"Jim Lux" napisal w wiadomosci
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On 11/16/2011 10:57 AM, Szczepan Bialek wrote:
"Jim napisal w wiadomosci
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On 11/15/2011 12:56 AM, Szczepan Bialek wrote:
"Jim napisal w wiadomosci
n
You mean when earth is generally heading "towards" the galactic center
vs
when earth is heading "away" from the galactic center?
Yes. But on the Earth orbit are places when this speed is 0.5 km/s
(only
rotation) or 30 km/s. (orbital speed).
People doing deep space navigation deal with this all the time, since
navigation is done by measuring the frequency of the received signal
from
the spacecraft. There's nothing special about it. spacecraft on some
heliocentric trajectory, Earth on a different heliocentric trajectory.
Like the Earth and Mars.
Yes, and, for instance, they measure the Doppler shift in the signals
radiated from spacecraft/rovers in orbit/on the surface of Mars as they
arrive at earth.
Do they published the results?
Sure..
Some are in that paper you cited.
As expected, the Doppler has several components: one from the rotation
of
Earth, one from the rotation of Mars (for a surface asset), and one from
the relative motion of Mars and Earth (which is periodic with about a 2
year, 2 month period)
I am asking about "one from the relative motion of Mars and Earth "
I imagine so, although I don't know where one get the data off hand. But
they archive and publish pretty much everything that comes down along with
all the radiometric data (doppler, phase, signal strength) in various and
sundry mission data repositories. getting it in a convenient translated
form might take some work.
I am not able to do any work in the data.
I will be waiting as somebody do it.
No surprises, nothing unusual. In fact, *tiny* variations in the
Doppler
are used to compute the orbit around planets, and from that, infer the
internal structure of the planet. Juno is going to Jupiter right now to
do
this, and the Doppler will be measured with a precision of about 1 part
in
1E15 (measured over 100-1000 seconds).
Measure frequency shift, they use to determine spacecraft trajectory
by
applying (mostly) Newtonian physics (you do have to use relativistic
corrections to get the last gnat's eyelash of precision).
They confirm the diurnal changings in the frequency. But what with the
annual?
All changes in frequency, of course. Load up the SPICE kernels, run the
numerical integration, and the expected frequency pops out.
I am interested only in the measured results.
Look for what's called Level 0 telemetry data from your missions of
choice.
Here they confirm the diurnal variation in the frequency.
Probably in this paper is also the answer for my question: "And what
about
the 365 days period (annual variation in the frequency)?
Unfortunately I am not an expert in radio. Do you know the answer?
Do you want to know the magnitude of the shift?
The measured value.
They wrote (page 37): "
Fig. 17, which shows the aP residuals from a value for aP of
(7.7760.16)31028 cm/s2. The data was processed using
ODP-SIGMA with a batch-sequential filter and smoothing algorithm.
The solution for aP was obtained using 1-day batch
sizes. Also shown are the maneuver times. At early times the
annual term is largest. During Interval II, the interval of the
large spin-rate change anomaly, coherent oscillation is lost.
During Interval III the oscillation is smaller and begins to die"
I "read the entire paper" but I do not and understand if the above
"During
Interval III the oscillation is smaller and begins to die" means that the
annual variation in frequency die when the spacecraft was very far.
Dunno..
I was ony trying to pick up if the annual variation in frequency take
place
or not.
The "anomaly" variation or the "variation due to earth in its orbit"? I
suppose the answer to both is "yes"
But it is not clearly stated.
The reason is simply. The diurnal variation are in agreement with the
Michelson-Gale experiment. The annuall should be null like the famous MM.
If you need raw data, you'll need to look for it. I'd suggest starting
with the Planetary Data System http://pds.jpl.nasa.gov/
Maybe the stuff at NAIF (Navigation and Ancillary Information Facility)
might help.
There's a lot of stuff out there, but, for instance, I ran across the raw
Radio Occultation Original Data Records from Ulysses. It has a
description including: "These data are
obtained from the Radio Science Support group at JPL. They consist
of time-ordered, high-time resolution Doppler data from special
radio science receivers (so-called 'open loop' data)."
There's a lot more description online and that's probably not a data set
you're looking for, but the data is out there, if you're willing to go
digging through it. I doubt anyone is going to give you exactly what
you're looking for, though.
They confirm the diurnal oscilations.
They do not mention the annual.
So I assume that the annual are null.
You'll have to do some conversion, and
you'll need to know a fair amount about how all the tracking systems work,
but that's all published. You might start with the DSN 810-005 online
document (google for it).. That will tell you how they record the data and
the format.
A more recent data set is from MRO
"This data set contains archival raw, partially processed, and
ancillary/supporting radio science data acquired during the Mars
Reconnaissance Orbiter (MRO) mission. The radio observations were carried
out using the MRO spacecraft and Earth-based receiving stations of the
NASA Deep Space Network (DSN). The data set was designed primarily to
support generation of high-resolution gravity field models for Mars and
secondarily for estimating density and structure of the Mars atmosphere.
Of most interest are likely to be the Orbit Data Files and Radio Science
Receiver files in the ODF and RSR directories, respectively, which
provided the raw input to gravity and atmospheric investigations, as well
as the ionospheric and tropospheric media calibration files in the ION and
TRO directories, respectively."
http://starbrite.jpl.nasa.gov/pds/vi...SS-1-MAGR-V1.0
Among the stuff in that particular data set is:
" The ODF is a compressed version of the TNF. It contains the most
important information (range, Doppler and frequency ramps)
needed by spacecraft investigators, and investigators interested
in determining gravity fields. Each ODF is accompanied by a full
PDS label which describes both the content and format of the
associated file. ODF data fields include:
Narrowband spacecraft VLBI, Doppler mode (cycles)
Narrowband spacecraft VLBI, phase mode (cycles)
Narrowband quasar VLBI, Doppler mode (cycles)
Narrowband quasar VLBI, phase mode (cycles)
Wideband spacecraft VLBI (nanoseconds)
Wideband quasar VLBI (nanoseconds)
One-way Doppler (Hertz)
Two-way Doppler (Hertz)
Three-way Doppler (Hertz)
One-way total count phase (cycles)
Two-way total count phase (cycles)
Three-way total count phase (cycles)
PRA planetary operational discrete spectrum range (range
units)
SRA planetary operational discrete spectrum range (range
units)
RE(GSTDN) range (nanoseconds)
Azimuth angle (degrees)
Elevation angle (degrees)
Hour angle (degrees)
Declination angle (degrees)
"
So there you have all the VLBI and doppler info you're looking for.
The actual data files are at
http://pds-geosciences.wustl.edu/mro...v1/mrors_0xxx/
(There's a link at the PDS catalog entry)
There's documentation on the format of the ODF files, and I see that they
actually give you Doppler and range observables, rather than raw counts,
which is nice.
The answer I am loking for is not important for me.
I have come accros an information that astronomers add the orbital speed of
the Earth to the radial speed of stars measured with the spectrographic
method.
The radio method are the same like the spectrography. But it contradicts
MMX. So I am trying to clear it.
S*