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Thot July 25th, 2017 07:07 AM

The Chemical Rocket Third Imperium
 
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 July 25th, 2017 08:09 AM

Quote:

Originally Posted by Thot (Post 570141)
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 July 25th, 2017 08:33 AM

Quote:

Originally Posted by Xerxeskingofking (Post 570143)
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.

Quote:

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.

Quote:

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? :)

Quote:

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 July 25th, 2017 10:47 AM

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/h...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 July 25th, 2017 01:02 PM

Quote:

Originally Posted by kilemall (Post 570154)
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).

Quote:

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 July 25th, 2017 01:04 PM

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

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

Ulsyus July 25th, 2017 01:37 PM

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 July 25th, 2017 01:44 PM

A stargate system would solve everything ...

Thot July 25th, 2017 02:36 PM

Quote:

Originally Posted by aramis (Post 570168)
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 July 25th, 2017 02:37 PM

Quote:

Originally Posted by Ulsyus (Post 570170)
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? :)


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