The ISV “Venturestar” is an example of “poly-propulsion”, using a Forward laser-sail to boost to 0.7c, and brake to a halt, in Sol-space, then using matter-antimatter, Powell/Pellegrino “Valkyrie” style, to brake at Alpha Centauri, then boost for the trip home.
I thought I’d work out the energy consumption of one of these babes. I like to compare starship energy budgets with global annual industrial energy production of about the present day, i.e. a year’s worth of energy at around 16 TW, coming to 5 x 10^20 J.
I get an energy consumption for a round trip to Alpha Centauri and back of at least 7.3 x 10^23 J, or 2.03 x 10^17 kW hr: equivalent to 1460 times current world annual usage. This makes a number of optimistic assumptions, particularly that the ship can be refuelled with both hydrogen and antihydrogen at Alpha Centauri, and that its initial mass is only 10,000 tonnes, falling to 1333 tonnes at the end of each main rocket propulsion phase.
In the story, the income from each flight is 350,000 x 40 million dollars, so 14 trillion dollars. If energy costs are less than about 0.007 cents per kW hr, then it might be a paying proposition. I wouldn’t mind if my home electricity bills were calculated on such a low tariff!
And clearly we are talking about electricity for the starship: electricity to drive the laser, and electricity to power the antimatter factory. (I am also assuming 100% efficiency in manufacturing antimatter, which may not be realistic.)
Stephen
Further on poly-propulsion, a little while ago I came up with the following plan. Beaming a laser onto a light sail is highly inefficient when the vehicle is moving at low speeds, but becomes more efficient at higher speeds. It only really works, however, to accelerate a ship away from the beam generator (Forward’s idea for reflecting the beam off an annulus to decelerate the ship strikes me as an impractical Heath Robinson idea). Nuclear fusion is fine for getting a ship started, but pegs out at a few per cent of light speed. Beamed energy which is captured by the ship and used to energise an onboard tank of hydrogen in something like a VASIMR engine works better for acceleration towards the beam generator (otherwise you are trying to capture the beam after it has passed thru your own exhaust stream).
Putting all these together, a one-way interstellar trip then might proceed as follows. (1) Launch the vehicle using nuclear fusion, get up to a few per cent of light speed. Discard the tanks and heavy fusion engine, and deploy a light sail. (2) Direct a beam of light from the Solar System onto the light sail and accelerate the ship further, to a high cruising speed. Finally (3) on approaching the destination, start up the beam again, but this time the ship captures it as electrical energy and uses it to drive a magnetoplasma engine, using an onboard hydrogen tank, to decelerate into the target system.
Not sure if this vague and complex plan deserves any further analysis!
Stephen
Thanks, Adam. Certainly, engineering is all about balancing the various trade-offs.
Yes, recycling the photons occurred to me, too, but since the light-sail would hardly be figured to optical accuracy, I would expect that this is impractical over distances of AU to light-years (but I have not seen this idea checked numerically). The beam reflected back to the region of the transmitter would be too widely dispersed.
Laser-powered rocket: how does the laser power get turned into rocket thrust? The only way I know is to capture it as electrical power, as one would in a solar power satellite, and use this power to run an ion thruster or electric magnetoplasma engine like VASIMR. One is then limited to an exhaust velocity of 500 km/s maximum; fine for pottering around the Solar System, but not capable of the speeds one would like for interstellar ships. Or is there another way?
Latest on Venturestar: my revised minimum energy budget for the ship for a round trip (!) to Alpha Centauri and back is now 8.6 x 10^23 J, or 1720 times current global annual industrial energy production.
Stephen
Since the Venture Star (two words) doesn’t seem to refuel at Alpha Centauri, we’d better calculate the energy cost of refilling there with hydrogen alone, and assume that all the necessary antihydrogen is loaded only in the Solar System. The energy cost triples to 2.6 x 10^24 J, equivalent to 5286 times current global industrial energy production. This assumes that the antimatter containment system masses the same as its contents, and that the vehicle returned to the Solar System is the same mass as in the calculation above. At Solar System departure, the ship now has a mass of 37,310 tonnes, and presumably needs a larger light-sail.
On return to the Solar System it has a mass of 562 tonnes, which is much too small to carry 200 passengers in “cryosleep” plus 350 tonnes of James Cameron’s fantasy mineral with a silly name. So better double or triple all masses, and hence all energy costs, in these estimates.
It would help if my source for this ship (http://james-camerons-avatar.wikia.com/wiki/Interstellar_Vehicle_Venture_Star) gave masses for the ship and its component parts, but it avoids doing so, probably because the ship seems to be built mainly out of “handwavium”…
Stephen
Astronist, can you guide me a little.
I am doing the same analisys for this ship.
First lets clear something..
The weight of the all ship including the 2 shuttles but not the antimatter fuel is 450 metric tons. And this is even a high extimation using materials for structures 40 times more heavier than the one than can be achieved usen carbon nanotubes or graphene.
But my question is about the ratio of antimatter that you need to reach 0,7c.
I am not sure what values are correct.
For example, taking the last beamed core nozzled design, this has an effiency of 86%.
The amount of energy release by matter antimatter is 100%, from this only the 61 %? is in pions charges.
What this mean?? That we can convert more than 40% into momentum?
There is a graphics that show g/kg and ?V, but this is taking an effiency of 38% for beamed core with a max velocity of 0,4 c
Can you help me with that?
Hi Adam, Thanks for the answer.
You have the souce of those analyses on pions rockets?
Becoz it said only 12 tesla to make the magnetic nozzled. This can be achievment with today technology with no need of unobtanium.
But make a photon engine to just use the gama ray with a 1/c of effiency seems a waste of energy. More talking in fact that in the paper use a lot of the energy to just storage and contain the antimatter, That give us so low effiency that can be compared with any other nuclear engine.
So why use antimatter??
Using different approaches we know that with only a few miligrams or micrograms of antimatter we can go to jupiter or more distant places at higher delta V.
Lets forget for a second of how contain the antimatter.
If the antimatter annihilation release a 60 % of charged pions (with mass) why we ignored them like propulsion???
That we need to take only a 40 % of gamarays with only 2/c “guessing” of effiency??
Many papers use their conclusion using the old frisbe study. The same happens with fordwards studies about beamed sail, but now there is a lot new ways higher improve those old studies.
But I found very difficult obtain basic data to make my own calcs.
About the ultra-dense deuterium I already read something, that can be used to produce high magnetic fields to be used in the contain. Not such to make the antimatter of this material.
About the weight, trust me, is not even a close estimation of how light can be a ship 140 years from now.
For example it will be like this:
shield 5 + crew 20 + habitation section 30 + both shuttles 60 + cargo 300 + ship structure 20 + engines 10 +? radiators 10 + spheres 5, sail 20.
For habitation section, i estimate 200 men/wommen, average weight 70 kg with an extra 70 kg on structure and cryo for each person.
You just need to read a lot more of graphene, nano-carbon materials, and other new materials that we are using all, even to day.
A japanese company is thinking seriusly in start to build a space elevator in the next 20 years using carbon nanotubes. You know the strength and weight parameters that you need to build something like that? It makes the ISS a lot more lighter.
No shit we are using low quality graphene in tenis rackets right now.
About the laser array, I already calc that, is about 2000 TW to accelerated a 1000 tons ship at 1,5 G. There is not heat problem or anothing else.
The beamed sail is the best aproach that we know to day to make interstellar trip a reality.
I read in some place that you need a 2/3 of the ship mass into antimatter-matter to reach 0,7 C.. But IDK, there is so much info at internet, that we need to take many sources to be sure. Since IDK what parameters they use to make that calc.
Hi AngelLestat
I presume you mean the paper by Zhang & Keane? Yes I do have it. And yes, if you go through the figures, the fraction of useable energy is rather low.
One uses a photon-rocket to achieve maximum efficiency for a rocket at any speed >0.63 c. And that’s what we’re talking about here.
You misunderstand. Friedwardt (Fred) Winterberg’s concept uses a system that can create a gamma-ray laser and a pure gamma-ray exhaust. No pions created, but the gamma-rays are highly collimated, so there’s no need for them.
You make some good points about the mass-budget. I guess that’s what the designers of the “Venture Star” had in mind.
As for laser-sails – they are pure photon propulsion, though not rockets as they don’t carry propellant. Not much different to a M-AM Photon Rocket in terms of efficiency issues at low speed. The design that the “Venture Star” is based on, the “Valkyrie” rocket design of James Powell and Charles Pellegrino, actually uses matter-rich mixes at low speeds, to maximise efficiency. Below 0.125c it uses a M-AM/Fusion hybrid system. As their design is a pion rocket when using a fuel-mix richer in anti-matter, there is considerable room for improvement in efficiency. Their magnetic nozzle concept seems rather inefficient, though I would like to see their original analysis.
regards
Adam
Looking info in other pages, I realize that you work in the icarus project, nice 🙂
Was funny how I notice, you did a note in the british interplanetary sociaty, and when I read “Adam Crowl”, it was not hard remember the page name and your nick.
I was reading again the Winterberg´s paper that you show me.
Of course, this paper exceeds my understanding on the topic, and my english level does not help me either.
And this seems like a very complex reaction to get this 100% collimated gamma ray beam. So this is mean that is the best option in theoretical physics to get momentum from an antimatter collision at speeds greater than 0,3c?
But if I understand correctly, this means that from a total energy of 300MJ you convert only 2J into momentum?
That’s where I get lost, how a magnetic nozzled that use the recoil of the mass particles like charged pions shooted to 0,8c be less effiency than pure photons?
If you said to speed higher than 0,7c is ok, I understand.. but if is not?
Or the collimated laser gets extra power from the ambiplasm medium bouncing photons until these can escape?
Yeah I understand that, there are like 3 or 4 methods to get high effiency at different low speeds.
One question: if you had a method to convert a high % into momentum, then it will be feasible to use the bussard concept to harvester hidrogen, so you only need to carry the anti-h reducing the half of the mass. It will be an option?
About the icarus project, Why it seems that beamed sail is not take it so seriusly like other project? In my opinion seems the best option for short (solarsail) or long distances.
If it is by the accuracy problem to brake at destination, there is a lot of new optics technologies that can give bigger improves in this fields like Metamaterials, dielectric, plasmonic, superlens, nonoantenas, etc.
Geoffrey Landis has also many great ideas in this matter. Like send a sail ship with only small fresnel lens, So the ship can drop them at different distances and velocities,
Then a new ship can made all the trip using these lens to focus the beam.
And sorry if I am making you spend time in this. You can finish the discucion wherever you want, I will no feel ofended of course.
Hi AngelLestat
Some more responses:
No one said it would be easy. But magnetic self-compression of the reactants allows very efficient momentum coupling of the gamma-rays to the vehicle.
The problem with a pion rocket is that most of the energy is not in the pions. Uncollimated gamma-rays and uncharged pions carry away a lot of energy.
The problem with magnetic-nozzles is that designing them to efficiently convert high-speed particles into an efficient jet-stream is difficult. A hemi-spherical nozzle, for example, only has a momentum efficiency of 50% – i.e. only 25% of the kinetic energy is converted into forward thrust. The One-loop magnetic nozzle studied by Callas (in that JPL Paper that no one can get a copy of) was only 35% efficient, meaning a very low energy efficiency. The adaptive design by Keane & Zhang resulted in a momentum efficiency as high as ~80% (64% energy efficient.)
Winterberg avoids nozzles with his gamma-ray laser system because it’s self-collimated by the magnetic-focussing. Thus the efficiency is (hopefully) very close to 100%.
A good analysis of how to compute rocket specific impulse can be found in Shawn Westmoreland’s fairly recent paper on M-AM rockets:
A note on relativistic rocketry
As for “Project Icarus” it’s specifically a fusion rocket study, due to its historical continuity with “Project Daedalus”. We have a spin-off Project, “Project Forward”, which is examining beam propulsion.
This time I take more time to think and read everything you sent me.
But I still have some questions if you dont mind.
I cant understand why in F. Winterberg study at the end says that to contain the necessary amount of antimatter would be needed a ship the size of a planet.
So a element a lot more dense is needed.
Why is that? If he has an engine with almost 100% of energy convertion, Why it needs that amount of antimatter?
About the avatar ship, it would not be more efficient make a bussard scoop to avoid carrying the hidrogen part, doing this it will help in the brake and reduce also the antihidrogen needed due to the low mass ratio. Of course, when the ship go back does not get any benefic of the scoop I assume.
After all, the venture star design seems feasible if we take a modest frame of technological advances.
But the heat generated (if they use a magnetic nozzled) at 1,5g seems like the bigger issue, I am right? Maybe they can use the sail to help in the cooling.
Carbon nanotube or something like graphene, are very good thermal conductors, and carbon resist high temperatures, like tungsten.
I dont know if is so good to absorb gamaray..
I was reading about subatomic black holes, like a way to power a starship.
What are your thoughts on that?
http://arxiv.org/pdf/0908.1803v1.pdf
Because if our assumptions are correct on how it may behave a SBH then looks like a more feasible idea than antimatter.
Then you have a machine who can convert anything into 100% energy. Seems ideal.
But it is hard to imagine how one could feed this SBH. With one atom side it will take a lot of time (in my opinion) to swallow a simple water glass. And the energy comming from the black hole it would shot and vaporize any matter you drop into before reach the core.
About the project forward I am wating until the end of the year to see the results.
Hi AngelLestat
Good questions and well worth answering – you’re not wasting my time.
He’s referring to the analysis by Frisbee, whose rockets were immensely long and thin, so the frozen anti-hydrogen could be kept cool enough (0.1 K) to remain storable via paramagnetism. The rockets were thousands of kilometres long, though only metres wide.
Perhaps it would be more efficient, but at best it would halve the antimatter needed, while adding the considerable mass of the ramscoop and thus potentially doubling the actual antimatter mass required.
Thus why I think the “Venture Star” would need a system more like Winterberg’s, which would have minimal waste heat issues.
You might have noticed that I made some helpful comments on that preprint that get acknowledged. So I do have a few thoughts on using black-holes – however it will be immensely more difficult than matter-antimatter, something that I disagree with Louis Crane on. Concentrating a million tons of energy into a near infinitesimal point is an immensely challenging task. Directing the decay products into useful thrust will be another immensely challenging task. And force-feeding such a tiny hole will be incredibly hard. Three “miracles” of physics will be required. If Louis is right with his Meduso-Anthropic Principle, then it must be possible.
Me again, thanks for the last answers.
I was doing some calculations and trying to learn a little more. But I still have some serious concepts problems.
If some of these are not easy questions to answer or it will take time, just tell me and I will understand them eventually.
Why the ISP in the case of a rocket with propellant at vacuum is equal to the Ve?
I can understand that in almost anycase, but not in this one:
An antimatter rocket that only convert the energy into photons (without pair production effect) and we get only the recoil efffect of these photons 2/c.
The Ve it will be close to C, but the ISP has to be very low. Am I right?
You tell me and I read it in many places, that if a shield absorb gamma rays these can be radiate it in a collimated way with ease. And in these case we will have the 100 % of the energy converted into momentum.
So why collimated in this case means 100% effiency?
A laser is also collimated and we get only a 2/c of its energy into momentum.
But the super conductor mesh it would weight a lot less than a sail.
The electrons will move across the mesh even if we not inject energy into the system.
Or I missing something?
Now I notice it 🙂
Yeah, I am agree with your comments on the topic.
I also find hard to imagine how we can “focus gamma ray” into a volume of 1 atom.
Or how to trap the BH and use their energy after created.
But is not very clear for me why we need to use gamma ray to make this BH.
If we need to focus the energy into such small point then I understand, but why we can not use a normal laser to focus the energy in a bigger area and then will let the gravity work to implode into its real size.
I was trying to calculate this radius using like parameter the max density of a neutron star, then I read that a lot of energy in the implode process is expelled into neutrinos and gamma rays, so I leave aside the numbers
But even if we need extra energy to make it in this way, it would be more easy in my silly and unreliable opinion.
Yeah it seems like the meduso-anthropic principle was made just like a defense mechanism to its meme.
But well, there is something in the light speed constant that seems to enclose a bigger truth, A connection between the real shape of the universe, black holes, the information and we.
Hi AngelLestat
Hopefully I can clear things up for you.
Isp – specific impulse – is a rocket engineer’s term for the amount of thrust a specific mass of fuel can produce. Usually it is divided by the gee-factor (9.80665 m/s2) as thrust is measured in “pounds force” or “kilograms force” instead of SI units like newtons. So 1 kilogram of mass-energy produces 1 kilogram of force (=9.80665 newtons) for 30,570,323 seconds from 1 kg of mass-energy. A photon rocket exhaust emits 299,792,458 joules of photons for every newton of thrust produced. The recoil isn’t 2E/c for a rocket, only a perfectly reflective mirror gets a double push.
No. I have said no such thing. Winterberg’s laser-design collimates the photons and that gives – within physical limits – as close to the maximum efficiency for a photon rocket as you can get. Uncollimated emission produces very little thrust – if any! The gamma-rays are emitted isotropically in all normal matter-antimatter reactions, unless a lasing effect is created, as in Winterberg’s design. But a photon rocket – like any rocket – has a maximum efficiency that is less than 100% – because it is a rocket! The maximum efficiency – defined as the ratio of the kinetic energy in the empty rocket to the energy in its expelled exhaust – is about 65%. But there are different efficiency terms being discussed in rocket designs – nozzle efficiency, fuel efficiency, rocket efficiency etc. These all multiply together. The Matter-Antimatter Pion rocket studied by Frisbee, for example, has a low nozzle efficiency – only about 12% of the pion kinetic energy is transferred to the rocket. And the fuel efficiency is low because about half of the mass-energy is lost as gamma-rays and uncharged pions.
Remember: Most Matter-Antimatter rocket designs are Pion rockets, not Photon Rockets. Uncharged photons can’t be directed by magnetic nozzles, but charged pions can.
As I have now explained it depends on which efficiency is being discussed – in this case it was thrust efficiency that I was talking about. The Gamma-Ray Laser points in one direction and the rocket moves in the opposite. Because the laser is almost perfectly collimated, the transfer of thrust to motion is nearly 100%. BUT that’s not energy efficiency. At low speeds a Photon Rocket is very inefficient in that sense. Only at speeds >0.63 c does PURE Photon propulsion dominate. Below that speed, and energetic particles moving at lower speeds are more efficient.
One doesn’t have to carry fuel at all during the laser acceleration phase. Only during the braking phase. Adding a ramscoop – which is not a mesh, but a rather heavy solenoid in most designs I’ve seen – to only save on half the fuel mass, seems an unnecessary complication. There’s also no guarantee there will be an efficient way of adding extra energy to the incoming mass, which is being scooped at relativistic speeds.
Rocket design and physics requires paying close attention to many different details and physical processes. That can be hard to communicate accurately 🙂
Yeah, one day after ask the question, I start to realize what was wrong with my interpretation. This energy is comming from matter, even if there become photons, We are obtaining the 100% of energy from them. Heh, I feel so silly right now.
No, you dont, sorry, what I read in many places is this:
“For example, a gamma ray absorbing shield will radiate back into space the energy it absorbs. Moreover, the re-emitted radiation coming from the shield will be in the form of photons at near-optical frequencies. Thereby, the re-emmitted radiation can be collimated into an exhaust beam with relative ease. We calculated that if a pion drive were so equipped that it could effectively utilize half of the gamma ray energy for propulsion, then it could achieve a ISP of up to nearly 0.77c.”
This was the root of my bad interpretation, somehow I compared with the beamed sail principle.
Now I understand better the phrase “this is rocket science” 🙂
Yeah, are not the same ramscoop and magnetic sail, now I know. But in some pages the people talk about them like it was almost the same thing.
Well, back to the ISV topic, I was doing some math.
The ISV speed is 0,7, so this is mean that the ISP is higher than 0,7c. It can use the uncharged pions with pair production effect to be able to focus these particles with the nozzle.
I take only 350 t for the ISV without fuel (yes I cut it a little more), Becoz why each ISV (total 12) needs to carry 2 shuttles? Is not better left 2 in pandora and 2 in earth?
I use the formule to know the fuel ratio that include the lorentz factor.
ISP TotalM FuelM Gray used Heat Release/s Heat Absorb/s
0,77c 1000 t 650 t 50% 742 TW 74 TW
0,95c 860 t 510 t 88% 139 TW 14 TW
1.0c 800 t 450 t 100% 0 0
To know the heat, I use the fuel mass, then x0.4(unchaged pions) x0,5(for 50% gama ray used) x1000xc2 (energy release) /15768000 (half year frame in seconds) then I “estimate” only a 10% of energy absorb becoz gamma ray are not easy to stop.
The radiation received by the crew is strongly reduced by the inverse square rule and I guess most of the radiation will escape to the opposite direction, becoz there is not much matter to produce the pair effect and is the shortest way to escape from the magnetic field.
Of course the acceleration is not constant becoz the heat will be variable.
Using P = e.A.?.(T14? T24) I calculate the max heat it can be dissipated by the radiators.
If we estimate 150m x 400m then both can dissipate 24 TW using a working temperature of 4500K (graphene melting point is 5500k at vaccum)
We also can use the sail 200 km2 “maybe” to dissipate heat, lets estimate a working temperature of 1000k (becoz we can not transfer much heat in thin structures), only 1 side and 0,1e. It give us 113 TW.
Of course this is just place numbers in an equation, But I dont have a clue what I am talking about 🙂
To calc the laser power, In the 0,77c case it will be 1000 tons to accelerate and 350 tons to brake, So the average is 650 tons, for that we need 1,2 Pw (using Landis´s estimation of 6,7N by gigawatt)
it will be 3,5 month to brake and 8,5 month to accelerate.
This give us the 12 years time frame for 12 ships.
I fear that these calculations have as much similarity as a child’s scrawl to represent their parents.
I said something very wrong about this last post? you can be honest 🙂
Well never mind, thanks for all your help than you already give me. I know that you had many publications, research on icaros project and other work to attend to.
regards,
Ariel.
Hi Ariel
Nothing wrong. I just got busy doing other things. I will do up a blog-post shortly covering some of it 🙂