The Chemical Rocket Third Imperium

[Thot]

I suspect OP is applying Tsiolkovsky's rocket equation to come up with some total delta-V figures for various portions of fuel on a ship. Essentially it takes a specific impulse value (efficiency of the engine) and calculates the delta-V as a function of the proportion of your total mass taken up by fuel.

Correct.

[...]
I think the most boring aspect of this in a role playing sense would be the transit times. With the delta-V available from rockets you would find yourself sitting around for quite a long time waiting to transit between jump points. Interplanetary journeys would take months much like they do now.

That's why I included the phrase about "adjusting safe jump distances" so that transit times remain the same. I haven't thought about how low the distance would then have to be, but I am assuming you need to be at least outside of orbit (so at escape velocity) to jump.

This will probably mean that you can safely jump within a system from one planet to another.

 

[Thot]

Because it's not going to be Cr20 per ton-displacement unless (and until) beanstalks.

Yes it is.

Fuel is 1Cr per ton. You need a ship with about 93% of its mass as fuel to deliver the cargo to orbit. Add 2% for the ship itself, and you have 5% as actual payload. That means you burn 19 tons of fuel for 1 ton of cargo. Assuming a very sturdy, durable, old, and written-off rocket ship, roughly 20 Credits per ton is a quite reasonable conclusion.

Note that the prices for shuttles are worked assuming gravitics and fusion plants... and still are in the Cr25/ton range. Get rid of that, and you're looking at least Cr250/ton.

No, that utterly depends on the price for the fuel (and the rocket, but I would propose that a chemical rocket is cheaper than a fusion reactor. A lot.)

Also, all fuel needs to be increased in cost, for it's not shippable cheaply.

Of course it is, if the technology AND infrastructure are there to make it cheap. And that is a lot safer to assume than broken laws of physics.

 

[aramis]

Yes it is.

Fuel is 1Cr per ton. You need a ship with about 93% of its mass as fuel to deliver the cargo to orbit. Add 2% for the ship itself, and you have 5% as actual payload. That means you burn 19 tons of fuel for 1 ton of cargo. Assuming a very sturdy, durable, old, and written-off rocket ship, roughly 20 Credits per ton is a quite reasonable conclusion.




No, that utterly depends on the price for the fuel (and the rocket, but I would propose that a chemical rocket is cheaper than a fusion reactor. A lot.)



Of course it is, if the technology AND infrastructure are there to make it cheap. And that is a lot safer to assume than broken laws of physics.

You're failing to amortize for the cost of the launcher. Fuel cost has ALWAYS been secondary to structure cost. And not leaving room for the controls.

Your math is majorly flawed. Overly simplistic, too.

Traveller shipping requires about 3% minimum for hab. That's 2% bridge, and 1% cabins.
Then the minimum drive is roughly 1%.
So, you're down to 0% payload after adding a pp and computer.
More realistically 1% payload, 94% fuel. Just the hull alone is MCr0.1 per Td for the shuttle. SO, a 200 Td Shuttle, and only 90% fuel... more generous than you're giving...

Using mongoose 1e as the friendliest
200Td SL hull MCr8.8
10 Td small ship bridge ... MCr1
1 Td MD A=1 MCr4
1 Td PP A=1 MCr8
180 Td fuel MCr0

MCr21.8 for 8 tons cargo. Fuel cost 180K/8Td = KCr22.5 per Td

Annual Payment, per month: KCr90.83. Assuming 1 trip per 4 hours 7 days per week, 4 weeks per month for 168 trips, KCr0.5 per trip, or Cr62.5 per ton.

Assuming 8 hour shifts for pilots, at KCr5000 for system pilots (vs 6K for jump pilots), we have 84 shifts, and most people will work 20 per month, so we need 4 pilots, and lose 4 shifts, but that's probably maintenance time. so all the above needs refigured for 160 instead of 168... KCr20/(160*8) = 15.62

Henceforth, rounding up to next quarter credit...
Pilots: Cr15.75 per td.
Payment share per trip becomes Cr71 per Td.

Maintenance - (0.1/12)% per month of base... so 21.8/12000 = 1816.666/mo, that's Cr1.5 per ton/trip.

So, using Cr100/ton for unrefined... 180 Td fuel is Cr18000, over 8 tons cargo... Cr2250 per ton.


Plus the costs of the tonnage on the ship of Cr88.25

Cr2338.25 per ton, no profit, full cargo (at 4% of ship)

 

[nobby-w]

Correct.

That's why I included the phrase about "adjusting safe jump distances" so that transit times remain the same. I haven't thought about how low the distance would then have to be, but I am assuming you need to be at least outside of orbit (so at escape velocity) to jump.

This will probably mean that you can safely jump within a system from one planet to another.

Have you tried playing Kerbal Space Program?

Spending a bit of time getting the hang of this will give you an appreciation of orbital mechanics and space flight with limited Delta-V. Playing with the orbital mechanics will be by far the most interesting aspect of your scenario and - If I might be so bold as to say so - KSP is a far better vehicle for exploring that.

 

[Thot]

You're failing to amortize for the cost of the launcher. Fuel cost has ALWAYS been secondary to structure cost. And not leaving room for the controls.

Because we build every rocket as a basically hand-crafted single piece, and throw large parts of it away (sure, some parts are reused after a lot of work) with each launch, instead of just having it land and refuel. SpaceX isn't doing their vertical landing for fun.

Traveller shipping requires about 3% minimum for hab. That's 2% bridge, and 1% cabins.
Then the minimum drive is roughly 1%.
So, you're down to 0% payload after adding a pp and computer.

That's just a matter of how you build. A ship with 5 tons of payload, 93 tons of fuel and 3 tons of actual empty ship mass is certainly a plausible construction.

What's more, even if you decide that you absolutely want 5% pure empty ship mass, you still have 2 tons of cargo. Then we are at 93/2= 46.5 Credits per ton, which is more, but not prohibitively so. Plus, if I absolutely think that I need it, I can just cut the fuel price by any factor.

And all that without any magic.

More realistically 1% payload, 94% fuel. Just the hull alone is MCr0.1 per Td for the shuttle. SO, a 200 Td Shuttle, and only 90% fuel... more generous than you're giving...

Using mongoose 1e as the friendliest
200Td SL hull MCr8.8
10 Td small ship bridge ... MCr1
1 Td MD A=1 MCr4
1 Td PP A=1 MCr8
180 Td fuel MCr0

MCr21.8 for 8 tons cargo.

You are using OTU numbers. Of course chemical rockets in such a setting must be cheap and durable, require less maintenance (if any at all), and be easily operated by not too highly qualified personnel. (Robots are everywhere, after all.) These are (comparatively) simple, mass-produced chemical rockets, not fusion reactors or Magic Drives built into armored steel hulls.

So the ship itself will likely cost more like a few hundred thousand, basically about 1% of what you assume, I would guess. And that's for all the launches over a 50 year (or more) lifetime. And if we need it to, the lifetime can be 100, 200, or 500 years. All several orders of magnitude (!) more plausible than Magic Drives.

We are probably looking at something more like 200,000 Credits/8 tons=25,000 Credits per ton of payload, written off over ten thousand launches or more.

Fuel cost 180K/8Td = KCr22.5 per Td

In your construction, you have 180 dtons, that's 180 Credits per launch under the above assumptions (you will just have to accept that, the same way though with less effort than drives that break natural laws). For 8 dtons, which boils down to just over 20 Credits, not kilocredits.

If you launch from a planet that is smaller and has lower escape velocity, or if you use a bigger rocket (which often, you will), the numbers get even better.

 

[Brandon C]

That's just a matter of how you build. A ship with 5 tons of payload, 93 tons of fuel and 3 tons of actual empty ship mass is certainly a plausible construction.

It's also an unmanned craft with no place for the characters.

And all that without any magic.

Again, you are replacing physics magic with economics magic. By drastically cutting the cost of starships, you are severely cutting into the revenue of the companies that provide the parts for starships and the labor costs to build them. Think about it -- if you reduce starship cost by 90% or 99%, you must also reduce the salaries of workers by 90% or 99%. Are the people who construct starships now just expendable slave labor who live in tents?

 

[Thot]

They are robots, more likely.

And I can try to explain it again: There is actually conceivable technology to make fuel (and rockets) that cheap. For the rockets, it is simple economics of scale, for the fuel, free energy (solar, for instance, collected with PV cells that have a lifetime of centuries - long lifetimes for mature technology increases economic viability greatly, both with production facilities and rockets) and automated production.

Player characters count as payload, so they are included. Also, keep in mind that in order to be equivalent to the Traveller ships that we are used to, rocketships will often be ten to twenty times bigger, which improves the payload percentage.

 

[Brandon C]

They are robots, more likely.

Then there is effectively no longer a labor force. If robots can build something as large and complex as a starship so cheaply, they should be building everything cheaply. All costs are driven down and manufacturing jobs vanish. What are all the Imperial citizens going to do?

Player characters count as payload, so they are included.

But not as crew. Merely being passengers while your robot ship is in vontrol is, IMHO, boring.

Also, keep in mind that in order to be equivalent to the Traveller ships that we are used to, rocketships will often be ten to twenty times bigger, which improves the payload percentage.

It also causes problems. That 100 ton scout is now a 1000-2000 ton scout., which requires more materials to build, takes longer to build, is more expensive to maintain, and requires larger berthing facilities.

 

[Thot]

The AI impact on the ecenomy is a much bigger field. Let's not dive too deeply into that (in this thread), but simply observe:
SpaceX's rockets TODAY work fully automated. A human cannot react fast enough anyway.

And no, the 2000dton-rocket will not be more expensive, unless you want it to be, which I am beginning to suspect.

Can you please accept the premise, and work from there?

 

[McPerth]

So.. what would your favorite military, scout, or merchant starship look like under such assumptions? What would your own noble PC's yacht be like?

I guess most ships would be unstreamlined, as interface is what will be mostly affected, and have limited maneuver drive time, so simply accelerating a little and keeping the speed up to the jump point at a more or less constant speed.

What would this Third Imperium look like? What about its rivals?

As Aramis points, probably so different to OTU 3I as not to be recognizable as the same...

As taking off/landing is where gravitics are most useful, wihout them I guess most ships will not be built for it, giving (as someone has already pointed) higher importance to highports and interface transport.

Things like orbital catapults, beanstalks and similar interface communications, nearly (if not outright) unheard of in 3I and OTU will be quite common, and as this will need at least TL 8-9 (so, higher than current Earth, as I don't believe we're able to build them right now), lower TL words will not be able to keep any level of regular inerplantary/interstellar trade. If this wil llead to those planets being scarcer (as anyone will try to rise TL to achieve interstellar trade) or poorer (as they cannot).

In some ways, this will be as setting 3I with 2300 rules (have you taken a look on how chemical drives work in MgT 2300AD?).

How would it affect warfare, commerce, politics?

As I guess I already answered (at least to a point) about commerce and politics, let me say how I think it will affect warfare:

The first effect will be to limit offensive opperations, as skimming fuel is based in Traveller on gravitics (non gravitic spacecraft will have serious trouble to do it), and so the fleet must either carry very specialized fuel takers (with will probably ned quite a lot of time to skim it, as their payload will be lower and the fuel consumed to get it higher), or depend on externa sources of fuel, as tankers will only last for that long, and going home for more fuel will take some time.

So, fuel will be the main concern on performing a thrust one enemy territory, and its scope will probably be limited for it to 3-4 jumps (no deep attack on Rhylanor will be posible in 5FW, just to give an example).

Also, due to interface problems already commented, planetary invasions will be quite different, as the ships able to land the troops will have quite less payload (in percentage) and troops carried by each of them will be fewer (again, in relation ot their size).

And, of course, on the dirtside, combat will be very different, without the grav vehicles and belts...

And I guess all of this is only the tip of the iceberg...

 

[mike wightman]

I still think the skylon/SABRE engine spaceplane will become the common interface vehicle of such a setting.
Add a TL or two and they could achieve mach 12 before the rocket mode has to be engaged, thus increasing payload to orbit.

Rockets would still have their place, as would electromagnetic 'first stage' rail gun launch systems - may as well use all that cheap fusion power plant electricity for something.

Actual spacecraft would be ion engine or plasma rockets - or possibly some sort of hybrid of the two for some vessels.

TL 12-15 material science should be able to solve the structural issues of building beanstalks and skyhooks.

A very different but very interesting setting.

 

[kilemall]

Hm, but why would the emperor spend his military budget on high cost fuel for one ship when he could buy ten extra ships instead, complete with fuel?

Several reasons.

3-4x the vee per fuel ton gives one several options-

• Push the ship faster to 'get there first/run down fleeing opponents/escape/evade' with strategic and tactical effects
• Burn the same vee as conventional ships but fit many times the payload into the same size ship
• Fit the same payload into a smaller ship

In the case of the latter two, not economical per se, but when the payload is extra armor and/or weapons, a polity's navy may find the tradeoff desirable.


I would expect most warship designs to be a combination of the above- more maneuver, more weapons capacity, in smaller hulls that require less overhead crew for the same mission.

 

[Thot]

I guess most ships would be unstreamlined, as interface is what wil lbe mostly affected, and have limited maneuver drive time, so simply accelerating a Little and keeping the speed up to the jump point at a more or less constant speed.

Indeed. That's why I wrote the battle rider concept, and starships basically staying at the jump point and do force projection via fighters and long-range weaponry from there would probably be a good guess.

As an extension of that, there'd probably be "jump ports", space stations at common jump points that allow for refuelling and changing cargo... that's actually something that might even be a worthy idea in the OTU.

As Aramis points, probably so different to OTU 3I as not to be recognizable as the same...

Is that so? The technofeudal society seems like a near-perfect fit to me. Travel times and cost are, after all, largely unaffected.

As taking off/landing is where gravitics are most useful, wihout them I guess most ships will not be built for it, giving (as someone has already pointed) higher importance to highports and interface transport.

Things like orbital catapults, beanstalks and similar interface communications, nearly (if not outright) unheard of in 3I and OTU will be quite common, and as this will need at least TL 8-9 (so, higher than current Earth, as I don't believe we're able to build them right now), lower TL words will not be able to keep any level of regular inerplantary/interstellar trade. If this wil llead to those planets being scarcer (as anyone will try to rise TL to achieve interstellar trade) or poorer (as they cannot).

I have reservations about catapults, beanstalks and the like - they have a vast array of problems that are commonly not addressed in the concepts. Among them: Extremely high capital investment required, extremely vulnerable to terrorist attack, warfare, and regular accidents, day-to-day operations are more complicated than many people imagine (as I wrote earlier, if you send something up the beanstalk, you have to send something of equal mass down at the same time, and if that other mass isn't available, you must wait, for just one example), and so on. Also, such installations would not have survived the Long Night.

Cheap fuel and cheap rockets, however, are easy to achieve, require little individual investment, are naturally redundant (because many people will have them), and allow for players to earn a buck with their own ship anywhere where they might go. Sure, a player ship will seem large compared to Traveller OTU deck plans, but in actuality, the ship they can live in will be the same size - just with a lot more (cheap) fuel attached.

In some ways, this will be as setting 3I with 2300 rules (have you taken a look on how chemical drives work in MgT 2300AD?).

2300 AD has been suggested already, and I have put it on my list for sure. I always found the whole concept interesting, but a deviating timeline and lack of ability made me never grab it. Thankfully, DTRPG has changed that.

[...]
So, fuel will be the main concern on performing a thrust one enemy territory, and its scope will probably be limited for it to 3-4 jumps (no deep attack on Rhylanor will be posible in 5FW, just to give an example).

Actually, that would be own concern: Given that I have removed the jump fuel requirement to not make things worse and replaced it with a 1 week cooldown, it should theoretically possible for the Zhodani to have a fleet parked in a comet cloud around Sylea just in case they need it...

Also, due to interface problems already commented, planetary invasions will be quite different, as the ships able to land the tropos will have quite less payload (in percentage) and troops carried by each of them will be fewer (again, in relation ot their size).

Depends. If you are willing to forego a chance for retreat, you might even require no fuel at all, and simply fall down in drop capsules with parachutes (unless it's a vaccum world, but those are usually smaller anyway).

And, of course, on the dirtside, combat will be very different, without the grav vehicles and belts...

Well, on the plus side, planetside combat would be more familiar to players.

And I guess all of this is only the tip of the iceberg...

There's always something one overlooks. That is, after all, the reason for this thread, to find out how such an interstellar society would work.

 

[mike wightman]

In the long run catapults, beanstalks etc work out cheaper - in much the same way as you are postulating rockets will become incredibly cheap.

e.g. by TL9 a material strong enough to build a beanstalk, once built all it costs is electricity to get a payload to the top, Cheap fusion power provides that electricity so your cost to orbit is basically paying back the investment in the materials to build the beanstalk. Cheaper than a rocket in the long run.

 

[Thot]

Several reasons.

3-4x the vee per fuel ton gives one several options-

• Push the ship faster to 'get there first/run down fleeing opponents/escape/evade' with strategic and tactical effects
• Burn the same vee as conventional ships but fit many times the payload into the same size ship
• Fit the same payload into a smaller ship

4 times the delta V per ton of fuel means an exhaust velocity of 18,000 m/s. That is only achievable with an ion drive, or some other kind of electric propulsion (or maybe a fusion rocket, but one that has other problems, such as killing the crew and onboard electronics with radiation). Again, 1/2m*v² applies, which means your drive needs a power source for, at the very least, due to mere physics, 162 Megawatts per kilogram of exhausted reaction mass per second.

One Hundred Sixty Two. Mega. Watts. Per. Kilogram.

For reference (once more), a 1970s Nimitz class aicraft carrier has a total reactor output of 200 MW. That ship displaces 100,000 tons of mass.

I could go on. Should I?

 

[Thot]

In the long run catapults, beanstalks etc work out cheaper - in much the same way as you are postulating rockets will become incredibly cheap.

I wouldn't doubt that it is cheaper on paper. But what in times of war, what when an accident happens, what when the Rule Of Terra selects it as their target? A broken beanstalk can destroy a planet's biosphere. Just to name one important point.

 

[mike wightman]

The 3I setting postulates cheap, clean fusion power, you would have to get rid of that too

1 EP = 250 MW, a 100t scout power plant produces 2EP, the same as a 200t type A free trader power plant.

 

[Xerxeskingofking]

4 times the delta V per ton of fuel means an exhaust velocity of 18,000 m/s. That is only achievable with an ion drive, or some other kind of electric propulsion (or maybe a fusion rocket, but one that has other problems, such as killing the crew and onboard electronics with radiation). Again, 1/2m*v² applies, which means your drive needs a power source for, at the very least, due to mere physics, 162 Megawatts per kilogram of exhausted reaction mass per second.

One Hundred Sixty Two. Mega. Watts. Per. Kilogram.

For reference (once more), a 1970s Nimitz class aicraft carrier has a total reactor output of 200 MW. That ship displaces 100,000 tons of mass.

I could go on. Should I?

the counter point is that trying to work out TL12+ technologies form a modern basis is like trying to work out the maxium endurance of (to use your example) the nitmiz class carriers by how long Erik the Red could keep food fresh.


I should say that several people here are suggesting alternative technologies, like SSTO planes based on SABRE or other such systems, that might a better fit for the setting your looking at.


or, even just look into MgT high guard, which has rules for working fuel hungry chemical rockets within the existing traveller M-drive paradigm (either addition).

I wouldn't doubt that it is cheaper on paper. But what in times of war, what when an accident happens, what when the Rule Of Terra selects it as their target? A broken beanstalk can destroy a planet's biosphere. Just to name one important point.

and the hryddogen cracking farms you are on about, able to produce many thousands of D tons of h2 and LOX, and presunably store these somewhere, are perfectly safe and reasonable?

 

[Thot]

The 3I setting postulates cheap, clean fusion power, you would have to get rid of that too

1 EP = 250 MW, a 100t scout power plant produces 2EP, the same as a 200t type A free trader power plant.

Yeah... think about that again. What's that Scout's effective accelleration, assuming about 1,000 tons of mass? What is the Delta V, assuming the same 93.1% of its mass as reaction mass that we used earlier for a chemical rocket?

 

[Thot]

[...]
I should say that several people here are suggesting alternative technologies, like SSTO planes based on SABRE or other such systems, that might a better fit for the setting your looking at.

I have considered them all. They fail, for various reasons.

[...]
and the hryddogen cracking farms you are on about, able to produce many thousands of D tons of h2 and LOX, and presunably store these somewhere, are perfectly safe and reasonable?

Yes, because even if you blow them up, you just destroy the downport, or even just a facility close to it, Not the whole planet. Sure, you could have them all explode by ortillery, but that's quite some effort.