Most orbital rockets, from the Saturn V carrying astronauts to the Lunar surface in the 1960s to a modern Falcon 9 or Ariane 5, are primarily covered in white. This is purposefully done, as this article explains.
Rockets are kept predominantly white in order to keep the cryogenic propellants inside the launch vehicle’s fuel tanks from heating up as a result of exposure to the sun’s radiation while on the launchpad and after liftoff during the vehicle’s ascent through the Earth’s lower atmosphere.
Most orbital launch vehicles use propellants that are extremely cold. Apart from the RP-1 fuel used in the first stages of most rockets, almost all other liquid propellants are cryogenic substances that need to be stored at subzero temperatures to remain in liquid form.
For example, liquid hydrogen used in many upper stages of orbital rockets needs to be cooled to temperatures below -253° Celsius (-423° Fahrenheit). Liquid oxygen, the oxidizer used with most liquid fuel types, needs to be cooled to -183° Celsius (-297° Fahrenheit).
Once these propellants are pumped into a launch vehicle, there is no form of active cooling, so they start to warm up. The fact that most launch facilities are situated in regions close to the Equator, with their associated warm tropical climates, accelerates the heating process.
As a result, launch service providers go to great lengths and use several techniques to make sure the propellants stay as cold as possible before liftoff at a launch site and within a rocket before and during launch (which you can learn more about in this in-depth article.)
This brings us to the choice of color used on orbital rockets, as the following section will illustrate.
Why Rockets Are Primarily White
Of all the colors in the visible spectrum, white is the most effective at reflecting heat produced by solar radiation (sunlight) away instead of absorbing it. Anyone spending time outside on a sunny day in a white as opposed to a dark shirt will notice this phenomenon.
Needless to say, rocket engineers were well aware of this phenomenon and realized that covering a launch vehicle in white is a relatively inexpensive way of slowing down the heating up of cryogenic propellants in the vehicle’s internal tanks.
The advantages of using a white coating on the exterior of an orbital rocket became very clear when the drawbacks of using darker colors on a launch vehicle were highlighted very early on in the United States Space Program during the development of the Saturn V rocket.
The Saturn 1, one of the first rockets used during the Apollo Program (whose goal was to put an astronaut on the Moon during the 1960s), had black & white stripes on its first stage, a checkered black & white pattern on the interstage, and an all-white upper stage.
(The use of black & white checkered patterns on rockets has a specific purpose, which dates back to World War II and will be explained in the next section.)
The problem with the extensive use of black colors on the rocket quickly became apparent. The color’s ability to absorb & conduct heat resulted in the fuel tanks located underneath to experience heat spikes, resulting in the fuel becoming dangerously warm.
As a result, the amount of black paint was dramatically reduced for subsequent Saturn V rockets, with the most prominent black markings visible on the vehicle’s interstage sections, which did not contain any propellants. The cryogenic upper stage was left entirely white.
Today, most modern launch vehicles like the Falcon 9, Ariane 5, and Antares rockets are all predominantly white, implementing the lessons learned during those early years of space exploration and saving unnecessary cryogenic propellant boil-off in the process.
(This is not the only technique deployed by rocket engineers to keep cryogenic propellants cold. A whole arsenal of methods is deployed to keep them from warming up, both at the launch site and in an orbital rocket, which one can learn more about in the following article.)
Why Rockets Displaying A White Color Is Not Always Painted
Stating that a rocket is painted white is not technically always correct, but rather that certain sections have a white coating. This is simply because the white appearance of a launch vehicle is not always the result of being painted.
Although paint is used in many cases, the white coating is often white-colored materials like white beta cloth blankets, which are widely used for thermal insulation on launch vehicles. The Space Shuttle and International Space Station (ISS) extensively used these materials.
Apart from the black silica tiles that protected the underside of the Space Shuttle from the extreme heat it experienced during re-entry into the atmosphere, it also made use of white LRSI (low-temperature reusable surface insulation) tiles to protect other parts of the vehicle.
(This means a large portion of the Space Shuttle’s visible white sections was not painted, but rather a combination of beta cloth blankets and LRSI tiles.)
Another common occurrence is that sections of a vehicle’s surface that are not white appear white as a result of ice forming on the surface of the rocket as the cryogenic temperatures of the propellants react with moist air outside.
If one considers that most orbital rockets use liquid oxygen as the oxidizer for the majority of liquid fuels and liquid hydrogen for their upper stages (and both are cryogenic liquids), it is clear that some portions of a rocket’s white appearance are the result of ice formation.
Paint is still regularly used, but it can come at the cost of additional weight. For example, the external fuel tank of the Space Shuttle was initially painted white to protect the propellants from the sun’s radiation, but only for the first two missions.
It was discovered that the paint wasn’t necessary, and the now familiar orange-brown foam insulation was sufficient to keep the propellants cold. This resulted in a weight saving of roughly 272 kg (600 pounds), which provided additional payload capacity.
Why Some Rockets Have Black & White Checkered Patterns
Probably the most well-known and iconic rocket in the history of spaceflight is the Saturn V rocket, which was not only memorable due to its sheer size and historical significance but also as a result of its familiar black & white checkered patterns.
The practice of putting black squares/rectangles on a predominantly white background dates back to World War II when Werner von Brauhn (former Nazi scientist and head of the American Space Program following the war) and his colleagues used it on the V2 rocket.
During World War II, the V2 rocket (which was the first human-made object to reach space) was developed by German engineers to attack Allied Forces over vast distances and was effectively used in attacks against London.
The rocket had a distinctive black-and-white pattern painted on its surface. (Similar to the patterns used on subsequent launch vehicles like the Saturn V and other modern rockets.)
There was a practical purpose for this. The contrasting black & white patterns allowed engineers on the ground to better track and record the vehicle’s motion, specifically the amount of roll on its vertical axis as it ascended into the atmosphere.
(There is a good reason why rockets roll on their vertical axis after launch, and controlling and monitoring this movement is crucial. Learn more about why rockets roll after launch and why it is so essential in this in-depth article.)
This provided valuable and accurate information about the rocket’s behavior in flight. This technique, known as photogrammetry, was also implemented by the team of former German engineers who worked on the Saturn V rockets during the Apollo Program.
Even today, different-sized black & white checkered patterns are used on modern rockets like NASA’s Space Launch System (SLS) to accurately track and record anything from measuring ground clearance to the vehicle’s movement in three-dimensional space and the amount of roll.
The markings are not just for live monitoring by engineers on the ground but also by multiple cameras located around the launch site as well as on the vehicle itself (to see how a rocket behaves in real-life circumstances compared to computer models and simulations.)
Conclusion
As this article clearly illustrated, using white as the predominant color on the surface of a launch vehicle effectively helps to reduce the amount of warming up that cryogenic propellants experience inside the rocket and the amount of boiling off and venting required.
The white color visible on many rockets is not necessarily the result of painting, and the familiar black & white checkered patterns also serve a specific and important purpose, as also illustrated.
This article was originally published on headedforspace.com. If it is now published on any other site, it was done without permission from the copyright owner.
