sevenperforce

For any realistic mission to Alpha Centauri, the nearest near-future tech would be beamed power. Build a massive solar farm and beam generator on the moon and use the beam to push a sail-based ship. If you want a boost out of the gate you can use Medusa-style Orion with a sun-skimming Oberth maneuver, and your Medusa sail can double as your solar sail for beamed propulsion.

Do you have evidence that this was, in fact, the Soviet approach during the N-1 launch program? The N-1 program was underfunded, rushed, and certainly not hardware-rich. The first two and final launches were all sent up with functioning spacecraft intended for either lunar flyby or orbit. Only with the third launch did they use dummy payloads, likely out of desperation. Just because the Soviets repeatedly spammed N-1s at the sky without success doesn't mean that they were intentionally using these launches as their initial non-operational test campaign. If those launches had succeeded, we wouldn't have characterized it as a launch vehicle test, but as a successful mission with an actual payload. In contrast, SpaceX's launch (and future planned launches) of Starship in its test campaign have been explicitly just that: tests, with no possibility of an actual orbital payload delivery. The sample size of 1 single flight (for Superheavy, which is the configuration we are talking about) isn't enough to reach any positive conclusions about "a quite high chance" of anything. Do you have inside information identifying when Raptor has suffered test stand RUDs, as opposed to rapid scheduled disassemblies in intentionally destructive tests to failure? Different engine, different vehicle, different configuration, different flight envelope. Where? You're moving the goalposts here. Above, you were talking about in-flight failures, but now you are including startup failures, which can be commanded by the vehicle due to sensor issues when the engine is just fine. We also have a brand new environment including the possibility of debris impact from the concrete pad, which is not an engine reliability issue either. Well, it was a successful first test flight. It cleared the tower; that was the primary objective. And more to the point, we have no specific evidence that engine reliability was a contributing factor to the outcome of OFT-1. There's circumstantial evidence to suggest it might have been engine reliability, but it also might have been overly-sensitive sensors, debris impacts, or issues with other parts of the vehicle. Presuming to know it is one thing or the other is a little silly.

If that's the case, then the same would apply to the Shuttle (would this have prevented Challenger?), Delta IV Heavy, Falcon Heavy, SLS, and many many other rockets that don't have full-duration static test fires.

It was definitely good to see a white cloud of water vapor instead of a brown cloud of concrete debris.

Core was doing almost 4 km/s (3,990 m/s) at MECO. Is that the fastest we've seen? **checks notes** Nope, not even close. USSF-44 had MECO at 3,966 m/s and USSF-67 had MECO at 4,029 m/s. But they are dwarfed (dwarved?) by Viasat-3, where all three cores were expended and the core reached 4,744 m/s at MECO.

Why does the interstage look used?

Smaller fairing means less articulated mass in the clamshell.

Nozzle size impacts efficiency but it wouldn't be particularly meaningful for operation duration. The longer-coasting upper stages have the grey solar-thermal band around the kerosene tank to prevent freezing, plus extra COPVs to support ullage repress and more engine restarts. I'm guessing long-coast simply has more extra COPVs than medium-coast.

They have posted some updated images of Neutron with changes to the OML. Differences: Same liftoff mass, so probably not a tank stretch, but they've done a height stretch and moved the fins up to the very top, shrinking the fairing relative to the rest of the vehicle. The upper stage is now even more fully contained inside the cylindrical portion of the vehicle: Significant leg design change too, perhaps to allow for a more aggressive booster stage re-entry profile. I'm just concerned about how much propellant they can reasonably have in that tiny upper stage.

Wow, they're building an FTL engine!?!? In all seriousness, this is great. Of course this is a pure marketing mockup and we shouldn't assume any engineering details from it. I wonder what kind of engine cycle they will go for. The NTR that was intended to serve as a Earth-Lunar ferry as part of the original STS architecture would have been a dual-mode version of NERVA, balancing LOX injection for high thrust at the start of the burn against the pure-LH2 low-thrust end burn for high efficiency. Nuclear engines have specific impulse to spare and so the usual challenge is trying to get high enough thrust to avoid Oberth losses. NERVA was a thrust chamber tap-off (or "hot bleed" since you can't say combustion tap-off) design, which is probably why the flight-configured engines in the above mockup and in the BWXT image below are depicted with the turbine exhaust injection manifold wrapped halfway around the nozzle like an F-1 or MVac: It's unclear why there are two separate flows from the tank and apparently two (or four?) separate turbopump assemblies as well. Maybe it's supposed to have two modes, one with a higher tap-off ratio and one without? Or are the turbopumps running in series? For ground testing the nozzle extension was not used and so the turbine exhaust had a separate nozzle: You can see that the tap-off comes from the very bottom of the reactor chamber right before entering the throat. An alternative approach for a flight-configured engine would have had dual turbine exhaust nozzles, presumably for roll control (or even all control authority if the main engine was fixed: With the thrust levels that you need from a NTR, a closed expander cycle really isn't possible. Granted, you make better use of the Carnot cycle power because you don't have to pump a bunch of heavy oxygen like closed expander hydrolox, but all that heavy oxygen is what's giving you most of your thrust, so you're right back where you started. Plus, the high mass of the nuclear reactor means that you're really not as concerned about squeezing out extra Isp as you are about getting more thrust. The LockMart promotional materials in that video depict four gold foil tanks surrounding the reactor. Even though we obviously shouldn't assume anything gratuitously from the pure promotional stuff, it makes me wonder if they're considering a dual-mode design like the STS ferry, or even something more creative like using a hydrolox gas-generator as an independent pump cycle for the main pumps. There are definitely some unique considerations for a nuclear engine, beyond just the obvious (like safety issues). In a conventional liquid bipropellant combustion engine, you have a limited amount of total thermal energy you can extract from a given mass of propellant, but maximizing the heat energy increases the average molecular weight in the exhaust, lowering the total specific impulse. As a result, a bipropellant combustion engine has to balance maximal thermal output against an optimally efficient propellant mix (which is why engines don't typically run stoichiometric). With a nuke, on the other hand, the total amount of thermal energy available is not a function of the amount of propellant you have: instead, total available energy is a function of reactor mass and propellant dwell time. So the baseline assumptions don't always work out quite the same way.

Surprising exactly…nobody. But I agree, we absolutely need it.

The same way SpaceX deals with all the water after a launch of Falcon 9 or Falcon Heavy.

Not without explanation, just without derivation. But then proven to the most rigorous of standards by every possible test (and by some tests thought to be impossible at the time the postulates were postulated). You're confusing observations with conclusions. You realize the Michelson-Morley experiment wasn't only done once, right? The laser interferometers at LIGO are the new and improved versions of Michelson-Morley, and they do quite a good job at detecting motion in the "aether" that is spacetime. Confirmed optically, no less. Dark matter is directly observable via objects like the Bullet Cluster. It would exist regardless of overall cosmology.

I don't think the scarfing will cause overmuch problems for differential throttling. It feels like you're imagining secondary plume interactions, but in a supersonic flow there is no upstream propagation of plume interactions, so any change in the wake pressure across the heat shield will be very very minor compared to the impact of the throttling itself. Thinking about it in the context of equal and opposite forces: The equal and opposite forces from each thruster are split between the forces on the chamber/injector, which have a significant medial-radial component (green) but balance each other out, and the forces on the scarfed expansion surface, which have a lower medial-radial component and progressively greater superior component (blue): By downthrottling on one side, the medial-radial component of the chamber force decreases on that side, causing a direct torque on the opposite side; it also causes the center of vertical force to shift away from that side, which also creates a torque. If anything, differential throttling of a design like this may result in too much authority and lead to oscillations that are hard to damp, like putting a Vector engine underneath too lightweight of a rocket in KSP. It will be less of an issue in space but it might cause issues with landing.

You're absolutely right. It looks like Stoke really started off with the idea of the actively-cooled heat shield and sort of stumbled onto an aerospike design, while BO appears to have been designing this as an aerospike from the ground up. Stoke may have better luck with its landing burns than BO, since they can just accept flow detachment.

My patent law experience is not extensive, but IMHO the levels of potentially infringing overlap aren't very significant. You can't patent physics, after all, and just because a patent might describe certain attributes in conjunction with its core aspects doesn't mean all of those attributes are protected. But yes, Stoke holds patent priority on everything here. The core of the Stoke patent is the dual use of the expander cycle with the heat shield cooling manifold to pump the coolant during re-entry. It's a truly novel idea and I think it will stick. The question is whether BO tries to copy that approach or not.

The latest patent from Stoke includes a depiction of a non-axisymmetric heat shield to provide lift during re-entry with 0° AOA: It's not immediately clear from the patent whether this orientation is imagined as fixed or as moveable. The patent doesn't discuss it moving, so it's a little tough to figure out exactly how this would interact with the plume coming off the engines themselves, if it's "stuck" like this.

JARVIS has emerged! I should note that the original Actively-Cooled Heat Shield System and Vehicle Including the Same patent by Stoke, establishing the concept of an engine which uses heat from an actively-cooled shield to circulate the coolant, was filed in August 2020 and claims priority to a prior filing from December 2019, and Stoke's Augmented Aerospike Nozzle, Engine Including the Augmented Aerospike Nozzle, and Vehicle Including the Engine patent was filed August 2021 and claims priority to November 2019. In contrast, Blue Origin's patent above was filed in July 2022 and claims priority to December 2021. So Blue Origin seems to be solidly behind the patenting curve here. Even Stoke's most recent Annular aerospike nozzle with widely-spaced thrust chambers, engine including the annular aerospike nozzle, and vehicle including the engine patent, despite being filed in April 2022, claims priority to April 2021, predating all priority by Blue Origin. I'll post more over in the Stoke thread, but I did note that their latest patent includes a depiction of a non-axisymmetric heat shield which would provide lift during re-entry at 0° AOA, although it's unclear how that would interact with the aerospike expansion in vacuum. One of the nifty things about BO's patent is the "plurality of scarfed nozzles" depicted around the heat shield: As Elon Musk has pointed out, one of the reasons that aerospikes suffer is that the primary challenge in rocket engine nozzles is getting the exhaust to go DOWN, and aerospikes aren't great at that. Actually angling and "scarfing" the nozzles into the heat shield like this will make the recessed nozzle surface present a more consistent surface against which the exhaust can expand, reducing intramolecular cosine losses, and it also protects the engines more directly than Stoke's design seems to. An element very similar to Stoke's design (and potentially grounds for a patent infringement battle) is that "The heat shield may be actively cooled [and] The heat shield may include a cooling circuit configured to dissipate heat encountered during reentry of the upper stage." They also suggest "secondary fluid injectors" which may eject fluid (presumably from an open/bleed expander cycle exhaust) along with the scarfed thrust nozzles to help shape the plume, which seems to be the configuration depicted here: Later on they contemplate that the heat shield would "be constructed of thin face sheets separated" by spacers and that "turbine exhaust gas is fed directly into the space between the face sheets and exhausted into the space . . . inside the annular engine exhaust stream through orifices in the outer sheet." Using some sort of base bleed in an aerospike design is a well-known way to improve efficiency (for example, here). It looks like they are considering both a closed expander design (using numerous BE-7 turbine units) and an open/bleed expander design (using one or more BE-3U turbine units), depending on whether they use the base bleed or not. The patent explicitly states that their design saves development time by "repurposing turbomachinery (e.g., powerpacks) and thrust chambers designed for other engines" and references designs being created "for use in other space vehicles." Later on, it gives the non-limiting example of using "two BE-3U powerpacks" to operate the nozzles but notes that as many as five or more powerpacks could be used. BO contemplates that they could "power down some number of powerpacks and/or nozzles to meet thrust requirements" for certain aspects of a mission; this would require that the various thrust nozzles be plumbed to alternating turbopumps so as to keep the thrust vector consistent. They suggest a 23-foot diameter vehicle and a 21-foot-diameter ring of engines which creates, effectively, a single 21-foot-diameter nozzle. They anticipate a specific impulse of 395-425 seconds in one configuration, 400-420 seconds in another configuration, and 405-415 seconds in a third configuration; these configurations are not clearly differentiated. They anticipate that for the two-BE-3U-powerpack configuration, only a single powerpack would be used for vertical landing, with sea level thrust of "about 100 klbf" and throttling capability down to as low as 20%. They talk about each thruster producing 2000 lbf in some configuration but it's not clear how many thrusters they are envisioning with that thrust level. Given that the BE-3U is expected to produce as high as 160 klbf in vacuum, this would imply probably thirty thrusters plumbed to each of the two powerpacks.

I have to wonder if the use of electric pumps paradoxically makes the engines more amenable to being dunked in seawater, simply because there is no complex turbine plumbing which could be impacted by incursions.

Ships in science fiction have such high specific impulse that fuel reserves are really never an issue unless they suddenly need to be a plot point. If you want them to be a plot point, make them so.

That might just do it.

Might be, I recall hearing that—but watch the vid, and the exhaust profile looks more like launch, not like the 3 engine entry burn which seems to read more linear to me. Can confirm that only three engines are plumbed for relights. The other engines (and those three, at launch) get their TEA-TEB from GSE. Also, I'm not sure even Falcon 9 could handle running all nine engines on a nearly-empty booster. Think about it -- 9x941 kN on a ~30 tonne stage is almost thirty gees. That's really getting into ridiculous materials stress. The upper stage is really doing most of the work to get to orbit.

Fictional spaceships depicted in film typically don't show any RCS thrusters at all -- the ships turn magically with engines running at full blast but without any forward impulse. Part of this was the combination of a lack of knowledge (film directors don't know how spaceships work) and rule of cool (it felt more "advanced" to have spaceships that turn without any visible means of rotation). The other part was the cost of CGI. CGI used to be incredibly expensive, and so any added animations drove up the budget. It is only in recent years that the cost of high-quality animation has dropped to the point that animating things like RCS pods is no longer a big-budget item. The decrease in CGI cost has combined with an additional desire to show space as grittier, with more realism and dynamic elements. The CGI ships in The Mandalorian and the rest of the Disney expansion of Star Wars are a good example of this. Prior to the Disney expansion, CGI ships in Star Wars basically just floated around without any visible propulsion or mechanisms, but now you see animations of stuff like RCS and vertical thrusters. For example, vertical thrusters on the Razor Crest here: Vertical thrusters on the N1 Starfighter here: And the use of active gimbal on the main engines, to control the ramming action of the Hammerhead Corvette: An astute observer will of course note that the engine plumes from the corvette appear to have Mach diamonds showing overexpansion, which is de facto impossible in the vacuum of space. Perhaps these aren't actually Mach diamonds but are instead some sort of magnetohydrodynamic vortices that just look like Mach diamonds? /s One possible in-universe reason we don't often see RCS in science fiction is that the inertial control mechanisms are just massively more powerful, or they have used some sort of magnetic field coupling as the primary orientation control. In real life, magnetic field coupling can be used to desaturate reaction wheels (the Starlink satellites use an electromagnetic rod to push against Earth's magnetic field for wheel desaturation to since they don't have any attitude thrusters), but you'd need immensely more power to do that for your primary mechanism. Science fiction, of course, is famous for huge power sources. The TIE fighters in Star Wars are said to be extraordinarily maneuverable, and the X-Wing pilots are always saying "Lock S-foils in attack position." Why? The X-Wings have their weapons mounted on the wingtips, so opening the wings would increase their field of fire...but that might not be the only reason. The X-Wings do have sings that look vaguely like they could provide aerodynamic lift, but the TIE fighter's wings certainly do not: What are those wings useful for, other than looking cool? They could be solar panels (at least, that's one in-universe answer offered in some of the extended universe stuff) but their utility would be meager given the enormous power requirements of Star Wars vehicles. They could also be thermal radiators of some kind, although we don't see them glow like radiators. My head-canon is that any flat, thin surfaces on Star Wars vehicles are high-energy magnetically-coupled reaction control planes, capable of pushing against any ambient planetary or stellar magnetic field in order to rapidly change orientation. That's why the X-Wings appear to maneuver in space just like ordinary aircraft: their "wings" are acting like real control surfaces. That's also why the TIE fighters are so maneuverable: they are basically just two giant RCS surfaces with a pilot and engine and blasters in a pod at the center. Even the Millennium Falcon's long, flat external surfaces are acting this way. This allows some aspects of basic physics to still apply. The moment of torque around the center of mass of a ship is going to depend on the physical orientation of those reaction planes. X-Wings and Naboo Starfighters have good roll and pitch authority ("let's try spinning, that's a good trick") but poor yaw authority and will probably rely on differential thrust for yaw. The TIE fighters have ridiculously good yaw and roll authority but very little pitch authority other than what phased gimbaling of their ion thruster can provide; this explains the strange, otherworldly way in which they seem to zip around through the sky. The Falcon has some yaw and roll control but FANTASTIC pitch control, which allows it to simply pitch its nose up and use its sublight thrusters to blast its way into space like a KSP spaceplane loaded down with oversized RCS wheels. To summarize, Star Wars ships basically use the following engines and maneuvering systems: Repulsorlifts: a "gravity brake" which "locks" to a particular point in the gravitational gradient and allows a vehicle to hover with little or no power consumption; similar technology is used for inertial dampening to keep the crew from getting smeared Reaction control planes: a magnetically-coupled "wing" which pushes against planetary or stellar magnetic fields to provide roll, pitch, and yaw authority as necessary Vertical turbine-based thrusters: a turbine bypass which sucks in atmospheric gases, diverts them through the main engine system, and then expels them downward at high velocity in order to provide vertical translation for liftoff when you need to ascend or descend vertically Sublight thrusters: extremely powerful reaction engines with ridiculously high specific impulse which somehow do not torch everything behind them...perhaps using a exhaust made of something which decays into non-interacting particles shortly after leaving the nozzle Hyperdrives: whatevermajiggy that lets you go to hyperspace It's a good head-canon anyway.

First methane-powered rocket to orbit...on my birthday! Not SpaceX, but not half bad either.

The clear disadvantages in this design are (a) no obvious abort mode and (b) overweight engines carried all the way to orbit. Every kg that can be moved off the orbiter is an extra kg of payload, so if there was a way to offload two of those three engines it would be a significant benefit. Obviously reducing dead weight carried by the first stage isn't a 1-to-1 benefit to payload, but it does something. If you can do crossfeed, it's absolutely worth doing a sustainer architecture IF it doesn't result in a less-efficient upper stage engine and IF it doesn't force other suboptimal design choices. A three-core crossfed design with the side boosters returning Falcon Heavy style and the center core going to orbit is the straightforward choice, but then EDL of the orbital stage (for the sake of reusability) becomes the challenge. With crossfeed and a potential tripropellant sustainer, the disadvantages of hydrolox are ameliorated because the nice thrusty boosters carry the fluffy hydrolox tanks out of the atmosphere where drag is no longer an issue, and drop them off full. Then the fluffy tanks help reduce heat load on EDL. I wonder how large and draggy a hydrogen tank would need to be in order to reduce heat load to the "hot structure" regime. Of course you still need descent control and a landing mode. You can do a standard biconic entry with split flaps but that doesn't provide a straightforward landing mode.