USA-193 decay predictions with public domain trajectory data
and assessment of the post-intercept orbital debris cloud

• The USA-193 satellite
• Observations of USA-193
• Reentry predictions
• Mass estimation
• Reentry risk assessment
• The destruction of USA-193
• The debris cloud

• Launch date - 14 December 2006
• Launch site - Vandenberg (California)
• Launcher - Delta II 7290
• Catalog number - 29651 (2006-057A)

• were determined from visual observations and freely distributed through the Visual Satellite Observers’s and the Heavens-Above web sites
• were mainly determined and issued in the TLE format by Ted Molczan, based in Toronto, Canada

• allowed the initial orbit determination: the dead satellite had been placed into a 351 x 367 km orbit, with inclination of 58.5°
• suggested a tumbling attitude, and telescopic CCD images showed an approximately 3 x 3 x 4 m box without solar panels (the premature satellite failure would have in fact prevented the solar arrays and main antenna deployment)
• confirmed, during the following months, that the orbit was not controlled, but decaying due to the effect of atmospheric drag

• The orbits used were those freely distributed through the Visual Satellite Observer’s and Heaven-Above web sites
• At the beginning of our analysis, on 22 January 2008, USA-193 had decayed to 275 x 280 km
• From 22 January to 21 February 2008, 20 TLE based on visual observations were issued (with observation gaps of 2-5 days), acquired and processed
• Also 11 “historical” TLE – from 15 December 2006 to 4 April 2007 – were found. They were used to model the satellite long-term decay and to characterize its aerodynamic properties
• Reentry predictions were obtained using a numerical special perturbations propagator, SATRAP, with a 16 x 16 gravity field, luni-solar attraction, direct solar radiation pressure with eclipses and atmospheric drag
• The Jacchia-Roberts 1971 thermospheric density model was selected for this specific event. In one case MSISE-90 was used as well for comparison
• The ballistic parameter B = C_DA/M was estimated by fitting, in a least squares sense, the semimajor axis decay described by a set of TLE (typically between 10 and 20), preceding the reentry prediction epoch

• The mean value obtained with JR-71 was
   
  B = C_D A / M = 0.012112 ± 0.000327 m²/kg

• The single value obtained with MSISE-90, on 17 February 2008, was
   
  B = C_D A / M = 0.011440 m²/kg

• The USA-193 estimated casualty area was ~ 60 m²
• The debris footprint was ~ 50 km wide and ~ 500 km long, in the direction of the sub-satellite ground track
• The macroscopic fragments able to survive the conditions encountered during the reentry would have hit the ground along the local vertical, neglecting the winds, with impact speeds in between 50 and 500 km/h
• Assuming an average population density of 15.34 inhabitants per km² in the applicable latitude band (± 58.6°), the estimated casualty area translated into a casualty expectancy of ~ 10^-3 (one order of magnitude more than the “alert threshold” informally adopted at international level)
• The a priori probability of debris fall in Italy remained well below 1%

• More then 50% of the fragments were not orbital and reentered within 45 minutes of the event [Johnson N.L., 26th IADC Meeting, Moscow, April 2008]
• Many reentering debris trails were in effect witnessed in Canada around 03:43 UTC [Visual Satellite Observer’s Home Page, 2008]
• During the day following the breakup, the orbits of 360 debris larger than 5 cm were determined [Orbital Debris Quarterly News, Vol. 12, N. 2, 2008; Johnson N.L. 26th IADC], but many of them decayed too rapidly, leading to only 173 officially cataloged objects
• One fragment was hurled into an orbit with an apogee altitude of 3250 km
• Inclination changes up to 3.8° were observed, therefore velocity variations up to ~ 700 m/s were imparted to the debris

• The liftoff from the Vandenberg Air Force Base of a classified reconnaissance spacecraft (NROL-28) atop an Atlas V rocket, initially slated for 29 February 2008, was delayed for at least two weeks to avoid the orbiting remains of USA-193
• The impact risk for the ESA’s Jules Verne Automated Transfer Vehicle (ATV), launched towards the International Space Station from Kourou, French Guiana, on 9 March 2008, increased by a factor 2 at the beginning of the cruise phase, although the background debris flux was moderate and the risk level decreased quickly [Krag H., 26th IADC Meeting, Moscow, April 2008]
• Concerning the International Space Station (ISS), at a mean altitude of about 335 km, the cumulative risk due to the USA-193 cloud of fragments was equivalent, according to the NASA estimates, to approximately 2-3 days of exposure to the pre-event space debris environment [Johnson N.L., 26th IADC Meeting, Moscow, April 2008]

• The lack of critical information
• The often exaggerated misconceptions of the general public, fed by a too complacent media system
• Competing security and safety needs
• International regulations and space policy concerns
• The secrecy surrounding military programs
• The phantom of an arms race in space
• The risk of causing casualties on the ground
• The risk of damaging precious satellite assets in orbit