level Mars atmospheric model. Applications include systems design, performance analysis, and operations planning for aerobraking, entry descent and landing, and aerocapture. Typical Mars aerocapture periapsis altitudes (for systems with rigid- aeroshell heat shields) are about 50 km. This altitude is above the 0-40 km height range covered by Mars Global Surveyor Thermal Emission Spectrometer (TES) nadir observations. Recently, TES limb sounding data have been made available, spanning more than two Mars years (more than 200,000 data profiles) with altitude coverage up to about 60 km, well within the height range of interest for aerocapture. Results are presented comparing Mars-GRAM atmospheric density with densities from TES nadir and limb sounding observations. A new Mars-GRAM feature is described which allows individual TES nadir or limb profiles to be extracted from the large TES databases, and to be used as an optional replacement for standard Mars-GRAM background (climatology) conditions. For Monte-Carlo applications such as aerocapture guidance and control studies, Mars-GRAM perturbations are available using these TES profile background conditions

Duvall, Aleta

Justus, C. G.

Keller, Vernon W.

NASA Technical Reports Server

ATMOSPHERIC MODELS FOR MARS AEROCAPTURE 
C. G. Justus"', Aleta Duvall"', Vernon W. Keller"' 
( I )  Morgan Research Corporation, 481 1 -A Bradford Drive, Huntsville, AL 35805- 
1948 (USA), Jere. Justus@msfc.nasa.Rov, Aleta. Duvall@msfc.iinsa.gov 
'2'NASA Marshall Space Flighr Center, EVI3, Marshall Space Flight Center, AL 
358I2 (USA), Vernon.Keller@nasa.gov 
ABSTRACT 
Mars Global Reference Atmospheric Model (Mars-GRAM) is a widely-used engineering- 
level Mars atmospheric model. Applications include systems design, performance 
analysis, and operations planning for aerobraking, entry descent and landing, and 
aerocapture. Typical Mars aerocapture periapsis altitudes (for systems with rigid- 
aeroshell heat shields) are about 50 km. This altitude is above the 0-40 km height range 
covered by Mars Global Surveyor Thermal Emission Spectrometer (TES) nadir 
observations. Recently, TES limb sounding data have been made available, spanning 
more than two Mars years (more than 200,000 data profiles) with altitude coverage up to 
about 60 km, well within the height range of interest for aerocapture. Results are 
presented comparing Mars-GRAM atmospheric density with densities from TES nadir 
and limb sounding observations. A new Mars-GRAM feature is described which allows 
individual TES nadir or limb profiles to be extracted from the large TES databases, and to 
be used as an optional replacement for standard Mars-GRAM background (climatology) 
conditions. For Monte-Carlo applications such as aerocapture guidance and control 
studies, Mars-GRAM perturbations are available using these TES profile background 
conditions. 
INTRODUCTION 
Mars Global Reference Atmospheric Model (Mars-GRAM) is an engineering-level 
atmospheric model widely used for diverse mission applications (Justus et al., 2003, 
2004a-e; Duvall et al., 2005). From 0 km to 80 km altitude, Mars-GRAM is based on 
NASA Ames Mars General Circulation Model (MGCM) (Haberle et a]., 1993), while 
above 80 km it is based on Mars Thermospheric General Circulation Model (MTGCM) 
(Bougher et al., 1990). Mars-GRAM and MGCM use surface topography from Mars 
Global Surveyor Mars Orbiter Laser Altimeter (MOLA) (Smith and Zuber, 1998), with 
altitudes referenced to the MOLA constant potential surface (areoid). 
Mars-GRAM 2001, the previous version of Mars-GRAM, has been validated (Justus et 
al., 2004a,d) against data from Radio Science (RS) observations (Hinson, et al., 1999), 
and from Thermal Emission Spectrometer (TES) nadir profiles (Smith et al., 2001). A 
just-released version of Mars-GRAM, Mars-GRAM 2005, is described here and is 
validated against RS data, nadir TES data, and TES data from Mars limb soundings 
(Conrath et al., 1999). While both the RS and TES nadir data extend up to an altitude of 
about 40 km, TES limb data reach altitudes of about 60 km or slightly higher. Results 
from comparison of Mars-GRAM with TES limb data are particularly relevant for 
https://ntrs.nasa.gov/search.jsp?R=20050207555 2019-08-29T20:48:03+00:00Z
aerocapture at Mars, since aerocapture periapsis altitude would typically be in the range 
of about 40-60 km, Le. above the height range covered by RS or TES nadir data. 
NEW MARS-GRAM FEATURES 
Two new features of Mars-GRAM 2005 that are of importance for aerocapture are: 
(1) Option to use input data sets from MGCM and MTGCM model runs that were 
designed to closely simulate the conditions observed during the first two years of TES 
observations at Mars (TES Year 1 = April 1999 through January 2001; TES Year 2 = 
February 2001 through December 2002). 
(2) Option to read and use any “auxiliary profile” of temperature and density versus 
altitude. 
In exercising the auxiliary profile Mars-GRAM option, the alternate data (i.e. values from 
the auxiliary profile) totally replace data from the original MGCWMTGCM databases. 
One example of an auxiliary profile would be data from RS or TES (nadir or limb) 
observations at a particular location and time. 
VALIDATION OF MARS-GRAM 2005 
For Mars-GRAM 2001 validation studies (Justus et al., 2004 a,d), 2,480 RS profiles were 
compared with Mars-GRAM results for the same location and time as each RS profile. 
Mars-GRAM 2005 climatology has been compared with over 12,000 RS profiles, 
approximately 5 times as many as for the 2001 comparison. The new, larger RS database 
provides more complete seasonal (Ls) coverage, over a wide range of latitudes, than 
represented in the earlier validation comparisons. Figure 1 presents results of average 
Mars-GRAM minus RS atmospheric density as a function of height and latitude, with all 
seasons (Ls values) combined. At almost all heights and latitudes, mean Mars-GRAM 
density differs by less than 10% from mean RS density. These results are slightly better 
than for the comparison of RS data with Mars-GRAM 2001, where a zone of slightly 
greater than 10% differences was seen at heights above about 32 km and latitudes 
poleward of about 50N. 
Comparisons of Mars-GRAM 2005 climatology with TES limb data (Conrath et al., 
1999) have also been conducted. Figure 2 compares atmospheric density profiles from 
Mars-GRAM 2005 and TES limb data at representative Phoenix landing conditions (Ls = 
78 degrees, latitude = 67.5N, longitude = 223.1E, for limb data from TES Year 1). The 
TES limb data profile in Figure 2 is an average of 17 individual limb profiles that are 
near this location and time. The average TES limb profile, formatted for use as an 
“auxiliary profile” in Mars-GRAM 2005, is also given in Table 1. Zero wind values in 
Table 1 indicate that no wind observations are available, so original MGCM wind values 
are assumed. Figure 2 shows good agreement between Mars-GRAM 2005 and TES limb 
60 
55 
50 
45 
40 
E x 35 
30 
2 25 
20 
15 
10 
5 
0 
0- 
MarsGRAM minus Radio Science Density, percent 
40 
35 
E 30 
Y 
25 
g 20 
E, 15 
f l o  
4 
.- 
5 
0 
%O 9 0  -30 0 30 60 90 
Latitude. degrees 
Figure 1 - Average Mars-GRAM minus RS atmospheric 
density as a function of height and latitude 
~ , - . ~ -  - - -  
, . . . . . . 
. . . . . . . . 
,.. . . 
4 6 6 7 1 0 4  2 3 4 6 6 7  105 2 3 4 6 6 7 1 0 - 2  2 
Density, kg/m3 
Figure 2 - Density profiles from Mars-GRAM 2005 and 
TES limb data at representative Phoenix landing conditions 
* 
Table 1 - Sample Mars-GRAM 2005 Auxiliary Profile (Average 
of 17 TES Limb Profiles at Phoenix Landing Conditions) 
Height 
2.172 
4.825 
7.408 
9 .921  
12.365 
14.744 
17.062 
19.326 
21.540 
23.709 
25.838 
27 .931  
29.992 
32.029 
34.048 
36.057 
38 .061  
40.051 
42.039 
44.019 
45.987 
47.948 
49.888 
51.825 
53.720 
55.646 
57.546 
Lat 
67.50 
67.50 
67.50 
67.50 
67.50 
67.50 
67.50 
67.50 
67.50 
67.50 
67.50 
67.50 
67.50 
67.50 
67.50 
67.50 
67.50 
67.50 
67.50 
67.50 
67.50 
67.50 
67.50 
67.50 
67.50 
67.50 
67.50 
Lon3 TempK P r e s W 2  Denskgm3 
223.10 209.39 4.7513+02 1.1873-02 
223.10 203.59 3.7003+02 9.5093-03 
223.10 197.79 2.8813+02 7.6223-03 
223.10 192.08 2.2443+02 6.1133-03 
223.10 186.63 1.7483+02 4.9003-03 
223.10 181.46 1.3613+02 3.9253-03 
223.10 176.77 1.0603+02 3.1383-03 
223.10 172.53 8.2553+01 2.5043-03 
223.10 168.64 6.4293+01 1.9953-03 
223.10 165.22 5.0073+01 1.5863-03 
223.10 162.06 3.9003+01 1.2593-03 
223.10 159.20 3.0373+01 9.9823-04 
223.10 156.83 2.3653+01 7.8913-04 
223.10 155.03 1.8423+01 6:2183-04 
223.10 153.86 1.4353+01 4.8813-04 
223.10 153 .15  1.1173+01 3.8223-04 
223.10 152.50 8.7003+00 2.9913-04 
223.10 151 .68  6.7803+00 2.3443-04 
223.10 150.77 5.2803+00 1.8373-04 
223.10 149.83 4.1103+00 1.4393-04 
223.10 148.78 3.2003+00 1.1293-04 
223.10 147 .71  2.4903+00 8.8513-05 
223.10 146.72 1.9403+00 6.9463-05 
223.10 145.76 1.5103+00 5.4463-05 
223.10 144.75 1.1803+00 4.2893-05 
223.10 143.68 9.1703-01 3.3603-05 
223.10 142.68 7.1403-01 2.6363-05 
mind . 00 . 00 
.oo 
. 00 
. 00 
. 00 . 00 
. 00 
. 00 . 00 
. 00 
. 00 
. 00 
. 00 
. 00 
. 00 
. 00 
. 00 . 00 
. 00 
. 00 
. 00 
-00 
. 00 
. 00 
. 00 
. 00 
Wind 
.oo 
. 00 
.oo 
. 00 
.oo 
. 00 
.oo 
.oo 
.oo 
.oo 
.oo 
.oo 
.oo 
.oo 
.oo 
. 00 
.oo 
.oo 
.oo 
.oo 
.oo . 00 
.oo 
.oo 
.oo 
.oo  
.oo  
densities for heights up to about 30 km, and above about 50 km. Mars-GRAM 2005 
density becomes about 15% higher than TES limb density near 40 km altitude. 
In contrast to the high latitude case shown in Figure 2, Figure 3 compares Mars-GRAM 
2005 density at equatorial conditions (for Ls=120) with both TES limb data and TES 
nadir data. TES limb and nadir data agree quite well with each other, over the full height 
range for which nadir data are available. Figure 3 shows that Mars-GRAM 2005 density 
agrees well with both types of TES data, up to a height of about 30 km. However, Mars- 
GRAM 2005 densities begin to deviate (on the low side) from TES limb data above about 
30 km, with Mars-GRAM densities being about 40% lower than TES limb data between 
about 45 km and 55 km. 
Figure 4 shows results from Mars-GRAM versus TES limb data density comparisons, 
averaged over all seasons (all Ls values), all latitudes, and both TES years 1 and 2. This 
figure shows average Mars-GRAM minus TES density (as percent of TES density) versus 
height and latitude. Figure 4 shows that results from Figures 2 and 3 are not atypical. At 
high northern latitudes, Figure 4 indicates that Mars-GRAM agrees closely with TES 
limb data, with Mars-GRAM being about 10% to 15% larger than TES near 40 km 
altitude. This behavior is similar to that shown in Figure 2. In contrast, Figure 4 shows 
TES and Mars-GRAM Density 
Ls=120 L a t a  L o n 3  Hr=14 Mapyear4 
50 
40 
E 
Y 
30 
I- s 
20 
10 
4 5 6 7 1 0 4  2 3 4 5 6 7  103 2 3 4 5 6 7 1 0 2  
Density, kg/m3 
Figure 3 - Density profiles from Mars-GRAM 2005, TES 
nadir data, and TES limb data, at equator, for Ls = 120. 
Mean Density Difference, (MG -TES)/TES, % 
TES Years 1 &2 Ls=AII LST=AII 
60 
50 
E 40 
& 
* 
-4 30 
z 
20 
10 
0 
40 -60 -30 0 30 60 90 
Latiude, degrees 
Figure 4 - Mean density difference, Mars-GRAM 2005 minus 
TES limb data, versus height and latitude 
TES Llmb Data vs MarsGRAM 2005 
60 
50 
40 
E 
Ea 30 x .- 
i 
20 
10 
0 
All Latitudes, All Seasons 
- Y18r.7 OInilty - Year 1 Tmpmmture 
4 0  -30 -20 -1 0 0 10 
Average Difference (MmGRAM - TES), percent 
Figure 5 - Comparison of Mars-GRAM 2005 density and 
temperature with TES limb data, for all seasons and latitudes 
that, over a broad range of low and middle latitudes, Mars-GRAM densities are 
significantly lower than TES limb densities for heights of about 40 km and higher, 
analogous to Figure 3. 
Figure 5 shows mean altitude profiles of Mars-GRAM 2005 versus TES limb density and 
temperature, averaged over all latitudes and seasons (all Ls values), separately for TES 
Years 1 and 2. In this figure, differences in both mean density and temperature are given 
in percent. A large, global-scale dust storm occurred during TES Year 2 (Smith, 2004). 
Note, however, that average Mars-GRAM versus TES comparisons for density and 
temperature are actually slightly better for TES Year 2 than for TES Year 1. This result 
would seem to indicate that Mars-GRAM (and MGCM on which it is based) represents 
dust effects at least as well during dust storm conditions as during non-storm conditions. 
Figure 5 confirms that the tendency of Mars-GRAM to underestimate density at high 
altitudes (especially at low-to-middle latitudes) is a feature of both TES Years 1 and 2. 
Figure 5 indicates that the tendency of Mars-GRAM to underestimate density at high 
altitudes (40 to 60 km) results from a “cold bias” in Mars-GRAM temperatures over this 
upper altitude region. If Mars-GRAM temperatures are colder than observed, over an 
extended altitude region, then hydrostatics forces Mars-GRAM density to become lower 
than observed, by a exponentially-increasing amount, as the depth of the cold bias layer 
increases. A “rule of thumb” approximation to estimate effects of such bias is that if a 
temperature bias = k x (in percent) persists over a layer of depth = n scale heights, then 
the density deviation at the top of the layer will be f x x n (in percent), assuming density 
deviation starts at zero at the bottom of the layer. For TES Year-1 data in Figure 5, we 
have x averaging about -5% over the layer from about 15 km to about 55 km altitude 
(roughly 5 scale heights). The rule of thumb thus gives a density deviation = -5% x 5 
scale heights = -25% at the top of this layer, is good agreement with observed density 
deviations at the 55-km layer top. 
Preliminary studies by Murphy (2005) using various vertical dust profiles suggest that 
MGCM's tendency to yield a cold bias results from too little dust at upper altitudes in the 
normal MGCM vertical dust distribution. Mars-GRAM 2005, which is based upon 
MGCM output, reflects this cold bias. For a given total dust loading (dust optical depth), 
increasing the relative amount of dust at higher altitudes in MGCM would produce 
additional heating of the upper altitude layers, thereby reducing or removing the cold bias 
and the resulting Mars-GRAM tendency toward low densities compared to observations. 
Until updated MGCM data are available for incorporation in Mars-GRAM, it may be 
advisable for aerocapture studies to use auxiliary profiles from TES limb data as Mars- 
GRAM input conditions. 
CONCLUSIONS 
The new Mars-GRAM option to use "auxiliary profiles" derived from TES limb data will 
be especially useful for aerocapture analyses. For aerocapture maneuvers with periapsis 
at low-to-middle latitudes, TES limb density data are typically larger than Mars-GRAM 
density by as much as 40% at periapsis altitudes (40 to 60 km). At high northern and 
southern latitudes, agreement is better between Mars-GRAM and TES limb densities. 
However, at high northern latitudes, such as planned for Phoenix entry and landing, 
Mars-GRAM overestimates density compared to TES limb data by about 10-15% in the 
30 to 45-km height range. 
ACKNOWLEDGMENTS 
The authors gratefully acknowledge support from the NASA Office of Space Sciences 
Mars Data Analysis Program (MDAP) and the MSFC In-Space Propulsion Technology 
Office. Particular thanks are extended to Jim Murphy, New Mexico State University, for 
providing MGCM output and comparative data. User feedback and suggestions from the 
following individuals are also greatly appreciated: Lee Bryant, Tim Crull, and Wyatt 
Johnson of NASA Jet Propulsion Laboratory; John Aguirre of Vigyan, Inc.; and Richard 
Powell of NASA Langley Research Center. 
REFERENCES 
Bougher, S. W., et al., "The Mars Thermosphere: 2. General Circulation with Coupled 
Dynamics and Composition", Journal of Geophysical Research, 95(B9), 14,8 11-14,827, 
1990. 
Conrath, B. J., Pearl, J. C., Smith, M. D., and Christensen, P. R., "Mars Global Surveyor 
TES Results: Atmospheric Thermal Structure Retrieved from Limb Measurements", 
American Astronomical Society, Division of Planetary Sciences Meeting #3 1, #49.08, 
September, 1999. 
Duvall, A. L., Justus, C. G., and Keller, V. W., "Global Reference Atmospheric Model 
(GRAM) Series for Aeroassist Applications", AIAA-2005- 1239, 43rd AIAA Aerospace 
Sciences Meeting and Exhibit, Reno, Nevada, January 10-13,2005. 
Haberle, R. M., et al., "Mars Atmospheric Dynamics as Simulated by the NASA Ames 
General Circulation Model 1. The Zonal-Mean Circulation", Journal of Geophysical 
Research, 98(E2), 3093-3 123, 1993. 
Hinson, D. P., Simpson, R. A., Twicken, J. D., Tyler, G. L., and Flasar, F. H., "Initial 
Results from Radio Occultation Measurements with Mars Global Surveyor", Journal of 
Geophysical Research (Planets), 104(El l), 26,297-27,012, 1999. 
Justus, C. G., Duvall, A. L. and Johnson, D. L., "Mars Global Reference Atmospheric 
Model (Mars-GRAM) and Database for Mission Design", in "Mars Atmosphere 
Modelling and Observations", CNESESA 1 1-5,2003. 
Justus, C. G., Duvall, A. L., and Johnson, D. L., "Mars-GRAM Validation with Mars 
Global Surveyor Data", Advances in Space Research, 34, 1673-1676,2004. 
Justus, C. G., Duvall, A. L., and Keller, V. W., "Engineering-level Model Atmospheres 
for Titan and Mars", International Workshop on Planetary Probe Atmospheric Entry and 
Descent Trajectory Analysis and Science, Lisbon, Portugal, October 6-9, 2003, 
Proceedings: ESA SP-544, February, 2004. 
Justus, C. G., Duvall, A. L., and Keller, V. W., "Atmospheric Models for Aerocapture", 
AIAA-2004-3844, 40th AIAA/ASME/SAE/ASEE Joint Propulsion Conference, Fort 
Lauderdale, Florida, July 11-14,2004. 
Justus, C. G., Duvall, A. L., and Keller, V. W., "Validation of Mars-GRAM and Planned 
New Features", 35th COSPAR Scientific Assembly, Paris, France, July 18-25,2004. 
Justus, C, G., Duvall, A. L., and Keller, V. W., "Atmospheric Models for Aeroentry and 
Aeroassist", 2nd International Planetary Probe Workshop, NASA Ames Research Center, 
August 23-26,2004. 
Murphy, J., private communication, 1/13/2005. 
Smith, D. E., and Zuber, M. T., "The Relationship between MOLA Northern Hemisphere 
Topography and the 6.1-mbar Atmospheric Pressure Surface of Mars", Geophysical 
Research Letters, 25,4397-4400, 1998. 
Smith, M. D., Pearl, J. C., Conrath, B. J., and Christensen, P. R., "One Martian Year of 
Atmospheric Observations by the Thermal Emission Spectrometer", Geophysical 
Research Letters, 28(22), 4263-4266,2001. 
Smith, M. D., "Interannual Variability in TES Atmospheric Observations of Mars during 
1999-2003", ZCUWS, 167, 148-165,2004. 


Atmospheric Models for Mars Aerocapture

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server