Bion-M2 Closes a 12-Year Loop After a Deadly First Flight

Russia’s Bion-M No. 2 biosatellite landed in the Orenburg steppes on September 19, 2025, with 65 of 75 mice still alive after 30 days in polar orbit.

The same Moscow institute had last opened a Bion capsule in 2013, when most of the rodents were dead. This flight was the delayed redo, flown on the high-latitude path Russia wants for its own station, and the first mouse atlas from the mission is already posted.

65 of 75 Mice Came Back From Polar Orbit

The 6.4-ton craft lifted off from Baikonur Site 31/6 at 17:13 UTC on Wednesday, August 20, 2025, on a Soyuz-2.1b. It spent 30 days and 464 orbits at 370-380 km and 96.6 degrees, then the descent module touched the Orenburg steppe at 11:15 local time (08:15 UTC) on September 19.

Roscosmos, the Russian Academy of Sciences, and the Institute of Biomedical Problems (IBMP) ran the mission. Photos from the grass show a small brush fire around the sphere. Crews put it out before three helicopters brought specialists in to pull the animals.

IBMP director Oleg Orlov spoke at the site for the institute’s press service. He said the capsule had landed normally and that the living specimens were in good enough shape to start the work already planned.

As for the results: we lost ten of the 75 mice. With such result, we are all satisfied, primarily scientists and the flight organizers.

Oleg Orlov, director, Institute of Biomedical Problems, landing-site remarks

Flies, plants, and microbes came back alive, according to the recovery team. First checks, including fly motor tests, ran in a medical tent on the steppe. The samples were due in IBMP labs in Moscow around midnight on September 20.

THE FLIGHT IN FOUR FIGURES

• Mouse tally: 75 launched in 25 automatic habitats, three to a box; 65 reached the grass.
• Other animals: about 1,500 fruit flies plus ants, cell cultures, seeds, fungi, and lichens.
• Work load: 29 experiments on a 30-day, 464-orbit polar pass.
• Measured dose: 9 ± 2 mGy inside the cabin, or 0.30 ± 0.06 mGy per day.

The mice were four-month-old C57BL/6 males from a Novosibirsk breeding station, raised in groups of three so they would share a cylinder in orbit. Most of them ate a high-water paste six times a day. A smaller group got dry bars and hydrogel. Implanted loggers tracked temperature, and some also recorded heart rate. IBMP got only short videos during the flight. Full cage recordings waited until the sphere was on the ground.

The Last Bion Flight Killed Most of Its Rodents

Bion-M No. 1 launched on April 19, 2013, and landed in the same Orenburg region on May 19 after 30 days at about 575 km and 64.9 degrees. That higher, lower-inclination path drove a proton-heavy trapped-belt dose roughly five times what Bion-M2 later recorded.

Of 45 mice on that flight, 16 of 45 mice survived Bion-M1. All eight Mongolian gerbils died after power, ventilation, and food cut out in their unit. All the fish died. Fifteen geckos lived, as did snails and microbes. IBMP scientist Evgeni Il’in said then that, with hardware working, natural deaths were not expected to exceed 5 percent.

A food-distribution failure wiped out 15 mice in one assembly right after launch. Other unit faults left the rest of the dead. The spacecraft itself, built by Progress in Samara on a Zenit-derived sphere with a Yantar propulsion section, had flown clean. The animal hardware had not.

NASA still ran a biospecimen sharing program on that flight. Nine U.S. investigators shared mouse tissues from the animals Moscow passed to them, and those shared mice reached the ground in good health. Ames teams later repeated a 30-day ground control in Moscow.

TWO BION LANDINGS IN THE SAME STEPPE

Bion-M2’s habitats were larger cylinders, 16 cm across and 12 cm high, with a day-night light cycle the 2013 boxes did not have. The May 2026 IBMP preprint, whose authors include Orlov, says the 10 losses came from a hardware malfunction that flooded one paste-fed habitat and then emptied the linked food reservoirs before the mission ended. That is the same class of failure that gutted Bion-M1, even if this time 65 mice still made it to the tent.

Why the Capsule Flew the Path of Russia’s Next Station

The polar path was the point of the redo. Roscosmos described the high-latitude track as a place where cosmic radiation runs about one-third higher than on the International Space Station, and as the kind of orbit drawn for the Russian Orbital Station. In the first half of 2025 the team dropped an earlier plan for an 800 km altitude so the biosatellite would sit closer to that future station’s height.

Passive dosimeters inside Bion-M2 recorded an absorbed dose of 9 ± 2 mGy, comparable to the ISS Service Module cabin at about 420 km. The mix was different. Relative to the station, the flight showed about a twofold rise in the galactic cosmic ray share and at least a 30 percent drop in trapped radiation. A moderate X-class solar flare on August 26, 2025, left no mark on the onboard dose. Chronic galactic rays, not a single storm, set the environment.

The IBMP authors call that mix a lower-bound analog for cislunar and interplanetary work, because Earth’s magnetosphere still shielded the cabin. Absolute heavy-ion fluences stay below a true deep-space cruise. For a country designing a polar station, the cheaper fact is simpler. This is the radiation field a future crew would see at 370-380 km and 96.6 degrees, measured in mice that could be opened on the grass.

Roscosmos General Director Dmitry Bakanov said before launch that experts would consider sending a person onto a polar orbit after the Bion-M2 results. RAS president Gennady Krasnikov later told a Kremlin meeting that the satellite’s launch had been postponed four times since 2013 and that the flight had gone well. Clips of mice floating in the cylinders spread as a zoo story. The dosimetry is what the orbit was bought for.

An Nrf2 Drug Kept Hindlimb Muscle on the Ground

Alexander Andreev-Andrievskiy of IBMP, who heads the animal phenotyping lab and is corresponding author on the preprint, had trained the mice on a simple task before they flew. After landing, the question was whether the skill survived the month upstairs.

For example, to get something pleasant, we teach mice to poke their noses into a button. Whether they will remember this after the flight is a question.

Alexander Andreev-Andrievskiy, head of IBMP’s Laboratory of Animal Phenotyping, prelaunch interview

The posted paper, dated May 6, 2026, is the first integrated mouse readout from the polar flight. It builds an atlas of 73 physiological endpoints across spaceflight, matched ground habitats, and ordinary vivarium cages. A tissue-sharing scheme took 158 samples from each mouse, more than 25,000 samples in all. Paste-fed mice were opened on landing and on days 1, 5, and 30. Dry-fed mice were watched for behavior and sampled later. The flooded paste habitat forced the team to cancel a planned day-15 collection for that group.

Paste-fed flight mice gained 7.3 ± 1.6 percent body mass in orbit, close to habitat ground controls at 6.1 ± 1.7 percent and far below vivarium mice at 21.4 ± 2.4 percent. After landing they put weight back on faster than both control groups. Early field videos still showed a mobility deficit in the first hours on the grass.

WHAT 30 DAYS IN POLAR ORBIT DID TO THE MICE

Most skeletal muscle had moved back toward control by day 5. Spleen, gut, and blood markers lagged, some still off at day 30. The authors write that after a long flight the bottleneck may be that slower visceral and immune reset, not the ability to stand.

Diet was not a background detail. Mice pulled 2.7 times more water from paste than from hydrogel. On paste, the 73 endpoints clustered into fairly separate muscle, stress, and visceral groups. On dry food the same measures collapsed into a tighter, stress-heavy network. The paper treats food and water as a primary control, not a logistics choice.

The sharpest drug result sits on Nrf2, a stress-defense pathway. Untreated C57BL/6 mice lost 18 ± 2 percent of rectus femoris mass against vivarium controls, one of the largest shifts in the set. Nrf2-knockout mice finished with the lowest muscle mass of any group. Mice given RTA-408, also called omaveloxolone, kept hindlimb mass at ground-control levels. The protection was selective. Muscle and several visceral organs improved. The usual blood and innate-immune pattern of spaceflight did not go away.

All of the flight mice were males of one inbred line, a limit the authors state outright. Group housing cuts isolation stress and adds fights and shared air. Thirty days is the early phase of adaptation, not a Mars cruise. Even with those bounds, the polar atlas is the first systems map Russia has from the orbit it wants to occupy.

Flies, Seeds, and a Meteorite in the Heat Shield

The mice were the main MLZh-02 payload. The sphere and its outer skin carried a second menagerie aimed at plants, microbes, and student kits, plus a reentry test that has nothing to do with rodent muscle.

WHAT ELSE RODE THE SPHERE

• Fruit flies: about 1,500 Drosophila, flown to test reproduction under the polar radiation mix after earlier Foton-M No. 4 and ISS generations.
• Seeds: 20 wild and crop species, including wheat, tomato, pepper, and lines grown from parents that had already flown on Bion-M1 in 2013 and Foton-M No. 4 in 2014.
• Meteorite: rock disks loaded with microbes, including extremophiles from Kamchatka hot springs and from Oymyakon, set into the lander’s heat shield to see what survives reentry heat.
• Lunar analog: 16 tubes of a new Moon-soil simulant, flown with the RAS Laboratory of Geochemistry of the Moon and Planets for later astrobiology work.
• Student kits: ants in a clear box billed as Ecosystem in Orbit, and a Russia-Belarus tomato-seed kit called Into Space with your Tomato.

Other runs tested cell cultures in controlled containers, microbes as a possible power source, and bugs that might break down clothing and waste. Mean cabin air sat at 25.1 ± 0.3°C with 66.3 ± 2.7 percent humidity. On December 14, 2025, a State Commission told Roscosmos that onboard systems had worked as planned and that the research program had been completed in full.

Bion-M No. 3 Is Aimed at 800 Kilometers

Bion started as Kosmos-605 in 1973, using Vostok-family spheres as unmanned labs. Primates left the line after the 1980s. Mice became the largest mammals the program still flies. After Bion-M1, officials talked about two more Bion-M craft in the 2016-2025 federal plan. Only one satellite was built. The second flight, promised for 2019, then 2021, 2023, and no later than July 31, 2024, left the pad on August 20, 2025.

FROM THE 2013 LANDING TO THE 2030 AIM POINT

1. May 19, 2013: Bion-M1 lands near Orenburg with 16 of 45 mice alive and all gerbils dead.
2. August 2014: At COSPAR, Space Research Institute director Lev Zeleny pledges Bion-M2 for 2019 and a third satellite around 2022.
3. 2015-2018: The federal program slips the pair to 2021 and 2025, then to 2023 after new French-built physiology gear is added to the plan.
4. 2023-2024: Assembly is largely done, with a no-later-than date of July 31, 2024, then a further slip into 2025.
5. August 20, 2025: Bion-M2 reaches polar orbit from Baikonur Site 31/6.
6. September 19, 2025: The sphere lands in the Orenburg steppe; 65 of 75 mice are alive.
7. December 14, 2025: The State Commission records a full success.
8. May 6, 2026: IBMP posts the first multisystem mouse atlas from the flight.

Vladimir Sychev, who leads the scientific direction at IBMP, said the next biosatellite, Bion-M No. 3, is being prepared for 2030 on a polar orbit about 800 km up, using a science complex based on the Bion-M2 gear and adding genetically diverse animals beside the usual inbred lines. Progress first deputy general designer Ravil Akhmetov said the platform is technically ready. An IBMP source also said there are no current plans for animal work on the Russian Orbital Station itself, though mice could fly there later, with Bion-M3 still the next dedicated shot.

The 2013 flight proved the sphere could come home and that the animal boxes could fail. The 2025 flight proved the boxes could mostly hold, then failed in one paste habitat in the last days, and still returned enough animals for a 73-endpoint map. The 800 km sequel is where that map is supposed to be tested against a harder radiation belt.

Frequently Asked Questions

How Many Mice Survived the Bion-M2 Mission?

Sixty-five of the 75 mice were alive at landing. The IBMP preprint says all 10 losses were in the paste-fed C57BL/6J group during the final days, after a hardware fault flooded one habitat with paste and then emptied the linked food tanks, a cut in sample size that also forced the team to drop a planned day-15 tissue collection for that diet.

What Orbit Did Bion-M2 Use, and Why Not 800 km?

The spacecraft flew 370-380 km at 96.6 degrees for 464 orbits. An 800 km polar altitude was the earlier plan; in the first half of 2025 the team lowered the target so the radiation and thermal environment would sit closer to the planned Russian Orbital Station, whose final inclination was still under discussion at launch.

How Did Bion-M1’s Mouse Losses Break Down?

Sixteen of 45 mice lived. Fifteen of the dead were in a single assembly whose food distributor failed just after launch; if that cage is set aside, survival in the remaining flight hardware was 16 of 30. Ground-control mice in the same paper lived at 38 of 45, and a preflight 30-day housing test had killed none of 15.

Did the Nrf2 Drug Change the Whole Spaceflight Pattern?

No. RTA-408 held rectus femoris mass at ground-control levels and helped several visceral organs, but the hematologic and innate-immune activation that marks spaceflight stayed in place. Nrf2-knockout mice had the worst muscle outcomes, and the authors treat knockout, baseline, and drug-boosted Nrf2 as three points on a stress-defense axis rather than a simple on-off switch.

Sychev’s 800 km aim point for 2030 puts the next sphere back on the altitude Bion-M2 abandoned, with a wider mix of mouse genetics and with the 2025 atlas as the baseline. That is the test the 12-year loop was built to reach.