The next space shuttle mission, scheduled for July 12, will reward two persistent scientist-astronauts who've waited a total of 36 years to make it into space.

At 58, Karl G. Henize will become the oldest man to fly in space. Anthony W. England, by comparison, is a mere pup at 43.

Henize and England are astronomers who joined the space program in 1967. Their upcoming mission -- the 19th shuttle flight -- will also be the third flight of Spacelab, the $1.1 billion laboratory built by the European Space Agency.

The flight will mark the eighth time that the shuttle Challenger has flown into space -- more than the other two spaceliners.

"Even though it has a lot of miles on it," Flight Commander Gordon Fullerton said the other day at Cape Canaveral, "the bird looks brand new."

The crew plans to study the sun, distant stars, other galaxies and Earth's atmosphere. For the first time, they will carry the German-built Space Instrument Pointing System, which is so accurate it can focus on a dime two miles away. It will be used to aim an array of three solar telescopes at the sun.

FLIGHT OF THE YEAR? . . . The mission after that one, now set for Aug. 24, is shaping up as the flight of the year for the National Aeronautics and Space Administration.

After the crew deploys three communications satellites from Discovery's cargo bay, it will attempt the most daring and ambitious shuttle mission to date. Two spacesuited astronauts will try to connect an electrical cable to a U.S. Navy communications satellite that has not functioned since it was launched in April. If the astronauts succeed, the satellite will be placed in a geostationary orbit 22,300 miles above the Equator -- where it was supposed to go when astronauts tried to launch it three months ago.

The risks are considerable. Two of the satellite's rocket motors are still unlit. Their fuel tanks are loaded, one with more than 1,000 pounds of hydrazine. There is a remote chance that the engines could light at any time. The hydrazine may also have frozen, which could damage the fuel lines. Leaking hydrazine can burn through spacesuits, which would have disastrous consequences for the people inside.

But the stakes are also high. Hughes Communications Services Inc., which built the satellite, will pay NASA between $10 million and $20 million to undertake the rescue mission. If it succeeds, Hughes has agreed to share the money it will receive from the Navy over the satellite's lifetime with the U.S. and British insurance firms that underwrote the April mission. If the salvage mission fails, the underwriters will pay Hughes $85 million.

INTERNATIONAL FLAVOR . . . The post-landing news conference of the last shuttle crew had a flavor as international as the crew itself. Most of the media attending were Saudi or French, and most of the questions were directed at Saudi Arabian Prince Sultan Salman Saud and French Air Force Col. Patrick Baudry.

Sultan was asked if his orbital photography had turned up any new oil fields in his native land. He replied, "I made a deal with a geologist in Saudi Arabia. Any new findings and our crew gets half."

Asked how he located Mecca each day so he could pray toward it, he responded, "It was easy. All I had to do was find Saudi Arabia, and since I was assigned to take photographs of Saudi Arabia, the ship was usually pointed in the right direction and I was able to locate it very quickly."

Baudry was asked what kind of wine he had smuggled aboard Discovery and when he planned to drink it. "It was a Medoc a red Bordeaux and the year was '75," he said. The crew plans to drink it when the astronauts visit France in September: "I want to see if there's any change in the taste after the time it spent in orbit."

Pilot John O. Creighton, who was married the day after Discovery landed, told reporters, "I'll get myself in hot water if I say which was my biggest thrill."

END OF AN ERA . . . University of Texas scientists recently held a farewell ceremony at the McDonald Observatory in the mountains of West Texas for a laser that has been used for the past 16 years to measure the distance between the Earth and the moon.

The Korad laser, one of the last experiments still in use from the days of the Apollo moon missions, measured that distance to within four inches. It will be replaced by the McDonald Laser Ranging System, which will compute the ever-changing distance to within two inches. However, the new laser will work the same way the old one did: firing a beam of laser light at a reflector left on the moon by pioneer astronauts Neil Armstrong and Buzz Aldrin. The light bounces back to the observatory's 107-inch telescope.