• 0 Posts
  • 4 Comments
Joined 2 years ago
cake
Cake day: July 17th, 2023

help-circle

  • Based on my image search engineering, the answer to your question is 2.

    Based on my one semester of air breathing propulsion that I took 25 years ago, I’m guessing there is more going on inside the turbine part of the engine that both allows sustainable fuels that current turbofans can’t and also allows compression ratios at lower fan speeds that allows an open fan with fewer blades. Again, I barely passed air breathing propulsion back then and haven’t used ANY of that knowledge since, so I’m mostly talking out of my ass.


  • GPS and Galileo satellites are in MEO, not GEO. GEO is a very specific altitude to keep a satellite directly over the same spot on Earth at all times (synced to the spin of Earth). MEO, on the other hand, is a wide range of altitudes roughly half the altitude of GEO. GPS sits right around 9800 nautical miles, which is 11200 miles. That’s still really far away, so your point stays the same. Galileo is in a similar orbit, I think around 200 miles lower but I can’t remember. GLONASS is there, too. Beidou from China has birds in both MEO and GEO. QZSS from Japan uses one GEO bird and three birds in a highly inclined orbit at GEO altitude.

    Your two points are good. I think a third point would be that this is a different RF spectrum, while GPS and Galileo are on roughly the same RF spectrum. Jamming GPS and Galileo at the same time isn’t difficult. Jamming a very different RF spectrum at the same time is much harder.


  • They were only able to receive signals from the bare minimum to achieve a solution (4 GPS and 1 Galileo). Their achieved accuracy was +/- 1.5km and +/- 2m/s. That is good enough in astronomic scales to get you to a planet, but it isn’t going to help failed landings or autonomous landings.

    I don’t think there was any new tech involved, just a receiver put on a moon lander to see if it could detect signals. And this won’t really do anything for Mars for two reasons: 1) the signal strength would be too small for any reasonable antenna to detect GPS L1/L5 at Mars distances, and 2) the distance would make the geometry be unusable to trilaterate a solution… think about a triangle where two lengths are 100 million miles and the third length is 100 miles. That is a completely worthless geometry for trilateration of a position solution. Even if we could somehow detect a GPS signal at Mars, best case is we get atomic clock time.