PASADENA, Calif., July 1 (UPI) -- The Ulysses spacecraft, a joint NASA-European Space Agency mission, has officially ceased operations, officials said.

The end-of-mission command was transmitted Tuesday to the spacecraft that operated for more than 18 years, charting the unexplored regions of space above the poles of the sun. When space shuttle Discovery launched Ulysses on Oct. 6, 1990, it had an expected lifetime of five years, NASA said.

"This has been a remarkable scientific endeavor," said Richard Marsden, Ulysses mission manager and project scientist at the European Space Agency. "The results Ulysses obtained have exceeded our wildest dreams many times over."

In addition to measuring the solar wind and charged particles, the spacecraft's instruments measured small dust particles and neutral gases from local interstellar space. NASA said Ulysses also had an unprecedented three chance encounters with comet tails, registering more than 1,800 cosmic gamma-ray bursts and providing findings for more than 1,000 scientific articles and two books.

Ulysses' orbital path is carrying the spacecraft away from Earth, progressively limiting the amount of data transmitted. That prompted Ulysses project managers, with the concurrence of the ESA and NASA, to decide it was an appropriate time to end the "epic scientific adventure," NASA said.

More information about Ulysses is available at http://ulysses.jpl.nasa.gov.

STATE COLLEGE, Pa., July 1 (UPI) -- U.S. scientists studying how some human DNA mutations are involved in inherited diseases say their findings may affect the way genetic counseling is offered.

Pennsylvania State University researchers said their study has shed light on the processes that lead to human DNA mutations implicated in such diseases as tuberous sclerosis and neurofibromatosis type 1.

The scientists, led by Associate Professors Kateryna Makova and Francesca Chiaromonte, examined mutations in which small fragments of DNA are either added or subtracted from the genome. They said they found patterns in the DNA sequences immediately surrounding those mutations.

Chiaromonte said the study is the first to detect patterns in the DNA sequences adjacent to insertions and deletions of DNA fragments at the genome-wide scale.

"We were surprised to find that the patterns … are unique because scientists previously have lumped the two types of mutations together," graduate student Erika Kvikstad said. "What's striking is that most insertions and deletions are thought to occur by replication errors and, while this is a primary source generating the mutations, we discovered that recombination also is very important."

The scientists said that if it's know that certain diseases are more likely to be caused by recombination than by replication errors, physicians can provide better advice to couples who want to have children.

The research is detailed in the July issue of the journal Genome Research.