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I never heard of a 'hypersonic tether assisted launch," although I endorse orbital-transfer tether assists, and orbit-to-escape velocity tethered launch schemes--which take place entirely in space--but "hypersonic" means atmosphere to me. Could you explain please?
Yes...and all that sunburn! But seriously, light sails gain you easy access to the volume of space above and below the plane of the ecliptic. Think of all that solar energy "going to waste" out there. Tempting maybe, as a new topic of discussion?
You mean: "We have met the aliens, and they are us?"
wouldnt this system lose effectiveness tremendously as the distance from the sun increases?
Yes, but out to distance of the asteroid belt, in a sphere surrounding the Sun, it should serve the purpose until other means not yet achievable are developed. My purpose is to attempt the do-able as soon as possible!
I say: stick with the U.N.
As long as the authorized inspection teams are free to come and go in Irak, allowed access wherever and whenever they want, able to follow-up any lead, substitute U.N. personnel at will...the situation will be containable. Healthcare and medical supplies dispensation inspection should be added to the weapons inspection, as a further condition of acceptance by the U.N.
If, and, or when, any unannounced inspection is resisted misdirected, prevented, hostages taken, whatever...the Security Council will have retained the final option of collective action, including invasion (as in the Balkans), and S.H., et al, placed on trial, as S.M. is now.
In the long run, the U.S. will have demonstrated by example that might does not mean right to unilateral actions; by avoiding unilateral military actions, preserved innocent lives; and by supporting collective U.N. actions and on-going efforts towards eliminating the despot-created conditions throughout the world that encourage international terrorism, eliminate this growing threat.
Light Sailing:
A Powered Light-sail, in the form of a gigantic "parachute," with tension lines attached to the metalized sail canopy at many points in a grid pattern which maintains the paraboloidal shape, such that the reflected sunlight will be reflected to a blackbody coated surface situated at the parabolic focus which covers the spacecraft, and from which the grid pattern of tension lines radiate, parachute-wise.
The heat resulting from the concentrated sunlight can (a) melt water-ice fueling a throttleable flash steam jet (b) generate thermal-electric current for an ion jet modirected sunwards. Payloads would be located outboard of the jet power assembly.
The sail and tension lines (according to recent internet disclosures) will comprise only a small percentage of the all-up mass of the "ship," to make the limiting light-powered acceleration as high as possible. Deformation of the canopy, when the jet-powered payload acceleration exceeds the limit will tend to de-focus the sunlight, thereby decreasing payload acceleration until its drag restores the parabolic shape, which re-focuses the sunlight, and so on.
Minimal steering capability would be possible by means of collectively programmed reeling-in or -out of the tension lines where they emerge surrounding the heat collector.
A bonus will be the ability of the huge canopy to receive and transmit microwave data.
Anyway, assuming this configuration of "powered light-sail" rig is practical, any number of relatively simple and reliable probes could be sent off, in any direction in-or-out of the ecliptic, chasing comets, etc.
Economical cargo transport out to Mars-space naturally comes to mind, as another application....
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I do not think there are things we can't know, given time to figure them out. Our lifetimes are so short, by the time we settle down to thinking for real, it's over. Imagine double or triple your lifetime, the last half devoted to figuring out stuff. Our minds are really something!
AltToWar: Nice try, appreciate the attempt to explain photons exerting force, but I wish you hadn't brought "magic" into it. But, don't delete for a while, I haven't print capability at this terminal...will get back to you when I've upgraded my physics theory regarding magic (oops, sorry, just kidding). I think you're a good sport, and besides, light (my preferred term) sails work. When I have a gut feeling about it, I'll be back to describe how I got it.
Soph: t
That's easy. It's because there is no roling friction to slow 'em down in space.
Shaun:
Incredible indeed. But before I delve into what I shall call "pre-relativity" where c is not the limiting velocity, why don't cosmology references mention inflation within the context of the Big Bang theory, expecially prior to distance-is-proportional-to-the-past? I'll get back to you, but I wish to describe a light-sailing rig your earlier post got me thinking about (see Interplanetary Transportation).
AlToWar (that's hard to type):
I'll respond point for point, not to act smart, but to try and get you to explain further.
A photon has no mass, period.
0 speed has no meaning in relativity.
None-mass-less objects is a cute term. But what's your point?
By angular momentum, is that due to spin? (Pls see below)
Reflected (not deflected) and/or absorbed?
Transfering angular momentum from a mass-less spinning(?) object would seem to be a contradiction in terms...but this may be where my hangup lies. Could you be more descriptive, please?
Photons diverted (not deflected) by gravity fields, and what kinds of particles (by reflection).
Space isn't empty, but it sure is transparent to lots of the electromagnetic "photons" including photons of light. My hangup is about "traveling for billions of years" (to us) taking "no time" (to photons) because of what you didn't mention in the first place, time shrinking to zero at light-speed.
If you could expound further on the "mass-less angular momentum transfer of photon energy to impart force to an opaque object...." And come to think of it, even frequency- or energy-wise according to whether it's infrared, visible, X-ray...since the material we use may want to be selectively transparent or opaque according to need. Great stuff!
Soph. Regarding gravity, my gut feeling is based upon the two dimensional, rubber membrane analogue which dimples to depths proportional to the mass of objects placed on it. Attraction by larger objects for smaller ones depends upon distance, along a line between, with no vectoring capability.
What I desire is more along the quantum line of thinking. I'm still getting over the shock of learning that the solar wind isn't the basis of "solar sailing," which could have been avoided by using the term "light sailing" in the first place. And then, when the "plasma sail" was described as capable of using the solar wind, but without vectoring being possible....
Thanks for your response. Hope this topic of "hangups" leads to others coming out of the gut-feeling-fix closet.
Thanks, Shaun. I shall dig into the sources you mention. I never, ever even heard of "inflation theory" wrt the Big Bang aftermath. You'd think they would at least mention it in the texts that devote so much space on the "looking back into time" theme! Any suggestion(s) as to source for hangup No 3? If not, thanks again for the time spent on Nos 1 and 2.
Some aspects of astronomy and cosmology just don't seem comprehensible to me, in spite of the knowledge obtained from available textbooks and journals. I mean gut-wise, not analytically as presented and proved mathematically. Here are a few "astronomy hangups" of mine, which I need help with.
Photons (1): Electromagnetic spectral "quanta" having no mass, capable of impinging physical mass at the "speed of light" to impart momentum. I know they do so on light sails, but isn't there a gut explaination as to how massless quanta exert force on inertial mass?
Photons (2): Emitted by luminous objects in space, they are capable of forming images on sensititive (CCD) arrays without distortion from any distance, in spite of having taken up to billions of years to arrive in the case of most distant observable objects. My gut interpretation of this is that, since they propagate at the "speed of light," to a photon regardless of frequency (energy), distance has no meaning and therefore no time exists for distortions to intervene. But I can't find anything in the literature that deals with astronomical image sharpness in terms of the medium (photons).
Photons (3): Images received of astronomical objects represent them at the instant of photon emission. Objects at distances requiring enough billions of years, at the "speed of light," for their emissions to arrive representing them less than a billion years (say) after the Big Bang...would seem to require the universe to have expanded faster initially than the speed at which the image propagated. I suspect that relativistic effects must be involved, but nothing I've read gives me the gut understanding of what's really happening.
Are there any other members with such hangups out there...and other, enlightened ones, able and willing to clear them up?
Try playing "what if" for a moment: What if the U.S. didn't have the military capability it has, to invade another nation (any nation) on its own initiative, with at least short-term impunity...wouldn't the U.N. be the only recourse, and by supporting it wouldn't the U.S. (and the world) be better off in the long run? Just because you have the power to do so shouldn't give you the right to use it willy-nilly. The world deserves and expects better from the "bastion of democracy."
I wonder if the obvious isn't being overlooked: a Segway-type stabilized literal pogostick!
Place doesn't have to be desolate, just settled and populated. By that time, nuclear ion-thrusters should be the norm, so time between planets, or whatever, tolerable.
Shaun: Anti/nul/shielded gravity schemes are so far fetched (to be generous) that even the most far-out physics don't contemplate the possibility. human-scale. The problem of routine access to LEO is urgently in need of do-able ideas before our ability to support a Mars program has past...makes me impatient with blue-sky dreams proposed as far back as H.G. Wells's "First Men in the Moon."
Nirgal: That machine needs power 100% of the time, or it falls out of the air. Of course, if you and Shaun....
Shame on me!
How about sleeping "upright" in a 20-foot (say) diameter electric motor driven centrifuge, powered from stationary bicycle generators pumped in tadem by the awake crew?
Shaun, I never considered returning...I thought the whole idea was to get out there as cheaply and soon as possible, to do stuff, in the case of Jupiter-space, with robot devices. But beyond Mars-space, "asteroid miners" of the human variety may want to return from time to time. In that case, I assume solar sails would permit retro-orbital vectoring until they dropped directly sunward to the distance desired, and then vector into orbit again. I'm pretty sure, the advent of high efficiency, nuclear-powered ion thrusters will put solar sailors out of business (except sport) just as steam did the tall ships. (I read that somewhere, it sounds like Clarke in fact.) But, solar-wind driven craft are being suggested as the initial stellar probes, for the very reasons you brought up. Great to hobnob with you!
Shaun: I just got interested enough to read your original offering...but your "six months" were up long ago. Shouldn't you delete the damn thing, and get back to serious proposals?
Solar (light) sailing: Forget the yacht analogy, which tacks by means of aerodynamic horizontal "lift" to sail windward. Solar sailing would use vectored photon thrust, either to accelerate orbital velocity to retreat from, or decelerate orbital velocity to approach, the Sun or whatever is being orbited. Of course, sailing with the Sun at your back would accelerate you away from the Sun faster than vectoring, and would permit "loitering" at any distance without orbiting the Sun, while eg. waiting for your destination of choice to arrive in your space. (Matching velocities and going into orbit arout it would be as difficult as navigating a tall ship into harbour without a tug, but isn't that what sailing skippers are for?) Sailing out of the plane of the ecliptic would be another great use for Solar sailing.
Solar (wind) sailing: The disadvantage of decreasing photon pressure with increasing distance from the Sun may not be too bad out to the Asteroid Belt. And I have read that the solar wind possibly can be used, instead of light pressure, by magnetizing the spacecraft and injecting hydrogen ions into the field, against which the solar-wind particles would impinge. I don't know if vector sailing would be possible, since the "surface" of the resulting ion bubble would resemble a cloud. But, the bubble apparently would expand with distance from the Sun in exact proportion with the decrease in Solar wind density, maintaining thrust constant to the outer planets. Pretty convenient, eh?
Researchers in Australia are currently testing a new type of wind turbine. Heres how it works: The device consists of a long tether; anchored to the ground, a helicopter-like turbine, and a small generator. It is launched by feeding power to the small generator, which doubles as a motor. The motor turns the turbine, which helicopters into the atmosphere. Once the tether is taught, and the turbine is at its highest altitude, the motor is turned off and is now kept aloft only by the continual pressure of the jet stream. The turbine is spun by the jet stream, and the power produced is sent back down the tether.
My question is whether or not mars has jet streams. Jet streams are often one-hundred times the speed of surface winds, and are therefore a much better source of wind power.
My only thought is, in Australia this should be considered a monumental hazard to air navigation!
And...and...Mars's surface is the same as Earth's land mass. Come to think of it, the Moon's gravity is one/half that of Mars--does that mean anything? I wish Earth had mountains that stuck as far out of our atmosphere as Mars mountains do, though, for acceleration-to-LEO rails to lean on. I can't think of anything about Venus along these lines, except maybe: it sure is nice that Earth didn't turn out to be like that! Funny about mushrooms, by the way, which consume oxygen and produce carbon dioxide--just the reverse of edible green plants: since both are edible doesn't this suggest a self-sustaining symbiotic relationship unnecessary to be attended by oxygen breathing humans? Oh, and isn't it great that all that water-ice that's suppose to be present on Mars is detectable from LMO, and doesn't have to be located by well drilliing! But, isn't it rotten, that Mars is so far away. and that I won't live to see it all happen. And finally--It sure was swell of someone to have thought up The Mars Society for me to take out all my frustration on. Thanks!
Cindy? Re. human{s) on Mars. Think of Mt. Everest, over a century ago. Just to get to the foothills took a year, what with the provisioning treks and acclimatization (assume no Sherpas already acclimated and able to help)...equivalent to getting to low Mars orbit, and perhaps "docked" to Phobos.
Now you crew-of-three (say) have a number of landers of various types, equipped with rovers with various mobilities (crawlers, aerostats, power gliders) all equipped for remote presence manipulation in realtime by any and/or all of you in concert, some with ability to take samples where your remote viewing from orbit via radar, hydrogen, visible/infrared daytime and nighttime scans indicate subsurface water-ice (say), and delivery to LMO-return launcher(s) for receipt by you, for initial analysis and consultations with Earth scientist, followed by repeats...until you are due for return trip back to Earth orbit, LEO, and docking to ISS isolation facility.
Now your equivalent of the Everest attack team, the second Mars expedition, have what they need to know and can be equipped to land, do what they have to do, leave resources for the third (colonization) expedition to build upon.
That shouldn't take more than six-to-ten Earth years to accomplish, and each trip an adventure. I woudn't mind going on a first trip without landing myself, if I had all those tools along for performing the initial exploration by means of remote presence, even to the extent of tactile sensing. The same vehicle(s) but with different payloads could be assembled in LEO, between trips. Imagine all the neat stuff you could carry if you didn't plan to land the first time out. Or is that too conservative for you? I never like to "go for broke" and fail, because it tends to turn people off who might otherwise provide long-term support....
As for wind-generated electrical power: Vertical wind-tunnels using Martian atmosphere in stretches of unpressurized canyon tributaries, with multistage turbo-electric generators within their bases, driven by the flow of Martian "air" warmed beneath low transparent roofs, with guy-wires from high canyon sides to prevent the kilometre-high "chimneys" from falling over.
With enough area roofed, the accumulated warmth could be made sufficient to supply electricity even during nighttime. East-west canyon alignment would of course be advisable for maximum solar exposure time, and trickle-charged battery and/or fuel cell alternatives (during duststorms) provided for.
(Updated 14 December 2002.)
Crawling Rovers: Has anyone of you not seen the multilegged insect-like like robots being shown on TV? They just seem to "flow" over obstacles. I would think them ideal, in principle, for unmanned Mars surface surveys--scaled-up to cope with the size of rocks strewn about in the terrain we have been shown so far. Being squat, they couldn't be tipped over, or toppled into gullies or from cliffs...if programmed to hesitate with their trailing-segment legs gripping surfaces already traversed by their leading-segment legs--until images of what had been encountered was transmitted (via whatever intermediate mother-vehicle to Earth) and interpretated by the remote-presence operator.
Watching these things move on TV--their top "scuttling" speeds are really prodigious--has pretty well convinced me that wheels will never match the match the advantages of "centipedal" propulsion, for Earth-based remote presence rover missions.
The current generic term adopted for these things is "Polypedal Robots." (Any suggestions for something more catchy?) They are being adapted from actual insects at the University of California at Berkely's PolyPEDAL Laboratory, by Professor Bob Full and a team of graduate students.
I invisage centipede-like rovers with segmented bodies--four or six legs per segment--with three or more per rover; individually powered by batteries allied with solar cells; remotely attachable and detachable for (a) maintenance replacement or (b) changing mid-mission demands requiring add-on manipulators, drills, tote-buckets and /or sensors; and interconnected wirelessly via digital FM radio (to avoid connectors) such that control can shifted end-for-end or to any segment between.
I hope this suggestion may stimulate a discussion about the pros and cons of unmanned crawler-type rovers. (For more background, search: "Polypedal Robots.")
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