Friday, March 19, 2021

The Other Milestone Yesterday

AFAIK, there has been virtually no general media coverage of this factoid.  After the SLS static fire yesterday, NASA Spaceflight (dot com) switched over to something happening at SpaceX Boca Chica.  SpaceX completed the stacking of the first Super Heavy booster.  The prototype has been in the works quite a while, and is referred to as Super Heavy BN1 (Booster Number 1).  This will eventually be the most powerful rocket in the world.  

Video here: I screen captured it before the top tank was fully in place; you can see a slightly darker (thicker) line right about the halfway up point where the cherry picker bucket is sitting.  A group of guys got out of the bucket and went inside the bottom section (the methane tank).  The process was interesting to watch.  Bluto the Crane lifted the top section (the LOX tank) until it cleared the bottom tank, which was over on the left in this view, then the bottom tank was rolled under the upper.  The upper tank was then lowered gradually while the guys inside the tank lined things up. 

There's still days of work to be finished: they need to weld the two tanks together, and connect their preinstalled plumbing and avionics runs.  Comprised of 36 of the steel rings also used to assemble Starships, the first Super Heavy prototype will stand roughly 70 meters (230 ft) tall from the top of its uppermost ring to the tail of its soon-to-be-installed Raptor engines.

Something that always puzzled me is that when they built the high bay and I found about its size, I realized it's too short to put a Starship prototype on the top of a Super Heavy booster.  I don't know if there are plans to make the high bay taller, but a Starship prototype like SN11 is 160 feet tall, and this SpaceX page says the stack of Starship and Super Heavy will be 394 feet. 

BN1 will not fly; it will be subject to all the static tests we've come to be used to and probably more.  It will be pressurized, and subjected to cryogenic temperature fluids like those it will carry.  At some point, the vehicle will get the four raptors it can accommodate.  The full payload-capable Super Heavy boosters will have 28 Raptors and there will be more on the Starship than the three engines the Starship prototypes have carried.  For test hops of the BN2 and perhaps BN3, they will apparently have four Raptors.  It's hard to keep up with these guys.

All of this is in preparation for a Starship Super Heavy orbital launch this summer.
First reported by NASASpaceflight and later confirmed by Musk himself, SpaceX hopes to be ready to begin orbital Starship launches as early as July 2021, just four months from now. Per NASASpaceflight, that first launch attempt will nominally use Super Heavy booster BN3 and Starship SN20. Super Heavy BN1 is expected to remain grounded, serving as a testbed for inaugural pressure and proof tests, as well as one or several possible Raptor static fires (Update: confirmed by Musk).

If that process goes according to plan, Super Heavy BN2 will pick up where BN1 leaves off and attempt at least one short hop test, among other qualification tasks. In the interim between that feat and Super Heavy BN3’s launch preparations, it’s safe to assume that either BN2 or BN3 will support some kind of iterative static fire test campaign similar to what SpaceX once did with Falcon 9, gradually building up from tests with a half-dozen or so engines to static fires with 20 or more – possibly up to and including a full complement of 28 Raptors.

From the SpaceX Starship page.


  1. With respect to stacking Starship on Superheavy, there is information that there will be a 450' tall tower built at Boca Chica. Someone commenting on the audio from Labpadre stated that he had a friend who was being hired as part of the crew that is going to build it. There seem to be preparations near the orbital launch pad to build something else that needs good foundations.

    1. They're actually laying the foundation for two 450' tall cranes at Boca Chica.

    2. I thought it wouldn't be hard to lift the roof on the high bay and add in another couple of hundred feet, so it's interesting they're going with cranes to hoist the Starship on top of its booster.

      BN1 doesn't have legs, and we don't know what they're planning to do. We know Elon thinks they should land without deploying legs, but have a tower catch it by the grid fins. It's hard to imagine that working the first time, so I think the first couple of boosters, will land on legs. Or they don't care if they crash the first few boosters trying to catch them.

  2. I am not a rocket scientist (ianars) but is seems some more attention to engines and fuel systems would be a good idea. Testing by explosion seems needlessly extravagant. But the scrap metal dealers are probably happy.

    1. In the case of the "crazy Elon" landing maneuver, I can appreciate that pulling off a new maneuver that no one has ever done may not model well in the software. The vehicle moves approximately as it should, but getting all the fluids in the system into the right place seems like the problem.

      But (big but) it seems at least one Raptor out of every set put on a prototype needs to be replaced. OK, partial credit again because it is in active development but if 1/3 don't work right, how long will it take them to get a set of 28 on Super Heavy to work? Put on 28, replace 9. Then replace 3 of the replacement 9 and 1 of the the final 3. Overly simplistic analysis of something best done with a Poisson distribution - but you get the point. Yeah, the Raptors don't look ready for prime time.

    2. But..I have to wonder if they are being overly cautious with the Raptors when there is any issue during static fires that strays farther than they want even though it is within design margins? That may be one reason they are so readily replacing them after static fires and then analyzing the physical area of the issue.