On Jun 21, 7:50 pm, Jeff Findley wrote:

snip

Henry Spencer has posted specific stages which meet the above criteria

in postings to these newsgroups. A Google search of these newsgroups

ought to turn up these postings. Of course, these stages were all

expendable. Making a reusable SSTO is quite a bit more difficult.

Jeff

Taking "orbit" as 9,000 m/s and SSME as 4,500 m/s, the mass fraction
is 1/7.4 or 13.5%

Gary Hudson has informally said that a mass fraction of 15% is about
as low as you can go for "reusable."

Skylon C1 design was 17.8% structure, (and ~4% payload) but they
cheat. Counting the rotation of the earth, they get to 1/4 of orbital
speed with an equivalent exhaust velocity of 10.5 km/s.

I have a graph of beamed energy exhaust velocity vs cost if I can
figure out how to make it into something I can put on a wiki.

Keith