Alpha Magnetic Spectrometer


The Alpha Magnetic Spectrometer is a particle physics experiment module that is mounted on the International Space Station. The experiment is a recognized CERN experiment. 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.
The principal investigator is Nobel laureate particle physicist Samuel Ting. The launch of flight STS-134 carrying AMS-02 took place on May 16, 2011, and the spectrometer was installed on May 19, 2011. By April 15, 2015, AMS-02 had recorded over 60 billion cosmic ray events and 90 billion after five years of operation since its installation in May 2011.
In March 2013, Professor Ting reported initial results, saying that AMS had observed over 400,000 positrons, with the positron to electron fraction increasing from 10 GeV to 250 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 in Physical Review Letters. Additional data are still being collected.

History

The alpha magnetic spectrometer was proposed in 1995 by the Antimatter Study Group, led by MIT particle physicist Samuel Ting, not long after the cancellation of the Superconducting Super Collider. The original name for the instrument was Antimatter Spectrometer, with the stated objective to search for primordial antimatter, with a target resolution of antimatter/matter ≈10−9. The proposal was accepted and Ting became the principal investigator.

AMS-01

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 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 and proved that the detector concept worked in space. This shuttle mission was the last shuttle flight to the Mir space station.

AMS-02

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 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 major particle 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 of dark matter along with other goals.
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- plan was to deliver AMS-02 to the ISS by space shuttle in 2005 on station assembly mission , but technical difficulties and shuttle scheduling issues added more delays.
AMS-02 completed final integration and operational testing at CERN in Geneva, Switzerland which included exposure to energetic proton beams generated by the CERN SPS particle accelerator. AMS-02 was then shipped by to ESA's European Space Research and Technology Centre facility in the Netherlands, arriving February 16, 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, United States, in late May 2010. This was, however, postponed to August 26, as AMS-02 underwent final alignment beam testing at CERN.
A cryogenic, superconducting magnet system was initially installed on the AMS-02. When the Obama 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 weaker field strength, its on-orbit operational time at ISS is expected to be 10 to 18 years versus only three years for the superconducting version. In December 2018, it was announced that funding for the ISS had been extended to 2030.
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. 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.

Installation on the International Space Station

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. 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. In 2006, NASA studied alternative ways of delivering AMS-02 to the space station, but they all proved to be too expensive.
In May 2008, a bill was proposed to launch AMS-02 to the ISS on an additional shuttle flight in 2010 or 2011. The bill was passed by the full U.S. House of Representatives on June 11, 2008. 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 September 25, 2008, and was passed again by the House on September 27, 2008. It was signed into law by President George W. Bush on October 15, 2008. 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 from CERN to the Kennedy Space Center by a Lockheed C-5 Galaxy jet.
It 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. 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.

Operations, condition and repairs

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. By 2019, the last pump was being operated intermittently. In November 2019, after four years of planning, special tools and equipment were sent to the ISS for in-situ repairs requiring four EVAs. Liquid carbon dioxide coolant was also replenished.
The repairs were conducted by the ISS crew of Expedition 61. The spacewalkers were the expedition commander and ESA astronaut Luca Parmitano, and NASA astronaut Andrew Morgan. Both of them were assisted by NASA astronauts Christina Koch and Jessica Meir who operated the Canadarm2 robotic arm from inside the Station. The spacewalks were described as the "most challenging since Hubble repairs".
The entire spacewalk campaign was a central feature of the Disney+ docuseries Among The Stars.

First spacewalk

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.

Second spacewalk

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.

Third spacewalk

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, 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 through swaging.
The astronauts also completed an additional task to install an insulating blanket on the nadir 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.
The duration of the spacewalk was 6 hours and 2 minutes.

Fourth spacewalk

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.
Ground teams worked to fill the new AMS thermal control system with carbon 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.
The astronauts also completed an additional task to remove degraded lens filters on two high-definition video cameras.
The duration of the spacewalk was 6 hours and 16 minutes.