Re: starship-design: HOTOL SeaDragon idea.

[KellySt@aol.com]

In a message dated 12/2/02 3:36:17 PM, KellySt@aol.com writes:

>Their was some studies of a mid orbit intercept by a nuclear powered tug.
> In theory you could do a factor of ten increase  cargo to orbit with a
>rocket based SSTO, overloaded into a suborbital capacity to intercept the
>boster tug.  NOt real sure I'ld recomend the idea though.  might as well
>just add the nuke to the upper stage or cary more fuel, and deal with a
>simpler system.
>
>
>
>Kelly


To: Mark Jensen
From: KellySt@aol.com
Hi everyone,
I just read the Fall 94 "Journal of practical applications in space".  (Yeah,
I know I'm behind.)  I finally finished Philip Chapman's artical on Reviving
Spaceflight.  It had some good ideas, but had bad writing.  One idea he had
sounded like half a good idea, and I wanted to know if anyone
confirmed/picked it apart yet.  

The idea was that given a basic SSTO at launch is 90% fuel, 9% ship, and 1%
cargo by weight.  (Its not quite that bac, but close.)  If you launch it to a
suborbital speed that takes 10% less fuel and have a orbital tug come down
and take the cargo (or give the ship a boost) you can save 9% of the total
weight and can get a tenfold upgrade in cargo capacity.  (1% standard cargo
capacity + the 9% saved fuel alotment.)  

Now he fiqured out that this could require 40% of your launches to be fuel
for the tug (specifically water to be processed into fuel), but he didn't
seem to realize that a 10% cut in orbital speed wouldn't save you 10% of your
fuel.
  
Anybody have any ideas as to how much fuel you could save?  Or for that
matter how much speed you could sacrafice and still have a reasonable chance
of intercept and boost?  The trick sounds like it could be usefull
(especially later if you get a nuclear rocket tug or Lunar water to cut down
up mass) but I wonder if he messed up his math somewhere.

Anyway thought somebody might know offhand, or just be curious. 


Subj:  Re:SSTO + Tug launcher?       
By: ==

On your SSTsub-O w/Tug idea, I ran some numbers:
At lift-off, 90K of fuel, 9K of structure, and 10K of payload.  With LOX/LH2, 
that ought to leave you just 6,000 fps shy of LEO.  A tug with 5.5K of fuel 
and 0.55K of structure could boost your 10K payload up to LEO.  For 
simplicity, let's say that the previous payload supplies the fuel.  10K 
payload minus 5.5K for fuel minus 0.3K of fuel to take the Tug from LEO to a 
rendezvous trajectory minus 0.2K for a fuel container, leaving 4K of usable 
payload.  That's a four-fold increase, IT WORKS!
  
==