May 13, 2009 -- A myriad of space debris combined with a 21-inch scratch across delicate thermal tiles has the seven-member crew of Space Shuttle Atlantis facing very real danger as it tries to repair and update the Hubble Space Telescope.
"Something the size of a pea could put a hole in the spacecraft," former astronaut Jeffrey Hoffman told "Good Morning America." "They can usually track [pieces of debris] down to two inches... What you really worry about are the pieces too small to track, but big enough to do damage."
How Dangerous Is the Mission?
In a region littered with thousands of pieces of space junk zipping around Earth at nearly 20,000 mph, the seven-member crew has more than a week to outfit the telescope with new batteries, gyroscopes and cameras, before scampering to safety.
With more pieces of shattered satellites and used-up rockets in the area than astronauts have ever encountered, the Atlantis could collide with one of the pieces of flying trash.
Hubble orbits about 350 miles above Earth, and its orbit is full of obstacles in a sort of space garbage dump. It's a far dirtier place than where shuttles normally fly with items like space rocks speeding by at five miles a second.
"Orbital debris is a threat to any operational spacecraft. A particle as small as a fraction of an inch can disable or disrupt spacecraft operation," said orbital debris scientist Nicholas Johnson.
"It's a riskier environment when we go to this altitude," NASA safety chief Bryan O'Connor told the Associated Press. However, the former shuttle commander added, it's a risk that NASA can handle.
But it's not just the debris that poses a risk to Atlantis and its crew. A 21-inch scratch on Atlantis' underbelly, that cuts across four of those delicate thermal tiles, occurred exactly 106 seconds after its Monday launch.
The scratch caused concern because the tiles protect the shuttle and the crew from temperatures exceeding 3,000 degrees upon re-entry. Fortunately, the scratch isn't deep.
"Damage appears to be very shallow and it's not a very large area," said NASA launch integration manager LeRoy Cain. "It's very preliminary and we're thinking we probably won't need a focused inspection on this, which is good news for us."
Even before damage was discovered, NASA was preparing shuttle Endeavour to rush to the astronauts' rescue if needed. Nothing so far has been found that would require a rescue.
And for at least one of the astronauts, the risk involved is worth it.
"I think in the big picture Hubble is something I think is worth risking my life for. It's about something so much bigger than all of us," Commander Scott Altman said in a 2008 interview.
Crew's Plan for Hubble
Today, the crew will grab the telescope and tuck it inside the shuttle's cargo bay, where spacewalking astronauts will make repairs and upgrades over the next week. The work begins Thursday.
On Tuesday the crew checked the outside of the shuttle for any damage from debris during launch, finding four nicks that initially seem minor.
The practice has become standard since the shuttle Columbia was hit by a piece of foam during launch in 2003 and later disintegrated during re-entry. But the biggest danger on any shuttle flight is getting hit with space junk or tiny space rocks at high speeds during orbit, not during launch.
"A lot of people have tried to dream up schemes of cleaning it up," Hoffman said. "The best thing we can do is avoid creating the debris."
The Associated Press contributed to this story.