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Post by AtomHeartDragon on Sept 13, 2018 12:03:26 GMT
In my experience the terms of engagement are completely dictated by higher acceleration party, while high dV can dictate if and where the battle happens. The fleet with higher acceleration can always change intercept velocity at the last moment or, if it is going to be intercepted at high velocity and doesn't like it, dodge the intercept without the low acceleration fleet having time to correct. In my experience, there is a low threshold of acceleration (around a few milligees), above which any additional is very nice but unnecessary. You can always force a change in intercept velocity or dodge a fast intercept if you have more acceleration. It's just a question of burning late enough. What you can't do is keep it up, but OTOH, defenders are going to have a supply chain on their side while attackers only the supplies they have brought.
Interesting, but I expect it to operate on very diffuse gases and generate absolutely pitiful thrust - even by ion drive standards.
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Post by phoenixzix on Nov 26, 2018 3:10:24 GMT
How would interplanetary tether system changes this scene?
Basically tethers exchange momentum with outgoing and incoming spacecrafts, and give or take the odd orbital boost,kinda acts like a low-tech stargate. Free dv, and the dv you can get are pretty impressive(several km/s by optimistical estimates)
Granted, these are impressive military target and gets shot up or mined once hostility starts, and the controller can control who takes tether or not, but maybe some treaty can declare these to Be Important Civilian Infrastructures Protected Under Protocol XX.C or something. Anyhow it eases long-haul for logistic and massive movement of fleets in friendly territory, encouraging a defensive oriented approach to fleet building.
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Post by eternalsorrow on May 7, 2020 22:48:26 GMT
I'm willing to revive this thread, since I consider this topic important (and VERY important during developing a new campaign and thinking about fleet movements), but poorly addressed both here and in the game itself. The reasonable travel time is under year or two, which is very hard to achieve everywhere further than the belt. There are 10 AU between Saturn and Uranus in confrontation, and to travel this distance under two years huge amounts of dV are needed, like 50-100 kms at least. I've been racking my brains for a week or more thinking about how did the uranium for the Ceres invasion get there from Uranus under 1.4 years. This is achievable by multi-gigawatt MPD crafts, but what to do with methane-propelled NTR ships? VCS fuel tank can achieve mass ratio ~70, which yields ~25 kms dV in optimum case. I've done some math with a 5 kt warship as a payload, and an asparagus-staged craft with 5 pairs of 10kt methane tanks and 6.1 km/s exhaust speed can achieve... 18.1 km/s. Crap.
Furthermore, fueled droptanks will cost in this case more than a craft itself.
I don't think any sophisticated tanker scheme may help in achieving greater speeds, I haven't found any way to do this and eventually return all ships home in reasonable time.
UPD Regarding the Ceres fleet fissiles, they may be delivered by an unmanned rocket, which doesn't require any crew and life support. 14t (arbitrary value for everything except droptanks) payload Hydrogen Deuteride NTR rocket may achieve 45 km/s dV with 10 x 1.0kt stages; that's about 3 times (very crude) less than required to deliver the cargo to the asteroid belt in 1.5 years.
Can someone do more advanced math and try to utilize the Oberth effect there?
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Post by cipherpunks on May 8, 2020 18:29:53 GMT
Tiny Reminders: - cost of materials in CoaDE - as it was - doesn't stand the examination from common sense PoV and is therefore ephemeral; needs to be revisited sooner or later. - crude vertical staging is possible using (eek) giant blast launchers - looks ugly but mostly works. Crewed ship can be launched from RC stage.
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Post by eternalsorrow on May 8, 2020 19:09:49 GMT
According to my math, vertical staging seems not to be a panacea and ~45-50 kms dV looks like the upper limit for NTR. You can achieve a bit more, but the fuel amounts become ridiculous.
These values are pretty nice for traveling and moving your forces between inner Sol bodies, but not enough to go further. I'm very interested, how the USTA managed to become an outer-Sol-based superfaction with such a logistic struggle. OTOH, 6-8MW/ton reactors fit into the supposed CoaDE tech level, and thus civilian 100-120 km/s MPD craft should be already possible to build. It seems that by doing an instant 25kms burn near Uranus pericenter at the escape velocity, you get 1.6 multiplier to your dV. That's already something, but methane-propelled invasion from there still has to be planned for 5 years or more.
UPD Well, I can't fly to Vesta or Ceres from Uranus to simulate the cargo run. The physics is completely broken on such a distance from Sun. That's pretty sad.
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Echo
Full Member
Posts: 141
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Post by Echo on May 18, 2020 9:03:16 GMT
I don't think any sophisticated tanker scheme may help in achieving greater speeds, I haven't found any way to do this and eventually return all ships home in reasonable time. Did someone say they returned? If no, then they don't have to.
Did someone say the tankers had to be manned? If no, then they could be drones controlled (but not launched!) by the cargo ship.
Did someone demonstrate that qswitched got this right? If no, maybe he didn't fact-check this particular thing. Also, did you check all the dates of all the missions and tried to see if it is possible to travel from where one mission ended to where the next mission started in the available amount of time, in order for the main character to be actually present on scene?
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Post by eternalsorrow on May 18, 2020 14:51:13 GMT
Such a drone seems useless, since it has to rendezvous with a ship on hyperbolic trajectory and still have decent amount of fuel to pass. It's even more irrational than put another stage. I did. Firstly, there is no need to be present on scene during most of missions. Qswitched mentioned that civilian missions may be controlled on the way to another combat mission, and some combat missions may be controlled over distance. Secondly, most of timings sit well until it comes to outer planets. Uranus-Ceres cargo run in 1.4 years seemed one of the most unplausible things there. While it's definitely possible to build a 200 km/s MPD cargo vehicle, I don't know if it's possible with the tech level assumed in the campaign. NTR-propelled invasion fleet movements between outer planets in less than 1-2 years also seem very weird.
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Echo
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Post by Echo on May 19, 2020 20:33:53 GMT
Such a drone seems useless, since it has to rendezvous with a ship on hyperbolic trajectory and still have decent amount of fuel to pass. It's even more irrational than put another stage. I was actually thinking that the drones are part of the fleet. Have the fleet burn just enough fuel so that a drone can be emptied, then refill the fleet and discard that drone; rinse and repeat a few times.
However, thinking more about it, probably this is going to waste more fissile fuel (in the drones reactors) than the cargo ship is actually carrying to Vesta or Ceres...
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Post by eternalsorrow on May 19, 2020 21:16:41 GMT
You've just re-invented staging. Such a drone is just a fuel tank which could be attached to a ship, but with its own engines and control systems.
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Post by AtomHeartDragon on May 19, 2020 21:43:26 GMT
You've just re-invented staging. Such a drone is just a fuel tank which could be attached to a ship, but with its own engines and control systems. It's a more flexible form of staging, just like tankers.
I'd divide delta-v into 4 tiers: - Crewed tankers - meant mainly to resupply fleets, crews complicate use for staging but can accompany fleets to resupply them between battles.
- Drone tankers - meant to accompany fleets and be discarded when spent providing nearly arbitrary amounts of extra delta-v without structural considerations of normal staging.
- Drop tanks (on warships) - meant to extend the range of warships, facilitate long range combat orbital maneuvers or get ships into CQB. Most likely popped once shooting starts, so use them or lose them
- Internal tanks - actual combat maneuvering delta-v reserve. Protected by armor.
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Post by eternalsorrow on May 20, 2020 10:26:18 GMT
I will be very grateful if you describe, how disposable drone tanker can help you achieve 100km/s+ dV for NTR fleet on its way to invasion. Because I see absolutely no advantages in comparison with staging except a possibility to maneuver between fleets.
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Post by AtomHeartDragon on May 20, 2020 12:01:12 GMT
I will be very grateful if you describe, how disposable drone tanker can help you achieve 100km/s+ dV for NTR fleet on its way to invasion. Because I see absolutely no advantages in comparison with staging except a possibility to maneuver between fleets. You don't need to engineer staging into all ships in the fleet (advantage over vertical staging and horizontal staging), you have the extra propellant carry itself (advantage over horizontal staging AKA droptanks) AND you have flexibility regarding the amount of extra delta-v carried.
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Post by eternalsorrow on May 20, 2020 13:39:01 GMT
It's not. Mass ratio will always be worse.
There are two possibilities to gain additional noticeable amount of dV during an interplanetary transfer, and no more:
1. Staging. By droptanks or (less efficient) drone tankers, but that's still a staging since you take fuel from a part of your fleet and discard it once it's empty. It's very difficult to obtain 50 km/s by an asparagus-staged methane NTR craft, and any drone tankers will have even worse mass ratio since they have to propel, power and control themselves.
2. Fly-by refueling near allied celestial bodies. But the tanker needs to align speeds with the target fleet (flying on hyperbolic trajectory) and pass a decent amount of fuel. In most of situations it won't be feasible.
Such fleet movements seem for me possible only by MPD-propelled vessels, but the game is quiet about MPDs on combat crafts, and there is no stock one.
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Echo
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Post by Echo on May 20, 2020 20:21:03 GMT
I stand corrected. I tried with 1 cargo freighter and 10 large methane tankers: - burned 9.74 km/s, then emptied 8 tankers to refuel the fleet;
- burned another 9.72 km/s, then emptied the remaining 2 tankers;
- finally burned another 4.42 km/s, then I run out of fuel
That's 23.88 km/s total, 2.45 times the freighter ΔV budget at 12.8 times the mass.
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Post by eternalsorrow on May 21, 2020 9:42:33 GMT
Try asparagus (or better "crossfeed") staging, that's the most efficient fueling scheme so far. 100 kt methane staged craft with 5kt payload should be able to reach ~40 km/s at least.
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