File image of the Progress spacecraft (right) at the International Space Station, ISS. Image credit: NASA

May 6, 2015 Progress mission failure, root cause still uncertain

Sen—For the past two weeks, the drama of Russia's stricken Progress cargo freighter has been gripping the space community and public at large. The Progress M-27M, which launched on April 28 loaded with supplies for the International Space Station (ISS), became stranded in orbit and is now heading for an uncontrolled plunge into Earth's atmosphere as early as Friday May 9, according to the latest estimates. Reentry experts agree that the majority of the spacecraft's components and its toxic propellant will burn up in the atmosphere, though some temperature resistant pieces such as the engine combustion chamber could make it all the way to the surface. Even then, the chances of hitting populated areas are extremely remote. However, for the rest of the Russian space program, the story is far from over.

As soon as the first details emerged about the accident, engineers were relieved that the mission failure had struck an unmanned cargo ship, rather than a Soyuz spacecraft—currently the only human transporter—carrying crew to the ISS. Although manned missions ride an older and supposedly more reliable Soyuz-FG rocket rather than a Soyuz-2-1a variant, the mechanics of the eight-minute launch scenario are very similar for both rockets. Ironically, the recent switch of Progress missions to the Soyuz-2-1a launcher was aimed at certifying the ill-fated rocket for human missions.

Had a manned Soyuz lost all its propulsion capability in the same way as the Progress M-27M mission, the only hope for the crew would be to survive long enough in the tumbling capsule for the headwind of the upper atmosphere to slow down the spacecraft and push it off its orbit. Given enough food, power and oxygen, the pilots could manually jettison the habitation compartment and the damaged propulsion module to parachute back to Earth inside their descent module.

The available resources onboard Soyuz afford it to function autonomously for slightly more than five days, though that capability likely assumes that the spacecraft can maintain a proper orientation toward the Sun in order for its solar panels to recharge the onboard batteries and for its thermal control system to maintain comfortable conditions for the crew and equipment.

The crippled Progress was hauled high enough to stay in orbit for around ten days. Surprisingly, as late as Tuesday May 5, the spacecraft still maintained a radio link with ground stations, the Russian mission control sources told Sen. However, such an endurance was attributed to the ship's onboard battery life rather than energy from its solar panels.

In the meantime, engineers are still struggling to find the culprit that caused the Progress freighter to break up communications with ground control and then to fail to respond to all the emergency commands.

Unfortunately, the available information is fragmented and investigators need to explain contradictory data. Part of the problem is that the accident happened at the moment of separation between the spacecraft and the launch vehicle. In the byzantine world of the Russian space industry it constitutes a border zone between the responsibilities of two teams: RKK Energia in Korolev, the organisation that builds the spacecraft, and RKTs Progress in Samara, which manufactures the Soyuz rockets.

Not surprisingly, in the first few hours of the crisis fingers were pointed in opposite directions. The rocketeers were saying that the spacecraft literally blew itself up after its separation from their vehicle, while the spacecraft developers immediately blamed the launcher. However, in the days since the failure, evidence has been mounting against the third stage of the Soyuz-2-1a rocket.

The picture which is still emerging points to a powerful explosion, which happened right in a middle of a three-second interval between the command to cut off the engine of the third stage and the separation of the spacecraft from the rocket. At that moment, the flow of data from a two-channel telemetry system nestled between the fuel and oxidizer tanks onboard the rocket suddenly stopped, while data coming from the spacecraft also became sporadic.

During three following passes over Russia, ground controllers were able to activate a TV camera onboard Progress which revealed that the cargo ship had been tumbling in space at high speed. In the meantime, a U.S. radar detected at least 44 pieces of debris emanating from the launch.

The rocket and the spacecraft were also found in a drastically different orbits—the ship around 40 kilometers higher than normal and the stage around the same distance lower than the projected altitude.

Surprisingly, the available telemetry indicates that the engine of the rocket obeyed the cutoff command, thus likely ruling out the rocket's propulsion system as a source of the explosion. However propellant tanks onboard the rocket still remained pressurized at the time of the separation, because the opening of a special valve to release the gas was scheduled few seconds later. In theory, this internal pressure could have provided explosive energy in the vacuum of space causing the structural disintegration of the stage.

According to one hypothesis, a rocket stage which was compromised by a structural defect stayed together as long as the engine thrust pushed it from behind and the spacecraft pressed on it from the front. In this scenario, as soon as the engine stopped firing, the internal pressure tore apart its body, possibly further exacerbated by the spacecraft's release on the opposite end. Under such a scenario, exploding bulkheads of the propellant tanks could have smashed sensitive telemetry equipment installed between the tanks and also crashed into the nearby spacecraft damaging the propulsion system.

Investigators face a difficult task finding the root cause of the problem in the politically sensitive field of manufacturing defects and quality control. They will also be under tight deadlines, because the next launch of the Soyuz-2-1a rocket with a Russian spy satellite was scheduled for May 15, while a fresh crew was slated to launch to the ISS on May 26. The latter mission could well be delayed until every question about the performance of the Soyuz rocket family has been settled, mission control sources said.