Pondering starship evolution

[Grav_Moped]

There's no reason why the fighter CAN'T be a box shape (or even a dispersed structure, for that matter) if the intent is pure combat.

However, for the purposes of what I'm researching here, I'm wanting a combination fighter and "external docking sky crane" VTOL lifter for the Boxes (cargo, etc.) to provide logistical support in austere locations for the loading/unloading of the starship. This means that entry into atmosphere (2+) becomes necessary, which then requires streamlining (configuration: 1, 2 or 6), even if the fighter isn't going to be transitioning from orbit through atmospheric entry with an external load (since that's the job of the starship to do orbital interface runs using internal loads). Of those choices, the "maximal" fighter option is configuration: 1 (which is only useful against meson guns, but still...). But it's still important for the fighter to be able to enter atmosphere and "be available" down near the surface as a VTOL sky crane for the marshaling of Boxes in the absence of ground support infrastructure (so as to be able to deploy outposts, make deliveries to austere locations and other "logistical services" as useful/necessary).

As a skyhook for cargo loading, it doesn't have to go very fast at all. It'd be a heavily-armed tugboat/GCarrier with a hard V_ne.

 

[Grav_Moped]

* Velocity (never exceed).

Had to manually code the subscript and don't want to mess with the post again...

Also, it does not need streamlining for fast atmospheric entry/departure since it can hitch a ride inside the freighter for that.

 

[Spinward Flow]

As a skyhook for cargo loading, it doesn't have to go very fast at all. It'd be a heavily-armed tugboat/GCarrier with a hard V_ne.

Also, it does not need streamlining for fast atmospheric entry/departure since it can hitch a ride inside the freighter for that.

Depends on your perspective, I guess.

A 30 ton small craft with A/A drives would be capable of lifting up to 170 (displacement) tons external load @ 1G of acceleration thrust (base, before accounting for local gravity), which functionally amounts to being up to 5x 30 ton Boxes when local gravity is ~0.9G or less. When dealing with local gravity closer to 1.0G or more, the external load lifting capability would be reduced to 60 (displacement) tons external load @ 2G acceleration thrust (base, before accounting for local gravity) ... or 30 (displacement) tons external load @ 3G acceleration thrust (base, before accounting for local gravity).

I'm thinking that "streamlining: yes" is operationally a more flexible option. It allows the fighter to enter atmosphere independently of the starship, which would be important in a variety of edge case scenarios. You REALLY don't want to have to use an internal docking inside the starship for transfers from orbit to surface if there are any kind of "hot LZ" type situations where some suppression/covering fire is needed. In overall "grander" terms of economics, the cost difference between configuration: 1 and configuration: 4 in terms of hull construction cost @ 30 tons of hull is MCr3.6 vs MCr1.8 ... and for reference, configuration: 2 would be MCr3.3.

For the 30 ton fighter design that I'm currently working up/putting through the wringer, that MCr1.8 savings on construction cost amounts to only ~6.3% of the total price of the small craft ... so not nothing, but also not something to be that worried about on the economics front.

 

[Condottiere]

Depends on the edition.

Currently, anything with a gravitational manoeuvre drive can renter an atmosphere, without needing heat shielding.

Probably, dead slow for dispersed structure.

 

[Spinward Flow]

Depends on the edition.

Currently, anything with a gravitational manoeuvre drive can renter an atmosphere, without needing heat shielding.

To be excessively fair, LBB2 (77 and 81) were written in the heyday of the Space Shuttle era. The basic notion underpinning LBB2.77 was that maneuver drives were reaction mass rocket engines, so delta-v potential was NOT "excessive" (with thrust burns on the order of days/weeks). In a paradigm where reaction mass for maneuver is QUITE FINITE ... inertial aerobraking into atmosphere for a descent to a world surface makes perfect sense. You just set up an intercept trajectory with the planetary atmosphere and let the aerobraking lower your perigee down to the world surface without needing to expend any reaction mass (brilliant!). However, in order to do that, you need a streamlined hull to be able to "ride the wave" through atmospheric entry transition from orbital velocities to "geosync at low altitudes over lithosphere" velocities.

It was basically the "CTOL of atmospheric entry" approach (the whole "touchdown THEN stop" solution).

But as soon as you've got gravitics technology available ... a lot of that "saving reaction mass by aerobraking" dance for delta-v just becomes obsolete. Instead, with gravitics, you can do more of a "VTOL for atmospheric entry" approach ("STOP ... then descend to touchdown"). With (sufficient) gravitic thrust available, you can "geosynch at ANY altitude above lithosphere" ... not just out at the inertial delta-v=0 geosync orbit for any given world. With gravitic thrust, you can "match world rotation rate" at any circularized orbit above the world surface so that you're "stationary in the sky" relative to the surface ... after which you just ease off on the gravitic thrust a little bit so as to sink/lower altitude down to the surface in a controlled way with no "massive orbital velocity" to scrub off when making contact with the atmosphere.



The aerobraking maneuver would continue to be a "quicker way to get down" from orbit ... but partially streamlined craft would ALSO be able to descend into atmosphere on gravitic thrust (provided that gravitic thrust exceeded local gravity), they would just do so slower than their fully streamlined counterparts.

However, all of those developments/realization happened AFTER the publication of CT, so CT still stipulates that partially streamlined craft are only allowed to land on worlds with atmosphere: 0-1 and are not allowed to land on worlds with atmosphere: 2+.

One way to interpret that would be that fully streamlined hulls (configurations: 1, 2 and 6) are designed to handle load bearing stress at the bottom of a gravity well, in addition to the atmospheric streamlining elements of their configuration. This means that the hulls are "safe to land" in gravity wells in excess of 1G (I think that world size: A = 1.25G according to CT).

By contrast, the largest world size that can (using LBB3) have an atmosphere: 1 would be a world size: 6, which would be a 0.75G maximum surface gravity (according to LBB2).

Point being that even if you can (logically) come up with a condition where a configuration: 4 (partially streamlined) craft can "VTOL down from orbit" without aerobraking, there can be additional factors at play such as the capability of the hull to bear up to the load bearing stresses of local gravity when on the surface, along with potential "wind gust" control hazards when making a descent from orbit (or vice-versa). High wind speeds could potentially buffet the partially streamlined hull in ways that could make control authority of the craft during descent/ascent "more dangerous than is acceptable" (not that it can't be done, just that the safety record is ... problematic ... to put it mildly). Therefore, the game RAW basically amounts to "atmosphere: 0-1 only" for partially streamlined hulls, without elaboration (to keep things simple).

And in CT, unstreamlined craft (configurations: 7-9) are not allowed to "land" on ANY world surfaces at all. Presumably a dispersed structure just isn't "rated" for that kind of local gravity load bearing stress on the construction under any circumstances.

 

[whartung]

The aerobraking maneuver would continue to be a "quicker way to get down" from orbit

Eh, we have power, and it's cheap, so there's no need to aerobreak. Let the thrusters do the work in advance, no need for a whole bunch of armor and heat mitigation, no need to suffer through all that. The trick is to just make sure nothing flies off in the high winds while interfacing.

And, yea, maybe it is a "quicker way down", but I'm betting its not that much quicker when you count all of the measures needed to survive it and coped with the risks in the first place. We'll be talking minutes of difference, not hours. "So, if I land 5 minutes later, the ship won't be incinerated? I think I can live with that."

 

[Spinward Flow]

And, yea, maybe it is a "quicker way down", but I'm betting its not that much quicker when you count all of the measures needed to survive it and coped with the risks in the first place. We'll be talking minutes of difference, not hours.

We've got the live video feeds of Starship testing from SpaceX to use as reference for an inertial aerobraking to surface as a real world example taking a bit over 20 minutes for an atmospheric entry to splashdown.

If you wanted to start your descent from a thrust controlled geosync at 100 km (100,000m) altitude above the surface and wanted to make a "controlled fall" at a constant sink rate of 10m/s (36kph) to the surface from that altitude, it would take over 2h 45m (9900 seconds) to make that controlled descent from orbit to surface.

So roughly 5-6x faster to get "down" from orbit using aerobraking (streamlined) rather than doing a "controlled sink" at a constant speed under gravitic control (partially streamlined) which also does not include the time required for deceleration to match world rotation prior to the vertical descent.

We'll be talking minutes of difference, not hours.

I'm thinking that an aerobraking ought to be able to "get down" to surface using aerobraking in 20-40 minutes (1-2 combat rounds), while a gravitic power "vertical" descent would take at least 4-5x as long to complete the maneuver (during which time the craft is highly vulnerable to incoming fire from either the surface or from orbit).

 

[kilemall]

We've got the live video feeds of Starship testing from SpaceX to use as reference for an inertial aerobraking to surface as a real world example taking a bit over 20 minutes for an atmospheric entry to splashdown.

If you wanted to start your descent from a thrust controlled geosync at 100 km (100,000m) altitude above the surface and wanted to make a "controlled fall" at a constant sink rate of 10m/s (36kph) to the surface from that altitude, it would take over 2h 45m (9900 seconds) to make that controlled descent from orbit to surface.

So roughly 5-6x faster to get "down" from orbit using aerobraking (streamlined) rather than doing a "controlled sink" at a constant speed under gravitic control (partially streamlined) which also does not include the time required for deceleration to match world rotation prior to the vertical descent.

I'm thinking that an aerobraking ought to be able to "get down" to surface using aerobraking in 20-40 minutes (1-2 combat rounds), while a gravitic power "vertical" descent would take at least 4-5x as long to complete the maneuver (during which time the craft is highly vulnerable to incoming fire from either the surface or from orbit).

An unexamined aspect is all of this time in atmo has to be coordinated by space traffic control.

Stacking em up in approach lanes means probably handling several at once, vs the much faster clearing but greater clearance and no one in the way of a hot landing.

Hot launch would be preferable as a way for clearing lanes fast, but may not be possible for the partially streamlined.

 

[Spinward Flow]

Well ...
I wasn't expecting THAT to happen ...

Looks like the 30 ton form factor has some ... unexpected "stacking advantages" in the way everything computes out in the context of the holistic package of design.

30 ton form factor = 5x single occupancy staterooms (20 tons) + Environmental Control Type V-c capacity: up to 5 persons (aquaculture, hydroponic wall gardens and carniculture) (10 tons)

• 30*14 = 420m3
• 9.3m x 7.5m x 6m = 418.5m³ = 6.4 deck squares x 5 deck squares x 2 decks high box form
• 18.6m x 7.5m x 3m = 418.5m³ = 12.4 deck squares x 5 deck squares x 1 deck high box form

Using F/F/F drives means that the code performance breakpoints are:

• code: 1 @ 1200 tons
• code: 2 @ 600 tons
• code: 3 @ 400 tons
• code: 4 @ 300 tons

Since I'm wanting to use a model/2bis as the starship computer (enables J3 but consumes EP=0), there is an incentive to "subtract the highest multiple of 30 from 400 without dropping below 300" ... which then (rather obviously) computes out to being a 310 ton starship hull form factor.

• 310 + 30*3 external load = 400 tons

That then means that the internal hangar bay has a "best fit" of 3x 30 ton (small craft) form factors for a total of 90 tons ... which can be loaded internally or towed externally without a loss of drive performance code factor(s).

• 310 tons + 0 tons external load = 310 tons = Drive-F performance codes: 3
• 310 tons + 90 tons external load = 400 tons = Drive-F performance codes: 3

But the curious thing is what happens when attempting J3+3:

• 400 * 0.3 = 120 tons J3 fuel consumption
• 310 * 0.3 = 93 tons J3 fuel consumption
• 120+93 = 213 tons J3+3 fuel consumption

With LBB2.81 drive fuel requirements in play, J3 @ 310 tons requires 93 tons and PP3 requires 30 tons, for a minimum internal fuel tankage of 123 tons.

• 213 - 123 = 90 tons of additional fuel reserve required for J3+3

And the hangar bay needs to be 90 tons for 3x 30 ton form factors ... which can be towed externally for the first jump, then moved internal for the second jump, allowing the 90 ton hangar bay to be filled with 90 tons of collapsible fuel tank reserve ...

Have a "little extra" fuel margin available above the 213 tons needed for J3+3 for "basic housekeeping power" over the entire transit plus enough for 2 days of full power maneuvering ... and it ought to be possible to complete a double J3+3 transit without refueling. My calculations are showing that as little as a 2 ton fuel margin beyond the 213 tons needed for the J3+3 (@400 tons and @ 310 tons, respectively) ought to be sufficient to complete a world surface to world surface maneuver across 6 parsecs, but that margin is going to be pretty tight, so additional "fuel reserve backup" options are preferred to widen the safety margin (in the event of mishap or adversity).

Crucially, neither the 16 ton nor 24 ton form factors (when used as basic building blocks, for this purpose) manage to achieve a similar result. The "stacking of the blocks" always winds up with a granular mismatch that fails to achieve sufficient fuel tankage (internal+additional) to achieve J3+3. That's because both the 16 and 24 ton form factors "stack" to 96 tons (6*16=96) (4*24=96) while the 30 ton form factor "stacks" to 90 tons (3*30=90). This then means that the 16 and 24 ton form factors "need a bigger hangar bay in a smaller starship" (400-96=304) versus the 30 ton form factor (400-90=310) and that differential is JUST ENOUGH to be "too big for too small a hull" at which point stuff doesn't fit anymore in a way that synergizes well further on down the line.

In other words, the 16 and 24 ton form factors manage to just miss the mark for the critical balance point needed to achieve J3+3 unrefueled performance out of the design. Mind you, the revenue tonnage available @ J3+3 is vanishingly small (2x high passengers, 10 tons or less of cargo), so it's not exactly economical to double jump over 6 parsecs like that ... but the capability IS THERE in the design refactoring when using the 30 form factor for modularized interstellar shipping containers.



I'll put the "text file of the spreadsheet" particulars into my next post (need to do some forum formatting to make it look good) for the requisite SHOW YOUR WORK to lay out all the particulars in an accessible layout of information.

 

[Spinward Flow]

Rule of Man Clipper
310 tons starship hull, configuration: 1
65 tons for LBB2.81 standard F/F/F drives (codes: 3/3/3, TL=10, EP=12)
123 tons of total fuel: 310 tons @ J3 = 93 tons jump fuel + 30 tons power plant fuel
8 tons for TL=10 fuel purification plant (200 ton capacity is minimum)
20 tons for bridge (1000 ton rating, MCr5)
2 tons for model/2bis computer
90 tons for internal hangar berths

1. Fighter Provincial = 30 tons
2. Stateroom Box = 30 tons (starship pilot, small craft pilot navigator, medic, gunner) (5x staterooms, V-c life support for 5 persons)
3. Stateroom Box = 30 tons (engineer/engineer, purser/purser, steward/steward, 2x high passengers) (5x staterooms, V-c life support for 5 persons)

* External Docking: 690 tons capacity

1. 
   
2. 
   

2 tons for cargo hold

• 92 ton capacity collapsible fuel tank = 0.92 tons

= 65+123+8+20+2+90+2 = 310 tons

Crew = 8 (Cr37,350 per 4 weeks crew salaries)

1. Pilot-1 = Cr6000
2. Ship's Boat-1 = Cr6000
3. Navigator-1 = Cr5000
4. Engineering-2/Engineering-2 = Cr6600
5. Steward-1/Steward-1 (purser) = Cr5400
6. Steward-1/Steward-1 = Cr4950
7. Medic-3 = Cr2400
8. Gunnery-1 = Cr1000

---

Fighter Provincial (Type-FP, TL=9)
30 ton small craft hull, configuration: 1 (MCr3.6)
0 tons for Armor: 0 (TL=9)
5 tons for LBB2.81 standard A/A drives (codes: 6/6, TL=9 civilian, EP=2) (Agility=6 requires EP: 1.8) (MCr12)
1.8 tons for fuel (19d 124h 50m endurance @ 1.8 EP output continuous)
6 tons for bridge (crew: 2) (pilot, gunner) (MCr0.15)
2 tons for model/2 computer (TL=7, EP: 0) (MCr9)
1 ton for triple turret: missile, missile, missile (TL=9, code: 1, batteries: 3, EP: 0, 3 missiles per battery, 12 reloads shared between batteries) (MCr3.35)
4 tons for 2 single occupancy small craft staterooms (MCr0.1)
* External Docking: 170 tons capacity (MCr0.34)
10.2 tons for cargo hold (5 ton Mail Vault installation ready)

• 0.1 tons for 15 person/weeks consumable life support reserves (2 crew=7.5 weeks endurance)
• 0.1 tons for 10 ton capacity collapsible fuel tank (MCr0.005)

= 0+5+1.9+6+2+1+4+10.1 = 30 tons
= 3.6+0+12+0.15+9+3.35+0.1+0.34+0.005 = MCr28.545

• 1G = 200 - 30 = 170 tons external load
• 2G = 100 - 30 = 70 tons external load
• 3G = 66 - 30 = 36 tons external load
• 4G = 50 - 30 = 20 tons external load
• 5G = 40 - 30 = 10 tons external load
• 6G = 3 - 30 = 3 tons external load

---

Revenue Tonnage @ J3/3G = 310 + 90 = 400 tons

• 2x high passengers
• 1 ton internal cargo
• 90 tons additional internal hangar cargo (when 1x Fighter Provincial, 2x Stateroom Boxes docked externally)
• 10 tons cargo/x-mail (1x Fighter Provincial)

Revenue Tonnage @ J2/2G = 310 + (90+200) = 600 tons

• 2x high passengers
• 1 ton internal cargo
• 90 tons additional internal hangar cargo (when 1x Fighter Provincial, 2x Stateroom Boxes docked externally)
• 200 tons external load charter capacity
• 10 tons cargo/x-mail (1x Fighter Provincial)

Revenue Tonnage @ J3+3/3+3G = 400 tons (J3) then 310 tons (J3)

• 2x high passengers
• 92 tons collapsible fuel tank in hangar and cargo hold (when 1x Fighter Provincial, 2x Stateroom Boxes docked externally)
• 10 tons cargo/x-mail (and/or collapsible fuel tank) (1x Fighter Provincial)

Drive Performances with External Loading

• (Starship tons) + (Multiplier*Small Craft tons*Quantity)
  • 310 + 1.0*30*0 = 310 tons = J3/3G/PP3
  • 310 + 1.0*30*3 = 400 tons = J3/3G/PP3
  • 310 + 1.0*30*9 = 580 tons = J2/2G/PP2
  • 310 + 1.0*30*23 = 1000 tons = J1/1G/PP1
• (Starship tons) + (Multiplier*Big Craft tons*Quantity) + (Multiplier*Small Craft tons*Quantity)
  • 310 + 1.1*100*1 + 1.0*30*6 = 600 tons = J2/2G/PP2
  • 310 + 1.1*200*1 + 1.0*30*2 = 590 tons = J2/2G/PP2
  • 310 + 1.1*300*1 + 1.0*30*12 = 1000 tons = J1/1G/PP1
  • 310 + 1.1*310*1 + 1.0*30*11 = 981 tons = J1/1G/PP1
  • 310 + 1.1*310*2 + 1.0*30*0 = 992 tons = J1/1G/PP1
  • 310 + 1.1*400*1 + 1.0*30*8 = 990 tons = J1/1G/PP1
  • 310 + 1.1*500*1 + 1.0*30*4 = 980 tons = J1/1G/PP1
  • 310 + 1.1*600*1 + 1.0*30*1 = 1000 tons = J1/1G/PP1

---

Although the starship's F/F/F drives are rated as:

• code: 1 @ 1200 tons
• code: 2 @ 600 tons
• code: 3 @ 400 tons
• code: 4 @ 300 tons
• code: 5 @ 240 tons
• code: 6 @ 200 tons

... the maximum external load the hull is designed to tow externally is only up to a combined 1000 tons (310 tons of starship, up to 690 tons of external load). This means that "200 tons of capacity" @ code: 1 is being "wasted" due to insufficient support elsewhere in the build details (bridge tonnage and cost, external "hangar" docking capacity and cost).



The reason why there are 4x Steward crew positions (being filled by 2 people) is because the regenerative biome life support systems require a Service Crew (3 positions per 1000 tons without Ship's Troops or 2 positions per 1000 tons with Ship's Troops). Since the "total amount of (combined) hull displacement" for the starship can vary from 310 tons (with zero external load) to 1000 tons (with 690 tons of external load), any Service Crew department section needs to be "sized" for the maximum (combined) displacement that the starship can move. That means that the Service Crew needs to be "sized" for 1000 tons ... not 310 tons ... and therefore, consequently, requires 3 crew positions for those (potential maximum) 1000 tons. Likewise, this is why the starship bridge is "rated" for 1000 tons (and therefore costs MCr5, instead of MCr1.55 for 310 tons), so being internally consistent and Intellectually Honest™ here.

My own headcannon on the subject is that the "3 Service Crew positions" have supercargo duties, in addition to "managing the farms" of the Environmental Control Type V-c capacity: up to 5 persons (aquaculture, hydroponic wall gardens and carniculture) regenerative life support biomes that are integrated into each of the 30 ton Stateroom Boxes (previous design iterations had these separated into different Boxes). The LBB5.80, p33 description of the Service Crew department duties are quite helpful in this regard:

Service Crew: The ship itself may have a requirement for other sections which provide basic services, including shops and storage, security (especially if there are no ship's troops aboard), maintenance, food service, and other operations.

The Purser fills a "4th Steward" crew position (separate from the 3 Service Crew positions responsibilities) and handles high passenger services (up to 8). Note that an additional 1x 30 ton Stateroom Box (5 staterooms, V-c regenerative life support for 5 persons) can be added (externally) to increase the number of high passengers that can be served per jump from 2 to 7 (at the loss of double jump maximum range) when operating routes that can take advantage of the increase in high passenger accommodations. If an additional 3x 30 ton Stateroom Boxes (5 staterooms, V-c regenerative life support for 5 persons, each), the number of high passengers who can be transported @ J3 increases from 2 to 16, although an additional Steward (single crew position) will need to be hired and accommodated in one of the additional Stateroom Boxes to support the increased number of high passengers. This means that it is possible for the starship class to operate as a high end J3 Liner in regions where high passage transport services are in demand, and/or if an operator can secure a long term interstellar charter contract to a third party to supply such services (devolving the responsibility for filling the transport manifests for those high passagenger accommodations onto the third party).



Of course, the REAL profit opportunities lie not within the passenger and cargo ticket revenues (those just "pay the bills" and defray operating costs in between windfalls) ... but rather within the possibilities for speculative goods arbitrage. Being able to transport up to 1+90+10=101 tons of speculative goods at J3 makes it VERY EASY to (quickly!) "link up" world with a variety of trade codes, enabling the wheeling and dealing of speculative goods to maximal advantage in fast turnaround times that yield quick profits for the savvy operator. With 3 parsecs of range available, being able to choose your next destination as a tramp merchant can become very lucrative indeed.

Operators who choose to purchase additional Cargo Boxes (for external towing) can choose to operate as J2+2 speculative tramp merchants in regions where the astrogation is more favorable to that mode of interstellar transport in order to "link up" between world markets.