Notes & Queries 3/29/08

by Paul Gilster on March 29, 2008

Did short supplies of oxygen and molybdenum slow down the evolution of animal life? Ancient oceans low on molybdenum would create problems for bacteria that use the element to convert atmospheric nitrogen into a form useful for living things. Brian Wang muses over these matters in his entry in the latest Carnival of Space, referring to a recent Nature paper and moving on to look at potential oceans in the Solar System, from Titan to Callisto, Ganymede, Enceladus, and of course, Europa.

Can life could develop in such places, and if so, how long would it take? Brian frames the question in relation to the Fermi paradox. Perhaps the universe takes a lot longer to evolve complex life than we have been assuming, with implications for what we might find on planets around other stars. We’re shooting in the dark on these questions, unable to say whether life exists off-planet in our own Solar System, but the day may not be so far off when results around nearby planets give us another evolutionary laboratory in which to study biology’s ability to adapt.

Plenty of interesting posts fill this week’s Carnival, but I was particularly taken by Stuart Atkinson’s reflections on Cumbrian Sky, recalling his early fascination with space and reflecting on how we have viewed Mars, and by extension many other astronomical objects, over the past few decades. It’s a long post, filled with reminiscence and reminding us that we can sometimes become all too blasé about the spectacular imagery now flooding the Internet from our space probes. Broadband has changed the landscape. Using his connection and the IAS Viewer available from the HiRISE site, Stuart can see Mars as never before:

“I can go to the HiRISE site, select a picture from the gallery, open it up with the IAS Viewer and literally look down upon single dust-covered boulders, stones and rocks, as if I was being flown over the cratered plains by Peter Pan or Superman.”

Read this post to be reminded of just how remarkable our tools have become, and see if you don’t recognize yourself, as I did, in the space-crazed youth described here.
——-
The Space Access ’08 conference in Phoenix is in its final day, and I notice that bloggers like Henry Cate, Rand Simberg and Clark Lindsey are keeping close watch on events. While the focus is on radically cheaper space transportation, I’ve seen some familiar names from the interstellar community on the agenda, from Gerald Nordley (discussing Tethers Unlimited) to Leik Myrabo, whose work on beamed energy propulsion can translate in the short term into efficient launch systems for Earth orbit, and in the long term into laser propulsion for deep space missions.

LaserMotive‘s Jordin Kare is also presenting, which reminds me of no end of interesting ideas, not the least of which is Kare’s SailBeam, a proposal to send tiny ‘micro-sails’ pushed by laser to drive an interstellar craft. The idea is a form of pellet propulsion of the sort first proposed by Clifford Singer back in 1979 and later developed into Gerald Nordley’s exquisite ‘snowflake’ pellets, using nanotechnology to steer their own course. Kare’s take was to cross pellets with lightsails, with each micro-sail becoming part of the fuel stream for the outbound spacecraft.

Why not a full sail? Kare realized that if you cut a large sail into tiny pieces and accelerate those fragments one after the other, you could bring the same amount of mass up to speed using a much less demanding optical system. The small sails can be accelerated much faster close to their power source, an idea that does away with deployment and maintenance issues in large sailcraft. The interstellar vehicle could use an onboard laser to vaporize the sails into plasma as they approached, deploying a pusher plate or magnetic field to absorb the energy.

Talk about acceleration — Kare’s diamond film sails would accelerate to close to light speed within seconds under an acceleration of thirty million gravities. The study Kare did for NASA’s Institute for Advanced Concepts, called “High-Acceleration Micro-Scale Laser Sails for Interstellar Propulsion,” is still available at the NIAC site even though the Institute is no longer in operation. For more, see this earlier Centauri Dreams post.

What I need to do next, now that Space Access ’08 has taken me so far afield from my earlier posting plans today, is to treat Kare’s interesting ‘fusion runway’ concept, one that would use impact fusion to accelerate a spacecraft to speeds that would make an interstellar journey possible. But I’m low on time, so we’ll get to that one down the road. How can I not discuss a propulsion system its designer refers to as the ‘Bussard Buzz Bomb?’ I’ll explain the origins of that name in the upcoming article.

dad2059 March 29, 2008 at 16:12

Talk about acceleration — Kare’s diamond film sails would accelerate to close to light speed within seconds under an acceleration of thirty million gravities…

Well, there’ll be negligible mass, enough to propel nanoprobes.

IMHO, any talk of interstellar exploration has to include nanotechnology.

Administrator March 29, 2008 at 17:03

dad2059, you’re exactly right in my estimation. Nanotechnology looms ever larger, as it were, as we look at potential mission concepts. Pushing a tiny probe laden with assembler technology — one that can build a scientific observatory around a distant star using local materials — seems to make great sense. Push as little mass as possible!

James M. Essig March 29, 2008 at 19:01

Hi Folks;

Imagine diamond fiber or carbon nanotube solar sails that have threads on the order of 0.5 to 1.0 nanometers wide and thick wherein the threads form a weave which has fibers spaced on the order of 0.1 micrometer to 1 micrometer apart to form a reflective sheet 0.5 to 1.0 nanometers thick that is as much as 99.95 percent empty space.

If a dive and fry manned space craft could pass somehow within 0.01 AU of the Sun and somehow deploy this sail all at once, the craft could excellerate to near C before it reached 1 AU providing the mass of the sail was about 1/2 an order of magnitude or more greater than that of the space craft itself. A 1,000 metric ton sail as such would have an area of approximately 10 EXP 15 square meters or the equivalent of 30,000 kn by 30,000 km. Now the sail would obviously have to be very reflective and be able to withstand a blackbody integrated spectral radiancy of that of a 5,800 K surface subtending a spherical angle of dual axial extent of roughly 90 degrees. I honestly think that all current forms of diamond, carbon nanotubes, even with those of high reflectivity would vaporize in an instant in this environment, but if future suitable material could be developed, that would be awesome.

Now imagine some unheard of, simmilarly low density, low mass per unit area, mesh sail could be developed to withstand the integrated spectral radiancy of an object with a surface temperature of say 75,000 K such as a high end temperature range Blue Supergiant star, upon a simmilar dive and fry manuever, the space craft could reach a location of about 10,000 AU from
such a star at which its gamma factor would be higher than the maximum of that which the protons will have in the LHC as it goes back on line this May.

Know we just need a way to deal with the billions of Gs that such space craft would experience with such Blue Supergiant sails without resulting in the shreading of the sails. especially their craft attachement mechanisms, and the integrety of the craft and its contents.

Thanks;

Jim

Adam March 30, 2008 at 2:06

Hi James

A gamma-factor of 14,000 in 10,000 AU? I don’t know as the drag from the star’s stellar wind would be incredible if speeds got too high. I’m not sure it’s feasible. Can you provide us with some figures?

Adam March 30, 2008 at 2:18

BTW James I’m not sure what an acceleration of 1 trillion gees (around the supergiant at 75,000 K) would do to the nanotubes. Ouch! And the case around the Sun has an initial acceleration of ~ 8.4 million gees – no way that’s manned. I’m not sure what the areal density of a sheet of pure graphene would be exactly, but I suspect it will be hundreds of times heavier than the 1,000 metric tons spread over 1.0E+15 sq.m you quote.

Sail-beams, anyone?

devicerandom March 30, 2008 at 6:16

Thirty million g? Do we need such an acceleration? What kind of complex object can sustain such an acceleration?

Administrator March 30, 2008 at 7:50

devicerandom, the 30 million g’s Kare is talking about would be applied to micro-sails — they’re essentially just being used as fuel for a departing spacecraft, vaporized upon arrival, and hence not complex objects. I’ll agree that the thought of 30 million g applied to anything gives one pause!

James M. Essig March 30, 2008 at 8:52

Hi Adam, devicerandom, and Paul;

Adam;

Thanks for asking for the numbers.

Paul;

I hope this post is not too long.

I was not sure how to more precisely convey the extreme accellerations possible, although I must admit the material science required is far beyond ours and likely even far beyond alteast virtually all ETI civilizations. However, if in the future, the materials science wizards come up with super strong, super refractive materials, with the right properties, here is the math not taken into account of solar wind drag which of course would be a strong gamma factor midigator.

Assuming a sail material density on the order of water at STP, a one metric ton sail could have an area of (10 EXP 3)(10 EXP 9) square meters or 10 EXP 12 square meters. A sail with a mass of 1,000 metric tons could have a mass of 10 EXP 15 square meters or an area 31,000 kilometers by 31,000 kilometers.

The force exerted by electromagnetic radiation on a surface is P/C or where P is total incident power and C is the speed of light. Radiation Pressure at Earth’s surface is 1370/c = (4.57 X 10 EXP-6) N/m2 in MKS units. Thus, at one A.U. from the Sun, the radiation pressure on a 10 EXP 15 square meter sail would be (4.57 X 10 EXP 9) Newtons or about 457.000 Tons of force to yield an accelleration of 457 Gs on the solar sail. If the mass of the space craft was assummed to be twice that of the sail, the accelleration would be about 228.5 Gs. For a solar sail dive and fry manuever where the sail craft would somehow dive to within 0.01 AU from the Sun, thereupon deploying the sail, the accelleration would be a whopping 2,285,000 Gs. At 0.1 AU, the accelleration would still be a whopping 22,850 Gs. As can be seen, the accelleration falls off as the inverse square of the distance of the craft from the sun for a constant area sail. Even at about 4.75 AU the craft would still have an accelleration of about 10 G. At 100 AU the craft would have an accelleration of 0.02285 G. If one integrates the total force applied to the craft over a distance traveled out to 100 AU. Thus, one can clearly see that the space craft would exit the solar system with relativistic velocites.

The space craft could be sent on trajectory to perform a dive and fry manuevure around a blue supergiant star with a surface temperature 10 times greater than that of the Sun or 10 x (5800 K) = 58,000 K. For a distance from the blue supergiant at which the spherical angle of the blue supergiant subtended with respect to the craft at minimum approach would be equaivalent to the same angle for a craft located at 0.01 AU from the Sun and given the same area specific mass for the sail, the radiation pressure would be 10,000 times as great thus yielding an accelleration at this location with respect to the blue supergiant of 22,,850,000,000 Gs. The craft could reach a gamma factor of about 2 or 0.86 C in roughly 1 millisecond! In about 0.1 second, the craft could reach a gamma factor of roughly about 10 taken into account relativistic dopplar redshift losses. The craft could no doubt leave the vacinity of the star with extremely relativistic velocities. The factor of the 10,000 fold increase in optical pressure for the case of the blue super giant is based on the T EXP 4 dependence of radiated power per unit area for temperature T.

Now comes the hard part. I think even the most advanced ETI technologies would be extremely inadequate to produce materials that can withstand these accellerations such as sail tethers and space craft.

Anybody up for using Quazars in a dive and fry manuever!

Best Regards;

Jim

david March 30, 2008 at 10:25

—————
we just need a way to deal with the billions of Gs that such space craft would experience with such Blue Supergiant sails
—————

I know very little about physics or math but is it possible for any material to survive such forces? Wouldn’t the material just vaporize, or even be crushed down into a mini blackhole that would immediately evaporate?

Micro-sails that are accelerated to even just 1 percent of light speed would be sufficient for driving a payload within the solar system, or even to the sun’s gravitational lens. Developing such a system would be good practice for building systems capable of sending payloads to another star. For such a system you would only need to keep the acceleration up for 0.1 seconds, or for a distance of 150km. You could use radio instead of light for the acceleration maybe. Or even maybe just give it a charge and use magnetic forces. A particle accelerate 150km in length.

Stu March 30, 2008 at 12:54

Thanks for your very kind words about my Mars post! Much appreciated! :-)

Stu

James M. Essig March 30, 2008 at 14:34

Hi David;

Thanks for the critical review of my previous posting. In short, there is no material in existence today that can with stand temperatures of 58,000 K without being vaporized. If the Earth was located much further away from the Sun than it is now, if the sun was even a low end mass supernova capable star, even at a great distance from the exploding star commensurate with the Earth being placed in the greatly cooled plasma of the supernova explosion, say at a greatly cooled temperature of 58,000 K, the thermal energy from the pulse would result in the ablative vaporization of the entire Earth starting with the Earths crust at a inward ablative vaporization rate of hundreds of meters per second. Note that silica rock has an even higher energy of vaporization than even the best hardened steels.

I know of absolutely no large craft that could ever come close to handling even a million Gs let alone 200 billion Gs. However, a good example of a macroscopic object that can handle 100,000 Gs that is big enough for us to see, touch, and handle in our hand is that of a high velocity sniper rifle bullet. Assuming the round reaches a muzzle velocity of about 1,500 meters/sec and thus travels down the length of the barrel on an interval of the order of one millisecond, it excellerates to 1,000 meters/sec in about one millisecond from a stationary state. This corresponds to about 1,000,000 meters/(sec exp 2) or about 100,000 Gs.

Now take among our biggest and baddest U.S. Navy ships such as modern nuclear powered aircraft carriers. If such a ship where to suddenly experience just 1 G of decelleration, it would likely be buckled and sink as if it ran into an huge iceburg at 20 knots. Rest assure that these ships are made as strong as they can reasonably and economically be designed and assembled.

In short, you make one heck of a good point about space craft not being able to do millions if not billions of Gs. But given billions or trillions of years in materials science developments, maybe something like this could be accomplished, but like you, I won’t hold my breath.

Thanks;

Jim

James M. Essig March 31, 2008 at 0:28

Hi Folks;

This is shaping up to be a popular thread with ten comments posted already.

The possibility, however improbable, of using a quazar as a electromagnetic energy source for a dive and fry space craft intrigues me as an ultimate example of the dive and fry type of manuever. I will not get into the specific numbers based on crude overly simplified propulsion models, however, when one realizes that a quazar can outshine a galaxy by perhaps as much as 1,000 fold, the potential of harnessing these energy sources in the distant future for intergalactic sailing ships (which ironically sounds like an oxymoron) seems to hold some promise in the far distant future.

Quazars are now known to be supermassive blackhole accretion disks which can extent outward of the blackholes for hundreds of lightyears thus providing a very long path for continuous outstandingly high G level accelleration assumming the craft and its sail can be made of material to handle the accelleration and extreme G force loading as well as the extreme temperatures within the blackhole accretion disks or within several radii of the accretion disk.

Obviously, there would be the issue of ionizing electromagnetic radiation produced within the superhot accretion disk plasma which would contain copious photon densities within the x-ray spectrum.

Hey, now there’s a good massive R&D project we could teem up with ETI space programs in the comming billions of years.

By the way, the possibility of one day making contact with ETI bodily lifeforms and sharing a lab space with them intregues me. To bad I will probably not live to see such happen but its a fun kind of thought anyhow.

Thanks;

Jim

Adam March 31, 2008 at 7:27

Hi David

The Large Hadron Collider will collide nucleii and maybe make them into black-holes – the dynamic pressure involved in those collisions is roughly a hundred thousand trillion trillion Newtons per square metre, many trillions of times what the solar-sail would experience. So it wouldn’t become a black-hole.

Would it vapourise? I think James is imagining very, very reflective material, so it might glow white-hot, but not vapourise. Very highly efficient reflective materials can be made for very specific frequency ranges of light, so what James imagines might be possible – though I don’t think it will be as light-weight as he hopes.

Jordin Kare’s micro-sails use transmittance to avoid over-heating – the material reflects some light, lets almost all the rest pass through it, and absorbs a very small amount. This might also work for the solar-sails James is imagining.

Finally, to work out the final velocity of a solar-sail roughly, all you need is the ratio of the radiation force to the force of gravity on the sail. The final velocity is the square root of that ratio times the escape velocity at that distance from the star. It’s a bit trickier for relativistic speeds, but James can probably figure that out himself.

Comments on this entry are closed.