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Re-Entry through satellite constellations
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Re-Entry through satellite constellations
JF Mezei wrote on Sat, 8 Jun 2019
00:48:55 -0400: On 2019-06-07 06:24, Jeff Findley wrote: Not any more than flying thousands of aircraft creates a "conflict" in the air. In flight, aircraft are assigned non conflicting flight paths, just like satellites. The difference is that a plane that is following another one on same path can be told to slow down to maintain its distance. Spacecraft, too. All the orbital elements are known. Missing them by a wide margin isn't difficult. And the bigger difference is that a plane can be told to circle airport until the plath to ;land is clear, planes on the ground can be held to create openings for planes to land. Musk can't just tell its satellites to hold on so some spaceship can re-enter. Actually he can. All his satellites have thrusters to allow them to 'dodge' orbital debris and thus they could presumably adjust orbits if necessary to allow something reentering to get past them. If a re-entering spaceship slows down or accelerates to avoid one satellite during de-orbit, it now has to deal with other satellites that may be in conflict. Take off your shoes and figure it out. There are only around 50 satellites per orbital plane. Go break out your crayons and figure out how far apart that puts the satellites. If you're landing anywhere in the Pacific, it is easier to dodge satellites below. But if you are tarketing an X on a landing pad, unless you are given lots of cross range like the Shuttle, you have 2 orbit opportunities per day. What happens when both have conflicts? Your premise is bull****. You can come down almost any time and miss all the satellites. These contellations are meant to provide coverage 24/7 in every area of covered continents. And because they are verlo low orbit, each satellite has small footprint, which means neighouring satelites need to be nearby. So is re-enty really that easy and without concern? Do the ****ing math. Given 50 satellites per orbital plan at around 400 km altitude (the lowest ones; higher ones will be further apart). That's around 7.2 degrees between satellites. The Earth has a radius of 12,742 kilometers. Add in the altitude of the orbits and you get around 13,100 kilometers for the radius of the circle and a circumference of around 82,300 kilometers for a spacing between satellites in the same orbital plan of around 1650 kilometers. If you can't hit a 1600 kilometer 'slot' to reenter, you probably have no business putting things in orbit. So yes, reentry is really that easy and without concern. You've been told three times now (once by Jeff and twice by me). Commercial aircraft have limits on how close they can be to each other when at same altitude. Yes, they do. So what? How close to a Starlink/Oneweb/other satellite would NASA allow a re-entering spaceship pass as it descends through their altitudes? Mostly that isn't NASA's say, since they don't own most of the vehicles. Are we talking a minimum of 1m% 100m? 1km? 100km? Even taking your preposterously large upper number of 100 km for a 'near miss' (the actual 'warning threshold' is about an order of magnitude smaller than that) there is more than 16 times as much space between even satellites in the lowest StarLink orbit. Again, THIS IS A NON ISSUE, SO ****ING DROP IT ALREADY. I once again did the basic math for you. You know, you could just do it for yourself and eliminate a lot of stupid questions on your part. Or you could believe it when someone gives you an answer and stop trying to push for your stupid questions. -- "Ignorance is preferable to error, and he is less remote from the truth who believes nothing than he who believes what is wrong." -- Thomas Jefferson |
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Re-Entry through satellite constellations
JF Mezei wrote on Sat, 8 Jun 2019
13:52:24 -0400: On 2019-06-08 05:05, Fred J. McCall wrote: Do the ****ing math. Given 50 satellites per orbital plan at around 400 km altitude One orbinal plane at 340km, 50 satellites. Each travels at roughly 27,000kmh covering circumference of roughly 42,000. Do the math. That is one satellite in that one orbital plane passing avery 1.9 minutes. Uh, so? You must have a hell of a time merging with traffic, since I'm pretty sure there is a lot less than 1.9 minutes between cars in the traffic stream. Now, the 340km altitude will be covered by 7500 satellites, at 50 per orbital plane, this means 150 orbital planes, or roughly one orbital plane every 2.5°, or about 300km apart. So if you target re-entry to pass between 2 satellites in one orbital plane, odds are there will be satellite in the orbital plane 300km away. So what? Remember that in order to provide reliable service, there needs to always be at least one low orbit satellite over any one spot in served areas. No. There needs to be at least one low orbit satellite with LINE OF SIGHT. This is not the same thing as 'over'. So if BFS is targeting a landing at the Wall Street heliport in Manhattan, odds are that there will be a satellite over Manhattan at any point in time. No. There will be a satellite with LINE OF SIGHT to Manhattan. Not the same thing as 'over'. The problem is that when you land on a target, your de-orbit time needs to be very precise to hit that target landing zone. This is really only true for a pure ballistic reentry. Nothing that reenters under control is pure ballistic. But if that time doesn't coincide with a 2 minute gap between satellites, what do you do? wait for an orbit where the de-orbit time does match a gap between 2 satellites? Think about it. A satellite will move roughly 7.5 km in ONE SECOND. So any given satellite is 'in the way' for something like 400 milliseconds, even if you adopt a preposterous 'safety window' of missing by at least a kilometer. If youa re targetting "somewhere" in the Pacific ocean, then you have much more leaway in when you de-orbit and thus can more easily find a gap through which you can pass. No. Space is mostly empty regardless of where you want to come down. Think about it. If you for some reason need to fly directly through the orbital plane of a group of satellites (already a bad assumption, as you could simply avoid that) your path to ground will be blocked for 0.4 seconds every 114 seconds even if you use a huge safety margin like 1 km. That's like you're blocked for 0.35% of the time. In other words, your flight path is clear more than 99.6% of the time. If you DON'T need to fly straight through one of those orbital planes, your flight path is clear 100% of the time. Now, add not only Starlink but also Oneweb. Does the math still resuilt in the "no brainer" you assume? Yes. And I didn't 'assume' anything. I understood the issue, which puts me far, far ahead of you. If you can't hit a 1600 kilometer 'slot' to reenter, you probably have no business putting things in orbit. How did you come up with 1600km? Circumference at 340km altitude is ~42000km. You have 50 satellites, that means 840km between satellites. It takes 1.9 minutes for a satellite at ~27,000kmh to travel 840km. I apologize. My number is a bit less than twice too large as I accidentally took a figure for Earth diameter as radius. My error should have been obvious to you, SINCE I GAVE THE BLOODY NUMBERS I USED (which you apparently 'cleverly' removed). Repeat this for the 1 or 2 orbital planes to the west, knowing that satellites in orbital plane are strategically phased to cover the gaps between 2 satelites in the orbital plane next to it (to ensure customers have continued connectivity). No. You still only have to fly through, at most, ONE orbital plane, which means you are blocked AT MOST for 400 milliseconds out of each 114 seconds. Even taking your preposterously large upper number of 100 km for a 'near miss' (the actual 'warning threshold' is about an order of magnitude smaller than that) So they are happy with 10km distance from another satellite during er-entry? Is re-entry considered with same standards for distance between objects in stable orbits with constant speeds and altitude? Actually they're 'happy' with much closer passes than that. That 10 km is the 'alert threshold' for DEBRIS. It's that big because debris aren't under active control and because it's merely a "you might want to start paying attention to this" alert. yourself and eliminate a lot of stupid questions on your part. If you know everything, yet unwilling to explain without insults, whyt do you even come here? If you know nothing, yet unwilling to do any work at all to inform yourself, why do you even come here? This isn't your personal teaching hospital, bucko. The rest of us don't exist to answer your stupid questions only to have you then argue about the answer because reality just isn't what you wanted. You need to do one of two things. You either need to actually inform yourself and then argue or else ask questions and say 'thank you' when someone exerts the effort to answer you. Note that your typical combination of ask questions and then argue with the answer is right out. -- "Some people get lost in thought because it's such unfamiliar territory." --G. Behn |
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Re-Entry through satellite constellations
JF Mezei wrote on Sat, 8 Jun 2019
13:55:35 -0400: On 2019-06-08 09:40, Jeff Findley wrote: That's not how this works. The reentry burn will be timed such that it avoids all tracked objects below the reentering vehicle. This isn't that hard. Doesn't that preclude precise landing for ballistic objects such as capsules ... Most capsules aren't pure ballistic objects. They can generate lift. ... since they have to time re-entry burn for "traffic" at 340km altitiude instead of timing it to land next to the recovery ship? 99.6% clear. The 400 ms at most that you can't fly through aren't going to appreciably affect anything. And for powered landings, doesn't that require much more fuel/cross range in order to paliate for doing a re-entry at a sub=obtimal time in order to avoid the traffic? Again, 400 ms, at most. It won't matter. -- "Some people get lost in thought because it's such unfamiliar territory." --G. Behn |
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Re-Entry through satellite constellations
On 9/06/2019 10:08 am, JF Mezei wrote:
On 2019-06-08 16:18, Fred J. McCall wrote: Most capsules aren't pure ballistic objects. They can generate lift. At 340km altitude, do they generate any lift? Aren't they pure ballistoc at that point? Near enough, but the deorbit burn can be timed/adjusted to put the spacecraft into a suitable gap between the satellites, while still allowing the targeting of a specific landing point. 99.6% clear. The 400 ms at most that you can't fly through aren't going to appreciably affect anything. So what you are stating is that NASA is perfectly OK with de-orbiting any any time because the odds of being at the wrong place and wrong time during that 400ms are so low as to not even bother? I don't think that was the point being made. Rather that any orbital modification required to achieve a 400ms change can be dealt with later during the non-ballistic phase. If they do "aim" to take the threat seriously and pass between 2 satellites based on their orbital elements, is there confidence that a de-orbit burn can not only start right on time (easy) but also decelerate at the exact rate (consider a capsule's mass may not be fixed depending on what cargo they are returning) such that they will cross path with Starlink orbit at just the right time? The craft can measure its deceleration, so it's not just dead-reckoning. Sylvia. |
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Re-Entry through satellite constellations
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Re-Entry through satellite constellations
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Re-Entry through satellite constellations
JF Mezei wrote on Sat, 8 Jun 2019
20:08:27 -0400: On 2019-06-08 16:18, Fred J. McCall wrote: Most capsules aren't pure ballistic objects. They can generate lift. At 340km altitude, do they generate any lift? Aren't they pure ballistoc at that point? As usual you totally miss the point. Let me try and explain it to you in detail even you will grasp. First, remember that any given bit of space I need to fly through is empty 99.6%. For the other 0.4% of the time I might have to do a reentry burn that is slightly suboptimal. If I'm really stupid I might have to use the OMS to avoid a collision. Now, once I pass that 340 km altitude, I don't carry those conditions with me what with me being reentering and all. Instead, I continue to go down and reach the point where the lift of the capsule can be used to adjust the impact point to precisely where I want it. THIS IS HOW IT WORKS NOW AND THERE'S NO REASON IT WOULD CHANGE BECAUSE OF STARLINK. Get it now? 99.6% clear. The 400 ms at most that you can't fly through aren't going to appreciably affect anything. So what you are stating is that NASA is perfectly OK with de-orbiting any any time because the odds of being at the wrong place and wrong time during that 400ms are so low as to not even bother? No, dear boy. I'm stating what I'm stating, not the stupid things you try to imply. In order to avoid that satellite you MIGHT have to do your reentry burn either 200 ms early or 200 ms late, worst case. Even on a pure ballistic reentry, how far does that move your landing point? It's certainly within the lift capability of the capsule to correct. If they do "aim" to take the threat seriously and pass between 2 satellites based on their orbital elements, is there confidence that a de-orbit burn can not only start right on time (easy) but also decelerate at the exact rate (consider a capsule's mass may not be fixed depending on what cargo they are returning) such that they will cross path with Starlink orbit at just the right time? Yes. The capsule's mass is always 'fixed' in that it doesn't change in flight. If you can't predict the reentry precisely then you cannot predict the landing point precisely and you cannot do spaceflight. Since we obviously CAN do spaceflight, your 'concern' is obviously not a real problem. -- "Some people get lost in thought because it's such unfamiliar territory." --G. Behn |
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Re-Entry through satellite constellations
Jeff Findley wrote on Sun, 9 Jun 2019
09:44:06 -0400: Again, look at the landing accuracy of Apollo capsules. This was achieved partly due to their ability to generate a significant amount of hypersonic lift. Or look at the landing accuracy of Dragon capsules, which do much better than Apollo did. -- "The reasonable man adapts himself to the world; the unreasonable man persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man." --George Bernard Shaw |
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