Elon Musk Shares Image of SpaceX Starship's Raptor Engine Attached to Mars Rocket Prototype

Testing of the SpaceX Starship prototype SN4 was ongoing at the Texas launch site this morning, as Elon Musk teased a glimpse of its Raptor engine.

Speculation mounted over the weekend that the "Serial Number 4" spacecraft prototype could soon be facing a static fire test, which would see one engine fired up at full thrust without an actual launch taking place at the site near Boca Chica.

Musk said on Twitter last week following a successful cryogenic proof trial that a static fire test using one of the firm's Raptor engines was planned for "later this week." Today he had another update, teasing: "SN4 [fire emoji] soon. Raptor looks so smōl."

A YouTube live stream video of the site by NASASpaceflight showed tests taking place on the latest iteration of the craft. The account touted an imminent "wet dress rehearsal fueling" of the SN4, but Musk later noted that it seemed "unlikely" for now.

"Liquid CH4 temp got too high this time. Offloading propellant. Will we retry later today," Musk tweeted, without elaborating on when that next stage would be.

A schedule for tests remained unclear at the time of writing, but the situation appeared to be fluid. SpaceX has been contacted for additional comment by Newsweek.

The Raptor is a full-flow, staged combustion engine powered by cryogenic methane and liquid oxygen. The launch component of the craft, the Super Heavy booster, will be powered by more than 30 Raptors, while Starship is powered by six.

Musk confirmed SN4 passed a cryogenic proof test last Sunday. It marked a milestone for the project designed to send crew and cargo to the Moon and Mars. The SN5 will be the first to see a multi-engine static fire and flight tests, Teslarati reported.

The SN4 became the first full-scale prototype to pass the cryo test after prior models failed. The SN3 faced issues during pressure tests in early April. The first full-scale build, the MK1, failed last November, while the SN1 was destroyed in February.

The SN2 passed the test, which packs the ship with liquid nitrogen to make sure that it will survive in flight pressure conditions, but it was not a full-scale build.

Musk's firm says: "SpaceX's Starship spacecraft and Super Heavy rocket (collectively referred to as Starship) represent a fully reusable transportation system designed to carry both crew and cargo to Earth orbit, the Moon, Mars and beyond.

"Starship will be the world's most powerful launch vehicle ever developed, with the ability to carry in excess of 100 metric tonnes to Earth orbit. Drawing on an extensive history of launch vehicle and engine development programs, SpaceX has been rapidly iterating on the design of Starship with orbital-flight targeted for 2020."

It is unclear if the 2020 target remains possible, although work at SpaceX facilities has largely continued despite the ongoing novel coronavirus outbreak across the U.S.

Musk hit the headlines last week after speaking out against lockdowns being enforced by state governments in response to COVID-19, which are aiming to limit the spread of the pandemic that has been tied to more than 67,600 deaths in the country.

The CEO wiped roughly $14 billion off the value of electric car firm Tesla after tweeting its "stock price too high imo" and vowing to sell "almost all physical possessions."