--- In space-elevator@yahoogroups.com, "Andreas" <awnd329@...> wrote:
>
> --- In space-elevator@yahoogroups.com, "Herbert Murray" <hcm1955@> wrote:
> >
> > Would replacing the jet engine with an electric ramjet allow scaled
> > down system? The ramjet would operate at supersonic velocities within
> > the atomsphere. The power for the ramjet could be feed from the hub.
> >
> An electric jet is interesting technology. It is quite likely easier to build
and more efficient than a regular combustion jet. However, it has no
applications. All the places were jets are used lack electric power. Thus,
electric jets don't exist.
>
> I think the weight of power cables prohibits electricity on the aerovator.
>
> The best bet for electric jets might be for solar airplanes. The DC current
from the PV cells could be fed directly to an arc inside the engine. It could be
the most lightweight and efficient way convert sunlight to thrust. Not sure if
it really beats an electric motor with propeller, though, especially considering
that a solar airplane would have to fly quite slowly.
>
> Andreas
>


A rough comparison of electric ramjet to a 747 Engine

A 100 miles aluminum dual conducter with a cross section 1 million circular mils
rated to carry 500 amps will weigh 8000 pounds. Operating a HVDC system at 1
million volts would allow the transmission of 450 to 500 Megawatts. A 500
megawatt electric ram jet develops at least 50,000 pounds of thrust or about the
same as a CF6 (typical 747 engine). At the hub the conversion of AC to DC would
be heavy and expensive. But at the ramjet, the dc could be directly connected to
the heating elements, as pointed out early. A 747 flying at 500 mph will burn
10,000 pounds of fuel per hour. So the eletrical conducter to carry the power
for Mach 3 would weigh less than 4 hours of fuel required for a 747 flying at
less than Mach 0.9


The whole point of this is to spin the tether faster using a Mach 3 ramjet
allowing a shorter tether, hence scaling down the system. The tradeoff is a more
complexe propulsion system.

Cheers,
Bert