The other day a very close friend and I were talking about re-entry for any manned mission entering the atmosphere. Anyone that reads my blog knows what my opinion is in regards to NASA. After having gone back and forth with my friend on the topic of the re-entry process of any object, manned or unmanned… I only have one question.
But, before I present my question, I want to point out that in the beginnings of NASA we are told that smashing into the atmosphere during re-entry can cause temperatures to rise above more than 5,000 degrees Fahrenheit (about 2,800 degrees Celsius). Not only does the exterior of the re-entry module reach above 5,000 degrees, but there are only a few inches of wall space between the exterior and interior of the cabin. Apparently NASA has developed a self consuming ablative heat shield that can withstand some pretty extreme temperatures (meaning that the heat experienced by the exterior of the object would not affect the temperature inside the object as it falls away from the craft).
But, don’t take my word for it… let’s ask NASA.
The initial conversation that I had with my friend was how I didn’t understand the mechanics of the heat shield they created and how it works so well. For example, in the above video the outside part is made of stainless steel. Stainless steel has a melting point of about 2,500 degrees Fahrenheit. Then, the honeycomb interior ablative heat shield in the video that is between the cabin and the stainless steel is nothing more than polymer fiberglass. Sadly enough, the melting point of this material also doesn’t even come close to being able to withstand 5,000 degrees (it has a melting point of about 2,200 degrees).
One other option that we are presented in the following video is pure silica-tiles (which again, sadly doesn’t have a melting point that reached 5,000 degrees). Although these tiles can withstand about 3,000 degrees, they were not used in the first video, but rather much later. Even still, that presents a problem.
The answer that finally clicked for me after having talked with my friend is the ceramic coating that was used. Apparently, NASA used a spray adhesive that was designed to melt away made of ceramic (which is pretty awesome considering the fact that it has a melting point of almost 6,900 degrees). If you spray enough of this stuff on and also consider the fact that re-entry time wasn’t anything more than a few minutes at most, this answer makes a lot of sense. However, the self consuming ablative heat shield in the first video was actually behind the stainless steel (notated throughout the entire first video with no mention of a ceramic outer layer). Again, the ablated material that was designed to dissipate upon re-entry in the first video was not on the outside of the stainless steel. But, that is beside the point. Just for argument’s sake, let’s assume that the ceramic coating was applied in the first video. It very well could have been despite not being mentioned. Although I am still looking, the farthest back that I have been able to find this ceramic ablation in use by NASA only goes back as far as the early 1990’s.
This 1960’s document shows that re-entry exceeded the melting point of silica by more than 1,000 degrees. While this 1960’s document shows that the primary ablator used during that time was 99.8% silica.
After having had this conversation with my friend and totally setting aside the conflicts that arise with re-entry (which was a lot of fun, because it made me evaluate and think, which is something I enjoy to do)… all it did was cause me to ask a new question.
Let’s assume that the stance my friend holds is the correct one.
With that, here is the question…
What happened to re-entry exceeding temperatures of 5,000 degrees Fahrenheit (about 2,800 degrees Celsius and above)?
I guess they realized that such a temperature was a little too outlandish, so they dropped it down a bit. Who knows… it’s probably just me being ignorant. Good ol’ Nye or Tyson can probably solve it for us.
I am not claiming to have answers. I am presenting questions.