Although an exact cause is not known, ISU experts say there are several possibilities to the cause of Saturday’s space shuttle Columbia catastrophe.

The leading theory for the cause of the crash is a piece of orange insulating foam on Columbia’s external fuel tank that came off and hit the leading edge of the shuttle’s left wing during liftoff on Jan. 16.

The crew never actually got to look at the area where the foam hit because the shuttle was not equipped with a robotic arm.

John Tannehill, ISU professor of aerospace engineering, did research on the space shuttle project in the early 1970s. His research was funded by grants from NASA. He said there were pictures taken from various satellites in space and there appeared to be no damage to Columbia. Tannehill said there may have been things that the satellites might not have seen.

Leroy Cain, lead flight director in Mission Control, said Friday that engineers had concluded the damage to the wing, if there was any, was considered minor and posed no safety hazard.

“[We] took a very thorough look at the situation with the tile on the left wing and we have no concerns whatsoever,” he said Friday.

Ron Dittemore, the shuttle program manager, said earlier there was no indication that hard metal, as well as foam, detached from the fuel tank.

This was not the first time that a piece of foam has come detached from the tank. In October 2002, the shuttle Atlantis lost a piece of foam and struck the rear section on one of two solid-fuel boosters. There was no indication that harm was done and the flight proceeded.

Tannehill said this situation is not as dangerous as a tile on the underbelly or leading edge of the wing being damaged.

Plans had already been made for flight managers to look at whether these events were indications of a more serious problem.

Saturday’s first indication of trouble with the left wing began when temperature sensor readings in the wing were not being communicated during re-entry.

NASA officials are looking into the left wing, but are not ignoring other possibilities.

“As we look at that now in hindsight, we can’t discount that there might have been a connection,” Dittemore said during a news conference on Saturday. “But we have to caution you and ourselves that we can’t rush to judgment on it because there are a lot of things in this business that look like the smoking gun but turn out to be not even close.”

It is also possible that one of 20,000 tiles on the underbelly and leading edges of the shuttle may have come loose.

“The tiles are a protection from the heat generated as the vehicle re-enters Earth’s atmosphere. If a tile had come loose, it’s totally gone, kind of like a blow torch put on the shuttle’s skin, it can eventually burn through,” Tannehill said. “What can happen if there is a hole is the hot gases start entering the structure. The structure can start melting and this is catastrophic if shuttle tiles are not in place.”

Tile damage on the underside of the shuttle as well as the leading edges of the wing are equally dangerous, Tannehill said. Both the underside of the shuttle and the leading edge experience high temperatures during re-entry.

A structural failure, another possibility that NASA officials are investigating, could occur when there was maximum pressure on the shuttle, Tannehill said. There is only aluminum skin and braces called ribs underneath the tiles, and a failure could cause an opening and start burning objects up inside the wing of the shuttle, he said.

A failure in the flight control system, another possibility, is unlikely because there are four computers working independently and Mission Control would have seen it in the telemetry, which is the general communication data, Tannehill said.

“The shuttle is on autopilot during re-entry, and if for some reason the computers malfunction and got the orbitor at a bad angle, it may have caused the shuttle to break up,” Tannehill said. “This is probably not likely because when all this was happening [Mission Control was] still contact with the shuttle crew.”

Tire pressure readings for Columbia’s landing gear were lost after the temperature sensor readings during re-entry, then there were indications of “excessive structural heating.”

The last communications to Columbia acknowledged the reading, and then all communication was lost.

A loss of communication is typical during re-entry.

“The shuttle starts to enter and it’s got tiles facing into the wind. An ionized envelope develops around the shuttle and you lose communication,” said William Byrd, director of the NASA space grant consortium. “The radio signal can’t penetrate and the shuttle will come out of it, but that didn’t happen.”

The moment communication was lost was probably the moment that the shuttle started breaking apart, Tannehill said.

Although there has never been problems during previous missions with the re-entry process, it is no less risky than going up — even though it is an “engineering wonder,” said Ping Lu, ISU associate professor of aerospace engineering and engineering mechanics.

“It is an engineering wonder because the flight is so flawless, and this is really the first time [trouble has occurred], but you have to keep in perspective that space is full of uncertainty, and the people involved fully understand and fully take the risk,” Lu said.

The shuttle was at a critical point of re-entry, flying at a speed of Mach 18, which is roughly 18 times the speed of sound. The shuttle had slowed down, but was still in the middle of re-entry, Tannehill said.

“It appears that somehow the thermal system broke down and led to structural failure, but that is speculation,” Tannehill said.

During re-entry, the heat surrounding the shuttle is about 3,000 degrees Fahrenheit, Lu said. It is very hostile and everything has to be very precise.

“Re-entry is always a critical moment for any spacecraft because the stress on the vehicle is so high,” Paul K. Harral, vice president and editorial page editor of the Fort Worth Star-Telegram, told the Daily on Saturday. Harral was a UPI space writer during the Apollo series, including the flight of Apollo 13.

“The issue is both the impact with the air, which at the speed of re-entry can be substantial … The resulting heat build-up, as the air begins to drag on the spacecraft, slows it down,” he said. “That friction causes heat, of course, and a critical element is dealing with that heat.”

Harral said NASA will next determine what happened and determine how to reduce the risk in future missions. There is no way to know how long the investigation could take, he said.

There may be some implications to the loss of Columbia for NASA.

A British Broadcasting Corp. correspondent said an immediate concern is the fate of the International Space Station. Three crewmen are currently living and working on the station.

Europe, Japan, Canada and Russia have all invested in this project, which relies heavily on the United States’ shuttle fleet. The correspondent said future plans will now be reviewed, and whether the station remains operational will be decided by experts.

Nikhil Murgai, ISU graduate student in aerospace engineering and president of the graduate student organization in the Department of Aerospace Engineering, said Columbia’s loss should not affect the future of space missions.

“Space research is one of the pioneering sciences,” he said. “There have been failures and mishaps, but that’s the human spirit — to discover what’s beyond. Mishaps don’t usually hinder the spirit. We’ll think of the people who made the sacrifice, but that sacrifice will lead us even further.”

Worldwide Reactions

U.S. Rep. Tom Latham, R-Iowa, expressed his condolences to the families of the seven astronauts, including Iowa-native Clark, on Saturday.

“Today’s space shuttle tragedy took one of Iowa’s native daughters, Laurel Clark, and six other brave heroes. Our thoughts and prayers are with Dr. Clark’s family and all of the families who lost their loved ones on this sad day,” Latham said.

ISU students also mourned the loss of the astronauts. Deepak Sahoo, a doctoral student in electrical engineering and president of the Indian Student Association, said his homeland is suffering the loss of a national hero.

“For the last two days programs in the Indian media [have been] about her and after the accident people all over the country were really sad about it,” he said.

Chawla also had Iowa ties. She had conducted space experiments for the University of Iowa on Columbia in 1997 and spoke to local schools in Iowa in 1998. She helped researchers study the effects of microgravity environment on the stability of flames.

Jonathan Gritz, president of Hillel, which is Iowa State’s Jewish student organization, said the loss of the astronauts, including Ramon, was unfortunate.

“It’s sad that it had to happen,” he said.

Because of the tensions between Israelis and Palestinians, the subject of a terrorist attack was brought up early and was immediately dispelled by Gordon Johndroe, spokesman for the Homeland Security Department in Washington, D.C.

“There is no information at this time that this was a terrorist incident,” he said.

Palestinian Information Minister Yasser Abed Rabbo said the Palestinians are “shocked at the news of the tragedy. We sympathize with the families of the astronauts.”

Ramon’s brother Gadi spoke to Israel’s Channel 10 television on Saturday.

“We are in shock and don’t know what to do,” he said. “This was a dream come true for Ilan.”

Minutes from home

The shuttle lost contact with Mission Control at 8 a.m. CST while traveling at an altitude of 203,000 feet and a speed of about Mach 18, or 12,500 miles per hour, above north central Texas. It was only minutes away from landing.

All seven astronauts were declared dead.

“These astronauts knew the dangers, and they faced them willingly, knowing they had a high and noble purpose in life,” President Bush said in a live address to the nation on Saturday. “Because of their courage and daring and idealism, we will miss them all the more.”

The last contact to the shuttle Columbia was made at 7:59 a.m. CST by Mission Control: “Columbia, Houston. We see your tire pressure messages. We did not copy your last.”

There was a delay before Husband responded, “Roger … ehrm … “

Radio and data communication were lost at this point, and Columbia did not respond to repeated messages.

Calls about debris from residents of north-central Texas to local authorities flooded the phone lines starting at about 8 a.m. CST. The debris stretches from the Dallas-Fort Worth area to more than 200 miles into central Louisiana.

At about 8:16 a.m. CST, when the shuttle was scheduled to land at Cape Canaveral, Fla., NASA declared that a contingency action plan for Columbia was being implemented.

NASA then assigned a former astronaut to each of the crew members’ families for support.

— The Washington Post, BBC, The Des Moines Register, Iowa City Press-Citizen, Houston Chronicle, The New York Times and NASA contributed to this article.