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Energy Paradox

do we really need that much fuel for orbiting earth ?
  (+3, -4)
(+3, -4)
  [vote for,

Hi !

This is my first halfbaken idea, so please be patient with me.

I always thought that the energy needed for (going to) orbit is one of the big miracles preventing cheap ways of getting to orbit.

Then I did some simple math (I'm a disbeliver - you will find out):

The kinetic energy E=mv²/2 The static energy E=mgh

If I calculate this (for 1 kg) I get for the total energy need of a 150km above earth orbit:

E=1*7851²/2 + 1*9,81*150000

7851 m/s² is the orbital speed needed for staying in a 150km above earth orbit.

If I do the above math I end up with E=32.008.613 Joule, or 32MJ

This looks like a lot of energy ('Mega'Joule) but actually I kg of simple jet fuel has 44MJ of termal/combution energy.

This would mean I need an Efficiency of 73% or the equivalent of 730g of jet fuel (which is less then 1 liter).

And yes, I know that the problem is converting thermic energy to speed & height . The Paradoxon is only about the AMOUNT of energy in orbit.

If I add this amount of energy to the object in kinetic energy it orbits, that's all.

And this 73% efficiency is high, but why should it not be achievable, as it is still <1?

And there are better energy holders then simple jet fuel ...

What is even more annoying is that if I would take a patient ride to orbit in 8h (no need for overtime here), then I need a power of 1111Watt to provide the neded energy to my 1kg - my vacuum cleaner can do better - and yes it can run for 8h eating 1kg dust.

PS: yes, I know I have to GET into orbit too - but this is still a Paradox that only this energy is needed for BEEING in orbit.

gutemine, Sep 09 2010


       The rocket has to lift itself too - in particular the rest of the unburnt fuel. See "Tsiolkovsky rocket equation".
Wrongfellow, Sep 09 2010

       it's a second-order differential equation, and the solution is widely regarded as non-trivial.
8th of 7, Sep 09 2010

       yes, but I'm not talking about a rocket - I'm talking about a simple piece in orbit.   

       We can discuss how to bring it there in another idea.   

       But anyway, what if this 1kg is the rocket/space ship ?   

       And I didn't say that the cerosine is the fuel (100% fuel would not make very much sense anyway)   

       This comparison is just for illustrating the needed energy/mass ratio of the paradoxon of an orbiting 1kg. But I'll update the post to make this less misunderstanding.   

       And I hate differential equations ...
gutemine, Sep 09 2010

       Welcome, gutemine!!   

       You're right about the very low energy needed to raise and orbit an object. A 20 gram satellite (N-Prize weight!) in orbit at about 100km possesses as much energy (mostly kinetic, some gravitational) as you would get from a teaspoon of petrol.   

       But that doesn't solve the problem of getting there. You have to punch through the atmosphere, for one thing.   

       After all, an elephant in New York has the same energy as an elephant in London, but nobody will move the elephant for free.   

       Also, what's a "paradoxon"?
MaxwellBuchanan, Sep 09 2010

       You are right. In English it is simply a paradox - I corrected the title   

       The paradox is actually what makes a Space elevator so attractive, no need for rocket fuel that just needs to be lifted too and ejected all the way up.   

       But puncture trough atmosphere suggests that it is extremely hard to move trought the atmosphere, but we all do it on a daily basis - and a 150km move in 8h is even something you can achive yourself if you buy a bike and do a little practice. And the paradox suggests that the energy balance is not so much worser if you move upwards.   

       And if I look at the DHL bill for 1kg from London to New York, maybe we should ask them for an orbit quote :-)
gutemine, Sep 09 2010

       The moon orbits the earth without using any fuel whatsoever, so I don't see the problem here.   

       There are two (and a half) things going on here
1) Lifting an object to a height where orbit is practical (i.e. where there's nothing in the way)

       2) Giving an object enough of a push in a horizontal direction (assuming you did 1) straight- up) so that the what-comes-up must-come-down paradigm is converted into an orbital one. (This, I think, is the energy referenced in your calculation)   

       2.5) Having kicked off a successful orbit, tweaking it every now and then to maintain it.   

       I'd venture that the most expensive one here is 1), and that 2) and 2.5) are significantly easier - in energy terms.   

       Also, cycling 150km may not be an issue, if you go sideways - but I think you'd find it significantly more difficult cycling the same distance vertically - unless it was downwards. Or to put it another way, gravity.
zen_tom, Sep 09 2010

       Hi gutemine.   

       //do we really need that much fuel for orbiting earth ?//   

       Yes. Come on, think it through. It's not exactly rocket science. Er...
Jinbish, Sep 09 2010

       thanks for the summary.   

       Actually the energy for changing the height E=mgh results in only 1.5MJ   

       The remaining 30,5MJ are the cinetic energy to move sidewards at orbital speed.   

       So you are wrong 1) is the easier part.   

       And don't forget that if you use bicycle speeed then air friction is nothing you can not handle with a few energy drinks during the 8h.   

       Maybe we should ask Red Bull to sponsor this approach :-)   

       I think putting one of their empty cans to space would make up for the minimum 9 gram of the N prize too.   

       I calculated solely the enegy difference between the 1kg on earth surface and 1kg orbiting.   

       Which simply means any fuel burnt on top of this is a WASTE if you view it from the orbiting point
gutemine, Sep 09 2010

       Wind resistance is non-trivial on a bicycle. 1 Calorie(food) is 4.18 kJ, if you are riding at 20kph for that 150km, you are going to burn ~4400 Calories, about half overcoming wind resistance. That's about 10MJ overcoming wind resistance. If you increase your speed to 30kph, your wind resistance Calories go up to ~6500, or 27MJ.   

       Unless you have a way to move up slowly, then add all your orbital velocity once you're above the atmosphere, you are going to have to be moving a lot faster than that before you leave it, and wind resistance scales as the square of velocity.
MechE, Sep 09 2010

       The other problem with using the bicycle analogy, is that the bicycle uses a rigid frame to hold itself against gravity. If you are going to launch a rocket, it needs to hold itself against gravity. That means in addition to whatever actual thrust you're using for acceleration, you need to provide a constant 1g thrust for the whole launch just to keep from falling back. If you do that for 8 hours, you are going to find that you need a lot of extra fuel.   

       And you're right, the energy of position is not nearly as high as the energy needed to get there. But as has been pointed out, the same thing is true of traveling between two points on earth. I can drive from Boston to DC and have exactly the same potential and kinetic energy at either end, doesn't mean I haven't spent quite a bit in between.
MechE, Sep 09 2010

       analogies are only good until they break - I agree.   

       I just wanted to point out that the hoursepower you need for the ride decreases if you simply take more time   

       Then you bring down a 1kg cerosine explosion (with unrealistic 73% efficiency in converting to cinetic energy - unless you call all the damage it causes a success) to a healthy 1kW job that any normal household device can do.   

       But let's use another analogy - it doesn't take a balloon any energy to float, and it nicely survives the 1g - pretty long if it doesn't leak.   

       We are living on the bottom of a sea of air - which unfortunately ends before it gets interesting for orbiting our planet, hence floating/ballooning to space is not a real option.   

       Until atmosphere would decide to reach out that far :-)   

       And by reading Jules Verne I learnt another interesting thing - even if you have orbital speed straight upright, you will still not fall back to earth but end up orbiting.   

       The reason is simply - you have already earth rotation when you sit on the ground, and this sidewards movement will be sufficient that while you fall back you end up in an already eliptic orbit.   

       So you don't need to pedall upwards and then explode to orbital speed - simply get faster as the rockets do - but take your time.   

       Then the 32MJ/kg would mean that you can do the job!
gutemine, Sep 09 2010

       No paradox. Energy is only one consideration, momentum is the other. Thus you need all that rocket fuel, and things become messy and inefficient. (Flying saucers obviously have a method of avoiding the momentum problem.) The problem here is that you haven't phrased this as an idea.
ldischler, Sep 09 2010

       Yes, I'm guilty.   

       Actually I HAVE also a real idea (wich is partly based on this 'paradox')   

       But I'm new here, so for me this thread is also for finding out how much expertise/feedback/inputs I can expect. If I'm misusing the site, or not following the rules I'm sorry (newbies always have good excuses - don't they?).   

       But I thought this is a bakery, so it should be OK just to show up with the incredients for the cake.   

       BTW I already gave away almost all the hints in my answers on a feasable alternative on how to solve the problem of getting to orbit in a different way (and no - Scotty will not beam us up).   

       Momentum is only a problem within vacuum, but for 150km this is a solvable problem, because you are still close enough to the pond.   

       So let's see where this discussion will lead us ...   

       Maybe another hint: why can some fishes fly or even walk on the shore?
gutemine, Sep 09 2010

       [marked-for-deletion] WIBNI
Wouldn't It Be Nice If we could ignore gravity and air friction during orbital insertion.
Plus, as [ldischler] has noted, no idea asserted.

       Welcome, [gutemine]! Sorry this seems harsh. However, if you frame your posting as an invention or specific idea, it becomes much easier to discuss.
lurch, Sep 09 2010

       what is // BEEING in orbit//?
xandram, Sep 09 2010

       I think this was supposed to be "peeing in orbit."
ldischler, Sep 09 2010

       //And by reading Jules Verne I learnt another interesting thing //   

       OK, put away the Jules Verne, or at least take Jules Verne off of the science shelf. He doesn't belong there.   

       I don't have time to do the math right now (it's been 10 years since I've worked orbital mechanics, I'd have to look up the equations), but suffice it to say, IF you "go straight up" with enough speed that your apogee velocity is equal to the equatorial velocity, your apogee (and thus gravitational potential energy) will be much greater than 150 km altitude.
Freefall, Sep 09 2010

       actually peeing in orbit is pretty close :-)   

       Let me explain and summarize our findings on the paradox term as I see it:   

       The actual energy needed for our hypothetical 1kg in orbit is not really exciting as we agree.   

       On the other hand for reaching (!) space with a rocket we burn hundreds of kg, up to maybe 1ton of fuel to get 1kg into orbit. Reason is that we use momentum for moving our 1kg, and that air resistance is our enemy.   

       For me the most polite word for this is a paradox (others would say crazy).   

       And regarding the upward shot:   

       If you have the kinetic energy of orbital speed of 7.8km/sec (30,5J as calculated above) and the height energy of 150km is only 1,5MJ, then this means you will go up for another approx 20,33x150=3050km. Meaning the apoge point of your eliptic orbit will be 3200km above earth. Don't ask me if this is sufficient that you don't hit the earth when going back because eliptic is to small. Probably the formulars for eliptic orbits including Keplers laws are not that simple math.   

       Only if you would have more then the second cosmic speed 11km/sec you would not fall back   

       PS: I would define beeing in orbit = beeing high and fast enough to stay there ?
gutemine, Sep 09 2010

       //Don't ask me if this is sufficient that you don't hit the earth //   

       If I remember correctly, any purely ballistic shot from the surface of the earth will create an orbit that passes through the surface of the earth. You have to go up a bit, then sideways a bit.
MaxwellBuchanan, Sep 09 2010

       By the way, [gute], if you're impressed by how easy it *should* be to get into orbit (at least in terms of energy budget), check out the N-Prize.
MaxwellBuchanan, Sep 09 2010

       well, buying the spoonfull of cerosine would be definitely within the N-prize budget :-)   

       As I cann't attach here my slides, I'll have to post my idea in the N-prize forum anyway (so just be patient), but it first needs some more basic checks.   

       If somebody here is good in gas dynamics he could volunteer for an early peek!   

       I could describe the idea in 1 sentence, but then we would spend pages on doing and checking the math - the slides are more efficient in explaining (and more entertaining too).   

       So let's first finalize our discussion here:   

       We cann't do it efficient with a rocket because Tsiolkovsky is against us.   

       A quick check in the Wiki on non-rocket space launch is not very motivating either:   

       * Space tower – too heavy * Space tether – I hate waiting for nano tubes * Inflatable tower – cool, but who pays the helium bill * Space fountain – cool, but I hate projectiles ... That's all folks ?   

       Or can we do better ?
gutemine, Sep 09 2010

       Bees. Obviously.
pocmloc, Sep 09 2010

       //If somebody here is good in gas dynamics he could volunteer for an early peek! //   

       Someone here must be, shirley?
MaxwellBuchanan, Sep 09 2010

       Bees would be perfect Nano satellite astronauts for the N-price :-)   

       Maybe if I put them in the Red Bull can it could go for an N-prize+ ?   

       But I would really need such an egghead to check if I didn't do a dumb mistake in my math and assumptions.   

       If he/she doesn't run away screaming (or laughing) we can discuss it anytime.
gutemine, Sep 09 2010

       sorry, my english vocabulary is not that great, maybe I will edit it to be simply jet fuel - OK ?   

       But kerosene should be also right ...   

       And I'm really sorry, if you had to use bing :-(
gutemine, Sep 09 2010

       Thanks for pointing out my typos/bad vocabulary. I'm not a native English speaker, so I have a good excuse anyway.   

       And don't spend to much time on the fuel - I included this only to illustrate that it is not really that much energy which is needed.   

       And burning something (even when it are explosives) is a pretty bad way to convert energy.   

       The real trick to solve the getting to orbit problem in a new way is to make the enemy your friend :-)   

       But nobody catches the hints ...   

       And no professor from Georgia Tech is volunteering for scientiffic advice either.
gutemine, Sep 09 2010

       //And burning something (even when it are explosives) is a pretty bad way to convert energy//   

       [8th_of_7] might disagree - or he might point out that some kind of plasmafication or obliteration or some other cat-to-antimatter-to-energy conversion process is far better.
Jinbish, Sep 09 2010

       I prefere low-tech solutions .... maybe because I recently ran out of the anti matter.   

       To be honest the N-prize webbpage picture with the paper plane was also one of the inspirations.   

       But if mankind could send their typos to space we would have much more space debris
gutemine, Sep 09 2010

       So, in point of fact a rocket can power its way into orbit but, AS YOU MAY OR MAY NOT HAVE NOTICED, tiny scale models of space ships are not able to replicate the orbital feats of their larger cousins. The FEAT of orbital space flight DOES require exponentially larger relative energy capacities with reduced scale. There is, in fact, an optimum size for a ship given the fuel density/thrust efficiency size of payload thus an optimum caloric output and it is huge. Your "energy math" excludes the weight of the fuel, rocket, structure, drag. Simply put it is meaningless.
WcW, Sep 10 2010

       //As I can't attach here my slides, I'll have to post my idea in the N-prize forum anyway (so just be patient), but it first needs some more basic checks.   

       If somebody here is good in gas dynamics he could volunteer for an early peek!   

       I could describe the idea in 1 sentence, but then we would spend pages on doing and checking the math - the slides are more efficient in explaining (and more entertaining too). //   

       OK, post a link to your slides, or tell us your idea in 1 sentence. The point of HB is that you tell us your idea, not tease us with riddles.
xaviergisz, Sep 10 2010

       look, I could be wrong, but if you cannot figure out how to get images onto the web where I can see them, I have doubts that you are going to be able to overcome the design hurdles of space flight. This is a matter of simple modern competence no longer a financial or technical challenge, you simply haven't tried.
WcW, Sep 10 2010

       OK- your are challenging, then I will try to condense it to 1 sentence:   

       Friction is your friend.   

       And I know how to post something in the web - if you would google a little bit you would find out :-)   

       But maybe I have a misunderstanding here how this place works - shouldn't we all be the bakers trying to get the cake finished or is it just about tasting some half baked stuff?   

       BTW the idea of the 'paradox' is that we should think about how to get away to add ONLY the energy really needed as calculated above.   

       And yes, I like riddles - it keeps the discussion fun and hopefully entertaining to the participants.
gutemine, Sep 10 2010

       You'll find that people here won't want to play teasing games for very long if they sense that there's no valid science behind the idea. In this household we usually obey the laws of thermodynamics.   

       Save yourself later grief and eventual cold- shoulders by reading the help file on the left.   

       Friction is both your friend and your enemy. Like your spouse.
RayfordSteele, Sep 10 2010

       Thanks for the feedback and inputs !   

       As I said already in another idea thread:   

       Because tomorrow we have 9/11 anniversary I decided that this will be the perfect date for discussing ideas on how to errect huge structures.   

       I'll therefore create a new idea thread for discussing it tomorrow, and you will then find the illustrating slides downloadable in the N-prize forum Technology advice section.   

       Thanks for your patience with me !
gutemine, Sep 10 2010

       I guess you don't need to be a rocket scientist to understand this idea... hmm... hang on... well, anyway, welcome to the b/2 [gutemine]
Fishrat, Sep 10 2010

       well it is an idea on how to build a space tower to win the N prize - so don't expect it to save the planet with a £999.99 budget :-)   

       And no, it is not rocket science.   

       But it should be scaleable ...   

       PS: Dave said that if the tower would be 100km high and stay there for 9 days (= 9 orbits) this would be within the rules if it delivers the 9,99 gram.
gutemine, Sep 10 2010

       so you don't actually have an idea.
WcW, Sep 10 2010

       Just a couple of minor points:   

       1) Technically, the "satellite" will have to be prevented from touching the sides of the tower during the nine days, but I think this would be doable?   

       2) Errrrr....it's Paul. (Oddly enough, Dave is my brother.)
MaxwellBuchanan, Sep 10 2010

       In don't really understand why it is iritiating to discuss a problem.   

       Wiki says about a paradox:   

       A paradox is a true statement or group of statements that leads to a contradiction or a situation which defies intuition.   

       Our intuition says we need lots of energy to go to space because it is so far out (are 100km far?) and we need so much rocket fuel to get there.   

       On the other hand the real mechanic energy needed to stay there is not exiting.   

       But I agree that pointing this out is not what you would classically call an idea, or better a discovery at all.   

       But to be honest I'm testing also a little bit the crowd - eg what kind of feedback/expertise somebody can get when asking dumb questions.   

       It is clear that such a thread will lead to some frustration on both sides.   

       I'm not questioning the approach you are using here by having a clear idea:discussion relationship, but for really complex problems this is also a limitiation in itself.   

       So I'm willing to excuse for this, but this would still not inhibit us to bake some more weird ideas on how to get to space in an energy efficient way.   

       At least for the next 3 hours until I promised already to post the Space Tower NT (working title) idea.   

       PS: and sorry for the Dave ... I'm mixing up threads. And yes this are two different things - using such a tower as a launch device which also adds orbital speed or just as a lifter. Both should be feasable - to some extent.
gutemine, Sep 10 2010

       'Pull' ist actually pretty close   

       All the discussion about strength for a space tower is that you have a problem finding a material which can handle the forces. So the tether approach came up to need only to withstand the pull forces and not push forces.   

       So there are 2 approaches in our brains to handle the weight of a space tower:   

       1. Bottom to Top = Tower (Push) 2. Top to Bottom = Tether (Pull)   

       But actually there is a 3rd one !   

       3. Continuously - this is the idea of the inflatable space tower or kite trains - BUT both have the problem that as soon as you go to vaccuum you run out of lift.   

       So you could call this only a 2.5 solution (and you get even a patent granted for this)!   

       I simply didn't stop here but tried to fix the problem how to get lift which works also in vaccum !   

       And there are not very much forces which work in vaccum too - so actually finding a potential solution wasn't that difficult at all. The space fountain idea already used electromagnetic forces - and it is a feasable solution. But I don't feel comfortable with projectiles just to keep a tower upright and getting a vaccum tube build - especially if you have the N-prize budget restriction in mind.   

       So I had to to move futher.   

       For thousand of years people thought water cann't flow upwards.   

       Until Archimedes invented his screw and proved them wrong - and it even worked with a crank handle and some slave labour.
gutemine, Sep 10 2010

       This is a forum where people post ideas for discussion. You have decided to use it for an annoying guessing game. Well, I'm not amused, and it's looking like I'm not the only one.   

       And it's starting to look like you're aiming to bring in a marketing stunt. (Which will be particularly offensive if you do it at the time you claim to be planning for.)   

       I hope I'm wrong - but if I'm not, don't be too surprised if your account gets deleted.
lurch, Sep 10 2010

       OK; I'll be quiet until midnight if you don't want to feed Trolls.   

       Then you get your Space Tower NT idea and I probably make a total idiot out of mine.   

       And every half baken idea in my understanding is a guess on the remaining ingredients
gutemine, Sep 10 2010

       Lost me after "Hi !" but I always give buns to newbies.
doctorremulac3, Sep 10 2010

       Here's a warmup to the halfbakery help file, since you apparently can't be bothered.   

       What is the halfbakery? The halfbakery is a communal database of poorly thought-out ideas for inventions. Its users can post their inventions and add links and commentary to other people's posts.   

       What the halfbakery isn't: This site is not a store, a game, or a business of any sort; if you think that, you're probably confusing the site with one of the postings on it. Sorry. The site is also not a resource to help people guide their inventions from conception to completion. This is the place where you post the things you're not going to be working on - because you can't be bothered, or you don't know how to, or because it's not such a stellar idea after all. The site is also not a marketplace where owners of patents find interested developers. Such sites exist (some are listed under links), but this isn't one of them.   

       Inventions Ideas for inventions for the halfbakery should be original to the poster and should, as far as the poster knows, not exist already. (Use search engines to check whether or not what you're about to invent already exists.) Do not post patents, product announcements or advertisements. Inventions are best if they're possible, or impossible in interesting ways. Obvious contradictions meant as a joke - e.g., "dehydrated water" - grow old quickly, and so do "magic wand" ideas that are blanket solutions for some well known problem without any functional link to the problem. ("A panic button that fixes my computer".) A cleverly disguised description of a "wheel" is posted about once a year; so's an idea for a recursive idea, for whose explanation - well, just click here. If you haven't seen one of those jokes this year, there's your chance to impress everybody with your wit and originality. Generally, the more you know (and can explain!) about the technology behind your invention, the more interesting the posting will be. As always, when in doubt, write about something you know. (More about which inventions fit here and which don't can be found in the section on [marked-for- deletion].)
RayfordSteele, Sep 10 2010

       Thanks for the explaination.   

       Space Hose idea is now blowing up as promised.   

       If somebody has spare venture captial - pelase donate it for disabled children, because this idea will NEVER be patented after making it public.   

       And I don't even know if it really works :-)
gutemine, Sep 10 2010


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