Shuttle Return to Flight Launch Planning with STK

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Shuttle Return to Flight Launch Planning with STK

• Harold Robertson
• NASA Johnson Space Center, Houston, TX

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Shuttle Return to Flight Launch Planning with
STKBackground

• The loss of the Space Shuttle Columbia during
  entry on Feb. 1, 2003 was attributed to a breach
  of the wing leading edge RCC by debris impact
• The debris source was determined to be a piece
  insulating foam that came off the external tank
  (ET) during ascent
• The first two return to flight missions (STS-114
  and STS-121) were designated as test flights to
  evaluate the changes made to the Shuttle system
  since the Columbia accident
• Approximately 39 test objectives were identified
  for STS-114 (including evaluation of ET changes)
• Besides engineering analysis, ET assessment after
  ascent was important in establishing if any
  debris was liberated that threatened the Shuttle
  

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Shuttle Return to Flight Launch Planning with
STKBackground (Continued)

• Daylight launches were baselined for the test
  flights to maximize usable imagery from ground
  based assets during ascent
• Some of the best instrumentation for evaluating
  the ET is on the Shuttle itself.
• Shortly after separation, two 16mm movie cameras
  and a still camera image the tank as it falls
  away
• A few moments later the Shuttle performs a pitch
  up maneuver and the crew uses both a still camera
  and camcorder to image the tank
• Orbital daylight was required to again maximize
  the chances of getting acceptable imagery from
  these cameras
• The still cameras were upgraded from 35mm film to
  digital (Kodak DCS 760) to allow same day
  downlink of the images

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Shuttle Return to Flight Launch Planning with
STKLaunch Opportunity Planning Constraints

• STS-114 and 121 are both support missions for the
  International Space Station (ISS)
• This requires a launch into an inertial plane at
  51.6 deg inclination that allows rendezvous with
  the ISS
• The daily launch window to achieve the required
  rendezvous plane moves about 25 minutes earlier
  each day due to nodal regression
• Phase window considerations cause additional
  small time shifts
• On an annual basis, roughly 40 of the daily
  launch windows result in darkness for ascent
• The post ascent requirements for orbital daylight
  removes several more days
• Several times a year, high Beta (angle between
  the sun and the orbital plane) make Shuttle/ISS
  attached operations impractical due to thermal
  management problems and further restricts
  available launch days

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Shuttle Return to Flight Launch Planning with
STKLighting Assessment (Initial Approach)

• Legacy mission planning tools were easily able to
  determine
• Daily planar launch window and rendezvous phase
  window times
• Beta angle
• Ascent and post ascent lighting
• The toolset had no easy way to assess the
  acceptability of the post ascent lighting
• Other software could generate highly precise CAD
  views and exact lighting conditions, but required
  considerable data preprocessing and setup for
  each day analyzed
• STK proved to be a useful tool to assess the post
  ascent lighting and screen available launch days
• The initial setup was to import the trajectory
  and attitude files from a powered flight ascent
  simulation for a given launch date and time.
• The Shuttle and ET were each modeled as separate
  satellites
• STK sensor tools were used to create camera
  sensors that allowed modeling each cameras field
  of view
• This setup worked well, but required a unique
  scenario build and trajectory files for each
  launch date evaluated

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Shuttle Return to Flight Launch Planning with
STK Post Ascent Lighting Assessment (Refined
Approach)

• To avoid having to manually creating multiple
  scenarios, a few simplifications allowed rapid
  generation of lighting conditions for each
  theoretical launch day of the year.
• 1st simplification even though the Shuttle is
  flying to a unique inertial plane for a
  rendezvous mission to ISS, the groundtrack shift
  across the 5 to 10 minute launch window is small.
  Liftoff was assumed to be at the same point in
  the launch window (coplanar). This potentially
  introduced a small spatial error.
• 2nd simplification chose to ignore the phase
  window and set the time relative to the daily 25
  minute shift (earlier) of the planar window
  (introduces a small temporal error)
• These two simplifications allowed the Shuttle and
  ET to be modeled as facilities (static objects)
  fixed at the points along their trajectories
  where the photos would be taken. The small
  errors introduced by the assumptions were
  considered acceptable with regards to lighting
  evaluation.
• The only time dependent variable left in the
  problem was the sun position.
• A new scenario was constructed which modeled the
  Shuttle Orbiter and ET as STK facilities
• A representative trajectory (such January 1,
  2005) was used to establish the Shuttle and ET
  facility locations and attitudes just after
  separation when the umbilical camera photography
  starts
• This was repeated in a separate scenario that
  located the static positions of the Orbiter and
  ET at the start of crew photography

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Shuttle Return to Flight Launch Planning with
STK Sample Image Output

• The scenario timestep was set to 23 hours and 35
  minutes (causing each frame to be 25 minutes
  earlier than the previous day)
• The software VCR module was utilized to generate
  a series of bitmaps (one for each launch
  opportunity) for the entire year
• Each bitmap image (or movie frame) represented a
  sample photo associated with the daily rendezvous
  plane launch window
• The images were then analyzed by JSC photo
  interpreters to evaluate the lighting
• This involved assessing key areas of the tank to
  see if that area was lit or in shadow
• The samples were posted on in internal website
  that allowed mission planners to see for
  themselves which days had adequate lighting

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Shuttle Return to Flight Launch Planning with
STK Areas of Interest on the ET and Sample
Image Assessment
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Shuttle Return to Flight Launch Planning with
STK Analysis Umbilical Well and Crew Camera
Lighting

• Good lighting for ET umbilical well photography
  requires the sun overhead or in the west.
• Good lighting for crew handheld photography
  requires the sun overhead or in the east.
• Result Few dates provide good lighting for both
  umbilical and crew handheld photography. (STS-114
  had good lighting for both on Jul 26, 2005)

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Shuttle Return to Flight Launch Planning with
STKResulting Launch Opportunities for STS-114

• Umbilical camera photography was selected as
  prime in establishing the launch windows
• Launch periods for 2005 that met all constraints
• March 16 to April 1
• May 15 to June 3
• July 13 to August 1 (STS-114 launched on July 26)
• September 9 to September 25
• November 7 to November 10

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Shuttle Return to Flight Launch Planning with
STK Comparison with STS-114 Imagery

• For the umbilical camera photos
• Unmodeled yaw rate in the tank produced a slight
  offset
• For crew photography
• There is no accurate preflight prediction of the
  ET attitude
• Times are approximate, based on internal camera
  clock
• The STK camera sensor was set up to boresight the
  ET model, so there were no framing issues. The
  actual photographer had to manually acquire and
  frame the ET in the viewfinder

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Shuttle Return to Flight Launch Planning with
STKSupplemental Analysis Umbilical Camera

• A detailed study was later conducted to see the
  lighting trend for the entire year
• The timestep advance was set to one minute. The
  view was manually stepped forward/backward to
  establish acceptable lighting boundary times for
  a couple of days each month
• The actual launch window times were ignored in
  this analysis

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Shuttle Return to Flight Launch Planning with
STK Additional Support

• Once built, the STK setup was used to generate
  several illustrations and videos for management
  presentations, crew training and Public Affairs
  

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Shuttle Return to Flight Launch Planning with
STK Summary

• STK allowed rapid generation of sample imagery
  for lighting analysis. New sets could be
  produced quickly when mission inputs changed.
• Greatly reduced the number of higher fidelity
  image program assessments required
• The STK 3D views and video clips allowed
  development of easy to understand presentations
  on the ET lighting topic