Captain James Lovell led the Apollo 13 mission

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An explosion on board Apollo 13 has caused one of the most critical situations in American space history and put the lives of the three astronauts on board in severe jeopardy.

The explosion happened in the fuel cells of the spacecraft's service module approximately 56 hours after lift-off.

This resulted in the loss of Apollo 13's main power supply which means oxygen and water reserves are now critically low.

The safety of the three astronauts, Captain James Lovell, Jack Swigert and Fred Haise, is uncertain although Nasa is hoping emergency contingency plans will ensure their safe return.

Certain death

The cause of the explosion is not yet clear although it is understood it could have been the result of ameteoritecrashing into the service module.

It is unlikely the exact cause will ever be ascertained as the service module will burn up before the spacecraft's re-entry into the earth's atmosphere.

The crew are currently surviving on the emergency battery power supply of the lunar module, Aquarius.

If the accident had occurred after the lunar module had been detached for the moon landing, the astronauts would have faced certain death.

The spacecraft's main computer has now been switched off to conserve what little power remains in the command module, Odyssey, as this part of the spacecraft will be required for re-entry into the earth's atmosphere.

Plans have been made to "slingshot" Apollo 13 around the moon and fire the spacecraft's last remaining booster engine to take it away from the moon's orbit and bring it back on course to earth.

This is a highly risky operation and there is no back-up should anything go wrong.

If all goes to plan Apollo 13 is due to splash down at approximately 1900 BST on Friday 17 April.

Geological experiments

The Apollo 13 mission was to have been man's third moon landing. The spacecraft was due to land in the Fra Mauro area of the moon on Thursday 16 April.

Captain Lovell and Mr Haise were due to carry out geological experiments on the moon's surface as part of an ongoing project to establish the true age of the moon.

Rock samples taken from previous missions have been dated as being 4,500 million years old.

During the 33-hour moon landing Mr Swigert would have been responsible for piloting the command module in lunar orbit.

Mr Swigert replaced Thomas Mattingly as command module pilot just hours before the mission began after it was found that Mr Mattingly had no immunity after exposure to German Measles.

Mr Lule asked people not to seek vengeance

Artificially 1969:
The A man driven into exile by former Uganda dictator Idi Amin has been sworn in as the country's new president.

Yusufu Lule was greeted by cheering crowds when he arrived back in Uganda yesterday from neighbouring Tanzania.

On Saturday Mr Lule took his presidential oath in a ceremony on the steps of the parliament building in Uganda's capital, Kampala.

The new president then called for a moment's silence for the estimated half a million people who had died under General Amin's rule.

Flanked by Tanzanian army commanders whose troops drove Idi Amin from Kampala, Mr Lule appealed to his countrymen not to seekvengeance.

"We must not indulge in the evil acts of the regime we have just removed," he said.

President Lule condemned the former leader as a rebel and ordered commando squads to track him down.

He urged troops still loyal to Idi Amin to surrender saying they would be "protected" if they handed over their weapons.

Elections

Last year Idi Amin precipitated his own downfall by sending troops to annexe part of Tanzania.

But Tanzania fought back, invaded Uganda and helped unify the various anti-Amin rebel groups.

Last month the dictator was forced to flee and is now believed to be in a remote area of the country with his remaining troops.

President Lule has said free elections will be held within two years -the first in the central African state since 1962.

The formation of the new government is being celebrated by the Ugandan people but it is a blow for Milton Obote, the man deposed by Idi Amin in 1971.

Mr Obote is a close friend of Tanzania's president Nyerere and many expected him to once again become president after Idi Amin's fall.

But Mr Obote's nine-year rule and his socialist reforms were almost as unpopular as Amin's regime.

Anti-Amin forces and exile groups told President Nyerere they would not tolerate Mr Obote beingreinstated.

meteorite:a stony or metallic mass of matter that has fallen to the earth's surface from outer space（陨星）

vengeance: infliction of punishment in return for a wrong committed; retribution（报复）

reinstate:to restore to a previous condition or position（复职，复位）