[Rhodes22-list] How Much Energy To Launch A Payload Into Space?

[Roger Pihlaja]

Michael,

It all has to do with how fast you have to accelerate the payload.  A rocket
can accelerate the payload over a distance of 100 km and several minutes of
time and so the power required is less.  For example, if you limited the
acceleration to "only" 16 g's (156.7 m/s^2), the acceleration time to reach
escape velocity is increased to 78.3 sec, the rail gun must be 39.8 km long.
The required total energy is the same at 5.677E11 joules; but, the power is
"only" about 8 megawatts because of the greater length of time involved.  At
10 km, I tried to choose a rail gun length that might be buildable up the
side of a real mountain.

Roger Pihlaja
S/V Dynamic Equilibrium

----- Original Message -----
From: "Michael Meltzer" <mjm at michaelmeltzer.com>
To: "The Rhodes 22 mail list" <rhodes22-list at rhodes22.org>
Sent: Wednesday, January 19, 2005 9:11 AM
Subject: Re: [Rhodes22-list] How Much Energy To Launch A Payload Into Space?


> Are you sure, seems a couple of orders of magnum off, The "standard"
> rocket lunches the finial payload in that range(10 ton), but lunch
> weight is many times that, mostly the need to lift the fuel to get is to
> the next level, the rail gun does not take the fuel along, were the moon
> rockets in that energy level??? as a crosscheck?, what about the probes
> they send out they are not using that type of energy budget?
>
> MJM
>
>
> Roger Pihlaja wrote:
>
> >Gentlemen,
> >
> >I don't think you folks appreciate how much energy it requires to lift a
payload into space.  Just for snicks and grins, I did the following rough
calculation:
> >
> >Suppose we want to be able to shoot 10 tons (9091 kg) off the earth into
the sun.  To do this, we must somehow accelerate the mass from rest up to
so-called escape velocity.  Escape velocity from the earth is about 25000
mile/hr (11176 m/s).  Suppose we build a "rail gun" up the side of a
mountain.  Now, once per day, the earth's rotation will have our rail gun
pointed in the correct direction to shoot a payload into the sun.  Let's say
we can build our rail gun 10 km long.  For the sake of simplicity, we will
assume the acceleration in the rail gun will be constant over the entire 10
km and there are no losses due to friction, magnetic coupling, electrical
resistance, etc.  How much power do we have to feed this rail gun?
> >
> >The required acceleration is 6245 m/s^2 or about 637 g's!  The payload
will have to withstand this acceleration for 1.79 seconds.  The energy
required is 5.677E11 joules and the power is 3.172E11 watts.  That's 31720
megawatts!  Keep in mind that a big nuclear power plant is typically rated
at around 1500 megawatts.  So, our rail gun facility needs about 211 world
scale nuclear power plants all operating at rated capacity to supply it with
sufficient power to launch one 10 ton payload per day into the sun.
> >
> >The power requirement for an explosive powered cannon is similarly
astronomical!
> >
> >Yeah I know, I need to get a life. :)
> >
> >Roger Pihlaja
> >S/V Dynamic Equilibrium
> >__________________________________________________
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> >
> >
> >
> >
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