201–210 of 276 posts
Earlier quoted context omitted.
You don't need a position prediction to remove an anomaly.
Actually, you kind of do, because how do you know it's an anomaly and not something you want to observe? Especially if it's just occluding things in its path, and you can't see it. It's really helpful to know where everything is.
Earlier quoted context omitted.
But that measurement is literally a dot that you know would not be there at time T-1, then should be there at time T and then shouldn't be there at time T+1. Astronomers are lazy.
It's not a dot, in a long exposure photograph, it's a line. You don't delete it spatially, you'll want to subtract off the extra photon counts along that line so you can retain whatever was in that part of the image. Now, I think that's possible - find lines one diffraction-spot wide, fit to its brightness and subtract it off. They should be damned near straight lines of constant brightness given how fast satellites…
Earlier quoted context omitted.
Yes, it might be that the astronomer community didn't expect Starlink to actually happen. A lot of people still haven't learned that SpaceX isn't just hyping things up.
it remains an experiment; if the network test proves useful, they ll have to mitigate this issue somehow. perhaps also make the satellites smaller
(I'm not speaking for any of my current or past employers, just for myself, and how I've seen this play out. One employer being a telescope impacted by Starlink, and the other being SpaceX, I want both sides to succeed.) First, astronomers know that satellites can disrupt observations. They've known for a while, and have had to deal with things like flares from Irridium satellites, which were probably when these prob…
This sounds to me like a new technology and a way of operating has come and we're trying to make it accommodate the old way of doing things. If we really have a way to launch thousands of satellites easily, can't we replace the terrestrial functionality with that? Let's launch hundreds of satellites observing near earth asteroids. If a private company can do it, governments definitely can
First, as others have pointed out, is size. Ground based mirrors are very large, in the 10s of meters, and those mirrors are extremely heavy, like tons. You can't lift one of those mirrors up on one rocket, so you'll have to figure out some kind of in orbit construction. Not impossible, but we haven't assembled a lot of things in space, probably the biggest would be the ISS. But telescopes have tricky tolerances...
Which leads me to the next issue: not only is it heavy, but telescopes are fragile. They have to be very carefully calibrated and put together. Launching something into space tends to be a very bumpy ride, and making something that can withstand that kind of vibration for launch, and then the thermal problems while in space would be certainly not trivial.
But let's say you could build something and get it to work in orbit. Then it's still hard to service. Servicing the hubble to fix the optics was a very hard mission, and the hubble is relatively close to the earth. And that was when we had the shuttle, which we don't now.
Cooling is very tricky for both telescopes and space. Since there's no air to radiate to, you can get big thermal gradients over the length of your craft and you have to be very careful how you point it. Same for the optics and the camera, you want to make sure they have as little thermal gradient as possible.
Unlike a lot of commercial satellites, many scientific probes and telescopes are constantly refitted and reused. Ground based telescopes frequently reuse the same expensive (typically one-off) mirrors and put better cameras on them all the time. This is pretty hard to do in space.
That being said, being in space does have a lot of advantages, the most obvious one being a lack of atmosphere to mess with your observations. But assembling large telescopes in space still isn't exactly easy.
I think over time though, we will be heading to more space based telescopes as the cost comes down. But many slower moving telescope projects (mostly slow due to government funding) were started before Starlink was even announced.
“No one thought of this,” she said. “We didn’t think of it. The astronomy community didn’t think of it.” I really have trouble believing that nobody mentioned adding thousands of satellites would go unnoticed. It is damn near impossible to take any image of the night sky without having a satellite streak through the frame. I have plenty of images with multiple satellites visible at the same time. In wide angle timela…
Yes, I’m an astronomer and I can tell you this SpaceX statement is pure BS. The astronomy community absolutely thought of this before any of these satellites were launched. I’ve personally talked about it at public outreach events (and it was members of the public who brought it up) and topic has definitely come up at professional meetings...but there is just a general feeling of powerlessness, both from the point of…
Why aren't you talking about any of the other constellations that are being built? They're all planning huge numbers of satellites, many of which are larger or in higher orbits than SpaceX's satellites. You can't single out Elon Musk's companies just because of a personal vendetta if you're actually trying to be fair and attack this from a technical perspective.
Earlier quoted context omitted.
since starlinks may change positions autonomously it's impossible to predict their positions. and they are so damn many
Starlink satellites are too small to do much orbital maneuvering. They only carry a small supply of krypton gas for their station keeping thrusters.
OTOH you can just ask SpaceX or the Air Force where they have been in the past, SpaceX uses GPS and the Air Force radar is accurate enough for knowing where they were.
Earlier quoted context omitted.
I'm well aware of the scale of starlink, but the speeds delivered by starlink won't be any faster than the existing GEO satellites at the time, not will it be cheaper. The OP talked about high speed internet, which, in most cases, the latency doesn't matter. Every cost estimate made by people in this industry say it will be much higher than geo to deliver a bit. If you have a source that says otherwise, please post i…
Can you point to some of those cost estimates? Latency absolutely matters for "high speed internet". Once you have reasonable bandwidth, that's the dominant factor in the user experience.
NSR estimates for SpaceX are higher than what SpaceX claims (Gwynne Shotwell just claimed some Morgan Stanley estimates of $1M launch + $1M to be way off [1]), but still, I wouldn't expect them to be able to launch the 4,409 satellites of their intial design for less than $10B. And it's not clear that they will be able to raise such amount of money without a clear path towards profitability.
I agree with the shaklee3, Tim's blog is very legit. As full disclosure, I am the first author of the MIT study he mentioned, and the more I look into LEO mega-constellations, the more skeptical I become.
[1] https://twitter.com/thesheetztweetz/status/11877454453611806...
Earlier quoted context omitted.
> It wasn't a "radio license." It's fundamentally a radio license: https://www.law.cornell.edu/cfr/text/47/25.114 > when they did consider increased collision risk Yup, they are supposed to evaluate orbital debris and collision risk, too, 47 CFR 25.114(d)(14). That, and equitable service (for some services) to Alaska/Hawaii are the only non-radio concerns they are permitted by regulation to consider.
> they are permitted by regulation Where is the restriction to only those concerns? 47 CFR § 25.156 has some pretty vague language about "the public interest, convenience and necessity." Thanks for pointing out that the FCC is required to evaluate orbital debris and collision risk, but I don't think the FCC is prohibited from considering other concerns (and i might be wrong on that).
The public comments relate to the adequacy of the application, which is required to address those points.
Yes, users of radio frequency spectrum do have public interest obligations. Thus far, for spacecraft this has been entirely confined to coverage requirements (aka, helping out Alaska when it's not infeasible).
It would be highly unusual-- and likely to be overturned in judicial review-- if the FCC were to decline to issue a radio license because of secondary impacts of the business. (Outside the specific areas where the FCC has been granted oversight-- environmental impacts of radio towers, space debris mitigation, safe operation of radio facilities, etc).
Earlier quoted context omitted.
The ground system is what will make or break starlink. Every phased array antenna to date is at a price point that would put starlink selling exclusively to enterprise customers. This means consumers won't be able to get it unless you're in the 1% and living very remote. SpaceX will not realize 20Gbps per satellite in useable bandwidth. It's more like 5Gbps. http://www.mit.edu/~portillo/files/Comparison-LEO-IAC-2018-…
OneWeb claims to have cracked that, for a price point of $200-300. https://spacenews.com/wyler-claims-breakthrough-in-low-cost-... Even if it winds up being more expensive, you might see a neighborhood getting an antenna and distributing it to a group of houses. > SpaceX will not realize 20Gbps per satellite in useable bandwidth. It's more like 5Gbps. Based on guesses made prior to the first launch of production hard…
I can say that the mass and volume of the satellites has changed quite a lot, and therefore the number of rocket launches required is pretty off in the paper. But I have not seen much info to invalidate the rest of results.