Figure 1. The Mir station, photographed from the Space Shuttle
For more than ten years, the Mir station has been the
World's only permanently manned laboratory in low earth orbit.
With an orbital inclination of 51.6°, its ground track
covers more than 85% of the Earth's surface, where approximately
95% of the population lives.
For the transfer of up to three crew members per trip to and
from Mir, the 6.9 t Soyuz spacecraft is used. In general, the
station's crew is changed every six months, with an overlap
during the exchange of between one and two weeks. A Progress
spacecraft (an unmanned derivative of the Soyuz vehicle) visits
the station every three months to resupply it, with up to 2.1 t
of payload, and to reboost it to maintain its nominal orbital
altitude.
The station's core module, injected into orbit in February
1986, contains the central control post for most onboard systems,
the computer for attitude control, and the telemetry and
communications system. It also contains the station's largest
work space, which is 7.0 m long and varies in width between 1.5
and 2.5 m.
The layout of the station during the Euromir 95 mission is shown in Figures 1 and 2. The Kvant module, which contains many astrophysical sensors and experiments, has been attached to the station (along the +X-axis) since April 1987. Three more modules have been docked to the central node of the station since then:
Figure 1. The Mir station, photographed from the Space Shuttle
Figure 2. Schematic of Mir's configuration at the time of the
Euromir 95 mission
During Space Shuttle flight STS-74 in November 1995, an Interface Module was permanently attached to Kristall's APDS-port (Androgynous Peripheral Docking System) to facilitate future Shuttle dockings. In March 1996, the station achieved its final configuration when the fifth module, Priroda, was attached along the +Z-axis. Two docking ports on the central node ( X) and the Kvant module (+X) are available for the Soyuz and Progress spacecraft. There are two more APDS-ports on the rear end of Kristall and on the Interface Module.
With Priroda's arrival, the total mass of the Mir complex reached 120 t and it now contains a hermetic volume of approximately 350 m³. A maximum of 35 kW of electrical power is provided by the station's solar arrays and the power supply to all modules is based on a 27 V direct-current bus.
The station's attitude is generally controlled with the help of 12 gyrodynes, located on the Kvant and Kvant-2 modules. Its reaction-control system is activated only briefly when the gyrodynes need to be desaturated.
The station has five generic ECLS systems on board:
Oxygen is produced by two electrolysis units one in Kvant and one in Kvant-2 which use water distilled from the urine- collection system. Nominally, these units are operated sequentially. A contingency system, also located in Kvant, uses pyrotechnic cartridges for oxygen production.
For the removal of carbon-dioxide and other detrimental pollutants from the station's atmosphere, a total of four systems are available. The two main units, located in Kvant, employ regenerative filters, which are periodically connected to vacuum venting lines. For contingency operations, there are two more systems in the core module which use LiOH catridges for carbon- dioxide filtering and cartridges containing other materials for the pollutants.
There are two air conditioners in the core module, one connected directly to one of the module's cooling loops and one using a conventional freon loop for efficient cooling and dehumidifying. If necessary, moisture removal from the station's atmosphere can be supported by the air conditioner in the Soyuz capsule.
To ensure a standard flow pattern within each module and air exchange between all modules, numerous ventilators are used (approx. 30 in the core module and 20 in the other modules). In the nominal flow pattern, air is routed from the region beside the front hatch through the free working space. Via lattices in the rear part of the modules, it enters the area behind the panels and moves in the opposite direction towards the front again, passing through air-liquid heat exchangers and dust filters.
Air exchange between the various modules takes place via flexible ventilation ducts (Fig. 3), driven by ventilators, installed at 5 to 7 m intervals.
Figure 3. Some of Mir's flexible ventilation ducting
There is a unit for regenerating distilled water from the urine collection system installed in the Kvant-2 module. As already mentioned above, this water is used for oxygen generation in the two electrolysis units. Another system installed in the core module regenerates drinking water from the condensate produced by the air conditioners. In this unit, the condensate is filtered, sterilized and re-mineralized, mainly for food preparation purposes.
Every module of the Mir station is equipped with its own thermal-control system. In general, internal thermal-control loops are used to maintain the temperatures of the station's atmosphere, internal structure and onboard systems within a given range. Excessive heat is initially transferred to external thermal-control loops via heat exchangers and then radiated into space.
In contrast to the Kvant module, which contains only one internal and one external circuit, all other modules are equipped with redundant internal and external thermal-control loops. The core module even contains two types of redundant internal circuits, namely two low-and two medium-temperature loops.
The Kristall module has a separate loop cooling the furnaces, while in Kvant-2 another separate loop removes heat from the electrolysis unit.
Discrete temperatures for the cooling fluid in the external thermal-control loops can be selected by the crew or by ground control. The selected temperature is then maintained by an electronic unit, regulating the flow of cooling fluid through the radiators. In this way, a constant temperature difference is maintained between the internal and external circuits in the heat exchangers. The radiators either contain coils of the cooling loop or a single cooling line to which heat pipes are connected.
The daily work routine onboard a space station is mainly determined by four factors:
Daily schedule and crew time
In contrast to short-
term missions, where the crew usually works in shifts, where the
daily networking time is comparatively high and where experiments
are run to a very tight schedule, long-term missions require more
balanced planning in order to maintain good crew performance.
Consequently, the daily work aboard Mir is planned in a very
similar way to that in a 'normal' working environment on the
ground.
During nominal operation, a Mir working day consists of 6.5 nett working hours (experimental work and/or system maintenance). In addition, 2 h per day are planned for physical fitness activities to counteract the effects of long-term weightlessness on the human body. One hour each evening is foreseen for debriefing sessions with the ground staff and preparations for the next day's activities.
This schedule is maintained for the 5 working days each week. At weekends, the work schedule is slightly reduced, to 3 5 h, including normal 'housekeeping tasks', but the 2 h of physical- fitness training is maintained.
Given that the two main objectives of the Euromir 95 mission were execution of the scientific programme and the acquisition of operational experience in conducting normal maintenance and repair work onboard Mir, approximately 70% of the total working time was allocated to the experiment programme, and the remainder to the onboard engineering tasks.
Experiment hardware and data handling
As there were
no spare payload racks available, all of the Euromir 95
experiment equipment had to be self-contained, apart from being
connected to the station's power supply. Only in two cases was
equipment connected directly to Mir's telemetry system (the TITUS
materials-science furnace and an active astrophysical sensor on
the ESEF platform).
Experiment control, as well as acquisition and storage of experiment data, was performed either by subsystems within the equipment or via a laptop computer connected to the hardware. The experiment hardware was not equipped with special diagnosis electronics, nor was the laptop configured to perform a detailed failure analysis in the event of a subsystem malfunction. Many of the experiment systems were equipped, however, with electrical connectors 'for ground test only'.
In most cases, experiment data were stored doubly-redundantly on different data carriers: primary data were either collected on the laptop's hard disk, on PCMCIA memory cards or on PCMCIA hard disks. Data compression and backup was performed automatically on PCMCIA hard disks and manually onto a magneto- optical disk via the NASA-MIPS2 (Mir Interface Payload System) controller. Data recorded manually on questionnaires or in tables were also typed into the laptop (.txt files) and backed-up electronically as described above.
Communication and telemetry
Voice communication
with the Russian Flight Control Centre (TsUP) was established via
three duplex channels: two UHF channels for a direct link via
different ground stations and one channel via a geostationary
satellite. All three channels used fixed frequencies. The ground
stations were mainly located on Russian territory. On a few
occasions, however, a UHF link with the TsUP was established via
an American and a German ground station. Communication times
ranged from 5 min to a maximum of 20 min for the direct (UHF)
links, depending on orbit orientation, and up to 40 min for the
satellite link. The UHF-2 channel was available to the Euromir
team only occasionally and over discrete ground stations.
In parallel with the UHF voice link, the daily schedule and procedures were uplinked via modem and printed with a teletype. This operation neither interrupted nor restricted normal voice communications on that channel. Packet file transfer to and from the station was also effected via one of the three voice channels, but no voice communication was possible on that channel while a transfer was in progress.
A video link (SECAM, down, up or up/down) was nominally arranged via a geostationary satellite, with duplex voice link at the same time. Black-and-white video could also be downlinked using one of the UHF channels.
Scientific data could only be downloaded offline via the NASA MIPS2 controller, connected to the Mir telemetry system. The controller was set up for data transfer using the crew's laptop. There was no online data downlink available whilst experiments were in progress during the Euromir 95 mission.
Onboard system maintenance
As several of the
station's modules have already spent a long time in orbit,
planned and unplanned maintenance and repair activities absorb
a considerable amount of crew time. Spare parts for all of the
different ECLS systems and the electrical power-supply system
were always available, with depleted stocks re-supplied via the
Progress spacecraft visits.
As only a limited number of system parameters were displayed to the crew, a thorough assessment of system performance could only be made at the TsUP, where the complete telemetry data set was available. All maintenance and repair activities were therefore performed in close consultation with the respective system specialists at the TsUP.
Figure 4. ESA Astronaut Thomas Reiter executing one of the many
life-science experiments
The combination of the specific working environment onboard the station and the designs of some of the Euromir 95 scientific equipment caused difficulties with the execution of some experiments. As a consequence, the allocated experiment time was exceeded and, in a few cases, the quantity and quality of the scientific data was degraded.
However, due to the extended mission duration and the fact that some of the time allocated for onboard engineering tasks could sometimes be used as a buffer for experiment operations, the additional unscheduled experiment time needed could be easily accommodated.
In general, three major problem areas, related to the allocation of space for equipment installation, the design of certain experiment equipment, and the technical means for communication, were identified during the Euromir 95 mission.
Allocation of space
Space for the installation and
stowage of equipment proved to be one of the most critical
resources aboard Mir. In a few cases, the locations foreseen for
the installation of particular equipment items during the Euromir
95 flight were not available in practice, because other equipment
had already been stowed there. Alternative locations therefore
had to be identified and prepared on an ad-hoc basis.
One biomechanical experiment required a large working volume with an unrestricted field of view. The only area in the Mir station that came close to fulfilling these requirements was the core module. However, as the requirements were difficult to satisfy even there, excessive time was needed both for the equipment's installation and calibration and for experiment execution.
Experiment hardware design
As already mentioned,
the Euromir 95 experiment equipment had to be largely self-
contained. Generally speaking, it was assembled at the beginning
of the mission, provisionally stowed and then installed in a
suitable 'working-position' each time an experiment run had to
be performed. With a few exceptions, the manufacturers had not
provided their systems with adequate means for easy handling
(loops, eyes etc.), nor were there sufficient aids for fixing the
equipment in its storage/working location (rubber bands, belts,
etc.). It turned out that adhesive velcro patches could rarely
be used, especially if the equipment was larger than about
30x30x30 cm³. Time was therefore lost in making improvised
installations.
The experiment hardware was operated for extended periods during this long-duration mission and consequently the probability of subsystem malfunctions increased with time. Of the total of 25 different experiment systems, 13 malfunctioned or behaved anomalously in the course of the flight. Five malfunctions were recovered exclusively with onboard means and ground support, four were resolved by uploading new equipment with Progress, and four could not be fixed at all as neither the means for an in-depth failure analysis nor appropriate tools were available. The technical documentation provided for the maintenance and repair of experiment equipment was often inadequate. In most cases the off-nominal procedures provided in the flight data file were insufficient to recover system malfunctions.
Communications and telemetry
Communication and
telemetry turned out to be a bottleneck during the mission. In
general, only the UHF-1 channel was used and the available
communication time had to be shared between the crew members.
Parallel use of the UHF-2 channel had to be requested separately
by the Euromir 95 project team. At times when the station did not
pass directly over Russian territory during daytime, only two or
three communications sessions were available early in the morning
or late in the evening, and total communication time was limited
to a few minutes. Exceptionally, a voice/video link via the
geostationary satellite could be organised during these periods.
The transmission of data for the setting-up of experiment equipment via the teletype system was not always reliable. Because transmission errors appeared as wrong alphanumeric characters on the printout, this data always had to be confirmed using the voice channel.
The file transfers from the ground to the station via one of the voice channels (usually UHF-1) and the packet controller system were reliable most of the time due to the inherent transmission error detection and correction. In the course of the mission, however, there were a few periods, of up to 7 days, when no up/down file transfers were possible at all.
The possibility to download scientific data files from the MIPS-2 controller via the Mir telemetry system was very helpful throughout the mission, even though the transmission rate was very low (in the order of a few kbit/s). However, the transfer of files larger than a few kilobytes appeared to be very prone to transmission errors. On some occasions, files had to be put into the telemetry queue up to five times before the information was correctly received on the ground, a process that could take up to two weeks.
During the Euromir 95 mission, as the European astronaut I was nevertheless involved in a variety of generic onboard engineering tasks, including routine maintenance work on the thermal-control system, on life-support systems and on the preparation and conservation of all EVA equipment (space suits and onboard systems). Because not all onboard system parameters are displayed to the crew, the effects of certain steps during maintenance and repair activities had to be confirmed by the specialists in TsUP before the crew could continue their work.
A few non-nominal situations were encountered in the course of the Euromir mission, including a leak in the Kvant module's internal cooling loop, which required unplanned maintenance and repair work. These occurrences allowed experience to be acquired in the fields of overall system structure and functionality, system maintainability, man/machine interfaces and the decision- making process especially during non-nominal situations.
The scientific programme foreseen for the Euromir 95 mission was successfully completed during the 179-day flight. The flight extension beyond the originally planned 135 days, combined with the possibility to upload additional experiment hardware, spare parts and consumables with a Progress spacecraft, provided the scientific community with additional experiment time and allowed the Euromir 95 project team to gain additional operational experience.
Despite minor deficiencies in terms of stowage/working space, the bottlenecks in communications and data up/download capacity and the extra crew time required to maintain the onboard systems, the Mir station is without doubt a very good platform for conducting research in all of the different scientific disciplines. It is also an excellent environment in which to validate the experiment hardware and operational concepts for the forthcoming International Space Station Programme.
For future missions, however, the prevailing conditions onboard the station have to be taken into account more fully during the development of stand-alone experiment equipment. Given the increased risk of system malfunctions and non-nominal system performance during long-duration missions, the maintenance concept for scientific hardware needs to be improved to allow the crew to perform thorough failure analyses and repairs for even complex electronic systems.
Commercially available laptop computers and software were used extensively and very successfully by the crew for experiment control, data acquisition and storage during Euromir 95. Further developments in this direction, including the improvement of electronic procedures and certain onboard management tools, the provision of detailed technical reference documentation, computer-based (in-orbit) training, and the application of voice control, are therefore highly desirable in order to boost overall mission effectiveness in the future.
ESA Bulletin Nr. 88.