The 3 kilometer question...

[Spacescifi]

In this scenario you have a 97000 ton spaceship that has been outfitted with a scifi FTL drive called Shift Velocity and Location drive (SVL).

Basically it moves moves vacuum over the ship's hull, shifting it's position in space without accelerating it. To drop out of SVL, the ship must encounter the three kilometer radius of another object in space (at least a kilogram or more). That is called shift lock (my play on mass lock), upon which your vessel drops out harmlessly with a speed and orbital vector identical to the object that shift locked you.

Basically, your ship is standing still relative to the object that shift locked you 3 kilometers away. Even though you gained it's speed and orbital heading, nulifying any you previously had.

Here is the question:

Your ship regularly docks with space stations in orbit of planets.

97,000 tons of spaceship is no joke. Therefore what would be the ideal fuel, rocket engine,and propellant you would have your spaceship stocked with ahead of time? Real fuels and engines only. Even nuclear is fine... antimatter or metallIc hydrogen is NOT. What will it be? A nuclear reactor with liquid methane?

How long will it take your 97,000 ton spaceship to cross 3 kilomoters from a relative dead stop?

EDIT: I know your not going to wanna burn tons of fuel. But at the same time I do not think waiting an hour to cross 3 kilometers and slow to dock will be acceptable to your passengers either.

You have 300 passengers.

Still the more you burn the more often you will have to refuel... so.

 

What do you think.

 

 

Edited July 3, 2019 by Spacescifi
Kilogram not kiligram

[insert_name]

trivial solution: make your ship 3km long, then just turn it with reaction wheels

[Shpaget]

Again with the 97 000. What's the deal with the false precission?

Have tug boats attach cables and winch your ship to the dock.

[KerikBalm]

3 km at 10 m/s is 5 minutes. At 5 m/s its 10 minutes. For a 10m/s acceleration, we can assume you need to decelerate again. So for a 10 minute trip, you need 10 m/s, for a 5 minut trip, you need 20 m/s.

Using storable chemical propellant with even a measly 300 Isp, this requires a fuel fraction of just 1.004. To get 20 m/s of dV with 300 Isp, you need a mass fraction of 1.007.

Lets say you want 5 min trips, and you want to be able to do 10 of them without refueling. So you need 10*20 m/s, ie 200 m/s.

Lets say you are using something like the Merlin 1D vacuum engine with 348 Isp, hydocarbon and lOx (relatively easy to store)

https://en.wikipedia.org/wiki/Merlin_(rocket_engine_family)#Merlin_1D_Vacuum

In that case you need a mass fraction of just over 1.06, ie 6% of your mass as Kerosene and Oxygen. So to move 97 tons of craft 200 m/s, you need 5.82 tons of fuel+ox. But why not say 100 kilotons dry mass and 6 kilotons of propellant?

Bump that up to a 800 Isp NERVA, and you only need a mass fraction of 1.026. For a single trip of 20 m/s total required, you need a mass fraction of 1.003, so lets say 0.3 kilotons of lH2.

If we go to more advanced solid cores of 1000 Isp, You need just over 1.002 mass fraction. Go to a LPNTR solid core, and you get to 1210s Isp, under 1.002 mass fraction, for 200 m/s, just over 1.01 mass fraction. Going hybrid with electric acceleration and monatmic designs, 1800 Isp: just over 1.001 mass fraction for 20 m/s, and 1.0115 mass fraction for 200 m/s

Liquid core or closed cycle gas core: 2000 Isp, 1.001 mass fraction for 20 m/s, and 1.01025 mass fraction for 200 m/s.

Open cycle gas core (may not want to use so close to a inhabited station), 3600 Isp: 1.0006 mass fraction for 20 m/s, and 1.0057 mass fraction for 200 m/s.

 

[kerbiloid]

4 hours ago, Shpaget said:

Again with the 97 000. What's the deal with the false precission?

from waybills = 100 000

dry = 96 000
antimatter = 3
official cargo = 997
contraband = 3000

P.S.
When they are walking the captain's elephant, then 99995.

Edited July 3, 2019 by kerbiloid

[magnemoe]

97.000 ton is very low for an 3 km long ship. more fitting for an 300 meter long one if you use seagoing ship as an template. 
Yes it would be engine and fuel then an 3 km grinder up to cargo and crew quarters. 
Radiators and stuff on the grinder. 

 

[Guest]

Based on numbers from COADE, an efficient 400m long warship is about 50-60 kilotons. So for a 97kT warship, you're looking at something between one and three fourths of a kilometer. However, this is for a fairly heavily armed, armored, methane-fueled NTR vessel (10km/s of dV). For a civilian ship, it could very well be much longer at that mass. That said, that depends on the exact volume of cargo you expect to carry.

Also, nowhere was it said that the ship is 3km, but rather, that it has to cross 3km. In which case, it's a matter of what acceleration you have to work with. For station docking, you'll be using RCS, and will not have your main engine running. As far as RCS go, in case of a nuclear engine, the most efficient solution is a bunch of arcjet thrusters using the same propellant as the NTR. Especially great if you have a bimodal engine that can generate power for the RCS. 

Edited July 3, 2019 by Guest

[cantab]

In solar or high planetary orbits, 3 km away is rendezvoused. You might just stationkeep and use smaller spacecraft to ferry between ship and station. In a low Earth orbit or if you must dock you'll want to close that distance, and yeah, RCS job.

Now if you're moving a hundred thousand tonnes, you will need some pretty beefy "RCS" thrusters. Scaling up to a thousand times what the Space Shuttle had, it's about 4 meganewtons for your primary RCS. And like any RCS propulsion system, you want to be responsive, capable of loads of ignitions and shutdowns.

Chemical engines will do the job, but obviously the fuel consumption is high in absolute terms, even if it's low compared to the mass of the ship as discussed.

A nuclear thermal rocket might do nicely. The big challenge is that the core either needs to be very responsive, or you need a way to keep it cool when not thrusting.

I'm sceptical about an arcjet or resistojet being able to provide enough power. A mass driver might do the thrusting but would be a menace to any nearby traffic.

Overall I think my pick would be nuclear thermal rockets using water as propellant and coolant. The NTRs would do double duty also providing the ship's electrical power, and when thrust is needed the exhaust is diverted out the nozzles. Water is less efficient than hydrogen but based on CoaDE it can run close if the reactor is hot enough to dissociate it, and it's abundant in the universe and is much denser and easier to store. So that we don't need a zillion reactors, I'll mount them in pods capable of swivelling to thrust in the direction needed. Unless we can run multiple nozzles off one reactor.

[Nightside]

11 hours ago, Spacescifi said:

97,000 tons

Please clarify do you mean:

- 97 tons to the thousandths place 

or 97 thousand tons?

Remember that in some places “,” is used as a decimal.

 

 

[Spacescifi]

11 hours ago, Shpaget said:

Again with the 97 000. What's the deal with the false precission?

Have tug boats attach cables and winch your ship to the dock.

 

Basically this, which is same weight.

3 hours ago, Nightside said:

Please clarify do you mean:

- 97 tons to the thousandths place 

or 97 thousand tons?

Remember that in some places “,” is used as a decimal.

 

 

97 thousand tons.

 

[natsirt721]

20 hours ago, Spacescifi said:

shifting it's position in space without accelerating it

This is called 'translating' I believe.

cantab is right - assuming that this vehicle is visiting infrastructure designed for other vehicles of its size, and using 500m as an estimate for length (COADE ships are usually spindly, a liner would be thicc) you're already very close to the station. 

The real question is, why bother with docking at all?

Most of the ship is probably dead mass - that is, for all intents and purposes it is part of the ship. It ain't going anywhere. Usually an appreciable fraction of the mass is fuel, but if you can translate outside of the atmosphere you don't really need a lot of fuel - we can put the upper boundary on a few tens of kilotons. Passengers and baggage mass is basically negligible. Cargo is probably similar to fuel, a 10-20 kt. Rather than bringing the behemoth to the station to transfer passengers/fuel/cargo, bring the passengers/cargo to the station and the fuel to the ship using tankers (or a really long hose :p). Cargo and fuel might be a little tricky - cargo is probably carried in standard containers, or at least not in bulk so you only need a ship (probably a fleet owned by the station) large enough to carry the largest denomination of cargo container. Tankers can carry a few kt of fuel at a time and make several trips - sure its not as convenient but provided there are enough tankers to be continuously filling your ship, it isn't going to be significantly slower. Passengers will wait however goddamn long you tell them to wait - I've spend two hours in an airliner on the tarmac waiting for a gate. But it's easier just to get them a shuttle.

I'll tackle the 'what is the RCS composed of' and hope that provides a good answer.

Exotics (antimatter, fusion, etc.) are out of the question. Too much dry mass per thruster.

Electric is too weak - even if you can a kilonewton per thruster, its going to take a while to build up any appreciable angular velocity, and equally long to negate it. You can basically forget about linear acceleration - even 10 of those 1 kN thrusters firing at once gets you about one-tenth of one millimeter per second squared.  

Nuclear thermal is probably impractical - you would need one core for every thruster block - between 6 and 8 reactors minimum. If you can afford the technological burden, this is probably your most fuel-optimal choice. Also, as cantab mentioned, throttle response would be poor, either sacrificing efficiency as you expel underheated propellant or mass for an active cooling system.

Chemical is easy. LOX fuels are a decent choice, but cryocooling can be a pain. Restarting them can also be problematic (but you can probably hand-wave that away). Personal bias steers me towards hypergolics, like N204/MMH. Isp near 330 is pretty poor, but you don't need any heavy turbopumps or cryocoolers for the fuel, and the engines are basically nozzles with a box on one end where the fire happens. Thrust is good enough - it won't be great, and you will have to fill up more than you would for LOX or NTR, but responsiveness and dry mass are stellar.

If you had a big ole nuclear reactor (or other convenient source of electricity), you could probably do an electrically-pumped thermal solution - like a steam rocket pumped by a megawatt laser. Those can be as efficient as NTR and you don't have to deal with nuclear problems.

[Spacescifi]

2 hours ago, natsirt721 said:

This is called 'translating' I believe.

cantab is right - assuming that this vehicle is visiting infrastructure designed for other vehicles of its size, and using 500m as an estimate for length (COADE ships are usually spindly, a liner would be thicc) you're already very close to the station. 

The real question is, why bother with docking at all?

Most of the ship is probably dead mass - that is, for all intents and purposes it is part of the ship. It ain't going anywhere. Usually an appreciable fraction of the mass is fuel, but if you can translate outside of the atmosphere you don't really need a lot of fuel - we can put the upper boundary on a few tens of kilotons. Passengers and baggage mass is basically negligible. Cargo is probably similar to fuel, a 10-20 kt. Rather than bringing the behemoth to the station to transfer passengers/fuel/cargo, bring the passengers/cargo to the station and the fuel to the ship using tankers (or a really long hose :p). Cargo and fuel might be a little tricky - cargo is probably carried in standard containers, or at least not in bulk so you only need a ship (probably a fleet owned by the station) large enough to carry the largest denomination of cargo container. Tankers can carry a few kt of fuel at a time and make several trips - sure its not as convenient but provided there are enough tankers to be continuously filling your ship, it isn't going to be significantly slower. Passengers will wait however goddamn long you tell them to wait - I've spend two hours in an airliner on the tarmac waiting for a gate. But it's easier just to get them a shuttle.

I'll tackle the 'what is the RCS composed of' and hope that provides a good answer.

Exotics (antimatter, fusion, etc.) are out of the question. Too much dry mass per thruster.

Electric is too weak - even if you can a kilonewton per thruster, its going to take a while to build up any appreciable angular velocity, and equally long to negate it. You can basically forget about linear acceleration - even 10 of those 1 kN thrusters firing at once gets you about one-tenth of one millimeter per second squared.  

Nuclear thermal is probably impractical - you would need one core for every thruster block - between 6 and 8 reactors minimum. If you can afford the technological burden, this is probably your most fuel-optimal choice. Also, as cantab mentioned, throttle response would be poor, either sacrificing efficiency as you expel underheated propellant or mass for an active cooling system.

Chemical is easy. LOX fuels are a decent choice, but cryocooling can be a pain. Restarting them can also be problematic (but you can probably hand-wave that away). Personal bias steers me towards hypergolics, like N204/MMH. Isp near 330 is pretty poor, but you don't need any heavy turbopumps or cryocoolers for the fuel, and the engines are basically nozzles with a box on one end where the fire happens. Thrust is good enough - it won't be great, and you will have to fill up more than you would for LOX or NTR, but responsiveness and dry mass are stellar.

If you had a big ole nuclear reactor (or other convenient source of electricity), you could probably do an electrically-pumped thermal solution - like a steam rocket pumped by a megawatt laser. Those can be as efficient as NTR and you don't have to deal with nuclear problems.

So with a ship of this weight (97000 tons), it really is impractical to fly around in space with rockets of current technology?

You would be better off with a ship that weighed less?

What would be an optimal large ship's weight with this translation drive? Since 97000 tons is evidently pushing the limits of steering and propulsion with rockets that need refueling too far?

[KSK]

Not enough information. SVL appears to be a Star Trek style warp drive in all but name, so journeys do take time. So?

How fast is your drive?

How far is this ship travelling and how long does it take to get there?

What is your ship doing? Are we talking 5 year missions where nobody has gone before or system-to-system hops starting and ending at a refuelling facility?

How many crew does your ship need?

How much cargo do you want it to carry?

What is your general technology level. Can you dispose of biowaste by using it as raw matter for a replicator or similar system, or  are you recycling it using more present day technology? Or are you simply storing it in a tank and offloading it at journey’s end?

At a bare minimum, your ship will require: the SVL drive and an energy source for it, some kind of reaction drive and propellant therefor, a habitation module, and sufficient life support consumables to support your crew for an expected journey length plus reserves.

Optional extras depending on role: Cargo space, a shuttle bay or other support craft hangar (or docking ports) plus fuel, spare parts and other consumables to maintain those craft, weapons and power/ammo supplies therefor, scientific equipment. 

Of all of those, you could get a rough idea of the mass of life-support consumables you need from looking up the comparable figures for the ISS.  You’ve already had some replies about maneuvering thruster fuel requirements. Everything else is handwaving and guesswork at this point.

Also - why the need for detailed figures? Unless you’re planning to write a technical manual for your ship, this level of expositionary detail can really bog a story down. Your readers / viewers won’t care about the exact mass of your ship except as a loose indication of size and capability relative to other ships.

Likewise, they probably won’t care about the tonnage of life support materiel it can carry but they might be interested in knowing whether it has a replicator system aboard for recycling, or whether it has a greenhouse or related biological recycling module. That sort of incidental detail helps to set the scene for your story - how advanced your setting is and therefore how dangerous or routine space travel is, for example.

Edited July 4, 2019 by KSK

[Spacescifi]

3 hours ago, KSK said:

Unless you’re planning to write a technical manual for your ship, this level of expositionary detail can really bog a story down. Your readers / viewers won’t care about the exact mass of your ship except as a loose indication of size and capability relative 

True. This was just an exercise to see what man could do if he jerry-rigged an SVL alien drive.

Lesson learned is... space travel is still hard. Just not as hard as before.

15 hours ago, natsirt721 said:

Usually an appreciable fraction of the mass is fuel, but if you can translate outside of the atmosphere you don't really need a lot of fuel - we can put the upper boundary on a few tens of kilotons.

Translation only works in vacuum. Grav-inverters make ship fall upward at same rate it would fall down. Translation drive does the rest in vacuum. Grav-inverters are also useful for gas giant refueling, since you can scoop falling down and fallling up.

Probably still need a compressor and tanks to make it liquid fuel though.

Edited July 4, 2019 by Spacescifi

[natsirt721]

14 hours ago, Spacescifi said:

So with a ship of this weight (97000 tons), it really is impractical to fly around in space with rockets of current technology?

Well, strictly speaking no. Technically there is nothing limiting you from building such a ship in Earth orbit today - it would be incredibly expensive and probably take a decade with current launcher technology and availability, but its not technically restricted (on-orbit construction woes aside). The problem is that while your engine choice dictates how much propellant you need, it also dictates how much propellant per kilogram of non-fuel you need for a given mission. That's where the problems set in. If you only need 2 kps of dV, you can achieve a mass ratio around 1.5 with hydrolox propellants. Strictly speaking this is not too bad, but for you that means 40 kt of propellant (assuming 97 kt is wetmass).

That's the beauty of the rocket equation - it doesn't really care about mass, it cares about mass ratio. You could make a ship that weighted 9.7 grams and it would need 4 grams of propellant. You could make a ship that weighed 9.7e13 tons, and you would need 4e13 tons of fuel. I read somewhere that for a non-bulk ship (i.e. a passenger liner or quick cargo vessel) you should try to keep the mass ratio below about 4. For you, this means about 80 kt of fuel maximum. From there, you can work backwards and try to figure out how much dV you think you need (in this example, basically none) and then how high your exhaust velocity can be to achieve that.

The handwave drive and the gravity inverter kinda throw a wrench in this process - most of your dV expenditures are still going to come during liftoff, but if you don't have to fight gravity then your engines can be significantly weaker. I would SWAG about 10 kt of chemical propellant for the main engines, and a few kt for attitude control.

Edit: I fully concur with KSK's analysis above, but it is important for the author to have a good grasp on the technical capability of the vehicle so they don't do anything too absurd. I would say that having translational drives and gravity inverters makes this sort of technical analysis meaningless, but if they are salvaged parts I can get behind it.

Edited July 4, 2019 by natsirt721

[Spacescifi]

11 minutes ago, natsirt721 said:

Well, strictly speaking no. Technically there is nothing limiting you from building such a ship in Earth orbit today - it would be incredibly expensive and probably take a decade with current launcher technology and availability, but its not technically restricted (on-orbit construction woes aside). The problem is that while your engine choice dictates how much propellant you need, it also dictates how much propellant per kilogram of non-fuel you need for a given mission. That's where the problems set in. If you only need 2 kps of dV, you can achieve a mass ratio around 1.5 with hydrolox propellants. Strictly speaking this is not too bad, but for you that means 40 kt of propellant (assuming 97 kt is wetmass).

That's the beauty of the rocket equation - it doesn't really care about mass, it cares about mass ratio. You could make a ship that weighted 9.7 grams and it would need 4 grams of propellant. You could make a ship that weighed 9.7e13 tons, and you would need 4e13 tons of fuel. I read somewhere that for a non-bulk ship (i.e. a passenger liner or quick cargo vessel) you should try to keep the mass ratio below about 4. For you, this means about 80 kt of fuel maximum. From there, you can work backwards and try to figure out how much dV you think you need (in this example, basically none) and then how high your exhaust velocity can be to achieve that.

The handwave drive and the gravity inverter kinda throw a wrench in this process - most of your dV expenditures are still going to come during liftoff, but if you don't have to fight gravity then your engines can be significantly weaker. I would SWAG about 10 kt of chemical propellant for the main engines, and a few kt for attitude control.

Edit: I fully concur with KSK's analysis above, but it is important for the author to have a good grasp on the technical capability of the vehicle so they don't do anything too absurd. I would say that having translational drives and gravity inverters makes this sort of technical analysis meaningless, but if they are salvaged parts I can get behind it.

 

Would gas giant scooping for refueling be as viable as I think it would be using grav-inverters?

Or have I overlooked something?

I know planets like Uranus are the places to go, since methane is easier to store than hydrogen.

[KSK]

14 minutes ago, natsirt721 said:

Edit: I fully concur with KSK's analysis above, but it is important for the author to have a good grasp on the technical capability of the vehicle so they don't do anything too absurd. I would say that having translational drives and gravity inverters makes this sort of technical analysis meaningless, but if they are salvaged parts I can get behind it. 

Thanks! And yes - I also concur that the author should have a decent grasp on the technical capabilities of the vehicle. If nothing else, it helps keep your worldbuilding consistent and consistency is also important if you're hanging any plot points on a limitation of your vehicle.

Incidentally, I would point to Apollo 13 as a relevant example here. As you'd expect, most of the story is underpinned by technical detail  but its notable that very few hard numbers are ever used - because they're not needed. Telling the reader that No.2 oxygen tank in the Service Module has gone boom, is more than enough to get the message across without digressing into how much oxygen that actually amounts to.

[Spacescifi]

41 minutes ago, natsirt721 said:

 

Edit: I fully concur with KSK's analysis above, but it is important for the author to have a good grasp on the technical capability of the vehicle so they don't do anything too absurd. I would say that having translational drives and gravity inverters makes this sort of technical analysis meaningless, but if they are salvaged parts I can get behind it.

Rockets delta v is not totally meaningless in this fictional scenario. Since how powerful your engines are and your mass ratio makes a diierence with how fast a vessel... or missile crosses 3 kilometers.

Civillan vessels may not mind taking 30 minutes or longer to cross 3 kilometers. Military vessels will. They will likely be ligher in weight, packed with weaponry and a minimum of crew and life support (if any).

In fact given the 3 kilometer range and factoring in inertia, missiles will be quite viable and nigh ustoppable if enough are launched.

This would provide the slow-mo boat spacebattles we see in visual scifi so often, only with newtonian physics.

 

Edited July 4, 2019 by Spacescifi
Military mass is lighter

[KerikBalm]

On 7/4/2019 at 7:31 PM, Spacescifi said:

 

Would gas giant scooping for refueling be as viable as I think it would be using grav-inverters?

Or have I overlooked something?

I know planets like Uranus are the places to go, since methane is easier to store than hydrogen.

Sure, if you need not worry about TWR or dV (you just use grav inverters to float, then jump to something in orbit, and can shut everything down and be in a stable orbit with no propellant use.

On 7/4/2019 at 7:56 PM, Spacescifi said:

Rockets delta v is not totally meaningless in this fictional scenario. Since how powerful your engines are and your mass ratio makes a diierence with how fast a vessel... or missile crosses 3 kilometers.

Civillan vessels may not mind taking 30 minutes or longer to cross 3 kilometers. Military vessels will. They will likely be light

er in weight, packed with weaponry and a minimum of crew and life support (if any). 

In fact given the 3 kilometer range and factoring in inertia, missiles will be quite viable and nigh ustoppable if enough are launched.

This would provide the slow-mo boat spacebattles we see in visual scifi so often, only with newtonian physics. 

For 3 km, the main thing here will be TWR/acceleration, not dV. A 10 m/s/s acceleration will get you to the target in 24 seconds, for only 240 m/s... not even enough dV to break the sound barrier on Earth. So modern missiles going multiple times the speed of sound are going to be more than viable. Consider an AIM-9 sidewinder:

http://www.designation-systems.net/dusrm/m-9.html 

Quote

Propulsion was provided by a Thiokol MK 17 solid-fuel rocket motor (17.8 kN (4000 lb) thrust for 2.2 s), which could propel the missile to a speed of Mach 1.7 above launch speed

This works out to about 250 m/s/s, or 25 G/s, with a dV of only about 560 m/s. The AIM-9 weighs 85.3 kg, so it seems its initial acceleration would be 208 m/s. Maintaining 25 G's, your missile impacts in 4.9 seconds from launch, with a dV of 1225 m/s. All these dV's are quite viable with current tech

On 7/3/2019 at 4:34 AM, Spacescifi said:

 To drop out of SVL, the ship must encounter the three kilometer radius of another object in space (at least a kilogram or more). That is called shift lock (my play on mass lock), upon which your vessel drops out harmlessly with a speed and orbital vector identical to the object that shift locked you.

Well, then any station can easily halve the dV requirements of a vessel that wants to rendezvous with it... Just have >1 kg masses that it can extend and retract at say... 10 m/s. Then you SVL to those masses, and you only have to gently brake to dock.

Also, you've now got a perpetual motion mobile. Want to accelerate? launch a >2kg mass out ahead of your ship... like out of a rail/coilgun, then shift lock to it.

Don't want to waste those? launch a more complex object ahead of you... it can have a mass the moves forward and backward cyclically (like bouncing balls, but with a spring or electromagnetic forces if the masses can't be touching for your SVL to work), you shift lock to a mass moving forward relative to the barycenter of what you launched forward... now you can SVL with a relative velocity to the barycenter of the masses you launched forward, and gain thousands of m/s each time.

Stations can have masses moving forward and back to allow vessels to SVL with relative velocity to the station. With proper timing, they can even launch masses to allow a vessel to SVL to break... ie have a mass going 10 m/s away from the station (you can catch it a moment later after the incoming vessel SVLs to it), and then an incoming vessel can SVL with a 10 m/s velocity relative to the station, before it SVLs, you can launch another mass at 10 m/s so that its 3km away from the station when the incoming vessel needs to SVL, and the incoming vessel can SVL again to a dead stop relative to the station.

With a pair of stations, you could just bounce this mass for SVL breaking back and forth between them... or give the mass a light sail to allow it to return on its own... or use velocities that allow you to launch the mass at resonant orbits, so it will come back and be caught later (10 m/s is slow enough to catch easily).

This magic drive that shifts velocity essentially allows for changing velocity with no propellant, just be shifting masses around at the destination. THe mass limit is so small, a vessel can launch its own mass for braking and accelerating at the target destination.

Incoming missiles? do they have more than 1 kg mass? SVL to the missile, and now you have the same velocity and it will never catch you TROLOLOLOLOL.

Want to trike a target? send in one vessel, have it fire a 1 kg mass at high velocity, then immediately SVL out, then the fleet comes in and SVLs to that projectile while its in flight, and they fire their projectiles at twice the relative velocity as the first (and immediately SVL out), repeat in stages until you break light speed/attack with a relativistic weapon TROLOLOLOLOL.

Sorry, but this drive is ridiculous.

[Spacescifi]

50 minutes ago, KerikBalm said:

Sure, if you need not worry about TWR or dV (you just use grav inverters to float, then jump to something in orbit, and can shut everything down and be in a stable orbit with no propellant use.

For 3 km, the main thing here will be TWR/acceleration, not dV. A 10 m/s/s acceleration will get you to the target in 24 seconds, for only 240 m/s... not even enough dV to break the sound barrier on Earth. So modern missiles going multiple times the speed of sound are going to be more than viable. Consider an AIM-9 sidewinder:

http://www.designation-systems.net/dusrm/m-9.html 

This works out to about 250 m/s/s, or 25 G/s, with a dV of only about 560 m/s. The AIM-9 weighs 85.3 kg, so it seems its initial acceleration would be 208 m/s. Maintaining 25 G's, your missile impacts in 4.9 seconds from launch, with a dV of 1225 m/s. All these dV's are quite viable with current tech

Well, then any station can easily halve the dV requirements of a vessel that wants to rendezvous with it... Just have >1 kg masses that it can extend and retract at say... 10 m/s. Then you SVL to those masses, and you only have to gently brake to dock.

Also, you've now got a perpetual motion mobile. Want to accelerate? launch a >2kg mass out ahead of your ship... like out of a rail/coilgun, then shift lock to it.

Don't want to waste those? launch a more complex object ahead of you... it can have a mass the moves forward and backward cyclically (like bouncing balls, but with a spring or electromagnetic forces if the masses can't be touching for your SVL to work), you shift lock to a mass moving forward relative to the barycenter of what you launched forward... now you can SVL with a relative velocity to the barycenter of the masses you launched forward, and gain thousands of m/s each time.

Stations can have masses moving forward and back to allow vessels to SVL with relative velocity to the station. With proper timing, they can even launch masses to allow a vessel to SVL to break... ie have a mass going 10 m/s away from the station (you can catch it a moment later after the incoming vessel SVLs to it), and then an incoming vessel can SVL with a 10 m/s velocity relative to the station, before it SVLs, you can launch another mass at 10 m/s so that its 3km away from the station when the incoming vessel needs to SVL, and the incoming vessel can SVL again to a dead stop relative to the station.

With a pair of stations, you could just bounce this mass for SVL breaking back and forth between them... or give the mass a light sail to allow it to return on its own... or use velocities that allow you to launch the mass at resonant orbits, so it will come back and be caught later (10 m/s is slow enough to catch easily).

This magic drive that shifts velocity essentially allows for changing velocity with no propellant, just be shifting masses around at the destination. THe mass limit is so small, a vessel can launch its own mass for braking and accelerating at the target destination.

Incoming missiles? do they have more than 1 kg mass? SVL to the missile, and now you have the same velocity and it will never catch you TROLOLOLOLOL.

Want to trike a target? send in one vessel, have it fire a 1 kg mass at high velocity, then immediately SVL out, then the fleet comes in and SVLs to that projectile while its in flight, and they fire their projectiles at twice the relative velocity as the first (and immediately SVL out), repeat in stages until you break light speed/attack with a relativistic weapon TROLOLOLOLOL.

Sorry, but this drive is ridiculous.

 

Well you understand the drive's abilities quite well.

Although you may have a misconception.

3 kilometer radius is set. Does not matter what it is.

If an object weighs a kilogram or more it WILL shift-lock your vessel. You CANNOT SVL until you clear the shift lock radius.

Thus if a station did not want a bunch of dangeous ships creeping up on it it only has to launch a bunch of satellites a few hundred kilometers out. Spread them out so that they only a few kilometers out from each other and you have a massive shift-lock net.

Space combat you have better grasp than I, as you understand just how lethal modern missiles are.

I can still see combat being a massive missile swarm battle. 

Although getting free speed won't be as easy as you think in combat. Because:

At SVL your ship will literally stay at SVL until you reach the 3 kilometer radius area of another  1 kilogram or more object. If you try dumping cargo, it will just SVL along with you. Now if you launched a missile or railgun slug, yeah, you could use that to shift-lock your vessel as soon as it hit the 3 kilometer radius.

In that case, you would retain your ship's true original speed and orbital heading before you went SVL.

So you may drift totally off target. Surely not at a relative stop to them this time. Yet it would be a tactic that could pay off if you hit your target.

Which is a big if considering SVL capabilities.

Two things seem to matter most here. Rate of fire and shift lock. With a good enough weapon loadout you could clear out the stuff shift locking you.

Missiles would be a mixed favor of sorts, since they will shift-lock your enemy ship the same as it will to you.

Worst case scenario? Shift-locked with a thousand missiles headed your way.

But you are right.

Something this huge get get away FAST from those missiles simply by launching high velocity railgun rounds and SVLing to them. Assuming the thousand enemy missiles were not already within 3 kilometers of your ship's radius. In that case you cannot even SVL.

I hope your vessel would have good countermeasures. It would need them.

 

Edited July 8, 2019 by Spacescifi
From each other

[Spacescifi]

I guess what I am saying is that shift-lock merely defaults to the closest object that weighs a kilogram or more. You really cannot choose what shift-locks you unless you launched the object yourself.

Edited July 8, 2019 by Spacescifi

[KerikBalm]

30 minutes ago, Spacescifi said:

You CANNOT SVL until you clear the shift lock radius

Ok, so you need to get 3km away from the station before SVLing away?

Still no problem. Have some telescoping poles. Extend one witha 1 kg mass, and start retracting it (if it needs to break contact with the target mass, no problem, it can do that momentarily). Incoming vessel SVLs to the mass, and is already on approach vector to the station. Now you only need a braking piston or EM system that can decelerate the ship by 10 m/s or some before collision. It can also push the vessel away again after wards. 5 minute dockings and departures, no reaction mass or chemical thrusters needed.

Quote

Thus if a station did not want a bunch of dangeous ships creeping up on it it only has to launch a bunch of satellites a few hundred kilometers out. Spread them out so that they only a few kilometers out from each other and you have a massive shift-lock net.

Ok, so this is a defensive net? In reality it just gives the opponent more opportunity to set up the SVL chain for a relativisitic weapon kill, without even losing their initial vessel.

Quote

Although getting free speed won't be as easy as you think in combat. Because:

At SVL your ship will literally stay at SVL until you reach the 3 kilometer radius area of another  1 kilogram or more object. If you try dumping cargo, it will just SVL along with you.

Huh, SVL will take stuff that you detached from your ship? what do you mean dumped cargo SVLs along with you?

Quote

Now if you launched a missile or railgun slug, yeah, you could use that to shift-lock your vessel as soon as it hit the 3 kilometer radius.
In that case, you would retain your ship's true original speed and orbital heading before you went SVL.

You previously said

Quote

your vessel drops out harmlessly with a speed and orbital vector identical to the object that shift locked you

So which is it, you retain the speed and heading before SVL, or you gain the speed and heading of the object you locked onto? these two statements are incompatible.

Its in the name that you shift velocity, so I'm just going to ignore the above statement as nonsense, and assume that yes, you can use SVL to gain speed easily. You accelerate a 1 kg projectile, and use SVL to make that velocity apply to your arbitrarily large vessel. Accelerating huge vessels is trivial now.

Disregarding the above quote as the contradictory nonsense that it is, I will also disregard the following as nonsense:

Quote

So you may drift totally off target. Surely not at a relative stop to them this time. Yet it would be a tactic that could pay off if you hit your target.

Which is a big if considering SVL capabilities.

And this also seems to be nonsense:

Quote

Two things seem to matter most here. Rate of fire and shift lock. With a good enough weapon loadout you could clear out the stuff shift locking you.

What do you mean clear out the stuff shift locking you?

Shoot things as they appear 3km away, stationary relative to you? The problem comes when the first ship sends the "pilot" projectile (recoil would move it from 3km away from the target to over 3km away), and then a ton of stuff shift locks to that projectile just before it hits, now everything appears coming in at high velocity, and you're screwed.

Want to come in at over 3km away? stagger your SVL jumps, first vessel comes in at 3km, backs up 1 meter, a 2nd vessel shift locks in, now 6 km away, and the first shift locks out (have a specialty vessel or two with 2 drives ready to go/ a quick operating specialty drive for just this tactical purpose). 3 vessels doing this chain blink in, puff the RCS, blink out get you to 9 km away, and ready for 3 stages of additive projectile shift locking for velocity stacking and wiping out the target with stuff blinking in at high velocity right on top of the target.

Quote

Something this huge get get away FAST from those missiles simply by launching high velocity railgun rounds and SVLing to them. Assuming the thousand enemy missiles were not already within 3 kilometers of your ship's radius. In that case you cannot even SVL.

I hope your vessel would have good countermeasures. It would need them.

This system highly favors offense. Anything on the defense is screwed.

You can just blink it, launch a swarm of 1 kg masses to pin down the target, then start a chain to get an un-dodgeable relativistic projectile that will obliterate the target.

With chained SVL, you easily reach relativistic velocities, and can wipe out entire planets.

Worst case scenario for the attacking party, you sacrifice your first ship to lock the target in place, and start the SVL chain. Then it will just be a fleet of the bruisers + the smallest and cheapest vessels capable of SVL, losing 1 per attack if the target is armed and the first vessel can't clear out in time. Obviously this will always be economically favorable, attrition favors the attacker.

Fleet vs fleet combat is pointless, and each side just tries to wipe out the enemy's home with relativistic weapons.

Its 1970's ballistic missile MAD, but in space.

 

Edited July 8, 2019 by KerikBalm

[Spacescifi]

1 hour ago, KerikBalm said:

Ok, so you need to get 3km away from the station before SVLing away?

Still no problem. Have some telescoping poles. Extend one witha 1 kg mass, and start retracting it (if it needs to break contact with the target mass, no problem, it can do that momentarily). Incoming vessel SVLs to the mass, and is already on approach vector to the station. Now you only need a braking piston or EM system that can decelerate the ship by 10 m/s or some before collision. It can also push the vessel away again after wards. 5 minute dockings and departures, no reaction mass or chemical thrusters needed.

Ok, so this is a defensive net? In reality it just gives the opponent more opportunity to set up the SVL chain for a relativisitic weapon kill, without even losing their initial vessel.

Huh, SVL will take stuff that you detached from your ship? what do you mean dumped cargo SVLs along with you?

You previously said

So which is it, you retain the speed and heading before SVL, or you gain the speed and heading of the object you locked onto? these two statements are incompatible.

Its in the name that you shift velocity, so I'm just going to ignore the above statement as nonsense, and assume that yes, you can use SVL to gain speed easily. You accelerate a 1 kg projectile, and use SVL to make that velocity apply to your arbitrarily large vessel. Accelerating huge vessels is trivial now.

Disregarding the above quote as the contradictory nonsense that it is, I will also disregard the following as nonsense:

And this also seems to be nonsense:

What do you mean clear out the stuff shift locking you?

Shoot things as they appear 3km away, stationary relative to you? The problem comes when the first ship sends the "pilot" projectile (recoil would move it from 3km away from the target to over 3km away), and then a ton of stuff shift locks to that projectile just before it hits, now everything appears coming in at high velocity, and you're screwed.

Want to come in at over 3km away? stagger your SVL jumps, first vessel comes in at 3km, backs up 1 meter, a 2nd vessel shift locks in, now 6 km away, and the first shift locks out (have a specialty vessel or two with 2 drives ready to go/ a quick operating specialty drive for just this tactical purpose). 3 vessels doing this chain blink in, puff the RCS, blink out get you to 9 km away, and ready for 3 stages of additive projectile shift locking for velocity stacking and wiping out the target with stuff blinking in at high velocity right on top of the target.

This system highly favors offense. Anything on the defense is screwed.

You can just blink it, launch a swarm of 1 kg masses to pin down the target, then start a chain to get an un-dodgeable relativistic projectile that will obliterate the target.

With chained SVL, you easily reach relativistic velocities, and can wipe out entire planets.

Worst case scenario for the attacking party, you sacrifice your first ship to lock the target in place, and start the SVL chain. Then it will just be a fleet of the bruisers + the smallest and cheapest vessels capable of SVL, losing 1 per attack if the target is armed and the first vessel can't clear out in time. Obviously this will always be economically favorable, attrition favors the attacker.

Fleet vs fleet combat is pointless, and each side just tries to wipe out the enemy's home with relativistic weapons.

Its 1970's ballistic missile MAD, but in space.

 

 

I will attemp to address some misconceptions.

1. It is not a jump drive.

2. It is a space moves past your vessel drive.

3. SVL navigation is as simple as steering your ship like a plane in space. Make no mistake. You are'nt accelerating, space is moving past your ship and you decide what direction space moves past based on your steering. Smaller mass ships are easier/quicker to steer. They can make tighter turns. Which is a relative thing, considering that base SVL speed is a lightsecond per minute. For FTL SVL, a vessel must clear a seven light second radius from the nearest planet. Then you can SVL at a lightyear per hour. Within a seven lightsecond radius of a planet you can only go a lightsecond per minute.

 

4. A vessel generates an invisible SVL field bubble while at SVL that is 3 kilometers wide. Any missiles or cargo dropped within it are subject to newtonian physics. But they will STAY in the bubble provided they do not drift out of or accelerate out of it. When that happens your vessel will shift lock to whatever mass it launched that cleared the 3 kilometer bubble first.

5. A vessel will literally stay at SVL forever until it either finds something to shift-lock to or the SVL generator overheats and melts it. Seven hours of SVL use is considered safe, but 8 hours is considered risking a meltdown. Leaving your vessel stranded in space unless it has a backup SVL generator.

6. A ship's SVL generator can cool down with heat sinks. Which may take hours or perhaps just 30 min if you have some expensive ones.

7. Say you SVL drove to a satellite and aquired it's orbital trajectory and speed. Next you SVL toward the moon, but detect four vessels trying to intercept you while in SVL. They turn tighter than your vessel and you know they WILL intercept you sooner or later since they are circling you from different vectors. You fire a missile that clears your SVL bubble radius and shift-locks you.

What speed and orbital heading do you aquire? 

Well... during SVL you do not get ANY orbital trajectory. You can only TRANSLATE to what you shift-lock to.

In your case it is the missile you fired from your own vessel. Thus you retain your previous orbital trajectory with the added speed of the missile thrown in. Just translocated to a totally different area in space, since you were halfway to the moon when you shift-locked to your missile.

That is how you can do that.

Now if you translated or shift-locked to the pirate vessels... yeah, you would match them for trajectory and speed at at a relative stop 3 kilometers away.

8. Pirates could still catch up to you but it would be hard if you keep spamming missiles to SVL away. Plus when not in SVL you're virtually standing still while SVL vessels are virtually making u-turns and loops at a lightsecond per minute.

Edited July 8, 2019 by Spacescifi
Bubble and translate catchup

[KerikBalm]

6 minutes ago, Spacescifi said:

I will attempt to address some misconceptions.

1. It is not a jump drive.

2. It is a space moves past your vessel drive.

3. SVL navigation is as simple as steering your ship like a plane in space. Make no mistake. You are'nt accelerating, space is moving past your ship and you decide what direction space moves past based on your steering. Smaller mass ships are easier/quicker to steer. They can make tighter turns. Which is a relative thing, considering that base SVL speed is a lightsecond per minute. For FTL SVL, a vessel must clear a seven light second radius from the nearest planet. Then you can SVL at a lightyear per hour. Within a seven lightsecond radius of a planet you can only go a lightsecond per minute.

1-3 make no difference as far as I'm concerned for the purposes of this discussion. How it changes its position is irrelevant. The point is that to the defending observer, it appears seemingly out of nowhere, and can seemingly disappear into nothingness provided it stays 3km away as well.

Quote

4. A vessel generates an invisible SVL field bubble while at SVL that is 3 kilometers wide. Any missiles or cargo dropped within it are subject to newtonian physics. But they will STAY in the bubble provided they do not drift out of or accelerate out of it. When that happens your vessel will shift lock to whatever mass it launched that cleared the 3 kilometer bubble first.
5. A vessel will literally stay at SVL forever until it either finds something to shift-lock to or the SVL generator overheats and melts it. Seven hours of SVL use is considered safe, but 8 hours is considered risking a meltdown. Leaving your vessel stranded in space unless it has a backup SVL generator.

Well, 4 makes it even easier to set up chains, as you can have a mass for other ships to lock on to 3 km behind the vessel that jumps in, so they can chain in 6km away, more safety and time to set up the relativistic kill chain.

It also means that you can have a nuke/antimatter weapon 2.99km in front of the SVL trive when activated, and then you jump in and nuke them from point blank immediately.

Bravo, you're making it worse.

Also, point 5 is easily over come by point 4. All you have to do to stop is to throw a 1 kg mass in front of you, it reaches the front of the bubble, and then causes the bubble to stop. You can now jump in at an arbitrary distance from your target. Awesome. BTW, what is the velocity of the mass when it leaves the bubble, if it hasn't shift locked to anything, it just drifted out of the bubble, its initial velocity?

If so, this means that you can now get relativistic velocities super easy: start falling towards a large mass (sun, black hole), then before getting within 3 km of 1 kg, shift drive farther away (and you can drop out at will by just ejecting a 1 kg mass in front of you to act as a brake), fall back towards the mass, repeat as needed, for only a few kg, you can now SVL anywhere you want and launch your projectile from an arbitrary distance, at an arbitrary velocity. Relativistic kill weapons made even easier, cool.

Now, FTL requires a 7 light second distance, within that distance, you're only going to get to 1/60 c using this method (still one heck of a fast first strike). Of course things are already going faster than this relative to each other, so SVL's speed limits make no sense, as if there is a preferred reference frame, but all this means is that you go FTL to reach something that is going fast relative to your desired target, match its velocity, then come at your target with that velocity.

Also note that earth is 500 light seconds from the sun. You'd get a lot of velocity repeatedly falling to 8 light seconds from the sun, and SVLing back away.

Quote

6. A ship's SVL generator can cool down with heat sinks. Which may take hours or perhaps just 30 min if you have some expensive ones.

Or you just double the size of your heat sinks, and allow it to fire off twice before your heat sinks are full and you need to cool your vessel down... but wait... you said earlier:

Quote

stay at SVL forever until it either finds something to shift-lock to or the SVL generator overheats and melts it. Seven hours of SVL use is considered safe, but 8 hours is considered risking a meltdown.

and

Quote

base SVL speed is a lightsecond per minute. For FTL SVL, a vessel must clear a seven light second radius from the nearest planet. Then you can SVL at a lightyear per hour

This implies heat is generated by unit time, and you only need 7 minutes to go FTL, and you have 8 hours worth of heat generation, which means you can do FTL SVL 68 times in a row before risking meltdown.

Also this implies an 8 light year drive radius, which isn't enough to cross some gaps between stars, so if you come up with a "rule change" to stop my easily thought of work around for stopping at will and building up to relativistic velocities (eject something out of the front of your bubble to stop you), then you also change the rules such that  many stars and star clusters are unreachable or inescapable with this drive.

This is the problem with fictional science... it always breaks down or leads to ridiculous capabilities that have to be ignored for story purposes.

PS, since this drive allows for FTL displacement (and no, moving space instead of the vessel doesn't change anything for this purpose, just as a point to point jump wouldnt), how are you going to deal with the resultant ability to time travel?

[Spacescifi]

8 minutes ago, KerikBalm said:

1-3 make no difference as far as I'm concerned for the purposes of this discussion. How it changes its position is irrelevant. The point is that to the defending observer, it appears seemingly out of nowhere, and can seemingly disappear into nothingness provided it stays 3km away as well.

Well, 4 makes it even easier to set up chains, as you can have a mass for other ships to lock on to 3 km behind the vessel that jumps in, so they can chain in 6km away, more safety and time to set up the relativistic kill chain.

It also means that you can have a nuke/antimatter weapon 2.99km in front of the SVL trive when activated, and then you jump in and nuke them from point blank immediately.

Bravo, you're making it worse.

Also, point 5 is easily over come by point 4. All you have to do to stop is to throw a 1 kg mass in front of you, it reaches the front of the bubble, and then causes the bubble to stop. You can now jump in at an arbitrary distance from your target. Awesome. BTW, what is the velocity of the mass when it leaves the bubble, if it hasn't shift locked to anything, it just drifted out of the bubble, its initial velocity?

If so, this means that you can now get relativistic velocities super easy: start falling towards a large mass (sun, black hole), then before getting within 3 km of 1 kg, shift drive farther away (and you can drop out at will by just ejecting a 1 kg mass in front of you to act as a brake), fall back towards the mass, repeat as needed, for only a few kg, you can now SVL anywhere you want and launch your projectile from an arbitrary distance, at an arbitrary velocity. Relativistic kill weapons made even easier, cool.

Now, FTL requires a 7 light second distance, within that distance, you're only going to get to 1/60 c using this method (still one heck of a fast first strike). Of course things are already going faster than this relative to each other, so SVL's speed limits make no sense, as if there is a preferred reference frame, but all this means is that you go FTL to reach something that is going fast relative to your desired target, match its velocity, then come at your target with that velocity.

Also note that earth is 500 light seconds from the sun. You'd get a lot of velocity repeatedly falling to 8 light seconds from the sun, and SVLing back away.

Or you just double the size of your heat sinks, and allow it to fire off twice before your heat sinks are full and you need to cool your vessel down... but wait... you said earlier:

and

This implies heat is generated by unit time, and you only need 7 minutes to go FTL, and you have 8 hours worth of heat generation, which means you can do FTL SVL 68 times in a row before risking meltdown.

Also this implies an 8 light year drive radius, which isn't enough to cross some gaps between stars, so if you come up with a "rule change" to stop my easily thought of work around for stopping at will and building up to relativistic velocities (eject something out of the front of your bubble to stop you), then you also change the rules such that  many stars and star clusters are unreachable or inescapable with this drive.

This is the problem with fictional science... it always breaks down or leads to ridiculous capabilities that have to be ignored for story purposes.

PS, since this drive allows for FTL displacement (and no, moving space instead of the vessel doesn't change anything for this purpose, just as a point to point jump wouldnt), how are you going to deal with the resultant ability to time travel?

 

You are not limited with FTL travel. Just cool your SVL generator and fly out again. 7 LY max to be safe yeah, but you can SVL again once you cool off.

Good math by the way, but your average reader won't dissect the heat generation with math anyway.

Time travel? No. Not doing that. 

Yet I am OK with going forward in time due to gravity like in the movie interstellar.

 

Also, FTL sensors exist. 7 LY range.

So any black hole shenanigans will likely be detected by a scout ship or probe in a nearby system anyway. They will be on high alert anyway. And the time it takes your ship to get here it can be intercepted and destroyed.

There actually is a tactical difference between translocation space moving past yoy and just blinking there.

Bliniking ia clearly superior. But with my drive, not only does it take time, but it can be detected.

Now if you did make a whole fleet of 24 relativstic vessels via black hole and SVL, the homeworld defebse force can send whatever spare vessels it has after you us put a bounty on your head.

Bobbing and weaving to evade numerous ships at FTL will make your attacks harder to pull off.

Since it only takes three kilometers to shift lock.

Once they do they have your speed and trajectory and can engage at 3 kilometers.

I guess the real battle will be won in detail.

Namely a lot of mano e mano, one vessel vs another, as most of fleet will likely scatter if you see a much larger one about to shift-lock you.