Slide1 : Earth Moon Libration Point (L1) Gateway Station –
Libration Point Transfer Vehicle Kickstage Disposal Options Presented to the International Conference On Libration Point Orbits and Applications
June 10-14, 2002, Parador d’Aiguablava, Girona, Spain G. L. Condon, NASA – Johnson Space Center / EG5, 281-483-8173, gerald.l.condon1@jsc.nasa.gov
C. L. Ranieri, NASA – Johnson Space Center
S. Wilson, Elgin Software, Inc.
Acknowledgements : Acknowledgements Chris Ranieri* – orbit lifetime analysis
Joey Broome# – STK/Astrogator validation/movie
Sam Wilson+ – software development / analysis
Daniel M. Delwood + – analysis * JSC Co-op # JSC Engineer + Elgin Software, Inc.
Outline : Outline Introduction
Expeditionary vs. Evolutionary Missions
Libration Point Transfer Vehicle (LTV) Kickstage Disposal Options
Geocentric Orbit Lifetime
Conclusion
Introduction : Introduction The notion of human missions to libration points has been proposed for more than a generation
The Gateway concept supports an Evolutionary vs. Expeditionary approach to exploration … A human-tended Earth-Moon (EM) libration point (L1) Gateway Station could support an infrastructure expanding human presence beyond low Earth orbit and serve as a staging location for human missions to:
The lunar surface
Mars
Asteroids, comets
Other libration point locations (NGST, TPF)
…
Expeditionary vs. Evolutionary : Expeditionary vs. Evolutionary Single mission or mission set
Completed mission satisfies mission objectives
Closed-end missions Examples
Expeditionary vs. Evolutionary : Expeditionary vs. Evolutionary Ongoing missions
Open-end missions on which other missions can build
Greater initial capital investment Examples
Earth-Moon L1 – Gateway for Lunar Surface Operations : Earth-Moon L1 – Gateway for Lunar Surface Operations Celestial park-n-ride
Close to home (3-4 days)
Staging to:
Moon
Sun-Earth L2
Mars
Asteroids
…
Sun-Earth L2 NGST
TPF Near Earth
Asteroids Mars
Gateway Operations – LTV Kickstage Disposal : Gateway Operations – LTV Kickstage Disposal Ongoing Gateway operations require robust capability for delivery & retrieval of a crew
Human occupation of the Gateway Station requires a human transfer system in the form of a Libration Point Transfer Vehicle (LTV) designed to ferry the crew between low Earth orbit and the Gateway Station. A key element of such a system is the proper and safe disposal of the LTV kickstage
Purpose : Purpose Identify concepts concerning the role of humans in libration point space missions
Examine mission design considerations for an Earth-Moon libration point (L1) gateway station
Assess delta-V (DV) cost to retarget Earth-Moon L1 Gateway-bound LTV spacecraft kickstage to a selected disposal destination
LTV Kickstage Disposal Options : LTV Kickstage
Diverted to Disposal Destination LTV Kickstage Disposal Options Options considered for LTV kickstage disposal:
Lunar Swingby to Heliocentric Orbit (HO)
Lunar Vertical Impact (LVI), typifies any lunar impact
Direct Return to Remote Ocean Area (DROA)
Lunar Swingby to Remote Ocean Area (SROA)
Transfer to Long Lifetime Geocentric Orbit (GO) LTV/Kickstage
Injection Toward L1 LTV Crew Cab
Continues to L1 LTV / Kickstage
Separation
Methodology : Methodology Evaluation Timeframe - 2006 Mission Year Chosen
Survey two week period of L1 arrivals yielding max (80.2o) and min (23.0o) plane changes ever possible at L1 for crewed spacecraft
28.6o lunar orbit inclination; coplanar departure from 51.6o ISS orbit
Moon goes from perigee to apogee during the chosen 2-week period; begins and ends on the equator
Combine max and min plane changes with arrivals at L1 perigee and apogee by looking at both choices of arrival velocity azimuth (northerly and southerly) for every arrival date (requires arbitrary ISS orbit nodes)
Methodology (continued) : Methodology (continued) HO, LVI, DROA, SROA, and GO maneuver times designed to minimize DV for stage disposal subject to imposed constraints
Solutions considered to be a practical attempt to minimize these maneuver DVs (e.g.: coplanar kickstage deflection maneuver assumed optimal for some disposal options) and not rigorous global optimizations Analysis
Analysis Tools
Earth Orbit to Lunar Libration (EOLL) scanner*
Four-body model
Earth, moon, sun, spacecraft
Jean Meeus's analytic lunar and solar ephemerides
Overlapped conic split boundary value solutions individually calibrated to multiconic accuracy
Validation with STK/Astrogator
* Developed and updated by Sam Wilson
Option 1. Lunar Swing-By to Heliocentric Orbit (HO) : Option 1. Lunar Swing-By to Heliocentric Orbit (HO) 1. Libration Point Transfer Vehicle (LTV)
spacecraft with Kickstage in
initial 407 x 407 km parking orbit L1 2. . Kickstage injects spacecraft
& kickstage onto transfer
trajectory toward L1 4. Jettisoned kickstage performs
maneuver to achieve close
encounter with moon 6. Kickstage flies behind trailing limb of Moon to achieve geocentric C3>0 (hence departure from Earth-Moon system)
Moon 3. Coast phase;
Kickstage jettison Earth 5. Spacecraft arrives
at L1 Nominal crew vehicle trajectory to Earth-Moon L1
Trip time = 3.5 days (84 hours)
Braking maneuver at L1 84 3.5 day transfer
Option 1. Lunar Swing-By to Heliocentric Orbit (HO) Video : Option 1. Lunar Swing-By to Heliocentric Orbit (HO) Video
Option 1. Lunar Swing-By to Heliocentric Orbit (HO) : Option 1. Lunar Swing-By to Heliocentric Orbit (HO)
Option 1. Lunar Swing-By to Heliocentric Orbit (HO) : Option 1. Lunar Swing-By to Heliocentric Orbit (HO) Advantages
No Earth or Lunar disposal issues (e.g., impact location, debris footprint, litter)
Relatively low disposal DV cost
Disadvantages
Heliocentric space litter (kickstage heliocentric orbit near that of the earth)
Periodic possibility of re-contact with Earth
Option 2. Lunar Vertical Impact (LVI) : Option 2. Lunar Vertical Impact (LVI) 1. Lunar Transfer Vehicle (LTV)
spacecraft with Kickstage in
initial 407 x 407 km parking orbit L1 2. Kickstage injects spacecraft
& kickstage onto transfer
trajectory toward L1 4. Jettisoned kickstage performs
maneuver to achieve
lunar impact 6. Kickstage impacts
Lunar surface Moon 3. Coast phase
Kickstage jettison Earth 5. Spacecraft arrives
at L1
Option 2. Lunar Vertical Impact (LVI) Video : Option 2. Lunar Vertical Impact (LVI) Video
Option 2. Lunar Vertical Impact (LVI) : Option 2. Lunar Vertical Impact (LVI)
Option 2. Lunar Vertical Impact (LVI) : Option 2. Lunar Vertical Impact (LVI) Advantages
No Earth disposal issues (e.g., impact location, debris footprint, litter, possible recontact)
Disadvantage
Lunar litter
Relatively high disposal DV cost
Option 3. Direct Return to Remote Ocean Area (DROA) : Option 3. Direct Return to Remote Ocean Area (DROA) 1. Lunar Transfer Vehicle (LTV)
spacecraft with Kickstage in
initial 407 x 407 km parking orbit L1 2. Kickstage injects spacecraft
& kickstage onto transfer
trajectory toward L1 4. Jettisoned kickstage performs
maneuver to achieve 20° atmospheric
entry angle and mid-ocean impact 5. Spacecraft arrives
at L1 Kickstage returns to Earth for ocean impact Moon 3. Coast phase;
Kickstage jettison Earth
Option 3. Direct Return to Remote Ocean Area (DROA) DV Budget Gives 240o Longitude Control : Option 3. Direct Return to Remote Ocean Area (DROA) DV Budget Gives 240o Longitude Control Entry flight path angle = -20o selected
Confines surface debris footprint
Impact latitude is determined by:
Spacecraft date of arrival at L1 and
Choice of northerly or southerly velocity azimuth at L1 arrival
From an established (e.g., ISS) earth orbit, these two degrees of freedom typically yield two or three transfer opportunities to L1 every month.
Impact longitude depends on (1.) and (2.) above, plus
3. Atmospheric entry time chosen for the kickstage
Minimizing the kickstage deflection DV determines an unique (and essentially random) impact longitude for an arbitrary transfer opportunity.
Kickstage budget gives 240 degrees of longitude control
If kickstage disposal is not to constrain the primary mission, the kickstage DV budget must be sufficient to allow the impact point to be moved from its minimum-DV location to an Atlantic or a Pacific mid-ocean line.
At any latitude, the maximum longitude difference between the chosen mid-ocean lines is 240 degrees (see next chart).
Option 3. Direct Return to Remote Ocean Area (DROA) Shaded Region Contains Max Longitude Difference (240o) Between Mid-Atlantic and Mid-Pacific Target Lines : Option 3. Direct Return to Remote Ocean Area (DROA) Shaded Region Contains Max Longitude Difference (240o) Between Mid-Atlantic and Mid-Pacific Target Lines x x x x x x x x x x x x x x x x x x x x Ocean Impact
demo location
Option 3. Direct Return to Remote Ocean Area (DROA) Video : Option 3. Direct Return to Remote Ocean Area (DROA) Video
Option 3. Direct Return to Remote Ocean Area (DROA) : Option 3. Direct Return to Remote Ocean Area (DROA)
Option 3. Direct Return to Remote Ocean Area (DROA) : Option 3. Direct Return to Remote Ocean Area (DROA) Data shown represent best of two solution subtypes
Generally there are two local optima for the location of the kickstage maneuver point in the earth-to-L1 transfer trajectory, of which the better one was always chosen
Advantages
Assuming kickstage disposal is not allowed to constrain the primary mission, this option is one of three (HO,DROA,GO) requiring the lowest DV budget that could be found (slightly more than 90 m/s in all three cases)
Avoidance of close lunar encounter, combined with steep entry over wide areas of empty ocean minimizes criticality of navigation and maneuver execution errors
Disadvantages
Not appropriate if kickstage contains radioactive or other hazardous material
Option 4. Lunar Swingby to Remote Ocean Area (SROA) : Option 4. Lunar Swingby to Remote Ocean Area (SROA) 1. Lunar Transfer Vehicle (LTV)
spacecraft with Kickstage in
initial 407 x 407 km parking orbit L1 2. Kickstage injects spacecraft
& kickstage onto transfer
trajectory toward L1 4. Jettisoned kickstage performs
maneuver to achieve close
encounter with moon 5. Spacecraft arrives
at Earth-Moon L1 Kickstage passes in front of Moon’s leading limb and returns to Earth for ocean impact 3. Coast phase;
Kickstage jettison
Option 4. Lunar Swingby to Remote Ocean Area (SROA) : Option 4. Lunar Swingby to Remote Ocean Area (SROA)
Option 4. Lunar Swingby to Remote Ocean Area (SROA) : Option 4. Lunar Swingby to Remote Ocean Area (SROA)
Option 4. Lunar Swingby to Remote Ocean Area (SROA) : Option 4. Lunar Swingby to Remote Ocean Area (SROA) Advantages
None identified
Disadvantages
This option requires a greater DV budget than any other one examined.
The DV values shown are minimum values for impact at an essentially random location.
The DV required for longitude control will be even higher
Inherent sensitivity of this kind of trajectory is almost certain to require extended lifetime of the control system to perform midcourse corrections before and after perisel passage
Option 5. Transfer to Long Lifetime Geocentric Orbit (GO) : Option 5. Transfer to Long Lifetime Geocentric Orbit (GO) 1. Lunar Transfer Vehicle (LTV)
crew module with Kickstage in
initial 407 x 407 km parking orbit 2. Kickstage injects crew module
& kickstage onto transfer trajectory toward L1 4a. Jettisoned kickstage performs
retargeted Earth parking orbit maneuver Kickstage continues on parking orbit Moon 3. Coast phase
Kickstage jettison Earth 5. Crew module arrives
at L1 L1 4b. Alternatively, kickstage may raise perigee with maneuver at/near apogee of Earth-L1 transfer orbit
Option 5. Transfer to Long Lifetime Geocentric Orbit (GO) Video : Option 5. Transfer to Long Lifetime Geocentric Orbit (GO) Video
Option 5. Transfer to Long Lifetime Geocentric Orbit (GO) : Option 5. Transfer to Long Lifetime Geocentric Orbit (GO)
Option 5. Transfer to Long Lifetime Geocentric Orbit (GO) : Option 5. Transfer to Long Lifetime Geocentric Orbit (GO) Advantages
Preferable to deliberate ocean impact if kickstage carries hazardous material
In 4 of the 22 cases studied, the DV requirement for GO disposal (into an orbit having a perigee altitude of 6600 km and an apogee altitude in the range of 300000 – 370000 km) was less than 12 m/s, which is much lower than that found for any other option considered.
Assuming the 22 cases represent an unbiased sample of all possible transfers between earth orbit and L1, this implies that a 12 m/s budget would suffice if it were permissable to forgo all but about 20% of the otherwise-available transfer opportunities.
Disadvantages
More orbital debris in the earth-moon system
The 12 m/s budget described above would increase the average interval between usable transfers to something like 50 days, as opposed to 10 days if transfer utilization were not allowed to be constrained by the disposal DV budget (which would then have to be more than 90 m/s).
To achieve acceptable orbit lifetime, lunar and solar perturbations may necessitate a higher perigee and/or lower apogees, either of which will increase the required DV.
Summary Results : HO, LVI, DROA, SROA, GO Transfer Delta-V vs. Libration Point Arrival Time D V Cost to Deflect LTV Kickstage from L1 Target to Disposal Destination 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 10/6/06 0:00 10/8/06 0:00 10/10/06 0:00 10/12/06 0:00 10/14/06 0:00 10/16/06 0:00 10/18/06 0:00 10/20/06 0:00 Libration Point Arrival Time (mm/dd/yy hh:mm) Deflection D V (m/s) Key: N=North L1 Arrival Azimuth S=South L1 Arrival Azimuth HO = Heliocentric Orbit LVI = Lunar Vertical Impact DROA = Direct Remote Ocean Area SROA = (Lunar) Swingby Remote Ocean Area GO = Geocentric (Parking) Orbit HO N GO N DROA N LVI N SROA N HO S GO S DROA S LVI S SROA S Moon at Perigee Moon at Apogee Summary Results
Geocentric Orbit Lifetime Study : Geocentric Orbit Lifetime Study
Slide37 : Spacecraft (kickstage) initial condition – Apogee of LEO to EM L1 transfer orbit
Apogee range: 300,000 km – 371,000 km
Perigee range: 6600 km – 20,000 km
45 test case runs
Results
56% of the test cases impacted the Earth within 10 years
Spacecraft cannot be left on transfer orbit
Further study to determine safe Apogee and Perigee Ranges
Geocentric Orbit Lifetime
LTV Orbit Lifetime : LTV Orbit Lifetime Note: A negative lifetime indicates LTV kickstage experienced either heliocentric departure from the Earth-Moon system or Lunar impact 45 transfer orbits in sample space
Summary : Summary Recommend Direct Remote Ocean Area impact disposal for cases without hazardous (e.g., radioactive) material on LTV kickstage
Controlled Earth contact
Relatively small disposal DV
Avoids close encounter with Moon
Trajectories can be very sensitive to initial conditions (at disposal maneuver)
DV to correct for errors is small
Recommend Heliocentric Orbit disposal for cases with hazardous material on LTV kickstage
No Earth or Lunar disposal issues (e.g., impact location, debris footprint, litter)
Relatively low disposal DV cost
Further study required to determine possibility of re-contact with Earth
Additional Slides : Additional Slides
Summary Results : Summary Results
Slide42 : Possible future missions to Earth-Moon (EM) L1 Libration Point – Gateway Station
Need to develop safe disposal guidelines for such a mission
Do not want nuclear payloads crashing into Earth Earth Moon L1 - Orbit Lifetime Study
Slide43 : Three orbit lifetime studies using STK/Astrogator:
S/c left on transfer orbit to EM L1 with low perigee and an apogee near EM L1 (343,000 km)
S/c left at EM L1 with no relative velocity to EM L1 and no station keeping
S/c left at EM L1 with a parametric scan of impulsive delta-Vs of varying magnitudes and directions (0 - 360 degrees; 0 - 500 m/s)
Propagation utilizes multiple gravitation sources
Earth (central), Sun, Moon, Mars, and Jupiter
Coordinate System defined with origin at EM L1
Earth Moon L1 Study
Slide44 : The spacecraft possesses zero initial position and velocity relative to Earth-Moon L1
With no station-keeping maneuvers, spacecraft drifts from L1 position
EM L1 location shifts as the Earth and Moon positions change
EM L1 Earth distance: 302830 km – 345298 km
No Earth Impacts found – Either lunar impacts or the s/c uses the lunar gravity to go heliocentric
Un-discernable pattern (given data sample space) Earth-Moon L1 - Orbit Lifetime
Spacecraft Initially at L1
L1 Orbit Lifetime vs. EM L1 Position in Lunar Cycle : L1 Orbit Lifetime vs. EM L1 Position in Lunar Cycle Orbit lifetimes <100 years result in either lunar impact or heliocentric trajectory (via lunar fly-by)
No Earth impacts occurred (for these 18 sample propagations)
Slide46 : Seven Total Earth Impacts
Earth Impact for a case with a Δv as small as 10 m/s
No discernible pattern to results by either magnitude, direction, or epoch for maneuver EM L1 Orbit Lifetime w/ Delta-Vs
Orbit Lifetime for Spacecraft at L1 Initial DV of 10-500 m/s; 360o Range Relative to Initial Velocity : Orbit Lifetime for Spacecraft at L1 Initial DV of 10-500 m/s; 360o Range Relative to Initial Velocity
Maneuver at Earth-Moon L1 (345,187 km apogee) DV = 100 m/s Over 360o Range of Direction : Maneuver at Earth-Moon L1 (345,187 km apogee) DV = 100 m/s Over 360o Range of Direction L1 Velocity Direction 100 Years In Earth Orbit
Slide49 : Further studies to better define safe disposal guidelines for s/c launched to EM L1
Further examine lifetimes for s/c at or near EM L1 position and velocity
Examine transfers to other disposal orbits, possibly b/w GEO and EM L1 that are less affected by lunar perturbations
Write for paper to be possibly presented in Spain on this work
EM L1 Orbit Lifetime – Future Work
Human Presence in Space : Human Presence in Space Demonstrated benefit to human presence
Hubble Space Telescope deploy and repair
Retrieval of Long Duration Exposure Facility
Retrieval of Westar and Palapa satellites
Libration Point Missions : Libration Point Missions Earth-Moon L1
Gateway station
Sorties to the Moon
Satellite deploy, servicing
Next Generation Space Telescope
Terrestrial Planet Finder
Staging area for interplanetary and asteroid missions
Earth-Moon L2
Robotic relay satellites for backside operations
Bent pipe communications
Navigation aid
Sun-Earth L2
Human missions to extend human presence in space
Lunar Mission: Libration Point vs. LOR : Earth-Moon L1
No lunar departure injection window
Reusability
Protection from failed station-keeping
Specialized vehicle design
Lunar Mission: Libration Point vs. LOR Lunar Orbit Rendezvous (LOR)
Shorter mission duration
Lower overall DV cost
Fewer critical maneuvers required Mission Scenario Advantages
Considerations for Human Lunar L1 Missions : Considerations for Human Lunar L1 Missions 18 year lunar inclination cycle
Eccentricity of lunar orbit
Performance cost versus time
Frequency of outbound & inbound opportunities
18 Year Lunar Inclination Cycle : 18 Year Lunar Inclination Cycle
18 Year Lunar Inclination Cycle : 18 Year Lunar Inclination Cycle
Eccentricity of Lunar Orbit : Eccentricity of Lunar Orbit
Performance Cost vs. Time : Performance Cost vs. Time
Frequency of Outbound and Inbound Opportunities : Frequency of Outbound and Inbound Opportunities
Frequency of Outbound and Inbound Opportunities : Frequency of Outbound and Inbound Opportunities
Total Transfer DV vs LPA Time : Total Transfer DV vs LPA Time
Transfer DV vs LPA Time : Transfer DV vs LPA Time