Soyuz-TM spacecraft motion control system

In my hubs, I want to tell you about the management of manned spacecraft. Mostly about the Soyuz and Space Shuttle ships. Over 15 years of studying these ships, I have gathered enough information about them, as well as the knowledge that I want to share with you.

On Habr I want to tell you about the mode of approach of the Soyuz spacecraft with the International Space Station (ISS). Since in space in 70% of cases of presenting information, abbreviations are used, I will have to use them the same way, but I will try to decipher and explain their meaning in the most complex and incomprehensible ones.

In order to talk about this mode, we need to describe the dynamics of the ship and the station, as well as describe the basic principles of ship control.

When approaching in space, the dynamics of the transport ship (TC) and the international space station (ISS) can be represented in the form of two independent movements:

  • rotation of each of the spacecraft around its center of mass (angular velocity assignment);
  • relative motion of the centers of mass of the TC and the ISS (linear velocity assignments).

Therefore, management includes:

  • control the movement of each spacecraft around its center of mass ( orientation control or control of the relative angular position )
  • control of the relative motion of the centers of mass of spacecraft (control of the relative path of convergence).

In practice, in the process of approaching the ISS moves in a known orbit and maintains a given orientation (in a previously set for convenient docking TC), so the ISS is called a passive ship (PC). The transport ship, which is an active ship (AK), has the task of maneuvering, that is, controlling rotation and movement relative to the center of mass relative to the ISS. Therefore, for the implementation of the approach of the TC to the ISS in the motion control system (CMS) of the TC, the approach mode (SB) is provided.

What tasks does the rapprochement mode solve?

  • selection of the optimal approach path (OTC) of the spacecraft with the ISS, based on the minimum fuel consumption for its implementation;
  • organization of control of the TC movement along the selected approach path;
  • providing automatic (discrete) or manual (analog) overflights to a given docking station of the ISS, hovering in front of it, approaching with relative motion parameters that ensure the normal operation of the docking mechanism;
  • providing automatic control over the state of the motion control system
  • TC in close mode. If a failure occurs, an automatic
  • switching to serviceable devices;
  • issue of information to the crew about passing the approach mode, parameters
  • the relative motion and failures of the COURT TC;
  • providing automatic or manual removal of the TC from the ISS in the presence of danger
  • collisions.

So, the approach system, like any other control system, must satisfy the following requirements:

  • minimum fuel consumption for rapprochement;
  • high precision control TC;
  • simplicity of software and instrument implementation;
  • minimum weight, dimensions and power consumption of the system;
  • high system reliability;
  • safety of the process of rapprochement.

In addition, I want to note that in order to ensure the passage of the approach mode and the operational intervention of the MCC in the control of the fuel cell in case of emergency situations (NShS) at the critical stages of approach (flyby, hovering, mooring, docking), it is desirable that these operations be performed in the light in sessions communications, that is, in the visibility zones of ground-based measuring points. But communication sessions are possible only at certain time intervals, due to the geographical location of ground-based measuring points and the orbit precession due to the daily rotation of the Earth. Therefore, it is necessary to create such a control of a transport ship in the approach mode in order to bring it into the vicinity of the ISS (relative distance less than 1 km) at a given point in time,

The purpose of the system, the requirements for it, and time limits, taking into account the cut-off situation, determine the principles of controlling a transport ship and the principles of
constructing a TRC TK in the approach mode.

Now, let's deal with you the principle of managing the TC in the SB mode.

Since the requirements for the approach control system are contradictory, it is completely impossible to satisfy them, because it is impossible to select a targeting method for controlling a transport ship that would ensure the simultaneous fulfillment of all requirements for the system. Therefore, in practice, the entire process of rapprochement is divided into two sections:

  • distant section (DU), whose task is to bring the TC to the area of ​​the ISS along the optimal approach path, that is, with minimal fuel consumption;
  • - the near section (CU), the task of which is to ensure control with a given accuracy of the orientation and movement of the center of mass of the TC towards the selected docking station and soft contact when docking. Based on the above considerations, for a transport ship, the proximity approach is realized using the free trajectory method, and the control unit is approaching it using the modified guidance method along the line of sight (here, under the line of sight (LP), the line connecting the centers of mass of the converging objects is adopted).

Guidance using the free trajectory method

The free trajectory method takes into account the orbital motion of the spacecraft in the Earth's gravitational field. It allows the transfer of a transport ship from the waiting orbit to the vicinity of the ISS using a multi-pulse maneuver, which consists of sections of the ballistic (free) motion of the spacecraft in the gravitational field and the controlled (with the propulsion system on) motion of the spacecraft. The direction, magnitude and moments of the output of these corrective pulses are calculated from the condition of ultimately getting into the vicinity of the ISS. It should be noted that the time for issuing corrective pulses is very short compared with the time of free movement of the TC. Thus, the approach trajectory consists of sections of free movement of the TC, at the interface points of which corrective impulses are issued. From here follows the name of the guidance method.

  1. two-pulse;
  2. three-pulse.

Of course, there are other schemes, but in this article we will consider only these.

1. In the case of a two-pulse scheme, the approach path is constructed using a 2-pulse maneuver, where
ΔV1 is designed to build an interception orbit that ensures that the TC enters the OK vicinity at a given point in time Tzad;
ΔV2 is designed to align the orbital speeds of the TC and OK.


2. In the case of a three-pulse circuit, the approach path is a belliptic transition realized by three correcting pulses ΔV1, ΔV2, ΔV3 .


In this case, ΔV1 is applied in the waiting orbit to transfer the TC to the internal
elliptical transition orbit,

ΔV2- is intended for the transition of the spacecraft to the vicinity of the ISS at a given
point in time Tzad,
ΔV3 - is necessary to align the orbital speeds of the spacecraft and the ISS.

In the following articles, we will examine guidance along the line of sight, parallel guidance, etc.

Also popular now: