Press Release

RSC Energia Report on Cause of Soyuz TMA-1 Reentry Problems

By SpaceRef Editor
May 28, 2003
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RSC Energia Report on Cause of Soyuz TMA-1 Reentry Problems

The findings of the technical commission established to analyze the causes of the Soyuz TMA-1 descent vehicle returning to Earth in ballistic mode were presented at a press conference held at S.P.Korolev Rocket and Space Corporation Energia for journalists of Russian and international TV companies and information agencies, as well as representatives from NASA and European Space Agencies. The chairman of the commission is the First Deputy General Designer of RSC Energia N.I.Zelenschikov. Present at the press conference were members of the commission – managers and specialists from RSC Energia, Federal Office of Aviation and Space Rescue and Recovery, Gagarin Cosmonaut Training Center and TsNIIMash.

The commission made a statement that basically all of the new systems and structural elements of the vehicle have been tested in flight during the mission. Fully tested were: the new control panel, refrigerating and drying units of the thermal control system, linear acceleration measuring unit, descent vehicle structure, the system for recording and storing telemetry and voice information and all the elements of landing system (baro unit, automatic equipment, upgraded gamma-ray altimeter, soft-landing thrusters, new seats). The new special computing unit KC020-M – the command unit of the controlled descent loop – has not been tested to the full extent because the descent vehicle switched from the automatic controlled descent mode into ballistic descent mode. However, telemetry data have shown that this computer unit, which was made to change from command mode into indication mode during switching over to the ballistic descent, generated all the necessary commands in accordance with its pre-programmed logic, so there have been no anomalies in its behavior.

Establishing Soyuz TMA-1 in-orbit orientation, starting propulsion unit, generating a retro burn, and running module separation operations have all been performed in accordance with the program and technical documentation and no anomalies have been found.

In the course of 183 seconds after separation of the spacecraft modules, the descent vehicle was moving along the controlled descent trajectory. Switching to the ballistic descent mode occurred automatically after the Motion Control System (MCS) generated the command on the basis of the spacecraft reaching the maximum allowable yaw angle. Operation of MCS and of the landing equipment, as far as roll and pitch channels were concerned, stayed within design limits.

The ballistic descent has been performed nominally, in accordance with the pre-programmed control logic. The maximum g-loads during descent did not exceed 8.1g. The descent vehicle landing system performed nominally and g-loads stayed within the design limits.

The descent vehicle of Soyuz TMA-1 landed in its target point for ballistic descent. The search and rescue service found the descent vehicle and the crew within prescribed timeframe. No anomalies have been found in the operation of the communications and direction finding systems during descent and landing.

During the descent the crew of Soyuz TMA-1 performed all the necessary monitoring and control operations in accordance with on-board instructions and recommendations from the Lead Operations Control Team (LOCT) displaying good teamwork and mutual understanding. The crew evinced high psychological stability, endurance and self-control. High professionalism of N.M.Budarin as the commander of the vehicle in this situation merits a special note here.

The commission findings: the cause of switching to the ballistic descent mode was an inadequate reaction of the descent control unit within the descent control system to the signals from gyroscope KI00-18 and the angular rate meter. As a result, the descent vehicle yawed to the limit angle, which caused the gyroscope end switch to issue the command to switch to the ballistic descent mode.

In the course of its work the commission has run tests on the descent control unit. During its electrical tests within the descent vehicle brought from the landing site to RSC Energia there have been many attempts to simulate the situation that occurred in flight, but they failed to reproduce it. Only when one channel of the unit was artificially disconnected, in one case (out of forty) a situation was achieved which was close to the one in flight.

The analysis has not revealed any connection between the situation and the descent vehicle modifications that have been introduced. The MCS hardware as far as the applicable control functions are concerned has not been modified since Soyuz T (since 1979). The descent control unit has no electrical interfaces with the newly added special computer unit and a unit for measuring linear accelerations.

Tests of the descent control unit after its return to Earth have showed that its electrical properties are fully compliant with the requirements of the technical documentation. However, an in-depth analysis of the descent control unit done in course of the commission activities revealed a peculiarity of its electrical design, which could, under a very rare combination of input signals in any of the three channels (pitch, yaw, roll), could lead to disabling the signal and stopping output of commands to the effectors. The occurrence of this problem is of very low likelihood, which is born out by the 48 successful controlled descents of the Soyuz-type vehicles, including the ones involving the descent control unit, which, before it was installed on Soyuz TMA-1, has passed flight tests in Soyuz TM-29 in 1999. The work to simulate and reproduce this situation in a stand-alone electrical test setup for the descent control unit continues.

The analysis of the on-board documentation, mission control documentation, LOCT actions, communication between search and rescue teams, MCC-M and the crew has revealed some problems that have not significantly affected the mission, but need to be resolved in the future.

The commission permits Soyuz TMA-2, currently operating in orbit within ISS, to continue its mission without any reservations regarding the on-board equipment of the spacecraft, however, it wants to draw attention to the need to take into account its recommendations about actions of the crew and LOCT, and communications between search and rescue team and MCC-M. The final version of the commission’s findings was submitted for approval.

It was recommended that, starting with Soyuz TMA-3, the descent control unit be modified to introduce into it additional elements which will rule out the unlikely but possible situation similar to the one that occurred.

After presenting the key findings of the commission, N.I. Zelenschikov, managers and specialists on that commission, answered journalists’ questions, and then, together with them they visited the Corporation’s test and check-out facility, where they provided additional explanations of the commission’s findings and told about the progress of work under the International Space Station project, including the on-going work at RSC Energia to build Progress and Soyuz TMA-3 spacecraft in support of ISS program for the year 2003.

The meeting continued for more than two hours.

SpaceRef staff editor.