PLEASE NOTE:
*
CCNet DIGEST, 2 September 1998
------------------------------
Please note that I will be in Kuala Lumpur for a week. I hope,
nevertheless, that I will be able to post a number of Digests
from the
Far East. Benny J Peiser
-------------------
(1) THE RISKY BUSINESS OF SPACE FLIGHT: ACCAPTABLE RISKS OF
PLANETARY DEFENSE?
ABCNEWS.com
(2) CAPTURE OF HALLEY-TYPE COMETS FROM THE NEAR-PARABOLIC FLUX
V.V. Emelyanenko*) & M.E. Bailey, SOUTH
URAL UNIVERSITY
(3) OBSERVING DUST AGGREGATES ONBOARD THE ROSETTA ORBITER
P. Oberc, POLISH ACADEMY OF SCIENCE
(4) SATELLITE ORBITS AROUND COMETARY NUCLEUS
D.J. Scheeres et al., UNIVERSITY OF PADUA
(5) LIGHTCURVES OF NINE ASTEROIDS
P. Denchev et al., NATIONAL ASTRONOMICAL
OBSERVATORY
=========================
(1) THE RISKY BUSINESS OF SPACE FLIGHT: ACCAPTABLE RISKS OF
PLANETARY DEFENSE?
From ABCNEWS.com
http://www.abcnews.com/sections/tech/DailyNews/rockets980828.html
By Michael J. Martinez
Aug. 28 — Two major unmanned-rocket explosions in the last
three
weeks have raised new questions about the U.S. commercial launch
program.
Since 1990, there have been 11 failures out of 167 launches in
the
Athena, Atlas, Delta, Pegasus, Taurus and Titan rocket classes—
including the Titan IV on Aug. 12 and the new Delta III on
Thursday.
How does that record compare with past decades, and with other
countries’ programs? Are rocket builders sacrificing
reliability in
the name of economy, or of cutting-edge technology?
They Were Expendable
In contrast to the early days of the space program, both the Air
Force and NASA now subcontract their rocket launches to aerospace
companies such as Lockheed Martin and Boeing. Prior to the 1986
Challenger disaster, NASA had planned to phase out “expendable”
rockets in favor of the space shuttles, says Karen Doniatowski,
director of expendable launch vehicles for NASA. “After
that, we
decided to continue utilizing these launch services, but we now
buy
those services from commercial vendors.”
Of the 40 or so unmanned missions NASA has contracted out since
the
Challenger disaster, only one has failed.
Launches contracted by other agencies and commercial carriers
have
been less reliable. Among the rocket classes currently in
service,
there have been 29 failures in 497 launches carrying payloads for
commercial services and the Air Force, a 5.6 percent failure
rate.
Failure, in space parlance, means anything from not achieving the
proper orbit to complete destruction of the spacecraft.
Self-Destructive Tendencies
In any event, most failures have an explosive end. No matter
whose
spacecraft is being launched, whether it’s the Air Force,
NASA or a
commercial carrier, an Air Force officer is always present, ready
to
send self-destruct signals to the rocket. If all communication is
lost, if there’s a navigational problem, if the rocket
suddenly
flares up or veers off course, the officer will destroy the
rocket to
protect people on the ground.
“When you’re essentially trying to balance a broomstick
on its end,
then light a bomb off under it, there’s a lot of things that
could go
wrong,” says John Cochran , head of the aerospace
engineering
department at Auburn University.
In the recent launches of the Titan IV and the Delta III, built
by
Lockheed Martin and Boeing, respectively, the self-destruct order
was
given by the Air Force officer on duty. The reason for both
mishaps
is still under investigation. Thursday’s failure dealt a
serious blow
to Boeing’s rocket launch service, which the aircraft giant
hopes
will compete with the European Space Agency for commercial
payloads.
Since the explosion, Boeing has been lobbying the Air Force to
continue Delta II launches.
Not Rocket Science
Mark Cleary, historian for the Air Force’s 45th Space Wing
at Cape
Canaveral, estimates there have been a total of 500 failures in
more
than 3,100 U.S. space flights, a failure rate of 16 percent. Most
of
them, he says, came in the 1950s and early 1960s, when rocket
science
was anything but exact. According to NASA and Air Force records,
early rocket classes had success rates as low as 30 percent.
“We had 32 losses just from 1951 to 1953,” Cleary says.
“You’ll find
that most losses occurred in the first few years of any given
program.”
Today, the United States has a 94 to 95 percent success rate in
launches, Doniatowski says. That compares to around 90 percent
for
Japan and the European Space Agency, and around 80 percent for
China
and Russia.
“Risk is a part of this business,” Doniatowski says.
“Of course, our
society isn’t all that tolerant of failure, but today they’re
certainly less frequent, especially considering the number of
launches and the frequent turnaround.”
Still, the question remains: Are U.S. rockets as safe as they
could
be? America’s superior success rate hasn’t prevented
some observers
from questioning whether rocket-builders are stretching the
technology too thin. “I guess engineers tend to overengineer
things a
little bit,” Cochran says. “Engineers like working with
BMWs and
Mercedes. They don’t like working with Volkswagens.”
Copyright 1998, ABCNews
================
(2) CAPTURE OF HALLEY-TYPE COMETS FROM THE NEAR-PARABOLIC FLUX
V.V. Emelyanenko*) & M.E. Bailey: Capture of Halley-type
comets from
the near-parabolic flux. MONTHLY NOTICES OF THE ROYAL
ASTRONOMICAL
SOCIETY, 1998, Vol.298, No.1, pp.212-222
*) SOUTH URAL UNIVERSITY, DEPT THEORET MECH, CHELYABINSK 454080,
RUSSIA
The dynamical transfer of comets from nearly parabolic to
short-period orbits is investigated, considering perturbations
by the major planets Jupiter, Saturn, Uranus and Neptune, for 5
Gyr.
The combined analytical and numerical scheme includes all the
essential features of the dynamical evolution, namely mean-motion
resonances, secular oscillations, secular resonances, and close
encounters with planets. The orbital evolution of similar to
10(5)
randomly oriented near-parabolic orbits is considered, with
initial
inclinations i and perihelion distances CI uniformly distributed
respectively in cos i and each of the five ranges 0 < q < 4
au, 4 < q
< 6 au, 6 < q < 10.5 au, 10.5 < q < 18 au and 18
< q < 31 au. The
objects which eventually evolve into Halley-type orbits primarily
originate from initial orbits of small perihelion distance, in
contrast to those that evolve to Jupiter-family orbits. Most
Halley-type comets originate from orbits with q in the range 0
< q <
4 au, with the majority coming from q < 2 au. The inclination-
averaged probability for evolution from a nearly parabolic orbit
with
0 < q < 4 au into a Halley-type orbit, assuming an
isotropic
distribution of initial inclinations, is about 0.01. When we
include
nongravitational forces (for example, taking typical values for
Halley-type, short-period, and nearly parabolic comets), this
figure
increases to 0.02, 0.04 and > 0.06 respectively. The
probability for
nearly parabolic orbits with initial perihelia in the range 10.5
< q
< 18 au to evolve into Halley-type orbits is about 0.0002,
again
assuming an isotropic distribution of inclinations. However, the
new-comet flux in the outer planetary region is expected to be
mush
higher than that in the inner Solar system, so the outer Solar
system
flux may be a significant additional source of Halley-type
comets.
Our results show that the number of Halley-type objects arising
from
the observed nearly parabolic cometary flux with absolute
magnitudes
brighter than H-10 = 7 and q < 4 au is hundreds of times
greater than
the number of known Halley-type comets. The resolution of this
discrepancy must lie in more observations and a deeper
understanding
of the physicalevolution of comets, which together become the key
issues for understanding the number of Halley-type objects and
the
terrestrial-planet impact rate due to both active and inactive
objects in Halley-type orbits. Copyright 1998, Institute for
Scientific
Information, Inc.
===============
(3) OBSERVING DUST AGGREGATES ONBOARD THE ROSETTA ORBITER
P. Oberc: Is it feasible to observe disintegrating dust
aggregates
onboard the Rosetta orbiter? ADVANCES IN SPACE RESEARCH, 1998,
Vol.21,
No.11, pp.1577-1580
POLISH ACADEMY OF SCIENCE, SPACE RES CTR, BARTYCKA 18A, PL-00716
WARSAW, POLAND
It is expected that disintegration of dust aggregates should
produce a
considerable fraction of the whole dust population in the coma of
Wirtanen. Secondary particles (fragments) have speeds of their
parent
grains and hence will be easily distinguished from primary
particles
owing to simultaneous size and velocity measurements by the Dust
Flux
Analyser. Thereby, an indirect detection of very large grains,
hardly
(or un-) detectable by DFA or other means, will become possible.
We
show that observations by DFA will allow to draw estimates on the
amission rate and size distribution of secondary particles
released
from aggregates with various masses, latent heat of the gluing
compound(s) etc. To improve measurements of disintegration
products by
DFA, it is desirable to extend the range of both velocity and
size
toward lower values, and widen the arrival direction range of
detectable particles. (C) 1998 COSPAR. Published by Elsevier
Science
Ltd.
==================
(4) SATELLITE ORBITS AROUND COMETARY NUCLEUS
D.J. Scheeres*), F. Marzari, L. Tomasella, V. Vanzani: ROSETTA
mission: satellite orbits around a cometary nucleus. PLANETARY
AND
SPACE SCIENCE, 1998, Vol.46, No.6-7, pp.649-671
*) UNIVERSITY OF PADUA, DIPARTIMENTO FIS, VIA MARZOLO 8, I-35131
PADUA, ITALY
This paper discusses the problem of orbiting a comet nucleus from
a
perspective of orbital stability. The main forces perturbing the
motion of the spacecraft around the comet: shape and rotation
rate of
the nucleus, comet outgassing, solar radiation pressure; are
derived
and quantified for the nominal case of the ROSETTA spacecraft at
the
comet Wirtanen. Their effects on the stability of the spacecraft
orbit are analyzed in detail and orbital stability criteria are
developed analytically. These criteria have been tested
numerically,
for select cases of interest, integrating the spacecraft orbit
about
a Wirtanen model constructed from mascons (mass concentrations at
a
point). This numerical model allows very irregular nucleus shapes
to
be modelled accurately if a large number of point masses is used.
The stability criteria derived in this paper denote stability of
the
spacecraft against crashing onto the comet surface or escaping
from
the comet on a hyperbolic orbit. They are developed and applied
only
over the relatively short time scales that are of interest to a
spacecraft mission. The stability criteria are expressed in terms
of
minimum periapsis radii for stability against the non-spherical
gravitational field, in terms of maximum semi-major axis for
stability against escape due to the solar radiation pressure, and
in
terms of preferred planes and orbit elements of a spacecraft
orbit
for stability against the combined non-gravitational forces of
comet
outgassing and solar radiation pressure. For orbits dose to an
irregular body the gravity perturbations are minimized, and
orbital
stability achieved, if the periapsis radius is above five mean
comet
radii if the inclination is close to 0 degrees and above three
mean
comet radii if inclinations are between 90 and 180 degrees with
respect to the comet rotation pole. When considering the combined
solar radiation pressure and comet outgassing forces, stable or
bits
can be found which ''freeze'' the orbit geometry with respect to
the
rotating reference frame defined along the comet-sun line. The
dependence of these stability criteria on the comet model
parameters
is discussed. The analysis in this paper is general enough to be
applicable to a wide range of orbital cases, including spacecraft
orbits about asteroids and natural satellites about comets and
asteroids. (C) 1998 Published by Elsevier Science Ltd. All rights
reserved.
======================
(5) LIGHTCURVES OF NINE ASTEROIDS
P. Denchev*), P. Magnusson, Z. Donchev: Lightcurves of nine
asteroids, with pole and sense of rotation of 42 Isis. PLANETARY
AND
SPACE SCIENCE, 1998, Vol.46, No.6-7, pp.673-682
*) NATIONAL ASTRONOMICAL OBSERVATORY, INST ASTRON, POB
136,BG-4700
SMOLJAN, BULGARIA
The results of photometric observations of 9 asteroids collected
from
1991 to 1997 are presented. The observations have been conducted
at
Belogradchik and Rozhen observatories, Bulgaria. For 42 Isis a
spin
pole determination has been performed: we derive a retrograde
sense
of rotation, a sidereal period of 0.5665417 +/- 0.0000005 days
and
two solutions for the spin vector: (P-1:lambda(0) = 288 degrees
+/- 5
degrees, beta(0) = -16 degrees +/- 2 degrees; P-2:lambda(0) = 117
degrees +/- 8 degrees, beta(0) = -5 degrees +/- 4 degrees). The
rotational period of 266 Aline is estimated to be 12.3 +/- 0.1
h. Composite lightcurves have been obtained for four objects (21
Lutetia, 24 Themis, 42 Isis and 266 Aline). Other lightcurves
have
been obtained for the asteroids 27 Euterpe, 38 Leda, 70 Panopaea,
173
Ino and 218 Bianca. (C) 1998 Published by Elsevier Science Ltd.
All
rights reserved.
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