To amplify a bit, faster-than-1-day turnaround tends to push toward
having a single vehicle returning directly to the actual launch site.
SSTO can do that, at cost of some increased propellant-per-payload-mass
consumption.
Both having to recover stages from remote landing sites, and having to
then reintegrate them, tends to make faster-than-1-day turnaround very
difficult (if not impossible.)
Put another way, at high enough flight rates SSTO's ground-ops
simplicity can save more cost than its (very likely) higher-tech
manufacture and somewhat higher propellant requirement incurs.
Henry V
On 2/11/2018 8:08 PM, William Claybaugh wrote:
Elivind:
SSTO is lower cost than all current attempts _if_ flight rates get past once per day; I can send you the class notes from a lecture I give annually at the Space Policy Institute which discusses both the methodology and the conclusions that can be reached. Those suggest that SSTO, if economically achievable, will be lower cost than any other chemical rocket based system.
They also suggest that an upper stage will be required for high inclination and above LEO orbits. SSTO is a chemical rocket optimized economic solution to low earth orbit at very high (by today’s standards) flight rates, only. But in the absence of new physics, that is where a capitalist economy must ultimately go.
I should also note that SSTO is technically “sweet”: it is the kind of problem that entices some engineers into insensible and uneconomic “solutions”....
Bill
On Sun, Feb 11, 2018 at 4:05 PM Eivind Liland <spookysys@xxxxxxxxx <mailto:spookysys@xxxxxxxxx>> wrote:
What’s the appeal of an SSTO over landing your multiple stages of
boosters? I’d think you’d get less payload to orbit for the same
fuel, so if you already solved re-use of the first stage.. what is it?
11. feb. 2018 kl. 21:13 skrev Craig Fink <webegood@xxxxxxxxx
<mailto:webegood@xxxxxxxxx>>:
On Sat, Feb 10, 2018 at 2:46 PM, William Claybaugh
<wclaybaugh2@xxxxxxxxx <mailto:wclaybaugh2@xxxxxxxxx>> wrote:
Today, I would want to carefully understand two technologies:
very low power thrusting during entry to provide a stand-off
gas blanket (and specially the mass of propellant required)
I too have been thinking about this one for a while, and seems to
me to be the way to go. If done right, I would think the mass
penalty would be minimal. But first, the vacuum engine bell has an
expansion ratio that is too large to operate deep in the
atmosphere, but it will run just fine without it's nozzle extension.
One solution fits
https://i.stack.imgur.com/uKx53.jpg
So, the extension needs to be replaced with a variable nozzle
extension similar to a jet, but designed for a rocket and able to
open much wider (even reversing) for the heat shield mode. The
weight of the much heavier variable nozzle extension could be
mitigated by removing the engine gimbals and traditional TVC and
using the variable nozzle extension for ascent, entry and
atmospheric flight TVC. Increasing the expansion ratio of the
variable nozzle increase ascent performance, while providing
additional "wake shielding" of the tanks. The second stage could
then land on the engine to nozzle extension joint, so landing gear
would not be required.
The "stand-off gas blanket" or film cooling of the variable nozzle
extension would be minimal for parts that are all ready built from
high temperature materials. I would think this type of entry would
favor a short high gee entry of a longer lifting low gee entry.
The CG of the second stage is at or near the engine resulting in a
dynamically stable entry and atmospheric flight. Plus, assent,
entry and landing forces are all in the same direction, the
structure was built to handle load in the +X direction.
-- Craig Fink
WeBeGood@xxxxxxxxx <mailto:WeBeGood@xxxxxxxxx>
