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MLM Nauka makes triumphant docking to ISS - NASASpaceFlight.com [nasaspaceflight.com]:

Russia’s Multipurpose Laboratory Module (MLM) Nauka, meaning “science,” has defied the odds to successfully dock to the ISS after a long and arduous journey dating back over 20 years and a problematic propulsion system after launch which had threatened the success of the mission.

The docking was not without issue, with Russian cosmonauts noting that Nauka wasn’t on the correct course less than an hour before docking; however, a retro burn quickly corrected the issue. After also troubleshooting an issue with the TORU manual docking system, which was used for the final seconds of the module’s approach, Nauka successfully docked to the Zvezda service module’s nadir port at 09:29 EDT / 13:29 UTC, marking the first major expansion to the Russian segment for over 20 years.

Nauka docking

Nauka had been chasing down the International Space Station (ISS) for the last eight days after being launched atop a Proton-M booster from the Baikonur Cosmodrome in Kazakhstan on 21 July. [nasaspaceflight.com]

Immediately after a successful orbit insertion of 190 x 350.1 km, issues with the module’s communications and propulsion systems were noted. Initial troubleshooting was complicated by limited communications during brief periods when the module came within range of Russian ground stations.

The communications issues were resolved in initial orbits; however, the propulsion system issue was more troublesome and believed to be related to a part of the module’s fuel supply being rendered unusable due to gases becoming mixed with the fuel for the main engine.

Reports indicated that pressure in the main engine’s propulsion tanks had risen to unacceptable levels due to an earlier-than-planned equalization of pressure between the tanks. Thus, use of the smaller engines would be needed to relieve tank pressure to a point where the main engine could be used.

The EDL phase of a Mars mission is often referred to as "7 minutes of terror”. After #Nauka [twitter.com] launch, the entire Russian space community experienced what I can call “8 days of terror”. But now it’s almost over! Let’s watch Nauka docking today at 13:26 UTC: https://t.co/LTfTe7XFch [t.co]pic.twitter.com/eMufXKVsun [t.co]

— Katya Pavlushchenko (@katlinegrey) July 29, 2021 [twitter.com]

That, coupled with continuous limited communications, resulted in several of the initially-planned orbit raising burns being cancelled and then later conducted using the module’s secondary engines.

These replanned first burns were enough to prevent Nauka from reentering the atmosphere within a few days, as was the fear given the low perigee insertion of 190 km. With those first burns, Russian controllers were able to stabilize Nauka, get the main engine working, and keep the module on track for a 29 July arrival at the Station as originally planned.

Approaching the ISS [nasaspaceflight.com], Nauka used its KURS automated rendezvous system as intended; however, the module was also equipped with a TORU manual docking system, which would have enabled cosmonauts Novitsky and Dubrov aboard the ISS to take control of Nauka and fly it manually if needed.

For the docking, the ISS was placed in a special attitude – essentially pitched up 90 degrees – in order to place Nauka’s docking axis along the velocity vector. This was not the original plan, which would have seen Nauka approach up the R-bar, or Radial velocity vector, with the nadir Zvezda port facing straight down at Earth.

The ISS orientation plan for docking was changed to accommodate Nauka’s as-is condition after launch.

Docking was made to Zvezda’s nadir docking port, which was recently vacated by the Pirs module on 26 July. [nasaspaceflight.com] This port uses a docking system called the Hybrid Drogue Adapter (HDA).

HDA is a Russian system which is essentially the combination of the traditional Probe & Drogue (SSVP) system and the Androgynous Peripheral Attachment System (APAS), on which the docking system of Dragon and Starliner is now based.

Specifically, HDA uses the docking collar from the APAS system, but rather than use a capture ring as is the case on the US segment, it instead uses a docking drogue as found on the SSVP system. This enables dockings to occur the same way as they do for Soyuz/Progress vehicles but gives a wider passageway through the hatch, which is useful for permanent modules.

Following docking and hard capture, the next immediate steps will be leak checks and vestibule pressurization followed by hatch opening, first ingress, and module activation.

Future plans:

A total of up to 11 spacewalks will be required in order to fully outfit and commission Nauka, with the first of these set to be performed in September.

Externally, after the module has been connected to the ISS via a series of cables, the first order of business will be to deploy the European Robotic Arm (ERA), which launched attached to the outside of Nauka. [esa.int]

This will involve removing external covers and launch restraints, following which the arm will be activated and fully checked out from the ground. ERA needs to be fully operational in order to proceed with the next phase of operations – which is transferring an airlock and radiator to Nauka.

This radiator and airlock were launched to the ISS attached to the outside of the Mini Research Module-1 (MRM-1) Rassvet on the STS-132 mission in May 2010 by Space Shuttle Atlantis. For the past 11 years, they have waited patiently for the arrival of Nauka.

The deployable radiator will be used to add additional cooling capability to Nauka, which will enable the module to host more scientific experiments. The airlock will be used only to pass experiments inside and outside the module, with the aid of ERA — very similar to the Japanese airlock on the US segment of the station.

The ERA will be used to remove the radiator and airlock from MRM-1 and transfer them over to MLM – with an extension boom being required to allow ERA to reach the airlock. This process is expected to take several months. A Portable Work Platform will also be transferred over, which can attach to the end of the ERA to allow cosmonauts to “ride” on the end of the arm during spacewalks.

Nauka also features a docking port on its nadir which other modules/vehicles can dock to. This port is also of the HDA type (passive side), however it features a special adaptor in order to convert it into a traditional Probe & Drogue port. This adapter converts the APAS docking collar into an SSVP docking collar, which will enable Soyuz and Progress vehicles to dock to MLM.

In November, Russia will launch the Node Module (NM) Prichal to the ISS, which will dock to the nadir port of Nauka and will add a further four HDA-type ports to the Russian Segment for future expansion – although any expansion plans are now somewhat up-in-the-air following Russia’s decision to focus their future efforts on constructing their own station to succeed the ISS, possibly in cooperation with China.

Prichal will dock to Nauka using the HDA system, which will first require the removal of the HDA-to-SSVP adapter ring from the nadir port of Nauka.

This ring was therefore added as an “insurance policy” in case Prichal failed to make it to orbit, which would have rendered Nauka’s nadir HDA port useless as Soyuz and Progress vehicles would not have been able to dock to it which would have left the Russian Segment with only three usable docking ports.

The first docking to Nauka is planned for September 28, when Soyuz MS-18 will be relocated from Rassvet to Nauka’s nadir port in order to clear Rassvet for the arrival of Soyuz MS-19. MS-18 will then depart Nauka on October 17, whereupon Progress MS-17 will be undocked from MRM-2 Poisk and relocated to Nauka on October 27.

Assuming Prichal is successfully launched on November 24, Progress MS-17 will then undock from Nauka, taking with it the APAS-to-SSVP adapter ring, which will convert Nauka’s nadir port back to HDA configuration ready for the arrival of Prichal.

In future, it will be standard practice to dock Soyuz vehicles to the nadir ports of Rassvet and Prichal and dock Progresses to the aft port of Zvezda and the zenith port of Poisk.

This is because the transfer chamber which connects to Zvezda’s aft port has a small leak which requires the hatches to remain closed as much as possible, which would block access to a Soyuz if it were docked to Zvezda’s aft port. In addition, Progress crafts are preferred for Zvezda’s aft port as this enables them to perform ISS reboosts using their main engines.

Progresses are also preferred for the Poisk zenith port as Poisk is now serving as the Russian Segment’s airlock following the departure of Pirs, and access to Soyuz craft docked to Poisk is blocked whilst Poisk is depressurized during spacewalks, which presents safety issues in an ISS evacuation scenario.

(Lead image: Nauka arriving at ISS. Credit: Mack Crawford for NSF/L2)

Also at phys.org [phys.org], www.nytimes.com [nytimes.com]

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