44

Not much research has been done on this question in recent years, but some researchers are worried enough to research into wooden satellites. The question on the environmental impact of deorbiting satellites burning up in the upper atmosphere was partly addressed in a 1994 report (warning: not peer reviewed) by the Environmental Management of the Space & ...


33

The mass of Earth's atmosphere is 5E+18 kg and the Troposphere alone has 3/4's of that. With an average height of 13 km that makes its volume $4 \pi r^2 h$ or about 6.6E+18 m^3. If we break up one thousand 100 kg satellites into semi-porous PM2.5 particles that works out to be 1.5E-08 micrograms per cubic meter, and we generally worry about tens of ...


32

No, 75 meters is not exceptionally close — several satellites show predicted passages that close or closer every single week of the year. But it is close enough to potentially appear in the top 10 list of satellite conjunctions for the week: http://celestrak.com/cgi-bin/searchSOCRATES.pl?IDENT=NAME&NAME_TEXT1=&NAME_TEXT2=&ORDER=MINRANGE&MAX=...


28

Exceptionally rare? No. Uncommon, well, yes. From what I can recall, these happened about once every 10 years per satellite for the constellation of satellites I worked with, at least, prior to doing a collision avoidance maneuver. That of course included debris/ satellite close approaches. Of course, I note that the two you listed are both live satellites,...


26

Nodal precession doesn't matter for a plane of satellites like this, they will rotate around in unison, so the coverage will remain the same. Okay, so why the unusual dual inclination constellation? The inclination of a satellite band tends to let you know what latitude it will work best at. A 0 degree satellite works best at the equator, a 90 at the poles. ...


22

EDIT: With the third Starlink launch happening about right now, it's time to update this answer! We now know that each satellite has a weight of 260kg, and that they launch 60 satellites per mission. They are flat packed, stacked 30 up side by side in the Falcon 9 Fairing, and far smaller than what I thought would be possible in my first answer. Elon Musk ...


22

Space Fence is what our current tracking system is called. This article claims that some companies and countries have an arrangement to receive tracking data, but few details. It appears that this in fact routine, but I don't know if companies have to pay in. To date, Strategic Command has announced data-sharing agreements with at least seven countries and ...


21

88! PSLV-C37 launched 88 identical satellites into a sun-synchronous orbit. These satellites were for an imaging company called "Planet Labs". Technically the only ones that were identical were the CubeSats (Which were named Doves) but they were launching 4 other types of satellites from this launch too. The rocket launched Cartosat-2D, a few other ...


19

Uhoh touches one side of the problem: "Why" - the lower the orbit, the less of Earth is covered in a single pass, and the closer to equator the orbit, the less do the passes vary further narrowing the area. MEO equatorial satellites make sense. The lower the orbit though, the less useful they become. Still, there's a slew of tasks that wouldn't be hurt by ...


16

75 meters isn't all that rare - for the full public catalog there are 75 meter predictions about 2-3 times per day. What you have to consider is the uncertainty in that number. For TLE data, that's 75 meters +- several kilometers. The 75 meter miss distance is from the nominal position of each object at closest approach. But TLE data has a significant ...


15

GPS satellite orbits go up to only 55 degrees inclination, so there are regions over the poles that they do not fly directly over (they are high up enough that they give coverage in the polar regions). If you were sitting up at the North Pole, you would never see a GPS satellite climb higher than 55 degrees from the horizon, whereas if you were on the ...


14

480,000,000!† †Depending on how you define satellite. I think Project West Ford is the current record holder, with 480,000,000 individual satellites. Well technically 480,000,000 copper dipole antennas, designed to act as an artificial ionosphere. Here is a photo of a few of the dipoles:


13

It's routine, and done as a service for the space community at large. Companies doing official business with the U.S. Government can get access to a variety of additional services, but the basic collision warnings to owners and operators of space vehicles are provided for the good of the world. You have to register for a free account on space-track.org to ...


13

Is there a webpage where I can see the list of LEO satellite constellations? Yes! Celestrak has several pre-arranged groups of satellites and many of those groups can be seen as constellations, and a few could be argued to be or not to be constellations as well. That's up to you. This is not exhaustive but it is probably 90%. The quickest way to get ...


11

Since 'right now' applies whenever this question is read,) even four years after the question was asked, the answer has to be Starlink, which has 1700 satellites deployed in its constellation. Authorization is for 4408 Ku and Ka band (12-18, 26-40ghz) satellites. Update: Just read an FCC filing that Starlink Gen2 plan is for 30,000 satellites operating in ...


11

Nothing physically prevents equatorial orbits at any altitude above the Kármán line. The question is really; what would be the point in flying over exactly the same equatorial band roughly every 90 minutes, when a higher-inclination orbit would let you cover much more of the planet (all of it, eventually, for polar orbits) or a higher orbit would let you ...


10

Basically they are not quite in the same plane. As a satellite raises or lowers, not only does it change the relative position within an orbital plane, it also will slowly shift the longitude of the ascending node with respect to the other satellites, called the "Nodal Precession". In fact, this happens every day. There is a lot in this, but the bottom line ...


9

Does each satellite slightly raise or lower it's orbit to start spreading out compared to one reference satellite? Yes. So off the bat there's a deltaV penalty for distributing the constellation? The ∆v required to phase the orbit can be arbitrarily small if you're not in a hurry to reach the final configuration, as described in this answer. I ...


8

I don't think anyone can give you a detailed answer on how they will make money, because their business plans are their own, and proprietary. But the premise of the question seems essentially flawed - There are huge areas of the world that do not enjoy reasonable (or any) broadband access. There are also existing markets for mobile broadband (passenger ...


7

I imagine the most difficult hurdle to overcome in a satellite recovery program like you describe would be the financial one, as there is very little incentive for SpaceX (or any company) to do so. First though, I think you're overestimating the problems/dangers of reentering space debris. Let me outline my reasoning: Any debris which survives reentry will ...


6

Bart's correct. To elaborate, I was part the USAF team that tested the first DoD acquired GPS receivers. From what I remember, the GPS and common to all positioning systems, the orbital geometry was mostly limited by economic practicality. + and - 55 degrees, as stated in the first answer, covered the planet's highest population density. The higher ...


6

While there is a currently accepted answer explaining why there are "no LEO satellites in the earth's equatorial plane", I found two of them with inclinations currently less than 3 degrees! Both are science missions and detect gamma rays. I don't yet know why equatorial orbits were chosen, but I can forward two theories until such time that I find ...


6

The space segment of the Cospas-Sarsat system has two components, SAR signal repeaters (SARR) and SAR signal processors (SARP). The Sarsat instruments [...], receive these messages. They are downlinked to the distress terminals — known as Local User Terminals (LUT) — distributed around the globe. The message are then processed and distress alerts ...


6

The answer is given within the question, the emergency signals are received by the the International Cospas-Sarsat Programme satellites. From wikipedia: Space segment The Cospas-Sarsat system space segment consists of SARR and/or SARP instruments aboard: Five satellites in polar low-altitude Earth orbit called LEOSARs Seven satellites in ...


6

Your arithmetic getting to 50 birds per plane about 7° apart seems reasonable. I would be surprised if 50 satellites could be put on a single launch, if for no other reason that I don't think they'd fit in the fairing. Regardless of how many go up on a single launch, I think we can safely assume it would be more than one, in which case the answer below is ...


6

I devised the plan for the ORBCOMM Gen 2 deployment while I was the Systems Design Lead for the spacecraft. Looking back on our plans and analysis, the first step was to select a scheme that met the customer requirements to first minimize the chance of recontact between the spacecraft (and also the LV) on subsequent orbits as well as allow the vehicles to ...


5

Planet Labs' Flock 3p, a constellation of 88 Dove satellites, was recently launched aboard ISRO's PSLV-C37, the record-breaking launch of 104 satellites. Wikipedia says: They head to a morning crossing time, sun-synchronous orbit (SSO) at an approximate altitude of 500 kilometres (310 mi). According to the Wikipedia Planet Labs article, Flock 3p is the ...


5

We are living in the 21st century now. One phased array can support a large number of beams, each pointing in a different direction, each moving at a different rate. All the steering can be done electronically. So no, you don't need one antenna for every link. Just a few spacecraft-fixed, phased arrays is all that's necessary. Here is a drawing of an ...


5

It's a valid question. The Starlinks would require larger tanks but we're still only talking about a few percent of their 227 kg mass because they use high solar-electric propulsion rather than conventional rockets. I estimated about 2.3 kg of liquid krypton for the lower orbiting Starlink satellites in this answer. That included orbit raising from 445 to ...


5

Satellite internet is a good way to avoid a lot of trouble building the ground infrastructure necessary to reach regions of the planet where logistics turn out to be very expensive and accessibility is highly limited. Until now, there was little care about the population of third world countries having internet access since it was perceived as a commodity in ...


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