binarycoffee

5 ms·

31.
by binarycoffee 6y ago
I am not sure I understand the objection (or maybe there wasn't one?) but since there seems to be some confusion in this thread on this point, the electrical efficiency of electric thrusters is very well defined, it is: η = ½Q·(Isp·g₀)
32.
by binarycoffee 6y ago
Not sure what was meant in the article, but Isp is not the same as efficiency. Also, high Isp is not desirable for a power-limited spacecraft such as cubesats because the input power scales with the square of Isp. The efficiency of an elect
33.
by binarycoffee 6y ago
So this is not what the article is about. It discusses a new method to generate integer values according to an arbitrary probability distribution, using as input a uniform random generator. Whether the input generator is truly random, pseud
34.
by binarycoffee 7y ago
I fear GP's post has not been fully appreciated. (I noted these words: [...] embrace [...] extend [...] extinguish [...])
35.
by binarycoffee 8y ago
Quite the opposite I would say: the harmonic mean can be seen as a very good justification for `1/0=inf` as the pragmatic choice. If, say, `a` is mathematically very small (and `x` is accordingly expected very small`) but `a` become
36.
by binarycoffee 9y ago
Yes, operating a Hall or ion thruster on O2 and/or N2 is not new (and Busek was not the only one that did it either). And it is definitely hard, but this is just part of the problem. The really tricky thing is to get the whole system w
37.
by binarycoffee 9y ago
Yes, this is related (not the author of the cited article but I know him well). There were also several precursor experimental studies funded by ESA, one of which [1] can be found in the same conf. proceeding. [1] http://erps.spa
38.
by binarycoffee 9y ago
Somewhat related is the E-sail [1] concept, a perhaps less ambitious but (probably) feasible idea to harness the momentum of solar wind particles with very long charged wires. [1] https://en.wikipedia.org/wiki/Electri
39.
by binarycoffee 9y ago
True, interesting idea. [Long edit] Thinking further about this idea, I realize this may even mitigate the catch 22 problem of very low orbits (<180km): the lower the orbit, the larger the drag and the required thrust power, meaning the
40.
by binarycoffee 9y ago
Absolutely, this is a passive compressor. It kind of works like an aerodynamic diode: it is much easier for the incoming particles to go through the intake tubes (because they are oriented along the spacecraft velocity vector) than to exit
41.
by binarycoffee 9y ago
This is still very much sci-fi at the moment for anything flying above a 250 km earth orbit because atmospheric density decreases dramatically fast with altitude. The missions targeted by this technology are GOCE-like spacecrafts which by d
42.
by binarycoffee 9y ago
This is a customized Hall thruster. Disclosure: I was involved in that project.
43.
by binarycoffee 10y ago
This is correct but incomplete: Vasimr may have a higher power density (be it power per thruster mass or per thruster volume) than ion thrusters but I am pretty sure it has lower power density than a Hall thruster, while being also much mor
44.
by binarycoffee 10y ago
I guess you mean the power-to-thrust ratio, which indeed scales roughly with the specific impulse. The thing is, pretty much every plasma propulsion device has the theoretical ability to throttle specific impulse. Gridded ion engines and Ha
45.
by binarycoffee 10y ago
fac = faculté, basically a French university. I guess what the parents refer to is that Universities in France are not as elitist as in other countries; the most prestigious higher education public schools are often considered to be the so-
46.
by binarycoffee 10y ago
Several comments have hinted at the possibility that this would be a over-unity device but as I couldn't find a specific demonstration, here is one that does not involve any fancy physics. Let's assume we have a spacecraft powered
47.
by binarycoffee 10y ago
easy: 1000000's of them rotating around a fixed point!
48.
by binarycoffee 10y ago
Interestingly, NASA used to have a group working on such projects. https://en.wikipedia.org/wiki/Breakthrough_Propulsion_Physic... And I believe they actually did a serious job, which is probably why they never found a
49.
by binarycoffee 10y ago
I doubt Mr debunkit is from TU Dresden or he would probably have posted the link to the article first (though it could have been a ruse of course). In any case, I am not from TU Dresden and have only a passing acquaintance with Tajmar, but
50.
by binarycoffee 10y ago
Hall thrusters typically operate around 50mN/kW. Gridded ion thrusters a bit lower, like 30-40mN/kW. That being said, some exotic thrusters like the FEEP still manage to be useful operating below 10mN/kW for precise positioni
51.
by binarycoffee 10y ago
True, that could have been brought up with greater diplomacy. That being said, I can understand the over-reaction, it is indeed frustrating to see relatively weak articles making front page because they originate from NASA when earlier, mor
52.
by binarycoffee 10y ago
Yes, sadly grand-parent appears to have been downvoted for posting one of the most insightful comment so far. To be fair, the authors did enlist Tajmar's paper in the state-of-the-art but they do not discuss despite it being the most r
53.
by binarycoffee 10y ago
As an electric propulsion engineer used to measure thrust in the uN range, what disturbs me much more than thrust levels close to the sensitivity threshold is the fact that thrust is only detected some 10-20s after the RF is turned on (figs
54.
by binarycoffee 10y ago
I can recommend "Exploring BeagleBone" by Derek Malloy which offers a very gentle introduction to the PRU with some mildly advanced examples. Also, a shameless plug with more PRU code examples in case you are interested to use Rus