The Starhopper, SpaceX’s prototype starship, is set to begin inaugural hop tests as soon as March or April of 2019. Starhopper’s design is unorthodox — and that’s why it’s expected to work so well.
Traditionally, carbon composites have been utilized for building spacecraft. For the Starhopper, engineers elected to replace carbon composites and an ablative heat shield with a stainless steel alloy and liquid cooling system. The Starhopper is still under construction in Boca Chica, Texas — where it has experienced minor repair delays due to weather — but SpaceX employees have been hard at work getting it built in time for its scheduled launch.
The SpaceX Starhopper Is Ready
The Starhopper is being utilized as a precursor to its own second stage — the Starship. The Starship is anticipated to be a reusable launch vehicle with the ability to operate effectively on long-term flights both within and beyond Earth’s orbit. Until that has been completed, however, the Starhopper is being built into three different versions for three different application options:
Spaceship
This version of the Starhopper will be large and will, in theory, possess the capability to move passengers or freight between interplanetary destinations. This version form of the Starhopper may also be used to travel in low earth orbit between destinations on Earth.
Tanker
The tanker will be smaller than the spaceship, and serve the purpose of refueling other vessels in orbit. It would also be a key step toward launching heavy spacecraft into interplanetary space.
Satellite Delivery Vehicle
This iteration of the Starhopper will feature a large cargo bay door. This door will be able to open in space, facilitating the placement of other objects into orbit, such as satellites. It could also be used in the recovery of space debris and spacecraft.
Key Materials Being Used for the Starhopper
The engineers behind the Starhopper are relying on former spacecraft designs from NASA and other organizations for inspiration, but are also trying out new and innovative concepts and materials on the Starhopper project. Stainless steel will be used for multiple applications on the starship, including:
Stainless Steel
Instead of traditional carbon fiber, designers chose stainless steel as the material for the ship’s structure and tank construction. The strength-to-mass ratio offered by stainless steel is widely believed to be an improvement over earlier carbon fiber composite designs. This strength-to-mass ratio is expected to hold up better against the extreme temperature ranges that the spacecraft will be exposed to. These range from cryogenic levels in space to 3000° F for atmospheric exit and reentry.
Cold-Formed Stainless Steel Alloys
These alloys will be used on certain components of the rocket. The alloys will also be provided with a cryogenic treatment before application to the spacecraft. Because this process cold-forms the metal into cryo-treated steel, it is expected to be markedly lighter and more wear-resistant than other steel options, such as hot-rolled steel.
Stainless Steel Heat Shields
Stainless steel alloys will see heavy use in the heat shields of the Starhopper. These heat shields will also be reusable. While these will be the same alloys used in creating the vehicle’s structure, the shield materials will be polished rather than coated. The polish allows for high reflectivity, which is crucial to safe atmospheric entry and requires less heat shielding than traditional materials.
The Value of Cold-Formed Steel in the Aerospace Industry
Steel has long been used by the aerospace industry, but cold-rolled steel is seeing more attention recently than before. This method of rolling adds on an additional step to traditional hot rolling techniques. After hot-rolled steel has cooled, it’s rolled again at room temperature.
This makes achieving precise dimensions easier and contributes to improved surface quality. Cold-rolled steels are also stronger than their hot-rolled counterparts thanks to it being shaped at lower temperatures.
Due to these properties, cold-rolled steel enables aerospace design engineers to achieve the following:
- Close tolerances
- Excellent resistance to tension breaking
- Optimal straightness and concentric uniformity
- A harder and stronger end product than hot-rolled steel
It’s clear why cold-formed steels are seeing high levels of use in the Starhopper project. With this material choice, engineers at SpaceX can improve the structural integrity of the spacecraft simply by incorporating cold-rolled steel into its design. Even though the public can expect multiple iterations of the Starhopper, it’s a safe bet that stainless steel alloys and cold-formed steels will be key components in each future model.
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