Something about my mass model of “Daedalus” didn’t sit right with me, so I recomputed the tankage from first principles. The percentages were more like 5%, thus meaning a slightly slower fastest time – 71.58 years with an initial mass of 281,181 tonnes.
While “Daedalus” can cruise at 0.12-0.14c, meaning speedy trips to Alpha Centauri, compared to the above, the problem is that there’s no way of stopping at such speeds – finite tank mass means an infinite mass of propellant would be required.
I went on to compute the performance of a magnetic sail equipped vehicle and got quite an encouraging result – which I’ll post here after the Symposium presentation itself, which is in a matter of days. Traveling to Alpha Centauri via fusion rocket in sub-50 years will be an immense engineering challenge, so one hopes better options will arise. Jonathan Vos Post has a paper online which is a good example of the extreme performance required for very rapid flybys – a perfectly efficient fusion motor, a five stage vehicle, and a mass-ratio of ~100,000 means a flight in ~9 years or so. Wildly unrealistic, but illustrative of the effort needed.
To do better will need something better than rockets, but not necessarily more powerful than fusion energy.
Currently I am working on a paper & presentation for the 100 YSS Symposium in Houston, to be presented by an Icarus colleague. I am examining the effectiveness of using a magnetic-sail to brake to low-speeds in the target system, but part of that is a comparison with a pure fusion rocket. As it is still the most detailed design for an interstellar fusion rocket I am using the performance characteristics of the “Project Daedalus” star-probe. The most economical use of propellant for pure-fusion is to boost up to cruise speed using the 1st Stage, drop the spent stage, then brake using the 2nd Stage after a period of cruising. “Daedalus”, due to its ignition system and the tricky physics of implosion ignited fusion, had two different exhaust velocities for the stages – 1st Stage was 10,600 km/s and 2nd Stage was 9,210 km/s.
A limiting variable on the possible mass-ratio was the mass of the cryogenic tankage required to keep helium-3/deuterium fuel at a chilly 3 K storage temperature. For the 1st Stage the tankage was 2.85% of the fuel mass stored and 4% for the 2nd Stage. As a critical mass-ratio is approached the required mass of propellant goes asymptotic – runs off to infinity. Thus there’s a maximum cruise speed for a single stage using “Daedalus” style storage systems. It works out as 0.1c for the 2nd Stage engine. To achieve that speed requires infinite propellant mass, so it’s not really practical.
A more practical question is the fastest trip to a given destination. Rockets are limited in how quickly they can burn their fuel – Stage 1 burns it at 0.72 kg/s and Stage 2 burns it at 0.0711 kg/s. To achieve higher speeds requires burn-times that are asymptotically rising, when the critical mass-ratio is factored in.
Alpha Centauri is 4.36 light-years away. A two-stage “Daedalus” vehicle can travel there in 68 years at a maximum speed of 0.075c and then brake to a halt at the destination. However the amount of fuel required is about 300,000 tonnes. Going a bit slower – arriving in 71 years – can reduce the fuel required to just 140,000 tonnes. “Daedalus” carried an immense payload by modern standards – 450 tonnes, the equivalent of the International Space Station. The recent paper on boot-strapping a robotic economy on the Moon only required delivery of 41 tonnes to kick-start things. A large exo-solar industrial base could be sent to other star systems in a decent time frame to build, in advance of human arrival, large laser or mass-beam facilities to decelerate a human-carrying star-ship. Such would allow much faster trip-times.
The preprint I mentioned is available online (thanks to Brian Wang’s “Next Big Future” post) and it’s here:
Affordable, rapid bootstrapping of space industry and solar system civilization
More discussion is coming. One preliminary idea is that 100,000 teleoperated robots on the Moon could have a volunteer Army controlling them to help build the Solar System economy. The pay-off for all involved would be long-term energy/resource security – and potential wealth.
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.
No. Not the mountain in the Himalayas. Kardashev II Civilization status – a civilization using the energy output of its star. Earth intercepts just 2.2 billionths of the Sun’s energy and presently we use ~1/10,000th of what Earth receives. Thus the plateau of K-II seems a long way off. However we could boot-strap our way there by developing an automated space economy. And the first step isn’t huge.
Philip Metzger and Robert Mueller have both been busy developing a Map of the way to K-II via quasi-self-replicating robotics on the Moon.
Here’s Phil’s 2011 100 YSS Presentation: Nature’s Way of Making Audacious Space Projects Viable
Abstract
Building a starship within the next 100 years is an audacious goal. To be successful, we need sustained funding that may be difficult to maintain in the face of economic challenges that are poised to arise during these next 100 years. Our species’ civilization has only recently reached the classification as (approximately) Type-I on the Kardashev scale; that is, we have spread out from one small locality to become a global species mastering the energy and resources of an entire planet. In the process we discovered the profound truth that the two-dimensional surface of our world is not flat, but has positive curvature and is closed so that its area and resources are finite. It should come as no surprise to a Type I civilization when its planet’s resources dwindle; how could they not? Yet we have gone year by year, government by government, making little investment for the time when civilization becomes violent in the unwelcome contractions that must follow, when we are forced too late into the inevitable choice: to remain and diminish on an unhappy world; or to expand into the only dimension remaining perpendicularly outward from the surface into space. Then some day we may become a Type-II civilization, mastering the resources of an entire solar system. Our species cannot continue as we have on this planet for another 100 years. Doubtless it falls on us today, the very time we intended to start building a starship, to make the late choice. We wished this century to be filled with enlightenment and adventure; it could be an age of desperation and war. What a time to begin an audacious project in space! How will we maintain consistent funding for the next 100 years? Fortunately, saving a civilization, mastering a solar system, and doing other great things like building starships amount to mostly the same set of tasks. Recognizing what we must be about during the next 100 years will make it possible to do them all.
He presents a stark choice and though it’s based an arguably finite resource base, the road to freedom surely lies with not being restricted to one planet.
Metzger, Mueller and their NASA colleagues have submitted a technical paper to the “Journal of Aerospace Engineering”:
Affordable, Rapid Bootstrapping of Space Industry and Solar System Civilization
Abstract:
Advances in robotics and additive manufacturing have become game?changing for the prospects of space industry. It has become feasible to bootstrap a self-sustaining, self-expanding industry at reasonably low cost. Simple modeling was developed to identify the main parameters of successful bootstrapping. This indicates that bootstrapping can be achieved with as little as 12 metric tons (MT) landed on the Moon during a period of about 20 years. The equipment will be teleoperated and then transitioned to full autonomy so the industry can spread to the asteroid belt and beyond. The strategy begins with a sub-replicating system and evolves it toward full self-sustainability (full closure) via an in situ technology spiral. The industry grows exponentially due to the free real estate, energy, and material resources of space. The mass of industrial assets at the end of bootstrapping will be 156 MT with 60 humanoid robots, or as high as 40,000 MT with as many as 100,000 humanoid robots if faster manufacturing is supported by launching a total of 41 MT to the Moon. Within another few decades with no further investment, it can have millions of times the industrial capacity of the United States. Modeling over wide parameter ranges indicates this is reasonable, but further analysis is needed. This industry promises to revolutionize the human condition.
Robert Mueller presented on the Plan at several different meetings, his presentation slides being available here:
Robotic, Self-Sustaining Architecture to Utilize Resources and Enable Human Expansion Throughout the Solar System
I got in touch with Phil and will hopefully have more to discuss in Part II of this blog post.
A pre-print from yesterday, submitted by Branislav Vlahovic:
Observed Cosmological Redshifts Support Contracting Accelerating Universe
Vlahovic, a Professor at NCCU, discusses the possibility that our Universe is Closed and has already passed its maximum radius, at 15 billion years of age. He explains that the observed red-shift would be observed even in a collapsing space-time and the Universe might be ~24 billion years old, with 6 billion years before re-collapse in an Anti-Big-Bang. The reverse of the Big Bang, typically called a “Big Crunch”, is when all the (negative) gravitational potential energy of the Cosmos will be returned to (positive) heat energy and the contents reduced to “pure-energy”. Not healthy for Intelligent Life like us.
To have a present day Hubble parameter of ~70 km/s/Mpc the Universe would need to have a mass-energy density about 4.4 times the critical density, Omega-Naught. That means a Cosmic census of about 50 billion Galaxies as massive as the Milky-Way and a Universe that’s presently 7.5 billion light-years hyper-radius, with the opposite side some ~11.8 billion light-years away. An interesting consequence of such a claustrophobic cosmos is that we might be seeing double images of quasars – one image being their hyper-luminous form billions of years before their current more sedate Galaxy form. If peculiar velocities (non-cosmological motions) off-set the most recent image from the position of their past form, then we’ll see a Quasar with a high red-shift near a “closer” Galaxy with a lower red-shift. This would answer the puzzle of why some Quasars appear to be springing from regular Galaxies.
This web-site isn’t afraid of exploring impending Cosmic Dooms – a Sudden Singularity a few million years from now has been discussed previously – but this one is interesting. It’s not far enough away for the Cosmos to be reconfigured for a controlled collapse, as per the Omega Point Theory, but it does invite exploring ways to break-out of our Cosmos. One option, also mentioned here, is to learn how to live in black-holes, which – if sufficiently large – can survive a Big-Crunch to spring-forth in the next Big-Bang. Alternatively we might learn how to harness the worm-hole created by the Ring-Singularity of rotating black-holes – in theory this will allow access to other Universes.
Can we survive the transition to other Universes, potentially with totally different laws?
Since the 1970s Dr. Michael Persinger has been developing a physical understanding of paranormal phenomena. More recently he has worked with modern neuroscience technology to study “anomalous cognition” – which he defines as gaining information via more than the usual five senses. Not exactly telepathy. Instead he proposes that the magnetic field around objects, especially the background terrestrial and interplanetary magnetic fields, can store information and human brains can retrieve it. To further communication of his work to the widest possible audience he has made it all available on-line:
Dr. Michael Persinger
…includes his early 1970s work on geomagnetic phenomena and UFOs, etc., which gave him a certain scientific infamy. Such “ultra-terrestrial” explanations for UFOs neither satisfy the sceptics or the believers, but does provide the basis for developing a scientific understanding of how humans and the Earth, as a collective entity, interact.
One can speculate further and imagine a bestiary of magneto-plasma based lifeforms which share this world with us, but tracking such elusive phenomena is incredibly difficult. I’ve had my own encounters and can understand the difficulty. My friend Andrew Collins isn’t as restrained about attempting to communicate with such possible entities and documents his ideas and experiences in his latest book:
Andrews Collins News… “LightQuest” book coming soon
LightQuest
…perhaps you can get in-touch with the Geo-Psyche? Just beware that all your attempts are through the most tricky communication medium of all – the human psyche.
Bussard Ramjet - One Option to the Stars, By Adrian Mann
The Official Announcement has arrived…
Mae Jemison and Team Establish 100 Year Starship With Goal to Make Interstellar Space Travel Reality by 2112
…also covered by Paul Gilster, at “Centauri Dreams”,…
100 Year Starship Organization Launches
…while Sharon Weinberger writes it up for the BBC’s International front page news…
100-Year Starship: Mae Jemison reaches for the stars
…the common thread is that this Organization is about finding a Way for humanity, as a whole, to turn their eyes to the stars. Reaching for the stars will enrich all our lives here on Earth, and 100 Year Starship will be looking for the best ideas to do that. Travelling to the stars requires creating a sustainable way of living for the years, probably decades, it will take to reach other star-systems. By learning to do that we’ll develop the technologies that will enable people to live well here on Earth.
Here’s one possible route – just one idea based on a talk by Mark Edwards at the September 2011 Symposium. He’s been advocating the use of algae as a means of creating food, pharmaceuticals and materials for years. The systems he has developed, using a bunch of algal species, can produce a broad variety of products – many of which we already consume without knowing it. His vision was food/drug/fabric/cosmetic “independence” for the average person – in a real way an automated Cornucopia, able to feed, treat, decorate and even clothe us, all through sunlight, carbon dioxide in the air, and some nutrients. Can you imagine doing away with the hit-and-miss of dirt-farming? And all perfectly suited for living in space for decades at a time.
That’s just one (very good) idea amongst probably thousands (millions) more. In time, as creativity is channelled into such concepts, I’m hopeful of a near total transformation of how we feed, clothe, decorate, house and power our selves and lives. Even with Crazy-Times ahead, thanks to the GFC 2.0 looming in Europe and beyond, I believe we can solve our problems and transform our lives. Our hope and self-belief need a common focus, and I think the 100 Year Starship is just the vehicle for that. What will make our lives better here, will enable us to take them There, to the Stars.
So join us in this journey, in whatever way you can.
Recently this website, Build the Enterprise, hit the news because of the author’s rather quixotic call to build a real interplanetary version of that most famous fictional starship lineage. Unfortunately the site’s Forum-ware is very cantankerous, so I posting my discussion of necessary redesigning of the concept (slightly reworded for clarity)…
Running the numbers, the figures are wrong, wrong, wrong.
Here’s a preliminary list.
(1) Wet mass is quoted as 84,822 tons. Propellant load is 12,474 tons. Yet elsewhere, in pounds, it’s 187 million/55 million. Inexplicably the propellant mass has been halved. To get to Mars in 90 days with the quoted mass-ratio, (187/(187-55))= 1.42, means a very high exhaust velocity is required. Exhaust velocity and jet-power are inextricably related by:
P = 1/2.T.v
where P is the jet-power, T the thrust and v the exhaust velocity. To get to Mars in 90 days requires a high delta-vee (dv) – enough to travel to Mars on a short trajectory, against the Sun’s gravity, then matching to Mars’ orbital velocity. With a VASIMR that low mass-ratio might get it to Mars in 90 days – with a dry tank. The 0.002 gee acceleration quoted however is IMPOSSIBLE. Thrust, T = M.a i.e. mass (84,822,000 kg) times 0.0196 m/s^2 = 1,662,511 newtons thrust. With a bit of algebra we find that with a 1.5 GW jet-power the exhaust velocity is an impossibly low 1,262 m/s. A reasonable exhaust velocity (high-thrust VASIMR mode) is 15,000 m/s – meaning a maximum acceleration of ~0.00024 gee or a jet-power of nearly 25 gigawatts.
However a lot more propellant will be needed if the vehicle thrusts all the way at that exhaust velocity, so on a typical trip to Mars a VASIMR steadily builds up the exhaust velocity to a maximum 300 km/s at the half-way point, then a steady decline as the vehicle slows down for Mars arrival.
Often people will say VASIMR can get to Mars in 39 days. They don’t often say what power and fuel that requires. To reach Mars in 39 days also required that particular VASIMR option to aerobrake into orbit around Mars – something not recommended for a large vehicle like “Enterprise”. The required propellant mass would be 230,000 tons, and the power source would mass 48,285 tons, while delivering 96.6 GW of electrical power to the engines. A 90 day mission is far less challenging in technological terms.
[Additional note: time under power over the same distance is related to the power by the 1nverse cube – thus taking 90 days means a power-supply that’s 8% the size of the 39 day trip.]
(2) In many ways the shape of the Enterprise is quite good. The frontal area is low, thus presenting a smaller target for potential meteoric impactors. Handy when going at high speed through our rather junky solar system. The original 1960s design also placed the antimatter reactors on booms as far away from the habitat as possible. The movies, and all later Trek, rather idiotically had the antimatter warp-core in the middle of the secondary hull – not a healthy idea at all. And plasma conduits all over the place… asking for trouble.
There is a major issue not addressed by the TV spaceship creators. Waste heat. Specifically for the Gen-1 “Enterprise” the VASIMR is essentially an externally powered fusion rocket – hydrogen plasma is heated and directed just like in an operating magnetic-mirror fusion reactor. The difference is that there’s no attempt at energising it all the way to fusion conditions. In theory, a VASIMR could be up-graded to be an actual fusion rocket. But without actually making its own fusion power, the VASIMR needs to get power from fission reactors, and they all put out excess heat. There’s only one way to get rid of excess heat in space when it’s not being thrown over-board in the rocket exhaust gases and that’s via radiators.
And the “Enterprise” – Gen1 or the fictional versions – don’t have them. A real “Enterprise” will need a set of “wings” – big radiators – to handle the heat or else the whole lot will cook.
(3) The back-up fuell-cells are a good idea, but for use in space they need an additional supply of oxygen of their own. A MW bank of fuel cells will use a lot of oxygen in a hurry, so you need to have a bank of liquid Oxygen (LOX) tanks to supply it.
(4) Why is the “Enterprise GEN-1” 3 times bigger than the fictional version? The fictional upgraded “USS Enterprise” was just over 300 metres long, yet its proposed namesake is ~950 metres long. I suspect an imperial-to-metric conversion error.
My preliminary, and hopefully friendly, critique. I look forward to dialogue with the concept creator.
