Payload description

The European Modular Cultivation System (EMCS)

A facility with a life support and an observation system, both of them operating by remote control on a centrifuge rotor, is deemed necessary for experiments with plants and other organisms in microgravity. This would enable the scientist on ground to study development and behaviour of organisms under microgravity and different accelerations in Space, with the possibility of a permanent on-board 1g-control. Under ESA contracts, the EMCS has been designed for these kinds of experiments, especially investigations of long term plant cultivations from seed-to-seed.

The EMCS consists of one Flight Model (FM), one Engineering Model (EM) and two Experiment Reference Models (ERMs); the three latter located on ground. The EM and one of the ERMs are located at the N-USOC site and the other ERM at NASA Ames Research Center in USA. The EMCS FM will hereafter be referred to as "EMCS". The "EMCS facility", which means the "pure" EMCS with no experiment components included, will be brought to the ISS by the launch of the space shuttle ULF 1.1, currently scheduled for May 2006.

The EMCS design

The EMCS consists of a gas-tight and temperature-controlled incubator, which contains two centrifuge rotors, that allows up to four Experiment Containers (ECs) to be placed on each rotor. The incubator is self-supported with air mix and CO₂ from the gas supply modules placed externally to the incubator, in addition to being connected to ISS' GN₂ supply. Together with other subsystems, the incubator forms the Holding Structure (HS), which is the main interface to the rack. The HS has the dimensions 93 x 56 x 66 cm³. All subsystems are mainly selfstanding and are controlled by the EMCS Standard Payload Computer (SPLC), which serves as the master controller of the facility and communicates with the EXPRESS Rack (ER), in which the EMCS will be located.

Figure 1. Picture courtesy: EADS-ST, Friedrichshafen, Germany

The figure above shows the front side of the HS, which has a main door that allows access to the internal volume for rotor mounting and maintenance. The main door has two EC Access doors, which gives access to Rotor A or B, respectively.

The EMCS sub-systems

The EMCS consists of the following sub-systems/ functions:

• Housing for the two rotors
• Pressure controlled, thermal housing for up to eight ECs
• Housing to control the ACS provided atmosphere

• Control of temperature of the incubator atmosphere
• and of the EC in the range of 18 °C– 40 °C

• Flushing with N₂
• Atmosphere setting and control of O₂ and CO₂
• Incubator pressure control
• Control of EC doors in the incubator

• Static part (Drive Unit, DU) with a motor drive for acceleration control

• Radius: 30 cm
• Liquid interface for water service of EC
• Gas interface for air flow through EC according to atmosphere settings
• Mechanical and electrical interface to the ECs
• Illumination system
• Video observation system
• RH-control of ECs via the Rotor Based Life Support System (RBLSS)

• Main controller power circuit breaker
• Connectors for EMCS cables on front panel
• Ethernet, power and video interface to EXPRESS rack on backside
• Centrifuge electronics, ACS electronic and video switch inside
• Analog video tape recorder (VTR)

• Master controller to monitor and control all subsystems according to predefined experiment schedules and/or manual commands. It provides monitoring of the facility status and safe operations of subsystems.
• Provides the I/F to the Rack Interface Controller (RIC) and thereby ground TM and TC.

Rotors providing µ-g

The figure shows an image of one of the rotors. Rotor A is identical to Rotor B and the two rotors have their ECs, RBLSS, cameras and water reservoirs facing towards each other. On each of the two centrifuge rotors, two or four ECs can be mounted. An even number of ECs must be mounted to prevent unbalance of the rotor. When the rotors are running, a centripetal acceleration will be applied to the ECs. In Space, this centripetal acceleration will simulate gravity inside the EC and the rotor speed determines the gravity level. The rotor speed may be varied to obtain gravity levels from about 10^-3g up to 2 g (at the rotor's outermost radius). This allows e.g. the performance of a micro-g experiment on one rotor and a 1-g reference experiment on the second rotor. Ground controls will be performed in the two dedicated ERMs.

Each rotor contains two rotor-based cameras and two sets of Rotor Based Life Support Systems (RBLSS), which provide the ECs with air humidity control, filtration and water supply. Each camera and RBLSS is shared between two ECs. The water reservoir is placed in the centre of the rotor. Each EC will be placed between one camera and one RBLSS, with one end pointing towards the Light Emitting Diode (LED) array next to the water reservoir.

Video

The EMCS contains a video system for observation and control of the experiments. The video sources in the EMCS are two cameras on each of the centrifuge rotors. The cameras are rotatable and each camera covers two ECs from its viewpoint. Rotatable mirrors allow these to adjust the view in the other axis.

Figure 3

The video system has three routing possibilities as shown in Figure 3:

1. Realtime downlink of analog video via ER I/F
2. Analog video to the EMCS VTR
3. Digitized still images embedded in the TM stream

The Experiment Containers

The ECs provide suitable interfaces for the scientists to accommodate their individual samples together with the Experiment Unique Equipment (EUE), which is placed inside the EC and is needed in addition to the services provided on the rotor for all ECs together. The EUE can be fixed mechanically to the baseplate of the EC and may be provided with water and gas exchange through openings in the baseplate, while processed on the rotor.

Figure 4

The EC consists of a baseplate and a cover with dimensions 60 x 60 x 160 mm³. Placing the EC on the rotor automatically connects it to the gas and water supply system of EMCS, and provides electrical power as well as data connections. The EC has the following specifications:

• Power: + 12 V DC, -12 V, DC, +5 V DC, max. continuous power per EC 1 W
• 5 analog out channels (1 of those assigned to built-in pressure sensor, 2 others assigned for an optional RH/T sensor, 2 optional)
• 4 digital lines (I/O)
• RS-485 interface
• Rotor-based pulsed water supply through internal filters (0.2 µm pore size)
• Built-in pressure sensor
• Separate RH/T sensor, to be connected at the EC internal connector
• EC Internal cameras for 2 positions

In order to provide a vital environment for biological samples and to enable observation of the samples, the EMCS is equipped with an illumination system. Through a transparent cover, each EC can be illuminated by the rotor based LED panel, on which illumination is oriented in the g-vector direction.

Illumination will be provided in the visible range to simulate daylight illumination and in the IR range to allow observation in the night modus. The following options exist:

• Full white illumination: >75 W/m2 in the range 400-700 nm with a peak at 468 nm and in the red range (see below)
• Reduced white illumination: about 50 W/m2
• IR illumination: 935 nm

Figure 5 shows the layout of the LED array. To stay in the visible light range, most diodes are white. However, six diodes are red in order to improve the emitted spectral distribution in the red range (650 nm).

Additionally the video camera provides camera IR illumination. This illumination is oriented in the camera observation direction (towards the top side of the EC cover, perpendicular to the g-vector).