[Prev][Next][Index][Thread]

(meteorobs) Excerpts from "CCNet DIGEST, 15 January 1999"


[Forwarded late, but nonetheless a very interesting edition! -Lew]

------- Forwarded Message

From: Benny J Peiser <b.j.peiser@livjm.acdot uk>
To: cambridge-conference@livjm.acdot uk
Subject: CCNet DIGEST 15/01/99
Date: Fri, 15 Jan 1999 16:25:19 -0500 (EST)

CCNet DIGEST, 15 January 1999
-----------------------------
...

(2) UNIVERSITY OF CHICAGO/ARGOS SATELLITE EXPERIMENT TO STUDY SPACE=20
    DEBRIS
    Steven N. Koppes <s-koppes@uchicagodot edu>=20
...

(4) LIGHTCURVES OF 26 NEAR-EARTH ASTEROIDS
    P. Pravec et al., ACADEMY OF SCIENCE OF THE CZECH REPUBLIC
...

(6) STARDUST PRESS KIT
    Andrew Yee <ayee@nova.astro.utorontodot ca>=20
...

-------------------------------------------------
(2) UNIVERSITY OF CHICAGO/ARGOS SATELLITE EXPERIMENT TO STUDY
    SPACE DEBRIS

>From Steven N. Koppes <s-koppes@uchicagodot edu>=20

January 13, 1999
For Immediate Release

Contact: Steve Koppes
         (773) 702-8366
         s-koppes@uchicagodot edu
=20
University of Chicago/ARGOS satellite experiment to study space debris
=20
Above the atmosphere bits and pieces of debris zip around the Earth at=20
tens of thousands of miles an hour. Some of these objects are natural
cosmic dust, produced by comets, meteoroid impacts or other natural=20
processes, while others are debris resulting from human activity in=20
space.

These objects have caused varying levels of damage  to space shuttles,=20
satellites and the Hubble Space Telescope. And although detection=20
systems currently track the largest pieces of man-made debris, many=20
more particles are too small to track, ranging in size from pebbles or=20
sand grains down to particles that can only be seen with a microscope.

"Many of these particles are produced by collisions between larger=20
debris objects, and so information about these particles is important=20
for understanding the whole debris population in Earth orbit," said=20
Bruce McKibben, Senior Scientist at the University of Chicago's=20
Laboratory for Astrophysics and Space Research.

A Chicago instrument designed to provide data to help reach that=20
understanding will be launched Jan. 15 on the Advanced Research and=20
Global Observation Satellite (ARGOS) from Vandenberg Air Force Base in=20
southern California. ARGOS's scientific payload will include the=20
University's space dust experiment (SPADUS), which will measure the=20
mass, speed and trajectory of dust particles in low-Earth orbit, and=20
will allow scientists to determine whether they are particles left in=20
the wake of comets or man-made orbital debris.

"This is the first active experiment where you can separate these two=20
phenomena," said John Simpson, Chicago's Arthur Holly Compton=20
Distinguished Service Professor Emeritus. "We will be able to tell=20
whether the debris is uniformly distributed or in clouds around the=20
Earth, and even whether there's a ring around the Earth, like Saturn's, =

but very weak. This is one of the discovery possibilities."

ARGOS, an unclassified U.S. Air Force satellite, will circle the Earth=20
for three years in a polar orbit at an altitude of 516 miles. This=20
altitude is near a region heavily used by commercial, scientific and=20
government spacecraft, where ground tracking of the larger objects=20
indicates a concentration of man-made debris. In addition to the=20
Chicago experiment, ARGOS will conduct high-temperature=20
superconductivity experiments,  upper atmospheric imaging and=20
environmental studies, and test electric propulsion methods.

Much of the current data regarding the quantity of debris particles in=20
low-Earth orbit was collected by NASA's Long Duration Exposure Facility =

(LDEF) from 1984 to 1990. But LDEF could not distinguish between=20
natural and man-made debris and could not determine where or when in=20
its orbit an impact occurred. SPADUS will be able to do this by=20
measuring the time of impact and the particle trajectory and velocity=20
of debris with enough sensitivity to detect particles smaller than the=20
particles contained in a puff of cigarette smoke.

Man-made debris  in a circular orbit races about the Earth at speeds of =
nearly 17,000 miles an hour. "This debris consists of everything from=20
rocket casings and dead satellites on down to the very small dust=20
particles that can result from the grinding down of these large objects =
as they collide with each other and with dust particles already in=20
orbit," McKibben said.

Cometary debris, on the other hand, travels more than 25,000 miles an=20
hour. There is also a remote possibility that SPADUS will be able to
detect dust particles entering the solar system from interstellar =
space.

"They'll have even higher velocities," McKibben said. "Very small ones=20
have been detected by spacecraft in the outer solar system right now.
We might see them, but I wouldn't count on it."

SPADUS will be used to study the Leonid meteor shower next Nov. 17. The =
Leonid meteor stream consists of the boiled off remains of Comet=20
Tempel-Tuttle and is usually fairly mild. But the shower was expected=20
to be far more intense in 1998 and possibly 1999, because last=20
February, the comet made its closest approach to the sun, which happens =
once every 33 years.

Last year, satellite controllers changed the orientation of their=20
satellites to reduce surface area exposed to the cometary stream. "The=20
meteor shower was not as strong as some predictions in 1998, so maybe=20
this year we'll get the whole works," Simpson said.

Earth's orbital path will take it across other cometary streams as=20
well, said Anthony Tuzzolino, Senior Scientist at Chicago's Laboratory=20
for Astrophysics and Space Research. "There are 15 or 16 streams that=20
are possible candidates for detection based on how close we'll come to=20
them," he said. "There are a lot of things to look for."

Helping in the data analysis will be Herbert Gursky and his associates=20
at the Naval Research Laboratory in Washington, D.C. The NRL=20
contributed the instrument's mechanical design and construction of the=20
experiment housing. Similarly,  important contributions were made by=20
Lockheed Martin, which provided the digital electronics box, including=20
the microchips that make the sophisticated SPADUS measurements possible =
in a package small enough for space flight.

H.N. Voss, then of Lockheed Martin and now a physics professor at=20
Taylor University in Upland, Ind., also led the effort to provide a=20
small radiation sensor system, known as the ADS as part of the digital=20
box. The ADS will monitor the radiation environment of the spacecraft,=20
and data analysis for will take place at Taylor University.

Instruments related to SPADUS are components on NASA's current Cassini=20
mission to Saturn and the Stardust mission to Comet Wild 2 (pronounced=20
"Vilt" 2). Similar Chicago-built dust instruments also flew aboard the=20
Russian Vega 1 and 2 spacecraft that visited Comet Halley in 1986.

Simpson and Tuzzolino built Cassini's High Rate Detector (HRD), part of =
a larger instrument, the Cosmic Dust Analyzer from Germany, which will=20
collect and analyze dust particles found in interplanetary space and
those that form the major components of Saturn's rings.

On Dec. 31, 1998, the HRD was turned on for the first time since=20
Cassini's launch on Oct. 15, 1997, for three weeks of testing. The HRD, =
which is working fine, will be turned on again in June to collect=20
several months of data as Cassini flies by Earth to gain=20
gravity-assisted momentum toward its destination.

Cassini will pass Earth at an altitude of 620 miles this summer.=20
"That's where the maximum of orbital debris is expected to be,"=20
Tuzzolino said. "The flyby will be a very exciting period." Tuzzolino=20
and Simpson, along with McKibben, also are providing the Dust Flux=20
Monitor instrument for Stardust, which is scheduled for launch Feb. 6.=20
The $2 million SPADUS instrument is funded by NASA, the Office of Naval
Research, the Naval Research Laboratory and Lockheed Martin.

###

Radio stations: The University of Chicago has an ISDN line.  Please
call for information. For more news from the University of Chicago,
visit our Web site at http://www-news.uchicagodot edu

sk/99-5

Steve Koppes
University of Chicago News Office
5801 South Ellis Ave. Room 200
Chicago, IL 60637-1473
773-702-8324 (fax)

-------------------------------------------------
(4) LIGHTCURVES OF 26 NEAR-EARTH ASTEROIDS

P. Pravec*), M. Wolf & L. Sarounova: Lightcurves of 26 near-Earth=20
asteroids. ICARUS, 1998, Vol.136, No.1, pp.124-153

*) ACADEMY OF SCIENCE OF THE CZECH REPUBLIC, ASTRON INST, CZ-25165=20
ONDREJOV, CZECH REPUBLIC

We present the results of our photometric observations of 26=20
near-Earth asteroids (NEAs) in the range of absolute magnitudes
H =3D 13.6-20.0 (diameters approximately 0.4-8 km). The synodic=20
periods in the range 2.3-230 h were detected for 25 of them; 21
periods are new and in 4 cases we confirmed earlier determinations.=20
In 20 cases the synodic periods are interpreted as being the rotation=20
periods.. Among the 5 exceptions, in two cases there remains an=20
uncertainty whether the detected period is not half or twice that of=20
the rotation period, and in another two cases-(3691) 1982 FT and 1997=20
BR-there were found large deviations of the lightcurve points from=20
the mean curves that can be due to possible complex rotations of the=20
small, slowly rotating asteroids. Overall, the short period end (2.3-
3.3 h) of the spin rate distribution shows characteristics that are=20
consistent with the hypothesis of their ''rubble pile'' structure, as=20
noted by Harris (Lunar Planet. Sci. XXVII, 493-494); specifically,=20
there is a ''barrier'' against spins faster than 2.3 h and the=20
amplitudes of the fast rotating NEAs are smaller in comparison with=20
the other, longer period NEAs. In the group of slow rotators (P > 12=20
h), the suggested presence of objects in excited rotation states must=20
be confirmed by further observations using also different techniques.=20
This slow rotators group may be actually more abundant than our=20
results suggest (6 of 25 objects, i.e., 20-30%), since there is a=20
bias against low-amplitude slow rotators in the groundbased=20
photometric program. (C) 1998 Academic Press.

-------------------------------------------------
(6) STARDUST PRESS KIT

>From Andrew Yee <ayee@nova.astro.utorontodot ca>=20

A 36-page PDF version of the Stardust press kit (621KB) is available at
http://www.jpl.nasadot gov/files/misc/stardust.pdf .

----------------------------------------
THE CAMBRIDGE-CONFERENCE NETWORK (CCNet)
----------------------------------------
The CCNet is a scholarly electronic network. To subscribe, please=20
contact the moderator Benny J Peiser at <b.j.peiser@livjm.acdot uk>.=20
Information circulated on this network is for scholarly and educational =

use only. The attached information may not be copied or reproduced for=20
any other purposes without prior permission of the copyright holders.=20
The electronic archive of the CCNet can be found at=20
http://abob.libs.ugadot edu/bobk/cccmenu.html

------- 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