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The Lyman Drive: An Alternative to the Standard Jump Drive

This article was originally posted to Freelance Traveller's website in May 2002, and was reprinted in the April 2013 issue.

Introduction

A major source of complaints in ship designs for Traveller, when using any of the standard rule sets, is the necessity for allocating major portions of hull space for fuel storage. At the same time, the reduced cargo capacity and increased cost of fuel makes most starships economically marginal at best, and impossible at worst. Given the description of purchasing a ship in the standard rules, it could be considered strange that most far and free traders aren't 'skips' (evading repossession for nonpayment).

The Lyman Drive offers a possible alternative that makes it easier for a small ship to be economically sustainable, while not completely eliminating the need to scrimp and save between payments. It also offers the possibility of designing small ships with extended jump range - ideal for exploratory ships.

Fuel Usage

The Lyman Drive requires more fuel for a Jump-1 than a standard Jump Drive, but the fuel requirements for higher jumps are significantly lower - a Jump-6 requires less than 15% of hull to be allocated to fuel carriage/storage. The fuel usage figures depend on jump range and tech level of construction, and are as follows:

Fuel Usage as % of Hull Volume

Jump Factor

TL10

TL11

TL12

TL13

TL14

TL15

1

13.6

10.2

10.2

10.2

10.2

10.2

2

-

13.6

12.1

12.1

12.1

12.1

3

-

-

13.6

12.7

12.7

12.7

4

-

-

-

13.6

13.1

13.1

5

-

-

-

-

13.6

13.2

6

-

-

-

-

-

13.6

Note that if no figure is given, a Lyman Drive of that capability cannot be constructed at that tech level. These are Traveller tech levels, rather than GURPS tech levels.

(If you want to simplify, just say that fuel usage is a flat 15% of hull volume.)

Gain in Available Tonnage

The decrease in required fuel means a potentially drastic increase in usable space in the hull - either for the comfort of the crew and/or passengers, or for increased cargo-carrying capacity. The amount of hull volume recovered (as a percentage of total hull volume) is as follows:

Recovered Volume as % of Hull Volume

Jump Factor

TL10

TL11

TL12

TL13

TL14

TL15

1

-3.6

-0.2

-0.2

-0.2

-0.2

-0.2

2

-

6.4

7.9

7.9

7.9

7.9

3

-

-

16.4

17.3

17.3

17.3

4

-

-

-

26.4

26.9

26.9

5

-

-

-

-

36.4

36.8

6

-

-

-

-

-

46.4

Observe that Lyman J1 drives actually result in a loss of available tonnage.

Note that if no figure is given, it is impossible to build a Lyman Drive with the indicated capability at the indicated tech level.

Increased Cost

The Lyman Drive, though having reduced fuel costs, does have higher purchase and operating costs.

The Lyman Drive must use refined fuel only. This requires either limiting the ship's ports of call to Class A/V and B/IV starports (C/III if the port is known to have refined fuel available), or the ship must be equipped with a refiner to allow the use of unrefined fuel (at Class C/III, D/II, and E/I ports) and/or wilderness refueling (anywhere). Standard ship refiners can be used.

'Jump governors' cannot be used with the Lyman Drive. All jumps use the same amount of fuel as the drive's rated maximum jump.

The cost of building the drive is higher, depending on both the desired maximum range and the tech level of construction, as follows:

Cost of Lyman Drive as Compared to Standard Jump Drive of the Same Capability

Jump Factor

TL10

TL11

TL12

TL13

TL14

TL15

1

115%

114%

113%

112%

111%

110%

2

-

128%

126%

124%

122%

120%

3

-

-

139%

136%

133%

130%

4

-

-

-

148%

144%

140%

5

-

-

-

-

155%

150%

6

-

-

-

-

-

160%

Note that if no figure is given, a Lyman Drive of that capability cannot be constructed at the given tech level.

Note that this increase is to be applied after all other cost factors associated with the drive (e.g., foreign manufacture costs, exchange rates, tech level effects, and so on).

Lyman Drives themselves take up the same amount of space on the ship as an equivalent Standard Jump Drive.

The cost of maintaining the Lyman Drive is higher than for standard jump drives. Apply the same increases from the construction costs table above to the cost for all parts and servicing, including annual maintenance.

(If you want to simplify, the cost of building and maintaining a Lyman Drive is 30% higher than a standard Jump Drive.)

All die rolls related to operating the Lyman Drive have an unfavorable DM of 1, effectively increasing the skill required of the engineer (and therefore the amount the engineer must be paid).

Economics

At J1, the Lyman Drive is strongly contraindicated, as it reduces revenue capacity while increasing costs.

At  J2, the increased cost of the Lyman Drive offsets the increased profitability from having additional cargo space, resulting in an increase in the CER (see Ken Pick's Commercial Efficiency Analysis of Selected Starfreighters) that is only marginal. In speculative trade, a Lyman Drive ship will still have to work to make ends meet, but may be able to survive on routes that would bankrupt a standard design. The advantage can be 'played up' by increasing the total hull volume (that is, larger ships will see a greater benefit than smaller ones).

In the case of the RL2 Stretch Fat Trader, using the TL15 version of the Lyman Drive does bring the ship from economically nonviable without subsidy to minimally profitable in unsubsidized speculative trade.

The advantage of the Lyman Drive makes itself felt at J4. At this level and above, incremental increases in hull volume are disproportionately allocatable to revenue generation, and profitability as a common-carrier at standard rates is virtually guaranteed.

Tech Level Ship Tonnage Price (MCr) CER
Gross Net

Jump-2 Examples (from Freelance Traveller Shipyard)

11

Type AL2 Far Trader

300

135

84

3.21

11

(Lyman Drive-211)

300

154

92

3.35

12

(Lyman Drive-212)

300

158

92

3.43

15

(Lyman Drive-215)

300

158

90

3.51

11

Type R2 Stretch Fat Trader

500

277

178

3.11

11

(Lyman Drive-211)

500

309

192

3.22

12

(Lyman Drive-212)

500

317

191

3.32

15

(Lyman Drive-215)

500

317

188

3.37

11

Type RL2 Stretch Fat Trader

600

317

228

2.78

11

(Lyman Drive-211)

600

355

245

2.90

12

(Lyman Drive-212)

600

364

244

2.98

15

(Lyman Drive-215)

600

364

240

3.03

Jump-3 Example (from The Traveller Adventure)

12

Oberlindes Type CT Cargo-carrier

1000

462

410

3.38

12

(Lyman Drive-312)

1000

626

469

4.00

15

(Lyman Drive-315)

1000

635

455

4.19

Jump-4 Example (from The Traveller Adventure)

13

Tukera Type AT Freighter

3000

1369

809

6.77

13

(Lyman Drive-413)

3000

2161

924

9.35

15

(Lyman Drive-415)

3000

2176

905

9.62

Non-Commercial Use of the Lyman Drive

Where commercial viability of the ship is not at issue, the Lyman Drive offers significant advantages. Extra space can be put to use to increase crew/passenger comfort, or to carry additional needed supplies or equipment.

Military Implications

At J2, military ships can use the additional space for loading ammunition, and may possibly be able to mount additional weapons batteries. Such a ship will have an advantage over standard designs of equivalent displacement.

At J3, another option becomes available: the ship can both fight and run, without the need for fuel tenders or on-site refueling. A fleet fully equipped with Lyman J3 Drives instead of standard J3 drives becomes eminently suitable for raiding hostile systems, or for fighting a war of attrition. It also becomes possible for such a fleet to attack the mainworld of a system without needing to fight outlying units to secure a fuel source.

At J4 and above, both capabilities become available together.

Again, incremental increases in hull volume can be disproportionately allocated to mission usage. A Battle Tender equipped with the Lyman Drive will be able to carry more Battle Riders than one equipped with standard jump drives.

Non-Military Implications

As with military ships, the benefits available will be increased mission tonnage, increased range, or both. The difference will be in how the benefit is applied.

Exploratory ships of J3 capability or greater immediately gain 'out-and-back' capability. This allows systems to be explored without the necessity of assuring the availability of fuel in the target system. Ships of J4 or greater capability also gain increased space for mission-related material (e.g., enhanced instrumentation, or increased supplies to allow a longer mission). J2 ships will gain mission capability, but not range.

Colonization vessels with J3 capability either allow for larger colonization efforts or for planting colonies at a greater distance from the launch point. This potentially allows for the selection of better colony worlds, or the staging of colonization missions from planets with better infrastructure or greater available resources.

Couriers, yachts, x-boats, and other similar non-military vessels travelling primarily between well-established worlds will gain both increased mission space (which may be devoted to increased comfort for crew and/or passengers) and increased range, if they are capable of J4 or more. J3 ships gain one or the other, but not both; J2 ships will gain mission space.