Heavenly Palace

Epoch now on Heav-Ab is 2018/3/28 10:56:31 UTC
Which I believe is 4 hours ago. (edit to 4; I had written 5)
Epoch before that was 8 hrs ago

 

Epoch? That's for sure!

 

I don't know why epoch is the term for 'time associated with a particular set of orbital elements'.
Astronomy jargon
It has very different meaning in Geology jargon
Different in common usage
(insert picture of Tower of Babel here)

 

I am scraping these into a spreadsheet, motivated by fuzzy1 since March 11. No doubt have missed many updates amongst. But the ones I have paint a sinky picture.

The 'orbits per day' follow a second order polynomial (is parabola a better term?) with an R^2 of 0.9965 For anything other than physics in a near-vacuum, such an R^2 would be effing absurd.

Another technical term.

In Biology, report an R^2 of 0.95 and journal reviewers are like, "You're lyin', man"

 

Perhaps this has become a tiresome thread, but soon to end. Allow me a few more comments.

Worth a look:

Tiangong-1 Reentry | The Aerospace Corporation

See the dashboard; it updates very fast. It also seems to have some internal contradictions. Yet TG-1 may be our best chance of getting PC minds into the subject.

AeroSp' latest orbit is 185/199 km. Heav-Ab (slower updating) is 187/203 km. The grail I have sought, perigee for last dance, might just be 165 km for typical space hardware.

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My flimsy estimate is that ~ one ton per week of human space junk re-enters per week. Mostly aluminium. Exo stuff may be a hundred tons per week. Mostly iron, mostly in sand-grain to pea (initial) size class. Irregular through time, see 'meteor showers'. If you want some 'exo', one word - magnets.

 

Just so readers know, Der Bob made this a topic I'd not have have pushed. But as such it helped me learn a lot about about thing falling. Where friction and aero-compression meet gravity.

This TG-1 is a small player. Ain't no Skylab; ain't no Mir. But things down here below have changed. Detecting, analyzing and communicating. We can realize more about infallings. Better, we might realize more about our self-imposed clutter in earth orbit where things can be learned and money can be made. Precious things, these orbital rings are. We pollute them at our peril just as all other pollution perils go.

Good night, sweet princess TG-1, and thanks.

 

Prediction now is for April 1 at ~4:30pm Chicago time over So. America.

 

Just who is making that particular prediction?

Here are some others. updated somewhat since Bob's post #86 (sorry for lousy formatting. First date-time per line is when prediction was updated, second is the predicted time):

" TIANGONG-1 Decay Predictions and current orbital parameters

Prediction Source Date of Prediction Predicted Reentry Date (UTC) ...*
SatFlare 29-Mar-2018 (15:25 UTC) 1 Apr 2018, 06:38 (±26 hours) ...
Aerospace Corp. 28-Mar-2018 1 Apr 2018, 07:15 (±20 hours) ...
US-StratCom 28-Mar-2018 1 Apr 2018, 01:57 (±19 hours) ...
Satview.org 28-Mar-2018 1 Apr 2018, 06:23 (±8 hours) ..."


... and another ...:
"Tiangong-1 is currently predicted to reenter the Earth’s atmosphere around April 1st, 2018 14:00 UTC ± 16 hours.
This prediction was performed by The Aerospace Corporation on 2018 March 29."

 

Fuzzy1 if you get a chance look at

Tiangong-1 Reentry | The Aerospace Corporation

scroll down to dashboard and see upper right corner graph. Last 4 predicted orbits have apogee decaying smoothly but perigee with a couple km uptick. I don't understand how that would be possible.

PS: on that page the prediction has moved up to 10:30 UTC +/-16 hrs (still 1 Apr)

 

Belay that. uptick@91 has disappeared and re entry is back to 14:00 UTC

 

Whoops... 16:59 UTC.

A psychic might even guess better, due to the enormous variables involved.

I'd still like to have a (small non-radioactive) chunk land in my backyard. Would make a great photo to post here.

 

By "couple km uptick" do you mean it's climbing a bit? Could it be "skipping off" the atmosphere (like a pebble on water), or is that not possible in this scenario? I've heard of that being a possibility, with returning Apollo missions.

 

OK. I must have had an older image in my local cache, and kept seeing the same old downtick, until forcing a full page reload and seeing a smooth progression. But it is showing me only 24 hours now, which isn't the full remaining life.

Apollo missions were coming in at close to escape velocity, high energy, so a skip off the atmosphere would make them go around again for several weeks in a very long elliptical orbit. That orbit would eventually decay to a future re-entry, but only long after the crew expired for lack of air/water/food.

This station barely has enough energy to stay aloft. A 'skip' (e.g. from a fortunate solar wing angle) would hold it up only briefly, probably just a few to tens of minutes.

For the rock-skipping analogy, an Apollo aiming error on the high side would have been equivalent to the very first bounce of a very fast skipping rock. This station is now getting close to its very last bounce, where multiple bounces start blending together just before it loses too much speed and sinks.

 

I don't know if that was ever real, or just some artifact of the page. I'll keep watch for it as the final orbits scroll into the display window that is now fixed to just 24 hours.

It is not possible for the semi-major axis (average of perigee plus apogee, plus Earth's radius) to take an uptick, that must be continually decaying. This axis defines the energy of the orbit. But it might be possible for the eccentricity to be reduced, i.e. making the orbit more circular. This could raise the perigee, though the apogee must fall to compensate, in additional to the regular drag decay.

This can be done with relatively small rocket boosts, which of course is not a choice for this station. I'm wondering if the 'solar wings' could cause a bit of lift at an opportune portion of the orbit, effectively 'skipping' a bit as Mendel asked. Or they might orient to maximum drag someplace mid-orbit, but not at either perigee or apogee. But predicting this means knowing the station's actual attitude pattern, which is inconsistent with a body tumbling out of control.

So most likely, the uptick you saw, and the downtick I saw previously, is a problem with the web page.
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P.S. Absent special circumstances, the greater drag at perigee than at apogee should also tend to circularize the orbit. But this would normally be seen only as apogee falling faster than perigee, not as perigee climbing.

And indeed, this has happened. Earlier this month (Mar 11), the apogee - perigee difference was 22 km. Now, it has shrunk to just 14 km. Considering that the semi-major axis (average orbit radius, i.e. from center of Earth) is now about 6560 km, this is a significant shift closer to a circle.

 

When the page was last updated, the display window width was 24 hours (was 72 hours this morning), but "Time to reentry" was 58 hours, so it isn't currently showing the predicted final orbits.

 

No resolving this until ~50 more hours pass. A recent burn-in was a 3U cubesat put in low orbit to explore how such burning in goes.

A diversity of rocket boosters (R/B by Heav-Ab) are most of described re-entrants. Not easy to know if these are 1 ton or 10, but they dominate Anthro-infall except when a purposeful sat de orbits. Such as TG-1 soon after now.

Spread of TG-1 predictions means that several predictors vary and they are not showing their work.

Each and every orbital re entry is net benefit because there are thus fewer kgs or tons that can bump into something else and get all Kessler.

Humans to date have poorly managed orbiting pollution. Just as we have near planet surface. But whoa I can't talk about such because it might drift political and snowflakes might melt.

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Cleaning Earth-orbital space may become a money proposition, but only for larger items. Human-source tinies are vastly exceeded by exo.