Hernandez is already posting updates on the micro-blogging site about his preparations for take-off and developments concerning the delayed launch of the space shuttle in both English and Spanish.
Yesterday, just before the Discovery's planned launch, Hernandez tweeted: "Folks this is my last tweet before I go into space! Will start to suit up in 30 minutes, listen to weather brief and head to the pad!"
But a few hours later, after the launch was delayed because of bad weather, his update was: "Well back [at] crew quarters! Try again tomorrow at 1:10:22 am!"
On Monday, Hernandez even tweeted about the chat he had with Mexico's president, saying: "Had a nice phone conversation with President Felipe Calderon of Mexico. He wished me good luck on our launch schedule for this Tuesday am."
It's hard to imagine Hernandez sending messages from a mobile phone or laptop when he's wearing his full astronaut gear, but once he and his fellow crew members are in orbit, those messages couldn't really be coming from anyone else.
And we can only assume that he and his colleagues have been set up with an Internet connection from which to tweet.
Discovery is scheduled to blast off at 1:10 a.m. Wednesday, according to the NASA website.
-- Deborah Bonello in Mexico City
Photo: From Jose Hernandez's Twitter profile.