Tests will inform whether Endeavour is cleared to return without repairs
Nasa is optimistic that the space shuttle Endeavour will not need repairs to a gouge on its underside before it makes the return journey to Earth.
Agency officials said it was unlikely they would have to send astronauts outside to repair the 9cm (3.5in) gash.
Meanwhile, the agency fulfilled its longstanding aim of a teacher talking to students from space.
Endeavour is carrying out a 14-day mission to continue the assembly of the International Space Station (ISS).
During launch on 8 August, a chunk of insulating foam hit the shuttle, creating a square gouge about the length and width of a business card.
A sliver of the wound penetrates through a pair of 2.5cm (1in) deep thermal tiles, exposing a thin felt fabric that forms the final barrier before the shuttle's aluminum frame.
US space agency managers have been carrying out tests back on Earth to determine whether two astronauts should be sent on a spacewalk to repair the damage.
The thermal heat shield is designed to protect the orbiter from the searing heat on re-entry, where temperatures can reach 2,000C.
Analyses carried out so far have shown that Endeavour could safely return to Earth as it was, said John Shannon, chairman of the mission management team. All tests and analysis should be completed by Wednesday, he added.
Foam damage has been a major concern for Nasa since the Columbia disaster in 2003 when a briefcase-sized chunk of foam insulation broke off during launch and pierced the shuttle's wing.
This caused the shuttle to disintegrate on re-entry into the atmosphere, killing all seven crew.
Teaching in space
On Tuesday, teacher-turned astronaut Barbara Morgan fielded questions from children via a link-up, realising a long-held dream.
Ms Morgan, 55, originally trained at Nasa as a back-up for Christa McAuliffe, who was selected for Nasa's Teacher in Space programme, announced by US President Reagan in the 1980s.
McAuliffe and six other astronauts were killed in 1986 aboard the shuttle Challenger, when a leaky booster rocket triggered an explosion 73 seconds into launch.
After the incident, Nasa asked Ms Morgan to stay on as its Teacher in Space representative and pledged a shuttle flight to fulfil McAuliffe's educational agenda.
When the agency banned civilians from flying in its spacecraft, Ms Morgan had to become a fully trained astronaut, joining Nasa's corps in 1998.
From the ISS, she spoke to an audience of hundreds of yougsters packed into the Discovery Center of Idaho in Boise, US, less than 160km (100 miles) from the elementary school where Morgan taught before joining the astronaut corps.
Asked by one child how being a teacher compared to being an astronaut, Ms Morgan replied: "Astronauts and teachers actually do the same thing.
"We explore, we discover and we share. And the great thing about being a teacher is you get to do that with students, and the great thing about being an astronaut is you get to do it in space, and those are absolutely wonderful jobs."
One child asked her about exercising in space: in response, Morgan lifted the two large men floating alongside her, one in each hand, and pretended to be straining.
Another wanted to see a demonstration of drinking in space. Ms Morgan and her colleagues obliged by squeezing bubbles from a straw in a drink pouch and swallowing the floating red blobs.
The mission was scheduled to last for 11 days but was extended to 14 thanks to a new piece of equipment that allows the shuttle to tap into the power grid of the ISS.