By Mikhail Kotov
Over the last year, the Russian space science made two achievements at once: made a flight of the Progress – unmanned cargo spacecraft to the International Space Station, using an ultra short scheme of three and a half hours, and returned to a short scheme, during manned flights, taking only six hours instead of more than two days.
Currently, the orbit of the International Space Station is approximately 400 kilometers. It’s impossible to say more precisely, as the stations often have to perform maneuvers to avoid colliding with space debris. In addition, even at such a height, the Earth's atmosphere influences the station’s orbit. The molecules of nitrogen and oxygen collide with the station, gradually inhibiting it, which leads to a decrease in the orbital altitude. From time to time, it is even necessary to turn on the engines of the spacecraft docked to the station, in order to return to the previous orbit.
This is precisely why the flight of spacecraft and docking with the station still remain to be a difficult task, requiring a large number of specialists. Each time one has to take into account many factors, in order to try to guess, as accurately as possible, the station position at the moment of docking. Even the sunspot activity affects it, under its influence the station can change its orbit by several meters from the calculated parameters in only several days.
Therefore, historically, flights to the Mir Station, and then the International Space Station, were carried out using a two-day method. In other words, from the time of take-off about two days pass, during which the spacecraft manages to make about thirty orbits. At the same time, the spacecraft shall gradually form such an orbit, in order to be close to the target, cut down relative speed, get close and dock. In order to reach the station with the appropriate speed and at the required orbit, the spacecraft performs a “Gomanovsky transition” to a phasing orbit, a bi-elliptical transition, then an approaching with the station and a speed equalization. In this case, of course, fuel, and, accordingly, the number of maneuvers are limited.
When it comes to a cargo unmanned spacecraft, this is not so important: food, water, and air containers can be kept for extra fifty hours. But regarding the crew, curled up in the cramped compartment of the Soyuz spacecraft, every extra hour is worth a lot. After a two-day flight, even the most trained specialists need to recover or they will operate with less efficiency.
Russian specialists have been working on reducing the flight time to the International Space Station for quite a long time. Now in 2018, finally we get a real breakthrough. On July 10, 2018, they managed to launch the Progress MS-09 cargo unmanned spacecraft to the International Space Station, using a new two-turn scheme – just three and a half hours from the start to the docking unit. New launch schemes, at first, are always to be evaluated with cargo unmanned spacecraft, and only after the specialists are convinced that it is completely safe, the scheme will be introduced on manned spacecraft.
The difference is more than fifteen times, as compared with thirty turns that are familiar and have been worked out over the years. How was this achieved? It is necessary to understand, that one of the main parameters, when performing a launch to the station, is the phase angle – the angle between the spacecraft and the station in-plane. The larger the phase angle, the less requirements are placed on the exact start time. In case of a two-day scheme, the angle is 200–400 degrees, and when a spacecraft is launched using a two-turn scheme, the angle is only 30±15 degrees.
Therefore, it appears, that the launch for such a scheme shall be performed almost a second per second. There is one more problem – the rocket does not place a spacecraft into orbit with an accuracy of one meter, it has to be corrected to ensure docking. Therefore, the spacecraft receives the first correctional impulse immediately after withdrawal. On the next turn, its orbit is analyzed and further adjusted. It takes place approximately 90 minutes later, when the spacecraft already goes to the docking process with the station.
The accuracy of the work is jewelry, any mistake immediately leads to the need to transfer the scheme to a two-day flight and adjust the orbit additionally. In 2013, for the first time, Russian manual crafts switched to a six-hour flight pattern (four turns). Then there was a rollback to the two-day scheme, and now, in 2018, the scheme is again a six-hour one. Thus, the Russian space science managed to fix a new record, albeit a subtle record outside the industry. An unmanned spacecraft is launched in a two-turn scheme for three and a half hours, and a manned one – for a four-turn scheme in more than six hours. Ahead, in theory, there is even the possibility of switching to a single-turn scheme. Although, this will be done only after the complete running of the two-turn scheme.
Why may this be required? The manned space science is understandable. This is not only the convenience of the process and reducing the load on astronauts, but also the possibility in the future, if necessary, to transfer specialists to the International Space Station, as quickly as possible, in case of urgent need, for example, in case of a serious illness of one of the crew members. Yes, for this we need a rocket with a fully automated launch, like Zenit once was. And it is expected that the Soyuz-5, which is generally created on its basis, will have such a function.
In addition, the reduced flight time will significantly save the work time of all ground services, reduce the load on astronauts and MCC personnel. And the possibility, in the shortest possible time, to ensure the assembly of spacecraft from several modules at the orbit can open up opportunities for military units. The possibility of prompt delivery of fuel or crew to the orbit for dual-purpose spacecraft will open up great opportunities in the future. In addition, it will provide an opportunity to keep uninhabited dual-purpose space stations in orbit, in order to activate them in just a few hours, if necessary, with the help of a manned mission.
One should not disregard the possible militarization of outer space in the future, and a short delivery scheme, a smaller logistics arm, are always very important. Now we have to wait for the manned spacecraft to be transferred to the double-turn scheme, which will make it possible to reach the orbital station in almost three hours after launching.
©New defence order. Strategy | 01 | 2019