Russians still troubleshooting ISS computers – EAS to be jettisoned

by Chris Bergin

Russian engineers are continuing to troubleshoot their computer systems onboard the International Space Station (ISS), which in turn discovered a new issue, this time with the KURS system.

A KURS/thruster test has now been added to the ISS schedule for July 21, with refinements to the arrival of Progress M-61/26P, potentially to the US EVA-9 spacewalk, and the subsequent timing for the jettisoning of the EAS (Early Ammonia Servicer) tank.

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The Russians have been working on finding a root cause to their computers issues since midway through the arrival of Atlantis during STS-117, with the temporary solution of installing bypass jumper cables which allowed a successful re-start of their systems, allowing normal ISS operations until replacement computers are delivered via the next Progress flight.

While that root cause remains illusive, another issue – not yet known if it’s related – appeared within the Ukrainian built KURS system in the Zvezda Service Module. The Russian ISS computers that caused issues last month are German built systems.

‘As part of the ongoing troubleshooting of the RS Terminal/Central (TVM/TsVM) computer lanes, RSC Energia today (Thursday) also tested the SM KURS automated rendezvous & approach radio system (which shares a component with the TVM computer) to investigate any possible connection to the recent computer failure,’ noted Thursday’s ISS On Orbit Status report.

‘Today’s test encountered a problem with KURS’ 2nd string (preliminary indications are that this issue may be KURS-internal and not linked to the TVM). A KURS/thruster test is being planned as a functionality check of the new Russian software version 7.05 which will be loaded on TsVM & TVM shortly (restart on v7.05 planned on 7/16).

‘Afterwards, installation of all bypass jumpers on the six lanes will be completed. After some operating time, the thruster test will be conducted tentatively on 7/21, before the next spacewalk, EVA-9.’

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While sources claim that EVA-9 will still take place as scheduled on July 23 at 10:30 UTC, the latest On Orbit information points to an under-review date in the second half of August. However, the new launch dates for the next Progress appear more solid, showing they will happen just prior to Endeavour’s arrival – as opposed to earlier in July, which was under review during the heights of the Russian computer issues.

’08/01/07 – Progress M-59/24P undocking (DC1) & re-entry. 08/02/07 – Progress M-61/26P launch. 08/05/07 – Progress M-61/26P docking (DC1 nadir),’ added schedule information, confirming the next Progress will dock two days before Shuttle Endeavour launches on STS-118 – arriving at the ISS on the 9th of August.’

Also now confirmed is the jettison of the 1412lb Early Ammonia Servicer (EAS) tank – which won’t be returned to Earth for re-fuelling – one of several options that were discussed by NASA.

The EAS consists of two nitrogen tanks that provide compressed gaseous nitrogen to pressurize the ammonia tank and replenish it, as needed, in the thermal control subsystems of the Station. It also contains additional stocks of ammonia for American Early External Ammoniac Thermal Control System (EEATCS).

The 680kg tank was launched on STS-105 with Discovery in August, 2001 – and installed by astronauts Daniel Barry and Patrick Forrester during two spacewalks.

The Servicer was to remain attached to the Station until a permanent system is activated on a future mission, or recycled on Earth before being returned later in the manifest.

However, due to relocation requirements of the Space Station Remote Manipulator (SSRMS) – the EAS either needed to be relocated. Given there is no where else for the tank to go, it will be jettisoned overboard. NASA since noted that the decision surrounding EAS related to the lifetime of the tank, rather than a problem with its current location.

‘The EAS was certified for an on-orbit life of five years which will run out this fall (2006),’ NASA’s Kylie Clem, International Space Station & Mission Operations Directorate Public Affairs, noted to this site back in June 2006. ‘Engineers are evaluating extending that for one more year as we work on a plan to safely remove it and return it or jettison it.

‘The timeframe we are currently evaluating is the 13A.1 (STS-118) stage. We originally planned to return it on shuttle when it was no longer needed. Other options are being discussed because of the limited number of shuttle flights remaining and considering it will have reached its certified structural limit.

‘It was put in place to service the early external active thermal control system and the photovoltaic thermal control system in the event either system had a leak. If there was a leak, a spacewalking crew would perform the necessary repairs or reconfigurations and then use the EAS to refill the cooling system with ammonia.’

However, while NASA didn’t officially note the decision of the EAS’ fate, it’s now confirmed it will be jettisoned from the ISS in conjunction with an re-boost of the station.

‘EVA-9 will be followed immediately by an altitude reboost, linked to the jettisoning of the 7A.1 EAS (Early Ammonia Servicer) of 1412 lb mass, with ~300 lb of ammonia & ~21 lb nitrogen),’ noted Thursday’s On Orbit status report.

The next milestone to take place onboard the ISS will be the welcomed addition of additional oxygen supply capacity via the US’ Oxygen Generating System (OGS). Work has been taking place since STS-117, ready for its activation on July 11.

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