Sunday, May 2, 2010
Mission
Mission Summary
ACE launched on a McDonnell-Douglas Delta II 7920 launch vehicle on August 25, 1997 from the Kennedy Space Center in Florida.
The Earth is constantly bombarded with a stream of accelerated particles arriving not only from the Sun, but also from interstellar and galactic sources. Study of these energetic particles contributes to our understanding of the formation and evolution of the solar system as well as the astrophysical processes involved. The Advanced Composition Explorer (ACE) spacecraft carrying six high-resolution sensors and three monitoring instruments samples low-energy particles of solar origin and high-energy galactic particles with a collecting power 10 to 1000 times greater than past experiments.
ACE orbits the L1 libration point which is a point of Earth-Sun gravitational equilibrium about 1.5 million km from Earth and 148.5 million km from the Sun. From its location at L1 ACE has a prime view of the solar wind, interplanetary magnetic field and higher energy particles accelerated by the Sun, as well as particles accelerated in the heliosphere and the galactic regions beyond.
ACE also provides near-real-time 24/7 continuous coverage of solar wind parameters and solar energetic particle intensities (space weather). When reporting space weather ACE provides an advance warning (about one hour) of geomagnetic storms that can overload power grids, disrupt communications on Earth, and present a hazard to astronauts.
The spacecraft has enough propellant on board to maintain an orbit at L1 until ~2024.
More details of the ACE mission can be found in the ACE Mission Paper, published in Space Science Reviews.
Science Goals
The nine scientific instruments on ACE are performing:
- Comprehensive and coordinated composition determinations
- Elemental
- Isotopic
- Ionic charge state
- Observations spanning broad dynamic range
- Solar wind to galactic cosmic ray energies
(~100 eV/nucleon to ~500 MeV/nucleon) - Hydrogen to Zinc (Z = 1 to 30)
- Solar active and solar quiet periods
- Solar wind to galactic cosmic ray energies
- Investigations of the origin and evolution of solar and galactic matter
- Elemental and isotopic composition of matter
- Origin of the elements and subsequent evolutionary processing
- Formation of the solar corona and acceleration of the solar wind
- Particle acceleration and transport in nature
Mission Status
ACE has been at the L1 point for over 10 years, and the spacecraft and instruments are still working very well, with the exception of the SEPICA instrument. Due to failure of the valves that control gas flow through the instrument, active control of the SEPICA proportional counter is no longer possible. At this time, we do not expect to deliver any SEPICA data beyond Feb 4 2005, unless one of the valves opens by itself, as has happened a few times in the past.
A fuel use strategy has been implemented that will allow continued operations through the year 2024 (see below).As of October 2006, 438 peer reviewed papers have been published by ACE science team members. See the ACE Publications List for more information.
Publication-quality data from the ace instruments are available on the web from the ACE Science Center.
The ACE Education and Public Outreach (E&PO) Committee, in cooperation with the cosmic ray group at NASA GSFC, has set up a page with ACE and other E&PO material on the web at: http://helios.gsfc.nasa.gov
Over 100 Science News items have been released by the ACE Science Center. You can check http://www.srl.caltech.edu/ACE/ACENews_curr.html
for the latest science news from ACE.
A Space Science Reviews book that contains all the ACE instrument papers has been published (vol. 86, Issue 1/4, 1998).
Also, the Advanced Composition Explorer (ACE) Lessons Learned and Final Report is out and available in pdf form (4.4 MByte).
On January 21, 1998, NOAA and the ACE project opened up the ACE Real Time Solar Wind (RTSW) monitoring capability to the public. The service provides continuous coverage of the solar wind parameters and solar energetic particle intensity. ACE's position a million miles upstream of earth gives as much as an hour's warning of CME's that can cause geomagnetic storms here at earth. See http://sec.noaa.gov/ace/index.html
ACE Orbit and Fuel Use Strategy
Initially, two Z-axis maneuvers using 16 lbm/y were used to prevent the Sun-Earth-Spacecraft (SES) angle from dropping below 4.75° due to natural evolution of the Lissajous orbit (see figure at right). This conservative Solar Exclusion Zone (SEZ) was designed to avoid solar radio interference with the downlink. As a result of discontinuing the Z-axis maneuvers after July 2001, ACE transited the SEZ with an SES angle of <2° every 3 months from September 2003 thru May 2005. Although the solar radio flux reduced the telemetry link margin to <3 dB during some of these transits, no science data were lost, as the ACE solid-state recorder has 86-hour capacity. Spacecraft commanding continued uninterrupted. Neither NASA nor NOAA has lost any data during SEZ transits, even in May 2004 when the minimum SES angle was 0.2° during a 21-hour crossing of the solar disk as viewed from Earth.
As the Lissajous orbit continues to evolve, the next SEZ transits within 2° will occur in 2011-2013 at solar maximum. Based on experience during 2003 - 2005, we expect minimal data loss at solar maximum. Should considerations warrant, it is possible to resume Z-axis maneuvers at any time prior to 2011. However, each year that the Z-axis is controlled requires an additional 16 lbm of fuel, shortening the remaining mission by 21 months.
History and Background
The proposal was resurrected at the instigation of Dr. Vernon Jones and officially resubmitted to NASA in 1986 as part of the Explorer Concept Study Program. In 1988, the ACE mission was selected for a one-year "Phase A" (concept) Study. This study was a collaborative effort between spacecraft design and science teams.
The ACE Mission officially began on 22 April 1991 when the contract between NASA/GSFC and the California Institute of Technology was signed. APL, designer and builder of the ACE spacecraft, was involved in planning for Phase B (definition). The early ACE Spacecraft effort (April to July 1991) was primarily for ACE mission support, spacecraft system specification and ACE instrument support and interface definition. Phase B of the ACE mission officially began in August 1992.
The Mission Preliminary Design Review was held in November 1993. Phase C/D (implementation) began shortly thereafter.
Mission and Spacecraft Characteristics
ACE launched on a McDonnell-Douglas Delta II 7920 launch vehicle on August 25, 1997 from the Kennedy Space Center in Florida.
In order to get away from the effects of the Earth's magnetic field, the ACE spacecraft has travelled almost a million miles (1.5 million km) from the Earth to the Earth-sun libration point (L1). By orbiting the L1 point, ACE stays in a relatively constant position with respect to the Earth as the Earth revolves around the sun.
- Communication Subsystem: Primary Mission, S-band, DSN;
- Communication Subsystem: NOAA - S-band @ NOAA Receiving Stations, TBD
- Total Onboard Data Storage in Two Solid State Recorders -- 2 Gigabits
- Primary Mission Downlink Rates: 78 & 6.9 kbps and 434 bps
- NOAA Real Time Solar Wind Mission: 434 bps
Authors: Eric R. Christian - erc@cosmicra.gsfc.nasa.gov and Andrew J. Davis -ad@srl.caltech.edu
Some content copied from the JHU/APL ACE Page
Curators: ACE Science Center - asc@srl.caltech.eduLast Updated: April 15, 2008
NASA's Ambitious New Space Telescope Passes Critical Test
By SPACE.com Staffposted: 01 May 2010 01:33 pm ET
NASA's hotly-anticipated new space observatory has passed its most significant mission milestone yet – a critical design review that sets the stage for a planned 2014 launch.
This means that the James Webb Space Telescope (JWST) a huge infrared telescope designed to peer farther back into the universe's history than ever before, has met all science and engineering requirements for its upcoming mission, NASA scientists said.
"I'm delighted by this news and proud of the Webb program's great technical achievements," said Eric Smith, the new telescope's program scientist at NASA Headquarters in Washington, D.C. "The independent team conducting the review confirmed [that] the designs, hardware and test plans for Webb will deliver the fantastic capabilities always envisioned for NASA's next major space observatory."
Meet the James Webb Space Telescope
The James Webb Space Telescope, pegged as the successor to the 20-year-old Hubble Space Telescope, is a next-generation space observatory for exploring deep space phenomena from distant galaxies to nearby planets and stars.
The new observatory is named after the late former NASA administrator James Webb, who led the space agency from 1961 to 1968. The telescope's entire mission, which has cost about $ 1 billion more than expected and taken a few years longer than planned, is estimated to cost about $5 billion.
But scientists have said the delays and overruns pale in comparison to the secrets of the universe the James Webb Space Telescope is expected to unlock.
The telescope is dedicated to studying the universe in infrared, rather than the optical light wavelengths dominated by Hubble. That means that while Webb telescope won't take the traditional photos Hubble has made popular, it will be able to observe older light and see deeper into the universe.
The telescope is designed to provide important clues about the formation of the universe and the evolution of our own solar system, from the first light after the Big Bang to the formation of star systems capable of supporting life on planets like Earth.
The review brought together multiple modeling and analysis tools. Because the observatory is too large for validation by actual testing, complex models are created to show how it will behave during launch and in the space environments in which it will be integrated.
These models are then evaluated against prior test and review results of the observatory's components.
More milestones ahead
The Mission Critical Design Review (MCDR) encompassed all previous design reviews, including the Integrated Science Instrument Module review in March 2009, the Optical Telescope Element review completed in October 2009, and the sun shield review completed in January 2010.
Next, the project schedule will undergo a review within the next few months. Final approval for the spacecraft design, which passed a preliminary review in 2009, is slated for next year.
"This program landmark is the capstone of seven years of intense, focused effort on the part of NASA, Northrop Grumman and our program team members," said David DiCarlo, sector vice president and general manager of Northrop Grumman Space Systems, located in Redondo Beach, Calif. "We have always had high confidence that our observatory design would meet the goals of this pioneering space mission."
While the MCDR approved the telescope design and gave the official go-ahead for manufacturing, hardware development on the mirror segments has been in progress for several years.
This month, ITT Corp. in Rochester, N.Y., demonstrated robotic mirror installation equipment designed to position segments on the backplane. The segments' position will be fine-tuned to tolerances of a fraction of the width of a human hair.
Additionally, the telescope's sun shield moved into its fabrication and testing phase earlier this year.
The three major elements of Webb – the Integrated Science Instrument Module, Optical Telescope Element and the spacecraft itself – will proceed through hardware production, assembly and testing prior to delivery for observatory integration and testing that is currently scheduled to begin in 2012.
The JWST is a joint project of NASA, the European Space Agency and the Canadian Space Agency. The mission is managed by NASA's Goddard Space Flight Center in Greenbelt, Md.
Saturday, May 1, 2010
Skywatching Highlights of 2010
By Joe Rao
SPACE.com Skywatching Columnistposted: 03 January 2010
09:09 am ET
Here are some of the more noteworthy sky events that will take place in 2010. Each will be covered in greater detail as the event approaches. Notes about terminology:
Magnitude: On this scale, smaller numbers represent brighter objects, with the brightest stars and planets represented by negative numbers.
Degrees: Distances in the sky, from our point of view, are measured in degrees. Your fist on an outstretched arm measures about 10 degrees of sky.
Jan. 15 – Solar Eclipse
An annular (ring) eclipse of the sun will take place over parts of Africa, India and China. Because the moon is near apogee (its farthest point from Earth in its orbit) and the Earth has just passed perihelion. So the moon appears much smaller than average, and the sun somewhat larger than average. The moon's circle is only about 92 percent as wide as the sun; so 4 percent of the sun's width shows on each side of the moon. Thus, the annular phase lasts a maximum of 11 minutes and 8 seconds. This is a very long duration indeed: nearly twice as long as some people got to watch last July's total eclipse. According to eclipse expert Fred Espenak of NASA's Goddard Space Flight Center, this is the longest annular eclipse of the 3rd Millennium – its duration will not be exceeded until the year 3043!
Jan. 29 – Mars Close Approach
Mars will be only 61.7 million miles from Earth, closer than it will be again until March 2014. Peaking at magnitude -1.3, Mars will outshine all stars and other planets except Sirius and Jupiter. Opposition to the sun occurs on the 29th. It's during January that Mars begins to become large enough to show, through telescopes, touches of dark surface detail and perhaps occasional white clouds or limb hazes in medium-sized amateur telescopes at the best moments on steady nights when it's fairly high. With time and practice you may see even more. Despite any rumors you might hear, Mars will not be "as big as the full moon" or anywhere near that large. To the naked eye, it will remain a star-like point in the sky.
Feb. 16 – Venus and Jupiter Get Together
Like two ships passing in the twilight, Venus and Jupiter come within about 0.5-degrees of each other this evening. Jupiter is heading toward the sun, while Venus is moving away from the sun. This would normally be a very striking sight, but unfortunately, this conjunction takes place with the two planets just 9 degrees east of the sun – probably too near to it to make a definite sighting. If you would still like to give it a try, then – immediately after sunset – concentrate on that part of the sky just above and to the left of where the sun has just set. Using binoculars sweep around this part of the sky; Venus (magnitude -3.8) will be sitting just below and to the left of Jupiter (magnitude -2.0).
Mar. 28 to Apr. 12: Venus and Mercury Pair Up
The two worlds make for an attractive pair in the west-northwest sky soon after sunset. Between these two dates these two planets are within 5 degrees of each other, Venus appearing to the left and slightly above the dimmer Mercury. On April 3, they will appear closest together, just a little over 3 degrees apart.
Jun. 6: Two Pairs to See
Orange-yellow Mars slides less than a degree north of the bluish star Regulus, a pretty conjunction easily seen in the middle of the evening sky. By then, Mars will have shrunk to a tiny ochre dot even in large telescopes. Also on this night, Jupiter will engage Uranus in the first of a series of three conjunction; there have been only six such triple conjunctions between 1801 and 2200. The last was in 1983 and the next will come during 2037-38.
Jun. 26: Partial Eclipse of the Moon
This eclipse favors the Hawaiian Islands, western Alaska, Australia, New Zealand, eastern portions of Malaysia and Asia. These locations will see the upper half of the moon darkened by the Earth's umbral shadow. Across parts of the eastern U.S., some evidence of the eclipse may become evident as the lighter penumbral shadow casts a "smudge" on the moon's left edge just before moonset.
Jul. 11: Total Eclipse of the Sun
Virtually the entire path of totality falls over water. It will pass within 15 miles of Tahiti (a great cruise ship opportunity) and scores a direct hit on tiny Easter Island, famous for its strange humanoid megalithic statutes. From this speck of land in the middle of the South Pacific Ocean, the sun will be totally eclipsed for 4 minutes 45 seconds. Talk about a photo-op! The only other landfall is near the very end of the totality track, over Patagonia.
Early Aug: Planetary Trio
Mars passes less than a couple of degrees south of Saturn on Aug. 1 and Venus slides just over 3 degrees to the south nine days later; on Aug. 8, the three planets will form what Jean Meeus defines as a "trio," when three planets fit within a circle with a minimum diameter smaller than 5 degrees. These three worlds are all well out (46 to 50 degrees) from the sun but, unfortunately for the Northern Hemisphere, south of it and therefore rather low to the sunset horizon.
source : www.space.com/spacewatch/100103-night-sky-events-2010.html
Saturday, April 24, 2010
Black holes
Black Holes: What Are They?
Black holes are the evolutionary endpoints of stars at least 10 to 15 times as massive as the Sun. If a star that massive or larger undergoes a supernova explosion, it may leave behind a fairly massive burned out stellar remnant. With no outward forces to oppose gravitational forces, the remnant will collapse in on itself. The star eventually collapses to the point of zero volume and infinite density, creating what is known as a “singularity ". Around the singularity is a region where the force of gravity is so strong that not even light can escape. Thus, no information can reach us from this region. It is therefore called a black hole, and its surface is called the “event horizon ".
But contrary to popular myth, a black hole is not a cosmic vacuum cleaner. If our Sun was suddenly replaced with a black hole of the same mass, the Earth's orbit around the Sun would be unchanged. (Of course the Earth's temperature would change, and there would be no solar wind or solar magnetic storms affecting us.) To be "sucked" into a black hole, one has to cross inside the Schwarzschild radius. At this radius, the escape speed is equal to the speed of light, and once light passes through, even it cannot escape.
The Schwarzschild radius can be calculated using the equation for escape speed:
vesc = (2GM/R)1/2
For photons, or objects with no mass, we can substitute c (the speed of light) for Vesc and find the Schwarzschild radius, R, to be
R = 2GM/c2
If the Sun was replaced with a black hole that had the same mass as the Sun, the Schwarzschild radius would be 3 km (compared to the Sun's radius of nearly 700,000 km). Hence the Earth would have to get very close to get sucked into a black hole at the center of our Solar System.
source :
Space Shuttle Challenger
History
Challenger was named after two previous vessels—first, HMS Challenger, a British corvettethat, from 1872 to 1876, was the command ship for the "Challenger expedition," conducting pioneering global marine research.[2]; and second, the Apollo 17 lunar module Challenger,which landed on the Moon in 1972.
Construction
Because of the low production of orbiters, the Space Shuttle program decided to build a vehicle as a Structural Test Article, STA-099, that could later be converted to a flight vehicle. In order to prevent damage during structural testing, qualification tests were performed to a factor of safety of 1.2 times the design limit loads. The qualification tests were used to validate computational models, and compliance with the required 1.4 factor of safety was shown by analysis.
NASA planned to refit the prototype orbiter Enterprise (OV-101), used for flight testing, as the second operational orbiter. However, design changes made during construction of the first orbiter, Columbia (OV-102), would have required extensive rework. Because STA-099's qualification testing prevented damage, NASA found that rebuilding STA-099 as OV-099 would be less expensive than refitting Enterprise.
Challenger (and the orbiters built after it) had fewer tiles in its Thermal Protection System than Columbia. Most of the tiles on the payload bay doors, upper wing surface, and rear fuselage surface were replaced with DuPont white nomex felt insulation. This modification allowed Challenger to carry 2,500 lb (1,100 kg) more payload than Columbia. Challenger was also the first orbiter to have a head-up display system for use in the descent phase of a mission
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