* Posts by Daniel 18

156 posts • joined 1 Apr 2011

Page:

Uncle Sam tells F-35B allies they'll have to fly the things a lot more if they want to help out around South China Sea

Daniel 18

Re: F16 vs F-35

Remember, no catapults... definitely no F-18, probably no Rafale.

SpaceX flings another 60 Starlink satellites into orbit in firm's heaviest payload to date

Daniel 18

Re: Think

1. Two hundred metres is not a sufficient separation given the various factors that can change an orbit.

2, 2.5 x 10^8 km^2 is big... but satellites are very very fast, so they get a lot of chances to collide with a lot of things. At the same time, the estimates for orbital debris as of 2013 were 21,000 objects 10 cm or more in size, 500,000 objects from 1 to 10 cm, and millions of pieces smaller than 1 cm. Only the first category can be tracked.

Most of this stuff is effectively invisible, It is also moving at 7 km/sec which is about 8 times the speed of a full power hunting round from a rifle. Thus, it carries 64 times the kinetic energy of such a bullet at the same mass. An impact from the rear cone will reduce the effective energy, while an impact from the front cone will increase it. I'm thinking that a collision at right angles will likely produce 1.4 x 64 times the energy of similar mass at rifle bullet speeds.

Some of those collisions will create debris that sticks around for a while...

Daniel 18

Re: 59 out of 60

"terrestrial astronomy is only a good option because of the lack of orbiting telescopes. If there were a dozen Hubble's"

Not any more. Orbital telescopes are now obsolete except for niche uses.

Thirty Metre Telescope:

"This system will produce diffraction-limited images over a 30-arc-second diameter field-of-view, which means that the core of the point spread function will have a size of 0.015 arc-second at a wavelength of 2.2 micrometers, almost ten times better than the Hubble Space Telescope"

(somewhat over one billion USD)

Giant Magellan Telescope:

"The telescope is expected to have a resolving power 10 times greater than the Hubble Space Telescope"

(about one billion USD)

(European) Extremely Large Telescope (name shortened a while ago):

"It has around 256 times the light gathering area of the Hubble Space Telescope and, according to the ELT's specifications, would provide images 16 times sharper than those from Hubble"

(a bit over one billion euros)

James Webb Space Telescope:

Originally supposed to launch in 2007 costing half a billion USD.

Now estimated to cost 9.66 billion if it launches in 2021.

Add in the ability to repair and upgrade the ground based telescopes leading to a much longer useful life.

If you don't really really need to be in space because of atmospheric absorption of some frequencies or a need to watch something 24 hours a day from one telescope,it is clear that you can build much better telescopes for a lot less money here on earth.

"(ditto the James Webb Telescope, but it's not an orbital instrument)"

Well, it is not orbiting the earth much, but it is orbiting the sun, at a distance chosen to keep it in the earth's shadow. It is orbiting the earth in that its path is changed by earth's gravity, which is why it can have the same orbital period as the earth while being farther from the sun. Thus it does go around the earth once a year.

The mod firing squad: Stack Exchange embroiled in 'he said, she said, they said' row

Daniel 18

"Just another case of SO being a members-only party"

I have to ask.... what is SO?

The top three attributes for getting injured on e-scooters? Having no helmet, being drunk or drugged, oddly enough

Daniel 18

"Cycling is a fast means of transportation"

Not really.

Going to work in morning traffic I average about 60 kph over the whole trip, with peak speeds of about 100 kph.

Going home after the worst traffic, it's 90 kph average, resulting in a trip time of less than half an hour.

I wouldn't want to try to do that on a bike.

Today's Resident Evil: Ransomware crooks think local, not global, prey on schools, towns, libraries, courts, cities...

Daniel 18

Even if you pay for an encryption key, how much time and effort is needed to make sure the entire IT operation has been cleaned of malware and updated/protected enough to make a simple repeat attack likely to fail?

It might be less expensive to toss out the hard drives, rebuild the systems with clean software, and restore from backups.

Android PDF app with just 100m downloads caught sneaking malware into mobes

Daniel 18

Re: "The Register has reached out to CamScanner's developer"

"Verbing weirds language"

Thank you, Calvin and Hobbes.

https://www.gocomics.com/calvinandhobbes/1993/01/25

British Prime Minister Boris Johnson moves to shut Parliament

Daniel 18

Re: I'm a leaver

Labour was selling unicorns too, only they were pink unicorns, and therefore better.

Also, Corbyn had no interest in stopping Brexit or having it go well. What he wanted was chaos he could blame on the Tories, and an election, hoping to become prime minister.

Daniel 18

As I understand it, he Queen is not allowed to withhold consent, barring something much more extreme.

To intervene in that manner would cause an immediate constitutional crisis.

If Boris were to order the military to nuke Europe, she could remove him from office, but that is the sort of thing that would be considered sufficient for breaking constitutional norms.

Electric cars can't cut UK carbon emissions while only the wealthy can afford to own one

Daniel 18

Re: Price equivalency

"and material prices collapse"

Of course, building hundreds of millions of EVs may push materials prices up a little.

Daniel 18

Re: A bit out of date?

"Cost of replacing an ICE engine, vs a battery pack or EV motor? Hmmm... Hmmmm."

In fifty years of driving IC vehicles, mostly second hand, typically 40,000 km/year, and keeping them an average of about 8 years, I have *never* had to replace an engine.

I could relegate my current car to longer trips only, and buy a Tesla S, but that would cost me about $40,000 more than I paid for my current vehicle, before looking into the insurance implications. I am sure my insurance would climb substantially, perhaps enough to pay for half my gasoline from that factor alone.

And $40,000 buys a lot of maintenance and fuel, particularly if you invest it. One might find that at the end of the reasonable ownership period for the Tesla you would still be $30,000 ahead of the game, enough to buy a reasonable IC vehicle new, and still have more than $10,000 left over.

Police costs for Gatwick drone fiasco double to nearly £900k – and still no one's been charged

Daniel 18

Re: Not just people with smartphones.

"Last time I went on a viewing roof at an airport the plane spotters had cameras that could have read the papers on the moon,"

I know I'd be out there with a 200 - 1000 mm lense....

Psst. Hey. Hey you. We have to whisper this in case the cool kidz hear, but... it's OK to pull your data back from the cloud

Daniel 18

Re: I smell a rat

Interesting.

I once had a chat with archivists from a government archive, and the only magnetic or optical media they considered 'archival', with a projected useful life of at least 50 years, was a specific type of magnetic tape.

This was a while ago, and I haven't seen that product in years.

Between bit rot and the death of compatible systems, we may leave less recorded history than the Victorian era.

Before we lose our minds over sentient AI, what about self-driving cars that can't detect kids crossing the road?

Daniel 18

"All of this re-inforces my opinion that autonomous vehicles have no place on the highway and should only be used on Special Roads, where traffic is restricted, regulated, controlled, streamed, with unexpected happenings minimised*. The problem is that most of the development research on auto-vecs is in the US where they don't have the legal concept of Special Roads, so they are being bogged down with trying to cope with being on the public highway."

This looks more like confirmation bias than logic to me.

Expecting autonomous vehicles to be perfect before letting them out on the road is like expecting doctors to be perfect before allowing medical practices.

You let the autonomous vehicles out when they are as good as a good human driver, across the usual mix of circumstances. Given that all drivers are not good drivers, this is a net safety win.

And yes, children are smaller and therefore harder to see. That's reality biting back.

Oh... and I am pretty sure that most countries don't have a lot of 'Special Roads', whatever those are. I've never heard of them. And no, I am not American.

Less than half of paying ransomware targets get their files back

Daniel 18

Re: Backups ...

"if they were running tapes on a 3 month basis then it should have been obvious that at the end of the 3 month cycle it was time for a new full backup"

More likely, it would be time for a full backup once a month, and those should be archived, every other one off site, and not re-used.

Office 365 user security practices are woeful, yet it's still 'Microsoft's fault' when an org is breached

Daniel 18

Spectre and friends? Sandbox escapes? Hypervisor escapes? Compromised hypervisor? Compromised physical server?

If anyone else has ever run on the physical box, you can no longer trust it.

Therefore, the safer cloud is private cloud.

Public cloud is for encrypted tertiary backups, and public facing read everything web sites.

Turn me up some: Smart speaker outfit Sonos blasted in complaint to UK privacy watchdog

Daniel 18

Re: (they don't last forever)

Surely if you have a macbook you can open an xwindows session between the pi and an X server on the mac, and use its screen, mouse, and keyboard?

SPOILER alert, literally: Intel CPUs afflicted with simple data-spewing spec-exec vulnerability

Daniel 18

Re: I am always disappointed in modern computing

"How the hell the modern world decided on the worst possible bollocks for the majority of modern computing is dumbfounding."

Not at all.

You can't always design to avoid a weakness that hasn't been thought of yet.

Indeed, the weakness only exists because a lot of smart people are looking for them in architectures as now implemented. If architectures were different, they would be finding different flaws.

At one time 'speculative execution' was one of the best practices for CPU design. Any design without it was either special purpose or a dud, from a cost/performance viewpoint.

The only way to avoid this in the future is:

1. Don't use good ideas other people come up with.

2. Design absolutely perfect products that are flawless under in any possible circumstances.

The first is silly and counterproductive.

The second requires God-like powers of intelligence and prediction.

Neither one is a good strategy for improving computers.

Three-quarters of crucial border IT systems at risk of failure? Bah, it's not like Brexit is *looks at watch* err... next month

Daniel 18

Re: Cheer up, what's the worst that could happen?

"If we hit leave with no deal, there is no backstop."

Only chaos.

YouTube's pedo problem is so bad, it just switched off comments on millions of vids of small kids to stem the tide of vileness

Daniel 18

Re: theregister.co.uk

"Why not use the entirely correct term "ephobophile" instead of the incorrect pedo- or paedo- forms?"

Because 98% of the people reading the article would not know what it meant.

I didn't, and the last time my language skills were checked they came in at 99.5 (percentile, at the limit of resolution of the test).

UK.gov tells companies to draft contracts for data flows just in case they screw up Brexit

Daniel 18

Re: A chocolate teapot that ignores the law

............EU businesses can simply refuse to exchange personal data with us after March 2019 unless this problem is fixed prior to Brexit............

The way I'm reading this, does it not mean that they have no choice but to refuse such data transfers, under EU law?

The glorious Brexit uncertainty: The only dead cert on data rules for tech biz in 2019

Daniel 18

Re: My prediction is...

"(we are subordinate to the US but that is to a large extent inevitable and apparently does not matter)"

Clearly.

But not nearly as subordinate as you will become if you leave the EU.

With ZERO input into decisions.

Boeing 737 pilots battled confused safety system that plunged aircraft to their deaths – black box

Daniel 18

Re: Hey software, get the fuck out of the way!

"The worst part was that the Airbus also silenced the stall warning when the AoA was out of range high - this caused the co-pilot to pull back on the stick whenever the nose came down, because that shut off the stall warning that would return when the AoA came back within range."

More irony here. The system was designed to avoid information overload by muting bad or irrelevant data - and the pilot was misinterpreting that.

Holy moley! The amp, kelvin and kilogram will never be the same again

Daniel 18

Re: SI

Just go on UTC for the planet and have done.

No more time zones, no more changes, just set your working hours when it makes sense in your location for your business.

Light and dark will happen the same regardless. and there is no real advantage to changing time to accommodate that, particularly in a connected world with ample electric lighting.

If the local light patterns make something reasonable, then do it - just don't mess with the clocks, change your times for events.

Tick-tock, tick-tock. Oh, that's just the sound of compromised logins waiting to ruin your day

Daniel 18

'Sticky' Fundamental Misconception

" and because it's so simple to put tools such as face recognition or fingerprint scanners on our devices – why not use it internally too?"

A lot of people think that biometrics can be used for authentication, but they are not really secure.

At best, they are an alternate form of user name, not an adjunct to passwords.

Revoking your face, fingerprints, or iris pattern is likely to be difficult and painful.

UK.gov finally adds Galileo and Copernicus to the Brexit divorce bill

Daniel 18

Re: Remind me...

"Cake? I'm sure I heard something about everybody getting to have their cake and eat it."

A sneaky ploy that will only work on people who have never played Portal.

Who knew games could be so educational?

Daniel 18

Re: The punishment beating will continue

"Having unicorns seems like such an awesome idea until you find yourself spending all your time cleaning unicorn sh!t off the carpet."

Oddly, I've never wanted unicorns.

Maybe that's why I found the version of unicorns in Glen Cook's "Sweet Silver Blues" so satisfying.

Phased out: IT architect plugs hole in clean-freak admin's wiring design

Daniel 18

Re: Bridge rectifier?

"This rectification was invariably done with a massive selenium rectifier about 8 inches long."

This sounds like some kind of transitional technology to me. What year were these built, roughly?

I remember taking apart old TVs - no solid state rectifier though, that part was done with a vacuum tube, and the right tube gave you a full wave rectifier.

Daniel 18

Re: Plot twist? What plot twist?

Indeed.

If single phase power is 120V, three phase will come in at 208V.

Instead, homes usually have a centre tapped feed, giving a choice of 120V or 240V single phase. The latter is used for things like clothes dryers, water heaters, central air conditioning, and stoves.

Other things - stuff plugged into wall sockets, furnace motors, lights, sump pumps, garage doors, etc. are generally 120V.

As a result connection is simpler and more compact than 240V, with no need for things like fuses in appliance plugs and the option of designing for a two prong plug.

Also, it seems like 120V doesn't bite as hard as 240 - the few times I've had undue excitement with 120V, it wasn't too bad, but rather startling.

The 208V stuff shows up in some moderately heavier commercial and industrial installations like store refrigeration systems, large AC units, I susect for elevators, some computer gear, and so on.

The 'big stuff' may use higher voltages like 400, 600, or 800V... steel mills, motors moving 1100 tonne bridges, lock gates, subways, and the like generally go for higher voltages.

(And while it may be a bit odd, if you put me in the motor room of a big lift bridge, I will actually go over and read the specification label on the motors...)

As for frequencies, originally it was 110V at 25 Hz, but back somewhere around the 1930s, they decided that was inefficient and changed to 60 Hz - much better for transformers.

When I was a kid, antique radio gear sometimes showed up with 25Hz transformers, which were way bigger and could be used at much higher loads on the newer 60 Hz current.

Rights groups challenge UK cops over refusal to hand over info on IMSI catchers

Daniel 18

Re: Three?

I suspect it will connect to another network's tower, in order to provide SIM free access to emergency numbers.

It just won't make ordinary connections for you.

FBI boss: We went to the Moon, so why can't we have crypto backdoors? – and more this week

Daniel 18

Re: Man on the sun

I suspect that most people who could understand the math around the halting problem could understand the math about crypto back doors.

It did take a year or two of university math to prepare to prove the relevant theorems. How many government funtionaries or politicians will have that? (which hints at a wider and deeper problem)

Official: AMD now stands for All the Money, Dudes!

Daniel 18

It all depends on what you are trying to do....

Nvidia does not provide adequate support and documentation for open source drivers, which means you are stuck with either slower drivers or whatever limitations the proprietary drivers carry, such as poor or no support for switchable graphics, and incompatibility with Wayland, which will likely replace X as the basis of windowing.

AMD provides the information before release of the GPUs, so open source drivers are about as good as proprietary drivers, Wayland works, and switchable graphics support is much better.

I have been quite irked by the complications of trying to get graphics on an Intel/Nvidia laptop do the things it should - particularly in driving multiple GPUs, Intel drivers also seem to fail to remove themselves properly when an un-install is triggered. Very messy.

I look forward to getting an AMD APU laptop, which will probably clear up a lot of issues.

I suppose I could get easier graphics by running the spyware that is Windows 10, but that's not really acceptable. Currently the only major operating systems for small (non mini/mainframe) devices that looks reasonably secure is a well chosen and configured Linux or BSD. Windows, MacOS, iOS, Android and Chromebook all look or have been proven inadequate.

Sysadmin sank IBM mainframe by going one VM too deep

Daniel 18

"I once heard someone refer to an exclamation mark as pling, which confused me somewhat!"

That's a new one.

I've mostly heard it referred to as 'bang' or 'shriek', depending on context / language.

Dear Samsung mobe owners: It may leak your private pics to randoms

Daniel 18

Re: Or you're worried about the bill?

"In Australia (not a country known for being a telecomms value leader) my $10 plan includes unlimited MMS to other Australian numbers."

Lucky you. My plan includes 150 SMS messages (out) a month, 100 prime time minutes, free nights and weekends, no data, for only $30 but I had to threaten to drop the carrier to get a special plan.

Galileo, here we go again. My my, the Brits are gonna miss EU

Daniel 18

Re: Fgs

"The Commonwealth already has one (IRNSS). Perhaps we could ask them nicely?"

The Commonwealth doesn't have one, India has one.

If you ask nicely and permit increased immigration they might let you join in... but it is a regional system with coverage of the area containing targets for their nuclear missiles.

I'm pretty sure the UK is farther away, and likely wants coverage for different target areas.

No fandango for you: EU boots UK off Galileo satellite project

Daniel 18

Re: Dictionary anyone?

"So the elected representative of any given area doesn't have to actually represent the will of the voters who elected him/her? And actual representation of the voters is bollocks? Wow! No wonder British people are totally disillusioned with their politicians if they only represent their own personal views."

------------------------------------------------------------------------------------------------------------

Like most words in English 'representative' has multiple definitions:

-------------------

Definition of representative: (Mirriam-Webster; other dictionaries similar or identical)

1 : serving to represent

2 a : standing or acting for another especially through delegated authority

b : of, based on, or constituting a government in which the many are represented by persons chosen from among them usually by election

3 : serving as a typical or characteristic example - eg - a representative moviegoer

------------------

You are using definition 3, in a somewhat inappropriate context, unless you assume the population in a given voting district is sufficiently homogeneous that a single person could be typical of them all.

In discussions of political systems, the normal definition is 2a - a person is given authority make decisions and act on behalf of the largest group of voters (somehow defined, or some other selection group).

In any first past the post system with more than two significant parties, elected representatives almost invariably receive fewer than half the votes - they are elected by a plurality*, not a majority. None the less, they are expected to represent the interests of everyone in their riding. Different groups in the riding may disagree on how to do that, but most people want broad benefits for everyone, not 'privilege me and be damned with everyone else'.

There are a number of reasons for representative rather than direct democracy, including the practical difficulties of the latter, delay, costs, the difficulty of meaningful discussions in groups the size of the whole electorate, and lack of expertise, time, and support resources for analysis on the part of the general population.

We want our government to represent us (definition 2a), not to be representative of us (definition 3).

We expect our professional representatives (politicians) to have above median skills, knowledge, contacts, time, research material, and focus on issues. We want them to be better than one random person plucked off the street and put in charge. That's why we elect them, why we have policies and platforms, why we go to or read transcripts of candidate' debates.

Making them robotic parrots of an 'opinion' expressed by a minority of the population and supposedly completely encompassed by a one time decision based on a few words of variable honesty, clarity, and meaning and answered in a binary manner will, more often than not, fail to serve the interests of the population as a whole.

Real life questions and even more, their answers, are longer and more complicated than can be answered by a 'yes' or 'no' to a brief sentence.

===================================================

* This is not necessarily bad.

While first past the post is not perfect, neither is any other voting system. Indeed, in political environments with more than two significant parties, proportional systems are usually less democratic.

The math is complex, and I can't reproduce the calculations and explanation from memory, but studies of voting in multiparty parliaments show that proportional systems tend to transfer power and control from the two largest parties to smaller, less broadly supported parties.

Consider, for example, the disproportionate per MP influence wielded by the DUP.

In most proportional systems with more than two parties, no party has a majority, pretty much forever.

I see a satellite of a man ... Galileo, Galileo, Galileo, Galileo, that's now 4 sats fit to go

Daniel 18

Re: Receiving the signal

"For now, all the separate systems require a separate receiver, so you need to check which ones they can actually use. GLONASS support is fairly common in addition to GPS, and Galileo isn't too unusual, so it's quite possible a current phone will work them all. Beidou and NAVIC are currently only regional, so you're unlikely to find support for them in phones not sold in the relevant regions."

Actually, if you look at the specifications for the available smartphones, most of the new ones have support for A-GPS, GLONASS and often BDS (see phonearena or gsmarena for specs on many phones). A few phones can receive Galileo, but it seems to be fairly uncommon.

I have some hopes that Galileo may be added to that list, but currently chipsets and integrated tri-band antennas for the three bands used by the A-GPS, GLONASS and BDS GNSS systems are widely available.

Given that there are a billion or more people in China buying smartphones, and most of the phones are built there, I expect that those three will remain the 'standard' set. It is possible that the Chinese government may even quietly encourage all phone manufacturers to include BDS.

BeiDou-3 currently has 9 satellites up, with 35 planned by 2020, giving global coverage. India's NAVIC and the Japanese QZSS are regional and likely will be ignored by most chipsets and most phones sold outside those regions.

If Galileo has sufficient advantages or can be added at insignificant cost it will likely become the fourth 'customary' GNSS in most devices.

A hypothetical British GNSS would probably come in after the other minor systems, given relative populations and sizes of economy... in other words, unless it can be handled by a receiver designed for one of the three or maybe four major systems, it will be a regional specialty item in phones and GNSS receivers.

'Incomprehensible failure' – Canada's $1bn Phoenix payroll IT fiasco torched by auditors

Daniel 18

The history of computing/IT is largely the history of failed 'magic bullets' which were going to make everything easy, solve all the problems, slash costs and delays, and often, eliminate programmers, analysts, IT professionals, etc.

Some highlights from the list include COBOL, subroutine libraries, time sharing, spreadsheets, relational databases (no need for IT pros getting between end users and their data if you have one of those!), remote computing, GUIs, structured programming languages, gotoless programming, object oriented languages, the cloud, microservices, agile, devops....

In many cases these fads are driven by a blind faith that a particular technique will solve all the major problems, or a desire to fix irritants that are the result of a solution to a previous problem... which often returns when the new magic bullet sweeps away the technique or practice that eliminated the older problem.

Often these ideas are 'validated' by anecdotal results achieved by the people who designed and built the new tools or techniques.

Curiously, random user populations with diverse skills and requirements often under-perform when compared with the developers or researchers using the tools they designed to solve the problems they are working on.

Daniel 18

Re: Let's just skip that step

"In the automotive assembly plant world, this would be going with production tooling and skipping prototype tooling."

Or going to production on F35s before making them actually work...

Is this one of those universally applicable errors?

Daniel 18

Re: Ouch

Am I the only one to suspect that a 6,000 page specification is too long to be a useful specification document?

Would anyone read, comprehend, and remember the whole thing? Would any group of people doing 'specification level' analysis be able to discuss it adequately in a week?

A detailed design document, possibly, but even that seems overly complicated for a payroll system, even one that can do retroactive payments.

Microsoft, Google: We've found a fourth data-leaking Meltdown-Spectre CPU hole

Daniel 18

Re: Its quite depressing really

"Federico Faggin designed the Z80 in 1974. It was, I'd bet, the last non-risc CPU that one person could get their head round. Since then people have designed bits of CPUs but how the hole thing works, along with the non too simple problem of the operating system running on it, is beyond one persons ability to fully understand."

Off hand I don't know the exact date or chip generation, but it's been decades since CPUs were designed directly by humans, rather than by human guided design tools. That has to translate to a lessened understanding of what is going on 'under the hood' in detail... not that humans could do all the circuit analysis the tools do, even in a lifetime, for a chip with tens or hundreds of billions of transistors, data paths, etc.

Daniel 18

Re: Its quite depressing really

"Maybe the engineers that design the CPUs think the same. They just want to design the fastest chip possible and not have to think about the security of it."

In part, it's a matter of metrics. Engineers are not particularly rewarded for producing theoretically secure chips, they are rewarded for producing faster chips on time for the sales types to hype them as faster than the competition.

In part, it's because a few engineers have months or years to design incredibly complicated chips, many many attackers, some lavishly supported by nation states, some by criminal organizations, some in a quiet basement somewhere have decades to find the small flaws that can be exploited.

Wanted that Windows 10 update but have an Intel SSD? Computer says no

Daniel 18

"Even then, I only run Windows in a NAS VM for the one application which the developer insists on using .NET. Everything else is either macOS or Linux."

Seems to me the last time I loaded something that wanted .net into WINE, it sent me away to download a .net package from the distribution repository... If you don't need a full VM, WINE may let you run it under Linux/WINE.

Blighty: If EU won't let us play at Galileo, we're going home and taking encryption tech with us

Daniel 18

Inherent limitations of LEO GNSS systems

"The attraction of doing a LEO GNSS constellation is that life for satellites and payloads at that altitude is relatively easy. It's below the Van Allen belts (low radiation), the orbit is only 90 minutes (easier thermal management), you still get a decent UV flux to make solar panels work well. Orbital decay is an issue, but that's not so bad really."

***

I have a suspicion that the accuracy issue might be a bit of a problem, particularly since you will need a lot more satellites due to horizon issues, if they are in a low orbit.

Suppose that you have 500 satellites in LEO rather than 25 in MEO.

Position is determined relative to the known location of each satellite according to the downloaded ephemeris.

Now the fun interactions begin.

Each satellite needs a highly accurate clock, which is not cheap, and probably bigger than a cubesat, all by itself.

Changes in orbit due to drag are not easily predicted - remember the problem deciding where the defunct Chinese space lab would come down, even just a day or two ahead? Drag varies with a number of factors, not all predictable. This causes errors in satellite locations, which causes errors in inferred position, and thus location, altitude, and speed. As a result the ephemeris must be recalculated and redistributed much more often, to avoid inaccuracy, and random inferred position changes as the set of satellites above the local horizon changes. In any case, satellite position accuracy will degrade much more rapidly than with MEO satellites, and the degradation is probably more rapid for smaller satellites (consider the square/cube law).

Any attempts at drag mitigation will add complexity, size, weight, and/or cost... and may introduce other sources of variation, particularly if mitigation success is variable.

The fun continues. Because there are 20, or 30, or 40 times as many satellites, the ephemeris is that many times larger, and takes longer to download. Cold start times for a GNSS receiver go up by a roughly similar factor. Warm start times go up, and warm start accuracy and validity - time in which a warm start is an option - decay faster.

All the satellites need to have the same ephemeris, because cold start times, and probably refresh times will exceed the time the same satellites are visible, or there has to be added complexity to handle an ephemeris where the data differs in recency and accuracy. This will also impact accuracy, and require more resources in both satellites and receivers, not to mention tracking and satellite updating.

This is more complicated, not only because of the size of data, but also because the satellites won't be visible to any one ground station for an extended period, so either upload speeds need to be faster, you need a lot of ground stations (or some unlucky LEO satellites will have stale data, because of a dearth of visible ground stations from their particular orbit for a random interval), or the update has to be relayed by satellites farther out that can see many LEO satellites for an extended period. Without the relay satellites you will probably need to implement rolling ephemeris updates, to get the data up in catch as catch can fragments.

How to manage that and the activation / use of the new data is an interesting exercise that will take more time to analyze than I have available now (and probably more knowledge and a system design to set the parameters).

I am not sure that an LEO constellation can deliver the consistent accuracy of a MEO constellation, and if it can, will probably require a lot more effort, complexity and cost in both hardware and software as well as operation. If some of this complexity lives in the receiver, the cost of that component may well go up.

The higher drag of LEO, particularly the effect on small satellites with a higher cross-section to mass ratio, may necessitate continuous replacement launches as the small packages re-enter. Increasing drag during orbital decay may also compromise positional accuracy for satellites that have not yet re-entered the atmosphere. Avoiding decay through active (thrusters or the like) or semi-active (drag minimizing attitude control, etc.) will add to size, weight, complexity, and cost while forcing another set of technical trade-offs onto the project while probably introducing resource dependent lifespan limits.

Any increases in receiver cost, or power draw, or greater accuracy limitations will make such a constellation a much less likely candidate for inclusion in any navigation system / receiver chipset when there are already several other GNSS systems that can deliver good quality service.

Page:

SUBSCRIBE TO OUR WEEKLY TECH NEWSLETTER

Biting the hand that feeds IT © 1998–2020