[smsm42]

Of course it's not "safe"! We put a ton of explosives into a huge can, put a small can with humans on top of it, set it on fire and try to control what happens and get the humans into space, and then we try to drop the same can from the space, while it's traveling at miles per second, and land it on the ground. It's not "safe" and won't likely be "safe" in our lifetimes, there's always big risk, that's why astronauts get so much respect - they take a lot of risks. These risks become smaller with time, but still they are quite serious. And of course anything that reduces risks - while not disabling the whole program - is good, but I don't think "safe" is the word that is justified when talking about those things.

[ballooney]

What he means and you're interpreting a bit too literally is that this [heatshield] is one subsystem where the risks are not well understood or quantified as, say, the propulsion system, for which we have a lot more experience and flight heritage.

[smsm42]

Yes, of course there are risky systems in there, and calling attention to one of them is fine. What I object to is framing it as a "safe/not safe" issue - as if without the tests the author proposed it were "not safe" and with them, by implication, it would become "safe". That's not like replacing old tires on your car with new tires - there are a lot of things that can go wrong, and many of them are "unsafe", and it's always a complex equation which can not be (at least at current level of technology) solved with doing more tests or anything else to make it "safe". The "safe" framing is the one I object to.