[AR] Re: Space-X landing not much to go on
- From: Bill Claybaugh <wclaybaugh2@xxxxxxxxxx>
- To: "arocket@xxxxxxxxxxxxx" <arocket@xxxxxxxxxxxxx>
- Date: Sat, 10 Jan 2015 21:22:28 -0500
Henry:
Sorry, but in my view this argument is at least specious and possibly just an
apologia:
The asset had a value that is certainly in the millions. Had it been reusable,
it would at least have saved the cost of building another. It is not "arguable"
that had this test succeeded--and the barge subsequently brought it proud back
to the Cape--that the value of that media would have been less than millions.
The economic loss is real. Once one starts down this path, it is not
appropriate to then claim that you didn't really mean it....
The rote assertion that quick turnaround test is cheaper than analysis is in
this particular example proven bogus: using open loop hydraulic systems is a
historically well established formula for failure. *If* that is what happened
here--I am relying on Rand's unconfirmed report--then brushing it off as the
price of experimentation is--in my view--a cheap shot. As ever, there is a
balance in these matters: if SpaceX used an open loop hydraulic system--as Rand
suggests--them they made a historically traceable mistake that points to a
failure in their systems engineering management.
Bill
Sent from my iPhone
On Jan 10, 2015, at 20:44, Henry Vanderbilt <hvanderbilt@xxxxxxxxxxxxxx> wrote:
> Two points:
>
> - The primary revenue mission succeeded. The precision-landing engineering
> test was an add-on, so "multi-million loss" is arguable. Not that the add-on
> test was free, it quite likely did cost a few million - the arguable point is
> "loss"; see second point.
>
> - Which is, given that it's an add-on engineering test, and also that SpaceX
> quite clearly is going for quick turnaround test-fly-test incrementalism
> rather than a traditional must-succeed-first-time approach, the costs of
> having systems engineering management "properly review _all_ trades" (for how
> many months? years?) before flying the test might well be higher than
> gaining the data on hydraulic system data quickly this way. IE, they now
> have this (and much other) data, rather than still being bogged down in
> design reviews.
>
> Henry
>
> On 1/10/2015 5:37 PM, Bill Claybaugh wrote:
>> To me, this sounds like inexperience speaking: neither weight nor complexity
>> nor pretty much any other factor justify a multi-million dollar loss.
>> Particularly when the addition weight is approximately less than 0.0% of the
>> stage dry mass....
>>
>> In my experience, this mistake occurs because the trade is made at the
>> sub-system level in consequence of the systems engineering management
>> failing to properly review _all_ trades. This is a PITA for management, and
>> because they can avoid this tedious process by fiat, they do...and that is
>> how the same stupid mistake keeps getting repeated.
>>
>> Bill
>>
>> Sent from my iPhone
>>
>> On Jan 10, 2015, at 19:06, Rand Simberg <simberg@xxxxxxxxxxxxxxx> wrote:
>>
>>> To expand, I'm not sure this is really a valid criticism in this case. They
>>> presumably did a trade, realized that pumps, plumbing, complexity etc.
>>> associated with recirculation weren't worth it for a system that operates
>>> for such a short period of time. They cut the margins a little too close,
>>> but they now know what it takes, and will budget for it in the future.
>>> Saying why use a hydraulic system that can "run out" in this context is
>>> like saying why choose a propulsion system that can "run out." You just
>>> need to know what the performance requirements are, and build in some
>>> margin. They learned today where they need to be.
>>>
>>> On 2015-01-10 16:02, Rand Simberg wrote:
>>>> Weight, I'd imagine.
>>>> On 2015-01-10 15:59, Bill Claybaugh wrote:
>>>>> So to turn this to a technical discussion; I've never understood
>>>>> why--in my experience, typically inexperienced--engineers have
>>>>> repeatedly chosen a hydraulic system design that can "run out".
>>>>> Given the historical consequences, why would anyone choose an open
>>>>> loop hydraulic system?
>>>>> Bill
>>>>> Sent from my iPhone
>>>>> On Jan 10, 2015, at 18:13, Rand Simberg <simberg@xxxxxxxxxxxxxxx> wrote:
>>>>>> It was a hard landing, reportedly because they ran out of hydraulic
>>>>>> fluid for the control fins. Elon said they came up about 10% short, and
>>>>>> the next flight will have much more margin. So I'd say odds for success
>>>>>> next time are pretty good, considering how close they came today.
>>>>>> On 2015-01-10 15:09, John Stoffel wrote:
>>>>>>> Edward> They landed in the fog. I wouldn't expect the video to show
>>>>>>> much of anything useful.
>>>>>>> So they made it down onto the Barge? Wow, that's awesome that they
>>>>>>> even got near there. I see from the web site that they say they
>>>>>>> landed hard, which is *still* damn impressive.
>>>>>>> I really like how they keep pushing the envelope here, it's inspiring.
>
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