dr_orpheus

9 ms·

31.
by dr_orpheus 2y ago
Interesting, TIL that Hubble uses gas-bearing gyroscopes. I been struggling to find any other spacecraft that use those gas-bearing gyros. The only other one that seems to be using them (that is still operational) is the Chandra X-ray Obser
32.
by dr_orpheus 2y ago
It's also not imaging all the time. The SAR imaging takes A LOT of power, so they can't run it constantly. If you look at the image in the article showing where the images were taken they are all near geopolitical hotspots, coastl
33.
by dr_orpheus 2y ago
It's not that it doesn't work, it is just prohibitively hard. The other comments here pointed out GEDI which is a LIDAR payload on the ISS. But it's resolution is only 25 m. This is compared to the resolution of the Umbra sat
34.
by dr_orpheus 2y ago
The accuracy of MEMS gyros is orders of magnitude worse than the gyros on Hubble. I suspect based on this article [0] that Hubble uses hemispherical resonator gyros (HRG [1]). The really high accuracy rate sensors that you find in spacecraf
35.
by dr_orpheus 2y ago
No, these are actually referring to the gyroscopic sensors on the spacecraft. This article [0] makes it a little bit more clear. While there are actuators that use gyroscopic torque, referred to as Control Moment Gyros (CMG) Hubble uses rea
36.
by dr_orpheus 2y ago
Certainly there is some bias, the other comments here have addressed some of the things we skim over. I don't know enough to speak to other countries specifically, but the US does now have the "de-orbited within five years" r
37.
by dr_orpheus 2y ago
Also, the US Operation Burnt Frost which shot down a non-functioning NRO satellite in 2008. Luckily this one was in a low orbit and everything decayed within a couple years. https://en.wikipedia.org/wiki/Operation_Burnt
38.
by dr_orpheus 2y ago
Yep, it was a dedicated satellite and it was an altitude of 283 km when they did the ASAT test. Everything from the test decayed within about 3 years [0]. [0] https://en.wikipedia.org/wiki/Mission_Shakti#Space_debris
39.
by dr_orpheus 2y ago
Yeah, it is an extremely sensitive accelerometer which it calls out about halfway through the article. "At the heart of the quantum compass – which could be ready for widespread use in a few years – is a device known as an acceleromete
40.
by dr_orpheus 2y ago
The Ars article linked below seems to indicate about 20x vs competing solid-state products and 2.5x vs liquid electrolyte batteries. "The new material provides an energy density...1,000 watt-hours per liter, which is about 100 times gr
41.
by dr_orpheus 2y ago
And even after you get past the manufacturing, titanium also seems to have some weird corner cases. I learned recently about metal induced embrittlement of titanium [0]. The Wikipedia article mentioned cadmium embrittlement of titanium, but
42.
by dr_orpheus 2y ago
Treatment, alloyed metals along with it, grain structure, manufacturing process. If you want an easily accessible intro to how metal treatment affects it's material properties go watch Forged in Fire. It is a blacksmithing game show wh
43.
by dr_orpheus 2y ago
The article mentions that the CoC may have been falsified, but I also wonder if part of this is they had falsified coupon testing/inspection documentation (or likely pulled a "good" coupon test and said it was for that batch)
44.
by dr_orpheus 2y ago
True, it's definitely feasible to make non-aluminum satellites. I do tend to go get up on my systems engineering soap box when people just talk about launch cost as it's a conversation I have too frequently in my job as well. The
45.
by dr_orpheus 2y ago
That is closer than I expected, and is specifically 47% of the re-entry mass (which is what we care about here) is from controlled. I would expect if you were just looking at # of satellites the numbers would be much more skewed as lots of
46.
by dr_orpheus 2y ago
> Most satellites are still under control and steered to a predetermined area for reentry over the South Pacific. This is not true, most satellites do not perform controlled re-entry. In order to perform controlled re-entry, you need to
47.
by dr_orpheus 2y ago
It is used quite a bit in the space industry already. But it is more expensive so it is usually confined to applications where you really need the weight savings, or you need something with a more controlled coefficient of thermal expansion
48.
by dr_orpheus 2y ago
But it's not just the cost of the launch, its also going to be the cost of the satellite itself. More mass means you need larger reaction wheels (or CMGs) to control the attitude of the spacecraft, larger reaction wheels means you need
49.
by dr_orpheus 2y ago
> I wonder if it's protected from gunfire in transit I would guess that it isn't. My assumption (without any data backing this up) is that making a specific, super rugged transport container would cost more (along with the addi
50.
by dr_orpheus 3y ago
The even more extreme version of this JPL has been working on with their Starshade program. Not specifically a cornograph, but same concept of blocking light from a star to look for something more dim, in this case its looking for exoplanet
51.
by dr_orpheus 3y ago
Yep, definitely power is an issue and a trade-off even with low levels of power. The other item is cost. Cold gas thrusters are super cheap and reliable. So the savings in amount of propellant in going to an electric propulsion system is no
52.
by dr_orpheus 3y ago
They need the milli-newton level of thrust control and so need tiny thrusters. Generally the simplicity of the cold gas thrusters in a small package is easy. Yes it is not as efficient, but moving up in efficiency and complexity to catalyze
53.
by dr_orpheus 3y ago
I think is the one you are looking for: https://beza1e1.tuxen.de/lore/index.html Also posted on HN awhile back: https://news.ycombinator.com/item?id=23005140 Edit: yep, here are your Crash Cows: https
54.
by dr_orpheus 3y ago
Previous HN Discussion: https://news.ycombinator.com/item?id=35643705
55.
by dr_orpheus 3y ago
Yes, using Day of Year for time GUIs and measurements is pretty common in spacecraft operations. Generally easier to do/plan operations for things like "we need to perform this maintenance activity every 5 days"
56.
by dr_orpheus 3y ago
Not its mass directly, but you can use it to calculate the moment of inertia. Move the CMGs a fixed angle and looking at the responding change in rate of the ISS. Mass can be determined from maneuvers when you fire the thrusters. Assuming y
57.
by dr_orpheus 3y ago
Reminds of when the "Fire Flowers" in Better off Ted: https://www.youtube.com/watch?v=P5rAOitj5_8 "Whoah! What was that? Uhh...fire squirrel"
58.
by dr_orpheus 3y ago
Also agreed, although I enjoyed some of the philosophical debate in the early portions of the book so I would put Anathem higher in books I enjoyed from Neal Stephenson
59.
by dr_orpheus 3y ago
"put the entire program on hold at least for 100 days" I don't think the wording here is quite right. The GAO has 100 days to decide if the protest is valid or not. If it is valid, then the program could be on hold for longer
60.
by dr_orpheus 3y ago
Somewhat, it will definitely tip the needle for those who are on the fence about their risk posture with radiation. But the surface of Mars is by no means the worst radiation environment. For overall dose levels, the surface of Mars is abou

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