See my reply to John, but he could conceivably launch an empty BFS on an
FH (it would be aerodynamically interesting, but not insurmountable, I
think, just a big hammerhead).
On 2018-02-10 11:46, Jonathan Goff wrote:
Rand,
Doing ground hops isn't the hard part of doing a reusable upper
stage--it's the orbital entry that's the hard part. I'd take Elon's
prospects of near-term full-RLV capability more seriously had he
started with making a reusable upper stage for Falcon 9. Even if it
was a tech demo with no intention of becoming an operational stage, it
would allow him to move a lot quicker to testing the hard parts --TPS,
control during reentry with CGs in different locations, etc. He
probably would have ~10mT of mass to work with (on a stage who's dry
mass is probably significantly less than that), assuming he wanted to
make sure the first stage could do a RTLS landing. That would allow
him to quickly test out the key risks he needs to retire.
But at the end of the day, I'm not heartbroken if Elon takes a
suboptimal path that gives his competition time to catch up. I'm more
interested in a competitive and healthy space transportation industry
than one dominated by a single player.
~Jon
On Sat, Feb 10, 2018 at 12:20 PM, Rand Simberg
<simberg@xxxxxxxxxxxxxxx> 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 [1]
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 [1]
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
Links:
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[1] tel:%28661%29%20718-0955