Digital Soyuz Return Could Be Rocky

First mission has some kinks to work out

4 min read

14 March 2011—The new ”digital” version of the Soyuz spacecraft is having some decidedly analog problems on its maiden voyage. Astronauts will test on-orbit repairs made to its troubled control systems ahead of a scheduled landing on Wednesday, 16 March. The tests will determine whether the Soyuz can perform a gentle guided descent or if it must rely on a backup emergency ”ballistic” landing instead, which would involve a much rougher deceleration and require the team to land several hundred kilometers short of the main recovery zone.

The digital Soyuz differs from its predecessors in that it has a computer upgrade, and the five incompatible analog processors for monitoring different spacecraft systems have been replaced 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 International Space Station (ISS) crew at six in the absence of the U.S. space shuttle fleet.

NASA quietly disclosed the situation on 10 March on its Web site in a routine and little-read daily ”On-Orbit Status Report” for the ISS. 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 most critical test was on 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.” Alexander Kaleri, Russia’s most senior flight-test engineer cosmonaut, was assigned command of this maiden flight because there were concerns that potential problems could arise.

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 that the astronauts will have to switch to manual control. The NASA report continued: ”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 ”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 needed to actively adjust its descent. Earlier manned vehicle upgrades, such as Soyuz-T and Soyuz-TM, made their first flights unmanned while performing an entire mission profile.

As 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 a passing reference to the Russian cosmonauts ”troubleshooting of the failed Analog/Digital converter of the Soyuz Descent Module’s ’Neptune’ console….” NASA added 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-19mission, which is not using a digital vehicle. A NASA internal report prepared in late October stated that the Russians believed 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 is that the cabin pressure rapidly increased while the new digital vehicle was on the launchpad. ”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 descent module compartment pressure rose to 933 mmHg [124 kilopascals] and 335 mmHg [44 kPa] ppO2 [partial pressure of oxygen] (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 101 kPa (760 millimeters of mercury), according to updates e-mailed within NASA at that time. Opening a vent valve could dump enough air to restore normal pressure. However, NASA documents did not address the implication of the elevated oxygen levels. With twice the normal partial pressure, the flammability hazard was more than doubled.

NASA documents said that ”the Russians have formed a commission” to address the display and oxygen regulator failures but had already concluded that 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 refusal of a once-in-a-lifetime photo op. The hope was for the Soyuz to fly by the ISS while the space shuttle Discovery and a European Space Agency ATV were docked—showing vehicles from all the international partners simultaneously at the station.

The Russians refused and said that 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 crew and more on the likelihood that certain failures would force the performance of backup procedures. These procedures could easily prevent 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 reentry and descent.

About the Author

James Oberg worked as an aerospace engineer at NASA for 22 years. He switched to journalism in the late 1990s and now makes his living reporting on space for such outlets as Popular Science, NBC News, and of course, IEEE Spectrum. In August 2010, he reported on how the repair of the International Space Station’s cooling system was a test of NASA’s ability to keep the station running.

This article is for IEEE members only. Join IEEE to access our full archive.

Join the world’s largest professional organization devoted to engineering and applied sciences and get access to all of Spectrum’s articles, podcasts, and special reports. Learn more →

If you're already an IEEE member, please sign in to continue reading.

Membership includes:

  • Get unlimited access to IEEE Spectrum content
  • Follow your favorite topics to create a personalized feed of IEEE Spectrum content
  • Save Spectrum articles to read later
  • Network with other technology professionals
  • Establish a professional profile
  • Create a group to share and collaborate on projects
  • Discover IEEE events and activities
  • Join and participate in discussions