NASA's huge six and a half ton Upper Atmosphere Research Satellite(UARS) continues to plummet towards the Earth and is expected to fall to the Earth sometime late Friday night or early Saturday morning.

The 20-year-old satellite was expected to fall to Earth sometime on Friday afternoon. However, changes in the school bus-size satellite's motion may push it to early Saturday, according to NASA's latest observations of the spacecraft, reports space.com.

Re-entry is expected between 11 p.m. Friday, Sept. 23, and 3 a.m., Sept. 24, Eastern Daylight Time (3 a.m. to 7 a.m. GMT), NASA said on its website. During that time period, the satellite will be passing over Canada, Africa and Australia, as well as vast areas of the Pacific, Atlantic and Indian oceans. The risk to public safety is very remote, said NASA.

Even though NASA had predicted that the satellite's debris would not strike North America, the space agency has not completely ruled out the possibility.

The satellite's orientation or configuration apparently has changed, and that is now slowing its descent, NASA officials wrote in a status update Friday morning. There is a low probability any debris that survives re-entry will land in the United States, but the possibility cannot be discounted because of this changing rate of descent.

According to an Associated Press report, The possible strike zone skirted Washington state.

The UARS was expected to fall faster due to increased solar activity which causes the atmosphere to expand and make low-flying satellites like UARS fall faster. But late Friday morning, NASA said the Sun was no longer the major factor in the satellite's rate of descent.

However, there is very little cause for concern over being stuck by the satellite's debris.

NASA officials had earlier said that the probability of a UARS debris hitting any one of the nearly 7 billion people on the planet were about 1 in 3,200. However, the personal odds of being hit by the satellite debris are 1 in several trillion, according to Mark Matney, a scientist NASA's Orbital Debris Program Office.

NASA expects around 26 pieces of the UARS satellite to come hurtling back to Earth, with the largest piece weighing about 300 pounds.

As of 7 p.m. EDT on Sept. 23, 2011, the orbit of UARS was 90 miles by 95 miles (145 km by 150 km), according to NASA.

It is still unclear as to where the satellite will fall. According to the space,com report, NASA orbital debris experts have said the satellite could fall anywhere between the latitudes of Northern Canada and southern South America, a region of Earth that encompasses much of the planet.

It is still too early to predict the time and location of re-entry with any certainty, but predictions will become more refined in the next 12 to 18 hours, NASA officials wrote in an update.

NASA officials believe that the UARS satellite could also fall over an ocean since three fourths of the Earth is covered in water.

UARS was launched Sept. 12, 1991, and was the first multi-instrumented satellite to observe numerous chemical components of the atmosphere for better understanding of photochemistry. UARS ceased its productive scientific life in 2005. It was put in a disposal orbit at that point, which reduced its lifetime by 20 years.