[X] My Assistant

[helvick]

Seems like Robert McNaught captured something else interesting in the Southern Skies last night.

[tty]

Oh dear, that's another load of unnecessary space debris on top of the chinese ASAT test. I thought boosters were supposed to depressurize to avoid this sort of thing.

[nprev]

Guess that the depressurization might've been what went wrong as the root cause...

Wonder if it might be wise to require (under what authority I can't imagine; UN?) deorbiting systems for upper stages using a small strap-on solid motor or something. Seems wise to get these beasts safely burnt-up as soon as possible after the job's done.

[mchan]

This is done in some cases where it is practical to do so. E.g., after spacecraft separatation, Delta upper stages in low earth orbit will burn remaining propellants to depletion to drop perigee as much as possible to increase atmospheric drag and hasten decay.

[ugordan]

SpaceWeather.com has a great movie taken by Gordon Garrard spanning nearly an hour.

Link to lower resolution video here (4 MB).

[Guest_PhilCo126_*]

Another " space debris " incident here:
http://www.dnaindia.com/report.asp?NewsID=1087543

[nprev]

Good grief... ! Well, at least it re-entered & isn't still up there posing an LEO hazard.

Still, can't have space junk threatening airliners & other things without adequate warning, and this sounds like a complete screw-up on the part of all agencies who's job it is to monitor these events. Might be time to consider establishing an international space junk alert system tied into the ICAO, national civil defense organizations and other concerned parties similar to the International Ice Patrol for maritime concerns...this would be in everyone's interest.

[ugordan]

"Flaming" space junk at a 10 km altitude? Wouldn't any significant kinetic energy be shed much, much higher up and be pretty much travelling at terminal velocity at that altitude? I'd imagine it wouldn't be "flaming" at all, too. How did the pilot determine it was in a 8 kilometer radius anyway? Radar?

[nprev]

Good questions, but I can buy off on the 'flaming' a bit...maybe it was still glowing from residual heat. I saw a booster re-entry almost from start to finish (180 deg across the sky!) in absolutely dark skies once when I was a kid in Montana, and when the main body broke up all the chunks were still quite luminous until they went below the horizon...pieces hit near Idaho Falls, ID.

[ugordan]

Yes, but how high were the booster pieces when they appeared to stop glowing? I don't know, it looks to me the pilot actually saw stuff many kilometers in altitude, much higher and farther than 8 km.
I wouldn't expect any junk to retain supersonic speeds all the way to 10 km altitude, let alone speeds to heat up the material.

Then again, I never witnessed anything of the sort so...

[nprev]

I agree with you there; seems unlikely that the stated range is accurate, and hard to understand where it came from. Most aircraft (esp. commercial airliners) have X-band weather-avoidance radars, so we're talking about a 3 cm wavelength, which of course could yield good resolution of chunks. However, the newer digital data processing schemes are designed to pick up diffuse rather than discrete targets; PPI mode just isn't the same as it once was.

The pilots might have seen some brief returns as the chunks transited their radar scan region (if they were indeed close enough to them), but I doubt that they persisted long enough to make an accurate range determination...if they showed up on the radar at all.

[edstrick]

In a *CLASSIC* UFO report from the mid to late 60's, a passenger plane somewhere over Kentucky took evasive action to avoid collision with what the pilot reported as a flaming craft. Passengers reported seeing glowing portholes in the "vehicle" and I think somebody said they could see faces looking out (or that's memory embellishment...)

In REALITY, it was a piece of space junk re-entering some 200 miles away over central or northern Ohio.

The Chilean pilot instinctively interpreted the flaming whatever as nearby due to it's relatively large size in the sky. He had no real idea how big or close it was. Jim Oberg has a column, I think on MSNBC, on the event.

[nprev]

Regardless, it's scary as hell to see something like that when flying, esp. if you can't accurately determine its range. Aircrews need to be warned about these events so they don't do anything stupid and/or impulsive in response which could jeopardize the safety of all on board. This is particularly true for heavily traveled transoceanic airspace such as that between the CONUS & Europe since the vertical separation distance between E-W routes has been decreased to 500 feet from 1000 feet; if somebody takes unneeded evasive action, you could have a midair....

[mchan]

The problem is that reentries due to orbit decay are difficult to predict accurately in location and time.

[nprev]

Even 24-hour warning that something was coming in somewhere would be sufficient to prevent aircrew over-reactions, though. The new reduced vertical separation minima (RVSM) I mentioned before increases the possibility of incursion if a plane suddenly climbs or dives to avoid space junk that's actually a few hundred km away. Better to alert & educate aircrews than accept this risk, because we could be talking about nearly a thousand people's lives if such an event involved two super-heavies.

[djellison]

It's not that easy - a re-entry might be within a 5 hour window on any one of 3 orbits at any place along a 5000 mile track.

Doug

[nprev]

I wasn't too clear in my last post. What I meant was just a general international warning (NOTAM) for aviators that a reentry was likely in the next 24 hours would be sufficient without specifying location, as well as some training for them about the events (i.e., it may look close, but it probably ain't).

[nprev]

I thought boosters were supposed to depressurize to avoid this sort of thing.

Speaking of that, how is this usually done exactly? Do most boosters have valves somewhere on the fuel manifold that open up on ground command or via preprogramming, or are there dump valves directly connected to the tanks themselves?

I'm sure there are several different methods, just curious about how this is supposed to work. You obviously don't want them opening up during powered flight...

[dvandorn]

Rocket stages in a vacuum are usually vented through the engine bell(s). That way, you don't need to design any separate venting system; all you have to do is activate the proper pumps (the ones that feed the fuels to the combustion chamber during flight) and your fuel or oxidizer goes flowing out of the bell. (You could actually vent hydrogen and oxygen at the same time, though I don't think they do that all that often... hypergolics, of course, you vent separately.)

Yes, these vents can be somewhat propulsive, but not nearly as propulsive as when the engine is actually operating (i.e., when the fuel and oxidizer are undergoing combustion). Apollo S-IVBs were sent on their post-TLI trajectories (often designed to crash into the Moon) using, in part, the propulsive effect of their fuel and oxidizer venting.

-the other Doug

[nprev]

Ah...makes sense, thanks, DV. So then, failures to fully purge are usually caused by lack of power, pump failure, or I'd imagine some stray moisture freezing & plugging the outflow path? Should add comm link failure as well, apparently.