IPB

Welcome Guest ( Log In | Register )

 
Reply to this topicStart new topic
Are there coordinates for where orbiters deorbited?
Antdoghalo
post Aug 10 2020, 03:48 AM
Post #1


Junior Member
**

Group: Members
Posts: 77
Joined: 13-October 09
From: Olympus Mons
Member No.: 4972



Are their sources providing tentative coordinates for where orbiters like Venera, Pioneer Venus, Venus Express, or Magellan may have entered the atmosphere much like those for the Pioneer Venus Multiprobe bus at 37.9S 290.9E? (Magellan maybe impossible due to it being a farside deorbit)


--------------------
"Thats no moon... IT'S A TRAP!"
Go to the top of the page
 
+Quote Post
Phil Stooke
post Aug 10 2020, 07:40 AM
Post #2


Solar System Cartographer
****

Group: Members
Posts: 8295
Joined: 5-April 05
From: Canada
Member No.: 227



I have been asking this question for years. Basically there should be answers to the questions in every case except Venera, whose orbiters might still be in orbit or will have decayed at an unknown date. For the other orbiters the orbit is known very well. The entry will be at periapsis and the latitude of periapsis will be known. The orientation of the orbit in space plus the time of the entry will give the longitude if somebody can put it together. I don't have the information to do it, but out there in spacecraft operations land the information must exist. But I have never seen it all put together. Please, orbit wizards, figure it out for us!

Now, with positional uncertainties and atmospheric uncertainties, the locations might only be accurate to a degree or so. But it would be really nice to be able to say 'Magellan burned up over Beta Regio' or 'Venus Express entered over Fortuna Tessera' and of course, to plot them on a map!

Phil


--------------------
... because the Solar System ain't gonna map itself.
Go to the top of the page
 
+Quote Post
Antdoghalo
post Aug 10 2020, 01:31 PM
Post #3


Junior Member
**

Group: Members
Posts: 77
Joined: 13-October 09
From: Olympus Mons
Member No.: 4972



It would be a lot like deorbit trajectories of Earth orbiting satellites, by having the orbit plotted as a line across Venus like that of the ISS on Earth, that greatly narrows down the coordinates. Next up would be the mathematical calculations of atmospheric drag using data from the dozen atmospheric probes we sent there and the Windmill Experiment (the solar cycles puffing up it's exposed atmosphere may need to be accounted for).
And yes I'd love to plot them on my 16K Google Earth overlay.


--------------------
"Thats no moon... IT'S A TRAP!"
Go to the top of the page
 
+Quote Post
Gerald
post Aug 10 2020, 06:33 PM
Post #4


Senior Member
****

Group: Members
Posts: 2292
Joined: 7-December 12
Member No.: 6780



I'm not sure, whether this will answer your question in the way you expect, but there are provided trajectory data in the SPICE kernel directories accessible via the anonymous FTP server naif.jpl.nasa.gov.
There are also reduced orbital data, for instance for Magellan in /pub/naif/MGN/misc/dnunes:
Attached File  mgn_nav.orb.txt ( 2.45MB ) Number of downloads: 70

For more detail, you'll need to evaluate the SPICE kernel SPK files.
According to /pub/naif/MGN/kernels/spk/nav/aareadme.txt,
/pub/naif/MGN/kernels/spk/nav/CYCLE6.BSP is ending at 1994 OCT 14 01:01:01.182.
Once you get significant atmospheric drag, further useful trajectory extrapolations through the atmosphere are probably not possible, since the integration of the applicable differential equations would diverge exponentially depending on spacecraft attitude and atmosphere detail. You would get very elongated ellipses, similar to the statistical outcome of stone skimming.
Go to the top of the page
 
+Quote Post
Antdoghalo
post Aug 12 2020, 03:24 AM
Post #5


Junior Member
**

Group: Members
Posts: 77
Joined: 13-October 09
From: Olympus Mons
Member No.: 4972



If I entered these in correctly and extrapolate, that would mean it would have start to break up over T'ien Hu Colles around 31N 15E (when it got down to 120km where Pioneer Venus multiprobe bus lost transmission because it was burning up). I'm not an expert in aerodynamics but I would assume due to the atmospheric high density, barring any "skips", it is likely any fragments landed not far to the east south east of that, no further than Bereghinya Planitia.


--------------------
"Thats no moon... IT'S A TRAP!"
Go to the top of the page
 
+Quote Post
JRehling
post Aug 12 2020, 03:16 PM
Post #6


Senior Member
****

Group: Members
Posts: 2276
Joined: 20-April 05
Member No.: 321



Thinking of a (somewhat) comparable example, I just did some light reading on the reentry of Skylab, which had a debris field about 280 km long. The details of the reentry were considerably different than had been planned, thereby reaching Australia rather than the Indian Ocean.

Of course, that's another case than the Venus orbiters. As for the difference in atmospheres, what would seem to be relevant is not the surface pressure but the scale height, in which respect, Earth and Venus are not very different. Skylab was greatly more massive than any Venus orbiter, making for a lot more fragmentation. Perhaps the most important difference is that Skylab's orbit was almost circular, which would make the location of periapsis less predictive of the reentry location.

https://www.nasa.gov/feature/40-years-ago-s...th-s-atmosphere
Go to the top of the page
 
+Quote Post
Antdoghalo
post Aug 12 2020, 05:10 PM
Post #7


Junior Member
**

Group: Members
Posts: 77
Joined: 13-October 09
From: Olympus Mons
Member No.: 4972



That's what I was thinking. Skylab had a nearly circular orbit while Magellan had an orbit with an apogee 1:1 2/3 it's perigee. Compared to Skylab, Magellan would have descended somewhat faster due to it's resulting higher angle. As for atmosphere, below a certain point, the density prevents much horizontal movement relative to the ground, same reason impact craters have relatively short range ejecta blankets on Venus.


--------------------
"Thats no moon... IT'S A TRAP!"
Go to the top of the page
 
+Quote Post
rlorenz
post Aug 13 2020, 01:30 AM
Post #8


Member
***

Group: Members
Posts: 503
Joined: 23-February 07
From: Occasionally in Columbia, MD
Member No.: 1764



QUOTE (Gerald @ Aug 10 2020, 01:33 PM) *
Once you get significant atmospheric drag, further useful trajectory extrapolations through the atmosphere are probably not possible, since the integration of the applicable differential equations would diverge exponentially depending on spacecraft attitude and atmosphere detail. You would get very elongated ellipses, similar to the statistical outcome of stone skimming.

Since I wrote a book on Stone Skipping, I couldn't resist following up to endorse your analogy! Yes, for a circular orbit there is very high downrange uncertainty due to atmospheric density variations and to the unknown attitude history (and thus drag) of the vehicle. You know it should be along the groundtrack somewhere, but not where (and you can even be several orbits off on the entry time, depending when the last orbit determination took place). That's less of an issue for Venus than for Earth, since the planet is rotating underneath the orbit plane much more slowly on Venus so successive orbits are not displaced cross-track by as much.

I suspect the only reason there is a coordinate for Pioneer Venus is that it was still in a very elliptical orbit, so the entry was relatively steep and so the uncertainty was low. Maybe the same would be true for the Veneras, but I dare say there isnt good orbit determination information to hand. Magellan and Venus Express both did aerobraking experiments and ended up in much less eccentric orbits so their destruction locations would be very uncertain in the along-track direction.

Even if you could determine an entry location, I can't imagine there being any debris that would be detectable by remote sensing : the scale height is pretty small and so the deceleration and heating peaks are pretty sharp.
Go to the top of the page
 
+Quote Post
Antdoghalo
post Aug 13 2020, 02:17 AM
Post #9


Junior Member
**

Group: Members
Posts: 77
Joined: 13-October 09
From: Olympus Mons
Member No.: 4972



I doubt anything landed of these satellites. If giant 100 meter boulders couldn't make it, many centimeter-sized fragments of metal sure didn't. and if they did, they likely got discolored or melted in the intense heat to where they would be indistinguishable from rocks to any rover that ever makes it one day.


--------------------
"Thats no moon... IT'S A TRAP!"
Go to the top of the page
 
+Quote Post
Phil Stooke
post Aug 13 2020, 03:51 AM
Post #10


Solar System Cartographer
****

Group: Members
Posts: 8295
Joined: 5-April 05
From: Canada
Member No.: 227



Not looking for debris - just to say 'it entered over Alpha Regio' or something like that. Also, I know how it might be done, I just want someone else to do it! I have enough stuff going on at the moment.

Phil


--------------------
... because the Solar System ain't gonna map itself.
Go to the top of the page
 
+Quote Post
rlorenz
post Aug 25 2020, 03:12 AM
Post #11


Member
***

Group: Members
Posts: 503
Joined: 23-February 07
From: Occasionally in Columbia, MD
Member No.: 1764



QUOTE (Phil Stooke @ Aug 12 2020, 11:51 PM) *
Not looking for debris - just to say 'it entered over Alpha Regio' or something like that. Also, I know how it might be done, I just want someone else to do it! I have enough stuff going on at the moment.


Per the first part of my post, I suspect the entry location is indeterminate - at best you could say it was somewhere along a great circle corresponding to the orbits when entry was predicted.
Go to the top of the page
 
+Quote Post
Phil Stooke
post Aug 25 2020, 03:23 PM
Post #12


Solar System Cartographer
****

Group: Members
Posts: 8295
Joined: 5-April 05
From: Canada
Member No.: 227



But most or all were in very elongated orbits, not circular, so periapsis should be the place where bad things happen. Therefore we know its latitude and can predict the longitude.

Phil



--------------------
... because the Solar System ain't gonna map itself.
Go to the top of the page
 
+Quote Post
Gerald
post Aug 26 2020, 12:00 AM
Post #13


Senior Member
****

Group: Members
Posts: 2292
Joined: 7-December 12
Member No.: 6780



You'll find a detailed discussion in "An Analysis of the Corridor and Guidance Requirements for Supercircular Entry into Planetary Atmospheres" by Chapman, Dean R, NASA Technical Report R-55, file name 20040030504.pdf.
The document applies to planets with an atmosphere, including Venus.
Note especially "Figure 13-Overshoot boundaries for single pass entries.", which also includes multi-pass atmosphere braking.

Overshoots can occur for all kinds of orbits that are supercircular, especially elliptical, parablic and hyperbolic ones, provided the entry angle is sufficiently shallow.

Actual numerical simulations for a given probe are beyond my ressources. I wouldn't expect any result other than rlorenz already stated, execept maybe for some probabilistic distribution of entry points on the basis of a large number of Monte-Carlo runs.
Go to the top of the page
 
+Quote Post

Reply to this topicStart new topic

 



RSS Lo-Fi Version Time is now: 18th September 2020 - 08:42 PM
RULES AND GUIDELINES
Please read the Forum Rules and Guidelines before posting.

IMAGE COPYRIGHT
Images posted on UnmannedSpaceflight.com may be copyrighted. Do not reproduce without permission. Read here for further information on space images and copyright.

OPINIONS AND MODERATION
Opinions expressed on UnmannedSpaceflight.com are those of the individual posters and do not necessarily reflect the opinions of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer UnmannedSpaceflight.com moderation team is wholly independent of The Planetary Society. The Planetary Society has no influence over decisions made by the UnmannedSpaceflight.com moderators.
SUPPORT THE FORUM
Unmannedspaceflight.com is a project of the Planetary Society and is funded by donations from visitors and members. Help keep this forum up and running by contributing here.