Place yourself in the cockpit of a shuddering space rocket re-entering the Earth’s atmosphere after a mission to mars. Temperatures of around 1,600°C are tearing at your vehicle, threatening to sear it into oblivion. What’s protecting you and your state-of-the-art space ship from disintegrating under such extreme temperatures? Believe it or not, it’s just a tile baked from sand! This tile is the only thing sitting between you and a guaranteed explosive demise. In this article we take a closer look at this wonder, and explore how the simple tile has become the Space Shuttle’s most celebrated component.
Photo: External Tiles on the Space Shuttle Endeavour (photo credit: Magnus Manske)
Why Space Rockets Require Thermal Protection Systems
The world’s leading engineers and scientists all agree that the optimal skin or shell material for rockets is an aluminium-graphite mixture. However, aluminium destabilises as temperatures rise, and structural failure takes place at 175°C. As temperatures reached on a rocket’s surface during re-entry are around 1,600°C, this critical point for aluminium is obliterated. Hence the requirement for an advanced thermal protection system for rocket skin is pretty obvious.
Possible Materials to Protect Rockets
Some metal alloys do exist which can handle the enormous re-entry temperatures. However the amount of alloy required would add considerable weight to any rocket and severely impact its performance. Ablative materials - which protect the shell of the rocket by burning off during re-entry - have also been experimented with. However the difficulty with these materials is that they are also very heavy, can impact on rocket aerodynamics as they burn off, and require re-application after each and every re-entry.
The Humble Tile - A High Tech Material to Protect the Space Shuttle
The principal material used in the thermal protection system of the Space Shuttle is a simple-looking tile made primarily of silica fibres, produced from high grade quartz sand baked at extremely high temperatures. A high percentage of the tile volume is empty space, making it light enough for spaceflight, while simultaneously enhancing its insulatory properties. These silica tiles are such exceptional insulators that the enormous heat generated on their outer surface during re-entry is not conducted through to the innermost layers, thus keeping the temperature of the aluminium rocket shell they protect below the critical point of 175°C. Indeed, they’re such woeful conductors of heat (and therefore wonderful insulators) that you could hold these tiles by their edges without suffering a burn, while their centre is red-hot. And I mean literally red-hot – just take a look at the following video if you need proof!
The Iconic Black and White Shades of the Space Shuttle
Even though tiles are exceptional insulators, those parts of the Shuttle that are exposed to the very highest re-entry temperatures still need further insulatory assistance. Thus the tiles at these critical areas of the Shuttle, such as on its underbelly, receive a protective coating of black glass which further assists in dispersing the huge heat generated. Meanwhile, those parts of the Shuttle, such as the upper fuselage, that are exposed to relatively lower temperatures (less than 650°C) are coated with a white mixture of silica compounds and shiny aluminium oxide. The white colour is not accidental, it was designed to reflect away heat generated by direct exposure to sunlight during orbit.
Thus the iconic black and white design of the Space Shuttle was not simply for aesthetics, but played an essential role in the thermal protection system provided by the tiles.
Photo: The Iconic Shades of the Space Shuttle
You Can Have Your Very Own Shuttle Tile
With the decommissioning of the Space Shuttle programme in 2011, NASA took the decision to offer a limited number of its thermal protection tiles to educational institutions and museums in the USA, offering the tiles as a loan while always maintaining ownership of them. In fact, distribution of the tiles is heavily controlled for a number of reasons. Firstly, the silica tiles generate a fine glassy dust on the surface which can damage eyes and lungs. Secondly, the tiles are considered under US law to be a class of technology requiring protection from foreign exploitation – and thus foreign distribution of any tile is prohibited.
But despite these legalities, you will be able to pick up a Space Shuttle tile relatively easily. This is because in the 1980's when one of the Columbia flights returned to earth, a number of its tiles were removed, broken down and encased in acrylic bars. Each bar was assigned a certificate of authenticity, and donated to every employee on the Space Shuttle programme.
In addition, spare tiles that had been manufactured for Columbia’s maiden flight were discarded without adequate care, and were subsequently recovered by interested parties. Since these events took place before limitations governing their procurement and sale were enacted, these tiles can still be traded lawfully today. So despite NASA’s later efforts to protect its own technology, the horse had already bolted during the 1980's when NASA had, to all intents and purposes, given the technology away. At the time of writing, there is one such tile available on ebay for a whopping $1,500. So if you really want one of these tiles badly enough, you can get one!
Once again, the humble tile flabbergasts those who’d thought it was merely a simple construction or design material. So, the next time your eye is caught by a dazzling light shooting across the sky, take a few minutes to allow yourself to marvel at the apparently limitless applications of the deceptively simple tile.
By The Tile Monk.
About The Author
The Tile Monk lives a simple life devoted completely to tile worship. He meditates on tiles, about tiles. He no longer lays tiles; that’s for his younger apprentices. You cannot follow him on Twitter or Facebook, as his time on this earth is dedicated solely to the contemplation of tiles, and occasional blogposts.