Fleet Tugs and Dropwarp: stutterwarp range extension

Roger Burton West
7 May 2008

Table of Contents

Note: Many thanks to John Dallman for the conversation which inspired this article.

The problem

The 7.7-light-year limit ("L" hereafter) of stutterwarp is a problem. It is specifically the sort of problem which vexes naval architects. While stutterwarp units are distinctly costly, so is losing ships because reinforcements aren't available.

Fleet Tugs

A large fleet tug can be a scarily fast vessel. Consider the Bridge-class fleet lifter (below), built round a 300MW stutterwarp drive and fusion plant. Unladen, this ship will outrun most missiles and fighters; she has no defences because she has no need for them. Carrying a Kennedy-class Guided Missile Cruiser she still makes 4.49, nearly as fast as the Kennedy alone; with a fully-laden Richelieu, she makes 2.27, versus the ship's own 2.33; with a Bismark, she makes 3.54, versus the ship's own 2.75. Certainly this is not a cheap ship, costing on her own as much as a large cruiser, but the implications for strategic mobility are immense.


The Bayern design of 2291 showed the potential for disposable stutterwarp units in extending a ship's range. These clearly have military applications as well. A stutterwarp drive for a warship may be her single most expensive component... but that's still a lot cheaper than a whole new warship.

While warships may well not be designed with disposable drive units, as they may be unnecessary in normal service, it seems very likely that such would be available for use in appropriate situations.

While full design specifications are not available for all ships, the Kennedy-class Guided Missile Cruiser may serve as an example; its 150MW drive masses 85 tonnes, takes up 72 cubic metres and costs MLv90. A hull module to contain this drive may cost around Lv200,000 - not really significant compared with the drive cost.

The total cost for our dropwarp unit is MLv90.2, 60% of the cost of a new Kennedy-class ship. This is not something that's likely to be built, and still less disposed of, during peacetime. However, when military needs dictate, the cost may seem trivial compared with the gains. The drop in warp efficiency from the small extra mass of the drive unit is insignificant; it would even be possible to carry multiple units and use them in succession. The only constraint is budget and the logistics of dropwarp pod delivery.

Transit points

A dropwarp unit is too expensive to be disposed of other than in very specific situations. Moving a fleet by tug needs multiple tug trips and discharges. How can these two be reconciled?

While a dropwarp unit (or other stuterwarp core) that has built up charge cannot be safely taken off-line outside a gravity well, it can be kept on-line indefinitely as long as it is not moved a significant distance. This allows a hybrid of the tug and dropwarp approaches: several dropwarp-equipped ships use the dropwarp pod to travel up to L/2. All ships rendezvous, and all their dropwarp units are transferred to a single ship (remaining on-line at all times). That ship takes the raft of dropwarp units L/2 back to their starting point, and allows them to be discharged safely; the remainder of the fleet carries on with its own drive capacity.

In extreme cases this can be extended asymptotically with multiple dropwarp pods; the next rendezvous point is at 3/4L from the starting system, the one after that at 7/8L, etc., thus producing a total fleet range arbitrarily close to 2L with all drive units recovered.

If such rendezvous-based transit operations were to take place on a regular basis, it seems likely that a permanent deep-space outpost would be constructed, and dropwarp pods shipped back periodically; they might even be made available for rent to civilians.


A tug group can shift its carried ships across a 1.5L gap, and a dropwarp pod can shift its ship across a 2L gap. These are the standard uses of range extension technology, and have obvious enough uses to "end run" a fleet round defending forces and allow access to enemy worlds.

However, potentially more significant is the possibility of allowing for retreat. In the conventional inter-system attack at distances beyond 0.5L, the attacker must win the fight or perish: if the defender can patrol potential discharge points effectively, the attacker will be unable to retreat over inter-system distances. Range extensions increase this, to 0.75L (for the tug) or L (for a single dropwarp pod).

All these tactics, and both range extension systems, must inevitably be used in the Kafer War even if not beforehand.

Bridge-class fleet lifter

The ship is built round a 300MW stutterwarp unit and a corresponding 300MW fusion plant (to simplify logistics, to minimise wet mass and to remove multiple-plant inefficiencies from the design).

Component Mass Volume Cost Surface
300MW fusion plant 10000 10000 200  
300MW nm stutterwarp 107 91 113.7  
10 bridge stations 50 80    
1 TAC station 5 8    
22 engineering stations 100 160    
63 25-m3 accommodations 167.5 1575    
Hamster cage spin hab 15.75 15.75    
180 days' supplies 11.34 56.7    
Navigation Radar 1 5 0.02 20
Advanced synthetic hull:        
27m hull section 34 17 1.275 850
24m hull section 30 15 1.125 750
15m hull section 20 10 0.75 471
Total 10541.59   316.87  

Drive efficiency table:

Load Speed
0 5.3428924
100 5.3261038
200 5.3095243
500 5.2609955
1,000 5.1838997
2,000 5.0422875
5,000 4.6943988
10,000 4.2776027
Bridge 4.2406565
20,000 3.7478418
50,000 2.9835079
100,000 2.4410119

Potential names in class: Tower Bridge, London Bridge, Southwark Bridge, Cannon Street Bridge, Blackfriars Bridge, Millennium Bridge, Waterloo Bridge, Hungerford Bridge, Westminster Bridge, Lambeth Bridge, Vauxhall Bridge, Grosvenor Bridge, Chelsea Bridge, Albert Bridge, Battersea Bridge, Wandsworth Bridge, Putney Bridge, Hammersmith Bridge, Barnes Bridge, Chiswick Bridge, Kew Bridge, Twickenham Bridge, Richmond Bridge, Kingston Bridge, Hampton Court Bridge, Walton Bridge