so,
hot air balloons are pretty great because they don't have
hard
to store leaky and expensive , or flammable gasses
air is everywhere . you just need to heat it up.
we all know how traditional propane baloons work.
otherwise there's 'solar' balloons.
solar hot air balloons have
been toyed with some time.
directly thermal balloons that work on soaking up the suns
direct rays and transmitting the heat to the internal air of
the
balloon.
meanwhile, the problem with propane powered hot air
balloons are they are heavy. solar balloons are not really
reliable nor does the air heat up all that much.
the upside is that, unburdened by lifting rigs, they are so
lightweight they don't need much lifting bouyancy from the
hot air gas. they are essentially big black garbage bags that
float when it's sunny out.
how about a new approach to creating an ultra lightweight
balloon that needs no propane and can stay tethered but
without bringing it down to resupply with lifting gas. PLUS
the balloon can generate electricity on site, without
electric
cables, or heavy solar panels mounted on the balloon.
simple-----get a rectenna to recieve microwaves with a
battery and an electric heating element in the balloon.
the microwaves can be directed precisely on target and
travel
directly into the balloon . the balloon is not propane
powered
and thus, between solar energy and microwave energy, the
balloon does not need to have a heat leaking
outport/inport.
a small valve for air can be designed into the balloon which
is
designed to keep heat IN the balloon as well as possible
while
being fairly light weight.
the balloon can convert solar and microwave radiation
directly to heat, and when needed convert the microwave
energy to electricity for whatever electrical needs the
balloon
might have. a small valve allows for air release and entry.
this sort of platform could also be ideal for a floating city
where these balloons are tethered to the mother platform
and are reheated as necessary. systems are designed for as
little heat leakage as possible.
BONUS POINTS
USE HELIUM INSTEAD OF AIR---AND
FOR HAVING IT BE A TOTALLY SEALED VALVELESS BALLOON
WITH INTERNAL HEAT SINK ( IF THE BALLOON GETS TOO
MUCH HEAT)
The bouyancy of HOT helium is such that you could probably
run the balloon on very little helium. problem is 'hot'
helium is probably especially leaky. however advanced new
thin films are especially impermeable and may one day
soon serve as appropriate skins for these types of hot
helium containing baloons.