Elon Musk says that SpaceX’s newest Starship prototype just passed its first test, clearing the way for the rocket to perform a form of testing that has destroyed all previously full-scale prototypes.
Known as a cryogenic proof test and reportedly scheduled to kick off as early as tonight (April 26th), SpaceX will fill some or all of the Starship SN4 prototype with ultra-cold liquid nitrogen. Used to simulate the similarly cold properties of Starship’s liquid oxygen and methane, liquid nitrogen (LN2) is chemically neutral and wont catch fire or explode in the event of a leak or total vehicle failure. SpaceX has performed many of those tests over the last six or so months, none of which were completed successfully with full-scale rocket tanks.
A series of test tanks (the same width as Starship but much shorter) did manage some impressive successes and proved that SpaceX’s current methods can technically build a rocket that’s up to the standards of spaceflight. Still, SpaceX needs to demonstrate that that remains true when multiple tanks and other components are attached to form a complete rocket. Enter Starship SN4’s April 25th and proposed April 26th tests.
Elon Musk says that Starship SN4 successfully finished an “ambient pressure test” early on April 26th, most likely referring to a test where the rocket’s tanks were filled with ambient temperature nitrogen gas. SpaceX technicians were eventually seen on mobile lifts spraying Starship with what appeared to be water (soapy water is a surprisingly simple way to find leaks in a pressure vessel – simply spray and look for bubbles).
It’s unclear if SpaceX actually pressurized the ship to the levels it has for past dedicated pressure tests, where verifying that the tank doesn’t burst is the main goal. If Starship SN4 did reach nominal flight pressures (6-8+ bar, 90-120 psi), it certainly bodes well for the test that’s to come.
Musk says that the next steps for Starship SN4 could begin – in the form of a cryogenic proof test – as early as April 26th, likely also in the late evening to early morning. During the ambient air test, Starship had some visible condensation on the exterior of its steel skin. The giveaway for the start of cryogenic testing will be the formation of frost on the rocket’s skin as the cold liquid nitrogen inside cools the steel to the point that it starts freezing water vapor out of the humid Texas air.
SpaceX has road closures optioned every day from April 26th to May 1st, leaving plenty of opportunities for a cryogenic proof test whenever Starship SN4 is deemed ready. If things go according to plan, Starship could be “physically” ready for a 150m (500 ft) hop test as early as a “few weeks” from now, though Musk says “approvals [from the FAA] may take longer.”