[AR] Re: Falcon 9 flight today
- From: Nathan Mogk <nm8911@xxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Sun, 6 Oct 2013 20:56:20 -0700
I like how Ben Brockert was included as a source on this article. You must
do a good job of getting your blog out there, Ben.
On Sun, Oct 6, 2013 at 4:16 PM, Henry Vanderbilt <hvanderbilt@xxxxxxxxxxxxxx
> wrote:
> On 10/6/2013 2:54 PM, Henry Spencer wrote:
>
>> On Sun, 6 Oct 2013, Henry Vanderbilt wrote:
>>
>>> ...the 2nd-stage restart attempt resulting in a hard start bad enough to
>>> disable the engine and scatter some debris, but not bad enough to
>>> rupture the stage tanks or feed lines.
>>>
>>
>> Hmm, yes, a very interesting possibility. A hard start can be violent
>> enough to do damage, e.g. by the acceleration transient, without actually
>> *bursting* anything. (Gemini 6's Agena target was lost due to a hard
>> start that damaged control electronics.)
>>
>> Speculative, of course, but it is worth noting that while they've
>>> acknowledged a restart problem, they've said nothing about its nature
>>> yet. It was FWIW apparently bad enough to immediately rule out a retry,
>>> given that remaining propellants were vented right afterward.
>>>
>>
>> If (dim) memory serves, there is at least one expendable item (igniter
>> hypergol cartridge?) needed for a start on the Merlin, and the engine has
>> fittings for only two of them, so two starts is all it's good for without
>> human attention. So the immediate propellant venting might not be
>> significant -- indeed, might have been pre-programmed -- because they
>> weren't going to be able to try again anyhow.
>>
>> Although, hmm. They said the stage "underwent a controlled venting of
>> propellants". In the spirit of hermeneutical analysis (read Arocket and
>> improve your vocabulary!) :-), note that they don't say it was on command,
>> or as planned, just that it was controlled. Maybe that *wasn't* meant
>> to happen immediately. If the tanks vented before anything could be done
>> about it, that would certainly explain why they quickly gave up on trying
>> again.
>>
>
> And yes, getting into the spirit of lawyerly parsing, I did deliberately
> phrase "It was FWIW apparently bad enough to immediately rule out a retry,
> given that remaining propellants were vented right afterward" to cover both
> commanded-venting and uncommanded-venting (at a "controlled" rate)
> possibilities.
>
> Looking at the video of the venting at http://www.nbcnews.com/**
> science/ufo-over-indian-ocean-**spacex-falcon-9-rocket-sparks-**
> sightings-4B11297922<http://www.nbcnews.com/science/ufo-over-indian-ocean-spacex-falcon-9-rocket-sparks-sightings-4B11297922>,
> by the way, I notice that the two-lobed effect I'd also seen in stills of
> the vent cloud is present pretty much through the first couple minutes of
> the video. It still may be (as I'd first thought from the stills) an
> optical effect of some sort, but it also looks consistent with
> bidirectional venting (via a T fitting or otherwise) intended to produce no
> net thrust. IE, more likely via the intended vents rather than via
> hypothetical damaged engine plumbing, if it's not just an effect of
> sunlight on the vent cloud or a lens effect.
>
> I hadn't known about the specific limit on Merlin starter cartridges
> though. A quick search didn't turn anything up. Any idea where to find
> out more about that?
>
> Henry
>
>
>
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