Space debris (space junk) encompasses both natural (meteoroid) and artificial (man-made) particles. While meteoroids orbit the sun, the artificial debris orbits the Earth. Hence, artificial debris is also called as orbital debris.
Orbital debris is any man-made object in orbit about the Earth that no longer serves a useful function. Such debris includes nonfunctional spacecraft, abandoned launch vehicle stages, mission-related debris, and fragmentation debris.
More than 500,000 pieces of debris, are tracked as they orbit the Earth. They all travel at speeds up to 23000 mph (37,000 kmph), fast enough for a relatively small piece of orbital debris to damage a satellite or a spacecraft. There are many millions of pieces of debris that are so small they can’t be tracked, which possess the greatest risk to space missions.
E.g: In 1996, a French satellite was hit and damaged by debris from a French rocket that had exploded a decade earlier.
Even tiny paint flecks can damage a spacecraft when traveling at high velocities. In fact, a number of space shuttle windows have been replaced because of damage caused by material that was analyzed and shown to be paint flecks.
To overcome such threats, NASA has Haystack radar to detect debris in the size range of 5 mm to 30 cm. It statistically samples the debris population by “staring” at selected pointing angles and detecting debris that flies through its field of view.
Debris composition:
Whenever a space mission occurs, it generates some unwanted waste e.g: solid fuel rockets deposit aluminum oxide particles, explosive bolts fragments into pieces due to stage releases, and also chunks of paints.
NASA did a post-mission analysis of space shuttles launches and reported that the damages from debris to the shuttle were as shown in figure 1:
Evasive measures:
Since only larger space objects can be cataloged and tracked, only these can be avoided through active measures or by evasive maneuvers. Smaller, uncatalogued objects can only be defeated by passive protection techniques, as used with the International Space Station (ISS).
NASA’s main source of data for debris in the size range of 5 mm to 30 cm is the Haystack radar, now known as HUSIR. HUSIR statistically samples the debris population by staring at selected pointing angles and detecting debris that flies through its field of view. The data are used to characterize the debris population by size, altitude, and inclination. NASA also collects data from the Haystack Auxiliary Radar (HAX) located next to the main HUSIR antenna, as shown in Figure 2.
Additionally, more than 100 different shields have been designed to protect the various critical components of the ISS, although all of the designs are modifications of three ISS primary shielding configurations: the Whipple bumper, the multishock (or stuffed Whipple) shield, and the mesh double-bumper shield.
Figure 3 shows a hole made in the solar panel of the ISS due to a space debris collision.
Way Ahead:
Many experts fear that debris in low-Earth orbit could reach a tipping point, known as an ablation cascade, (also dubbed the Kessler Effect) where debris from one impact could trigger a chain reaction of additional impacts. This was famously depicted in the movie Gravity.
Though space is quite large, the images of debris surrounding space are exaggerated to an extent. But, if the problem continues to grow as space activities grow, the potential loss will motivate nations and organizations to look for solutions. Because, entire economies have been built on the services they provide: military application, communication, space exploration, and remote sensing in fields of hydrology, ecology, meteorology, oceanography, glaciology, geology.
The best step to start with is to have satellites that have twin capabilities: first, able to de-orbit themselves after the end of their life-cycle. Secondly, to dodge debris when required. SpaceX’s Starlink satellite is one such example.
If not considered seriously, then later there will be a need for an active clearance mechanism, currently under experimentation or conceptual stage (Earth-based lasers to track and ablate the debris, e.Deorbit mission, CleanSpace One, electrodynamic tether, Sling-Sat Space Sweeper, SpaDE, RemoveDebris spacecraft, etc). But this will require additional costs and international cooperation & collaborations to make it happen on a large scale. Hence, the time has come to think and plan accordingly, it’s rightly said, stitch in time saves nine.
What techniques do you think, can help in solving the issue of space debris? Please let us know by replying to this mail.
References:
https://www.skyandtelescope.com/astronomy-news/what-indias-anti-satellite-test-means-for-space-debris/
https://sattrackcam.blogspot.com/2019/03/debris-from-indias-asat-test-how-long.html
https://www.nap.edu/read/5532/chapter/6#31
http://www.esa.int/spaceinimages/Images/2014/06/ATV_shielding_after_impact_test
https://arstechnica.com/science/2013/07/how-nasa-steers-the-international-space-station-around-space-junk/
Real Engineering video on Space Debris: https://www.youtube.com/watch?v=itdYS9XF4a0
