Inna lillahi wa inna ilayhi raji'un. Surely we belong to God and surely we will return to Him. My prayers go out to the families of the Columbia astronauts. May God ease their pain and help them come to terms and be at peace with their loss.
Right now, officials and scientists are saying that it doesn't look like terrorism, just another tragedy like the explosion of the space shuttle Challenger. Time online has an article that discusses various possible causes of the explosion: Aerodynamics May Explain Space Shuttle Breakup. At this time, I don't think anyone knows enough to say more.
There's a lot of speculation swirling because of the Israeli astronaut Ilan Ramon, of course. I personally don't think that's a significant factor whether or not this was terrorism; what matters is the shock and horror that people feel when they hear about what happened and watch the coverage on TV. That would be why they would do it, I think, not because of the number or nationality of the astronauts who died.
What it does do, and this makes me cry, is complicate the responses of people to what happened. Istighfirullah1 at anybody who thinks this is a good revenge on Israel because Ramon died. Istighfirullah at anybody who says they're not sorry Ramon died because he's an Israeli military officer. Istighfirullah, istighfirullah, istighfiruallah! Will you not fear Allah? What has happened to your humanity?
O you, those who have faith, stand up for Allah and be witnesses in equality and do not let hatred for a folk swerve you so that you do not do justice. Do justice, that is the most pious (thing) and fear Allah. Surely He is aware of what you do - Surah al-Ma'ida ayah 8
1 Istighfirullah: An Arabic word meaning roughly "may God forgive you for what you have done wrong"