Re: accelerations
Bart De Pontieu (BDP@MPE.MPE-GARCHING.MPG.DE)
Thu, 11 Jan 1996 03:39:53 +0100 (CET)
Kurt Jonckheere writes :
>Paul Maley wrotes:
>>Kurt reports possible accelerations in 18096 (87-49B),...
>It seems that we have catched up this acceleration from the very beginning!
Which is great. Too bad there are some major gaps in the time coverage.
We could use some more observers here. Who helps out ?
>>Per Kurt's message of January 7, I would offer up the thought that the
>>accelerations may be caused by a leaky propellant valve rather than fuel
>>corrosion.
>I wonder if you or someone else knows the exact mechanism of opening and
>closing the valves to see it this is possible.
>Some years ago we thought that another reason for accelerations might be
>a fuel leak through a hole formed by an impact of a meteorite.
A leaky valve is indeed a possibility, and contrary to what Kurt thinks,
it was mentioned before in our newsletter Flash. Dr. Hermann Boehnhardt even
wrote an article about fuel leaks in (I think) Astrophysics and Space Science
in the seventies, using data from Jean Meeus and Horst Koehnke (all in the
PPAS now), and assuming a leaky valve. One of his results was (I think) that
the acceleration is caused mainly by the effects of the mass loss on the
moments of inertia. Another result was that better time coverage was needed
to check for the effects of external torques. So, it is quite important to
have daily coverage of these accelerations if we want to improve on models.
It should also be possible to deduce an order of magnitude estimate of the
force exerted by the outgassing, by taking into account the change or
semi major axis.
Certain Soviet rockets do suffer from corrosion. I remember reading some-
where (Spaceflight ?) that there were several cases of fragmentation ascribed
to corrosive fuel (or oxydizer?) eating its way through pipes, which then
comes into contact with oxydizer with an explosion as a result. I will have
to look up where I read this. Maybe Jim Varney can shed some light on this,
since he has access to this professional article about fragmentation. In any
case, viewed the above, my guess would be that corrosion can be a reason for
certain accelerations. Just a guess ;-)
>- there seems to be no relation with major meteor showers
>( something against this it that over the year the showers are still
> in minority compares with the daily activity)
And there is enough man-made debris out there. On the other hand, I
seem to remember there was a report of MIR being hit by Perseids a few
years back. Don't know if this was a hoax or not. And didn't ESA's
Olympus satellite (in geostationary orbit) start tumbling out of control
on August 11/12 (I forget the year) ? Hermann Boehnhardt, who was working
on the Olympus project at that time, didn't exclude the possibility of a
meteorite hit, when I asked him a few years back.
>- a lot of objects have multiple accelerations! This is again confirmed
>by 87- 49 B and 88-53B. I should think that this is difficult to explain
>with a hole because when a hole is formed all fuel escapes and there remains
>no fuel for later accelerations. The idea of Paul can solve this if we
>assume that when pressure lowers (as fuel escapes through the valve) the
>valve can close again. When the valve mechanism suffers more from its age
>it might open again.
If the fuel goes through cycles of freezing and sublimatio due to different
lighting conditions, repeated accelerations can be explained. It may be worth
trying to calculate how much time the satellites spend in sunlight these
days. And see whether this time is exceptionally high. It is well known that
some of the MIDAS satellites went through cycles of acceleration/de-
celeration. There was a correlation between the time of the maxima of the
flash period and the angle between the sun and the ascending node of the
satellite's orbit.
>I'm not sure but think that we assumed the thickness of the rocket
>to be about 1 to 2 millimeters.
I don't remember where the thickness came into our very crude models ?
>Maybe it is a combination of valve-corrosion-impacts over the years...???
I'm not sure whether it means anything, but there are accelerations that
last for 2 weeks, and there are those that last for more than 1 year.
Maybe those are caused by different things, or just a manifestation of
the same process, with different numbers ?
Now that Kurt has shed some new light on these accelerations, I hope to
work on the subject a bit more, as soon as I have more time (in 3 months
maybe ?). At that time I also hope to revive the DRAP project (Determi-
nation of Rotation Axis Project) that was started last year, but which
has been dormant due to illness/lack of time. Knowing the temporal
evolution of the direction of the rotation axis should help establishing
whether external torques are involved in these accelerations.
Cheers,
Bart De Pontieu <bdp@mpe.mpe-garching.mpg.de>