Musing: Battery Powered Rocket???

[mikejz]

I’ve been reading about research into ultra capacitors and would like to throw out the following idea<br /><br />What if capacitors or batteries ever achieved a higher energy density than conventional liquid fuels?<br /><br />It seems to me that such a technology would enable electric-thermal rockets to be a possibility. They would be much like nuclear-thermal with the benefit of actually being able to ‘light’ them on the ground.<br /><br />Any thoughts? <br /><br /><br />

 

[mrmorris]

There are a couple of problems.<br /><br />First -- even if the batteries were to achieve par, or even exceed chemical energy density -- the chemicals have a huge advantage. As the chemicals are expending their energy -- the mass of said chemicals is being shot out the back of the rocket. Once the chemical reaction is over -- all the mass is gone. By contrast -- the batteries are getting lifted all the way to orbit. The energy density would have to be <b>***much***</b> greater to compensate.<br /><br />Second -- electricity really isn't an efficient means of creating heat. This is why electric water heaters really bite. They're only about 30% efficient at best on converting electrical energy to heat energy (nuclear reactions on the other hand generate heat with great efficiency). Again -- this doesn't <b>preclude</b> the concept, it just ups the ante again on the energy density required.

 

[henryhallam]

<font color="yellow">Second -- electricity really isn't an efficient means of creating heat. This is why electric water heaters really bite. They're only about 30% efficient at best on converting electrical energy to heat energy</font><br /><br />Read the First Law recently? <img src="/images/icons/wink.gif" /><br /><br />Any electric heater is 100% efficient at converting electrical energy into heat. The reason they suck is that electricity is much more valuable than heat, you're throwing away the ability to do more useful work.

 

[qso1]

Maybe one day, but if history is any guide so far...look at electric cars. They really haven't changed all that much in the 60 or more years the idea has been around. They are still less efficient than gasoline engines and come with battery banks rather than a single battery and certainly have not replaced gasoline powered cars.<br /><br />I'm not sure what or how your looking to employ a battery or capacitor based system as a substitute for chemical propulsion but seems if we were anywhere near being able to develop such propulsion, either NASA or private enterprise/industry would be developing it. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[mrmorris]

<font color="yellow">"The reason they suck is that electricity is much more valuable than heat, you're throwing away the ability to do more useful work. "</font><br /><br />Actually -- I was doing one of the things I always try never to do -- namely making the assumption that the data I got from a single source was correct. In this case, it was my father-in-law. He's an engineer, and is generally *very* good about providing data on efficiencies and such. He'd indicated that electric water heaters were about 30% efficient and gas about 60-70% efficient. However, in this case, he was mistaken, and after a bit of Googling research, I know where he came up with the 30% figure:<br /><br /><i>"Electric resistance heating converts nearly 100% of the energy in the electricity to heat. However, most electricity is produced from oil, gas, or coal generators that convert only about 30% of the fuel's energy into electricity. Because of electricity generation and transmission losses, electric heat is often more expensive than heat produced in the home or business using combustion appliances, such as natural gas, propane, and oil furnaces. "</i><br /><br />Since the factors above don't have any bearing on electricity delivered to resistance heaters via batteries -- the second argument is null. The first problem is still applicable.

 

[mikejz]

Of course a chemical rocket has an oxidizer, so the weight penalty would be along the same lines.<br /><br />Second, it is possible that the propulsion be magnetic rather than thermal--basically hurling stuff magnetically out the back end.

 

[mrmorris]

<font color="yellow">Of course a chemical rocket has an oxidizer, so the weight penalty would be along the same lines."</font><br /><br />I don't see where you're going with this. The oxidizer gets thrown out the rear along with the propellant. The mass of the oxidizer is part of the action-reaction equation that makes a rocket go. So where's the penalty?<br /><br /><font color="yellow">"Second, it is possible that the propulsion be magnetic rather than thermal"</font><br /><br />You specified thermal when you likened it to a nuclear-thermal rocket. As for magnetic -- what are you going to be throwing out magnetically? Water is <b>weakly</b> magnetic and wouldn't kend itself to that kind of acceleration. What are you considering?

 

[docm]

Whatever would work in an ion or plasma drive, which are by their nature electric, but of course they're limited to operating in space. Batteries don't have the capacity for them either except for temp. storage for a solar panel array. Nuclear reactors are better <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> </div>