Interstellar Propulsion Analyses
Oct 20, 2017 21:38:02 GMT
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Post by Kerr on Oct 20, 2017 21:38:02 GMT
Interstellar Propulsion Analysis:
Relativistic Propulsion
This analysis focuses on several propulsion system that allow velocities at which time dilation significantly reduces travel time, these system are necessary to allow +10 Ly manned trips without using much of an humans life time, and possibly allowing flights across the galaxy assuming biological immortality.
1. Laser-Sails
Laser Sails utilize the concept of external propulsion or "leaving your engine home". Laser Sail produce acceleration by utilizing an coherent beam of light which imparts momentum on the sail when reflected. Achieving high fractions of c requires thousand of AU up to light years worth of acceleration distance, also efficiency increases as the sail approaches c, but this effect is cancelled out by the red shifting of the laser beam which results in significant power loss at velocities over 0.99. This effect has to be compensated to increasing the power output proportional to the redshift. Another problem that is often ignored when talking about relativistic photon sail is interstellar drag. As an example we take the hypothetical ship “Horizon”, it is equipped with an 100x100km sail which accelerated the ship to 0.999c, at 0.999c each kilogram of matter carries an momentum of 6.7 giganewtons and 1.92 exajoules of energy. Each second the ship encounters roughly 50 grams of interstellar medium, which results in 335MN of drag and 23 Megatons worth of cosmic radiation every second.
Laser Sail performance depends on the Beam quality (range and power) and the sail material. Reflectivity is ,as often falsely assumed, not an important factor in relativistic sails. The two most important factors of an relativistic sail are areal density and max. force/laser flux. Two examples of excellent sail materials are CVD Diamond and Glass.
Glass: 125kN/m², 100TW/m², 406mg/m²
CVD: 5kN/m²,740GW/m², 200mg/m²
CVD has a 5x better reflectivity than the glass-film sail, CVD also has a higher yield strength which translates into better structural integrity. The absorption of the glass-film is 3 magnitudes lower than the absorption of the CVD film.
Yet another problem is deceleration, but there are two plausible solutions,
1. Multi-stage Laser Sail, this solution from Robert Forward utilizes multiple sails which decouple and can be used to decelerate the craft. An ship capable of accelerating and decelerating requires two-sails. The craft is accelerated to relativistic speeds, cruises at the speed for a few years/decades and decouples, the laser are reactivated and use the first sail to focus the laser beam on the second sail which is decelerated. The use of three-stages allows the vessel to return.
2. Mag-Sail, this solution tries to slow down ionized hydrogen of the interstellar medium with magnetic fields to produce drag. The very low density of the interstellar makes this method rather hard to use on low velocities, but works extremely well at relativistic velocities, remember the 335MN drag from the 10,000km sail? An simple 100t Mag-sail could create up to 16.75GN of Drag. This means that at 0.999c an 65kT Mag-sail can decelerate an one gigaton vessel at one Gee. The performance decreases as the vessel slows down.
The problem with the multi-stage sail is that at relativistic velocities it may not be possible to deploy an light sail without destroying it in the process, the problem with the Mag-Sail is that it gets miserable performance at speeds below 0.95-0.99c. These two can be combined to fix the problems of both methods.
2. Antimatter Beam Core
The Antimatter Beam core annihilates equal amounts of matter and antimatter to produce a mix of neutral and charged pions. The neutral pions are very short lived in decay nearly instantly into multi-hundred MeV gamma-rays, the charged pions live on long enough to travel several meters and be directed by an magnetic nozzle before they decay into mouns and neutrinos. The work of Robert Forward and Robert Frisbee showed that the effective exhaust velocity of a antimatter beam core engine is equal to 0.33c. Which translates into 100MN per kilogram of fuel. More recent work using CERN's particle simulation software Geant4 showed that the effective exhaust velocity is equal to 0.69c [1]. After analysis of the report I found out that the simulation indicated an average pion multiplicity of 6.5 for neutral pions and 3 for the charged pions. Resulting in an exhaust velocity of 0.31c and 0.265c after including inefficiency of the magnetic nozzle. This found indicates that the Beam Core concept may be too inefficient to be realistically used in interstellar travel. Using the Antimatter beam core allows an trip to Trapist-1 (40Ly) in 38.6 years, the maximum velocity achieved is 0.93c.
3. Kugelblitz Drive
The Kugelblitz Drive utilized Micro Black Hole which are radiating multiple Petawatts of power, the ideal kugelblitz drive assumes an black hole that only radiates photons and an dyson cap which works as an reflector, the concept basically was a photon rocket powered by Hawking radiation. But because there is no way of reflecting gamma rays, short of using electron gas at white dwarf densities, most concepts used an giant cumbersome titanium dyson cap to absorb the photons to produce thrust, the problem with this is that you can't have an relativistic rocket because the dyson cap often out-massed the black hole and had pretty low thermal limits, producing extremely low accelerations and corresponding Delta-v's.
In the article called "Acceleration of a Schwarzschild Kugelblitz Starship" I witnessed a high average energy flux carried out by electrons-positron and proton-antiproton pairs. After a few short calculation I found out that the momentum/energy ratio of relativistic particles is roughly equal to the momentum of photons. 300MW/N. Assuming an 85% Efficient magnetic nozzle the exhaust velocity will be 0.255c. Very close to the fuel efficiency of an antimatter beam core.
How does this compare overall to the beam core concept?
The MBH's are fail-safe contrary to antimatter storage,
It releases 45% of its energy as Neutrinos and 25% as Gamma-rays, creating 2.5x less waste heat than a comparable Beam Core design.
The enormous density of the MBH also saves structural mass which can be added to the crew quarters.
Antimatter Beam Core rockets have the advantages of being able to throttle and to deactivate when needed, the use of an drag less magnetic scoop can double the effective Isp of the Antimatter beam core, meaning it requires only half the mass an MBH would require.
A trip to Trapist-1 using an Kugelblitz drive would take 39 years and reach an maximum velocity of 0.928c.
An AM Beam Core RAIR would require 29 years and reach an max velocity of 0.964c
4. Antimatter Photon Core
A while ago I came across the preprint called
“Matter-Antimatter GeV Gamma Ray Laser Rocket Propulsion”
Describes a carefully controlled magnetic implosion called Pinch discharge of a proton-antiproton ambiplasma down to near nuclear densities, with non-gamma ray annihilation modes largely suppressed. The recoil of the gamma-rays is
transferred by the Mössbauer effect. This creates an near total annihilation and near perfect collimation of a pure gamma-ray exhaust.
This concept allows for an nearly perfect Antimatter powered photon rocket. With an Isp=c and the high collimation makes the drive very hard to detect. Making it ideal as an RKKV Drive, while also being able to create Gamma-ray laser with light-second ranges, this engine performs twice as good as the AM-RAIR at half the antimatter consumption and 4 times as good as the AM-Beam Core at the same antimatter consumption.
A trip to Trapist-1 using this drive only takes 22.6 years, and reaches an max velocity of 0.98c.
A. Interstellar Medium
“The worst part of travelling in the interstellar vacuum is that it isn't a vacuum” -Isaac Arthur.
At speeds above 0.99c impacts with interstellar hydrogen gas would be comparable to re-entry, dust particles will do more damage than a high-caliber anti-material round and something the size of an paperclip will create an explosion dozens of times more energetic than the bomb dropped on Hiroshima.
There are several ways of dealing with the dangers of the interstellar medium, I will present 3 possible methods.
1. Lasers. An pulsed laser with sufficient power could be used to vaporize dust particles and small objects, using ultraviolet frequencies it will also allow to efficiently ionize hydrogen, which can then be deflected by an magnetic field.
2. Whipple Sails. Using solar sail like whipple shield can protect an vessel from micrometeorites by impacting with said objects, at relativistic speeds this will result in a cone-shaped explosion which will expand at several kilometers per second because of electrostatic and thermal blooming. Hundreds to thousand of these sails could be deployed each having masses as low as 16kg/km².
3. Drones. Drones can be equipped with their own lasers , sensors, whipple sails and propulsion systems which makes them a viable method of protection a larger vessels, around a few megatons to a gigaton, drones can be used to repair damaged whipple sails, relay laser power from the mainship and destroy specific targets directly by using kinetic weaponry.
All those three methods can be combined to produce an effective overall safety-system for relativistic spaceships.
Example:
The Beam craft “Horizion” utilized an 1TW UV Pulsed FEL with a effective range of 2,000 light-seconds. Capable of completely ionizing anything smaller than a fist. 10 light-seconds in front of the mainship is a series of 100 graphene whipple shields each separated by a light-second. Each whipple shield is equipped with an small D-He³ Z-pinch drive to give them enough delta-v to stay in their position for years, they are also equipped with small repair drones which repair damage caused from sustained impacts.
At a distance of 150 light-seconds is a swarm of drones equipped with super conductive electromagnets, laser relays, bubbleguns, thousands of small whipple sails and sensors to locate massive objects which might cause a thread. The system provides enough protection from the interstellar medium to allow velocities up to and even beyond 0.999c, while not even using 1% of Horizon's mass.
Notes: All the travel time examples used constant acceleration ranging from 0.8m/s² to 1.95m/², Using 1G or higher acceleration enable the ship to coast most of the ´trip at their maximum velocity utilizing their time dilation.
0.93c=2.53Ly/y
0.928c=2.49Ly/y
0.964c=3.62Ly/y
0.98c = 4.92Ly/y
[1] “Beamed Core Antimatter Propulsion: Engine Design And Optimization“
Relativistic Propulsion
This analysis focuses on several propulsion system that allow velocities at which time dilation significantly reduces travel time, these system are necessary to allow +10 Ly manned trips without using much of an humans life time, and possibly allowing flights across the galaxy assuming biological immortality.
1. Laser-Sails
Laser Sails utilize the concept of external propulsion or "leaving your engine home". Laser Sail produce acceleration by utilizing an coherent beam of light which imparts momentum on the sail when reflected. Achieving high fractions of c requires thousand of AU up to light years worth of acceleration distance, also efficiency increases as the sail approaches c, but this effect is cancelled out by the red shifting of the laser beam which results in significant power loss at velocities over 0.99. This effect has to be compensated to increasing the power output proportional to the redshift. Another problem that is often ignored when talking about relativistic photon sail is interstellar drag. As an example we take the hypothetical ship “Horizon”, it is equipped with an 100x100km sail which accelerated the ship to 0.999c, at 0.999c each kilogram of matter carries an momentum of 6.7 giganewtons and 1.92 exajoules of energy. Each second the ship encounters roughly 50 grams of interstellar medium, which results in 335MN of drag and 23 Megatons worth of cosmic radiation every second.
Laser Sail performance depends on the Beam quality (range and power) and the sail material. Reflectivity is ,as often falsely assumed, not an important factor in relativistic sails. The two most important factors of an relativistic sail are areal density and max. force/laser flux. Two examples of excellent sail materials are CVD Diamond and Glass.
Glass: 125kN/m², 100TW/m², 406mg/m²
CVD: 5kN/m²,740GW/m², 200mg/m²
CVD has a 5x better reflectivity than the glass-film sail, CVD also has a higher yield strength which translates into better structural integrity. The absorption of the glass-film is 3 magnitudes lower than the absorption of the CVD film.
Yet another problem is deceleration, but there are two plausible solutions,
1. Multi-stage Laser Sail, this solution from Robert Forward utilizes multiple sails which decouple and can be used to decelerate the craft. An ship capable of accelerating and decelerating requires two-sails. The craft is accelerated to relativistic speeds, cruises at the speed for a few years/decades and decouples, the laser are reactivated and use the first sail to focus the laser beam on the second sail which is decelerated. The use of three-stages allows the vessel to return.
2. Mag-Sail, this solution tries to slow down ionized hydrogen of the interstellar medium with magnetic fields to produce drag. The very low density of the interstellar makes this method rather hard to use on low velocities, but works extremely well at relativistic velocities, remember the 335MN drag from the 10,000km sail? An simple 100t Mag-sail could create up to 16.75GN of Drag. This means that at 0.999c an 65kT Mag-sail can decelerate an one gigaton vessel at one Gee. The performance decreases as the vessel slows down.
The problem with the multi-stage sail is that at relativistic velocities it may not be possible to deploy an light sail without destroying it in the process, the problem with the Mag-Sail is that it gets miserable performance at speeds below 0.95-0.99c. These two can be combined to fix the problems of both methods.
2. Antimatter Beam Core
The Antimatter Beam core annihilates equal amounts of matter and antimatter to produce a mix of neutral and charged pions. The neutral pions are very short lived in decay nearly instantly into multi-hundred MeV gamma-rays, the charged pions live on long enough to travel several meters and be directed by an magnetic nozzle before they decay into mouns and neutrinos. The work of Robert Forward and Robert Frisbee showed that the effective exhaust velocity of a antimatter beam core engine is equal to 0.33c. Which translates into 100MN per kilogram of fuel. More recent work using CERN's particle simulation software Geant4 showed that the effective exhaust velocity is equal to 0.69c [1]. After analysis of the report I found out that the simulation indicated an average pion multiplicity of 6.5 for neutral pions and 3 for the charged pions. Resulting in an exhaust velocity of 0.31c and 0.265c after including inefficiency of the magnetic nozzle. This found indicates that the Beam Core concept may be too inefficient to be realistically used in interstellar travel. Using the Antimatter beam core allows an trip to Trapist-1 (40Ly) in 38.6 years, the maximum velocity achieved is 0.93c.
3. Kugelblitz Drive
The Kugelblitz Drive utilized Micro Black Hole which are radiating multiple Petawatts of power, the ideal kugelblitz drive assumes an black hole that only radiates photons and an dyson cap which works as an reflector, the concept basically was a photon rocket powered by Hawking radiation. But because there is no way of reflecting gamma rays, short of using electron gas at white dwarf densities, most concepts used an giant cumbersome titanium dyson cap to absorb the photons to produce thrust, the problem with this is that you can't have an relativistic rocket because the dyson cap often out-massed the black hole and had pretty low thermal limits, producing extremely low accelerations and corresponding Delta-v's.
In the article called "Acceleration of a Schwarzschild Kugelblitz Starship" I witnessed a high average energy flux carried out by electrons-positron and proton-antiproton pairs. After a few short calculation I found out that the momentum/energy ratio of relativistic particles is roughly equal to the momentum of photons. 300MW/N. Assuming an 85% Efficient magnetic nozzle the exhaust velocity will be 0.255c. Very close to the fuel efficiency of an antimatter beam core.
How does this compare overall to the beam core concept?
The MBH's are fail-safe contrary to antimatter storage,
It releases 45% of its energy as Neutrinos and 25% as Gamma-rays, creating 2.5x less waste heat than a comparable Beam Core design.
The enormous density of the MBH also saves structural mass which can be added to the crew quarters.
Antimatter Beam Core rockets have the advantages of being able to throttle and to deactivate when needed, the use of an drag less magnetic scoop can double the effective Isp of the Antimatter beam core, meaning it requires only half the mass an MBH would require.
A trip to Trapist-1 using an Kugelblitz drive would take 39 years and reach an maximum velocity of 0.928c.
An AM Beam Core RAIR would require 29 years and reach an max velocity of 0.964c
4. Antimatter Photon Core
A while ago I came across the preprint called
“Matter-Antimatter GeV Gamma Ray Laser Rocket Propulsion”
Describes a carefully controlled magnetic implosion called Pinch discharge of a proton-antiproton ambiplasma down to near nuclear densities, with non-gamma ray annihilation modes largely suppressed. The recoil of the gamma-rays is
transferred by the Mössbauer effect. This creates an near total annihilation and near perfect collimation of a pure gamma-ray exhaust.
This concept allows for an nearly perfect Antimatter powered photon rocket. With an Isp=c and the high collimation makes the drive very hard to detect. Making it ideal as an RKKV Drive, while also being able to create Gamma-ray laser with light-second ranges, this engine performs twice as good as the AM-RAIR at half the antimatter consumption and 4 times as good as the AM-Beam Core at the same antimatter consumption.
A trip to Trapist-1 using this drive only takes 22.6 years, and reaches an max velocity of 0.98c.
A. Interstellar Medium
“The worst part of travelling in the interstellar vacuum is that it isn't a vacuum” -Isaac Arthur.
At speeds above 0.99c impacts with interstellar hydrogen gas would be comparable to re-entry, dust particles will do more damage than a high-caliber anti-material round and something the size of an paperclip will create an explosion dozens of times more energetic than the bomb dropped on Hiroshima.
There are several ways of dealing with the dangers of the interstellar medium, I will present 3 possible methods.
1. Lasers. An pulsed laser with sufficient power could be used to vaporize dust particles and small objects, using ultraviolet frequencies it will also allow to efficiently ionize hydrogen, which can then be deflected by an magnetic field.
2. Whipple Sails. Using solar sail like whipple shield can protect an vessel from micrometeorites by impacting with said objects, at relativistic speeds this will result in a cone-shaped explosion which will expand at several kilometers per second because of electrostatic and thermal blooming. Hundreds to thousand of these sails could be deployed each having masses as low as 16kg/km².
3. Drones. Drones can be equipped with their own lasers , sensors, whipple sails and propulsion systems which makes them a viable method of protection a larger vessels, around a few megatons to a gigaton, drones can be used to repair damaged whipple sails, relay laser power from the mainship and destroy specific targets directly by using kinetic weaponry.
All those three methods can be combined to produce an effective overall safety-system for relativistic spaceships.
Example:
The Beam craft “Horizion” utilized an 1TW UV Pulsed FEL with a effective range of 2,000 light-seconds. Capable of completely ionizing anything smaller than a fist. 10 light-seconds in front of the mainship is a series of 100 graphene whipple shields each separated by a light-second. Each whipple shield is equipped with an small D-He³ Z-pinch drive to give them enough delta-v to stay in their position for years, they are also equipped with small repair drones which repair damage caused from sustained impacts.
At a distance of 150 light-seconds is a swarm of drones equipped with super conductive electromagnets, laser relays, bubbleguns, thousands of small whipple sails and sensors to locate massive objects which might cause a thread. The system provides enough protection from the interstellar medium to allow velocities up to and even beyond 0.999c, while not even using 1% of Horizon's mass.
Notes: All the travel time examples used constant acceleration ranging from 0.8m/s² to 1.95m/², Using 1G or higher acceleration enable the ship to coast most of the ´trip at their maximum velocity utilizing their time dilation.
0.93c=2.53Ly/y
0.928c=2.49Ly/y
0.964c=3.62Ly/y
0.98c = 4.92Ly/y
[1] “Beamed Core Antimatter Propulsion: Engine Design And Optimization“