Quote from: Bananas_on_Mars on 08/22/2020 02:12 pmMy feeling is we might see automated on orbit assembly with dedicated Starships.The following is an example how this could work.For example solarpanels that don’t need to deploy(fold themselves open) could be paired with the rest of the satellite shortly before release.Sun shades possibly the same.This could be combined with a last health check, thruster check while in the largest vacuum chamber you can imagine, and then release.Satellites that fail this test can be brought back and repaired.I cannot imagine any scenario in which this makes any sense. What does it solve that justifies this complexity?
My feeling is we might see automated on orbit assembly with dedicated Starships.The following is an example how this could work.For example solarpanels that don’t need to deploy(fold themselves open) could be paired with the rest of the satellite shortly before release.Sun shades possibly the same.This could be combined with a last health check, thruster check while in the largest vacuum chamber you can imagine, and then release.Satellites that fail this test can be brought back and repaired.
Quote from: AC in NC on 08/22/2020 02:59 pmI cannot imagine any scenario in which this makes any sense. What does it solve that justifies this complexity?It can shift complexity from the satellites to the „deployment mechanism“. Build the machine that builds the machine is an Elon Musk credo that might extend into space.On Falcon 9, everything that goes to orbit is gone and not reusable. On Starship, you can get stuff back and reuse it, not only the second stage/Spacecraft, but also the other stuff you might put on there.The Starlink satellites are currently really optimised for Falcon 9. We shouldn’t expect the satellites that are launched by starship to simply look the same.Starship doesn’t even have to use a satellite deployment similar to anything that has been done before. It could easily deploy 400 satellites over the course of 2 weeks, one satellite at a time. More like the cubesat deployments from the Spacestation than current Starlink deployment.
I cannot imagine any scenario in which this makes any sense. What does it solve that justifies this complexity?
Build the machine that builds the machine is an Elon Musk credo: Fine. When you need that. Not where you don't. Best part is no part.Of course Starship can enable novel modalities. But they have to make sense. Ungrounded idle speculation with might's and could easily's isn't very interesting unless you can articulate a problem to be solved. Two-week deployments with Starship doesn't sound like any rational use of resources.What problem are you trying to solve?
Depending on how quickly they get to orbit, and how far down range they are when they achieve orbit, the time period when the instantaneous debris path crosses over populated areas may be short enough to greatly reduce risk. The actual performance of Starship is evolving as they make improvements to Raptor, so I doubt that they have definitive numbers to be able to calculate trajectories with associated risk calculations. Could be wrong, maybe their projections are close enough.
Well, best part is no part is true... for the finished product.The launcher or the deployment system is just a means to the finished product - an operational satellite on orbit.How many parts are only there on the satellites because they have to fold flat? How many parts are overengineered for on-orbit requirements because of requirements from launch?Assuming the design of the current satellites is not changing when they switch over to starship might be conservative, but also speculative.SpaceX has shown with their first generation of Starlink satellites that they’re willing to design for an end-to-end optimum.I remember no-one predicted they would be able to put 60 satellites on a single launch. Almost no-one predicted their deployment method.In the first post, OP said he couldn‘t fit 400 Starlink satellites into Starship, which was a publicly stated number from SpaceX. My answer to that is that the assumption that SpaceX doesn’t change anything about the form factor might be wrong.
It can shift complexity from the satellites to the „deployment mechanism“. Build the machine that builds the machine is an Elon Musk credo that might extend into space.On Falcon 9, everything that goes to orbit is gone and not reusable. On Starship, you can get stuff back and reuse it, not only the second stage/Spacecraft, but also the other stuff you might put on there.The Starlink satellites are currently really optimised for Falcon 9. We shouldn’t expect the satellites that are launched by starship to simply look the same.Starship doesn’t even have to use a satellite deployment similar to anything that has been done before. It could easily deploy 400 satellites over the course of 2 weeks, one satellite at a time. More like the cubesat deployments from the Spacestation than current Starlink deployment.
..Yes, but even an impact zone that's moving close to orbital speed (which it should be, by the time it reaches Panama) can generate a fairly high probability of casualties if it crosses an area with a population density of 3200 p/km²...
unlike Falcon 9, Starship has Vertical Integration by design.The whole tension rod stuff isn’t necessarily needed on Starship.
If you're worried about debris, they're deployed so low (well under 300km, even though that's what I used above), that the tensioning rods, which have low ballistic coefficients, will deorbit in less than a month.
Quote from: TheRadicalModerate on 08/22/2020 09:31 pmIf you're worried about debris, they're deployed so low (well under 300km, even though that's what I used above), that the tensioning rods, which have low ballistic coefficients, will deorbit in less than a month.Last I checked only the tensioning rods from the v0.9 launch have deorbited, so they have a demonstrated orbital lifespan of many months.
Quote from: Bananas_on_Mars on 08/22/2020 02:12 pmunlike Falcon 9, Starship has Vertical Integration by design.The whole tension rod stuff isn’t necessarily needed on Starship.Without the tension rods tying the satellites down, you risk the stack shifting during stage separation. The obvious counterargument is that during stage separation you're in zero g (not negative g) so there's no force to pull the satellites upward, but there's still non-trivial "bumps" during stage separation. You wouldn't want the satellites just floating there, held in place only by inertia and a prayer.
There has been a lot of discussion over the ability to overfly land while keeping the probability of loss of life below 1 in 10,000. I thought a very high-level summary of how this is done might be useful. For anyone wishing the gory details, I refer you to SAE ARP 4761, which describes in more detail than you will ever want the tools used to calculate the relevant probabilities.One starts with a Functional Hazard Analysis (FHA). In this document, one identifies every functional failure that can result in the worst-case loss of mission or loss of life, but also lower failure modes, e.g. serious injuries, or serious damage etc. This is very much a top-down document, but it serves to identify the failure modalities that can lead to violating the 1:10,000 probability requirement.Once that is established one performs an FTA, Fault Tree Analysis for each hazard identified in the FHA, which can lead to loss of mission or loss of life. The fault tree for each hazard is the chain of events that must occur for the event of interest. This is almost always a chain of events, each of which has its own probability and at each step, is connected to the rest of the tree by logical AND or OR events, allowing eventual calculation of the associated probabilities. A fault tree can be done either qualitatively or quantitatively. The former is used when the expected result does not include loss of mission, or loss or life or serious injury. If loss of life, serious injury, or loss of mission seems near or above the 1:10000 threshold, (above in the sense of the likelihood of occurrence violates the FAA requirement) then a quantitative analysis of the fault tree is required. When the FTAs for each of the hazards identified in the FHA are in hand, and one has identified the trees for which a quantitative analysis is required, one performs a Failure Modes, Effects, and Criticality Analysis, or FMECA. The FMECA is very much a bottom-up analysis starting from the lowest level parts list for the vehicle, and generating a failure probability for every component (This is a very large task for a system with thousands of parts). There are agreed failure models for both electronic and mechanical parts, and for a few novel processes or parts, one might have to construct a new model!?) Once all the models are identified, then there are software programs that will calculate the failure probabilities and put all of them into a database.Now, using the database of failure probabilities for all the parts, one combines them using the rules of combinatorial logic, to generate for each step in the Fault Tree, for each hazard in the FHA a probability of failure. Once all the probabilities are known, then they are inserted into each step of the Fault Tree, and a final probability for each hazard identified. As long as that probability does not violate the 1:10,000 requirement one is golden. If it does, then some mitigation plan must be developed. For a system as complex as the starship, this requires man-years of effort, by experts in various engineering disciplines, but I strongly suspect SpaceX already has built the models and as the design matures, can update them to keep the analysis as best known at a particular point. For each launch trajectory, the final steps of the analysis where one includes the probability of injury or death to individuals on the ground is updated.As one gets actual flight reliability data, the model failure modes are replaced with actual field data, and overtime one tweaks the design to improve the reliability of one's worst five or worst ten issues, which over time also change but this is normal sustaining engineering.It is very much not known by us (but may be by SpaceX) what will be needed to overfly a particular spot on the earth but based on my experience, it might not be as hard as some here expect to achieve the 1:10,000 probability. After over a hundred years of effort, the goal for aircraft is not 1:10,000 but rather 1 in a billion for the equivalent hazards, and it is achieved. I hope this oversimplified process description can inform the interested reader.
There‘s tying something down so it doesn‘t float away in microgravity, and then there‘s stacking satellites until the stack is 7m high and weighs almost 8 tons, and turning the stack horizontal, mating it with a rocket, transporting it up a hill, turning it up vertical at the end of a 60m stick.Look at pictures of the rods and tell me honestly which design criteria you think is driving the design of the rods?With vertical integration, they could be using a totally different concept to secure the satellites.
I suspect it may be a lot fewer Starlink satellites on Starship, at least at first. Maybe like 200 or so. Preserves more propellant margin. Plus early Starships might be really heavy.
