It's been six long years since world-famous physicist Stephen Hawking got a taste of weightlessness during a zero-G airplane flight from NASA's Kennedy Space Center — but he still wants to feel the real deal aboard Virgin Galactic's SpaceShipTwo rocket plane.

The 71-year-old Hawking has been living with neurogenerative disease for decades, but his illness hasn't kept him from taking on adventures that might tax younger, fitter humans. On Tuesday, during a London talk sponsored by the charity Breathe On UK, Hawking noted that he has required assistance with his breathing since his tracheotomy in 1985.

"Being on a ventilator has not curbed my lifestyle," he told the audience, using his instantly recognizable computer-generated voice. "I have been to Brussels, the Isle of Man, Geneva, Canada, California ... and I hope to go into space with Richard Branson's Virgin Galactic. It is possible to have quality of life on a ventilator."

That's music to the ears of Breathe On UK, which was created to help kids who need long-term breathing assistance. It's also a compliment to Virgin Galactic, which put SpaceShipTwo through its supersonic paces for the first time this week. If all the tests go right, SpaceShipTwo could be taking passengers on suborbital space trips as early as next year.

Richard Branson, Virgin Galactic's billionaire founder, promised to consider Hawking for one of those trips even before the good doctor took his ride into weightlessness in 2007. The invitation still stands, according to George Whitesides, the company's president and CEO.

"Richard and the team would love to welcome him on board," Whitesides told NBC News on Tuesday.

Hawking's health is the big issue for any future spaceflight, just as it was for the zero-G flight years ago. The physicist would have to be fully checked out, and even if he was cleared for takeoff, medical staff would almost certainly have to ride along. Deceleration could be the toughest part of the trip. SpaceShipTwo's flight profile calls for up to 6 G's of force on the way down. That's more force than most space shuttle astronauts have felt, and it ranks right up there with the world's rockiest roller-coaster rides.

If Hawking were to fly into space sometime in the next few years, he'd take the No. 2 spot on the list of the world's oldest astronauts. The only person older would be senator-astronaut John Glenn, who flew on the space shuttle Discovery at the age of 77 and is now 91 years old.

Six years ago, Hawking declared, "Space, here I come!" Should he keep that dream alive, or should he focus on earthly adventures instead? Feel free to register your opinion in our informal survey, and weigh in with your comments below.

More about Stephen Hawking:

• Hawking lays out his case for a godless big bang
• Stephen Hawking visits LA stem cell lab
• Cosmic Log archive on Stephen Hawking

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

The fight over the final disposition of King Richard III's 528-year-old remains has escalated to the point that people are sending hate mail to York's cathedral, the police are being called in to investigate, and a member of Parliament is pleading with the rivals to avoid sparking another "War of the Roses."

On strictly legal grounds, the matter was resolved even before the remains were unearthed in a parking lot near Leicester Cathedral last year. Britain's Justice Ministry granted researchers from the University of Leicester a license to conduct the excavation there and to determine the disposition of any human remains found there.

Last month, the researchers announced that a skeleton found at the site belonged to Richard III, based on DNA tests. The discovery resolved a longstanding mystery over what happened to Richard's remains after his death in the Battle of Bosworth in 1485. That battle marked a turning point in the Wars of the Roses, a decades-long contest between the houses of Lancaster and York for the English throne. 

Richard III has gotten a bad rap through the centuries — in part because William Shakespeare's play about the monarch cast him as a hunchbacked villain. But historians say he wasn't that terrible of a guy, and since last month's announcement, Richard III's fans have been arguing over whether he should be reburied in Leicester, where he was found; in York, where he had family ties; or in London's Westminster Abbey, the resting place for many of England's kings.

The University of Leicester is already working to arrange a burial at Leicester Cathedral next year, but some of the opponents of that plan — including nine descendants of Richard III's siblings — have taken up York's case. The arguments are apparently getting uglier: Hugh Bayley, a member of Parliament representing York Central, said that York Minster's dean, Vivienne Faull, has received some letters "so extreme that she has referred the correspondence to the police."

Faull was dean of Leicester Cathedral before coming to York, and she has shied away from contesting Leicester's claim to the remains. "It has been suggested that opponents have accused her of bias because of her previous links to Leicester Cathedral," The Telegraph reported.

The Yorkshire Post quoted a spokesman for the Dean and Chapter of York as confirming that "a small number" of the letters relating to the fuss over Richard III's remains have been abusive. "These have been passed to the Minster Police, and they continue to monitor the situation closely," the spokesman was quoted as saying.

The British government's current view is that Richard III's final disposition is up to the University of Leicester, but during Tuesday's speech in the House of Commons, Bayley urged the government to establish an independent commission to decide the matter. In the meantime, he called for what Shakespeare might have termed "some little pause" in the battle. 

“I would say to everybody — calm down," Bayley said. "Let us all respect the memory of a former king of our country, and let us discuss, in a dignified and sober way, where his remains should finally be put to rest. We do not want to reignite the Wars of the Roses.”

More about Richard III:

• Study suggests Richard III spoke with a lilt
• King Richard III's face revealed after 500 years
• Richard III's 'discovery' was reported in 1935, too

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

Reuters file

The sun sets behind England's Stonehenge monument.

LONDON — British researchers have proposed a new theory for the origins of Stonehenge: It may have started as a giant burial ground for elite families around 3,000 B.C.

New studies of cremated human remains excavated from the site suggest that about 500 years before the Stonehenge we know today was built, a larger stone circle was erected at the same site as a community graveyard, researchers said.

"These were men, women, children, so presumably family groups," said University College London professor Mike Parker Pearson, who led the team. "We'd thought that maybe it was a place where a dynasty of kings was buried, but this seemed to be much more of a community, a different kind of power structure."

Tale of two Stonehenges
Parker Pearson said archaeologists studied the cremated bones of 63 individuals, and believed that they were buried around 3,000 B.C. The location of many of the cremated bodies was originally marked by bluestones, he said. That earlier circular enclosure, which measured around 300 feet (91 meters) across, could have been the burial ground for about 200 more people, Parker Pearson said.

The team, which included academics from more than a dozen British universities, also put forth some theories about the purpose of the second Stonehenge — the monument still standing in the countryside in southern England today.

Various theories have been proposed about Stonehenge, including that it was a place for Druid worship, an observatory for astronomical studies, or a place of healing, built by early inhabitants of Britain who roamed around with their herds.

Parker Pearson said the latest study suggested that Stonehenge should be seen less a temple of worship than a kind of building project that served to unite people from across Britain.

Solstices drew thousands
Analysis of the remains of a Neolithic settlement near the monument indicated that thousands of people traveled from as far as Scotland to the site, bringing their livestock and families for huge feasts and celebrations during the winter and summer solstices.

The team studied the teeth of pigs and cattle found at the "builders' camp," and deduced that the animals were mostly slaughtered around nine months or 15 months after their spring births. That meant they were likely eaten in feasts during the midwinter and midsummer, Parker Pearson said.

"We don't think (the builders) were living there all the time. We could tell that by when they were killing the pigs — they were there for the solstices," he said.

The researchers believe that the builders converged seasonally to build Stonehenge, but not for very long — likely over a period of a decade or so.

The mass monument building is thought to end around the time when the "Beaker people," so called because of their distinctive pottery, arrived from continental Europe, Parker Pearson said.

More about Stonehenge:

• Building Stonehenge: A new timeline
• Stonehenge scan puts focus on solstices
• Stonehenge's eerie sounds revived

Copyright 2013 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

Experts say DNA analysis supports their claim that the bones dug up last year under a parking lot in the English city of Leicester are the last mortal remains of England's King Richard III.

"It's the academic conclusion of the University of Leicester that beyond reasonable doubt the individual exhumed at Greyfriars in September 2012 is indeed Richard III, the last Plantagenet king of England," Richard Buckley, the project's lead archaeologist, said during a Monday news briefing in Leicester.

The project used 21st-century forensic science to solve a 500-year-old mystery surrounding one of William Shakespeare's best-known villains. Shakespeare's play, "Richard III," made the king out to be a scheming monster who killed children to get to the English throne. The bard gave Richard III dramatic lines that are still evoked today, ranging from "the winter of our discontent" to "A horse! A horse! My kingdom for a horse!"

In real life, Richard III's battlefield death in 1485 marked the end of England's Wars of the Roses, a decades-long conflict between the houses of York and Lancaster. Tradition held that he was buried in the choir of Leicester's Greyfriars Church, but the precise location of his remains was lost in the mists of time. Some even speculated that Richard's bones were thrown into the River Soar during Henry VIII's reign.

It was only in the past few years that archaeologists have been able to zero in on the location of the Greyfriars site again. Last year, a team led by the University of Leicester excavated a city parking lot and found a wealth of intriguing evidence — including a skeleton with a battle-scarred skull and a spine that was curved due to scoliosis. There was no evidence of a coffin, a shroud or clothing that was buried with the body.

All those clues suggested that the skeleton could have been that of the historical Richard III, but to firm up the connection, scientists put the bones through genetic tests, radiocarbon dating and more detailed osteological analysis.

"The skull was in good condition, although fragile, and was able to give us detailed information about this individual," University of Leicester archaeologist Jo Appleby reported Sunday in a news release. During Monday's news briefing, Appleby said experts identified 10 injuries to the bones, including eight wounds to the skull and "postmortem humiliation injuries." Such wounds are "highly consistent" with the accounts of Richard III's death, she said.

"Historical sources tell us that Richard's body was stripped," hacked and put on public display after the battle, Appleby noted.

The skeleton's relatively delicate structure was consistent with descriptions of Richard III's physical appearance, University of Leicester historian Lin Foxhall said. 

University of Leicester

A photo shows the Greyfriars skeleton lying in the site where it was found.

University of Leicester

The Greyfriars skeleton is laid out for forensic analysis. Experts believe the foot bones were separated from the rest of the body after burial.

University of Leicester

The Greyfriars skull was found by researchers during a search for the remains of King Richard III.

Buckley told journalists that the position of the hands suggested that they might have been bound together. Initially, the team reported that an arrowhead was found among the bones, but Buckley said a closer look determined that the object was a nail that was apparently mixed in with the remains.

Radiocarbon dating showed that "the individual could have died in 1485," Buckley said. Two tests yielded dates possibly ranging from 1455 to 1540.  

The team's genetic analysis reinforced the link to Richard III: DNA was extracted from bone samples and compared with modern-day mitochondrial DNA from two direct descendants of Richard III's family, including an anonymous donor as well as Michael Ibsen, a Canadian-born cabinetmaker who is a 17th-generation descendant of Richard III's eldest sister, Anne of York.

"The DNA evidence points to these being the remains of Richard III," said Turi King, a geneticist at the University of Leicester. She said additional DNA tests were still in progress.

Genetic matches based on mitochondrial DNA aren't as clear-cut as, say, a paternity test — but a mismatch would have ruled out any family connection. Similar techniques were used to identify the remains of Czar Nicholas II and other members of Russia's royal family, who were killed in 1918 during the Russian Revolution.

A documentary about the Leicester project, "Richard III: The King in the Car Park," is to be aired by Britain's Channel 4 on Monday night. But this isn't the end of the story. For one thing, the results announced on Monday will have to go through review and publication in scientific journals. The announcement also could lead to a reassessment of Richard III's reign, which some historians say wasn't nearly as terrible as Shakespeare made it out to be.

"I think this could be the moment where Richard III's reputation actually turns," British historian Andrew Roberts told NBC News. "This could be the moment where we look at his achievements and the positive aspects of Richard III, and don't just see him as one of the old Dark Ages kings."

And then there's the matter of reburying the remains: Authorities said the skeleton would get a proper interment in Leicester Cathedral, not far from the parking lot where it was found. The cathedral's canon chancellor, David Monteith, said planning for an interment ceremony in 2014 has already begun, and he expressed the hope that after more than 500 years, Richard III "may come to rest in peace, and rise in glory."

More about the search for Richard III:

• PhotoBlog: Reconstruction reveals Richard III's face
• Skeleton was almost destroyed in 19th century
• Dispute erupts over skeleton's future resting place
• Hunt for king's grave turns up garden

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.