NASA Waits For Answers As Russia Investigates "Razor's Edge" Soyuz Landing
- From: spacearium <matt@xxxxxxxxxxxxxxxxx>
- Date: Thu, 24 Apr 2008 19:28:00 -0700 (PDT)
(From The Spacearium, http://www.spacearium.com and reprinted with
permission)
JOHNSON SPACE CENTER, TX - It will take one to three months before
NASA knows what caused a series of problems during the re-entry of
Soyuz TMA-11 that put the three astronauts on board in significantly
more danger than had been reported at the time.. The Interfax news
agency reported one Russian official as likening the situation to
being on a "razor's edge." Russia has formed a state commission to
study the bone-rattling landing and determine what may need to be done
to ensure such a hard landing doesn't occur again.
On board the Soyuz was the Expedition 16 crew of the space station,
commander Peggy Whitson and flight engineer Yuri Malenchenko. With
them was the first South Korean astronaut, spaceflight participant So-
yeon Yi.
Several problems occurred during the spacecraft's descent to Earth,
which may or may not be related.
For some reason, the Soyuz hit the atmosphere at the wrong angle, with
its hatch facing forward rather than its heat shield. Apparently, the
re-entry capsule failed to separate from the rest of the craft
correctly, which left it in the wrong orientation. Soyuz was already
entering the upper atmosphere before its attitude control system was
able to re-orient the vehicle.
As a result, the hatch was severely damaged, although, fortunately,
not breached. In addition to the damaged hatch, the communications
antenna on the outside of the capsule burned off completely, leaving
the crew unable to communicate with ground controllers until they were
on the ground and able to use a satellite phone kept on board.
During the descent, smoke started to fill the crew cabin. Indicative
of a potential electrical fire, the smoke cleared once Malenchenko
turned off display lights.
During re-entry, perhaps because of the improper orientation of the
spacecraft, the Soyuz' onboard guidance computer experienced some
anomaly that caused the spacecraft to switch to a "ballistic entry".
In a normal landing, the guidance computer uses the Soyuz' reaction
control system to keep the vehicle from entering too steeply and guide
the spacecraft to a precise landing target.
If the guidance system fails, the capsule reverts to a mode called
ballistic entry, essentially an uncontrolled plunge through the
atmosphere that's much steeper than a guided entry.
The re-entry trajectory of the Soyuz is designed to limit the forces
of deceleration to about 5 G's, or five times the force of Earth's
gravity. During Expedition 16's re-entry, the crew experienced forces
nearly 10 times that of normal Earth gravity for several minutes
coupled with bone-rattling vibrations. For astronauts returning from
six months in weightlessness, a ballistic re-entry is extremely
uncomfortable at best, and poses some level of risk for injury to the
crew.
This was the second ballistic re-entry in a row and the third since
2005. The problem during the previous Soyuz landing was traced to a
short-circuit in a hand controller cable on the spacecraft. Smoke in
the cabin of Soyuz TMA-11 may be an important clue if TMA-11
experienced a repeat of the wiring problem.
Malenchenko emphasized the crew took no pro-active action that led to
the ballistic entry. "There was no action of the crew that led to
this," said Malenchenko.
The Soyuz landed 295 miles off target due to the ballistic entry. In
the days after the crew returned to the cosmonaut training center in
Star City, Russia, details of the hair-raising landing began to
emerge.
"During descent, I saw some kind of fire outside," said So-yeon Yi.
"At first I was really scared because it looked really, really hot and
I thought we could burn."
Had the crew hatch on the capsule been breached or if the Soyuz failed
to right itself early in re-entry, the spacecraft would have burned up
and killed all three space travelers. Damage to the landing parachutes
could have led to the capsule slamming into the Kazakh Steppes at 200
mph, with a similar outcome.
However, NASA and Russian officials as well as the Expedition 16 crew
stressed the need to not overreact and let the state commission figure
out what happened, why it happened and what corrective action to take.
"They are doing everything we would do. We'll get good result from
this (investigation)," said NASA Associate Administrator for space
Operations Bill Gerstenmaier. "We just need to get through this
investigation."
So far, there's been no suggestion of grounding the Soyuz. Indeed,
such an option doesn't seem possible. Soyuz is critical to maintain
the 6-month rotation of crews on the space station. In fact, beginning
next year the rate of Soyuz flights will have to double in order to
support the increase in the size of the station crew from three to six
members.
Also, the current Expedition 17 crew will return home on board the
same Soyuz they rode to orbit. Landing of Soyuz TMA-12 is slated for
late October. Russian and U.S. officials expect to have completed
troubleshooting efforts on Soyuz TMA-11's hard landing by then.
(The Spacearium, http://www.spacearium.com)
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