DW said it best. Like how several technologies work in EP, we know that they could be a thing, and roughly how that would work, but obviously if we knew how to go from A to B, we'd probably have it already. Based roughly on the tech as described, I assume refueling moves stored MH in a holding tank to the tank on the ship. All of this would require very delicate magnetic containment along the way - so this will be as rugged as can be built, but if exsurgents with monkey wrenches bang on stuff too much, you'll break containment and high pressure hydrogen will violently rush out. And god forbid you have, like, an open flame somewhere. If, say, the normal lines from the holding tanks to the ship are broken, they'll have to rig something, which means they might just get a straight up equipment failure, no monkey wrenches. There are probably safeties in place to prevent cascading failures, but you never know, maybe those are broken.

Moving and transferring the stuff would be... Pretty challenging. Perhaps the fuel tanks themselves are interchangable - IE, hydrogen is compressed into MH [i]inside[/i] the fuel tank into which it is being transferred, and this is then treated like a solid rocket fuel "cell" that can be moved in one discrete unit, plugged in above the rocket motor? In which case, the proper equipment for fuel transfer would consist of a forklift truck and/or a Daitya morph. (Or, you know, fuel handling armatures and such.) It would also suggest that fuel tanks themselves are not-infrequently recycled and refactored in the fueling bays, since the fuel tank that went into that Autonomist-made GEV probably isn't the same one that goes into a hypercorp-made SLOTV. Alternatively, you use varying magnetic fields to [i]carefully[/i] decompress MH into liquid hydrogen, pump it into the fuel tank and compress it again. Frustratingly, I could envision [i]both[/i] approaches being used by different manufacturers, so your players should RTFM before they go to the trouble of securing the fuel pumps and pipes, only to find out that they could have/need to have gone and manufactured an empty tank to-spec, filled it, and moved it with a Power Loader.

It is stated that metallic hydrogen is kept stable through the use of electromagnetic fields. (Main Rules p. 347). Because of that I came up with the following concept of metallic hydrogen and how it is stored and used on ships: Metallic hydrogen for ships is typically stored in curved plates. The standard plate is a common length (I never really decided on a length but as an example we could say that all plates are 25 cm long) with a more or less common arc (my idea was somewhere in the neighborhood of 55 degrees). The radius of the plates would vary by the thickness of a standard plate so as an example if a standard plate was 1 cm thick then you would have plates with a radius of 4 cm, 5 cm, 6cm, etc. What this all means is that if you stack up a bunch of plates you would get a chunk of metallic hydrogen that looks like 1/6th of a cylinder 25 cm tall (assuming 25 cm was our standard length). The ultimate diameter of the cylinder would depend on how many plates were used and the size of the innermost plate (you would never use all the 'inner' plates although whichever was the innermost plate would vary depending on the size of the engine). Six of these stacks would make up a 'ring' and multiple rings would make up the entire engine. This means that a wide variety of engine configurations can be built using these standard plates just by varying the precise plates used to create a ring and the number of rings in the engine. So for refueling my take is that a ring or series of rings is stored in a 'sleeve' that includes the EM generators necessary to keep the metallic hydrogen stable. You're probably looking at redundant systems along with a physical design that will 'fail safe' as the final safety (the sleeve wouldn't be strong enough to prevent the hydrogen from expanding but it is strong enough to prevent uncontrolled expansion and then vents pressure so that instead of the metallic hydrogen sublimating in a fraction of a second in a huge shockwave it sublimates over several minutes). This is probably almost identical to the general construction the fuel tank/motor except that it lacks nozzles to focus the escaping hydrogen into thrust. So while a 'sleeve' could be damaged badly enough to explode it isn't any more likely to happen from a stray bullet than it is for a metallic hydrogen engine to explode from a stray bullet. It would probably take either criminal negligence on the part of the handlers or else deliberate sabotage. Refueling would be accomplished by moving aside the engine's nozzle, pressing the end of the sleeve up against the opening to the engine, then opening the top of the sleeve and pushing the plates into the engine. Stability of the hydrogen would be maintained by the field generated by the sleeve and the field generated by the fuel tank/engine and not by pressure. While it sounds like that can be done quickly it probably takes time to make sure that the two overlapping fields are working together. You will also have an issue with removing the old remaining plates if they exist. How long it takes to refuel probably varies really widely depending on circumstances. For instance I would imagine that smaller military vessels are probably designed so that remaining hydrogen can be dumped/vented quickly in combat conditions (time being much more critical than fuel recovery at that point). Because you would have a very small number of likely configurations you could have 'sleeves' sitting around designed for those specific craft. Because the possible field generators is a small set of military grade equipment and because under combat conditions you don't follow the same safety protocols of civilian agencies the military can probably slam a new load of fuel into one of those ships pretty quickly. On the other hand if you are recovering unused plates to minimize operations costs and you need to have a new set of plates assembled for your ship because your ship is one of a thousand different designs you are probably looking at leaving your ship somewhere while you go out and get something to drink, maybe have some dinner and get some sleep in a bed that isn't in a ship's cabin. Of course none of this is official. It's just my best guess based on the description of the drives in the rules, my very limited knowledge of rocket motors, and my assumptions on practices and procedures. I'm also simplifying some of the design elements such as omitting components that help align the plates and keep them together because while I'm sure they exist they are not necessary for this level of theorizing.

nostromo1a1 wrote:

compressing is easy, you have heard of air conditioning right? basically a compressor adds pressure and heat then this gas goes to a heat exchanger where the heat is rejected and the gas turns liquid while being under pressure same idea just depends on how it would need to be done such as what pressure and heat exchange are necessary.

That's kind of like saying going to orbit is easy because you can jump a foot in the air. 30 PSI air conditioning and 500 megabar compression are significantly different. (More than 100 million times as much pressure) I really like bent plates being used for building rocket engines. I was thinking the housing for MH fuel needed to be a lot closer but I like that idea, especially as MH might be metastable, so you could just use the plates alone, without stabilizing fields.

dare wrote:

DW: That only kind of solves the problem - I prefer my approach to be world-oriented, not scenario-oriented. That's why I'm looking for a world-consistent way for the metallic hydrogen storage & transport to work, so that it'll work the same way the next time the same thing comes up, and that I have a bit of an explanation on how the tech works, in case someone comes up with something unexpected.

Unfortunately, the books are quite lite on "world-oriented" details. Unless the books specializes on the topic, like gate crashing, don't expect much specifics. The books tends to do things abstract, like prices for stuff being in price categories, like [Low] being 250 cr, and [Expensive] being 20,000 cr. Or how fabrications times in nanofabs being 1 hour * price category. Annoying I know, but its what we have to work with.

to be more correct some a/c units operate at more than 500 psi and some even operate at negative atmospheric pressure or barely above absolute pressure which is very different. Depending where you were when you make a vertical jump physically you could jump into orbit. As for necessary pressure that is dependent on the temp or the gas you are compressing to liquid or otherwise manipulating and changing it's current state. before I forget it's not actually metallic it's more correctly called "Exotic Solid Phase"

nostromo1a1 wrote:

to be more correct some a/c units operate at more than 500 psi and some even operate at negative atmospheric pressure or barely above absolute pressure which is very different. Depending where you were when you make a vertical jump physically you could jump into orbit. As for necessary pressure that is dependent on the temp or the gas you are compressing to liquid or otherwise manipulating and changing it's current state. before I forget it's not actually metallic it's more correctly called "Exotic Solid Phase"

Metallic hydrogen is estimated to require in excess of around 14.5 million psi for formation, so that's about 5 orders of magnitude more than those 500 psi ac units. Also, it is absolutely impossible to jump into orbit with a vertical leap. If you leapt vertically gravity would either draw you back down and you would pass through your launching point and impact the surface or else you would exceed escape velocity for your locale and continue away from the body. In neither case would you orbit. You would have to have a horizontal component to the leap to orbit but even that would not truly work as with nothing to provide impulse once your feet leave the surface you are using for propulsion your energy you would have no way to increase your energy state meaning that the absolute best you could do in theory was to return to your launching point which would now be in your way (and that's ignoring the fact that miniscule drag forces will almost certainly degrade your orbit). And it is more correctly called 'metallic hydrogen' over 'exotic solid phase' in the same way that it would be more correct to refer to something as 'salmon' instead of 'fish'. Metallic hydrogen is an exotic solid phase but there are also other forms of exotic solid phase matter.

I would recommend looking at the wikipedia page on solid-fuel rockets (https://en.wikipedia.org/wiki/Solid-fuel_rocket) to get an idea about how a metallic hydrogen engine probably works. It won't be 100% accurate since there's no oxidizer and the thrust is provided by relaxing the EM field instead of igniting the mixture but it should probably get people a long way to thinking about how the engine probably works. That said, I'm not so sure about my whole curved plates idea any more. It seems more likely that you would just have standard size 'motors' which are a combination of casing and grain. The engine proper would contain the EM generators that surround the casing, the seal and the nozzle. The 'motor' would be contained by device that is essentially the same as the engine's EM generator and 'refueling' would be a matter of removing the expended motor, mating the transport container to the engine, and sliding the new motor into place. Curved plates just seems a little too convoluted with too many potential points of failure.

Quote:

It is only stated that the electromagnetic fields stabilize the metallic hydrogen. Formation of metallic hydrogen requires significantly more than just refrigeration. It requires massive pressure as well. Now it is possible that the pressure is also replaced by EM fields but if that is the case it seems like the implication is that the EM fields for a ship's tank only stabilize the metallic hydrogen. Perhaps it is inefficient to mount the much more powerful field generators that would be required for MH creation to a ship so they only mount ones strong enough to stabilize the MH. That being the case you would not be able to fill a ship's tanks with gaseous or liquid hydrogen and then convert it to metallic hydrogen. It would have to be metallic hydrogen as it is loaded which would prevent 'pumping' in any form.

I looked at the phase diagram and went with solid phase instead of metal phase. I'm guessing the metal phase would be better for propulsion due to the pressure difference, which is considerable. Whatever the system is, there's also got to be one for morph scale, otherwise Rovers (space fighter variant) and Courier start to loose some luster. If it is cylinder sections, they'd be getting the middle bits. Edit: Courier, not Ring Flier

base3numeral wrote:

I looked at the phase diagram and went with solid phase instead of metal phase. I'm guessing the metal phase would be better for propulsion due to the pressure difference, which is considerable.

Exactly. These engines are using metallic hydrogen, not just solid hydrogen. The greater pressure translates to a greater amount of stored energy which translates to a higher specific impulse, and by and large for the purposes of what we are dealing with specific impulse is your God. It is usually a far more critical figure than thrust to weight (and yes, there are exceptions such as combat applications and launch/landing, but overall you will get somewhere faster with a high Isp than with a low Isp, even if the low Isp has a much higher acceleration).

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Whatever the system is, there's also got to be one for morph scale, otherwise Rovers (space fighter variant) and Courier start to loose some luster. If it is cylinder sections, they'd be getting the middle bits. Edit: Courier, not Ring Flier

I'm not quite sure what you mean by 'middle bits'. Unfortunately we do run into a bit of a problem with metallic hydrogen engines and morphs, mainly the amount of fuel that they have to carry. Unfortunately we don't know the full Δv of that fuel because it isn't stated but we are told that they can accelerate at 'up to .25g' for an hour and a half. In the world of physics that is a little vague because a rocket will actually gain acceleration (not just velocity but its actual acceleration increases) as fuel is consumed and mass of the accelerating object is diminished. If we assume an Isp of 1600 and that the figures represent a total Δv of 13.23 km/sec (9.8m*.25*3600*1.5) then 57% of the morph's initial weight needs to be metallic hydrogen. That's an awful lot. If we assume that the total Δv is around 7.5 km/sec (which means we end with an acceleration of around .25 g) then we 'only' need about 38% of the morph to be metallic hydrogen, which is still an awful lot but less than before. In either case it doesn't really seem like you should have enough free space inside the morph for an internal engine of this size. It seems like the modification should be for an external engine or else an internal engine with far less Δv (meaning it runs for far less than an hour and a half). These large requirements become even sillier when you consider that metallic hydrogen engines for ships seem to have a thrust to weight ration somewhere in the neighborhood of 45:1. Using our first figures that means that 57% of the morph is the fuel but only .55% of the morph is the rest of the 'engine' (it gets a little complex because part of that figure should also be representing the stabilizing fields which are not technically considered part of the engine when calculating thrust to weight which is why I put that in quotes). If I'm devoting that much of my morph to fuel why am I devoting such a tiny, tiny amount to trust production? It seems to me like I would want to devote at least 3-6% of the morph to thrust production so that I have between 1.5-3 g's of acceleration, which would be very useful talking off from Mars (which has a surface gravity of .38 G) or Titan (which with a .14 G surface gravity can be overcome with the .25 G metallic hydrogen engine but which sacrifices nearly 60% of its thrust fighting gravity as opposed to 10% of its thrust if the engine produced 1.5 G's). As a result I sort of handwave the internal rocket for morphs in my game and say that aren't really metallic hydrogen engines like those used by spaceships. They are a modified metallic hydrogen engine which have to do something to excite the expanding hydrogen to produce an even greater Isp at the cost of a lower thrust to weight ratio. As a result the exact methods for refueling a ship's metallic hydrogen engine may not work on the internal engines of a morph. Of course this is just my own handwave/houserule. It occurs because I can get a little obsessed with the physics and the minutiae of how things would be working. Since the initial question was the kind of thing my quirk tries to answer I am providing all the details for how to generate a 'real world' answer. If you enjoy the level of 'realism' this kind of process brings, feel free to use my answer and ideas (or even expand off of them). If it is too cumbersome and it is going to get in the way of your enjoyment of the game, feel free to ignore them. The biggest issue is to just be sure you are creating a fun and compelling scene/scenario for you and your players.

Depending on how intensive the field setup need to be, you might be able to use MH powder as the fuel. Simply dump it into an ignition chamber and let it become H2 gas again and you have a rocket. You'd have a lot of options for refueling in that case, with the added bonus that the same fuel powder can be used for many engines. I lean towards something like that because there's some evidence that metallic hydrogen could be metastable, so you wouldn't need EM fields to keep it metallic, you'd need to jolt it somehow to make it revert.

An important question here (that I didn't see answered) was the question of how much of the ship mass is fuel. For a ship launching from the surface into orbit, IRL most of the ship is fuel (this is called the payload fraction). For example, the mass of the space shuttle is twenty times smaller than the mass of the fuel spent getting the shuttle into orbit. Hydrogen is fuel-efficient (high ISP) but low-thrust, so you need less (by mass) compared to rocket fuel. It's also usually very large, which is why metallic hydrogen is so nice, but compressing it like that will actually increase the mass, as you now need bigger equipment to store it. A GEV of course must be small, and isn't expected to get into orbit or do any fancy-pants maneuvers. Having played a ton of Kerbal Space Program, and looking at real-life examples, to support simple maneuvers like changing orbit from the Moon to the Earth, about 20-50% of the mass would be propellant. That's lower if the expected maneuvers are more like RCS, for docking between neighboring ships or brief maneuvers. The GEV is slightly smaller than a soviet BTR-80, so that gives us a ballpark of 15 tons, making its fuel weight /around/ 6 tons. I expect compressing hydrogen to the point of becoming metallic--a feat we haven't achieved yet IRL--probably takes some heavy duty equipment, as well as an easy source of hydrogen and lots of power. I don't think it makes sense to build that onto the GEV itself (it might make sense for larger craft). So either the metallic hydrogen is one or more large tanks with battery power that are manually put on the GEV, or the GEV docks into a larger machine and that machine "fills" it. Because of the complexity, danger, and business reasons, I would assume the latter is most common. So what is the time required to extract 6 tons of hydrogen from the atmosphere or water and compress it to 3,500,000psi? Well it would take about 60 tons of water. On earth, it would take more than 600,000 tons of atmosphere. We don't know how much electrical power it would take, but I imagine it would be "a lot". Requiring a GEV be docked and charged at least 24 hours doesn't seem unreasonable to me. Of course, if you don't need a full tank, it would be easier. And the less you need, the less pressure you need to reach, the less power and time it takes to process. (Note; fuel requirements are hard--they are limited by the mass of hydrogen and our ability to accelerate it. But lower vehicle mass and less maneuvering capability both reduce the fuel tank size. Keeping the same payload ratio, dropping the vehicle mass by half would drop the fuel requirements by more than half, without reducing its performance.)

Semi related: Can you make a metallic version of any gas?

Hydrogen doesn't fit well anywhere, even in the metal group. When you've only got one single electron to hide that naked proton, most of the rules go out the window. Metals are metals because they'd (mostly) rather give up some electrons to get stable orbitals than take them. This works okay because their nuclei are still screened by the rest of their electrons. All those electrons that the metals don't really want just hop around, atom to atom, free to flow with any electric field that's imposed on them. Non-metals want electrons quite a lot, so it's almost impossible to knock them free. You can make solid hydrogen with... moderately absurd pressures, and temperatures a few hairs above absolute zero (14K). It doesn't act like a metal at all, because the H-H bonds are the dominant force, and the electrons are still bound in their orbitals. To actually make a metallic solid you have to force all those nearly-bare protons into such close proximity that the electrons just can't decide what nucleus they're actually part of.

Can you tell me where you read this? Diamonds aren't a create example because carbon is a solid at standard temperature and pressure. Engines in EP don't maintain metallic hydrogen at high pressure, either, because they are electromagnetically stabilized so if it turns out that there's other ways that hydrogen can be kept in a metallic state without high pressure the actual impact is probably somewhat minimal. Without the requirement for EM generators you would probably get a better thrust to weight but since the thrust to weight for MH engines is already pretty good my guess is that they don't take up that much mass in the EP universe.

Lazarus wrote:

. . .3 tons would be almost enough fuel to establish circular orbit around Mars and 1.5 tons would be enough to establish circular orbit around Luna. . .

So this thread has caused me to look around and find some new information. To take up an orbit 50 km above the surface of Luna a GEV would need 4.92 km/s of Δv which requires about 4 tons of metallic hydrogen remass and for Mars it would take about 17.9 km/s of Δv which requires about 10.5 tons of metallic hydrogen. An awful lot of that is caused by the fact that the GEV's rocket produces only .1 G of thrust. If it was capable of the 3 G of thrust that a standard ship has it would only require 2 tons and 4 tons of metallic hydrogen respectively. Because of that difference I have to kind of assume that the GEV probably uses a modified metallic hydrogen engine similar to the modified engine that I think morph's have to use. That explains the much lower thrust but probably results in a much higher specific impulse.

Lazarus wrote:

the amount of the ship dedicated to fuel is really difficult to estimate because it depends an awful lot on the needs/design of the vehicle.

Agreed on that. I have to imagine on a GEV, the purpose would be to launch from an airless, low-gravity moon, or for minor maneuvers close to a mother ship. Having a full-blown rocket would seem to defeat the purpose of having a dedicated roving vehicle. Something smaller would make sense though--imagine of the lunar buggies had turbo boost.

To reach low Earth orbit using an engine with a specific impulse of 450 (Hydrogen-Oxygen rocket) takes about 89% of the vehicle's mass.[/quote] You focus a lot on ISP, but not on TWR. Remember, if your TWR is below 1, you could have an ISP of a million and it won't do you a lick of good. For a GEV's rocket to be useful on a planet or moon, it will need to have some oomph, and that limits the maximum feasible ISP. [quote wrote:

Hydrogen isn't much of anything.

ISP is limited by the mass of the remass. Hydrogen, being the lightest of the elements, is ideal for maximizing ISP. You can of course burn it in lower-ISP methods though. Atomic Rockets goes into way too much detail: http://www.projectrho.com/public_html/rocket/engines.php (if you search for exhaust velocity or hydrogen)

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That's actually makes about 40% of the vehicle its fuel weight (assuming 15 tons is the combined weight of payload and fuel) for a Δv of 8.01 km/s. That's actually quite a lot. That would get you into Earth orbit if Earth didn't have an atmosphere (Δv to reach circular orbit around Earth ignoring atmosphere is about 7.9 km/s). 3 tons would be almost enough fuel to establish circular orbit around Mars and 1.5 tons would be enough to establish circular orbit around Luna. My guess is you are looking at around 1 ton of metallic hydrogen since I don't think a GEV's engine is even good enough to establish orbit around Luna but you might be looking at closer to 3 tons. I doubt you are looking at 6 tons based on the performance characteristics you were outlining.

As before, are you tempering your ISP values with the necessary thrust to overcome gravity?

Quote:

You seem to be working on the idea of turning the hydrogen metallic inside the engine. I'm not saying you can't do it that way but it seems to me to add a lot of complication, sort of like refining petroleum and feeding the distillate straight into the gas tank of a car.

Maybe I wasn't clear, but I agree with you; the conversion inside of the GEV would probably not be reasonable. I assume there would be a refinery or ISRU on-site the GEV would "plug into". By "in situ", I mean on the moon or whatever where the GEV is operating. Not loaded on the GEV itself.

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It is very unlikely you would reduce the fuel requirements by more than half without reducing performance.

By fuel requirements, I mean the mission requirements which would determine how much fuel you need; i.e., if you decide instead of your GEV needing to go 20 km/s it only needs to go 10 km/s, you can load less fuel on it.

Lazarus wrote:

You are actually incorrect in the assumption that your Thrust to Weight has to exceed gravity. For one thing it completely ignores assisted launches.

That's true. For this example though, I assumed the GEV, which is noted as a ground vehicle, has at least enough thrust to reach escape velocity from a Luna-sized body, without the benefit of an outside assist.

Quote:

Hydrogen gas feeds through an 'compression chamber' where it is stripped of its electrons, excited, and then channeled through an electromagnetic choke.

Honestly, this is what I had assumed all along. It makes a lot more sense than any sort of conventional 'burning rocket' sort of design. Could be I just forgot what the book actually says :P Ultimately, metallic hydrogen is a propellant, so it could be used in just about any sort of engine you might imagine. (I actually sort of blacked out on that one too--metallic hydrogen and anti-matter aren't mutually exclusive in my mind, since one is a propellant, one is a fuel source, and neither are an engine type).

A cursory google search shows the real life metallic hydrogen rocket design is basically a bottle filled with metallic hydrogen which they just let decompress out. Ostensibly terrible, unless the alternative is an RP-1 rocket. Are you referencing a different design I don't know about?

hey MAD Crab, I think it would appear that the real world is forgotten or overlooked here for it's inconvenience, good try though, and good luck getting it across. Metallic Hydrogen is not solid, it's still a liquid state more or less. There is the subject discussed years ago of Metastable Hydrogen now days thrown in the same basket. The idea of Metastable Hydrogen was to compress it to a solid then use it like a solid rocket motor or use lasers to strip it inside the motor housing.

nostromo1a1 wrote:

hey MAD Crab, I think it would appear that the real world is forgotten or overlooked here for it's inconvenience, good try though, and good luck getting it across. Metallic Hydrogen is not solid, it's still a liquid state more or less. .

Nothing is being forgotten or overlooked (except perhaps manners). Metallic hydrogen may be liquid depending upon temperature and pressure. However, most phase state diagrams that I have been able to locate indicate that the absolute lowest temperature is still above room temperature (I believe the absolute best I found was about 320K or about 110 F. What is more, those graphs are extremely theoretical. We are still not really sure what they are like because we aren't producing metallic hydrogen in any real quantities that lets us be sure what those graphs will ultimately look like. So why do I (and others) work on the idea that the hydrogen is solid when there is a possibility that it is liquid? Because the game designers already stated that the fuel used in the engine is solid. It is right there in the book where it says 'Metallic Hydrogen Rocket (MH): Metallic hydrogen is a solid form of hydrogen created using exceedingly high pressures.' Maybe it turns out that the graphs are wrong and the minimum temperature is higher. Maybe it is because the metallic hydrogen is under higher pressure than that particular point and as a result the transition point requires a higher temperature. Maybe the electromagnetic stabilization does something that causes the metallic hydrogen to be solid at a higher temperature for the same reason it is remaining metallic at lower pressures. Whatever the reason, the game is making an assumption and we are trying to remain within that assumption. This isn't 'forgetting or overlooking the real world' because in the real world we don't have metallic hydrogen lying about, so unless you can produce some please stop saying 'this is how it is'. Yes, you may have some diagrams showing a lower temperature for transition between solid and liquid metallic hydrogen but at present those are at odds with graphs from other perfectly reputable (please note, I am not saying 'more reputable'. Your scientists may be perfectly reputable, but so are a lot of others who don't agree with you) scientists. And please realize, I'm not saying you can't suggest that perhaps people houserule something. I myself have talked several times about houseruling aspects of metallic hydrogen engines to make them work better and to explain certain inconsistencies that occur when they are used by morphs. However, when I do that you may notice I am very clear that what I'm proposing is a houserule. I don't say 'you can't just say that morphs use standard metallic hydrogen rockets because of these problems'. I say 'I see these problems and this houserule is a solution'. If you want to suggest a houserule that ships use liquid metallic hydrogen instead of solid then go right ahead. Just don't try and act like we have to do it that way.

ThatWhichNeverWas wrote:

In my headcannon, MH is stored/pumped as a superfine powder, magnetically suspended in the tank. Fuel is moved to the Nozzle by altering the configuration of the field. Showing my ignorance here , but why is a "hybrid" MH engine necessary? Because it's a pure propellant, a given amount of MH will provide a set ISP, with thrust scaling to the size of the nozzle, or rather how much propellant can be expelled at once. I'm also not entirely sure why the mass requirements are problematic for morphs, or at least those designed to incorporate them from the get go.

The hybrid engine is necessary exactly because of the mass requirements. Metallic hydrogen has a theoretical specific impulse of around 1600. Without some sort of extra energy entering the equation (such as the conversion to a plasma state and the use of an electromagnetic choke) the ISP remains unchanged no matter what you do. This means that to get the performance stated for internal rocket engines the over half the morph's weight would need to be reaction mass. Now you are correct that someone could build a dedicated space travel morph that has large amounts of remass like that but if that was the case why does it have such tiny nozzles? It actually has to use significantly more remass when trying to launch from surfaces such as the Luna because of the low acceleration. Using Luna as an example a morph would require about 18% of its mass to launch from the surface to a 50 km orbit around Luna with .25 G of acceleration. It would only require about 13% with 3 G of acceleration. Using some back of the envelope guesstimate calculations the difference in nozzles between .25 G and 3 G is less than 5%, so there is no real reason for a morph designed for space travel to have the lower acceleration of the internal rocket motor unless it has a lower thrust to weight ratio than a standard metallic hydrogen engine (and the primary reason for that would be because of some attempt to increase your ISP). Additionally, while that much reaction mass is tenable for a dedicated morph the robotic implant can be put into any synth morph. Assuming nothing else changed on that morph the new morph would need to be around 2.3 times more massive than the original morph to accommodate that much remass and it seems like that should be mentioned in the description (of course in fairness it should also be mentioned that it isn't a pure metallic hydrogen engine if it is a hybrid like my assumption).

Lazarus wrote:

The hybrid engine is necessary exactly because of the mass requirements. … This means that to get the performance stated for internal rocket engines the over half the morph's weight would need to be reaction mass. Now you are correct that someone could build a dedicated space travel morph that has large amounts of remass like that but if that was the case why does it have such tiny nozzles? It actually has to use significantly more remass when trying to launch from surfaces such as the Luna because of the low acceleration. … Using some back of the envelope guesstimate calculations the difference in nozzles between .25 G and 3 G is less than 5%, so there is no real reason for a morph designed for space travel to have the lower acceleration of the internal rocket motor unless it has a lower thrust to weight ratio than a standard metallic hydrogen engine (and the primary reason for that would be because of some attempt to increase your ISP).

I can think of two reasons why a smaller nozzle could make sense: The engine as written isn't intended for orbital insertion, but rather travel in microgravity, and a larger nozzle means more exhaust, increasing the risk of damage to the morph. The latter combines neatly with the admitadly odd limit on acceleration – the limit is [i]programmed[/i] safety feature, not a physical element of the engine. Extending from this, I think it's perfectly reasonable for us to simply say that it's a pure MH engine (preserving the ISP), with a nozzle capable of up to 3g accelerations but [i]unlocking[/i] it requires a Piloting or Freefall check.

Lazarus wrote:

Additionally, while that much reaction mass is tenable for a dedicated morph the robotic implant can be put into any synth morph. Assuming nothing else changed on that morph the new morph would need to be around 2.3 times more massive than the original morph to accommodate that much remass and it seems like that should be mentioned in the description (of course in fairness it should also be mentioned that it isn't a pure metallic hydrogen engine if it is a hybrid like my assumption).

I suppose the question here is how much the augment alters the morph's basic structure, since Morph mass is never mentioned in any case.

haha I was just about to post about this