[AR] Re: SpaceX F9 Launch/Update -- Live Link
- From: David McMillan <skyefire@xxxxxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Tue, 22 Dec 2015 12:41:05 -0500
On 12/22/2015 8:28 AM, William Claybaugh wrote:
Marcus:
As I recall, two SRB's sank. The remainder were recovered and reused.
There is enough remaining hardware to do the first couple of SLS
launches; I believe the pacing item is rear fulcrum's.
In our enthusiasm for SpaceX's impressive achievement we should not
overlook that reuse of the SRB's never made economic sense: flight
rates needed to hit about 18 per year to reach break even. While the
recovery costs were around $300k per SRB, refurbishment cost many
millions--more than the cost of a new motor. That is the issue
SpaceX--and Blue Origin--now confront.
I'm not really sure the SRBs are the correct comparison here,
though. After all:
1. Water recovery vs dry-land (or barge deck) recovery -- saltwater
corrosion was a significant cost driver on SRB refurb, IIRC
2. Solid vs liquid -- As I understand it, the inspection and cleaning
process for an SRB is much more involved than what it's likely to take
for a liquid stage (once multi-flight MTBF numbers have been established
with some reliability). And the refueling process is *definitely* simpler.
3. Re-testing. Test-firing one of the SRBs left you with just as big
a cleanup and refurb task as a full-up STS flight. SpaceX can (and has,
for static test-firings) just keep re-fueling and re-lighting. About
the only thing they can't ground-test is the hypersonic reentry
stresses. In fact, one rumor I heard is that this stage will be moved
to NM and put through multiple "hop" flight tests, Grasshopper-style,
precisely to see what performance post-recovery looks like relative to
baseline.
4. Infrastructure. An RTLS F9 stage recovery is nearly as simple as
driving the TEL over and grabbing it -- just like the trip from Hangar S
to SLC40, but in reverse. The SRBs required substantially more.
Of course, the STS orbiter itself isn't a great comparison either,
although I've heard it claimed that near the end of the STS life cycle,
the latter marks of the RS-25 were coming close to the original
re-usability specs. But even if that's true, there's so many other
differences as to make direct comparison problematic.
What good baselines *do* we have for a near-apples-to-apples
comparison? The closest thing I can think of is the DC-X, although that
never went to the kinds of altitudes and velocities that the F9 booster
has to endure. Are the DC-X data for engine life and MTBF public? Of
course, the *closest* data is probably the Grasshopper and F9R results,
but SpaceX has held those close to their vest, AFAIK. And, again, no
hypersonic phase.
Still, SpaceX has already demonstrated that the first-stage Merlins
can be re-fired multiple times, and clock up several flights' worth of
firing time, without requiring substantial overhaul (so far as the
publicly available information indicates). They've also demonstrated
(IMO) that landing the first stage is entirely within reach, although
barge landings are still questionable and they still need to prove they
can do it reliably. The only major unknown, from my seat in the
bleachers, is what effect flight stresses (particularly Max Q and the
hypersonic reentry phase) have on the vehicle life. My guess is that
the tentpole items there are metal fatigue on the vehicle as a whole,
and possible damage to the engines from taking re-entry heating and
aerodynamic stress "in the teeth," as it were.
Given what we *do* know, I don't see any reason to expect that F9
first-stage re-use costs would be anywhere close to that of an STS SRB.
I also think there's good reason to be cautiously optimistic about the
re-use costs, relative to the costs of a new-build F9 first stage. The
good news here, of course, is that we (well, SpaceX) now have actual
flight hardware in hand to get hard data from, and little stopping them
from getting another 2-4 recovered boosters over 2016.
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