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.

27 thoughts on “Why is SpaceX Working Around the Clock on the Starship Prototype?”

  1. There won’t be any shiny skin. That is only tinfoil to prevent workers from roasting inside. It would be too frail to withstand an actual reentry.

  2. I can’t help think that he has some sort of a means of heat shrinking the stainless sheet metal to make it look better. Here is a video of such a process done in a low tech shop:


    After all, why would he tease such a beautiful picture, if it only makes what he is building, and eventually flying, look like total junk. I think we are in for some more surprises.

  3. The hopper will not go into orbit. It has no control surfaces needed for a guided reentry. Space X has stated the front wings and two of the tail fins will move to control reentry. However all the landing legs on the upper are welded in fixed positions. Also the front wings are not present and there doesn’t appear to be any holes for the control mechanism. From what I am seeing now and what Space X has stated about the BFS the hopper will not go into orbit.

  4. “A Starship without any payload could reach orbit by itself in one stage.”

    I was unaware of that fact. Even with no payload, a single stage to orbit space craft is incredibly impressive, especially with an ability to reenter and land.

    “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).”

    “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).”

    The fact of the matter is, SLS has already been technologically leapfrogged by Falcon Heavy. There is nothing you can do with SLS that can not be done with two, or at most three, Falcon Heavy launches, for about a third of the price. When Congress mandated the SLS, it made sense, because President Obama was merely wanting to make believe we had a Mars program, with no launcher to carry it out. Nobody, at that time, could have foreseen the incredible progress SpaceX was going to make. If BFS (I refuse to use Elon’s stupid new names) achieves single stage orbital flight, especially a manned flight, before SLS even flies, hopefully that will create the political climate necessary to finally cancel the project. Let Orion launch on Falcon Heavy, although it will then also be obsolete.

  5. I think the hopper will at some point do nose first dives into the atmosphere, to test the shiny skin, hot structure strategy in the real world. This is why the upper part of the hopper is mirrored. The lower part will likely get sooty anyway during retrorocket burns. Climb to 20 km, come back down very fast, let the atmospehere slow the hopper down, log lots of data while doing so. Repeat……..
    One thing about the dual purpose nozzle, I think the larger nozzle will protect the motor, and “undercarriage” during the tail first part of reentry.

  6. Mat… I’m going with the idea that he’s showing people what it is as an example. He knows its going to work. We know it’s going to work. If he just wanted to build a regular hopper there’s no point in building an elaborate nosecone at all. To test the rocket engines alone its not needed. The computer would guide that to landing if it had a corkscrew for a nose cone. That nosecone is most likely for the real deal. Afterwards he’s going to double the body length of that slap a sticker on it launch it at 4:20 am or pm when done. One other thing. That dude your going to send around the moon. At that price surprise him. Send around venus and back. That would be awesome.

  7. There is something remarkably Heinlein/Bradbury (or Wright Brothers) about building a jumbo-get equivalent Mars rocket prototype, in the desert, in a few months, in a tent. Doubly so when SLS has taken over a decade and will only launch a small capsule.

  8. There is a picture of what Elon intends the test vehicle to look like here: engadget_com/2019/01/05/elon-musk-teases-spacex-starship-test-vehicle/
    And it is way cleaner and more elegant than what Elon is currently building. I am not sure if he has a trick up his sleeve to smooth out the mirror finish at a latter point but right now it sure looks cheapo and junky especially compared to the what is intended.

  9. My guess is that he wants to start his “hopper” tests while the (presumably successful) orbbital test of the Crew Dragon is still in the news, and in the mind of the public. That way, when Boeing does its “Starliner” tests later in the year, the public will be thinking “What’s the big deal? SpaceX did the same thing six months ago, and where’s Boeing’s super-heavy-lift launch vehicle/spacecraft?”

  10. please edit for consistent temperature measurements – either C or F. Nice to be able to know that 1000C is within range of the 2000F alloys

  11. Nice write-up. You write:

    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.

    And the best blunt body is our classic space capsule … and Starship appears to be half-way between the Shuttle and a capsule … so less than 90% and far less on the control surfaces edges.

    Why working around the clock? Elon Musk has a push-push-push style of management backed by a lot of money for parts. He works 70 Hours Per Week and has high (maybe unrealistic) expectations of his staff. He probably hates idle staff … so this project is his place to put hours when hours are available. I think Tesla Model 3 production hell (thankfully over) had a flavor of this.

  12. Everyone knows its not going to space Orange, Just like the grasshopper its basically there to test idea’s.

  13. They are going for a more realistic test … that heavy outer plating will change the moments of inertia of the craft that the control system must manage. Maybe also to work with putting the Stainless Steel shell together.

    There will be no “public-private program” it’s SpaceX and Elon Musk money. The Crew Dragon delays shows how public money at least doubles the cost and the time. I think the “doing-it-for-show” theory is negated by the pickup trucks and dirt mounds in front of the ship.

  14. The photos of SpaceX laying thin sheets of mirror material over the base is, I think, telling. This hopper is to going to be doing re-entries from orbit so it doesn’t need to be mirrored aluminum. Mirrors on the Starhopper are right now for appearance. So, why does SpaceX need to have the appearance but not the reality of an orbital-class Starhopper? They are trying to make the appearance of great progress to sway the minds of the “dumb money” people especially the policy makers. Money from a public-private program could easily be more than enough to fund the development of the full Super Heavy Starship. That is why they are working so hard for appearance.

  15. “There would be more mass to re-radiate away the heat.”

    Heat isn’t radiated away by mass, but instead surface area. The key advantage of a hot metal structure is thermal capacity: It can take more BTUs of heat to get the structure to a dangerous temperature than reentry delivers to the craft.

    An insulated surface will reach thermal equilibrium during reentry due to its very limited heat capacity. So it gets VERY hot. But an uninsulated steel structure won’t reach that equilibrium, won’t get as hot, because reentry will be over before it can finish heating up. Due to the much larger mass available to soak up the heat.

  16. Series 300 stainless sheet seems amenable to your suggestion, as long as the remainder of the air-frame avoids stress induced by a differential rate of cooling.

  17. Insulation behind the surface plates could be multiple metal foils. Major structural members near the hot area could be titanium.
    I’d have a special landing service vehicles that upon landing of the starship would quickly approach the starship, and use forced convection of cool air to quickly lower skin temperatures, as well as duct cool air into the ship.

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