Oscar Holverson was traveling on the ship with his wife, Mary Alice.
The letter is one of the last known correspondences to have survived the sinking of the doomed ocean liner, Reuters reported.
The Titanic tragedy occurred on April 14, 1912, on its voyage to NY from Southampton.
The Holverson family made a decision to sell the letter at an auction in the Southern English town of Devizes and was hosted by Henry Aldridge & Son.
Halverson, as is evident from the letter obviously was in awe of everything around, describing the mother, "this giant ship, equipped like a luxury hotel".
Astor was the American financier and real-estate investor.
"He looks like any other human being even tho (sic) he has millions of money", he wrote. "They sit on the deck with the rest of us", - writes Halverson.
His wife survived the disaster, Aldridge said.
Aldridge, twenty years engaged in the sale of relics from the Titanic, noted that the content of the writing brings this lot to a new level due to standing on it a special date, personal observations of its author and the fact that it has been in the waters of the Atlantic.
A hand-written letter found on the body of a man killed in the sinking of the Titanic is expected to fetch up to £80,000 ($105,000) at auction on Saturday.
More than 1,500 people died.
It still has traces of seawater and logo of the shipping company White Star.
In his letter, Mr Holverson also described his experiences rubbing shoulders with one of the ship's most famous passengers.
She never remarried - and according to Encyclopaedia Titanica, she was buried with her husband in NY after dying of kidney failure in 1918 at the age of 41.
In April 2014, a letter written just hours before the ship's encounter with the iceberg, was sold at auction for £119,000.
Henry Aldridge & Son auctioneer Andrew Aldridge told Fox News in an email Tuesday that he believes it is the most important letter written aboard the Titanic ever to come to market.
A set of rusty locker keys that belonged to a Titanic cabin steward also sold at the auction for €85,000.