The Alpha Magnetic Spectrometer (AMS-02) is a particle physics experiment module that is mounted on the International Space Station (ISS).

[5][6] The module is a detector that measures antimatter in cosmic rays; this information is needed to understand the formation of the universe and search for evidence of dark matter.

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."

[11][12][13][14][15][16][17] The alpha magnetic spectrometer was proposed in 1995 by the Antimatter Study Group,[18][4] led by MIT particle physicist Samuel Ting, not long after the cancellation of the Superconducting Super Collider.

By not detecting any antihelium, the AMS-01 established an upper limit of 1.1×10−6 for the antihelium-to-helium flux ratio[21] and proved that the detector concept worked in space.

After the flight of the prototype, the group, now labelled the AMS Collaboration, 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.

[24][25] AMS-02 was then shipped by specialist hauler [26] to ESA's European Space Research and Technology Centre (ESTEC) facility in the Netherlands, arriving February 16, 2010.

[31] 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 $2 billion.

[43] 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.

[45] In November 2019, after four years of planning,[45] special tools and equipment were sent to the ISS for in-situ repairs requiring four EVAs.

Both of them were assisted by NASA astronauts Christina Koch and Jessica Meir who operated the Canadarm2 robotic arm from inside the Station.

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 flight control team on Earth initiated power-up of the system and confirmed its reception of power and data.

[52] The astronauts also completed an additional task to remove degraded lens filters on two high-definition video cameras.

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 measuring cosmic rays.

AMS-02 was designed to search with a sensitivity of 10−9,[19] an improvement of three orders of magnitude over AMS-01, sufficient to reach the edge of the expanding Universe and resolve the issue definitively.

AMS-02 operates on the ISS, 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 understanding the radiation protection required for astronauts during interplanetary flight, this data will allow the interstellar propagation and origins of cosmic rays to be identified.

[57] The AMS paper reported the positron-electron ratio in the mass range of 0.5 to 350 GeV, providing evidence about the weakly interacting massive particle (WIMP) model of dark matter.

The accompanying Physics 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.

The AMS team presented for 3 days at CERN in April 2015, covering new data on 300 million proton events and helium flux.

[65] A study from 2019, using data from NASA's Fermi Gamma-ray Space Telescope discovered a halo around the nearby pulsar Geminga.

[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 the high-energy data regarding elementary particles such as electrons, positrons, protons, and antiprotons, which presents challenges to theoretical frameworks.

The extensive dataset collected by AMS necessitates a reevaluation of existing models of the cosmos, as discussed at the APS April meeting in 2024.