ISS managers prepare for possible de-crew – launches to resume soon
International Space Station (ISS) Program managers are continuing with precautionary preparations for station operations without the presence of on-board crewmembers, in the event that a de-crewing of the ISS is needed should Russia be unable to return the Soyuz booster to flight by mid-November.
Soyuz failure latest:
The Soyuz failure that caused the loss of the Progress M-12M/44P spacecraft on 24th August was attributed by a Russian investigation to a blocked fuel line leading to a gas generator in the Soyuz booster third stage’s RD-0110 engine. As a precaution, all third stages at the Baikonur Cosmodrome in Kazakhstan were transported back to their assembly plant in Russia for a full inspection.
According to Russian media reports, Roscosmos head Vladimir Popovkin confirmed to the Russian Government last week that the inspections have revealed no issues with any other third stage engines, and thus the third stage engine failure on the Progress M-12M flight has been attributed to a random one-off manufacturing defect.
This clears the way for the return to flight of the Soyuz booster, which is set for 30th October when a Soyuz-U booster will loft the un-crewed Progress M-13M/45P spacecraft. Although a Soyuz booster launched a Russian GLONASS satellite into orbit last week, that booster carried a Fregat upper stage which was different to the third stage that failed in August.
Providing the Progress M-13M launch is successful, crewed flights aboard Soyuz boosters will resume on 14th November, when a Soyuz-FG booster will launch the Soyuz TMA-22/28S spacecraft carrying Russian cosmonauts Anton Shkaplerov & Anatoly Ivanishin, and US astronaut Dan Burbank.
The docking of Soyuz TMA-22 to the ISS on 16th November will temporarily boost the ISS crew back up to six crewmembers, since it is currently operating at a reduced three crewmembers following the departure of Soyuz TMA-21/26S on 16th September. Despite this reduced crew, the target of 35 crew hours per week of scientific research continues to be met aboard the orbital outpost.
Following a crew handover period of less than one week, the ISS will once again be reduced to three crewmembers when Soyuz TMA-02M/27S, carrying Russian cosmonaut Sergey Volkov, US astronaut Mike Fossum, and Japanese astronaut Satoshi Furukawa, departs the ISS on 22nd November for a landing in Kazakhstan.
Soyuz TMA-03M/29S will then launch on 21st December, carrying Russian cosmonaut Oleg Kononenko, US astronaut Don Pettit, and European astronaut André Kuipers. This will put the ISS back up to six crewmembers by year-end. This, however, is a best-case scenario that assumes the Soyuz booster returns to flight successfully.
ISS de-crew preparations:
In the event that Soyuz TMA-22/28S does not reach the ISS by the time that Soyuz TMA-02M/27S has to depart on 22nd November, ISS Program (ISSP) managers are continuing with precautionary preparations for a de-crewing of the station.
“The ISSP will continue to work two separate paths, de-crew and not de-crewing, until 28S launches. Utilization is not top priority during this time frame as certain de-crewing activities need to be performed to keep multiple options open” stated recent L2 notes. “Two de-crew sims are planned for Flight Directors (FDs) and the flight control team”, continued the notes.
There are many concerns relating to leaving the ISS in an un-crewed configuration, mitigations for which were recently reviewed in a set of ISS de-crewing preparation presentations, available to download on L2.
A major area of concern relates to the atmosphere of the ISS, both in event of a Micro Meteoroid Orbital Debris (MMOD) strike, and the long-term effects of stagnant air inside the station.
In order to protect against the risk of ISS depressurisation in the event of an MMOD strike, all hatches in the US and Russian Segments of the ISS would be closed prior to de-crewing of the ISS. This would prevent the whole station from depressurising in the event that one module were to suffer an MMOD strike.
The Oxygen (O2) and Nitrogen (N2) system on the station would also be isolated. The Common Cabin Air Assembly (CCAA), essentially the station’s dehumidifier, would be left active in order to prevent any potential issues with temperature, humidity, condensation, and resulting microbial growth in the absence of crewed presence.
The presentations note that all trash items that will pose long-term odour, fungal and/or microbial growth issues will be disposed of on Progress M-10M/42P when it undocks from the ISS on 29th October, in order to reduce some of the risks associated with microbial growth. Microbial growth would present an issue for crews returning to the ISS, since it would present them with a hazardous atmosphere.
Inter Module Ventilation (IMV) fans would remain active in order to provide cooling to all modules, although leaving IMV fans on does increase the risk of on-board fires due to increased airflow, at a time when no crews would be present to extinguish them.
The IMV valves – essentially valves between modules – would remain open, so as they could serve as Positive Pressure Relieve Valves (PPRVs) to prevent positive pressure differentials building up between sealed-off modules. The IMV valves could be commanded closed by the ground in the event of an MMOD strike on a module, in order to prevent depressurisation of the entire station.
To further reduce the risk of fire, many pieces of equipment would be shut off prior to crew departure, including Portable Computer System (PCS) and Station Support Computer (SSC) laptops.
Environmental Control & Life Support System (ECLSS) hardware such as the US Carbon Dioxide Removal Assembly (CDRA) and Oxygen Generation System (OGS), and Russian Electron oxygen generator and Vozdukh carbon dioxide removal system would also be shut off, since there would be no crews aboard the ISS to require oxygen or produce carbon dioxide.
The US Water Processor Assembly (WPA) and Urine Processor Assembly (UPA) would remain active and would periodically be used to process urine into water, in order to keep fluids flowing through the lines in the WPA and UPA, preventing stagnation.
Essential science hardware would remain powered on in order to preserve valuable scientific samples. This hardware includes the Minus Eighty-degree Laboratory Freezer for ISS (MELFI), GLACIER and MERLIN freezers.
Numerous other risks are presented by operating the ISS without any crews, since no crews would be aboard to deal with any issues that may arise, such as vital hardware replacements in the event of a failure.
Perhaps the most serious risk would be a loss of attitude control by the ISS, since it could potentially lead to a complete loss of the station. While a string of failures would be needed for such a situation to occur, a loss of attitude control could cause the ISS to enter a tumble, which would prevent future spacecraft from docking to the ISS, and also preclude ISS reboosts from occurring.
Communications between the ground and the ISS could also be lost since the ISS’ antennas would not be able to maintain a lock on orbiting satellites or ground stations. This situation would mean that the ISS would slowly lose altitude and eventually enter into an uncontrolled re-entry, possibly endangering populations below.
Another less serious risk would be the loss of three US Segment Command & Control (C&C) Multiplexer/Demultiplexers (MDMs), a situation that has occurred before on the ISS. Such a loss would cause the Node 1 C&C MDM to take over the primary C&C MDM, however the Node 1 MDM does not provide for commanding of the US Segment via S-Band, which is the usual method of commanding the US Segment.
This means that the US Segment would need to be commanded through the Russian Segment as it passes over Russian Ground Sites (RGSs), but this is limited in capability. The ISSP is currently evaluating the potential to command the US Segment via the station’s Ku-Band antenna.
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A leak inside a station module (such a water coolant) is another risk that would be increased if no crew were aboard the station to clean it up. Prior to crew departures, jumpers would be installed between critical hardware (such as avionics) and the station’s Low Temperature Loop (LTL) water coolant loop, to protect against the loss of the Moderate Temperature Loop (MTL).
Any batteries aboard the station would also need to be disposed of prior to crew departure, to prevent against their degradation. The Mobile Transporter (MT) would be prevented from translating along the station’s truss during an un-crewed period, since no crewmembers would be available to conduct an EVA to repair the MT in the event that it became stuck.
Another potentially very serious risk involved in un-crewed operations relates to Progress resupply vehicles. Prior to crew departure from the station, BZV clamps that help hold Progresses onto the ISS would be removed.
This would allow Progresses to depart the station so that new Progresses could be launched with additional propellant, enabling indefinite ISS reboosts to occur, allowing the ISS to stay aloft for years in an un-crewed configuration.
However, during Progress dockings, no crewmembers would be available aboard the ISS to take control of incoming Progresses via the TORU manual control system should the automated KURS system fail, as has happened on many occasions in the past. Thus, Progress dockings would become single fault tolerant, and risks associated with a collision between a Progress and the ISS, as occurred on the Mir space station in 1997, would be increased.
According to recent L2 notes, NASA ISS Program Manager Mike “Suff” Suffredini wants the capability to dock a European Automated Transfer Vehicle (ATV) to the ISS in the un-crewed configuration, in addition to Russian Progress vehicles.
“Suff asked the team to protect for doing an ATV docking in an unmanned configuration. The idea is that we need a method for getting new propellants on the ISS if a Russian vehicle cannot be launched.
For this to be necessary, the ISS would need to be unmanned for about 9 months. It is very unlikely that the Russians would not be able to launch a Progress by then” stated the notes (L2).
Upcoming resupply flight schedule issues:
While the issue of ISS crewing is worked by the ISSP, the issue of station resupply flights and associated issues is also being diligently worked by the ISSP and their commercial partners.
Even commercial resupply flights have been affected by the Progress M-12M launch failure, since SpaceX have been forced to move their Dragon D2/D3 demo into what is likely to be a January 2012 timeframe, since the Soyuz launch delays meant that a full crew trained to berth Dragon to the ISS would not have been present on the station on Dragon’s original 9th December arrival date.
However, another issue affected by the Progress M-12M failure, which has knock-on effects for the commercial resupply flight schedule, is the series of software updates that were planned for the ISS, which will enable the station to support the new commercial vehicles.
The current version of ISS software is X2_R9. Prior to the Progress failure, the plan was to transition the ISS to X2_R10, which would add support to the station for new Enhanced Processor and Integrated Communications (EPIC) cards.
An upgrade called PEP R10 would have followed that, and then X2_R11 would have been uploaded to the ISS, which would have upgraded the Mobile Servicing System (MSS) software from its current version of 6.3, to the new version of 7.1, which is capable of supporting robotics operations for the new commercial vehicles.
However, the Progress failure and subsequent impact on crew schedules scuppered that plan, since crews are needed for EPIC installation, testing, and diagnostic activities. The EPIC transition has encountered problems, with a recent L2 note stating “for the EPIC cards, no real discovery of route cause, looking at modification to resistor output logic voltages”.
The new plan will see PEP R10 uploaded to the ISS first, which will add some support for the EPIC cards, and also enable the current MSS 6.3 to support robotics operations for the new commercial vehicles. This is currently planned for February 2012. X2_R10 and X2_R11 would follow sometime afterwards.
This means that if any commercial vehicles fly to the ISS before or during February, before the PEP R10 transition can take place, they will have to use the current ISS software, X2_R9, for which they are not designed to be compatible. Orbital’s Cygnus vehicle also needs the EPIC cards in order to be compatible with the ISS.
According to related presentations (L2) “the biggest impact is probably to Orbital because they do not have any telemetry in X2_R9”. Another L2 note related to Cygnus software stated that “the Orbital sim checkout last week did not go well. The data flow problem still exists, so telemetry is not populating as expected. Orbital thought their software update would solve the problem, but it did not. We will talk with them this week about revamping the sim schedule”.
L2 notes also detail another issue facing Orbital in development of their Cygnus vehicle software: “During a TIM (Technical Interchange Meeting) with Orbital 3 to 4 weeks ago, there was a scenario where the vehicle was close to ISS, and there was a 55-second-delay to abort.
This is how much time it takes to wake up the vehicle, because their command shuts down the entire propellant system. Orbital said that this could be cut down to 30 seconds, but the PCS (Portable Computer System) command takes 20 seconds, getting us back up to 50. This is an issue he will be discussing with them”.
Future ISS cargo/stowage issues:
A recent ISS stowage status presentation, available to download on L2, detailed some of the concerns relating to cargo deliveries and stowage from the realigned flight schedule.
According to the presentation, the loss of Progress M-12M/44P didn’t have an adverse effect on on-board cargo, with the presentation noting “Priority cargo replanned for other vehicles. Consumable supplies not impacted due to surplus on ISS” – the surplus referring to the massive delivery of cargo by the final Space Shuttle flight, STS-135.
What was lost, however, is the trash capability of Progress M-12M/44P. As previously mentioned, ISS managers would like to dispose of as much cargo as possible prior to a potential de-crew. As such, plans are being formulated to dispose of a high amount of US trash on Progress M-10M/42P, which docked to the ISS back in April and is currently set to depart on 29th October.
According to the presentation, 60 Cargo Transfer Bag Equivalent (CTBE) of cargo will be disposed of on Progress M-10M/42P, whereas the historical average of US trash disposed of on Progresses is 25 CTBE, with the remainder of Progresses 90 CTBE capability being taken up by Russian trash. “Russian agreement that all US trash will be accommodated” noted the presentation.
Looking ahead to upcoming resupply flights, Progress M-13M/45P, set to launch on 30th October, will carry 37 CTBE of US cargo to the station. The SpaceX D2/D3 flight will deliver 41 CTBE, although it has a capacity of 50 CTBE. Orbital’s D1 flight will carry 20 CTBE of cargo, although it has a capacity for 66 CTBE. Japan’s HTV-3 will launch 58 CTBE of cargo, with a capacity for 160 CTBE. And Europe’s ATV-3 will launch with a full complement of 160 CTBE of cargo.
The reason that the full cargo capability of some vehicles is not being exploited is due to trash concerns, with the presentation noting regarding the SpaceX D2/D3 flight “launching empty bags (18 CTBE of the 41) to facilitate maximum disposal capability for SpaceX and Orbital demo flights”.
The trash concerns stem from the possibility that the rate of cargo deliveries aboard the ISS may surpass the disposal capabilities of the vehicles, leading to an “overstow” situation. One CTBE of common trash per three crewmembers – or two CTBE per six crewmembers – is created every day on the ISS.
The presentation notes that Russia’s Progress M-13M/45P flight will accumulate 80 CTBE of stowage aboard the ISS, but only dispose of 42 CTBE, leaving a leftover of 38 CTBE aboard the ISS.
The SpaceX D2/D3 flight will accumulate 67 CTBE, but only dispose of 16 CTBE, leaving a left-over of 51 CTBE (although the Dragon vehicle has the capacity to dispose of 50 CTBE). Orbital’s D1 flight will accumulate 78 CTBE, and dispose of 66 CTBE, leaving a leftover of 12 CTBE.
The current plan of altering vehicle manifests to include less cargo is done in order to create less on-board stowage impacts and preserve trash opportunities. The presentation notes that under this plan, the “next foreseeable stowage issue is at ATV-3 arrival in March 2012”.
If resupply vehicles were launched with more cargo aboard in order to utilise their full capacity, then the “spacing” between the cargo vehicle flights would need to be increased to allow for more cargo to be launched. This however would mean that “trash levels on ISS will increase and may surpass disposal opportunities. Trash issues could start as soon as Jan 2012”.
Although the ISS now has a storage closet in the form of the Permanent Multipurpose Module (PMM), the effects of the loss of the massive disposal capacity of the Space Shuttle are already being felt aboard the station.
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