# The great conversion of MegaTraveller starships back to High Guard

#### Spirit of 1977

##### Cosmic Mongoose
This thread is in response to views that MegaTraveller (MT) made too many compromises from its Classic Traveller (CT) origins. Specifically, MT starship construction was initially based upon Book 5 High Guard (HG), but made many changes that did not sit well with many older players. While my initial view was that the MT changes were fine, I was intrigued enough to take up the challenge of trying to bring MT back to something more like HG. The results are very interesting, as I will show in future posts.

TL;DR: Unless you are very familiar with MegaTraveller and CT High Guard starship construction rules, you can safely ignore all of this!

In preparation for some example starships I will be posting based upon MegaTraveller (MT) rules but modified to retain as much of the CT High Guard (HG) rules as possible, these are the conversion rules I am using. You will need to be familiar with both HG and MT. I would appreciate any commentary or error detection so that I may incorporate them into my examples.

HG to MT assumptions (note that ton always means 1000 kg; the volume D-ton will always be specified and equals 13.5 kl):

1) Maneuver Drives (MD) and Power Plants (PP): HG assumes that MDs consume a certain volume of hull per G rating, and PPs of sufficient size will both power the MD and supply excess energy points (EP), and Striker tells us that 1 EP = 250 MW.

In MT, PPs supply some fixed amount of MWs. MDs are constructed from maneuver units with fixed parameters, except for the actual thrust produced. This is because MT wanted to maintain the MD = % of hull logic. We will dispose of this, and by consulting the grav drive data for vehicles, it is easy to see that a maneuver unit (anti-grav or thruster) produces 675 tons of thrust. We will then compute Gs of thrust as (tons of maneuver thrust)/(loaded craft tonnage). This produces interesting results, particularly at high TLs. Note that under this construction, 1G MDs may not be able to land on worlds with gravity > 1G, though Agility would allow it.

1a) Agility: HG Agility (<= max Gs of acceleration) = excess EPs per 100 D-tons of hull. MT Agility = 5.4 x excess MW / loaded tons. While these may seem unrelated, the MT formula is a completely faithful translation of the HG formula assuming that 1 D-ton in HG = 13.5 tons on average in MT. Thus the move from HG to MT is from volume to mass, which is appropriate, and all acceleration calculations in my examples use mass. This produces different results from HG, but they make sense (e.g., lower TL craft require larger PPs to obtain maximum Agility).

1b) Minimum PP Size: In HG, the PP number had to be the larger of the MD number or Jump number. To replicate this, the minimum size of the PP that powers the MD is 67.5 MW per MT jump unit. The PP is assumed to run while in jumpspace and reinforces a 30 day fuel requirement. Such a PP may have excess MWs vis a vis the MD and thus might add to Agility.

2) Fuel Usage: MT PP fuel consumption is much higher than HG, and so jump fuel was reduced to compensate. For these examples, we restore the HG jump fuel requirement of 10% hull volume x jump number. It turns out that once a MT PP is at least 1 D-ton and gets the full 3x efficiency bonus, MT PPs and HG PPs are almost identical with respect to MW, tons, and D-tons. Only fuel consumption is different: MT fusion PPs consume 6.67x the fuel of HG PPs. Thus, all that is required to replicate HG is to multiply MT fuel consumption by 0.15. I'm still debating whether this should apply to all fusion PPs, including vehicles, but I might do so given the alternative of fuel cells produces interesting tradeoffs (this is otherwise beyond the scope of this exercise).

3) Armor Volume: There is a strong view that armor ought to take up hull space. I'm adding this back though honestly it does not matter much for adventure class ships. It is likely much more meaningful for capital ships, which may feature in later examples.

In HG, armor A is a factor starting at 0. Armor takes up V(1+A)% of hull volume, where V=4 for TL 7-9, 3 for TL 10-11, 2 for TL 12-13, and 1 for TL 14-15. For MT, the minimum Armor Factor is 40 for spacecraft, corresponding to a mass multiplier of 33.6 for hard steel in Striker (and MT). Let A be our Armor Factor >40 and M the corresponding mass multiplier. Then armor takes up the following percentage of the hull: [8 x Armor Type Mass Multiplier x M/33.6]%. The corresponding V values for MT are 3.5 for TL 7, 2.8 for TL 9, 2.5 for TL 10, 2.1 for TL 12, and 1.1 for TL 14, so rather close overall and more generous at lower TLs. The advantage of this MT method is we can compute armor density and perhaps use that.

4) Bridge: HG imposed a 2% of hull volume bridge requirement, 20 D-tons minimum. I am using a more flexible rule via Duty Stations. A Duty Station is 2 D-tons (like a small stateroom), and all starships require a minimum of (10/active crew) Duty Stations. The active crew requirement is based upon the MT rules for crew count and could produce deviations from the 2% of hull requirement, which I think is fine given the better model of Duty Stations. But for ships <=1000 D-ton, the bridge is always 20 D-tons (10 Duty Stations).

5) Computers: HG computers were gigantic, likely including other systems like control panels, comms, and sensors. In MT, the latter systems are explicit and computers are much smaller. We use the MT rules without modification, which likely results in lower overall volume than HG.

Example starships are forthcoming!

2) MegaTraveller craft design owes many of its foibles to it being a derivative of Striker. Fuel usage, but more specifically the power requirements of drives and weapons being *really high*, is a direct pull from Striker. The problem arose because Striker treated its starship power numbers as approximations to fit ship weaponry and armor into the tech and power progression of Striker's vehicular weaponry and armor. Approximations that MegaTraveller then read as gospel.

The power slice fix, late in MegaTraveller in a Challenge article, refutes the 30 day "requirement" in very specific ways, and makes many CT designs possible in MT that are not possible with just the Craft Design chapter and reader's assumptions.

4) and 5) MT splits the CT Bridge volume into *many* explicit slices, not just things that are involved in command and control. Most notably, airlocks and life support (including gravitics) are also part of that, as they are not at all part of CT design.

2) MegaTraveller craft design owes many of its foibles to it being a derivative of Striker. Fuel usage, but more specifically the power requirements of drives and weapons being *really high*, is a direct pull from Striker. The problem arose because Striker treated its starship power numbers as approximations to fit ship weaponry and armor into the tech and power progression of Striker's vehicular weaponry and armor. Approximations that MegaTraveller then read as gospel.

The power slice fix, late in MegaTraveller in a Challenge article, refutes the 30 day "requirement" in very specific ways, and makes many CT designs possible in MT that are not possible with just the Craft Design chapter and reader's assumptions.

4) and 5) MT splits the CT Bridge volume into *many* explicit slices, not just things that are involved in command and control. Most notably, airlocks and life support (including gravitics) are also part of that, as they are not at all part of CT design.
Yes, I am aware of all these points. The purpose of this exercise is to make the smallest number of changes to MT to reproduce results closer to CT/HG. You definitely can make MT versions of nearly all classic models, but some do require major compromises. I am/was fine with that, many weren't.

I'll have my first examples up later today. I'm quite pleased with the results, to the point where I may just adopt this new procedure. Particularly how lower TLs come out. But you shall see!

Quick note:
1a) Agility: HG Agility (<= max Gs of acceleration) = excess EPs per 100 D-tons of hull.
There is no excess involved, it's just powering the M-drive and weapons at the same time.

As a minimum you must have the power plant to power the M-drive or all the weapons. If you have power for the M-drive after weapons are powered, that is called Agility = available acceleration.

In effect you can choose to power weapons first (Agility) or M-drive first (Emergency Agility), if you don't have power for both.

MT Agility = 5.4 x excess MW / loaded tons. While these may seem unrelated, the MT formula is a completely faithful translation of the HG formula assuming that 1 D-ton in HG = 13.5 tons on average in MT.
MT agility is just ridiculous, as it is unrelated to the M-drive. It's just excess power pumped into thin air...
A MD-1 ship can have Agility-6, just by wasting power.

You are already powering the M-drive fully as part of the basic power requirement, so there is no choice in MT.

While my initial view was that the MT changes were fine, I was intrigued enough to take up the challenge of trying to bring MT back to something more like HG. The results are very interesting, as I will show in future posts.
As far as I can see from a quick summary, you are basically proposing to use HG with MT (&house ruled) crew and bridges?

OK, here are the first two examples, which of course have to be the Type S Scout and Type A Free Trader. One thing I had forgotten is that GDW grandfathered in Book designs and did not redesign them using HG. So in Supp9, Fighting Ships, the Type S is simple the Book 2 design stated in HG notation, and they even say so. This adds even more confusion, as things like fuel do not work the same between Book 2 and HG.

Here are summarized statistics. The three designs are original Book 2, and my revised MT/HG rules (given previously) for a TL 11 and TL 15 version of each ship.

Things to notice:

1) I had no difficultly reconstructing these ships. No compromises were needed to obtain full HG Agility or 30 day fuel duration.

2) TLs work like you would expect. The TL 15 versions are light and sleek, the TL 11 versions massive, clunky, and much more expensive.

3) The Type S is most interesting. As I suspected, a HG version of the Scout would be a lot better than Book 2 because HG uses a lot less fuel, and this shows in the TL 15 version. But the TL 11 version requires a HUGE power plant to reach Agility 2. Yet it still has about the same cargo as Book 2, whereas the TL 11 is positively spacious.

4) The Type A results are less different because less power is needed to achieve Agility 1. But the TL 11 version is still more massive and expensive, which makes complete sense to me.

I really LIKE these results, particularly how lower TL ships turn out. I'll be interested to hear any comments. My next build will likely be a SDB and something else with more armor, as I suspect extra armor could produce some complications.

As far as I can see from a quick summary, you are basically proposing to use HG with MT (&house ruled) crew and bridges?
First examples are up, take a look. Re. Agility, the MT formula is not only not ridiculous, it is a completely faithful conversion of the HG formula under the assumptions that 1) 1 EP = 250 MW (which is true from Striker), and 2) 1 HG D-ton weighs 13.5 tons on average (i.e. the MT cargo weight assumption). That last is an assumption, but it's not a bad one.

3) Armor Volume: There is a strong view that armor ought to take up hull space. I'm adding this back though honestly it does not matter much for adventure class ships. It is likely much more meaningful for capital ships, which may feature in later examples.

In HG, armor A is a factor starting at 0. Armor takes up V(1+A)% of hull volume, where V=4 for TL 7-9, 3 for TL 10-11, 2 for TL 12-13, and 1 for TL 14-15. For MT, the minimum Armor Factor is 40 for spacecraft, corresponding to a mass multiplier of 33.6 for hard steel in Striker (and MT). Let A be our Armor Factor >40 and M the corresponding mass multiplier. Then armor takes up the following percentage of the hull: [8 x Armor Type Mass Multiplier x M/33.6]%. The corresponding V values for MT are 3.5 for TL 7, 2.8 for TL 9, 2.5 for TL 10, 2.1 for TL 12, and 1.1 for TL 14, so rather close overall and more generous at lower TLs. The advantage of this MT method is we can compute armor density and perhaps use that.
We don't have to guess at armour volume as it's defined in Striker:

Just divide the MT volume by the "Weight" to get the volume in m³ (=kl)?

Does this solve the armour problem in HG - volume based armour gives the same protection to a 10t fighter and a 100,000t BB?

Armout factor should be based on thickness and configuration - which means you need to know the approximate surface area of the hull

Does this solve the armour problem in HG - volume based armour gives the same protection to a 10t fighter and a 100,000t BB?
Mostly: MT armour is basically Striker armour calculated for a sphere of the given volume. There is no configuration modifier though.

We don't have to guess at armour volume as it's defined in Striker:
View attachment 1653

Just divide the MT volume by the "Weight" to get the volume in m³ (=kl)?
Right, I did this, though I used the multipliers from MT. I did reproduce the calculation from Striker and got the MT multipliers within rounding.

Mostly: MT armour is basically Striker armour calculated for a sphere of the given volume. There is no configuration modifier though.
Since multiplication is associative, I don't think it matters which order you apply the multipliers. So MT changes mass both for configuration and armor, and that means a config that increases mass also increases armor mass by an additional amount from the config. In MT, I THINK what happens is you select an armor factor, and that dictates mass, from which I then computed volume. So in my version, I don't THINK volume determines anything, as it is derived last.

BYW, as this has been raised multiple times:

Theorem: The Agility formulas in HG and MT are equivalent under the assumption that 1 HG D-ton weighs 13.5 tons (i.e., 1 liter = 1 kilogram).

Proof: In HG, Agility = excess EP per 100 D-tons. So 1 Agility = 1 EP per 100 D-tons. Per Striker, 1 EP = 250 MW. If we now assume that 1 D-ton weighs 13.5 tons, we get: 1 Agility = 250 MW per 1350 tons = 18.52 MW per 100 tons. As 100/18.52 = 5.4, 5.4 x 18.52 MW per 100 tons = 100 MW per 100 tons = 1 MW per 1 ton. In other words, 1 Agility = 1/5.4 MW per ton, so multiplying by 5.4 converts the units to just MW per ton, as in MT.

Thus, Agility = excess EP per 100 D-tons (HG) = 5.4 x excess MW per ton (MT). QED.

Now, IS this a good assumption? Does the average D-ton of a ship weigh 13.5 tons? In most cases, the average mass appears to be LESS than this, so the MT formula would SEEM to boost Agility. But because RAW MT has super high fuel requirements compared to HG, in practice you could not install enough power plant to max out Agility. My recalc fixes this completely: as I noted, I had no difficulty reproducing Agility at each TL, and it has the right "feel" of getting bulky (but still doable) at lower TLs. We'll see how that holds up for heavily armored ships.

You do realise that a 13.5 cubic metre deckplan "ton" means you will need to allocate more volume to the fuel since 1000kg of liquid hydrogen requires 14 cubic metres...

You do realise that a 13.5 cubic metre deckplan "ton" means you will need to allocate more volume to the fuel since 1000kg of liquid hydrogen requires 14 cubic metres...
I am not changing that one. Too many other changes for a 3% difference. Sorry.

OK, first failure! As I feared, heavily armored ships could be an issue. But in this case, I also think there is a size problem. Before I go further, I'd like opinions on where you would compromise.

I tried to reconstruct the System Defense Boat (SDB) from Supp 9 Fighting Ships. The problem is both its small size (200 D-tons) and high armor (HG 13). The way MT treats armor, every 3 MT factors equal 1 HG factor, so HG 13 = MT 40+3x13 = MT 79, which is a LOT of armor.

I can produced a 300 D-ton model with Armor 67 that gets us to 6G and Agility 6. The MT version was 400 D-tons, Armor 67, and Agility 1, so my version is a big improvement over RAW MT, but not as small as the HG original. Would people like me to post this version, or is there a different tradeoff you would like to see instead? Thanks

You do realise that a 13.5 cubic metre deckplan "ton" means you will need to allocate more volume to the fuel since 1000kg of liquid hydrogen requires 14 cubic metres...
Theorem: The Agility formulas in HG and MT are equivalent under the assumption that 1 HG D-ton weighs 13.5 tons (i.e., 1 liter = 1 kilogram).
1 m³ ≈ 1 tonne => 1 Dt ≈ 13.5 tonne average for total ship mass is reasonable.

Some systems are lighter, some are more massive, it averages out.

Not when doing the deck plans that include the jump fuel tankage...

Thus, Agility = excess EP per 100 D-tons (HG) = 5.4 x excess MW per ton (MT). QED.
Irrelevant:
HG Agility is calculated on power production - weapons power, hence on power for the m-drive. HG Agility is limited by m-drive. It's all about the m-drive.

MT Agility is calculated on excess power when the m-drive is already fully powered, it's not limited by m-drive. MT Agility has nothing to do with the m-drive, and that's ridiculous.

Not when doing the deck plans that include the jump fuel tankage...
We are not doing deck plans over mass, but over volume?

The volume of 1 Dt fuel is 13.5 m³ (two squares), just as any other Dt, whatever the mass of the particular system.

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