John:
While better propellants do seems a distance away; I’m inclined to think
that printed staged-combustion engines (a la Ursa Major) are a big enough
performance (and cost) benefit to count as a propulsion improvement worth
including in a today technology SSTO.
I was at the time impressed by the honeycomb inconel and Titanium
(respectively) TPS panels developed for X-33; they aced arc jet testing and
were both much lighter and appeared much more operable than ceramic
alternatives. The ARC inconel warpped ceramic tiles seemed—to me—a
possibly heavier and less operable backup technology. The need for
carbon-carbon ceramic at the hottest spots on some designs seemed to me,
twenty years ago, sporty: I would have designed c-c out of my personal
SSTO; I still hold that view.
I agree that Al-Li would be a today baseline. Northrop’s follow-on (to
LM’s X-33) composite H2 tanks worked fine in limited cycle testing and
might be an option. I remain deeply skeptical of using composites with Lox
for a 1000+ flights vehicle.
Highly reusable H2 tank insulation seems to me an issue: none of the three
X-33 proposals did much more than assume that the existing (or proposed)
corporate experience would last forever on an RLV. This was specially
problematic—in my view—wrt the DC-X insulation technology which was known
to shed into the plumbing.
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) and the exact trade between
landing propellant and wings: one existing trade suggests that wings weigh
about as much as landing propellant for two very specific designs.
Would you baseline tripropellant?
Bill
On Sat, Feb 10, 2018 at 12:44 PM John Schilling <
john.schilling@xxxxxxxxxxxxxx> wrote:
Hopping the upper stage doesn't help with the high-energy recovery
problem, which I think is going to be the hard part. He'll need the BFR
booster for that. Recovering an F9 or FH upper stage would get him a
head start there, as well as making a better general-purpose launch
vehicle in the near term, so I'm somewhat disappointed that he has moved
away from that.
John Schilling
john.schilling@xxxxxxxxxxxxxx
(661) 718-0955
On 2/10/2018 11:20 AM, Rand Simberg wrote:
But he's working the upper stage first, because he recognizes that as
the harder problem, given Falcon experience. He said he wants to start
hopping it next year.
On 2018-02-10 11:12, John Schilling wrote:
Elon said it was "conceivable" that BFR could have its first orbital
flight in four years, and Elon's schedule performance suggests that he
is already thinking in Mars years. So, mid-2025 at the earliest, and
I'd wager against even that.
John Schilling
john.schilling@xxxxxxxxxxxxxx
(661) 718-0955
On 2/10/2018 10:42 AM, Rand Simberg wrote:
Not far in the future, judging by what Elon said this week at the
launch. BFS is a reusable orbital stage.
On 2018-02-10 09:38, John Schilling wrote:
I believe it was achievable 20 years ago, just more trouble than it
was worth. It is probably more achievable now, but may still be more
trouble than it is worth.
One useful change has been improved materials and manufacturing
techniques to reduce structural mass, which is critical for SSTO.
Friction stir welding of Al-Li, for example. And maybe LOX-compatible
composites, depending on what happens with XCOR's "Nonburnite".
Another, I think underrated, change is increased skepticism through
hard experience of shiny technologies that we probably don't need,
like air-turboscramwarp drives and tankage shaped into elaborate
aerodynamic shapes.
Operational validation of VTVL reusables is a good thing to have,
given that given that expendable SSTO is an economic non-starter. The
best answer may still involve wings (attached to cylindrical tanks!),
but demanding wings because that's how Shuttle worked and we don't
trust anything else is a needless and possibly crippling constraint.
The biggest obstacle I see remaining, is the ability to safely and
reliably recover an orbital stage without excessive TPS mass.
Unfortunately, SpaceX seems to have pushed their work on that one
farther into the future, so maybe that's one for DARPA, Blue Origin,
or some newcomer to the field.
Propulsion is, I think, not a major constraint. We've got at least
marginally reusable rockets with adequate performance. There are some
nice-to-haves we could work for on that front, but no showstoppers for
a Mark 1 SSTO.
John Schilling
john.schilling@xxxxxxxxxxxxxx
(661) 718-0955
On 2/10/2018 9:01 AM, William Claybaugh wrote:
Dr. Schilling’s comments on SSTO got me thinking about Have
Region, DC-X, and X-33.
Technology is now about 20 years further down the road; is
chemical rocket reusable SSTO now achievable?
What is different?
Bill