China’s ASAT – The Problem With Debris

Lots of press these past few days over China’s ASAT test/demonstration vs. a defunct FY-1C weather satellite. Some may ask why the big deal — space after all, is not the province of but a few privileged nations and the target satellite was theirs, so why the concern? In a word, debris. The rather violent impact (and we are assuming a hit to kill intercept) generated thousands of debris particles of varying size. Where this is a problem lies in the orbit of the FY-1C. As a weather satellite it was in a polar orbit which in turn, exposes a huge number of satellites (including the ISS and if on orbit, the shuttle) to running a barrier of debris in their orbits. The illustration below(from the ArmsControlWonk blog which first broke the news) provides insight into this issue:

The launch path is the heavier purple path closer to the Earth, the intercept point is pretty clear and the threaded looking paths are the initial plots of debris. To give a better feel for what this constitutes, consider the infamous USAF “Needles” experiment or Project West Ford.

At the height of the Cold War in the late 1950s, all international communications were either sent through undersea cables or bounced off of the natural ionosphere. The United States military was concerned that the Soviets (or others) might cut those cables, forcing the unpredictable ionosphere to be the only means of communication with overseas forces. The Space Age had just begun, and the communications satellites we rely on today existed only in the sketches of futurists. Nevertheless, the US Military looked to space to help solve their communications weakness. Their solution was to create an artificial ionosphere. In May 1963, the US Air Force launched 480 million tiny copper needles that briefly created a ring encircling the entire globe. They called it Project West Ford. The engineers behind the project hoped that it would serve as a prototype for two more permanent rings that would forever guarantee their ability to communicate across the globe.

The project itself was a virtually unqualified success. Though the first launch ended in failure, the second launch went without a hitch on May 10th, 1963. Inside the West Ford spacecraft, the needles were packed densely together in blocks made of a naphthalene gel that would rapidly evaporate in space. This entire package of needles weighed only 20 kg. After being released, the hundreds of millions of copper needles gradually spread throughout their entire orbit over a period of two months. The final donut-shaped cloud was 15 km wide and 30 km thick and encircled the globe at an altitude of 3700 km:

The West Ford copper needles were each 1.8 cm long and 0.0018 cm in diameter and weighed only 40 micrograms. They were designed to be exactly half of the wavelength of 8000 MHz microwaves. This length would create strong reflections when the microwaves struck the copper needles, in effect making them tiny dipole antennae each repeating in all directions the exact same signal they received. Most of the West Ford dipoles re-entered Earth’s atmosphere sometime around 1970, according to theoretical and observational evidence. The needles slowly drifted down to the Earth’s surface, unscathed by re-entry because of their size (unlike the current mess left on orbit by China).

This is in studied contrast to the intercepts conducted by the US using either SM-3s or GBIs as part of the development of the Ballistic Missile Defense System (BMDS). Those intercepts were against ballistic targets and the debris carried back in to the atmosphere in short order. Even when the US first demonstrated the ASAT concept in the late 50’s/early 60’s (Bold Orion, which was tested by the Air Force starting in October 1959, launched rockets from a B-47 bomber while in the two Hi-Ho tests in 1962, the Navy launched rockets from an F4D and F4J fighter) the intercepts were near hit and satellites not destroyed. If the intention was proof of concept, the Chinese ASAT could relatively easily have been flown to a near hit position and verified test criteria without target destruction and the resultant debris.