USA 193 Post-Shootdown Analysis

Coverage started 2008 February 27

Updated 2009 May 26

On 2008 February 21, the US Department of Defense reported the successful intercept of USA 193 by an SM-3 missile launched from the USS Lake Erie, positioned northwest of Hawaii. The missle was launched at on 2008 February 20 at approximately 22:26:47.36 EST (2008 February 21 at 03:26:47.36 UTC).

The following NOTAM (NOtice To AirMen) was released on the Defense Internet NOTAM Service prior to the event restricting the area to be used for launch:

02/062 (A0038/08) - AIRSPACE CARF NR. 90 ON EVELYN STATIONARY RESERVATION WITHIN AN AREA BNDD BY 3145N 17012W 2824N 16642W 2352N 16317W 1909N 16129W 1241N 16129W 1239N 16532W 1842N 17057W 2031N 17230W 2703N 17206W SFC-UNL. 21 FEB 02:30 2008 UNTIL 21 FEB 05:00 2008. CREATED: 18 FEB 12:51 2008

The restricted area and time agreed well with orbital data released on the SeeSat list just prior to the intercept. I am providing an STK Viewer file (see bottom of this page for more information on STK Viewer) which shows the area restricted by the NOTAM and the SeeSat orbit of USA 193 during the NOTAM period to illustrate the agreement.

The Viewer file shows the NOTAM area to an altitude of 300 km and the green dashed line is the ground track of USA 193. The position of USA 193 is also shown. Based on the video of the intercept from the Satellite Shootdown Briefing [no longer available] given by Gen Cartwright on Feb 21, the position of the observing plane and its heading is shown at the time of launch.

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Screen shot from STK Viewer file of Observing Aircraft and USS Lake Erie

Note that the observing aircraft is flying along the boundary of the NOTAM area, just outside the restricted area and looking at the USS Lake Erie just inside the restricted area. Using the pointing angles of the video sensor, seen at the bottom of the video, the position of the USS Lake Erie is determined to be 23.48137 N, 163.28272 W, about 23 km from the aircraft.

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Screen shot from STK Viewer file of Video View of USS Lake Erie

From the video, it appears that the SM-3 launch occurred at 03:26:47.36 UTC, 38.5 seconds after USA 193 rose above the horizon as seen from the USS Lake Erie.

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Screen shot from STK Viewer file of Engagement Geometry at Time of SM-3 Launch

Download USA 193 Intercept Scenario

On 2008 February 27, Air Force Space Command began releasing orbital data labeled as "USA 193 DEB" via the Space Track web site (which requires a user account to access). As of this update, orbital data (TLEs) has been released for 173 pieces of debris (they still have not released any TLEs for the original satellite, however, which is still shown to be in orbit). An initial analysis of this debris is unable to determine an intercept time, due to the poor quality of the data. However, according to a story in the Omaha World-Herald, the intercept occurred approximately 170 seconds after launch (roughly 03:29:35 UTC).

A check of the Gabbard plot for this event shows debris ranging from 147 km altitude at perigee all the way up to 2,689 km at apogee. Of particular concern, however, is that the relatively small number of conjunctions (close approaches within 5 km of a satellite on orbit) reported for this debris so far has included satellites such as LANDSAT 5 and 7, SPOT 5, SAR-LUPE 3, QUICKBIRD 2, OFEQ 7, METOP-A, TIMED, WORLDVIEW-1, TERRA, GRACE-1 and -2, ENVISAT, IKONOS 2, several Iridium and Orbcomm satellites, and even the International Space Station and ATV-1 (Jules Verne). For the latest conjunction report, please check SOCRATES.

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Screen shot from STK Viewer file of Debris Orbits at Time of SM-3 Launch

Analysis of the orbital lifetime of this debris is particularly difficult, too. According to open sources, the original USA 193 spacecraft was approximately 4.6 m long and 2.4 m wide. Assuming a cylindrical shape, that would give it a volume of 21.4 cubic meters. Those same sources reported a mass (presumably including the hydrazine fuel) of 5,000 lbs or 2,300 kg. Subtracting out the fuel, reported by the US DOD as 1,000 lbs, would yield a dry mass of about 1,800 kg. That would yield an average density of 85 kg/m3.

Reports by the US DOD cite "no parts larger than a football survived the strike." A regulation NFL football is 11 inches long and 21 inches in circumference, so the diameter of a sphere with the same volume works out to about 20 cm. Since the US Space Surveillance Network typically cannot track objects smaller than 10 cm, these USA 193 debris pieces should range from 10–20 cm in diameter. Assuming these are spheres, the total mass of the pieces cataloged so far (using the average density of the original spacecraft) would be between 7.7 kg and 61.9 kg—or only 0.4 to 3.4 percent of the original dry mass.

Assuming this information is correct and using the same approach as applied to the analysis of the orbital debris of from the Chinese ASAT test, we obtain the following chart. It shows the percent of the 174 objects which decay over time (at least 152 of which are reported to have already decayed), based on our analysis. The black line represents 10-cm objects and the blue line represents 20-cm objects. In the 10-cm case, the last object decays 81 days after the intercept; in the 20-cm case, the last object decays 99 days after the intercept (these estimates do not include the original piece for which we have no TLE data). If any of the pieces are larger than reported, they will take progressively longer to decay. (Note: the 'glitch' above 85 percent is the result of debris pieces still being shown as in orbit, according to the NORAD catalog, but which our calculations show should already have decayed. The data below 85 percent is based on reported decay dates and suggests that our calculations might be optimistic or the pieces might be larger than reported.)

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Plot of Orbital Decay Rate of USA 193 Debris
(black = 10 cm diameter, blue = 20 cm diameter)

For comparison, we provide our original analysis, based on the first data available for each debris object, in the figure below. The current data shows the decay to be taking somewhat longer than originally estimated but far closer than the 40-day estimate initially provided by the US Department of Defense.

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Plot of Orbital Decay Rate of USA 193 Debris (based on original data)
(black = 10 cm diameter, blue = 20 cm diameter)

This analysis will be updated as additional information becomes available.

Note: Larger versions of all the images provided on this page are available by clicking the images. The interactive STK Viewer files of these scenes are also provided to give you a far better sense of the overall environment by allowing you to zoom in and out and move around the Earth while watching all the satellites moving in their orbits.

Note: STK Viewer is a free product which allows anyone with a Windows computer to view an STK (System Tool Kit) scenario. With it, you can animate a scenario forward or backward, pause the animation, and zoom or pan the view for a more complete understanding of the event. Just like with Adobe Acrobat, where the authoring software requires a license but the Adobe Reader is free, STK can produce STK Viewer files—also known as VDFs—which can then be viewed by anyone with the STK Viewer software. You can find the free STK Viewer on CelesTrak here. - TS

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