Space Flight, Simulation of

the creation (reproduction) on earth of conditions close to those of space and space flight. Such a simulated space environment is used for testing materials and equipment, for checking the correctness of their selection and design, and for determining their suitability for use in space, as well as for training future astronauts. The space environment is also simulated in order to test the structural components of launch vehicles (upper stages) and space vehicles (satellites and manned spacecraft), rocket motors, and radio equipment (antennas and so on) and for conducting other studies.

Chambers in which the environment of space is simulated are usually called simulators. Various types of simulators make possible reproduction of individual parameters of space with a certain degree of accuracy. They include machines used to simulate the environment of other planets (for example, Mars and Venus); to study the problem of manned space flight and the functioning of the man-machine system (particularly to optimize operations on orbital stations), as well as the repair of equipment and the performance of emergency rescue; and to reproduce the forces acting on a launch vehicle during the orbital insertion phase (noise, accompanied by vibration, g-loads, and high temperatures). For example, an altitude chamber, in which an entire spacecraft is tested, is a simulator.

Electronic and mechanical equipment is tested in centrifuges. A “hydrogen cannon” is used to create conditions resembling reentry into the atmosphere of earth or other planets. The cannon is a wind tunnel in which a hydrogen stream with a speed of 48,000 km/hr flows past the spacecraft. It is used to study the effect of micrometeorite particle bombardment on various materials. Large simulators use computers for automatic control of the testing process according to a preset program. The recording, storage, and processing of information obtained during the tests are also automated. Altitude chambers exist for testing space equipment under conditions simulating the combined effect of various factors of space flight, such as solar radiation, vacuum, and temperature variations.

However, no machine exists in which all the conditions of space flight can be simulated simultaneously. It is virtually impossible to construct an altitude chamber of large volume with a vacuum of up to 10−¹⁴ newtons per sq m (N/m²), or the order of 10−¹⁶ mm of mercury (mm Hg). The pressures created in such altitude chambers are 10−¹⁴ N/m² (10−6 mm Hg), which corresponds to the pressure at an altitude of about 330 km. Such conditions are fully adequate for testing most launch vehicle and spacecraft components. To create the rarefaction, air is pumped out in stages by means of mercury or oil-diffusion and cryogenic vacuum pumps. In addition to low pressure, the illumination and temperature of space are also simulated. Solar radiation is simulated by mercury, xenon, or carbon arc lamps, which are usually situated outside the chamber. The light and heat from the sources are directed at the quartz windows of the chamber through a system of reflectors and then focused on the object under test through a system of mirrors and lenses located inside the chamber. For the simulation of temperatures as low as — 200°C, the chamber walls are equipped with panels or coils cooled by liquid nitrogen flowing through them.

Astronauts must be protected from the dangerous effects of vacuum, weightlessness, meteor dust, and various types of radiation, which ranges over a broad spectrum. Chambers for testing spacecraft designed for manned flight are similar to and operate in the same way as chambers for testing materials and equipment, but provision is made for rapid depressurization in the event of an emergency. For example, as part of preparations for the first manned lunar flight, the USA developed special altitude chambers. The Apollo spacecraft were tested in a stainless-steel altitude chamber 36.5 m high and 19.7 m in diameter. Arc lamps in the ceiling and walls with cryogenic cooling made possible the creation of a temperature range from −180° to + 125°C in the chamber, which is close to that on the lunar surface. The vacuum in the chamber can be as low as 10−5 N/m² (of the order of 10−7 mm Hg). An altitude chamber 13 m high and 10.6 m in diameter was used to test the astronaut’s equipment for extravehicular activity and for temperature tests of the lunar module of the Apollo craft with a man aboard. Carbon arc lamps in the ceiling of the chamber simulate solar radiation, and the cooled walls make it possible to create the temperature conditions of space. A pressure as low as 10−⁴ N/m² (of the order of 10−6 mm Hg) can be maintained in the chamber. Studies of the effects of g-forces on astronauts and spaceship components and systems are carried out in centrifuges, on which accelerations of more than 30 g can be produced, with various rates of onset. The centrifuge cabin has three degrees of freedom, which makes possible the generation of g-loads acting on the astronauts in different directions. A change in the rate of rotation results in g-loads resembling those encountered during liftoff, staging of the launch vehicle, and so on. Studies of the effect of short-term g-loads with very high rates of onset are conducted in linear acceleration simulators, which are also used to study the effect of g-loads resulting from braking (for example, during atmospheric reentry or landing).

Weightlessness, which accompanies any space flight, is simulated in specially modified aircraft. A mockup of the spacecraft is placed in an aircraft flying along a ballistic curve, and the astronaut learns how to enter and leave it and to eat, drink, and so on. The brevity of the period of weightlessness (25-35 sec) is a drawback of such simulation.

The comprehensive and complete simulation of the space environment on earth is impossible. Therefore, during preflight training astronauts receive instruction on a number of specialized pieces of equipment, called trainers. Trainers are classified as static or dynamic, depending on their type of mounting (fixed or movable). In addition, three groups of trainers are distinguished according to purpose: to acquaint the astronauts with the operation of the spacecraft’s primary systems; to study the jobs an astronaut must perform in space and to accumulate the experience needed to accomplish them; and to train the spacecraft’s crew in order to carry out all the tasks of the flight program (flight trainers). Trainers belonging to to the third group are stationary pieces of equipment that are essentially spacecraft mockups, which duplicate precisely the interior of the full-scale craft. The noise accompanying launch vehicle liftoff is reproduced. In addition, views of the earth, moon, and sky and changes in them resulting from the spacecraft’s motion along its trajectory are simulated through the use of motion-picture projectors and systems of mirrors. Instruments on the control panel provide the astronauts with the necessary information. Instrument readings are recorded by computers, which compare them with the predetermined parameters and make appropriate corrections.

Space flight simulators provide a saving in time and money during the development of launch vehicles and manned spacecraft and acquaint the astronauts with conditions to be encountered on future flights.