Every month aboard the International Space Station (ISS) is packed with activity, science, and research and April was no exception. Astronauts and cargo ships departed, a spacewalk was conducted and the total eclipse was observed from this incredible vantage point.

The month began with 10 astronauts aboard the orbiting outpost, although three were due to depart soon. Flight Engineer Tracy Dyson arrived in late March on the Soyuz MS-25 from the Baikonur Cosmodrome in Kazakhstan. She will spend six months in space on this, her third visit to space, whereas her companions were due to spend only 13 days on the station. Commander Oleg Novitsky was on his fourth visit to space, while spaceflight participant Maryna Vasileuskaya became the first Belarusian woman in space.

In addition to photographing different locations on the Earth, Vasilevskaya also conducted research on how diet affects microbes living in a crew member’s gut system. The pair accompanied US astronaut Loral O’Hara back to Earth on the MS-24 Soyuz, departing on April 6 and landing under a parachute on the ground in Kazakhstan.

The Soyuz MS-24 spacecraft with three crewmates aboard slowly backs away from the space station after undocking from the Rassvet module. (Credit: NASA)

Expedition 71 officially began with the undocking of the Soyuz MS-24 spacecraft, comprising NASA astronauts Michael Barratt, Matthew Dominick, Tracy Dyson, and Jeanette Epps, together with Roscosmos cosmonauts Nikolai Chub, Alexander Grebenkin, and Oleg Kononenko. They will remain on the station until this fall.

Science and Research Investigations

Loral O’Hara has spent a total of 204 days and over 3,000 orbits aboard the station since she arrived on Soyuz MS-24 last September. In that time she’s performed many science experiments and investigations from 3D printing human heart tissues and investigating cancer treatments to manufacturing new materials. These include the production of flawless optical fibers in space — an experiment that arrived with the NG-20 cargo mission.

Early parabolic research showed that optical fibers manufactured in microgravity are of superior quality to those made on Earth and the investigation has produced more than 11 kilometers (seven miles) of fibers. These will be returned for analysis now that the CRS-30 Dragon has returned to Earth. The Flawless Photonics manufacturing platform will, however, stay on the space station for future use.

Expedition 70 Flight Engineer and NASA astronaut Loral O’Hara conducts tries on the Sokol launch and entry suit she will wear when she returns to Earth aboard the Soyuz MS-24 crew ship. (Credit: NASA)

O’Hara joined several of her crewmates in contributing to the study known as the Complement of Integrated Protocols for Human Exploration Research on Varying Mission Durations (CIPHER). This is comprised of 14 different experiments covering all aspects of human physiology and psychology in space to study how the human body is affected by and adapts to long-duration spaceflight. Taking advantage of the fact that we age faster in orbit, researchers have been studying what happens in our cells. This could help improve life on Earth for people with tissue degradation as we age, and help to improve the health of astronauts on longer-duration missions such as to the moon or a three-year round-trip to Mars.

In the Columbus laboratory module, NASA Flight Engineer Mike Barratt took part in CIPHER studies that checked his eye function and blood pressure as well as using the Ultrasound 2 device to scan his veins. Coordinating with a team on the ground, Flight Engineer Tracy Dyson monitored Barratt wearing specialized goggles that tracked eye movements as he moved. This is part of a vestibular exam that seeks to understand better how weightlessness affects the crew’s sense of motion and perception.

As part of the study, Jeanette Epps has been wearing a specialized thigh cuff, similar to a blood pressure cuff. This helps study the upward flows of fluids in the body which can create head pressure and eye issues for astronauts. Dominick and Dyson both donned a specialized cap and sensors to simultaneously measure blood flow and pressure and electrical heart activity to inform a study of blood pressure issues such as light-headedness or fainting, both in space and here on Earth.

NASA astronaut Jeanette Epps using the BioFabrication Facility (BFF) glovebox (Credit: NASA)

The crew took turns operating the BioFabrication Facility in the Columbus laboratory module to 3D print cardiac tissue samples and process them for incubation. The results of this tissue engineering study could offer future crews the ability to print food or medicines and may assist with the donor organ shortage by enabling doctors on Earth to bioprint replacement organs and tissues.

Crew members kept a close eye on each other this month, performing eye scans of the cornea, retina, and optic nerves using standard optometrist equipment, together with a team on the ground, as part of the B Complex eye health investigation. This explores a condition experienced by some astronauts called Spaceflight-Associated Neuro-ocular Syndrome, or SANS, which may be alleviated using a Vitamin B supplement. The study could help maintain vision and health on long-duration missions in the future. Mice on the station have been treated with gene therapy that could address the reduced vision and retinal conditions that are associated with living in space. They returned on the CRS-30 Dragon for further analysis, where they will be compared to a control group.

Barratt, Dominick, and Epps have also been testing a garment that may help crews adjust quicker to Earth’s gravity on their return from a long-term space mission. Epps has also been swapping samples in the Electrostatic Levitation Furnace — a high-temperature research device enabling observation of the thermophysical properties of materials which is difficult in Earth’s gravity environment.

Flight Engineer and NASA astronaut Mike Barratt processes brain organoid samples inside the Life Science Glovebox for the HBOND neurodegenerative disorder study. (Credit: NASA)

The Human Brain Organoid Models for Neurogenerative Disease and Drug Discovery (HBOND) studies neuroinflammation, a common feature of neurological disorders. Using brain organoid samples from people who have Multiple Sclerosis or Parkinsons’ Disease, the crew used the station’s Life Science Glovebox to test the effects of a drug injection. This could improve diagnosis as well as the development of treatments for those suffering from these conditions. The study also aims to help researchers to understand how microgravity affects the central nervous system. Scientists on the ground remotely viewed the samples and operated a specialized microscope.

The Ecosystem Spaceborne Thermal Radiometer Experiment, or ECOSTRESS, will accurately measure the temperature of plants on Earth throughout daylight cycles using infrared. Researchers have found that photosynthesis in plants will begin to fail at 46.6 degrees Celsius (114 degrees Fahrenheit). The data collected is hoped to answer some key questions about water stress in plants and how certain regions of the Earth, such as rainforests, may respond to climate change. It is not known whether temperatures in tropical vegetation could reach this threshold but the study is expected to raise awareness of the need to mitigate climate change.

The Moon’s shadow, or umbra, is pictured covering portions of Canada and and the U.S. from the ISS soared into the solar eclipse. (Credit: NASA)

Total Eclipse

The astronauts aboard the ISS were treated to a special view of the total eclipse that passed over Mexico, the United States, and Canada this month and were on the day side of the Earth three times during the event. Unlike those in the path of totality, the Expedition 71 crew witnessed only a partial eclipse from the windows of the station.

However, during their orbital passes, they were able to see, and photograph, the moon’s shadow as it raced across the Earth 420 kilometers below them. Traveling at 2,400 kilometers per hour, the 185-kilometer-wide shadow, or umbra, gave those on the ground four minutes of shadow whereas the astronauts experienced this celestial event for a shorter period of time with each pass.

Five Expedition 70 crew members wear solar eclipse viewing glasses aboard the ISS. (Credit: NASA)

Extravehicular Activity (EVA)

Russian cosmonauts ventured out of the Poisk airlock on April 25 to perform the station’s 270th spacewalk, otherwise known as an Extravehicular Activity, or EVA. This was the seventh EVA for Station Commander Oleg Kononenko and the second for Flight Engineer Nikolai Chub. Preparations for this four-and-a-half hour spacewalk began two weeks prior, with suit pressure leak and battery checks, collecting tools, and configuring their spacesuits.

Flight Engineer Alexander Grebenkin assisted the duo in and out of their Orlan spacesuits and monitored his crewmates as they worked outside the space station. The pair completed the objectives, deploying one panel for a synthetic radar system on the Nauka module and installing experiments and hardware on the Poisk module. These will analyze the level of corrosion on station surfaces and modules.

Cosmonauts Oleg Kononenko and Nikolai Chub during their spacewalk installing equipment and experiments on the space station’s Roscosmos segment (Credit: NASA)

Meanwhile, the four cosmonauts onboard the orbiting outpost have been collecting blood and saliva samples for a space immunity study and practicing spacecraft and robotic piloting techniques that may be used on future planetary missions and could help inform future cosmonaut training. They also observed Cosmonautics Day this month — the anniversary of Yuri Gagarin’s first spaceflight on April 12, 1961. Enjoying an off-duty day, the trio transmitted a video message commemorating that historic mission.

NASA concluded an investigation this month into the stanchion used to mount batteries onto a cargo pallet that made news when it survived re-entry in early March and impacted a house in Naples, Florida. The object is made of the metal alloy Inconel and is roughly the size of a soda can. It comes from a cargo pallet containing a number of aging nickel hydride batteries which have since been replaced by more efficient lithium-ion batteries as part of a major overhaul of the ISS power systems. The pallet had a mass of around 2,630 kilograms and was released by the station’s robotic arm back in March 2021 with the expectation that it would entirely disintegrate during eventual re-entry.

The recovered Stanchion is inspected by the NASA investigation team. (Credit: NASA)

Usually, these pallets would arrive at the ISS with fresh batteries on an expendable Japanese H-II Transfer Vehicle (HTV) which would later depart with the same pallet loaded with expired batteries. This pallet was from HTV-9, the last of this series of cargo supply spacecraft until HTV-X comes online early next year.

Things got out of sync following the abort of Soyuz MS-10 two minutes after launch in Oct. 2018 which meant that astronaut Nick Hague did not arrive in time to perform the complex EVA required to change the batteries. As a result, the HTV-7 vehicle departed without the usual pallet, which NASA decided to instead return on the following HTV-8 mission. This staggered approach remained in place up to the pallet from HTV-9 in May 2020 but, with further delays to the HTV-X craft of at least a year, it was then stored on the outside of the station until a decision was eventually made to dispose of it in 2021 by releasing it.

The cargo pallet containing expired batteries from HTV-9 is released by the robotic arm in March 2021 (Credit: NASA)

Departures and Arrivals

Jeanette Epps spent several days installing a small cubesat deployer inside the Kibo laboratory module’s airlock. Ten small satellites were deployed into low-Earth orbit between April 11 and 18, including Killick-1 and others that had been delivered on CRS-30 for a variety of technology and communications studies.

Release the CubeSats! Last week two Earth-observing CubeSats deployed from @Space_Station to help monitor Earth’s changing landscape.

KILLICK-1, seen below, measures sea ice and wave height to better understand important ocean phenomena and improve weather and climate models. pic.twitter.com/MsxK1LrJ9e

— ISS Research (@ISS_Research) April 23, 2024

The Cargo Dragon C209-4, which brought supplies and research to the station in late March, was expected to autonomously undock from the Harmony module and depart on April 28 but was delayed due to weather. Undocking took place on Sunday, April 28 at 1:10 PM EDT (17:10 UTC), with splashdown expected on April 30 around 1:00 AM  EDT (05:00 UTC) off the coast of Florida. This was the first Dragon 2 craft to be launched from SLC-40 using the new access arm and tower.

It takes days of preparation to stow away and secure everything that is making the return journey — over 1,860 kilograms of science and supplies. Matthew Dominick closed the ‘basement’ on the spacecraft in preparation, after which the crew then spent a further couple of days packing more bags on the mid-deck and strapping them all in.

Your science is ready for delivery.

NASA astronaut Matthew Dominick closes out the Dragon spacecraft in preparation for its scheduled departure in late April. Dragon will return to Earth with samples and hardware from several experiments for further study. pic.twitter.com/CJWb9ZBuUh

— ISS Research (@ISS_Research) April 26, 2024

The upper compartment has stowage room too, including a bank of refrigerators known as Polars — these keep important samples at the required temperature for their journey home. Some final science will be conducted directly before closing out the Dragon, and immediately frozen for analysis soon after Dragon makes splashdown back on Earth. The most critical science is loaded last, and nearest to the side access hatch.

One of the experiments on this return trip has been exposed to the harsh environment of space for the past six months. This is the eighteenth series of experiments for the Materials International Space Station Experiment (MISSE) series. The MISSE project has tested some 4,000 material samples and specimens since 2001 including paints, lubricants, container seals, and fabrics, sometimes for up to four years at a time, to test their durability in the punishing space environment. The latest tests include insulation materials that could be used on the planned Gateway outpost or the lunar surface and a coating that could help to prevent the salt corrosion seen on vehicles at Cape Canaveral while they await launch.

The Cargo Dragon C209-4 awaits departure from the ISS (Credit: NASA)

The Dragon is also returning microbe samples which Dominick has taken by swabbing surfaces throughout the US segment of the ISS. The specimens will be treated and analyzed on Earth to help determine microbial resistance to antibiotics and any risk to crew health. The crew has been working on bacteria samples in the Kibo laboratory module which may help researchers understand how bacteria adapt to weightlessness and why microbes are more resistant to antibiotics in space.

Looking forward (and back)

Preparations are underway for the first crewed flight test of the Boeing CST-100 Starliner, which is due to launch from SLC-41 at Cape Canaveral on May 6. The spacecraft has been hoisted on top of the Atlas V rocket that will carry it into low-Earth orbit to certify the vehicle for crew rotation missions to the ISS. With a diameter of 4.56 meters, the capsule can carry up to four astronauts, or a mix of crew and cargo and can be steered manually or automatically.

The Starliner will carry its first two passengers, Barry “Butch” Wilmore and Sunita “Suni” Williams, who will become the first woman to fly on a maiden flight of a new orbital vehicle type. The mission will include docking to the ISS before departing to land under a parachute on the ground in the United States. It is the first time an Atlas V will carry a crewed spacecraft and the first mission for NASA’s commercial crew program that isn’t conducted with a SpaceX capsule.

Sunita Williams, seated in the foreground, and Barry Wilmore, seated next to her, in their blue spacesuits, gloves, and headsets. (Credit: NASA)

The duo will spend about a week on the station during their mission and entered pre-flight quarantine on April 22 in advance of the launch. During this time, contact with the astronauts is limited, and most interactions are remote with the exception of certain team or family members. They conducted a full mission dress rehearsal on April 26.

Following the departure of the Cargo Dragon, Crew 8 will suit up and relocate Dragon Endeavour from the forward-facing port on the Harmony module to the space-facing zenith port on May 2, to free up the port for Starliner’s arrival. The Progress 87 resupply ship fired its engines for almost seven minutes on April 26 to increase the station’s altitude. This orbital reboost is in readiness for the Roscosmos Progress 88 cargo craft which is expected in late May.

NASA also announced the crew for the next rotational Soyuz crew which will launch this fall on the MS-26 craft. NASA astronaut Don Pettit will be making his fourth visit to space alongside Roscosmos cosmonauts Alexy Ovchinin and Ivan Vagner. Pettit has already spent almost 370 days in space, and over 13 hours of experience on two EVAs. He is well known for his passion for photography, inventions such as the zero-g coffee cup, and for sharing his love of physics in video demonstrations.

Star trail time exposure from my third mission to @Space_Station. Solar panels blur into the exposure, creating a ghostly afterimage.

City lights streak to the right, and disappear in rural plots to the left, dividing the image into a black and gold mosaic of human presence.… pic.twitter.com/Y3wJelhdGG

— Don Pettit (@astro_Pettit) March 30, 2024

Pettit first served as Science Officer on Expedition 6 back in 2003, during which he conducted both of his EVA missions and became one of the first US astronauts to arrive on a Shuttle and depart on a Soyuz, following the loss of Columbia, which extended his mission by a further two months. He then returned to space on the STS-126 Shuttle Endeavour mission and, as part of the Expedition 30/31 crew, operated the Canadarm 2 with André Kuipers to grapple the first Dragon 1 and berth it to the Harmony module. This was the first time a private spacecraft had ever made a rendezvous with the ISS. Don’s time on the ISS is sure to be memorable, educational, and will hopefully deliver more stunning astrophotography.

Looking back, SpaceX launched the CRS-3 mission to the ISS 10 years ago this month. This was the first Dragon capsule to fly on the Falcon 9 v1.1 and the first time a Falcon booster had flown with landing legs. Booster B1006 achieved the first successful ocean soft touchdown of a liquid rocket engine orbital booster on this mission, simulating landing. This was only the fifth flight of an uncrewed Dragon and the company’s third mission to the space station under the Commercial Resupply Services contract, its predecessor having launched over a year prior in March 2013.

This is how I make my star trails. Sequences of still images assembled until the beauty of Earth from @Space_Station reshapes into a new form by the forces of time, nature, and physics.

Thanks to Christopher Malin for making this video clip from my Expedition 30 photographs. pic.twitter.com/GGdGxY6LgJ

— Don Pettit (@astro_Pettit) April 24, 2024

(Lead image: The Kibo laboratory module from the Japan Aerospace Exploration Agency, from which various cubesats were deployed this month. It is comprised of a pressurized module and exposed facility, a logistics module, a remote manipulator system and an inter-orbit communication system unit, and is pictured as the International Space Station orbits over the southern Pacific Ocean east of New Zealand. Credit: NASA)

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