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Luna-Glob mission

Nearly half a century after the last Soviet probe visited the Moon, a new-generation lunar lander launched from the Russian Far East with a destination in the southern polar region of the Earth's natural satellite. Originally dubbed Luna-Glob, the new spacecraft was publicly renamed Luna-25 to symbolize its historical connection to the Luna-24 mission in 1976, which effectively concluded the Soviet robotic lunar program.


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Luna-Glob launch at a glance:

Payload Luna-Glob (Luna-25)
Launch vehicle Soyuz-2-1b No. B15000-003/Fregat No. 122-10
Payload fairing 81KS B15000-047
Launch site Vostochny, 1S
Launch date and time 2023 Aug. 11, 02:10:57.189 Moscow Time (actual)

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Liftoff and ascent to orbit

A Soyuz-2-1b/Fregat rocket, carrying the Luna-Glob (Luna-25) lander, lifted off from Pad 1S in Vostochny on Aug. 11, 2023, at 02:10:57.189 Moscow Time (08:10 Local time at the launch site). It was 23:10 UTC and 7:10 p.m. EDT on August 10.

After a few seconds of vertical ascent under the simultaneous thrust of the four RD-107 engines of the first stage and the single RD-108 engine of the second stage, the Soyuz steered due east so that its ground track matched an orbit with an inclination 51.7 degrees toward the Equator. It was the first mission from Vostochny heading in a strictly eastern direction, instead of flying along a north-northwest corridor as did all previous launches from the site targeting near-polar orbits.

(By entering orbit with the lowest possible orbital inclination accessible from Vostochny, the launch vehicle preserved the maximum payload available for the subsequent insertion into a trans-lunar trajectory.)

The first stage of the rocket separated 1 minute and 59 seconds into the flight (L+118.93 seconds), leaving it to the second (core) stage of the Soyuz rocket to continue accelerating the vehicle. The four boosters of the first stage were to impact the ground at Drop Zone No. 511 around 340 kilometers downrange from the launch site. Local authorities later confirmed that three of four boosters were discovered 28 kilometers from the town of Shakhtinsky, between rivers Desh and Tastakh. All 18 residents of Shakhtinsky were evacuated an hour before launch and "were returned to their homes at 10:30" a local official said.

The payload fairing protecting the lander then split into two segments and separated as well 3 minutes and 32 seconds after liftoff (L+211.95 seconds). Its remnants were projected to fall at Drop Zone No. 513 extending across the Verkhnebureinsky, Ulchsky and Vaninsky districts in the Khabarovsk Region on Russia's Pacific Coast.

In the meantime, the propulsion system of the third stage was pressurized, and just moments before the scheduled separation of the second stage, the RD-0124 engine of the third stage ignited and fired through a lattice structure connecting the boosters. The empty second stage separated 4 minutes and 48 seconds into the flight (L+287.86 seconds) and seconds later, the aft skirt of the third stage split into three segments and fell off (at L+292.46 seconds). All these fragments were to splash down in the Sea of Okhotsk at Drop Zone No. 515.

The third stage continued firing until around nine minutes into the flight (until L+560.64 seconds), followed by the separation of the Fregat upper stage with the lander over the Pacific Ocean 9 minutes and 24 seconds after liftoff (L+563.94 seconds). Just short of orbital velocity, the third stage quickly reentered the atmosphere and splashed down in the Pacific.

Upper stage maneuvers

Just five seconds after parting ways with the third stage, Fregat was to fire its main propulsion system to enter an initial parking orbit around the Earth at 02:22 Moscow Time or around 11 minutes after liftoff from Vostochny. The US Space Force later reported an object associated with the Luna-Glob launch in a 267 by 281-kilometer orbit with an inclination 51.73 degrees toward the Equator.

Then, after a period of passive flight, 59 minutes 52 seconds into the flight (at 03:07:52 Moscow Time on Aug. 11, 2023), Fregat was programmed to restart its engine to enter a trans-lunar trajectory exactly an hour after reaching the initial orbit. If everything went as planned, the Luna-Glob lander would be ready for separation from the Fregat 1 hour 19 minutes 47 seconds after liftoff (03:30:44 Moscow Time on August 11) and for autonomous flight into the vicinity of the Moon (INSIDER CONTENT) along a 350 by 400,000-kilometer elliptical orbit around the Earth. Fregat's second maneuver was also designed to reduce the orbital inclination of the mission by 0.8 degree.

Another eight minutes later, at 03:38 Moscow Time, the near-empty Fregat was scheduled to perform its final maneuver to enter a safe trajectory away from its former passengers.

Minutes after the planned separation time, Roskosmos confirmed that the spacecraft had been on the trans-lunar trajectory with the lunar orbit insertion scheduled for August 16, at 12:03:30 Moscow Time, followed by a landing attempt on the surface of the Moon on Aug. 21, 2023.

After separation from Fregat, the mass of the Luna-Glob spacecraft was reported to be 1,648 kilograms.

According to the operator of the Luch data-relay satellite system, Luch-5A and Luch-5B satellites were used to transmit telemetry from the Fregat upper stage after the mission had left the communications range of the ground stations on the Russian territory. A total 115 minutes of transmission time had been provided by Luch satellites, according to the provider.

Trans-lunar flight

During the day on Aug. 11, 2023, Roskosmos said that Luna-25 had maintained stable communications with ground control and its telemetry confirmed that all systems aboard the spacecraft had functioned normally.

Industry sources also confirmed that an optional orbit correction on the second day of the mission to adjust possible inaccuracies in trans-lunar injection would indeed be required, using DKS engines (INSIDER CONTENT) and delivering six meters per second in velocity change. The lander's engine firing was scheduled for 16:00 Moscow Time on Aug. 12, 2023.

Also, the Fregat upper stage was confirmed performing a maneuver that precluded its crash into the Moon. According to the estimates based on tracking data by the US Space Force, Fregat was expected to pass between 10,000 and 6,000 kilometers from the center of the Moon on Feb. 22, 2024.

Roskosmos then announced that Luna-25 had fired its propulsion system as planned for 46 seconds on Aug. 12, 2023. At the time, the spacecraft was 230,000 kilometers from Earth.

Roskosmos also said that the first activation of the science complex (INSIDER CONTENT) aboard Luna-25 had been successfully performed on August 13 and that the service telemetry from all the instruments had shown their good operation. First measurement data (from the instruments) during a cruise to the Moon had also been received and the scientific team had began its processing, Roskosmos said. According to the Space Research Institute, IKI, the ADRON-LR instrument (INSIDER CONTENT) had been used to measure the radiation environment around the spacecraft.

Luna-25 performed its second trajectory correction maneuver on Aug. 14, 2023, at 06:40 Moscow Time (11:40 p.m. EDT on August 13). This time, the lander's propulsion system fired for 24.3 seconds, according to Roskosmos.

Luna-Glob enters lunar orbit

First color image from Luna-Glob released on Aug. 16, 2023. It was produced by one of the STS-L cameras (INSIDER CONTENT) on Aug. 15, 2023, at 00:00:22 Moscow Time (5 p.m. EDT) at a distance of 380,000 kilometers from Earth. Credit: IKI RAN


According to unofficial reports, the Luna-25 (Luna-Glob) spacecraft was expected to enter an initial orbit around the Moon at noon Moscow Time (5 a.m. EDT) on Aug. 16, 2023. According to an unofficial report on the Novosti Kosmonavtiki web forum, posted around 1.5 hour after the expected lunar orbit insertion maneuver and citing available telemetry, the probe's engine fired as scheduled and the spacecraft maintained correct attitude during the maneuver.

Around two hours after the event, Roskosmos confirmed that two engine firings starting 11:57 Moscow Time (4:57 a.m. EDT) had successfully put Luna-25 into orbit around the Moon by 12:03 Moscow Time (5:03 a.m. EDT). The first maneuver was performed with the KTD engine (INSIDER CONTENT) and lasted 243 seconds. The second firing used soft landing engines and lasted 76 seconds.

According to Roskosmos, all systems aboard the spacecraft were functioning normally. The spacecraft was reported to be in the 91.4 by 112.6-kilometer orbit around the Moon with an inclination 82.087 degrees toward the lunar Equator and the ascending angle of 270.53 degrees longitude (a point where the spacecraft's ground track crosses from the sourthern to the northern hemisphere).

The mass of the spacecraft after reaching lunar orbit was reported to be 1,237 kilograms.

The first lunar orbit correction was expected to be performed two days after entering the initial lunar orbit and upon exact calculation of orbital parameters.

Also, on August 17, the Space Research Institute, IKI, released first image of the lunar surface produced by Luna-Glob's STS-L TV system (INSIDER CONTENT) at 08:23 Moscow Time (1:23 a.m. EDT). According to IKI, aboard the spacecraft, instruments ADRON-LR (INSIDER CONTENT), PmL and ARIES-L (INSIDER CONTENT) conducted test observations. In particular, they registered gamma-ray and neutron flows from the lunar surface and measured parameters of space plasma, gas and dust content in the lunar exosphere.

As of August 17, Luna-Glob was scheduled to perform a correction of its lunar orbit on August 18, at 13:00 Moscow Time (6 a.m. EDT), followed by another maneuver to form the landing orbit on August 19, at 14:18 Moscow Time (7:18 a.m. EDT), a poster on the Novosti Kosmonavtiki forum said.

On August 18, Roskosmos confirmed that the 40-second orbit correction maneuver had been performed, but with the engine firing starting at 09:20 Moscow Time (2:20 a.m. EDT). The State Corporation also said that all systems aboard Luna-25 had functioned well, but no orbital parameters or any details on the timeline of the mission had been released.

Luna-Glob crashes

Luna-Glob's final descent trajectory and impact site as calculated by Keldysh Applied Mathematics Institute, IPM.


On August 19, around 18:35 Moscow Time (11:35 a.m. EDT), Roskosmos reported that another orbital maneuver had started at 14:10 Moscow Time (7:10 a.m. EDT) to transfer the spacecraft to a "pre-landing orbit", but "during the operation, an emergency situation occurred on board... which did not allow the maneuver to be performed with the specified parameters." According to Roskosmos, the management team was analyzing the situation.

A few hours after the first official announcement about a problem aboard Luna-Glob, an unofficial Telegram channel, Zakryty Kosmos, reported that the spacecraft had broken communications with ground control during the orbit correction but Roskosmos had continued its attempts to contact the spacecraft. Before the end of the day on August 19, Aleksandr Ivanov, First Deputy Director for the Development of Orbital Assets and Advanced Projects at Roskosmos, arrived at NPO Lavochkin, the prime contractor in the Luna-Glob project with its own mission control facility. Ivanov reportedly chaired a meeting on the status of the Luna-Glob mission.

Around the same time, another Telegram channel Yura Prosti claimed that a computational error led to the final engine firing to be 1.5 times longer than required and thus resulting in deorbiting and crash of the spacecraft on the Moon.

The Moon set over the Russian territory around 21:00 local time (2 p.m. EDT) on August 19, precluding further possible communications between the spacecraft and three deep-space ground stations operated by Roskosmos. The new opportunity to hear from the lander came on the morning of August 20, first over the NIP-15 site near Ussuriisk in the Far East, followed by NIP-14 in Medvezhi Ozera near Moscow and NIP-16 near Yevpatoria in the occupied Crimea (where Russia was expected to operate some deep-space communications equipment).

At 09:47 Moscow Time on Aug. 20, 2023, Roskosmos announced that the communications with the spacecraft had been interrupted at 14:57 Moscow Time on August 19, during the orbit correction. According to the State Corporation, all attempts to contact the spacecraft made on August 19 and August 20 had failed. The preliminary analysis showed that the spacecraft had entered into an unplanned orbit and had crashed into the surface of the Moon, the State Corporation said. (According to an unofficial source, the impact took place at 15:01 Moscow Time on Aug. 19, 2023.)

According to Roskosmos a special inter-agency commission was being formed to investigate the cause of the failure.

According to one rumor surfaced on August 20, the Onboard Flight Control System, BKU (INSIDER CONTENT) of the lander mishandled the so-called variable thrust controller (privod regulyatora tyagi), which manages the operation of the propulsion system (INSIDER CONTENT) on Luna-Glob. Around the same time, the official Russian media quoted IKI scientist Natan Eismont as saying that the problems with the spacecraft had been discovered well before the fatal orbit-lowering maneuver, which would have to be postponed to deal with the problem. According to some speculations on the Russian social media, the mission managers were pressured not to postpone the transfer to a lower orbit in order to beat an Indian lander to the lunar surface, which was scheduled to touch down near the South Pole of the Moon on Aug. 23, 2023.

On August 21, Yuri Borisov, Director General at Roskosmos blamed an engine failure for the Luna-Glob crash. According to Borisov, the engine fired for 127 seconds instead of planned 84 seconds. According to unofficial sources at the time, all the commands radioed to the spacecraft ahead of the fateful maneuver were found to be correct, including the one for the timing of the engine cutoff, but for a yet unknown reason, the propulsion system kept firing and was shut down by the emergency timer, when it was too late.

On the same day, Keldysh Applied Mathematics Institute, IPM, reported that its ballistic center calculated that the crash of the Luna-Glob spacecraft had taken place at 14:58 Moscow Time on Aug. 19, 2023, at the Pontecoulant G crater located in the Southern Hemisphere of the Moon at 61 degrees 26 minutes 59.95 seconds East longitude, 57 degrees 54 minutes 36.65 seconds South latitude.

Luna-Glob crash site likely found

crash

On Aug. 31, 2023, NASA published an image from the Lunar Reconnaissance Orbiter, LRO, showing a fresh crater on the surface of the Moon likely owing its origin to the Luna-Glob crash.

According to the agency, the LRO team sent commands to the spacecraft on August 22 to snap photos of the expected crash site. The LRO conducted imaging on August 24, from 2:15 p.m. EDT to 6:12 p.m. EDT. The comparison of the new imagery to the previous photos of the area taken in June 2022, revealed a new crater with a diameter of around 10 meters. It was located at 57.865 South latitude and 61.360 East longitude.

NASA said that the impact point was on a steep (greater than 20-degree grade) inner rim of Pontecoulant G crater, around 400 kilometers short of the lander's intended landing site.

Luna-Glob failure scenario emerges

Speaking at a press-conference in Baikonur after the launch of the Soyuz MS-24 mission on Sept. 15, 2023, Head of Roskosmos Yuri Borisov said that the orbit correction engine of the Luna-Glob (Luna-25) lander had failed to cut off as planned due to (lack of) data from an accelerometer that measures velocity changes (critical for the accuracy of orbit correction). According to Borisov, the accelerometers had failed to activate (during the maneuver, preventing the on-time engine shutdown).

Borisov also said that Roskosmos specialists had evaluated 11 out of 16 possible failure scenarios and planned to complete the investigation by the end of September. However, by that time, Borisov's disclosure combined with various rumors and details surfaced on the Internet during the mission and in the subsequent weeks made it possible to ascertain an overall picture of the accident.

During the trans-lunar cruise phase of the flight, when the Luna-Glob lander had to perform some corrections of its path from the Earth to the Moon, ground controllers noticed unexplained switches from the primary to the secondary set of the BIUS-L instrument, which measures angular velocity and linear acceleration for the lander's flight control computers (INSIDER CONTENT). Upon the second attempt to activate BIUS (and with growing acceleration induced by the maneuver), the primary instrument would return to action. However, ahead of the fateful lunar orbit correction on August 19, both accelerometers worked correctly, but once the maneuver started, one set failed again, while the flight control system never switched to data from the second set. As a result, onboard computers were not receiving data about critical parameters required for properly completing the orbit correction, such as orientation of the spacecraft in space, velocity and altitude.

If confirmed, this crash scenario would likely implicate deficiencies in the development or testing of the flight control system and its software rather than any mechanical problem of the propulsion system, which was implied in the initial statement about the incident.

Roskosmos confirms Luna-Glob failure scenario

On Oct. 3, 2023, Roskosmos reported that the investigation into the Luna-25 mission failure was entering its final stage.

The official statement essentially confirmed that the most likely culprit in the accident had been the incorrect functioning of the Onboard Flight Control System, BKU, (INSIDER CONTENT), associated with the non-activation of the accelerometers unit in the BIUS-L instrument (Lunar Angular Velocity Measurement Unit), possibly, due to infiltration of commands with varying implementation priorities into the command data stream to the instrument. It was accompanied by the fact that the distribution of commands in the data stream had a random nature, the statement said. "Under these circumstances, the Onboard Flight Control System was receiving zeroed signals from the BIUS-L's accelerometers." As a result, the flight control system missed the moment when the spacecraft reached the necessary velocity and failed to perform its timely engine cutoff, in turn leading to the (late) engine shutdown based on the timer marker.

According to Roskosmos, "recommendations had been formulated for additional measures excluding such contingencies in the subsequent lunar missions."

Luna-Glob's space tug to reenter

The Fregat upper stage No. 122-10 that delivered the ill-fated Luna-Glob lander into its trans-lunar trajectory and remained on a high elliptical orbit around the Earth was expected to reenter the Earth's atmosphere and burn up on Feb. 26, 2024, according to calculations by the Keldysh Applied Mathematics Institute, IPM. The space tug was predicted to hit the dense atmosphere at 18:43:09 UTC (21:43 Moscow Time, 1:43 p.m. EST) some 400 kilometers north/north-west of the American Samoa in the Southern Pacific Ocean. The reentry forecast was produced based on the tracking of the Fregat made with the help of IPM's telescopes.

 

 

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Page author: Anatoly Zak; last update: February 27, 2024

Page editor: Alain Chabot; Edits: August 10, September 16, October 3, 2023

All rights reserved

 

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The fully assembled Soyuz-2-1b/Fregat launch vehicle with the Luna-Glob lander shortly before rollout to the launch pad in Vostochny. Click to enlarge. Credit: Roskosmos


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The Fregat upper stage (left) and the Luna-Glob lander attached to the launch vehicle adapter. Click to enlarge. Credit: Roskosmos


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A close-up view at the interface between the Fregat upper stage and the Luna-Glob lander. Click to enlarge. Credit: Roskosmos


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Luna-Glob lifts off on Aug. 11, 2023. Credit: Roskosmos


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A half of the payload fairing found at the drop zone of the Luna-Glob mission several hours after its launch on Aug. 11, 2023. Credit: Roskosmos


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A cloud of gas formed during the second firing of the Fregat upper stage sending Luna-Glob spacecraft toward the Moon as seen by a Russian ground-based telescope. Credit: KIAM & ISON


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Click to enlarge. Credit: Roskosmos

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Click to enlarge. Credit: Roskosmos


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First images from the Luna-Glob probe. According to the Space Research Institute, IKI, photos were taken on Aug. 13, 2023, at a distance of 310,000 kilometers from Earth. Click to enlarge. Credit: Roskosmos


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On Aug. 17, 2023, IKI released first image of the lunar surface produced by Luna-Glob's STS-L TV system (INSIDER CONTENT) at 08:23 Moscow Time. It showed Zeeman Crater near South Pole with a center at 75 degrees South latitude and 135 degrees West longitude. Click to enlarge. Credit: Roskosmos


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Several days after Luna-Glob crash, Roskosmos head Yuri Borisov held a meeting at NPO Lavochkin, prime developer of the project. Click to enlarge. Credit: Roskosmos


 

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