ASEN 5050 SPACEFLIGHT DYNAMICS Mission Orbits, Constellation Design

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ASEN 5050SPACEFLIGHT DYNAMICSMission Orbits,
Constellation Design

• Prof. Jeffrey S. Parker
• University of Colorado Boulder

2
Announcements

• STK Lab 3 due Friday 12/5
• STK Lab 4 due 12/12
• Planetary ephemerides should be changed to DE421
  instead of Default
• Final Exam on 12/12, due 12/18
• Take-home, open book open notes
• Final project and exam due 12/18

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Schedule from here out

• 12/3 Mission Orbits, Constellation Design
• 12/5 Spacecraft Navigation
• 12/8 Final Review, part 1
• 12/10 Final Review, part 2
• 12/12 Deep Impact

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Final Project

• Due 12/18. If you turn it in by 12/12, Ill
  forgive 5 pts of deductions.
• Worth 20 of your grade, equivalent to 6-7
  homework assignments.
• Final Exam is worth 25.
• Find an interesting problem and investigate it
  anything related to spaceflight mechanics (maybe
  even loosely, but check with me).
• Requirements Introduction, Background,
  Description of investigation, Methods, Results,
  Conclusions, References.
• You will be graded on quality of work, scope of
  the investigation, and quality of the
  presentation. The project will be built as a
  webpage, so take advantage of web design as much
  as you can and/or are interested and/or will help
  the presentation.

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Final Project

• Instructions for delivery of the final project
• Build your webpage with every required file
  inside of a directory.
• Name the directory LastName_FirstName i.e.,
  Parker_Jeff/
• there are a lot of duplicate last names in this
  class!
• You can link to external sites as needed.
• Name your main web page index.html
• i.e., the one that you want everyone to look at
  first
• Make every link in the website a relative link,
  relative to the directory structure within your
  named directory.
• We will move this directory around, and the links
  have to work!
• Test your webpage! Change the location of the
  page on your computer and make sure it still
  works!
• Zip everything up into a single file and upload
  that to the D2L dropbox.

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Space News

• Japans Hayabusa 2 launched last night!

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Space News

• Japans Hayabusa 2 launched last night!

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Space News

• Orions Exploration Flight Test 1 Thurs 12/4 at
  704 am Eastern Time (504 am Mountain!).
  Duration 4.5 hours.

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ASEN 5050SPACEFLIGHT DYNAMICSMission Orbits

• Prof. Jeffrey S. Parker
• University of Colorado Boulder

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Satellite Populations
Molniya
51.5
28.5
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Satellite Populations
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Satellite Populations
Molniya, GNSS
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Satellite Populations
Gabbard classes
GEO
GNSS
GTO
ISS
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Satellite Populations
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Frozen Orbits

• Molniya orbits are designed to have a critical
  inclination, such that the argument of perigee
  does not change over time.
• Example plots for NROSS frozen orbit
  characteristics

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Repeat Groundtracks

• Exact Repeat Groundtracks
• A satellites ground track returns to exactly the
  same latitude/longitude that it began.
• Should occur within 50 days for this
  classification
• The satellite never flies over much of the Earth.
• Near-exact Repeat Groundtracks
• A satellites ground track returns to a point
  very near its starting point.
• The drift provides a dense coverage of the Earth.

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Repeat Groundtracks

• Example exact repeat groundtracks

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Repeat Groundtracks
The nodal crossings occur in a pattern
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Some Period Definitions
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General Perturbation Techniques

• The secular change of the orbital elements due to
  J2 is given from the Lagrange Planetary Equations
  as

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Nodal Period
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Exact Repeat Constraint
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Altitude/Inclination vs NERP/K
NERP/K
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Groundtrack Drift
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TOPEX Crosstrack Drift
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Altimetry Missions

• Consider Topex/Poseidon, Jason, Jason-2, and the
  like.
• They perform remote sensing operations of the
  ocean surface, including measuring the sea
  surface height, sea surface smoothness,
  temperature, etc.
• Driving requirements
• The orbit must be very well known and well
  determined.
• A meter error in height may make the ocean height
  estimation off by a meter very significant!
• The orbit should pass over a large portion of the
  oceans surface.
• The orbit should pass over the same points within
  a reasonably short time period.
• The fly-over period should not alias any effects
  that significantly contribute to the motion of
  water in the ocean, such as tides.

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Altimetry Missions

• Parke et al. (1987) developed the following
  requirements for the orbit of Topex/Poseidon
• The satellites altitude must be known to within
  14 cm
• The orbit should be compatible with that sort of
  OD requirement. I.e., it would not work to orbit
  too close to the atmosphere or in an unstable
  resonance with the gravity field.
• Minimize the spatial and temporal aliases on
  surface geotrophic currents, geoid variations,
  etc.
• Subsatellite groundtrack should repeat within 1
  km.
• Tidal aliases will not be aliased into
  semiannual, annual, or zero frequencies or to
  frequencies close to these.
• The global grid of subsatellite points must
  extend as far south as the southern limit of the
  Drake Passage (62 deg S)
• The ascending and descending tracks must cross at
  sufficiently large angles to resolve the 2D
  geostrophic current.

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Altimetry Missions

• Station Keeping
• Atmospheric drag is one of the largest effects
  that drives the ground track away from its
  reference, and therefore must be compensated for
  using maneuvers.
• For a circular orbit and neglecting the Earths
  rotation
• The loss of energy over time due to drag

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Altimetry Missions

• The loss of energy over time due to drag

Varies with time
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Altimetry Missions

• The change in energy over time
• Integrate
• Integrate over one orbit period

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Altimetry Missions

• The change in energy over time
• Integrate
• If drag were estimated with 50 accuracy, then
  the orbit error for the satellite will be lt 1 cm
  for a satellite above 1100 km.
• Recommendation remain above 1100 km and
  preferably above 1300 km.

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Altimetry Missions

• Effects of Solar Radiation Pressure.
• Since solar panels are virtually always pointing
  toward the Sun, there is always a force acting on
  the satellite, and it changes the circular
  orbits semimajor axis

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Altimetry Missions

• Circular orbits

Minimum between 1200 1300 km
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Altimetry Missions

• Altitude
• Desirable to be as high as possible for OD
• Desirable to be 1200 1300 km for station
  keeping
• Good for link budgets too
• Desirable to be below 1500 km for radiation Van
  Allen Belts!

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Altimetry Missions

• Polar Crossing Angle psi

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Altimetry Missions
Desirable gt 40 deg
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Altimetry Missions
Less Desirable
Desirable gt 40 deg
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Altimetry Missions

• Orbit Period Considerations
• Tidal Aliasing
• Want to avoid this

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Altimetry Missions

• Tidal Aliasing, the frequencies, periods, and
  amplitudes of the most significant tidal
  constituents

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Primary Lunar Tide
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Vertical displacement

• If the Earths surface was in equilibrium with
  the potential from the moon, the vertical
  displacement of the surface would be in the shape
  of an ellipsoid elongated toward the moon.

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The Principal Tide M2

• The largest component of the tides is associated
  with the potential due to the moon and with the
  frequency of the motion of the Earth-moon system
  around its center of mass.
• The time from high moon to high moon1 lunar day
  (1 1 day/ 27.5 days) 24 hours 50.47 minutes
• High tide separation is half of this
• 12 hours 25 minutes
• However, this component, like all of the
  semi-diurnal (and diurnal) tides is not in
  equilibrium with the potential.
• A phase difference between high moon and high
  tide has been known for centuries. The high tide
  generally lags behind the high moon.

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Tidal friction

• If there were no dissipation in the Earth
  systems, tides would lie directly under MP
• However, friction creates a delay in the tidal
  response.
• The Earths surface reacts to the tidal potential
  due to MP with a lag. The tides peak 30 minutes
  later.

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Altimetry Missions

• Tidal Aliasing, the frequencies, periods, and
  amplitudes of the most significant tidal
  constituents

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Altimetry Missions

• Tidal Aliasing, the frequencies, periods, and
  amplitudes of the most significant tidal
  constituents

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Altimetry Missions

• In each cycle, the altimeter samples the phase of
  each tide.
• A sun-synchronous altimeter sampling the S2
  constituent would find a frozen tide with an
  infinite aliasing period.
• ERS-1, ERS-2, Envisat, and NPOESS all did this.
• Otherwise, the change in phase of the tide during
  one repeat period T is
• The primary alias period

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Altimetry Missions

• For Topex/Poseidons 9.916-day repeat period
  orbit, the primary alias periods are

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Altimetry Missions

• For Topex/Poseidons 9.916-day repeat period
  orbit, the primary alias periods are

Each of these is different by at least several
days
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Altimetry Missions

• If tidal aliasing does occur and/or the tidal
  frequencies or their aliasing frequencies
  overlap, there are ways to resolve the alias.
• Use along-track data
• Use cross-over points

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Altimetry Missions

• Spatial vs. Temporal Resolution

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Altimetry Missions

• Tide Gauges and Ground Track Placement

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Altimetry Missions
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Topex/Poseidons Options

• 1335 km, 64.80 deg inclination
• 1252 km, 62.01 deg inclination
• 1255 km, 65.84 deg inclination
• 1173 km, 62.69 deg
• Option 1 first choice, Option 3 as backup if a
  frozen orbit is desired.
• Topex/Poseidon was placed in an exact repeat
  groundtrack orbit with 127 revolutions per 10-day
  cycle.

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ASEN 5050SPACEFLIGHT DYNAMICSConstellation
Design

• Prof. Jeffrey S. Parker
• University of Colorado Boulder

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Constellation Designs

• GPS
• 6 circular orbits, 12-sidereal hour period, 55
  deg inclination
• 4 satellites per orbit, evenly spaced over 360
  deg
• Galileo, a Walker Delta 56 deg27/3/1
• 3 orbital planes, 56 deg inclination
• 9 satellites per orbit, evenly spaced over 360
  deg
• Iridium, a near-polar Walker Star
• 6 orbital planes, 86.4 deg inclination
• 11 satellites per orbit, evenly spaced over 180
  deg

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Constellation Designs

• A-train (Afternoon Sun-Synch, coordinated)
• BGAN
• Compass Navigation system
• Disaster Monitoring Constellation
• Globalstar
• GLONASS
• Orbcomm
• RapidEye
• Sirius Satellite Radio
• TDRSS
• XM Satellite Radio

And others!
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A-Train

• Coordinated constellation of French, American,
  Japanese, Canadian satellites
• Sun-Synch
• 98.14 deg inclination
• 130 pm solar time equatorial crossing
• GCOM-W1 (SHIZUKU), JAXA
• Aqua (4 min behind), USA
• CloudSat (2.5 min behind), USA and CSA
• CALIPSO (15 sec behind), CNES, USA
• Aura (15 min behind Aqua)
• PARASOL (now retired)
• OCO-2

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Compass / BeiDou-1

• Chinese navigation system
• Geostationary orbits
• The area that can be serviced is from longitude
  70E to 140E and from latitude 5N to 55N.

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BeiDou-2

• Chinese navigation system
• Supersedes BeiDou-1
• 35 satellites, completed by 2020
• 5 in geostationary orbit
• 27 in MEO
• 3 in inclined geosynch orbit
• Plans for up to 75 or more satellites, covering
  urban canyons

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GPS

• 6 circular orbits, 12-sidereal hour period, 55
  deg inclination
• 4 satellites per orbit, evenly spaced over 360
  deg

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Disaster Monitoring Constellation

• International, coordinated, Sun-Synch orbit
• 1015 am local time Northward equator crossing

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Globalstar

• LEO
• 50 satellites
• Inclination 52 deg
• 1400 km altitude
• Communication, short latency
• 5 ms 1-way light time.

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Iridium

• 66 active satellites
• LEO 781 km altitude, inclination 86.4 deg
• 11 satellites in each of 6 orbital planes
• Iridium NEXT 2nd generation communication system
• 66 more satellites, launched 10 at a time on
  Falcon 9 launches

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Orbcomm

• 29 satellites
• LEO 775 km altitude
• Telecommunication system

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RapidEye

• German geospatial information provider.
• 5 satellites in the same orbital plane.
• Altitude 630 km
• Sun-synchronous, 1100 am ascending time, 97.8
  deg inclination

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Sirius

• 3 satellites
• Highly elliptical, geosychronous orbits (Tundra
  orbits)
• Each satellite spends 16 hours over the
  continental US per orbit.
• XM Satellites 2 geostationary satellites.

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TDRSS

• Tracking and Data Relay Satellite System
• A dozen GEO satellites some equatorial and some
  just off of the equator.
• Navigation and communication, largely of NASAs
  assets.

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Announcements

• STK Lab 3 due Friday 12/5
• Any issues with v9 versus v10?
• STK Lab 4 due 12/12
• Any issues with v9 versus v10?
• Final Exam on 12/12, due 12/18
• Take-home, open book open notes
• Final project and exam due 12/18