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(meteorobs) Excerpt from "CCNet 125/2000 - 1 December 2000"
------- Forwarded Message
From: Peiser Benny <B.J.Peiser@livjm.acdot uk>
To: cambridge-conference <cambridge-conference@livjm.acdot uk>
Subject: CCNet, 1 December 2000
Date: Fri, 1 Dec 2000 11:42:08 -0000
CCNet 125/2000 - 1 December 2000
--------------------------------
[...]
(4) LIQUID MIRROR TELESCOPE OBSERVATIONS OF THE 1999 LEONID METEORS
Andrew Yee <ayee@nova.astro.utorontodot ca>
(5) EXCHANGE OF LIFE BETWEEN PLANETS
Michael Paine <mpaine@tpgi.com.au>
[...]
(7) LEAPING INTO THE FUTURE: ONE HOP AT A TIME
Ron Baalke <baalke@jpl.nasadot gov>
(8) REENTRY SURVIVABILITY
Andrew Yee <ayee@nova.astro.utorontodot ca>
[...]
====================================================================
(4) LIQUID MIRROR TELESCOPE OBSERVATIONS OF THE 1999 LEONID METEORS
>From Andrew Yee <ayee@nova.astro.utorontodot ca>
[From October 2000 issue of ORBITAL DEBRIS QUARTERLY NEWS, NASA JSC,
http://www.orbitaldebris.jsc.nasadot gov/newsletter/v5i4/v5i4.html#news5]
Liquid Mirror Telescope Observations of the 1999 Leonid Meteors
By J. Pawlowski
The November 1999 Leonid Meteor Shower was observed and videotaped using a
Liquid Mirror Telescope (LMT) located at the Johnson Space Center (JSC)
Observatory near Cloudcroft New Mexico. This is the largest aperture optical
instrument ever used for meteor studies. The sensitivity of the LMT along
with its automated meteor detection software enabled detection of Leonid
meteors in the 5 to 12 magnitude range. Leonids of such faint magnitudes
were unable to be seen using our low light level video camera which was
operating concurrently at the same location. Our purpose was to use the data
from both sources to validate the Leonid Mass Distribution Model derived at
JSC by Dr. Mark Matney. This model along with other meteor and orbital
debris models is used for meteoroid and orbital debris risk assessment
performed prior to every Space Shuttle Mission.
A total of 151 Leonids were detected by the LMT over three nights of
observations (November 17, 18, & 19). Their masses were estimated to be
between 10**-4 and 10**-8 grams using meteor analysis software also
developed at JSC. A mass distribution of these lightweight Leonids was
calculated, and the slope of their mass distribution was compared to the
slope of mass distribution of the Leonid Meteor Mass Distribution Model.
There was excellent agreement over the 0.002 to 0.02 milligram range. This
agreement along with the agreement in the 0.02 to 0.2 gram range based on
data from our low light level cameras reported in the April issue of this
publication supports our continued use of the model.
====================================================================
(5) EXCHANGE OF LIFE BETWEEN PLANETS
>From Michael Paine <mpaine@tpgi.com.au>
Dear Benny,
Further to comments from Paul Davies and I about "lifeboats in space", the
idea is also raised in a recent paper published in Planetary and Space
Science. The PDF can be downloaded from
http://www.elsevier.com/inca/publications/store/2/0/0/ (until 1 Dec 2000)
Details and a relevant extract are below.
regards
Michael Paine
Planetary and Space Science
Volume 48, Issue 11, 01-September-2000
Curt Mileikowsky, Francis A. Cucinotta, John W. Wilson, Brett Gladman, Gerda
Horneck, Lennart Lindegren, Jay Melosh, Hans Rickman, Mauri Valtonen, J.Q.
Zheng,
Risks threatening viable transfer of microbes between bodies in our solar
system,
Planetary And Space Science (48)11 (2000) pp. 1107-1115
With relatively long viable flight times in space of about 100,000 years,
the following conclusions can also be drawn:
* Even if life originated only once, either on Earth or on Mars, it
would still have had a very high probability of avoiding catastrophic
extinction by the largest impactors during the heavy bombardment period
by orbiting around its planet (or the Sun) inside ejecta and returning to
its planet tens of thousands of years later once conditions there had again
become habitable. (This life-saving orbiting could be caused by the same
impact that caused the extinction or by earlier impacts.)
* And if longer times of absence from a planet were necessary for
survival, then desendants of microbes that had originated on say
Earth, been transported to Mars and proliferated there, could be
moved back to Earth again and again for periods of up to tens or hundreds
of millions of years, thus preserving the original life.
* In the biological evolutionary literature a lot is written about
extinctions that were possibly caused by impacts.They are always presented
as partial extinctions, for special groups of species, special
environments, etc., never of course as complete extinction of all life on
Earth... with one exception: a very early collision with a Mars-sized
planet, assumed to have created the Moon, would certainly have
extinguished all life on Earth had any been there.
* The early, very few giant impacts on Earth and Mars which caused
large-scale boiling off of oceans might have extinguished either most
life on the planet except microbes dwelling in rock deep under the surface,
near the temperature wall, or all of life. The first of these
two alternatives may seem more probable, but the second cannot be
excluded.
* If all early life was extinguished by impact on the Earth or Mars,
it is very improbable that it happened at the same time on both of them.
If it happened on one of them, life could probably have returned from
the other via ejecta carrying viable microbes.
One consequence of this: hypotheses as to whether the origin of life was
relatively easy and frequent or not need not be in influenced by the idea of
early life being often extinguished.
====================================================================
(7) LEAPING INTO THE FUTURE: ONE HOP AT A TIME
>From Ron Baalke <baalke@jpl.nasadot gov>
MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109 TELEPHONE (818) 354-5011
http://www.jpl.nasadot gov
Contact: Carolina Martinez (818) 354-9382
FOR IMMEDIATE RELEASE November 28, 2000
LEAPING INTO THE FUTURE: ONE HOP AT A TIME
A small hopping robot with froglike abilities that moves by a combination of
rolls and hops to its desired destination may someday hop a ride to an
asteroid and leap its way to other planets in the search for water.
The frogbot, featured as the "robot of the month" in the Robot Watch news
section of Discover magazine's December issue, weighs in at 1.3 kilograms (3
pounds) and is powered by a single motor. It is equipped with a camera,
solar panels, sensors and onboard computer that executes commands
autonomously, making the robot ideally suitable for exploration of distant
planets, comets and asteroids.
Under development jointly by NASA's Jet Propulsion Laboratory and the
California Institute of Technology, both in Pasadena, Calif., the frogbot
can steer and right itself.
"Hopping is a more efficient form of transportation in low-gravity
environments," said Dr. Paolo Fiorini, an engineer in the robotics group at
JPL. "Our hopping robot performs much like a frog, except that it only has
one leg and no tongue. It has a spring between its knees that makes it bend
its legs and hop. When the spring releases, the frogbot takes a 1.8-meter
(6-foot) hop on Earth, which could become a 6- meter (20-foot) leap under
low-gravity conditions on planets like Mars, depending on terrain."
Engineers believe that in low-gravity environments, such as small planets,
and in micro-gravity environments, such as asteroids, wheels successfully
used on rovers may not be the most efficient form of locomotion. In
laboratory experiments, slithering, rolling and hopping have been shown to
be alternative methods of propulsion.
In the future, NASA envisions missions involving dozens of small robotic
vehicles. "To be effective, a small exploratory robot vehicle must
frequently go over obstacles that are many times its body size," said Joel
Burdick, the Caltech co-inventor of the robot. "Hopping or leaping motions
are some of the few effective ways for small vehicles to overcome such
relatively large obstacles."
"Our goal was to come up with a locomotion method and design that would use
a minimal number of instruments and that would be small, compact,
lightweight and still be able to perform useful scientific study," said Dr.
Neville Marzwell, head of the Advanced Projects Office at JPL. Researchers
at Sandia National Laboratories in Albuquerque, N.M., have also developed a
hopping device, with more limited maneuverability.
The frogbot has shown better mobility than rovers on certain terrain. It can
be developed to reach canyon walls and other remote areas, be manufactured
at a lower cost and multiple numbers of the device can be released onto a
planet's surface to cover large distances and communicate with each other.
One frogbot could be lost without hindering the whole network.
The hopping robot technology will be ready in about three to five years and
could help scientists capture images and collect ground samples. One of the
major challenges facing engineers is precision navigation necessary to
control the hopping robot. Engineers are also developing a
hopper that adheres and climbs vertical walls and are testing prototypes on
different ground terrains.
Pictures are available at
http://technology.jpl.nasadot gov/gallery/robotics/robot_index.html
The Advanced Projects Office of Space Flight at NASA Headquarters is the
primary source of funds for this work, which was also sponsored by a
National Science Foundation grant through the Center for Neuromorphic
Systems Engineering at Caltech. Managed for NASA by Caltech, JPL is the lead
U.S. center for robotic exploration of the solar system.
====================================================================
(8) REENTRY SURVIVABILITY
>From Andrew Yee <ayee@nova.astro.utorontodot ca>
[From October 2000 issue of ORBITAL DEBRIS QUARTERLY NEWS, NASA JSC,
http://www.orbitaldebris.jsc.nasadot gov/newsletter/v5i4/v5i4.html#news3]
Reentry Survivability Analysis of Extreme Ultraviolet Explorer (EUVE)
By R. O'Hara
A reentry analysis of the Extreme Ultraviolet Explorer (EUVE) spacecraft was
performed using the Object Reentry Survival Analysis Tool (ORSAT) - Version
5.0. The analysis was done in response to a request by NASA Headquarters and
Goddard Space Flight Center (GSFC) after a preliminary assessment had shown
that the EUVE reentry may produce a debris area greater than the limit set
within the NASA Safety Standard 1740.14 guidelines.
NASA's 3243 kilogram EUVE spacecraft was launched on June 7, 1992 from Cape
Canaveral Air Station on board a Delta II launch vehicle into a 528
kilometer, 28.5 degree inclined orbit. With the spacecraft nearing its end
of mission and a possible reentry into the Earth's atmosphere expected as
early as October 2001, personnel at Goddard Space Flight Center performed a
reentry analysis using the NASA Johnson Space Center Debris Assessment
Software (DAS) - Version 1.0, in accordance with NASA Policy Directive
8710.3. In the GSFC analysis, there were 18 individual objects predicted to
survive. The total casualty area calculated for these surviving objects was
12.41 m**2, which exceeds the 8 m**2 limit set in the NASA safety standard.
The large debris area implies a potential human casualty risk of
approximately 1 in 5,300. The EUVE spacecraft was not designed with a
propulsion system and therefore cannot perform a controlled reentry. In
order to mitigate the potential risk to human safety from an uncontrolled
reentry of the EUVE spacecraft, a retrieval of the spacecraft using the
Space Shuttle was considered. However, since DAS is a lower fidelity model
and tends to produce a more conservative result, the Orbital Debris Program
Office at JSC was asked to perform a more detailed reentry study using the
higher fidelity NASA-Lockheed Martin ORSAT model to determine if taking such
a measure would be necessary.
Several sophisticated material and thermal properties are included in ORSAT
but do not exist in the DAS code. These enhancements tend to result in fewer
objects surviving reentry when using ORSAT as opposed to DAS for a reentry
analysis. For example, the emissivity is set to 1.0 for all materials
available in DAS, implying blackbody radiation for each component analyzed.
Thus, objects in DAS tend to lose heat faster and are more likely to
survive. In ORSAT, however, the emissivity can be adjusted based upon what
type of material the object is composed of. ORSAT also considers heat of
oxidation during reentry, which means that the object gains heat faster and
will demise more readily. Heat of oxidation is not considered in DAS. ORSAT
also allows for thermal conductivity. With this enhancement and using a
layered approach to modeling the fragments, ORSAT can reduce the overall
debris area by allowing for objects to partially ablate. In contrast to this
method, DAS will allow the entire fragment to survive. And finally, ORSAT
enables the user to supply a wall thickness for an object, making it easier
to model hollow objects. DAS treats all objects as solid and therefore
requires a workaround to approximate the reentry heating to a hollow object.
This workaround has been validated using comparisons with ORSAT runs, though
the more direct approach used by ORSAT is more reliable.
In the ORSAT analysis, only the objects shown to survive with the DAS model
were evaluated, and the high fidelity features of ORSAT were applied to the
reentry analysis. Reentry of the EUVE spacecraft was considered to occur at
an altitude of 122 kilometers with breakup occurring at 78 kilometers. All
of the objects were considered exposed to reentry heating at this breakup
altitude. Objects were also analyzed for possible shielding affects by other
components. Any object shown to demise at the breakup altitude, but was
considered shielded by other spacecraft components, was reanalyzed starting
at the demise altitude for the object shielding it. This allowed for some
conservatism since in reality these objects would have experienced some
heating and possible ablation prior to the demise of the object shielding
it. The final debris area calculated from the more sophisticated ORSAT
analysis of the surviving fragments came to a total of approximately 5.95
m**2, which is well under the 8 m**2 NASA constraint.
The more detailed reentry study of the EUVE spacecraft done using ORSAT has
shown the future uncontrolled reentry of EUVE to be of an acceptably low
risk to human safety and therefore mitigation measures are unnecessary.
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