_Alpha_Magnetic_Spectrometer.jpg) AMS-02 on the truss, as viewed during anExpedition 50 spacewalk | |
| Module statistics | |
|---|---|
| Part of | International Space Station |
| Launch date | 16 May 2011 13:56:28 (2011-05-16UTC13:56:28)UTC[1][2][3] |
| Launch vehicle | Space Shuttle Endeavour |
| Berthed | May 19, 2011; 14 years ago (2011-05-19) |
| Mass | 6,717 kg (14,808 lb) |
TheAlpha Magnetic Spectrometer (AMS-02) is aparticle physics experiment module that is mounted on theInternational Space Station (ISS).[4] The experiment is a recognizedCERN experiment (RE1).[5][6] The module is a detector that measuresantimatter incosmic rays; this information is needed to understand the formation of theuniverse and search for evidence ofdark matter.
Theprincipal investigator isNobel laureate particle physicistSamuel Ting. The launch ofSpace Shuttle Endeavour flightSTS-134 carrying AMS-02 took place on May 16, 2011, and thespectrometer was installed on May 19, 2011.[7][8] By April 15, 2015, AMS-02 had recorded over 60 billion cosmic ray events[9] and 90 billion after five years of operation since its installation in May 2011.[10]
In March 2013, Professor Ting reported initial results, saying that AMS had observed over 400,000positrons, with the positron to electron fraction increasing from 10 GeV to 250 GeV. (Later results have shown a decrease in positron fraction at energies over about 275 GeV). There was "no significant variation over time, or any preferred incoming direction. These results are consistent with the positrons originating from the annihilation of dark matter particles in space, but not yet sufficiently conclusive to rule out other explanations." The results have been published inPhysical Review Letters.[11] Additional data are still being collected.[11][12][13][14][15][16][17]
The alpha magnetic spectrometer was proposed in 1995 by theAntimatter Study Group,[18][4] led byMIT particle physicist Samuel Ting, not long after the cancellation of theSuperconducting Super Collider. The original name for the instrument wasAntimatter Spectrometer,[4][18][19] with the stated objective to search for primordial antimatter, with a target resolution of antimatter/matter ≈10−9.[18][19] The proposal was accepted and Ting became theprincipal investigator.[20]
An AMS prototype designatedAMS-01, a simplified version of the detector, was built by the international consortium under Ting's direction and flown into space aboard theSpace Shuttle Discovery onSTS-91 in June 1998. By not detecting anyantihelium, the AMS-01 established an upper limit of 1.1×10−6 for the antihelium-to-heliumflux ratio[21] and proved that the detector concept worked in space. This shuttle mission was the last shuttle flight to theMir space station.
After the flight of the prototype, the group, now labelled theAMS Collaboration, began the development of a full research system designatedAMS-02. This development effort involved the work of 500 scientists from 56 institutions and 16 countries organized underUnited States Department of Energy (DOE) sponsorship.
The instrument which eventually resulted from a long evolutionary process has been called "the most sophisticated particle detector ever sent into space", rivaling very large detectors used at majorparticle accelerators, and 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 a better chance of discovering evidence ofdark matter along with other goals.[22]
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 onstation assembly missionUF4.1, but technical difficulties and shuttle scheduling issues added more delays.[23]
AMS-02 completed final integration and operational testing atCERN inGeneva, Switzerland which included exposure to energeticproton beams generated by the CERNSPS particle accelerator.[24][25] AMS-02 was then shipped byspecialist haulerArchived January 17, 2022, at theWayback Machine[26] toESA'sEuropean Space Research and Technology Centre (ESTEC) facility in theNetherlands, arriving February 16, 2010. Here it underwent thermal vacuum,electromagnetic compatibility, andelectromagnetic interference testing. AMS-02 was scheduled for delivery to theKennedy Space Center inFlorida, United States, in late May 2010.[7] This was, however, postponed to August 26, as AMS-02 underwent final alignment beam testing at CERN.[27][28]
A cryogenic,superconducting magnet system was initially installed on the AMS-02. When theObama administration extended International Space Station operations beyond 2015, the decision was made by AMS management to exchange the AMS-02 superconducting magnet for the non-superconducting magnet previously flown on AMS-01. Although the non-superconducting magnet has a weakerfield strength, its on-orbit operational time at ISS is expected to be 10 to 18 years versus only three years for the superconducting version.[29] In December 2018, it was announced that funding for the ISS had been extended to 2030.[30]
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.[31] After theSpace ShuttleColumbia 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 $2 billion.[32][33]
For several years it was uncertain if AMS-02 would ever be launched because it was not manifested to fly on any of the remainingSpace Shuttle flights.[34] After the 2003Columbia 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.[20] In 2006, NASA studied alternative ways of delivering AMS-02 to the space station, but they all proved to be too expensive.[34]
In May 2008, a bill[35] was proposed to launch AMS-02 to the ISS on an additional shuttle flight in 2010 or 2011.[36] The bill was passed by the full U.S.House of Representatives on June 11, 2008.[37] The bill then went before theSenate Commerce, Science and Transportation Committee where it also passed. It was then amended and passed by the fullSenate on September 25, 2008, and was passed again by the House on September 27, 2008.[38] It was signed into law by PresidentGeorge W. Bush on October 15, 2008.[39][40] The bill authorized NASA to add another space shuttle flight to the schedule before the space shuttle program was discontinued. In January 2009, NASA restored AMS-02 to the shuttle manifest. On August 26, 2010, AMS-02 was delivered fromCERN to theKennedy Space Center by aLockheed C-5 Galaxy jet.[41]
It was delivered to theInternational Space Station on May 19, 2011, as part of station assembly flightULF6 on shuttle flightSTS-134, commanded byMark Kelly.[42] 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 theIntegrated Truss Structure, on USS-02, thezenith side of theS3-element of the truss.[43]
_Luca_Parmitano_carries_the_new_thermal_pump_system.jpg)
By April 2017, only one of the 4 redundant coolant pumps for the silicon trackers was fully working, and repairs were being planned, despite AMS-02 not being designed to be serviced in space.[44][45] By 2019, the last pump was being operated intermittently.[45] In November 2019, after four years of planning,[45] special tools and equipment were sent to the ISS for in-situ repairs requiring fourEVAs.[46] Liquid carbon dioxide coolant was also replenished.[45]
The repairs were conducted by the ISS crew ofExpedition 61. The spacewalkers were the expedition commander andESA astronautLuca Parmitano, andNASA astronautAndrew Morgan. Both of them were assisted by NASA astronautsChristina Koch andJessica Meir who operated theCanadarm2 robotic arm from inside the Station. The spacewalks were described as the "most challenging since [the last]Hubble repairs".[47]
The entire spacewalk campaign was a central feature of theDisney+ docuseries Among The Stars.
The first spacewalk was conducted on November 15, 2019. The spacewalk began with the removal of the debris shield covering AMS, which was jettisoned to burn up in the atmosphere. The next task was to install three handrails in the vicinity of AMS to prepare for the next spacewalks and remove zip ties on the AMS' vertical support strut. This was followed by the "get ahead" tasks: Parmitano removed the screws from a carbon-fibre cover under the insulation and passed the cover to Morgan to jettison. The spacewalkers also removed the vertical support beam cover. The duration of the spacewalk was 6 hours and 39 minutes.[48][49]
The second spacewalk was conducted on November 22, 2019. Parmitano and Morgan cut a total of eight stainless steel tubes, including one that vented the remaining carbon dioxide from the old cooling pump. The crew members also prepared a power cable and installed a mechanical attachment device in advance of installing the new cooling system. The duration of the spacewalk was 6 hours and 33 minutes.[50]
The third spacewalk was conducted on December 2, 2019. The crew completed the primary task of installing the upgraded cooling system, called the upgraded tracker thermal pump system (UTTPS), completed the power and data cable connections for the system, and connected all eight cooling lines from the AMS to the new system. The intricate connection work required making a clean cut for each existing stainless steel tube connected to the AMS, then connecting it to the new system throughswaging.[51]
The astronauts also completed an additional task to install an insulating blanket on thenadir side of the AMS to replace the heat shield and blanket they removed during the first spacewalk to begin the repair work. The flight control team on Earth initiated power-up of the system and confirmed its reception of power and data.[51]
The duration of the spacewalk was 6 hours and 2 minutes.[51]
The fourth spacewalk was conducted on January 25, 2020. The astronauts conducted leak checks for the cooling system on the AMS and opened a valve to pressurize the system. Parmitano found a leak in one of the AMS's cooling lines. The leak was fixed during the spacewalk. Preliminary testing showed the AMS was responding as expected.[52][53]
Ground teams worked to fill the new AMS thermal control system withcarbon dioxide, allowed the system to stabilize, and powered on the pumps to verify and optimize their performance. The tracker, one of several detectors on the AMS, began collecting science data again before the end of the week after the spacewalk.[52]
The astronauts also completed an additional task to remove degraded lens filters on two high-definition video cameras.[52]
The duration of the spacewalk was 6 hours and 16 minutes.[52]
About 1,000 cosmic rays are recorded by the instrument per second, generating about oneGB/s of data. This data is filtered and compressed to about 300 kbit/s for download to the operation center POCC at CERN.
A mockup of the machine is present inside the operations center at CERN.
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:[56]
The AMS-02 uses 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 measuringcosmic rays.[43]
Experimental evidence indicates thatour galaxy is made ofmatter; however, scientists believe there are about 100–200 billion galaxies in the observable Universe and some versions of theBig 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 anantihelium 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 was designed to search with a sensitivity of 10−9,[19] an improvement of three orders of magnitude overAMS-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, ordark energy, which makes up the balance. The exact nature of both still is unknown. One of the leading candidates for dark matter is theneutralino. 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 backgroundpositron,antiproton, orgamma ray flux could signal the presence of neutralinos or other dark matter candidates, but would need to be distinguished from poorly knownconfounding astrophysical signals.
Six types ofquarks (up,down,strange,charm,bottom andtop) 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 asstrangelets. 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 during transit is a significant obstacle tosending humans 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 operates on theISS, 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 fromprotons toiron. In addition to understanding the radiation protection required for astronauts duringinterplanetary flight, this data will allow the interstellar propagation and origins of cosmic rays to be identified.
 | This section needs to beupdated. Please help update this article to reflect recent events or newly available information.(April 2024) |
By late 2016, it was reported that AMS-02 had observed over 90 billion cosmic rays.[10]
In February 2013, Samuel Ting reported that in its first 18 months of operation AMS had recorded 25 billion particle events including nearly eight billion fast electrons and positrons.[57] The AMS paper reported the positron-electron ratio in the mass range of 0.5 to 350GeV, providing evidence about theweakly interacting massive particle (WIMP) model of dark matter.
On March 30, 2013, the first results from the AMS experiment were announced by theCERN press office.[11][12][13][14][15][16][58] The first physics results were published inPhysical Review Letters on April 3, 2013.[11] A total of 6.8 millionpositron andelectron events were collected in the energy range from 0.5 to 350 GeV. The positron fraction (of the total electron plus positron events) steadily increased from energies of 10 to 250 GeV, but the slope decreased by an order of magnitude above 20 GeV, even though the fraction of positrons still increased. There was no fine structure in the positron fraction spectrum, and noanisotropies were observed. The accompanyingPhysics Viewpoint[59] said that "The first results from the space-borne Alpha Magnetic Spectrometer confirm an unexplained excess of high-energy positrons in Earth-bound cosmic rays." These results are consistent with the positrons originating from the annihilation of dark matter particles in space, but not yet sufficiently conclusive to rule out other explanations. Ting said "Over the coming months, AMS will be able to tell us conclusively whether these positrons are a signal for dark matter, or whether they have some other origin."[60]
On September 18, 2014, new results with almost twice as much data were presented in a talk at CERN and published inPhysical Review Letters.[61][62][63] A new measurement of positron fraction up to 500 GeV was reported, showing that positron fraction peaks at a maximum of about 16% of total electron+positron events, around an energy of 275 ± 32 GeV. At higher energies, up to 500 GeV, the ratio of positrons to electrons begins to fall again.
The AMS team presented for 3 days at CERN in April 2015, covering new data on 300 million proton events and helium flux.[64] It revealed in December 2016 that it had discovered a few signals consistent with antihelium nuclei amidst several billion helium nuclei. The result remains to be verified, and the team is currently trying to rule out possible contamination.[65]
A study from 2019, using data from NASA'sFermi Gamma-ray Space Telescope discovered a halo around the nearbypulsarGeminga. The accelerated electrons and positrons collide with nearby starlight. The collision boosts the light to much higher energies. Geminga alone could be responsible for as much as 20% of the high-energy positrons seen by the AMS-02 experiment.[66] The AMS-02 on the ISS has, as of 2021, recorded eight events that seem to indicate the detection of antihelium-3.[67][68]
Over a twelve-year period aboard the ISS, the AMS has accumulated a dataset of more than 230 billion cosmic rays, spanning energies reaching multi-TeV levels. The precise measurements obtained by the magnetic spectrometer enable data presentation with an accuracy approaching ~1%. Particularly significant is thehigh-energy data regarding elementary particles such as electrons, positrons, protons, and antiprotons, which presents challenges to theoretical frameworks. Additionally, observations of nuclei andisotopes reveal energy dependencies that deviate from theoretical predictions. In a presentation at the 2024 APS April meeting, the AMS collaboration argued that the dataset they have collected necessitates a reevaluation of existing models of the cosmos.[69]
This article incorporatespublic domain material fromAMS project page.National Aeronautics and Space Administration.
{{cite web}}: CS1 maint: archived copy as title (link)
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