Solid core nuclear rocket

Atomic Fission Drives are commonly used in The Frontier as a practical method of reaching Void velocity, crossing the Void and decelerating at the destination system. These engines are indisputably the most powerful drives any ship can mount.

Atomic engines work through the harnessing of atomic fission. Through the use of advanced technology, this power is collected and concentrated, resulting in significant acceleration capable of reaching void velocity in under 5 days.[1]

Atomic FuelEdit

Atomic engines use solid pellets of radioactive material, usually plutonium or uranium, of a standardized shape and size.[2] Each pellet costs 10,000 Credits, and is available for purchase at Class I and II Construction Stations, but due to their intrinsic value in the interstellar trade, are also found in Class III centers, most major spaceports and at locations where uranium is refined.

Accelerating and decelerating at 1g, each engine consumes one pellet, leaving enough power for 1-10 additional days of thrust at 0.5g and twice that powering ship's systems before it is reduced to depleted uranium, which provides no power to ship's systems.[3]

If the ship accelerates to void velocity and decelerates at 0.5g or less at the destination, the pellet may provide 1d5 x 20 days of 1/2 g acceleration (twice that powering ship's systems).[4] These "half-spent" fuel pellets are also traded and sold and are commonly used in shuttles and orbiter/landers equipped with atomic drives instead of chemical rockets and also used to power some types of power generators.[5]

Although each engine consumes 1,130 Cr less worth of fuel than an equivalent ion engine per jump, the overall greater availability of hydrogen and (far more economical) alternate fuels, as well as their simpler maintenance schedule, along with other factors, make atomic engines less common than their ion counterparts, though some newer designs with fewer atomic engines than the maximum (and correspondingly reduced performance) are significantly reducing these costs and relegating ion-drive engines to secondary roles in merchant fleets.

Fractional Acceleration Fuel ConsumptionEdit

It can be assumed that since a an atomic drive ship can maintain 1 g acceleration with a fewer number of engines than the maximum required by the Hull Size, that the shared load reduces the fuel consumption on each individual engine correspondingly. This would mean that a ship with an ADF of 3 could make three consecutive 1 g jumps before expending the fuel pellets. The ship would still require an overhaul after every 1, 3, or 12 jumps[6] as normal.

Accelerating to Void Velocity at more than 1 g consumes proportionally more fuel. Likewise, low-g acceleration conserves fuel accordingly.

No ship can have acceleration greater than its ADF.


Official RulesEdit

Knight Hawks Expanded Rulebook pp.13

The most powerful type of engine that can be installed on a spaceship is an atomic fission engine. Atomic engines propel the ship by splitting atoms and using the tremendous amount of energy released as thrust. Atomic drives use either uranium or plutonium as fuel. An engine will burn a 10 cm diameter chunk of fuel in the course of an interstellar jump.

Atomic engines are mounted on struts that keep them away from the ship's hull.[8] This is because these drives are a source of dangerous radioactivity, and must be isolated from the crew and living quarters of a ship. A fighter is the only ship that has an atomic drive mounted in the spaceship's tail. Fighter pilots must wear special suits that resist radioactivity.

The struts that atomic drives are mounted on are equipped with explosive charges. These charges enable the pilot or engineer to jettison the engines if this should become necessary. This obviously will be done only in extreme emergencies, such as an engine meltdown or overload.[9]

Acceleration/Deceleration Factor (ADF)Edit

If a ship has a full complement of atomic engines, both its ADF and MR (Maneuver Rating) will be the number indicated on the Hull Specification Chart. For each engine less than the maximum, however, either the ship's ADF or MR (player's choice, at time of construction) must be lowered by 1. The ship's MR cannot be more than one higher than the ADF. Also, the ship's ADF and MR never will be less than 1, even if the ship has only one engine.

EXAMPLE: Hargut Lance, a hull size 6 ship, can carry three atomic engines. With all three engines, its ADF is 3 and its MR is 3. If one engine is removed, either its ADF or its MR must be reduced to 2. The owner, Snar Latm, reduces the MR. If a second engine is removed, the ship's ADF must be reduced to 2, or its MR reduced to 1.

Atomic Fuel (official rule)Edit

A pellet of atomic fuel is a 10 cm diameter piece of radioactive material, either plutonium or uranium. One pellet costs 10,000 CR. They can be purchased only at Class I or Class II ship construction centers. A pellet is burned out in a single interstellar jump. A ship that does not decelerate appreciably after a jump will still have power for 1d5 x 20 days.

An atomic engine can automatically replace the fuel pellet after a jump, if the engine has been loaded with an additional pellet. Depending on the size of the engine, from 3 to 10 pellets can be loaded into it before a voyage begins (for the exact figure, see below). Additional pellets can be loaded only by a Spaceship Engineer (see Spaceship Skills). Refueling an engine takes 2d10 hours, minus the engineer's skill level. Because most of this time is spent removing access panels and shielding, the time is the same no matter how many fuel pellets are loaded.


Besides refueling, atomic engines must be overhauled regularly by an engineer. To determine how much time the overhaul takes, roll a number of d10s equal to the engineer's skill level. Subtract the result of this roll from 60 hours. The difference is the number of hours needed to overhaul the engine.

EXAMPLE: A level 3 starship engineer needs to overhaul a starship's engine. The player rolls 3d10 and gets 15. Subtracting 15 from 60 hours determines that overhauling the engine will take 45 hours.

The Atomic Drive Information Table lists the number of trips each type of atomic engine can make between overhauls.

Multiple EnginesEdit

If more than one atomic engine on a ship needs either refueling or overhauling, each must be worked on separately. For example, if only one engineer is aboard a twin engine ship that needs both overhauling and refueling, that engineer must perform four operations consecutively. This could take several weeks.

Skipping OverhaulsEdit

If an atomic engine is not overhauled on schedule and the ship tries to make an interstellar jump, there is a 60% chance the engine will fuse itself into a worthless lump of iron. If a second jump is made, this risk increases to 80%. A third jump cannot be made, and an attempt will automatically ruin the engines. If there is an engineer on board, he has a chance to realize that the engines are about to become fused. This chance is equal to his Logic score plus 10% x his engineering skill level. A successful roll means the engineer can shut down the engines before they are ruined. However, no further acceleration will be possible until the engines are overhauled.


Due to different capabilities, atomic drives have different costs depending on the construction center used.

Engine Size A (HS 1-4):

Cost per Engine at Class I Center: 200,000 Cr
Cost per Engine at Class II Center: 250,000 Cr
Fuel Fuel Pellets Carried: 3
Trips Between Overhauls: 1
  • Number of Engines by Hull Size (Min/Max):
    • 1: 1/1
    • 2: 1/1
    • 3: 1/2
    • 4: 1/2[10]

Engine Size B (HS 5-14):

Cost per Engine at Class I Center: 400,000 Cr
Cost per Engine at Class II Center: 500,000 Cr
Fuel Fuel Pellets Carried: 6
Trips Between Overhauls: 3
  • Number of Engines by Hull Size (Min/Max):
    • 5: 1/3
    • 6: 1/3
    • 7: 1/2
    • 8: 1/2
    • 9: 1/2
    • 10: 1/3
    • 11: 1/3
    • 12: 1/4
    • 13: 1/4
    • 14: 2/6

Engine Size C (HS 15-20):

Cost per Engine at Class I Center: 750,000 Cr
Cost per Engine at Class II Center: N/A
Fuel Fuel Pellets Carried: 10
Trips Between Overhauls: 12
  • Number of Engines by Hull Size (Min/Max):
    • 15: 2/4
    • 16: 4/6
    • 17: 4/6
    • 18: 4/6
    • 19: 2/4
    • 20: 6/8

Notes and ReferencesEdit

  1. Using KH game scale, 1 ADF equals 16,666 meters per second squared. Since 1g = 9.80665 meters per second squared, 1 ADF equals approximately 1,700g's, which is absolutely not survivable for any known sentient species. For purposes of linear acceleration to void velocity, using a 6km hex results in 1 ADF = 1g acceleration.
  2. 10cm diameter cylinder weighing approximately 5kg (depending on actual composition) and is kept in a secured, lead-lined case; total weight of pellet and case is 10 kg)
  3. Landing does not appreciably use up the remaining power, but takeoff consumes a day's worth of 1/2 g acceleration.
  4. This is a slight modification of the official rule.
  5. Half-spent pellets may be only obtained in the secondary market; cost is usually 50-100 Cr per day of 1/2g thrust.
  6. As determined by engine size.
  7. This rule reflects in-game physics, as well as the relative economy of Star Frontier commerce. It makes atomic engines much more economical to operate than corresponding ion drives for commercial use, while keeping both competitive, depending on application.
  8. Ships with only one engine mount it on the tail, but with a buffer zone between the ship and the hull; essentially a "strut" out the tail that might or might not be sheathed for aesthetic purposes.
  9. Before this point is reached, the fuel pellet can be ejected as part of a crash shutdown.
  10. Originally misprinted as "1", official errata published in Polyhedron #16
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