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6.1990-2932

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ROUND-TRIP MARS TRAJECTORIES
New Variations on Classic Mission Profiles
off
John K. Soldner
Science Applications International Corporation
Houston, TX
Downloaded by UNIVERSITY OF NEW SOUTH WALES (UNSW) on October 27, 2017 | http://arc.aiaa.org | DOI: 10.2514/6.1990-2932
Abstract
human exploration of the solar system. The Lunar
and Mars Exploration Office at the Johnson Space
Center is the top-level architect for mission
development and definition, and system engineering
for the space exploration initiative (SEI).
Ballistic round-trip Mars stopover missions are
generally categorized as "opposition-class" or
"conjunction-class". These two trajectory types have
widely disparate trajectory characteristics, including
energy requirements and trip-time profiles, such that
they are generally not compatible in an evolving
mission strategy. However, by varying interplanetary
transit times and Mars stay times, a set of trajectories
have been developed which are referred to as "500-day"
and "1000-day missions." These two sets of
trajectories have "normalized AV budgets which can
then accommodate a common vehicle, and allow
incorporation into a long-term mission strategy for an
evolving outpost at Mars.
The goal of these studies was to develop the database
from which subsets could be applied to a defined
approach. The material to be presented in this paper
was generated as part of the FYI989 studies, as well
as, during the intensive 90-day study period that
concluded in November 1989. The results to be
presented are new design approaches to well-known,
classic ballistic Earth-Mars round-trip trajectories.
11. Classic Earth-Mars Trajectorv Options
I. Introduction
The two major classes of Earth-Mars ballistic roundtrip trajectories that are well documented in the
literature are "opposition-class"and "conjunctionclass", so-called according to whether the midpoint of
the mission more closely corresponds to the date of
Earth-Mars opposition or conjunction. The
significant characteristicsof each type are summarized
below.
The year 1990 marks the beginning of at least the
fifth decade of serious technical discussions about
concepts for human missions to Mars, beginning
with Wernher von Braun's Mars Project proposal in
1953 up through the recently completed NASA 90day study. While each succeeding study reflects our
increasing knowledge in the field of human space
flight, the one constant in all of the studies has been
the Earth-Mars trajectory analyses. There have been
no new breakthroughs in the way one travels to Mars;
the laws of orbital mechanics governing the motion
of a spacecraft in interplanetary space have not
changed since the days of Kepler. (In fact, the reader
is directed to Reference 1 (February 1967) for a very
thorough discussion of ballistic Mars mission
profiles.) The point of this discussion is to
emphasize to the reader that the trajectory concepts
presented in this paper represent slight variations on
the classic mission profiles. It will be demonstrated
how these trajectories can be applied to a long-term
approach to a Mars outpost emplacement.
Opposition Class: This class of trajectory is
characterized by "short" Mars stay time (-30-60 days),
and by "short" round-trip flight times (-500days); however each one-way leg can be 200long depending upon the launch opportunit
orbit plot of an opposition-class trajec
from above the ecliptic plane, is provi
A Venus gravity assist is typically em
energy reduction; either outbound or i
depending upon the launch opportuni
gravity assist is not employed the traject
passes by the Sun at approximately Venu
distance (-0.7 AU). A "sprint" trajectory
be discussed later in more detail, is a sub
class of trajectory, characterized by round'
times of approximately one year. Opp
missions are also high energy mission
propulsive AV requirements of 12-20 k
total AV is the sum of: (1) departure fr
altitude circular parking orbit at Earth, (
For the past two years, the NASA Headquarters Office
of Exploration (OEXP) has been leading a NASAwide effort to provide recommendations and
alternatives for a decision on a focused program of
Copyright 0 1990 by the American Institute of Aeronautics
and Astronautics, Inc., All rights reserved.
497
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L-
Figure 1.
Example Opposition Class Trajectory
EARTH-MARS
MARS STAY
MARS-EARTH
TOTAL MISSION
Figure 2.
Example Conjunction Class Trajectory
498
into a low-altitude circular orbit at Mars, (3) departure
from the same parking orbit at Mars, and (4) braking,
when necessary, to a maximum allowable Earth
approach velocity of 9.5 km/sec.l
This class of trajectory is
characterized by "long" Mars stay time (-350-500
days), and "long" round-trip flight times (-900-1000
days). One-way trip times are typically 200-300 days
long depending upon the launch opportunity.
Conjunction class missions, since they are quasidouble Hohmann transfers, are by definition
minimum energy round-trip mission profiles. The
total propulsive AV requirements for conjunctionclass missions are 7-9 km/sec. An orbit plot of a
typical conjunction-class trajectory is provided in
Figure 2.
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:-
Again, the reader is directed to Reference 1 for a
complete discussion concerning the peculiarities of
opposition and conjunction-class missions. From
these two broad classes of trajectories, a subset
having energy and flight time characteristics
appropriate for piloted missions was developed.
It should also be noted that these trajectories were
developed assuming aerobraking at Mars for orbit
insertion. Different trajectory solutions within the
two major classes of trajectories will be obtained
depending upon assumptions about the transfer
vehicle propulsion system. For example, a trajectory
optimized assuming aerobraking at Mars will have a
much higher approach velocity at Mars, than a
trajectory assuming propulsive capture. Even two
trajectories that assume propulsive capture at Mars
could differ depending upon whether Nuclear Thermal
Rocket propulsion or advanced chemical propulsion
is assumed for the Mars orbit insertion bum.
111. 500-Dav and 1000-Dav Trajectories
The FY 1988 OEXP studies (Reference 2) employed a
splitlsprint mission strategy for the human missions
to Phobos and Mars. A representative mission
profile is illustrated in Figure 3. This strategy is
advantageous for reducing the required initial mass in
low Earth orbit for "fast" piloted missions with short
stay times at Mars. For a detailed discussion about
the utility of the splitlsprint concept for Mars
missions, the reader is directed to Reference 3.
Briefly, all the cargo not required by the crew for the
outbound leg, i.e., the massive trans-Earth injection
(TEI) stage, along with all the mass destined for the
Mars surface, is sent to Mars on a minimum energy
cargo mission. The crew is then launched separately
during the next opportunity on a fast "sprint" profile
having a total round-trip mission duration of 440
days. In this way, the large cargo mass requires only
a small propulsive maneuver, while the mass for the
high energy piloted sprint has been reduced to the bare
minimum, thereby allowing the round-trip time to be
decreased from the 500-600 days, typical of
opposition-class missions, to slightly over one year,
for the comparable mass in low Earth orbit.
For mission safety reasons, the FYI989 studies
assumed that the TEI stage could not be separated
from the crew's transfer vehicle, i.e., the crew would
not be sent to Mars on a separate trajectory from their
return propulsion system. The performance
calculations based upon this change, i.e., the cargo
flight now delivers only the Mars lander (the TEI
stage is included in the piloted flight), showed that
the advantage of splitting the mission was now
greatly reduced. Also, returning to an all-up strategy
greatly reduced mission complexity by avoiding the
rendezvous of the piloted and cargo vehicle at Mars.
However, as noted above, an all-up mission of
approximately one-year duration is prohibitively
massive. (Hence, the reason to split it in the first
place.) By extending the sprint trajectory total
mission duration to approximately 500 days a Venus
swingby could be found in every opportunity (this is
not always possible for sprint trajectories), and the
resulting trajectories' energy were reduced
significantly. The 500-day trajectory profile is a
compromise between the classic opposition class
trajectory and the "sprint", in terms of both mission
energy and flight time.
The question posed was: if a transfer vehicle were
designed for a 500-day class mission AV budget, what
flexibility does it offer if flown on a conjunctionstyle mission? A major realization in the FYI989
studies was that reducing conjunction class mission
one-way trip times (both outbound and return) by up
to 100 days can be achieved for very modest (-5%)
increase in departure AV. This result is shown
graphically in Figure 4. The total round-trip mission
duration remains approximately 900-1000 days;
however the Mars stay time is increased by as much
attractive from a life sciences (sh
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CARQO
-
CREW
- 1.15 YR OPPOSITION CL
CONJUNCTION CLASS
T
3 0 DAY
STAY
I-
i
I
Figure 3.
Mars SplitISprint
(2018 Launch Opportunity)
5000
I
@
Minimum Energy
Return (Mars - Earth)
One-way Flight Time (days)
Figure 4.
Flight Time Effect on Departure AV
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It should be pointed out that decreasing the one-way
trip time, while not significantly impacting the
departure AV, does increase the arrival velocity at the
target planet. As a result, this particular strategy may
be attractive only for missions which employ
aerobraking at Mars, and direct entry at Earth, and not
for all-propulsive missions. This fact is displayed
graphically in Figure 5. A trajectory plot of the
1000-daytrajectory corresponding to the conjunction
class mission in Figure 2 is shown in Figure 6.
From the 500-day and 1000-day class of trajectories a
subset with a free-return abort capability was
developed for d piloted missions. This means that
once the trans-Mars insertion bum is performed, the
piloted transfer vehicle can return to Earth without
any further propulsive maneuvers required. The 3year free-return abort trajectories corresponding to the
1000-day class missions are shown in Table 1. The
abort trajectories that correspond to the 500-day class
missions are still in work at this time.
Increasing the AV budget for conjunction-class
missions allows faster one-way trip times; extending
the "sprint" round-trip times allows AV budgets
compatible with the 1000-day class. Thus, the
resulting 500-day and 1000-day class trajectories for
the launch opportunities 2015-2030 that were
developed as part of this study are presented in Tables
1 and 2. Please note the following assumptions and
constraints under which these trajectories were
optimized: (1) aerocapture at Mars, (2) direct entry at
Earth return, (3) launch from Space Station Freedom
orbit, (4) Mars orbit sue for arrival and departure 250
km apoapse x 1 sol (Period = 24.62 hours; an
elliptical parking orbit was chosen at Mars, vs. low
circular, to reduce the initial mass required in low
Earth orbit), (5) V-infinity at Mars arrival < 7.0
kmlsec, and (6) V-infinity at Earth return < 7.0
kmlsec ( ~ 9 . 5kmlsec for the abort trajectory). The
results in Table 2 show that these constraints could
not always be met for the 560-day class missions, a
fact which is discussed in more detail in the
paragraphs to follow.
There are really three trajectory types presented in
Tables 1 and 2: (1) 1000-day, (2) 500-day, with
Venus swingby outbound, and (3) 500-day, with
Venus swingby inbound. It is important to note that
there is a launch opportunity every synodic period for
& trajectory type. Since the launch dates of the
three types do not necessarily coincide, this means
that there is an opportunity to launch to Mars at least
every calendar
and sometimes
year. Since the AV budgets have been normalized
across the trajectory types, important backup launch
opportunities now potentially exist.
However, as previously noted, the results presented in
Table 2 demonstrate that many 500-day class
missions are not viable from an energy point of view,
i.e., the AV requirements are greater than the
normalized AV budget and/or the arrival velocities are
outside the constraint envelope. They have been
included here for completeness. Applying double
Venus swingbys, i.e., both outbound and inbound for
the same round-trip mission, is a possible solution in
these difficult years although not addressed in this
study. The reader is directed to Reference 4 for a
survey of double Venus swingby opportunities.
Finally, the AV budget employed in the 90-day study
is presented in Table 3. All of the 1000-day class
missions presented in Table 1 are within this budget;
at least one 500-day mission every two years is
within the budget.
Table 3.
Normalized AV Budget
Flight Phase
Pre-injection preparation
Trans-Mars injection (TMI)
Trans-Mars coast
Mars orbit insertion
Mars orbit rendezvous
Mars orbit operations
Trans-Earth injection (TED
Trans-Earth coast
Earth orbit insertion
Earth orbit operations
AV Cmlsec)
200
.....................................................................
Inintial Mass In LEO
700
w
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NTR TMI,
9..
Earth to Mars Flight-time (days)
* 2005 Launch Opportunity
*
Launch from SSF orbit
* 250 km x 1 sol orbit at Mars
* 37 t payload delivered to Mars surface
*
Aerobrake to 500 km circular phasing orbit,
then deorbit
Figure 5. Advantage of Aerobraking at Mars
2018 Launch Opportunity
- -- -
MASS STAY TIME
T
lood
EARTH-MASS
MASS STAY
MARS-EARTH
133d
TOTAL MISSION
894d
65gd
Figure 6. 1000-Day Class Trajectory
Table 1
EARTH-MARS
1000-DAY CLAS
-
Outbound
Flight
rime, days
Mars
Stay
rime, days
6.786
6.786
190
190
0
5 12
7/1/14
7/1/14
6.933
6.933
181
181
0
555
1/8/16
3.687
3.687
7/30/16
7/30/16
6.940
6.940
150
150
0
635
4/26/18
61.5118
6/5/18
4.287
4.287
9/13/18
9/13/18
7.008
7.008
100
100
0
566
7/20/20
7/5/20
7/5/20
4.217
4.217
11/21/20
11/21/20
5.974
5.974
139
139
0
630
8/13/22
9/6/22
9/6/22
4.051
4.05 1
3/6/23
3/6/23
4.734
4.734
181
181
0
540
8/27/24
10112/24
Round-Trip 10/12/24
4.025
4.025
4/24/25
4/24/25
5.455
5.455
194
194
0
515
9/16/26
11/13/26
Round-Trip 11/13/26
3.983
3.983
5/14/27
5/14/27
7.196
7.196
183
183
0
516
10/11/28
12/14/28
Round-Trip 12/14/28
3.791
6/12/29
6/12/29
7.537
3.791
-
180
180
0
54 1
12/4/30
Delta V
TMI
kmlsec
Arrival
Date
3.836
6/1/12
6/1/12
1/1/14
1/1/14
3.672
3.672
3/2/16
3/2/16
Launch
Date
3.836
11/24/11
Abort
Round-Trip 11/24/11
Abort
Round-Trip
Abort
Round-Trip
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-
Abort
Round-Trip
Abort
Round-Trip
Abort
Round-Trip
Abort
Abort
Abort
Mars
arrival
Vinf
-
7.537
-
Departure
Date
Abort
Abort
Abort
Abort
Abort
Abort
Abort
1 1 1
Delta V
TEI
km/sec
R;z
1 1 1
0
1.069
12/19/16
7/6/16
1 1 1
Return
Flight
Time, days
Total
Mission
Duration, days
949
220
1139
922
3.450
7.341
902
180
1083
916
0
1.699
2/27/19
8/24/18
3.412
7.456
942
120
1092
905
2.:75
6/9/21
11/7/20
5.460
6.845
1000
120
1100
886
0
2.180
8/30/23
1/10/23
8.488
7.458
1013
150
1152
919
0
1.684
10/26/25
3/5/25
9.238
7.W
965
190
1146
911
0
1.352
12/1/27
4/14/27
9.072
7.183
951
210
1145
914
0
1/3/30
1.068 15/19/29
9.220
7.168
965
220
1148
9 19
0
0.999
6.386
7.242
957
200
1137
92 1
1 1 1
1 1 1
1 1 1
1 1 1
1
1
Abort
Earth
Return
Vinf
1/25/32
6/22/31
Table 2
EARTH-MARS TRAJECTORY OPTIONS
500-DAY CLASS
Launch
Date
Venus
Swingby
5/23/15 (0) 10/20/1:
11/28/15 (I) 3/14/17
Venus
Swingb
Delta '\
Delta V
TMI
kmlsec
--
Arrival
Date
Mars
Arriva
Vinf
-
Outbound
Mars
Flight
Stay
Time, days Time, day
Departure
Date
Delta V
TEI
km/sec
6.967
334
30
5/21/16
2.723
7/30/16
5.125
245
30
8/29/16
3.383
0.0
3.889
4/21/16
0.048
4.348
3/23/17
(0) 9/8/17
0.0
4.027
2/9/18
8.095
322
30
311 1/18
0.815
11/7/17
(1) 2/11/90
0.0
5.850
7/11/18
5.910
246
30
8/10/18
4.620
4/15/19
(0) 8/24/19
4.137
7.129
2/29/20
9.921
320
30
3/30/20
1.735
7/29/20
(1) 8/4/21
0.0
4.354
11/18/20
7.133
112
30
12/18/20
2.717
11/2/21
(0) 1/5/22
0.0
5.155
6/29/22
8.163
239
30
7/29/22
6/14/22
(I) 8/15/23
0.0
7.183
11/26/22
8.568
10/1/23 (0) 3/12/24
0.0
4.814
10/23/24
8.409
0.405
6.162
2/15/25
1/15/26 (0) 6/26/26
2.223
14.306
11/19/26
11/17/26 (I) 12/6/27
0.0
4.049
5/9/27
(0) 8/28/28
0.575
5.228
1/6/29
10/22/28 (I) 12/3/29
1.796
8/28/24
1/3/28
(0 9/4/25
4/15/29
6.508
-
(0) Swingby on Outbound leg to Mars
(I) Swingby on Inbound leg back to Earth
Return
Date
Mission
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OUTBOUND TRANSIT
MARS STAY TIME
Figure 7. Mars Outpost
Flight 1
Piloted
5/15
Flight 2
Cargo
3/17
Flight 3
Piloted
5/18
--- Human Exploration
Flight 4
Piloted
712 0
Timeline
Flight 5
Cargo
9/22
Figure 8. Mars Outpost Mass Requirements
Flight 6
Piloted
10124
Flight 7
Piloted
11/26
expeditionary missions, and long stay-times for the
evolutionary missions.
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- These missions are characterized by
es at Mars, and relatively short roundtrip missions. The mission characteristics of the
00-day class mission is appropriate for the first
several missions to the martian surface. The crew's
surface time and total mission duration are minimized
consistent with a conservative strategy for the first
piloted mission to another planet. Surface tasks
conducted by the crew include reconnoitering the
landing region for final site selection of the surface
outpost infrastructure.
Evolution - The evolutionary strategy employed
during the FY 1989 studies assumed that once the
outpost site has been selected, the surface
infrastructure h k been delivered and deployed, and
human long duration habitability issues have been
resolved at the lunar outpost, a Mars crew will be
committed to a long duration stay at the Mars
outpost. Long-duration stays on the surface,
characteristic of the 1000-day class missions are a
more efficient strategy for the human resource given
the capital investment in the initial mass in low
Earth orbit (IMLEO) for a piloted Mars mission.
(Expedition missions require 800-1000 t IMLEO vs.
600-750 t for long duration stay missions.)
An option currently under development at the Lunar
and Mars Exploration Program Office at JSC is to
conduct several "expedition missions" to the surface
during one Mars stopover of a 1000-day mission.
During the 500-600 days that the crew and transfer
vehicle spend in the Mars vicinity, two or three
separate manned landings, of 30-60 day surface
duration, could be conducted. The use of human
expeditions in concert with robotic explorers
teleoperated from Mars orbit provide a framework in
which an entire "expedition phase" could be
completed in just three years.
Given mission requiremen
timelines, expeditio
can be combined to
The "discovery" of the 1000-day class missions, with
their very quick one-way transit times, has important
implications on future piloted
planning. If crew physiologic
to be dependent solely upon the amount of time spent
in zero-g, then two important re
First, the need for an artificial-g
Vehicle may be obviated. (Crew psychological
conditioning may require artificial-g for adequate
quality of life during interplanetary transit. This
subject is beyond the scope of th
the need for advances in propuisi
beyond Chemical (Isp = 480 sec
may not be necessary. Nuclear thermal rockets
(NTR) will not provide an
one-way trip times. How
theoretically provide
as little as 100-200 days w
a variety of reasons not related to crew health.
1. Wilson, S.W. and Lee, V.A., "A Survey of
Ballistic Mars-Mission Profiles,
,Volume 4, Numb
pp. 129-142.
2. Office of Exploration, "Exploration Studies
Technical Report, FY1988 Status, Volume 2: Study
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