Monday, April 27, 2020

Starship SN4 Breaks “The Cryo Test Barrier”

Late last night through early this morning, SpaceX Starship prototype Serial Number 4  achieved something the first three serial numbers never did.  It survived a fueling test with liquid nitrogen (in place of methane).
Late on Sunday night, SpaceX completed a critical cryogenic test of a Starship prototype at its launch site in South Texas. The successful test, during which chilled nitrogen was loaded into pressurized fuel tanks, was reported on Twitter by SpaceX founder Elon Musk.

The vehicle, dubbed SN4—which stands for Serial Number 4—was pressurized to 4.9 bar, or 4.9 times the atmospheric pressure at the surface of the Earth. This pressure is not as high as Starship's fuel tanks and plumbing system are designed to withstand, but it is enough for a basic flight.
The test of SN3 failed back on the night of April 3rd, which was explained to have been due to a testing error, specifically loading the liquid nitrogen by volume not weight, if I understood them.  As with SN3, the plan was to run these cryogenic tests, and then strap one of their Raptor engines to the protoype for a static test.  That could happen by this weekend.  Once the static tests pass, there will be a test flight of the vehicle.  No, seriously. 
Should the static fire test be successful, Musk has said the SN4 vehicle will make a 150-meter "hop" test, much as the "Starhopper" prototype performed in August 2019. The company has yet to receive regulatory approval for this test, so it may not happen for several weeks.
Serial Number 5, well into construction already, has been earmarked for a higher altitude test flight. Musk has said, if all goes well with SN4, the plan is to attach three Raptors to SN5 for a higher flight test later this spring.  How much spring is left?  Seven weeks?

It helps to remember that Starship is just the upper stage for something much, much bigger:  Starship Super Heavy shown here between the Saturn V and a Falcon 9, the Starship Super Heavy's ancestor.  The vehicle was originally named the BFR, which was cleaned up for public consumption by explaining it as Big Falcon Rocket.  Although the corporate website refers to the rocket as Starship and Super Heavy, they also call it the BFR. 

Starship is the "upper stage" of a two-part, fully reusable launch system that SpaceX is developing. The company's goal is for the "Super Heavy" rocket to boost Starship into orbit, where this vehicle can either carry cargo to some destination or carry dozens of passengers.  
I read somewhere recently that Starship is considered much harder to get right than the Super Heavy booster, so that's why all the prototyping to date has been for the upper stage.  I guess SpaceX regards something with liftoff capability along the lines of a Saturn V, but fully reusable instead of three disposable stages, as their expertise or knowledge base, something they have a pretty good idea of how to do.  I expect their development will continue being fun to watch.


  1. Look at the size of the BFR! We am living in exciting times!!

  2. All the difficulties of internal structure that BFR has are easily testable in Starship simulation stages. Same fuel, same engines (only atmospheric, not vacuum-rated,) same construction, same landing issues.

    Really, all the booster is is a larger Starship with a flat nose. Yes, the booster will need to be structurally stronger, as it will be carrying a Starship, but, really, tanks, plumbing, pressure and vacuum issues, computer programs and computer controls, all the inners, all the outers, easily same same. Actually, realistically, the Starship is the more difficult vehicle.

    Go, go SpaceX!

  3. These are exciting times with respect to space flight. I am rooting for SpaceX also. I really hope they get to Mars in the next 10 to 20 years and I live long enough to see it.

  4. Having watched this from the beginning, I don't call this the BFR, though the name lingers on. The original Mars Colonial Transporter was a true monster, 12 meters in diameter. That name evolved into the Interplanetary Transport System when Musk realized that it could go much farther than Mars, and when it was downsized by reality to 9 meters in diameter.

    Finally, in 2018, the system was officially renamed "Starship" and "Super Heavy", but the diameter stayed at 9 meters. "Super Heavy" was also once used to refer to a Falcon Heavy design with more than two side boosters.

    Like all his products, Musk updates continuously and sometimes his naming conventions can be difficult to follow. Or irrelevant. I'm waiting for all this little stuff to pass into history so we can get to work on the STS -- the "Stupid Tall Starship" ;-)

    1. It's getting to be fun to watch these guys. They seem to get a good balance of fail quickly, fix it and keep going, without tearing up everything and starting over.

      Starship/BFR/STS was originally composite, I think. The look has changed over the years and I expect more will change as we go along. The concept of being so reusable that they can fly again in less time than it takes to recycle an F9 is pretty much one of those "I'll believe it when I see it" things.

      OTOH, if they're going to use it for hypersonic air travel, like that webpage says, it will have to be that reusable. Halfway around the world in 30 minutes is only marginally more useful than an 8 hour airplane ride if you're stuck there for a couple of months while they get the ship ready to take you back home.

  5. I think everyone who buys a Tesla is funding this. Whenever I see a Tesla owner (not a lot here, but there are a few) I want to say "Thank You!"

    1. There might be a buck or two off each Tesla, but I think the people who are paying for this are all the launches they've done. By launching satellites for everyone but themselves. They're testing out the long flight life boosters on their Starlink satellites rather than for paying customers.

      A Tesla Model 3 costs like $35,000 while a satellite launch is over $35 Million. More profit there to use.

      Nowadays, we can't even say NASA is supporting SpaceX; they're another contractor to NASA and NASA is supporting them less than old-line contractors like Boeing. I think they say SpaceX has outperformed Boeing at 30% less than Boeing charges.