A New Starship Construction System – part 5 – Engines Revisited

This post is a result of me thinking about the smaller ships: shuttles, fighters, even assault scouts. But especially the tiny hull size one and two ships. We’re going to look at an expansion of the engine size chart presented in part 2, adding in some new sizes and more data on the existing engines.

The first thing I was contemplating, and that I’ve know for a while, is that the Class A engines were way overpowered for the very small craft. If you took the stats for a fighter, it comes out to a total mass of about 263 tons. The thrust for a Class A Atomic or Chemical drive is 6250 and an Ion drive has a thrust of 3000. That mean the maximum potential ADF is 23.7 for the atomic and chemical drives and 11.4 for the ion drive. Well over the 6 ADF maximum and the 5 ADF specified for the ships. These smaller ships could easily get by with much smaller engines and still have the same performance. It had always been my intention to add in the smaller engine sizes.

The other issue that has been nagging at me lately is docking, specifically in bays inside a larger vessel. The system takes this into account and allocates bay sizes based on the size of the ship and includes the mass of the docked ships in the ADF calculation. Except the final sizes of the ships don’t include size or mass of the engines! I had originally hand-waved that away saying that the engines were rated to propel themselves plus provide X amount of thrust depending on the size and type of engine. For the larger ships, that’s fine. The engines are external to the ship and it’s really not going to dock inside anything else. But for the little ships, this is an issue and I need mass and volume values to make it all work out.

So that’s the task for today: Calculate the data for some smaller engines for the little ships, and come up with mass and volume values for all the engine types.

And then we can properly build and design assault carriers to hold our fighters (and maybe our assault scouts) and any ship that has one or more shuttles it houses internally. So let’s get started.

Smaller Engines

This is actually the easy part. I intended to make two additional sizes of engines, one about half the performance of the Class A engine, and a second one at half the performance of that.

The hardest bit for me was coming up with a nomenclature. Do I go with the engine size labels from model rocketry (1/2A, 1/4A) to match the A, B, and C sizes of model rockets? Or do I go the battery route and call them AA, and AAA engines. In the end, I decided to go the battery route. So the Class AA engine has about half the performance of the Class A engine, and the Class AAA engine about 1/4 the performance.

The only real constraint I had was that I wanted at Class AAA engine to still provide and ADF of 5 to the standard UPF fighter. Since that fighter has a mass of 274 tons (when configure, it has to provide a thrust of at least 1370.

The thrust ratios between the Class A, B, & C engines are on the order of 3-4. If I maintained that same ratio, then our AA engine at best would only have a thrust rating of 6250/9 = 694, about 700 which is too small. Of course 2 of them would give us the required thrust but all the depictions of the smaller ships are single-engined and I wanted to go with that.

So instead of going down by thirds, decided to go down by halves. Actually a little more in the case of the step from Class A to Class AA with the atomic and chemical drives. With that decision made, it was time to work out the values. That gives us the following table.

Engine Performance Table

	Class A		Class AA		Class AAA
Engine Type	Thrust	Cost (cr)	Thrust	Cost (cr)	Thrust	Cost (cr)
Chemical	6,250	50,000	3,000	28,000	1,500	15,000
Ion	3,000	100,000	1,500	55,000	750	30,000
Atomic	6,250	250,000	3,000	130,000	1,500	70,000

The values for the Class A engines are simply taken from the original post and provided for comparison. Additionally, we need the cost of fuel for each of these new engines types.

Fuel Cost Table

Engine Type	Class A	Class AA	Class AAA
Chemical	300	150	75
Ion	5	3	2
Atomic	10,000	6,000	3,000

As with the larger engines, the atomic engines require the atomic fuel pellet at the prices listed plus a load of Chemical fuel as well.

Unlike the larger atomic engines, which can hold more than a single fuel load, the AA and AAA atomic engines can only hold a single load. Additionally, the smaller ion engines can only hold 5,000 fuel units instead of 10,000 like their full-sized siblings.

Volumes and Masses

Now for the harder part. Generating volumes and masses for these various engines.

Engine Volume

There really isn’t much go to on here. I could look at the miniatures, but they were created more for style than with any eye for consistency between the ships. There are also a few drawing in the game books that might be used as a reference. In the end, I did the following.

I started with my 3D model of the assault scout which is based on the drawings of the ship all through the books. I then assumed that this plus the wing of the assault scout represented the volume of the engine plus the fuel tanks needed to hold the three units of fuel for the engine. This gave me a volume, based on my models of 657 cubic meters. We’ll round that down to 600 cubic meters and call it good. That’s the volume of a Class A atomic engine and its associated fuel tanks.

Now, anyone who looks at real rockets will immediately realize that that isn’t a lot of volume for fuel. For example, the space shuttle’s external tank had a volume of just over 2000 cubic meters. And that’s enough to make one trip up, not one and back, let alone three trips. So we’re dealing with some amazing rocket propellant here (and really cheap too). But that’s okay, I’m willing to have handwavium as a fuel additive in our rockets.

The next thing we need is a scaling relation for the larger (and smaller) engines. It has to account for the larger fuel load in the larger engines, And remembering that for the atomic engines, we can hold additional loads over the three in the Class A engines. At the very least, it has to scale up as the thrust scales. But I want to add a little more on top of that.

At one point in the past, I had made 3D models of Class A, B, & C atomic engines. At some point when I created them, I had some rationale for why they were the size they were. I don’t remember that rationale now (and it may have been purely aesthetic), but I figured I could at least look at them and see what the relationships were.

In the end I decided that the scaling for the volumes would be 1.45 times the scaling in the thrust. That would provide a baseline and then I’d adjust the numbers slightly to get nice “round” numbers (i.e. 2800 instead of 2782.5). On the smaller engines, I adjusted things up bit making the engines slightly larger to account for “minimum” sizes for some of the components and fuel tanks. I also made some adjustments to the various types of engines to account for the type and amount of fuel they carry.

Engine Mass

This one was much easier as it was to be based off of the volume. In this case I just assumed an “average” density for each type of engine and its fuel. The question was what to pick.

Modern rocket fuels are actually very light, on the order of 0.7-1.0 tons per cubic meter, less dense than water. And liquid hydrogen, the primary fuel in ion engines, is amazing light at only 0.07 tons per cubic meter. On the other hand, the actual engine parts are going to be much more dense to withstand the forces and pressures being exerted.

So in the end I compromised. Chemical engines would have an average density of 2 tons/cubic meter, ion engines would be 1.5 to reflect their much lighter fuel, and atomic engines would be 2.5 to represent the additional components that give them their special properties.

Engine Data

With all of those items figured out we can now build the full data table on each of the engine types.

Chemical Engines

Size	Thrust	Cost (cr)	Fuel Cost (cr)	Volume (m³)	Mass (tons)
AAA	1,500	15,000	75	100	200
AA	3,000	28,000	150	200	400
A	6,250	50,000	300	400	800
B	20,000	175,000	1,000	2,000	4,000
C	80,000	770,000	4,200	12,000	24,000

Ion Engines

Size	Thrust	Cost (cr)	Fuel Cost (cr)	Volume (m³)	Mass (tons)
AAA	750	30,000	2	100	150
AA	1,500	55,000	3	200	300
A	3,000	100,000	5	500	750
B	10,000	400,000	17	2,500	3,750
C	40,000	200,000	70	15,000	22,500

Atomic Engines

Size	Thrust	Cost (cr)	Fuel Cost (cr)	Volume (m³)	Mass (tons)
AAA	1,500	70,000	3,000	100	250
AA	3,000	130,000	6,000	200	500
A	6,250	250,000	10,000	600	1500
B	20,000	400,000	32,000	2,800	7,000
C	80,000	6,000,000	125,000	16,000	40,000

Impacts

So how does this impact our smaller ships? Most importantly, I want to see what it does for fighters and digger shuttles, the two small ships that are explicitly included inside larger vessels.

Using this system before the changes to the engines, we had the following characteristics for the two ships:

Fighter – mass: 274 tons, volume: 136 m³, 1 Class A Atomic engine, Max loaded ADF: 22.8
Digger shuttle – mass: 1330 tons, volume: 641 m³, 1 Class A Chemical engine, Max loaded ADF: 4.7

If we were to just update these vessels with the data for the original engines, the volume of the fighter would jump to 736 m³ with a mass of 1774 tons, an increase of 441% and 547% respectively. The digger shuttle isn’t quite as bad as it was bigger to begin with but it would increase to 1041 m³ and 2130 tons, increases of 62% and 60%.

However, these ships don’t need this large of an engine. If its occupants could handle it, the Class A engines on the fighter give it a maximum possible ADF of 22.8. Since it is only supposed to have an ADF of 5, we can swap out the Class A engine for a Class AAA engine. It will still have a maximum ADF of 5.5. With that change, the the fighter now has a volume of 236 m³ (a 74% increase) and a mass of 524 tons (a 91% increase). Still larger, but much more reasonable and easier to pack into our assault carriers. It also reduces the cost of the fighter by 180,000 credits. Since the original cost was 528,151 cr., reducing that by 180,000 is a savings of 34%. And that makes the bean counters at Spacefleet happy.

The default Class A chemical engine on the digger shuttle gives it a maximum ADF of 4.7, well within the species limit of 5. However, it only really needs an ADF of at least 2 to get on and off planets, so here we can get away with a Class AA chemical engine. This still leaves the shuttle with a max ADF of 2.3, reduces the cost of the shuttle by 22,000 cr., and put the final volume and mass at 841 m³ and 1730 tons (increases of 32% and 30% over the original), making them easier to store in the mining ships. Since the digger shuttle was original 140,320 cr., the 22,000 cr. reduction saves nearly 16% off the cost of the shuttle.

And for the curious, the Assault Scout has a volume and mass of 3455 m³ and 2458 tons. Adding in its two Class A atomic engines brings its total volume up to 4655 m³ and total mass up to 5558 tons (increases of 35% and 126%). That makes it 20x larger and 11x more massive than a fighter. So it’s not unreasonable that special carriers might be designed to transport the larger ships.

Final Thoughts

I definitely like the direction of this change. The size of the fuel storage is probably unreasonably small, but that’s just going to be part of the fiction of our science fiction. The exact values might change as this sees a bit more play but I think it serves as a solid baseline to build on.

What are your thoughts and ideas on this update to the engines? Let me know in the comments below.

A New Star Ship Construction System – part 4 – Hull Types, Armor, and Sensor Systems

This is a continuation of the excerpts from the starship construction system. I had originally planned to have the how to draw a star system map post ready for today but I didn’t quite finish it. So I’m posting this one in its place and will have that one up next week.

This article will be about the various type of hulls that you can make you ship out of and the effects they have on the hull points and mass of the ship. In the new system I expand on the basic hull from the original rules to four different types that have different characteristics and costs.

While not related, I’m also including the section on the radar and energy sensors as that is another deviation from the standard system

Hull Type

There are four different hull types. Each type has a mass and cost associated with it depending on the hull type selected. Different hulls provide different amount of hull points for a given ship size.

Hull Type	Cost multiplier	Mass Multiplier	Hull Point Multiplier
Light	35 cr * total volume	0.15 tons * total volume	0.6
Standard	50 cr * total volume	0.25 tons * total volume	1
Armored	100 cr * total volume	0.50 tons * total volume	1.4
Military	200 cr * total volume	0.40 tons * total volume	2

Light Hull – This is a light duty hull. It costs and weighs less than a standard hull but only provides sixty percent of the hull points of a standard hull.

Standard Hull – This is the standard type of ship hull and provides the standard number of hull points. This is the typical hull used on most civilian vessels

Armored Hull – This is the highest grade hull available to civilians. It is twice as massive and twice as expensive as a standard hull and provides a forty percent increase in hull points over a standard hull.

Military Hull – Combining specialized materials and designs, the military grade hull is not available for civilian ships. It is more expensive than even the armored hull although it doesn’t contain as much mass and provides double the number of hull points of a standard hull.

Example: Obar Enterprises is designing a new mid-sized freighter that has 100 cargo units of space. After selecting all the ship’s, the total volume of the ship is 18,453.2 cubic meters. Selecting a standard hull gives a cost of 18,453.2 x 50 = 922,660 credits and a mass of 18,453.2 x 0.25 = 4613.3 tons. This hull would have the standard number of hull points.

If the cost or mass were a concern, they could go with a light hull, which would have a cost of only 18,453.2 x 35 = 645,862 cr (saving nearly 300,000 cr) and have a mass of only 18,453.2 x 0.15 = 2767.98 tons saving nearly 2000 tons. However, this hull would have a hull point multiplier of 0.6 or only 60% of the standard hull points.

Additional Armor

Sometimes even the strongest hull just isn’t enough and you want to add more armor to the ship. Once you have your base hull, you can add additional layers of protection to the ship as desired. This will greatly increase the cost and mass of your ship but won’t affect the volume.

You can add armor on to the ship to increase its hull points by up to 25% in 1% increments. The cost of additional armor is 8 cr. per cubic meter of volume per percentage increase. Thus to get a 5% HP increase it would cost you 40 cr. per cubic meter of the ship, nearly doubling the cost of a standard hull. The armor adds an additional 0.016 tons of mass per cubic meter of volume per percentage increase. Thus that 5% increase above would also add 0.08 tons per cubic meter of the volume of the ship.

The armor modifier for calculating the ships final hull points is just 1+(armor bonus/100). So if my armor bonus is 20% the modifier is 1+(20/100) = 1.2. This will be multiplied by the ship’s base hull points to determine the actual number of hull points the ship has.

Long Range Detectors

Radar

Radar systems are combination active/passive systems. In active mode they send out pulses of radio waves and detect the reflected pulses. In passive mode, they scan space for emissions from other ships. The range of the radar system depends on its rating. The higher the rating the more distant an object it can detect due to stronger emitters and more sensitive receivers. It takes a lot of power and large transmitters to get returns from objects in the larger areas covered by the higher rated systems. The listed range is the range for the active system. In passive mode, the ranges are at least 10 times larger but can only detect targets that are radiating at radio frequencies.

Rating	Range (km)	Multiplier
1	300,000	1
2	600,000	8
3	900,000	27
4	1,200,000	64
5	1,500,000	125

Cost: 10,000 cr x Multiplier, mass: 15 tons x Multiplier, volume: 5 cu m x multiplier (7 cu m if aerodynamically streamlined)

Energy Sensors

These are broad spectrum radiation detectors that look at multiple wavelengths to detect radiation from ship systems. They scan radio, optical, infrared, x-ray, and microwave wavelengths and have gamma-ray detectors to look for signatures from ships’ engines and power plants. These are completely passive systems and like radar come in different ratings that have increased sensitivity. The ranges listed are for detecting shielded, ship-sized energy sources against the cosmic background. If an object is putting out energy emissions that are stronger than typical radiation leaked from ship systems, the detection range could be much larger. For example, even a type 1 energy sensor suite will still be able to detect the system’s star at ranges of billions of kilometers. Exact details are left up to the referee.

Rating	Range (km)	Multiplier
1	500,000	1
2	1,000,000	8
3	1,500,000	27
4	2,000,000	64
5	2,500,000	125

Cost: 200,000 cr x Multiplier, mass: 50 tons x Multiplier, volume: 20 cu m x multiplier

Thoughts

That’s it for the hull types, armor, and long range detectors. It’s a fairly simple change but allows for a wide range of ships with various characteristics and costs. Obviously the heavier hulls, armor, and larger sensors are going to require bigger, more expensive engines or suffer a performance penalty but sometimes you just need more hull points or a larger sensor range.

Share your thoughts, suggestions, and questions in the comment section below.

A New Starship Construction System – part 3 – Life Support

My previous posts about my new starship construction system generated a bunch of interest and several people expressed a desire to see more. So I thought I’d post up bits and pieces of this over a series of posts. I’ll start by posting the things that are new relative to the starship construction system in the Star Frontiers Knight Hawks Campaign Book.

I already posted the introduction the the “A New Starship Construction System” post back in early November. Although it wasn’t labeled as such, the “Starship Engines” post that came shortly after the first one was part 2 as that was taken from the new system as well.

The timing of these posts will be probably be fairly sporadic as I’m using them as filler between posts on other topics and when I’m working on things that I’m not ready to post about.

I’ve already posted about the engines. The next major change is the life support system which is the topic of this post. With each of these posts going forward, I’ll try to include some of the rationale and thinking behind the choices I made and the way I designed it. So let’s get going.

Design Considerations

One of the things that I found problematic with the life support system as described in the standard rules was that it always felt way too small. For example say you had a ship that could support 9 people. According the the standard rules, all of the life support equipment for the entire ship, including all the food, oxygen, and water for 200 days of operation would weigh only 9 kg (20 lbs)!

That 9 kg is split half and half between the equipment and the consumables so there is 4.5 kg (10 pounds) of equipment to get all that food, water, and air throughout the ship and then 4.5 kg of the food and water itself. Now I don’t know about you, but there is no way I can feed my family of 9 for a week, let alone 200 days on 10 lbs of food. Maybe if it was all just a nutrient pill that you took once a day that had all your calories, vitamins, and minerals. But I think even that is stretching it and definitely not very satisfying.

One could argue for transmutation/replicator technology ala Star Trek but that just doesn’t jive with the feel of Star Frontiers for me and I don’t want that in my game. Beside the rules state that the life support systems “include food storage and preparation, and water, atmosphere and wast processing and disposal.” (KHCB p 14) That sounds like it should include a bunch of machinery and storage space.

So looking at the life support systems I saw two things that needed to address. One was food storage and preparation, and the other was water, air, and waste circulation and processing. All of that was going to take up space. I needed to make sure the system had enough mass and volume associated with it to include all the various bits of machinery and storage and pipes and duct work needed to get the various bits around the ship as needed.

Another aspect was that I wanted it to be completely configurable by the ship designer. The default rules were for a 200 day supply in the system. Since I knew this new system was going to be bulkier, I wanted to give the option to go for a smaller system if you knew that was all your needed. For example, a shuttle, that just goes up and down from the ground to orbit probably doesn’t need a life support system that can go 200 days without recharging. It probably only needs a few days at most and so can have a much lighter system.

Related to that I wanted to have different types of system for shuttles, system ships, standard interstellar ships, and first class accommodations. Each of those have different requirements and therefore should have different costs, volumes, and masses.

Taking all of that into account results in the following system. The excerpt of the rules that follows assumes that you’ve determined the crew size and number of the various passenger cabins you will have on the ship before to select the life support system.

Life Support Equipment

Now that you know the number of crew and passengers, you can select the amount of life support equipment the ship needs. It is recommended that you have at least one backup life support system in case there are problems with (or damage to) the primary system. The life support system includes a variety of systems such as air filtering and circulation, food preparation, sanitation facilities, and waste management. Life support on starships are mostly a closed system, almost everything gets recycled. However there are some consumables that do need to be replaced (mainly foodstuffs) every so often.

Your life support system needs to be at least large enough to support the crew and passengers. Typically, ships are designed with a little extra capacity as a safety margin or for emergencies. There are four basic levels of life support available for ships, depending on the ship’s needs:

Rudimentary – This is an air supply system only. It doesn’t handle food or waste materials and just provides an air supply and air circulation system with filtering. This is the life support system you find on launches, workpods, fighter craft, and other ships that are not designed to be occupied for a long time.

Basic – This level of life support adds basic food storage and preparation, sanitation facilities, and waste management to the air supply system of the rudimentary life support level. Supplies are stored and consumed and waste material has to be removed regularly. There is little to no recycling of materials except for air and water. This level of life support is typical of shuttles and some short distance system ships that typically operate for only short periods of time between calling on bases where their life support can be resupplied and waste material removed. It may also be found on some lifeboats. While you could equip a starship with this type of life support system, making it large enough to support long missions uses up valuable space in the ship and tends to be more expensive in the long run.

Standard – This is the typical system for any starship. It consists of complete air and water recycling, as well as recycling of waste material. It typically includes some sort of hydroponics system for both growing fresh food and recycling carbon dioxide back into oxygen. There are full food preparation facilities as well as complete sanitation facilities. This level of life support is required for Journey class passenger accommodations.

Deluxe – This is a more advanced version of the Standard system. It provides better recycling, larger food preparation facilities, more variety in the fresh foodstuffs, and better (nicer) sanitation and waste management facilities. This level of life support is required for any First Class passenger accommodations.

A ship can have different life support levels for different parts of the ship. This is quite common on passenger liners. For example, if a passenger liner has 20 First Class cabins and 100 Journey class cabins. It is not very likely that the owners will invest in Deluxe life support for the entire ship (although if they did, it would figure prominently in their advertising). Rather they would invest in a Deluxe life support system to cover the First Class cabins and a standard system to cover the Journey Class cabins and the crew.

The volume listed for the life support system includes both the machinery and hardware for processing the air, water, food, and waste material as well as storage space for raw materials and duct work to move material around the ship.

Every life support system has two ratings. The first is the maximum number of beings the system can support. This determines the amount of mass and volume allocated for the life support machinery (pumps, filters, ducts, pipes, etc.). The second is the maximum number of days that the system can support those beings without being refilled/recharged. This determines the amount of volume committed to storage of life support supplies.

Base hardware costs and volumes per being supported

All values except base system volume are multiplied by the maximum number of beings the system can support at one time.

Type	Cost	Mass	Base system volume	Volume
Rudimentary	500 cr	0.2 tons	1 cu m	0.1 cu m *
Basic	1500 cr	2 tons	6 cu m	5 cu m
Standard	3000 cr	4 tons	15 cu. m	8 cu m
Deluxe	5,000 cr	6 tons	30 cu. m	10 cu m.

* This volume assumes you are equipping a small one or two room craft with this system like a fighter or launch. If you try to put this into a larger ship the volume goes up by a factor of 10 for the ducting and pipes needed.

For example, our passenger liner has 20 First Class cabins and 100 Journey class cabins for crew and passengers. It would need two life support systems. The Deluxe system would support 20 beings. It would cost 20 x 5000 = 100,000 cr, have a mass of 20 x 6 = 120 tons, and take up 30 (base volume) + 20 x 10 (volume per being) = 230 cubic meters. The Standard system for the Journey class cabins would cost 100 x 3000 = 300,000 cr, have a mass of 100 x 4 = 400 tons and take up 15 + 100 x 8 = 815 cubic meters. Thus the Standard system while being just a little more than 3x the size of the Deluxe system, supports 5x as many beings.

Supply cost per being per day

In addition to the base machinery costs, there is the cost of the food, air, and water needed for the beings on board. Multiply each value times the maximum number of beings the system can support and then by the number of days you want to be able to support those beings without a reload/refill of the system.

Type	Cost	Mass	Volume
Rudimentary	10 cr	0.05 tons	.1 cu m
Basic	15 cr	0.15 tons	.4 cu m
Standard	25 cr	0.1 tons	.15 cu m
Deluxe	40 cr	0.15 tons	.25 cu m

So if our passenger liner wanted to support its full complement of crew and passengers for 200 days without a resupply, the cost of the supplies and storage areas would be as follows: For the Deluxe system the cost is 40cr x 20 beings x 200 days = 160,000 cr, the mass would be 0.15 tons x 20 x 200 = 600 tons, and the volume would be 0.25 cu m x 20 x 200 = 1000 cubic meters. The standard system supplies would cost 25 cr x 100 beings x 200 days = 500,000 cr, the mass would be 0.1 tons x 100 x 200 = 2000 tons, and the volume would be 0.15 cu m x 100 x200 = 3000 cubic meters.

Thoughts and Comments

That’s the life support system rules in the the new system. Let me know what questions or thoughts you have in the comments below.

A New Starship Construction System – part 2 – Starship Engines

I was going to post another ship next but realized that I should probably talk a little bit about the way I redesigned the engines in my new starship construction system. Otherwise, some of the bits of information about the ships won’t make sense. I’ve published some of this on-line before but I don’t remember exactly where so I’m repeating it here for completeness. Here is the section on engines from the starship construction system document.

Engines

Now that we know the mass of our ship, it’s finally time to determine its propulsion. Each type and size of engine is rated to have a specific thrust and fuel capacity. Your ship’s hull size determines the maximum number of engines it can support. You don’t have to have to fill all your engine slots if that number of engines is not needed to achieve the performance you desire. And regardless of hull size and engine type, the maximum acceleration of any ship is 6g.

Hull Size	Max Engines
1	1
2-4	2
5-8	4
9-12	6
12+	8

(Note: I didn’t even follow my own rules when I created the PGC C-10 Fast Courier as I gave it 4 engines at HS 4. This is something I’m still thinking about/working on.)

Engine thrust is given as an arbitrary thrust rating that has been scaled to work with the mass of the ship as given in tons. To determine the maximum acceleration of your ship, add up the thrust ratings of all your engines and divide that by the total mass of your ship in tons. The resulting number is the maximum acceleration of your ship in multiples of one standard gravity (10 m/s/s). Round all fractions down to the nearest tenth of a g.

Chemical Engines

These engines use a high efficiency chemical fuel that burns and is expelled out the engine nozzle to provide thrust. These engines are relatively cheap and easy to produce. While very powerful, because of the large volume of fuel needed, these engines have limited capability in regards to how long the engines can operate on a single fuel load. These engines are typically used for ground-to-space shuttles and system ships.

Ion Engines

Ion engines work by ionizing hydrogen and accelerating the resulting protons and electrons to high velocity and expelling them out the back of the engine to provide thrust. Each engine contains a small nuclear reactor to provide the power needed to ionize the hydrogen and accelerate the particles to the relativistic speeds needed to generate thrust. This reactor uses the same atomic fuel pellet as an atomic engine but only needs to be replaced once every 10 years. The initial fuel pellet is included in the cost of the engine.

While not as powerful as chemical or atomic engines, Ion engine fuel is relatively cheap and if a ship is properly equipped, can be harvested from any gas giant for free.

Because of the nature of the engine, ships with ion engines cannot land on or take off from planets.

Atomic Engines

An Atomic engine is a supercharged version of the chemical engine and uses the same fuel. The engine works by generating a quantum field that temporarily increases the momentum of particles by a factor of hundreds. These temporarily super-massive particles are ejected out of the back of the engine to generate thrust for the ship. Because each particle is effectively much more massive, less fuel is needed to achieve the same thrust and instead of a single fuel load lasting for only few minutes of thrust, it can last for days and allow the ship to accelerate to Void jump speeds.

However, generating this field requires a huge amount of energy (which is transferred to the particles) during operation. To provide this power, each engine contains its own nuclear reactor, similar in design to the reactor in the ion engine. However, the large power requirement of the atomic engine means that it consumes one atomic fuel pellet after only 10,000 minutes of full thrust operations (about 8.5 days) instead of the 10 year life span for the atomic fuel pellet in an ion engine.

In addition, atomic engines require an overhaul every few jumps, again depending on the size of the engines. This overhaul is necessary to make sure that the quantum field generators are properly aligned and positioned to only affect the fuel and not the body of the engine itself. The number of trips that a ship can go between overhauls depends on the size of the engine and is given in the table with the fuel costs below.

Engine Costs

The following table gives the cost and thrust values for each of the different types and sizes of engines. Determine the number, size, and type of engines your ship will use and then record the engines chosen for your ship.

	Class A		Class B		Class C
Engine Type	Thrust	Cost	Thrust	Cost	Thrust	Cost
Chemical	6,250	50,000	20,000	175,000	80,000	770,000
Ion	3,000	100,000	10,000	400,000	40,000	2,000,000
Atomic	6,250	250,000	20,000	1,100,000	80,000	6,000,000

Fuel

Next you need to provide fuel for your engines and determine how much acceleration each fuel load will provide for your ship. Each engine uses different types of fuel and has different storage capabilities and requirements.

Chemical Engines

Each fuel load allows a chemical engine to operate at maximum thrust for 60 minutes. This is typically enough to allow the ship to make one round trip between the ground and orbit or limited acceleration and maneuvering in space. Each engine can only hold a single fuel load and must be refueled after each load is expended. The cost of a fuel load depends on the size of the engine and is given in the following table.

Engine Class	Cost of a fuel load
Class A	300 cr
Class B	1000 cr
Class C	4200 cr

Ion engines

Although not as powerful as chemical or atomic engines, these engines are reliable and can hold more fuel. While they can technically run off any material, the fuel of choice is hydrogen. Using any other fuel source decreases the thrust provided by the engines by a factor of two. Each engine can hold 10,000 fuel units and each unit provides 10 minutes of operation at maximum thrust (A fully fueled ion engine can operate continuously for over 80 days without refueling). A fuel unit costs 5, 17, or 70 cr per unit for Class A, B, or C engines respectively.

Once every 10 years, the atomic fuel pellet in the ion engine’s reactor needs to be replaced, the cost for this fuel pellet is the same as that for a similarly sized atomic engine.

Atomic engines

Like the other engines, Atomic engines store all their fuel internally. The fuel for these engines consists of two parts. The first is a load of fuel like the chemical rockets, the second consists an atomic fuel pellet (typically uranium) to power the reactor. The amount of fuel that can be stored depends on the size of the engine and is given in the table below.

Each atomic fuel pellet and load of chemical fuel provides enough fuel for 10,000 minutes (about 8.3 days) of operation at maximum thrust. The cost of a fuel pellet depends on the size of the engine, given in the table below. The cost of the chemical fuel is identical to that of the chemical engines of the same size.

Consult the table below to determine the number of fuel loads & pellets held and time between each overhaul for each engine size.

Engine Class	Trips between overhauls	Maximum Fuel Loads & Pellets loaded	Cost per pellet (cr)
Class A	1	3	10,000
Class B	3	6	32,000
Class C	10	12	125,000

Compute total acceleration per fuel load

Acceleration is measured in ADF. One ADF is defined as 10 minutes of acceleration at 1g. (For you Star Frontiers grognards out there, I’ve redefined the boardgame hex scale to 3600 km so that 1 ADF does equal 1g acceleration for 10 minutes, and 1 g is defined as 10 m/s/s not 9.8.)

If you want to keep it simple, you can simply assume the following:

a load of fuel in a chemical rocket provides just enough thrust to make one round trip between the ground and orbit around a planet or can provide a total of 8 ADF in space.
Ion engines use one fuel unit per engine per ADF and a total of 1000 fuel units per engine for a single interstellar jump
Atomic engines use one chemical fuel load and one atomic fuel pellet for a single interstellar jump or the same fuel provides enough thrust for a total of 1000 ADF if operating solely in-system.

If you want to be a bit more exact and track the exact fuel usage you can do the following to compute the total number of ADF that a load of fuel will provide for your ship. This will depend on the type of engine you have. It requires more bookkeeping but actually results in less fuel being needed in the long run, sometimes significantly if the ship has a high maximum ADF.

Chemical Engines – Take the maximum acceleration you calculated for the ship earlier and multiply it by 6. This is the total number of ADF your ship gets from using one load of fuel in each engine.
Ion Engines – The maximum acceleration calculated above is the number of ADF provided by expending a single ion fuel unit in each engine.
Atomic Engines – Take the maximum acceleration calculated earlier and multiply by 1000. This is the total ADF provided by using one unit of chemical fuel and one atomic fuel pellet in each of your engines.

Round all fractions down. Assume that that small difference is used up in minor station keeping and maneuvering

Examples

Chemical Engine

Fully loaded a Digger Shuttle (HS 2) has one Class A chemical engine and a maximum acceleration of 4.7g. Since it has chemical engines, the total ADF provided by the single load of fuel in its engine is 4.7 x 6 = 28.2 or 28 ADF.

Ion Engine

A small (HS 7) freighter is equipped with four Class B ion engines. Fully loaded, its maximum acceleration is 1.1g. Thus by using up one fuel unit in each of its four engines, it has 1.1 ADF available. If each engine carries it’s maximum fuel load (10,000 units each), the total ADF available to the ship is 11,000 ADF. Since each interstellar jump typically takes 1000 ADF to complete, the ship can make 11 trips without refueling if it needed to.

Atomic Engine

The newly designed Swift class assault scout has a total mass of 2470.83 tons and two Class A atomic engines for a total thrust of 12500. This gives a maximum acceleration of 5.059g which rounds to 5.0. The total ADF available to the assault scout from one load of fuel in each engine is therefore 5×1000 = 5000 ADF. After expending this much thrust, the assault scout will have used two loads of chemical fuel and two atomic fuel pellets, one in each engine.