Crops under solar panels can be a win-win

I subscribe to Aviation Week magazine. They are astoundingly professional; when they want to review a new aircraft, they fly one.

There was an article last week about the several companies that are trying to develop hydrogen-powered airplanes. You might read it.

Qualitative ideas are fine, but eventually the numbers matter. Engineering is like that.

His usage still isn't clear to me. "On the Shuttle, LH2 takes out the main part of the ET and still you need those SRBs as the first stage." Is he trying to say it makes the Shuttle smaller? I don't know what he means by "takes out".

so familiar with the material that the acronyms pop up automatically.

s opposed to impressing them - spells out that kind of acronym. For one thi ng short acronyms are ambiguous - ET tends to mean "extraterrestrial" more often than "external tank".

in part of the ET and still you need those SRBs as the first stage." Is he trying to say it makes the Shuttle smaller? I don't know what he means by "takes out".

roughly 3/4 of the giant external tank is liquid hydrogen

Sorry for the confusion, apparently I spent too many decades in sci.spce.shuttle and sci.space (now defunct) newsgroups.

Liquid hydrogen has a much lower density than liquid oxygen or kerosine. When burning substances the critical thing is the _mass_ ratio between fuel and oxidizer. Thus, to get the sufficient number of kilograms of liquid hydrogen, a very large tank volume is needing, which also requires heavier tank structures.

Most parts of the external tank (ET) are thus required for hydrogen, a much smaller part is occupied by oxygen. If the Shuttle would take off solely with hydrogen, the tank size would have to be many times larger. To avoid this, the solid rocket booster (SRB) will create the most trust during liftoff.

On Sunday, September 8, 2019 at 1:16:06 PM UTC-4, snipped-for-privacy@downunder.com wr ote:

ote:

s water for the amount of food produced the solar panels stay cooler improv ing their electrical production. True win-win.

ally anything is an improvement. It is not a general recommendation.

it takes to run irrigation pumps, and they really want to be using drip ir rigation in places like this, and drip is low power.It probably drove the i dea of using the panels for shading in the first place, although a lot stuf f doesn't do well in shade. Notice they didn't mention any of the economics , but the crummy vegetable crop isn't going to make up for the loss of reve nue due to greatly reduced panel density.

so many ways. They have HUGE problems. Here is a story about their plastics problem:

etting unsustainable.

roy the

roblem. There really aren't enough private planes to create a problem, but international tourism probably has to go.

ems to be true.

r liquid hydrogen fuel - rather lower energy density than liquid hydrocarbo ns - might save the tourist industry, but it would take a while and a great deal of expensive development.

y to

ocket fuel.

ol to allow them to land and be recovered.

se pointed out those examples were single use, but there is nothing inheren t in hydrogen fuel that makes a reusable rocket impractical.

So why use hydrogen fuel? Was it the enviromental issues? They don't stop people from using other, not so environmentally friendly fuels in other ro ckets. Didn't someone post here that Musk is using kerosene? Is that why his rockets landing look like movie props from the 50's? Anyone else notic e that?

Or maybe it's just because they are landing rather than taking off?

ess water for the amount of food produced the solar panels stay cooler impr oving their electrical production. True win-win.

erally anything is an improvement. It is not a general recommendation.

ty it takes to run irrigation pumps, and they really want to be using drip irrigation in places like this, and drip is low power.It probably drove the idea of using the panels for shading in the first place, although a lot st uff doesn't do well in shade. Notice they didn't mention any of the economi cs, but the crummy vegetable crop isn't going to make up for the loss of re venue due to greatly reduced panel density.

n so many ways. They have HUGE problems. Here is a story about their plasti cs problem:

getting unsustainable.

stroy the

problem. There really aren't enough private planes to create a problem, bu t international tourism probably has to go.

seems to be true.

for liquid hydrogen fuel - rather lower energy density than liquid hydrocar bons - might save the tourist industry, but it would take a while and a gre at deal of expensive development.

way to

rocket fuel.

ble

trol to allow them to land and be recovered.

else pointed out those examples were single use, but there is nothing inher ent in hydrogen fuel that makes a reusable rocket impractical.

op people from using other, not so environmentally friendly fuels in other rockets. Didn't someone post here that Musk is using kerosene? Is that wh y his rockets landing look like movie props from the 50's? Anyone else not ice that?

Rick C wrote in news:d5c46a04-9f9e- snipped-for-privacy@googlegroups.com:

external tank. That's my guess.

Are you not the twerp that does the "lol" thing so often?

It has been a long established norm for mil and space gear to have a lot of acronyms (and acronymic like abbreviations). Hell the US governement et al.

Because the single-use rockets are *fragile*. They are simply not engineered to work at the duty cycle that commercial aviation needs, and would be four times heavier if they were.

Even those are not likely to last a dozen launches, and that's good engineering, since the failure rate from other causes is still higher than that. They certainly couldn't approach the safety and duty cycle needed for commercial aviation.

Clifford Heath.

Hydrogen/Oxygen has a low molecular mass exhaust (very high energy/momentum ratio), and the shuttle main engine is basically just idling while the SRBs are firing . SRBs use rubber to produce a very high molecular mass exhaust - high momentum/energy ratio suitable for lower-speed (atmospheric) flight. When the SRBs are gone, the main engine ramps up. I've tried to explain this before, but it matters because at high speed, you're throwing out exhaust from a fuel you previously had to spend energy accelerating. It's not an adequate analysis to just look at the frame of reference of the rocket in flight, you must consider how it reached that point. Low velocity high molecular mass (= momentum) works better at slower speeds.

Clifford Heath.

e:

ote:

e:

nels-can-be-a-win-win/

ter for the amount of food produced the solar panels stay cooler improving their electrical production. True win-win.

anything is an improvement. It is not a general recommendation.

takes to run irrigation pumps, and they really want to be using drip irriga tion in places like this, and drip is low power.It probably drove the idea of using the panels for shading in the first place, although a lot stuff do esn't do well in shade. Notice they didn't mention any of the economics, bu t the crummy vegetable crop isn't going to make up for the loss of revenue due to greatly reduced panel density.

any ways. They have HUGE problems. Here is a story about their plastics pro blem:

ng unsustainable.

the

em. There really aren't enough private planes to create a problem, but inte rnational tourism probably has to go.

to be true.

quid hydrogen fuel - rather lower energy density than liquid hydrocarbons - might save the tourist industry, but it would take a while and a great dea l of expensive development.

t fuel.

to allow them to land and be recovered.

That's putting the cart before the horse. You engineer your product for the job it has to do. If the parts need to last for more than dozen launches t hen they get designed to last longer.

LOL Yes, but literally everyone knows what that means to the point of it b eing the equivalent of a word. It's the not so often used abbreviations th at are counter productive.

I'm not in the aerospace world as are most people here. In case you didn't know, this isn't an aerospace group, so when discussing aerospace topics i t makes no sense to think everyone will understand your abbreviations. Kin da like expecting you to understand anything anyone posts that isn't along your main line of thought.

Are words too hard for you?

Is "four times" the official aerospace number provided by NASA or someone??? The lady doth protest too much, methinks...

I'm still not sure what your point is. Single use rockets have their purpose. Multi-use rockets have their purposes. Both are practical.

Failure rate from all other causes? Are you saying they are likely to blow up before being used 12 times? I'd hate to be the astronaut to go up the 12th time!!! Usually it's 13 that is the unlucky number.

I think it is funny you are arguing a point without having any information to base your opinion on. Do you have any sources? Has Space-X said they only expect their rockets to last 10 flights?

stop people from using other, not so environmentally friendly fuels in othe r rockets. Didn't someone post here that Musk is using kerosene? Is that why his rockets landing look like movie props from the 50's? Anyone else n otice that?

You have me confused. Momentum is the name of the game, no? Isn't that th e product of velocity and mass?

I thought the issue was a bit like nuke power plants vs. gas turbines. Sol id rocket boosters can't be controlled once ignited. Liquid fuel can be co ntrolled. So you can't do the whole job with solid rockets unless you don' t care about the end game as is the case in missiles as weapons.

Doing a bit of searching...

"Compared to liquid engines, solid motors have a lower specific impulse ? ?? the measure rocket fuel efficiency that describes thrust per amount of fuel burned. However, the propellant is dense and burns quite quickly, g enerating a whole lot of thrust in a short time. And once they?ve b urned their propellant and helped propel SLS into space, the boosters are d iscarded, lightening the load for the rest of the spaceflight."

So the real difference is that solid rockets have more thrust because the b urn more rapidly. While they actually have lower specific impulse which me ans at the end of their burn they impart less energy to the space craft tha n a liquid fueled rocket would have, they do it more quickly getting the sp ace craft up to speed faster.

So it doesn't seem to do with there being any advantage to "high molecular mass exhaust", rather simply the faster burn rate. In other words, solid f uels don't actually require a rocket engine as such, so their thrust is not limited by the same factors as liquid fueled rockets.

Ok, I'll try again, because you still haven't got it.

Consider a Hydrogen/LOX motor at subsonic/transsonic speeds. The fuel is light, but bulky, and the exhaust velocity is very high, much higher than the speed of the rocket. The exhaust has residual kinetic energy in proportion to the (speed delta) squared, and returns momentum proportionate to speed times mass flow rate as with any rocket.

Now introduce a high molecular mass gas into the exhaust stream, for example by burning something that doesn't burn very well. It doesn't use much LOX, but it produces a greatly increased exhaust density, which means for the same peak nozzle temperature, you get a much slower exhaust stream. Now you need less heat to produce the same momentum change, so you can replace some of the H2/O2 fuel with the solid that you're burning. You have to expend energy lifting (accelerating) that extra reaction mass as you go.

If you run the numbers on this, it turns out that optimum performance is achieved when the exhaust is at a slower velocity than H2/O2 alone; as long as the rocket itself is still in small Mach numbers.

When you get to higher Mach numbers, the amount of energy you have to expend in accelerating the extra reaction mass (in order to have brought it with you) increases to the point it's not worth doing it. There's little or nothing to be gained by using a high molecular mass exhaust gas.

This is how the space shuttle works. The SRBs lift the shuttle through the atmosphere to around Mach 2 or so, then the main engine ramps up to full power for higher speeds.

I suspect that NASAs scientists understand this a lot better than your high-school physics allows you to. Please don't respond again unless you're actually prepared to write a program that crunches the numbers on it, as I have done (for a related problem also in rocketry). I won't respond to further displays of ignorance.

Clifford Heath.

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t stop people from using other, not so environmentally friendly fuels in ot her rockets. Didn't someone post here that Musk is using kerosene? Is tha t why his rockets landing look like movie props from the 50's? Anyone else notice that?

t,

ar

t the product of velocity and mass?

Solid rocket boosters can't be controlled once ignited. Liquid fuel can b e controlled. So you can't do the whole job with solid rockets unless you don't care about the end game as is the case in missiles as weapons.

? the measure rocket fuel efficiency that describes thrust per amo unt of fuel burned. However, the propellant is dense and burns quite quickl y, generating a whole lot of thrust in a short time. And once they? ve burned their propellant and helped propel SLS into space, the boosters a re discarded, lightening the load for the rest of the spaceflight."

he burn more rapidly. While they actually have lower specific impulse whic h means at the end of their burn they impart less energy to the space craft than a liquid fueled rocket would have, they do it more quickly getting th e space craft up to speed faster.

lar mass exhaust", rather simply the faster burn rate. In other words, sol id fuels don't actually require a rocket engine as such, so their thrust is not limited by the same factors as liquid fueled rockets.

I'm not trying to be a jerk, but your explanation is terrible. You state t hings as important without explaining why they are important. "which means for the same peak nozzle temperature, you get a much slower exhaust stream" . You say things like "If you run the numbers" without explaining why the numbers come out that way. Some very broad points are just stated without explanation at all, "When you get to higher Mach numbers, the amount of ene rgy you have to expend in accelerating the extra reaction mass...".

Here is a particular point you don't connect. "Now you need less heat to p roduce the same momentum change". That ratio is not the important ratio. It is MASS to momentum change, otherwise known as specific impulse... to te chnically in this case the inverse, specific fuel consumption.

Specific impulse is the change in momentum divided by the mass of the fuel used. Or this can also be calculated by the thrust (momentum change rate) divided by the mass flow rate. You are suggesting at low speeds the ratio (specific impulse) is not as important at the mass flow rate which you seem to be saying is maximized by the solid fuel. You totally fail to explain why this is more important than the specific impulse at low speeds.

In fact, with the greater mass flow rate of the solid fuel the correspondin g increase in thrust is less since the specific impulse is lower. This mea ns the solid fuel requires MORE fuel to be carried and burned to achieve th e same acceleration. Certainly this is less of a detriment in the early pa rt of the flight.

Maybe you are right, but from what I read the important point is specific i mpulse. That tells you how much acceleration you can get from a given amou nt of fuel, all other factors being the same (mass ratio, etc). The only d istinguishing factor I found that anyone stated was important was the fact that you could get a much higher thrust from the solid fuel rockets than li quid and so the actual acceleration would be faster with a higher burn rate . This is more a factor of the engines rather than an intrinsic property o f the fuel.

Nothing in your explanation above actually addresses *why* the solid fuel i s better at "small Mach numbers" or why liquid fuel was better at higher Ma ch numbers. Your explanation is simply incomplete with large gaps in logic .

I might think you are saying the same thing as I except with a lot more wor ds, but I don't see anything in your explanation that could be construed as addressing the fact that the solid rocket boosters burn more rapidly and p roduce a much greater thrust than the liquid fuel rockets. Everything you are talking about is in regard to intrinsic characteristics of the fuel its elf.

Your BS about my "high school physics" is just that. Rocket science is lar gely high school physics.

One thing I learned, a bit later than high school, is that few concepts are actually hard to understand or explain and that when someone can't explain a concept clearly, it is because they don't actually understand it themsel ves. QED.

Please don't bother to respond until you have actually reached the point of understanding your argument yourself. I won't respond to further displays of intellectual ineptness and an inability to explain your thoughts.

Hey Bozo, those "electric" cars are really fancy coal-fired vehicles. We will NEVER have so-called carbon neutral electric power.

Liquid hydrogen requires tanks over FOUR TIMES as large as jet fuel. This makes is UNUSEABLE as an aircraft fuel.

More climate alarmist bullshit.

Gnatguy doesn't seem to have heard of solar cells and wind turbines, and isn't aware that the electric power they generate is now cheaper than the power you can get by burning fossil carbon.

Presumably back when his brain of capable of absorbing new information this might not have been true, and he now can't overwrite the obsolete data.,

With planes that look like ones we have,

The fossil carbon extraction industry is spending a lot on spreading lying propaganda to this effect. Gnatguy is gullible enough to believe it.

Plants don't need UV light. Just red and blue. They'll do just fine.

"UVA is a part of the visible light spectrum that we see as white or yellowish light."

How can you trust any web page that says UV light is visible? Such a fundamental mistake makes everything from this source suspect.

Also, why are you resurrecting a three year old thread?