Digital Soyuz Return Could Be Rocky

First mission has some kinks to work out

4 min read
Digital Soyuz Return Could Be Rocky

The new “digital” version of the Soyuz spacecraft is having some decidedly analog problems on its maiden voyage. Astronauts will test on-orbit repairs done to its troubled control systems ahead of a scheduled landing next Wednesday. The tests will determine whether the Soyuz can perform a gentle guided descent or instead must rely on a backup emergency “ballistic” landing, involving a much rougher deceleration and landing several hundred kilometers short of the main recovery zone.

The “digital Soyuz” differs from its predecessors by a computer upgrade and the replacement of five incompatible analog processors for monitoring different spacecraft systems with a single digital device called MBITS (the Russian acronym for "small-sized onboard informational telemetry system"). MBITS promises to make transmission of spacecraft parameters much more efficient, so that Russia can meet the rapid launch demands needed to keep the ISS crew at 6 in the absence of the U.S. space shuttle fleet.

NASA quietly disclosed the situation Thursday on its website in a routine and little read daily “On-Orbit Status Report” for the International Space Station.

According to the NASA report: “Teams in Moscow and Houston are conducting final analyses of some tests being planned for the new-design Soyuz 24S immediately upon undocking,” the report revealed. The most critical test was required by the “on-orbit installation of new M4294M Microamperemeter rate measurement assemblies (“ammeters”) by Alex Kaleri on February 2 in the Neptun-ME crew console in response to an instrumentation failure during ascent last year.”

Alexandr Kaleri, Russia’s most senior flight test engineer cosmonaut, was assigned command of this maiden flight because of concerns over potential problems cropping up.

If the test of the roll rate instruments is successful, the crew will have all four landing modes—two automatic and two manual, but any additional problem with the automated descent will mean astronauts must switch to manual control. Continued NASA, “if the rate gyros in the ammeter test are not operational then we will go into a ballistic descent.”

The upcoming descent will be the first-ever manned use of an upgraded guidance system for atmospheric entry without the prudent practice of making an unmanned test run first.  Before this current mission, the so-called digital avionics had been flight tested several times aboard unmanned Progress cargo drones and had worked well. But those vehicles had neither crew systems nor a landing module that needs to actively adjust its descent.  Earlier manned vehicle upgrades such as Soyuz-T and Soyuz-TM made tgheir first flights unmanned while performing an entire mission profile, but not this time.

As was to be expected, the vehicle’s first flight uncovered some shortcomings. A few weeks after the ship’s 7 October launch, a Russian press agency reported “a host of emergencies” on board. It quoted an internal source as saying, “The pressure rose inside the spacecraft’s descent vehicle because of an oxygen leak before the launch, the switchboard [display] computer reloaded before docking, and the analog-digital converter [for the display panel] broke down during the autonomous flight [on the second day].” This was entirely accurate –according to subsequent NASA disclosures but was denied by Moscow mission control officials.

The NASA “On-Orbit Status Report” of 3 November made passing reference to the Russian cosmonauts “troubleshooting of the failed Analog/Digital converter of the Soyuz Descent Module’s ‘Neptune’ console….” NASA reported, adding that “preliminary results from the Russian specialists have indicated the problem is hardware related.”

Earlier in 2010, the same display failure had occurred on the Soyuz TMA-19 mission, which is not a “digital” vehicle. A NASA internal report prepared in late October stated that the Russians believed that that problem had been caused by a synchronization conflict between the new-model panel and the old-model Soyuz. The introduction of the digital version of the spacecraft was supposed to eliminate the problem. But it happened again with the digital version too.

Another problem that has come up is that the cabin pressure rapidly increased while the new “digital” vehicle was  on the launch pad. “When the primary O2 isolation valve was opened, O2 flowed unexpectedly into the descent module,” explained one memo. A NASA safety review document prepared in January gave further details: “They reported a loud sound from the valve and a rapid pressure increase,” the on-line document disclosed. “The descent module compartment pressure rose to 933 mmHg and 335 mmHg ppO2 (35.9% PPO2).”

Two weeks earlier, during the Soyuz TMA-18 landing on 25 September, that crew also had to manually bleed down cabin pressure to 760 mmHg, according to updates emailed within NASA at that time. Opening a vent valve could dump enough air to restore normal pressure. However, NASA documents in my possession did not address the implication of the elevated oxygen levels. With twice as much partial pressure, the flammability hazard was more than twice normal.

NASA documents described how “the Russians have formed a commission” to address the display and oxygen regulator failures but had already concluded the problems were minor. “The Russians state there is no concern with nominal or contingency return capability.” After examining returned regulators, they reportedly have identified a fabrication material flaw in all the pressure regulators currently installed.

The lurking problems with the digital Soyuz, which neither NASA nor the Russians have been entirely candid about, were probably the major motivation for Moscow’s disappointing demurral for a once-in-lifetime photo op.  The hope was for Soyuz to fly by the ISS while the shuttle Discovery and a European Space Agency ATV were docked—showing vehicles from all the international partners simultaneously at the station.

The Russians refused, because, they say, there had not been enough time for them to fully analyze the flight plan and all its possible failure and backup modes. This was certainly true, as far as it went. But the hidden history of digital Soyuz’s problems and the expectation of new ones made the veto the only prudent choice, sources say. The issues center less on immediate hazards to the lives of the crew, but instead to the too-high likelihood that failures that could occur would force the performance of backup procedures. These procedures could easily have prevented the ship from redocking, leading to an emergency return to Earth. Further, techniques developed to accommodate some of these failures would have forced the crew to select a much more severe re-entry and descent.

The Conversation (0)