Coverage started 2007 January 19
Updated 2012 June 22
Several sources have reported a Chinese ASAT test was carried out against the Chinese FENGYUN 1C polar-orbiting weather satellite on 2007 January 11. For details, see:
These reports were confirmed by the Chinese government on January 23:
In order to illustrate the circumstances of this attack, I have produced an STK Viewer file (see bottom of this page for more information on STK Viewer) which confirms the basic facts reported by AW&ST. It shows the period from 2007 January 11 at 22:26:10 UTC (which analysis shows as the most likely time of the event, slightly different than the time of 22:28 UTC reported by AW&ST) until January 12 at 0600 UTC. The orbit of FENGYUN 1C (pre-attack) is shown in red and the location of the Xichang Space Center is also shown. I am also providing a Google Earth location file for the Xichang Space Center, with recently released details of the launch complex and surrounding facilities.
FENGYUN 1C and the other pieces of debris now catalogued by NORAD are shown in green. From this animation, it is easy to see the spread of the resulting debris cloud for the first couple of orbits. It should be noted that the spread of debris at the time of the event is due to the error associated with propagating the TLEs back from the time they were released to the time of the event.
Screen shot from STK Viewer file of Chinese ASAT scenario (five minutes post-attack)
As of 2012 June 22 (another 10 TLEs were released on this date), 3,312 pieces of debris—including whatever's left of the original payload—have been catalogued by NORAD. Only 256 have decayed as of this date. That makes this event the largest debris-generating event on record—far surpassing the 713 pieces cataloged when the Pegasus rocket body that launched STEP 2 exploded on 1996 June 3. NASA's Orbital Debris Program Office now estimates more than 150,000 pieces of debris larger than 1 cm from this event:
Updating the initial analysis by CSSI just after this event was first reported shows pieces in the debris cloud ranging from below 200 km in altitude up to almost 4,000 km (see Gabbard plot), posing a threat to many operational satellites, due to the polar orbit of the debris cloud. Potential conjunctions with satellite payloads currently on orbit can be found by searching for "FENGYUN 1C" using SOCRATES or by generating an automatic search. Using the SOCRATES run from 2008 January 22 at 1300 UTC, there were 3,100 occasions predicted where a piece of FENGYUN 1C debris would come within 5 km of a satellite payload in low-Earth orbit over the next week—over 28 percent of all predicted conjunctions over that period. We are now routinely seeing about 3,000 conjunctions within 5 km over a seven-day period between the FENGYUN 1C debris and payloads in Earth orbit.
The figures below (from 2007 December 5) give a sense of the risk to other satellites in low-Earth orbit (LEO), including the International Space Station (ISS). The first figure shows how the orbit of the ISS passes through the ring of debris at the southern part of its orbit. The second figure shows the larger population of LEO satellites—payloads, rocket bodies, and debris (size exaggerated for visibility)—which could also be affected.
View of ISS Orbit (green) and Debris Ring (red) from Chinese ASAT Test
View of LEO Satellites (green) and Debris Ring (red) from Chinese ASAT Test
This debris event is so large that the debris can still be fairly easily seen without doing anything to emphasize the debris cloud, although the debris ring has widened considerably over the past eleven months.
View of All Satellites including Debris Ring from Chinese ASAT Test Readily Visible
As of 2008 January 22, an analysis of the current SATCAT shows there are 3,231 payloads in Earth orbit or beyond (see SATCAT Boxscore for details). Of those, we have orbital data for 2,864 payloads in Earth orbit. Of the missing 367 objects, some are in deep-space orbits around the Sun or other planets and some are not released by the US government, for whatever reasons. Of the 2,864 payloads we do have data for, 1,899 of these payloads pass through the regime now affected by the debris from the Chinese ASAT test—fully two-thirds of all payloads in Earth orbit.
Despite several statements by NASA officials that the ISS is not at risk due to this event, UPI reported 2007 February 2 that US and Russian officials maneuvered the ISS specifically to avoid a piece of debris from this event. For details on this report, see:
At this point, however, I am unable to independently verify this story via official sources at NASA or the Russian Space Agency and analysis of the TLE data for 2007 does not support the claim that the ISS has been maneuvered since the ASAT test was conducted. UPI subsequently revised their original story to say that the Russian Mission Control Center spokesman "was describing a general policy." (The ISS was maneuvered on 2007 March 15 in preparation for the arrival of Soyuz-TMA 10, as reported in ISS Status Report SS07-13.)
The first acknowledged maneuver to avoid a piece of debris from the Chinese ASAT test occurred on 2007 June 22 when flight controllers at NASA's Goddard Space Flight Center briefly fired the thrusters on their TERRA satellite to avoid a 7 percent chance of being struck the following day:
Several analysts have suggested that the debris from this event would be relatively short-lived and only remain in orbit for ten years or less. Unfortunately, nothing could be further from the truth. A detailed analysis of the orbital lifetime, performed on 2007 October 10, of the debris cataloged so far—using the Lifetime model implemented in STK—predicts that just over 6 percent of the debris (136 pieces) will have decayed within ten years and 79 percent will still remain in orbit 100 years from now. As of 2008 January 22, only 23 of the 2,377 pieces cataloged to date are shown as having decayed from orbit—less than one percent in the first year. The majority of the debris from this one event will remain a hazard for centuries to come. (Note: This analysis was only done for 2,150 of the 2,247 pieces catalogued as of 2007 October 10 since it appears that 97 pieces were missing from the catalog at that time.)
The graph below shows a prediction of the percent of the total Chinese ASAT test debris population which has decayed from orbit over time based on our analysis. The baseline orbital lifetime analysis results are shown in blue along with high-drag (upper line) and low-drag (lower line) excursions to help assess the impact of uncertainty in the baseline assumptions.
Plot of Orbital Decay Rate of ASAT Debris
Without specific information on size, mass, and shape of individual debris pieces resulting from this test, it was necessary to make a number of assumptions to complete the orbital lifetime analysis. First, it was assumed that all pieces were large enough to be tracked by US SSN (approximately 10 cm) which, given the size of the original satellite, meant that each piece would be roughly the same size. Assuming they had roughly the same densities, the total dry mass of the satellite prior to the test (850 kg) was divided by the number of pieces in the public SATCAT (2,247) at that time, yielding an average mass of 0.38 kg. These assumptions were used for the baseline analysis.
Next, it was necessary to select an appropriate atmospheric model to estimate drag. STK has nine atmospheric models which can be used in its Lifetime tool. Sensitivity analysis using the various models showed differences on the order of months, which was expected (and can be seen from the graph) to be a small difference when compared to the overall lifetime of most of the pieces. Therefore, the Jacchia-Roberts model was chosen, since it is an analytical model and runs much faster than the other models, most of which are numerical or not as sophisticated.
The analysis used the latest Schatten space weather predictions for the period 2006 October until 2030 May. STK/Lifetime replicates this cycle throughout the analysis period beyond the Schatten predictions (2030–2107). In fact, the effects of the solar cycle can be seen throughout the curves in the graph above, especially in the high-drag case. Considerable variability is likely in these predictions, though, since our ability to predict solar and geomagnetic cycles is still quite crude. The impact, however, should not be as significant for the majority of debris pieces, which are above the original FY 1C orbit. In fact, the chart supports this assumption since the variability due to the solar cycle is far less than the uncertainty in the drag due to the ballistic coefficients of the debris.
The baseline analysis also assumed a coefficient of drag of 2.2. However, due to the uncertainty in the size, mass, shape, and coefficient of drag for each of the pieces, additional runs (excursions) were conducted which varied the ballistic coefficient by a factor of two relative to the baseline assumptions. That is, the ballistic coefficient—which is the product of the coefficient of drag and the cross-sectional area divided by the mass—varied from half the baseline ballistic coefficient (low-drag case) to twice the baseline value (high-drag case). The results indicate that while there may be considerable variability due to the uncertainty in the debris characteristics, even doubling the drag on all the debris still only results in 36 percent of the debris decaying from orbit within 100 years.
As of 2009 June 10, only 50 pieces of this debris have decayed from Earth orbit.
An excellent one-minute video (42,414,214 bytes bytes, HD WMV format, playing time 1:31) of the Chinese ASAT test and resulting debris (1,710 pieces shown) is also available, courtesy of AGI's video team. This video is a 2007 Film/Video Silver Winner of the 28th Annual Telly Awards!
Other high-bandwidth (including broadcast quality) and low-bandwidth videos can be found on the CSSI web site at http://www.centerforspace.com/asat/.
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
Expanded coverage of CSSI analysis:
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