Fobos-Grunt EOM Re-Entry Latest

[mdo]

Below plots were created using GMAT. Since I find this stuff fascinating and educating let me share those:

The first two plots show the altitude above ground vs. time up to reentry. The zigzagging is primarily due to the eccentricity of the orbit as the spacecraft swings up and down between apogee and perigee. There are also secondary maxima and minima when crossing the equatorial bulge. The lower the altitude the more pronounced it gets. When closely examining the curve another effect becomes apparent: The differential drag changes the shape of the orbit rendering it more circular. Therefore the distance between low and high points progressively shrinks to the right of the figure. In the past 24 hours, for instance, the high point changed by 7 km and the low point decreased by 5 km. 

Plot two zooms in on the entry interface at ~120 km which is marked by the cross. Since FG is a relatively compact object it can take up to a full orbit from first crossing the 120 km mark before it succumbs to drag.

The final screenshot shows the stretch it covers from the point where it first crosses the entry interface at a speed of 7,84 km/s until it descends to 105 km where drag finally takes over (and my propagator settings get numerically unstable). Please note that the underlying world map is misleading as the timing is uncertain and therefore one cannot deduce an impact point. Owing to its daily motion the Earth will be rotated anywhere between +/- 180 deg with respect to the shown ground track.

So, as disappointing as it may be, my plots do not say when impact will happen and therefore where. Consequently, time axis labels were removed. Experts for that are on the seesat list. Plot two shows part of the reason - a small change in the start conditions will determine whether FG will climb over the equatorial bulge one more time and survive a good fraction of another orbit or not. The reasons for the uncertainty are manifold though and include at least the following and likely more: Lack of space weather forecast, spacecraft orientation may change and therefore its cross section and drag coefficient, the remaining mass is unknown (propellants used/vented).

[ChileVerde]

Another reentry predictor:

http://celestrak.com/events/reentry/phobos-grunt.asp

[input~2]

http://celestrak.com/events/reentry/phobos-grunt.asp

Updated 2012 Jan 12 14:00:37 UTC
 the current estimated reentry date/time is now 2012 Jan 15 17:38:08 UTC.

[input~2]

Updated 2012 Jan 12 18:33:25 UTC
      the current estimated reentry date/time is now 2012 Jan 15 21:02:19 UTC

In other words, the precise time is "to be defined"

[Lee Jay]

The rule-of-thumb the folks on seasat use is the uncertainty is about plus or minus 20% of the time until reentry.  So putting seconds (or even minutes) on there right now is a bit silly!

[olasek]

The rule-of-thumb the folks on seasat use is the uncertainty is about plus or minus 20% of the time until reentry. 

I hope 20% of the approximate time remaining to reentry, right? In other words 20% of the 3 days remaining is about .... 17 hours. So say during the final 24 hrs 20% should be roughly 5 hours or 3 orbits. By the way plus or minus 20% is huge it is really 40% window of uncertainity. Perhaps it is only plus or minus %10.

[ChileVerde]

I hope 20% of the approximate time remaining to reentry, right? In other words 20% of the 3 days remaining is about .... 17 hours. So say during the final 24 hrs 20% should be roughly 5 hours or 3 orbits. By the way plus or minus 20% is huge it is really 40% window of uncertainity. Perhaps it is only plus or minus %10.

20% is somewhat arbitrary and is chosen to be conservative, but I don't think it's all that excessive. 10% is probably too optimistic, although as you get into the final hours it might be OK.

FG is giving us a lot of data to use in a retrospective analysis once the actual time of reentry is known.

[olasek]

20% is somewhat arbitrary and is chosen to be conservative, but I don't think it's all that excessive.

Plus or minus 20% is however a bit excessive (it amounts to 40%) hence my question above. If +/- 20% were true then even today we could be more than a full day off in predicting the reentry time.

[ChileVerde]

Plus or minus 20% is however a bit excessive (it amounts to 40%) hence my question above. If +/- 20% were true then even today we could be more than a full day off in predicting the reentry time.

Yes, from one end of the uncertainty period to the other, that's close. On each side of the middle of it, like half a day, I see that the current projections are running for 12 passes or so, so they seem to be using 3/4 day uncertainty, 3/8 day or 9 hours on each side. Considering the uncertainties in the uncertainties (pace Rumsfeld), those don't seem too much different than 1 day, 1/2 a day. We really don't know the time of the fall much better than that, and orbital mechanics translates that time uncertainty into place uncertainty.  At this time, I think we can be fairly sure of many parts of the Earth where it isn't going reenter/fall, but that leaves many places where it might.

[kevin-rf]

Still to many places for Chris to cover with his catcher's mitt

[Chris Bergin]

Still to many places for Chris to cover with his catcher's mitt

More inclined to Cricket, personally

So this is the weekend where this poor spacecraft meets its end. We'll rely on this thread for the updates and hopefully we'll get a more accurate estimate of entry in the coming hours.

[Chris Bergin]

Sunday or Monday is what the UKSA is going with:

http://www.bis.gov.uk/ukspaceagency/news-and-events/2012/Jan/phobos-grunt-to-re-enter-earths-atmosphere-between-sunday-and-monday

[Michael J]

Roscosmos has issued a public notice of measures being taken in preparation for Phobos-Grunt's reentry.  Looks like they are doing CYA just in case it doesn't fall in the ocean. (Google translated)

http://translate.google.com/translate?hl=en&sl=ru&tl=en&u=http%3A%2F%2Fwww.federalspace.ru%2Fmain.php%3Fid%3D2%26nid%3D18552

[JimO]

Roscosmos has issued a public notice of measures being taken in preparation for Phobos-Grunt's reentry.  Looks like they are doing CYA just in case it doesn't fall in the ocean.

I must stress again that the Russian word 'kontrol' does
NOT mean 'control' in the sense of the English word.

This 'obvious' but incorrect interpretation OFTEN creates very bad
mistakes in the minds of people.

It refers to "monitoring" of an activity, NOT active influence
on the course of that activity -- think "passport control".

To actually actively modify an activity, as in 'Mission Control',
the word is 'upravleniyeh', where 'prav' is the root meaning
'correct, and the word particles imply a process of 'correcting out'
something.

[edkyle99]

Sunday or Monday is what the UKSA is going with:

http://www.bis.gov.uk/ukspaceagency/news-and-events/2012/Jan/phobos-grunt-to-re-enter-earths-atmosphere-between-sunday-and-monday

It states that "The aluminium fuel tanks are expected to melt and the unused fuel destroyed/dispersed in the upper atmosphere."

It seems likely to me that the largest percentage of the propellant would be "dispersed" rather than "destroyed", but I'm not sure what happens to a hypergolic propellant when it is sprayed into a superMach-whatever heated plasma stream in the upper reaches of the atmosphere.   It's going to slow down rapidly and be heated to probably extreme temperatures, but only briefly.  Perhaps this is a question best posed to a chemist?

 - Ed Kyle

[input~2]

USSTRATCOM reentry window reported at 2012-01-13 15:30:00 UTC is as follows:
15 JAN 2012 0804UTC - 16 JAN 2012 0304UTC

[Antares]

What are the exact constituents of Russian hypergols?  N2O4 and N2H4 would definitely become N2, O2, H2O, and NOx.  If there's carbon in the hydrazine, CO and CO2 depending on how quickly it cools.  Hypers are pretty delicate molecules.  A little temperature or the right reactant and they dissociate quickly.

[Jorge]

What are the exact constituents of Russian hypergols?  N2O4 and N2H4 would definitely become N2, O2, H2O, and NOx.  If there's carbon in the hydrazine, CO and CO2 depending on how quickly it cools.  Hypers are pretty delicate molecules.  A little temperature or the right reactant and they dissociate quickly.

The Russians typically use UDMH (C2H8N2) rather than straight N2H4 or MMH.

[olasek]

It seems likely to me that the largest percentage of the propellant would be "dispersed" rather than "destroyed",

I would bet the opposite - most will actually ignite and burn out simply because how fuel is confined in tanks and the first burn-through should ignite whatever is inside. This is just my opinion but regardless - I don't think any of the fuel will reach ground.

[pippin]

I must stress again that the Russian word 'kontrol' does
NOT mean 'control' in the sense of the English word. 

Hehe, interesting
A misconception shared by German/English languages ("Kontrolle" in German also usually is being used with a "monitoring" or "surveillance") meaning.

It's a misconception that works in both directions, btw.