ggreer

5 ms·

31.
by ggreer 3mo ago
Aluminum alloy and carbon fiber, because both have high strength to weight ratios. Steel is denser, so its specific strength isn't as high. But it retains strength at both lower & higher temperatures, and it's much cheaper. It
32.
by ggreer 3mo ago
Solid motors are simpler, but I wouldn't say they're more reliable. It was the solid booster failure that caused the Challenger disaster, and solid booster failures that have caused ULA's Vulcan Centaur rocket to be grounded.
33.
by ggreer 3mo ago
I'm not sure how that would help. If you're descending it's probably to land, and then you can recharge the batteries with electricity from the ground. That would be more efficient (and cheaper) than burning fuel to charge th
34.
by ggreer 3mo ago
The talk about AI water usage exists because in Karen Hao’s book Empire of AI , she got water usage wrong by three orders of magnitude.[1] For data centers that use water cooling, it's almost always non-potable water, and it's us
35.
by ggreer 3mo ago
Increasing global electricity production by 1.5% (or 500 terawatt-hours) would also be a solution. Production from solar power increased by 600TWh from 2024-2025 and its rate of adoption is increasing as costs go down, so this doesn't
36.
by ggreer 3mo ago
I agree with those comments and my vehicles are a 1990 Mazda Miata that I fixed up[1] & and a Model 3 Performance. The Model 3 looks boring, but is ridiculously fast. The Miata has the stock engine, intake, & exhaust, so it's n
37.
by ggreer 3mo ago
Are they fast DC chargers or level 2 chargers? If it's the former, then that is cheap. If it's latter, then that is some expensive electricity. I'm in Washington where electricity is cheaper, so 29 cents per kWh is not much c
38.
by ggreer 3mo ago
I can think of several practical uses. It would be very useful immediately after a disaster. Lighting up the night would make search & rescue much more effective. It would also allow for more solar power generation in an area, reducing
39.
by ggreer 4mo ago
I picked 30mph because that's the current threshold for what is considered a motorcycle in the state of Washington. Until recently, e-bikes were exempt from this because the old law was made back when e-bikes were rare and couldn'
40.
by ggreer 4mo ago
The law doesn't ban them. It classifies fast e-bikes as motorcycles (which require registration, insurance, and a motorcycle endorsement).[1] This seems reasonable to me. The previous laws for e-bikes were based on outdated assumptions
41.
by ggreer 4mo ago
For sprints, shoes give additional traction for faster starts, but don't increase running efficiency. For distance events, shoes were just extra weight, and barefoot runners have won Olympic competitions.[1] Recently, springy "sup
42.
by ggreer 4mo ago
This quirk of competition is why swimmers can win a ridiculous number of medals. If swimming only had freestyle, Michael Phelps would have 7 gold medals instead of 23.
43.
by ggreer 4mo ago
Allowing a bicycle would be like if swimming competitions allowed fins. A more accurate mapping to the swimming strokes would be race walking, which is widely ridiculed.
44.
by ggreer 4mo ago
Space gets you 24/7 solar power. To run a data center for 12 hours without sunlight, you'd need massive batteries. Also oceans have weather and corrosion. The issue with putting stuff in space isn't the kinetic energy require
45.
by ggreer 4mo ago
Tesla's valuation is high because investors expect them to sell goods & services other than cars, such as autonomous vehicle rides and humanoid robots for domestic & industrial use. Who knows if they'll be able to pull it
46.
by ggreer 5mo ago
Rocket engines can’t throttle down very much. Raptor can go down to 40% of its rated thrust, which for V3 would be 100 tons. The ship’s mass is maybe 150 tons with remaining propellant at the start of the landing burn, and probably around 1
47.
by ggreer 5mo ago
This is the third time in two days that you’ve made this exact same comment.[1][2] 1. https://news.ycombinator.com/item?id=48215414 2. https://news.ycombinator.com/item?id=48220491
48.
by ggreer 5mo ago
Just FYI the sizes of the planets, stars, and their orbits are not to scale at all. To get an idea of how empty space is, there are 63,360 inches in a mile, and 63,239 astronomical units in a light-year. So if you scaled everything down suc
49.
by ggreer 5mo ago
Only one of them is working right now. Their original tower needs to be overhauled to support Starship V3.
50.
by ggreer 5mo ago
They can build new boosters pretty quickly. New launch/catch towers take a lot longer, and they don't have any redundancy yet. Also they weren't going to reuse their V2 boosters once V3 was ready, so they could learn more by
51.
by ggreer 5mo ago
They won't use barges because the booster has no landing legs (to save weight), and because the booster is massive compared to Falcon 9. Also Starship is meant for rapid reusability, and it can take days to return a barge to port and u
52.
by ggreer 5mo ago
That's because they use other terms like "Falcon 9/Heavy", "Starship", "Super Heavy", "launch vehicle/system", "booster", "upper/lower stage", and "spacecr
53.
by ggreer 5mo ago
The measured levels of arsenic, strontium, and vanadium are below the limits for drinking water, even in California. And 4% of drinking water sources in California have higher hexavalent chromium content than the water in that ditch.[1] Bes
54.
by ggreer 5mo ago
Hexavalent chromium can come from many industrial sources, including welding stainless steel. If you go to Tesla's lithium refinery in google maps[1] and follow the drainage ditch along highway 77 (to the northeast) about a half mile,
55.
by ggreer 5mo ago
Different states have different rules about what sort of things insurers are allowed to charge different rates for. In the states that allow it, Tesla does offer insurance discounts for FSD usage.[1] Lemonade also offers discounts for FSD u
56.
by ggreer 6mo ago
Your first link is for the bus budget in Portland, Maine. The system cost for busses in Portland, Oregon in 2025 was $453 million.[1] 1. https://trimet.org/about/pdf/trimetridership.pdf
57.
by ggreer 6mo ago
The $812 million figure for 2025 did not include the cost to build the rail system. Nor did it include many other expenses. TriMet's expenditures for this year are $1.185 billion.[1] If you divide passenger miles for TriMet busses (141
58.
by ggreer 6mo ago
In 2025, TriMet had 262 million passenger miles at a system cost of $812 million, for a cost of $3.09 per passenger mile.[1] Fares covered 7.8% of their costs. The other 92.2% came from payroll taxes and federal grants. For comparison, a Ly
59.
by ggreer 6mo ago
Even when just looking at marginal costs, I doubt Waymo is half that of a human driven vehicle. If we assume a robotaxi lasts 200k miles before being retired, then the cost of the vehicle alone ($75k) is 37.5 cents per mile. If a vehicle dr
60.
by ggreer 6mo ago
It's not clear to me if their costs are lower yet. Waymo's vehicles are rather expensive (estimates for their newer Zeekrs are around $75k each), and they need to pay some number of remote monitors for exceptional situations (as n

More ›