While it's a nice answer, it's wrong. Badly wrong.
The first animal in space, as far as we know, was Laika, a dog. She was also the first fatality in space, because no provision had been made to return her. And *I* for one would consider dogs sentient. So right from the outset, we sent sentient beings into space knowing they would die.
The US initially sent chimpanzees, which I'd also call sentient. They were used to test the Mercury capsule, so they at least were returned alive.
However, the US also recently (June 1996) flew STS-78, which involved 12 white mice on a "Life and Microgravity Spacelab (LMS)" mission. The mice were euthanized and dissected immediately on return.
The US just pulled out of the Bion 11 mission, but we've been involved in the earlier missions. Monkeys were flown with electrodes (pointy ones) through their skulls into their brains. (ick.)
We (humanity) have used "lower life forms", whether sentient or not, as expendible experimental subjects, and continue to do so. To claim otherwise is naive at best.
My apologies for tromping on human nobility ....
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