sevenperforce

Got to watch Sunday's Super Blood Wolf Moon (phew) which was cool, as always. Made me think...what would it be like to watch a solar or lunar eclipse from the moon? How about seeing a lunar eclipse from high lunar orbit? What about a Phobosian eclipse from Mars? Wrote this article for Medium about how it would look to stand on the surface of the moon during an eclipse.

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With only a single engine, is there any active roll control, or is it just down to the actuated lower fins? The capsule speed readout reached 0 mph at T+4:05. That's got to be a display element; if they don't have SOME downrange velocity, then they would risk falling back onto the pad. Unless they did a dogleg with corrections...in which case the capsule risks falling back onto the landing pad, which also is a problem. 350,342 feet is 66 miles is 106.8 km. Maximum speed during ascent was 2,226 mph; maximum speed during booster descent was 2,603 mph. Landing engine ignites at 376 mph, probably just a few moments from when the booster would reach lower-atmosphere terminal velocity. Terminal velocity for the capsule reaches a relatively steady 210 mph well before chute deployment.

The one silver lining is that the accident prompted Elon to identify the top piece as a fairing, specifically. This strongly implies that even the cylindrical portion of the "upper" piece will be empty; until now, it was uncertain whether tankage might protrude upward. This, along with some higher-quality drone footage, means we can now do a little more evaluation. This shot shows the placement of what appears to be the central bulkhead separating LOX from CH4. Possible tracing of bulkhead outline: We already know that the upper bulkhead has been sitting outside, waiting to be added, which means it will be added on top of the triangular leg support beams: The beams will be therefore be immersed in the liquid methane. A possible cutaway: Anyone with more time than me want to run the numbers and see what kind of propellant volume we're potentially looking at? The placement of the upper and lower bulkhead is a guesstimate; the placement of the central bulkhead is placed by visual/pixel count on the most recent image. Remember that liquid oxygen is 2.4x more dense than liquid methane and the Raptor will use 3.8x as much LOX by mass.

The problem there is tipover. Chutes bring the vehicle down with substantial horizontal velocity. New Shepard has a shape that is extremely tipover-resistant, so it's not an issue, but Soyuz can tumble and roll pretty hard. Rolling on impact would damage Dragon 2 and make reuse much more difficult. Yeah...on the one hand, it would suck to have a chute failure and not have propulsive landing programmed...yet it would suck much, much more to have a successful chute-pop get torched by a computer glitch. I mean, LOCV either way, but the latter just feels worse. Depends on how much orbital maneuvering they do. I think that using rockets to touchdown at surface is something SpaceX has gotten pretty good at.... Innnnnnnteresting.

Yeah, umm.......that's actually not so bad at all. The face shields were only black because there was a manikin in them before. Accents are whatever. Close enough. Also note that they look overly bulky because Behnken's gloves are folded back into his cuffs and Hurley's are hanging loose, whereas during flight they would be properly engloved. But yeah, it looks like a proper bridge flight suit. Knee pads are cool. I could see someone saluting that! On another note... Granted, we already knew this. But it got me thinking: in the event of catastrophic chute failure, the SuperDracos could absolutely kick in and make splashdown survivable. I wonder if there is contingency programming for this. Granted, the risk of chutes failing in triplicate are unbelievably low, but I don't think adding that programming would cause any problems.

Presumably something like LANTR? They were never interested in propulsive landing for Earth. NASA contractors proposed numerous VTVL designs. None ever got the nod, obviously, but I'm sure they were considered at some level. Douglas and Boeing both made such proposals, as well as perhaps Grumman. I misread @Xd the great's post and thought he said SLS. NASA has never been interested in earth-propulsive landing for the SLS since it was all about reusing STS hardware. There were definitely early STS designs that were VTVL. Restartability and throttleability of rocket engines was considered problematic, which is why the Chrysler SERV would have carried no less than forty turbine jet engines for hover-light touchdown after entry and descent. The DC-X program started a decade after STS was already flying.

They were never interested in propulsive landing for Earth. Also, EDL in a lawn dart is no small challenge.

I gave up on this a while back. "Dark" can, after all, be a metaphor...like the Dark Ages. If it's unseen, it's "dark" to us even if the sun might be lighting it quite nicely. Are the seeds growing under direct sunlight?

Air drag ullage. the fuel pools at the bottom on the tank because the rocket is being slowed by the air it passes through. Turbopumps can manage it from there. What's going to be interesting is how you keep it in the tank right after staging, when air resistance is going the other way. You'd have to use ullage thrusters continually throughout staging.

All tanks will be autogenously pressurized. The CH4 tanks will be pressurized with vaporized CH4 run through cooling channels around the engine bell; the LOX tanks will be pressurized with vaporized LOX run through cooling channels around the combustion chamber (or I may have that flipped). Pressurant gases will be vented into spark-ignited ten-tonne methane-GOX thrusters for RCS.

Well as long as you had ullage thrusters, the acceleration vector IS in the right direction...

The bulkhead is the tank. Well, it's the top of the tank. Elon has already confirmed that the Starhopper will use autogenous pressurization and monocoque tanks (i.e., the vehicle wall is the tank wall) just like the Starship. The fact that they installed non-flight article engines means they are testing attachments, which means the base of the vehicle is already airtight and plumbed. So they need two bulkheads: one concave-up bulkhead to separate LOX from CH4 (it needs a hole in the bottom to feed CH4 down to the engines) and a concave-down bulkhead to separate the top of the CH4 tank from the "cone" and all the flight computers, etc. My guess is that we see the concave-down bulkhead installed just above the level of the cylindrical portion of Starhopper. Starship will have some significant design changes in comparison to the 2017 IAC version and the 2018 #DearMoon version, so it's not yet certain how the header tanks will be arranged. One major LOCV vulnerability for the Starship is a non-catastrophic hull breach during ascent or entry. If SpaceX adds cylindrical tanks with valves between them, then it builds in the capacity to feed the Raptors from multiple tanks, thus reducing LOCV risk dramatically. It also allows for the possibility of using CoM shifts to control pitch during EDL. They are only validating hover, approach, and landing. They may test pitchover with the Starhopper, but probably only to evaluate recovery modes in the event of a control surface failure a la CRS-16. They will use spent F9 upper stages to test feathered canard entry. Then they put those two datasets together to get what they need for the first Starship test article. LOX freezes at 54 K and boils at 90 K; CH4 freezes at 91 K and boils at 112 K. Better than kerolox, but still not ideal. This is one reason (out of several) why the lower tank will definitely be LOX; this way you can have warm oxygen gas autogenously pressurizing the lower tank just across the bulkhead from the liquid methane. Otherwise you have very warm methane gas in contact with the coldest LOX which is not great. It does make concentric tanks challenging.

I assume the top is not welded together. NSF's L2 already confirmed they are using 9M tanks, so all they need are bulkheads. The hopper will have a LOT of dV, likely enough to go suborbital though they will not do so. Will likely use common bulkhead for simplicity. The bulkhead shown has a hole in the center -- this may be a column for piping of methane down through the center of the LOX tank. Elon said that the three engines currently in place are not flight articles, meaning that they are there only to test pipe fittings. So that implies that the piping is already completed and is simply hidden inside the lower portion of the vehicle.

If any hopper bulkhead is installed such that it is visible when the "cap" is off, we should be able to get a surprisingly good estimate of dV.

Guilty as charged. In other news... That was in commentary on this: IT'S HAPPENING I mean we knew that, but still. It looks like there's one bulkhead there and another one in construction, with the pieces laying around it. This hopper is so f'in kerballed. Super Heavy is expected to stage the Starship somewhere between 1.8 and 2.5 km/s, with sufficient reserve to perform boostback, entry, and landing burns. Starship is expected to be able to complete orbital insertion with enough dV remaining for orbital maneuvers, deorbit, and landing.

Relatively accurate identification of the emergence of clothing can be made by identifying the genetic divergence of head lice and clothing lice.

Vibranium only absorbs kinetic energy, not thermal energy, right?

That's what I have heard most.

First time I heard about KSP was from the alt-text on #1106. Second time I heard about KSP was from the above.

YESSSSSSSSSSSSSSSSS

Alternately: The tailfins must be in stall for the entirety of the aerodynamic regime or the whole vehicle will uncontrollably lawn-dart. The only way I know to maintain a controlled stall would be a conventional yawed tailspin. From Wikipedia: Tailspins are dangerous for conventional aircraft because most control surfaces are stalled. With very high roll authority via RCS, however, the StarShip may have a better time of it.

Maybe they did some fancy modeling that gives a flight and lift profile which permits fixed fins. At hypersonic entry, all lift is compression lift; there is no aerodynamic (Bernoulli) lift at all. Increases in atmospheric pressure and decreases in speed both exchange compression lift for aerodynamic lift, but they do so with different functional profiles. The transition from compression to aero may therefore be adjustable based on entry profile. Of course the same thing needs to work on Mars...though on Mars, the thrusters are going to have way more control authority than in the low Earth atmosphere. Recalling the Shuttle's S-curves...it may be possible to point V-stab ventral and then use roll authority only to execute a controlled tailspin all the way through the compressive-to-aerodynamic transition. Transitioning from prone to tail-first is going to be a challenge regardless. A lot depends on where the CoM is. I do not know that putting the V-stab ventral vs dorsal would produce any difference in lift-induced torque around the CoM in the low atmosphere, though it probably would do so in the upper atmosphere during compressive-lift entry. Useful comment by Lars from NSF: Makes a lot of sense. Getting all the right parts in place so they can swap out with stand-tested flight engines.

Elon suggests that the hopper will fly with this mottled appearance but the operational starship will be nice and shiny: https://twitter.com/elonmusk/status/1081662202124296192 ^^for some reason this is not pasting in properly. Also: https://twitter.com/elonmusk/status/1081676911066017793

Oh god that's too much. So Elon's render is quite true. Mold lines around the fins are interesting...those are the areas that would take a lot of entry heating. If the holes in the central fuselage section are thrusters, that's a good place for roll control. I really do wonder if we will see fixed fins on the orbital version as well.