What was the reason behind the death of kalpana chawla(Astronaut)??

Introduction

Kalpana Chawla was an American astronaut, engineer, and the first woman of Indian descent to go to space. She first flew on Space Shuttle Columbia in 1997 as a mission specialist and primary robotic arm operator. She was very brilliant in his works, she also won the various medals in field of astronomy and robotics.

Cause of her death

US space shuttle Columbia disintegrated shortly before landing on Saturday morning, killing the seven crew members on board, including Indian-American Kalpana Chawla.
Witnesses in and near Waco and Dallas, Texas, reported seeing the space shuttle breaking up around 8 am local time, about 16 minutes before its scheduled landing at Cape Caneveral, Florida. Local cameramen captured several vapour trails in a clear blue sky as the shuttle broke up.
Columbia was returning to earth after a 16-day mission and was commanded by Texan Rick Husband, who was on his second mission. It was also the second mission for Karnal, Haryana-born Kalpana Chawla after her debut flight in 1997.
In fact, it was possibly the most diverse space mission ever. Besides Husband and Chawla, the shuttle carried African-American Michael Anderson, Israeli astronaut Ilan Ramon, and woman doctor Laurel Clark.
About an hour after the shuttle was seen disintegrating, witnesses reported seeing debris scattering in the Texas hinterland between several small remote towns.
Nasa mission control said the flight was at 200,000 feet altitude and traveling at 12,500 miles an hour when they lost contact after a last garbled message. At that time, the seven astronauts would have been strapped in for landing and tremendous gravitational force would have been at work.
This was Columbia''s 28th space flight. Each shuttle is good for at least 100 flights. Columbia was returning to the earth after a 16-day space mission in which the crew carried out nearly 80 experiments. Chawla was the shuttle''s flight engineer and was also tasked to carry out several scientific experiments.
Columbia''s landing was happening just after the 17th anniversary of the Challenger disaster (January 28, 1986) in which seven American astronauts died when the shuttle exploded shortly after take-off.

Although Chawla was married (to Frenchman Jean Pierre Harrison, a flying instructor and aviation writer) and settled in the US, she had close ties to India.
In fact, among the items she carried into space on this mission was a banner from the Nehru Planetarium in India, one from the Aero Club of India, and pins and patches from some of the schools and colleges she attended both in India and the United States.
Chawla showed an interest in flying and space from her earlier years growing up in Karnal, Haryana. Her school projects and papers were all about the stars, planets, and outer space. Her businessman father encouraged her to join the Karnal Flying Club, while she took up engineering and became Punjab Engineering College''s first woman aeronautical engineer in 1982.
She moved to the US soon after for her graduate and post-graduate studies and joined Nasa''s Ames Space Center in 1987. She was selected by Nasa in 1994 to be an astronaut.
In pre-flight interviews, she had spoken about how Commander Husband, she, and Anderson were all from the same class at the Johnson Space Center, while Brown and Clark were from the class that followed them.

The whole crew went on a ten-day backpacking trip to the Wind River mountains in Wyoming to get to know each other better.