Spent upper stages left in orbit these days in general have their leftover propellants vented, to prevent the stages eventually exploding and adding to the orbital debris problem.
Vented propellants in orbit will tend to disperse rapidly to densities too low to do much other than provide a free show if the extremely diffuse cloud happens to be in sunlight while it's dark on the ground below. Several tons of kerosene dispersed over a 108-mile sphere has a an effective density of zero for most practical purposes.
Henry On 10/6/2013 11:57 PM, qbert@xxxxxxxxxxxxxxx wrote:
These maybe some dumb questions, but, 1) does this mean that they will be venting all the time if the don't get the rocket to relight? And 2), does venting present a danger to satellites or other rockets, considering it's fuel? Robert At 11:14 PM 10/6/2013, you wrote:I wasn't so much a source as the instigator. As far as I know from the blogs and news sites that I watch, I was the first one in English to point out the cloud and definitely show from orbital parameters that the UFO was the Falcon 9's cloud. I know Alan Boyle in real life, I guess he saw my post about it and thought it was worth a story. With some further work on other images I found that the propellant cloud was 108 miles wide. http://wikkit.tumblr.com/post/63351208465/how-big-was-the-cloud-of-propellant-from-the Ben On Sun, Oct 6, 2013 at 9:56 PM, Nathan Mogk <nm8911@xxxxxxxxx> wrote: > 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, >> 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 >> >> >
