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Did you ever watch the mini-series 'Ascension'?
https://en.m.wikipedia.org/wiki/Ascension_(miniseries)It is technically possible, using a fission-fusion hybrid approach. A direct fission fragment rocket would have exhaust velocity up to about 4% of c. If you could design an engine that uses fast neutrons from fusion reaction to fast-fission 238U or 232Th in thin fibres and then direct the released fission fragments using a magnetic field, then there is enough fissionable material on Earth to build a crewed space craft able to reach a few percent of c. So you could reach the nearest stars in a couple of centuries, when factoring in acceleration times. An orion type vehicle would probably be used to launch the star ship from Earth surface to solar escape velocity. After Orion separation, the much more efficient, but lower thrust fission fragment drive would activate.
Whether it would be financially affordable is another question. Given that our knowledge of the closest exoplanetary neighbourhood is poor, you have to ask why it would make sense to undertake such a mission instead of colonisation of our own inner solar system. Especially given how much it is likely to cost. Colonisation of near Earth space, the asteroids and Mars, would offer direct benefits to people on Earth, in terms of orbital infrastructure and access to new resources. In building a starship, we would be sending a very small group of people on a multi generation journey into an uncertain environment. I think that would be a hard sell for any government to its people.
It makes sense to leave the Sun's gravity well with an Orion-drive, the change to a FF-rocket, sparing years of spiralling outward. But why not to accelerate to 0.04 C with a laser sail, then decelerate with a FF-rocket at the destination star?
P.S.
As a second thought, I like your idea: Orion is perfect to transport huge payloads, so why not to use your combo to send the deceleration laser-station to the destination star?
Mercury would have any transmitter not able to point towards its target ship for more than half og the orbital time as the sun is blocking the laser from shining on the target sail....Also other planets that get into the path of the sail will as well block the beam from reaching its target as well.
https://en.wikipedia.org/wiki/List_of_v … ed_recordsOnly if the star is on the same plane of the orbit of the planets. Proxima for example would be ever tracked by an array located in the south pole of Mercury. Anyway, for an orbital laser station, you need to correct the error of parallax, that is bigger at short distance, so some fraction of power is wasted in corrections. That's why I think the best solution is the statite-station, which can be perfectly aligned to the point where the star will be at the time of arrival (to send a starship we need to perfectly know the proper motion of the stars).
https://en.wikipedia.org/wiki/Space_tra … celeration
https://sciencetrends.com/the-accelerat … to-use-it/
acceleration = (vFinal−vInitial)/(tFinal−tInitial) or a=Δv/Δt
for acceleration to relativistc velocity these formulas work better:
a=v*c/(t*sqr(c^2-v^2))
and
t=v*c/(a*sqr(C^2-V^2))
As you can see, to reach c, you need either an infinite instantaneous acceleration, or an infinite time at constant acceleration
For Quaoar re SpaceNut's post #37
Do I understand correctly that you are proposing to install the laser system on the surface of Mercury?
If that is correct, it would address the issue raised by SpaceNut, of the installation falling into the Sun.
You need multiple installation on the planet for continually tracking the starship and sometimes, if the star is on the orbital plain of Mercury, it will be some short eclipses. Another possibility is the statite, which never miss the star.
In the next issue raised by SpaceNut ... How long would the acceleration be needed?
In your earlier post you provided velocity values, but if you provided times for acceleration and deceleration I missed it.
If I understand your post correctly, you have addressed SpaceNut's point about needing to go all the way out to Pluto by explaining that the effects of gravity on the beam are minimal (ie, vanishingly small) and the issue of dispersion raised by GW Johnson you address by giving the relatively uncluttered environment of space itself (in the vicinity of Mercury) as a reason to expect the cohesion of the laser beam to hold up for the distances involved in acceleration
The dispersion of the beam depends by the diameter of the sail (Ds) the diameter of the laser array (Da) and the wavelength (Lw) of the light (which increase with velocity due to relativistic doppler effect).
The max distance at which the beam con be focused on the sail is given by this formula Dmax=Ds*Da/(2*Lw). So to focus a at thousands of UA you needs some thousands kilometer wide array. And you also have to trade-off between long wavelength, which gives the best reflectivity, and short wavelength, which can be focused at longer distance with a smaller array (I found the best compromise near 12 micron). Gravitational red shift is negligible: what matters is the red-shift due to doppler effect.
During the simulation, I found two strategies for a manned interstellar sail-ship:
1) constant acceleration of 1 g with the laser station that increases its optical power output as the ship increases its speed, to compensate for the red-shift. This strategy consents to reach the target velocity in a shorter distance, giving a less wide laser array, but needs much more power and a wider photovoltaic array. Acceleration distance and acceleration times are easy to calculate using the simple formulas of relativistic kinematic
2) variable acceleration at constant power, with the ship that gradually decreases its acceleration due to the red-shift of the laser beam. This strategy needs less laser power and a less wide photovoltaic array, but the distance at which the ship reaches the target velocity is increased, so the laser array has to be wider. Acceleration distance and acceleration times are very hard to calculate, due to the fact that the acceleration decreases with the red-shift, while the reflectivity increases, because graphite is more reflective at longer wavelength: I'm not so good in math to do the integral, so I wrote a spaghetti-code for the integration by part, which works quite well.
The first probe needs to include the deceleration component you've described, because there won't be a laser at the receiving solar system.
In my simulation I considered a laser station at both ends, because that is the scenario of my next novel. But you're right.
Going back to SpaceNut's points ... pointing the laser at the receding starship/mirror while moving wth Mercury in it's orbit will require some clever engineering.
(th)
I've many doubt about the feasibility of decelerating a starship at the destination star with a sun based laser station.
Do you have some preliminary thoughts about how you would design that feature of the system?
(th)
I imagine a dish shaped starship, surrounded by a ring shaped carbon-carbon drum with the furling sail. The instruments and the cargo at the center, the habitats are two nacelles attached to the ring, and the life support radiator is integrated in the surface of the dish. Two trusses are attached on the dish, one in the bow and one in the aft, with a compact fission reactor and a set of furling graphite anti-meteoroid shields at both ends (the aft shields are also used to shadow the ship from the laser beam). At the center of the last shield there are the laser point defense for meteoroids. The ship is symmetric so she has not to flip for the deceleration, but just to unfurls the sail and aligns whit the laser station of the destination system. The drum contains three sails: the main sail and two spare sails.
Re. the deceleration phase, what are the objections to using a magnetic sail to slow down? Not enough drag from the solar wind at the destination?
Also, I'm now wondering what the Isp limits of ablative sails are. Mind, targeting issues (you're talking about vaporising it into a very hot plasma and then directing that with a magnetic nozzle) probably make it a non starter.
The idea was from Robert Zubrin and Dana Andrews: they found that neutral hydrogen atoms become ionized, in presence of a magnetic field traveling at relativistic velocity, because electrons and nuclei are accelerated in opposite directions. Here is a more recent article that uses a combination of a magnetic sail and an electric sail for deceleration: the magnetic sail for hi-speeds and the electric sail for slow speeds.
https://arxiv.org/pdf/1603.03015.pdf
Tomorrow I'll read it (now in Italy is 1 AM)
Still, I don't think you should give up on Orion just get. Fusion bombs + magnetic nozzles could potentially get 0.08c exhaust velocity? Enough if you pile them on to reach 0.2c, if you can use a magsail to decelerate...
For fusion bombs do you mean pure fusion bombs or conventional two stage hydrogen bombs?
I was wondering if we could use the in a configuration that is like a tunnel in which the ship sets in the center a just ahead of the many lasers that would push it to speed. The corner lasers would be a multi type point unit with ability to push the unit ahead of it as well as push the ship which is in the center of them.
https://i.pinimg.com/originals/8b/d6/54 … c7f33f.jpg
Another concept I was thinking was to have a parabolic sail that is also pointed at by multiple lasers but it connects to a fixed laser assembly on the ship facing aft. The dish would scooped up particles and focus them back towards the ship. The laser would be unfocused onto the dish but via reflection the particles would be heated and reflected back out a center hole in the dish.
http://www.see.murdoch.edu.au/resources … age007.jpg
This is missing the center exit hole but ahead of the reciever is the nuclear power and laser assembly to make it work like a star trek deflector dish...picking up the incoming particles and accelerating them aft as it heads towards its target destination...
For particles do you mean space neutral hydrogen atoms?
Our nearest star system, Alpha Centauri, is 4.4 light-years away and physicists believes probes can make the interstellar trip in just 20 years on the wind from the sun at 60 million meters a second, seems fanciful. You need to boost the power of the light source to brighter than the Sun and shrink the mass of the spacecraft.
Now making an array of high powered lasers that are spread out point like a cone towards the sail means more force striking the same target even if they do get weaker with distance there is still more of them to push the sail.
Of course the issue is that the lasers will need to stay focused on the light sail for the entire boosting phase with a target size that is shrinking with every passing kilometer that the sail moves away from the laser.https://www.space.com/29950-lasers-powe … craft.html
https://www.space.com/40512-breatkthrou … ology.html
So large nuclear powered stationary lasers point to a common target out past the influence of the suns solar winds could get to speed if we do not burn a hole into it....
An small unmanned probe has far fewer problems than a big manned spaceship: it can be busted at thousands of gee, without crushing the crew, so all the acceleration phase takes place near the laser beam source: a gram-sized probe, busted with an initial acceleration of 5000 G, reaches 0.25 C just in 32 minutes in at 0.52 UA from the laser.
Viceversa, a manned 10,000 ton sail-ship, with a 14 km wide, 260 ton C-C sail, with a 15 PWo 12 micron IR laser array, has an initial acceleration of 9.8 m/s2 and reaches 0.25 C in 111 days at 2601 UA from the laser station, so she needs a 1100 km wide laser array, to focus a redshifted 15.49 micron beam on her sail at that distance*
I see no need of nuclear powered lasers in space, where sunlight is abundant and ever present: why not a high efficient diode pumped-solid state laser powered by an array of solar panel or alternatively a solar pumped-solid state laser, which doesn't need to convert solar energy in electricity?
*in these days I perfected my spaghetti-code and now I can simulate real sails with non complete reflectivity: during the simulations, I discovered that the tungsten coating doesn't work very well when the sail reaches its exercise temperature. So I eliminate it and make an uncoated graphite-fiber-reinforced-graphite sail, that become almost 0.95 reflective over 3000 K in the mid-infrared spectrum, resulting a lighter and more efficient sail.
I also write a code for the integration by parts, so now I can calculate the time and the final distance of the acceleration phase at constant power output, with an acceleration that decreases progressively due to relativistic doppler effect, while the sail increases its reflectivity with the increment of the light wavelength.
Mercury orbits the Sun at an average distance (semi-major axis) of 0.387 AU (57,909,050 km; 35,983,015 mi) so a laser station of 0.25 Au is inside the orbit of mercury and is not on mercury's surface at all....
Red shift is what happens to the lights color as something is receding which is shining as well while blue shift is approaching..
edit
https://solarscience.msfc.nasa.gov/SolarWind.shtmlAs predicted and measured by the voyagers
https://www.sciencedaily.com/releases/2 … 102033.htmHowever, when New Horizons traveled beyond Pluto, between 33 and 42 AU, the solar wind measured 6-7% slower than at the 1 AU distance, confirming the effect.
https://www.discovermagazine.com/the-sc … from-pluto
Pluto's orbit is also highly elliptical, stretching from 4.4 billion km to just over 7.3 billion km from the Sun. Doing the math again, that means the Sun goes from being 0.0012 to 0.0004 as bright as it is from Earth: a range of roughly 150 to 450 times as bright as the Moon from Earth. That's a change in brightness by a factor of three!
Sure I put it more inside to spare panels surface. Maybe the best station to propel a sail-ship is not an orbital station but a statite, with a solar sail to keep it aligned with the ship course.
For Quaoar re #35 above ...
In trying to follow your presentation, I note that the result quoted is different by only .00000019 micron ... The start was 4.8 micron wavelength, and the value you derived was that plus the small shift of 19 to the minus 8 (if I counted digits correctly).
In other words, not much! Am I missing a digit somewhere?
(th)
I've approximate z: the real value is 3.9482514879433695243028286559985*10^-8 so it's possible to have some wrong decimal
Does laser affected by gravity?
https://www.science.org.au/curious/space-time/gravity
https://www.needforscience.com/physics/ … a-quantum/
https://www.physlink.com/Education/AskExperts/ae661.cfm
https://solarsystem.nasa.gov/system/resources/detail_files/14745_PIA12375.jpg
To have a beam unaffected means we are beyond the suns strong influences that shape how waves travel from a point due to its time space shape as caused mostly by the suns mass.
Nothing is truly stationary when it comes to the subtle effects of wind, gravity or its waves and thats not only from our sun but from all sources....
We can calculate the gravitational redshift due to the Sun's gravity for a IR laser beam of 4.8 micron of wavelength, with this approximate formula, that is valid for distances far grater than the Scwartzschield radius (luckily, our Sun is not a black hole so it's OK):
z= GM/(c^2*R) (1)
with z=(Le-L0)/Le (for a beam going away from the celestial body)
where GM is the Sun's standard gravitational parameter (132712440018 km^3/s^2); c is the speed of light (299792.458 km/s); R is the distance of the laser station from the Sun 0.25 UA = 37399467.675 km; L0 is the initial wavelength of 4.8 micron; Le is the red-shifted wavelength we have to find; and z is an adimensional number.
the result is
z=3.95*10^-8
resolving 2 for Le we found Le=L0/(1-z)
resulting 4.80000019 micron. So a 4.8 micron laser cast from a laser station at 0.25 UA from the Sun will become 4.80000019 micron due to Sun's gravitational redshift.
Hi Quaoar:
We did pretty good out here on the farm in central Texas, but many of my fellow Texans did not. Statewide, the polar vortex event was pretty much a disaster. A really bad one, too.
We did as well as we did out here on the farm because we never lost power. We're on a country co-operative for our power (and another one for our water). Over the years, those have simply proven to be more reliable. But city dwellers do not have that as a choice.
It is extremely rare to see temperatures get near 0 F (-18 C) here in central Texas. Not that it doesn't happen, it is just extremely rare. When it did, it was usually a 1-3 day event. This one was 9 days below freezing without a break. It reminded me of what I experienced in Minnesota about a quarter century ago (which was 2.5 months continuously below 0 F = -18 C).
We lost some garden plants and some in the greenhouse, too. But not everything. Some of the shrubs and trees suffered damage, particularly the ones that got coated solid with re-freeze ice coming off the roof.
This event had 3 ice events embedded in it, coming after a separate system had already snowed us in before. That's 4 significant icing events (so far) in one winter. We normally see only one of those per winter here.
GW
-18 °F is -27.8 °C!!! As I remember, we never have temperatures so low in Rome. I'm happy your farm didn't suffered heavy damage and I hope your plants can recovery as soon as possible.
The Planetary Society recently flew a solar sail. It works, but the accelerations are miniscule with just sunlight. More of a whisper than electric thrusters. You can improve the effect by shining a laser on the sail, if the sail is reflective enough not to be destroyed by the beam, but across interplanetary distances, the beam spreading renders this notion rather infeasible. Too strong up close, too weak far away.
As a reality check, the beam spreading I observed with a 2-4 milliwatt helium-neon laser was from 2mm to about 6 inches beam diameter, in only 12,000 feet. This was shining one at night down the main runway at TSTC airport, Waco, Texas, 3 or 4 decades ago. The beam was still bright enough to give you a headache, so it would still have far more effect than ordinary sunlight on a solar sail. But imagine how diffuse it becomes over 12 million miles instead of 12 thousand feet. Beam spread is proportional to distance.
GW
The beam needs to be projected from space and to be focused on the sail: we can imagine actively cooled adaptive mirrors like those of the big telescopes (I perfectly know it will be a monstrous task to build a multi kilometer sixed space array of this devices). Gas lasers like helium-neon have worst beam quality than diode pumped solid state lasers due to the turbulence of the medium. In Earth's atmosphere the laser beam spreads a lot due to diffraction, but in space it encounters only few hydrogen atoms for cubic cm so, if the beam comes from a space laser station, I think the diffraction should be far less (I used the formulas of this old work to calculate the maximum distance at which the beam can be focused on the sail https://www.amazon.it/Laser-driven-ligh … 07Y8H8MV8) .
P.S.
Hi, GW nice to hear you. How it's going in Texas?
I guess we're playing something of a semantics game here. I was aware of the JAXA solar sail demonstrator, but I'm considering the engineering involved as well as the theoretical concepts. Building a solar sail many kilometers in diameter and thin enough to be carried to space is Engineering. I don't think we're there yet.
Sure but we can start to work on the problem, build demonstrators in scale, make simulations, then try to go bigger and bigger as we gain experience on lightsails.
Obviously the first laser sail station will be build in a optimistic future where we have avoided to nuke each other and we have succeeded in colonizing the solar system, and we have gained experience in mining asteroids for raw materials and building space habitats.
Using a Thermonuclear propulsion unit to slow down--that's possibly doable later in this Century. After all, Fusion energy is "just 10 year away," and it has been for several decades.
At the moment we have nothing but another laser station in the destination star system to slow down from 0.25 C, and that is the weak point of my arguments. As GW posted, there is no rocket able to reach 0.25 C of deltaV.
A Clark-Sheldon dusty plasma FF-rocket has a predicted exhaust velocity of 15000 km/s, 0.05 C, so an hybrid system, with a sail for acceleration and a two stages FF-rocket for deceleration can travel at 0.1 C and reach Proxima in about 43 years.
We have never built a dusty plasma FF-rocket, but we have the knowledge and the technology to start working on the topic, as Robert Bussard did for the NTRs at the time of project Rover.
For quaoar re #24 (answer to SpaceNut)
SearchTerm:SolarSail Quaoar on power from Mercury to accelerate ship at 1 go to .25 C
SearchTerm:Interstellar Quaoar series on how to send a probe to Proxima CentauriNote that the series above includes discussion of a hybrid approach, using laser power to accelerate from the Solar System, and a form of fission propulsion to decelerate at the destination.
For Quaoar ...
Would you be willing to show the amounts of time required to reach your target velocity of .25 C and ...
the time the vessel would coast at .25 C and ...
the time the vessel would be decelerating to reach Proxima at a velocity low enough to achieve orbit?
It is possible to show graphs in this forum. Would you have any interest in learning how to do that.
(th)
Destination: Proxima Centauri
Distance: 4.2441 light years
Constant acceleration of 9.8 m/s2
Variable laser power
Vmax 0.25 C
Earth reference frame
Acceleration time: 91 days, 10 hours
Coast time: 16 years, 265 days, 0 hours
Deceleration time: 91 days, 10 hours
Total trip time: 17 years, 82 days, 28 hours
Starship reference frame
Acceleration time: 90 days 10 hours
Coast time: 16 years, 69 days, 18 hours
Deceleration time: 90 days 10 hours
Total trip time: 16 years, 250 days, 14 hours
In this simulation, I've slightly simplified the problem, assuming that departure and destination laser stations are both statites (non orbital station kept stationary by a solar sail) so acceleration is from 0 to 0.25 C and deceleration is from 0.25 C to 0.
For orbital maneuvers the starship has to angle the sail at 45° from the laser station and use the beam power to gain or lose orbital velocity. She's not a ship of low orbit, so she parks herself in the high orbit of Proxima b, not so deep in the gravity well of the planet. Then a shuttle may detach from the mothership and reaches the low orbit. At this point a three stage lander (two stage and a capsule) detaches from the shuttle, performs a deorbit maneuver, enters in the atmosphere and lands near a river or a lake (in this simulation I assumed Proxima b has an Earth like ecosystem). When the mission is finished the lander uses a compact fission reactor to produce LOX-LH2 from electrolysis and reaches the low orbiting shuttle in three stages (Proxima b is a super Earth with almost 1.3 G of surface gravity, so a SSTO is impossible).
That's a simulation. A real travel must also take account of the relative motion of the destination star to not miss the target. This is not an easy task and implies a perfect knowledge of the motion of the target star.
The Star Trek warp drive is made of antimatter and energy to cause the speed to change. Its a far off future for when we can control the combination for sure.
The trials of solar sails are still in the infancy and its unknown as to just how much payload can be moved for a give sail size and distance from the source that propels the ship.
Of course solar wind in moving the heavier part of the equation in the particle from the sun that the striking the sail and its that atom which gives it more energy into the sail for motion.Lasers over distance continue to spread and would need to be continually refocused to keep the beam not only on target but concentrated to force the sail speed to keep increase as a beam that is spread or diffusing will cause the speed to drop.
The max distance depends on the diameter of the array, the diameter of the sail and the wavelength of the light (plus realtivistic redshift):
Distmax=Dlaser*Dsail/(2*Lwl) all in the same units.
For example, if a 4800 nm mid infrared laser-array needs to push a 10000 ton starship at 0.25 C under constant accelaration of 9.8 m/s2, the acceleration phase ends at 2010.5 UA of distance, so if the sail has a diameter of 19 km and the laser-array has a diameter of 260 km, it can keep the beam focused on the sail up to 2064 UA, so the acceleration distance of 2010.5 is in the range (4800 nm become 8000 at 0.25 C due to relativistic redshift).
Graphite at 3200 K has a reflectivity of 0.918 at 4800 nm of wavelengh, so the initial laser optical power would be about 15.3 PW
At 8000 nm the reflectivity of the sail rises to 0.937, so the final optical power to keep 9.8 m/s2 of acceleration would be about 25.3 PW (8000 nm photons has less momentum than 4800 ones)
Considering a plug to wall laser efficiency of 0.9, the final electric power would be about 27.2 PW, which is very huge, but in space energy is abundant. Considering a laser station orbiting at 0.25 UA from the Sun, where the solar irradiance is 21.792 KW/m2, and 0.8 efficient solar panels: to have 27.2 PW we need a 1409.4 km diameter array.
So what is the solar wind, can it be created, are there sufficient particles in space to cause energy to be transferred to a sail if a simulated wind could be only a short distance from the ship to keep it moving....
Solar sail is a proven technology and works very well: JAXA's probe IKAROS use a 7.5 micron thick square sail of aluminized polyamide of 25 meters of diagonal to reach Venus. It was a photonic sail.
https://it.wikipedia.org/wiki/IKAROS
Solar wind is composed by ions (mainly hydrogen and helium) and can be captured by magnetic sails
https://www.colorado.edu/faculty/kantha … _paper.pdf
article not quite what I would think would be a source for the warp drive content
scientists-announce-a-physical-warp-drive-is-now-possible-seriously
The answer I gave was premised on the statement "with today's technology." We don't really have workable Solar sails and the big battery of high power lasers to beam at them. Robert Zubrin also "did the math," and concluded that the power consumption of the lasers was unreasonable, hence unaffordable.
GW "did the math," and clearly demonstrated that chemical propulsion isn't "in the ballpark."
Nuclear Thermal has been worked on, but it too, is anemic for powering interstellar vehicles in a meaningful time frame.
Maybe ther's a misunderstanding: today's technologies doesn't mean we can build the ship tomorrow. It only means that with many year of R&D and a lot of money we will able to build it in a near future, only perfecting the technologies and the materials we just have today, and without inventing some handweavium technology like antimatter.
We have high efficient diode lasers (the best reaches 0.67 plug to wall and we don't need to build a single terawatt laser but only to stack many megawatt lasers in an array) and we can perfect them to reach 0.9 in CW at high power; we have multi-juncion solar panel and we can perfect them to reach 0.8 of efficiency (the theoric limit is 0.85); we have graphite fiber reinforced graphite composite to build a micron thick kilometer sail; we have compact fission reactors to power the spaceship during coasting; we can build space stations and we also have the SEP technology to slowly move them near the orbit of Mercury where the sunlight is 5500 KW/m2. Combining all these techs, in a near future we will build a laser powered 0.24 C a sail-ship.
For Quaoar re #15 ...
Thank you for considering SPS.
Your cautions about the use of laser systems strong enough to accelerate a star ship seem well thought out. I would put them in the category of atomic energy on Earth .... it needs to be carefully managed and kept away from persons who might be tempted to use them for evil purposes.
Huge laser stations needs hug amount of money so they will be likely built by a strong and centralized government: some kind of Wittfogel's hydraulic empire.
https://en.wikipedia.org/wiki/Hydraulic_empire
I don't like autocratic states, but in case of relativistic sail-ships, a centralized empire might be the lesser evil: consider a laser station with a 327 km wide photovoltaic array, orbiting near a star, able to produce 909 TWe, powering a 818 TWo laser: this station can accelerate a 300 ton spaceship to 0.3 C, under the constant acceleration of 1 g, and that is OK, but the same station can also accelerate a 10 ton sailing torpedo (8 ton of sail and 2 ton of stuff) to 0.9 C, resulting a completely unstoppable planet killer, able to deliver 1.16 Yj on the target. 0.9 C is too close to C to be detected by a radar and destroyed with a laser shot, so there is no defense and in case of cold war between star systems, whoever delivers the first shot wins.
On the positive side, such a system should be quite useful for regular service inside the Solar System.
For one thing, it can boost intra-Solar-System transport which is intended for outward movement.
For another, it can provide welcome bursts of useful power to human (or automated) "customers" out-system ....
This kind of system needs to be funded and managed as a Solar System resource.
It would be practical if humans achieve sufficient maturity to forego the kinds of evil-doing they are still engaged in all over the planet today.
Sure: laser stations can also be used to accelerate interplanetary sailing-ship: in this case the requirements are far less challenging.
Accelerations of about 0.1 m/s2 are good for interplanetary travel outside the gravitational wells (i.e. Lagrange Zone): a 300 ton spaceship needs only 4.5 TW of optical power and a 80-kg-250-meter-wide sail.
Edit#1: I finally scheduled some time to look at the paper on "dusty" fission rocket design.
This is a (to me) very interesting paper from 2005, which describes the evolution of a concept through several versions. The "current" one seeks to address the problem of heating of the fuel by reducing the size of individual components/particles to nano size.
In light of the need for small size, I am pretty sure there is an error in Table 2 Rigidity of various fission fragments.
In the line for "Dust" the Atomic weight is given as 10 to the 8th.
I'm pretty sure the intention was to publish as 10 to the ** minus ** 8th.
However, I'm certainly open to being corrected if ** I ** am in error.
My reasoning is that the progression of atomic weight is from 140 through 95 and 4 to the bottom row for dust.
I'm not an expert, but I think 10^8 might be quite correct because the weight is not given in kg but in atomic units: it only means that a dust gran weights 10^8 times a hydrogen atom, which is likely because it contains many uranium atoms.
By any chance, do you have resources available where you could set up shop to work on your idea in a public way?
GW Johnson is an example of a member who has created an independent repository of his writings... You can see his work at his exrocketman Wordpress blog.
There is a big difference: GW is an experienced aerospace engineer and a rocket scientist, while I'm a SF writer: I can do some rough math using formulas, but I've no idea how to really do things.
Have you any thoughts about the SPS in LEO topic?
Italy would be a beneficiary of the system, if it is brought into existence.
(th)
I like SPS and I use it for my laser stations: I've make a little upgrade so my starships can now reach 0.3 C (above this speed, realtivistic red-shift become prohibitive for laser power and the ship needs meters thick shields to stop neutral hydrogen atoms).
A 300 ton starship with 2 people and 150 ton of cargo, with a 2400 meters and 8 ton sail, requires a 370 km wide solar array (in an orbit where solar radiation is 10 KW/m2) to produce 816 TW of electric power for a 250 km wide laser array.
There are two unintended consequences:
1) a 300 ton starship flying at 0.3 C can be easily turned in a weapon of mass destruction: 300 ton at 0.3 C become 314.4855, giving a kinetic energy of about 1.3 Yj (1.3 x 10^21 joule!!!) which can crush a planet in case of collision.
2) A 350 km wide orbital laser station with a 250 km wide laser array of 734.5 TW of optical power is also a weapon of mass destruction (it's impossible not to think to Darth Vader's Death Star). It can also be used in mode-lock (burst of short pulses) to vaporize an erratic starship on a collision course with a planet.
For Quaoar re #9 and topic in general
First, thank you for considering my hybrid suggestion ...
I hesitate to risk imposing upon your generosity ....
Could you develop your "Voyager sized probe" idea a bit more? If humans (ie, you) were to design a space probe with the mass that Voyager had, using modern technology, ** and ** if humans (ie, you) were to to plan to boost the ship using lasers at Mercury, ** and ** if the ship were designed to slow down to go into orbit at Proxima, what would that system look like?
Such a vessel could (presumably) operate under conditions that humans would find difficult, and (if properly designed) such a probe could (presumably) return useful information from the destination solar system.
In reflecting a bit more, I think that it might be a good idea to increase the mass of your (hypothetical) probe slightly, to accommodate a power supply able to operate reliably for a couple of hundred years. That would allow commands from Earth to (hopefully) direct activities of the probe after arrival at the destination.
***
Would you be willing to comment upon the SPS in LEO concept, in the Solar Power topic?(th)
I have many doubts about the feasibility of a two stage laser sail probe able to decelerate in the destination system. First of all, the deceleration takes place at 4 LY from Earth, so if the beam is misaligned it would be impossible for the AI in control to call the laser guys and tell them to move the beam, because it will take 8 years.
Even if the alignment is perfect, at 0.25 C the beam arrive at 60% of its power due to relativistic red shift. At this point, the big sail of stage 1 has to change its shape from flat to concave, to focus the beam on the smaller sail of stage 2. But stage 1 still continues to accelerate in opposite direction of stage 2, further decreasing the power of the beam.
I think it's more practical a laser sail for acceleration and a Clark-Sheldon stage for deceleration. We can imagine a five stages probe: a laser-sail stage able to reach 0.2 C and four Clark-Sheldon deceleration stages with a 800 kg probe as payload.
You may take a look at Isaac Arthurs "Laser Highways" as well.
I am not likely to survive to the day when interstellar becomes very possible. .
Me too. I'm 57, but I hope my son and my daughter will be still alive that day.
For quaoar ... re #7
Thanks for the implied ending of the story << grin >> .... I expect to find that Clark-Sheldon ships can slow down.
However, I'm surprised by your answer, in this sense ... while your novel presumes the earlier trips by Clark-Sheldon ships, you have not (as nearly as I can tell) imagined ** those ** ships would receive a laser boost.
Since that seems eminently feasible, it would seem reasonable to me to build all the "slow down" capability you need into the vessel, and give it the needed boost when leaving Earth.
That is ** exactly ** the same scenario I've proposed for the Earth-to-Mars trip ... there is no reason (other than tradition) for the ship departing for Mars to consume ** any ** of it's mass or fuel to achieve transfer velocity. All of the needed momentum can be imparted by a pusher tug, which can then return to Earth and refuel for the next trip.
In the case of your proposed journey to Proxima, a hybrid solution would bring the future you are "seeing" into being a whole lot sooner.
Yes, it's feasible to build an hybrid spaceship with a laser sail for acceleration and a two stages Clark-Sheldon rocket for deceleration: in this case we will have a maximum speed of 0.1 C, that's very exiting and can reach Proxima in about 43 years. But in my novel, during the Age of Diaspora there was no laser stations. They will be built some centuries later in the Age of Reconnection.
As a follow up ... others have proposed slowing a laser powered ship. I'm reminded of the work of Dr. Robert Forward. As I remember, the plan called for a double reflector design ... energy from Earth would impact a reflector, which would send the photons back to the arriving vehicle, whose smaller mirror would accept the slowing momentum.
A serious problem with that proposal and with all of the similar ones I have seen is that they depend upon accuracy of beam pointing over interstellar distances and many years that I think is unreasonable.
The hybrid solution which I infer from your description of the laser boost launch idea is NOT dependent upon laser energy after departure from Earth. If you are so inspired, please compute the distance needed to give a vessel 1 g of acceleration until it reaches velocity that would put it at Proxima in 100 years (including slowing)
It is ** that ** distance the laser facility on Mercury would have to cover, not the far greater distance Dr. Forward was considering.
(th)
The problem with this approach is that you need a 5200 km wide laser array of 216 nm of wavelenght to focus on a 3.35 km wide sail at 4.2 LY. 5200 km is quite less than the diameter of Mars which is 6800 km. It's very impractical with a big manned starship, but it may work with a voyager-sized probe.
For Quaoar re #5
Thank you for the reminder of the Orion drive, and the new (to me at least) link to the Clark-Sheldon design.
I'm looking forward to following the link, but if you are willing to hive a hint of the ending of the story, does the vehicle slow as it approaches Proxima? I'm assuming it does, but your brief summary did not include that important detail.
I bring this up because (if it does) then a combination of your laser launch proposal with their slow down to dock method (assuming it works) might provide the best of both .... Your solution is terrific for the launch phase but has a problem slowing at the destination. Their design (if I understand the implications) may have the ability to slow down to arrive safely at the destination.
Taking the concept a bit further ... If a vehicle is given a massive start, and then waits until the last possible moment to begin slowing, the travel time could be reduced to the lowest possible value. A 1 G boost away from earth would presumably allow the ship itself to separate from the sail, while the sail could be collected and returned to Earth for another boost operation.
That would be a one way trip for the vessel ... it would depart with enough fuel and mass to slow at the destination, and it would set up shop there for exploration of the destination, reporting back to Earth, and potentially development of the destination if that is feasible.
PS ... would you be willing to stop in at the Solar Power topic and offer your feedback on the SPS in LEO concept?
(th)
By the moment we are only able to accelerate at 0.25 C but not to slow down: in my novel the nearest stars have been already colonized by Clark-Sheldon ships, so the colonists communicated via radio and agreed to build laser stations in every system, creating a high-way laser network.
I was always quite taken by the atom bomb rocket. You just have a succession of atom bombs that are periodically placed on the "engine" side of a big radiation shield. Each one accelerates the craft. I guess you could fine tune so G forces aren't too bad. Can't recall the name given to the concept. It's not Nerva. I seem to recall the atom bomb rocket could get you up to interstellar speed pretty quickly.
The Orion drive is a very promising technology, but the original work by General Atomic gave a maximum exhaust velocity of 200 km/s, which is fantastic for interplanetary travels but too small for going interstellar.
http://ntrs.nasa.gov/archive/nasa/casi. … 085619.pdf
Excluding handweaving technologies like antimatter (we still have no idea about how to mass produce it and how to safely store it at reasonable density) or fusion (we are always ten years from doing it) at the moment the only rocket we can mount on the aft of a generation ship is a Clark-Sheldon dusty plasma fission-fragment rocket, whose exhaust velocity is about 15000 km/s. A two-stage-three-generations-starship with this rocket can reach 5% of C and travel to Proxima in almost 90 years.
As an hard SF writer, I was looking for a realistic starship for my next novel which will be set between the local stars. The ship should be about 600 ton of mass and she should be able to reach Proxima in about 16-17 years, traveling at 0.25 C.
Can we build such a ship with slightly ameliorated current technologies?
After making some rough math, I found the answer and I was quite shocked: yes we can build it using a laser sail like the mini probe of Yuri Milner, but bigger.
A 600 ton starship needs almost 880 TW of optical laser power to accelerate at 1 g.
We can image a one-micron-thick carbon-carbon sail, coated with 10 nm of molibdenum on the aft side: such a sail would weight 0.0018 kg/m2 and would have a power load of 100 MW/m2 at 2000 K. So the total sail area would be 8814000 m2, the diameter 3350 m (or a square of 2970 m of side) and the mass 15.9 ton. The sail would be furled like the sail of JAXA's IKAROS: stowed on a rolling drum like an origami, then extended and kept in shape by centrifugal force. We can image carbon nanotubes artificial muscles, embedded in the sail as stiffening ribs, that fold it again during the coasting phase of the trip.
The ship will have also four fission reactors for electrical power, a 20 T superconductive magnetic coil to shield the habitat from GCR, a passive shielding of 30 cm of water, ten one-micron-thick carbon-carbon shields for space dust, laser as point defense against debris, lidars radars and quite powerful chemical RCS rockets to dodge bigger objects.
The accelerating laser array will be build on the polar regions of Mercury: the best diode lasers have a plug to wall efficiency of 76% and we can imagine they might reach 90%. So, to have 880 TW of optical power, we need 978 TW of electrical power, that become 1632 TW due to the red shift, to keep the ship accelerating at the same rate when she reaches relativistic speeds (at 0.25 C a 216 nm laser becomes 360 nm so the beam power is at 60%).
With a constant acceleration of 1 G and 0.25 C of cruise speed, the acceleration phase ends 5765 AU away from the Sun, so the laser array needs an aperture of almost 120 km (imagine a field of lasers of 120 km of diameter) to be focused on a sail of 3350 (the lasers have 216 nm of wavelength).
The photovoltaic array will be put near the equator: at Mercury the sun power is 6600 W/m2. We can image that in a near future solar panels will become 85% efficient: so to get 1632 TW of electrical power we need a square array of panels of 1386 km of side, and we need many of these due to the rotation of the planet.
Laser and solar PP also need radiators.
All this stuff will be very expensive and difficult to build, but not impossible.
The weak point of my dream is that my spaceship needs also a laser deceleration station in the orbit of the destination star.
We can imagine three possibilities: they are built in our solar system then sent to the destination system at 0.03 C with a fission-fragment propelled spaceship. They are built in the destination system with local materials after sending robots. They are built in the destination system by intelligent aliens in communication with us.
A couple of problems occur to me. So long as the hydrogen remains close to absolute zero, it is effectively trapped within the lattice of the crystal or fullerine molecule. However, in any material at apparently uniform temperature, there can be local variations in molecular energy. If even one fullerine molecule fails within your fuel pellet, the result may end up being a detonation wave. Secondly, such a concentrated source of energy, failing catastrophically, would produce a fireball hot enough to produce x-rays. I believe GW has written in the past about the EMP hazards of nuclear explosions in the upper atmosphere. That hazard occurs because fission generates gamma rays that ionise the upper atmosphere, creating electric field gradients which interact with powerlines. An intense x-ray source in the ionosphere could do the same thing.
All of this is conjecture on my part. So take it with a large heap of salt.
That's not a big problem: MMI fullerenes need in any case to be diluted with liquid hydrogen to lower the chamber temperature, so you can use them to obtain a gelled liquid hydrogen and store it at 10 K with a zero-boil-off active cooling system.
For Quaoar re #16
It is a privilege for me to be able to offer encouragement for you to PLEASE continue your thinking!
Also, if you have not been aware, this forum is actively recruiting new "high value" members, and existing members are in the very best possible position to identify prospective members and to encourage them. You are the ONLY active member from Italy, so I hope you will keep a watch for candidates you'd like to see 'enrolled' in whatever process this forum is engaged in.
You've noted the creative thinking of Void, the expertise of GW Johnson and kbd512, and the Engineering capabilities of Calliban.
It is not only possible but likely I am failing to mention talents of many other existing members.
We have need of volunteers to help with projects by RobertDyck, Calliban, and (importantly to me) development of a Tutorial on Celestial Mechanics for Mission Planning that I hope will be led by GW Johnson.
We are holding a collection of work by GW Johnson that is packed with the knowledge he has accumulated over decades, and it is just sitting in archive waiting for development.
If you know of a professor who might be interested in helping to develop this material into a formal curriculum, please let that person know of the opportunity.
Clearly we need serious students to help to provide the incentive for volunteer work to build this tutorial. The candidates will see themselves as preparing to navigate manned and unmanned spacecraft between Earth and Mars (or anywhere in the Solar System).
If you would care to do so, you can become a lead for development of the Hydrogen storage method you've described. It may not be possible to engineer the storage system you've imagined, but since there is no way to know without actually trying, now is a good time to begin the effort.
(th)
Thanks, I'm happy to collaborate, but I don't know if a SF writer like me, who likes hard fiction and dreams about interplanetary and interstellar spaceships, might be useful to a real project
