Hubble’s shocking life alongside space debris

During its 30 years in orbit around Earth, the NASA / ESA Hubble Space Telescope has witnessed the changing nature of space flight as the skies have been filled with increased numbers of satellites, the Space Station was born. International and space accidents and explosions have created clouds of fast-moving space debris.

Hubble himself has felt the impact of these debris, accumulating small impact craters in his solar panels that show a long and hectic life in space. So what can we learn from these impacts and what does the future hold for Hubble?

In 1993, Shuttle’s first mission was to ‘fix’ Hubble. By providing the space observatory with corrective optics, he was suddenly able to take incredibly sharp images of the Universe loved by everyone.

While the astronauts were there, they replaced the observatory’s solar panels that had been ‘shaking’ due to temperature fluctuations. One of the panels was removed in orbit, then burned in Earth’s atmosphere, but the other was returned to Earth.

Part of ESA’s contribution to Hubble was to design, manufacture and supply its solar panels in exchange for observation time, which means that the returned group was available for inspection by the Agency.

This was one of the first opportunities in the history of space exploration to see the impact of more than two years in space on an orbiting satellite. The team discovered hundreds of impact craters that accumulate on the surface of just a small section of the solar array, ranging from microns to millimeters in diameter.

Nine years later, the solar panels were again replaced and returned to Earth this time, accumulating nearly a decade of impact craters.

This matrix is ​​now on display at the ESA Technology Center (ESTEC) in the Netherlands, but a small piece came under the control of the ESOC mission in Germany, home of the Office of Space Debris.

Evidence matrix of the early Hubble bombardment

Although we don’t know exactly when each impact crater formed, they must have occurred during the period of the orbiting solar array. As such, imprinted on them, is unique evidence of the activity of space flight during your time in space.

Impact craters were studied to determine their size and depth, but also to search for potential new debris. Since the chemical composition of the solar cell was known, the impactor could have introduced “foreign” materials or elements into the crater.

Metals like iron and nickel would suggest an impact from a natural source: fragments of asteroids and comets known as micrometeoroids. However, the craters found in Hubble’s solar panels contained small amounts of aluminum and oxygen, a strong indication of human activity in the form of ‘solid rocket engine’ firing debris.

The space debris team, as part of a larger effort with partners in industry and academia, was able to match the shape and size of these craters with the rocket fire models known to have occurred at the time, finding a coincidence between the observed craters and the expected craters.

Hubble hurt?

These tiny particles, ranging from micrometers to a millimeter in size, would have hit Hubble at enormous relative speeds of 10 km / s, however they did not have a big impact on the spacecraft that continues to take incredible pictures of our Universe.

Such impacts occur quite frequently for all satellites, the main effect being a continuous but gradual degradation in the amount of energy that solar panels can produce.

The new missions use a model created by the space debris team, based on Hubble’s first impact data, to predict how many impacts can be expected for each mission and what effect it will have on solar energy.

Hubble still lives with the threat of collision.

Imagine the Hubble spacecraft in orbit, residing within a 1 km x 1 km x 1 km cube. On average, at any time, a single micron-sized piece of debris shares that cube with Hubble, because for every cubic kilometer of space around Earth, there is approximately a small debris object.

This doesn’t sound like much, but Hubble itself travels 7.6 km / s relative to Earth, and so do these little pieces of debris. A large fraction of collisions between the two occur not from the front, but at an angle, leading to relative impact speeds of approximately 10 km / s.

For simplicity, imagine that these particles travel at 10 km / s relative to an immobile Hubble. This is the same as ten of these fast-moving objects that cross in and out of Hubble cubic space every second. Because Hubble’s solar panels occupy a large area, measuring approximately 7x2m, they are more likely to come face-to-face with large numbers of these projectiles.

Today, Hubble faces a similar threat from small pieces of debris as it did shortly after launch. Although micron-sized particles are still being created, the atmosphere at this low altitude, 547 km above Earth’s surface, also sweeps away some of them.

However, unfortunately the risk of larger objects is also increasing. The debris fragments ranging from 1 to 10 cm in size are too small to be cataloged and tracked from the ground, but have enough energy to destroy an entire satellite. At Hubble’s altitude, the probability of a collision with one of these objects has doubled since the early 2000s, from 0.15% probability per year to 0.3% today.

Hubble lives where mega-constellations plan to reside

Some satellites are launched today without the ability to change their orbit. Instead of maneuvering at the end of their life, they can insert themselves at relatively low altitudes so that over time Earth’s atmosphere will propel them to burn, including the region Hubble calls home.

Furthermore, it appears that the total number of operational satellites deployed in this region will increase rapidly. Some broadband internet constellations, the largest of which are planned to contain thousands of satellites, have their sights set on these heights.

Space security at ESA

To help prevent the accumulation of new debris through collisions, ESA’s Space Safety program is developing ‘automatic collision avoidance’ technologies that will make the collision avoidance process more efficient by automating decision processes in the ground.

But what about the rubble that’s already out there? In a world first, ESA has commissioned an active debris removal mission that will safely remove a debris element currently in orbit. The ClearSpace-1 mission will target a portion of the 100kg Vespa rocket, which went into orbit after ESA’s second Vega launcher flight in 2013.

With a mass of 100 kg, the Vespa is similar in size to a small satellite. Its relatively simple shape and sturdy construction make it a suitable first target, before moving on to larger and more challenging captures via follow-on missions, which eventually include capturing multiple objects.