Sexual reproduction is likely to be impossible in space due to cosmic radiation bombarding the human body.
Researchers at the agency’s Ames Research Centre in California found that without effective shielding on spacecraft, powerful proton particles would probably sterilize any female embryo conceived in deep space.
They also concluded that male fertility was likely to be negatively affected, with the particles damaging the sperm count.
Given that travel to distant planets is likely to take decades, centuries or longer, this could make any mission to colonise other environments a non-starter.
The scientists noted that space shield technology is currently not sufficiently advanced to offer enough protection from this type of radiation.
Dr Tore Straume, a radiation biophysicist at the centre, said: “The present shielding capabilities would probably preclude having a pregnancy transited to Mars.”
The DNA which manages the development of all the cells in the body is particularly susceptible to the kinds of radiation found in space.
Studies on animals have shown that exposure to ionising radiation can kills egg cells in a female fetus as far on as the second or third trimester.
Dr Straume added: “One would have to be very protective of those cells during gestation, during pregnancy, to make sure that the female didn’t become sterile so they could continue the colony.”
Nasa has a strict code of conduct on sexual relations, stating that “relationships of trust” among astronauts are to be maintained at all times.
The research was published in the Journal of Cosmology.