sevenperforce

I'm very close but unfortunately it will be cloudy.

Well I often see you asking whether rocket nozzles need to be bigger or smaller or whatever because of "heat" or some other reason, so how would I know? Well, that's not necessarily true. You can have an toroidal aerospike which uses a single annular combustion chamber but discrete nozzle throats. Such a configuration could be used for gimbal control or additional altitude compensation or just overall structural stability. In a similar vein, there were a number of early ballistic missile designs which used one sustainer nozzle inside of a larger annular boost nozzle, both of which (I believe) were fed at least in part from the same chamber: This is from the Lance missile. I'm not 100% sure that it is a single combustion chamber, but even if it isn't, you could still imagine an engine with such a configuration, especially if it was solid-based. The popular RPG-7 antitank missile has a single solid-fueled combustion chamber that feeds multiple nozzles: And the same is true of the solid-fueled escape motors for the Apollo and Orion capsules, which have multiple nozzles fed from one central combustion chamber (ignore the bit up top, that's a separate solid-fueled steering motor): In other theatres you have the R-5 air-to-air missile that used multiple nozzles fed from a single combustion chamber: And in a rocket-combined-cycle airbreathing engine, you can absolutely route the exhaust gases of a single chamber through multiple nozzles or multiple geometries. That's sort of what an afterburner is, in a way; you're using the nozzle from the primary combustion chamber as a secondary combustion chamber. But let's not forget the most famous single-chamber multiple-nozzle engine of all, the 1970s Mars Viking lander engine: So when I said that "there would never be any need for multiple rocket nozzles attached to a single combustion chamber" I wasn't entirely right. There would probably never be any need for such a design as the main boost engine of an orbital launch vehicle. But there are clearly plenty of situations where there is some specialized purpose that requires multiple nozzles with a single chamber.

Zero of those have clustered nozzles coming from a single combustion chamber. Multiple engines or multiple chambers make perfect sense. Multiple nozzles just for the sake of clustering nozzles makes no sense.

Nope, they aren’t. Multiple rocket nozzles are never clustered in place of a larger nozzle. Multiple rocket CHAMBERS, on the other hand, are often clustered, either in connection to a single turbopump or as a cluster of completely separate engines. There are a variety of reasons for this, mostly related to combustion stability but also for economies of scale and additional thrust. But of course the multiple rocket chambers will need multiple rocket nuzzles. There would never be any need for multiple rocket nozzles attached to a single combustion chamber.

Plus, the X-37 really doesn't have the payload capability for an orbital launch platform, either. It could carry a few physics packages, sure, but not with what would be needed for independent deorbit and re-entry.

Oh, I don't think this is a sign of rocket gardening at all. Maybe they just need to make some final modifications to the pad that they can't do with B7 still there. I imagine there might be parts that need to be craned in through the center ring.

Supposedly they are preparing for a chopstick lift of B7: Let's hope they are doing "now we know the last thing we need to do before launch" work and not "that was fubar, back to the drawing board" work.

The Hanford Site was selected because (among other, lesser important reasons) it was very close to a hydroelectric dam but reasonably far from population centers. They needed lots of space, lots of electricity, and not many people. It would absolutely have been feasible to knock out the Hanford Site by a one-way strategic bomber mission (assuming the Soviets could have penetrated American air defenses and radar, which was quite formidable), but it would have only set back the nuclear weapons production by the amount of time that was invested in the Hanford Site. If the Soviets actually launched an attack on American soil, we would have put up plutonium production everywhere that had electrical power, population centers be damned.

I did not hear the term being used, at least not regularly, until SX started dumping multiple satellites per mission. I know that GPS and Iridium can be called 'constellations' - but my impression was that each of those were large satellites that were (effectively) individually placed by different rocket launches. So - is there a different term for that? Or does 'constellation' simply refer to a group of related satellites? The Iridium constellation launch campaign delivered between two and seven satellites to LEO per launch, depending on the launch vehicle capabilities. They used a variety of launch vehicles, including Delta II, Proton-K, and Chang Zheng 2C. Iridium's replacement constellation, Iridium-NEXT, began launching on Falcon 9 rockets in 2017, with approximately 10 satellites being delivered per launch. The Globalstar constellation started launching in 1998 and had about a dozen satellites go up in each launch. I was actually incorrect about the first GPS satellites; the original GPS launch was in 1978. Of course those particular satellites have long since been retired. The GPS sat launch campaign only sent up a single satellite per launch until the USA-66 mission in 1990, which launched two at the same time. Yeah, you could do this easily enough. A simple relay like Quequiao needs a mass of no more than half a ton with enough propellant to brake itself into a lunar orbit, and so a Falcon 9 could definitely send four of them to TLI with enough margin for first-stage recovery.

A real object does have a real trajectory but you can have a real object with a real trajectory that is on an escape trajectory such that it will never again form a closed orbit relative to any object, due to the expansion of the universe.

Constellations have been around for quite a while now. The GPS constellation was launched beginning in 1993 and the Iridium communications constellation was launched beginning in 1997. We haven't had much in the way of a need for a lunar relay constellation. All crewed landings took place on the near side of the moon, as well as all robotic landers up until Chang'e 4 (which had a dedicated communications link to Earth via a separately-launched relay, Queqiao, at L2). The orbiters we have (like the LRO) are out of communications with Earth half the time, but that's fine since they can just uplink whenever they come back around. You wouldn't need six smallsats; you can get away with three. That's because you're on the "Earth" side of the moon half the time anyway, so as long as one of the satellites has line-of-sight to a satellite that has line-of-sight to Earth, you're fine. One problem with constellations around the moon, at least in low lunar orbit, is the distribution of mascons that make it hard to maintain orbit. There are a handful of frozen orbits, though, or you could put the constellation in a more distant orbit. For Artemis II, the crew in Orion will be isolated from Earth briefly during the flyby, but not for very long. It's a free-return after all. Artemis III will place Orion in NRHO which has constant communications with Earth, and the landing will be on the south lunar pole with line-of-sight to Earth. In subsequent missions, Gateway will be in NRHO, and it will have relay capability if NASA wants to do landings on the far side of the moon.

With the same success we can say that they are orbiting Crab Nebula, or any other reference point, because there is infinite number of open trajectories and reference points. The closed trajectory differs from them principally, as you can have only one unique reference point (letting alone the reference point own motion and orbital perturbations, let the Universe be considered static for this purpose). The eccentricity of an orbit can be greater than 1. As long as your trajectory is still along a path which can be defined as an orbit with a periapsis and an eccentricity, it's still an orbit. That condition remains until your object gets close enough to another massive body to cause its trajectory to deviate, at which point the periapsis and eccentricity relative to the original reference point are lost. There's no static "bulky mass of matter" in a globular cluster; everything is just orbiting the stars which happen to be closer to the center than they are at any given point. The same is true of galaxies. Our own cluster, the Local Group, has essentially nothing in the center; it's basically dumbbell-shaped, with the Milky Way and a number of smaller galaxies on one end and Andromeda and a number of smaller galaxies on the other end. At one level up from the Local Group you have the Virgo Supercluster, which includes the Local Group. The clusters in the Virgo Supercluster orbit the Virgo Cluster, which is the heaviest cluster in the Virgo Supercluster. Unlike the Local Group, the Virgo Cluster does have a single giant galaxy in the center, the supergiant elliptical galaxy Messier 87: The supermassive black hole at the center of Messier 87, M87*, produces the relativistic jet shooting out of the galactic core. It was the first black hole ever imaged by the Event Horizon Telescope. The black hole at the center of Messier 87 is probably the "most-orbited" discrete object that we orbit. Although the Virgo Supercluster is considered to be a lobe of the Laniakea Supercluster, the latter is no longer gravitationally bound and has already begun to disperse due to the dark-energy expansion of the universe. So we are not in any closed orbits above the level of the Virgo Supercluster (to answer @kerbiloid's question). The largest gravitationally-bound object in our local universe is the Shapley Supercluster, a collection of dozens of major galaxy clusters with a total mass more than 10,000 times that of the Local Group. We are close enough to it that its gravity is still tugging the Virgo Supercluster in its general direction, but not so strongly that it will be able to overcome dark energy expansion.

Well, interstellar rogue objects are orbiting Sagittarius A* and the rest of the galactic core directly, but I don't think that answers your question. Objects which are ejected from their galaxy of origin are still technically orbiting that galaxy, just on the outgoing leg of a hyperbolic trajectory. Until they get close enough to something for their orbit to deviate so that they're now on a hyperbolic trajectory around THAT thing, this condition remains.

How about "in orbit around one or more stars"?

Could have been an early shutdown or maybe Elon just got it wrong or the plans changed. I believe he previously said that the second static fire would be 16 engines but they ended up doing 14 instead.

Yep, that's what I get when posting at 4 AM We've tossed this about before, but if I had my druthers, I'd use something like the following nomenclature: Star. Any body which currently or in the past sustained nuclear fusion in its core. Main sequence star. Any star in hydrostatic equilibrium which is currently fusing hydrogen in its core. Giant star. Any star in hydrostatic equilibrium which was previously a main sequence star but has exhausted the hydrogen in its core. Red giant. Any giant star with an inert core which is fusing hydrogen or helium in shells. Supergiant. Any giant star large enough to fuse helium into heavier elements via the alpha process. Failed star. Any star which was unable to sustain sufficient nuclear fusion to reach hydrostatic equilibrium. Stellar remnant. Any star which formerly reached hydrostatic equilibrium but no longer sustains nuclear fusion. Degenerate star. Any stellar remnant which is supported by quantum degeneracy pressure. White dwarf. A degenerate star supported by electron degeneracy pressure. Neutron star. A degenerate star supported by neutron degeneracy pressure. Black hole. Any stellar remnant which has collapsed to be smaller than its Schwarzschild radius. Stellar nebula. Any stellar remnant or portion of a stellar remnant which has been ejected into a diffuse cloud. World. Any gravitationally-rounded body which is not a star. Rogue world. Any world which is not in orbit around a star. Giant world. Any world too large to have a solid surface or crust, in which the transition between gas and liquid occurs above the critical point. Gas giant. A giant world comprising primarily hydrogen and helium. Ice giant. A giant world comprising primarily elements heavier than helium. Terrestrial world. Any world with a solid surface. Ethereal world. A terrestrial world with a persistent troposphere. Ice world. A terrestrial world with a surface composing of icy volatiles and no persistent troposphere. Rocky world. A terrestrial world which is neither an ethereal world nor an ice world. Planet. Any world in orbit around a star which is not a natural satellite. Major planet. Any planet which, together with its natural satellites, makes up the vast majority of the mass in its orbital neighborhood. Planet binary. Any pair of planets in orbital resonance, neither of which are a major planet, but which together with their natural satellites make up the vast majority of the mass in their orbital neighborhood. Minor planet. Any planet which is neither a major planet nor a member of a planet binary. Natural satellite. Any body in orbit around a star which is in orbital resonance with a larger body, other than a planet binary. Moon. Any natural satellite which stays within the Hill Sphere of a larger body. Planetary moon. Any moon which is also a world. Dwarf moon. Any moon which is not a world. Trojan satellite. Any natural satellite, other than a moon, which is in a 1:1 resonance with a larger body. Leading trojan. A trojan satellite at the L4 point of a larger body. Trailing trojan. A trojan satellite at the L5 point of a larger body. Resonant satellite. Any natural satellite with a resonance other than 1:1 with a larger body. Orbital neighborhood. The orbital neighborhood of a body is the set of objects orbiting the same star as that body which crosses the orbit of the body or of one of its natural satellites. Comet. A body with a sufficiently eccentric orbit that it experiences cycles of visible mass loss near periastron. Asteroid. Any body in orbit around a star other than stars, comets, planets, and the natural satellites of planets. Belt asteroid. Any asteroid which orbits entirely between the orbits of adjacent major planets. Centaur. Any asteroid which crosses the orbit of a major planet. Distant asteroid. Any asteroid which orbits a star at a greater average distance than any major planet.

I'm not here to say I told you so. But I did bloody tell you.

Back to the OP, we had a new engine test over Thanksgiving: Lovely Mach diamonds. I'm guessing that this is still a low-throttle test. Those plumes are extremely orange, which suggests low combustion temperatures and a lot of molecular hydrogen burning in the ambient air.

Oh, it’s terribly hackneyed. FWIW, it’s strictly the Pluto/Neptune problem, not the Pluto/Uranus problem. Virtually all of the Plutoids and other bodies in the Kuiper belt are in resonance with Neptune. By all rights, Pluto should be considered a satellite of Neptune, just like the trojans of Jupiter should be considered satellites of Jupiter. It feels very icky to think that Pluto would be a planet if it was close to the orbit of Mercury, and Earth would be a dwarf planet if it was out there near the orbit of Pluto. I’m all for categorizing things based on the role they play in stellar system evolution, but you’ve gotta have a limit somewhere.

One of the problems with the OP (and with science fiction in general) is that there’s a disconnect between what ecosystems could exist and how ecosystems form. Even the deserts of Earth (the Sahara, Antarctica, etc.) weren’t always deserts. By the way, @Beamer, are you new? You seem uncommonly smart and I’m not sure why I haven’t interacted with you before. The best working hypothesis is that they formed close and got themselves ejected into more distant orbits by any number of interactions, but there are other possibilities.

Titan has lakes and rivers and rainclouds. Of course these lakes and rivers and rain clouds are all full of liquid methane, not liquid water, but that’s beside the point. Jupiter, Saturn, Uranus, and Neptune are gas giants. Gas giants do not have oceans anywhere; they are so heavy that the gases which compose them transition gradually through supercriticality, so there is never any sharp surface transition (like the transition between air and liquid/solid like on Earth, Mars, Venus, and Titan). It should be noted that Uranus and Neptune are also commonly referred to as ice giants. Ice giants are still gas giants and there is nothing particularly icy about them since they are extremely hot. But unlike the “classic” hot gas giants, they just are composed mostly of heavier elements. It is believed that during the formation of stellar systems, the largest accretors suck up the majority of the hydrogen and helium in the protoplanetary disc, achieving a substantial amount of internal heat production through Kelvin-Hemholtz contraction. These form the gas giants, which rob the rest of the protoplanetary accretors the opportunity to grow in mass. Slightly smaller accretors are able to capture heavier elements in the hot disc and grow to significant size, but cannot hang onto hot hydrogen and helium and thus stop growing out at much lower masses. These smaller giants will be either completely ejected from the system or will be flung into more distant orbits, where they cool relative to the gas giants.

Well so actually that’s one of the reasons the definition is what it is. We wanted to be able to decide whether exoplanets should be characterized as planets or not, and so the concept of “big enough to be round” and “has the right location and size to clear its orbit” were chosen because those things could be measured from far away. Planetary astronomers are divided to some degree between the study of body composition and the study of orbital mechanics and system evolution. The current definition largely reflects consideration of the latter before the former.

The vertices are above you in absolute altitude but they are "below" you in the sense that they are beneath the plane tangent to the surface at your feet. So regardless of how it came to be, or if it once started out as a natural planet, once you make/magic this thing, it is not technically a planet anymore... Well, technically, this definition merely says "big enough" to have enough gravity to force it into a spherical shape. It doesn't have to be spherical.

Stationkeeping for NRHO is minimal, and that's what the PPE is for. Stationkeeping for NRHO is the result of gravitational perturbations and nothing else. There's no atmosphere up there. In comparison, the ISS is so close to Earth that it is basically scraping the surface of the atmosphere. That's why it needs periodic reboosting.

Then you'll hate how it looks from Earth's inertial reference frame. Funny that it makes a retrograde re-entry to Earth. I wonder why.