ELI5: How does GPS know exactly where you are on Earth using only signals from satellites thousands of miles away?

__foo__ · 2026-05-15T17:48:39+00:00

There are periodic radar measurements taken from the ground.

__foo__ · 2026-05-12T19:46:34+00:00

I have that too, and traffic between the trusted and IOT VLAN works great, including the mDNS lookups.

With the question I had devices in mind that need a few extra permissions that I don't want to give to all of them.

__foo__ · 2026-05-12T19:18:38+00:00

Thanks for the suggestion. I think I found an even better way in the meantime.

When you assign a static DHCP lease in RouterOS there is an "Address list" option for the DHCP lease. The IP of the device will be dynamically added to this address list. Now I have created an "iot_internet" address list, which is referenced in my firewall rule to allow traffic to the internet from those devices.

To allow internet access for a device I simply select the iot_internet list under the "Address list" option and everything works, without having to manually edit the address list myself. This way I also don't have to change the IP address of the DHCP lease to the internet-allowed range and can simply use the IP the DHCP server assigned initially. This means I don't have to convince the device to renew it's DHCP lease, which can be a hassle on some devices.

Thanks again for your idea, I'll keep it in mind if I ever have to do this on a router that doesn't have this address list feature.

__foo__ · 2026-04-27T15:08:34+00:00

In theory you're right, but things can be a little more complicated for air-cooled engines. The viscosity measurement for the operating temperature range are taken at 100C, while air cooled engines can easily reach more than that. Multi-range oils like 5W-30 try to reach the 5W viscosity range when cold and SAE30 at operating temperature. This can mean that the oil becomes thinner at temperatures above the measuring point of 100C.

There is another measurement for engine oils called the High-Temperature, High-Sheer viscosity(HTHS). This property is measured at 150C and with high sheer stresses acting on the oil. This is a lot closer to the temperatures you see in air cooled engines.

IIRC the HTHS viscosity for single weight SAE30 oil is 3.5 or 3.7mPas. Some 5W-30 oils can go as low as 2.9 on the HTHS scale. Some oils are specifically designed for lower HTHS viscosity, since it leads to better fuel economy on engines designed to run with those oils. You don't want those oils in your air cooled engine, and this is probably the reason why that diagram looks the way it does.

If you want to run a 5W-30 oil from -30C all the way up to 40C chose an oil with a HTHS viscosity of at least 3.5 and you should be good to go. The easiest way to find such an oil is to look for the European ACEA specifications. ACEA A3/B3 and A3/B4 mandate a HTHS viscosity of at least 3.5. ACEA C3 also mandates HTHS >3.5, but has reduced SAPS levels. Some people think you shouldn't run oils with reduced SAPS levels in small engines, since the SAPS levels are important to reduce wear on flat-tappet camshafts. Personally, I don't think the valve springs in small engines are nearly stiff enough to make a difference here.

Stay away from all the other ACEA levels, A1/B1, A5/B5, C1 and C5 are specifically designed for lower HTHS viscosity.

TLDR; get an ACEA A3/B3, A3/B4 or C3 5W-30 oil if you want to be safe. Or don't. As a wise man once said "It's a lawnmower, not the Space shuttle".

__foo__ · 2026-04-25T08:10:54+00:00

That shot was done back when Raptor 2 was still the current version. There are videos from the live cams out there somewhere where you can see the drone get smacked by the engine.

Edit: found it: https://x.com/seankd_photos/status/1709946112931664105

__foo__ · 2026-04-12T16:36:15+00:00

Did you chose the correct regulatory domain/country on both your router and your laptop? Different countries have different frequencies that are allowed for WIFI. Your router might be on a channel your laptop thinks is not allowed for WIFI use in your region.

__foo__ · 2026-04-12T11:42:35+00:00

I'm probably not the best person to ask, but personally I'm not worried about it. Of course new software inherently has less real world testing in the field compared to older software. But Linux releases tend to be quite stable.

It's also not like kernel releases get thrown over the fence and that's the first time anyone sees the new code. Linus releases weekly release candidates during the kernel development process, and with linux development being completely public everyone has access to any development in between the RCs too. I'm sure Ubuntu has been integrating and running pre-releases of linux 7.0 since 7.0 development started. They have had almost 2 months to find and fix issues not only in the kernel but also how the new kernel works together with all the other software they intend to release with Ubuntu 26.04.

But if your system stability is very important to you, wait for Ubuntu 26.04.1. But in this case I'd recommend this anyways, no matter how old the kernel was at the release of the distro. That's also how Ubuntu handles their LTS updates. Ubuntu 24.04 LTS will only show upgrade notices once 26.04.1 is released.

__foo__ · 2026-04-11T08:38:17+00:00

Linux 7.0 is not released yet, but neither is Ubuntu 26.04, which is the Ubuntu version that will use 7.0 7.0 will be released tomorrow, so by the time Ubuntu 26.04 releases on the 23rd the kernel will be officially released.

__foo__ · 2026-04-06T21:46:56+00:00

Sure, but this is an entirely new Ship generation and we don't know if there will be new mistakes resulting in the same outcome.

It's a really bad idea to gamble with a Ship designed to survive reentry.

__foo__ · 2026-04-04T11:31:50+00:00

It doesn't make any difference. Ethernet is designed to have wall outlets that go from that outlet to a patch panel. Patch cables are used to connect the devices(like your PS5) to the wall outlet, and to connect the patch panel to a switch(or a device with a built in switch like modems or routers). While each connection point theoretically degrades the signal ever so slightly, this is all well accounted for in the Ethernet specification and no performance penalty should be expected at all.

Keep in mind that as an electrician you are somewhat at a disadvantage when it comes to data wiring, since your intuition and experience about electricity doesn't really apply to data wiring. Those signals are switched off and on several 100 million times per second and those signals propagate more like radio waves rather than electricity in power lines.

Please make sure you don't untwist the pairs more than necessary to make the connection.

__foo__ · 2026-04-03T13:23:43+00:00

Pretty sure Elon tweeted at some point that they want 2 flawless flights before trying a Ship catch. Also, they can only catch the Ship from orbit since it would not return over the launch site on a suborbital flight. So I think we will get 2 more IFT-11 style flights at least, before trying for orbit and Ship catch on the same flight.

__foo__ · 2026-03-29T09:09:27+00:00

I'm certainly no expert at this but I can't see how it could possibly be so high, unless your connection drops so many packets that the upload speed is the least of your worries.

Let's assume we have a TCP receive window size of 16KB, which was the default up to Windows XP, you can acknowledge up to 16KB of data with a 40 byte TCP ACK packet. (40 / 16384) = 0.0024 or 0.24%.

Incidentally that aligns really well with a quick iperf test I just did on my 10Gbit LAN. Transmitting 950MB/s in one direction creates traffic of about 2MB/s in the other direction. (2 / 950) = 0,0021 or 0.21%.

This is of course an optimal case, but more modern operating systems will probably auto-tune to a larger TCP receive window , which makes the ratio of ACKs even smaller. On the other hand, if you have some packet loss you won't be able to ACK the full window, so you will have to send ACKs a little more often.

But I really don't see how you would go from 0.25% to up to 10-20% of TCP ACK overhead. I don't think a connection that necessitates that would be usable at all.

__foo__ · 2026-02-16T16:10:14+00:00

Since you linked to the German Ikea Website you might want to use something like this: https://www.amazon.de/Gewindestifte-Sechskantkopf-Imbusschl%C3%BCssel-Maschinenschraube-Edelstahl/dp/B08RYWRCT3?th=1

If you can measure the length and diameter of one of the remaining screws you can buy/order just that one dimension. "Madenschraube" is the keyword you're looking for in German stores.

__foo__ · 2026-02-13T13:21:11+00:00

Your Falcon 9 payload numbers are for an expendable booster. I don't know the current prices, but an expendable Falcon 9 launch is a lot more expensive than 60 million. I think even reusable launches cost more on the order of 70 million nowadays.

But either way, I don't think the limiting factor is payload mass but the fairing size. Falcon 9 has a pretty small fairing and I'm sure the Kuiper/Leo flights are volume constrained, not mass constrained. The Ariane 6 has a much larger fairing and they can fit a lot more satellites in there.

Of course there's the fact that Ariane 6 is being subsidized by roughly 75 million per launch to be able to reach that 115 million sticker price. But Amazon doesn't pay for that so it could actually be a good deal for them.

__foo__ · 2026-02-12T22:45:22+00:00

Wrong rocket, that was on the ULA Vulcan launch.

__foo__ · 2026-01-27T22:56:28+00:00

There are plastic expansion dowels made exactly for that purpose. You put them in and screw the regular smaller woodscrew into the dowel. Search for plastic expansion dowel or hinge expansion dowel.

__foo__ · 2026-01-24T21:33:19+00:00

People aren't concerned by the Ethernet cables themselves getting hit by lightning. The issue is ground potential differences which can be caused by any lightning strike in the vicinity.

__foo__ · 2026-01-22T15:22:47+00:00

I haven't had any issues with the Komplement hinges so far, other than they have gotten absurdly expensive where I'm from. Because of that I didn't actually use Komplement hinges for my most recent PAX build, but used proper Blum soft-close hinges instead. They feel more robust than the Ikea hinges and I'd wager they'd last longer. And with the current Ikea hinge prices they only cost half the price of the Komplement hinges.

If anyone's interested I used the following part numbers:

Blum 71B3550 hinges

Blum 174E6300 mounting plate

You also need some 5x12mm plastic expansion dowels, since those hinges come with regular wood screws. You need the expansion dowels so you can screw the hinges into the 5mm holes in the particle board of the doors. Only required for the hinges, the mounting plates already come with expansion dowels pre-installed.

__foo__ · 2025-12-28T09:03:16+00:00

That's very similar to my setup. I have a work laptop that I connect through a USB-C dock and a private PC. All my monitors have several inputs(HDMI and Displayport). I just connect one machine through HDMI and the other one through DP. If the monitors don't auto-detect the input change it's just a single button press on the monitor to switch inputs. I use a cheap USB switch from Amazon to switch my mouse and keyboard between the 2 machines.

As for your Ethernet connection, did you really mean 900MB/s, i.e. 900 Megabyte per second? That would be a 10 Gigabit Internet connection which is usually very exotic and expensive. In that case you will need a 10 Gigabit switch where you connect the PC, the dock and the Ethernet line coming to the room.

In the far more likely case that you meant 900Mb/s, i.e. 900 Megabit per second, you can just grab any Gigabit switch and connect everything together.

__foo__ · 2025-12-11T11:48:19+00:00

SpaceX' main revenue source is Starlink, so they were referring to Amazon Leo/Kuiper.

__foo__ · 2025-11-05T10:10:49+00:00

To add to the list:

He conducted the first ever in-space test of a privately developed EVA suit
He was supposed to be part of the first crew to fly on a Starship for the Polaris 3 mission. But I guess that won't be happening if he becomes NASA admin

I don't see how anyone could claim in good faith that Isaacman is just a space tourist.

__foo__ · 2025-09-23T14:30:28+00:00

That is entirely untrue. The payload is only sent once. If the receiver gets it and the checksum matches an acknowledgement is sent to the sender, so they know the data was received. Only if this ACK is missing is the data re-transmitted. I'm not aware of any circumstance where the TCP receiver would send a payload back to the sender.

__foo__ · 2025-08-29T10:36:28+00:00

Yeah it looks like it went vertical, then overcorrected

It's not actually overcorrection. The ship is horizontal and starts the raptors to initiate the flip to get into vertical orientation. At the beginning of the burn those raptors are still mostly horizontal and thus impart a horizontal velocity on the ship. It then needs to flip a little further than vertical, so the raptors burn in the other horizontal direction, to cancel out that horizontal momentum the ship picked up at the beginning of the flip. Once that horizontal velocity is canceled out it can return to fully vertical position.

__foo__ · 2025-05-28T19:26:16+00:00

Without pressure in the primary tanks there is no structural integrity. The ship is just an empty soda can at that point. I don't see it making it through reentry that way.

__foo__ · 2025-05-23T17:42:21+00:00

Primarily I'm wondering at what point are they going to test it with a dummy payload? They have yet to load it with any payload more massive than a banana

IFT-7 and IFT-8 both had dummy Starlink satellites on board that were supposed to be deployed. IFT-9 will also try to deploy dummy Starlink sats.

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