sevenperforce

I wanna see someone stitch together all the videos of the payload deployments. It looked really cool.

Okay, nice. That helps with some of the speculative maths....

Oh, you misunderstand. The goal would not be to change throttle, but to alter the expansion pattern without an altitude-compensating nozzle. Let’s take the Falcon 9 as an example. The SL Merlin 1D is slightly overexpanded at sea level but it rapidly becomes underexpanded as it climbs, eventually creating that very large plume shortly before MECO. That plume from underexpansion represents an efficiency loss. The nine engines on the Falcon 9 don’t have enough clearance to all angle in together, but if they did, would that direct the plume more in the correct direction and thus increase efficiency?

I agree. The only argument for SSTO over TSTO is that an SSTO can loop around to the launch site and land, while a TSTO either has to land downrange (and be transported back) or expend extra propellant for RTLS. The former option takes time and the latter is inefficient. But I think it can probably be mathematically proven that you get more payload to LEO with a reusable TSTO, including RTLS boostback inefficiency, than with a reusable SSTO.

So here’s a question. Suppose you had a clustered rocket like the Electron or Falcon 9, set up as a sustainer stage. Could you start out with the engines gimbals pointed straight down and then gradually gimbal the engines inward to approximate an aerospike/altitude-compensating nozzle?

The X-37 uses TUFROC, a single-piece ceramic shield. It is repeatedly reusable from LEO entries, but it is very heavy (at least, compared to lightweight silica tiles). There's just no way you can get a heat shield into that mass fraction.

It's happening!! Seriously, though, this is really cool. The column structure is...interesting. I would love to see the maths that went into designing the load paths for that. It looks like these crossbeams handle a compressive load. The changing angle for each of these columns would make them want to buckle inward and so you need a lot of compressive loading capacity in the crossbeams. If I had to guess I would say that the angle in the lower column serves to eliminate bending or leaning moments that would otherwise decrease stability. If they were perfectly vertical, then the entire platform would be much more prone to leaning or rotating. You could eliminate those with additional stability structures but a big part of this structure being the shape it is must be to reduce the overall footprint so that there's as little as possible for Superheavy's exhaust plume to interact with. Each of those columns needs to support about 850 tonnes, plus their own mass and the launch table. Actually seeing these hot gas thrusters is just incredible. I don't know why but I've really been anticipating seeing them and they are...cool. Is that Ben Shapiro or Sheldon Cooper on the central thruster? I suppose that based on Elon's tweet, cold gas thrusters will be sufficient to perform the flip and provide ullage for Superheavy's boostback burn. Curious, though, that there is no prograde nozzle shown. It shouldn't need retrograde authority for separation from Starship because the pusher rod(s) and Starship's own thrusters will handle that, but you'd need prograde for ullage, no? <thinks for a moment> Actually, wait -- I've got it, I think. Immediately after separation, these thrusters fire to rotate Superheavy back toward the launch site. Because these thrusters are quite hefty, this causes rotation around the center of mass. Because the center of mass is (at least slightly) above the engine cluster, this causes a centrifugal acceleration at the engine cluster, pulling propellant down toward the engines to provide ullage. The core engines ignite and gimbal to cancel the rotation, which provides all the ullage needed. Obviously no ullage is required for the landing burn since you have the air slowing you down at that point. Looking more closely at the hot gas thrusters, it appears that the GOX and CH4 lines enter the engine near the top of the chamber, so there probably isn't any regenerative cooling going on. This is fine since they will be used in short bursts. I would really like to know whether the hot-gas thrusters are fed from an accumulator COPV (which in turn would be fed from the autogen press lines) or are tapped straight from the tank. I would assume the former. Tapping them straight from the tank ullage would be simpler, but would run the risk of liquid ingestion and would also be a waste of the nice high pressures coming off the autogen lines.

It looked like it came down pretty distant from the centerpoint in comparison to what we usually see. I wonder why.

The fact that they use the same 9+1 configuration as the Falcon 9 probably contributes. Most teensy rockets use numerous stages with a single engine or a two-engine cluster at most on the first stage. Electron (and now Relativity with its Terran 1) are bucking that tradition with clusters.

I am very interested in whatever cycle they’re going to come up with for the Aero R. If I was going to design a methalox engine of that thrust level from scratch, I would go with a dual split bleed expander augmented by a gas generator, but with the gas generator downstream of the bleed with dual heat exchangers. That way you extract ALL the heat from the chamber first, THEN extract precisely as much additional heat as you need from the gas generator, but you are still able to keep your oxidizer and fuel pumps completely separate and you don’t need any nasty shaft seals. The gas generator empties into the nozzle so it doesn’t need high pressure, and it’s very accommodating of changing mixture ratios so you have a lot of variability during flight.

Maybe that would be part of Congressman Gohmert's new plan to adjust Earth's orbit. In all seriousness I think the typical issue with doing this is that you'd have weird accelerative gradients on the engine gimbal.

They look TINY (like, beer-bottle-sized) in all the diagrams, so I always assumed they were significantly bigger, like at least the size of a 5 gallon bucket. These are more like large wine bottles.

That's what I thought, too, but apparently not: Relativity has completed hundreds of tests on its Aeon 1 engines that will power Terran 1 – but Terran R will feature a “new engine called Aeon R” that the company has begun developing, Ellis said. “We’ve also tested the engine for the upper stage,” Ellis said. “It’s a copper chamber engine ... and it’s actually now the same engine on the upper stage of Terran R as on Terran 1.” The article showed this image, which it said was the upgraded Aeon Vac firing without its nozzle extension. That said, this upgraded Aeon Vac would either (a) need to be fully regeneratively cooled like the Raptor Vac or (b) have an extensible (and retractable) nozzle like the RL-10B-2. The latter option would save on space in the interstage/engine bay and it would probably save on weight too. I wonder how they'll keep it from tumbling during re-entry. Those strakes are nice and all but with a very fluffy forward payload bay I'd expect it to tend to go tail-first. Maybe the strakes are designed to keep it passively aerodynamically stable? The Aeon 1 is a methalox gas generator. I don't see any exhaust on any of the firing videos, though, so it must use partial exhaust film cooling or something. I don't think there's any word yet on what cycle they'll use for the Aeon R. With 3D printing and methalox they could do some fun things with a dual bleed expander cycle engine. Closed expander cycles are limited to about 150 kN but a bleed expander cycle can get up to 270 kN and a GG-augmented bleed expander cycle could go even higher.

Starship physically can't flip in the thick parts of the atmosphere; that's why it has to use engine gimbal. The ITS would have had an easier time doing an aerodynamic flip because it didn't have the heavy header tank in the nose. It would have been more likely to go tail-first. That's where all the heavy stuff (including the header tanks) would have been. It would have been a chaotic tail-first, though, so it would need to fire up the engines for control just after the flip initiated. I'm a little confused by only having a single Aeon Vac engine on the upper stage, though. Terran 1 uses nine Aeon 1 engines on the first stage and a single Aeon Vac on the second stage, while the graphics say that Terran R uses seven Aeon R engines on its booster and a single Aeon Vac on the second stage. The Aeon Vac only produces 126 kN which hardly seems anywhere near sufficient for pushing 20 tonnes into LEO. For reference the Merlin 1DVac is around 900 kN IIRC. Plus, they can't use the standard Aeon Vac because its radiative nozzle won't work inside the engine bay. Perhaps they will rig up the Aeon Vac with an extensible and retractable nozzle like an RL-10 to allow it to do a landing burn? Maybe they will add a couple of Aeon 1 engines on the second stage to increase thrust at separation and then use the Aeon Vac by itself for the final push to orbit?

My training was also physics but I worked as a telecommunications test engineer for a while, so I was (at that point) an engineer. I would not call myself an engineer now because that is not my job. IMO if you have education that qualifies you to do engineering, and you work in an engineering field, you are an engineer; if you do not have education that qualifies you to do engineering and you work in an engineering field, you are a technician. If you pass the PE exam, you are a licensed professional engineer regardless of what kind of work you do. Chemistry and physics are tricky. I wouldn't call someone a chemist or a physicist just because of a BS or MS degree unless they are actually doing chemistry or physics for their jobs. That being said, if you have a PhD in either, then you could legitimately be called a "PhD physicist" or "PhD chemist" and people understand that it sticks with you even if that's not your job at any given point in time. This is very accurate. Rocket science is different from rocket engineering. All titles are made up to begin with. "Licensed Engineer" just has meaning because the government decided it does, and the government has power because we decided to believe it does.

And, three rocket science videos back to back.... (okay so this forum embed function is NOT working properly, so I'm going to post links) Rocket Science Sunday 4 (Why Are Mach Diamonds?) Rocket Science Starts Simple From RL-10 to Raptor -- Power Cycles Everyday Astronauts is great and all but I can do it in under two minutes, so.....

A nice little rocket engine primer for anyone who wonders why rocket science is complicated...reposted because the first one didn't load. (Posting here because I’m using the Kestrel and Merlin 1D as inspiration.)

Oh that’s true without question. I think Bezos would be amused to hang out with someone and not tip them off about who he was, and that’s not necessarily a good thing. I think engineers have their own version of Dunning-Kruger that tends to manifest in precisely these situations. I assume multibillionaires must be actively evil to get that much money in the first place.

That’s what I thought about Gates until I heard about the Epstein business. Musk is neurodivergent and overestimates his expertise in some areas but is generally good at the things he understands. Bezos has a lot more sense than Musk but he’s not quite as smart. Strikes me as the sort of person who you could hang out with and never know who he was. Zuckerberg is an evil lizard person escaped from Area 51. It feels like the anti-nuclear lobby has gotten quieter over the past couple of decades. I think a lot of the old guard died out. Chernobyl would have been less dangerous (at least in the long-term) if it had magically transmuted into a bomb. And by now the danger has mostly passed. The main reactor site itself will be *SPICY* for another 20,000 years or so, but the exclusion zone already has low enough radiation that it’s being resettled.

Agreed. It's not gonna be raw tonnage delivery; it's gonna be niche. Starship can do two things aircraft can't do. First, it can get there a lot faster and doesn't require coordination of refueling assets. Second, it can take larger payloads than an aircraft, though not by any massive factor. It is admittedly hard to come up with a monolithic payload that the US military would need moved halfway across the world and wouldn't already have local assets for. So the speed is going to be the biggest factor. Another possibility we haven't discussed as much is whether they would dispense with Starship's re-entry altogether. If what you have can be shielded to survive re-entry, then Starship can boost to a suborbital trajectory, open the chomper and drop it off in empty space, and then boost itself into a full orbit so it returns to the launch site. Then you don't have to worry about landing Starship in a war zone.

The aircraft carrying capacity of a supercarrier is primarily belowdecks in the aircraft hanger. Large carriers have several hangar decks and can hold aircraft in close quarters. So removing aircraft from the flight deck doesn't even come close to halving the number of planes. In reality, you'd barely even notice. Also remember that the purpose of an aircraft carrier is not to "move" planes, but to operate them. It is a floating airport. Starship can land on the flight deck and then move via onboard crawler to an area clear of the main angled flight deck. It doesn't even have to be a carrier, per se. Amphibious assault ships like the USS Nassau can support V/STOL landing fighters.

I suspect that the tiles only snap on one way. In other words, once they’re on, the only way for them to come off is to break them.

Carriers are designed to have giant flying bombs plummet toward them at terrifying speed and slam onto the deck violently. They’re also designed to easily absorb surface explosions. A nuclear supercarrier can easily produce LOX from seawater and is already accustomed to tanking large amounts of fuel for a number of different vehicles, but it could also just take the empty Starship back to land. Existing carriers can easily be equipped with cranes capable of unloading cargo rapidly from a Starship as soon as it has safed. I suspect most military equipment can handle plenty of stress, yes.

Here’s a thought. Where are they intending to land Superheavy again? That’s right, on a floating platform. If they can land the boosters on a floating platform, they can readily land Starship on a floating platform. If they can land Starship on a floating platform, they could readily land Starship on an aircraft carrier. It should be quite safe. I assume that with a negligible payload penalty, starship can perform the same off-target maneuver that the Falcon 9 boosters perform, correcting for a landing burn at the last second. A landing failure wouldn’t necessarily do much damage to a carrier. The carrier can either refuel Starship and allow it to fly back under its own power, or it can carry the empty Starship back to US soil. Landing at sea on a carrier in the center of a battle group ensures that Starship isn’t flying into enemy territory. It’s not going to get shot down. It has a safe place to land and the ship can even be equipped with a crane to offload cargo. I am sure that if you asked the US Navy, “hey, if you could deliver 150 tonnes of cargo from US soil to any carrier group on the world in under two hours, would you have a use for that?” they would say “Uh yep definitely.”

This is very accurate. It is trivial for the United States to set up complete air superiority when we are dealing with tiny insurgencies. Not so much in a hypothetical battle with another superpower. [snip]