Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > sci.physics > #691110

Re: Shooting to the Moon

Show all headers | View raw

Edward Prochak <edprochak@gmail.com> wrote:
> On Sunday, June 17, 2018 at 10:07:28 PM UTC-4, Arindam Banerjee wrote:
>> On Monday, June 18, 2018 at 11:44:42 AM UTC+10, Edward Prochak wrote:
>>> On Sunday, June 17, 2018 at 9:13:39 PM UTC-4, Arindam Banerjee wrote:
>>>> On Monday, June 18, 2018 at 10:04:56 AM UTC+10, Edward Prochak wrote:
>>>>> On Friday, June 15, 2018 at 9:21:25 PM UTC-4, Arindam Banerjee wrote:
>>>>>> Did 3200 amps with own two brown hands
>>>>> 
>>>>> you are off by 3 orders of magnitudes!
>>>> 
>>>> No.
>>>> 
>>>> I shorted with a 16.5 V 250F capacitor bank with a low milliohm
>>>> circuit resistance to get 3200 amps on the average.  The 3200 A
>>>> was calculated from the drop in the voltage across the capacitor
>>>> bank. Say when it dropped from 16.5 V to 7.5 V then the charge
>>>> discharged is 250 (16.5 - 7.5) = 2250 coulombs.
>>>> 
>>>> Agreed?
>>> 
>>> Yes, but
>>> That is still 3 orders of magnitude less than the
>>> 25,000,000 Amps needed for the 1km rail gun.
>>> I don't know what materials will carry that high a current.
>>> 
>>> ED
>> 
>> In my PhD work, my guide asked me to do a worksheet showing
>> how much a conductor of a given dimension will heat up over
>> time with current.
>> 
>> That I did, and with that help I designed my 3200A gun. It does not
>> become hot by the way, thanks to the dimensioning.
>> 
>> Extending that to my motor (the IFE) I worked out that with a
>> 500mm*500mm copper cross section, the heat increase would be manageable
>> for 3 million amperes.
>> 
>> I can use the same worksheet to work out the dimensions for 25million amps.
>> 
>> My guess is that it would be around 2000mm*1000mm.
>> 
>> That is a lot of copper, for 2000m rails, but it will carry 25 million
>> amps. Note, this are rough figures. We also need to know that the whole
>> barrel will be vacuum sealed and as cold as possible. Colder the
>> temperature, better the conductivity, lower the contact resistance, etc.
>> I am not talking about superconductivity, just higher conductivity with lower temperature.
>> 
>> I am giving over-the-top back of the envelope estimates. Naturally, when
>> we get down to the calculas and do the fine slicing, the actual figures
>> for a given design will emerge. Reducing the contact resistance is the key. 
>> 
>> Another point - we need existing defunct mineshafts going down 1-2Km for
>> this gun. No point creating a 1000 m vertical structure, what! Natural
>> side-support, in a hole!
>> 
>> I think we can with a limited budget make a gun that can launch small
>> satellites into space. It can compete with rocket launches. 
>> 
>> Cheers,
>> Arindam Banerjee
> 
> Earlier you Arindam) posted:
> "25 million amps is nothing but 25000 volts divided by 1 milliohm. 
> No problem at all, both in theory and practice."
> 
> the total resistance needs to be 1 milliohm (or less)
> 
> So what is the resistance?
> to obtain a voltage drop of 25000V over 2 kilometers,
> R=rl/A
> l - length 2 km (=2000 m)
> A - cross-sectional area 2000mm by 1000mm (2m*1m= 2m^2)
> r - rho resistivity for copper is 0.000 000 017 ohm-meter
> 
> R= 0.000 017 ohm = 0.017 milliohm.
> 
> I'm impressed. about a factor of 5 margin of safety.
> 
> Now 2 Km by 2m^2 is a volume of 4000 m^3
> Density is 8.96 g/cm^3 * 1kg/1000g * (100 cm)^3/m^3 =8960 kg/m^3
> total weight 35,840,000 kg
> Now I'm impressed again. Cost is a little over $25 million.
> 
> Of course it will be the assembly costs that swamp the material costs.
> You'd likely want the rails to be continuous. so you'd want to caste the
> rails in place maybe?Or can it be multiple parallel sheets of copper?
> (how big is a roll of copper 1km long?)
> 
> Physically doable, though challenging. that the navy gave up on their
> railgun, suggests there are other challenges we haven't identified.
> 
> Nothing better be around the launch tip, that is going to be
> one hell of a sonic boom!
> 
> Ed
> Meaning the resistance needs to be 
> 

I think the copper is going to melt the second you make a single firing.
Well, melt maybe is not the right word. Explosively vaporize is perhaps
better. Fairly simple to calculate the heating load and then ask whether
copper’s thermal conductivity is anywhere near what it would need to be. 

Quenching of accelerator superconducting dipoles is an object lesson. 

-- 
Odd Bodkin — Maker of fine toys, tools, tables

Back to sci.physics | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Shooting to the Moon Arindam Banerjee <banerjeeadda1234@gmail.com> - 2018-06-15 05:20 -0700
  Re: Shooting to the Moon Wally W. <ww84wa@aim.com> - 2018-06-15 08:55 -0400
    Re: Shooting to the Moon Edward Prochak <edprochak@gmail.com> - 2018-06-15 08:34 -0700
      Re: Shooting to the Moon Sergio <invalid@invalid.com> - 2018-06-15 13:42 -0500
        Re: Shooting to the Moon Arindam Banerjee <banerjeeadda1234@gmail.com> - 2018-06-15 14:26 -0700
        Re: Shooting to the Moon benj <benj@nobody.net> - 2018-06-15 19:17 -0400
          Re: Shooting to the Moon Arindam Banerjee <banerjeeadda1234@gmail.com> - 2018-06-15 18:21 -0700
            Re: Shooting to the Moon Arindam Banerjee <banerjeeadda1234@gmail.com> - 2018-06-16 05:55 -0700
            Re: Shooting to the Moon Edward Prochak <edprochak@gmail.com> - 2018-06-17 17:04 -0700
              Re: Shooting to the Moon Arindam Banerjee <banerjeeadda1234@gmail.com> - 2018-06-17 18:13 -0700
                Re: Shooting to the Moon Edward Prochak <edprochak@gmail.com> - 2018-06-17 18:44 -0700
                Re: Shooting to the Moon Arindam Banerjee <banerjeeadda1234@gmail.com> - 2018-06-17 19:07 -0700
                Re: Shooting to the Moon Edward Prochak <edprochak@gmail.com> - 2018-06-18 13:35 -0700
                Re: Shooting to the Moon Odd Bodkin <bodkinodd@gmail.com> - 2018-06-18 21:02 +0000
                Re: Shooting to the Moon Edward Prochak <edprochak@gmail.com> - 2018-06-19 10:39 -0700
                Re: Shooting to the Moon Arindam Banerjee <banerjeeadda1234@gmail.com> - 2018-06-19 15:35 -0700
                Re: Shooting to the Moon Arindam Banerjee <banerjeeadda1234@gmail.com> - 2018-06-19 21:09 -0700
                Re: Shooting to the Moon Edward Prochak <edprochak@gmail.com> - 2018-06-20 10:49 -0700
                Re: Shooting to the Moon Arindam Banerjee <banerjeeadda1234@gmail.com> - 2018-06-20 16:18 -0700
                Re: Shooting to the Moon Edward Prochak <edprochak@gmail.com> - 2018-06-21 15:05 -0700
                Re: Shooting to the Moon Arindam Banerjee <banerjeeadda1234@gmail.com> - 2018-06-21 16:57 -0700
                Re: Shooting to the Moon Sergio <invalid@invalid.com> - 2018-06-18 16:18 -0500
                Re: Shooting to the Moon Steve Carroll <frelwizzen@gmail.com> - 2018-06-19 10:40 -0700
                Re: Shooting to the Moon Arindam Banerjee <banerjeeadda1234@gmail.com> - 2018-06-19 15:20 -0700
                Re: Shooting to the Moon Arindam Banerjee <banerjeeadda1234@gmail.com> - 2018-06-18 22:40 -0700
      Re: Shooting to the Moon Arindam Banerjee <banerjeeadda1234@gmail.com> - 2018-06-15 14:29 -0700
        Re: Shooting to the Moon Wally W. <ww84wa@aim.com> - 2018-06-16 11:10 -0400
          Re: Shooting to the Moon Arindam Banerjee <banerjeeadda1234@gmail.com> - 2018-06-16 15:13 -0700
          Re: Shooting to the Moon Arindam Banerjee <banerjeeadda1234@gmail.com> - 2018-06-16 19:04 -0700
            Re: Shooting to the Moon Arindam Banerjee <banerjeeadda1234@gmail.com> - 2018-06-16 20:05 -0700
              Re: Shooting to the Moon Arindam Banerjee <banerjeeadda1234@gmail.com> - 2018-06-16 21:18 -0700
              Re: Shooting to the Moon Wally W. <ww84wa@aim.com> - 2018-06-17 05:35 -0400
                Re: Shooting to the Moon Arindam Banerjee <banerjeeadda1234@gmail.com> - 2018-06-17 03:08 -0700
                Re: Shooting to the Moon Arindam Banerjee <banerjeeadda1234@gmail.com> - 2018-06-17 06:00 -0700
                Re: Shooting to the Moon Wally W. <ww84wa@aim.com> - 2018-06-17 13:28 -0400
                Re: Shooting to the Moon Arindam Banerjee <banerjeeadda1234@gmail.com> - 2018-06-17 16:15 -0700
    Re: Shooting to the Moon benj <benj@nobody.net> - 2018-06-15 11:48 -0400
  Re: Shooting to the Moon numbernumber1964@gmail.com - 2018-06-18 15:29 -0700
  Re: Shooting to the Moon numbernumber1964@gmail.com - 2018-06-19 12:21 -0700
    Re: Shooting to the Moon Odd Bodkin <bodkinodd@gmail.com> - 2018-06-19 21:47 +0000
  Re: Shooting to the Moon numbernumber1964@gmail.com - 2018-06-19 12:29 -0700
  Re: Shooting to the Moon furthermore7990662@gmail.com - 2018-06-19 16:03 -0700
  Re: Shooting to the Moon furthermore7990662@gmail.com - 2018-06-19 16:03 -0700
  Re: Shooting to the Moon carleto4157990662@gmail.com - 2018-06-19 16:05 -0700
  Re: Shooting to the Moon carleto4157990662@gmail.com - 2018-06-19 16:06 -0700

csiph-web