laser propulsion

Pure airbreathing vehicles cannot enter orbit. That particular
design is airbreathing, and as such is no use for that
application. The reason is due to orbital mechanics- orbits
necessarily intersect the last point where thrust occured.
For pure airbreathing vehicles this is within the atmosphere.

Therefore, to allow it to enter orbit, it *must* carry fuel
with it in some way.

Secondly, that design requires a pulsed laser. Pulsed lasers of
the relevant power are very expensive. The heat exchanger idea
does not require pulsed lasers. Cheap semiconductor lasers can
be ganged up and shone through telescopes at the vehicle from
several different locations.

Thirdly, with the system that was demoed the laser was shone
from below. To make orbit you must go sideways very fast, and
just a bit upwards. The angles are quite awkward- you have to
supply enough velocity before it goes over the horizon.

panamabob wrote:

> I seem to recall successful launches using a laser that heated normal air and the expansion of that air creating the thrust. The "vehicle looks like a thrust nozzle super polished on the interior and the laser aimed up inside.
>
> As I said it already has launched successfully. Why complicate with additional hydrogen? It would seem to defeat the concept of not requiring the weight of fuel to be added to payload and hence additional costs.
>
> Curious
>
> Bob
> SLF
> -----
>

--
- Ian Woollard (ian.woollard@...)

"Is a planetary surface the right place for an expanding
technological civilization?"
- Gerard O'Neill