(meteorobs) A real Earth-grazer

[Esko Lyytinen]

Hi,

How the angular velocity would change during the flight would in 
principle tell this. So, a single photograph is not enough for this, but 
a video is, if this can be measured well enough and if the observed arc 
is long enough. This typically is long for any level grazers.
If an individual photograph would show individual frames as detectable, 
then it could be measured with mutual timing data.
We in the Finnish fireball group, if not capturing video, make besides a 
normal "sum-image" also an image with every third or every fifth frame 
only recorded. These can typically be masured individually, if not then 
it probably was a slow moving satellite flash ;)

So, if there is a long enough capturing arc, with accurate enough 
astrometric positions and mutual timings for these available, then this 
is possible. My own Excel sheet model is capable of solving this.
In this Earth-grazer case I first got the single station data from Jari 
Tuukkonen and derived the flight direction (with assumed velocity of 
15km/s) . I got to know that this had the lowest point around the 
observation and then started to escape into space.
After I got the observations of Timo Kantola also, then the actual 
velocity and height could be derived, but the direction of the flight 
did fit to the one station-only derivation within about half a degree. 
Because the possible deceleration (by the atmospheric "drag") also 
affects the angular velocity change, this might make the one station 
result less reliable, depending on the case, but in this case, the 
escape was almost certain from one station data only.

The model has for example flattened (oblate spheroid) Earth, for 
accurate multiple station results. And there is a direct fit into the 
observations. Actually I have made NOT a bit of coding for the solving. 
The Excel solver ("Add-Inn") can do the job of solving this to find (in 
essense) the least squares fit to the observations. The same model can 
be used for one station data or multible station data.
In principle this Excel sheet would be available, but there are no 
instructions written on this, at least yet. This is not a program for 
fixed form input and to get the output. One has to put the observations 
into lines at correct cells and do the mutual linking timings into the 
cells for example. So a relatively good understanding of the principles 
will be needed. Because the solving method (by Excel solver) is only 
iterative, it may need some reasonable start values and/or some manual 
"help" to get into it (might start to converge into some unreasonable 
solution), but with some experience this seems to be no problem.

Esko

> Date: Wed, 24 Sep 2008 22:45:41 -0700
> From: "stange" <stange34 at sbcglobal.net>
> Subject: Re: (meteorobs) A real Earth-grazer
> To: "Global Meteor Observing Forum" <meteorobs at meteorobs.org>
> Message-ID: <003b01c91ed1$f27a4fb0$e294364b at NAMELESSONE>
> Content-Type: text/plain; format=flowed; charset="iso-8859-1";
> 	reply-type=original
>
> Esko,
>
> Other than by calculation from altitude triangulation Esko, do you know any 
> way in which an earth grazer (might) be identified from a single photograph 
> from one site?
>
>  YCSentinel
>
>