Just like in I guess a large portion of human history after farming started. You abandoned the fields and retreated to the walled hilltop when the enemy came. Maybe that's what we have been genetically conditioned to expect and that's why we have these zombie films and series.
Not really. You're correct inasmuch as it increases collision energies. But it also increases momentum, which maintains orbital integrity within predictable bounds. Nobody is maneuvering around satellites, they–and their debris–stay where the math tells them to.
Thought experiment: Let's say you are simulating ten thousand satellites on your computer, and the simulation runs until there is a crash. Now let's say the simulation runs for an hour normally. If you increase the speed of the simulation, you get to a crash in a shorter time. Satellites move about 30x the speed of airliners. Hence, if everything else was similar, one would expect 30x the amount of collisions.
> Satellites move about 30x the speed of airliners. Hence, if everything else was similar, one would expect 30x the amount of collisions
Not how orbital mechanics work.
Planes maneuvers, get tossed around and have hubs they circle. A plane under my left wing can’t be relied on to continue in a straight line. The satellite can.
> your comment that speed is not a factor was incorrect
It would be if I had said this.
Speed doesn’t matter “a lot”. (Orbits around a small object get crowded quicker. The speeds are less. But the volumes are way less. Volume absolutely dominates speed when it comes to orbital cross sections.)
Orbits are predictable, but they intersect and decay [at different rates] and occasionally get perturbed by space weather. This already needs periodic conjunction avoidance manoeuvres, and whilst orbits are fast satellite manoeuvres are slow, so the notice you need to avoid a conjunction is measured in hours rather than seconds. Can't imagine a scenario in which it would be sustainable for LEO to even approach the density of commercial aviation, except perhaps for a hypothetical where a single entity actually managed all the satellites.
The other underestimated dimension is that satellite manoeuvres use up a finite supply of expensively-launched propellant. That's tolerable when Starlink is doing 50k conjunction avoidance manoeuvres in six months across its constellation, but once it becomes each satellite moving at least weekly you either need bigger satellites carrying more propellant or have to accept significantly higher collision risk than they currently do.
> and whilst orbits are fast satellite manoeuvres are slow
This is something people unfamiliar tend to misconceive in their limited thinking on the subject. You can't just tap the breaks to slow down. Changing altitude of satellites is done by speeding up to increase altitude and slowing down to lower altitude. Once you change the velocity and reach the desired altitude, you have to then undo that acceleration to get back to orbital velocity. Fuel is required in both directions. The less fuel used the better for the maneuver. Most satellites EoL is defined by remaining maneuvering fuel vs functionality of the hardware.
My first understanding of accelerating in space was from the old Asteroids game. To slow down, you had to rotate 180° and start accelerating in that direction. Others might learn it from Kerbal.
> This is something people unfamiliar tend to misconceive in their limited thinking on the subject
I have a background in astronautical engineering. While you can't tap the brakes to 'slow down', you can impart miniscule amounts of impulse which, over the course of hundreds of orbits, will change your plane by an imperceptible amount from a distance, but tens or hundreds of kilometers up close. OM being OM, you can predicts these collisions in advance.
I had a professor who referred to orbits not in altitude but in expected decay time. We're currently in the months to single-digit years orbits. (We will stay there for telecommunications due to latency.) If we were doing at decades or centuries what we're doing in LEO, this would be a problem. At LEO, it's a nuisance and barely more.
> you can impart miniscule amounts of impulse which, over the course of hundreds of orbits
right. this is what is counter-intuitive for those that are not familiar with space. they don't just light the burner and boost to a new altitude. the part about stopping the acceleration with an opposite burn is often not considered. most think you can fly a space ship like a jet fighter, but in space. can't blame them since that's how sci-fi portrays it. real life space flight is really boring in comparison. jumping out of FTL to land in orbit around a planet makes me laugh every. single. time.
> whilst orbits are fast satellite manoeuvres are slow, so the notice you need to avoid a conjunction is measured in hours rather than seconds
I'm not arguing against collisions becoming more likely. I'm arguing aginst it becoming commonplace to the point that it becomes a commercial concern.
> satellite manoeuvres use up a finite supply of expensively-launched propellant
Nobody is plane changing out of a collision. And for the foreseeable future, in LEO, the birds are not propellant constrained. (And launch is getting cheaper.)
> you either need bigger satellites carrying more propellant or have to accept significantly higher collision risk than they currently do
We're decades away from this being a problem. That gives ample runtime to developing e.g. magnetic station-keeping (if we go reactionless) or more-efficient engines.
> what's the state of solar powered magnetorquers these days?
Academic. We don't currently have a pressing need for reactionless thrust in the magnetosphere. Each of semiconductors, launch vehicles and telecommunications standards are moving faster than satellites last.
> Each of semiconductors, launch vehicles and telecommunications standards are moving faster than satellites last.
That's certainly a pragmatic cost based argument for not using them in the fast moving world of commercial magnetosphere constellations.
> Academic.
I feel they've moved past academic and transitioned to deployed .. at some evolution of implementation. Not commercially relevant is certainly one state of play.
I guess I was more interested in the nonlinear control issue in a field of highly variable intensity.
A bit pedantic here.. I think you might be thinking about space tether propulsion. I don't know if that has been deployed yet. Magnetorquers, as in a device that uses magnets to rotate the satellite are very common in cubesats, you can buy it off the shelf
I first encountered space tethers in 1980 reading an Introduction to Engineering text where the example was given of unrolling a flat spool of thin metal through shaping rollers to extrude a very long boom with a spring on the end to stabilise the orientation of a satellite.
That was one of the first times I noodled about with the dynamics of a pendulum in a potential field.
These days, of course, there's a few more tricks that can be done with a dangling lasso, including interacting with the magnetic field via a looped current.
That aside, I was curious about traditional magnetorquers and their variations actively providing force in the magnetosphere.
The Earths magnetic field has a lot of diurnal pulsing .. the gravitational field is lumpy but stable.
There's a control challenge in getting a smooth desired response from a choppy field.
Cheer's for the lookout though, it hadn't occurred to me that some would be talking about magnetic force against the field using "space tether" as the base description - my background was more about the field equations than the physical implementation.
( Magnetorquers are also used in the US Navy for twisting controls inside a fully sealed container. )
> I'm not arguing against collisions becoming more likely. I'm arguing against it becoming commonplace to the point that it becomes a commercial concern.
Minimising collision risk already is a commercial concern, and the number of conjunction avoidance manoeuvres SpaceX takes in order to achieve this has been growing exponentially (which presumably is a major factor driving their move of 4k satellites to a lower orbit which involves more station keeping) Obviously this gets harder when most of the satellites avoiding their orbits coming too close don't have the same owner, particularly if some of the other megaconstellations aren't even particularly cooperative (hi China!)
> Nobody is plane changing out of a collision. And for the foreseeable future, in LEO, the birds are not propellant constrained. (And launch is getting cheaper.)
No which is why I mentioned the fact that constellations pre-emptively plane change to avoid conjunctions. The frequency with which they have to do this scales superlinearly with the number of satellites operating in or intersecting the orbital plane. Ultimately propellant use for those manoeuvres and station keeping defines the satellite lifetime: agree it's not a huge problem when a satellite is only making small orbital changes a handful of times a year and its got a decent sized delta-v budget for station keeping and EoL deorbiting anyway, but another 70k satellites in the same plane would require quite a lot more adjustments, never mind them operating at aircraft density as proposed earlier.
> We're decades away from this being a problem. That gives ample runtime to developing e.g. magnetic station-keeping (if we go reactionless) or more-efficient engines.
Depends how fast the satellites get put up there (and also whether orbital megastructures become a reality, although non-trivial numbers of them actually might be decades away). There's some scope to improve propulsive efficiency (hi colleagues!), but within the power/mass constraints of a smallsat, you're not likely to see orders of magnitude more improvement in specific impulse over current gen EP, and we are forecast to need orders of magnitude more avoidance manoeuvres, which is generally going to mean more reaction mass. Sure, if we get reactionless propulsion suited for precise orbital changes in LEO then we can forget all about the tyranny of the rocket equation, but hey, if we perfect flying cars we won't have to think about the implications of congestion on the roads!
Yeah, since there's lots of countries and some are very dynamic and modern, maybe they could act as early adopters. But don't stop there: if it works for the early adopters, others could also apply their lessons. For example Estonia is often mentioned in electronic government etc.
A financialization example: Somehow some company's stock became the go-to for investors that had continuous expectations just for the stock, and not about actual company health. And the company chose to prop up the stock quarter per quarter, instead of investing in long term development, until it crashed.
This is somewhat similar to dangers of gamblification I guess. Where the expectations of the investors (gamblers) start shaping the decisions of the professional management of the company.
I wonder how expensive it would be to get widespread usage of better stoves, heat pumps or co-generation + district heating with centralized gasified burning. Everything could be locally built.
I don't know about electricity prices there either.
Gas for heating is something every European nation should steer clear from, for strategic reasons.
> I wonder how expensive it would be to get widespread usage of better stoves, heat pumps or co-generation + district heating with centralized gasified burning. Everything could be locally built.
Do you want cheap and efficient, or do you want locally built?
Very expensive. If you want to invest, first step would be making inefficient houses efficient, aka insulation. Problem is that, a lot of older housing ventilation is built on it being leaky...
Hmm this comment gives the impression that electric Porsches are bad to drive and are only bought for the badge and convenience, like the SUV:s. I haven't driven a Taycan so can't say but I would assume it's not so. (And also it doesn't look like a convenient car.)
I own a Panamera and my husband owns an M850i. The Panamera drives like a Porsche, while the M850i is comparatively a boat. I'm not a big fan of how much suspension travel the M850i has; the Panamera has exactly the right amount to feel sporty but still comfortable, just like our 718 has.
Also Porsche SUVs regularly rank at the top of luxury SUV reviews. I've never driven one but the consensus is that they're great - it's not just badge engineering.
The Cayenne has no right to be as fast as it is. The stupid thing will powerslide out of corners at 120 kmh and fly at hot hatch speeds through twisty cobblestone roads. The brakes were also wonderful and surprisingly cheap for the size. Didn't have air suspension so it rode like a fast car though.
Car enthusiasts caring about the driving experience doesn't just mean drivability. Engine sound is a huge part of it. All the classic Porsche 911 have flat-6 engines which make a distinctive sound that is totally part of the brand.
FTR I don't care about this myself, I'm happy with my EV. But the importance of this aspect is easily missed by people not part of the target demographic.
It feels like engine sound has become more important to these people since EV's entered the market. I'm sure it was there before but not to the same extent.
The huge uproar about the 718 having a flat four turbo engine was mostly about the sound. (I don’t have a problem with it.) I think it has always been there.
It became more of a selling point as regulation came for it. OPF, stricter modification control, etc. Prior it didn't matter as much since it was always decent and you could do whatever you want to it. Now, a pops and bangs tune with a straight pipe will get your car impounded in most countries the first time a cop sees/hears you.
It's societal. I don't really have a way I can translate it for someone raised in the Western culture.
Counter example:
While westerners would look at 996 with confusion, Chinese would look at Western "intellectual property" constructs with confusion. To them it's not "copying", it's they figured out a better way to do it and the rest is fair game.
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