Transcript Document

Satellite Drag Variability at Earth, Mars and Venus
Due to Solar Rotation
Jeffrey M. Forbes
Department of Aerospace Engineering Sciences, UCB 429 University of Colorado, Boulder, Colorado
Sean Bruinsma
Department of Terrestrial and Planetary Geodesy, Centre Nationale D'Etudes Spatiales, Toulouse, France
Frank G. Lemoine
Planetary Geodynamics Laboratory Code 698, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
Bruce R. Bowman
Space Analysis Division/A9A, US Air force Space Command, Colorado Springs, Colorado 80914
Alex Konopliv
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA.
Objective: Utilize thermosphere densities deduced from precise orbit
determination (POD)* of the Mars Global Surveyor (MGS), Pioneer Venus Orbiter
(PVO) and Magellan satellites, and 6 Earth-orbiting satellites during
contemporaneous time periods, to perform a comparative analysis of the satellite
drag environments of Earth, Mars and Venus due to the rotation of the Sun.
*See papers by Lemoine (this session), Bowman (previous Astrodynamics conferences), and Konopliv on specific POD
methodologies for Mars, Earth, & Venus, respectively
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Average Temperature Profiles for Earth, Mars & Venus
Venus
Mars
Earth
CO2
cooling
to space
O + CO2 --> O + CO2*
CO2* --> IR emission
Motivations:
(1) In the context of Thermosphere General Circulation Models (TGCMs)
(e.g., Bougher et al.), comparative thermosphere data analyses can help to
constrain the poorly-known rate coefficient for O + CO2 --> O + CO2*
(2) Improved thermosphere density models are needed for aerobraking, re-entry,
satellite ephemeris prediction, and mission planning.
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Our study focuses on thermosphere density variations
related to rotation of the Sun.
The Sun’s atmosphere rotates with a period of ≈ 25 days near the
equator and 35 days near the poles, with an average rate of ≈ 27 days.
This differential rotation
causes magnetic field lines to
twist, resulting in the
formation of active regions
that release enhanced solar
energy in various forms,
including the extreme
ultraviolet (EUV) radiation
responsible for heating the
hot outermost region of a
planetary upper atmosphere,
the thermosphere (ca. ≥ 100
km for Earth, Mars, Venus).
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19.5 nm EUV
emission
3
The rotation of solar active regions produces quasi-27-day
periodicities in EUV flux emanating from the Sun and subsequently
absorbed by planetary thermospheres.
Relatively little is known
about the response of Mars’
neutral thermosphere
to short-term solar flux
variations.
Quasi-27-day cycle
Since EUV solar radiation
can only be measured from
space, the 10.7 cm solar
flux that has been observed
from the ground for several
decades is often used as a proxy for the EUV flux. In our study, the 10.7
cm solar flux (‘F10.7’) measured from Earth is adjusted to Mars and Venus
taking into account relative angle and relative distance with respect to the
Sun.
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March 11, 2003
19.5 nm EUV emission
10.7 cm radio flux
March 21, 2003
March 21, 2003
Day in 2003
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Data
Mars:
Daily density values at 390 km were inferred from (POD) of MGS during two
intervals of particularly pronounced quasi-27-day variability of solar flux:
days 75-150 and 270-365 of 2003.
Venus:
(1) Exosphere temperatures from drag analyses of Pioneer Venus Orbiter
(PVO) were obtained directly from the NASA Planetary Data System, for
two daytime intervals: days 100-220, 1979, and days 320-75 of 1980-1981.
(2) Daily density data from one daytime interval (days 250-365 of 1992) was
obtained from POD of the Magellan satellite.
Earth:
Drag analyses of the following 6 satellites, covering all of the above periods:
NORAD
06073
04053
06895
00829
03827
00011
INTL
1972-023E
1969-064C
1973-078C
1964-038A
1969-015E
1969-001A
NAME
INCL
Venus Lander 52.1
Intelsat
30.2
Delta-1 R/B
28.8
Elektron 3
60.8
OV1-19 R/B 104.8
Vangua rd 2
32.9
APOGEE
9800
5400
2320
6450
5450
3000
PERIGEE
220
265
350
415
500
560
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Methodology
In order to compare relative responses,
density variations are converted to
equivalent temperature variations using
empirical models of each thermosphere:
DTM-Mars, Hedin (1983) Venus Model,
and J70.
Phasing varies from cycle to cycle so that
it is difficult to find a single linear
coefficient that simply relates the solar and
temperature variations.
T
F10.7
To circumvent this problem in the interest
of obtaining some quantitative results, we
considered each positive and negative
excursion of temperature (T) and F10.7
(F10.7) as a pair, and calculated the
corresponding value of T/F10.7.
For this purpose the average of all 6
Earth-orbiting satellites were used to
obtain a single data point for each
T/F10.7 calculation.
AIAA/AAS Astrodynamics Specialist Conference, 21 - 24 Aug 2006,
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AIAA/AAS Astrodynamics Specialist Conference, 21 - 24 Aug 2006,
Keystone Resort & Conference Center, Keystone, Colorado
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AIAA/AAS Astrodynamics Specialist Conference, 21 - 24 Aug 2006,
Keystone Resort & Conference Center, Keystone, Colorado
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AIAA/AAS Astrodynamics Specialist Conference, 21 - 24 Aug 2006,
Keystone Resort & Conference Center, Keystone, Colorado
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AIAA/AAS Astrodynamics Specialist Conference, 21 - 24 Aug 2006,
Keystone Resort & Conference Center, Keystone, Colorado
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Thermosphere response of Earth, Mars and Venus to changes in solar flux
due to the Sun’s rotation. F = change in 10.7 cm solar radio flux (F10.7)
received at the planet; T = change in exospheric temperature (K).
P lanet &
Time Period
T/F
T/F
Ratio to
Earth
Earth
075-150, 2003
270-360, 2003
100-220, 1979
320-75, 80-81
250-365, 1992
All periods
2.95
1.73
1.20
1.77
2.46
2.060.83
1.00
1.00
1.00
1.00
1.00
1.00
Mars
075-150, 2003
270-360, 2003
All periods
0.77
0.59
0.700.36
0.26
0.34
0.34
< 0.15
< 0.20
< 0.21
<
0.200.12
< .125
< .113
< .085
< .097
Venus
100-220, 1979
320-75, 80-81
250-365, 1992
All periods
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Conclusions concerning the thermosphere responses of
Earth, Mars and Venus to quasi-27-day variations in
solar flux due to rotation of the Sun
• Mars’s thermosphere response is approximately 1/3rd that of Earth.
• Venus’s response is barely discernible, approximately 1/10th that of Earth.
• The above differences are likely due to the differing efficiencies of CO2 cooling
in these upper atmospheres. Our results can therefore be used to constrain
planetary atmosphere models that seek to self-consistently and inter-consistently
simulate the thermospheres of these planets.
Our tabulated data might be used for that purpose. However, additional insight
might be gained by attempting to model the actual experimental data, as this
better retains the value of contemporaneity. In particular, different effective local
times and latitudes correspond to each illustrated data set, and numerical
models attempting to emulate these results may need to similarly sample the
model output to optimize the fidelity of the comparison.
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• The results presented here should prove valuable in validating and/or updating
the parameterization of short-term solar flux variations in empirical models of
Earth’s, Mars’, and Venus’ thermospheres, especially for the purposes of
specifying or predicting atmospheric drag on satellites.
Future Work
• The effects of long-term solar flux changes on the thermospheres of these
planets, using expanded data sets, i.e., MGS, Odyssey, MRO, Magellan, Venus
Express, etc..
• Improved proxies for EUV solar variability effects, such as E10.7, MgII,
Soho EUV, etc.
• Incorporation into DTM-Mars
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Average Temperature Profiles for Earth, Mars & Venus
Mars
Venus
Earth
CO2
Cooling
O + CO2 --> O + CO2*
CO2* --> IR emission
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Keystone Resort & Conference Center, Keystone, Colorado
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