraft near the Earth–Sun L1/L2 point carrying a payload of a proof mass, two telescopes, two 1–2 W lasers with spares, a clock and a drag-free system ranging coherently among one another using lasers. ASTROD I is a first step towards ASTROD. Its scheme is to have one spacecraft in a Venus-gravity-assisted solar orbit, ranging optically with ground stations with less ambitious, but still significant scientific goals.

ASTROD–AN OVERVIEW

2002 ◽  
Vol 11 (07) ◽  
pp. 947-962 ◽  
Author(s):  
WEI-TOU NI
Keyword(s):  
Angular Momentum ◽  
Solar System ◽  
Gravitational Wave ◽  
Reference System ◽  
Precise Determination ◽  
The Sun ◽  
Gravitational Wave Detection ◽  
Wave Detection ◽  
The Earth

The objectives of the Astrodynamical Space Test of Relativity using Optical Devices (ASTROD) Mission concept are threefold. The first objective is to discover and explore fundamental physical laws governing matter, space and time via testing relativistic gravity with 3-6 orders of magnitude improvement. Relativistic gravity is an important cornerstone of physics, astronomy and cosmology. Its improved test is crucial to cosmology and modern theories of gravitation including superstring theories. Included in this objective is the precise determination of the relativistic parameters β and γ, the improved measurement of Ġ and a precise determination of an anomalous, constant acceleration directed towards the Sun. The second objective of the ASTROD mission is the high-precision measurement of the solar-system parameter. This includes: (i) a measurements of solar angular momentum via Lense-Thirring effect and the detection of solar g-mode oscillations via their changing gravity field, thus, providing a new eye to see inside the Sun; (ii) precise determination of the planetary orbit elements and masses; (iii) better determination of the orbits and masses of major asteroids. These measurements give better solar dynamics and probe the origin of our solar system. The third objective is to detect and observe gravitational waves from massive black holes and galactic binary stars in the frequency range 50 μHz to 5 mHz. Background gravitational -waves will also be explored. A desirable implementation is to have two spacecraft in separate solar orbit carrying a payload of a proof mass, two telescopes, two 1-2 W lasers, a clock and a drag-free system, together with an Earth reference system. the two spacecraft range coherently with the Earth reference system using lasers. When they are near, they range coherently to each other. The Earth reference system could be ground stations, Earth satellites and/or spacecraft near Earth-Sun Lagrange points. In this overview, we discuss the payload concept, the technological requirements, technological developments, orbit design, orbit simulation, the measurement of solar angular momentum, the gravitational-wave detection sensitivity, and the solar g-mode detection possibility for this mission concept. A simplified mission, Mini-ASTROD with one spacecraft ranging optically with ground stations, together with Super-ASTROD with four spacecraft of 5 AU (Jupiter-like) orbits, will be mentioned in the end. Super-ASTROD is a dedicated low-frequency gravitational-wave detection concept. For Mini-ASTROD, the first objective of ASTROD will be largely achieved; the second objective will be partially achieved; for gravitational wave detection, the sensitivity will be better than the present-day sensitivity using Doppler tracking by radio waves.

scholarly journals Encounters involving planetary systems in birth environments: the significant role of binaries

2020 ◽  
Vol 499 (1) ◽  
pp. 1212-1225
Author(s):  
Daohai Li ◽  
Alexander J Mustill ◽  
Melvyn B Davies
Keyword(s):  
Solar System ◽  
Significant Role ◽  
Cross Sections ◽  
Binary Stars ◽  
Open Cluster ◽  
Planetary Systems ◽  
The Sun ◽  
Crowded Environments ◽  
Stellar Density

ABSTRACT Most stars form in a clustered environment. Both single and binary stars will sometimes encounter planetary systems in such crowded environments. Encounter rates for binaries may be larger than for single stars, even for binary fractions as low as 10–20 per cent. In this work, we investigate scatterings between a Sun–Jupiter pair and both binary and single stars as in young clusters. We first perform a set of simulations of encounters involving wide ranges of binaries and single stars, finding that wider binaries have larger cross-sections for the planet’s ejection. Secondly, we consider such scatterings in a realistic population, drawing parameters for the binaries and single stars from the observed population. The scattering outcomes are diverse, including ejection, capture/exchange, and collision. The binaries are more effective than single stars by a factor of several or more in causing the planet’s ejection and collision. Hence, in a cluster, as long as the binary fraction is larger than about 10 per cent, the binaries will dominate the scatterings in terms of these two outcomes. For an open cluster of a stellar density 50 pc−3, a lifetime 100 Myr, and a binary fraction 0.5, we estimate that Jupiters of the order of 1 per cent are ejected, 0.1 per cent collide with a star, 0.1 per cent change ownership, and 10 per cent of the Sun–Jupiter pairs acquire a stellar companion during scatterings. These companions are typically thousands of au distant and in half of the cases (so 5 per cent of all Sun–Jupiter pairs), they can excite the planet’s orbit through Kozai–Lidov mechanism before being stripped by later encounters. Our result suggests that the Solar system may have once had a companion in its birth cluster.

scholarly journals The Nasa Solar Probe Mission: In Situ Determination of Interplanetary Out-of-The Ecliptic and Near-Solar Dust Environments

1991 ◽  
Vol 126 ◽  
pp. 29-32
Author(s):  
Bruce T. Tsurutani ◽  
James E. Randolph
Keyword(s):  
Solar Cycle ◽  
Solar System ◽  
Solar Eclipse ◽  
Orbital Period ◽  
High Velocity ◽  
Scientific Community ◽  
The Sun ◽  
Probe Mission

AbstractThe NASA Solar Probe mission will be one of the most exciting dust missions ever flown and will lead to a revolutionary advance in our understanding of dust within our solar system. Solar Probe will map the dust environment from the orbit of Jupiter (5 AU), to within 4 solar radii of the sun’s center. The region between 0.3 AU and 4 Rshas never been visited before, so the 10 days that the spacecraft spends during each (of the two) orbit is purely exploratory in nature. Solar Probe will also reach heliographic latitudes as high as ~ 15 to 28 above (below) the ecliptic on its trajectory inbound (outbound) to (from) the sun. This, in addition to the ESA/NASA Ulysses mission, will help determine the out-of-the-ecliptic dust environment. A post-perihelion burn will reduce the satellite orbital period to 2.5 years about the sun. A possible extended mission would allow data reception for 2 more revolutions, mapping out a complete solar cycle. Because the near-solar dust environment is not well understood (or is controversial at best), and it is very important to have better knowledge of the dust environment to protect Solar Probe from high velocity dust hits, we urgently request the scientific community to obtain further measurements of the near-solar dust properties. One prime opportunity is the July 1991 solar eclipse.

The gravitational field of a rotating cohesive system

1947 ◽  
Vol 43 (2) ◽  
pp. 164-177 ◽  
Author(s):  
G. L. Clark
Keyword(s):  
Periodic Solution ◽  
Gravitational Field ◽  
Gravitational Waves ◽  
External Fields ◽  
Velocity Of Propagation ◽  
Gravitational Equations

In this paper a periodic solution of the gravitational equations is examined. The solution, which is valid throughout all space, is such that the internal and external fields and their derivatives are continuous at the boundary of a spheroid rotating about an axis other than that of symmetry. At great distances from the system the solution has the same form as the field due to a rotating rod and can be applied to problems like the determination of the velocity of propagation of gravitational waves and the loss of energy of a rotating cohesive system.

scholarly journals Lunar Libration Tables and Determination of Crater Coordinates

1997 ◽  
Vol 165 ◽  
pp. 281-286
Author(s):  
Natasha Petrova
Keyword(s):  
Gravitational Field ◽  
Solar System ◽  
Angular Position ◽  
Theoretical Description ◽  
Laser Ranging ◽  
Radio Sources ◽  
Space Technology ◽  
The Moon ◽  
Lunar Rotation

The study of lunar rotation has attracted considerable interest with the advent of the epoch of exploration of the Solar system by space technology. A series of works on an investigation of the lunar gravitational field carried out with the help of artificial lunar satellites have greatly advanced our possibility for that study. The problem concerning the landing on the lunar surface of spacecraft, and the creation of durable lunar bases, impose heavy demands on the accuracy of theoretical description of orbital and rotational motion of the Moon.The development of the observational technology with the help of radio-and laser ranging (LLR) provides at the present time measurements of the distance to a given point on the Moon with an accuracy of about 2 cm, probably improved in the future to about 5mm (Banerdt, 1995). By using differential VLBI measurement with extragalactic radio sources angularly near the Moon, it should be possible to obtain routine estimates of angular position of the beacon to 0.1 mas from each observation (Baudry, 1995). Therefore, combining VLBI and LLR techniques will provide a means of achieving new objectives, and that calls for the development of the theories adequate to an accuracy for observations.

Fingerprints of the protosolar cloud collapse in the Solar System: Refractory inclusions distribution and isotopic anomalies in meteorites

2019 ◽  
Vol 15 (S350) ◽  
pp. 100-102
Author(s):  
Francesco C. Pignatale ◽  
Emmanuel Jacquet ◽  
Marc Chaussidon ◽  
Sébastien Charnoz
Keyword(s):  
Thermal Properties ◽  
Solar System ◽  
Building Blocks ◽  
Homogeneous Distribution ◽  
The Sun ◽  
Relative Age ◽  
Show Evidence ◽  
Collapsing Cloud ◽  
Isotopic Anomalies

AbstractIncreasing evidences suggest that the building blocks of Ca-Al-rich inclusions (CAIs) could have formed with the Sun, during the collapse of the parent cloud. However, determination of the relative age of CAIs relies on the homogeneous distribution of their short-lived radionuclide 26Al that is used as a chronometer. Some CAIs show evidence of 26Al/27 Al variation that is independent of decay.We investigate the dynamical and chemical evolution of refractories from the collapsing cloud to their transport in the protoplanetary disk focusing to the predicted isotopic anomalies resulting from 26Al heterogeneities.The interplay between the thermal properties of the dust, the isotopic zoning in the cloud and disk dynamics produce aggregates that resemble chondrites. An abrupt raise of 26Al close the center of the cloud followed by a plateau throughout the cloud best matches the observations. As a consequence, the 26Al -chronometer retains validity from the formation of canonical CAIs onward.

A proposal for an electrical connection between the gravitational field and light

2020 ◽  
Vol 33 (3) ◽  
pp. 271-275
Author(s):  
Michael J. Curran
Keyword(s):  
Gravitational Field ◽  
Magnetic Fields ◽  
Gravitational Waves ◽  
Building Block ◽  
Electromagnetic Waves ◽  
Direct Photon ◽  
The Sun ◽  
Speed Of Light ◽  
Electrical Connection ◽  
The Relationship

Based on well-established equations, we provide evidence of an electrical connection between the gravitational field and light. Each is modeled using the inductance‐capacitance ( <mml:math display="inline"> <mml:mrow> <mml:mi>L</mml:mi> <mml:mi>C</mml:mi> </mml:mrow> </mml:math> ) circuit as the building block. A proposed direct photon force (not a pressure and not by means of a force carrier), the relationship between the speed of light and gravity, the frequency and wavelength of gravitational waves, gravitational redshift, the trajectory of planets around the sun, and equations of plane electromagnetic waves may all be expressed with the assistance of an ideal (no resistance) <mml:math display="inline"> <mml:mrow> <mml:mi>L</mml:mi> <mml:mi>C</mml:mi> </mml:mrow> </mml:math> circuit model of light. Each begins with the Planck‐Einstein relationship. Each suggests that gravity and electromagnetism interact directly through fluctuating electrical and magnetic fields from both sources. With this perspective Einstein's concept of the warping of spacetime may not be needed to explain gravitation.

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