My take: Hopping a BFR boilerplate upper-stage mass-balance/aero model
is technically useful, relatively cheap, and a great marketing aid for
gathering the seriously large chunks of investment it'll take to develop
BFR overall.
RE a reusable F9 U/S, my guess is that they may have found that stable
reentry in an attitude that'd require only a tolerable mass of thermal
protection can't easily be backed in to the existing design. If they're
going to have to design from scratch, might as well go direct for BFR
second stage, would be the thinking.
If so, they may be overlooking their own example of doing F9
risk-reduction subscale on the cheap with F1. Testing the BFR 2nd stage
config subscale on F9 may make development sense - could actually bring
in BFR faster and cheaper than going straight to full scale - totally
aside from market utility of an F9 reusable U/S.
Henry
On 2/10/2018 12:43 PM, John Schilling 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