In the near future, manned spaceflight activities will be dedicated to assembly flights for the International Space Station (ISS) with the European contribution of the Columbus Orbiting Facility (COF). During these assembly flights of the US Space Shuttle and Russian launchers, only limited flight opportunities are available for microgravity researchers, including biologists, to conduct their science. Therefore there is a need for small sophisticated payloads which provide scientists with experiment platforms to conduct experiments during the ISS assembly phase, making use of the limited resources. Space Shuttle Middeck Locker-based payloads are the most suitable payloads in this respect. A newly designed payload called 'Biopack' is such a Locker-based facility which builds on already existing hardware and infrastructure, and provides scientists with a research facility for biological experiments under varying gravity conditions.
Although the Biopack builds on ESA's very successful facilities Biorack (flown already three times in Spacelab and three times in Spacehab) and Biobox (flown three times in the Russian retrievable capsules), its design and operations scheme overcomes some of the disadvantages of the previous facilities. Biopack is aiming for flights in the Space Shuttle middeck, in Spacehab, and in the long-term in the European Drawer Rack (EDR) in COF.
The Biopack provides experimenters with a versatile research tool which includes an incubator with three centrifuges, a cooler, and a freezer. The facility is being designed with the standard Type-I/E and Type-II/E experiment containers in mind. On board an orbiting spacecraft, such as the Space Shuttle, or ISS, biological samples in the Biopack can be exposed to gravity levels ranging from microgravity to at least 2g.
The Biopack is designed to accommodate small biological samples e.g. mammalian cell and tissue cultures, small plants or insects. And although the majority of these experiments are primarily of academic interest, studying the effect of gravity and microgravity on various processes on a systemic and cellular level could reveal basic phenomena also relevant in non spaceflight-related sciences. Moreover, especially in areas such as plant and animal research involving biomechanical issues, the microgravity environment of space is essential for studying the effects of mechanical stress on growth and development of biological systems as a baseline value. The microgravity condition during orbital spaceflight is unique for studying cells and tissues in the lowest possible mechanical stress environment for a prolonged period.
Essentially, Biopack consists of two units, the Biopack Interface Frame (BIF) and the Biopack Experiment Insert (BEI) (see Figure 1). The BIF encompasses all spacecraft interfaces and the full Biopack electrical and thermal infrastructure; it accommodates the BEI. The BEI is the actual payload; it includes three experiment compartments: the incubator with centrifuges, the cooler, and the freezer. The experiment samples in their dedicated Experiment Containers (ECs) are housed in these compartments.
Figure 1: The Biopack general view
2.1 Biopack Interface Frame (BIF)
The BIF occupies the volume of two Space Shuttle Middeck lockers. It is the primary interface to the spacecraft, mechanically, thermally (air and/or water cooling), and electrically (28 VDC power and telemetry/telecommand data), and to the crew.
All Biopack functions can be controlled and monitored by the astronauts from the Control and Monitoring Panel (CMP). On the CMP, controls for main power, for stopping and starting each individual centrifuge and for setting the incubator temperature are located. Indicators are available for major Biopack status information. In addition, a palmtop computer which forms part of the CMP, will be used for controlling Biopack's operations and displaying housekeeping and experiment data.
2.1.1 Data handling
The Biopack will be capable of displaying, downlinking, and locally storing all parameters available in the facility. These include various temperatures, centrifuge speeds, door indicators, experiment sensor values and switch settings. During flight, status and sensor information can be down-linked to ground controllers. Biopack and experiment operations can be adjusted in flight through telecommands when necessary.
2.2 The Biopack Experiment Insert (BEI)
An Incubator which is temperature controlled between 20° and 37°C can accommodate twenty standard Type I/E and four Tpe-II/E containers (see Paragraph 2.3), ten Type I/E and two Type II/E containers in static positions and another ten Type I/E and two Type II/E on individual centrifuges. Each of the three centrifuges is software controlled and can be programmed to provide any acceleration value between microgravity and 2g. Static as well as dynamic gravity profiles can be generated providing the experimenter with an unlimited range of experiment scenarios.
To store samples before or after the incubation period, two temperature controlled areas are available. Ten Type I/E containers can be stored in the 4°C cooler, while the same number of containers can also be kept frozen in a -15°C freezer. Transfer of ECs between incubator and freezer or cooler requires astronaut actions (see Figure 2).
All static as well as the centrifuge positions of the ECs in the 20° to 37°C incubator have electrical connectors which interface with the Type-I/E and Type-II/E containers. There are power and data line connections to the experiments. Activation signals can be issued to experiment units either automatically via pre-programmed time lines or can be manually started by a crew member or ground controller.
Figure 2: Biopack with open incubator drawer
2.2.1 On-board centrifuges
In the early days of microgravity experimentation, only microgravity samples were brought into orbit. Results obtained from the flight samples were compared to the ground 1g controls. For the first time during the Cosmos series of flights, on-board 1g centrifuges were used for control samples. By applying these centrifuges, a distinction could be made between 1g ground and 1g in-flight samples. For various reasons, in-flight 1g samples plus 1g ground controls are essential for evaluating microgravity effects.
First of all, launch accelerations and vibration to which flight samples are exposed are not experienced by ground samples. In-flight gravity disturbances are not simulated for ground samples. There is also the always present cosmic radiation outside the Earth's atmosphere/magnetosphere. This radiation could have an impact on the spaceflight/microgravity samples, while it would be absent in ground samples. Also environmental differences in a particular payload, such as small differences in temperature and gas composition or operations, may vary between in-flight and ground-based controls. Besides the 1g gravity level used for in-flight controls, the centrifuges may also be used for more detailed studies on biological processes under reduced gravity conditions. (See also paragraph 3.2'Acceleration profiles').
2.3 Experiment Containers (EC)
For their biological research facilities, ESA has defined two standardized ECs known as Type-I/E, with an internal volume of approximately 65 ml, and Type-II/E with a volume of 385 ml. This standard has been adopted for the development of payloads dedicated to biological research. The most successful and best known payload in this respect is Biorack. Besides Biorack, also the Biobox and sounding rocket payloads such as the Cells in Space (CIS) module adopted the Type-I/E standard. By now, not only European but also US/NASA experimenters are familiar with the compact but versatile experiment possibilities in these containers. Experiment inserts for mammalian cells, bacteria, fish, plants, and small insects have already flown. And it is this collection of hardware now available for Type-I/E containers which provides a catalogue of experiment modules readily adaptable for future experiments. This hardware know-how reduces the development time and costs for future experiments which can make use of already qualified modules. For the Biopack, the successful Type-I/E and II/E ECs have been adopted as standard experiment containers.
2.4 Experiment lead time
A drawback for many scientists conducting microgravity experiments, is the prolonged time between sample preparation and final experiment incubation. This experiment lead time encompasses:
- integration of the biological samples in ECs,
- hand-over to the Agency authorities, e.g. ESA
- transfer to the launch authorities, e.g. Spacehab,
- transport to the launch site,
- integration into the launcher/spacecraft,
- the launch window,
- facility start-up in orbit,
- temperature equilibration, and finally
- the start-up of the experiment.
The Biopack facility should drastically reduce this lead time.
First of all, the Biopack Experiment Insert (BEI) remains as one unit throughout the integration process. All experiment containers are loaded into the BEI, after which it is transferred to the launch site and integrated into the Biopack Interface Frame (BIF) already mounted in e.g. the Space Shuttle Middeck or Spacehab module. Secondly, the temperatures in the BEI will remain at the preset value throughout the lead time. Thirdly, the accelerometer in the Biopack will detect microgravity as soon as the Shuttle reaches its orbital phase. When microgravity is reached the Biopack automatically switches to experiment activation without delay or crew intervention. Finally, because the Biopack is a relatively small payload, only a limited amount of experiments can be accommodated. Integration time and logistic complexity is reduced compared to larger facilities.
The time scenario for future microgravity studies in the International Space Station puts high constraints on experiment design. Experiment lead times are substantially increased when one assumes a consecutive experiment performance sequence in facilities such as Biolab (ESA) or the Gravitational Biology Facility (NASA). Delicate experiments that cannot endure any extensive storage periods can hardly be performed in typical ISS facilities. The Biopack facility could be used to accommodate this special group of lead-time sensitive studies. Samples capable of surviving prolonged storage at low temperature, dehydrated conditions, or in arresting phase such as seeds or spores, are better suited for Space Station scenarios.
To the extent feasible, the Biopack is an automated research facility in which autonomous experiments can be performed with minimum crew intervention. However, it is necessary that crew members manually transfer containers from one location within the Biopack to another, either for handling and inspecting samples or for moving them from the incubator to e.g. the cooler.
3.1 Experiment profile
A typical profile for a complete Biopack flight experiment with mammalian cells from preparation until retrieval after the mission could be as follows:
- At the principle investigators' (Pis') laboratories, samples are prepared at room temperature,
- After accommodating the cells in the ECs, these will be temperature-conditioned at +20°C and transferred to the BEI. This transfer could be in temperature (+20°) conditioned transport containers, if necessary.
- The fully assembled BEI, ready for flight with the incubator at +20°C, the cooler at +4°, and the freezer at -15°, will be transferred to the launch site and integrated in the BIF, already installed in the spacecraft. This will happen as shortly as possible before the launch of the Space Shuttle.
- After launch, the Biopack will be automatically activated as soon as microgravity is reached. The incubator will heat up to its preset temperature while centrifuges start to generate their preset gravity profiles.
- As planned, the experiment containers are handled by a crew member. Samples can be inspected and subsequently transferred to new locations or back to the incubator for a second incubation period.
- After incubation, the experiment will be transferred by the crew to either the +4°C cooler or to the -15°:C freezer.
- At the end of the mission, the Biopack will be deactivated, but temperatures will be maintained until removal of the BEI from BIF and spacecraft. This will be a few hours after landing of the Space Shuttle.
- ECs will be removed from the BEI for immediate return to the PIs. Transfer of the ECs will be in conditions as specified by the PIs.
3.2 Acceleration profiles
Besides the static positions for the microgravity samples, the Biopack with its centrifuges can generate gravity levels up to, at least, 2g. The centrifuges are software controlled offering many experiment acceleration profiles as depicted in Figure 3.
Figure 3: Acceleration profiles
Experiments located in the static microgravity position in the incubator in combination with 1g samples on the centrifuges, provide the standard set-up of spaceflight experiments (Figure 3 A and B).
If a microgravity response has already been demonstrated, experiments can be conducted in the hypogravity area between microgravity (µg) and 1g (Figure 3C). In such a scenario, threshold values for the various responses can be explored. A comparable phenomenon is known as gravity presentation time in plant studies. Accelerations beyond the Earth's 1g can be applied to evaluate whether the changes found in the hypogravity area continue in the hypergravity domain (Figure 3D).
To overcome a possible effect of microgravity (countermeasure), an exposure for shorter or longer times to 1g can be evaluated (Figure 3E). In addition, profiles could be applied sequentially to verify whether the exposure to 1g as such is responsible for the response, or whether the transition and change in acceleration levels is capable of producing similar effects (Figure 3E versus 3F).
Peak pulses of gravity or microgravity at preset intervals could be applied to define any gravity-sensitive windows within the samples under investigation (Figure 3G and H).
To investigate whether biological systems are sensitive to various accelerations, the impact of the total sum of different loads given by the gravity level multiplied with exposure time could be analysed. Although the total loads are similar, it could be interesting to investigate how biological samples will respond to different acceleration profiles (Figure 3I and J) and compare these data to an average of 1g as per Figure 3K. Gravity perception can also be investigated by determining if the perception of accelerations is due to sudden changes, as compared to gradual changes (Figure 3L). It may be clear from the profile plots in Figure 3 that any other gravity profile could be applied by the Biopack centrifuges, enabling scientists to explore biological phenomena in more detail.
At present, the Biopack is in Phase-B of development. Phase C/D is anticipated to start in early 1999. The aim is to have the Biopack maiden flight in Spacehab/STS-107 in September 2000.
ESA is developing further facilities for research in biology and exobiology, and for research on the impact of cosmic radiation on biological systems including man in space. These are the Modular Cultivation System (MCS) and the Space Exposure Biology Assembly (SEBA), both for flight on different sections of the ISS as from 2002.
Information on results of earlier biological experiments in ESA facilities can be found in:
Biorack on D1. ESA SP-1091, Eds. N. Longdon, V. David, February 1988, ESA/ESTEC, Noordwijk, the Netherlands.
Biorack on Spacelab IML-1. ESA SP-1162, Ed. C. Mattok, March 1995, ESA/ESTEC, Noordwijk, the Netherlands.
Biological Experiments on Bion-8 and Bion-9. ESA SP-1190, R. Demets. September 1996, ESA/ESTEC, Noordwijk, the Netherlands.
