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I get how tiny that is compared to space, even that in Earth's orbit. But since these satellites are super precise, could we make a plan where two of them zoom

I get how tiny that is compared to space, even that in Earth's orbit. But since these satellites are super precise, could we make a plan where two of them zoom past each other with just a 5-meter gap without fearing them colliding? I mean, if robocars can do it driving centimeters apart, why not satellites?

HPsquared 3y ago
Their movements are also very smooth and predictable. Probably more a "what if there's a slight disturbance" thing, or "this is within our measurement / prediction error range and they could collide"
orbital-decay 3y ago
Two problems are orbit determination accuracy (bottlenecked by the amount of ground stations and the low quality of public NORAD data) and prediction of perturbations (dominated by the atmosphere and space weather at low orbits). Both areas progressed greatly in the last decade, but still not enough.
- araes 3y ago
  Other than purely technical issues, there's also social issues. Lot of folks won't have the ability to meet those specs anyway. Many countries simply will not care that much, and launch whatever to wherever, because "tragedy of the commons." And, many are openly antagonistic, and will simply test anti-satellite missiles, because the USA already has em, and tested em, so we can too.
aaronmdjones 3y ago
Cars can maneuver much more readily, travel at much lower velocities, have road traction so aren't affected by their gravitational attraction to each other, and don't have a third axis of separation (altitude) to deal with, including changes in that axis due to micro-gravity and atmospheric fluctuations. This makes long-term modelling of orbits/intersections very difficult, and the error bounds are much too large to give any reliable projections on the order of 5 metres. We would know that they came within 5 metres of each other when they come within 5 metres of each other; not long before.
cfraenkel 3y ago
also, in this case (as with all 'debris'), one of the vehicles is dead, so you can't do active ranging on it, just passive radar. Much less accurate. Active rangefinding is good to ~ meter accuracy at geosynch, passive radar is nowhere near that close. The two factors for how good your orbit fit are how good your range data is, and how frequently you get samples. To get accurate orbits, you need to look often, and there are lots of objects up there - way more than there are antennas on the ground keeping track of them.
- bagels 3y ago
  If you are using onboard radar to avoid collisions in LEO, you probably won't find it useful for this purpose.
bagels 3y ago
Space weather and positional measurement accuracy limits how precisely you can predict your orbit, especially over longer time periods. Maneuvers use precious fuel. Not all objects can make maneuvers (debris). If there are two active sats, they have to coordinate as to not make it worse.
- Buttons840 3y ago
  I bet the clouds of Earth shifting the mass and gravity of the planet could change orbits by a few meters this way or that.
  - bagels 3y ago
    Atmosphere expands and contracts with solar activity and day night cycles, changing drag. That is the primary factor. Top forces in Leo are gravity (lumpy earth, sun, moon Jupiter), drag, solar radiation pressure
  - JPLeRouzic 3y ago
    I am a layperson and never heard about that phenomenon, please could you provide a pointer?
    - bagels 3y ago
      I am not a layperson, and I don't think any of the models take this in to account. Lumpy earth and drag are much larger effects. https://svs.gsfc.nasa.gov/3655/ https://svs.gsfc.nasa.gov/3655/ https://www.swpc.noaa.gov/impacts/satellite-drag https://www.swpc.noaa.gov/impacts/satellite-drag
    - Buttons840 3y ago
      It was just a guess. On second guess the atmosphere is a fluid so maybe it has very little effect. But when a satellite is traveling billions of miles, a little effect could easily move it a few feet one way or another, maybe. As others mentioned, there are larger effects.

HPsquared 3y ago

Their movements are also very smooth and predictable. Probably more a "what if there's a slight disturbance" thing, or "this is within our measurement / prediction error range and they could collide"

orbital-decay 3y ago

Two problems are orbit determination accuracy (bottlenecked by the amount of ground stations and the low quality of public NORAD data) and prediction of perturbations (dominated by the atmosphere and space weather at low orbits). Both areas progressed greatly in the last decade, but still not enough.

araes 3y ago
Other than purely technical issues, there's also social issues. Lot of folks won't have the ability to meet those specs anyway. Many countries simply will not care that much, and launch whatever to wherever, because "tragedy of the commons." And, many are openly antagonistic, and will simply test anti-satellite missiles, because the USA already has em, and tested em, so we can too.

aaronmdjones 3y ago

Cars can maneuver much more readily, travel at much lower velocities, have road traction so aren't affected by their gravitational attraction to each other, and don't have a third axis of separation (altitude) to deal with, including changes in that axis due to micro-gravity and atmospheric fluctuations. This makes long-term modelling of orbits/intersections very difficult, and the error bounds are much too large to give any reliable projections on the order of 5 metres. We would know that they came within 5 metres of each other when they come within 5 metres of each other; not long before.

cfraenkel 3y ago

also, in this case (as with all 'debris'), one of the vehicles is dead, so you can't do active ranging on it, just passive radar. Much less accurate. Active rangefinding is good to ~ meter accuracy at geosynch, passive radar is nowhere near that close. The two factors for how good your orbit fit are how good your range data is, and how frequently you get samples. To get accurate orbits, you need to look often, and there are lots of objects up there - way more than there are antennas on the ground keeping track of them.

bagels 3y ago
If you are using onboard radar to avoid collisions in LEO, you probably won't find it useful for this purpose.

bagels 3y ago

Space weather and positional measurement accuracy limits how precisely you can predict your orbit, especially over longer time periods. Maneuvers use precious fuel. Not all objects can make maneuvers (debris). If there are two active sats, they have to coordinate as to not make it worse.

Buttons840 3y ago
I bet the clouds of Earth shifting the mass and gravity of the planet could change orbits by a few meters this way or that.
- bagels 3y ago
  Atmosphere expands and contracts with solar activity and day night cycles, changing drag. That is the primary factor. Top forces in Leo are gravity (lumpy earth, sun, moon Jupiter), drag, solar radiation pressure
- JPLeRouzic 3y ago
  I am a layperson and never heard about that phenomenon, please could you provide a pointer?
  - bagels 3y ago
    I am not a layperson, and I don't think any of the models take this in to account. Lumpy earth and drag are much larger effects. https://svs.gsfc.nasa.gov/3655/ https://svs.gsfc.nasa.gov/3655/ https://www.swpc.noaa.gov/impacts/satellite-drag https://www.swpc.noaa.gov/impacts/satellite-drag
  - Buttons840 3y ago
    It was just a guess. On second guess the atmosphere is a fluid so maybe it has very little effect. But when a satellite is traveling billions of miles, a little effect could easily move it a few feet one way or another, maybe. As others mentioned, there are larger effects.