6 ms·

That sounds very scary to me. If they don't care whether a single satellite is working or not, they are basically asking Kessler syndrom to start within years.

by patall 9y ago

That sounds very scary to me. If they don't care whether a single satellite is working or not, they are basically asking Kessler syndrom to start within years. Multiple start-ups (etc.) and the article covers not even have a tiny bit about what happens at the end of life of the satellites, what could go wrong ...

InclinedPlane 9y ago
This is simply ignorant of the plans. Firstly, there are levels of functionality, being able to provide service being the highest one. Out of service satellites are still most likely to be able to execute a controlled re-entry. Secondly, these satellites will be in low Earth orbit. If they become completely inoperable they have an orbital lifetime of only a few years before they re-enter. Only with routine station keeping maneuvers can they stay in orbit for even their sub-decade planned lifetimes. So there's very little risk of a Kessler syndrome type situation developing. At any given time the number of derelict satellites in orbit would be quite small if not zero.
- kobeya 9y ago
  > Out of service satellites are still most likely to be able to execute a controlled re-entry How? By a burn? That's a lot of fuel reserve to use up.
  - InclinedPlane 9y ago
    How much reserve fuel does an out of service satellite need to use after it burns up in Earth's atmosphere? How much fuel do you imagine it takes a satellite to re-enter if it will happen automatically in a matter of a few years? The answer to both is, of course, not much, not much at all.
  - Retric 9y ago
    It takes minimal energy to deorbit from LEO. By changing the shape of the orbit you spend some time in denser atmosphere which increases drag which quickly deorbits you. Controlled just means they start the processes at a specific time.
jamesaross 9y ago
You don't have to worry too much about the low Earth orbit (LEO) sateillites as they will deorbit soon enough. My understanding is that there is also ongoing research into methods to deorbit them at end of life.
- kobeya 9y ago
  In the case of a Kessler syndrom event it remains a concern. Collisions will push some debris higher while causing other pieces to enter early. The result would be a debris cloud that persists for decades even in LEO.
  - snaily 9y ago
    From first principles, I'm not seeing how a LEO collision pushes a significant amount of debris notably higher, but I'm certainly missing something: Post collision, all debris orbits will still be passing through the point of collision. Any deflection with a vertical component (up or down towards the earth) will have a part of their orbit go through thicker atmosphere, which will make them deorbit faster. That leaves deflections which are in the plane spanned by the two orbits ("sideways" and "forwards/backwards"). If those deflections in any way slow down the piece of debris, that will also go through lower atmosphere and deorbit. Disregarding debris under those effects, the remaining debris will have two more things going for it: They'll be out of the LEO orbit for a large part of their (now elliptic) orbits, and they'll be smaller so they'll slow down more from friction (due to the square-cube law). Of course, cascading effects could still affect all satellites in LEO (and humanity's access to orbit for years), but it doesn't seem to me like it'd be a "permanent" issue in LEO? What am I not seeing?
    - kobeya 9y ago
      When collisions are more frequent than once per orbit you get effects where more than one collision cause a bit of debris to have itself lifted. MOST debris is deorbited, but a small fraction is lifted into a higher orbit overall. As these collide with other objects the total mass of the system might go down (from reentry), but the number of objects and the frequency of collision goes up, continuing the process of some objects getting into higher energy orbits. This is not too dissimilar to the process of evaporative cooling in a liquid, or gas escape from an atmosphere.
currydove 9y ago
The other comments that are replying to you have it fairly accurate. It's not widely known but it isn't a secret either: the point of the doves is to be deployed en masse and with more capability with every subsequent build. A quick refresh in the constellation means there is fresh hardware in space every so often. This means the intention is indeed for re-entry into the atmosphere after the operational lifespan of the dove has lapsed. (They physically stay in space only a few years depending on altitude, orbit, exposed atmospheric drag and a couple of other things) The last two flocks alone have put close to 130 sats in space so the debris issue is something that is taken quite seriously at the company. Source: I work at planet. I generally lurk on HN but I created an account just now to reply to this :) EDIT: Relevant blog post from a couple years ago - https://www.planet.com/pulse/keeping-space-clean-responsible-satellite-fleet-operations/ https://www.planet.com/pulse/keeping-space-clean-responsible...
- a_d 9y ago
  Unrelated and probably a stupid question -- but I am curious. What would these satellites see if they looked the other way - i.e. Outwards towards space. Would they see just darkness? Some stars? Lots of stars? Would you know?
  - llccbb 9y ago
    I don't work for Planet but I know the doves have a space-looking camera that is used to help understand the satellite's orientation based on the location of stars in the image.
  - teh_klev 9y ago
    I'd hazard a guess at probably not a lot. The onboard telescopes and cameras are likely calibrated to look at and focus on specific sized patches (say 15km by 15km) of the earth between certain altitudes (say LEO distance + -450m to 9000m). Turning them to look outwards might just capture something if it happened to be inside the size of patch and whatever the telescope/camera combo can focus on (which would be the LEO distance plus or minute a bit). But space is big, even at 500km above the earth, so the likelihood of finding something in your field of view such as another satellite is probably quite low. Stars and other astronomical objects might be too dim/out of focus. [Disclaimer: not a rocket scientist]
JoeDaDude 9y ago
Maybe this is a good time to bring up the European Space Agency film about space debris [1]. [1]. http://www.esa.int/spaceinvideos/content/view/embedjw/484820 http://www.esa.int/spaceinvideos/content/view/embedjw/484820

by patall 9y ago

InclinedPlane 9y ago

This is simply ignorant of the plans. Firstly, there are levels of functionality, being able to provide service being the highest one. Out of service satellites are still most likely to be able to execute a controlled re-entry. Secondly, these satellites will be in low Earth orbit. If they become completely inoperable they have an orbital lifetime of only a few years before they re-enter. Only with routine station keeping maneuvers can they stay in orbit for even their sub-decade planned lifetimes. So there's very little risk of a Kessler syndrome type situation developing. At any given time the number of derelict satellites in orbit would be quite small if not zero.

kobeya 9y ago
> Out of service satellites are still most likely to be able to execute a controlled re-entry How? By a burn? That's a lot of fuel reserve to use up.
- InclinedPlane 9y ago
  How much reserve fuel does an out of service satellite need to use after it burns up in Earth's atmosphere? How much fuel do you imagine it takes a satellite to re-enter if it will happen automatically in a matter of a few years? The answer to both is, of course, not much, not much at all.
- Retric 9y ago
  It takes minimal energy to deorbit from LEO. By changing the shape of the orbit you spend some time in denser atmosphere which increases drag which quickly deorbits you. Controlled just means they start the processes at a specific time.

jamesaross 9y ago

You don't have to worry too much about the low Earth orbit (LEO) sateillites as they will deorbit soon enough. My understanding is that there is also ongoing research into methods to deorbit them at end of life.

kobeya 9y ago
In the case of a Kessler syndrom event it remains a concern. Collisions will push some debris higher while causing other pieces to enter early. The result would be a debris cloud that persists for decades even in LEO.
- snaily 9y ago
  From first principles, I'm not seeing how a LEO collision pushes a significant amount of debris notably higher, but I'm certainly missing something: Post collision, all debris orbits will still be passing through the point of collision. Any deflection with a vertical component (up or down towards the earth) will have a part of their orbit go through thicker atmosphere, which will make them deorbit faster. That leaves deflections which are in the plane spanned by the two orbits ("sideways" and "forwards/backwards"). If those deflections in any way slow down the piece of debris, that will also go through lower atmosphere and deorbit. Disregarding debris under those effects, the remaining debris will have two more things going for it: They'll be out of the LEO orbit for a large part of their (now elliptic) orbits, and they'll be smaller so they'll slow down more from friction (due to the square-cube law). Of course, cascading effects could still affect all satellites in LEO (and humanity's access to orbit for years), but it doesn't seem to me like it'd be a "permanent" issue in LEO? What am I not seeing?
  - kobeya 9y ago
    When collisions are more frequent than once per orbit you get effects where more than one collision cause a bit of debris to have itself lifted. MOST debris is deorbited, but a small fraction is lifted into a higher orbit overall. As these collide with other objects the total mass of the system might go down (from reentry), but the number of objects and the frequency of collision goes up, continuing the process of some objects getting into higher energy orbits. This is not too dissimilar to the process of evaporative cooling in a liquid, or gas escape from an atmosphere.

currydove 9y ago

The other comments that are replying to you have it fairly accurate. It's not widely known but it isn't a secret either: the point of the doves is to be deployed en masse and with more capability with every subsequent build. A quick refresh in the constellation means there is fresh hardware in space every so often. This means the intention is indeed for re-entry into the atmosphere after the operational lifespan of the dove has lapsed. (They physically stay in space only a few years depending on altitude, orbit, exposed atmospheric drag and a couple of other things) The last two flocks alone have put close to 130 sats in space so the debris issue is something that is taken quite seriously at the company. Source: I work at planet. I generally lurk on HN but I created an account just now to reply to this :) EDIT: Relevant blog post from a couple years ago - https://www.planet.com/pulse/keeping-space-clean-responsible-satellite-fleet-operations/ https://www.planet.com/pulse/keeping-space-clean-responsible...

a_d 9y ago
Unrelated and probably a stupid question -- but I am curious. What would these satellites see if they looked the other way - i.e. Outwards towards space. Would they see just darkness? Some stars? Lots of stars? Would you know?
- llccbb 9y ago
  I don't work for Planet but I know the doves have a space-looking camera that is used to help understand the satellite's orientation based on the location of stars in the image.
- teh_klev 9y ago
  I'd hazard a guess at probably not a lot. The onboard telescopes and cameras are likely calibrated to look at and focus on specific sized patches (say 15km by 15km) of the earth between certain altitudes (say LEO distance + -450m to 9000m). Turning them to look outwards might just capture something if it happened to be inside the size of patch and whatever the telescope/camera combo can focus on (which would be the LEO distance plus or minute a bit). But space is big, even at 500km above the earth, so the likelihood of finding something in your field of view such as another satellite is probably quite low. Stars and other astronomical objects might be too dim/out of focus. [Disclaimer: not a rocket scientist]

JoeDaDude 9y ago

Maybe this is a good time to bring up the European Space Agency film about space debris [1]. [1]. http://www.esa.int/spaceinvideos/content/view/embedjw/484820 http://www.esa.int/spaceinvideos/content/view/embedjw/484820