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I think you could do a solar VASIMR, but I'd bet it ends up about as heavy as a nuclear source VASIMR, by the time one builds arrays to generate power in the dimmer sun out near Mars. It gets worse the further you go from the sun.
I don't see chemical VASIMR as a viable option. You burn the same propellants either way, why not get the 99% thermal efficiency of a high-thrust chemical rocket engine instead of the Carnot efficiency (in the 30-40% range) of an electric power plant, and for low thrust that increases the delta-vee required?
I was hoping VASIMR might be a breakthrough in terms of thrust for the power, but it is not. It is instead just a very practical arrangement to build an electric thruster. It will have about the same propulsive characteristics as are typically calculated for any of the electric items.
What VASIMR and the other electrics need is a high-power power supply that is lightweight. That's the needed breakthrough. Hasn't happened yet, to my knowledge.
GW
Hi Russell:
I'm using a variant of the old early-1950's scale-height approximation warhead entry model, which is a 2-D Cartesian thing. I corrected the convective heat transfer part, the dynamics were OK as they were. Gees and velocity vs range-or-altitude look good. I do it as slant range plots. There is no radiation heat transfer model, so a rule of thumb might be to triple the calculated convective loads.
Real warheads follow a curved path during entry, it is true, but the Earth curves away beneath them, too. So, as it turns out, the flight path angle at entry and the flight path at M3 are pretty close to equal. That's why the stupid oversimplified model works so well anyway.
It's only good for what it was intended, entry from low orbit or fractional-orbit trajectories. But it sure is easy to do on a spreadsheet. One needs a better model for aerobraking and other sophisticated stuff like that.
GW
Louis:
In my modeling, with entry from low Mars orbit, the delta-vee for a transfer ellipse from 200 km to the surface was only 50 m/s. That's attitude thruster system work. You don't need a big stage to do this.
If you did aero-braking of some kind from some more energetic orbit, I think what you want to end up with is "about circular" at "about 200 km". Justus & Braun claim the entry interface altitude for Mars is 135 km. So, you cannot orbit that low. I see some others using 300 km, but I do not see anything to prevent mission success when using "a few months" at 200 km circular. Pick an inclination. Cover a lot of Mars's surface. Do multiple landings in a single mission.
Elliptical orbits lead to steeper entry angles, which means lower altitudes at local Mach 3, for any given ballistic coefficient. That's bad, as near as I can tell. You do need sufficient time and path length to rocket-brake to something survivable for landing. There is a human limitation to how fast this can happen.
The model I have is for entry from low altitudes at low speeds, and it "models" as constant path angle in 2-D Cartesian coordinates. This sort of thing worked pretty well for warheads in the 1950's and early 1960's. It is not extrapolatable to other entry conditions. So, don't ask.
As for post-local-Mach-3 braking, I analyzed it as vacuum-trajectory stuff, which is a small over-estimate of required rocket impulse, since the drag numbers are so low compared to practical landing masses for manned (or big cargo) missions on Mars. Plus drag coefficient gets cut roughly by factor 2 when you use retro thrust during the supersonics.
All this stuff is posted over at "exrocketman": http://exrocketman.blogspot.com for a nominal 60 metric ton manned lander with a crew of 3. Or an unmanned cargo lander with a very large payload fraction-to-ignition weight. Same basic hardware works on the moon or Mercury. Nothing more than MMH-NTO storable chemical propellants. Not reusable, though. Real reusability comes from a variant of NERVA for the lander engine.
GW
In my crude model, if you enter at 1.6 degrees depressed below horizontal, you "terminate" at M3 and near 1.6 degrees below horizontal. That might not be "right" but it's close to true. Point is, with a shallow entry, you come out of hypersonics moving a lot closer to horizontal than vertical. You do not have to slow from 0.7 km/s to zero in only 5 km altitude-as-path-length. You have a whopping lot more path length available to slow down. I was using under 1 gee for my calculations.
GW
OK, my post 11-26-12 above was based on a science news story I saw on the internet. Since then, I have run across the source for it: a “perspective” article by Alan Simmons of U. Nevada, published in the 16 November 2012 issue of AAAS’s peer-reviewed journal “Science”. That would be volume 338, page 895.
The article indicates geologic dates for paleolithic-technology stone artifacts based on soil context of around 170,000 years on Crete, and around 110,000 years on the southern Ionian islands, in the Aegean Sea. At those times, neither location was connected to the mainland, and both were well out of sight of land, as viewed from the mainland. (This is well before the peak glaciation of the last ice age, which started around 100,000 years ago, and peaked around 20,000 years ago.)
The article does make the point that these conclusions are still not accepted. There is much work to do before the community will accept this result. But those dates do correspond to paleolithic technology stone tools found in those places. There was a second set of “old” stuff found that dated to about 12,000 years ago, which was definitely neolithic stuff (usually associated with species homo sapiens), and a third set neolithic stuff dating to around just before the time of the Mycenaens (about 9000 years ago). That’s 3 different occupations of these sites that are older than what was believed before.
The problem with the paleolithic stone artifacts is that they definitely pre-date homo sapiens in those locations. They may possibly pre-date homo neanderthalensis, since we think Neanderthals got their start around 100,000 years ago in the middle east and Europe. But nothing is proven. Whatever species it was, it does indicate that seafaring was possible then, and this does agree with early non-modern-human seafarers reaching Australia and the Flores Island region of Indonesia. That is truly remarkable.
Other things I have read in these refereed journals indicate the earliest seafarers to reach Australia and Flores Island were homo erectus, somewhere in the neighborhood of 50,000 to 100,000 years ago, at least, perhaps far earlier. Who knows?
We are quite literally talking people capable of building sailing boats and navigating well out of sight of land, perhaps as early as a million years ago. They may not have looked so very much like us, but they certainly seemed to have behaved like us, and a very long time ago at that.
That’s why I think basic human cognitive abilities have been relatively unchanged for a very long time.
GW
On Mars there are problems with solar flare radiation, cosmic ray radiation, and very harsh UV in direct sunlight. That suggests the greenhouse should have an opaque roof and transparent walls. The roof could be a few feet of regolith, which provides the radiation shield. Using scattered and surface-reflected sunlight would cut down the harshness of the UV to something tolerable by Earth plants and the people who tend them. And you won't need some exotic transparency material to filter out the excess UV. Being in a shallow crater or other depression will increase the surface-reflected sunlight.
Round is better as a pressure vessel, so you are probably looking at clear-wall cylinders, but with plain flat roofs ballasted against the air pressure inside by thick regolith cover. Put your solar thermal and PV panels up there. They'll look more like artificial button-stage mushrooms than the classic domes of science fiction. You'll need some arches inside to hold it all up until you pressurize. I'd leave them there. Use more ballast than you need to counter the air pressure. Safer that way, in the event of an overpressurization accident.
The atmosphere inside will have to be more than just compressed Mars CO2, for Earth crops. There will have to be some oxygen and water vapor content, and possibly a diluent for the CO2. I dunno the details, I am not a biologist. But I do know our plants here are adapted to our air, in which CO2 is a trace, not a major component. I have heard of experiments with higher CO2 concentrations, and I seem to remember that too much CO2 had bad effects. So, I rather suspect the air inside these greenhouses on Mars will resemble Earth air more strongly that Mars air, although the pressure might be much lower than here, and the CO2 percentage much higher.
Just educated guesses on my part. Nothing more.
GW
Myself, I'm less worried about methane detection-or-not, and more worried about the fossilized presence of organic compounds in some of the obviously-water-deposited mudstones and conglomerates. Surface samples probably have had the organics destroyed by the harsh environment, but subsurface samples could yield results, especially those not just buried by transient dust. They gotta dig in the right places. That's why they picked Gale Crater. It'll take a while.
The recent "noise" in the news about something "for the history books", with the subsequent downplaying, sounds like another Allan Hills meteorite microbe fossil thing. I'd bet they found something, maybe some organics, but haven't been able to confirm it yet at an incontrovertible level of proof. So, rather than repeat the debacle they went through over the meteor fossil incident, the managers have quashed the initial enthusiasm that leaked out from the actual researchers. But, they did find something. It will be very interesting to hear what it really is.
BTW, I still think the traces in the Allan Hills meteorite might well have been microbe fossils. I thought those two NASA researchers were badly treated by the science establishment back then.
If Curiosity did find organics, and they can duplicate and prove it, then we may have to revise our history books regarding the Viking results. I rather doubt Viking actually found life that close to the surface. Probably just organics in some kind of an activated chemical state, made so by the harsh environment. But it would not surprise me to learn someday that there really is active microbial life deeper underground. It would be a remnant from much earlier times when the climate was better on Mars, and microbial life was all over the surface, leaving fossil organic traces everywhere.
GW
For landing big items on Mars, I like entry from low orbit better than direct entry or entry from a high orbit. This is because the entry angle is enforced to be very shallow and the speed at interface minimum, with no risk of ricochet off into space. Shallow entry angle and minimal interface speed lets the hypersonics slow you down to around local Mach 3 at altitudes you can cope with, even at truly enormous ballistic coefficients. Up around 1000 kg/sq.m. Entry speeds that way are around 3.5 km/sec. The local M3 speed is around 0.7 km/sec.
For the numbers I have been running, I get a Mach 3 terminal altitude (at a very shallow flight path angle) in the neighborhood of 5 km for craft massing 60 metric tons. That's too low for a chute or ballute (or any other aero decelerator) to work, but it is low enough for simple rocket braking to be quite practical. All that is needed is supersonic retro thrust. NASA looked at this in the wind tunnel about 1960, but has since forgotten all about those results. It's an ancient NASA TN cited in Hoerner's old "drag bible" ca. 1965, which shows the data. Retro thrust reduces supersonic drag coefficient by about half. So, plan your retro thrust as if you were landing in vacuum, and you'll have a small kitty of extra emergency propellant. Which is the smart thing to do, anyway.
There is a plume stability issue: an axial retro plume does not "know" which way to bend when it reverses into the slipstream. So it flip-flops around. That induces side forces and moments that could tumble the craft out of control. The "fix" is multiple thrust nozzles, each canted a bit off-axis. It will be stable because each plume "knows" which way to bend. We've already seen this with the thrusters on shuttle, the X-15, and a few SR-71's so equipped. We're about to see it again when Spacex puts the big Super-Draco thrusters on their Dragon capsule.
In short, there's no technical reason this cannot be done. It ought to be tried in the next unmanned Mars probe lander, before we commit to landing men with it. That would be the smart way to do it, but it requires breaking with traditional practices. Tradition dies hard. Landing big things on Mars is not nearly as hard as been recently ballyhooed. But it does require doing something different than the same aeroshell and chute family we have used since Viking.
As for the cradle idea, what do you do about crew bailout if there is an ascent or descent failure? The separable crew capsule idea can be made to handle that as a one-shot "ejection-seat" item. Just a question, not a claim that it cannot be done. I have never before considered hypersonic bailout in nothing but a suit. I dunno whether it can be made to work or not, here or Mars. The Baumgartner jump recently does suggest there might be hope.
GW
What got me started was the problem of extreme low vehicle thrust/weight (acceleration) that seems to be inherent with VASIMR and all the other electric propulsion devices. When you include the power supply for a very long "burn", the engine system T/W seems to be a very tiny number: N's of thrust vs tons of equipment. You never get to climb out of a gravity well rapidly that way, so mission delta-vees get increased, since you have what amounts to a huge gravity loss term.
For cargo-only, long transit times are no real problem, but they certainly are with men. Either you pack a whole lot more life support supplies, or you figure out how to provide (reliably) a closed recycling ecology. Both seem to be very heavy items, adding greatly to dead-head payload. This compounds the departure weight exponentially, high Isp notwithstanding. That's why I think the cargo can be sent with some-or-all electric propulsion, if advantageous, but probably not the men. For them, you need high-thrust / high Isp propulsion. We gotta fly much faster with men.
Thus, from a zero-order standpoint, what one should focus on for future manned fight developments should be devices with high-thrust / high Isp potential. I know of only two that exceed current chemical propulsion, and which could actually be built and tested quickly (less than a decade). Those are solid-core nuclear thermal, and nuclear pulse propulsion. Both have downsides: the nuclear thermal we knew as flight-ready 4 decades ago has less T/W and Isp than we would like, uses a propellant with availability and storability issues, plus has real safety issues with retained reactor cores; while nuclear pulse propulsion seems to work best at gigantic ship sizes for which we as yet have no use (we aren't ready to do major colony flights yet).
Yet, those two propulsion items seem to me to be the place to start. I would like to see NERVA put into service ASAP with a quick follow-on to a simple water NERVA. I'd bet a talented team could get both T/W up above 5 and Isp up above 500 sec in a very few years with a water NERVA. By the time they get that working, I'd bet they would have a path to a gas core version identified. There's the real potential for much higher T/W and Isp out of nuke thermal (think engine T/W way above 10 and Isp way above 2000 sec, although these are probably inversely related). The pulse propulsion needs refinement and update to something beyond 1950's fission technology. That was over half a century ago. We can do better, and quickly, too. We just need a good place to test stuff like this, and that's the moon.
Nuke propulsion tests, space/planetary science, and possible mining-for-profit; there's some good reasons to plant bases on the moon. No one, but all 3 together, make a pretty good case. And we can get there with rockets we already have, or will have soon.
We should have been doing this all during the last 4 decades after the Apollo landings, instead of poking our heads in the sand the way we did. Every decade lost not doing these things was another decade's delay getting men to Mars and other places. (20-20 hindsight is wonderful, ain't it?)
GW
The last 500 years' e4xperiences here suggests that explorations and technology development are best done by government agencies working with certain business contractors.
The kinds of visits that lead to colonies (or not) seem to have been most successful when there was a partnership between government and industry. This allowed both to share risks and expenses, and gave the companies the potential for monopoly profit. The Dutch and British East India companies come to mind.
Colony-planting was actually best done by companies, and with an eye toward creating a mutual trade network that would persist through independence for the colonies. The Spanish and French weren't so good at that last point, while the British and Dutch were. Which explains why mostly-English-speaking North America did better than mostly-Spanish-speaking Central and South America. Even though the Spanish got there first.
I think history has a lot to teach us about how to really do the exploration and utilization of space.
GW
The evidence would suggest that we have had essentially-constant cognitive abilities for a very long time now. They found some human-worked stone tools on Crete that were in sediments significantly older than 100,000 years. That predates homo sapiens in Europe by 50,000 years, and may be (or even predate) neanderthals or denisovans. Could even have been homo erectus, no one knows. Erectus dates back over a million years.
Point is, Crete, even then, is 100 miles sailing distance out of sight of land. These guys could build boats and cross significant chunks of ocean, navigating without seeing land. It takes more than poles or paddles on a log to do that. It takes real boat hulls and sails. That's the same as our abilities today. Only the technologies have changed. And we used sails until about a century ago.
GW
Hi JoshNH4H:
The only concern about shooting high-level waste off-earth (other than cost) is flight safety. What do you do about a launch failure? There's a way to make the containers survive without leaking, of course, but it will be heavy and more expensive. They did it in the 1950's with that crashworthy reactor vessel that flew in the old NB-36.
GW
Not being a nuclear rocket engineer, I do not know what the design of a "water NERVA" might have in the way of performance. I know there is a square root of molecular weight decrement of Isp for the heavier water. But, the far higher heat capacity of the steam, even as it ionizes, should allow a lot more reactor power and thus a higher effective "chamber" temperature. An LH2 NERVA, if resurrected from the old plans, would be around 900-1000 sec Isp at engine T/W 3.6. A wild guess for a "water NERVA" might be 600-700 sec Isp at similar engine T/W. Maybe the "atomic rocket" site has data on this, maybe not. I dunno.
The thing is, our probes and observations are telling us that there is water available almost everywhere. All you have to do is dig it up, melt it, and filter out the dirt (mostly just a settling tank). It probably does not matter very much if it is contaminated with admixtures of ammonia, methane, and/or carbon dioxide. You have readily available "fuel" everywhere you want to go, and in a form (water or ice) that is easily stored and transported, easier than any other imaginable propellant.
Try those numbers (600-700 sec) and engine T/W = 3.6 in your mission calculations, knowing that vehicle T/W's way above 0.1 are very easily possible. This is impulsive-burn stuff. There is no low-acceleration effect on velocity increments or on transit times.
My educated guess is that the original NERVA could be resurrected and made flight-ready in about 5 years. About 5 years or so after that, there could easily be a water NERVA made ready by the same team. That's about 1 decade or so to some very practical interplanetary propulsion, even for manned vehicles. Water for propellant is just about everywhere.
Then, dream about a gas core nuclear thermal engine running on water propellant. 1500-6000 sec Isp at engine T/W from 4-ish on down to maybe 0.01 at the high-Isp end. "Filling stations" nearly everywhere you go. And the water NERVA (or its gas-core offspring) can be your reusable landing boat propulsion, too.
Working on atomic rockets looks to me like it holds a lot more promise than an SLS made of recycled shuttle technology.
GW
There are bullets spraying across the border into at least 3 Texas towns across the Rio Grande from 3 big Mexican towns. The druggies seem to be more heavily armed than the police. If that's not a threat to at least local and regional government in Mexico, then I don't know what is a threat to anything. That violence drives a significant fraction of the illegal immigration. We're still in a "main-street" economic depression up here, and everybody around the world knows it. It's in some large part the drug-related violence that drives the impetus to cross the border. With a depression up here, why else would they even want to come?
As for Venezuela, they're at risk of the most idiotic things, even going to war with whoever they can reach, as long as that idiot popinjay Hugo Chavez stays in control. He borders on the irrational, and from the wrong side of it.
GW
I thought OPEC was over 50% of the world's oil, close to 2/3 of it not many years ago is what I remember. Nobody truly controls prices entirely, outside of a monopoly or oligopoly, but he who has the lion's share of the product has the lion's share of influence over its price. That would be true even at 40% share for OPEC oil. I see decreasing stability throughout the middle east in perpetuity now. I don't see much possibility for stability in Mexico or Venezuela, not for a long, long time. Russia (not OPEC, but might as well be) has a lot of oil, but still has difficulties extracting it, and problems with regional political instabilities (like Chechnya).
There are only two approaches to using less oil for transportation fuel: raise fuel mileage and use something else. We have improvements we could still make in fuel efficiency, but I rather doubt we'll obtain anything super dramatic, like factor-3+ items. As for alternatives to oil, they are still too hung up in money politics to become mature and help a whole lot. Where I live, McLennan County (Texas) is a square roughly 30 miles on a side. That's 900 square miles of territory. In all of that, there is but one single filling station selling E-85 from one single pump, and nobody selling any biodiesel at all. Availability of these things is just not very good yet. And that's after over 30 year's effort (arbitrarily dating from the establishment of DOE-NREL about 1980).
As for electric vehicles, we still lack a decent battery, although there are some promising laboratory items. If these work at all (not a trivial question), they usually take 20-40 years to reach a significant market share, based on past experiences. You can speed that up by tilting the "playing field" with subsidies and tax consequences, but that's been rather politically unpopular in recent years, excepting petroleum, which still retains its massive start-up subsidies after over 150 years of existence. The best we have with electrics right now is the series ("plug-in") hybrid, which runs all-electric over short ranges and burns fuel over long ranges. The Chevy Volt is the first of these that I know have hit the market. I'm not sure Toyota yet offers a Prius like that; mine is a parallel hybrid, with a very small battery and no all-electric operation capability other than crossing a parking lot at walking speed. Time will tell whether Chevy "did it right". (It can be done right, that series hybrid propulsion has been in diesel locomotives since 1933, and diesel submarines since about 1919).
GW
I'd be surprised if we found extant microbial life on the surface, due to the harsh UV radiation and the extreme-dessication of the atmosphere and top few cm of surface.
Because I think it likely there was once lots of microbial life when the climate was more benign, I would be very unsurprised to hear we found extant microbial life underground.
I'd be surprised to hear (someday) we found fossils of multicellular life on Mars, because the climate there "went bad" so very long ago. Things were equable (as we understand it) for only a billion or two years. Here, it took nearly 4 billion to reach multicellular forms. (Only data point we have.)
GW
Bob:
I don't have the Justus and Braun link in front of me. It's a NASA paper cited in one or more of the ballistic coefficient / Mars lander articles I posted over at "exrocketman". I think I formally cited it in a references list in the 6-30-12 article titled "Atmosphere Models for Earth, Mars, and Titan". It's probably cited again in some of the subsequent articles.
GW
I've seen some very strange-looking photos of rocks posted here. Definitely not anything resembling igneous stuff-as-I-know-it. But, I am not a geologist. Mudstone-looking items make me think of lakes, of course, or at least streams. Definitely persistent over years to lay down what must have been layers of the stuff. Which in turn suggests some kind of seasonality to the sedimentation process. That's what happens here, anyway.
Dunno about methane-or-not. It was my understanding from the detection-from-orbit stuff that the sources were both highly localized and transient. Maybe irregularly-transient. If my understanding of those prior detections is correct, then having Curiosity find nothing quickly means very little. It'll have to search long and hard to find anything, statistically speaking.
Warmer-than-expected weather on Mars is quite interesting. If it gets significantly above 32F / 0 C, then some ice somewhere is going to melt. The air pressure is too low for liquid water to be anything but a brief transient, but the measurable absolute humidity should rise sharply, in localized zones on a transient basis. Might even see frost or snow transients, who knows?
To keep the water stable for anything but a brief transient, the water vapor partial pressure (only a small piece of the total air pressure!) has to exceed 6.1 mbar above a free liquid surface at 0 C. If the liquid is warmer, the required vapor (partial) pressure is even higher, right out of the standard steam tables. For ice sublimation, the 6.1 mbar at 0 C vapor pressure requirement decreases as the ice temperature decreases, again, right out of the standard tables.
GW
I think you're probably right about NASA's choice between SLS and Falcon-Heavy. Too bad little gets done that actually makes sense.
I found and posted a plot using NASA's own best cost projections for SLS last month over at "exrocketman". I think the article is dated 9-13-12. They look like $2-4 K/lb when anything else in that payload mass range, built and operated the way the commercial launchers are, would be well under $1000/lb.
It's all in the simplicity and small logistical tail. I've never dealt with any government lab anywhere that really understood those two things. Although, I never dealt with NASA JPL. Maybe they do.
GW
Those definitely look like some kind of mudstones, heavily eroded by wind. Is there any data on composition?
GW
Falcon-Heavy is listed as 53 metric tons to LEO out of Canaveral. It's supposed to fly for the first time out of Vandenburg next year. Why not do the same mission even sooner with the rocket we already will soon have in hand, and at far lower launch cost?
Check prices: at full load, Falcon-Heavy is projected at $1000/lb ($2200/kg). Do you really think a government rocket will ever be that cheap? I don't. Titan-IV was not. Atlas (originally an ICBM) and Delta (originally the old Thor IRBM) had to be extensively "reworked" in the commercial launch business to be as cheap as they are today (full load about $2500/lb for 18-25 ton payloads to LEO out of Canaveral).
Just a thought.
GW
Raw data is deceptive, as I said. US population grew by about 50% between 1975 and 2010, from near 200 million to over 300 million. Normalize your park visit numbers by population to get a percentage of the population visiting the parks. You will see the recent dip with the great recession.
Our only hope to stop exporting ever-larger amounts of cash for foreign oil is a two-pronged strategy. We need higher-mileage vehicles, as you say. We also need more domestic production of fuels. The problem with domestic production of oil is price: we don't set it, OPEC does. Even if we went to all-North American sources and bought nothing from OPEC (Mexico is OPEC, B.T.W.), that would not affect its market price by any material amount. The way out of that dilemma is fuels made from something other than oil. We've been screwing around instead of doing that, for over 40 years now. It's a bit late to be starting. But better late than never, I guess.
I know about the Prius, we have one. We have some far older vehicles, too. Everything I drive on the street (and all my lawn and garden equipment) runs totally unmodified on an E-30 to E-35 blend, made from the E-10 that is today's regular, and E-85 where it is available, splash-blended in the tank at the pump. That's about a 1/3 reduction in petroleum fuel usage by this family. I've been doing this for 7 years now, ever since E-85 first became available in this area.
The 220,000-original-miles-on-it catalytic converter in my '98 Sentra shows a check-engine / cat-converter-not-working code whenever I have to drive that vehicle on plain gasoline. That light goes out about a week after I use E-30+ blend again. It takes about that long for the solvent action of the alcohol to clean the accumulated soot off the cat converter bed. It's soot buildup that kills cat converters, you know.
My 1944 Farmall-H tractor has run on straight E-85 for 7 years now. I did the conversions myself, they were very simple. That old corroded steel gas tank is now sparkling clean inside, something the "corrosive ethanol" was not supposed to do. All I know is that it runs cleaner, more powerfully, and with less degradation in its lube oil, than it ever did on gasoline. And its petroleum use has been reduced by 85%.
That being said, we need ethanol not-from-food crops. Food vs fuel is a stupid thing to perpetuate, although we had to start with what we knew how to do. I have great hopes for cellulosic ethanol, although it's "not there yet". There is also ethanol fermented directly from spoiled grocery store produce, something that should be about as easy and efficient as sugar cane. Nobody seems to be doing that yet. In fact, Texas has a law against using spoiled produce that way. How stupid is that?
We need the other alternatives too. Things like "grassoline", etc. Biodiesel can play a role in both trucks and turbine aircraft, too. You just have to get away from the food-vs-fuel dilemma, which is where we had to start.
GW
I have never understood how or why people will read more into what is written, than what is actually written.
I never, never, never said that cheap fuel is mentioned in any work by Adam Smith himself, or in any other person's works. I said that our western economies were "designed" by the "dead hand of Adam Smith". That's a colorful way of saying nobody "designed" anything, it was simply unconsciously "worked out" more-or-less at random, under prevailing market forces. All of our fuels for over 2 centuries have been cheap, relative to even poor family incomes, until shortly after 1973. Nothing has been cheap since for very long, and we had good times during the short interval that it was once again cheap. We have had bad times otherwise, ever since.
I didn't say "oil prices", I said fuel prices, specifically gasoline prices, and I did say "inflation-adjusted prices". Raw (unadjusted) data tells you very little. Average people don't buy crude oil. Most of them buy gasoline. A very few buy diesel. Whatever it is, it is a finished fuel, ready to use. Everything about our economies depends upon transport of goods, in turn dependent upon finished fuels. I chose to look at gasoline prices over time, because that's what most folks have to buy. Plain common sense. Nothing else is implied.
There is a second more recent problem with US diesel, which is now around 30% more expensive than gasoline, when it used to be about 10% cheaper. This is also quite important for family budgets (especially poor folks), because about 40% of the price of your box of corn flake cereal is diesel used in the transport of corn and finished product, when the corn itself is only around 2-3%. The food price spikes blamed on ethanol production were really caused by diesel fuel price hikes. Sad, but true.
To see the inflation-adjusted regular-grade gasoline price plot, you can go to zfacts.com, and get one for yourself. It will not have the set of current events added to it that I used. The most recent form of the version I used is posted at http://exrocketman.blogspot.com, in an article dated 8 March 2012, and titled "Iran, Oil, and Economies". Go there, scroll or navigate down, and see for yourself what actually happened, the same as I did. All the political ideologies about what government policies might and might not do relative to economic good times versus depression turn out to be lies (surprise, surprise!!!!). Finished fuel prices has been the real driver since 1973. OPEC formed as a price-fixing cartel in 1963. US oil production peaked about 1970, ceding “control” over prices to OPEC thereafter. Simple as that.
Consumer fuel demand is "very inelastic", by-and-large. You'll find that term in a lot of business school and management textbooks. Except for upper middle class to rich, there is not a lot of “by-choice” driving going on out there in the US anymore. Most folks just go to work, to school, and to the grocery store. They go occasionally to the doctor when they can afford it. Almost nobody drives all over the country for vacations anymore; ask the national parks, they'll confirm what I say.
There still is no viable alternative product available to the public, to gasoline made from oil. Doesn't really matter why. Effectively, gasoline fuel is a monopoly cartel product, whose price depends upon three things. There is a base supply-and-demand signal, which until around 2004, was about $1.80-$2.00/gal of gasoline, I am pretty certain (from examining the graph), as expressed in early 2012 dollars. Superposed upon top of that since the beginning have been various speculator "bubbles" that spike and crash, usually around 50 cents a gallon or less, in 2012 dollars. Also superposed on top of all those effects are the two OPEC punitive pricing spikes, which are quite large, and which were intended to crash our economies (they did). One was from 1979 to 1986, the other since 2003. These are trivially easy to see from the graph, once you “spot” the right current events upon it.
The thing that bothers me is the distinct possibility that OPEC supply (the largest remaining on the planet) is peaking just as Chinese and Indian demand is spiking up for the next few decades. That puts us western civilization folks into a supply-shortfall-at-any-price situation for the very first time in history. Dangerous territory indeed, for economies "designed" to run on cheap fuel.
THAT was my point.
GW
Hi Bob:
The answer depends upon the ballistic coefficient of what you are trying to land, which in turn depends on the mass you are trying to land. That answer also depends very strongly on whether you do a direct entry from "deep space" vs an entry from low Mars orbit. The detailed "critical variables" are velocity and trajectory angle (relative to horizontal) at the entry interface altitude. I've been using Justus & Braun's interface altitude of 135 km, entered from a 200 km circular orbit, for which the entry angle is about 1.6 degrees and the de-orbit burn delta-vee is about 50 m/s maximum. The Mach at end-of-hypersonics (with severe heating) is about 3 (local). The M3 altitude ranges from near 30 km at around 100 kg/sq.m to around 5 km at around 1000 kg/sq.m.
If you come out of hypersonics below about 20 km, there's not time to deploy a chute, much less have the time for it to do any good. So, I was looking at direct rocket braking to touchdown from the M3 altitude. No chutes at all. It actually seems to be feasible. There's about 3 km/s delta vee required to touchdown from that M3 point, by the time you get all the speed killed, do the final slow approach with some hover, and throw in a kitty for contingencies. It varies from scenario to scenario, but you are moving around 2 km/s more or less horizontally at that M3 point. That puts a sort of lower bound on it.
Hope that helps.
GW
Glandu:
I think you and I actually agree on point 3 above. My point is that the correlation between economic troubles and fuel prices is not random. From 1973, decreasing toward 1978, then even more strongly from 1979 to 1986, fuel prices were well above the inflation-adjusted supply-and-demand level of 1.80 to $2.00 per gallon (American, which is a different tax structure than Europe). After 2001, prices once again skyrocketed and have stayed above $3.00/gallon (American) since then, except for a dip during the 2009 crash.
The numbers are different in Europe, but the trends are the same. These two big price spikes are OPEC punitive pricing for the US and/or NATO getting crosswise with onbe or more OPEC members. Remember, all westerners are "infidels", so it only takes one of us getting all of us hurt.
The other smaller spikes are speculator bubbles.
The different shape of the trends post-2001 relatrive to 1973-1986 suggests there might be an upward trend in supply-demand pricing buried underneath the punitive pricing spikes.
Note that there was no punitive pricing spike after the Soviet (1980) or US (2002) invasions of Afghanistan. Not an OPEC country, no oil to speak of, OPEC didn't care. Note also that there was no spike-up (other than a small speculator bubble) after the 1991 US invasion of Iraq: OPEC begged NATO to do that. But the 2003 invasion of Iraq prompted a big one. Most of OPEC and the rest of the world was against that one.
You can get an inflation-adjusted price history of US regular-grade gasoline from about 1970 to the present at zfacts.com. They will have some historical events on their graph, but you have to spot most of these in this discussion on their graph yourself. Again, the numbers in Europe are different, but the trends are identical. European prices reflect the environmental and health costs of oil in product prices, in the US we fund those out of taxes not collected in fuel prices.
GW