| AMS-02 patch | |
| Alpha magnetic spectrometer | |
| Organization | AMS Collaboration |
|---|---|
| Mission Type | Cosmic Ray |
| Host Satellite | International Space Station |
| Launch | 16 May 2011 8:56:28 AM EDT[1][2][3] (13:56:28 UTC) |
| Launch vehicle | Space Shuttle Endeavour |
| Launch site | Kennedy Space Center Launch Pad 39A |
| Mission duration | 10 years or more[2] |
| Mass | 14,809 lb (6,717 kg |
| Max length | |
| Power consumption | 2000–2500 watts |
| Webpage | AMS-02 homepage |
| Orbital elements (ISS) | |
| Inclination | 51.6 degrees |
| Orbit | LEO |
| Min altitude | 341 km (184 nmi) |
| Max altitude | 353 km (191 nmi) |
| Period | ~91 minutes |
The Alpha Magnetic Spectrometer, also designated AMS-02, is a particle physics experiment module that is mounted on the International Space Station. It is designed to search for various types of unusual matter by measuring cosmic rays. Its experiments will help researchers study the formation of the Universe and search for evidence of dark matter as well as investigate antimatter. The principal investigator is Nobel laureate particle physicist Samuel Ting. After final testing at ESA's European Space Research and Technology Centre (ESTEC) facility in the Netherlands,[4] delivery to the Kennedy Space Center in Florida took place on 26 August 2010.[5] The launch of Space Shuttle Endeavour flight STS-134 carrying AMS-02 took place on 16 May 2011, and the spectrometer was installed on 19 May 2011.[6][7]
Contents |
The alpha magnetic spectrometer was proposed in 1995 by MIT particle physicist Samuel Ting, not long after the cancellation of the Superconducting Super Collider. The proposal was accepted and Ting became the principal investigator.[8]
An AMS prototype designated AMS-01, a simplified version of the detector, was built by the international consortium under Ting's direction and flown into space aboard the Space Shuttle Discovery on STS-91 in June 1998. By not detecting any antihelium the AMS-01 established an upper limit of 1.1×10−6 for the antihelium to helium flux ratio[9] and proved that the detector concept worked in space. This shuttle mission was the last shuttle flight to the Mir Space Station. The photograph was taken from Mir.[10]
After the flight of the prototype, Ting began the development of a full research system designated AMS-02. This development effort involved the work of 500 scientists from 56 institutions and 16 countries organized under United States Department of Energy (DOE) sponsorship.
The instrument which eventually resulted from a long evolutionary process is "the most sophisticated particle detector ever sent into space", rivaling very large detectors used at major particle accelerators, and it has cost four times as much as any of its ground-based counterparts. Its goals have also evolved and been refined over time. As built it is a more comprehensive detector, which has (among other goals) a better chance of discovering evidence of dark matter.[11]
The power requirements for AMS-02 were thought to be too great for a practical independent spacecraft. So AMS-02 was designed to be installed as an external module on the International Space Station and use power from the ISS. The post-Space Shuttle Columbia plan was to deliver AMS-02 to the ISS by space shuttle in 2005 on station assembly mission UF4.1, but technical difficulties and shuttle scheduling issues have added more delays.[10]
AMS-02 successfully completed final integration and operational testing at CERN in Geneva, Switzerland which included exposure to powerful nuclear particle beams generated by the CERN particle accelerators.[12] AMS-02 was then shipped to ESA's European Space Research and Technology Centre (ESTEC) facility in the Netherlands where it arrived 16 February 2010. Here it underwent thermal vacuum, electromagnetic compatibility and electromagnetic interference testing. AMS-02 was scheduled for delivery to the Kennedy Space Center in Florida, U.S.A. in late May 2010.[6] This was however postponed to August 26, as AMS-02 underwent final alignment beam testing at CERN.[13][14]
A cryogenic, superconducting magnet system was developed for the AMS-02. This was a critical technology, enabling a high sensitivity needed to achieve mission objectives.[15] Late in its development, poorly understood anomalous heating in the cryogenic magnet system was discovered. The anomalous heating would place additional demand on the cryogenic cooling. This characteristic significantly reduced the original system design lifetime and contributed to a decision to abandon the cryogenic system in favor of a previously developed but less capable permanent magnet system.[16]
With Obama administration plans to extend International Space Station operations beyond 2015, the decision has been made by AMS management to exchange the original AMS-02 superconducting magnet for the non-superconducting magnet previously flown on AMS-01. Although the non-superconducting magnet has a weaker field strength, its on-orbit operational time at ISS is expected to be 10 to 18 years versus only 3 years for the superconducting version. This additional data gathering time has been deemed more important than higher experiment sensitivity, despite the fact that the abandoned cryogenic system was originally described as critical technology to mission success.[17] Whether the ISS will operate long enough for AMS to take full advantage of its extended lifetime is also unclear.
Activities relating to payload integration, launch, and deployment of AMS-02 are managed by the Alpha Magnetic Spectrometer Project Office at NASA's Johnson Space Center in Houston, Texas, U.S.A.
AMS-02 was delivered to the International Space Station on May 19, 2011 as part of station assembly flight ULF6 on shuttle flight STS-134, commanded by Mark Kelly.[18] It was removed from the shuttle cargo bay using the shuttle's robotic arm and handed off to the station's robotic arm for installation. AMS-02 is mounted on top of the Integrated Truss Structure, on USS-02, the zenith side of the S3-element of the truss.[19]
In 1999, after the successful flight of AMS-01, the total cost of the AMS program was estimated to be $33 million, with AMS-02 planned for flight to the ISS in 2003.[22] After the Space Shuttle Columbia disaster in 2003, and after a number of technical difficulties with the construction of AMS-02, the cost of the program ballooned to an estimated $1.5 billion.[23]
The cost of the program was criticized heavily during the period when it appeared that it would not be flown,[8] and remains controversial.
The detector module consists of a series of detectors that are used to determine various characteristics of the radiation and particles as they pass through. Characteristics are determined only for particles that pass through from top to bottom. Particles that enter the detector at any other angles are rejected. From top to bottom the subsystems are identified as:[24]
The AMS-02 will use the unique environment of space to advance knowledge of the Universe and lead to the understanding of its origin by searching for antimatter, dark matter and measuring cosmic rays.[19]
Experimental evidence indicates that our galaxy is made of matter; however, scientists believe there are about 100–200 billion galaxies in the Universe and some versions of the Big Bang theory of the origin of the Universe require equal amounts of matter and antimatter. Theories that explain this apparent asymmetry violate other measurements. Whether or not there is significant antimatter is one of the fundamental questions of the origin and nature of the Universe. Any observations of an antihelium nucleus would provide evidence for the existence of antimatter in space. In 1999, AMS-01 established a new upper limit of 10−6 for the antihelium/helium flux ratio in the Universe. AMS-02 will search with a sensitivity of 10−9, an improvement of three orders of magnitude over AMS-01, sufficient to reach the edge of the expanding Universe and resolve the issue definitively.
The visible matter in the Universe, such as stars, adds up to less than 5 percent of the total mass that is known to exist from many other observations. The other 95 percent is dark, either dark matter, which is estimated at 20 percent of the Universe by weight, or dark energy, which makes up the balance. The exact nature of both still is unknown. One of the leading candidates for dark matter is the neutralino. If neutralinos exist, they should be colliding with each other and giving off an excess of charged particles that can be detected by AMS-02. Any peaks in the background positron, antiproton, or gamma ray flux could signal the presence of neutralinos or other dark matter candidates, but would need to be distinguished from poorly known confusing astrophysical signals.
Six types of quarks (up, down, strange, charm, bottom and top) have been found experimentally; however, the majority of matter on Earth is made up of only up and down quarks. It is a fundamental question whether there exists stable matter made up of strange quarks in combination with up and down quarks. Particles of such matter are known as strangelets. Strangelets might have extremely large mass and very small charge-to-mass ratios. It would be a totally new form of matter. AMS-02 may determine whether this extraordinary matter exists in our local environment.
Cosmic radiation is a significant obstacle to a manned space flight to Mars. Accurate measurements of the cosmic ray environment are needed to plan appropriate countermeasures. Most cosmic ray studies are done by balloon-borne instruments with flight times that are measured in days; these studies have shown significant variations. AMS-02 will be operative on the ISS for at least 3 years, gathering a large amount of accurate data and allowing measurements of the long term variation of the cosmic ray flux over a wide energy range, for nuclei from protons to iron. In addition to the understanding the radiation protection required for manned interplanetary flight, this data will allow the interstellar propagation and origins of cosmic rays to be identified.
According to its original design, AMS-02 was to be returned to Earth on a shuttle flight after its superfluid helium supply (used to cool the superconducting magnet solenoid) was exhausted. Because the superconducting system could not be made to work reliably, lower sensitivity non-superconducting magnets were employed, eliminating the need for superfluid helium. The experiment additionally is too large and heavy to return to Earth after the retirement of the shuttle, and the plan is therefore now to leave the unit in place on the space station exterior.
For several years it was uncertain if AMS-02 would ever be launched because it was not manifested to fly on any of the remaining Space Shuttle flights.[25] After the 2003 Columbia disaster NASA decided to reduce shuttle flights and retire the remaining shuttles by 2010. A number of flights were removed from the remaining manifest including the flight for AMS-02.[8] In 2006 NASA studied alternative ways of delivering AMS-02 to the space station, but they all proved to be too expensive.[25]
In May 2008 a bill was proposed to launch AMS-02 to ISS on an additional shuttle flight in 2010 or 2011.[26] The bill was passed by the full House of Representatives on 11 June 2008.[27] The bill then went before the Senate Commerce, Science and Transportation Committee where it also passed. It was then amended and passed by the full Senate on 25 September 2008, and was passed again by the House on 27 September 2008.[28] It was signed by President George W. Bush on 15 October 2008.[29][30] The bill authorized NASA to add another space shuttle flight to the schedule before the space shuttle program is discontinued. In January 2009 NASA restored AMS-02 to the shuttle manifest. On 26 August 2010, AMS-02 was delivered from CERN to the Kennedy Space Center by a Lockheed C-5 Galaxy,[31] and it was launched into space on STS-134 on 16 May 2011.
This article incorporates public domain material from websites or documents of the NASA.
|
||||||||