The Chemical Rocket Third Imperium

[Thot]

Imagine the OTU - without reactionless thrusters, without Contragravity or anything like it, not even with fusion rockets, but instead, with extremely cheap chemical rockets and chemical rocket fuel. Yes, no artificial gravity either. Instead, there is side-effect-free medication that prevents atrophy and all that.

The whole Imperium offers infrastructure to operate chemical-rocket-propelled spaceships. You can buy the fuel for a credit a ton, as automated ultra-cheap facilities produce it even on remote unihabitated worlds within the Imperium's borders, as long as they have at least a class E starport.

Starships are very usually pure space dwellers, they never land, possibly don't even leave a jump point. They, too, have big chemical rockets attached, but of course they use them rather rarely.

Jump distance is adjusted so that a ship at escape velocity can reach a safe jump distance in about the same time as it would need in the OTU with a standard Traveller maneuver drive. There are no (meaningful) jump fuel requirements, but jump engines need to cooldown for about a week after a jump.

There are landing craft with re-launch capability (small shuttles with massive rockets attached to them, which land vertically and can produce their own fuel once on the ground), escape pods with heat shields that can do a single atmospheric entry and parachute down safely.

No space elevators. The concept is dubious at best, and requires careful balancing even under optimistic assumptions (when you send something up, something of equal mass must come down, which is highly impractical and prone to failure).

Everything in normal space is done with ultra-cheap chemical rockets on H2/O2 basis. Even the most advanced starships of the Ancients used this basic technology.

For reference, here is the % of the ship that is fuel and the delta V that comes out of it (assuming a fairly advanced chemical rocket with 4500m/s exhaust velocity; Terra's escape velocity is a bit over 11 km/s):

Reaction Mass Percentage	Delta V
10,0%	474 m/s
20,0%	1,004 m/s
30,0%	1,605 m/s
40,0%	2,299 m/s
50,0%	3,119 m/s
60,0%	4,123 m/s
70,0%	5,418 m/s
80,0%	7,242 m/s
90,0%	10,362 m/s
95,0%	13,481 m/s
98,0%	17,604 m/s
99,0%	20,723 m/s
99,5%	23,842 m/s
99,9%	31,085 m/s

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?

How would it affect warfare, commerce, politics? What would this Third Imperium look like? What about its rivals?

 

[Xerxeskingofking]

Imagine the OTU - without reactionless thrusters, without Contragravity or anything like it, not even with fusion rockets, but instead, with extremely cheap chemical rockets and chemical rocket fuel. Yes, no artificial gravity either. Instead, there is side-effect-free medication that prevents atrophy and all that.

The whole Imperium offers infrastructure to operate chemical-rocket-propelled spaceships. You can buy the fuel for a credit a ton, as automated ultra-cheap facilities produce it even on remote unihabitated worlds within the Imperium's borders, as long as they have at least a class E starport.

Starships are very usually pure space dwellers, they never land, possibly don't even leave a jump point. They, too, have big chemical rockets attached, but of course they use them rather rarely.

Jump distance is adjusted so that a ship at escape velocity can reach a safe jump distance in about the same time as it would need in the OTU with a standard Traveller maneuver drive. There are no (meaningful) jump fuel requirements, but jump engines need to cooldown for about a week after a jump.

There are landing craft with re-launch capability (small shuttles with massive rockets attached to them, which land vertically and can produce their own fuel once on the ground), escape pods with heat shields that can do a single atmospheric entry and parachute down safely.

No space elevators. The concept is dubious at best, and requires careful balancing even under optimistic assumptions (when you send something up, something of equal mass must come down, which is highly impractical and prone to failure).

Everything in normal space is done with ultra-cheap chemical rockets on H2/O2 basis. Even the most advanced starships of the Ancients used this basic technology.

For reference, here is the % of the ship that is fuel and the delta V that comes out of it (assuming a fairly advanced chemical rocket with 4500m/s exhaust velocity; Terra's escape velocity is a bit over 11 km/s):

Reaction Mass Percentage	Delta V
10,0%	474 m/s
20,0%	1,004 m/s
30,0%	1,605 m/s
40,0%	2,299 m/s
50,0%	3,119 m/s
60,0%	4,123 m/s
70,0%	5,418 m/s
80,0%	7,242 m/s
90,0%	10,362 m/s
95,0%	13,481 m/s
98,0%	17,604 m/s
99,0%	20,723 m/s
99,5%	23,842 m/s
99,9%	31,085 m/s

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?

How would it affect warfare, commerce, politics? What would this Third Imperium look like? What about its rivals?

it would put a large premium on highport space, and would massively increase the value of orbital infrastructure, due to the much, much lower costs of moving stuff around in orbit as opposed to up out of a grav well.

like you say, spacecraft will be spilt between high fuel "interface" craft that have the Delta V to get onto and off planets, and lower fuel jumpships that can travel between stars.

the very high fuel percentages mean that traditional smallcraft are pretty much useless. if your 100 ton shuttle can only carry less than 10 tons of cargo theirs really not much point in making one instead of going for a 1000 ton ship and being able to move a 150-200 tons at once.


lower gravity worlds gain a significant trade advantage due to the much lower surface to orbit costs. the classic GG fuel skimming is much, much harder to do, and frankly pointless if your going to have to burn a huge amount just to get into positon to even try it.

once a ship is decided on a route and started its burn, its pretty much committed, and it cant really change course mid way.


have you considered SSTO and other such technologies? they might offer a way to reduce the fuel percentages down a bit to allow for interface craft to do more than just about limp into orbit.

 

[Thot]

it would put a large premium on highport space, and would massively increase the value of orbital infrastructure, due to the much, much lower costs of moving stuff around in orbit as opposed to up out of a grav well.

Probably, but note how I set the cost of a ton of liquid hydrogen or oxygen to a single Imperial Credit per ton. That means you pay roughly 20 Credits to get a ton (!) of payload into orbit and beyond.

like you say, spacecraft will be spilt between high fuel "interface" craft that have the Delta V to get onto and off planets, and lower fuel jumpships that can travel between stars.

In fact, we might be able to keep using the non-streamlined standard Traveller ships... like the Xboat tender, for instance.

the very high fuel percentages mean that traditional smallcraft are pretty much useless. if your 100 ton shuttle can only carry less than 10 tons of cargo theirs really not much point in making one instead of going for a 1000 ton ship and being able to move a 150-200 tons at once.

That's true - the larger the ship, the bigger the payload can be even in percent of the total mass.

A completely new field of application for battle riders and their carriers?

lower gravity worlds gain a significant trade advantage due to the much lower surface to orbit costs.

Indeed. In fact, asteroid belts will probably be premier industry sites.

 

[kilemall]

I'm not quite getting your mass percentage/delta vee chart, the missing part would appear to be how much time at X accel is assumed.

I think it's a bad assumption that similar ratios of mass and energy to modern fuels will obtain, even with no fusion/grav. For example, Metallic Hydrogen could have 3-4x the output of conventional fuels.

https://dash.harvard.edu/bitstream/handle/1/9569212/Silvera_Metallic.pdf?sequence=2

The other thought I had was assuming this tech mix, I would likely go with a Mongoose rules/10D jump limit. Given the slower speeds, there will be plenty of time for shootin drama.

 

[Thot]

I'm not quite getting your mass percentage/delta vee chart, the missing part would appear to be how much time at X accel is assumed.

No, the raw delta V (the total speed change that the ship can perform) is unrelated to the amount of acceleration. It only comes into play when a force counteracts it (such as gravity), where it substracts from acceleration (and thus delta v) every second. For a launch, that might affect the first few dozen seconds, after which the rocket will be flying not straight up, but more and more horizontally (in a very low, but increasing orbit).

I think it's a bad assumption that similar ratios of mass and energy to modern fuels will obtain, even with no fusion/grav. For example, Metallic Hydrogen could have 3-4x the output of conventional fuels.[...]

Sure, but you won't be able to produce it cheaply, whereas H2/O2 could be produced by solar powered, long-life automated facilities everywhere- facilities that might be so well-built that they last for thousands of years and can thus sell their product for basically nothing.

 

[aramis]

The 3I without gravitics wouldn't be the 3I...

The price penalty is too high to have the high trade empire.

 

[Ulsyus]

So if you find beanstalks dubious, how do you feel about skyhooks? The only require a fraction of the resources required of a full-blown space elevator, reduce the need to explain why rocket fuel needs to be so cheap, and still allows you to have all the other components of your concept. Additionally, where the technology is too low to allow for them you could still have big rockets tearing holes in the clouds.

 

[Brandon C]

A stargate system would solve everything ...

 

[Thot]

The 3I without gravitics wouldn't be the 3I...

The price penalty is too high to have the high trade empire.

Why is 20 Credits per ton "too high"?

 

[Thot]

So if you find beanstalks dubious, how do you feel about skyhooks? The only require a fraction of the resources required of a full-blown space elevator, reduce the need to explain why rocket fuel needs to be so cheap, and still allows you to have all the other components of your concept. Additionally, where the technology is too low to allow for them you could still have big rockets tearing holes in the clouds.

Why can't fuel just be that cheap? Isn't that a lot easier to assume than everything else SF does in order to have star-spanning empires?

 

[Brandon C]

Why can't fuel just be that cheap? Isn't that a lot easier to assume than everything else SF does in order to have star-spanning empires?

A physics breakthrough is easier to work past than an economics breakthrough. The first sidesteps the laws of nature, the second sidesteps human nature. Why wouldn't people charge the most they could for fuel rather than the least? If here is no longer any desire to be wealthy, then why are independent traders operating anyway?

 

[Thot]

[...] Why wouldn't people charge the most they could for fuel rather than the least? If here is no longer any desire to be wealthy, then why are independent traders operating anyway?

The assumption is that 1 Credit per ton (of fuel, translating to roughly 20 Credits per ton of payload) is "the most they can charge".

Because there are fifty automated facilities in the system, protected by High Imperial Law since the time of the Ziru Sirka (and this is the basis of interstellar society, so the Imperium really, really means that one), and most of those facilities have been in operation basically since the law was established and are utterly written off. They are just printing money, with zero operation cost, and they are so numerous that anyone who demands more will just be outcompeted by the others. What's more, they are cheap to build should it, for whatever reason, become necessary: You just buy a self-extracting standard container that builds the facility near a large body of water. Plus, as mentioned, many ships come with on-board facilities to fill their tanks, albeit more slowly.

 

[Brandon C]

The assumption is that 1 Credit per ton (of fuel, translating to roughly 20 Credits per ton of payload) is "the most they can charge".

So the Imperial government controls fuel distribution?

 

[Thot]

So the Imperial government controls fuel distribution?

No. The market is so full of supply that 1 Credit per ton is the equilibrium price.

It may vary locally, but 1 Cr per ton should be a reasonable average.

 

[nobby-w]

Imagine the OTU - without reactionless thrusters, without Contragravity or anything like it, not even with fusion rockets, but instead, with extremely cheap chemical rockets and chemical rocket fuel. Yes, no artificial gravity either. Instead, there is side-effect-free medication that prevents atrophy and all that.

Something like Kerbal Space Program, I should think. Try spending a little time setting up a Munar fuel mining operation and refuelling station, and then transferring fuel to a fuelling station in Kerbin Orbit.

Figure out how to make SSTOs that can transfer between ground and Kerbin Orbit. Build some lighters that can dock with the SSTOs and transfer passengers to the stations. Lug some payloads into orbit with the SSTOs.

Run some missions out of that setup. That should give you a feel for what an interplanetary economy might look like under those circumstances. I can post a couple of save games and some ship files if you want.

 

[kilemall]

No, the raw delta V (the total speed change that the ship can perform) is unrelated to the amount of acceleration. It only comes into play when a force counteracts it (such as gravity), where it substracts from acceleration (and thus delta v) every second. For a launch, that might affect the first few dozen seconds, after which the rocket will be flying not straight up, but more and more horizontally (in a very low, but increasing orbit).

Guess I'm not following you- the value you are positing in the second column is TOTAL potential vee?

Sure, but you won't be able to produce it cheaply, whereas H2/O2 could be produced by solar powered, long-life automated facilities everywhere- facilities that might be so well-built that they last for thousands of years and can thus sell their product for basically nothing.

Okay, you could have a commercial fuel/rate, and then a military/scout/rare corps spec ops high cost/high performance fuel.

Differentiating orgs and people operating on a budget vs. power and subtle prices like the high performance ships tied to supporting bases makes IMO for a more sense of unique reality I believe you are striving for.

Thinking of how such a milieu would look like and operate, a classic SF short story came to mind, Cold Equations.

https://en.wikipedia.org/wiki/The_Cold_Equations

A Twilight Zone adaptation....

https://www.youtube.com/watch?v=SBgEil5qEAc

 

[Thot]

Yes, I read tons of good stuff about KSP. Unfortunately, my time to spend on computer games is rather limited, so I'll just stick with some spreadsheets. Also, KSP doesn't have an FTL component, so that part would be really missing.

Hm, let us think a bit about the Imperial Navy under such assumptions.

With the low delta V that we have to expect for interstellar ships, and with the fact that only really large ships will be able to deliver a meaningful mobile punch, battle riders will be even more important, though the riders will look quite differently (while the battle rider carriers might be able to stay largely the same). However, for some tasks, such as trader-raiding cruisers, that will not be viable.

So this might be that universe's version of the Azhanti High Lightning class (I am using GT Starships as a blueprint for my own considerations, since it conveniently lists mass):

Total loaded mass without drop tank: 660,000 tons
Internal fuel mass: 30.000 tons (4.5%, delta V is about 200 m/s before refuelling)
Empty mass without drop tanks: 630,000 tons
Jump 5, 1.7 g accelleration fully loaded without drop tank.

Adding a 240,000 dtons drop tank, delta v rises to 1600m/s, jump goes down to 1, iniitial acceleration drops to about 1.2 g.

Will she carry fighters? Most likely, but a lot fewer and bigger ones, so as to have some meaningful delta V on them. Standard AZHL's fighter hangar is 800 dtons, so maybe 8 fighters, with 100 dtons each, consisting of a cockpit, some weapons, a rocket engine and 90-95% fuel for a delta v in the range of 10-13 km/s.

Tactics for such a ship would be to jump into a system and stay at the jump location (assuming jump drive puts the ship from the orbit around one star into another orbit around another star), where it will use its spinal mount to control the surrounding area of space, destroy merchant ships and smaller warships until it has caused enough trouble to force the opposition to react and burn a lot of fuel (or do an in-system jump to its location, more likely), and then jump away to repeat the exercise elsewhere.


What about landing operations? How to invade a system? Jump in with a fleet, hope that you either subdue or avoid an enemy FTL fleet at the arrival point, send out your battle riders (who will approach the planet at 1/4th of their delta v, to allow for a full return without refuelling should it be necessary - this might take a while, depending on the exact number for the jump distance). and have them fight through any opposition for a good drop position in orbit, then land the troops with drop pods (invasions will mostly be "no retreat possible" affairs, though).

Actual space combat will be mostly artillery duels without much maneuvering - maneuvering is done in the days and weeks that lead to the battle (including tactical jumps), but once the shooting starts, not much is going to change in terms of relative speeds, usually, for simple lack of delta V. Things like "sand" casters might gain additional relevance.

System defense boats and fighters will of course be a bit better off in terms of delta V, which they could have in excess of 10 km/s, but they will be either much weaker or much larger than OTU's versions.

 

[Thot]

Guess I'm not following you- the value you are positing in the second column is TOTAL potential vee?

Yes, of course. The simple result from the rocket equation.

Okay, you could have a commercial fuel/rate, and then a military/scout/rare corps spec ops high cost/high performance fuel.
[...]

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?

 

[nobby-w]

Guess I'm not following you- the value you are positing in the second column is TOTAL potential vee?
[ . . . ]

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.

L-Hyd and L-Ox is about as efficient as rocket fuel gets, and is likely the easiest to manufacture from resources in space. One could add nuclear engines and high-efficiency, low-thrust ion engines into the mix. Reaction mass for ion engines is tricky - Xenon or Cesium, neither of which is particularly easy to mine in space.

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.

 

[aramis]

Why is 20 Credits per ton "too high"?

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

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.

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

The ripple effect adds up VERY VERY fast once you get rid of continuous thrust drives and gravitics.