In 2013, balloons were launched by NASA near the North and South poles to study X-rays in Earth’s atmosphere

In 2013, balloons were launched by NASA near the North and South poles to study X-rays in Earth’s atmosphere. The work was part of a balloon-based NASA mission called the Balloon Array for Radiation-belt Relativistic Electron Losses, or BARREL. The mission focused on X-rays produced when electrons from the radiation belts around Earth move down into the atmosphere. These electrons can enter the atmosphere from the Van Allen Belts, which are regions of charged particles held around Earth by its magnetic field.

BARREL used balloons to measure the X-rays and other signals linked to these electrons. The measurements helped scientists study how radiation moves between space and Earth’s atmosphere. The information also supports work on protecting satellites that operate around Earth.

What was the BARREL mission?

The Balloon Array for Radiation-belt Relativistic Electron Losses was a balloon mission designed to study electron precipitation and X-rays in Earth’s atmosphere. The mission type was a balloon-based campaign. Its destinations included Antarctica and Sweden. The airborne campaigns took place from 2013 through 2020.

The main objective was to study X-rays in Earth’s atmosphere. The X-rays examined by BARREL are connected to electrons that fall, or precipitate, from the Van Allen Belts into the atmosphere. Scientists study this process to understand radiation belts and how they interact with the atmosphere.

Radiation belts are important for space missions because spacecraft and satellites can pass through regions containing energetic particles. Understanding how electrons move through these regions can help scientists improve knowledge of the space environment around Earth.

In 2013, balloons were launched near the North and South poles

BARREL began in 2013 with balloon campaigns over Antarctica. Antarctica is the southernmost continent and contains the South Pole. For the Antarctic campaigns, balloons were launched from the South African Antarctic Station, known as SANAE IV. They were also launched from the British Halley VI Research Station.

The balloons carried instruments that collected measurements while they remained in the atmosphere. Several balloons could operate at the same time during a campaign. The Antarctic campaigns allowed scientists to observe electrons moving into Earth’s atmosphere near the South Pole. These measurements were used along with observations from spacecraft studying the radiation belts.

The mission later moved to the Northern Hemisphere. In Sweden, BARREL balloons were launched from the Esrange Space Center above the Arctic Circle. The launch site was near Kiruna, Sweden’s northernmost town.

When did the primary BARREL mission end?

The primary BARREL mission ended after the final balloon was sent over Sweden on August 30, 2016. The mission did not end all BARREL-related balloon activity at that point. Recovered BARREL payloads were later used on three additional flights as targets of opportunity.

One of these flights was a piggyback flight involving the HIWIND payload from Sweden in 2018. Two other flights used ultra-long-duration balloons launched from Antarctica. One took place in December 2018, while another took place in 2019.

These flights lasted for different periods. The 2018 flight lasted 70 days. The 2019 flight lasted 100 days. This extended the use of BARREL instruments and provided additional measurements after the primary mission had ended.

How BARREL worked with NASA spacecraft?

BARREL was designed to add to observations made by NASA’s Van Allen Probes spacecraft. The Van Allen Probes were launched on August 30, 2012. Their mission focused on studying Earth’s radiation belts and the particles within them.

BARREL provided measurements from balloons in the atmosphere, while the Van Allen Probes collected measurements from space. Scientists could compare these observations to study how electrons moved from the radiation belts into the atmosphere.

The balloon measurements were planned around the position of the spacecraft. Scientists wanted the balloon array and spacecraft to be magnetically connected, or conjugate, so that measurements from both locations could be compared. This approach gave researchers information from different parts of the same space environment.

BARREL also worked with the MMS mission

The BARREL team also coordinated its work with NASA’s Magnetospheric Multiscale mission, known as MMS. MMS studies how the magnetic fields of the Sun and Earth connect and disconnect. This process is linked to changes in the space environment and the movement of energy and particles.

Coordinating BARREL observations with MMS gave scientists another way to study the movement of charged particles and electromagnetic energy around Earth. The different missions focused on different parts of the same system. Together, their observations helped scientists examine how activity in space can affect particles around Earth and their movement toward the atmosphere.

What instruments did the BARREL balloons carry?

The BARREL balloons carried X-ray instruments to measure radiation produced when energetic electrons entered the atmosphere. Some of the balloons also carried instruments built by students. These instruments provided additional measurements. One student-built instrument was designed to study the total electron content of Earth’s ionosphere.

The ionosphere is a layer containing charged particles that overlaps with Earth’s neutral atmosphere. Measuring its electron content can provide information about changes in the upper atmosphere. Another student-built instrument measured low-frequency electromagnetic waves.

These waves are connected to the movement of electrons in space. They can help scatter electrons from space into Earth’s atmosphere. Measuring these waves gave scientists information about another process involved in electron precipitation.

Why were several balloons used together?

During each BARREL campaign, several long-duration balloons were kept in the air at the same time. The balloons could remain aloft over a period of about one month during a campaign. Operating several balloons together created an array of measurements across different locations. The purpose was to measure electron precipitation and help estimate the total number of electrons lost from the radiation belts.

Scientists also planned observations for periods when the balloon array was conjugate with spacecraft. This allowed direct comparison between balloon measurements and spacecraft observations. The combination of balloon and spacecraft data helped researchers connect events observed in space with the X-rays and other signals measured in Earth’s atmosphere.

Who led the BARREL mission?

Dr. Robyn Millan of Dartmouth College was the principal investigator for the BARREL mission. Her role involved leading the scientific work associated with the mission. BARREL brought together balloon observations, spacecraft measurements and instrument data to study electron precipitation. The mission also included student-built instruments, which allowed students to take part in collecting measurements related to Earth’s ionosphere and electromagnetic waves.

Why does the BARREL mission matter?

BARREL provided measurements of a process that connects Earth’s radiation belts with the atmosphere. Energetic electrons can move out of the Van Allen Belts and enter the atmosphere. When they do, they can produce X-rays. Measuring these X-rays gives scientists a way to study electron precipitation. The information can improve understanding of Earth’s radiation environment. This is relevant to satellites because radiation can affect spacecraft systems and instruments.

BARREL therefore added another source of information to the study of the Van Allen Belts. Its balloon measurements complemented the work of the Van Allen Probes and were coordinated with observations from MMS. The mission also showed how balloons operating near the North and South poles can provide measurements that connect events in space with changes and signals observed in Earth’s atmosphere.

Key mission details

• Mission name: Balloon Array for Radiation-belt Relativistic Electron Losses (BARREL)
• Mission type: Balloon
• Destinations: Antarctica and Sweden
• Airborne campaigns: 2013–2020
• Main objective: Study X-rays in Earth’s atmosphere
• Antarctic launch sites: SANAE IV and Halley VI Research Station
• Swedish launch site: Esrange Space Center near Kiruna
• Primary mission end: August 30, 2016
• Additional 2018 flight: HIWIND piggyback flight from Sweden
• Additional Antarctic flights: December 2018 and 2019
• Flight duration: 70 days in 2018 and 100 days in 2019
• Related spacecraft: NASA’s Van Allen Probes and Magnetospheric Multiscale mission
• Principal investigator: Dr. Robyn Millan, Dartmouth College