Jump to content

"Optical/3D Rectennas"


Recommended Posts

On Saturday, August 06, 2016 at 2:30 PM, shynung said:

That's the plane I meant. Reaction Engines called that plane the A2. Like you said, it's basically Skylon, minus the rocket mode.

I don't think so. An older thread in this forum discussed about the feasibility of capturing CO2 from the air to create hydrocarbon-based fuels. The process itself is energy-hungry for sure, not least because of the generally low concentration of atmospheric CO2 compared to O2, but it could produce hydrocarbons. If the OP there considered using more concentrated forms of carbon, like coal or biomass, and avoiding burning some of the carbon feedstock for energy, we can improve the efficiency of the process.

In the end, if cheap fusion power became a reality, I'd imagine these would fuel future jet airliners. LH2 would still be somewhat silly (flying fuel tanks), but microwave thermal jets? We don't even have a working prototype right now.

 

It's not a matter of the cost of LH2.  It simply has too low a density to be practical.  Microwave-powered aircraft make sense from a practicality standpoint, on the other hand, if you can bring down the cost to where it beats jet fuel (unlikely).  Their primary utility is in building spaceplanes, where their superior performance (when used to power a rocket with LH2 a microwave thermal rocket can achieve ISP's of 850-1000 seconds...  And a microwave thermal turbojet has essentially unlimited fuel-economy, as the atmosphere is its only propellant...) justify their massive cost.

And microwave-electric aircraft *have* been prototyped- just not at scale.  People have built working toy-sized electric helicopters powered by microwaves, and if I remember correctly a tiny thermal turbojet aircraft as well...  The thrusters have been tested in laboratory settings as well, and work as expected (which is rare in engineering...)

 

Regards,

Northstar

Edited by Northstar1989
Link to comment
Share on other sites

On Sunday, August 07, 2016 at 0:46 AM, shynung said:

There are other concerns with the LH2 plane approach. As they're practically flying fuel tanks, an airplane fuel by LH2 with the capacity of a B777 or A340 would be humongous. They might be large enough to necessitate new infrastructure - wider/longer runways, larger aprons, larger hangars - which means these LH2 airplanes are limited to airports which can handle their size.

Also, abandoning fossil fuels doesn't necessarily means abandoning Jet-A. We have ways to create synthetic equivalents of crude oil from solid carbon sources, such as coal or biomass.

I agree with this though.  I doubt LH2 will ever become common for commercial aviation, short of suborbital jumpers.  Rather, I made the point about microwave aircraft because I think LH2 is so far-fetched that microwave aircraft are actually more likely (and hey, since they contain no flammable fuels and just use the atmosphete for propellant, they're safer in a crash due to the lack of  abundant flammables...)

Link to comment
Share on other sites

@Northstar1989 I'd hold back my expectation on microwave thermojets until there's a working full-scale prototype. We have quadcopter drones for a few years, but no full-scale versions have been developed today that are objectively better than the classic helicopter design.

I do agree on microwave thermojet planes being more feasible than LH2, since we don't need to build new airports for them. I still think syncrude-derived jet fuel would be the less logistically-intensive alternative, though, since we don't have to refit/replace the airplane propulsion system for a new fuel/energy source, or the entire fuel supply infrastructure. We do need a reliable source for the carbon, however.

There are far better uses for optical rectennas than flight, however.

Edited by shynung
Link to comment
Share on other sites

On 8/6/2016 at 9:46 PM, shynung said:

There are other concerns with the LH2 plane approach. As they're practically flying fuel tanks, an airplane fuel by LH2 with the capacity of a B777 or A340 would be humongous. They might be large enough to necessitate new infrastructure - wider/longer runways, larger aprons, larger hangars - which means these LH2 airplanes are limited to airports which can handle their size.

Also, abandoning fossil fuels doesn't necessarily means abandoning Jet-A. We have ways to create synthetic equivalents of crude oil from solid carbon sources, such as coal or biomass.

Currently, our means of producing biomass consume more fuel than it provides, because we use so much of it in agriculture. Only exceptions are third world countries which can't possibly produce enough to export without switching to first world agricultural methods. Granted, it's easy enough to switch most of agricultural machinery to electric, but it still means that any bio-fuel is going to be many times more expensive than electrolytic H2. As for coal, it's already expensive. Sure, it's much cheaper than oil, but coal-burning power plants are already on a comparable price point to solar. With environmental taxes, coal is more expensive than solar in some parts of the world. (California, much of Europe.) Optical rectenas are going to bring down price of solar by nearly two orders of magnitude. Stop and think about that figure. Nearly 100 times cheaper electric production. Price of electricity will be due to infrastructure only. Nothing we have can compete with this. The only method we know of storing this energy without increasing its cost ten-fold is electrolytic H2. We might come up with something, given that it's going to be an important limitation, but we don't have anything like it yet.

And yeah, we'd need new infrastructure for these flying monsters. Just like 747 did. Just like many planes before it. This is not a new problem. Since we are talking about replacing only intercontinental - or equivalent range - flights only, this isn't a problem. They are already tending towards monstrous because they are trying to save on fuel costs. This is exactly the same motivation. Nothing new. We are talking a handful of airports around the world. From there, local flights will connect with either conventional jets or something else, like the aforementioned electric replacements for regional turboprops.

This is a projection going entirely off technology we have in experimental stages in the lab. We are going to start producing massive quantities of cheap solar power. We will have hard time storing it. While batteries are going to improve by about a factor of 3 in the near future, most promising being graphene batteries, this is nowhere near enough. Next best thing is hydrogen. We are likely going to see power companies building major LH2 storage facilities to balance the grid. Hopefully, this will allow recycling much of the existing infrastructure. This will mean that large quantities of LH2 will be available really cheap for anyone who wants to purchase it for fuel. Aircraft manufacturers are unlikely to just watch this untapped energy source sit in storage tanks.

But like with any projection, any significant change could throw it all off. Maybe we'll figure out how to tap into nuclear isomer energy in the next decade. Maybe we'll have 178m2Hf batteries to store these massive quantities of energy. Seems unlikely, given how much research went into it with limited success, but it's just one of hundreds of parameters that can change. But if things go the way they are going now, little details like requirements for larger airfields, completely new hangars, new safety standards, and new equipment, aren't going to stand in the way of massive capital gains on paying next to nothing for fuel.

Link to comment
Share on other sites

On Monday, August 08, 2016 at 1:39 AM, shynung said:

@Northstar1989 I'd hold back my expectation on microwave thermojets until there's a working full-scale prototype. We have quadcopter drones for a few years, but no full-scale versions have been developed today that are objectively better than the classic helicopter design.

I do agree on microwave thermojet planes being more feasible than LH2, since we don't need to build new airports for them. I still think syncrude-derived jet fuel would be the less logistically-intensive alternative, though, since we don't have to refit/replace the airplane propulsion system for a new fuel/energy source, or the entire fuel supply infrastructure. We do need a reliable source for the carbon, however.

There are far better uses for optical rectennas than flight, however.

Fully in agreement there.  I was actually talking about microwave rectennas there, though, because microwaves are less affected by clouds than visual light...

On Monday, August 08, 2016 at 3:20 AM, K^2 said:

Currently, our means of producing biomass consume more fuel than it provides, because we use so much of it in agriculture. Only exceptions are third world countries which can't possibly produce enough to export without switching to first world agricultural methods. Granted, it's easy enough to switch most of agricultural machinery to electric, but it still means that any bio-fuel is going to be many times more expensive than electrolytic H2. As for coal, it's already expensive. Sure, it's much cheaper than oil, but coal-burning power plants are already on a comparable price point to solar. With environmental taxes, coal is more expensive than solar in some parts of the world. (California, much of Europe.) Optical rectenas are going to bring down price of solar by nearly two orders of magnitude. Stop and think about that figure. Nearly 100 times cheaper electric production. Price of electricity will be due to infrastructure only. Nothing we have can compete with this. The only method we know of storing this energy without increasing its cost ten-fold is electrolytic H2. We might come up with something, given that it's going to be an important limitation, but we don't have anything like it yet.

And yeah, we'd need new infrastructure for these flying monsters. Just like 747 did. Just like many planes before it. This is not a new problem. Since we are talking about replacing only intercontinental - or equivalent range - flights only, this isn't a problem. They are already tending towards monstrous because they are trying to save on fuel costs. This is exactly the same motivation. Nothing new. We are talking a handful of airports around the world. From there, local flights will connect with either conventional jets or something else, like the aforementioned electric replacements for regional turboprops.

This is a projection going entirely off technology we have in experimental stages in the lab. We are going to start producing massive quantities of cheap solar power. We will have hard time storing it. While batteries are going to improve by about a factor of 3 in the near future, most promising being graphene batteries, this is nowhere near enough. Next best thing is hydrogen. We are likely going to see power companies building major LH2 storage facilities to balance the grid. Hopefully, this will allow recycling much of the existing infrastructure. This will mean that large quantities of LH2 will be available really cheap for anyone who wants to purchase it for fuel. Aircraft manufacturers are unlikely to just watch this untapped energy source sit in storage tanks.

But like with any projection, any significant change could throw it all off. Maybe we'll figure out how to tap into nuclear isomer energy in the next decade. Maybe we'll have 178m2Hf batteries to store these massive quantities of energy. Seems unlikely, given how much research went into it with limited success, but it's just one of hundreds of parameters that can change. But if things go the way they are going now, little details like requirements for larger airfields, completely new hangars, new safety standards, and new equipment, aren't going to stand in the way of massive capital gains on paying next to nothing for fuel.

Biomass =/= current biofuels technology.  What shymung's talking about is producing octane and ethanol from cellulose, basically (or at least I hope so...)

That's *very* different and much higher-yield than stupid corn-based ethanol...  You can use grasses that grow 12 feet high before you harvest them then, which means you use way less fuel per ounce of biofuel produced than with corn...

Current biofuels are just a handout to the corn lobby.  Take it from a biologist with a little knowledge of agriculture- corn is about the worst crop imaginable for producing cellulosic biofuel...

We can bring the cost of biofuel down an order of magnitude, which could well make it cheaper than LH2 which (which has MAJOR storage issues).  And, it has the advantage of not requiring more infrastructure spending.  When you look at the true cost of air travel and ignore stupid stuff like government paying for airports (and pretend airlines were footing the bill), ground infrastructure is a HUGE part of air travel costs, whereas fuel is only a tiny portion...

Edited by Northstar1989
Link to comment
Share on other sites

1 minute ago, Northstar1989 said:

Fully in agreement there.  I was actually talking about microwave rectennas there, though, because microwaves are less affected by clouds than visual light...

Something else to consider: airport radars used for ATC uses the microwave spectrum, and so does aircraft radios and transponders. Using microwaves to power the craft would throw a spanner to the workings of these equipment.

Also, I'm not entirely convinced that microwave beamed power would be used at a large scale in the foreseeable future. I'm betting that we'll get the first fusion rocket spaceborne before microwave thermal rockets.

Also, I think you played too much KSP Interstellar. Try Near Future Technology for a while.

Link to comment
Share on other sites

19 minutes ago, shynung said:

Something else to consider: airport radars used for ATC uses the microwave spectrum, and so does aircraft radios and transponders. Using microwaves to power the craft would throw a spanner to the workings of these equipment.

Also, I'm not entirely convinced that microwave beamed power would be used at a large scale in the foreseeable future. I'm betting that we'll get the first fusion rocket spaceborne before microwave thermal rockets.

Also, I think you played too much KSP Interstellar. Try Near Future Technology for a while.

KSP-Interstellar Extended is based tightly on real-world data (the original Interstellar is not).  Like it or not, Microwave beamed power works.  But it has a few problems:

- It's very expensive (this is accurately reflected in KSP Interstellar).  You have to launch a LOT of rockets each year (over 100) to pay back the cost of the ground infrastructure with the lower cost of the rockets themselves.  And that's based on CURRENT launch-costs: it doesn't ever pay for itself at all if you compare it to what SpaceX hopes to do, which is cheaper- unless you can develop a spaceplane based off the technology... (which is at least feasible, since microwave thermal rockets can get over 850 seconds ISP with Hydrogen)

- It sounds scary.  Who wants to be in an air/spaceplane powered by microwaves?  Most people still falsely believe your microwave oven give you cancer...

- it does, as you point out, create problems for current ATC systems

 

But the engineering and technology DOES work, we know that beyond a reasonable doubt...

Edited by Northstar1989
Link to comment
Share on other sites

The better usage of Microwave Beamed Power is for orbital operations, actually.  Badically take anything you would normally use a nuclear reactor for and replace it with a ground-based microwave transmitter and a thermal receiver or rectenna.  Examples:

- Propulsive Fluid Accumulators in Low Earth Orbit

- Thermal Rocket propulsion (pure LH2 for 850-1000 s ISP, or Liquid Nitrogen at low to mid 300's ISP for better fuel density, thrust, and the ability to use all the Nitrogen you collected with a Propulsive Fluid Accumulator- which you would otherwise throw out, if you were just keeping the Oxygen for use in chemical rockets...)

- High powered electric propulsion (stuff like multi-MW VASIMR, or plasma thrusters using nothing but Nitrogen...)

 

The main problem with using 2 or 3 for, say, a manned Mars mission, is that while you get plenty of power from ground-based transmitters in Low Earth Orbit, the beam will be far too diffuse to produce usable power-levels (unless you want to spend MONTHS on a return-burn) out by Mars orbit...

Lasers coupled with optical rectennas (if we can develop them) or existing thermal rocket technology would work better, but then you have the problem that lasers diffuse too much when passing through the atmosphere... (whereas microwaves diffuse more over long distances)

Could work nicely for a Lunar tug, though...  Propel the thing with ground-based microwaves and Nitrogen (collected by a Propulsive Fluid Accumulator in LEO) sent through a plasma thruster, or even Hydrazine (since it doesn't require active cooling to store) launched from Earth, for ultra-cheap transport of cargo from LEO to Lunar orbit and back... (still have to get the cargo to LEO though, even if you don't have to launch the fuel to get it from there to the Moon if you use a Propulsive Fluid Accumulator for the Lunar transit fuel...)

Edited by Northstar1989
Link to comment
Share on other sites

@Northstar1989 Let me clarify that I don't, for a moment, doubt the effectiveness of microwave beamed power. We've used microwave for cooking, and microwave energy rectifier tech has been demonstrated. What I doubt is the feasibility of integrating the technology into our current aviation transport system, which already uses the microwave spectrum for other purposes.

I agree that microwave beamed power would be very useful in space applications. Up there, we can communicate using methods that wouldn't be feasible on earth, such as laser communication systems, though maybe not for broadcasts.

2 hours ago, Northstar1989 said:

What shymung's talking about is producing octane and ethanol from cellulose, basically (or at least I hope so...)

I was talking about biomass gasification and Fischer-Tropsch process, actually. The end result is very similar to crude oil, and can be processed with existing petrochemical technology. The gasification process can use carbon from almost any source, not just biomass. Nutzi Germany once processed coal in the same manner when it faced oil embargoes during WWII to supply themselves with energy and materials.

Edited by shynung
Link to comment
Share on other sites

3 hours ago, shynung said:

@Northstar1989 Let me clarify that I don't, for a moment, doubt the effectiveness of microwave beamed power. We've used microwave for cooking, and microwave energy rectifier tech has been demonstrated. What I doubt is the feasibility of integrating the technology into our current aviation transport system, which already uses the microwave spectrum for other purposes.

I agree that microwave beamed power would be very useful in space applications. Up there, we can communicate using methods that wouldn't be feasible on earth, such as laser communication systems, though maybe not for broadcasts.

I was talking about biomass gasification and Fischer-Tropsch process, actually. The end result is very similar to crude oil, and can be processed with existing petrochemical technology. The gasification process can use carbon from almost any source, not just biomass. Nutzi Germany once processed coal in the same manner when it faced oil embargoes during WWII to supply themselves with energy and materials.

Biomass gasification and Fischer-Tropsch to produce long-chain hydrocarbons including Octane.  From cellulose (the main component of plant biomass).  Basically exactly what I was referring to...

Interestingly enough there's a lot of overlap between that and soil biology and Mars colonization.  For one, you can actually produce the syngas (mixture of CO and H2) needed to run the Fischer-Tropsch process by pyrolyzing the biomass instead of just gasifying it...  The advantage of pyrolyzing is you also get:

- Biochar, which you can burn like coal (it even looks similar to coal!) or use as a powerful soil amendment to drastically and permanently (at least as permanently as you get with soil anyways.  Archaeologists have found patches of manmade biochar-enriched soul in the Amazon over a thousand years old and still going strong...  They call it "terra preta" there.) improve soil fertility.  It does a bunch of things, including improving soil nutrient/ion and water-retention, reducing evaporative losses from sunlight, and providing an excellent porous microscopic surface for beneficial soil bacteria to grow on...  Using it we could make depleted farmland fertile again, and make jungles (which get too much rain- normally causing nutrients to wash right out of the soil once we chop the rainforests down), and deserts bloom (with much less water needed for irrigation in deserts, due to the greatly reduced evaporative losses...)  Speaking of, once you cover land up with pressurized and mildly-heated spaces, growing crops on Mars would be a lot like growing crops in a cold desert...

- Bio-"Oil", which is really just a suspension of variable-weight tars in water.  But it can be refined using existing petrochemical technology as a raw hydrocarbon feedstock into the refining process, and in fact is already done so when it is produced as a valuable byproductof certain industrial processes...

All of this is in addition to syngas.  So, it makes a lot more sense to pyrolyze at least some of the biomass for the valuable byproducts.  It's a positive feedback loop that way, as you can actually plow a lot of the Biochar into the soil to increase crop yields if you're growing biomass crops like those massive 12-foot grasses I talked about before... (essentially, it grows faster and you get more frequent harvests- it doesn't necessarily grow in any thicker or taller...)

Edited by Northstar1989
Link to comment
Share on other sites

By the way, before I move on to what any of yhis has to do with Mars; some more on biomass-crops because they're really fascinating.   Here's a list of a few particularly high-yield biomass crops.  I suggest reading up more on them when you get the chance:

Giant Miscanthus- a relative of sugarcane, this grass grows in dense stands (it basically completely covers the ground) 12-15 feet high.  It has low water and fertlizer requirements, excellent pest resistance, yields 6-20 tonnes of biomass per year depending on soil and rainfall conditions, and can be harvested with existing farm machinery designed to collect hay...

Arundo Donax- this crop is a cane rather than a thin-stalk grass. It grows 20 feet high, and yields around 20 tons of biomass per acre per year, making it even more productive than Miscanthus in many cases.  However is is somewhat less hardy than Miscanthus, a potentially invasive species, and more difficult to harvest and process...

Switchgrass- this biomass crop grows in a thick ground cover 4-6 feet tall.  It only yields 6-10 tons of biomass per year once well-established and requires extra potassium and phosphorus as fertilizer, but is a reasonably hardy and *very* long-lived perennial grass, remaining highly productive for up to 20 years without the need for replanting...  Due to its lower yields, it is best grown only where crops like Miscanthus are not viable, however...

 

In short, plant some Giant Miscanthus or Arundo Donax, harvest it once it's established in a couple years, stick it in a pyrolysis unit, and VOILA!, cheap and sustainable syngas production, along with plenty of Biochar and Bio-Oil...

 

Later, I'll get to what the Fischer-Tropsch process has to do with Mars ISRU.  But I'm tired of writing for now, and have given plenty to think about...

 

Regards,

Northstar 

 

 

Edited by Northstar1989
Link to comment
Share on other sites

On 8/8/2016 at 1:39 AM, shynung said:

@Northstar1989 I'd hold back my expectation on microwave thermojets until there's a working full-scale prototype. We have quadcopter drones for a few years, but no full-scale versions have been developed today that are objectively better than the classic helicopter design.

I do agree on microwave thermojet planes being more feasible than LH2, since we don't need to build new airports for them. I still think syncrude-derived jet fuel would be the less logistically-intensive alternative, though, since we don't have to refit/replace the airplane propulsion system for a new fuel/energy source, or the entire fuel supply infrastructure. We do need a reliable source for the carbon, however.

There are far better uses for optical rectennas than flight, however.

From looking at what escape dynamics tried to do, I'd recommend waiting for the US Navy to start building its massive laser program.  Even that sounds like it wouldn't quite provide the power escape dynamics needs, and the Navy blasters only need fire for milliseconds while the launch vehicle will need minutes of constant power (and don't ask about how the tech is supposed to get out from under wraps, even using a foreign spy's leaked data is iffy in the US).

Did that need optical rectennas anyway?  All it needed was to absorb the power and turn it into heat, while an antenna typically absorbs power as electricity (well, really as a signal, but I've used stuff powered by near field power).

Quadcopters are based on the issue that four small electric engines typically require the same number of windings as a single motor four times more powerful, and don't require the fancy (and extremely expensive once scaled up, those forces are huge) gimballing on any rotor.  They really aren't expected to scale, and any "scaled up" version would have the same issues that the Moeller "aircar" (and any less scamy competitors) would have had for decades.

 

Link to comment
Share on other sites

Wouldn't a scaled quadcopter still only require 4 smaller rotors than a traditional helicopter, and thus require less expensive gimballing?

 

Anyways, as for MARS ISRU, the Fischer-Tropsch process is great on Mars because you have readily available carbon and hydrogen sources in the atmosphere and the water ice in the soil, and a *very* high value of fuel produced on Mars in that it saves a massive cost getting it there by more traditional means.

If you run the Fischer-Tropsch process on Mars, you can easily produce Kerosene and LOX to burn it with (the LOX from electrolyzing the water byproduct, as well as extra water you dig up just for that purpose, or CO2 from the atmosphere) right there on Mars.

Since Kero/LOX is a good deal denser than Meth/LOX and doesn't require any heavy/expensive insulation or active-cooling systems for the Kerosene component, it's a superior fuel for a Mars return, even before you consider that Kero/LOX engine technology is already much better-developed and more widely used than Meth/LOX is...

It's worth noting that the Fischer-Tropsch Process can also eventually be used to produce feedstocks for the production of structural plastics fit for use in construction of permanent buildings on Mars, as well as to produce petrochemicals for various more mundane uses...  So developing the reaction for propellant-production now also has knock-on benefits for eventual base-construction and colonization efforts decades later...

 

Regards,

Northstar

Edited by Northstar1989
Link to comment
Share on other sites

10 minutes ago, Northstar1989 said:

Wouldn't a scaled quadcopter still only require 4 smaller rotors than a traditional helicopter, and thus require less expensive gimballing?

Anyways, as for MARS ISRU, the Fischer-Tropsch process is great on Mars because you have readily available carbon and hydrogen sources in the atmosphere and the water ice in the soil, and a *very* high value of fuel produced on Mars in that it saves a massive cost getting it there by more traditional means.

If you run the Fischer-Tropsch process on Mars, you can easily produce Kerosene and LOX to burn it with (the LOX from electrolyzing the water byproduct, as well as extra water you dig up just for that purpose, or CO2 from the atmosphere) right there on Mars.

Since Kero/LOX is a good deal denser than Meth/LOX and doesn't require any heavy/expensive insulation or active-cooling systems for the Kerosene component, it's a superior fuel for a Mars return, even before you consider that Kero/LOX engine technology is already much better-developed and more widely used than Meth/LOX is...

It's worth noting that the Fischer-Tropsch Process can also eventually be used to produce feedstocks for the production of structural plastics fit for use in construction of permanent buildings on Mars, as well as to produce petrochemicals for various more mundane uses...  So developing the reaction for propellant-production now also has knock-on benefits for eventual base-construction and colonization efforts decades later...

Regards,

Northstar

Yes an scaled quad copter would have the same restrictions as an helicopter, you could save some in having tubes around the fans, this is far simpler on an quad copter you could even put the fans in an wing structure, giving aerodynamic lift once you get up to speed. 

Agree with you, on Mars fuel is very expensive. 
On Earth it don't make much sense as its energy intensive and its not much co2 in the atmosphere. 
Think its to energy intensive to use for cleaning co2 from power plants too, one exception would be processes like iron or cement making where you have to produce lots of co2 anyway. 
 

Link to comment
Share on other sites

18 minutes ago, Northstar1989 said:

Wouldn't a scaled quadcopter still only require 4 smaller rotors than a traditional helicopter, and thus require less expensive gimballing?

Except that this gives a scaled quadcopter 4 times the chances to crash thanks to an engine failure.  With toy quadcopters, a quadcopter with an broken motor is thrown away regardless of how much it is broken in the fall.  A scaled quadcopter is likely to have greater issues when crashing.  You *could* employ some other means of altering the power levels to each propeller, but that would still likely be as complex and prone to failure as four motors.  While the gimballing is expensive, I didn't think it was a major source of failure in helicopters.

Even so these only help make a cheaper (if more dangerous) helicopter, which seems an extremely specialized form of flight.

I think the existing NASA Mars Architecture still lists ISRU of oxygen and stored hydrogen, without suggesting how to maintain enough hydrogen at the end of the mission while stored form months in a containment system shipped to and landed on Mars.  I'd expect kerosene would be a better choice myself.

Link to comment
Share on other sites

23 hours ago, Northstar1989 said:

Biomass =/= current biofuels technology.  What shymung's talking about is producing octane and ethanol from cellulose, basically (or at least I hope so...)

Doesn't matter. With current farming techniques, plant matter takes up more fuel than you could possibly make carbon-for-carbon. Even if you convert cellulose in addition to all the sugars, you're still in the deficit. And we don't produce enough waste cellulose as byproduct to account for our fuel use. Again, we presumably want to convert farming to consume electricity only, but this gives you the idea of the scale of effort required to make synthetic fuel.

There is absolutely no way to make any carbon-based fuel remotely as cheap per calorie stored as LH2, provided that you have a source of next-to-free electric power, which is what we're talking about. Synthetic fuels might be a stopgap during transition, and I'm sure there are applications where we'll keep using them, but at the levels of global energy consumption, it's not long-term viable. Primary storage will be hydrogen until something better comes along.

Link to comment
Share on other sites

1 hour ago, shynung said:

@K^2 I recall that you once mentioned nuclear isomer batteries somewhere?

Many times. At least once in this thread. But there have not been any significant breakthroughs since DARPA's TRIP, just some incremental improvements. Enough to where we might be able to replace radiothermal isotope generators at some point in observable future, but nowhere near enough to make them viable for energy storage in commercial vehicles.

Of course, there are other metastable isomers and probably quite a few we haven't discovered yet. Or maybe we have, and it's just classified. After all, a lot of Hafnium research went dark very suddenly right after the first paper claiming stimulated emission got published.

The capacity is definitely there. Again, using Hafnium 178 as an example, its m2 isomer stores 2.5MeV of energy (1.36 GJ/g, or about 28,000 more energy per weight than gasoline). At the same time, it has half-life of 31 years, emits only gamma radiation, and decays to ordinary 178Hf, which can then be "recharged" to its m2 form. Fact that the only way we know to recharge it is with a particle accelerator and the costs are astronomical, as well as limited quantities of this isotope being available in the first place, are what makes this non-viable as a consumer battery. As indicated, even military was so convinced they can't afford to make any practical use of it that they unclassified all experiments.

But if we were to find something with, say, tens of keV energy range and similar half-life? Well, then you could recharge it with an equivalent of a dentist x-ray and radiation from it would be completely safe with minimal shielding. And it would still be about hundred times better than gasoline. This is currently the golden grail of nuclear isomer energy. If we find it, all our problems might get solved just like that. Unfortunately, unlike chemical energies where you can come up with new properties by just bringing a few atoms together, and we can come up with all kinds of "just right" configurations for all sorts of interesting optical phenomena, with nuclear energy we are limited to what's already there. Which is less than a hundred of stable elements with at most a few stable isotopes each. The good news is that it will only take so long to try all of them in all sensible energy ranges. The bad news is that we might just be out of luck on the right isomer existing.

So best possible scenario, we'll figure out high energy density nuclear isomer batteries and we'll have minivans capable of making orbit. Worst case, we'll have to figure out controlled fusion or be stuck with chemical energy.

Link to comment
Share on other sites

10 hours ago, wumpus said:

Except that this gives a scaled quadcopter 4 times the chances to crash thanks to an engine failure.  With toy quadcopters, a quadcopter with an broken motor is thrown away regardless of how much it is broken in the fall.  A scaled quadcopter is likely to have greater issues when crashing.  You *could* employ some other means of altering the power levels to each propeller, but that would still likely be as complex and prone to failure as four motors.  While the gimballing is expensive, I didn't think it was a major source of failure in helicopters.

Even so these only help make a cheaper (if more dangerous) helicopter, which seems an extremely specialized form of flight.

I think the existing NASA Mars Architecture still lists ISRU of oxygen and stored hydrogen, without suggesting how to maintain enough hydrogen at the end of the mission while stored form months in a containment system shipped to and landed on Mars.  I'd expect kerosene would be a better choice myself.

True, larger helicopters tend to have two engines for this reason, latest helicopter crash in Norway was because of gearbox fail and they are fatal. 
With an quad or more copter you would need electrical engines as they fails rarely and is easy to tune, you could use the opposite engine for balance and land on two, with an small parachute  you could get enough stability to use the two remaining engines for landing. 
now with 5 or more engines you could land if loosing one rotor or engine. Not sure if the larger professional 6 engine drones has engine fail software. In drones think its more about communication and software fails, also wind or maneuvering who push the drone into an position it can not recover from before hitting the ground. 

Link to comment
Share on other sites

16 hours ago, K^2 said:

Doesn't matter. With current farming techniques, plant matter takes up more fuel than you could possibly make carbon-for-carbon. Even if you convert cellulose in addition to all the sugars, you're still in the deficit. And we don't produce enough waste cellulose as byproduct to account for our fuel use. Again, we presumably want to convert farming to consume electricity only, but this gives you the idea of the scale of effort required to make synthetic fuel.

There is absolutely no way to make any carbon-based fuel remotely as cheap per calorie stored as LH2, provided that you have a source of next-to-free electric power, which is what we're talking about. Synthetic fuels might be a stopgap during transition, and I'm sure there are applications where we'll keep using them, but at the levels of global energy consumption, it's not long-term viable. Primary storage will be hydrogen until something better comes along.

That's an absolutely and completely false statement about cellulosic biofuel.  Even with corn-based ethanol, you only use marginally more fuel than you produce- and that's when you're throwing the majority of your calories away!  With crops like Giant Miscanthus you get many times the yield at a fraction of the fertilizer and pesticide usage (almost none, in fact) and don't throw the vast majority of your calories away as farm-waste.  As the majority of current farming caloric expenditures are on fertilizer and pesticides, this leaves the calorie balance squarely in the positive even with current farming techniques...

As for optical rectennas, this *isn't* next-to-free electrical power, and LH2 is *not* going to ever be a cheap fuel.  You bring down the costs of the panels themselves by up to an oder of magnitude with optical rectennas vs. traditional photovoltaics, but installation and maintenance costs are still significant, as are the costs of water-electrolysis equipment capable of capturing and storing the hydrogen on an industrial scale...

LH2 is also difficult and dangerous to safely transport or store for long periods of time, and the places you would need it for LH2-based air travel (mainly urban airports) are likely to be a LONG ways from your solar farms.  Not to mention, solar panels don't work at night, so the entire argument about using surplus electrical power produced by optical rectennas to make LH2 at night is totally and completely bunk...

LH2 might still be cheaper than cellulosic biofuel derived from Giant Miscanthus fed into a pyrolysis unit, but you don't need to completely rebuildair-travel infrastructure for the biofuel option.  As the majority of air-travel expense is actually in personnel costs and ground infrastructure, LH2-based air travel makes zero economic sense.

Edited by Northstar1989
Link to comment
Share on other sites

On Wednesday, August 10, 2016 at 7:42 PM, wumpus said:

Except that this gives a scaled quadcopter 4 times the chances to crash thanks to an engine failure.  With toy quadcopters, a quadcopter with an broken motor is thrown away regardless of how much it is broken in the fall.  A scaled quadcopter is likely to have greater issues when crashing.  You *could* employ some other means of altering the power levels to each propeller, but that would still likely be as complex and prone to failure as four motors.  While the gimballing is expensive, I didn't think it was a major source of failure in helicopters.

Even so these only help make a cheaper (if more dangerous) helicopter, which seems an extremely specialized form of flight.

I think the existing NASA Mars Architecture still lists ISRU of oxygen and stored hydrogen, without suggesting how to maintain enough hydrogen at the end of the mission while stored form months in a containment system shipped to and landed on Mars.  I'd expect kerosene would be a better choice myself.

LH2 keeps just fine if you keep it cold enough.  You lose a little, but it's certainly feasible to store a sizeable quantity of LH2 for the duration of a Mars mission...

But they're talking ISRU- that means, by *definition* of In Situ Resource Utilization that they're *NOT* shipping it from Earth and just using it to take off again as-is...

The most likely source of Hydrogen on Mars is from electrolysis of the substantial deposits of water-ice found in the soil a couple meters down in many places on the planet.

And, once you get LH2 on Mars, whether by mining it from the soil or shipping it from Earth in an insulated and actively-cooled container, you *don't* just keep it that way.  You react it with CO2 to make Methane (for Meth/LOX combustion) or with CO to make Kerosene- neither one of which needs to be kept nearly as cold as LH2 for storage (in fact Kerosene, you don't have to cool at all!)

If you were *really* worried about your precious LH2 boiling off, and you didn't want to mine it on Mars instead, you'd ship Hydrogen to Mars in the form of Ammonia, which has the next-best mass fraction of Hydrogen after Methane and doesn't require active-cooling; or Hydrazine- which has the nice property that it actually *releases* energy when you break it down...

Of course in that case, you'd probably just be better off taking a Particle Bed nuclear reactor with you (such reactors were designed for Project Timberwind) and feeding a CO2/O2 mixture through your reactor to get back to orbit (this isn't all that dissimilar to a recent proposal to build a CO2/CO Mars 'hopper' with an RTG as its heat-source...)  CO2 is available on Mars without needing to carry out any chemical reactions, and O2 is necessary to clean the soot out of your reactor that tends to form as CO2 pyrolyzes to leave behind graphite...

You'd need to coat the uranium pellets in a material that won't oxidize when exposed to hot O2, though- or risk spewing radioactive material all over Mars' surface...

Alternatively, you could just use CO2 on its own.  Your reactor would gunk up with graphite by the second or third launch back to orbit, so you'd lose all hope of re-using your lander for future Mars missions, but then all you'd have to do is pressurize and cryogenically store CO2 as a liquid in order to have propellant to get you back to orbit.  No mean task, but virtually any Mars ISRU plan calls on collecting and storing CO2, and it can be stored at much higher temperatures and in much smaller tanks (due to its higher density) than LH2, which means a solar array sent down with the Mars Cargo Module of a Constellation-style mission should be more than up to the task of collecting and storing the CO2 over a period of several months, or years (if you send the Cargo Module a Hohmann Transfer Window ahead of the crew, to start making propellant for the lander to launch back into orbit in advance...)

 

Regards,

Northstar

Edited by Northstar1989
Link to comment
Share on other sites

On 8/11/2016 at 4:11 PM, Northstar1989 said:

That's an absolutely and completely false statement about cellulosic biofuel.  Even with corn-based ethanol, you only use marginally more fuel than you produce- and that's when you're throwing the majority of your calories away!  With crops like Giant Miscanthus you get many times the yield at a fraction of the fertilizer and pesticide usage (almost none, in fact) and don't throw the vast majority of your calories away as farm-waste.  As the majority of current farming caloric expenditures are on fertilizer and pesticides, this leaves the calorie balance squarely in the positive even with current farming techniques...

Lets start with the fact that photosynthesis is less than 10% efficient, whereas optical rectenas start at about 40%. This is a death sentence for biofuels already, since land availability is the biggest bottleneck in civilized world. But then you have to add farming costs in machinery, labor, and energy consumption. Corn ethanol is not viable in US and Europe by a huge margin. It is not viable everywhere else by a much narrower margin, but then you add transportation costs on top of an already expensive fuel. So lets say with cellulose in the mix you can pass the break-even point. We are talking about net efficiency of less than 1% at this point. Even with free electricity, if you can make this actually cheaper than Jet-A from oil, I'll be impressed.

On 8/11/2016 at 4:11 PM, Northstar1989 said:

LH2 is also difficult and dangerous to safely transport or store for long periods of time, and the places you would need it for LH2-based air travel (mainly urban airports) are likely to be a LONG ways from your solar farms.  Not to mention, solar panels don't work at night, so the entire argument about using surplus electrical power produced by optical rectennas to make LH2 at night is totally and completely bunk...

Yeah, solar power works only during the day. Which means you need to store it during the day. Got any idea how to store the massive amounts of energy we consume during a typical night without increasing a cost dramatically? I'll give you a hint. Power companies already have gas turbines. Yeah, you'd be taking a loss of over 50%, but given that infrastructure is already there and energy itself is almost free, it's stupid not to do it. Each modern power plant is going to become a giant battery using H2 generated during the day to power the place during the night.

The surplus H2 isn't going to be there because of power usage fluctuations. It's going to be there because electric companies will already need to make huge quantities of it, meaning they'll be able to sell it cheap as well, thanks to economy of scale.

So the options for airline companies is going to be LH2 at $0.05/gallon or Jet-A (bio or fossil) at $5/gallon. Long range variants of 777 take nearly 50,000 gallons of fuel and its longest flights use up almost all of it. So even with the fact in mind that you need about 4x the quantity of LH2 by volume, your options are paying about $200,000 to put 40k gallons for a flight or about $8,000 worth of LH2. You'll want to do at least one flight per day minus maintenance, so lets say 3,500 flights in 10 years, and you are looking at savings of over half a billion dollars. For comparison, the plane we are talking about costs about $300 million. If we throw in maintenance and man power, we are looking at saving about half of the airplane's ten year cost. Half. Multiply this by the size of the long-range fleet and you have enough money to build new airports, refueling infrastructure, and roll out new planes leaving just enough for each CEO to cut themselves a huge bonus check.

There are other considerations, of course, like that pesky safety factor. But it's going to be cheaper for airline companies to just get lobbying groups to talk about how much greener this is for the environment, and everyone will forget about the few unfortunate accidents caused by poorly trained technicians and really dangerous flammable gas. If you think little things like human lives are going to stop corps from pushing this through, given the insane amounts of money at stake, then you don't know anything about modern corporate politics.

Link to comment
Share on other sites

7 hours ago, K^2 said:

Lets start with the fact that photosynthesis is less than 10% efficient, whereas optical rectenas start at about 40%. This is a death sentence for biofuels already, since land availability is the biggest bottleneck in civilized world. But then you have to add farming costs in machinery, labor, and energy consumption. Corn ethanol is not viable in US and Europe by a huge margin. It is not viable everywhere else by a much narrower margin, but then you add transportation costs on top of an already expensive fuel. So lets say with cellulose in the mix you can pass the break-even point. We are talking about net efficiency of less than 1% at this point. Even with free electricity, if you can make this actually cheaper than Jet-A from oil, I'll be impressed.

How about coal-sourced synthetic Jet-A? It's not quite clean, but it's cheap, and the US alone have about 200 billion tons in her reserves, able to last for more than 2 centuries at current production rates.

Link to comment
Share on other sites

11 hours ago, shynung said:

How about coal-sourced synthetic Jet-A? It's not quite clean, but it's cheap, and the US alone have about 200 billion tons in her reserves, able to last for more than 2 centuries at current production rates.

Coal is fundamentally expensive. If demand drops, digging it out will be even more expensive. Yes, if we suddenly stop needing it for power plants, the reserves will be a source of cheap carbon for a while. But I don't see it working out long term.

Link to comment
Share on other sites

  • 1 month later...
On Saturday, August 13, 2016 at 0:55 AM, K^2 said:

Lets start with the fact that photosynthesis is less than 10% efficient, whereas optical rectenas start at about 40%. This is a death sentence for biofuels already, since land availability is the biggest bottleneck in civilized world. But then you have to add farming costs in machinery, labor, and energy consumption. Corn ethanol is not viable in US and Europe by a huge margin. It is not viable everywhere else by a much narrower margin, but then you add transportation costs on top of an already expensive fuel. So lets say with cellulose in the mix you can pass the break-even point. We are talking about net efficiency of less than 1% at this point. Even with free electricity, if you can make this actually cheaper than Jet-A from oil, I'll be impressed.

Yeah, solar power works only during the day. Which means you need to store it during the day. Got any idea how to store the massive amounts of energy we consume during a typical night without increasing a cost dramatically? I'll give you a hint. Power companies already have gas turbines. Yeah, you'd be taking a loss of over 50%, but given that infrastructure is already there and energy itself is almost free, it's stupid not to do it. Each modern power plant is going to become a giant battery using H2 generated during the day to power the place during the night.

The surplus H2 isn't going to be there because of power usage fluctuations. It's going to be there because electric companies will already need to make huge quantities of it, meaning they'll be able to sell it cheap as well, thanks to economy of scale.

So the options for airline companies is going to be LH2 at $0.05/gallon or Jet-A (bio or fossil) at $5/gallon. Long range variants of 777 take nearly 50,000 gallons of fuel and its longest flights use up almost all of it. So even with the fact in mind that you need about 4x the quantity of LH2 by volume, your options are paying about $200,000 to put 40k gallons for a flight or about $8,000 worth of LH2. You'll want to do at least one flight per day minus maintenance, so lets say 3,500 flights in 10 years, and you are looking at savings of over half a billion dollars. For comparison, the plane we are talking about costs about $300 million. If we throw in maintenance and man power, we are looking at saving about half of the airplane's ten year cost. Half. Multiply this by the size of the long-range fleet and you have enough money to build new airports, refueling infrastructure, and roll out new planes leaving just enough for each CEO to cut themselves a huge bonus check.

There are other considerations, of course, like that pesky safety factor. But it's going to be cheaper for airline companies to just get lobbying groups to talk about how much greener this is for the environment, and everyone will forget about the few unfortunate accidents caused by poorly trained technicians and really dangerous flammable gas. If you think little things like human lives are going to stop corps from pushing this through, given the insane amounts of money at stake, then you don't know anything about modern corporate politics.

You drastically underestimate just how expensive those airport additions you're talking about would be...  And how expensive LH2 is to store so it doesn't boil off...

Also, LH2 won't sell for $0.05 a gallon.  No way.  That simply would never happen.  The transportation costs alone of getting the stuff from the countryside where the solar farms would be to the city airports would dwarf that...

Anyways, I started this thread to talk about Optical Rectennas.  Particularly their applications for spacecraft.  Maybe we could get the discussion back on-track?

 

Regards,

Northstar 

Edited by Northstar1989
Link to comment
Share on other sites

This thread is quite old. Please consider starting a new thread rather than reviving this one.

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...