Help identifying this Tumbling object in a night sky photo from Namibia

[timmdeeg]

Sorry my English isn't so good. What is a tumbling booster? Part of a rocket?

 

[Vanadium 50]

which shows two stars on the track, not hidden by something

Bur this is a long-time exposure. Most of the time the object is not blocking the stars.

Frankfurt, air-traffic central for Germany.

Frankfurt aspires to be as confusing as Heathrow, but only manages to be as bad as Pearson.

And if we mean "rotate" we should say "rotate" and not "tumble".

 

[chemisttree]

Sorry my English isn't so good. What is a tumbling booster? Part of a rocket?

Yes

 

[DaveC426913]

And if we mean "rotate" we should say "rotate" and not "tumble".

Just my curiosity but I don't understand why the term "tumbling" has met with so much objection.
Is it a technical term I am not aware of?

Because 'apparently rotating, uncontrolled, on multiple axes' seems to be quintessentially 'tumbling' where I come from.

In fact, "rocket boosters" and "tumbling" seems to be not uncommon phraseology on NASA (number #2 Google hit) and other rocket-centred sites:

 

[Vanadium 50]

The unstable motion of a body rotating about its middle axis is called "tumbling".

 

[chemisttree]

“Unstable” is implied when using “tumble.”, yes?

 

[Devin-M]

If it’s a satellite, what’s the minimum plausible deflection length of the reflection? If it’s 350 miles away, 100 ft long, how many pixels is that?

 

[Devin-M]

I think 100 ft at 350 miles is 0.00309 Degrees or 11.1 arc seconds (a little more than half the apparent size of Saturn viewed from Earth). What’s the arc second per pixel on the telescope? I think with a Nikon D800 36MP sensor full frame on a 2175mm focal length scope I get theoretically 0.46 arc sec per pixel. That could conceivable lead to a 24 pixel wobble (12 pixel each direction side to side) from centerline of trajectory.

Saturn:

 

[Devin-M]

It would be traveling 7800 m/s… if it’s 30 meters long it’s covering 260 body lengths per second. At what RPM would it need to be rotating to match the observed curve? Would it be able to withstand those centrifugal forces?

 

[jbstratman]

TL;DR Summary: Question: What tumbling object causes this trajectory?

I have received this image from someone in Namibia recently at the Kiripotib Astrofarm.

Has anyone an idea what could cause such a strange trajectory?

View attachment 334010

Perhaps a cylindrical object that is reflective only on one end?

 

[timmdeeg]

Sorry for being absent for some time.

Perhaps a cylindrical object that is reflective only on one end?

This I have been thinking too, but the explanation seems much different after some discussion with a former astronomer at the university of Heidelberg.

There are two traces, a broad one like a snaky line and above a thin one which ist straight. Imagine a vibration of the mount (which I have never experienced myself though) and that both lines originate from satellites. But why then snaky and straight?

The duration for satellites to go through the image section is about seconds (remember 1000 mm focus length). Now two assumptions: First, the satellite above (straight line) went through after the satellite below. Second, the mount vibration was finished before the above satellite went through. Indeed the amplitude of the snaky line is decreasing at the lower side of the line, before passing through.

Why the broad line? It seems it can be shown that's due to a very rapid satellite motion/tumbling.

Please let me know in case above conclusions are not consistent.

This issue will be most probably be discussed in the magazine "Sterne und Weltraum". I'll keep you informed.

 

[Devin-M]

You can estimate the minimum body lengths per second (assuming it’s orbital) and from this the rpm— I suspect it’s quite high. If it comes out to 10 revolutions per second or more is that still plausible? If we try putting a rocket booster on a turntable at 100 revolutions per second (6000rpm) I think it flies apart.

 

[sophiecentaur]

There's an awful lot to look through here but has anyone determined the possible speeds of the object, given the angle traversed in 3 minutes(?) and the likely radius of rotation?. I'd bet it's a small, slow object. I remember being fascinated by what turned out to be a sky lantern - in the early days before they were popular. My distance perception suggested it was massive and very fast when it was actually just across the valley from me and drifting by on a light wind.

 

[Devin-M]

Imagine a vibration of the mount

I think telescope wobble for part of the exposure can be ruled out because the other stars are round.

 

[timmdeeg]

I think telescope wobble for part of the exposure can be ruled out because the other stars are round.

This is a crop from which I roughly calculate the amplitude of the curved line to be 15 arc s using the Astrometry.net data below. This shouldn't be a problem with Autoguiding.

Center (RA, Dec):	(312.617, 31.896)
Center (RA, hms):	20h 50m 28.049s
Center (Dec, dms):	+31° 53' 45.233"
Size:	18.8 x 19.5 arcmin
Radius:	0.226 deg
Pixel scale:	0.796 arcsec/pixel
Orientation:	Up is 88.2 degrees E of N

 

[Devin-M]

This is a crop from which I roughly calculate the amplitude of the curved line to be 15 arc s using the Astrometry.net data below. This shouldn't be a problem with Autoguiding.


View attachment 334791

Based on the last photo, If you want to assume it’s orbital & 350 miles (563.2km) away, 15 arc seconds gives a size of 134 ft (40.8m). If it’s traveling 8000 m/s at orbital velocity that’s 196 body lengths per second or 2940 arc seconds per second. The path width is about 8px giving about 1.8arc sec per pixel (assuming path width 15 arc sec). The path length is 336 px giving a 604.8 arc sec path length. This implies a path time of 0.205 seconds. I count 19 potential rotations in that time giving 92 rotations per second or 5520rpm, rotating faster than a car engine at freeway speeds. This seems implausible as a 40m long rocket body would likely not be able to tumble 92 rotations per second without rapid disassembly. Since the stars are round we can rule out telescope wobbling for part of the exposure. For me, this leaves firefly flapping its wings as most plausible explanation.

 

[Devin-M]

0.796 arcsec/pixel

Ps after you uploaded it here, the image size was scaled down to 1.9 arc seconds per pixel.

Pixel scale:

1.9 arcsec/pixel

 

[timmdeeg]

Since the stars are round we can rule out telescope wobbling for part of the exposure. For me, this leaves firefly flapping its wings as most plausible explanation.

I don't have this experience myself but guess that autoguiding would keep the stars round.

Other opinions?

 

[timmdeeg]

This issue will be most probably be discussed in the magazine "Sterne und Weltraum". I'll keep you informed.

Here comes Ulrich Bastian's comment, he is one of the founding fathers of Gaia:

My translation:

It seems most probably the trace of a satellite. It begins in the middle of the image and from there sloping to the bottom. It is parallel to the second satellite trace, not shown here. The wobble motion is for sure not due to the motion of a sky object but caused by a fast vibration of the optical instrument or the mount:
Assuming the usual angular velocity of a satellite the wobble period would be around 0.01seconds. The full amplitude is around 8 to 10 arc sec corresponding to 13 - 16 meters assuming a distance of 300 km of the object. Probably the vibration was cause by touching the instrument ... . It was already decayed when the second satellite went through the picture. At its end its amplitude is recognizably decreasing already.

I would like to add guiding was good enough to keep the stars almost round.

 

[chemisttree]

The stars might be round because they are significantly dimmer than the satellite. Their round appearance was an image built up from an extended exposure for which the vibration contributed very little.