Why is SpaceX Working Around the Clock on the Starship Prototype?

SpaceX is working through weekends to complete the Starship prototype. They are targeting a first flight as early as the end of January.

Scott Manley has a video about the SpaceX stainless steel starship prototype. Scott is confused as to why SpaceX is pushing so hard to complete the starship and why it is built out of stainless steel.

Elon Musk still operates SpaceX and Tesla as startup companies. SpaceX is not at the point where they can not hit aggressive operational and development targets.

SpaceX can divert staff from the crewed launch while there are delays because of the government shutdown.

SpaceX can make great progress on the Starship and try to hit lower development costs. Keeping development costs at $1 to 2 billion allows for SpaceX to self-fund the development.

Making great progress will encourage more investors and funding for the SpaceX Super Heavy Starship. The project is still not fully funded and complete development might cost up to $10 billion.

The top portion of the new rocket is the Starship portion. A Starship without any payload could reach orbit by itself in one stage. This could be the 2020 orbital test mentioned by Elon Musk. Reaching orbit with a seven raptor engine Starship in 2020, would be ahead of the first test flight of the Space Launch System (SLS).

Beating SLS to orbit would seem to ensure additional private or government funding to complete the full development of the SpaceX Super Heavy Starship.

Why Stainless Steel?

SpaceX has shifted to stainless steel to enable hot metal structures for re-entry. What was considered in the when the Space Shuttle was being designed was to make the airframe of the rocket with high-temperature alloys. There would be far less insulation to protect the crew. The main structure would reach about 1,000 degrees Celsius. There would be more mass to re-radiate away the heat. Hot metal structures were tested with early x-planes.

During re-entry a blunt body about 90% of friction heat is carried away by the bow shock wave and only 10% of the energy would reach the spacecraft.

All the reusable heat shields have had insulation behind the heat shield. The airframe of the rockets has usually been light-weight aluminum. The thinking was to protect the aluminum from heat but carry the weight of the insulation. The hot-metal approach uses less insulation to compensate for the steel being heavier than aluminum.

SpaceX is using 300 series stainless steel. Stainless steels have good strength and good resistance to corrosion and oxidation at elevated temperatures. Stainless steels are used at temperatures up to 1700° F for 304 and 316 and up to 2000 F for the high-temperature stainless grade 309(S) and up to 2100° F for 310(S).

X-15 was the Fastest Manned Plane Ever Built and It Used Hot Metal Structures

Some of the advantages, disadvantages and history were discussed at the Reddit SpaceX forum and at the Nasa flight forum. Gary Hudson (Designer of Phoenix SSTO) mentioned recently on the NASA forum.

Paul Werbos has been a proponent of the Boeing hot structures system designs. Ray Chase of ANSER did a lot of materials testing for hot structures.

It has been discussed on the Power Satellite Forums and on the Lifeboat Foundation mailing lists.

The Super Heavy Starship will be able to deploy over five times the number of Starlinks satellites per launch and the cost per launch will be three to ten times less. The lower launch cost will be because of the full reusability and larger payload.