HOUSTON -

The search is on for the vandals who wrote graffiti on the space shuttle replica outside Space Center Houston.

Scrawling graffiti on the space shuttle in this town is something akin to going to Paris and defacing the Eiffel Tower. But someone did just that overnight; crawled up on the shuttle replica with a can of spray paint. It may have been meant as a joke but no one found it funny.

Wilkins Roman from Arkansas spotted it immediately when he and his family arrived at the Space center Wednesday morning. Someone painted a racial slur on the fuselage, and the phrase, "Houston we are the problem."

"I just can't believe that people would do stuff like that. What was the motive to do something like that? It's not right," Roman said.

From Sky 2 aerials, workers could be seen painting over the graffiti on the shuttle. That Space Center Houston crew had it cleaned up by noon. It may have been meant as a joke, but visitors told us they aren't amused.

Mike Bishop said, "It's an icon!"

"I don't know why anyone would use that as their way of expressing their discontent about anything," said Paul Joplin.

Whoever did it managed to get past Space Center Houston security overnight. Administrators say that may be because surveillance cameras were turned since the shuttle mockup is scheduled to be moved soon.  That's also means there's no video of the vandals.

Houston has deep ties to the nation's space program and is home to Johnson Space Center and Mission Control. The shuttle mockup came from Kennedy Space Center, arriving here in June 2012.

It will be coupled soon with the 747 that carried it for a permanent display.

Space Center Houston added that they are working with authorities to determine who is responsible for the vandalism.