Future propultion systems for spacecraft

[Night_Wing_Zero]

So i've been reading some articles as well watching some documentaries that scientists are developing multiple ways to travel in deep space, however what would be the requirements for such engines to exist and keep the crew safe and sound without having a disaster?

 

[Nibb31]

Requirements would depend on the technology.

So far, we have to choose between chemical propulsion and electric propulsion, but in the end, the only way to obtain thrust is to throw stuff out the back, which requires an amount of energy proportional to the thrust that you want to get.

[p1t1o]

53 minutes ago, Night_Wing_Zero said:

So i've been reading some articles as well watching some documentaries that scientists are developing multiple ways to travel in deep space, however what would be the requirements for such engines to exist and keep the crew safe and sound without having a disaster?

 

Welcome to the forums!

First, 2 links:

http://www.sciencemadness.org/library/books/ignition.pdf (can take a while to load, I just tested the link and it works)

http://www.projectrho.com/public_html/rocket/

The first is a book detailing some wonderful anecdotes in the history of rocketry development. Its very well written and straight from the horses mouth. Its a very good primer for how modern rocketry came to be and what real rocket science is really like. My favorite part is the part about lemons  

The second is a great repository of rocketry science. Intended as a resource for people writing science fiction, it has great current information on various types of modern, projected and hypothetical space propulsion - and it also has chapters on other interesting things such as space weaponry, navigation etc.

You might find that either of these links answer a lot of your questions.

Happy spacing!

[PB666]

3 hours ago, Night_Wing_Zero said:

So i've been reading some articles as well watching some documentaries that scientists are developing multiple ways to travel in deep space, however what would be the requirements for such engines to exist and keep the crew safe and sound without having a disaster?

 

 

The biggest problem is ISP or for pure space traveling exhaust velocity.

So the problem is that we can come up with options that over long periods of time can develope great velocity. For example you could use a proton accelerator to throw out a proton with a relativistic mass of several psuedo-daltions

So imagine that we could say 'fix a position very close to the sun' then you could use panels to drive your speed up over a couple of generations, release and off into space you go and 4 decades later your at alpha centauri where you reverse the process.

But . . . .we cannot wind your ship up around a star because inertia pitches you out in space. So its really about a power supply more than a propulsion system . . . . We don't have one. Most of the engines current in design or out there that can allow carry a load into deep space do not have a power supply for the engine VASIMR is an example. 

So the next best thing is to look at nuclear energy as a source of propulsion. Two reasons, the mass fraction of nuclear material released is smaller, ISP is higher and more power per unit mass.

TNR in the best conceived scenarios is 1000s ISP, That will get you in theory about double the speed outbound of V1 and V2 (though really what you want is to crunch out velocity at the planetary transfer gravity turns and TNRs have poor thrust). So this technology is really interplanetary such as Earth / Mars cargo.

The next are the Nuclear pulse rockets, which in deep space offer the opportunity to really crunch up the speed, need not worry about transfers, just point along an escape trajectory and go.
However the machinery for doing that is heavy and you need to launch from earth or build in space (say 100 SpaceX missions, a space factory, and a crew that operates in EVA or more advanced space robotics).
The nuclear test ban treaty kind of forbids using it for a surface launch propulsion system. (Requires Uranium, Neutron generators, H, Li, Plutonium, etc.). Its very messy launching from the surface, might need to take over a desert country or part of Antarctica to accomplish this without causing a revolution.

Finally you have hybrid fusion reactors were they use a combination of plasma technology and isotope inject for direct expansion and ejection of low atomic weight isotopes. This is more of popular science thing that acctually anything close to space use at the present. 

Next you have always 20 years in the future Fusion Reactors -> electric power generation -> ION drive (possibly isolation and ejection of the nuclear waste). This provides electricity for the entire craft and carries some risk, the problem with fusion reactors is the high velocity neutrons are hard to contain, so the power systems need to be isolated from everything else. The smallest function EP fusion reactor in design is about 50,000 lbs, so that represents a pretty heafty cost in engine, if it produced 50 MW, than at about optimal efficiency if can produce about 0.3N of thrust (at an ISP 1500000000s) or higher if you want to blow some fuel. Problem is fuel weighs. 0.3N divided over a vehicle that weights 150 tons (1/3 power, 1/3 fuel, 1/3 else), not a hell of alot of acceleration.  0.000002 a For a year is 63.112 M/S. So to get 0.1C would take 480000 years. This number can be brought down with more effecient reactors, none the less we are still looking at an awfully long trip to the closest star, which really and truely is not a good candidate for which to travel.

Then there are other schemes. For example why carry a reactor when you can create a system of photonic rely points, simply carry long lived photo cells. And somehow mysteriously light is delivered. The problem is that you need about 10 football fields worth of solar panels to do anything, and there is a problem in that solar panels have the bizarre thing called mass and they also have momentum and structural constraints. So if you alot 1kg per meter than your mass is 50,000 kg about the same as the fusion reactor. Of course you can increase the beam but then the panels are shorter lived. The other problem is that unless your beam ships are properly staged, there is no way to slow down when you get to the target. There has been a proposal of using a space parachute, but for a human colony in space, the chute would need to be kilometers across to have any affect in deep space. Also there was electromagnetic means, but again the system would need to project a great distance into space.

Finally there is space fantasy.

1. Star Trek warp style feild. Needless to say its based on physics that DOES NOT EXIST (i.e. forces that are not observed, potential reversal of time, and particles that have not been observed)

2. Star Gate style wormholes. Violates the time restraints.

So in modern space flight design there is always risk, craft break down into things like calculable risk, we can build a station, a space factory and stage conventional fuels in space.

Then there are politically risky things that have little testing in space such as Nuclear Thermal Rockets.

Then there is politically suicidal technology like nuclear pulse rockets, potentially doable, but crew may not be protected.

Then there basically very high risk of failure because not currently doable (such as Fusion of any kind).

Then there are fantasies in which have not the foggiest clue as to how to start a design and testing process.

Given this there is a risk aversion strategy to make current systems more efficient, more bang per payload buck, and combine systems utilizing the greatest advantage for each system in the type of space where it is most advantageous (like Ceres exploration mission). Musk is trying new ways of more efficiently lowering cost to put more payload up, potentially enabling space assembly and staging and supply mission to marginally accomplishable goals. As of yet no-one is planning trips to human colonies on Pluto (and of course we know from new horizons is that once you get momentum to reach pluto, you have no power to stop so . . . . ) Basically it shows that you probably can get maybe 5000dV of stopping power and upto 25000dV launch to intercept and thats about it for our current landing targets. When you talk about manned you can cut that in half, reasonable targets.
 

 

[Night_Wing_Zero]

1 hour ago, PB666 said:

 

The biggest problem is ISP or for pure space traveling exhaust velocity.

So the problem is that we can come up with options that over long periods of time can develope great velocity. For example you could use a proton accelerator to throw out a proton with a relativistic mass of several psuedo-daltions

So imagine that we could say 'fix a position very close to the sun' then you could use panels to drive your speed up over a couple of generations, release and off into space you go and 4 decades later your at alpha centauri where you reverse the process.

But . . . .we cannot wind your ship up around a star because inertia pitches you out in space. So its really about a power supply more than a propulsion system . . . . We don't have one. Most of the engines current in design or out there that can allow carry a load into deep space do not have a power supply for the engine VASIMR is an example. 

So the next best thing is to look at nuclear energy as a source of propulsion. Two reasons, the mass fraction of nuclear material released is smaller, ISP is higher and more power per unit mass.

TNR in the best conceived scenarios is 1000s ISP, That will get you in theory about double the speed outbound of V1 and V2 (though really what you want is to crunch out velocity at the planetary transfer gravity turns and TNRs have poor thrust). So this technology is really interplanetary such as Earth / Mars cargo.

The next are the Nuclear pulse rockets, which in deep space offer the opportunity to really crunch up the speed, need not worry about transfers, just point along an escape trajectory and go.
However the machinery for doing that is heavy and you need to launch from earth or build in space (say 100 SpaceX missions, a space factory, and a crew that operates in EVA or more advanced space robotics).
The nuclear test ban treaty kind of forbids using it for a surface launch propulsion system. (Requires Uranium, Neutron generators, H, Li, Plutonium, etc.). Its very messy launching from the surface, might need to take over a desert country or part of Antarctica to accomplish this without causing a revolution.

Finally you have hybrid fusion reactors were they use a combination of plasma technology and isotope inject for direct expansion and ejection of low atomic weight isotopes. This is more of popular science thing that acctually anything close to space use at the present. 

Next you have always 20 years in the future Fusion Reactors -> electric power generation -> ION drive (possibly isolation and ejection of the nuclear waste). This provides electricity for the entire craft and carries some risk, the problem with fusion reactors is the high velocity neutrons are hard to contain, so the power systems need to be isolated from everything else. The smallest function EP fusion reactor in design is about 50,000 lbs, so that represents a pretty heafty cost in engine, if it produced 50 MW, than at about optimal efficiency if can produce about 0.3N of thrust (at an ISP 1500000000s) or higher if you want to blow some fuel. Problem is fuel weighs. 0.3N divided over a vehicle that weights 150 tons (1/3 power, 1/3 fuel, 1/3 else), not a hell of alot of acceleration.  0.000002 a For a year is 63.112 M/S. So to get 0.1C would take 480000 years. This number can be brought down with more effecient reactors, none the less we are still looking at an awfully long trip to the closest star, which really and truely is not a good candidate for which to travel.

Then there are other schemes. For example why carry a reactor when you can create a system of photonic rely points, simply carry long lived photo cells. And somehow mysteriously light is delivered. The problem is that you need about 10 football fields worth of solar panels to do anything, and there is a problem in that solar panels have the bizarre thing called mass and they also have momentum and structural constraints. So if you alot 1kg per meter than your mass is 50,000 kg about the same as the fusion reactor. Of course you can increase the beam but then the panels are shorter lived. The other problem is that unless your beam ships are properly staged, there is no way to slow down when you get to the target. There has been a proposal of using a space parachute, but for a human colony in space, the chute would need to be kilometers across to have any affect in deep space. Also there was electromagnetic means, but again the system would need to project a great distance into space.

Finally there is space fantasy.

1. Star Trek warp style feild. Needless to say its based on physics that DOES NOT EXIST (i.e. forces that are not observed, potential reversal of time, and particles that have not been observed)

2. Star Gate style wormholes. Violates the time restraints.

So in modern space flight design there is always risk, craft break down into things like calculable risk, we can build a station, a space factory and stage conventional fuels in space.

Then there are politically risky things that have little testing in space such as Nuclear Thermal Rockets.

Then there is politically suicidal technology like nuclear pulse rockets, potentially doable, but crew may not be protected.

Then there basically very high risk of failure because not currently doable (such as Fusion of any kind).

Then there are fantasies in which have not the foggiest clue as to how to start a design and testing process.

Given this there is a risk aversion strategy to make current systems more efficient, more bang per payload buck, and combine systems utilizing the greatest advantage for each system in the type of space where it is most advantageous (like Ceres exploration mission). Musk is trying new ways of more efficiently lowering cost to put more payload up, potentially enabling space assembly and staging and supply mission to marginally accomplishable goals. As of yet no-one is planning trips to human colonies on Pluto (and of course we know from new horizons is that once you get momentum to reach pluto, you have no power to stop so . . . . ) Basically it shows that you probably can get maybe 5000dV of stopping power and upto 25000dV launch to intercept and thats about it for our current landing targets. When you talk about manned you can cut that in half, reasonable targets.
 

 

So in any case if you had to design your deep space exploration vessel, which type of energy would you use to power up and keep your ship running?

[KSK]

1 hour ago, Night_Wing_Zero said:

So in any case if you had to design your deep space exploration vessel, which type of energy would you use to power up and keep your ship running?

Nuclear fission, probably using a bimodal nuclear-thermal rocket Use it as an engine and a generator as needed. The requirements for building relatively compact fission reactors with acceptable safety margins are known and have been for a long time. 

A fusion reactor would be even better once somebody works out how to build a working one that delivers an energy surplus and then figures out how to make it small enough to launch into space. Which probably won't happen any time soon.

Edit: I presume we're talking properly deep space exploration here? Chemical propulsion combined with sufficient in-situ resource utilisation infrastructure might work otherwise.

Edited January 9, 2017 by KSK

[wumpus]

2 hours ago, PB666 said:

Next you have always 20 years in the future Fusion Reactors -> electric power generation -> ION drive (possibly isolation and ejection of the nuclear waste). This provides electricity for the entire craft and carries some risk, the problem with fusion reactors is the high velocity neutrons are hard to contain, so the power systems need to be isolated from everything else. The smallest function EP fusion reactor in design is about 50,000 lbs, so that represents a pretty heafty cost in engine, if it produced 50 MW, than at about optimal efficiency if can produce about 0.3N of thrust (at an ISP 1500000000s) or higher if you want to blow some fuel. Problem is fuel weighs. 0.3N divided over a vehicle that weights 150 tons (1/3 power, 1/3 fuel, 1/3 else), not a hell of alot of acceleration.  0.000002 a For a year is 63.112 M/S. So to get 0.1C would take 480000 years. This number can be brought down with more effecient reactors, none the less we are still looking at an awfully long trip to the closest star, which really and truely is not a good candidate for which to travel.

[Standard] interplanetary ion drives work fine: for cargo going *slooooowly*.  At least two spacecraft have been launched with that type of propulsion and are doing fine.  Just don't expect to use one to get to Mars *yourself* (or Proxima Centauri for that matter).  These pretty much all have four figure Isp numbers and nearly-zero thrust values (although going *this* slow allows for some interesting gravity tricks that negate the lack of Oberth effect on delta-v).

* I've heard that they [or rather the solar panels they need] have issues with the Van Allen belts.  If true, this makes them wildly less useful than they could be.  Expect a slow cargo ship hauling from low Earth orbit to *anywhere* to spend most of its time in the Van Allen belts.

[PB666]

4 hours ago, Night_Wing_Zero said:

So in any case if you had to design your deep space exploration vessel, which type of energy would you use to power up and keep your ship running?

First off the modern day technologies work fine for Mars mission as long as we consider the two halves, getting there and getting back.

So for initial flight phase I think standard chemical repertiore is fine.

You need a small equitorial orbiting station to basically assemble a mars ready rocket. So that is fine. YOu can use rocket thrusters in LEO to HEO and you can use ION drives or chemical drives to manage the transmartian transfer. 

To get to LEO requires 8000dv, to get to HEO another 4000 or so dV and 2000 to transfer. A smaller amount to insert into martian HMO (smaller mass further from sun). If you can capture mars L1 and have fuel stage that will probabily get humans down to LMO. This way they don't have to worry about timing the intercept.

We could in theory have refuelling stations as Earth L2, Mars L1, So these fuel supplies could be shipped by transfer ships that are ION driven/Solar panel for mars and conventional fuel on earth. Since L2 is behind the earth its easier to cool the liquid oxygen,

Landing on Mars is problematic no matter what, but a Space X like landing system seems to be credible (remember however SpaceX is not carrying a payload while landing, so either you land humans piecemeal and station separately or you have a major hastle getting the lander to Mars.

Once you get humans to LMO then you can transfer to L1 station and refuel and headback to earth (Its like 500 dV or something).

One possiblity is to have a Manned observatory at Earth L2 that can act also as a space station. This would allow ships to carry passengers (shuttle) between LEO and L2, which is 2 million miles from earth with a lower DV than earth HEO. Once at the station, for example a nice rotating platform, that always points in the direction of the sun, no need to shift the solar panel. An analogous station could be a mars L1 that is unmanned. basically vessels would come in dock, so you could have multiple vessels docked with fuel until passengers arrive. The fuel tanks on the station load up, release the ships which return to Earth, and the station waits till passengers come, then starts spinning. After a few weeks of that they return to the MEO ships. Of course this might alleviate the gravitation-less sickness, but the stations would have to be armored also to protect from cosmic radiation, at 2 million miles from earth the magnetic field wanes. How the journey might be done is at LEO the ship is boosted to reach GSO requiring 3000 dV, Launch and this consume the overwhelming amount of DV. From there the ship is traveling a few  km/sec but it will have to slow down considerabily to intercept L2. Thus it would add another 500 to 1000 dV and remove that dV at L2. so  a budget of 4500dV from LEO should suffice to get to L2. Considering an average speed of say a km/sec and 3 m km to travel 34 days. Consider station times its not that much. They would then get on their station and grav up. Next Get on the transfer ship also at L2. SInce the ship is 2 million miles closer to mars and the mars station is 2 million closer to earth it reduces speed but not transfer time (basically the average orbital periods of the two planets divided by 2); however because they are close high energy transfers are possible. Given the transfer is only 200 days or so, the the astronauts would reach MARS L1 station. Here they would again Grav up. The station would be set to spin, only occasionally stopping to take on fuel and supplies and the Mars LEO transfer ship. The ship they used from Earth L2 could be that ship, and take them down to LEO.

Thats the easy part, expensive but Easy the next part is not easy at all.

From mars LEO a pre-manned station needs to be targeted to a predefined landing site.
From mars LEO the survival package and supplies need to landed on the planet, complete with solar panels, food, water, fuel.
From mars LEO a return ship or a fuel supply for the return ship needs to be landed, given O2 is likely part of the package an O2 recyclig system needs to be landed

Finally the crew would be landed. They would be largely enginneers technicians etc with minimal research science training. THis first crew would craft the station into working condition. After a few months and rock gathering they would return to fuel waiting LMO ship which would wisk them back to the mars L1 station were they grav up once more while they wait for a transfer window back to earth. Given that mars has some gravity, I would presume the gravity-less problems will be alleviated to some degree than spending a year in zero gravity. The mars station could be equiped with a Merry-go-round were astronauts spend a few days in or a few hours a day. SInce the return trip back to earth is pretty much payload they could go for a direct earth atmosphere intercept provided a reentry vehicle is attached at Mars L2. Basically this might mean that the ship detaches the station, then attaches to the reentry vehicle and goes back the same way it came, except intercept earths atmosphere where it burns and lands on the oceans with Martian rocks.

 

 

[Nuke]

you can do a lot with ion drives if you can solve the power problem. if you have a couple megawatts to work with things get easier and you get a drive capable of in system travel. they will never work for heavy lift though. a high output power plant also lets you do isru and colonization.

Edited January 10, 2017 by Nuke

[Night_Wing_Zero]

19 hours ago, KSK said:

Nuclear fission, probably using a bimodal nuclear-thermal rocket Use it as an engine and a generator as needed. The requirements for building relatively compact fission reactors with acceptable safety margins are known and have been for a long time. 

A fusion reactor would be even better once somebody works out how to build a working one that delivers an energy surplus and then figures out how to make it small enough to launch into space. Which probably won't happen any time soon.

Edit: I presume we're talking properly deep space exploration here? Chemical propulsion combined with sufficient in-situ resource utilisation infrastructure might work otherwise.

Well mine would be solar sail, I remember that either NASA or the ESA tested it on a probe as far as know, yet the drawback of this is as farther you are of the sun, the less enegry you get and colder it gets when theres no light at all

I dont know how solar panels would react to extremely low light levels

[wumpus]

42 minutes ago, Night_Wing_Zero said:

Well mine would be solar sail, I remember that either NASA or the ESA tested it on a probe as far as know, yet the drawback of this is as farther you are of the sun, the less enegry you get and colder it gets when theres no light at all

I dont know how solar panels would react to extremely low light levels

I think for a solar sail, the bigger issue would be how high you have to get (out of Earth's gravity well and away from the atmosphere) before your light gains exceed your aero losses.  Assuming low thrust and long travel times, your biggest challenge is getting from LEO to L2 or so for funky gravity tricks (even if you are moving faster than the typical "Lagrange gravity tricks" require, you still are going to use multiple planetary slingshots, which mean at least escape velocity or more than L2 delta-v).

A sail is going to have nasty aero dynamic resistance (and can't be simply held normal to the atmosphere unless you are willing to rely on "black and white" sides.  I'd expect problems in LEO for sufficiently low values of "Low".

[PB666]

1 hour ago, Night_Wing_Zero said:

Well mine would be solar sail, I remember that either NASA or the ESA tested it on a probe as far as know, yet the drawback of this is as farther you are of the sun, the less enegry you get and colder it gets when theres no light at all

I dont know how solar panels would react to extremely low light levels

They don't work beyond the asteroid belt, too far away, and the surface area to mass area for solar sails has to be screaming high, the problem with that is that probes can be light and structural issues can be dealt with. For larger craft the structural issues for a stable solar sail are problematic, they would have to cover kilometers to be effective.

 

Edited January 10, 2017 by PB666

[PB666]

9.08 μN per  Meter at earths radius, lets be generous, lets say that majically we imparted no energy to get to an earth mercurian transfer. And we have to reflect most of the light so 79.08 but we get half of that and if we get any massive power the outbound velocity crossing earth will get to use about all of the 9.08 because the ellipse will be almost vertical.

Now lets say our acceleration 50 uN /1 kg per meter of sail. thus we have 50 um/sec2 of acceleration  So the transit time is about 100 days we can generate a declining amount of power. That gives us an increase speed of 432 meters per second., ah but as we travel down the transect that acceleration needs to fall because sunlight goes to back to 9 so that if we take the average its about 200 m/s added acceleration. 
Now the transfer orbit since most of the energy does not come at mercury you would have a gravity boost yes, but you would have to wait another 100 days to get back to mercury to repeat the process. Also remember that our vectors later in the orbit are pushing us further from mercury so we are loosing optimal acceleration so basically we have a complex spiral out of the solar system.

You can get substantially more acceleration if you cut the payload and this benefits greatly at mercury's orbit because of the gravity well affect on adding dv.

So lets say we are traveling 65km/s and this gets us back to orbit, the KE is  2.115E9 per kg so if we could put all that 200dv in an periapsis we gain 1E7 joules per kilogram, at earths orbit, the problem is that

1. the velocity of at apoapsis is high 10,000s of meters per second. Which means in terms of energy that is a small amount

2. we cannot impart that much power in the depths of the gravity well.

Consequently as we reach about the orbit of Venus, we need to stop capturing power and wait till we get close to Mercury's orbit again.

Rinse, repeat, rinse.

Each time you do this you loss nine months, each time you fly by mercury you gain less E*t because your orbital velocity increase and each time you are spending time in space longer waiting to fall back to mercury. Over many years you eventually get enough speed to leave the inner solar system and reach the outer planets, were the massive planets will distort the hell out of the gravity assist, and course correction will be required, therefore some of that solar sail energy will have to be spent avoiding the gas giants.

The sun produces a tremendous amount of energy, there is no doubt about that, the big problem is we have no effective means of storing (except in hydrocarbons). Even if you have 15 kw per meter, that means diddly in space were your orbital momentum is 10 magnitudes greater.

Lets imagine the perfect solar driven system

1. We start at a submercurian orbit.
2. Our sail or panel weight is infinitly low, all energy goes to payloads
3. The impulse is prograde to orbital motion
4. We can indefinitely hold orbit until reaching desired interstellar velocity and 5. can we obtain and indefinity amount of energy from the sun.

So now lets take at look at the reality

A. Submercurian orbit is very difficult to achieve, for human inhabitants it takes time.
B. Panels and sails need structural rigity either via bracing or panel rigidity.
C. The impulse of sails is only partly prograde some is radial, however with ION drive much more is prograde there is inefficiency in the conversion. 
D. We cannot indefinitely hold an orbit until we gain speed, the ship takes on an elleptical orbit that takes it away from the energy, the power time in each orbit decreases and the idle time increases, eventually until we are talking 100s of years, such a scheme is basically only good until you reach escape velocity, much less than is needed to reach the next star
E. the energy gain per surface are under the most ideal circumstance is nothing compared to the energy required to gain velocities to reach a star, less say we had 100mt ship that had a kilometer of sail and the sail weight nothing. 1000000 of sail would impart at best 50uN * meter2/ 0.1 kg  = a of 0.0005. So at periapsis we are accelerate  1.8 m/hour*sec or 44 meters/day*sec. When you think about the speed of light you would need to hold that orbital radius for 1866 years to reach 0.1C.

So reality check 1.
Its a generational ship
check 2
It spends most of its time at large distances from the sun with little power input

check 3
passengers get stranded in interstellar space where they expire.

So lets just say that we take with us 50,000 dV of fuel and do a burn at mercurial orbit.

50,000 m/s has a kinetic energy. So at any particular orbit you like the amount of energy in velocity is equal to half the amount of energy to escape.

1/2 50,000^2 = 1250000000 J/kg if we add 50,000 it becomes

1/2 100,000^2 = 5000000000 J/kg

We need only 2500000000 j/kg to escape at mercuries orbit, thus we have 2500000000 which is 70710 m/s interstellar velocity. 

So the bottom line is that we need a propulsion system (either ION driven or Sail) which can achieve say in a period of a month these kinds of stats for a 100,000 kg vessel (BTW the size is too low probabily by a factor of 100, but lets just assume that we bioengineer a race of space tolerant microhumans).

Here is what we would want.

At least 100N of thrust. Given the rated thrust per meter of Sail of 50 uN per meter we need 4,000,000 or about 4 square kilometers but preferably something like 400 square kilometers or a sail 20km x 20km. About the size of a medium size city. Again it has to be virtually weightless. That gets us up to par with the voyager speeds. However voyager would need 40,000 years to reach the closest star. We want to achieve that distance in 40 years. OK so how much area would you need to accelerate much higher speed. So the acceleration time is drastically cut, in a month of 0.05 average C the ship is way outside the system. In addition humans aren't too happy if they are place at more than 1 g for a great length of time. So we might set the practical limit at 1.5g or 15 m/s squared.

We need an arc of say 20 degrees from Mercury to accelerate. for the sake of argument lets say it strait. This solves one problem however we can use the sail to easily reach a close orbit, but the question is what are the parameters of the sail.

1. 57.9 x 2 x pi = 20.24 million kilometers

20.24 billion meters = 50k*T +  1/2 15 T*2 (hope you see the problem with this right off but I will walk through it). roughly 49000 seconds

Okay so how much V will we generate in that amount of time? 50k + 49000*15 = 729000 m/s (less than 1/400th the speed of light) and that would roughly get you 4 light years 4E16 in 1740 years, beyond that 20' arc you can still get energy from the sun but it, because of the radial speed (increasing) and the inclination (increasing) of the escape vector declines rapidly. So a lousy escape velocity like this how much sail do you need at mercury. We need a =15

15 x 100,000 kg = 1.5E6 N/5E-5NperMeter =  a sheet of about 180km x 180km. We could design a super thin kind of plastic, but that plastic would not support the acceleration of the ship and would require structural beams, eventually eating up the payload to nothing. So talking about ships that could take humans to alpha century taking even 1000 years, much more than 100,000 kg in mass its structually impossible to make a sail that can accomplish the task.

So think in terms of a power supply that can deliver 0.001 to 0.1c and can deliver that speed at 9.8 a  over a time frame of a few days to years.

This eliminates all kinds of methods of transport for substantive mass objects. THe only valid choice I have found is fusion powered nuclear waste driven ion propulsion.  

 

 

Edited January 10, 2017 by PB666

[KSK]

Solar sails are great in that they don't need propellant but the acceleration on a solar-sail powered craft would make a solar-electric propelled craft (think Dawn ion drives in KSP) look turbocharged. A solar sail craft would be a thing of beauty though, no doubt about it.

[Night_Wing_Zero]

22 hours ago, PB666 said:

They don't work beyond the asteroid belt, too far away, and the surface area to mass area for solar sails has to be screaming high, the problem with that is that probes can be light and structural issues can be dealt with. For larger craft the structural issues for a stable solar sail are problematic, they would have to cover kilometers to be effective.

 

This gets me to ask the following, how in the world does Count Dooku ship is able to travel long distances having a solar sail?

 

 

Edited January 11, 2017 by Night_Wing_Zero

[Gkirmathal]

4 minutes ago, Night_Wing_Zero said:

This gets me to ask the following, how in the world does Count Dooku ship is able to travel long distances having a solar sail?

 

Cause it maybe is a 'plot device'?

 

Quote

however what would be the requirements for such engines to exist

Regarding technologies that are in the realm of being technically feasible in the near future (Nuclear Thermal Rockets), IMO a major aspect is political willingness to put funds into development of said technology.

That willingness became very biased, also to the public, because of the former cold war nuclear arms race, the fear of it, it's effects and the few nuclear disasters/incidents the world has seen. All tainted the idea of having nuclear tech used for something good.

For the more short term timescale I think PB666 really explained it excellently, with what is needed and what can be done now with what we have.

[wumpus]

I guess it depends on your definition for "deep space".  If you want to head out to Proxima Centauri (better hope it has a non-1:1 tidal locking, plus a ton of other things to knock it off the "acceptable planets" list) you are pretty much limited to an Orion*.  Even if you manage to build a hydrogen zero-boiloff storage that lasts for decades, there still doesn't exist any material that hydrogen won't leak through over that time period nor any reason to expect any.  If you use something other than hydrogen, say goodbye to your 4 digit ISP and any hope of stopping when you get there.

Interplanetary space has a little more hope, but is still likely chemical rockets (unless you build an Orion or nuclear thermal rocket.  They have outstanding technical issues, but politics is likely the biggest hurdle).  I'm still holding out hope for hauling [chemical] fuel (and other cargo) from LEO to where ever, but understand that any slow cargo ship from LEO will spend nearly all its time in the Van Allen belts (trouble).  This is true even for trips to Mars, thanks to the nature of gravity wells, acceleration, and delta-v.

* by "Orion" I mean the original "Project Orion" headed by Freeman Dyson in the 1960s.  Pure kerbal design, and were well on their way to building an interstellar ship in the 1960s.

[Oliverm001x]

An option for the potential of interstellar travel would be the theory of photonic propulsion. This is a relatively simple concept that could warrant interstellar travel at 25% of the speed of light. The process works by constructing a solar sail, depending on size and optimisation of the sail, a laser mounted onto multiple satellites would be situated in multiple orbits on the multiple bodies in our solar system, to ensure full satellite availability and the potential for additional usage in the case of 1 or more laser failures. 

As science has shown lasers can travel for near indefinite distances in the vacuum of space, as it consists of a concentrated beam of light, and decays occurs at inconspicuous levels. 

The solar sail would be engineered out of aluminized mylar or other materials at a thickness of 5 microns. To put that into proportion, an average human hair is 50 microns thick. Once launched and placed in an interstellar coast by a conventional chemical propellant engine, the concentrated laser beam(s), would be directed onto the sail, thus propelling the spacecraft much in the same nature as wind propels a yacht's sail. 
 

Now comes the question of keeping the crew alive. Due to the vast level of radiation present within space, it is imperative to shield the crew of the high energy. This could be accomplished by encapsulating the crew module in H2O or water. Furthermore, in situations of grave danger coming from (for ex. a coronal mass ejection) fecal matter and/or any other human waste of a hydrogen base could be utilized to protect the crew from radiation. Recycling has its benefits  

In addition, if the technology would be available, then administering a cryonic stasis and lowering the metabolism to a state of cryptobiosis, would result in the potential of the humans being "animated" during the travel not ageing during that period. However all of this is still to come in the future  . 

[TheEpicSquared]

Alcubierre Drive (very, very futuristic propulsion)

[Night_Wing_Zero]

19 hours ago, TheEpicSquared said:

Alcubierre Drive (very, very futuristic propulsion)

I've heard of it but never got the time to investigate, what is it and how it works?

[TheEpicSquared]

Just now, Night_Wing_Zero said:

I've heard of it but never got the time to investigate, what is it and how it works?

It's a theoretical form of propulsion that involves warping space and time around the spacecraft, by contracting space in front of the spacecraft and expanding space behind it. Through some complex equations/concepts, this enables the craft to move at up to 10 times the speed of light (don't quote me on that, though), all without breaking the laws of physics! 

[FleshJeb]

@Oliverm001x Have you seen the solar sail design for the novel Rocheworld?

 

[Oliverm001x]

Just now, FleshJeb said:

@Oliverm001x Have you seen the solar sail design for the novel Rocheworld?

 

Wow! Looks cool, and realistic  ! 

[Nuke]

4 hours ago, TheEpicSquared said:

It's a theoretical form of propulsion that involves warping space and time around the spacecraft, by contracting space in front of the spacecraft and expanding space behind it. Through some complex equations/concepts, this enables the craft to move at up to 10 times the speed of light (don't quote me on that, though), all without breaking the laws of physics! 

mach effect may allow for the negative mass requirement if it can produce wide enough mass fluctuations to allow the mass to be negative for at least part of its duty cycle. but doesn't alcubierre drive require a huge negative mass, like jupiter sized? and i dont think anyone has come up with how this kind of drive would work other than theory behind how to make a warp bubble, so i dont know how the negative mass is leveraged in the design. of course if mach effect proves viable we will have reactionless thrusters based on it long before we can build an alcubierre drive. but were back to our original problem we faced with ion propulsion. power. you can crack that problem and we can just use mpd thrusters and get absurd amount of high isp thrust. thats enough to explore and colonize the solar system, and we can just nuke out way to the next star system with an orion drive, we just got to want to do it and not blow ourselves up in the process. alcubierre will require a few more generations of power plants beyond that, terrawatt matter antimatter reactors for example.

Edited January 16, 2017 by Nuke

[Bill Phil]

Sadly, the best thing we've got involves nuclear detonations behind the spacecraft. Thus, no one will go for it, at least for a while. Maybe once we have a larger infrastructure and can build/deploy ships far from Earth. So... In like a hundred or more years. By then, however, we'll probably have better tech.