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 Discussion on question by Pablo: What…

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asdfex
Wed 09:49
It's like driving your car: Always wear your belt. In case of the ISS, it's a van-Allen-belt. Or, in more serious words: The magnetic field of the Earth.
 

 Discussion on question by Cyrille Cor…

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asdfex
Mar 6, 2024 09:06
If it's in a residential area, why not put a note close to the dumpster to ask? People are likely to use the same bin again :)
 

 Discussion on answer by Weather Vane:…

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asdfex
Oct 27, 2023 19:33
I guess this table would look completely different if we compare numbers for the same trip in each vehicle. I.e. look at a 1000 km cross country trip where there is actually a choice between different transports. It's quite obvious that it is rather difficult to have a lethal accident in a bus traveling 30 km/h in a city, but not so much on the highway.
 

 Discussion on answer by Sten: How do …

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asdfex
May 28, 2023 15:08
@armand If this is what your question was about, I suggest to rephrase it. As it is now you asked for reasons to assume that Hubbles law is true. But it seems you wanted to ask why Hubbles law implies that expansion looks the same from everywhere.
asdfex
May 28, 2023 15:08
@ARaybould These observations regarding my desk translate into traveling a billion light years and measure the movement of galaxies from there. An option I have because my desk is slightly smaller, but not with Hubble. Without the option we can only state that the formula as-is describes observations from Earth, and that there are good reasons to assume it is valid elsewhere. But "because the formula says so" is not a proof that the universe actually obeys its results in every place.
asdfex
May 28, 2023 15:08
A mathematical equation designed to describe observations made from Earth can't be used to prove that the same law is valid elsewhere. And exactly this is what is asked @armand (Unless I misunderstand the question). I could equally well write an equation describing the flatness of my desk and extend it to assume that everything is flat.
asdfex
May 28, 2023 15:08
And where is the proof of Hubble's law? It's also only valid to describe observations made by us, unless you add assumptions.
asdfex
May 28, 2023 15:08
This doesn't answer the question. You just assume that the situation is the same elsewhere - but the question asks for prove of this assumption.
 

 Discussion on question by Quora Feans…

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asdfex
Jun 3, 2022 16:37
@EarlGrey It's the only means of transportation where you expect such a tight limit. You won't do that if you travel by car, plane, bike or foot. Sure, connections should work out to not get stranded for hours somewhere, but being ten minutes late after hundreds of kilometer travel should not raise any complaints.
asdfex
Jun 3, 2022 16:37
@Polygnome Every day, including long-distance. Colleagues traveling by car have a much higher amount of unexpected delays. Defining on-time as "5 minutes delay after 2 hours journey" is just ridiculous. That's just 4% of the total travel time, I don't even get this precise by foot or bicycle.
asdfex
Jun 3, 2022 16:37
@HagenvonEitzen I don't know which trains you usually take, but in Germany you can expect 90% and more to be not more than 10 minutes late and about 80% to be on time plus a couple of minutes.
 

 Discussion on answer by snoopy: What …

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asdfex
May 14, 2021 12:17
About mass, Kuiper wrote in 1950 that a mass of 0.5 Earths is estimated from the distortion of the orbit of Neptune. Maybe they lost another 0 and intended to write 9/100?
asdfex
May 14, 2021 12:17
About rotation, this should have been known well before Charon was discovered, by the changes in brightness. You don't need precise measurements, just many of them and search for a period in them.
 

 Discussion on question by DevanshS: D…

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asdfex
May 12, 2021 19:33
I think this is a perfectly valid question. The issue is a bit about wording - you can't ask for a discussion here, but you can ask for design recommendations. And you might want to change the "detector blinks" to something like "detector gives a signal / detector is triggered".
 

 Discussion on question by uhoh: Is it…

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asdfex
Nov 19, 2020 16:01
Unique cables can help, but don't forget that also these cables are all custom made (possibly by hand), so you just shift the point where the error can happen from assembly to manufacturing of components.
 

 Discussion on answer by Marcus Müller…

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asdfex
Sep 13, 2020 21:18
Unfortunate sizes. The implementation costs 3520 slices in a Lattice FPGA. Just a tiny bit more than the available in a MachXO2-7000 in QFN.
 

 Discussion on answer by Bob Jacobsen:…

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asdfex
Apr 15, 2020 13:48
Nothing contradicts your calculations. It's just that there is a lot more to it than voltage and $v_e$. It's all written in this answer.
asdfex
Apr 15, 2020 13:48
No, that's wrong. Xenon is chosen because it's heavy.
asdfex
Apr 15, 2020 13:48
@uhoh I don't see a wrong statement there. Heavy atoms are better. There is no way for any reasonably-sized, close-future technology probe to be better off using light ions.
asdfex
Apr 15, 2020 13:48
You might want to add in the weight of solar panels. That should be in the order of at least 4 kg/m², including support structures. That makes the He-Dawn a lot heavier than Xe-Dawn, reducing acceleration, needing a larger launcher.
asdfex
Apr 15, 2020 13:48
This is exactly the correct answer - it just doesn't make sense to use light gases because of power requirements to get the same acceleration. Nobody cares about dv alone, net acceleration is the crucial factor.
 

 Discussion on question by uhoh: How t…

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asdfex
Feb 11, 2020 13:50
@uhoh Leaving out information makes it for all of us much more complicated to understand what you did. Essentially we have to recreate all your work to get started. With labels and such one can start right ahead.
asdfex
Feb 11, 2020 13:50
Please add a key describing what the 3 colors represent, and don't forget the units on the y-axis.
asdfex
Feb 11, 2020 13:50
The tiny difference between straight ahead and ahead in orbit shouldn't result in a large change like this.
asdfex
Feb 11, 2020 13:50
This doesn't seem right. The guy 100m in front of ISS is still exactly in the same orbit, just with a slight phase shift. His distance shouldn't change. The guys above and sideways are in elliptical orbit and at a different inclination, repsectively, these curves seem about right.
 

 Discussion between Russell Borogove a…

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asdfex
Jan 3, 2020 19:28
I just tried to get something reasonable out of flightclub.io. Something's wrong with my settings. 20% more fuel give 15% more dv, that doesn't seem right. And the fuel mass change rate doesn't change with the amount of engines....
asdfex
Jan 3, 2020 17:47
Sorry 'larger height and lower speed'.
asdfex
Jan 3, 2020 17:44
I guess our two "high performance" versions is what we have to compare. The net dv is just 1% different, so I would call them identical in performance. You have to land 16.4t from a larger height and speed compared to 14.3t from a lower one.
asdfex
Jan 3, 2020 15:54
We're talking about different things. I'm talking about two identical rockets, one with a modified engine that has more power. You scale the tanks, I scale the engine.
asdfex
Jan 3, 2020 15:54
More impulse (also) means more speed to cancel during landing. High TWR on the other hand means short burn time and less height at MECO which is favorable for landing. I think we have to compare boosters with identical performance here, i.e. same payload, same dv. (NB, I'm not arguing here, just collecting things to take into account)
asdfex
Jan 3, 2020 15:54
Speed should be larger with high TWR - the booster spent the same dv, but in less time so gravity losses are lower.
asdfex
Jan 3, 2020 15:54
@RussellBorogove Sure, you're right, but you get a high TWR booster with a worse mass/fuel ratio. And fuel needed for landing is larger, adding an other penalty on the amount of fuel to be used for the launch itself.
 

 Discussion on answer by asdfex: How w…

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asdfex
Jan 8, 2019 20:08
@Old_Fossil Only during a few days per year - most of the time Earth would be outside the beam. With high gain antennas there is almost no signal outside the intended opening angle, the falloff is very steep.
asdfex
Jan 8, 2019 20:08
@hobbs Sometimes the radial velocity is larger than 0.003 - when Sun, Earth and Pluto form a line. 3 months later the apparent speed is 0.
asdfex
Jan 8, 2019 20:08
@Wipqozn right, I added it to the answer as well as Hennings comparison.
asdfex
Jan 8, 2019 20:08
@user New Horizons moves almost straight out of the solar system, it's not in a circular orbit like the planets. The only thing that moves quickly is Earth, From the probes perspective from Pluto, it moves by 2.6° within half a year, or 0.003° during the six hours the light needs - that's only about 1% of the beam width.
asdfex
Jan 8, 2019 20:08
@david-hammen Thanks, I added the other antennas.
 

 Discussion on question by hacker804: …

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asdfex
Jul 25, 2017 10:46
This looks all fine to me. Don't worry about the crystal too much. You might want to choose one in a smaller package though...
 

 Discussion on question by uhoh: Who d…

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asdfex
Mar 8, 2017 15:57
I'm pretty sure there was no actual shader (or just a primitive 2d one) used in the pictures - just a certain area of the image of the Moon has been darkened. If it were a real 3d model, you would see the outline of craters greatly pronounced around the terminator.
 

 Discussion on question by uhoh: Is th…

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asdfex
Feb 7, 2017 21:25
Last paragraph here gives some information on post-processing: epic.gsfc.nasa.gov/epic
asdfex
Feb 7, 2017 21:13
No, it's a combination of some of the 10 chromatic channels, taken as 10 separate images.
asdfex
Feb 7, 2017 21:09
I have to agree with @uhoh There is no "seeing around the secondary mirror". I guess it is just some unusually bright reflection from somewhere in the atmosphere