New Soviet space station `Mir' marks crossroad in spaceflight. Once operating, it will host permanent human presence on orbit

The new Soviet space station, called ``Mir,'' marks another significant step on that nation's carefully planned program of space exploration and exploitation. But in a broader sense, Mir may be ending a 5 billion-year-long chapter in Earth's history. The time that passes while Mir awaits its first crew may represent the final days in the history of the planet when all earthborn life was restricted to its biosphere.

When people board Mir and activiate it, and later when the United States space station and its successors are set up, there may never again be a moment when outer space is devoid of earthborn life.

If earlier stations in the Salyut series were pioneering pathways, Mir is going to be a six-lane thruway. It builds on 15 years of flight experience and careful planning. The operating mode it inaugurates may continue into the next century.

Physically, the Mir module is clearly an evolutionary outgrowth from its Salyut predecessors: It is cylindrical, about 40 feet long, and 14 feet in diameter at its widest point. It weights about 20 tons and is launched by the standard Proton booster. The aft end houses a docking port and maneuvering engines, and a set of solar panels sprouts from the midsection. The front end of Mir, however, has an 8-foot diameter sphere instead of a cylindrical airlock module. And instead of one docking port facing forward, it has that plus four new ``lateral docking ports'' arranged around the waist of the sphere, in addition to an aft port.

These additional ports are the key to Mir's flexibility and utility. Instead of cramming it with scientific gear and slipping in crew equipment wherever there was leftover space, Mir's central module is devoted entirely to crew systems. Scientific gear will be located in special modules that link up to the new ports.

Soviet specialists have described these special modules as being devoted to astrophysics, biology, materials processing, Earth-resources surveys, or other research. The modules, each equal in size to Mir and launched separately, can remain linked up for months or can fly in parallel orbits and then dock with Mir for refurbishment and resupply.

Such modules have already been tested on earlier missions. The first prototype was orbited in 1977 and performed 200 days of solo maneuvers. In 1981 a module named Kosmos 1267 linked up to the abandoned Salyut 6 space station, and in 1983 the Kosmos 1443 module docked with Salyut 7 for the first manned operations of the hardware. Last year, after Salyut 7 had been repaired following a cripping power breakdown, the Kosmos 1686 module docked to it.

Mir is currently in a parallel orbit to the Salyut 7/Kosmos 1686 complex, so joint operations are obviously planned. While a linkup of all three modules is unlikely (they don't seem to have compatible docking equipment), observers believe that the relatively new Kosmos 1686 module will soon be undocked from the aged Salyut 7 and flown over to Mir.

Prior to that, Mir may receive a checkout team of cosmonauts, riding a standard Soyuz manned spacecraft. On the day of Mir's launch on Feb. 20, the TASS news agency had described an ``initial stage'' of testing in both automatic and manned modes, to be followed by advanced work. ``In the future,'' TASS said, ``it is envisaged to attach specialized modules.'' Although some Western newsmen interpreted this to mean that the module's checkout crew would return to Earth and then be replaced by a long-term crew, the Soviet account actually gave no indication of any such interruption of the habitation of the station.

Space engineer and former cosmonaut Konstantin Feoktistov also suggested that a full five-module complex might not be set up immediately. ``The design of the station itself envisages the possibility of its being gradually built up,'' he told an interviewer. Only two add-on modules would be needed, one on either side of the multiple-docking sphere, to create a symmetric and thus controllable configuration. Two more might be sent up sometime later this year or next.

Late last year, European scientists had disclosed that they had delivered astrophysics equipment to the Soviets for use in a specialized module devoted to astronomy. The project was called ``Salyut-HEXE,'' for High Energy X-Ray Experiment. The module is to be launched this spring. If so, together with Kosmos 1686 it could form the first symmetric operational configuration of Mir. Soviet spokesmen also pointed with pride to Mir's special new interior. Boasted cosmonaut Alexander Serebrov, ``It is absolutely all new -- new life-support systems, new interior, new living quarters.'' Without the clutter of scientific apparatus, the module was designed from the start with people in mind. There is a control console and a dining area, as well as a small repair shop with a steel table, vises, soldering equipment, and other tools. There are also small private bedrooms, much as on the US Skylab facility in 1973-74.

Mir also represents major improvements in automation. Tasks such as vehicle orientation control, which formerly took direct and tedious manual operation, can now be performed by computers. Equipment can be turned on and off, and controlled in operation, by computer. This approach is intended to free the many man-hours a day that previously had been spent on such repetitive tasks.

A new communications system has also been implemented on Mir. Until now, radio contact with Mission Control near Moscow was possible only when a station was flying over tracking sites in the Atlantic. Starting with Mir, the Soviets are using a communications relay satellite to allow continuous radio contact when the station is over the Eastern Hemisphere.

The Soviets obviously intend to use the Mir complex for commercial as well as research activities. They have spelled out profitable tasks in manufacturing, mapping, and climate/weather forecasting. The unending arguments over cost-vs.-value that still bedevil the US space station's funding efforts have quite clearly been settled in the affirmative in Moscow.

The Soviets will clearly continue to push human orbital endurance records beyond the current 237 days. However, experienced cosmonauts and space-medicine specialists have said that for normal missions, three to four months is an optimal duration; after that, fatigue and stress can mount dangerously. Also, now that Mir is to be permanently occupied by rotating crews, experimental animals can be left on board for very long periods, and then examined much later for the effects of such lengthy exposures.

Longer-range values of Mir can also be forecast. More advanced closed-loop regenerative life-support systems, including special ``greenhouse modules,'' are certain to be tested as early as possible. These technologies, together with the medical data on years-long space-exposure effects, are crucial to planning for manned interplanetary flight.

James Oberg is a professional spaceflight engineer with a life-long interest in Soviet space technology. He is the co-author of the recently released ``Pioneering Space'' (McGraw-Hill).