[Spaceship] Query: Traveller Jump Sled Performance

[DaltonS]

I'm designing a Traveller style J-2 Jump Sled to deliver a payload to an empty parsec using RPK's "GURPS Spaceships In Traveller" rules. The payload is a large Modular Section taking up the first 2 hull sections with everything else in the rear hull section. The J-2 Jump Drive requires 3 fuel tanks with the payload attached. Without the payload module would it only need 1 full tank for the return trip? (This fuel would have to be carried in the payload module since there is no room for it in the drive section.) Note that the following design can be scaled down for a smaller payload.

MALAMUTE (MARINER-CLASS HEAVY FRAME CARRIER)
PILOTING/TL10 (HIGH-PERFORMANCE SPACECRAFT) or PILOTING/TL10 (STARSHIP) Page:

 TL    Name    dST/dHP  Hnd/SR  HT      Move       LWt.       Load       SM       Occ        dDR   Range    Cost   
10^  Malamute    300     -4/4   13  0.333333G/c  100,000  63,027.4 [1]  +12  214ASV [2,3]  0/0/23    —    $5.357B

Length: 200 yd. (600 ft.) Crush Depth: 0.0 Atmospheres (0 ft.)
Power Points: +1⅓ / -1⅔
Energy Bank: 1 PPh / 180 PPt
Space Performance #1: Hnd/SR: -4/4 sAccel: 0.333333Gs
Space Performance #2: FTL Rating: FTL-2

SHIP SYSTEMS

   FRONT     
[1-6, Core]  Large Modular Section
               SM+11.5 / 60,000 Tons

   CENTER    
[1-6]        Large Modular Section
               (continued)

    REAR     
[1]          Smaller SM Systems
               SM+11
  [a]        Advanced Metallic Laminate Armor
               dDR 23
  [b‡‡]      Super Fusion Reactor
               4 Power Points / 400 yr Fuel [4,7,TL11]
  [c!]       Standard Reactionless Engine
               0.333333 Gs [3,4]
[2]          Smaller SM Systems
               SM+11
  [a]        Hangar Bay
               Cap.: 1,000 Tons / SM+7 / Launch: 800 Tons/min [4,5]
  [b]        Cargo Hold
               1,500 Tons / SM+6 Bay Doors
  [c!]       Tertiary Battery
               ten 100 MJ improved rapid fire laser turrets [4]
[3!]         Jump 2 J-Drive
               7,500 Tons Hydrogen per Parsec / 15,000 Tons per Jump [3,4,6]
[4-6]        Fuel Tank
               15,000 Tons of Hydrogen
[Core]       Smaller SM Systems
               SM+11
  [a]        Control Room
               Comp: C9 / Comm/Sensor: 10 / 15 Stations [4]
  [b-c]      Habitat
               15 bunkrooms, ten cabins, 60 hibernation chambers, ten luxury cabins, 47 passenger cabins, one sickbay [4]
               five bunkrooms, one establishment, 30 hydroponics bays, 90 life pods, one ops center, 30 power cells, 500 tons of steerage cargo

User Notes: J2 drive charges in 15 minutes. Without the modular section the ship can accelerate at 1G and requires 1 tank (5,000 tons) of fuel to jump 2 parsecs.
Design Switches, Features, & Notes: 8 Airlocks (Capacity: 8 people each), Fuel Cost: $30,000,000; Auxiliary Craft Cost: $25,977,500; Total Cost: $5,412,977,500
IR SIGNATURE: +7 Super Fusion Reactor
CAMPAIGN OPTIONS: EBS's Unofficial rules, RPK's Traveller rules
SHIP OPTIONS: Artificial Gravity, Gravitic Compensators, Total Life Support
[1] Load includes: 27.4 tons of Crew & Passengers, 500 tons in Steerage Cargo, 1,500 tons in Cargo Hold, 60,000 tons in Modular Section, 1,000 tons in Hangar Bay
[2] Plus 60 in Hibernation Chambers, [3] Crew Requirement (114 total): 15 Control Stations (1 Captain, 1 Executive Officer, 1 Helmsman, 1 Chief Engineer, 1 Navigator, 1 Communication Operator, 1 Sensor Operator,
5 Tertiary Battery Gunners, 1 Flight Officer, 2 Cargo Masters), 31 Technicians, 10 Gunners, 10 Auxiliary Craft Crew, 19 Passenger Care, 2 Entertainment, 1 Medical, 20 Office Workers, 6 Gardeners
SYSTEM NOTES: [4] 10 Workspaces per Full system, 3 per Smaller SM system, [5] Optimized for Modular Cutter
FUEL USED: [6] Hydrogen (15,000 tons), [7] Hydrogen/Helium Isotopes
RADIATION PROTECTION FACTOR (PF): 200/100/1,000, Non-Mass Shielded PF: 100 (see p. SS5:41)

AUXILIARY CRAFT

Qty.       Ship       Location     Cost     Mass  Crew  
   5  Modular Cutter  Rear      $25.9775M  1,000  10

HABITATS

Qty.   Location          Type          SM          Notes          
  15  Rear [Cb]  Bunkrooms             +0              60 person
  10  Rear [Cb]  Cabins                +0              20 person
  60  Rear [Cb]  Hibernation Chambers  +0            60 chambers
  10  Rear [Cb]  Luxury Cabins         +0              20 person
  47  Rear [Cb]  Passenger Cabins      +0              94 person
   1  Rear [Cb]  Sickbay               +0        1 bed; +2 Skill
   5  Rear [Cc]  Bunkrooms             +0              20 person
   1  Rear [Cc]  Establishment         +0    20 patrons, 2 staff
  30  Rear [Cc]  Hydroponics Bays      +0  120 person production
  90  Rear [Cc]  Life Pods             +0     360 person (4/pod)
   1  Rear [Cc]  Ops Center            +0    20 person; +1 Skill
  30  Rear [Cc]  Power Cells           +0        1 PPh / 180 PPt
 100  Rear [Cc]  Steerage Cargo        +0               500 tons

WEAPONS TABLE
Range Scale: Basic Combat Ranges Turn Length: 20-Sec

Qty.        Location        Weapon   Mount    Options    Size       Damage     sAcc [1]  Rcl    RoF   Shots  Range  

  10  Rear [2c] - Tertiary   Laser  Turret  Rapid Fire  100 MJ  5dx2 (2) burn   +0 (+4)   1   20 [2]    ∞     S/L

[1] Parenthetical value is the Rapid Fire bonus (p. SS1:60), [2] Includes x2 RoF for Improved

Created using the GURPS Spaceships Design Spreadsheet Version 2.0 RC 33 copyright © 2009-2017 Eric B. Smith. This spreadsheet is based on information contained in the GURPS Spaceships series of books.

Dalton “asking the experts” Spence

[Pomphis]

Originally Posted by DaltonS

Without the payload module would it only need 1 full tank for the return trip?

IMO that would be a sensible house rule, but under RAW it would require 3. It is a SM+12 ship, even if 2/3 are empty.

[malloyd]

Originally Posted by Pomphis

IMO that would be a sensible house rule, but under RAW it would require 3. It is a SM+12 ship, even if 2/3 are empty.

Although in principle you could design something that could carry a payload in a framework that could be folded up (or telescoped closed), erasing the volume the payload would normally occupy when it was empty.

Somewhat the same principle as a collapsable "drop" tank I suppose, which has a long controversial history in Traveller ship design.

[Fred Brackin]

Originally Posted by Pomphis

IMO that would be a sensible house rule, but under RAW it would require 3. It is a SM+12 ship, even if 2/3 are empty.

Yes, if you did this you'd have to change fuel use based on whether or not a cargo bay was empty or full.

For ultimate realism on reaction drives you'd do that but Spaceships is a simplified game.

Come to think of it you probably shouldn't be changing performance for CT even more than in Spaceships. CT is volume based.

[Donny Brook]

I don't have the whole Spaceships series; are there rules for towing anywhere? This might be analogous.

[Fred Brackin]

Originally Posted by Donny Brook

I don't have the whole Spaceships series; are there rules for towing anywhere? This might be analogous.

Towing would be like an External Clamp though obviously only for ships without energetic exhausts.

External Clamps definitely refigure normal space performance but Spaceships mostly just puts in placeholders for individual GMs to insert FTL rules.

[DaltonS]

I based this concept on "System Defense Boat Jump Shuttles" (T:S page 83) which described the combination as 700 dtons and said "Note that, when empty, the jump shuttle behaves as a ship of 300 tons (its actual hull size), which improves its sAccel, jump number, and fuel endurance." The "modular section" is actually a separate hull which is detached from the drive section upon arrival thus reducing the ship's mass by 2/3rds. How this would affect it's volume I don't know but in RPK's "GURPS Spaceships In Traveller" rules this isn't an issue.

Dalton “it's a Traveller vs GURPS thing” Spence