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AT: Space debris impact

Status quo solves space debris- NASA and NOAA prove

On an otherwise quiet Sunday on September 28, the Suomi NPP mission team was monitoring a possible close approach of a debris object. By early evening, the risk was assessed to be high enough to start planning a spacecraft maneuver to put the satellite into a safer zone, out of the path of the object classified in a size range of 4 inches up to 3.3 feet.

It was determined that the object (travelling at almost 17,000 mph) was approaching at a nearly "head on" angle, and could potentially only miss the Suomi NPP satellite by approximately 300 feet on Tuesday, September 30, if no action was taken. With that knowledge, the decision was made at 1:30 p.m. on Monday, September 29, for NOAA's Satellite Operations Facility, or NSOF, in Suitland, Maryland, to reposition Suomi NPP. Operational control as well as planning and execution of all Suomi NPP maneuvers take place at NSOF.

"Because Suomi NPP moves at a similar speed as the debris object, if there had been an impact, it would have occurred at a combined speed of nearly 35,000 mph. This would have been catastrophic not only to the satellite, but would result in thousands of pieces of new debris," said Harry Solomon, Mission Manager for Suomi NPP at NASA's Goddard Space Flight Center.

Space around Earth is littered with numerous man-made objects that could potentially collide with operating spacecraft and each other (creating more debris). There are more than 20,000 objects being monitored by the U.S. Department of Defense for satellite managers around the world.

Only about 1,000 of those 20,000 objects are operating spacecraft. The rest of the monitored space debris ranges in size from the size of a softball, to massive rocket bodies, all orbiting uncontrolled at relative speeds averaging about 22,300 mph in low-Earth orbit, where the majority of the objects reside.

Yet it is the unknown, often smaller, untracked objects that pose the biggest threat. "If a spacecraft is lost due to being hit by debris, the odds are the satellite will be hit by something the trackers can't see," said Nicholas Johnson, NASA chief scientist (retired) for orbital debris at Johnson Space Center in Houston.

That is exactly the scenario Solomon and his counterpart, Martin England, mission operations engineering lead at NSOF hope will never happen.

Risk Team Monitors Unmanned Missions Threats for NOAA and NASA

While NASA's Johnson Space Center manages monitored debris threats for spacecraft related to U.S. manned missions such as the International Space Station, the responsibility for unmanned missions managed by NASA falls to the Conjunction Assessment Risk Analysis, or CARA, team operating out of NASA Goddard.

Since Suomi NPP's launch in October 2011, this recent reposition was the fourth Risk Mitigation Maneuver to avoid space debris. In this case, the object was a section of a Thorad-Agena launch vehicle used between 1966 and1972 primarily for Corona U.S. reconnaisssance satellites.

A previous Suomi NPP risk mitigation maneuver in January 2014 avoided a discarded booster from a Delta 1 launch vehicle, a type of rocket made in the United States for a variety of space missions from 1960 to 1990. There is also a significant amount of debris in Suomi NPP's orbit from the Chinese Fengyun-1C, a meteorological satellite China destroyed in January 2007 in a test of an anti-satellite missile. Another threat near Suomi NPP's orbit is the debris resulting from a 2009 collision of a functioning commercial communications satellite and a defunct Russian satellite.

Suomi NPP's job is to collect environmental observations of atmosphere, ocean and land for both NOAA's weather and oceanography operational missions and NASA's research mission to continue the long-term climate record to better understand the Earth's climate and long-term trends.

To accomplish those goals, the satellite maintains a position on orbit such that the desired path across the ground does not vary by more than 20 km (12 miles) on each side. This orbit is adjusted with regular planned maneuvers to maintain the proper orbit and angles for best information collection. But if a Risk Mitigation Maneuver to avoid space debris were to necessitate moving out of that desired collection zone, then yet another maneuver would be necessary to return to the optimum orbit position. These unplanned maneuvers tap into the finite amount of fuel on satellites and could potentially shorten mission life of a spacecraft if fuel is used more quickly than anticipated.

The amount of space debris is not constant. It generally increases every year, sometimes generated from debris collisions, which can potentially create additional debris fragments. But there are also debris reductions. One tracked object generally falls back to Earth daily, sometimes burning up to nothing upon re-entry, or falling into water or the large areas of low population density.

In addition, there are also natural events that help control debris. The sun is currently going through a period known as solar maximum, the term for a high period of solar activity. The increased number of sunspots and solar storms during solar maximum takes place approximately every 11 years. During this period, the extent of Earth's atmosphere increases due to solar heat generated by the increased amount of solar activity. As the atmosphere extends to higher altitudes, debris at these altitudes are then subjected to increased friction, known as drag, and as a result, space debris typically fall to Earth at a higher rate during solar maximum.

The Suomi NPP mission is a bridge between NOAA and NASA legacy Earth observing missions and NOAA's next-generation Joint Polar Satellite System, or JPSS. The next satellite, JPSS-1, is targeted for launch in early 2017.

Status quo mechanisms being strengthened now to solves space debris threats

On Feb. 10, 2009, the operational Iridium 33 and decommissioned Kosmos-2251 satellites collided at a speed of 42,120 kilometers per hour, destroying both satellites. In July 2011, more than 2,000 large debris fragments resulting from this collision were detected.

Space debris constitutes a continuously growing threat to satellites and manned spacecraft. Very small debris creates potentially nonthreatening damage. Large debris can be detected by ground-based radars and avoided by spacecraft maneuvers. However, small- to medium-sized debris in low or medium Earth orbits constitutes the biggest threat. These orbits have the largest density of debris and the highest relative speeds, while the atmospheric drag is small enough that it may take centuries to have the debris re-enter the atmosphere.

In 1978, NASA scientist Donald J. Kessler showed that if the density of space debris in low Earth orbit is high enough, each collision generating space debris would increase the likelihood of further collisions. One serious implication is that the multiplication of debris in orbit will render space exploration, and even the use of satellites, increasingly dangerous and costly for many generations.

Multiple solutions to remove space debris have been explored and published.

One of these solutions involves physical contact between debris and the spacecraft:

Shielding of in-orbit spacecraft has been considered. However, the satellite community has recognized that the sheer weight of any reasonably efficient shielding would make launch not economically viable. Furthermore, the speeds involved in physical contacts would generate a cloud of additional debris.

“Catcher” spacecraft have also been proposed. Conceptually, highly mobile and agile spacecraft equipped with a “catching device” like a net or a robotic arm could be launched from Earth to intercept and catch debris. However, unless the catcher spacecraft are able to precisely match the speed and direction of the debris, any high-speed physical contact between a component of the catcher spacecraft and space debris will result in a collision, multiplying the debris. The cost of designing, developing, testing and launching such a spacecraft, with sufficient fuel onboard to repeatedly intercept multiple debris fragments at different speeds, orbits and altitudes, does not seem to be economically viable.

Other solutions would use high-power lasers that could vaporize the surface of the debris in space, deflecting it and possibly changing its orbit to intersect the atmosphere. These solutions have the advantage of not requiring physical contact with the debris.

Space-based laser systems require designing, building, launching and operating a spacecraft equipped with a very high-power laser system. Such a design is utterly complex and expensive and very likely will not be economically viable.

Airborne laser systems are facing the same obstacles: The Boeing YAL-1 Airborne Laser Test Bed program, which was designed as a missile defense system to destroy tactical ballistic missiles, was terminated because of cost.

Ground-based laser systems are handicapped by the very long propagation distance, atmospheric absorption and distortion of the laser beam. Such parameters make this solution also not economically viable. Furthermore, being located in a single country, a ground-based laser system would raise serious political issues within the international community because of its implied antisatellite capability.

In summary, the cost/benefit ratio of the above solutions appears to be the main reason none has been implemented to date to proactively mitigate the most dangerous debris.

A more affordable approach for cleaning low and medium Earth orbits of small- to medium-sized orbital debris may be achievable. This approach would use the principle of deflecting an electrically charged, moving object in a magnetic field. The old television tube is probably the most common example of this principle, where electrical charges (electrons) are deflected by the magnetic fields generated by the tube deflection coils.

The application of this principle would use a space-based electron gun to generate an electron beam directed at the orbital debris. The beam would remotely impart an electric charge to the debris. Earth’s magnetic field would exert a force on the electric charge of such debris crossing the magnetic field at high speed, modifying its orbit. Over time, the orbit would become highly elliptical and would intersect the upper atmosphere, where the debris would vaporize or fall to Earth. Preliminary calculations have shown that this concept is sound. The benefits include:

Cost: Lower cost is the major advantage of electromagnetic deflection.

Feasibility: There is no new or speculative technology to develop. Used in particle accelerators and in millions of old-style television tubes, the electron gun technology is very mature. The energy used to generate the electron beam is orders of magnitude lower than high-power lasers.

Risk: It would reduce the probability of creating additional debris by avoiding any physical contact.

The electron gun device could be integrated in an add-on module to the international space station.

The ISS is already in space, and there would be no new spacecraft to develop and launch.

The ISS has a large power-generation capability, while the electron gun would require only intermittent and modest amounts of energy to operate.

This solution would be more easily adopted by the international space community, since it does not have the capability to damage or destroy a spacecraft. This feature would be expected to encourage support and funding of the project by all the nations involved in space operations. The electromagnetic deflection concept would best be implemented as an international program, managed and coordinated by the space agencies of several countries.

As with any new technology development, there are still open questions associated with the deployment of this concept. A formal study would have to be conducted by space specialists to validate and test the concept and determine the optimum design parameters.

Areas that should be explored include:

The ability to precisely direct the electron beam at the debris. Although electrons can be sent at near-light speed, they are also deflected by the very magnetic field that will act on the debris, requiring precise aiming of the electron gun.

The ability of the target to store the electrons.

The retention of the charge by the target. Due to the constant bombardment of the target by the solar wind that comprises ionized particles, it is expected that the charge of the target will dissipate over time.

The dynamic response of the target trajectory under the influence of the deflecting force.

In conclusion, civil and government satellites as well as manned missions are currently exposed to the growing risk of collisions with debris, which may result in costly incidents, or accidents that could take human lives. It is essential to have a solution implemented as soon as possible. As of today, the electromagnetic deflection approach seems to be one of the most cost effective, most realistically achievable and least risky. It deserves to be further evaluated and pursued.

Space debris not a threat to humans

Since 1957, when the first artificial satellite was launched into space, the amount of space debris has increased year by year. As of this week, there are more than 16,000 pieces of debris with a diameter of more than 10 centimeters in space, according to observation data from the United States.

This debris is distributed in different earth orbits: low orbit, hundreds of kilometers away from the earth; moderate-altitude orbit, thousands of kilometers away, and high orbit, tens of thousands of kilometers away. Because of this, the debris is not concentrated in a dense region of space.

Generally speaking, space debris is divided in three categories: large space debris, with a diameter of more than 10 centimeters; small space debris, with a diameter of less than 1 millimeter, and dangerous debris, with a diameter between large and small debris.

"If the debris falls to the earth, most of it will be burned away by the high temperature of thousands of degrees produced by the high-speed friction with the atmosphere. Even if a large chunk of space debris penetrated the atmosphere and posed a threat to the earth, mankind should be capable of defending against it," Gong said.

First, we can roughly estimate its orbit. With the estimation of its orbit, we can intercept it. Gong said that the U.S. has successfully intercepted a failed satellite using a missile. That satellite contained highly toxic substances. In order to prevent it from falling into the sea, the U.S. destroyed the satellite by a missile launched from a warship. China also has similar technologies and can disintegrate it in the space before it causes harm."

However, these technologies are not very mature. It is still uncertain when they will come into use, he said.