An inspection of the space shuttle Atlantis has uncovered some "minor" damage to the vehicle's right side, Nasa officials say, BBC reported.
Atlantis appears to be in good overall shape, but Nasa engineers in Houston are still studying the 53cm (21in) line of chips on the shuttle's right side.
More analysis will be needed to assess whether another inspection is needed.
Atlantis was launched on Monday to begin a risky repair mission intended to save the stricken space observatory.
Hubble has been hit by failures to its science instruments and to gyroscopes.
These gyros are used to point the observatory at targets in the sky. If successful, the mission could extend Hubble's lifetime beyond 2014.
During their first full day in orbit, Atlantis's crew used a laser-tipped boom to look for any damage to the orbiter in a 10-hour inspection.
The line of chips uncovered by the astronauts are in thick tiles that make up the protective heat shield on Atlantis' starboard side.
The damage is located where the right wing joins the shuttle's fuselage. Nasa said the chips could be related to a "debris event" detected by the wing's leading edge sensors 104-106 seconds into the lift-off.
Officials said the damage did not appear to be serious: "To my untrained eye... I would think [the chips] were minor," lead flight director Tony Ceccaci told reporters at a news conference in Houston.
But more analysis by engineers would determine whether a "focused inspection" was needed in that specific area. If so, astronauts would use sensors to determine the exact depth of the damage to the heat shield tiles.
Nasa has placed the space shuttle Endeavour on stand-by to rescue the crew of Atlantis if they are endangered.
If something goes wrong on this mission, Atlantis's crew will not be able to shelter on the International Space Station (ISS).
The station orbits at around 350km (220 miles) above Earth, while Hubble occupies an orbit about 560km (350 miles) up.
Impacts from micrometeoroids and space debris present one of the most pernicious threats to the astronauts.
There is more space junk - from old satellites and rocket stages - at Hubble's altitude than at the ISS's.
But a successful mission would make Hubble up to 90 times more powerful than it was in its original guise.
Atlantis roared up into the sky at 1901 BST (1401 EDT) on Monday from Florida's Kennedy Space Center. Nasa discovered a surprising amount of damage from Monday's launch at the pad used by Atlantis.
Managers wanted to make sure none of the material blasted off during launch hit Atlantis.
Atlantis is due to rendezvous with Hubble just after 1700 BST (1200 EDT) on Wednesday.
As the shuttle approaches Hubble, astronaut Megan McArthur will use the shuttle's robotic arm to grab the 13.2m- (43ft-) long telescope.
She will then mount the observatory on a work platform in the shuttle's cargo bay to allow the spacewalkers easy access to Hubble.
The next day, astronauts will begin the first of five gruelling spacewalks planned for the 11-day mission.
Crew members will install new instruments and thermal blankets, repair two existing instruments, replace gyroscopes, batteries and a unit that stores and transmits science data to Earth.
Astronauts will remove the existing Wide Field and Planetary Camera 2 instrument to make way for the new Wide Field Camera 3 (WFC3).
This camera, able to take amazingly sharp images over a broad range of colours, will enable astronomers to carry out new studies of dark energy and dark matter, searching for remote galaxies previously beyond Hubble's vision.
Spacewalkers will also swap the Corrective Optics Space Telescope Axial Replacement (Costar) device for the new Cosmic Origins Spectrograph (COS).
COS is designed for ultraviolet spectroscopy and will probe the origins of large scale structure in the Universe as well as the formation and evolution of galaxies.
Nasa plans to make repairs to the Space Telescope Imaging Spectrograph (STIS), which suffered a power failure in 2004, and to the Advanced Camera for Surveys (ACS), which was hit by an electrical short in 2007.
After the work to Hubble is complete, Atlantis will boost the telescope to a higher altitude, ensuring that it survives the tug of Earth's gravity for the remainder of its operating lifetime.
Launched in 1990, the Hubble Space Telescope is now regarded as one of the most important instruments in the history of astronomy. It has made a remarkable contribution to our understanding of the origin and evolution of the Universe.
Following the Columbia disaster in 2003, which claimed the lives of seven astronauts, another mission to service Hubble was considered too hazardous.
The reason was astronauts would not be able to use the space station as a safe haven if the shuttle sustained damage on launch.
Nasa has now accepted the risk of the mission, but will have the shuttle Endeavour ready to launch immediately to bring the crew home if the servicing mission is put at risk.
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