Vintage MS Specs: What Does The Zack Weigh?

[toysdream]

So over the last couple of years, I've littered this poor board with a series of little threads about One Year War-era mobile suit specs. To make a long story short, these are basically a Big Confusing Mess. Just for ease of access, here are some of the notable ones related to mobile suit weights...

Heavy Mobile Suits
MSV-R and Vintage MS Specs
Vintage MS Specs: 2013 Edition
Vintage MS Specs Forever

This gets especially complicated where First Gundam and the MSV series are concerned because, after all these decades, we still don't have a single set of official specs. Instead, we basically have three competing sources that keep getting mixed and matched and swapped around.

Entertainment Bible 1: Published in 1989, and based in part on The Anime's Zeta Gundam Part 3. This gave us full specs for most of the mecha from First Gundam and the MSV and MS-X series.

Gundam Mechanics: A card file series published by Hobby Japan, starting in 1998. The specs from this series were also featured in Hobby Japan's Gundam RPG books around the same time. For the most part, the new specs here just filled in gaps left by Entertainment Bible 1.

MS Encyclopedia 98: Also in 1998, a new edition of the MS Encyclopedia listed heights and base weights for every mobile suit. In some cases, these agreed with those listed in Entertainment Bible 1 and/or Gundam Mechanics, but in some cases they didn't.


Now that Bandai is releasing lovely new HG-UC versions of the old MSV machines, we're seeing these conflicts at work in the accompanying specs. In particular, the MS-06R-1A and MS-06R-2 specs are a mishmash of figures from these competing sources - base weights from the MS Encyclopedia, thruster outputs and full weights from Gundam Mechanics, assorted bits from Entertainment Bible 1 where available. Here's how they just listed the MS-06R-2:

Base weight: 58.2t
Full weight: 75.0t
Generator output: 1,340 kW
Thruster output: 60,000 kg

Those are basically the Gundam Mechanics specs, but with the base weight from MS Encyclopedia 98. The end result, if you've been following the arcana of mobile suit weight math, is an extremely small propellant capacity!

Briefly put, the difference between base weight and full weight - 16.8 tons in this case - equals weapons payload plus propellant. The "mass ratio" specs that were included in the Zeta and ZZ specs were a measurement of full weight divided by (base weight + weapons payload), thus enabling us to figure out the precise payload and propellant weights. In almost every case, the payload figures turn out to be whole numbers of tons, suggesting that they're actually estimates - 5.0 tons for the GM II, 6.0 tons for the Hizack and Galbaldy Beta, so on and so forth.

At the start of Zeta Gundam, most of the machines we see - the Nemo, Hizack, Galbaldy Beta, Rick Dias, Gundam Mark II, etc - have about 5-6 tons of weapons payload and 15-16 tons of propellant. (Thus, the difference between their base and full weights is about 20-22 tons; the GM II is a little below this range, the Marasai a little above.)

Compared to this, the new R-2 specs put it way below trend for the older Zeta suits, to say nothing of the truly heroic propellant capacities we've seen assigned to some other vintage mobile suits. But it's not entirely alone...


Although MS Encyclopedia 98 shaved five tons off its base weight, the specs listed for the MS-06R-1A in Entertainment Bible 1 were similarly skimpy:

Base weight: 61.8t
Full weight: 76.8t

That's a difference of just 15.0 tons. What's more, the old MSV info said that the R-2 type had 18% more propellant than the R-1A, which suggests the following breakdown:

MS-06R-1A: 61.8t + 5.0t payload + 10.0t propellant = 76.8t
MS-06R-2: 58.2t + 5.0t payload + 11.8t propellant = 75.0t

And we can find a few more examples of teeny tiny propellant capacities in the vintage MS family tree:

MS-09: 62.6t + 6.0t payload + 11.3t propellant = 79.9t
MS-14B: 53.5t + 6.0t payload + 17.3t propellant = 76.8t
YMS-15: 52.7t + 5.0t payload + 10.9t propellant = 68.6t

Dom full weight as per HG-UC kit and latest MS Encyclopedia; Dom and Gelgoog payloads are guesses based on Dowadge and Galbaldy Beta; Gyan payload is guess based on GM and R-Jarja.

By most standards, these are pretty lousy numbers, and it's hard to square them with the specs of other vintage mobile suits. On the other hand, this makes the higher capacities of the Zeta suits a clear improvement...

-- Mark

[Zeonista]

Heh, based on much of the animation we've seen of OYW MS, the load-out weights are ridiculously low. That's not enough weight for the weapons, let alone the fuel! Obviously no one was using MEKTON rules to calculate fuel & weapon weights, eh Mark? Although the anime for the first series seems to justify fuel economy; AMBAC uses movement instead of apogee thrust, and in the Side 6 fight Amuro mostly circles & spins in place to fight the Doms, instead of chasing them all over the battlefield. The most the White Base MS move is when they advance to destroy the remaining Zeon cruisers.

This makes me more likely to support the idea that MS tech in terms of nerd-physics was an evolving idea in the first decade of Gundam history, before Gundam Sentinel and War in the Pocket yanked things into truly proportionate consideration. After all, the guys who knocked together MS Gundam on the fly were interested in cool action first, and developed stats later as some fun extras for the fans, right? So the original MS & MSV stats got jotted down by people who didn't exactly work at JPL. And once in print, they were enshrined forever in the otaku rote memory of Holy MS Statistics. But by the time of Zeta, the mechanical designers had some more experience, and could allow for a different load scheme. The stat quoted for early Gryps War MS is accurate, in as much that their weaponry was mostly an energy ranged weapon and an energy melee weapon. The extra fuel would be allowed because of the technology that permitted lower-weight armor and power plants. Ergo, more fuel & faster MS as depicted in the anime.

[toysdream]

Everything related to mobile suits is ridiculously light, though. If you doubled everything across the board, it might start to seem slightly less absurd, but under the circumstances the weapon weights could still be *proportionally* reasonable.

As for scientific plausibility, the figures in Gundam Century - which the MSV writeups are referencing - are actually a lot more sensible than the later ones in Zeta Gundam. I'd say they kind of walked the physics accuracy backwards a bit with the Zeta specs, but now we're stuck with it.

-- Mark

[Zeonista]

I am not sure the Zeta allowances are backward. If MS are like aircraft, then the dry weight to loaded weight gap should be small. If MS are like tanks, then the dry weight and loaded weight gap would be closer. Tanks don't move over half speed unless they are in combat, then they go to full speed versus enemies with similar weapons. (In the infantry support role without AT weapons involved, they slow down more to track two-legged targets.) Tanks burn fuel at an impressive rate, but not so much as aircraft, so a basic combat can be played out without sweating the fuel gauge. Aircraft move fast, even at cruising speed, and acceleration to combat (or in space, de-acceleration) makes them burn a lot of fuel very quickly!

Of course, that is pre-supposing MS are like conventional vehicles in that allocation to begin with. If they are an entirely new class of vehicles (as per the story), then a new ratio of performance weights should be established. The role of a MS might also determine its loaded weight specs as well. The MS-14B Gelgoog is a battlefield superiority machine issued to skilled pilots, so the highest amount of propellent listed makes sense. The Gyan doesn't have as much because it's a close-combat brawler, so its fuel consumption is mainly used for quickly closing to the target, without a lot of positional maneuvering.

[Arbiter GUNDAM]

Where is all the fuel/propellant kept anyway?

[toysdream]

Mobile suits aren't like tanks or aircraft; they're spacecraft, which have a whole other set of parameters. Unlike a tank with its treads, or an aircraft with its wings, they have no way to move without using their rocket engines, and unlike an aircraft - whose jet engines mix their fuel with external air - everything that comes out of that rocket engine has to be loaded into the spacecraft when it takes off.

So rocket-powered spacecraft, even ones with pretty high-efficiency rocket engines like those of mobile suits, need to carry a lot of propellant! The fuel requirements of tanks or aircraft are minute by comparison.

As far as propellant tank locations, sometimes they have clearly identified cylindrical tanks, and sometimes the internal tanks are shown in cutaways or model kits, but otherwise it's mostly guesswork. In the case of the Zaku series, there's some propellant space inside the chest, some in the backpack (depending on the type), and a lot in the legs - if the MG kits are to be believed, much of it in the thighs, which are enlarged in the MS-06R type.

-- Mark

[Zeonista]

Looking at the MS as spacecraft does explain the need to carry tons of fuel yes, in the probable ratio required to sustain flight and combat capability. In that respect I would say the more fuel, the better. (I will save the catgirls by not asking whether the amount of fuel required is actually adequate for its intended use. ) It would make the various external drop tank configurations and base jabbers a definite practical article!

On the location of fuel tanks, a MS pilot should probably not think too much about the close proximity of cockpit, Minovsky plant, and torso fuel tank. I would say the backpack and rear torso would hold most of the fuel, probably adding to the size of the backpacks in later UC history, although there also has to be some space for all those larger rocket motors. We know the fuel is there, since any attack which penetrates the rear torso and/or backpack produces the obligatory explosion. I never thought about fuel for calf and foot thrusters being stored in thighs, but it makes obvious sense in consideration.

[Brave Fencer Kirby]

Actually, since the stuff is propellant (aka "reaction mass") rather than fuel, it's likely that it's not combustible at all. Propellant is the stuff that you feed into your rocket nozzle so that it's heated up and thrown out the back in order to propel the ship forward via Newton's third law (the "equal and opposite reaction" one). Fuel is what you use to heat up the propellant. In chemical rockets fuel and propellant are the same stuff (eg, the space shuttle used liquid hydrogen and liquid oxygen; when they're mixed in the combustion chamber, they explode, which provides the energy needed to send the mix out the exhaust nozzle, which provides the thrust), but in nuclear rockets like Gundam uses the fuel would be the stuff in the reactor (deuterium and helium-3 in Gundam's case, IIRC) and the propellant would be... something else; Gundam doesn't specify, to my knowledge.

The only two real requirements for propellant are low atomic weight (which makes it more efficient) and high density (which makes it easier to store); making it something explosive isn't necessary, and should probably be avoided if possible for obvious reasons. Of course, even if it's not explosive due to its chemical composition, your propellant is still going to be extremely hot and at extremely high pressure while it's making its way from the reactor to the thrusters, which is an explosive combination in and of itself. A boiler explosion is decidedly non-combustible water acting explosively due to the heat and pressure involved, after all. The inevitable-torso-explosion could also be caused by a breach of the reactor vessel itself -- even if it doesn't involve an actual detonation from a beam weapon/Minovsky reactor interaction, releasing the plasma inside a fusion reactor is going to cause a sizable mess.

[Nebfer]

Well I'm not expert of Rocket engines, However the most effective Nuclear rocket fuel would be Hydrogen, at lest form a efficiency stand point, though it's handling and storage problems makes this a bit problematic (mostly by being not dense, flammability is largely moot be it's use in space, though in a pressure vessel (I.e. Earth or colony) well...). Methane and Ammonia are viable contenders, as is Water (but water is only half the ISP as H2), though Methane produces carbon as a byproduct which can supposedly clog the pipes, Ammonia is good as it dose not produce problematic byproducts and is fairly dense (~ eight times that of regular hydrogen IIRC).

Interestingly enough IIRC A solid core Nuclear rocket engine can have enough nuclear fuel to undergo fission (if it was all in the same spot).

The ISP for Gundam Engines seem to be above 2,000, though likely less than 6,000.
An ISP of 3,500, and a fuel fraction of ~15% (roughly 10 tons in the Zaku IIs case), would net about 5km/s of Delta V (at that you would need about 26% mass ratio for 10km/s or easily reach earths orbit), If I got it right.
A intersting ISP, fuel fraction, & Delta V chart can be found here.

[Brave Fencer Kirby]

The ISP for Gundam Engines seem to be above 2,000, though likely less than 6,000.

How'd you come to that conclusion? Not criticizing, I'm just wondering what your logic is.

[Nebfer]

The ISP for Gundam Engines seem to be above 2,000, though likely less than 6,000.

How'd you come to that conclusion? Not criticizing, I'm just wondering what your logic is.

Well lets see Nuclear engines typically have higher ISPs than Regular rocket engines. To get something like 5km/s Delta V out of 10 tons of reaction mass on a Zakus Mass, is going to result in an ISP of around 3,500...

Theirs actually a few ways to do these, one of the common ways is Delta V = Exhaust velocity * ln (full mass / empty mass)

Exhaust velocity = ISP * 9.8
ln = Natural log
Full mass is 76.8 tons
Empty mass is 66.8 tons
So 3500*9.8*ln(76.8/66.8 ) = ~4,785 m/s of Delta V
I believe at .68Gs (6.67m/s) it would (Zaku II R1A) reach that velocity is roughly 12 min.

Alternatively you can go to these web pages for ISP/Delta V calculators
http://www.strout.net/info/science/delta-v/
http://www.quantumg.net/rocketeq.html
Also
http://en.wikipedia.org/wiki/Rocket_equation

ISPs of 2,000 to 6,000 is random but reasonable (it's not out of reach in some engine designs, don't think they use them though) to get relatively decent Delta Vs and not making it to easy to reach orbital velocity (~7.8ish km/s +2ish km/s for drag functions, though I would think a MS would have a bit higher drag penalty...). For example an ISP of 2,000 will result in said Zaku II to have a DV of 2.7km/s, 6,000 results in 8.2km/s.
For easy interplanetary numbers I could of used the values you get for Battletech Aerospace fighters (an ASF with that same 10 tons of reaction mass would have a Delta V of 240km/s, and a ISP in the six digits).

[toysdream]

I guess we've thrown around some delta-v figures for mobile suits and warships in previous threads. We have less to go on for specific impulse specs - there are some hints on this in Gundam Century, which indicates that most One Year War mobile suits use chemical rockets with a specific impulse of roughly 280-420 seconds; the Rick Dom is virtually the only one with nuclear thermal rocket engines, which are said to have 2-3 times the fuel efficiency of chemical rockets and would thus come in about 850 seconds.

Given that mobile suits never seem to run out of propellant in the animation - let alone after just 30 seconds of full thrust, as Gundam Century would indicate - we can probably assume they all use nuclear thermal rockets, and that these have a much better specific impulse, along the lines of Nebfer's suggestions.

-- Mark

[Nebfer]

I guess we've thrown around some delta-v figures for mobile suits and warships in previous threads. We have less to go on for specific impulse specs - there are some hints on this in Gundam Century, which indicates that most One Year War mobile suits use chemical rockets with a specific impulse of roughly 280-420 seconds; the Rick Dom is virtually the only one with nuclear thermal rocket engines, which are said to have 2-3 times the fuel efficiency of chemical rockets and would thus come in about 850 seconds.

Given that mobile suits never seem to run out of propellant in the animation - let alone after just 30 seconds of full thrust, as Gundam Century would indicate - we can probably assume they all use nuclear thermal rockets, and that these have a much better specific impulse, along the lines of Nebfer's suggestions.

-- Mark

IIRC is their not a mention of one of the Zaku line having like a 15ish minute burn time with it's engines?

But as you said running out of fuel is some what rare in gundam, just as rare is mentions of reaching the point of no return in regards to fuel limits. This seems to indicate that fuel endurance is not measured in seconds or a few minutes. And given that we generally know how much fuel a mobile suit has we can at lest get a rough idea of their ISP


A few examples based of a 3,000 to 3,500 ISP
Zaku II 73.7 max load with a 10 ton fuel load, 3,500 ISP, gives a 5km/s DV and 14.4 min at it's .59Gs of thrust
Rick Dom at 78.6 tons full load with a 28 ton fuel load with a ISP of 3,000 gives us a DV of 12.95km/s, with an accel rate of .67G providing some 32 mins of endurance
GM 58.8 tons full, with 11 tons fuel an 3,400 ISP gives 6.9km/s of DV and a and a .94 accel. rate provides 12.5 min of endurance
Hizack At 59.6t full load and ~14.8 tons of fuel, and assuming a 3,220 ISP has a DV of 9km/s, with it's 1.09G acceleration rate allowing for a 14 min burn time
GM III 56.2 tons full with 11.5 tons fuel, and a 3,500 ISP gives 7.85km/s of DV a 1.45G accel only allows a 9.2 minute endurance.
Jegan 47.3 tons loaded with 20 tons fuel and a ISP of 3,000 gives us a DV of 16.16km/s it's 1.03 acell rate allows for 26.6 minutes of full thrust (an ISP of 3,500 provides 18.85km/s of DV and 2,000 gives 10.77km/s by the way)

Not exactly perfect as I doubt units like the Jegan can reach earth orbit from the ground...
Provides some interesting perspectives like if accurate the Zaku II seemingly having a better endurance (mostly due to it's low thrust) than the GM but the GM having better performance.
Though the numbers are largely pulled out of thin air...

[toysdream]

It's actually really easy to figure out the duration of maximum thrust, if you know the propellant weight and specific impulse - just multiply the propellant by the Isp, and then divide by thrust (in tons). In other words, if your rocket engine has an Isp of 1000 seconds, then one ton of propellant can produce one ton of thrust for 1000 seconds. (This is where Gundam's unscientific practice of listing thrust in kg, rather than Newtons, actually simplifies the math.)

Thus the Hizack, which has 14.9 tons of propellant and 64,800 kg of thrust, can sustain full thrust for (14.8/64. x Isp, or .2284 x Isp. So with an Isp of 3000 seconds, that's a duration of 685 seconds (11.4 minutes); with an Isp of 3500 seconds, a duration of 799 seconds (13.3 minutes).


As you mention, the one specific claim we've been given concerns the MS-06R-1A Zaku II. As per the first MSV book, "the fuel that can be used in combat is limited to 15 minutes at full thrust." Since that's 15 minutes combat duration, there should also be an extra margin for launching, landing, and traveling to and from the combat zone.

Despite what I suggested in the first post, I think 10 tons of propellant is probably too low for the R-1A. The standard Zaku has at least 10 tons, and the Hizack has almost 15, so I think the R-1A should probably be toward the latter end of that range. Going by current official specs, we have a base weight of 56.8 tons and a full weight of 76.8 tons, so let's assume for the sake of argument that it has 15 tons of propellant (56.8t base + 5.0t weapons + 15.0t propellant = 76.8t).

As we've previously discussed, there are a bunch of estimates for its thrust, including 49,800 kg (Entertainment Bible 1) and 52,000 kg (Gundam Mechanics). But since it's supposed to be somewhat under-fueled, the R-1A really should have a lower propellant-to-thrust ratio than the Zaku or Hizack - you'll note that the Hizack has about 50% more thrust and 50% more propellant than the MS-06F Zaku II, so the ratio is similar for both machines. So I'll use my pet figure of 76,800 kg for the MS-06R-1A's total thrust.


And so, a very rough estimate:

76.8 tons of thrust x 900 seconds duration / 15.0 tons of propellant = 4,608 seconds specific impulse

This estimate is inflated a bit by my high thrust figure - if you used the EB1 or Gundam Mechanics thrust, you'd end up with an Isp closer to 3000 seconds. On the other hand, the Isp should also be adjusted up to allow for a few more minutes of launch, landing, and travel acceleration. But if we ignore those factors for the moment, we can generate lots more comparative figures...

MS-06F Zaku II: 10.2t x 4608 sec / 43.0t = 1093 sec (18.2 minutes)
RMS-106 Hizack: 14.8t x 4608 sec / 64.8t = 1052 sec (17.5 minutes)
MSZ-006 Zeta Gundam: 25.6t x 4608 sec / 112.6t = 1048 sec (17.5 minutes)

Interesting. On the one hand, we can assume that engine performance (and thus Isp) increases over time. On the other hand, this shows that a lot of mobile suits have a similar propellant-to-thrust ratio, with about 1 ton of propellant for every 4,000 kg of thust. By my numbers, the MS-06R-1A carries 1 ton for every 5,000 kg of thrust, so perhaps that's representative of a "lightly fueled" mobile suit.

Another example would be the ReGelgu - it has 172,600 kg of thrust and 34.9 tons of propellant, which is 4,950 kg of thrust per ton of propellant. Perhaps that's what the ZZ specs meant when they said that the ReGelgu's high mass ratio was necessary "to cover the poor performance of the rocket engines."

-- Mark

[toysdream]

As a bit of visual reference, here's a scaled comparison of a bunch of mobile suits that have clearly visible propellant tanks:

http://www.ultimatemark.com/gundam/imag ... arison.jpg

I've grayed out the armament and propellant weights in those cases where I had to guess.

Of particular interest is the EWAC-Zack, which as you can see has exactly 13.0 tons more propellant than the Hizack. Since the only change is the addition of two extra tanks on its backpack, this gives us a clear idea what a 6.5-ton propellant tank looks like.

You'll note that the MS-06S Zaku II has 30% more propellant than the MS-06F, exactly covering its 30% increase in thrust.

As I've previously noted, the latest MS Encyclopedia lists the same base weight for the MS-14A and MS-14B versions of the Gelgoog, suggesting that the MS-14B specs may actually reflect the backpack-less MS-14S. In this case, the MS-14S would have exactly 30% more thrust than the standard MS-14A, accompanied by a similar increase in propellant.

-- Mark