Microgravity Facilities

1.1.1 Balloon Flights

While balloon flights cannot provide a microgravity environment directly, they can be used to expose samples to radiation similar to those encountered in orbit. They can therefore be used to provide information to complement results from orbiting experiments. While it is highly desirable to have a control 1-g centrifuge on every microgravity mission in order to separate the effects of the space environment from those of microgravity (see this Chapter, Section 2.3), this is not always possible. The more easily available, and considerably cheaper, stratospheric balloon can then be used as a means of providing a 1 g, cosmic-ray-irradiated control. It has the additional advantage that larger and more numerous samples can be carried than on a space mission. Flights lasting up to 24 h, carrying payloads of 2,000 kg up to altitudes of 40 Km, have been used to expose biological samples to cosmic ray levels close to those experienced in low Earth orbit (LEO) (Planel 2004).

1.1.2 Drop Towers/Shafts

The most economical and easily available way to provide microgravity are drop towers or shafts up to 100 m in height wherein the air can be evacuated so that an experiment capsule can fall freely for a short time before being decelerated. Drops can typically provide 2-5 sec of microgravity, but this period can be doubled by using a catapult system at the base of the shaft, such as the one at the ZARM scientific institute in Bremen, Germany.

However, not all types of scientific inquiry are appropriate for the drop facilities. Meaningful microgravity research in biology and biotechnology can seldom be conducted in drop experiments, because the duration is very short and the deceleration too violent. Living organisms are not used. Crystals grow too slowly for such short-term microgravity exposure. On the other hand, these conditions are sufficient for many physics and material sciences experiments.

Figure 3-02. The ESA-CNES Airbus A300 Zero-G initiating a parabola. The insert shows the complete trajectoiy. Photo courtesy of Novespace.

1.1.3 Parabolic Flight

To achieve a parabolic trajectory from a steady horizontal flight, an aircraft gradually pulls up its nose and starts climbing at an angle of approximately 45 deg (Figure 3-02). This "injection" phase lasts for about 20

seconds, during which the aircraft experiences an acceleration of about 1.8 g. The engine thrust is then reduced to the minimum required to compensate for air-drag, and the aircraft then follows a free-fall ballistic trajectory, i.e., a parabola, lasting approximately 20 seconds, during which weightlessness is achieved. At the end of this period, the aircraft must pull out of the parabolic arc, a maneuver which gives rise to another 20-s period of 1.8 g on the aircraft, after which it returns to normal level flight attitude.

Sequences between 30 and 40 parabolas are normally flown on each mission, so allowing repetition of experiments. Relatively large pieces of apparatus can be carried and operated by the experimenter on these flights. Parabolic flights have been used extensively to investigate human and animal physiology, and gravitational biology under low gravity.

1.1.4 Sounding Rockets

Sounding rockets are sub-orbital rockets that carry a payload above the Earth's atmosphere for period of up to 15 minutes, but which do not place the payload into orbit around the Earth. Typically, such rockets reach an altitude of 250-350 km at which point the payload is separated and undergoes stabilized free-fall, finally landing by parachute. Payloads can be quite large, thus containing a number of individual experiment modules.

One of the benefits of this type of carrier is that late access to the payload is available until about 2 hours before launch, thus allowing studies on time-critical biological processes, or samples requiring complex preparation. Such facilities have been used to study gravity-sensing mechanisms in a number of plants and animals.

Not only are sounding rocket missions carried out at very low cost, but the payload can also be developed in a very short time frame, sometimes as quickly as three months. This rapid response enables scientists to react quickly to new observed phenomena and to incorporate the latest, most up-to-date technology in their experiments.

1.1.5 Biosatellites

Some space biology studies require the presence of human to carry out the experiments in orbit. Others simply require that animals be kept in space for some period of time. The latter "passive" type of study is a very efficient utilization of animals providing many investigators with specific tissues from the same animals. The Russian Biosatellite flight series, which began in 1966 with Voslchod (see Chapter 2, Table 2-02), is currently the only facility dedicated to biological experimentation using unmanned, Earth-orbiting satellites for missions lasting for up to 15 days.

The earlier Biosatellites used by the former Soviet Union were the so-called Cosmos or Bion biosatellites. Their design was based on the famous Vostok spacecraft, which carried Yuri Gagarin as the first man into space in

Figure 3-03. Artist drawing of a Foton capsule. The spherical compartment in the middle is the one that is housing the biological specimens. Source ESA.

1961. Unmanned recoverable capsules of the Foton type were introduced in 1985 (Figure 3-03). Foton was envisaged as a microgravity platform for physics and materials science to complement the very similar Bion capsules that were aimed at life science studies. However, in later years an increasing number of biology and non-microgravity experiments were transferred to Foton, while the Bion program was discontinued.

Foton capsules are pressurized and temperature-controlled, can host a payload of 700 kg in a volume of 4.3 m3 with 800 W of electrical power provided for the entire duration of the mission. The capsule is composed of three compartments: the landing module, the instrument assembly compartment, and a hermetically sealed unit that contains additional chemical sources of energy. The landing module is a complex, autonomous spherical compartment that can house plants, animals, and cell cultures. The samples can be loaded in the capsule only 14 hours before the launch. After the flight, the biological specimens are immediately removed from the capsule by a ground team and placed in refrigerated containers. The Foton capsule is then transported, first by helicopter, then by aircraft. The samples are then dispatched to the participating science teams via Moscow. The scientific instruments are removed from the capsules a few days later and transported back in the investigators laboratories.

Figure 3-03. Artist drawing of a Foton capsule. The spherical compartment in the middle is the one that is housing the biological specimens. Source ESA.

The Foton capsules provide unique opportunity for flying biological specimen (animals, cells, and plants) when no crew activity is needed. Telemetry can be used to activate some procedures during the flight, such as fixation of cells, or turn on or off the light. Small onboard centrifuge generating centripetal accelerations of up to 1 g can also be utilized to provide comparison with ground controls and make sure that the observed effects of the flight on the specimen are not due to the stress of launch and landing or to atmosphere changes. The samples are loaded in the capsule up to a few hours prior to launch.

Because the spacecraft is an unmanned biosatellite, all experiment operations, spacecraft subsystems, and life support systems for experiment subjects must be automated. Experiment materials and subjects cannot be directly manipulated during the flight, and viewing is possible only by means of video. Malfunctioning hardware cannot be repaired during a mission, and life support equipment cannot be manually regulated. These limitations place special demands for quality and reliability of flight hardware and allow the experiments somewhat less flexibility than those flown on manned vehicles.

There are, however, significant advantages to conducting life sciences experiments on unmanned spacecraft. The cost of flying an unmanned mission is markedly less than that of a manned mission. Hardware can be built relatively inexpensively, using a wider range of materials, without jeopardizing crew safety. Similarly, missions can often be extended or shortened to maximize science return and animal welfare, since crew requirements do not have to be considered. Also, they allow mission management to control the launch date and thereby allow payload readiness to be a significant factor.

1.1.6 Soyuz

The Soyuz "Taxi" flights are dedicated to exchange the Soyuz emergency return vehicle on ISS and are therefore planned exactly every six months. Two to three cosmonauts (with one seat being commercially available for about 20 million dollars!) participate in such flights, offering approximately five effective experiment days on board the ISS.

The total length of flight is around 10 days with 2 days in orbit before docking with ISS. The time between de-orbit and recovery is in the order of a few hours. The Soyuz capsule has a pressurized volume of about 4 m3. The mass of payload that can be carried to the ISS is about 250 kg, and the mass that can be brought back to Earth is about 150 kg. However, most of this mass is used to carry supplies to the ISS cosmonauts (water, food, and personal items). Therefore, only a limited number and simple experiments can be accommodated. Based on the European experience, a passenger of a Soyuz "Taxi" mission is allowed to carry 12 kg of equipment or samples up (volume 0.4 x 0.4 x 0.4 m), and to return 4 kg of equipment (e.g., tapes, films) or samples down to Earth. However, scientific equipment can be sent in advance to the ISS using a Progress unpressurized vehicle.

The experiments are usually performed in the Russian section of the ISS. Crew time can also be used to perform experiments using hardware already on board the ISS, in the Russian module, or brought up by the Progress cargo re-supply ship. Sample return immediately after termination of the mission is extremely limited and without temperature control capability

(room temperature only). These flights are best suited for the activation of automatic experiments.

1.1.7 Space Shuttle

For the period until complete construction of the ISS, all Space Shuttle flights are dedicated to assembly and operation of the ISS. Therefore, opportunities for Shuttle-based experiments are limited. Nevertheless, the Space Shuttle can accommodate flight experiments with typical flight duration of 8 to 12 days. Equipment can be stored in the storage lockers (up to 27 kg and 0.36 m3) on the forward bulkhead of the middeck (Figure 3-04). Each drawer has foam-rubber spacers to hold the contents in place. The experiments themselves must require only limited crew training and involvement to execute. Experiment hardware occupying or requiring a large volume to operate will not likely be accommodated. Experiments that do not require Shuttle power (i.e., battery-operated) are more easily accommodated, since in general there is no power available in the middeck lockers during ascent and reentry.

Figure 3-04. The Spacelab and

SpaceHab modules are pressurized laboratoiy facilities that can be placed in the Space Shuttle cargo bay. The middeck contains pressurized living quarters for the crew as well as locker space for holding small payloads. Source NASA.

The Small Self-Containers (SSC), or "Getaway Special" payloads, can also be used to conduct space life science experiments. The SSC are small (90 kg, 1.4 m3) cylindrical containers attached to the inside wall of the Space Shuttle cargo bay. There are placed on board when allowed by space and weight restrictions. These containers must contain their own systems for power, handling data, and environmental control. Some of the systems may be turned on or off from the flight deck, but otherwise they are completely automatic. They must, however, adhere to flight safety guidelines. Many biological experiments proposed by students have flown in these containers.

Time-critical supplies or specimens can be loaded in the Space Shuttle between 40 and 20 hours before launch. It is possible to retrieve equipment, supplies, and data that have time- or temperature-critical sensitivities after landing plus 3 hours. Note that there are periods of time before the flight and after landing when no access to the experiment is possible and maintenance of the equipment integrity must be assured. The availability of Shuttle resources for experiments that require animals as subjects is also extremely limited for short-duration experiments.

1.1.8 Spacelab & SpaceHab

Spacelab was built by the European Space Agency for use in the Space Shuttle cargo bay. Spacelab was a pressurized module, 4 m in diameter and 7 m in length equipped with standard experimental racks (0.48 m) that held up to 290 kg of equipment and instruments. Spacelab mainly flew during dedicated life and material science missions of the Space Shuttle Columbia (Figure 3-04). A Spacelab module was even flown as a cargo carrier, during the first docking of the Space Shuttle with the Russian space station Mir. The first Spacelab flew on STS-9 in 1983, and the last on STS-90 in 1998. Over its 15-year flight history, the Spacelab program hosted pay loads for practically every space research discipline. In all, 19 Space Shuttle missions carried life and microgravity sciences research into orbit and resulted in more than 750 experiments and more than 1,000 peer-reviewed articles, as well as numerous talks, abstracts, and Master's and Doctoral theses. The International Microgravity Laboratory missions (IML-1 and -2) carried not only international research but also international crews. One mission was dedicated solely to Japanese research (Spacelab-J) and two missions dedicated to German research (Spacelab D-l and -2).

SpaceHab is designed for housing a four-person crew in a pressurized laboratory within the Space Shuttle cargo bay. This laboratory includes temperature and moisture control, and power supply with AC and DC current supplied to all experiment locations, and high-data rate communications. The Research Double Module (RDM) is proposed on a commercial basis to microgravity experiments: it includes six standard double-rack locations, and storage lockers (up to 27 kg and 0.36 m3), for a total payload capacity of approximately 4,000 kg. The crew has access to the RDM through a pressurized tunnel connected to the Shuttle middeck airlock.

Like its older brother Spacelab, SpaceHab relies on the high bandwidth Ku-band signal processing of the Space Shuttle. However, during periods of communication blackout (Loss of Signal, or LOS) data can also be stored onboard and downlinked later.

Up to the STS-107 mission, SpaceHab was particularly useful to conduct life and material sciences experiments during dedicated missions while waiting for the completion of the ISS (Figure 3-05). None of these missions are currently manifested. Today, SpaceHab modules are added to Space Shuttle missions visiting the ISS to carry supplies requiring a pressurized environment.

Figure 3-05. Photograph showing an astronaut inside the SpaceHab module on board the Space Shuttle Columbia STS-107 mission. Photo courtesy of NASA.

1.1.9 International Space Station (ISS)

While we are writing these lines, the entire Space Shuttle fleet is grounded following the foam problems that occurred again during the launch of the STS-114 Return-to-Flight mission. So, it is difficult to predict the final state of the ISS. The following are the supposed capabilities of the ISS after completion, as of September of 2005.

More than four times as large as the Russian Mir space station, the completed International Space Station will have a mass of about 450 tons and more than 1200 m3 of pressurized space in six laboratories. The United States will provide two laboratories (the United States Laboratory and the Centrifuge Accommodation Module). There will be two Russian research modules, one Japanese laboratory referred to as the Japanese Experiment

Module (JEM) named Kibo (for "Hope"), and one European Space Agency (ESA) laboratory called the Columbus Orbital Facility (COF).

All six laboratories together will provide 37 International Standard Payload Racks (ISPR). An ISPR, about the size of a home refrigerator, holds research equipment and experiments. Additional research space will be available in connecting nodes and the Russian modules. The JEM also has an exterior "back porch" with 10 spaces for mounting experiments that need to be exposed to space. The experiments will be set outside using a small robotic arm on the JEM. There are also four attached payload sites on the truss and two spaces on the COF for mounting external experiments.

ISS Flight Equipment

Research Area

Advanced Animal Habitat (AAH)

Development

Aquatic Animal Experiment Facility (AAEF)

Gravitational; Development

Aquatic Habitat (AQH)

Gravitational; Development

Biolab

Cell; Radiation

Biopack

Cell; Biotechnology

Biotechnology Mammalian Tissue

Culture Facility (BMTC)

Cell; Gravitational; Biotechnology

Biotechnology Research Facility (BRF)

Biotechnology

Cell Biology Experiment Facility (CBEF)

Cell; Gravitational; Radiation

Cell Culture Unit (CCU)

Cell; Gravitational; Radiation

Centrifuge Accomodation Module (CAM)

Gravitational; Development

Compound Microscope

All

Crew Health Care System (CHeCS)

Biomedical research

Dissecting Microscope

All

Egg Incubator (EI)

Development

European Physiology Modules (EPM)

Human physiology; Biomedical

Gravitational Biology Facility (GBF)

Gravitational; CELSS

Habitat Holding Racks

Gravitational; Development

Human Research Facility (HRF)

Biomedical

Insect Habitat (IH)

Gravitational; Development

Life Sciences Glovebox

All

Matroshka

Radiation

Microgravity Sciences Glovebox

Biotechnology

Modular Cultivation System (EMCS)

Cell; Gravitational; Development

Plant Research Unit (PRU)

Gravitational; Development

Small Centrifuge

Gravitational; Development; CELSS

Space Station Incubator

Cell; Biotechnology

2.5-m Centrifuge

Gravitational, Development; CELSS

X-Rciy Crystallography Facility

Biotechnology; Gravitational

Table 3-02. Equipment dedicated for space life sciences research on board the ISS after assembly phase is complete, and the corresponding research areas.

Table 3-02. Equipment dedicated for space life sciences research on board the ISS after assembly phase is complete, and the corresponding research areas.

Table 3-02 lists the experimental facilities that will fit inside the science laboratories of the ISS, and the research area concerned by this equipment. Some of these facilities, along with their pictures, are detailed in the Section 3 of this Chapter. A list of Internet websites describing these facilities in more details is also provided at the end of the References list (this Chapter, Section 5).

There are severe limitations for operating science facilites in space. For example, there is a minimum storage period of 5-6 days before starting an ISS experiment, since the Shuttle has to travel to (2 days) and dock with the ISS after which the experiment must be transferred to the ISS facility. The experiment can then stay on board the ISS for the duration of one or several increments. After the last increment, the samples will be transferred back into the Space Shuttle for a minimum of 5-6 days, and then returned to Earth, where they will be made available to the scientists approximately 3 to 5 hours after landing. Samples and specimens can also be transferred to and from the ISS using the Soyuz "Taxi" flights.

Today, the two-person crew allowed on board the ISS is so small that the astronauts spend the vast majority of their time on maintenance, leaving little room in their schedule for actual experiments. Once completed, the ISS will house an international crew of up to seven for stays of approximately three months. Emergency crew-return vehicles will always be docked with the ISS while it is inhabited, to assure the return of all crewmembers.

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