Hmm I thought they were small, countertop microwave sized,
the version 1 satellites which constitute the majority of the current constellation are just a touch under 600 pounds and before you unfurl the solar panel are roughly the size of a refrigerator. The major revision currently being launched is over twice the weight (but has much more than twice the capability).
Hmm I thought they were small, countertop microwave sized,
the version 1 satellites which constitute the majority of the current constellation are just a touch under 600 pounds and before you unfurl the solar panel are roughly the size of a refrigerator. The major revision currently being launched is over twice the weight (but has much more than twice the capability).
This is exactly the field I work in now. These kinds of near misses happen very often, I have actionable events like this at least once a month (our satellites are maneuverable). I can't really say if this event was exceptionally high risk or not, without knowing the covariances and resulting Pc involved.
We've had events with calculated misses less than 10m. but the miss alone isn't all of the story. you have to look at the error bars (covariance) for both the primary and secondary object, hard body radius (HBR) of both objects, and some other metrics to determine how much of a risk this really is. a miss is a miss. if you don't hit it, you're fine, even if it's by 1ft. if the error is huge, then the probability of collision (Pc) goes down a lot due to uncertainty, if the error is very small (less than the miss), then the Pc also goes down a lot because you are more certain that you will actually miss, so it's a delicate balance of all these factors.
Re: de-orbiting. most missions do not have enough fuel to fully de-orbit in the way many might be thinking of, ie, burning until you hit re-entry and burn up in the atmosphere. I believe there is a rule for newer LEO missions that they need to re-enter in 25 (or is it 50?) years. most missions will only reserve enough fuel to get themselves out of their constellation and away from (below) other active missions and left to naturally decay from drag the rest of the way over many years.
most missions will only reserve enough fuel to get themselves out of their constellation and away from (below) other active missions and left to naturally decay from drag the rest of the way over many years.
I'll add a few Starlink specific comments to this overview. Notice that the comments mention "most missions" as distinct from "most satellites". The Starlink constellation is so big and growing so fast that by most measures they are the majority or soon to be majority of live active full satellites (I'm not counting fragments and debris, though both are important).
The Starlink orbit (soon there will be more than one, but for the time being not) is quite low. Formally LEO and not VLEO, but still the atmospheric drag is so much that they carry a very considerable fuel supply (for ion thrusters--originally krypton and transitioning to argon {the more efficient Xenon was ruled out from the beginning as too scarce and too expensive}). Mostly this fuel supply is station keeping fuel, as the orbit is low enough that drag would put them out of place in short order. Some is avoidance fuel (the topic of this thread) and some is in fact intended for active deorbit, which SpaceX has done many dozens of times.
Again because the orbit is so low and the shape quite draggy (high surface to volume in particular) the Starlinks fall down on their own in far less than "many years". I've seen references to few months up to a year or so--the drag at their altitude is not at all constant, with solar events in particular moving it around.
Satellites another couple of hundred kilometers up are still considered to be in a rather low orbit, but have drastically longer decay times, and present a much higher risk of long-term hazard.
I stand ready for correction if I got some of this wrong.
not really anything to correct. different orbits have different situations. and different satellites have different capabilities. context matters. drag gets exponetially worse the lower you are. no arguing that.
my satellites are at ~705km, and are huge (schoolbus size, ~5000kg), use 5lb hydrazine thrusters with tank pressure less than 1/3 what it was at launch 25 years ago. current plan is for "perigee lowering maneuvers" in 2026-2027ish to deplete the rest of our fuel in retrograde, which will only push us down another few km. it'll have to drift the rest of the way, which will take a long time. drag down re-entry predicted for sometime in the 2040s or 2050s
the mission in the article (TIMED) is medium (~660kg) was launched to at 650km without maneuvering capability. currently at around 600km best i can tell from a quick search.
Starlink is at 550km, also medium (260kg) (800kg), probably more overall delta-V available at EOM to de-orbit. from what i remember, they have the Ion thrusters and can leave their thrusters on for months on end at a very low thrust, which compounds over such a long time.
mikey wrote:Hmm I thought
)
the version 1 satellites which constitute the majority of the current constellation are just a touch under 600 pounds and before you unfurl the solar panel are roughly the size of a refrigerator. The major revision currently being launched is over twice the weight (but has much more than twice the capability).
archae86 wrote: mikey
)
WOW they are BIG!!
This is exactly the field I
)
This is exactly the field I work in now. These kinds of near misses happen very often, I have actionable events like this at least once a month (our satellites are maneuverable). I can't really say if this event was exceptionally high risk or not, without knowing the covariances and resulting Pc involved.
We've had events with calculated misses less than 10m. but the miss alone isn't all of the story. you have to look at the error bars (covariance) for both the primary and secondary object, hard body radius (HBR) of both objects, and some other metrics to determine how much of a risk this really is. a miss is a miss. if you don't hit it, you're fine, even if it's by 1ft. if the error is huge, then the probability of collision (Pc) goes down a lot due to uncertainty, if the error is very small (less than the miss), then the Pc also goes down a lot because you are more certain that you will actually miss, so it's a delicate balance of all these factors.
Re: de-orbiting. most missions do not have enough fuel to fully de-orbit in the way many might be thinking of, ie, burning until you hit re-entry and burn up in the atmosphere. I believe there is a rule for newer LEO missions that they need to re-enter in 25 (or is it 50?) years. most missions will only reserve enough fuel to get themselves out of their constellation and away from (below) other active missions and left to naturally decay from drag the rest of the way over many years.
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Ian&Steve C. wrote: This is
)
I'll add a few Starlink specific comments to this overview. Notice that the comments mention "most missions" as distinct from "most satellites". The Starlink constellation is so big and growing so fast that by most measures they are the majority or soon to be majority of live active full satellites (I'm not counting fragments and debris, though both are important).
The Starlink orbit (soon there will be more than one, but for the time being not) is quite low. Formally LEO and not VLEO, but still the atmospheric drag is so much that they carry a very considerable fuel supply (for ion thrusters--originally krypton and transitioning to argon {the more efficient Xenon was ruled out from the beginning as too scarce and too expensive}). Mostly this fuel supply is station keeping fuel, as the orbit is low enough that drag would put them out of place in short order. Some is avoidance fuel (the topic of this thread) and some is in fact intended for active deorbit, which SpaceX has done many dozens of times.
Again because the orbit is so low and the shape quite draggy (high surface to volume in particular) the Starlinks fall down on their own in far less than "many years". I've seen references to few months up to a year or so--the drag at their altitude is not at all constant, with solar events in particular moving it around.
Satellites another couple of hundred kilometers up are still considered to be in a rather low orbit, but have drastically longer decay times, and present a much higher risk of long-term hazard.
I stand ready for correction if I got some of this wrong.
not really anything to
)
not really anything to correct. different orbits have different situations. and different satellites have different capabilities. context matters. drag gets exponetially worse the lower you are. no arguing that.
my satellites are at ~705km, and are huge (schoolbus size, ~5000kg), use 5lb hydrazine thrusters with tank pressure less than 1/3 what it was at launch 25 years ago. current plan is for "perigee lowering maneuvers" in 2026-2027ish to deplete the rest of our fuel in retrograde, which will only push us down another few km. it'll have to drift the rest of the way, which will take a long time. drag down re-entry predicted for sometime in the 2040s or 2050s
the mission in the article (TIMED) is medium (~660kg) was launched to at 650km without maneuvering capability. currently at around 600km best i can tell from a quick search.
Starlink is at 550km, also medium
(260kg)(800kg), probably more overall delta-V available at EOM to de-orbit. from what i remember, they have the Ion thrusters and can leave their thrusters on for months on end at a very low thrust, which compounds over such a long time.(strikethrough note, sorry grabbed the v1 size)
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