Bob Clark:
Correct. Only partially fueled and using 3 sea level Raptors, BFS could
still roughly match X-33's trajectory, and thus should be able to
characterize the TPS for orbital-reentry-like conditions.
-Chris
On Wed, Mar 14, 2018 at 10:06 PM, Robert Clark <rgregoryclark@xxxxxxxxx>
wrote:
Do you mean only partially fueled to take off with only three of the
engines firing?
Bob Clark
On Wednesday, March 14, 2018, Chris Stelter <robotbeat@xxxxxxxxx> wrote:
Jon,
I think you're under-estimating the ability of a near-term BFS to
simulate orbital entry.
Doing ground hops isn't the hard part of doing a reusable upperstage--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.
From my calculations, a BFS with 3 sea level Raptors should have enough
thrust and roughly enough delta-v to do an X-33-like suborbital reentry
trajectory, which in some ways was more challenging (from a heat flux
standpoint) than an optimized LEO reentry.
Now, BFS is, of course, much larger than a reusable upper stage for
Falcon 9 would be and thus more expensive to fabricate, but it's perfectly
appropriate for orbital-like testing of the TPS.
In a 3 engine configuration, it'd have less thrust than a Falcon 9 (and
so /possibly/ fits in their current Boca Chica EIS which I think was
originally made with the idea of possibly doing F9R/F9Rdev tests), and it
gives them practice with austere launch conditions (i.e. launching from a
relatively-unprepared patch of ground), which is basically what Mars will
be. And marginally, should be cheaper than a Falcon 9 launch for testing
per-launch with less need for integration in between tests. More like
Grasshopper/F9Rdev1/DC-X than a typical TSTO orbital launch.
-Chris
On Sat, Feb 10, 2018 at 2:46 PM, Jonathan Goff <jongoff@xxxxxxxxx> 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
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
