What pushes NASA chief Mike Griffin's buttons? Poor grammar, he admitted on Monday at the Lunar and Planetary Science Conference in Houston, Texas.

In a short speech to hundreds of scientists at the meeting, Griffin described his fondness for the mission statement of the starship Enterprise in Star Trek: "To explore strange new worlds, to seek out new life and new civilisations, to boldly go where no man has gone before."

He joked that it would be great to use as NASA's own mission statement, except that the split infinitive in the last phrase offends his inner pedant. "I will catch split infinitives almost as a reflex," he said, adding that he often berates others for grammatical errors.

An audience member later asked him to turn his critical eye on himself and comment on his own performance as NASA chief.

"I can't grade my own paper," he protested at first. "I have a deep ethical aversion to self-assessment."

But he gave it a go anyway, saying that his greatest achievement was putting space experts in top posts at NASA. He said that previously, those posts were often filled by people with no previous experience in space science or engineering.

"I would like people to say that I repopulated NASA headquarters with people who were at the top of the space business," he said. "You may agree or disagree with some of the decisions . . . but none of them took their job at headquarters as a nervous virgin."

As for his greatest disappointment, he said he regretted having failed to persuade US policy makers to give higher priority to ensuring a quick and smooth transition between the space shuttle's retirement and its replacement. He has previously said that at current funding levels, the new Orion spacecraft and Ares rocket will not be ready for service until 2015, five years after the shuttle's last flight.

But a few minutes later, responding to repeated questions about how supporters of space exploration could help win a bigger NASA budget, he argued that the agency's existing level of funding was something to be grateful for.

"There is not another advanced nation in the world where their space community wouldn't kill to have the budget that NASA has," he said, adding that the space agency is getting about the same amount of money today as it was during the Apollo era. (That's roughly true if you adjust for inflation and simply compare the number of dollars spent in the 15 years including Apollo with the most recent 15 years. But US budgets were much smaller back then, so Apollo was a much bigger fraction of overall government spending - peaking at more than 4% compared to 0.6% today.)

"We get as much money today," Griffin said. "If we have less to show for it than we remember from looking back, then to quote Shakespeare, the fault lies not in our stars but in ourselves."

David Shiga, online reporter (Image of Griffin on his first day as chief in 2005: NASA/Renee Bouchard)