4 ms·

When I first read about SpaceX's plan to launch up to 42,000 satellites, I actually wondered if we'd end up with a night sky filled with artificial objects. The

When I first read about SpaceX's plan to launch up to 42,000 satellites, I actually wondered if we'd end up with a night sky filled with artificial objects. Then I looked at the size of the earth: 197,000,000 square miles. Which is basically one satellite for 4,690 square miles. And that's at ground level. Add in more distance for low earth orbit height, and it becomes even bigger. The cubic space between two of these objects (which I'm not sure where to begin to calculate) must be pretty massive. The sky is huge. And though it's probable that one thing will hit another up there, it doesn't seem very probable, even if something were to explode into a billion tiny bullet -like projectiles.

Ididntdothis 7y ago
It has happened already so it’s a pretty realistic event.
- DanBC 7y ago
  I don't understand why you got downvoted. NASA release photographs of damage caused by space debris.
kqr 7y ago
This is the sort of thinking that made us first pollute our cities, then the seas, and then the atmosphere. Humans are great at saying, "Look at all this amount of space. Let's dump junk in it!" until it becomes untenable.
- yummypaint 7y ago
  By the time its untenable commercial enterprises have already made their profit, and it's up to the public to foot the bill for cleanup.
ThisIsTheWay 7y ago
https://en.wikipedia.org/wiki/Tragedy_of_the_commons https://en.wikipedia.org/wiki/Tragedy_of_the_commons
Sanzig 7y ago
The issue isn't that there isn't a lot of space up there (as the name would imply, there's a lot of room). The issue is that nothing up there stays still: everything is orbiting the earth, moving at velocities in excess of 7 km/sec (sometimes well in excess at very high altitudes). Different space missions have different orbit requirements, so there is a wide range of inclinations, altitudes, eccentricities, and ascending nodes. Take a look: http://stuffin.space/ http://stuffin.space/. It's a very dynamic system with a dizzying amount of pieces in it. The issue isn't so much mega-constellations in and of themselves, since presumably with good operations automation and standardized communications between operators we can thrust and avoid potential collisions as they arise, even with very large constellations. The issue is reliability: applying a small burn to nudge out of the way isn't an issue when one or both of the two spacecraft in a potential collision is operating and has propellant (although accidents still happen [1]), but if they're both dead, that's a recipe for a hypervelocity trainwreck. That's why it's important to ensure reliable fail-safe de-orbiting of end-of-life spacecraft. The FCC is moving in this direction, but unfortunately the rulemaking is still pending. [1] https://en.wikipedia.org/wiki/2009_satellite_collision https://en.wikipedia.org/wiki/2009_satellite_collision
- ben-schaaf 7y ago
  > sometimes well in excess at very high altitudes High circular orbits move a lot slower than lower circular orbits (eg: geostationary orbits basically don't move at all relative to the ground). It's the highly elliptical orbits that have massive velocities.
  - histriosum 7y ago
    FWIW, geostationary orbital velocity is like 3km per second. I'm not sure that being stationary relative to the ground is very relevant since we are talking about stuff colliding in space. The more stable orbits seem like they might be less prone to issues, though.
  - Sanzig 7y ago
    Yep, I was referring to highly eccentric orbits like Molniyas... apologies, I should have been more clear!
woodandsteel 7y ago
SpaceX's satellites will be in relatively low orbits, which means that atmospheric drag will pull them out of orbit, like in a decade or two. Even better, SpaceX's new Starship super rocket will make it vastly cheaper to put mass into orbit. That means it will become possible to put up a bunch of satellites that will collect dead satellites and other space debris and return them to the ground.
- Ididntdothis 7y ago
  I doubt it will be affordable to collect space debris. Space is huge and orbital maneuvers need a lot of fuel.
- Rebelgecko 7y ago
  For the higher orbital shells they're using, it can easily take 100+ years to deorbit from atmospheric drag alone
jakeinspace 7y ago
I think you're vastly underestimating the amount of surface area covered by a satelite: A quick check of Wikipedia[1] told me that the orbit altitude of Starlink satelites is 550km. The earth has a radius of 6371 km. Based on some trig calculation (which can be done on this[2] little php web applet I found), the visible percentage of the Earth from 550km is 4%! That's a lot. Of course, that's a significant overestimate, since it counts surface area which is just barely technically visible at a nearly 180 degree angle, and assumes a spherical Earth. Let's be generous, and say that only 5% of that area is both reasonably visible from StarLink (I apologize for this crudeness, I'm too lazy to do the math) and above trees/buildings/mountains. So that's .2% of the Earth visible from each satelite at an azimuth which is possibly visible for an average human observer on the ground. That gives an average number of 84 satelites observable, assuming a normal distribution, and likely many more for an average observer in an above-average-density area. Obviously these aren't going to be as visible and bright as the ISS or Iridium flares, but they aren't gonna be sparse. [1]https://en.wikipedia.org/wiki/SpaceX_Starlink https://en.wikipedia.org/wiki/SpaceX_Starlink [2]http://www.neoprogrammics.com/spheres/visible_fraction_of_surface.php http://www.neoprogrammics.com/spheres/visible_fraction_of_su...
mhh__ 7y ago
Even if there is a fair amount of sky (solid angle per satellite?), there isn't that much space in the useful areas e.g. If you want a gazillion geostationary satellites or in molniya orbits then there's much less orbit per satellite.
- m4rtink 7y ago
  The initial ideas for geostationary satellites dating back to their invention by Arthur C Clark envisioned basically manned space stations with communication enquipment attached. Only technological advances later on enabled the current ring of large independent satellite that are long lived yet still eventually expandable. Given that the GEO ring space is indeed finite & should be kept free of debris (even crossing one) at all costs I can imagine eventually reverting to the idea of large communication stations instead of individual satellites. The stations will likely still not be manned will support automated & possibly even manned servising. It could look likey large truss, kinda similar to the one used on the ISS. Inside it would host power & fuel interconnects. Attached to it would be the communication payloads, solar power modules, engines and fuel tanks. Periodically a resuply/repair craft would visit, replenishing fuel & swapping any failed modules. Depending on your launch costs broken mpdules would either be tossed to a safe graveyard orbit or brought back (possibly to a LEO space station) for refurbishment. The first steps of this might be already happening with the recently launched Mission Extension Vehicle: https://en.m.wikipedia.org/wiki/Mission_Extension_Vehicle https://en.m.wikipedia.org/wiki/Mission_Extension_Vehicle The MEV will grapple a satellite that is low on fuel and will act as it's replacement propulsion unit. In this way it can serve at multiple satellites and ppssibly even serve as a tug for satellites that have failed & are are likely to fail soon, to make sure they reach the designated graveyard orbit. And other similar & more ambitious missions are already planned and being built.
deleted 7y ago
[deleted]
DanBC 7y ago
Orbital debris covers stuff large enough to be monitored by U.S. Combined Space Operations Center’s (CSpOC) Space Surveillance Network (SSN). It also covers stuff too small (from about 5mm to about 30cm) to be monitored by CSpOC but large enough to pose risk to human and robotic space missions. This smaller debris would be monitored by ODPO. https://orbitaldebris.jsc.nasa.gov/measurements/radar.html https://orbitaldebris.jsc.nasa.gov/measurements/radar.html > NASA's main source of data for debris in the size range of approximately 5 mm to 30 cm is the Haystack Ultrawideband Satellite Imaging Radar (HUSIR). The HUSIR radar, operated by the Massachusetts Institute of Technology’s Lincoln Laboratory, has been collecting orbital debris data for the ODPO since 1990 under an agreement with the U.S. Department of Defense. HUSIR statistically samples the debris population by "staring" at selected pointing angles and detecting debris that fly through its field-of-view. > The data are used to characterize the debris population by size, altitude, and inclination. From these measurements, scientists have concluded that there are approximately 500,000 debris fragments in orbit with sizes down to one centimeter. https://orbitaldebris.jsc.nasa.gov/faq/# https://orbitaldebris.jsc.nasa.gov/faq/# > 3. How much orbital debris is currently in Earth orbit? > More than 23,000 orbital debris larger than 10 cm are known to exist. The estimated population of particles between 1 and 10 cm in diameter is approximately 500,000. The number of particles larger than 1 mm exceeds 100 million. Orbital debris is already causing damage. Here's some examples from Hubble: https://orbitaldebris.jsc.nasa.gov/measurements/in-situ.html https://orbitaldebris.jsc.nasa.gov/measurements/in-situ.html The photo gallery shows other examples of impact damage as well as examples of debris: https://orbitaldebris.jsc.nasa.gov/photo-gallery/ https://orbitaldebris.jsc.nasa.gov/photo-gallery/

Ididntdothis 7y ago

It has happened already so it’s a pretty realistic event.

DanBC 7y ago
I don't understand why you got downvoted. NASA release photographs of damage caused by space debris.

kqr 7y ago

This is the sort of thinking that made us first pollute our cities, then the seas, and then the atmosphere. Humans are great at saying, "Look at all this amount of space. Let's dump junk in it!" until it becomes untenable.

yummypaint 7y ago
By the time its untenable commercial enterprises have already made their profit, and it's up to the public to foot the bill for cleanup.

ThisIsTheWay 7y ago

https://en.wikipedia.org/wiki/Tragedy_of_the_commons https://en.wikipedia.org/wiki/Tragedy_of_the_commons

Sanzig 7y ago

The issue isn't that there isn't a lot of space up there (as the name would imply, there's a lot of room). The issue is that nothing up there stays still: everything is orbiting the earth, moving at velocities in excess of 7 km/sec (sometimes well in excess at very high altitudes). Different space missions have different orbit requirements, so there is a wide range of inclinations, altitudes, eccentricities, and ascending nodes. Take a look: http://stuffin.space/ http://stuffin.space/. It's a very dynamic system with a dizzying amount of pieces in it. The issue isn't so much mega-constellations in and of themselves, since presumably with good operations automation and standardized communications between operators we can thrust and avoid potential collisions as they arise, even with very large constellations. The issue is reliability: applying a small burn to nudge out of the way isn't an issue when one or both of the two spacecraft in a potential collision is operating and has propellant (although accidents still happen [1]), but if they're both dead, that's a recipe for a hypervelocity trainwreck. That's why it's important to ensure reliable fail-safe de-orbiting of end-of-life spacecraft. The FCC is moving in this direction, but unfortunately the rulemaking is still pending. [1] https://en.wikipedia.org/wiki/2009_satellite_collision https://en.wikipedia.org/wiki/2009_satellite_collision

ben-schaaf 7y ago
> sometimes well in excess at very high altitudes High circular orbits move a lot slower than lower circular orbits (eg: geostationary orbits basically don't move at all relative to the ground). It's the highly elliptical orbits that have massive velocities.
- histriosum 7y ago
  FWIW, geostationary orbital velocity is like 3km per second. I'm not sure that being stationary relative to the ground is very relevant since we are talking about stuff colliding in space. The more stable orbits seem like they might be less prone to issues, though.
- Sanzig 7y ago
  Yep, I was referring to highly eccentric orbits like Molniyas... apologies, I should have been more clear!

woodandsteel 7y ago

SpaceX's satellites will be in relatively low orbits, which means that atmospheric drag will pull them out of orbit, like in a decade or two. Even better, SpaceX's new Starship super rocket will make it vastly cheaper to put mass into orbit. That means it will become possible to put up a bunch of satellites that will collect dead satellites and other space debris and return them to the ground.

Ididntdothis 7y ago
I doubt it will be affordable to collect space debris. Space is huge and orbital maneuvers need a lot of fuel.
Rebelgecko 7y ago
For the higher orbital shells they're using, it can easily take 100+ years to deorbit from atmospheric drag alone

jakeinspace 7y ago

I think you're vastly underestimating the amount of surface area covered by a satelite: A quick check of Wikipedia[1] told me that the orbit altitude of Starlink satelites is 550km. The earth has a radius of 6371 km. Based on some trig calculation (which can be done on this[2] little php web applet I found), the visible percentage of the Earth from 550km is 4%! That's a lot. Of course, that's a significant overestimate, since it counts surface area which is just barely technically visible at a nearly 180 degree angle, and assumes a spherical Earth. Let's be generous, and say that only 5% of that area is both reasonably visible from StarLink (I apologize for this crudeness, I'm too lazy to do the math) and above trees/buildings/mountains. So that's .2% of the Earth visible from each satelite at an azimuth which is possibly visible for an average human observer on the ground. That gives an average number of 84 satelites observable, assuming a normal distribution, and likely many more for an average observer in an above-average-density area. Obviously these aren't going to be as visible and bright as the ISS or Iridium flares, but they aren't gonna be sparse. [1]https://en.wikipedia.org/wiki/SpaceX_Starlink https://en.wikipedia.org/wiki/SpaceX_Starlink [2]http://www.neoprogrammics.com/spheres/visible_fraction_of_surface.php http://www.neoprogrammics.com/spheres/visible_fraction_of_su...

mhh__ 7y ago

Even if there is a fair amount of sky (solid angle per satellite?), there isn't that much space in the useful areas e.g. If you want a gazillion geostationary satellites or in molniya orbits then there's much less orbit per satellite.

m4rtink 7y ago
The initial ideas for geostationary satellites dating back to their invention by Arthur C Clark envisioned basically manned space stations with communication enquipment attached. Only technological advances later on enabled the current ring of large independent satellite that are long lived yet still eventually expandable. Given that the GEO ring space is indeed finite & should be kept free of debris (even crossing one) at all costs I can imagine eventually reverting to the idea of large communication stations instead of individual satellites. The stations will likely still not be manned will support automated & possibly even manned servising. It could look likey large truss, kinda similar to the one used on the ISS. Inside it would host power & fuel interconnects. Attached to it would be the communication payloads, solar power modules, engines and fuel tanks. Periodically a resuply/repair craft would visit, replenishing fuel & swapping any failed modules. Depending on your launch costs broken mpdules would either be tossed to a safe graveyard orbit or brought back (possibly to a LEO space station) for refurbishment. The first steps of this might be already happening with the recently launched Mission Extension Vehicle: https://en.m.wikipedia.org/wiki/Mission_Extension_Vehicle https://en.m.wikipedia.org/wiki/Mission_Extension_Vehicle The MEV will grapple a satellite that is low on fuel and will act as it's replacement propulsion unit. In this way it can serve at multiple satellites and ppssibly even serve as a tug for satellites that have failed & are are likely to fail soon, to make sure they reach the designated graveyard orbit. And other similar & more ambitious missions are already planned and being built.

deleted 7y ago

[deleted]

DanBC 7y ago

Orbital debris covers stuff large enough to be monitored by U.S. Combined Space Operations Center’s (CSpOC) Space Surveillance Network (SSN). It also covers stuff too small (from about 5mm to about 30cm) to be monitored by CSpOC but large enough to pose risk to human and robotic space missions. This smaller debris would be monitored by ODPO. https://orbitaldebris.jsc.nasa.gov/measurements/radar.html https://orbitaldebris.jsc.nasa.gov/measurements/radar.html > NASA's main source of data for debris in the size range of approximately 5 mm to 30 cm is the Haystack Ultrawideband Satellite Imaging Radar (HUSIR). The HUSIR radar, operated by the Massachusetts Institute of Technology’s Lincoln Laboratory, has been collecting orbital debris data for the ODPO since 1990 under an agreement with the U.S. Department of Defense. HUSIR statistically samples the debris population by "staring" at selected pointing angles and detecting debris that fly through its field-of-view. > The data are used to characterize the debris population by size, altitude, and inclination. From these measurements, scientists have concluded that there are approximately 500,000 debris fragments in orbit with sizes down to one centimeter. https://orbitaldebris.jsc.nasa.gov/faq/# https://orbitaldebris.jsc.nasa.gov/faq/# > 3. How much orbital debris is currently in Earth orbit? > More than 23,000 orbital debris larger than 10 cm are known to exist. The estimated population of particles between 1 and 10 cm in diameter is approximately 500,000. The number of particles larger than 1 mm exceeds 100 million. Orbital debris is already causing damage. Here's some examples from Hubble: https://orbitaldebris.jsc.nasa.gov/measurements/in-situ.html https://orbitaldebris.jsc.nasa.gov/measurements/in-situ.html The photo gallery shows other examples of impact damage as well as examples of debris: https://orbitaldebris.jsc.nasa.gov/photo-gallery/ https://orbitaldebris.jsc.nasa.gov/photo-gallery/