Beginner

Two Russian astronauts, called cosmonauts, went outside the International Space Station on May 27. The International Space Station, or ISS, is a large laboratory that travels around the Earth in space. When astronauts go outside a space station, it is called a spacewalk.

The two cosmonauts are named Sergey Kud-Sverchkov and Sergei Mikaev. They wore special spacesuits to protect them from the cold and emptiness of space. Their spacewalk lasted about five hours. This was the 279th time someone has walked in space near the ISS.

Their main job was to install a special science experiment on the outside of the space station. The experiment is called a solar terahertz sensor. It will study the Sun by measuring a type of energy called terahertz radiation. Scientists want to learn more about powerful solar events called flares.

Solar flares are big explosions on the Sun that send energy and particles toward Earth. They can affect satellites and power systems on Earth. By measuring what happens during a flare, scientists can better understand the Sun and protect our technology.

cosmonaut

a Russian astronaut; a person trained by Russia to travel and work in space

spacewalk

when an astronaut or cosmonaut goes outside a spacecraft to work in space

International Space Station

a large spacecraft that orbits Earth and is home to astronauts from many countries who do science experiments

spacesuit

a special protective suit that allows a person to survive in space

solar flare

a sudden powerful explosion on the Sun's surface that releases energy and particles into space

radiation

energy that travels in waves or particles through space or matter

satellite

a machine that orbits Earth, used for communication, weather forecasting, and navigation

experiment

a scientific test done to learn something new or to check if an idea is correct

Elementary

Expedition 74 commander Sergey Kud-Sverchkov and flight engineer Sergei Mikaev exited the International Space Station on May 27, 2026, for a five-hour spacewalk that began at 10:15 a.m. Eastern time. NASA broadcast the excursion live on NASA Plus and YouTube. This was Kud-Sverchkov's second career spacewalk and Mikaev's very first. To tell them apart, mission controllers used a simple color code: Kud-Sverchkov wore a suit with red stripes and Mikaev wore one with blue stripes.

The spacewalk was the 279th in support of the ISS since the station began operations. The cosmonauts' main task was to install a new solar-terahertz experiment on the exterior of the Zvezda service module, which is the Russian-built core living and working section of the space station. The experiment contains specialized sensors designed to measure the Sun's terahertz electromagnetic radiation, a range of energy between radio waves and infrared light.

Scientists are particularly interested in terahertz emissions from the Sun during solar flares and coronal mass ejections, or CMEs. A CME is a large cloud of magnetized plasma that the Sun sometimes releases into space. When a CME reaches Earth, it can disrupt GPS signals, satellite communications, and electrical power grids. The new experiment will help scientists predict these space weather events more accurately.

If time allowed, the cosmonauts were also asked to photograph the Kurs rendezvous antennas on a recently docked cargo spacecraft called Progress 94. Those antennas had failed to deploy correctly after the spacecraft launched in March 2026, and mission planners wanted visual confirmation of their current position before deciding whether to attempt a mechanical repair on a future spacewalk.

Expedition 74

the current long-duration mission aboard the International Space Station, identified by a sequential number

Zvezda module

the Russian-built core living and working section of the International Space Station, launched in 2000

terahertz radiation

electromagnetic energy in the frequency range between radio waves and infrared light, used in imaging and scientific research

coronal mass ejection

a large, fast-moving cloud of magnetized plasma released from the Sun's outer atmosphere that can affect Earth's technology

plasma

a high-energy state of matter consisting of electrically charged particles, found in the Sun and in lightning

space weather

conditions in near-Earth space driven by the Sun's activity, which can affect satellites, power grids, and communications

Kurs system

a Russian automated radar docking system used by Soyuz and Progress spacecraft to approach and dock with the ISS

rendezvous antenna

a communication device that helps a spacecraft navigate and align itself precisely for docking with another spacecraft

Intermediate

Expedition 74 commander Sergey Kud-Sverchkov and flight engineer Sergei Mikaev egressed through the Pirs docking compartment airlock at 10:15 a.m. EDT on May 27, 2026, beginning the 279th spacewalk in support of ISS assembly and maintenance. The excursion, broadcast live on NASA Plus and the agency's YouTube channel, was scheduled for approximately five hours. Kud-Sverchkov, wearing the Orlan-MKS suit marked with red leg stripes, was on his second career extravehicular activity, while Mikaev, wearing the suit with blue stripes, executed his first.

The primary objective was mounting a new science payload, designated STEHel-T (Solar Terahertz Emission Heliolab), on the exterior of the Zvezda service module's Poisk-facing panel. STEHel-T contains a broadband terahertz receiver covering the 0.1 to 10 THz spectral range and a narrowband heterodyne detector optimized for the 0.55 THz water-vapor absorption feature that acts as a diagnostic of the solar chromosphere. Scientific interest is centered on characterizing the terahertz signature of impulsive-phase solar flares and the prompt electromagnetic emission component that precedes the main CME plasma arrival by eight to twelve minutes, since this early warning window could extend operational lead times for satellite operators and power grid managers.

Solar terahertz research has historically been constrained by atmospheric absorption of terahertz frequencies: the same water-vapor bands that make terahertz useful for solar diagnostics also prevent ground-based observatories from making broadband measurements below approximately 10 kilometers altitude. Mounting STEHel-T on the ISS, which orbits at a mean altitude of approximately 408 kilometers, places the instrument entirely above the absorbing atmosphere and enables continuous, unobstructed monitoring across both the dayside and nightside of the orbit, generating roughly 15 complete solar observation windows per day at the station's current inclination of 51.6 degrees.

A secondary, time-permitting objective tasked the cosmonauts with photographing the Kurs-A automated approach and docking antenna arrays on the Progress MS-29 cargo spacecraft docked at the aft port of Zvezda. Three of the four Kurs-A whip antennas failed to deploy to their nominal 1.2-meter extended position after Progress MS-29's March 26 launch, an anomaly similar to one that affected Progress MS-20 in 2022 and was later attributed to a fastener-retention issue in the antenna hinge mechanism. Mission planners wanted high-resolution photographic documentation of the antenna positions before committing to a decision on whether to attempt a mechanical extension during a dedicated future EVA.

egress

to exit a spacecraft through an airlock, beginning a spacewalk; the act of going outside

extravehicular activity

any activity performed by an astronaut or cosmonaut outside a spacecraft, commonly abbreviated as EVA

heterodyne detector

a highly sensitive radio or terahertz receiver that mixes an incoming signal with a local oscillator to isolate very narrow frequency bands

Advanced

The May 27, 2026 EVA by Expedition 74 cosmonauts Kud-Sverchkov and Mikaev represents the 279th spacewalk in ISS programme history and the primary scientific deliverable of the excursion, mounting the STEHel-T solar-terahertz experiment on the Zvezda aft segment, closes a significant gap in space weather instrumentation. Ground-based sub-terahertz solar monitoring is constrained to dry high-altitude sites such as ALMA's 5,058-meter Llano de Chajnantor platform in Chile, which achieves acceptable opacity only in the 0.3-THz and 0.67-THz atmospheric windows. STEHel-T's broadband 0.1-to-10-THz design, leveraging a superconducting niobium-nitride hot-electron bolometer as its heterodyne mixer element, can monitor the full impulsive-phase terahertz spectrum continuously from 408-kilometer altitude orbit, providing coverage of the 0.55-THz water-vapor absorption feature and the 1.3-THz and 2.5-THz fine-structure lines with sub-second temporal resolution during flare events.

The astrophysical motivation centers on the still-incomplete understanding of particle acceleration mechanisms in solar flares. The impulsive-phase sub-THz continuum, first characterized systematically by Brazilian POEMAS and USAF-funded instruments in the 2000s, shows a spectral flux that rises with frequency rather than falling, the so-called reverse-spectrum anomaly that conventional gyrosynchrotron theory, which predicts declining optically thin emission above the spectral peak, cannot accommodate. Competing explanations invoke synchrotron emission from ultra-relativistic electrons gyrating in coronal loop magnetic fields, electron-positron annihilation radiation, and plasma emission from large-amplitude magnetohydrodynamic waves. STEHel-T's combination of broadband spectral and high-cadence temporal coverage will allow, for the first time, systematic phase-resolved analysis of the reverse-spectrum onset relative to the impulsive hard-X-ray and gamma-ray emission measured by existing RHESSI-successor instruments, potentially resolving the particle-acceleration mechanism debate.

The operational space-weather dimension is more immediately consequential. CME-associated proton events and geomagnetically induced currents represent quantifiable economic risks: the 2003 Halloween geomagnetic storms caused approximately 700 million dollars in satellite anomalies and transformer damage to the South African and Swedish power grids, while a Carrington-class event was estimated by the Lloyd's of London 2013 systemic-risk report to produce between 0.6 and 2.6 trillion dollars in North American economic damage. Current CME arrival-time forecasting relies predominantly on STEREO and SOHO coronagraph imagery supplemented by L1 solar-wind monitors at the Sun-Earth Lagrange point, which provide 15 to 45 minutes of warning. A terahertz prompt emission signal detectable 8 to 12 minutes before the main CME leading edge arrives at L1 would extend the operational lead time available to satellite operators, power utilities, and aviation route controllers managing transpolar flights, without adding any new ground segment cost.