GURPS Spaceships TL9 SM+15 Orbital Giga-Lifter

[Peter Knutsen]

This is a truly gigantic TL9 ship intended to lift very large ships up into low orbit (and it might have enough delta-V to lift into high orbit, even) and then land again, being crewed. It uses the volatile and somewhat expensive HEDM fuel, but it is a very robust ship, and with its powerful 4G acceleration it can probably cope with bad weather. Also I'd guess that during routine operations, the ship does not use the full acceleration, but makes do with 3G or maybe even just 2.5G.

Hull: SM+15, streamlined
TL: 9
dDR ??? / 100 / 0 (or go with "overall armour" ??? / 50 / 50 instead)
Payload: One SM+14 ship, as upper stage


Front section
[1 to 6] Upper stage (streamlined SM+14)

Mid section:
[1] Streamlined metal laminate armour, dDR 100, 3G$
[2] Control room, 60 stations, 300 workspaces, 6G$
[3 to 6] HEDM fuel, base delta-V 0.5 mps per tank, 150k tons fuel per tank, 1G$ per empty tank
[c] HEDM fuel, base dV 0.5 mps, 1G$

Rear section:
[c] HEDM fuel, base dV 0.5 mps, 1G$
[1 to 4] HEDM fuel, base dV 0.5 mps per tank, 1G$ per empty tank
[5] HEDM reaction engine, 2 G acceleration, 300 workspaces, 9G$
[6] HEDM reaction engine, 2 G acceleration, 300 workspaces, 9g$

Number of tanks: 10
Delta-V modifier for number of tanks: x1.4
Final delta-V: 7.0 miles per second
Amount of fuel: 1.5 million tons (HEDM fuel)
Cost of fuel: 9G$ to fill tanks

Total cost of empty ship: 37 billion dollars (assuming large production runs, which is highly unlikely. The fuel would be mass-produced, however, and so be available at unmodified cost)

Total crew: 960 (900 in workspaces, 60 at control stations)


This ship is actually overpowered in terms of delta-V, and could easily sacrifice one fuel tank for something else, but I'm at a loss as to what it should be. It doesn't seem to need anything much, given its highly specialized function of climbing up the gravity well.

A habitat would enable it to do longer missions, but what should that be? Long missions in this kind of ship doesn't make much sense.

One change would be to switch from a large upper stage (SM+14) to a small one (SM+13) so as to get 1 habitat, and 3 additional fuel tanks. That helps us reach the important fuel tank breakpoint so as to get a final delta-V of 10.4, which enables the ship to not just climb up into orbit but also send the payload on its way to somewhere, then turn around and fly back to Earth and land.


One could also scale the ship down, of course. Reducing by 1 SMs divides all costs by 3, reducing by 2 SMs divides by 10, and so forth.

One of the most interesting things I've found out (although I strongly suspected it earlier) is that it simply isn't possible to do a two-stages-to-orbit design at TL8. The delta-V of ordinary rocket fuel (0.15 mps per tank) simply isn't high enough. HEDM fuel, on the other hand, has plenty of delta-V to make it feasible.

(Or, thinking some more, what about an SM+X ship that launches just a single SM+X-3 ship? For instance an SM+11 ship that lifts one SM+8 ship to orbit? That might be doable at TL8 after all, although only barely)

[thtraveller]

Good idea. Though SSTO is possible with HEDM you don’t want to be dragging around the deadweight of empty tanks etc for the main mission craft.

Cost of fuel: 9G$ to fill tanks

Ouch!

Total crew: 960 (900 in workspaces, 60 at control stations)

Given the volatile nature of HEDM fuel I would want this to at least have limited automation and most likely full automation.

One change would be to switch from a large upper stage (SM+14) to a small one (SM+13) so as to get 1 habitat, and 3 additional fuel tanks. That helps us reach the important fuel tank breakpoint so as to get a final delta-V of 10.4, which enables the ship to not just climb up into orbit but also send the payload on its way to somewhere, then turn around and fly back to Earth and land.

Mission simplicity says do it this way, whereas design efficiency says use a space-capable only second stage with a different and much more efficient engine. Tough call. I guess given the cost of HEDM we would be looking at a second stage for budget reasons.

I could see delivering fuel to orbit to refuel the orbital fleet being a major part of HLVs mission at early TL9. I assume late TL9 we capture an ice asteroid or two to enable space refuelling.

Having a large hangar bay is another approach you could take?

One of the most interesting things I've found out (although I strongly suspected it earlier) is that it simply isn't possible to do a two-stages-to-orbit design at TL8. The delta-V of ordinary rocket fuel (0.15 mps per tank) simply isn't high enough. HEDM fuel, on the other hand, has plenty of delta-V to make it feasible.

A single-stage-to-orbit is possible with Nuclear Thermal Rockets at TL9 and they are much cheaper on the fuel, or a two-stage-to-orbit using dirt cheap water as reaction mass. So I would expect to see a few “spaceports of convenience” arise that allow nuclear launches from their territories.

EDIT: your stats look spot on btw.