Example: Designing Your First Beam Cruiser

Updated: v2026.01.30

This worked example walks through the complete design process for a 10,000-ton beam cruiser optimized for medium-range engagement. We will make every decision step by step, showing the math behind each choice and explaining the trade-offs involved.

Objective

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Design a 10,000-ton beam cruiser capable of:

  • Engaging hostile warships at medium beam range (~200,000-400,000 km)
  • Sustaining combat for multiple volleys
  • Operating independently within a star system (reasonable fuel endurance)
  • Surviving return fire from comparable opponents

Starting Conditions

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  • TN Start: Nuclear Thermal Engine technology (5 EP/HS), Pressurised Water Reactor
  • Laser Technology: 10cm focal size available, Ultraviolet wavelength (1.0x range modifier)
  • Fire Control: Beam FC with tracking speed up to 5,000 km/s
  • Engine Power Multiplier: 5 EP/HS (base, no boost applied yet)
  • Fuel Consumption Modifier: 1.0 (standard – lower values improve range but increase engine size)
  • Armor: Duranium (strength 5 per layer)
  • Shipyard: Naval yard capable of 10,000 tons

Step 1: Determine Role and Engagement Range

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Our cruiser is a medium-range beam combatant. This means:

  • We want to fight at 150,000-300,000 km (close enough for beam accuracy, far enough to maneuver)
  • We need weapons that deal meaningful damage at this range
  • We need speed to dictate engagement terms against slower opponents
  • We need enough armor to survive several volleys while trading fire

Design target speed: ~2,500 km/s or better (fast enough to dictate engagement terms, competitive in the “Moderate” speed class for early-game cruisers)

Step 2: Engine Sizing

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We want at least 2,500 km/s from a 10,000-ton hull (200 HS). Let us start by checking what 4,000 km/s (a “Fast” speed) would require, then work down to what is achievable. Using the speed formula (see Section 8.3 Engines and the Aurora wiki):

Speed (km/s) = Total_Engine_Power * 1000 / Ship_Size (HS)

Where 1 EP is the power required to propel 1 HS (50 tons) at 1000 km/s against Trans-Newtonian drag. Equivalently, since Ship_Size (HS) = Ship_Mass (tons) / 50:

Speed (km/s) = Total_EP * 50,000 / Ship_Mass (tons)

Solving for required Engine Power at our target speed:

Required EP = Speed * Ship_Size (HS) / 1000
Required EP = 4000 * 200 / 1000
Required EP = 800 EP

But this assumes the final ship size is exactly 200 HS. In practice, the engines themselves add mass. We need to iterate. Let us start with the engine calculation.

With Nuclear Thermal Engine at 5 EP/HS, we can apply a power boost. Let us try a 1.25x boost (the sweet spot per Appendix D – 25% more power with ~56% more fuel consumption):

Boosted EP/HS = 5 x 1.25 = 6.25 EP/HS

Using fuel consumption modifier of 1.0 (standard) – lower values improve range but increase engine physical size for the same power, a poor trade-off for warships. A 25 HS engine (the maximum starting size) produces:

Engine Power = 25 HS x 6.25 EP/HS = 156.25 EP per engine
Engine Mass = 25 HS x 50 tons/HS = 1,250 tons per engine

We need 800 EP. Let us check how many engines that requires:

Engines needed = 800 / 156.25 = 5.12 engines

Six 25 HS engines would provide enough power but consume 7,500 tons (75% of our hull) – far too much. Let us calculate what speed is actually achievable at a reasonable engine allocation.

Revised approach: Dedicate ~40% of tonnage to engines (a reasonable warship allocation):

Engine tonnage: 4,000 tons = 80 HS total
Split into 4 engines of 20 HS each (for redundancy)
With 1.25x boost: EP per engine = 20 x 6.25 = 125 EP
Total EP = 4 x 125 = 500 EP
Engine HTK = sqrt(20) = 4.47 per engine (good redundancy)

Speed at 200 HS total ship size:

Speed = 500 * 1000 / 200 = 2,500 km/s

2,500 km/s is solidly in the “Moderate” speed class and very competitive for a TN-start beam cruiser. This is fast enough to dictate engagement terms against heavy ships and keep pace with most early-game threats.

However, 4,000 km/s (the “Fast” speed class) would require either higher tech or a much larger engine fraction. Let us check what a 50% engine allocation gives:

Engine tonnage: 5,000 tons = 100 HS total
Split into 4 engines of 25 HS each
With 1.25x boost: EP per engine = 25 x 6.25 = 156.25 EP
Total EP = 4 x 156.25 = 625 EP
Speed = 625 * 1000 / 200 = 3,125 km/s
Engine HTK = sqrt(25) = 5 per engine

3,125 km/s is excellent, but 50% of the hull in engines leaves tight margins for weapons and armor. The 40% allocation at 2,500 km/s is the better balance for a cruiser that needs to carry weapons, armor, and sensors.

Final engine decision: 4x 20 HS Nuclear Thermal Engines at 1.25x boost

  • Total engine mass: 4,000 tons (80 HS)
  • Total EP: 500
  • Speed (at 10,000 tons / 200 HS): 2,500 km/s
  • Engine HTK: 4.47 each (17.9 total – good redundancy)

Note: 2,500 km/s is a strong speed for TN-start technology. Researching Nuclear Pulse (8 EP/HS) would boost this same engine allocation to 4,000 km/s, making engine technology research a high priority.

Step 3: Weapon Selection – Laser vs Particle Beam

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At this tech level, our choices are:

10cm Laser (UV wavelength):

  • Damage: 10 per shot (focal size = damage)
  • Power required: 10
  • Range: base UV range for 10cm (approximately 160,000 km at starting tech)
  • Size: approximately 3 HS (150 tons) at base recharge rate
  • Damage pattern: Gradient 3 (focused – excellent armor penetration)

Particle Beam-4 (if researched):

  • Damage: 4 per shot
  • Power required: 10
  • Range: 200,000 km
  • Size: 7 HS (350 tons)
  • Damage: single-column (all damage to one armor location)
  • No damage falloff within range

Decision: Lasers win at this tech level. Here is why:

  1. Lasers deal 10 damage vs particle beam’s 4 damage for the same power draw
  2. Lasers are smaller (3 HS vs 7 HS) – we can fit more weapons
  3. Laser gradient-3 damage pattern already focuses damage well for penetration
  4. Particle beams shine later when armor is thicker and single-column penetration matters more

Weapon loadout: 6x 10cm Lasers

Weapon tonnage: 6 x 3 HS x 50 = 900 tons (18 HS total)
Total power draw: 6 x 10 = 60 power
Total damage per volley: 6 x 10 = 60 damage

Step 4: Fire Control Matching

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The fire control must:

  1. Track at or above target speed – if our FC tracks at 5,000 km/s, it has full accuracy against targets moving up to 5,000 km/s
  2. Have sufficient range to cover our weapon envelope
Tracking modifier = min(1.0, FC_Tracking_Speed / Target_Speed)

With FC tracking 5,000 km/s vs a target at 2,500 km/s (our own speed class):

Tracking mod = min(1.0, 5000 / 2500) = 1.0 (full accuracy)

Even against faster targets at 4,000 km/s:

Tracking mod = min(1.0, 5000 / 4000) = 1.0 (still full accuracy)

Our 5,000 km/s tracking is more than adequate for this era. It would only degrade against targets faster than 5,000 km/s.

Fire control range: We need the FC to cover at least our laser maximum range (~160,000 km). From the formula:

FC_Range = FC_Size x Resolution x FC_Tech_Level x 10,000 km

A standard beam FC provides range based on its size. We need range >= 160,000 km. With starting tech, a 2 HS beam FC should provide adequate range for our weapon envelope.

Fire control allocation: 2x Beam Fire Controls (2 HS each = 4 HS total = 200 tons)

  • 3 lasers assigned per FC (provides redundancy – if one FC is destroyed, half the weapons still fire)

Step 5: Sensor Selection

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Our cruiser needs to detect targets at engagement range or beyond. We need:

  • Active sensor to detect enemy ships
  • Resolution matched to expected target size

From the active sensor formula \hyperlink{ref-ex-beam-1}{[1]}:

Detection_Range (km) = sqrt((Active_Strength x HS x EM_Sensitivity x Resolution^(2/3)) / PI) x 1,000,000

For a resolution-100 sensor at 5 HS with Active_Strength=10, EM_Sensitivity=5:

= sqrt((10 x 5 x 5 x 100^(2/3)) / 3.14159) x 1,000,000
= sqrt((250 x 21.54) / 3.14159) x 1,000,000
= sqrt(1,714) x 1,000,000
= 41.4 x 1,000,000
= 41,400,000 km (~41M km)

This detects a 5,000-ton ship (matching resolution 100) at approximately 41 million km – well beyond any beam engagement range. A 10,000-ton ship would be detected at even greater range due to the cross-section scaling.

Sensor allocation: 1x Active Sensor (5 HS = 250 tons), resolution 100

  • Detects 10,000-ton ships well beyond weapon range
  • Detects 5,000-ton ships at full rated range
  • Smaller targets detected at reduced range per the sqrt scaling

Step 6: Armor Selection

Updated: v2026.01.30

With Duranium armor (strength 5 per layer), we need to decide on thickness. Our expected threats are similar-era beam weapons dealing 4-10 damage per hit.

Armor depth analysis:

  • A 10-damage laser hit vs 5-strength Duranium: penetrates 2 layers per hit
  • A 4-damage particle beam: does NOT penetrate even 1 layer (4 < 5)
  • Multiple hits to same column will progressively strip armor

Per the guidelines in Section 8.2.3 Armor Thickness, 4-5 layers is “moderate protection, good for cruiser-weight combatants.”

Decision: 4 layers of Duranium armor

Armor weight for a 10,000-ton ship at 4 layers (approximate from Section 8.2.3 Armor Thickness):

Armor mass: approximately 2,500-3,500 tons

Let us estimate 3,000 tons for our calculations.

Armor allocation: 4 layers Duranium = ~3,000 tons

  • Stops particle beam hits completely (4 damage < 5 strength)
  • Requires 2 laser hits to same column to penetrate (10 damage strips 2 layers)
  • Provides 20 total armor strength per column before internals exposed

Step 7: Shield Consideration

Updated: v2026.01.30

Trade-off analysis:

A 10 HS shield generator (the starting maximum size) provides:

Shield Strength Modifier = sqrt(10/10) = 1.0 (standard reference strength)

This costs 500 tons (10 HS x 50 tons) and:

  • Provides an energy buffer before armor takes hits
  • Generates EM signature (Shield_Strength x 3) making us visible to passive EM sensors
  • Requires Corbomite (may be scarce early)
  • A single 10 HS generator has HTK = sqrt(10) = 3.16 – could be destroyed by a few hits

Decision: Skip shields on this design. Reasons:

  1. At this tech level, shield generators are relatively weak (max 10 HS)
  2. The 500 tons is better spent on additional armor or weapons
  3. EM signature increase makes us detectable at greater range
  4. Corbomite may be needed for other projects
  5. A single 10 HS generator is a fragile single point of failure

Note: Revisit this decision once Maximum Shield Generator Size research allows 20+ HS generators, where the sqrt scaling provides meaningful efficiency gains.

Step 8: Power Plant Sizing

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Our 6 lasers each draw 10 power = 60 total power required.

Using Power Plant output formula:

Power_Output = Power_Tech x Size_HS x sqrt(Size_HS / 10)

At starting Pressurised Water Reactor tech (let us assume Power_Tech = 5):

For a 10 HS power plant:
Output = 5 x 10 x sqrt(10/10) = 5 x 10 x 1.0 = 50 power

That is short of our 60 power requirement. Options:

  1. One 10 HS plant (50 power) + one small supplemental plant
  2. One larger plant (if tech allows)
  3. Apply boost

With 20% boost (manageable explosion risk at 15%):

Boosted output = 50 x 1.2 = 60 power (exactly what we need)
Explosion chance when hit = 5% + (20/2)% = 15%

Decision: 1x 10 HS Power Plant with 20% boost

  • Output: 60 power (matches weapon draw exactly)
  • Mass: 500 tons
  • HTK: sqrt(10) = 3.16
  • Explosion risk: 15% when hit (acceptable)

Redundancy concern: A single power plant is a vulnerability. If destroyed, all weapons lose power. Consider adding a 2 HS backup:

Backup: 2 HS plant, output = 5 x 2 x sqrt(2/10) = 5 x 2 x 0.447 = 4.47 power

That only powers a fraction of one laser. Not worth the tonnage for such minimal backup. Accept the single-point-of-failure at this tonnage constraint.

Power plant allocation: 1x 10 HS reactor (20% boost) = 500 tons

Step 9: Fuel Tankage

Updated: v2026.01.30

We want enough fuel for sustained system operations. The warship guideline from Section 8.3.5 Fuel Consumption recommends 15-25% of hull tonnage devoted to fuel.

Fuel consumption with 1.25x engine boost and 20 HS engines (fuel consumption modifier = sqrt(10/20) = 0.707):

Boost penalty at 1.25x: approximately 1.56x fuel consumption
Base fuel rate per EP/hour = Fuel_Consumption_Modifier x Boost_Penalty
Base fuel rate = 0.707 x 1.56 = 1.103 litres per EP per hour
Fuel per hour = 500 EP x 1.103 = 551.5 litres/hour (approximate)

Range calculation at our speed of 2,500 km/s:

Range (billion km) = Fuel_Capacity / Fuel_per_Hour x Speed x 3600 / 1,000,000,000

Allocating 15% of hull tonnage to fuel (1,500 tons = 30 HS):

Fuel capacity: 6 standard tanks x 50,000 litres = 300,000 litres
Range = 300,000 / 551.5 x 2,500 x 3600 / 1,000,000,000
Range = 300,000 / 551.5 x 9,000,000 / 1,000,000,000
Range = 544.0 x 0.009 = approximately 4.9 billion km

This provides workable operational range for inner system defense. For reference, Earth-to-Jupiter distance averages about 0.8 billion km, so 4.9 billion km covers multiple round-trips within a solar system.

Fuel allocation: 1,500 tons (300,000 litres, ~4.9 billion km range)

Step 10: Bridge, Engineering Spaces, MSP Storage

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Bridge: Mandatory on all ships. 1 HS = 50 tons.

Engineering spaces: Critical for maintenance and damage control. Per the Annual Failure Rate formula:

AFR_Without_Engineering = 0.2 x Ship_Tonnage (percent)
AFR_With_Engineering = (0.04 / Engineering_Tonnage_Percent) x Ship_Tonnage

Targeting 5% engineering (500 tons):

AFR = (0.04 / 0.05) x 10000 = 0.8 x 10000 = 8000...

Actually, the percentage is of total tonnage. With 500 tons engineering on a 10,000 ton ship (5%):

Engineering_Tonnage_Percent = 500 / 10000 = 0.05 (5%)

This provides reasonable maintenance support. The MSP stored:

MSP_Stored = floor(12.5 x Ship_Build_Cost_BP x Engineering_Tons / Total_Ship_Tons)
MSP_Stored = floor(12.5 x [Build_Cost] x 500 / 10000)

The exact MSP depends on total build cost, but 5% engineering gives decent damage repair capability.

Allocations:

  • Bridge: 50 tons (1 HS)
  • Engineering: 500 tons (10 HS, 5% of hull)

Step 11: Final Design Review

Updated: v2026.01.30

Initial Mass Budget

Component Mass (tons) HS
Engines (4x 20 HS) 4,000 80
Lasers (6x 10cm) 900 18
Fire Controls (2x) 200 4
Active Sensor (1x) 250 5
Power Plant (1x 10 HS) 500 10
Armor (4 layers Duranium) ~3,000 –
Fuel Tanks 1,500 30
Bridge 50 1
Engineering 500 10
Subtotal ~10,900 –

Problem: We are ~900 tons over budget. This is the fundamental iteration loop of ship design. Options:

  1. Reduce armor (3 layers instead of 4, saves ~750 tons)
  2. Reduce weapons (5 lasers instead of 6, saves 150 tons)
  3. Trim fuel (reduce to 1,000 tons, saves 500 tons but reduces range)

Revised design – applying option 1 (reduce armor to 3 layers):

Component Mass (tons) HS
Engines (4x 20 HS) 4,000 80
Lasers (6x 10cm) 900 18
Fire Controls (2x) 200 4
Active Sensor (1x) 250 5
Power Plant (1x 10 HS) 500 10
Armor (3 layers Duranium) ~2,250 –
Fuel Tanks 1,500 30
Bridge 50 1
Engineering 500 10
Subtotal ~10,150 –

We are now only ~150 tons over. Trimming fuel tanks to 1,350 tons (27 HS, ~270,000 litres) brings us under budget with a small margin for crew quarters.

Final Iteration (Verified)

Component Mass (tons) HS
Engines (4x 20 HS) 4,000 80
Lasers (6x 10cm) 900 18
Fire Controls (2x) 200 4
Active Sensor (1x) 250 5
Power Plant (1x 10 HS) 500 10
Armor (3 layers Duranium) ~2,250 –
Fuel Tanks 1,350 27
Bridge 50 1
Engineering 500 10
Crew Quarters 50 1
Total ~10,050 –

Close enough to 10,000 tons (the ~50 ton excess can be absorbed by minor sizing adjustments in the ship designer). Final speed calculation with 200.5 HS effective size:

Speed = 500 EP * 1000 / 201 HS = 2,488 km/s (approximately 2,500 km/s)

Final Performance Characteristics 

Speed: 500 EP * 1000 / ~200 HS = 2,500 km/s
Armor: 3 layers x 5 strength = 15 damage to penetrate per column
Firepower: 60 damage per volley (6 lasers x 10 damage)
Power: 60 (exactly matching weapon draw)
Range: ~4.4 billion km (inner system defense)
Engine redundancy: 4 engines, HTK 4.47 each (17.9 total)

Speed Upgrade Path

Once Nuclear Pulse Engine (8 EP/HS) is researched, the same 80 HS engine allocation produces:

EP = 80 * 8 * 1.25 = 800 EP
Speed = 800 * 1000 / 200 = 4,000 km/s

This makes engine technology research the single highest-impact upgrade path for this design.

Key Decisions Explained

Updated: v2026.01.30

Why Laser Over Particle Beam?

At early tech, lasers deal 2.5x more damage per power unit (10 vs 4) and occupy less than half the hull space per weapon. Particle beams become competitive when armor reaches 6+ layers and single-column penetration matters. At 3-4 layers of Duranium, raw laser damage is more effective.

Speed vs Armor Trade-Off

We chose 3 layers (moderate protection) over 4+ layers (heavy armor doctrine). At 2,500 km/s, we can dictate engagement terms against most early-game opponents and outrun heavily armored battleships. The 3 layers stop particle beams cold (4 damage < 5 armor strength) and require 2 laser hits per column to penetrate – reasonable for trading fire at medium range.

Why 40% Engine Allocation Works

Dedicating 40% of tonnage to engines at TN-start provides 2,500 km/s – solidly in the “Moderate” speed class. This leaves 60% of hull for weapons, armor, sensors, and support systems. Going to 50% (3,125 km/s) would require sacrificing either weapons or armor, weakening the ship’s core combat role.

Number of Weapons vs Individual Size

Six 10cm lasers provide better sustained firepower than fewer larger weapons because:

  • More individual shots means more chances to hit
  • If one laser is destroyed, you lose only 1/6 of firepower
  • Six weapons spread across 2 fire controls gives redundancy
  • Overkill on each shot is wasted; more smaller shots is often better than fewer large ones

Common Mistakes

Updated: v2026.01.26

  1. Forgetting Power Plants: Without a reactor, beam weapons cannot fire. Every laser, railgun, and particle beam requires power. Always calculate total power draw before finalizing weapons.

  2. Undersizing Fire Control Tracking: If your FC tracks at 3,000 km/s but the target moves at 5,000 km/s, your hit chance is reduced to 60%. Always match or exceed expected target speeds.

  3. No Engineering Spaces: Ships without engineering suffer high failure rates and cannot repair damage in the field. The formula AFR = 0.2 x Tonnage without engineering means a 10,000-ton ship has a significant annual failure chance.

  4. Insufficient Fuel for Concept of Operations: A system defense ship needs 5-15 billion km range minimum. Calculate your actual range, not just fuel mass. At low speeds, even large fuel loads provide short range.

  5. Ignoring the Iterative Nature of Design: Your first pass will almost always exceed tonnage. Budget overruns of 10-30% are normal in the initial draft. Plan for 2-3 iterations trimming components.

  6. Single Point of Failure Components: One power plant, one fire control, or one engine means a single hit can cripple your ship. Where tonnage allows, distribute critical systems across multiple components.

  7. Designing in Isolation: If your cruiser moves at 2,500 km/s but your destroyers move at 4,000 km/s, the task group is limited to cruiser speed. Design your fleet as a system.

References

\hypertarget{ref-ex-beam-1}{[1]}. Aurora C# active sensor formula from Appendix A: Detection_Range (km) = sqrt((Active_Strength x HS x EM_Sensitivity x Resolution^(2/3)) / PI) x 1,000,000. The x 1,000,000 multiplier produces detection ranges in the tens of millions of km for standard military sensors.

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Aurora 4X Manual & Guide - Unofficial community documentation for Aurora C# (game by Steve Walmsley)

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