[Prev][Next][Index][Thread]
(meteorobs) Excerpts from "CCNet 81/2001 - 22 June 2001"
------- Forwarded Message
From: Peiser Benny <B.J.Peiser@livjm.acdot uk>
To: cambridge-conference <cambridge-conference@livjm.acdot uk>
Subject: CCNet 81/2001 - 22 June 2001
Date: Fri, 22 Jun 2001 09:52:02 +0100
CCNet 81/2001 - 22 June 2001
----------------------------
[...]
(2) LIFT OFF FOR ROSETTA AT LE BOURGET [in 2003]
ESA News, 20 June 2001
(3) ARIANE TO LAUNCH ROSETTA EXPLORATION SATELLITE
Yahoo News, 19 June 2001
[...]
(7) ASTEROIDS RATHER THAN COMETS
Richard Taylor <richard.taylor3@virgindot net>
[...]
==============================================================================
(2) LIFT OFF FOR ROSETTA AT LE BOURGET
>From ESA News, 20 June 2001
http://sci.esa.int/content/news/index.cfm?aid=1&cid=1&oid=27505
The January 2003 launch of ESA's Rosetta comet chaser by an Ariane 5 rocket
was confirmed on Tuesday, 19 June, at the Paris Air Show. Ariane 5 is one of
the few rockets in the world with the payload lift capability required to
send the three tonne Rosetta spacecraft towards the distant comet.
The signatories at the official ceremony marking the completion of the
Rosetta launch services contract negotiations were the ESA Science Director,
Professor David Southwood, and Arianespace Chairman and CEO, Jean-Marie
Luton.
Ariane 5 is one of the few rockets in the world with the payload lift
capability required to send the three tonne Rosetta spacecraft towards the
distant comet.
"The 2003 launch will mark the first time an Ariane 5 has launched a
spacecraft beyond Earth orbit," said Dr John Ellwood, the ESA project
manager for Rosetta.
Other key factors were the willingness of Arianespace to do everything
possible to ensure that the launch will take place within the three-week
launch window and the launcher's ability to perform an extended coast phase
with its EPS upper stage.
After launch from Kourou spaceport in French Guiana, the EPS stage and its
Rosetta payload will remain in a 4000 km x 200 km coast orbit for just under
two hours. Prior to reaching perigee (the closest point to the Earth), the
upper stage will be ignited, injecting Rosetta into the required Earth
escape trajectory towards Mars.
"We're very happy to be able to use this extended coast phase capability of
Ariane 5, which is critical to the Rosetta mission," said Professor
Southwood.
Rosetta is one of the Cornerstones in ESA's long-term scientific programme.
Its objective is to carry out the most intensive and detailed studies ever
made of a comet, and hence hopefully unlock the mystery of how life evolved
on Earth. The small cosmic snowballs we know as comets are generally
regarded as the most primitive objects in the Solar System, the building
blocks from which the Earth and other planets were formed some 4.6 billion
years ago.
During its eight-year odyssey to Comet 46P/Wirtanen, Rosetta will swing by
Mars once and Earth twice, using their gravity to provide the energy needed
for its voyage into deep space. The extended trek will also include flybys
of two unusual asteroids, Siwa and Otawara.
Rosetta will eventually rendezvous with Comet 46P/Wirtanen in November 2011.
While the Rosetta Orbiter's payload of scientific instruments studies the
comet from close range - with the closest observations made from a distance
of about 1 km - a small lander will be released onto the comet's surface to
make direct observations of the solid nucleus.
The Orbiter's comet reconnaissance mission will continue for nearly two
years, during which it will monitor the dramatic changes that take place as
the nucleus begins to vapourise in the warmth of the Sun.
==============================================================================
(3) ARIANE TO LAUNCH ROSETTA EXPLORATION SATELLITE
>From Yahoo News, 19 June 2001
http://biz.yahoo.com/rf/010619/0574212.html
LE BOURGET, France, June 19 (Reuters) - Western Europe's Arianespace launch
company said on Tuesday it had won a contract to launch the Rosetta
interplanetary exploration satellite for the European Space Agency (ESA).
Rosetta will be launched in early 2003 aboard an Ariane-5 rocket from
Ariane's launch centre in French Guiana on South America's northeast coast.
Rosetta's eight year mission will be to rendezvous with the comet
46P/Wirtanen.
``Rosetta will swing by the earth twice, and Mars once, using their gravity
to provide the energy needed for its long voyage and send it on the right
path,'' Arianespace said in a statement released after a signing ceremony at
the Paris air show.
``During its eight year voyage, Rosetta will perform flybys of two
asteroids, Otawara and Siwa,'' it said.
John Ellwood, Rosetta project manager for ESA, said the final cost of the
Rosetta programme, launch, satellite, payload and ground centres, could
approach $1 billion.
The satellite will be built by Italy's Alenia Spazia, a division of
Finmeccanica and will weigh three tonnes at launch.
Also on Tuesday, Arianespace signed a letter of intent with London-based
satellite operator Inmarsat for the launch in 2003/2004 of an Inmarsat-4
satellite for the organisation's global satellite network.
The contract brings Arianespace's backlog to 41 firm satellite launch orders
worth over $3 billion.
Earlier on Tuesday International Launch Services (ILS), Arianespace's
arch-rival, also signed a letter of intent for the launch of another
Inmarsat-4 satellite. Inmarsat officials said the status of the ILS's
contract was more advanced than Arianespace's but expected both to become
firm orders in the next several weeks.
Copyright ) 2001 Yahoo! Inc.
==============================================================================
* LETTERS TO THE MODERATOR *
==============================================================================
(7) ASTEROIDS RATHER THAN COMETS
>From Richard Taylor <richard.taylor3@virgindot net>
Richard L. S. Taylor - Probability Research Group
e-mail: probability.rgroup@virgindot net and richard.taylor3@virgindot net
Dear Benny,
In his comments on Michael Paine's opening discussion about "the ejection
of surface rocks from Mars during impacts by large asteroids", Duncan Steel
points out that the feasibility of material being thrown off Mars, or
indeed off any other planetary target, depends critically upon the impact
speed. He goes on to cite the result of an analysis he performed using a
sample of over 600 observed Mars-crossing asteroids from which he calculated
a mean impact speed of 9.3 km/sec, with less than five percent of the
impacts at greater than 20 km/sec and rather less than one percent occurring
at greater than 30 km/sec. Using the relation given by Melosh (H.J. Melosh,
"The rocky road to panspermia", Nature, volume 332, pp.687-688, 1988) Steel
suggests that an impact speed in excess of 20 km/sec is necessary to achieve
any substantial ejection from Mars. Duncan then goes on to argue that only
comets have Mars-impact velocities capable of producing a significant
quantity of Earth-crossing ejecta.
It is important, however, to clarify just what is meant by a 'substantial
ejection' from Mars. Do we speak in terms of total mass, or the number of
high velocity spallation fragments, generated by the impact. These are quite
distinct aspects of the collision process. In his monograph 'Impact
Cratering - A Geologic Process' OUP (1989) pp72 - 74 et seq. Melosh
discusses the high speed ejecta that is produced by spallation and although
low in terms of total mass spallation fragments fairly typically attain
velocities twice that of the impactor. As the escape velocity of Mars is
5km/sec Duncan Steel's calculated mean asteroid velocity of ~9km/s could
produce spallation plates - that then fragment through the action of elastic
forces - with velocities of ~4 times that of Mars escape. As spallation
fragments come from at or near the target's surface they are ejected in the
very early stage of the formation of the impact crater. Because of this they
are generally only lightly shocked and this may allow organic materials, or
living cells, to survive far more readily than would be the case for heavily
shocked material produced by the far higher cometary impact velocities.
This suggests that asteroid collisions will be quite capable of getting
low-mass high velocity fragments off Mars and into Earth-crossing orbits.
The question is whether or not any of these small fragments can survive the
descent through Earth's atmosphere and conserve any living Mars-bugs.
Richard Taylor
-------------------------------------------------------------------
THE CAMBRIDGE-CONFERENCE NETWORK (CCNet)
--------------------------------------------------------------------
The CCNet is a scholarly electronic network. To subscribe/unsubscribe,
please contact the moderator Benny J Peiser <b.j.peiser@livjm.acdot uk>.
Information circulated on this network is for scholarly and educational use
only. The attached information may not be copied or reproduced for
any other purposes without prior permission of the copyright holders. The
fully indexed archive of the CCNet, from February 1997 on, can be found at
http://abob.libs.ugadot edu/bobk/cccmenu.html
DISCLAIMER: The opinions, beliefs and viewpoints expressed in the articles
and texts and in other CCNet contributions do not necessarily reflect the
opinions, beliefs and viewpoints of the moderator of this network.
------- End of Forwarded Message
To UNSUBSCRIBE from the 'meteorobs' email list, use the Web form at:
http://www.tiacdot net/users/lewkaren/meteorobs/subscribe.html