[AR] Re: NASA test of quantum vacuum plasma thruster (was "Anyone heard of this?")
- From: Keith Henson <hkeithhenson@xxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Tue, 5 Aug 2014 17:13:06 -0700
On Tue, Aug 5, 2014 at 3:00 PM, Peter Fairbrother <zenadsl6186@xxxxxxxxx> wrote:
> On 05/08/14 19:31, Keith Henson wrote:
snip
>> I have not seen the paper, but someone quoted to me that they were
>> seeing 30-50 micronewtons.
>>
>> Let's assume the power level was on the order of a kW and gave ~40
>> micronewtons or ~40 micronewtons per kW.
>
> The power level was 28 watts. They also report a peak thrust of 116 uN at
> 16.9 watts.
That's seriously better. 6100 uN/kW, ~6% of an ion engine
snip
> Though the paper does discuss a Mars mission, even so, the drive would not
> really be suitable for solar system use, except perhaps the further reaches.
>
> It would only come into its own where final velocities above about 50 km/s
> are needed, and even a Vasimr drive would need a mass ratio well above 10.
Wait, VASIMR engines reach 50 km/s exhaust velocity. 1-1/e is about
63% reaction mass.
> It might be most useful in a nuclear-powered interstellar probe, at about 1%
> of the speed of light.
>
> That's if it works at all ..
Right.
Keith
> -- Peter Fairbrother
>
>
>
>>
>> For electric thrusters, a kg of reaction mass per second accelerated
>> to 20 km/s (typical VASIMR) acquires a Ke of 1/2 mV^2. This takes 200
>> MW (at 100% efficient).
>>
>> The force is 1kg x 20,000 m/s or 20,000 Newtons, 100 N/MW or 0.1 N/kW,
>> which is 100,000 micronewtons per kW.
>>
>> Reducing this number is the VASIMR efficiency (~70%) and the reaction
>> mass fraction, which for LEO to GEO and this exhaust velocity is
>> around 20%. Earth to Mars is similar.
>>
>> It's still 1000 times more energy effective to use ion engines,
>> assuming I have not made some boneheaded error.
>>
>> Keith Henson, L5 Society founder and EE (if you still need one)
>>
>>
>
>
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