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    Capsule Communicator

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  1. Three is enough. Extra signals allow for an estimate of the error (by comparing solutions from the different sets of three), and also allow for fine tuning of the GPS receiver's internal clock (by tweaking the time to minimize the error). The computation of position using three distances from three known points is called trilateration. It is how my old Kerbal GPS mod (Figaro) does it. In that mod, just like in the real GPS system, extra combinations of three are used to estimate the error. (A relevant link for anyone who's interested: https://gisgeography.com/trilateration-triangulation-gps/)
  2. Not everywhere. Many EFIS displays even have a button to allow the crew to switch between metric and imperial altitudes, for use when operating in airspace of countries that use metric altitudes. That, and the International Nautical Mile (the one that counts) is defined as EXACTLY 1852 metres.
  3. Enhanced video shows dust being kicked up during Ingenuity's flight:
  4. 11:00 Pacific Daylight Time (1800 UTC) news conference link: (Sadly, will probably also including introduction by overdone PR lady™...)
  5. A media briefing about the Ingenuity helicopter will start in about 45 minutes from the time of this writing:
  6. I caught a glimpse of this during the tribute montage at the end of the briefing that I linked to above. I'm surprised it didn't make bigger headlines (it impresses me, anyway): The cliff face on the left (The Eiger's North Face in Switzerland) that the red Perseverance logo is projected onto is over 5000 vertical feet high. All three peaks that have images projected onto them (The Eiger, Jungfrau and Mönch) exceed 13,000 feet (~4000m) in height. This would have been quite the sight to see!
  7. Another news conference going live in about 50 minutes of this writing:
  8. Speaking of nerds... I went back and refined my estimate of Perseverance's entry trajectory. I initially went with the simplifying assumption that the path between data points was linear (rather than hyperbolic) and that the speed over that distance was just the average of the speeds at the two data points. Unfortunately, the solution is quite sensitive to the angular distance between the data points used in the system of equations, so the small error introduced with that assumption turns out to be significant. That assumption did provide a good seed value for a couple of rounds of iterations, however. To make a long story short, I refined the solution by computing the actual distance along the hyperbolic curve between the two data points, and computing the actual average speed over that distance. I then adjusted the angular distance between the two points iteratively, so that the distance traveled was correct for the speed and elapsed time between the points. The solution converged quickly. It only took two iterations to settle onto a result that was consistent, all around. I also used the most widely spaced values from the mission control video that were still consistent with the vis-viva equation, in order to minimize the error that results from not knowing the exact elapsed time between the data points. (I used the video's elapsed time at each data point as my time measurement, so I was probably only accurate to +- a second or so.) Anyhow, the new estimate was that: The periapsis point of the hyperbolic trajectory was about 76 km below the Martian surface The hyperbolic eccentricity "e" was about 1.327 The velocity at periapsis (in the absence of pesky atmosphere and rocks) would have been about 5.473 km/sec The entry interface angle (at the entry interface time cited during the landing) was -14.6 degrees And just for completeness, I plotted it. The heavy read line represents the Martian surface, the dotted red line the Martian atmosphere, and the blue solid line is the entry trajectory. The two pluses show the computed locations of the data points that I used for the estimate.
  9. I recall that Bombardier tried active noise cancellation in the cabin of the Dash-8 Q400 aircraft, but it struck me more as a gimmick... and we're getting off topic.
  10. That thing really is going down like a greased piano... no messing around.
  11. And admittedly not a planet, but I recall that Huygens recorded audio on Titan?
  12. So I nerded out yesterday evening and attemped to compute the hyperbolic trajectory that Perseverance followed to the entry interface. I used the data that was shown on mission control's readouts in the mission control livestream. I ended up having to make some simplifying assumptions but I arrived at an eccentricity of about 1.3 and a periapsis point about 130km below the Martian surface. The entry interface angle worked out to about 18 degrees. That's a bit steeper than the value of ~15 degrees that I heard quoted during the livestream. The data from the early part of the entry in the livestreams was still consistent with the vis-viva equation (i.e. aerobraking wasn't having a significant effect yet), so I don't think my numbers will be too far off. But it would be interesting to know the actual values. Anyone have any idea what they might have been? ------------------------------------------------ Next press conference is at 10:00 Pacific Time today. Hopefully they'll show them then?
  13. Post landing briefing going live shortly (they seem to be running late):
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