31–40 of 69 posts
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This sattelite was some 8000kgs, vs. 4000-ish kgs for the previous-generation GPS satellites, if I remember correctly.
Any idea why their weight increased so much?
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Two things: 1. A GPS satellite is in a very high orbit compared to LEO, and so all stages were requested to burn to completion, to ensure the satellite has enough margin to reach that orbit. 2. The second stage ends at a ~800 km orbit, while the satellite itself needs to increase this to ~12,000 km (I'm rounding these numbers). The sat has to carry enough on-board propellant to raise it's orbit that much which necess…
Still SpaceX routinely recovers the first stage after launching geostationary communication satellites. I thought GPS should be lighter as they are closer to Earth and needs to send much less information in their signal, so the power requirements and size of Solar panels should be lower.
The only information I can find on why this one was so energy intensive has to do with the high inclination the GPS satellite has to be in (55 degrees), which is pretty far off from inclination of the launch pad in Florida.
Wikipedia says this launch was originally planned on a Delta IV. That would make sense because it has higher specific impulse hydrogen engines. The Falcon does well in LEO, but improved Isp really helps as you go farther out.
Here's a video comparing ULA's rockets to SpaceX: https://www.youtube.com/watch?v=QoUtgWQk-Y0
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yeh cause doing DOD projects from an American Company to increase GPS is a good thing
Not for those on the receiving end of JDAMs SpaceX is taking defense money to launch satellites that are primarily for military use in guiding platforms that deliver things to lethal terminal effect. That's just as martial as Raytheon building the Tomahawk guidance module. Thought experiment: would SpaceX take Russian money to launch GLONASS birds? I'd wager not because it would be 'immoral'.
Even if there's no novel or unusual technology on the Glonass sat, learning that is intelligence in itself.
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I think it is mostly about the path the rocket is allowed to travel during launch. In the US, for equatorial orbits, one launches from Cape Kennedy to the east, and for polar from Vandenburg to the south. Maybe off angle launches aren't allowed so a lot of correction is needed after the satellite reaches orbit to get to an inclined orbit? I am not an orbital mechanics specialist or space launch planner. Corrective co…
Vandenberg is mostly used for polar orbit launches because it's a path over the ocean. Not possible to launch eastbound from there because first stages would fall on populated areas. This is also the reason why the Israeli space program launches into rare retrograde orbits (opposite direction of earth's rotation), westbound over the ocean, because they don't want to drop 1st stages on their eastern neighbours.
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Vandenberg is mostly used for polar orbit launches because it's a path over the ocean. Not possible to launch eastbound from there because first stages would fall on populated areas. This is also the reason why the Israeli space program launches into rare retrograde orbits (opposite direction of earth's rotation), westbound over the ocean, because they don't want to drop 1st stages on their eastern neighbours.
Correct. But the question is, if one wants an inclined orbit, why can't you launch out of Kennedy to the northeast or out of Vandenberg to the southwest. Wouldn't this save all the delta v correction you need to do after getting into an equatorial or polar orbit and then transitioning to an inclined orbit?
no employee protests against DOD projects :)
yeh cause doing DOD projects from an American Company to increase GPS is a good thing
Earlier quoted context omitted.
This sattelite was some 8000kgs, vs. 4000-ish kgs for the previous-generation GPS satellites, if I remember correctly.
Any idea why their weight increased so much?
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GPS is lofted and maintained by the DoD. It's primary purpose is military. It would not exist as a free service without DoD's investment. Other satellite constellations with far fewer sats cost considerable amounts of money to use, and few of our modern applications for GPS would be very appealing at $xxx a month. Civillian GPS is a generous charity from US taxpayers to the rest of the world
No, its primary purpose is civilian. Its original and occasional purpose is military, sure, but as I mentioned, it is used far more widely now, by several orders of magnitude. Its military applications are so eclipsed now by non-war-related uses that the military origins are practically irrelevant.
Keeping track of the boats and missiles pays the bills. Everything else is just a happy accident of zero marginal use cost.
SpaceX had to use a fully expendable Falcon for this launch. What makes a GPS satellite so heavy?
Two things: 1. A GPS satellite is in a very high orbit compared to LEO, and so all stages were requested to burn to completion, to ensure the satellite has enough margin to reach that orbit. 2. The second stage ends at a ~800 km orbit, while the satellite itself needs to increase this to ~12,000 km (I'm rounding these numbers). The sat has to carry enough on-board propellant to raise it's orbit that much which necess…
Looks like they use a liquid fuel thruster lift it to its final orbit[0]. Some other missions have used ion engines for orbit raising[1]. I wonder why that wasn't incorporated into the GPS design.
[0] https://en.wikipedia.org/wiki/Lockheed_Martin_A2100 [1] https://space.skyrocket.de/doc_sdat/ses-12.htm
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No, its primary purpose is civilian. Its original and occasional purpose is military, sure, but as I mentioned, it is used far more widely now, by several orders of magnitude. Its military applications are so eclipsed now by non-war-related uses that the military origins are practically irrelevant.
Civilian use is wide yes, but this is only because it is provided for free by DoD. None of those uses would be economically viable if they had to bear the costs of developing, launching and maintaining the system. Keeping track of the boats and missiles pays the bills. Everything else is just a happy accident of zero marginal use cost.
Doing war stuff with GPS does not generate any revenue. It costs American citizens the same amount of dollars regardless of whether it is used for war or not.
It’s not national, and it’s not security.