The last few weeks of SpaceX’s work on Starship and Starhopper prototypes has been marked by less visible progress relative to the past few months. The changes that are visible, however, confirm that its Boca Chica engineers are working around the clock to complete the first orbital Starship prototype.



At the same time, it appears that SpaceX’s South Texas facilities are preparing for a rapid period of expansion and build-up. New work around the ad-hoc Starhopper pad has recently begun, while construction of a second concrete jig for concurrent prototype fabrication and what will likely be a more permanent hangar and control facility are also ramping up. Things have been quiet news-wise for SpaceX’s McGregor and Hawthorne facilities but there is reason to believe that Raptor production and testing is going smoothly.

And over at its pal’s place, the orbital prototype (and the build-up of another jig)



📸@BocaChicaGal



Dedicated Updates: https://t.co/FYHRkwZ2dd pic.twitter.com/glg8Yr6oO6 — Chris B – NSF (@NASASpaceflight) April 20, 2019

Starship Alpha

The most obvious visible progress made in April is centers around SpaceX’s first orbital Starship prototype, soon to begin its third month of active construction. As of mid-March, the shells of two large steel barrel sections – together about 18 m (60 ft) tall – were fully erected at the build site, with a handful of other sections in various states of welding. The height of those two cylinders has remained unchanged since then but it’s safe to assume that a ton of work has been going on inside them, invisible to anyone viewing from public perspectives since drones were effectively banned in March. In other words, the two pieces – most likely the barrel sections of Starship’s liquid methane and liquid oxygen (LOX) tanks – are likely being carefully transformed into actual propellant tanks.

A look inside SpaceX’s 2017 version of a 9m-diameter Starship.

There is also a good reason for their height differential: the larger (LOX) section is almost exactly a third larger than the small section (methane) in part because of the physical reality that Starship will need almost exactly 33% more LOX than methane by volume. Large propellant tanks – particularly those meant for cryogenic fluids and spaceflight applications – are often quite complex, with the vast majority of that complexity happening under the hood. The above render was made while SpaceX was still planning on carbon fiber tanks and also appears to be significantly simplified, but it still offers a small look at some of that complexity.



Aside from successfully completing thousands of welds throughout the assembly, a lot of the effort of building an advanced tank is put into plumbing – both internal and external – needed to load, unload, pressurize, depressurize, and generally manage cryogenic (i.e. super cold) liquid propellant. SpaceX decided to utilize a partial balloon tank design to keep the steel skins of its stainless steel Starship and Super Heavy as thin as possible, adding yet another level of internal work due to the need for stringers and longerons on top of baffles and hardware to mount COPVs or header tanks.

Starship glows red and white-hot as it reenters Earth’s atmosphere. (SpaceX)

SpaceX already uses stringers (the grid-like structure) in Falcon 9’s RP-1 tank. (SpaceX)

Adding further complexity to the internal structure of Starship is the presence of major aerodynamic surfaces and landing legs, both of which will need to survive extreme stresses if they are to function as intended. Those structures must be aerodynamically streamlined and attach to the outside of Starship’s hull, likely requiring significant structural reinforcements both inside the spacecraft’s nose and rearmost propellant tank.

Super Heavy?

SpaceX began construction of a second concrete fabrication jig just a handful of days ago. Effectively a copy of a jig occupied with the larger of the two barrel sections of the orbital Starship prototype, the simple structure acts as a mount and includes a large door that allows scissor lifts to get inside the steel structure. The new jig is being built directly adjacent to Starship’s smaller barrel section, suggesting that it could simply be a way to concurrently work on both the LOX and methane tanks. Given the inherent simplicity of a concrete jig, it could also end up being used to support the simultaneous assembly and integration of the first Super Heavy booster prototype.

Both, but demo Starship is being built now, whereas Super Heavy hardware will start getting built in spring — Elon Musk (@elonmusk) December 9, 2018

Back in December 2018, SpaceX CEO Elon Musk indicated that the first Super Heavy prototype would start production in “spring” (i.e. NET April 2019). Musk has also indicated that Starship and Super Heavy will be simultaneously built both in Boca Chica, Texas and Cape Canaveral, Florida. In general, SpaceX is clearly beginning another round of expansion and improvement for its Boca Chica facilities, including the new concrete jig and an entirely new building on the same plot of land.

SpaceX began filling the new jig with concrete on April 24th. (NASASpaceflight – bocachicagal)

Starhopper

Last but not least is SpaceX’s Starhopper prototype. After completing an inaugural round of multiple wet dress rehearsals (WDRs) and two Raptor static fires/hops, SpaceX technicians removed the vehicle’s lone Raptor engine on April 8th. Starhopper has remained more or less inactive in the last two weeks, aside from some work going on inside the vehicle (per the open access hatch).

Meanwhile, in Boca Chica, Mary has paid Starhopper a visit. Still waiting for a Raptor to return into its aft.



📸@BocaChicaGal https://t.co/wuQANNGRo4 <–Heh, that single thread with just photos and started just this year is now at 1,092,119 reads. #HopperFans pic.twitter.com/Z2vIrFikXS — Chris B – NSF (@NASASpaceflight) April 20, 2019

Without a Raptor engine, there is admittedly not a whole lot that SpaceX can do with Starhopper, aside from additional WDRs if the first handful of tests were not enough. Instead, some minor work has been going on around the Hopper’s ad hoc pad, mainly taking the appearance of dirtmoving. Without aerial views, its hard to tell what exactly is taking shape, but it’s safe to say that Starhopper is simply waiting for additional Raptors to be produced, tested, and delivered to Boca Chica. Once more Raptors are ready, it’s understood that SpaceX will move into multi-engine (likely 3+) hop tests, perhaps loosing Starhopper from its tethers.

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