273 research outputs found
Photographic Observations of the Hayabusa Re-entry
We analyzed photographic observations of the re-entry of the Hayabusa
spacecraft and capsule over Southern Australia on June 13, 2010, 13:52 UT.
Radiometric measurements of the brightness of the associated fireball were
obtained as well. We derived the trajectories and velocities of the spacecraft,
its four fragments and the capsule. The capsule trajectory was within a few
hundred meters of the trajectory predicted by JAXA prior the re-entry. The
spacecraft trajectory was about 1 km higher than the capsule trajectory. Two
major fragments separated from the spacecraft at a height of about 62 km with
mutual lateral velocity of 250 m/s. The maximum absolute magnitude of the
fireball of -12.6 was reached at a height of 67 km. The dynamic pressures
acting on the spacecraft at the fragmentation points were only 1 - 50 kPa. No
spacecraft fragment was seen to survive below the height of 47 km. The integral
luminous efficiency of the event was 1.3%. As expected, the capsule had a very
low luminous efficiency and very low ablation coefficient. The ablation
coefficients and masses of the major spacecraft fragments are discussed.Comment: Accepted for publication in PASJ, 16 pages, 8 figures, 5 table
Anomalous Change of y\u27 and z in Na_x(H?O)_zCoO?・y\u27H?O at x ? 0.33
Abstract: We prepared some Nax(H?O)zC0O?・yH?O with BLH single phase and examined the Na content (x), H?O content (z)and H?O content (y). Nax(H?O)zC0O?・yH?O with BLH single phase and 0.28≦x≦0.36 were prepared by changing the amount of Br? used. The drastical changes in the c-axis length and z, Co valence, y around x=0.33 were observed, strongly suggesting that there exists a phase transition here
Near-Ultraviolet and Visible Spectroscopy of HAYABUSA Spacecraft Re-entry
HAYABUSA is the first spacecraft ever to land on and lift off from any
celestial body other than the moon. The mission, which returned asteroid
samples to the Earth while overcoming various technical hurdles, ended on June
13, 2010, with the planned atmospheric re-entry. In order to safely deliver the
sample return capsule, the HAYABUSA spacecraft ended its 7-year journey in a
brilliant "artificial fireball" over the Australian desert. Spectroscopic
observation was carried out in the near-ultraviolet and visible wavelengths
between 3000 and 7500 \AA at 3 - 20 \AA resolution. Approximately 100 atomic
lines such as Fe I, Mg I, Na I, Al I, Cr I, Mn I, Ni I, Ti I, Li I, Zn I, O I,
and N I were identified from the spacecraft. Exotic atoms such as Cu I, Mo I,
Xe I and Hg I were also detected. A strong Li I line (6708 \AA) at a height of
~55 km originated from the onboard Li-Ion batteries. The FeO molecule bands at
a height of ~63 km were probably formed in the wake of the spacecraft. The
effective excitation temperature as determined from the atomic lines varied
from 4500 K to 6000 K. The observed number density of Fe I was about 10 times
more abundant than Mg I after the spacecraft explosion. N2+(1-) bands from a
shock layer and CN violet bands from the sample return capsule's ablating heat
shield were dominant molecular bands in the near-ultraviolet region of 3000 -
4000 \AA. OH(A-X) band was likely to exist around 3092 \AA. A strong shock
layer from the HAYABUSA spacecraft was rapidly formed at heights between 93 km
and 83 km, which was confirmed by detection of N2+(1-) bands with a vibration
temperature of ~13000 K. Gray-body temperature of the capsule at a height of
~42 km was estimated to be ~2437 K which is matched to a theoretical
prediction. The final message of the HAYABUSA spacecraft and its sample return
capsule are discussed through our spectroscopy.Comment: Accepted for publication in PASJ, 22 pages, 7 figures, 6 table
Reducing nonideal to ideal coupling in random matrix description of chaotic scattering: Application to the time-delay problem
We write explicitly a transformation of the scattering phases reducing the
problem of quantum chaotic scattering for systems with M statistically
equivalent channels at nonideal coupling to that for ideal coupling. Unfolding
the phases by their local density leads to universality of their local
fluctuations for large M. A relation between the partial time delays and
diagonal matrix elements of the Wigner-Smith matrix is revealed for ideal
coupling. This helped us in deriving the joint probability distribution of
partial time delays and the distribution of the Wigner time delay.Comment: 4 pages, revtex, no figures; published versio
Detection of Earth-impacting asteroids with the next generation all-sky surveys
We have performed a simulation of a next generation sky survey's (Pan-STARRS
1) efficiency for detecting Earth-impacting asteroids. The steady-state
sky-plane distribution of the impactors long before impact is concentrated
towards small solar elongations (Chesley and Spahr, 2004) but we find that
there is interesting and potentially exploitable behavior in the sky-plane
distribution in the months leading up to impact. The next generation surveys
will find most of the dangerous impactors (>140m diameter) during their
decade-long survey missions though there is the potential to miss difficult
objects with long synodic periods appearing in the direction of the Sun, as
well as objects with long orbital periods that spend much of their time far
from the Sun and Earth. A space-based platform that can observe close to the
Sun may be needed to identify many of the potential impactors that spend much
of their time interior to the Earth's orbit. The next generation surveys have a
good chance of imaging a bolide like 2008TC3 before it enters the atmosphere
but the difficulty will lie in obtaining enough images in advance of impact to
allow an accurate pre-impact orbit to be computed.Comment: 47 pages, 16 figures, 2 table
Initial Results for Science Instruments Onboard EQUULEUS During the Cruising Phase Toward the Earth Moon Lagrange Point
EQUULEUS (EQUilibriUm Lunar-Earth point 6U Spacecraft) is a spacecraft to explore the cis-lunar region including the Earth-Moon Lagrange point L2 (EML2). The spacecraft is being jointly developed by JAXA, the University of Tokyo, and several other universities in Japan. After being launched into a lunar transfer orbit by NASA\u27s SLS (Space Launch System) Artemis-1 on November 16, 2022, the spacecraft successfully performed a first Delta-V and a trajectory correction maneuver. This enabled a precise lunar flyby and successful insertion into the orbit toward EML2.
Although the size of EQUULEUS is only 6U CubeSat, the spacecraft carries three different science instruments. The spacecraft can effectively demonstrate science missions during and after the flight to EML2 by using these instruments; the plasmasphere observation around the Earth by PHOENIX, the space dust flux detection in the cis-lunar region by CLOTH, and the lunar impact flash (LIF) observation at the far side of the moon by DELPHINUS.
All instruments have already completed its checkout. During the cruising phase, PHOENIX conducted Earth observations and successfully identified the Earth\u27s plasmashere. CLOTH has started regular standby operations. DELPHINUS obtained impressive images such as the far side of the Moon at lunar closest approach and long-period comet, Comet ZTF. This poster presents the details of these scientific missions and the initial checkout and observation results of the science instruments
AC resistivity of d-wave ceramic superconductors
We model d-wave ceramic superconductors with a three-dimensional lattice of
randomly distributed Josephson junctions with finite self-inductance. The
linear and nonlinear ac resistivity of the d-wave ceramic superconductors is
obtained as function of temperature by solving the corresponding Langevin
dynamical equations. We find that the linear ac resistivity remains finite at
the temperature where the third harmonics of resistivity has a peak. The
current amplitude dependence of the nonlinear resistivity at the peak position
is found to be a power law. These results agree qualitatively with experiments.
We also show that the peak of the nonlinear resistivity is related to the onset
of the paramagnetic Meissner effect which occurs at the crossover temperature
, which is above the chiral glass transition temperature .Comment: 7 eps figures, Phys. Rev. B (in press
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