Dissecting Mgt personal Grav vehicles

[sideranautae]

In trying to figure out how/if Mgt grav vehicles can operate in deep space in a prior thread it was discovered that they can and do according to the CRB.

The two smallest grav vehicles listed are the TL 12 Grav Belt (see Vehicles Chart on pg. 103) and the TL 14 Long Range Thruster package for Vac Suits (pg. 97).

Neither of the entries list a volume for these vehicles. The Grav Belt delivers a performance of 300 kph (assumptions; Standard atmos. & 1 G planet) for 4 hours using batteries. Cr. 100,000

The Grav Thruster pack gives 1/10 G acceleration for 48 hours using L-hyd only fueled power-plant (fusion is only thing that fits that bill). Cr. 20,000

The price difference makes sense when one examines the performance difference. The Grav belt must deliver in excess of 1G of "Grav" lift/thrust. The Thrust Pack only delivers 1/10 G thrust.

The missing component is the volume/size of these vehicles. Considering both without their fuel+power plant (Thruster pack), batteries (Grav Belt) it would make sense for the latter to be larger in size as it delivers probably 12X the G's of the less expensive vehicle. The other item to consider for size/volume is the batteries and the fuel + fusion PP on the other.

Any ideas as to volume for these rigs?

 

[sideranautae]

Found a funny one in MT:

TL 15 PETER PAN CHILD'S FLOAT CHAIR
Parents may rest assured when they tuck their children
into the Peter Pan commuter bubble. Young passengers
are guaranteed to reach the destination that has been programmed
at home, since the computer will not accept program
changes in flight without radio authorization from the
parent. There is an automatic distress signal in case of
mechanical failure and forced landing. A child can literally
go anywhere in the world on one fuel tank, and refills cost
less than two credits. The use of rest stops is necessary,
however, as there are nO extended life support facilities in
the bubble.

CrattlD: Imperial Peter Pan Float Chair, TL15,
Cr76,200
Hull: 1/1, Disp=0.25, Config=5SL, Armor=4F,
Unloaded.0.47 tons, loaded=0.56 tons
Power: 1/2, Fuel Cells=0.54Mw, Dur=4/12
Loco: 1/2, Grav, Thrust=2 tons, NOE=240kph,
Cruise=720kph, Top=960kph,
MaxAccel=O.8G
Comma: Radio=VDist (50km)
Sensors: Radar=Dist (5km), ActObjScan=Form,
ActObjPin=Form
Off/Def: Hardpoints.1 (squirt gun, maybe?)
Control: Computer=O, Elect link
Accom: Crew.1, Seats.Cramped x 1, Env_Basic env

Other: Fuel=0.04kl, Carg.5kl, ObjSize_Smal,
Emlevel_Moderate

 

[sideranautae]

Came up with Volumes for the Grav Belt. 25 Liters at TL 12. 15 for the TL 15 model.

 

[sideranautae]

The Thruster Pack power plant supplies enough power for 4.8 G hours. The TL 12 batteries on the Grav belt provide 6 G hours of power.

Batteries will be less energy dense than a Fusion PP + fuel by at least 5X. (but there will be a minimum size for the FPP's)

So we'll call the batteries 20 liters and the Grav modules 5 liters for 25 liters at TL 12. The batteries drop by half at TL 15 for 10 liters.

The Thruster pack Grav modules put out ~7% of the "thrust" as the Grav belt. So 1 Liter (minimum size) for those Grav modules. But 20 Liters minimum size for the Fusion PP + 2 Liters for fuel (close to standard amount per other FPP specs) for a total of 23 Liters for the Thrust Pack.

Although IMTU man portable fusion PP's appear at TL 15, MGT has them at TL 12...

 

[sideranautae]

The fusion reactor for the Thruster Pack size also gibes with the CRB vis-a-vis The Plasma Gun, Man Portable: The RAW states that, "It is powered by a built-in micro-fusion generator."

I guess there are quite a few rules in MGT that haven't been explored...

 

[phavoc]

Neither of the entries list a volume for these vehicles. The Grav Belt delivers a performance of 300 kph (assumptions; Standard atmos. & 1 G planet) for 4 hours using batteries. Cr. 100,000.

TL-12 thruster pack is 10kg. TL-14 thruster pack is "much smaller".

The Grav Thruster pack gives 1/10 G acceleration for 48 hours using L-hyd only fueled power-plant (fusion is only thing that fits that bill). Cr. 20,000

TL-12 thruster pack and the TL-14 thruster pack both use L-Hyd. Only the TL-14 uses gravity plates for locomotion. L-Hyd, by itself, can be used as the thruster fuel. It doesn't have to be fusion.

The price difference makes sense when one examines the performance difference. The Grav belt must deliver in excess of 1G of "Grav" lift/thrust. The Thrust Pack only delivers 1/10 G thrust.

Grav belts are expected to operate within a planetary environment. Thruster packs are only operable in zero-g. It takes a great deal more energy to lift/move a mass in a gravity well than it is to propel mass in zero-g

The missing component is the volume/size of these vehicles. Considering both without their fuel+power plant (Thruster pack), batteries (Grav Belt) it would make sense for the latter to be larger in size as it delivers probably 12X the G's of the less expensive vehicle. The other item to consider for size/volume is the batteries and the fuel + fusion PP on the other.

Any ideas as to volume for these rigs?

A parachute harness, minus a parachute, is quite small volume wise. Assuming one takes the description at face value. The webbing itself would be holding the A/G modules, batteries and control units. To determine volume you need mass and density. I would say that the grav belt is no more encumbering than heavy-duty climbing gear of the type of web gear (minus canteen, grenades, first aid pack and ammunition) that a soldier carries. Empty it all weighs around 7 lbs or so, which would give it a mass of about 3kg with rounding.

 

[Jeraa]

Grav belts are expected to operate within a planetary environment. Thruster packs are only operable in zero-g. It takes a great deal more energy to lift/move a mass in a gravity well than it is to propel mass in zero-g

Grav belts use the Zero-G skill. That doesn't sound like something that usually operated in a planetary environment. And Scoundrel mentions using grav belts during boarding actions.

 

[sideranautae]

Grav belts use the Zero-G skill. That doesn't sound like something that usually operated in a planetary environment.

Grav Belts are listed as vehicles used on planets for personal transportation. You need zero G skill as you are in a null gravity field while in use.

 

[sideranautae]

TL-12 thruster pack is 10kg. TL-14 thruster pack is "much smaller".

kg is a measure of mass not volume. So a bit difficult there.

TL-12 thruster pack and the TL-14 thruster pack both use L-Hyd. Only the TL-14 uses gravity plates for locomotion. L-Hyd, by itself, can be used as the thruster fuel. It doesn't have to be fusion.

No, in space there is nothing you can do with L-hyd alone as fuel. (except to fuse it) It is inert.

Thruster packs are only operable in zero-g. It takes a great deal more energy to lift/move a mass in a gravity well than it is to propel mass in zero-g

Thruster pacs are usable anywhere where 1/10 G will move you. If you are on a 1G planet and on a Floater it would push you are 1/10 G accel... The rating gives what it will actually do. Environment is not relevant. It supplies a thrust equivalent of 98 cm/sec/sec.

A parachute harness, minus a parachute, is quite small volume wise. Assuming one takes the description at face value. The webbing itself would be holding the A/G modules, batteries and control units. To determine volume you need mass and density. I would say that the grav belt is no more encumbering than heavy-duty climbing gear of the type of web gear (minus canteen, grenades, first aid pack and ammunition) that a soldier carries. Empty it all weighs around 7 lbs or so, which would give it a mass of about 3kg with rounding.

Batteries supplying that much energy are going to be a bit larger maybe. But, sounds about right per description.

 

[Jeraa]

TL-12 thruster pack and the TL-14 thruster pack both use L-Hyd. Only the TL-14 uses gravity plates for locomotion. L-Hyd, by itself, can be used as the thruster fuel. It doesn't have to be fusion.

No, in space there is nothing you can do with L-hyd alone as fuel. It is inert.

I have to disagree with you there. The whole "equal and opposite reaction" thing. Its what makes a gun recoil when fired, or what pushes you back when you push someone else. If you propel something such a liquid hydrogen (or for that matter, water or simple air) out one end of an object, the object itself will be propelled in the other direction.

The liquid hydrogen isn't fuel, it is reaction mass.

 

[sideranautae]

The liquid hydrogen isn't fuel, it is reaction mass.

The amount of L-hyd being discussed (under pressure) it not near enough, by MANY orders of magnitude, to supply the Δv listed for the vehicle. Therefore, it is dismissed out of hand.

 

[Jeraa]

The liquid hydrogen isn't fuel, it is reaction mass.

The amount of L-hyd being discussed (under pressure) it not near enough, by MANY orders of magnitude, to supply the Δv listed for the vehicle. Therefore, it is dismissed out of hand.

Granted they are for starships, but lets run the numbers using the reaction mass required for starship-grade reaction drives. They need an amount of reaction mass equal to a certain percentage of the ships size:

2.5% x Maximum Thrust x hours at Maximum Thrust.

Now your average human is roughly 100 liters in volume. In order to travel at 0.1g acceleration for 48 hours would therefore require 10% of the humans volume, or 10 liters of reaction mass. (100x.025 = 2.5 x thrust 0.1 = 0.25 x 48 hours = 12). Now, 1 liter of water has a mass of 1 kg. So that 12 liters of reaction mass has a mass of 12 kg. Which is only 2 kg more than the mass of a TL 12 thruster pack. Now that doesn't leave any mass for the actual thrusters, but those shouldn't be too much. Liquid hydrogen should be much less dense than water, so have a lower mass per liter, which means that all of the reaction mass and the thrusters themselves could possibly have a mass of only 10 kg.

Yes, granted, the rules are for starship reaction drives. But they almost work for this. Maybe not realistic, but we are talking about a game, not real life. And the rules (kind of) say its possible.

 

[sideranautae]

The liquid hydrogen isn't fuel, it is reaction mass.

The amount of L-hyd being discussed (under pressure) it not near enough, by MANY orders of magnitude, to supply the Δv listed for the vehicle. Therefore, it is dismissed out of hand.

Granted they are for starships, but lets run the numbers using the reaction mass required for starship-grade reaction drives. They need an amount of reaction mass equal to a certain percentage of the ships size:

2.5% x Maximum Thrust x hours at Maximum Thrust.

Now your average human is roughly 100 liters in volume.

You have to use mass not volume. ALSO, "standard starship fuel is NOT what is used for the reaction drive in HG. It would HAVE to use L-Hyd AND an oxidizer (probably LOX), LOTS of it. The reaction rockets aren't just shooting l-hyd out the back. (The description would state that it is using standard REACTION drive fuel)

Use the specific impulse formula as we don't have the nozzle velocity

where:

m_0 is the initial total mass, including propellant,
m_1 is the final total mass,
v_\text{e} is the effective exhaust velocity,
\Delta v\ is delta-v - the maximum change of velocity of the vehicle (with no external forces acting),
\ln refers to the natural logarithm function.

(The equation can also be written using the specific impulse instead of the effective exhaust velocity by applying the formula

where

is the specific impulse expressed as a time period and

is Standard Gravity.)


BUT, if you want to go HG reaction drive. Figure at least 150 liters for person, EVA suit, et al. = ~2,700 liters of "fuel" to get 48 hours of 0.1 G accel..

That would be 2.7 CUBIC meters of fuel... :shock:

 

[Jeraa]

You have to use mass not volume.

Conveniently, mass and volume in this case is the same, as the human body is mostly water (which has a mass of 1 kilogram per liter). A 100 liter human has a mass of 100 kg.

ALSO, "standard starship fuel is NOT what is used for the reaction drive in HG. It would HAVE to use L-Hyd AND an oxidizer (probably LOX), LOTS of it. The reaction rockets aren't just shooting l-hyd out the back. (The description would state that it is using standard REACTION drive fuel)

The rules disagree with you. Specifically, the sidebar in High Guard called "Burning Your Bridges (or using Jump Fuel in an Emergency)." Jump fuel is pure liquid hydrogen, and can be used as reaction mass. No mention is made of a oxidizer anywhere.

Again, real world physics vs game physics. Game physics trump real-world physics. Traveller is in no way a real-world simulation.

BUT, if you want to go HG reaction drive. Figure at least 150 liters for person, EVA suit, et al. = ~2,700 liters of "fuel" to get 48 hours of 0.1 G accel..

That would be 2.7 CUBIC meters of fuel... :shock:

Using High Guard rules? No. I have no clue how you got that result.

Its 2.5% of volume per G-Rating per hour.
That is 0.25% volume for 0.1G acceleration for one hour. That is 12% of total volume for 48 hours, or 12 liters for a normal, 100 liter person.

2.5% of 150 liters is 3.75 liters. Multiply that by the 0.1G acceleration and you get 0.375 liters. Multiply that by 48 hours and you get 18 liters. Not 2,700 liters.

 

[sideranautae]

So, after reviewing all MGT rules it is clear that the Grav drives scale from personal vehicle size all the way up to space ships. And that no matter the scale, they all work the same and in the same environments.

Also, man portable (micro-fusion PP's) are introduced in MGT at TL 12! Too early for my game. I'll set at TL 14.