CCNet DIGEST, 29 June 1999


     "For the Cerise collision and the 830 m estimated miss-distance we
     get from the TLE orbital data available before the event, the
     maximum collision probability we could have was about 10(-6),
     which shows the necessity of an improved orbit determination for a
     correct assessment of the collision risk" (N. Berend in:
     ADVANCES IN SPACE RESEARCH, 1999, Vol.23, No.1, pp.243-247)

    Andrea Milani <>

    SpaceViews, 29 June 1999

    CNN INTERACTIVE, 28 June 1999

    BBC ONLINE NETWORK, 28 June 1999

    Ron Baalke <>

    Neil Bone <>

    Michael Paine <>

    K. Morishige et al., INST SPACE & ASTRONAUT SCI

    P. Jenniskens, NASA, AMES RES CTR


     D. McNally & R.H. Rast, UNIV LONDON OBSERV

     SpaceDaily, 28 June 1999


From Andrea Milani <>

Dear Benny,
as I had anticipated to you, we have solved the 1998 OX4 problem. You
should have received the announcement of the paper we just completed
on this. The paper as such is a bit technical, but I guess you could
extract from it the less mathematical parts, e.g. Section 1, for
posting on CCNeT; if you think this is too hard, the abstract and a
pointer to my preprint page would do.
Yours Andrea

Andrea Milani
Dipartimento di Matematica
Via Buonarroti 2
tel. +39-050-844254 fax +39-050-844224


To the participants of the Torino "IMPACT" meetings

In the last session of the meeting we announced that the small asteroid
1998 OX4 had the possibility of impacting the Earth, although with a
very low probability. For the announces such as this one, see the
impact risk home page of the NEOdyS online information system at

Unfortunately this asteroid is lost, and the recovery appears almost
impossible with the present telescope resources and technologies. We
were very unhappy with this unpleasant conclusion, and therefore
immediately after the meeting we begun work on a possible solution.

We can now announce that we have found a solution to the problem raised
by 1998 OX4; the same method could be applied to other similar cases of
lost potential impactors which might be discovered in the future. In
short, the idea is to replace a full recovery campaign, requiring an
inordinate amount of observational resources, with a targeted search
for only those, among the possible orbital solutions for 1998 OX4,
which can have impacts; we call these the Virtual impactors (VI). We
have proven that it is possible to define a campaign of negative
observations, to show that the virtual impactors do not actually exist,
by using a very limited amount of telescope and observer time. Thus the
impact risk could be eliminated, even without actualy recovering the
lost asteroid.

This result is announced in a paper now submitted for publication, with
the title "VIRTUAL IMPACTORS; SEARCH AND DESTROY", by Milani, Chesley,
Boattini and Valsecchi. The preprint is available online from

(HTML version for WWW browsers)

(PostScript version for laser printers).


Andrea Milani, Steven Chesley, Andrea Boattini, Giovanni Valsecchi



Andrea Milani e-mail:
Dipartimento di Matematica, UniversitÓ di Pisa
Via Buonarroti 2, 56127 PISA, ITALY

Steven R. Chesley e-mail:
Dipartimento di Matematica, UniversitÓ di Pisa
Via Buonarroti 2, 56127 PISA, ITALY

Andrea Boattini e-mail:
IAS-Planetologia, Area di ricerca CNR
Via Fosso del Cavaliere, 00133 ROMA, ITALY

Giovanni B. Valsecchi e-mail:
IAS-Planetologia, Area di ricerca CNR
Via Fosso del Cavaliere, 00133 ROMA, ITALY

Submitted for publication, June 29, 1999


If, for an asteroid which has been observed only over a short arc
then lost, there are orbits compatible with the observations 
resulting in collisions, recovery would be desirable to decide if it
will actually impact. If recovery is essentially impractical, as is
the case for many small asteroids in the 100 m to 500 m diameter
range, the next best thing is to make sure that the lost asteroid is
not on a collision course. We propose a method to achieve this
guarantee, with an observational effort far smaller than the one
required for recovery. The procedure involves the computation of an
orbit which is compatible with the available observations and, by
hypothesis, results in an impact at some later encounter; this we
call a Virtual Impactor (VI). The collision at some future time is a
strong constraint, thus the VI has a well determined orbit. We show
that it is possible to compute for each given time of observation the
skyprint of the VI, that is the set of astrometric positions
compatible with an impact (or a near impact). The skyprint needs to
be scanned by powerful enough telescopes to perform a negative
observation; once this has been done for the skyprints of all VIs,
collisions can be excluded even without recovery. We propose to apply
this procedure to the case of the lost asteroid 1998 OX4, for which
we have found orbital solutions with impacts in the years 2014, 2038,
2044 and 2046. Suitable observing windows are found when the VI would
be close to the Earth in 2001 and in 2003, and the corresponding
skyprints are small enough to be covered with very few frames. This
procedure might become more and more necessary in the future, as the
number of discoveries of small potentially hazardous asteroids
increases; we discuss the general principles and the validation
procedures that should apply to such a VI removal campaign.

    Who counts the wampum of the night
    To see that none is due?
    --Emily Dickinson, 1859, poem 128.



From SpaceViews, 29 June 1999

A planned NASA mission to land a spacecraft on the nucleus of a comet
will soon be canceled, SpaceViews has learned.

Top project officials told SpaceViews that the Space Technology 4
(ST4) mission, also known as Champollion, will be canceled as part of
a budget-tightening effort by NASA.

"We understand that NASA Headquarters has proposed [canceling
Champollion] to the Office of Management and Budget and we think that
Office of Management and Budget will accept that," ST4 project
manager Brian Muirhead said.

Other sources, including the Associated Press, have reported that
Champollion has already been canceled, but Muirhead said late Monday,
June 28, that he has received no official notification of the
project's cancellation. However, he noted, "everybody from [JPL
director] Ed Stone on down is speaking as if that were the case."

The Planetary Society and the scientific community are organizing
efforts to lobby Congress to save the mission, but Muirhead said that
the chances of reinstating the project that way are low, "given all
the other challenges that exist in Washington these days."

Champollion faced possible cancellation earlier this year, when NASA
headquarters officials expressed concern that the mission would not
be able to meet its planned cost and mass goals. However,
Muirhead and team members redesigned the mission, combining a planned
orbiter and lander into a single spacecraft to land on a comet
nucleus, that won approval from NASA officials.

Muirhead said the expected cancellation of Champollion had nothing to
do with the project or the team or "any force outside of the budget
forces that NASA is struggling with."

The cost of the extra Hubble servicing mission planned for October,
along with costs associated with delays with the launch of the
Chandra x-ray telescope, have put pressure on NASA's space
science budget. In addition, Congress may impose caps on all federal
budgets as part of an earlier deficit-reduction deal that could cut
NASA's budget by up to 10 percent -- despite an expected $100
billion budget surplus for this year.

Champollion may be the first victim of NASA's belt-tightening, but
Muirhead said it's unlikely to be the last. "They can kill ST4 but
that doesn't fill the bucket," Muirhead said. "There are still other
problems that exceed our level of funding."

The Planetary Society reported earlier in June that both Champollion
and the 2001 Mars Surveyor lander were in danger of cancellation. The
society later reported that the Mars lander was out of

Other sources have indicated that NASA may cut funding from proposed
extended missions for spacecraft currently in operation, including
Deep Space 1 and Galileo. Extended mission funding allows spacecraft
to continue operations at a lower level after the originally planned
mission comes to an end.

Champollion is part of NASA's New Millennium Program, an effort to
flight-test advanced technologies that could be utilized on future
missions. Scheduled for launch in 2003, Champollion would have been
the first spacecraft to land on the nucleus of a comet when it
touched down on Tempel 1 in 2005.

The mission would have returned key information about the composition
and structure of a comet nucleus while testing advanced instruments,
solar panels, and other technologies, including an advanced version
of the ion engine tested on Deep Space 1, another New Millennium
Program mission.

"It's certainly a very challenging mission, one that not only had
great technology and great science but a level of public interest
that would blossom as people came to know more about it," Muirhead

News of the impending cancellation has left the team very
disappointed. "We just assembled a really incredible group of
people," Muirhead said, "and if anyone could pull this off we could."

"People will go on to other jobs, but I think it will be hard to find
anything as exciting as anything we had just been attempting."

Copyright 1999, SpaceViews


From CNN INTERACTIVE, 28 June 1999

By Robin Lloyd
CNN Interactive Senior Writer

(CNN) - NASA's next rover can leap small buildings in a single bound
but weighs just a little more than Superman's cape.

Unlike its Mars-touring cousin Sojourner, the latest rover, called a
nanorover because it is so small, is being designed to hop around an
asteroid measuring a kilometer, or about a half-mile, in diameter. The
red planet is about 6,774 kilometers, or 4,200 miles across.

Engineers at NASA's Jet Propulsion Laboratory are refining the advanced
rover in preparation for a mission called MUSES, overseen by the
Japanese space agency and set for launch in January 2002. The trick is
learning how to drive on an asteroid.

"You've got the same problem as a car on Earth on a sheet of ice," said
Don Yeomans, NASA's project scientist for the mission. "There is very
little friction between the wheels and the surface."

"So you can creep along at 1 millimeter per second or you can take
these enormous leaps, and that's the preferred mode of operation," he

A more sophisticated rover

The MUSES rover, about the size of a fat paperback novel, hops by
squeezing its struts together like scissors. The asteroid's small
gravitational field would allow it to hop up to tens of meters, or
yards, high and land in a new spot, Yeomans said.

If the rover lands on its back, it is designed to right itself. "The
trick is to not be too enthusiastic, to start off with a little jump,"
he said. "We don't want to put this thing in orbit."

The MUSES rover is 10 times smaller than the Mars Pathfinder mission's
Sojourner, has a more sophisticated on-board computer and has a color
camera, not black and white, Yeomans said.

And where Sojourner had to settle for detecting the basic elements
found in surface rocks, the MUSES rover will have an infrared
spectrometer that can detect more complex minerals at the asteroid's

The MUSES rover also will have a grid of wires on its solar panels that
can be charged up to reject dust and keep it from mucking up the

Asteroids to get lots of traffic

Many people became more aware of asteroids in 1998 with a false alarm
for an asteroid-Earth collision and the release of asteroid movies
"Deep Impact" and "Armageddon."

NASA is sponsoring other missions involving asteroids, including Deep
Space 1 which is set to pass by asteroid 1992KD next month and the Near
Earth Asteroid Rendezvous mission which is set to enter the orbit of
the asteroid Eros on Valentine's Day, 2000. The European Space Agency
also plans to send up a spacecraft to land on a comet and fly-by two

Yeomans says MUSES is uniquely challenging.

"We hope to bring back surface samples for study in Earth-based
laboratories," he said. "And we intend to drop the little nanorover on
the surface and have it run around and make TV images and detect what
the thing is made of in terms of minerals and the elemental components
of the rocks -- iron, calcium, magnesium and oxygen in a particular

MUSES is set to visit an asteroid called Nereus which orbits near
Earth. At the time of the craft's arrival to the object, it will be
about 245 million miles from Earth.

Up to three asteroid samples will be collected by the lander. After a
two-month stay on the asteroid, the plan is for a capsule with the
samples to separate from the lander and eventually parachute to Earth's
surface in 2006.

The NASA portion of the mission costs about $30 million. A team of six
U.S. scientists was named this week to work on the rover part of the
mission, including Peter Smith of the University of Arizona, who
oversaw the camera on Sojourner.

Copyright 1999, CNN


From the BBC ONLINE NETWORK, 28 June 1999

By BBC News Online Science Editor Dr David Whitehouse

Scientists hope to solve the mystery of the greatest cosmic impact of
the century by undertaking an expedition to a remote region of

The impact happened on 30 June, 1908, at Tunguska in central Siberia.
With no warning, a small comet or meteor hurtling through space
collided with the Earth and exploded in the sky.

The impact had a force of 20 million tonnes of TNT, equivalent to
1,000 Hiroshima bombs. It is estimated that 60 million trees were
felled over an area of 2,200 square kilometres. If the explosion had
occurred over London or Paris, hundreds of thousands of people would
have been killed.

The first expedition to reach the site was led by Russian scientist
L.A.Kullik in 1938. His team was amazed to find so much devastation
but no obvious crater.

So began the mystery of Tunguska: What was the object that caused
such destruction and why did it leave no crater?

Lake bottom

It may have been a small comet, made of rock and ice, that was
fragile enough to be vaporised in the explosion before it struck the
ground. Alternatively it may have been a low-density meteorite.

To search for answers, the second University of Bologna expedition is
about to travel to the isolated region taking with them a battery of
high-tech equipment.

One of the team, Dr Luigi Foschini, told BBC News Online that one of
their main aims will be the study of sediments at the bottom of Lake

This lake is 8km (five miles) away from the centre of the 1908
explosion. The lake is about 500 metres wide and 47m deep.

"We will be using a 'sub bottom penetration system,' to make a
structural map of it to decide where to drill for samples from the
lake bed," he said.

At the same time, a "side scan sonar" will take ultrasound 
photographs of the lake bottom. A remotely-controlled, underwater
telecamera will also be used in the research.

Large fragments

Undisturbed samples will be collected by using a "box corer." Dr
Foschini hopes to collect microparticles from the disintegration of
the cosmic body to determine once and for all what it was.

They will also continue a search for microparticles preserved in tree
resin. This was carried out on the earlier expedition in 1991. The
researchers will also undertake an accurate aerial survey of the 
region and compare their data with that obtained in 1938 by Kullik.

The comparison between the 1938 pictures and the new survey should
give further information on the direction of the tees felled by the

Some scientists believe that large fragments may have reached the
ground before the main impact. If the cosmic body was a meteorite,
then it may be possible to find these fragments.

A search will be made for them among the ground rocks of Tunguska
using neodymium magnets together with a metal detector.

Copyright 1999, BBC


From Ron Baalke <>

Leonids on the Horizon
Marshall Space Flight Center

What's in store for the 1999 Leonid meteor shower? Experts make their

June 22, 1999: Go outside after sunset this month and look high in
the sky above the southwest horizon. The bright star shining about 20
deg. above, and to the south of Venus is Regulus, the brightest star
in the constellation Leo. The dim, sickle-shaped collection of stars
that make up Leo may not seem impressive now, but in November 1999
they could serve as the backdrop for a once-in-a-lifetime sky show --
a full-fledged Leonid meteor storm.

The Leonid meteor shower takes place every year around November 17
when Earth passes close to the orbit of comet Tempel-Tuttle. Usually
not much happens. The Earth plows through a diffuse cloud of old
comet dust that shares Tempel-Tuttle's orbit, and the debris burns up
harmlessly in Earth's atmosphere. A typical Leonid meteor shower
consists of a meager 10 to 20 shooting stars per hour.

If this were always the case, the Leonids would be known to a small
number of meteor enthusiasts only. Instead they are famous. At
roughly 33 year intervals the Leonid meteor shower can blossom into
what astronomers call a meteor "storm," when hundreds of thousands of
shooting stars per hour rain down from the sky.

Leonid storms occur at intervals separated by multiples of 33 years,
the period of comet Tempel-Tuttle's orbit around the sun. Whenever
the comet swings through the inner solar system it brings a dense
cloud of debris with it, so that for 3 or 4 years after its passage
the Leonids can be very active. Curiously, there isn't a full-fledged
storm every time Tempel-Tuttle passes by.

Sometimes there's simply a stronger-than-average shower, never quite
rising to the level of a storm, and sometimes nothing much at all
happens to mark the comet's passage. This capricious behavior makes
predicting Leonid meteor storms a bit tricky.

The last great Leonid meteor storm was in 1966. It was, predictably,
somewhat unexpected. The comet had passed by Earth's orbit in 1965,
so astronomers were aware that something might happen. But, judging
by the paucity of the 1899 and 1932 showers, it was widely thought
that the orbit of the debris stream had been deflected so much by
gravitational encounters with other planets (mainly Jupiter) that a
close encounter with Earth's orbit was no longer possible. The best
predictions suggested a strong shower over western Europe with 100 or
so meteors per hour.

Instead, there was an stunning display of shooting stars over western
North America. This recollection by James Young at JPL's Table
Mountain Observatory in California gives a sense of what the storm
was like:

     "This very noteworthy [1966] meteor shower was nearly missed
     altogether... There were 2-5 meteors seen every second as we
     scrambled to set up the only two cameras we had, as no real
     preparations had been made for any observations or photography.
     The shower was expected to occur over the European continent.

     The shower peaked around 4 a.m., with some 50 meteors falling per
     second. We all felt like we needed to put on 'hard hats'! The sky
     was absolutely full of meteors...a sight never imagined ... and
     never seen since! To further understand the sheer intensity of
     this event, we blinked our eyes open for the same time we normally
     blink them closed, and saw the entire sky full of streaks ....

The 1966 return of the Leonids was one of the greatest displays in
history, with a maximum rate of 2400 meteors per minute or 144,000
per hour.

Tempel-Tuttle visited the inner solar system most recently in late
1997 and early 1998. The subsequent Leonids display, in Nov. 1998,
was marvelous as observers all over the world were treated to a
dazzling display of fireballs (shooting stars with magnitudes
brighter than -3). Nevertheless, the 1998 Leonids were a shower, not
a storm. The maximum rate of meteors last year was about 250 per
hour. Scientists have learned that if Earth crosses the orbit of
Tempel-Tuttle too soon after the comets passage, then there is no
storm, just a strong shower. Apparently that's what happened in 1998.
In recent history no Leonid storm has ever occurred less than 300
days after Tempel-Tuttle passed by Earth's orbit. In 1998, Earth
followed the comet to the orbit-crossing point by only 257 days

The period of maximum activity during the 1998 Leonid shower took
place about 12 hours before the earth crossed Tempel-Tuttle's orbital
plane. The early activity caught many observers by surprise, but it
was business as usual for the unpredictable Leonids. Rainer Arlt of
the International Meteor Organization noted that while the maximum
activity came early, there was a secondary maximum when the Earth
passed the comet's orbit (see left). This pattern is similar to that
observed in 1965, the year that preceded the great Leonids storm of
1966. In his report Bulletin 13 of the International Leonid Watch:
The 1998 Leonid Meteor Shower, Arlt wrote:

     [T]he radar, visual, and photographic records of the 1965 Leonids
     indicate an activity profile which resembles that of the 1998
     Leonids. Even the low population index seems comparable. Judging
     from these phenomenological facts, we may expect 1999 to show a
     similar shape of activity as in 1966. The actual maximum meteor
     numbers are hardly predictable. [ref].

Joe Rao, a Leonids expert who lectures at New York's Hayden
Planetarium, also advocates 1999 as possibly the best year for a
storm during this 33 year cycle. Writing for Sky &Telescope he says:

     Based on what happened last November, I will venture a prediction.
     If a meteor storm is to take place at all, 1999 would appear to be
     the most likely year for it to happen. But even if this year's
     Leonids are richer in number, observers should not expect the same
     high proportion of fireballs that were seen in 1998. Instead, a
     more even mix of bright and faint meteors is likely. [ref]

Rao bases his argument on historical precedent and the Earth-comet
geometry. During the seven most recent Leonid storms when Earth
crossed Tempel-Tuttle's orbit soon after the comet, the average
distance between the comet and Earth was 0.0068 astronomical unit.
The average number of days between the comet's passage and the
Earth's arrival at the plane of the comet's orbit was 602.8 days.
With the 1999 values of 0.0080 a.u. and 622.5 days, Rao says we ought
to be in a prime position to see significant, if not storm-level,

Rao is also a meteorologist for News 12 Westchester, which seems a
suitable occupation for predicting meteor showers.

In 1999, the Earth will pass nearly three times as far from the
comet's orbital path as it did in 1966 and more than six times
further than it did during the great storm of 1833. If the peak of
the Leonids arrives exactly when the Earth passes through the comet's
orbital plane, Donald Yeomans of JPL gives 01:48 UT on November 18,
1999 as the most likely time for the 1999 maximum [ref]. That would
make Europe and North Africa the best places to watch the show.
However, Leonid meteor showers frequently arrive much earlier or
later than predicted, so any place on the globe could be favored.

A blast from the past reveals the future

The spectacular display of fireballs in 1998 was a treat for
observers, but it posed some interesting questions for astronomers.

According to David Asher of the Armagh Observatory and his
colleagues, the intensity and duration of this exceptional event
indicated that the Earth must have passed through an extremely dense,
narrow stream of large dust grains and particles. The timing implied
that these debris particles occupied an orbit somewhat different from
the main stream, and that they left the comet's nucleus many hundreds
of years ago. But in that case, how did the stream has hold together
so tightly for so long?

To solve the problem, Dr David Asher and his co-workers calculated
the motion of large dust grains ejected from comet Tempel-Tuttle at
each of the last 42 occasions when it made its closest approach to
the Sun. They checked to see whether any of the particles could
explain the fireballs seen in 1998, and identified September 1333 as
the time when most of the observed particles must have been released.

The particles were kept in a tight stream by a process known as
"gravitational resonance." A similar phenomenon gives rise to the
fine structure seen in Saturn's rings. In this case, grains ejected
from the comet in 1333 were kept in step by the gravitational
influence of Jupiter. Instead of spreading around the whole orbit,
they were nudged by periodic "kicks" from Jupiter's gravity into a
rather short arc of large particles, distinct from the 'normal'
stream of small particles ahead of and behind the comet. Their
calculations showed that in November 1998 most of the resonant arcs
missed the Earth by a wide margin, but the arc of particles released
in 1333 cut right through the Earth's orbit, and the calculated time
for when this happened matched the observed fireball maximum to the

Armagh and co-workers are not expecting a repeat performance of
bright fireballs in November in 1999. All the resonant strands in the
meteoroid stream will be well past Earth in space. However, a strong
'normal' display is likely, peaking at about 2 a.m. on November 18th,
due to meteoroids ejected from Comet Tempel-Tuttle in the years 1866,
1899 and 1932, which have not yet had time to disperse around the
comet's orbit.

Rob McNaught of the Research School of Astronomy and Astrophysics at
the Australian National University and colleagues have examined the
motions of Tempel-Tuttle debris particles ejected from the comet
within the last 200 years. Their calculations predict that the
maximum hourly rate of meteors in 1999 will be 1000 to 1500 per hour
-- not exactly a major storm, but still a remarkable display -- and
that the best years to observe could be in the next millennium when
hourly rates might reach 10,000 - 35,000 in 2001 and 25,000 in 2002.
These conclusions differ from most other recent studies which predict
greatest activity during the years 1998 - 2000, but the Leonids do
not always adhere to conventional wisdom.

Ready or not, here they come!

     All sorts of conjectures were made by all sorts of people ... We
     may learn of this that, when men are in a high state of
     excitement, their testimony must be taken with many grains of

First-hand account of the 1833 Leonid Meteor Shower.
Elder Samuel Rogers

There seems to be plenty of room for debate about the upcoming Leonid
meteor showers. The exact timing of the display, the number of
fireballs vs. fainter meteors, and the best observing sites are all
uncertain. Nevertheless, even the most pessimistic predictions for
1999 presage a memorable show.

One thing seems sure, no matter where you live: The Leonids are
coming and, on Nov 17, 1999 the place to be is outside, looking up!


From Neil Bone <>

BAA Meteor Section Meeting
Institute of Astronomy, Madingley Road, Cambridge
Saturday October 30 1999, 1.30 pm

An afternoon of talks and discussion timed just a couple of weeks 
ahead of what could be the meteor display of the 1990s, the Leonid 
maximum of Nov 17-18. The programme is at an early stage of 
construction, but will include a review of last year's spectacular
Leonid return and what it might mean for forecasting this year's
peak, and contributions from the Section's triangulation group which
netted some excellent results in November 1998. Further details
should be available soon.

General enquiries can be addressed to the Meteor Section Director: 
Neil Bone, The Harepath, Mile End Lane, Apuldram, Chichester, West
Sussex, PO20 7DZ. Tel. (01243) 782679.

Local arrangements are being handled by the Comet Section Director:
Jonathan Shanklin, 11 City Road, Cambridge, CB1 1DP.

Best wishes,
Neil Bone


From Michael Paine <>

Dear Benny,

Given the fence-sitting of the UK government and the situation in
Australia I consider it is very important that the report of the IMPACT
Workshop includes some strong recommendations for an international
Spaceguard Survey. It seems that the government policy makers need the
whole matter set out simply, possibly as a project that can be
rubber-stamped. Although it is not customary for a scientific
conference, I would like to see the report nominate responsibilities
and a BUDGET for each key nation. For example:

Country         Implementation  Annual        Comments
US                 $XXX         $XXX         Coordination through MPC...
(sorry if I have missed some)

In this way the relatively low cost of Spaceguard will be apparent to
each nation. It might also then be possible to get the project endorsed
by the UN. For some ideas about presenting the issue to politicians

UK Parliament Report of May 1999

Clark Chapman's Action Plan, presented to a US Congress Science
Subcommittee in 1998

My own proposal for Australia

Michael Paine


K. Morishige*), H. Yano, Y. Maekawa, S.P. Deshpande, M.J. Neish,
S. Kibe: Three dimensional analysis of impact crater profiles on the
SFU spacecraft's Teflon radiators. ADVANCES IN SPACE RESEARCH, 1999,
Vol.23, No.1, pp.113-117


We report on three dimensional morphology of about 100 hypervelocity
impact craters on the Teflon radiators of the SFU spacecraft measured
by scanning laser microscope and X-ray CT technique. We also
performed impact calibration experiments using a two-stage light-gas
gun at ISAS with alumina, glass and copper bead projectiles of
diameters 50 to 80 mu m at velocities from 3.5 to 4.5 km/s, in order
to reproduce impact crater profiles formed in space. As a result, the
depth to diameter ratio of these impact craters constrains bulk
density, velocity and size of impactors, which are complementary
information to elemental analysis regarding the origin of the
impactors, namely meteoroids or space debris. (C) 1999 COSPAR.
Published by Elsevier Science Ltd.


P. Jenniskens: Update on the Leonids. ADVANCES IN SPACE RESEARCH,
1999, Vol.23, No.1, pp.137-147


Meteor storms are of concern to satellite operators because they are
a natural impact hazard. Little is known about their cause and
effect. Meteor storms are rare and have never been studied by modern
techniques. Now, the upcoming Leonid returns of November '98 and '99
offer a once-in-a-lifetime opportunity to gather data that can help
assess the impact hazard of meteor storms and provide a wealth of
data on the physics and chemistry of meteoroids accreting into the
Earth's atmosphere. Three months before the Nov. '98 return, we here
give gn update of what to expect and what observing efforts are going
to be made. (C) 1999 COSPAR. Published by Elsevier Science Ltd.


N. Berend: Estimation of the probability of collision between two
catalogued orbiting objects. ADVANCES IN SPACE RESEARCH, 1999,
Vol.23, No.1, pp.243-247


This paper deals with the estimation of the probability of collision
corresponding to a single predicted close approach between two
catalogued orbiting objects. By assuming normally distributed
position uncertainties at the estimated closest approach time and a
quasi-rectilinear relative trajectory about this time, we get a
simple formula that takes into account the dynamics and the geometry
of the close approach. The validity of the method has been verified
with Monte-Carlo simulations for close encounter configurations
derived from the Cerise collision that occurred on July 24, 1996. If
we do not know the global amplitude of the position uncertainties, we
can nonetheless estimate the highest value the probability can reach.
For the Cerise collision and the 830 m estimated miss-distance we get
from the TLE orbital data available before the event, the maximum
collision probability we could have was about 10(-6), which shows the
necessity of an improved orbit determination for a correct assessment
of the collision risk.


D. McNally*), R.H. Rast: The effect of spacecraft and space debris on
astronomical observation. ADVANCES IN SPACE RESEARCH, 1999, Vol.23,
No.1, pp.255-258


It is shown that debris trailing of astronomical fields results from
field crossing by on orbit spacecraft and larger pieces of debris
capable of reflecting sufficient sunlight to register on astronomical
detectors. Such incursion into observed fields of view leads to
degradation or loss of the observation. Measures to mitigate the
problem are suggested. The paper is prefaced by expressing concern at
recent proposals for efficient thin film solar reflectors which could
have very serious long term consequences for optical astronomy. (C)
1999 COSPAR. Published by Elsevier Science Ltd.


From SpaceDaily, 28 June 1999

by Bruce Moomaw

Cameron Park - June 28, 1999 - There was a huge furor earlier this
year over whether the International Astronomical Union should allow
Pluto to keep its official title as a planet, or officially
redesignate it an asteroid because of its small size -- or perhaps
even a giant comet, given the fact that it is composed largely of

After an acrimonious dispute among the astronomical community, the
IAU decided to keep things as they are. But was the IAU's decision
correct, or was it an unwise surrender to an outcry from an
uninformed public?


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