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From: JR Tate <fr77@dial.pipex.com>
Subject: Clementine II Science Meeting
Date sent: Tue, 15 Apr 97 22:20:23 GMT
Here are some preliminary notes on the Clementine II Science
meeting that I
recently attended in the USA. They are far from complete, but
should give you
a flavour for the sort of things that were discussed.
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Notes on the Clementine II Science Meeting
Held at HQ US Air Force Space Command, Peterson AFB, Colorado
Springs
27th - 28th March 1997
INTRODUCTION
Colonel SP Worden, the Deputy Director Requirements, US Air Force
Space
Command, introduced the meeting, and gave an overview of the
Clementine
programme.
Clementine I was designed to demonstrate military technology,
and, at the
same time managed to do some "neat science". It was,
however, a shame that
the asteroid fly-by element of the mission failed.
There is high interest in Congress in the programme. $45 million
has been
allocated, along with funds from the US Air Force budget, for a
follow-on
mission (Clementine II). The White House has directed that this
mission is to
be a collaborative effort with NASA. This cold result in a
shuttle launch,
allowing a larger payload.
The USAF has recommended that Clementine II should be a deep
space mission,
with a launch date in late 1999 or early 2000, and should include
interaction
with an Earth crossing asteroid. NASA will lead the science
aspects of the
mission, while AFSPC will be the overall mission leaders.
Hopefully Clementines I and II are the first of a series of joint
missions.
The Clementine II mission will be totally unclassified, and there
are
possibilities for international co-operation.
There is, as yet, no DoD approval for an asteroid rendezvous, but
Congress
has expressed its interest in asteroid research. A decision of
the mission
profile will be announced in August 1997. There are three
possibilities:
a. Earth Orbit mission
b. Full mission, including at least one asteroid encounter.
c. A hybrid mission.
A treaty compliance meeting has already taken place, and there
seem to be no
problems with any of the planned mission profiles.
Planetary Defence is not yet a formal DoD mission, but there is a
study
underway at the moment, and it seems likely that it will become
so in the
near future.
An interagency agreement is expected to say the necessary
surveillance
technology and assets exist, and that the planned asteroid
science to be done
by Clementine II is necessary.
NASA PRESENTATION
The NASA director, Dan Goldin, regards Clementine II as a very
exciting
mission, and this feeling is echoed by the NASA senior
management.
NASA welcomes involvement, as long as:
a. NASA is to lead on science matters.
b. The science cost is affordable.
c. All treaty commitments are observed.
Dr Eugene Shoemaker will lead the science definition team, to
report to NASA
in September 1997. The final NASA decision will be published in
the same
month.
A NASA Science Announcement of Opportunity (AO) will be published
soon
thereafter.
Foreign institutions may apply, but will require governmental
support to be
considered.
JPL will provide engineering and programme support.
NASA has a number of related missions in train:
NEAR
Fly-by of Mathilde in Jun ’97
Rendezvous with Eros in Jan ’99
Stardust
Launch in Feb ’99
Sample and return mission to Comet Wild 2 in 2004
Deep Space 1 (a New Millennium Mission)
Launch Jul ’98
Fly-by of asteroid McAuliffe in Jan ’99
Fly-by of a DS1 will fly by comet West-Kohoutek-Ikemura and the
planet Mars
in 2000
As an aside, it was stated that the official view is that an
asteroid or
comet passing within 7.5 x 106 km of the Earth is regarded as a
Hazardous
Object.
USAF PL/SX - DAVID BARNHART
Clementine II is primarily a military mission, but there is, and
will be a
synergistic relationship with NASA.
Instrumentation will be designed for dual military/science roles.
A microsatellite is defined as a 3 axis stabilised device, with a
"wet" mass
of between 2 and 20 kg.
There was a funding shortfall in FY 96/97 resulting in
contingency planning
for reduced mission profiles. The current options are:
a. Earth orbit
b. Asteroid mission
c. Hybrid mission.
The final choice will depend on funding decisions made in
September 1997.
A Titan II launch has been "booked" for Clementine II,
but a free Shuttle
launch would be a much better option, assuming that
"HAZMAT" safety problems
can be resolved.
DR. EUGENE SHOEMAKER
The Science Definition Team will have to look at two things:
a. What science can be achieved with the Air Force mission
hardware?
b. What extra instrumentation can be fitted to the spacecraft?
LLNL - DR. ARNO LEDEBUHR
The Clementine II bus will go for a 50-100 km fly-by of the
target asteroid.
There will be a suite of Integrated Mission Sensors.
Bus range at probe impact will be 100-300 km, before closest
approach.
Probes will be released about 3 hours before impact.
Bus navigation system will be switched off when the target
asteroid fills the
CCD field of view.
The asteroid capable probes will be 30"-40" long,
weighing 19.6 kg.
There is, therefore, not much opportunity to fit additional
science packages
on the impact probes.
Optical sensors have been chosen, as they are not anti-ICBM
capable, and the
probes will only be capable of low relative velocities. These
measures are
required for treaty compliance.
The Clementine I sensor suite weighed 7.5 kg and consisted of:
Star tracker
Near IR camera
UV/visible camera
Long wave IR camera
Laser ranger
The Clementine II package will include a telescope with five
channels:
High resolution visible
Medium resolution near IR
Medium resolution Long Wave IR
Profiling LIDAR (ranger)
Flash spectrometer
The mothership will have 8 Gb of memory on board.
MISSION TARGETS
The optimal distance for asteroid targets is 0.2 AU to give
useable radar
data.
The nominal Clementine II mission will visit two asteroids.
Best fit for the mission so far would be:
1986 JK - a C-type asteroid, possibly a dormant or extinct comet
(dynamic and
spectral evidence available).
c. 1 km diameter in an orbit typical of Jupiter family comets.
4179 Toutatis - S-type (from the inner asteroid belt and Earth
crossing).
Possibly the best known ECA and the location of its centre of
mass is known
to within 10 cm at any time.
1.92 x 2.40 x 4.60 km in size.
Launch opportunities for missions to both of these are 4 June
1999 and 10
November 1999.
Dr. Eugene Shoemaker
Dr Shoemaker described what he called "the ECA zoo".
Many of the asteroids that we see now are fragments of the cores,
mantle and
crust of larger, differentiated parent bodies. In addition there
are extinct
comets from both the Oort cloud and the Kuiper belt.
We need data on asteroid compositions, sizes and spin states.
Questions on Structure
Asteroidal fragments
Are they structurally coherent?
Do they have fractures or faults?
Are they debris piles?
If so, what is the size distribution of fragments?
Were the primitive parent bodies homogenous or heterogeneous?
If the parent bodies were differentiated, compositional or
volcanic
stratification?
Craters and regolith indicate the age of a body and its
evolution.
Extinct Comets
Are they homogenous or heterogeneous?
Are they single or multiple bodies?
What is their surface structure?
Do they have vents or fissures?
Will the probe impact "turn on" cometary activity?
There followed a discussion on impact science led by Dr Greg
Canavan who
pointed out that the vapour effect indicates compressional
strength of the
target, while rubblisation indicates tensile strength.
Dr Tom Ahrens explained that the cratering of small asteroids is
controlled
by their structural strength. For larger bodies gravity is the
controlling
influence. The threshold between the two is at an approximate
diameter of 150
metres. He added that structural strength decreases with
decreasing size as
fault configurations become more critical.
The fact that shocked gasses from an impact fluoresce may be
useful in
determining compositions. However, the spectra obtained from the
gas plume
from the impact would be contaminated by vaporised material from
the
microsatellite.
POTENTIAL SECONDARY MISSION OBJECTIVES
Dust Studies - Dr. Tom Economou
Interstellar
Interplanetary
Cometary
Asteroidal
Planetary / Satellites
Man made space debris
Various dust detectors were described.
Survey for Asteroids - Dr. Duncan Steel
Dr Steel discussed the advantages of searching for Earth crossing
asteroids
from the spacecraft, but noted that the detection rates would
probably be
low.
He pointed out that meteoroid orbits do not resemble those of
comets, but
look like those of the Aten family. There appear to be two main
source
directions, anti-helion and helion.
He warned all present of the likelihood of a major meteor storm
on 17th
November 1999, the Leonids. This storm recurs at 33 to 34 year
intervals, and
is expected to be particularly heavy in 1999. This event could
pose a
considerable threat to satellites or other assets in Earth orbit.
Search for Microlensing Effects
It was suggested that the Clementine II spacecraft would make a
good platform
for observing microlensing effects caused by Dark Matter. This
would be
achieved by measuring parallax effects. Similar research has
already
indicated the presence of MACHO’s in the galactic halo, and
that the Milky
Way is a barred spiral galaxy.
OPTIONS FOR AN EXTENDED MISSION
Assuming that the primary mission objectives are achieved there
may be
potential for extending the spacecraft mission to achieve further
scientific
goals. A number of possibilities were discussed.
Return to the Moon
The spacecraft could be inserted into a low polar orbit around
the moon. It
would then use its LIDAR to accurately determine the topographic
configuration of the lunar surface.
One major task would be the production of an accurate radar map
of the
possible ice deposits at the lunar pole discovered by Clementine
I.
Confirmation of the existance of substantial quantities of ice
could have a
profound effect on the future exploration of the solar system.
Ice would be
detected by using the Coherent Backscatter Opposition Effect,
probably using
the spacecraft’s main communication dish as a radar antenna.
Deep Space Profiles
The possibility that the spacecraft could be configured to travel
to Mars, or
the inner asteroid belt were discussed. It was agreed that these
profiles
were possible, and would be considered further.
OTHER MATTERS
Ground Based NEO Surveys
There then followed a briefing on Ground Based NEO Surveys,
including:
Spacewatch
NEAT
LONEOS
European Activity - Richard Tremayne-Smith (BNSC)
It was stated that the European position is that mitigation of
potential
impacts is not an issue until Clementine II and Rosetta type
missions have
been completed.
ESA is undertaking a study of the NEO threat.
The Spaceguard Foundation - Dr. Duncan Steel
The Spaceguard Foundation currently has 53 members, with 13
pending
applications.
There are associate organisations in Japan and the UK, with
organisations in
Germany, France and Finland pending.
ESA has allocated $100,000 to the Foundation to help establish a
central node
for NEO data.
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If you have any questions or comments, please get in touch.
Jay Tate
Spaceguard UK