However many astronomers believe it is from a different mission due to the size and markings.
Local boatmen towed the section to Tresco where it has now been removed from the beach.
Rocket splits but doesn't disintegrate
Joseph Thomas, from Tresco Boat Services, found the section of rocket while travelling around the north end of the island.
He said: "There were lots of gulls on the water and I thought initially it was a dead whale and the birds were feeding off it."
Mr Thomas found the debris, which was "covered in goose barnacles", at about 14:00 GMT on Thursday about 100m (328ft) from the shore.
"I didn't know what it was. We tried to drag it ashore using a hook, but it bent it.
"First thoughts were that it was part of a plane, but then we scraped the barnacles off and we saw it was part of a rocket.
Definitely not a beached whale
"It's not every day part of a rocket washes ashore at home."
"It was too heavy for us to tow."
Coastguards issued a warning to shipping in the area after the discovery.
Spokesman Martin Leslie said: "The markings show an American flag. It looks like it's an American rocket and seems most likely to be the unmanned SpaceX Falcon 9 which blew up shortly after take-off from Cape Canaveral in June.
"We're grateful for all those who helped in its recovery, it was a great example of the community working together."
That rocket, which broke up shortly after take-off and landed in the sea about 4,100 miles from the Isles of Scilly, was in the process of sending a cargo ship to the International Space Station.
However Jonathan McDowell, an astronomer at the Harvard-Smithsonian Center for Astrophysics, said many experts believed, due to the size and markings which have now been revealed, it was from a different mission.
"All the geeks have been getting together and looking at fine details, and we're pretty sure it's a launch from September 2014 that successfully sent a cargo mission to the space station.
"It didn't look like an exploded rocket to me, it looked like a fairly normal piece of space junk when the lower stage of a rocket falls from a hundred miles up and hits the ocean. Large sections can remain in tact and it's really quite normal," he said.
Islander Pete Hicks, who towed the debris to shore, tweeted: "Towed in and beached a piece of flotsam earlier. Thoughts were could be aviation parts ..didnt imagine space race."
I have written for the travel, entertainment, and culture sectors, both on-line and in the local press.
For over twenty-five years my day-job consisted of slugging away, making other people rich, in the world's most ruthless, yet strangely boring and inept corporate finance environments. Those included international banking, new-IT, and advertising.
As freelance writer, and critic, in my spare time, I helped run a workshop for local writers. Admittedly, I am no-longer writing the on-line movie review blog ‘Celluloid Seduction’, having no time to hang around the entertainment sites as I use to.
After the devastating and unsolved death of my younger brother on 09/09/1994, I continue to exorcise feelings of powerlessness, and loss that plague my psyche, by creating modern literal performance poetry, using traditional rhythmic forms, following in the footsteps of my late grandfather, the Cypriot 'Red Village' poet 'Vasilis'.
Recently, I jumped a milestone and found myself travelling back in time to my old haunts from the 80s. I even landed a job back in Government... but don't worry, nothing exciting to write about yet. I'm just a small cog in a big wheel.
I have many interests including the cinema, music, writing of all kinds, political and religious debate, new and weird science and the occult, plus a lot of other things that just don't fit in this box. Twitter comes in handy for disseminating views.
Although this Blog is a reflection of the strange world I find myself living in, it's also full of memories and opinions.
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