North Korean rocket debris aboard a South Korean ship as sailors stand guard on Dec. 14, 2012. The debris is believed to be the fuel container of the first stage of North Korea’s latest rocket launch. Photo: AP/Yonhap
Last week, North Korea finally managed to put an object into orbit around the Earth after 14 years of trying. The event was greeted with hysterical headlines, about how the whole thing was a likely a missile test and most certainly a failure of Western intelligence. Most of those headlines were dead wrong.
There are many questions yet to be answered about this launch and what it means. Some of them will take weeks or months to determine, others may never be answered satisfactorily. But there’s enough information already in the public domain to answer basic questions about the launch. News flash: Most of the initial reports about it were total misfires.
Was This a Ballistic Missile Test or a Satellite Launch?
Some of the same technologies are needed for long-range missiles and for space launches — most notably rocket motors, high strength-to-weight fuselages, and guidance software. But they’re not the same thing. All evidence points to a satellite launch, despite headlines like these.
The goal of a space launch vehicle is to insert payloads into orbit and to do so they must perform two functions. They must first lift a payload to a desired altitude above the Earth and then give that payload enough forward speed to remain in orbit at that altitude. The final speed required for this is determined by the altitude and pull of the Earth’s gravity. With enough speed, the payload moves forward equal to the distance it is pulled towards the Earth by gravity. It moves in an ellipse around the Earth, continually falling towards the Earth but missing (“free fall”).
A comparison of space launch and missile test trajectories. Illustration: UCS/Google Earth
Ballistic missiles, on the other hand, have a different goal. Their objective is to deliver a payload to another spot on the Earth. To do so, they need to accelerate the payload to a very high speed, although significantly slower than the space launch vehicle, and after separation from the rocket, the ballistic missile’s payload follows an elliptical path through space similar to a satellite. However, the ballistic payload is not in orbit — part of its elliptical path is inside the Earth’s atmosphere. The payload coasts along its elliptical path and instead of “free-falling” around the planet, it re-enters the atmosphere and impacts a spot on the surface of the Earth.
From a practical perspective, these different goals result in significant differences in the flight profile of a space launch versus a ballistic missile launch. Look at the illustration of the North Korean launch compiled by Dr. David Wright. The green trajectory in this illustration is for a ballistic missile trajectory while the red and yellow trajectory is for a space launch trajectory. The most striking difference is in the altitude — a long-range ballistic missile actually goes much higher into space than a typical space launch into low-Earth orbit (LEO), sometimes as high as 1,500 kilometers (930 miles).
Within these parameters, the North Korean rocket launch was most certainly a space launch and not a ballistic missile test. This can be verified by multiple sources before, during and after the launch. Prior to the launch, North Korea notified international agencies of the splashdown zones for the first two stages and the payload shroud, as is standard practice. These splashdown zones corresponded to a space launch trajectory, indicating beforehand that the North Koreans planned to try and place a satellite into orbit. During the launch, heat from the rocket was picked up by constellations of U.S. military infrared satellites in orbit. Tracking of the burn phase of the launch by those satellites allows the U.S. to verify that it was on a space launch trajectory. After the launch, remnants of the first stagewere recovered in the pre-announced splash zone by the South Korean Navy.
Was the Test Illegal Under International Law?
The most like answer is yes, but it is not likely enforceable. Although all countries do have the right to pursue peaceful exploration and use of outer space, that right is subject to international law. The United Nations Security Council has adopted two resolutions — 1718 and 1874 — demanding the North Korea refrain from further launches using ballistic missile activity. And those resolutions are binding under international law on countries that are members of the UN. What’s less clear is whether the international community has the tools to enforce these UNSC resolutions.
UNSC Resolution 1718, adopted on October 14, 2006, levied sanctions on North Korea as a result of their test of a nuclear weapon earlier that month. Contained within the text of the resolution is a demand that North Korea cease testing and development of its ballistic missile program. UNSC Resolution 1874, adopted on June 12, 2009, implemented further sanctions on North Korea after their second test of a nuclear weapon in May 2009. It repeats many of the same prohibitions as Resolution 1718, including a demand that North Korea not conduct any launch using ballistic missile technology.
North Korea’s position is that it is simply exercising its rights to peaceful exploration and use of outer space in accordance with the rights given to all nations under Article I the 1967 Outer Space Treaty, to which it is a Party. However, the actual text of the Article is as follows:
Outer space, including the moon and other celestial bodies, shall be free for exploration and use by all States without discrimination of any kind, on a basis of equality and in accordance with international law, and there shall be free access to all areas of celestial bodies
The important piece is the phrase “in accordance with international law.” UNSC Resolutions are considered binding international law on countries that are members of the UN. That includes North Korea.
However, whether or not the launch was illegal is only part of the issue. The real crux is what can or will be done about it. North Korea is gambling that the punishment for violating international law is further sanctions, which it has shown it can withstand or manipulate to some degree. It is possible that the UNSC could authorize stronger measures, including direct military action by the United States or other countries, in additional UNSC resolutions. North Korea is betting that the gun it has pointed at South Korea’s head, along with the existing commitments of the American military in Afghanistan and elsewhere, will deter a military response.
Did the North Koreans Catch Everyone Napping?
That’s what you’d believe if you read reports like these. It’s what you’d think if you learned that key Asian policy members of the Obama Administration were in the middle of a cocktail reception at the Japanese Ambassador’s residence in Washington, DC, when the launch occurred. But the fact that the North Koreans were preparing to launch a rocket was of no surprise to anyone. It’s only the specifics of the timing that may have caught some a little flat-footed. It’s highly unlikely that people at the top levels of the U.S. government and its key allies were surprised.
That’s because the launch window was fairly long, between 7 a.m. and noon local Korean time each day from Dec. 10 to Dec. 22. This launch window is driven by the orbit that the satellite needs to be placed into. A satellite orbit is fixed in space relative to the Earth and so you need to wait until the Earth rotates under the desired orbital plane before you can launch. The length of the window each day is based on the desired precision of the final orbit, the performance of the booster, the weight of the payload, and a number of other factors.
There is evidence that North Korea attempted a disinformation campaign that may have played a role in generating surprise. On December 8, U.S. intelligence satellites spotted a train carrying rocket components en route from a missile plant to the launch pad. On December 9, North Korea stated that it had discovered a problem with the rocket and it was delaying the launch and extending the window by nearly a week. The next day, the South Korean government stated that there was “no sign” of an imminent launch and another report stated that the rocket had been removed from the pad. That last statement was provably false at the time – analysis of imagery from commercial remote sensing satellites showed the rocket was still on the pad. However, the same imagery also indicated possible maintenance work on the rocket, leading to an assessment from a former U.S. intelligence analyst that a launch was at least a week out.
An example of a highly elliptical Earth orbit. Illustration: NASA
To take advantage of this disinformation campaign, it also appears that North Korea timed the launch to correspond to a significant gap in coverage of the launch site by imaging satellites. An analysis done by Marco Langbroek, a Dutch hobbyist satellite observer, shows that the launch occurred at the end of a one-hour gap with no coverage by any known American intelligence, Japanese intelligence, or commercial imaging satellites in LEO. Other portions of the launch window had at most fifteen minutes between satellite overflights. This is backed up by a quote from an unnamed U.S. official, who said they relied too much on overhead satellite imagery for their warnings about the launch.
Despite this, it is doubtful that the disinformation campaign was effective on everyone. As anyone in the imagery analysis field can tell you, LEO imagery satellites have their limitations. They exist in limited numbers, travel in predictable orbits, can only observe what’s directly underneath them, and have a revisit time measured in many hours to days. It is relatively simple to either cease activities when they come overhead, or in some cases, to actually create a false situation on the ground for them to capture.
However, these are not the only tools governments like the United States have at their disposal. While satellites in LEO only have limited viewing windows, satellites in other orbits can stare at specific locations for extended periods. Satellites in highly elliptical Earth orbits (HEO), often called Molniya after the Soviet satellites that were the first to widely use them, can hang over a specific part of the Earth for hours at a time as shown in illustration above. Three satellites spaced out in the same orbit can monitor a region continuously, with two in the upper part of the orbit on either side of apogee (red dot number 6) and one in the lower part of the orbit swinging through perigee (red dot number 0).
The U.S. has at least two infrared sensors in HEO orbits as part of the Space-Based Infrared System (SBIRS). Open source information indicates that they are hosted on two classified satellites, USA 184 and USA 200. The same satellites are also believed to carry a signals intelligence payload that cancollect electromagnetic emissions. Observations from amateur satellite observers indicate that their orbits “hang” over Asia, indicating that they likely could have been used to monitor the launch site and observe the launch. An image seen below and right, released by the U.S. military, is of one of the SBIRS payloads in HEO tracking a missile launch.
An infrared satellite image of a missile launch taken from the Space Based Infrared Systems Highly Elliptical Orbit-2 sensor. Photo: Air Force
In addition to the SBIRS payloads in HEO, the U.S. has a number of satellites in geostationary Earth orbit (GEO), orbiting 36,00 kilometers (about 22,000 miles) above the Equator that likely provided critical data on the North Korean launch. These satellites orbit around the Earth at the same rate the Earth rotates, giving the impression that they are “fixed” relative to a particular spot on the Earth. In the case of the North Korean launch, the U.S. satellites in GEO collection signals intelligence and electronic intelligence could have monitored the launch site for preparations and the infrared warning satellites would have detected the launch.
The important issue in the case of North Korea is that very few people have access to the information from these satellites. They are considered critical to U.S. national security and their very existence is highly classified, along with any intelligence products created from the data they collect. Additionally, they are often stovepiped into different sets of indicators with little integration between different sources, leading to the possibility of conflicting conclusions.These factors likely worked in the North Koreans’ favor. Very few within the U.S. government, and no one outside the U.S. government with the possible exception of close allies, would have had access to the intelligence from these satellites. Most governments would have to rely on either declassified or sanitized intelligence or their own intelligence sources, and outside observers had to rely on the handful of commercial imaging satellites for information. It is this last group, along with lower-level government officials, that fell victim to the North Korean disinformation campaign, and the reliance on the media for quotes and information from these sources created the impression that the North Koreans had fooled everyone.
Within the U.S. government, top national security officials likely had access to data sources that were unaffected by North Korean disinformation. However, it is possible that different intelligence sources could have been driven conflicting conclusions, leading to disagreement over what the reality was. This may have played a role in catching some within the U.S. government off guard.
What did the North Koreans Put into Orbit?
A satellite, primarily. Plus a third-stage rocket body and two small pieces of debris.
Shortly after the launch, the North American Aerospace Defense Command (NORAD) stated that it had U.S. missile warning systems had detected a launch and that the rocket had apparently placed an “object” in orbit.
The objects from the launch were on a trajectory that took them south over the Philippines, Western Australia, and the South Pole, before coming back north again along the east coast of South America and flying over the North Pole. Along the way, it would have been spotted by several radars belonging to the U.S. Space Surveillance Network. Likely candidates include the phased array radars at Cape Cod Air Force Station in Massachusetts, Thule Air Base in Greenland, and Royal Air Force Fylingdalesin the UK, along with the mechanical tracking and imaging radars at Massachusetts Institute of Technology’s Haystack Observatory.
By 9:18 p.m. EST, less than three hours after launch, orbital analysts working in the Joint Space Operations Center (JSpOC) were able to use the tracking from these sensors to catalog the objects from the launch. Shortly thereafter, two-line elements (TLEs) with the orbital parameters for these objects were published by the U.S. military on the Space Track website and echoed elsewhere, such as the detailed charts here. In total, four objects were cataloged:
For the most part, the North Korean launch is similar to many other satellite launches. In most launches, after the first two (or sometimes three) rocket stages finish burning and fall back to Earth, the upper stage continues to burn and provide the final push to place the payload in its planned orbit. It then separates from the payload and often remains in orbit itself for significant periods of time. It is also fairly standard for there to be a few small pieces of debris in orbit as well.
What might these objects look like? Prior to the April 2012 launch attempt, North Korea showed reporters the satellite that it claimed was being launched into space at that time. Although there weresome doubts as to whether what was shown was the actual satellite or a model, the size, shape, and outward appearance of the satellite corresponded to the function given by North Korea of a crude Earth-observing satellite.
The North Korean satellite previously launched in April, seen at the Sohae Satellite Station in Tongchang-ri, North Korea, on April 8, 2012. Photo: AP/David Guttenfelder
A detailed analysis of the satellite based on photos taken by reporters in April 2012 can be found here. It is roughly rectangular, measuring 0.75 meters squares by 1.1 meters tall (2.5 feet square by 3.5 feet tall) and weighing about 100 kg (220 lbs). On the top of the satellite as shown in the images are four low-bandwidth UHF antennas likely used for telemetry and command and control of the satellite. They could also be used to transmit music. The silver tower sticking up is likely a GPS receiver that enables the satellite to calculate its position and velocity in orbit, and the solar panels on the sides appear to be hinged, suggesting they may swing out on orbit.
A closer view of the satellite’s equipment. Photo: via the Federation of American Scientists
The gold tube pointing up in the closeup photo is a 10 centimeter (4 inch) wide video camera covered by a black lens cap, estimated to provide imagery of around 100 meters resolution. The gold tube on its side is either a Sun or Earth sensor that enables it to determine its attitude and point sensors at the Earth. Behind the camera is the squat metal tube for the X-Band antenna that has the bandwidth needed to send any imagery taken by the satellite to the ground. None of this gear is very sophisticated and similar or more advanced components are commercially available over the Internet or being built and flown by universities around the world.
There is no way to confirm if the satellite placed in orbit by North Korea is the same as what was shown to reporters in April. However, the data being collected so far indicates that the satellite in orbit is at least the same general size and shape and the orbit is consistent with an Earth-observing mission. While the U.S. military has yet to release information on the radar cross section (RCS) of any of these pieces which would provide a good estimate of their size, optical tracking done by amateur observers indicates that the satellite is much smaller than the rocket body. Their observations of the size and shape of the object cataloged as the rocket body also correlate to the known size and dimensions of the third stage of the Unha-3.
That leaves only the mystery of the two small pieces of debris. As mentioned earlier, it is common to have additional pieces of debris associated with the payload separation in orbit. In some cases, they can be straps or parts there were used to fasten the payload to the upper stage. In other cases they are weights on a rope that are used to de-spin the payload after separation or covers used to protect the small engines that separate the payload from the upper stage. After release of the payload, these motors are used to decelerate the rocket body slightly to separate it from the payload.
The orbital data published by the U.S. military supports the notion that the two pieces of debris are somehow related to separation. Their area-to-mass ratio, calculated from the drag information in the TLEs, indicates that they are small, lightweight, and very similar. They have nearly the same perigee as the rocket body, indicating that they separated at the same time as the payload. They appear to be spaced on either side of the rocket body, which analysts have noted is consistent with covers for the separation engines that were blown to the side so as not to impact the satellite.
Comparison of apogees of the four North Korean space objects.
The only apparent anomaly at this time is the relative orbits of the four objects. Usually the satellite is in the highest orbit, with the rocket body and other objects in slightly lower orbits. In the case of the North Korean launch, the rocket body and one of the pieces of debris are in slightly higher orbits than the payload. This in and of itself does not indicate a significant problem, but there may be an aspect to the separation method used that played a role. The rocket body being in a higher orbit than the satellite did however led to some confusion by the orbital analysts at the JSpOC, who initially cataloged the satellite and rocket body backwards and had to swap element sets several hours after launch.
This mis-categorization should not have happened. Given the relative sizes of the satellite and rocket body, it should have been easy to distinguish one from the other even if they were in an unusual configuration. As the objects were tracked by the various radars, the amount of radar energy returned over the course of the track would have varied with the size and any rotation of the objects. With minimal training, it is fairly easy to distinguish a large, rotating, oblong rocket body from a much smaller, nearly cube-shaped satellite using such information.
Is the North Korean Satellite Functional?
It doesn’t look like it, no. Pyongyang promised that the satellite would start playing “The Song of General Kim Jong-Il.” But so far, amateur observers haven’t heard any transmissions from the satellite at all.
The North Korean government also stated before the launch that the satellite was supposed to monitor forest resources, watch out for natural disasters, assist in food crop planting, and forecast the weather. These are all missions that a satellite like this one could pull off, theoretically. So we have to examine the spacecraft’s flight path and transmissions to tell if it’s really doing those jobs.
Earth observation satellites are usually placed in what are called sun-synchronous orbits (SSO). These are special LEO orbits that are designed to maintain the same angle between the Sun, satellite, and a spot on the ground by using the Earth’s gravitational field to rotate the satellite’s orbit around the Earth at the same rate the Earth rotates around the Sun. This allows for consistent lighting and overflight times for the places on the ground the satellite is observing, as well as consistent illumination of the satellite’s solar panels. To accomplish this, the satellite needs to be placed into a precise inclination and matching altitude as shown in this graph.
The inclinations and matching altitude corresponding to sun-synchronous orbit.
North Korea was successful in placing their satellite in a SSO orbit at an altitude of roughly 500 kilometers (310 miles) and an inclination of 97.4 degrees. To do so, they needed to execute a fairly complex maneuver of the third stage. The inclination of a satellite’s initial orbit is a function of the latitude of the launch site and the direction (azimuth) of the rocket. It is possible to directly launch into an inclination equal to or higher in value than the launch site latitude. So for example, a launch site at 28 degrees North can directly launch into any orbit of 28 degrees inclination or higher, while a launch site on the Equator can launch into any inclination.
Most countries also avoid flying their rockets over populated areas and other countries if they can help it. That can lead to further constraints on which direction the rocket can take, and thus which orbits you can access. In the case of North Korea, rocket launches from their original east coast launch site overflew Japan, creating a lot of political problems. So they moved to a new launch site on the west coast of North Korea that allows them to launch south, away from Japan.
However, the new west coast launch site still doesn’t allow North Korea to launch directly into SSO. Doing so would require either overflying Taiwan or the Philippines. As amateur observer Bob Christy pointed out, North Korea solved this problem by launching the rocket in a direction that kept it away from other countries during the most dangerous part of the launch, and after separation of the second stage the third stage was turned before igniting. This led to a new trajectory that placed the satellite in the correct orbital inclination as shown in the illustration.
This is sophisticated stuff from a country that’s never had a successful space launch before. But it’s not the only indicator of whether the North Korean satellite is working. Pyongyangstated before the launch that the satellite would be transmitting scientific data when orbiting over the DPRK and the hymns of Kim Il Sung and Kim Jong Il the rest of the time. Scientific data transmission involving images would take place over X-Band microwave radio frequencies and other transmissions would take place in the UHF band.Although it is known that North Korea has registered for an X-Band license with the International Telecommunications Union (ITU), the precise frequency is not known. Moreover, such transmissions would only take place where there are ground stations that can receive the data. This presents a problem for North Korea, as the satellite is only over their territory for a short period of time. Most other countries solve this problem by either building their own ground stations all over the globe, such as the U.S. military’s Air Force Satellite Control Network, or by contracting with an existing network. Polar-orbiting satellites often make use of the extensive ground station operated byKongsberg Satellite Services in Svalbard, Norway near the North Pole and McMurdo Station in Antarctica near the South Pole, since their satellites overfly one of these two areas roughly every 45 minutes.
We don’t know if North Korea signed contracts with Kongsberg or made a deal with someone else for additional ground stations outside of North Korea. However, amateur satellite observers around the world have been listening to the satellite for any hints of music or other signals in the UHF. So far, their results have been negative.
Lacking any evidence of transmissions from the satellite, the final indication of whether or not it is functioning comes from its stability on orbit. Although some satellites are intended to rotate freely as they orbit around the Earth, many are increasingly designed to orient themselves in a certain direction and maintain that orientation. This can be done in a number of ways, from complex systems such as gyroscopes to simpler, passive methods such as gravity gradient booms. Gravity gradient booms are appendages sticking out of a satellite that use the Earth’s gravity to orient a satellite towards the Earth.
Before the launch, North Korea stated that its satellite was designed to be 3-axis stabilized, meaning it would not have significant rotation in any of the three axes of movement relative to the Earth. This is common for Earth observing satellites to keep their cameras pointed at the Earth and away from the Sun. The satellite shown by North Korea to reporters in April also indicates it was meant to be 3-axis stabilized. The camera and most of the antennas are all on a single face of the satellite, presumably the one that was meant to be pointed at the Earth.
Shortly after launch, unnamed U.S. officials were quoted in the media stating that the North Korean satellite was tumbling out of control, while South Korean officials reported that the satellite is orbiting normally. The phrase “tumbling out of control” was a poor choice of words, as it gave the impression that the satellite might somehow crash back to Earth or off into another satellite. That is not the case. Even if a satellite is spinning wildly, it is still moving along a predictable orbit. This is similar to theteacups-style amusement park rides where each individual car can rotate while still moving on a fixed path among the others.
Optical observations of the satellite taken by amateur observers indicate that the North Korean satellite is tumbling, but not at an alarming rate. They report a regular flashing every few seconds, consistent with a tumbling object. The regularity indicates that it is about the same size in length, width, and height and the time between flashes indicates that it is not tumbling very fast. The flashes are likely the result of reflective surfaces, such as solar panels, catching the sunlight.
The tumbling indicates that either the satellite has malfunctioned or perhaps North Korea has not yet established control. However, it should be noted that tumbling at this stage does not definitively mean that the satellite is nonfunctional or will remain so. Some of the simpler techniques for stabilizing a satellite, such as passive magnetic systems, require a bit of time to slowly stabilize the satellite. It could also be that the satellite is functional, but the tumbling is preventing ground controllers from communicating with the satellite.
The final bit of evidence that could indicate whether or not the satellite is functional is if it maneuvers. An increasing number of satellites, even university-built cubesats, are being deployed with maneuvering capability. However, the satellite presented to journalists by North Korea in April showed no signs of any maneuvering capabilities. Given its current orbit and estimated area to mass ratio, it is expected that all the North Korean space objects will re-enter the atmosphere within several years.
Do the North Korean Space Objects Pose a Threat?
Not right now, and maybe not ever. All four North Korean space objects are in normal, predictable orbits and are being tracked regularly by both the U.S. military and amateur observers around the world.
For the moment, none of the North Korean space objects pose a collision threat to any other objects on orbit. They are all orbiting nearly a hundred kilometers (60 miles) above the International Space Station and well below the most crowded SSO region of 700 to 900 kilometers (430 to 560 miles) where many of the Earth observation satellites are. They are being included in the daily collision avoidance runs conducted by the Joint Space Operations Center and other satellite operators will be warned if one of the North Korean objects does pose a threat to another satellite.
In a few years when their orbits naturally decay enough to re-enter the atmosphere, the North Korean objects are not expected to present an unusual threat. The satellite and the two pieces of debris are small enough that they are unlikely to survive atmospheric re-entry in a significant manner. Sizeable pieces of the rocket body may survive and impact the ground, but the North Korean upper stage is significantly smaller than many of the other rocket bodies in orbit. In any case, the JSpOC will be monitoring their re-entry and providing warning to governments if they should potentially re-enter over populated areas and pose a threat. Hundreds of space objects re-enter each year, and to date none has resulted in significant damage to people or property.
Bottom line: North Korea’s space launch is likely illegal and provides Pyongyang with important know-how that they’ll need for long-range missile launches. But in the short term, this one little (mostly) dead satellite isn’t going to hurt anyone.
N Korean Space Launch References –
 Two Line Element Set –
 Yo-yo De Spin –
 Outer Space Treaty –
 Defense Support Program –
Courtesy : Wired