Odds of Hanging On
"You're fired," is a phrase you're not likely to hear as an astrophysicist, unless you quit your day job for a chance to be on The Apprentice.
Seriously, if you make it through college, grad school, and a Ph.D. program without freaking out and running off to make a new life for yourself, there's no reason you won't be a shoo-in for tenure before long.
Even if you don't make it that far and simply grab an industry job, you still won't have to worry about unemployment. Your skillset will apply to a wide range of industries, from other forms of physics and engineering to climatology, meteorology, and teaching. At a bare minimum, you'd be a great candidate for custodian at the planetarium.
In short, you don't have to be an award-hoarding, innovation-churning Commander of the Stars to hang on in this field. If you're hired in the first place, you clearly know what you're doing, and your employer probably needs you more than you need them.
Opportunities do end, but job growth is steady, so you can count on something coming along for you if you're looking. Hey, if you wanted to be unemployed, you wouldn't have gotten so insanely well-educated. Right?