SpaceX CEO Elon Musk announced via Twitter that Starhopper’s first untethered hover tests – flying as high as ~20 meters (65 ft) – could be attempted as early as Tuesday, July 16th.



SpaceX engineers and technicians have been working around the clock the last several months to prepare Starhopper for flight and – even more importantly – prepare the company’s next-gen Raptor engine to ensure it is reliable enough to risk losing the Hopper in flight. Neither task is a small challenge, with both pushing SpaceX’s workforce into new and (partially) unfamiliar territory, ranging from Starhopper’s use of steel propellant tanks to Raptor’s adoption of liquid methane and oxygen instead of the kerosene/oxygen or hydrazine SpaceX’s workforce is familiar with

~20m up & sideways for first flight. Mk1 Starship hopefully 20km up in a few months. — Elon Musk (@elonmusk) July 12, 2019

Back in April 2019, SpaceX – having installed Raptor SN02 roughly two weeks prior – static fired Starhopper for the first time ever, simultaneously lifting the massive craft a few inches off the ground as it strained against its tethers. Three and a half months later, SpaceX engineers appear to have finally solved a mechanical resonance (vibration) issue that plagued all Raptors that came before SN06, forcing aborts, limiting test length, and even destroying or damaging engines beyond repair.

Exciting progress in Boca! Hopper almost ready to hover. Based on tonight’s test, looks like 600 Hz Raptor vibration problem is fixed. pic.twitter.com/9bLWOHG0sV — Elon Musk (@elonmusk) July 7, 2019

As previously discussed on Teslarati, Starhopper’s first true flight tests have been a long time coming. 9m (30 ft) in diameter and perhaps 25m (80 ft) tall, Starhopper is an extremely unusual and visually bizarre test article, effectively acting like a (vaguely) mobile Raptor test stand and a full-fidelity way for SpaceX’s aluminum-focused welding and fabrication crews to gain experience building a moderately functional stainless steel rocket.



Last month, there was some hope that Raptor SN05 would be capable of supporting Starhopper’s first hover tests as early as mid-to-late June, but it’s understood that the vibrational issue described above by Musk damaged the engine during one of its final acceptance tests, delaying Starhopper testing by several weeks. Had that resonance issue been solved months ago, it’s probable that Raptor SN02 could have taken Starhopper directly from its first static fires to untethered flight operations in April.

Starhopper completed its first successful (tethered) hop test and Raptor ignition on the evening of April 3rd. (NASASpaceflight – bocachicagal)

According to CEO Elon Musk, SpaceX’s Raptor manufacturing team is rapidly moving from a development-focused line to something more like mass-production. Once the design has been more thoroughly pinned down, the production ramp could max out with up to two Raptor engines completed daily, averaging out to an annual production rate of an incredible ~500 engines.



Additionally, Musk tacitly acknowledged that SpaceX’s recent development Raptors likely cost around $2M apiece, but the final mass-production cost could drop as low as $200,000 per engine, almost unfathomable for such a high-performance, cutting-edge engine.

Raptor liberated its oxygen turbine stator (appears to be mechanical, not metal combustion failure), so we need to update the design & replace some parts. Production is ramping exponentially, though. SN6 almost done. Aiming for an engine every 12 hours by end of year. — Elon Musk (@elonmusk) June 24, 2019

For the time being, SpaceX will be focused on wringing out any subtler design flaws and general bugs in Raptor as the engines are gradually produced and tested at increasing volumes. This includes hop/hover tests like those Starhopper is scheduled to attempt next Tuesday, as well as even wilder ~20-km suborbital flight tests that could come once one or both of SpaceX’s “orbital” Starship prototypes are fully integrated.

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