Traveling to space is a lot of fun, but can also be a headache. Literally.

A new study of 17 astronauts found that the majority of them experienced painful headaches when they traveled beyond Earth. The findings prompted doctors to call for designating space headaches as a new "secondary disorder."

Space headaches have been reported before, but until now they were thought to be related to the common motion sickness astronauts experience in space. The new study found that the two maladies are not actually connected.

"Our research shows that space flights may trigger headaches without other space motion sickness symptoms in otherwise super healthy subjects," said lead researcher Alla Vein of the Leiden University Medical Center in The Netherlands.

Doctors aren't sure exactly why so many astronauts experience these pains, but they think it has to do with the effects of microgravity on the human body, which include disrupting a person's sense of balance and equilibrium.

The study followed one female and 16 male astronauts, ranging from 28 to 58 years of age, during flights to the International Space Station. During their space missions, 12 of the 17 astronauts (71 per cent) reported headaches. Nine astronauts experienced headaches during launch, nine while onboard the space station, one while spacewalking outside the station, and two during landing. None of the astronauts had a history of recurrent headaches on Earth.

Headache severity ranged from mild to severe, with some astronauts describing the feeling as "exploding" and "heavy feeling." They sometimes lasted for hours.

"Although headaches in space are not generally considered to be a major issue, our study demonstrated that disabling headaches frequently occur during space missions in astronauts who do not normally suffer from headaches on Earth," Vein said. "Previous research has shown that astronauts can be reluctant to reveal all the physical complaints they experience in space, so the actual incidence could be even higher than our study suggests."

The study is detailed in the June issue of the journal Cephalalgia.