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"930525.DFC" (62280 bytes) was created on 05-25-93
25-May-93 Daily File Collection
These files were added or updated between 24-May-93 at 21:00:00 {Central}
and 25-May-93 at 21:00:15.
=--=--=START=--=--= NASA Spacelink File Name:930525.REL
5/25/93: HUBBLE LOOKS AT THE HEART OF A GALAXY COLLISION
Paula Cleggett-Haleim
Headquarters, Washington, D.C.
M
Jim Elliott
Goddard Space Flight Center, Greenbelt, Md.
Ray Villard
Space Telescope Science Institute, Baltimore, Md.
RELEASE: 93-97
NASA's Hubble Space Telescope has looked into the heart of a galaxy
created by the collision of two galaxies and peering deeply into its nucleus,
discovered a remarkable pinwheel-shaped disk of gas surrounded by clusters of
young stars born as a result of the merger.
The star clusters apparently were born as a result of the collision of
two disk-shaped galaxies. The galaxy merger, which occurred about 1 billion
years ago, triggered an infall of the gas which fueled the birth of new stars
around the center of the galaxy.
"This may unlock the key for understanding how all globular clusters
formed in ellipticals," said Dr. Brad Whitmore of the Space Telescope Science
Institute (STScI), Baltimore, Md. "The Hubble observation also shows how tiny
disk-like structures might have formed in many other galaxies."
This discovery provides some of the best evidence to date for
explaining the origin of giant elliptical galaxies. For more than a half
century, astronomers have theorized about how such galaxies formed. Some
theories propose that ellipticals formed from collisions between disk galaxies
-- flattened stellar systems resembling the Milky Way galaxy.
These results are being presented in a press conference today at NASA
Headquarters, Washington, D.C., by Whitmore and Dr. Francois Schweizer of the
Carnegie Institution of Washington. Co-investigators are Claus Leitherer, Kirk
Borne and Carmelle Robert of STScI.
Pinwheel of Stars and Gas
The striking Hubble image shows a spiral pattern at the galaxy's core,
surrounded by bright star clusters. "I knew I had a major result within 10
seconds of looking at the Hubble picture," said Whitmore.
The pinwheel shaped disk has an uncanny resemblance to a face-on spiral
galaxy, yet it is only 10 thousand light-years across -- about 1/20 the size of
the total galaxy. The gas and stars in the disk swirl around the nucleus,
making a spiral pattern like cream poured in a cup of coffee. The mini-spiral
contains enough gas to make 8 billion stars like the sun. Though several of
the clusters were first spotted from ground- based telescopes, their true
nature was uncertain until the Hubble observations.
Hubble's resolution is so good that the astronomers can measure the
diameters (0.04 arc seconds, the apparent size of a dime at a distance of 80
miles) of the bright star clusters seen in the same image as the spiral disk.
They turn out to be about 60 light years across, the same size as globular
clusters that orbit the Milky Way galaxy.
The globular clusters found in NGC 7252 are considered the progenitors
of similar clusters that orbit the Milky Way galaxy. Since globular clusters
normally contain ancient red giant stars, they provide a fossil record of the
formation and evolution of galaxies. Globular clusters contain about 1 million
stars each, arranged in a tight, spherical swarm and generally are found to be
about 15 billion years old.
However, the "ultra-luminous clusters" found in NGC 7252 contain hot
bluish stars. Because these blue stars are short-lived, the clusters in NGC
7252 are estimated to be mostly between 50 and 500 million years old.
The blue stars make the globular clusters up to several hundred times
brighter than the clusters that orbit the Milky Way galaxy. If the Milky Way's
globular clusters were as bright, they could be seen with the naked-eye and
would be brighter than the stars in the Big Dipper.
In the 1920's, American astronomer Edwin Hubble classified galaxies
according to their spiral or elliptical shape. A key difference is that stars
are concentrated in a disk in spirals, but are distributed in a diffuse,
roughly spherical distribution in ellipticals.
Since Edwin Hubble's time, astronomers have sought an explanation for
why there are two different types of galaxies. During the past decade, the
hypothesis that spiral galaxies can collide and merge to form elliptical
galaxies has become increasingly popular.
Located 300 million light-years away in the constellation Aquarius, NGC
7252 has been considered the prototypical example of a merger between two
disk-shaped galaxies. The galaxy has a pair of long tails that are unambiguous
evidence of the effects of gravitational tidal forces from a galaxy merger.
The galaxy NGC 7252 is nicknamed the "Atoms-for-Peace" galaxy because
its stars form a bizarre loop-like structure that resembles a schematic diagram
of an electron orbiting and an atomic nucleus. (In December 1953. U.S.
President Dwight D. Eisenhower made his "Atoms for Peace" speech to foster
peaceful applications of nuclear energy.
If globular clusters can be born during galaxy collisions, it
reinforces the theory that disk galaxies merge to make giant elliptical
galaxies. One argument against this theory is that elliptical galaxies have
more globular clusters than expected if disk galaxies were simply combined,
since disk galaxies have relatively few clusters.
Hubble Picture Helps to Solve Mystery
The new Hubble Space Telescope observation solves this dilemma by
showing that when disk galaxies collide they can form new globular clusters.
Rather than being a problem for the merger scenario, an increase in the number
of globular clusters is a natural consequence of galaxy mergers.
The existence of a "mini-disk" also fits with the merger scenario since
similar disk-like features appear to exist in many elliptical galaxies.
Another clear indication that the material originated from the collision of two
galaxies is that the mini-spiral is rotating in a direction opposite to the
rest of the galaxy.
This discovery is the latest in a series of disk-like structures that
Hubble has uncovered at the cores of galaxies. Previously, HST found a giant
disk of cool dust and gas orbiting a suspected black hole in the active galaxy
NGC 4261 and discovered an edge-on "donut" of dust in the spiral galaxy M51.
The astronomers predict that in a few billion years the gas in NGC 7252
will be exhausted. The galaxy will look like a normal elliptical galaxy with a
small inner disk.
Source:NASA Spacelink Modem:205-895-0028 Internet:192.149.89.61
=--=--=-END-=--=--=
=--=--=START=--=--= NASA Spacelink File Name:930525.SHU
KSC SHUTTLE STATUS REPORT 5/25/93
KENNEDY SPACE CENTER SPACE SHUTTLE STATUS REPORT
Tuesday, May 25, 1993
KSC Contact: Bruce Buckingham
-----------------------------------------------------------------
Mission: STS-57/Spacehab/EURECA-Retrieval Orbital Alt. 287 miles
Vehicle: Endeavour/OV-105 Inclination: 28 degrees
Location: Pad 39-B Crew Size: 6
Target Launch Date/Window: June 3, 6:17 - 7:28 p.m.
Target KSC Landing Date/Time: June 11, 5:14 p.m.
Expected Mission Duration: 7 days/23 hours (if cryogenics allow)
IN WORK TODAY:
* Pad cleared of all non-essential personnel
* Pressurization of hypergolic fuel and oxidizer tanks
* Ordnance installation
* Aft engine compartment closeouts
* Continue analysis of flexible joints in main propulsion system
* Launch countdown preparations
WORK SCHEDULED:
* External tank purges
* Final ordnance installation
WORK COMPLETED:
* Helium signature test
* Hypergolic line purges
-----------------------------------------------------------------
Mission: STS-51/ACTS-TOS/ORFEUS-SPAS Orbital Alt.: 184 miles
Vehicle: Discovery/OV-103 Inclination: 28 degrees
Location: OPF bay 3 Crew Size: 5
Mission Duration: 9 days/22 hours Target Launch Period: mid-July
IN WORK TODAY:
* Freon coolant loop servicing
* Orbiter/payload pre-mate check-outs
* Potable water servicing
* Lower nose landing gear
* Auxiliary power unit leak and functional checks
* Stacking of right hand solid rocket booster in VAB
WORK SCHEDULED:
* Orbiter/FRCS interface verification checks
* External tank doors functional checks
WORK COMPLETED:
* Freon coolant loop checks/temperature transducer replacement
* Orbital maneuvering system redundant electrical verifications
* Main engine installation preparations
* Integrated hydraulic operations
-----------------------------------------------------------------
Mission: STS-58/SLS-2 Orbital Altitude: 176 miles
Vehicle: Columbia/OV-102 Inclination: 39 degrees
Location: OPF bay 2 Crew Size: 7
Mission Duration: 14 days
Target launch period: Early September
IN WORK TODAY:
* Configure payload bay for SLS-2
* Hypergolic deservice
* Remove dome heatshields
* Replace landing gear tires
* Main engine post flight inspections
* SLS-2 mission sequence test
WORK SCHEDULED:
* Auxiliary power unit lube oil servicing
* TACAN system test
WORK COMPLETED:
* Open payload bay doors
* Preparations for hypergolic deservice
* Installation of waste water tank
Source:NASA Spacelink Modem:205-895-0028 Internet:192.149.89.61
=--=--=-END-=--=--=
=--=--=START=--=--= NASA Spacelink File Name:930525.SKD
Daily News/TV Sked 5/25/93
Daily News
Tuesday, May 25, 1993
Two Independence Square,
Washington, D.C.
Audio Service: 202/358-3014
% New radiation belt located;
% STS-51 mission status;
% NASA F/A makes first flight.
Scientist from the Goddard Space Flight Center and the California Institute of
Technology report the location of a radian belt of cosmic rays several hundreds
miles above the Earth.
The Solar, Anomalous and Magnetospheric Particle Explorer (SAMPEX) was orbiting
375 miles (600 kilometers) above the Earth when it measured the belt. The belt
is composed of particles known as anomalous cosmic rays. The rays are the
result of the sun's interaction with tenuous gas that exists between the stars
in the Milky Way galaxy.
Scientist of the SAMPEX team will use this recent discovery to study the
properties of interstellar matter.
* * * * * * * * * * * * * * * *
Specifically modified to test new and advanced system technologies, a NASA
F/A-18 made its first research flight on May 21 at the Ames-Dryden Flight
Research Facility.
The plane's first mission involved testing of an electric actuator used to
monitor the position and control of one of the aircraft's ailerons. Future
missions will involve investigating the use of optical systems on future
aircraft and developing new ways to measure an aircraft's speed, altitude and
other air data parameters. Researchers hope the project will help ensure that
new aerospace concepts are transferred to U.S. industry quickly.
* * * * * * * * * * * * * * * *
Still targeted for launch in mid-July, technicians at the Kennedy Space Center
continue to prepare Space Shuttle Discovery for the STS-51 mission. Workers
yesterday conducted freon coolant loop checks and replaced the temperature
transducer. Pre-mate check-outs on the orbiter and payload were conducted
yesterday as well. With the completion of the forward reaction control system
installation (FRCS), technicians are scheduled to begin orbiter and FRCS
verification checks on Discovery.
Space Shuttle Discovery will carry the ACTS payload and a crew of 5 during the
upcoming mission. Mission duration is planned for 9 days and 22 hours.
* * * * * * * * * * * * * * * *
Here's the broadcast schedule for Public Affairs events on NASA TV.
Note that all events and times may change without notice and that all times
listed are Eastern.
Tuesday, May 25, 1993
NOON NASA Today news program including stories on the STS-57
mission; HST; SEDS and the Internat'l Space & Engineering Fair.
12:15 pm Aeronautics & Space Report.
12:30 pm Pictures in the Mind.
Live 1:00 pm Space Astronomy Update
(From HQ).
2:00 pm Shaping Tomorrow.
2:30 pm Human Machine in Space.
3:00 pm Gemini, The Twins.
3:30 pm Around the Moon.
Wednesday, May 26, 1993
NOON NASA Today news program featuring stories on the EURECA
retrieval; the Data Egg and Shuttle astronaut health.
12:15 pm Aeronautics & Space Report.
12:30 pm Quieter, Faster, Safer Aircraft.
Live 1:00 pm Magellan Press Briefing
(From HQ).
1:30 pm Pioneer/Saturn Encounter.
2:00 pm Adventures in Research.
2:30 pm Viking Expeditions.
3:00 pm Transition Years.
3:30 pm Regaining the Edge.
NASA TV is carried on GE Satcom F2R, transponder 13, C-Band, 72 degrees West
Longitude, transponder frequency is 3960 MHz, audio subcarrier is 6.8 MHz,
polarization is vertical.
Source:NASA Spacelink Modem:205-895-0028 Internet:192.149.89.61
=--=--=-END-=--=--=
=--=--=START=--=--= NASA Spacelink File Name:930525B.REL
5/25/93: SCIENTISTS LOCATE NEW RADIATION BELT AROUND EARTH
Paula Cleggett-Haleim
Headquarters, Washington, D.C.
M
Michael Finneran
Goddard Space Flight Center, Greenbelt, Md.
Jay Aller
California Institute of Technology, Pasadena, Calif.
RELEASE: 93-94
The location of a radiation belt of cosmic rays -- particles from
beyond the solar system -- has been pinpointed several hundred miles above the
Earth, according to scientists from the California Institute of Technology,
Pasadena, and NASA's Goddard Space Flight Center, Greenbelt, Md.
A NASA satellite called Solar, Anomalous and Magnetospheric Particle
Explorer (SAMPEX), was orbiting 375 miles (600 kilometers) above the Earth when
it measured the belt.
The belt is most intense above a 5,000-mile (8,050- kilometer) strip of
Atlantic Ocean between the southern tips of South America and Africa, Caltech
and NASA scientists said at the annual meeting of the American Geophysical
Union in Baltimore, Md., on Tuesday, May 25.
The belt is composed of particles known as anomalous cosmic rays, which
are the result of the sun's interaction with tenuous gas that exists between
the stars in the Milky Way galaxy.
"We were pretty sure the belt was there, and now we've pinned it down
along with its location, which we didn't know before," said Goddard's Dr. Tycho
von Rosenvinge, a member of the SAMPEX team.
The first clear evidence for such a raof Russian and U.S. scientists in
1991 using information from a series of Russian COSMOS spacecraft.
They were unable, however, to determine directly the location of the
belt, which is composed of different high-energy particles than another region
of radiation, the Van Allen radiation belts discovered by James A. Van Allen in
1958 using data from NASA's Explorer 1 satellite.
The belt in which the anomalous cosmic rays collect is embedded within
the inner of the two Van Allen belts. The geometry of these belts is
determined by the Earth's magnetic field lines, which connect the North and
South magnetic poles.
"The cosmic rays become trapped in this field, where they bounce back
and forth between the poles of Earth's magnetic field," said Caltech's Dr.
Richard Mewaldt, a member of the SAMPEX team along with Caltech colleagues Drs.
Jay Cummings, Alan Cummings, Richard Selesnick and Edward Stone.
The rays are the most intense in the 5,000-mile (8,050- kilometer)
strip between South America and Africa, Mewaldt said, because the Earth's
magnetic field is not centered perfectly, and this is where it allows the
trapped particles to get closest to the planet's surface.
SAMPEX scientists said trapped cosmic rays can be stored in the belt
for weeks or more, so the intensity can build up over time as more arrive.
More of the cosmic rays collect in the belt during periods of minimum solar
activity, which follows an 11- year cycle.
The trapped radiation has doubled between August and November 1992,
according to SAMPEX measurements, and now is about 100 times the intensity of
the anomalous cosmic rays in interplanetary space.
"This long-term storage will give the SAMPEX team a unique opportunity
to study the properties of interstellar matter right in Earth's back yard,"
Mewaldt said.
SAMPEX was launched in July 1992 on a Scout rocket from Vandenberg Air
Force Base, Calif. The satellite is managed by Goddard for the Office of Space
Science at NASA Headquarters in Washington, D.C.
Source:NASA Spacelink Modem:205-895-0028 Internet:192.149.89.61
=--=--=-END-=--=--=
=--=--=START=--=--= NASA Spacelink File Name:930525C.REL
5/25/93: HUBBLE SERVICING MISSION STUDY COMPLETED
Mark Hess/Jim Cast
Headquarters, Washington, D.C. May 25, 1993
RELEASE: 93-96
A task force established by NASA Administrator Daniel S. Goldin to
review plans for the Hubble Space Telescope servicing mission concluded that,
"the mission is achievable." This conclusion was driven by the fact that the
spacecraft and most of its subsystems were designed for on-orbit maintenance.
The Task Force on the Hubble Space Telescope Servicing Mission,
chartered in late January, reviewed all aspects of the first servicing mission
which is currently scheduled for December 1993. Dr. Joseph F. Shea was
Chairman of the task force.
"We were asked to arrive at a judgement as to the likelihood of success
of the repair and servicing mission," said Shea. "In our opinion, we think the
mission is achievable."
The task force pointed out, however, that the mission is complex and
will require more EVA (spacewalk) time than any mission to date. Given this
complexity, the task force recommended that a second HST servicing mission be
planned 6 to 12 months after the STS-61 flight to handle tasks that might not
be completed during the first mission or respond to failures that occur in the
intervening months.
Shea said planning and management changes, which have taken place over
the past few months, will improve the likelihood of success. "We support the
appointment of a Mission Director, and believe that such a position, with
authority and resources, is necessary if the mission is to be carried out with
confidence," Shea said.
The task force report also concluded that a full end-to-end simulation
of the EVA in the Neutral Buoyancy Simulator at the Marshall Space Flight
Center, Huntsville, Ala., which is currently in the planning stage, is
"essential to a successful mission."
"There are some areas, like schedule, where we still have some
concerns," Shea said. "We think the timelines for the EVAs are very tight and
some of the hardware is not fully assembled. But we were very pleased to see
that NASA extended the mission duration and the number of EVAs for the flight."
Source:NASA Spacelink Modem:205-895-0028 Internet:192.149.89.61
=--=--=-END-=--=--=
=--=--=START=--=--= NASA Spacelink File Name:6_2_18_5.TXT
NOTE: This file is too large {27551 bytes} for inclusion in this collection.
The first line of the file:
- Current Two-Line Element Sets #197 -
Source:NASA Spacelink Modem:205-895-0028 Internet:192.149.89.61
=--=--=-END-=--=--=
=--=--=START=--=--= NASA Spacelink File Name:6_2_2_45_6.TXT
STS-57 TV SCHEDULE
***********************************************************************
NASA SELECT TV SCHEDULE
STS-57
5/25/93
***********************************************************************
NASA Select programming can be accessed through GE Satcom F2R, transponder 13.
The frequency is 3960 MHz with an orbital position of 72 degrees West
Longitude. This is a full transponder service and will be operational 24 hours
a day.
Two hour edited programs of each flight day will be replayed for Hawaii and
Alaska on Spacenet 1, transponder 17L, channel 18. The orbital position is 120
degrees West Longitude, with a frequency of 4060 MHz. Audio is on 6.8 MHz. The
programs will begin on launch day and continue through landing airing at
11:01PM Central Time.
This NASA Select Television Schedule of mission coverage is available on
COMSTORE, the mission TV schedule computer bulletin board service. Call
713/483-5817, and follow the prompts to access this service.
------------------------- Monday, May 31 -----------------------------
L-3 Days
SUBJECT SITE CDT
------- ---- ---
COUNTDOWN STATUS BRIEFING KSC TBD
CREW ARRIVAL KSC 3:00 PM
------------------------- Tuesday, June 1 -----------------------------
L-2 Days
COUNTDOWN STATUS BRIEFING KSC 8:00 AM
SPACEHAB PAYLOADS BRIEFING KSC 8:30 AM
SPACEHAB PAYLOADS BRIEFING KSC 12:30 PM
SPACEHAB PAYLOADS BRIEFING JSC 1:00 PM
SPACEHAB PAYLOADS BRIEFING KSC 1:30 PM
------------------------- Wednesday, June 2----------------------------
L-1 Day
COUNTDOWN STATUS BRIEFING KSC 8:00 AM
EURECA BRIEFING KSC 8:30 AM
OACT/SPACEHAB BRIEFING KSC 9:00 AM
GAS BRIEFING KSC 9:30 AM
SHOOT BRIEFING KSC 10:30 AM
PRE-LAUNCH NEWS CONFERENCE KSC 11:45 AM
------------------------- Thursday, June 3 ----------------------------
FD1
ORBIT SUBJECT SITE MET CDT
----- ------- ---- --- ---
NASA SELECT COVERAGE BEGINS KSC 01:00 PM
LAUNCH KSC 00/00:00 05:17 PM
NASA SELECT ORIGINATION SWITCHED JSC 00/00:08 05:25 PM
TO JSC
MECO JSC 00/00:08 05:25 PM
1 NASA SELECT ORIGINATION SWITCHED KSC 00/00:13 05:30 PM
TO KSC
1 LAUNCH REPLAYS WILL OCCUR KSC 00/00:13 05:30 PM
APPROX. 5 MIN. AFTER MECO
(T=30:00)
1 POST LAUNCH PRESS CONFERENCE KSC 00/00:58 06:15 PM
1 NASA SELECT ORIGINATION SWITCHED JSC 00/01:28 06:45 PM
TO JSC
2 SPACEHAB ACTIVATION 00/02:30 07:47 PM
(Not Televised)
3 Ku BAND ANTENNA DEPLOY 00/03:15 08:32 PM
(Not televised)
4 VTR DUMP OPPORTUNITY/CREW CHOICE TDRE 00/05:45 11:02 PM
T=10:00
4 NASA SELECT ORIGINATION SWITCHED KSC 00/06:13 11:30 PM
TO KSC
4 ENGINEERING LAUNCH REPLAYS KSC 00/06:13 11:30 PM
(T=30:00)
--------------------------- Friday, June 4 ----------------------------
FD2
NOTE: ADDITIONAL SPACEHAB ACTIVITIES MAY BE DOWNLINKED
THROUGOUT THE DAY.
5 NASA SELECT ORIGINATION SWITCHED JSC 00/06:43 12:00 AM
TO JSC
6 CREW SLEEP 00/08:30 01:47 AM
8 REPLAY OF FD1 ACTIVITIES JSC 00/11:43 05:00 AM
11 CREW WAKE UP 00/16:30 09:47 AM
12 MISSION UPDATE JSC 00/18:43 12:00 PM
14 P/TV02 LEMZ-1 ACTIVATION TDRW 00/21:10 02:27 PM
T=5:00
15 P/TV02 EFE ACTIVATION TDRW 00/22:26 03:43 PM
T=15:00
15 MISSION STATUS BRIEFING JSC 00/22:13 03:30 PM
16 P/TV01 RMS CHECKOUT TDRE 01/00:28 05:45 PM
T=30:00
17 P/TV02 SCG OPERATIONS TDRE 01/01:20 06:37 PM
T=20:00
17 P/TV01 RMS PAYLOAD BAY SURVEY TDRE 01/01:20 06:37 PM
T=18:00
(May be pre-empted by SCG science tv)
18 P/TV02 SPACEHAB ACTIVITIES TDRE/W 01/02:50 08:07 PM
T=20:00
20 REPLAY OF FD2 ACTIVITIES JSC 01/05:43 11:00 PM
-------------------------- Saturday, June 5 ---------------------------
FD3
NOTE: ADDITIONAL SPACEHAB ACTIVITIES MAY BE DOWNLINKED
THROUGHOUT THE DAY.
22 CREW SLEEP 01/08:30 01:47 AM
24 REPLAY OF FD2 ACTIVITIES JSC 01/11:43 05:00 AM
27 CREW WAKE UP 01/16:30 09:47 AM
28 MISSION UPDATE JSC 01/18:43 12:00 PM
30 P/TV02 TDS-SE SOLDER ACTIVITY TDRW 01/22:07 03:24 PM
T=10:00 (May be pre-empted by MSB)
30 MISSION STATUS BRIEFING JSC 01/22:13 03:30 PM
31 P/TV02 TDS-SE SOLDER ACTIVITY TDRE 01/22:17 03:34 PM
T=50:00 (May be pre-empted by MSB)
34 P/TV06 BELO STATIONS INTERVIEW TDRW 02/03:05 08:22 PM
T=15:00
34 P/TV02 LEMZ ACTIVITY TDRE 02/03:50 09:07 PM
T=5:00
35 P/TV05 EMU CHECKOUT DOWNLINK TDRE 02/04:55 10:12 PM
OPPORTUNITY
T=59:00
(May not be televised/crew choice)
35 REPLAY OF FD3 ACTIVITIES JSC 02/05:43 11:00 PM
--------------------------- Sunday, June 6 ----------------------------
FD4
NOTE: TELEVISION DOWNLINK OF EURECA RETRIEVAL ACTIVITIES
WILL OCCUR ORBITS 44 - 49 AS TDRSS AND GSTDN
COVERAGE ALLOWS. ADDITIONAL SPACEHAB ACTIVITIES
MAY ALSO BE DOWNLINKED.
37 CREW SLEEP 02/08:00 01:17 AM
39 REPLAY OF FD3 ACTIVITIES JSC 02/11:43 05:00 AM
42 CREW WAKE UP 02/16:00 09:17 AM
43 MISSION UPDATE JSC 02/18:43 12:00 PM
44 P/TV02 EFE OPERATIONS TDRE 02/19:00 12:17 PM
T=20:00
44 ORBITER NH BURN (Not Televised) 02/19:24 12:41 PM
45 ORBITER NC4 BURN (Not Televised) 02/20:11 01:28 PM
45 RENDEZVOUS DOWNLINK OPPORTUNITY MIL 02/20:14 01:31 PM
T=14:00
46 Ku BAND TO RADAR MODE (Not Televised) 02/21:15 02:32 PM
46 RENDEZVOUS DOWNLINK OPPORTUNITY MIL 02/21:53 03:10 PM
T=9:00
46 ORBITER NCC BURN (Not Televised) 02/22:20 03:37 PM
47 Ti BURN (Not Televised) 02/23:19 04:36 PM
47 RENDEZVOUS DOWNLINK OPPORTUNITY GDS, 02/23:27 04:44 PM
T=17:00 MIL
47 RMS POISE FOR CAPTURE (Not Televised) 02/23:32 04:49 PM
48 RENDEZVOUS DOWNLINK OPPORTUNITY GDS, 03/01:05 06:22 PM
T=22:00 MIL
48 Ku BAND TO COMM (Not Televised) 03/01:15 06:32 PM
48 P/TV07 EURECA GRAPPLE TDRE 03/01:35 06:52 PM
48 P/TV07 EURECA BERTH (Not Televised) 03/02:00 07:17 PM
49 P/TV07 EURECA BERTH CON'T TDRE 03/02:43 08:00 PM
T=32:00
50 MISSION STATUS BRIEFING JSC 03/04:13 09:30 PM
50 P/TVO7 VTR DUMP OPPORTUNITY TDRW 03/04:22 09:39 PM
CREW CHOICE (Replay of this
downlink to follow MSB if req'd)
51 REPLAY OF FD4 ACTIVITIES JSC 03/05:47 11:04 PM
--------------------------- Monday, June 7 ----------------------------
FD5
NOTE: TELEVISION DOWNLINK OF EVA ACTIVITIES WILL OCCUR
ORBITS 59 - 65 AS TDRSS COVERAGE ALLOWS. SPACEHAB
ACTIVITIES MAY ALSO BE DOWNLINKED.
52 CREW SLEEP 03/08:00 01:17 AM
54 REPLAY OF FD4 ACTIVITIES JSC 03/11:43 05:00 AM
57 CREW WAKE UP 03/16:00 09:17 AM
58 P/TV05 EVA PREP DOWNLINK TDRW 03/18:00 11:17 AM
OPPORTUNITY
T=10:00
59 P/TV05 EVA PREP DOWNLINK TDRE/W 03/18:25 11:42 AM
OPPORTUNITY
T=55:00
59 MISSION UPDATE JSC 03/18:43 12:00 PM
62 P/TV05 EVA PREP DOWNLINK TDRW 03/23:00 04:17 PM
OPPORTUNITY
T=10:00
62 P/TV05 AIRLOCK DEPRESS TDRE 03/23:40 04:57 PM
T=7:00
62 P/TV05 AIRLOCK EGRESS (Not Televised) 04/00:00 05:17 PM
EVA BEGINS
63 EVA & RMS ACTIVITIES TDRW/E 04/00:22 05:39 PM
T=63:00
64 EVA & RMS ACTIVITIES TDRW/E 04/01:45 07:02 PM
T=56:00
65 EVA & RMS ACTIVITIES TDRW/E 04/03:26 08:43 PM
T=32:00
65 AIRLOCK INGRESS TDRE 04/04:00 09:17 PM
T=5:00
65 MISSION STATUS BRIEFING JSC 04/04:43 10:00 PM
66 REPLAY OF FD5 ACTIVITIES JSC 04/05:43 11:00 PM
--------------------------- Tuesday, June 8 ---------------------------
FD6
NOTE: ADDITIONAL SPACEHAB ACTIVITIES MAY BE DOWNLINKED
THROUGHOUT THE DAY.
67 CREW SLEEP 04/08:00 01:17 AM
70 REPLAY OF FD5 ACTIVITIES JSC 04/11:43 05:00 AM
73 CREW WAKE UP 04/16:00 09:17 AM
74 MISSION UPDATE JSC 04/18:43 12:00 PM
75 P/TV02 EFE ACTIVITIES TDRE 04/19:50 01:07 PM
T=10:00
76 P/TV02 EFE ACTIVITIES TDRW 04/21:45 03:02 PM
T=15:00 (May not have Ku coverage)
77 MISSION STATUS BRIEFING JSC 04/22:13 03:30 PM
78 P/TV08 FARE TEST #5 DOWNLINK TDRW 05/00:00 05:17 PM
OPPORTUNITY
T=19:00
78 P/TV02 LEMZ-3 ACTIVITIES TDRW 05/01:03 06:20 PM
T=5:00
80 P/TV06 CNN INTERVIEW TDRW 05/03:45 09:02 PM
T=15:00
81 REPLAY OF FD6 ACTIVITIES JSC 05/05:43 11:00 PM
------------------------- Wednesday, June 9 ---------------------------
FD7
NOTE: ADDITIONAL SPACEHAB ACTIVITIES MAY BE DOWNLINKED
THROUGHOUT THE DAY.
82 CREW SLEEP 05/07:00 12:17 AM
85 REPLAY OF FD6 ACTIVITIES JSC 05/11:43 05:00 AM
87 CREW WAKE UP 05/15:00 08:17 AM
90 MISSION UPDATE JSC 05/18:43 12:00 PM
90 P/TV02 EFE ACTIVITIES TDRE 05/19:00 12:17 PM
T=15:00
92 MISSION STATUS BRIEFING JSC 05/22:13 03:30 PM
92 P/TV02 LEMZ-4 ACTIVITIES TDRE 06/00:00 05:17 PM
T=5:00
97 REPLAY OF FD7 ACTIVITIES JSC 06/05:43 11:00 PM
97 CREW SLEEP 06/06:00 11:17 PM
-------------------------- Thursday, June 10 --------------------------
FD8
NOTE: SPACEHAB ACTIVITIES MAY BE DOWNLINKED THROUGOUT THE DAY.
100 REPLAY OF FD7 ACTIVITIES JSC 06/11:43 05:00 AM
102 CREW WAKE UP 06/14:00 07:17 AM
105 MISSION UPDATE JSC 06/18:43 12:00 PM
107 CREW CONFERENCE TDRW 06/22:00 03:17 PM
T=30:00
107 MISSION STATUS BRIEFING JSC 06/22:43 04:00 PM
110 Ku BAND STOW 07/02:20 07:37 PM
(Not televised)
112 CREW SLEEP 07/05:30 10:47 PM
112 REPLAY OF FD8 ACTIVITIES JSC 07/05:43 11:00 PM
---------------------------- Friday, June 11 --------------------------
FD9
116 REPLAY OF FD8 ACTIVITIES JSC 07/11:43 05:00 AM
117 CREW WAKE UP 07/13:30 06:47 AM
120 MISSION UPDATE JSC 07/18:43 12:00 PM
122 DEORBIT BURN (Not Televised) 07/21:48 03:05 PM
123 LANDING KSC 07/22:56 04:13 PM
POST LANDING PRESS CONFERENCE KSC L+TBD
LANDING REPLAYS KSC L+TBD
------------------------ DEFINITION OF TERMS -----------------------
CAN-DO: Variety of experiments located in two canisters in payload bay
CDT: Central Daylight Time
EFE: Environmental control and life support system
Flight Experiment
EURECA: European Retrievable Carrier
EVA: Extra-vehicular activity
FARE: Fluid Acquisition and Resupply Experiment
FD: Flight Day
GBA: GAS Bridge Assembly
GDS: Goldstone Tracking Station
GSTDN: Ground Spacecraft Tracking and Data Network
JSC: Johnson Space Center
KSC: Kennedy Space Center
LEMZ: Liquid Encapsulated Melt Zone
MECO: Main Engine Cut-off
MET: Mission elapsed Time. The time which begins at the moment
of launch and is read: Days/Hours:minutes. Launch= 00/00:00
MIL: Merrit Island Tracking Station
MSB: Mission Status Briefing
NC4: Orbital correction burn
NCC: Orbital correction burn
NH: Orbital height adjustment burn
TI: Terminal Initiation burn
P/TV: Photo/Television Scene
RMS: Remote Manipulator System
SCG: Solution Crystal Growth
SPACEHAB:Commercial module carried in payload bay
STS: Space Transportation System
TDS-SOLDER:Tools and Diagnostic System Solder
TDRE,W: Tracking and Data Relay Satellite, both East and West
longitudes
TDRSS: Tracking and Data Relay Satellite System
T=: Time event duration equals
VTR: Video Tape Recorder
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5/25/93: HUBBLE LOOKS AT THE HEART OF A GALAXY COLLISION
Paula Cleggett-Haleim
Headquarters, Washington, D.C.
M
Jim Elliott
Goddard Space Flight Center, Greenbelt, Md.
Ray Villard
Space Telescope Science Institute, Baltimore, Md.
RELEASE: 93-97
NASA's Hubble Space Telescope has looked into the heart of a galaxy
created by the collision of two galaxies and peering deeply into its nucleus,
discovered a remarkable pinwheel-shaped disk of gas surrounded by clusters of
young stars born as a result of the merger.
The star clusters apparently were born as a result of the collision of
two disk-shaped galaxies. The galaxy merger, which occurred about 1 billion
years ago, triggered an infall of the gas which fueled the birth of new stars
around the center of the galaxy.
"This may unlock the key for understanding how all globular clusters
formed in ellipticals," said Dr. Brad Whitmore of the Space Telescope Science
Institute (STScI), Baltimore, Md. "The Hubble observation also shows how tiny
disk-like structures might have formed in many other galaxies."
This discovery provides some of the best evidence to date for
explaining the origin of giant elliptical galaxies. For more than a half
century, astronomers have theorized about how such galaxies formed. Some
theories propose that ellipticals formed from collisions between disk galaxies
-- flattened stellar systems resembling the Milky Way galaxy.
These results are being presented in a press conference today at NASA
Headquarters, Washington, D.C., by Whitmore and Dr. Francois Schweizer of the
Carnegie Institution of Washington. Co-investigators are Claus Leitherer, Kirk
Borne and Carmelle Robert of STScI.
Pinwheel of Stars and Gas
The striking Hubble image shows a spiral pattern at the galaxy's core,
surrounded by bright star clusters. "I knew I had a major result within 10
seconds of looking at the Hubble picture," said Whitmore.
The pinwheel shaped disk has an uncanny resemblance to a face-on spiral
galaxy, yet it is only 10 thousand light-years across -- about 1/20 the size of
the total galaxy. The gas and stars in the disk swirl around the nucleus,
making a spiral pattern like cream poured in a cup of coffee. The mini-spiral
contains enough gas to make 8 billion stars like the sun. Though several of
the clusters were first spotted from ground- based telescopes, their true
nature was uncertain until the Hubble observations.
Hubble's resolution is so good that the astronomers can measure the
diameters (0.04 arc seconds, the apparent size of a dime at a distance of 80
miles) of the bright star clusters seen in the same image as the spiral disk.
They turn out to be about 60 light years across, the same size as globular
clusters that orbit the Milky Way galaxy.
The globular clusters found in NGC 7252 are considered the progenitors
of similar clusters that orbit the Milky Way galaxy. Since globular clusters
normally contain ancient red giant stars, they provide a fossil record of the
formation and evolution of galaxies. Globular clusters contain about 1 million
stars each, arranged in a tight, spherical swarm and generally are found to be
about 15 billion years old.
However, the "ultra-luminous clusters" found in NGC 7252 contain hot
bluish stars. Because these blue stars are short-lived, the clusters in NGC
7252 are estimated to be mostly between 50 and 500 million years old.
The blue stars make the globular clusters up to several hundred times
brighter than the clusters that orbit the Milky Way galaxy. If the Milky Way's
globular clusters were as bright, they could be seen with the naked-eye and
would be brighter than the stars in the Big Dipper.
In the 1920's, American astronomer Edwin Hubble classified galaxies
according to their spiral or elliptical shape. A key difference is that stars
are concentrated in a disk in spirals, but are distributed in a diffuse,
roughly spherical distribution in ellipticals.
Since Edwin Hubble's time, astronomers have sought an explanation for
why there are two different types of galaxies. During the past decade, the
hypothesis that spiral galaxies can collide and merge to form elliptical
galaxies has become increasingly popular.
Located 300 million light-years away in the constellation Aquarius, NGC
7252 has been considered the prototypical example of a merger between two
disk-shaped galaxies. The galaxy has a pair of long tails that are unambiguous
evidence of the effects of gravitational tidal forces from a galaxy merger.
The galaxy NGC 7252 is nicknamed the "Atoms-for-Peace" galaxy because
its stars form a bizarre loop-like structure that resembles a schematic diagram
of an electron orbiting and an atomic nucleus. (In December 1953. U.S.
President Dwight D. Eisenhower made his "Atoms for Peace" speech to foster
peaceful applications of nuclear energy.
If globular clusters can be born during galaxy collisions, it
reinforces the theory that disk galaxies merge to make giant elliptical
galaxies. One argument against this theory is that elliptical galaxies have
more globular clusters than expected if disk galaxies were simply combined,
since disk galaxies have relatively few clusters.
Hubble Picture Helps to Solve Mystery
The new Hubble Space Telescope observation solves this dilemma by
showing that when disk galaxies collide they can form new globular clusters.
Rather than being a problem for the merger scenario, an increase in the number
of globular clusters is a natural consequence of galaxy mergers.
The existence of a "mini-disk" also fits with the merger scenario since
similar disk-like features appear to exist in many elliptical galaxies.
Another clear indication that the material originated from the collision of two
galaxies is that the mini-spiral is rotating in a direction opposite to the
rest of the galaxy.
This discovery is the latest in a series of disk-like structures that
Hubble has uncovered at the cores of galaxies. Previously, HST found a giant
disk of cool dust and gas orbiting a suspected black hole in the active galaxy
NGC 4261 and discovered an edge-on "donut" of dust in the spiral galaxy M51.
The astronomers predict that in a few billion years the gas in NGC 7252
will be exhausted. The galaxy will look like a normal elliptical galaxy with a
small inner disk.
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4/23/93: HUBBLE TELESCOPE SERVICING MISSION SCHEDULED FOR ELEVEN DAYS
Ed Campion
Headquarters, Washington, D.C. April 23, 1993
Kyle Herring
Johnson Space Center, Houston
RELEASE: 93-76
The December flight of Endeavour on Space Shuttle mission STS-61 to
service the Hubble Space Telescope (HST) has been scheduled as an 11 day
mission designed to accommodate a record five spacewalks with the capability
for an additional two, if needed.
The decision to schedule five extravehicular activities, or EVAs, was
reached following extensive evaluations of underwater training, maneuver times
required using the Shuttle's robot arm based on software simulations and actual
EVA tasks on previous missions.
"Basically what we've done by going to five EVAs rather than three is
to repackage our margin so that we have the capability to respond to the
dynamics, or unknowns, of spacewalks," Mission Director Randy Brinkley said.
"It improves the probabilities for mission success while providing added
flexibility and adaptability for reacting to real-time situations."
In laying out the specific tasks to be completed on each of the
spacewalks, officials have determined that changing out the gyros, solar arrays
and the Wide Field/Planetary Camera (WF/PC) and installing the Corrective
Optics Space Telescope Axial Replacement (COSTAR) are priority objectives
during the mission.
"When we looked at accomplishing all of the tasks, highest through
lowest priority, and recognizing that the major tasks -- gyros, solar arrays,
WF/PC and COSTAR -- would consume most of the time set aside for each
spacewalk, five EVAs were deemed appropriate," said Milt Heflin, Lead Flight
Director for the mission.
While the five spacewalks will be unprecedented, the use of two
alternating spacewalk teams will alleviate placing more stress on the crew than
previous missions requiring two, three or four EVAs.
"We have paid close attention to lessons learned during previous
spacewalks and factored these into our timeline estimates for five EVAs,"
Heflin said. "In planning for all Space Shuttle missions, it is necessary to
formulate a work schedule that represents as realistic a timeline as possible
to accomplish the mission objectives."
Planning currently calls for at least five water tank training sessions
that include support from the Mission Control Center, called joint integrated
simulations, lasting between 10 and 36 hours. In addition, many stand alone
underwater training "runs" will practice individual tasks in each spacewalk.
Various refinements to the specific tasks on each spacewalk will be
made based on actual training experience during the months prior to the
mission. Also, lessons learned from other spacewalks leading up to the flight
will be valuable in assisting the STS-61 crew in its training techniques.
Endeavour's June flight and Discovery's July mission both will include
spacewalks to evaluate some of the unique tools to be used on the HST mission.
The evaluations will help in better understanding the differences between the
actual weightlessness of space and the ground training in the water tanks at
the Johnson Space Center, Houston, and the Marshall Space Flight Center,
Huntsville, Ala.
Also, the inflight spacewalking experiences will assist in gaining
further insight into the time required for the various tasks and expand the
experience levels among the astronaut corps, the flight controllers and
trainers.
Designed to be serviced by a Space Shuttle crew, Hubble was built with
grapple fixtures and handholds to assist in the capture and repair procedures.
The telescope was launched aboard Discovery in April 1990. At that
time the NASA mixed fleet manifest showed the first revisit mission to HST in
1993 to change out science instruments and make any repairs that may have
become necessary.
- end -
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5/25/93: HUBBLE SERVICING MISSION STUDY COMPLETED
Mark Hess/Jim Cast
Headquarters, Washington, D.C. May 25, 1993
RELEASE: 93-96
A task force established by NASA Administrator Daniel S. Goldin to
review plans for the Hubble Space Telescope servicing mission concluded that,
"the mission is achievable." This conclusion was driven by the fact that the
spacecraft and most of its subsystems were designed for on-orbit maintenance.
The Task Force on the Hubble Space Telescope Servicing Mission,
chartered in late January, reviewed all aspects of the first servicing mission
which is currently scheduled for December 1993. Dr. Joseph F. Shea was
Chairman of the task force.
"We were asked to arrive at a judgement as to the likelihood of success
of the repair and servicing mission," said Shea. "In our opinion, we think the
mission is achievable."
The task force pointed out, however, that the mission is complex and
will require more EVA (spacewalk) time than any mission to date. Given this
complexity, the task force recommended that a second HST servicing mission be
planned 6 to 12 months after the STS-61 flight to handle tasks that might not
be completed during the first mission or respond to failures that occur in the
intervening months.
Shea said planning and management changes, which have taken place over
the past few months, will improve the likelihood of success. "We support the
appointment of a Mission Director, and believe that such a position, with
authority and resources, is necessary if the mission is to be carried out with
confidence," Shea said.
The task force report also concluded that a full end-to-end simulation
of the EVA in the Neutral Buoyancy Simulator at the Marshall Space Flight
Center, Huntsville, Ala., which is currently in the planning stage, is
"essential to a successful mission."
"There are some areas, like schedule, where we still have some
concerns," Shea said. "We think the timelines for the EVAs are very tight and
some of the hardware is not fully assembled. But we were very pleased to see
that NASA extended the mission duration and the number of EVAs for the flight."
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MAGELLAN STATUS REPORT 5/25/93
PUBLIC INFORMATION OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109.
MAGELLAN STATUS REPORT
May 25, 1993
The Magellan spacecraft was lowered into the top of the Venus atmosphere today
for an "aerobraking" maneuver, the first of its kind in planetary exploration,
to begin the process of circularizing its highly elliptical orbit.
The operation began at 10:31 a.m. Pacific Daylight Time with a thruster burn
lasting until 10:41 a.m. to slightly slow the spacecraft. The high-gain
antenna was turned toward Earth at 10:54 a.m. and the spacecraft first struck
the outer atmosphere at 12:00 noon. The atmospheric contact on the first orbit
lasted until 12:36 p.m.
The operation, to continue over about 80 days, will slowly bring the spacecraft
from its current orbit ranging between 170 kilometers (105 miles) and 8,500
kilometers (5,300 miles) from Venus, to a new, more circularized orbit of 200
by 600 kilometers (125 by 375 miles). The change will alter the time taken by
each orbit from 3 hours, 15 minutes to about 90 minutes.
If the maneuver is successful, the new orbit will permit high-resolution
gravity studies at Venus's poles as well as at its equatorial latitudes.
The second "drag pass," when the spacecraft will again dip into the atmosphere
to continue the circularizing process, was scheduled for 3:14 p.m. to 3:50 p.m.
PDT today.
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5/25/93: SCIENTISTS LOCATE NEW RADIATION BELT AROUND EARTH
Paula Cleggett-Haleim
Headquarters, Washington, D.C.
May 25, 1993
Michael Finneran
Goddard Space Flight Center, Greenbelt, Md.
Jay Aller
California Institute of Technology, Pasadena, Calif.
RELEASE: 93-94
The location of a radiation belt of cosmic rays -- particles from
beyond the solar system -- has been pinpointed several hundred miles above the
Earth, according to scientists from the California Institute of Technology,
Pasadena, and NASA's Goddard Space Flight Center, Greenbelt, Md.
A NASA satellite called Solar, Anomalous and Magnetospheric Particle
Explorer (SAMPEX), was orbiting 375 miles (600 kilometers) above the Earth when
it measured the belt.
The belt is most intense above a 5,000-mile (8,050- kilometer) strip of
Atlantic Ocean between the southern tips of South America and Africa, Caltech
and NASA scientists said at the annual meeting of the American Geophysical
Union in Baltimore, Md., on Tuesday, May 25.
The belt is composed of particles known as anomalous cosmic rays, which
are the result of the sun's interaction with tenuous gas that exists between
the stars in the Milky Way galaxy.
"We were pretty sure the belt was there, and now we've pinned it down
along with its location, which we didn't know before," said Goddard's Dr. Tycho
von Rosenvinge, a member of the SAMPEX team.
The first clear evidence for such a raof Russian and U.S. scientists in
1991 using information from a series of Russian COSMOS spacecraft.
They were unable, however, to determine directly the location of the
belt, which is composed of different high-energy particles than another region
of radiation, the Van Allen radiation belts discovered by James A. Van Allen in
1958 using data from NASA's Explorer 1 satellite.
The belt in which the anomalous cosmic rays collect is embedded within
the inner of the two Van Allen belts. The geometry of these belts is
determined by the Earth's magnetic field lines, which connect the North and
South magnetic poles.
"The cosmic rays become trapped in this field, where they bounce back
and forth between the poles of Earth's magnetic field," said Caltech's Dr.
Richard Mewaldt, a member of the SAMPEX team along with Caltech colleagues Drs.
Jay Cummings, Alan Cummings, Richard Selesnick and Edward Stone.
The rays are the most intense in the 5,000-mile (8,050- kilometer)
strip between South America and Africa, Mewaldt said, because the Earth's
magnetic field is not centered perfectly, and this is where it allows the
trapped particles to get closest to the planet's surface.
SAMPEX scientists said trapped cosmic rays can be stored in the belt
for weeks or more, so the intensity can build up over time as more arrive.
More of the cosmic rays collect in the belt during periods of minimum solar
activity, which follows an 11- year cycle.
The trapped radiation has doubled between August and November 1992,
according to SAMPEX measurements, and now is about 100 times the intensity of
the anomalous cosmic rays in interplanetary space.
"This long-term storage will give the SAMPEX team a unique opportunity
to study the properties of interstellar matter right in Earth's back yard,"
Mewaldt said.
SAMPEX was launched in July 1992 on a Scout rocket from Vandenberg Air
Force Base, Calif. The satellite is managed by Goddard for the Office of Space
Science at NASA Headquarters in Washington, D.C.
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SPACE ASTRONOMY UPDATE: NGC 7252 5/25/93
NGC 7252 is a galaxy located 310 million light years away in the direction of
constellation Piscis Austrinus, the Southern Fish. This galaxy, also known as
Arp 226, is shaped very differently than the spiral-shaped Milky Way; it also
is nearly eight times as luminous.
NGC 7252 has a single bright nucleus containing billions of stars. The nucleus
is embedded within the main body of the galaxy, a bean-shaped object marked by
delicate ripples of starlight, dust lanes, and six unresolved but very blue
star clusters. The entire galaxy is surrounded by faint loops of gas and two
slender tails of gas and stars that extend more than 260,000 light years from
the nucleus of the galaxy.
It has been called the "crumpled spider," but its most enduring nickname is the
"Atoms for Peace Galaxy," a name astronomer Alar Toomre, of the Massachusetts
Institute of Technology, bestowed upon it because of its resemblance to the
nuclear energy logo.
NGC 7252's unusual shape is believed to be the result of a merger between two
separate galaxies more than a billion years ago. Toomre, who surveyed merging
galaxies during the early 1970s, cited NGC 7252 as one of the best and least
ambiguous examples. He also performed some of the first computer simulations
of colliding and merging galaxies and produced many examples that looked
similar to NGC 7252.
The nucleus of the galaxy shows a spectrum typical of young stars less than a
billion years old. It also contains a disk of rotating gas extending 13,000
light years from the core, moving at 230,000 miles per hour.
The interstellar gas outside this disk, however, moves in the opposite
direction of the stars and gas in the galaxy. This "counter-rotating disk"
also contains more than eight billion times the mass of the Sun, making it and
the nucleus of NGC 7252 a potent star-forming nursery even today.
In 1982, Francois Schweizer studied this galaxy in detail using ground-based
telescopes and was able to discern six bluish knots of light in the galactic
nucleus, which he interpreted as young star clusters formed after the merger.
From Earth, however, resolution is limited. Schweitzer's observations hinted
at how the galaxy was formed, but did not reveal any of the important details
predicted by computer models over the years.
Each of these galaxies was probably about the same size as our Milky Way before
the encounter. As they fell closer together, the delicate spiral arms, with
their billions of stars, were distorted and scattered into space to form the
two tails that now emanate from NGC 7252.
The upheaval caused the motions of some of the stars within the newly forming
galaxy to create concentric rings of light centered on the nucleus of NGC 7252.
Similar rings have been seen in the outskirts of many elliptical galaxies,
leading some to believe that mergers formed all elliptical galaxies.
As the gas and dust clouds in these galaxies continued to collide and fall into
the center of the newly forming nucleus, their original motions dictated that
they circulate in the opposite direction of the other stars in NGC 7252. Over
the years, the production of new stars will subside as the great reservoir of
gas is transformed into new stars. Yet these stars will be marked by the
motion they shared with the original gas disk out of which they formed.
As a result, the nucleus of NGC 7252 will contain two distinct populations of
stars moving in opposite directions. The shape of this galaxy will settle into
the round, snowball form common to most elliptical galaxies.
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SPACE ASTRONOMY UPDATE: GLOBULAR CLUSTERS 5/25/93
A globular cluster is a dense spherical collection of stars. Most clusters
have up to one million stars packed in a region 10 to 100 light years in
diameter. A typical globular cluster is 500,000 times as bright as the Sun. In
the Milky Way's globular clusters, the stars are crowded closer together than
anywhere else in the Galaxy. If Earth orbited a star in a globular cluster, our
darkest night would be as bright as partial moonlight. Elliptical galaxies
have many globular clusters: the giant elliptical M87 has 16,000 globular
clusters. Spiral galaxies have fewer: we have more than 150 globular clusters
in the Milky Way. These clusters are old, formed early in our Galaxy's history.
The clusters orbit about the Galactic center like electrons around the nucleus
of an atom, preserving evidence of the Galaxy's primordial shape. We can
determine the age of clusters by looking at the colors of the stars inside
them. Old clusters have only red stars, while younger ones have bluer stars.
Clusters with young stars have traditionally been called Open Clusters because
they are not so densely packed.
Some of the Milky Way's clusters can be seen with the naked eye. One, M13 in
the constellation Hercules, appears as a faint fuzzy star. With a ground-based
telescope, we can see thousands of stars in the outer region of this cluster.
Those stars near the cluster core, however, are concentrated so tightly that
individual stars cannot be resolved from the ground. NASA's Hubble Space
Telescope (HST), with its higher resolution and vantage point above Earth's
obscuring atmosphere, has resolved the individual stars in a similar globular
cluster M15.
How do globular clusters form? We don't know. We have observed the early
stages in the formation of individual stars and the smaller collections of Open
Clusters that contain up to several hundred stars. The Orion Nebula is one
such example. But we have never seen the progenitor of a globular cluster.
Until recently, evidence supported the idea that all globular cluster systems
were ancient. We now know that the nearby galaxy, the Large Magellanic Cloud,
is home to clusters about one hundred times younger than those in our Galaxy.
While these clusters provide an opportunity to study young star systems, they
do not contain as many stars as "normal" globular clusters, so their
classification is still somewhat uncertain.
HST has provided an even better example: the peculiarly shaped galaxy, NGC
1275. In January 1992, astronomers announced they had discovered young
globular clusters in this galaxy. Apparently the clusters were spawned by the
collision of two galaxies now making up NGC 1275.
By studying globular clusters, astronomers are trying to develop a better
understanding of how even larger collections of stars, such as galaxies, form.
And now we have both young and old globular clusters to study. Globular
clusters also provide a unique laboratory for the study of the stellar life
cycle. Because their thousands of stars are similar in age and composition,
but have varying masses, astronomers can study stars in a globular cluster to
see how mass influences the life of a star.
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SPACE ASTRONOMY UPDATE: COLLIDING GALAXIES 5/25/93
Galaxies are rarely loners as they move through the vast depths of
intergalactic space. Many are found in great clusters, with dozens and even
thousands of neighbors that gravitationally jostle one another. Our own Milky
Way belongs to a family of more than 30 galaxies, called the Local Group, which
spans a volume of space some five million light years across. Our Local Group
has two hefty galaxies: the Milky Way and Andromeda. The rest are smaller
galaxies galaxies such as the Magellanic Clouds. Studies of spiral galaxies
show that most of them have several smaller galaxies swarming around them the
way the two Magellanic Clouds orbit the Milky Way.
Although galaxies rarely travel at speeds more than a 1,000 km per second (2
million miles per hour) within these clusters, they can be separated from their
neighbors by as little as two times their own diameter. In such close
proximity, it is inevitable that collisions between galaxies occur. These
collisions can last millions of years and span over a trillion cubic light
years of space. When finished, the galaxies are almost completely transformed.
And yet the collisions themselves are gentle encounters when seen on a planet's
scale. The mere planet dweller may never notice that the galaxy has been
transformed. The distance from star to star is so great that a galaxy
collision will produce very, very few star collisions. Only one pair of stars
out of trillions are likely to collide, condemning whatever planetary systems
they harbor to the cold depths of space.
The situation is quite different for the gas and dust between the stars. Great
rifts are torn in the otherwise smooth fabric of galactic starlight as the gas
and dust are compressed into great clouds and shock waves. Delicate balances
within the core of the galaxy may also be upset, with titanic consequences.
The nuclear regions of galaxies are often the sinkholes where huge gravity
tides pull in gas and dust clouds. When galaxies collide, so too do these
clouds, triggering great episodes of star forming activity in the compressed
gas.
Source:NASA Spacelink Modem:205-895-0028 Internet:192.149.89.61
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