ALICE contributes to NASA's Orion mission

Panos Charitos

On Friday, 5 December, NASA's new Orion spaceship, a capsule built to take humans farther into space than ever before, made its first test flight. The flight marked the first time, since Apollo 17 was launched to the moon in 1972, that a spacecraft built for humans traveled out of low-Earth orbit. Behind the Orion mission there is a flavour of High Energy physics, following in the tradition of synergies between the two fields. More specifically, following the previous success of the Timepix project on the Inernational Space Station (ISS), CERN scientists worked closely with their colleagues at NASA to integrate Timepix into the Orion spaceship.

Pivotal for this effort was Lawrence Pinsky, who started his career in heavy-ion physics at the NA48 and later NA49 fixed target experiments, before joining the ALICE collaboration. Later, he became involved with NASA's APOLLO programme, where he was mainly responsible for heavy particle dosimetry. He worked as a postdoc at NASA's space programme from 1977 to 1990. At that time, he became interested in the simulation of cosmic rays events with the use of GEANT3. His colleagues were also trying to do the same simulations of heavy particles coming from cosmic rays with FLUKA and he joined them. They developed the first Monte Carlo code to simulate transport phenomena of heavy cosmic rays.

In 2006, when NASA invited him to give a series of lectures, he met Michael Campbell. Strangely, even though they worked in neighbouring buildings, they never had the chance to interact before and realize the possibility of using some of the technologies developed at CERN in space programmes. Michael showed MEDIPIX2 to Pinsky, who immediately realized its potential and demonstrated the chip to his colleagues in Houston. During a workshop held by NASA, they advertised it to experts in space radiation and monitoring from all over the world. Various other projects were presented during the workshop, but it was MEDIPIX2 that had the most advantages and outclassed the rest. For the non-experts, the Medipix2 ASIC is a high spatial, high contrast resolving CMOS pixel read-out chip working in single photon counting mode. It can be combined with different semiconductor sensors which convert the X-rays directly into detectable electric signals. This represents a new solution for various X-ray and gamma-ray imaging applications.

NASA and Huston joined MEDIPIX2 in 2007 and worked actively in the development of the new chip. In 2010, during the Workshop on Radiation Monitoring for the International Space Station – an annual meeting to discuss the scientific definition of an adequate radiation monitoring package and its use by the scientific community on the International Space Station (ISS) – a sequence of lectures on MEDIPIX took place. As the funding necessary for the project to continue was approved, more institutes joined the MEDIPIX2 collaboration that later developed the Timepix chip. The chip was finally installed on ISS in October, and started collecting data and sending them to physicists for analysis.

Image of the Timepix USB system in operation on the International Space Station (Image Courtesy of NASA). 

The ISS Timepix detectors gather data to characterize the radiation field as a function of time, taking precise measurements of the spectrum of charge and velocity of particles present inside the spacecraft. These Timepix units are compact USB powered devices, based on Medipix technology and controlled via Flight Software that is deployed on existing ISS Computers. Configuration settings can be modified and uploaded from the ground to adjust data-taking parameters on orbit, and minimal crew time is required for deployment and operation. The flight software displays total dose and dose rate based on LET information compiled from individual particle tracks. In addition, full measurement data is saved and downlinked for further analysis.

Larry Pinsky and undergraduate physics major Christina Stegemoeller, who worked with the group, display the Timepix detector.

Timepix technology could improve or replace older devices by helping scientists analyse the particles and energy spectrum and then calculate the risks of exposure to heavy-ion radiation. This first trip was an opportunity to gain experience on the use of detectors in space, contributing to the development of the next generation of Timepix.

During the test flight, mission controllers extensively checked Orion's systems. The capsule orbited Earth twice, with its second orbit taking it about 5,793 kilometres away from the planet's surface — 14 times farther than the orbit of the International Space Station.

NASA scientists were particularly interested in seeing how the spacecraft behaves during important events, such as separations, once in space. Moreover, they also used the approximately 1,200 sensors aboard Orion to monitor the way the capsule's computers and other technology behave in the harsh space environment. Orion flew through belts of radiation twice (on the way out, and again on the way back to Earth), allowing scientists to see how the spacecraft's computers behave in a high-radiation environment.

NASA has plans for another uncrewed mission in 2017 or 2018, which will be the first flight of Orion with the Space Launch System, a mega rocket, still in development. And in 2021, astronauts will travel with Orion and SLS for the first time to test some of the technologies needed for a trip to Mars. This test flight was just the beginning for Orion.

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