30
$\begingroup$

This answer says:

GPS Block III satellites are being launched to replace failed or aging Block II satellites, which doesn't require launching more than one at a time. A Falcon Heavy could fill up an orbital plane with six satellites in a single launch, but there's no need for it.

Could a FH really do done in a semi-standard way?

  • Could you fit all six into a FH fairing? If not, would a slightly larger one be enough?
  • Is there enough lifting power to get all six to some place where they could reach MEO? Could the FH 2nd stage get them all the way to that altitude and inclination?
$\endgroup$
  • 1
    $\begingroup$ Fixed your link, but with a link that gives me credit for the views, so feel free to re-fix it. $\endgroup$ – Russell Borogove Nov 26 '19 at 4:20
  • $\begingroup$ @RussellBorogove thanks! $\endgroup$ – uhoh Nov 26 '19 at 5:30
  • 2
    $\begingroup$ Just a side remark: Would you want to risk 1.2 billion worth of satellites (refundable by insurance) in a single launch and years of production time (non-refundable), if you could send them in batches of two for just about 10% more money? $\endgroup$ – asdfex Nov 27 '19 at 13:16
  • $\begingroup$ @Bill thanks for the edit! Since the FH is reusable, a "single FH" could also do it in six flights! So I've edited the title even further. $\endgroup$ – uhoh Nov 28 '19 at 22:23
41
$\begingroup$

Could you fit all six into a FH fairing? If not, would a slightly larger one be enough?

I can't find dimensions for GPS III sats, but this Lockheed Martin image shows how much of a Delta Medium 4-meter fairing is taken up by a single one:

enter image description here

Looking at the dimensions of the fairing in the Payload Guide, I think the satellite is about 5m long by 2.5m wide.

The Falcon "long fairing" has a payload envelope of 4.6m internal diameter up to 12.2 m of length, then tapering to 1.45m diameter at 16.5 m. Unfortunately, I can only find these dimensions in a drawing in a Quora posting with no source citation:

enter image description here

Thus you can fit two GPS sats stacked lengthwise with a little margin for a deployment rack of some kind, but a third wouldn't fit without a stretched fairing.

Six is Right Out.

Is there enough lifting power to get all six to some place where they could reach MEO? Could the FH 2nd stage get them all the way to that altitude and inclination?

GPS III sats mass around 4.4 tons. The transfer orbit for a GPS III on Delta IV is 1200 km x 20185 km. Silverbird tells me Falcon Heavy can do 26.7 tons to 1200 km x 20185 km 55º in fully expendable mode -- because of the high inclination, the payload capacity is just about the same as it is for an equatorial GTO insertion, so it appears FH can just barely put the mass of 6 satellites into that orbit.

As far as I can tell, the satellites do their own circularization, so presumably the six could get into independent phasing orbits and drift into their assigned slots at leisure once delivered into the target plane.

| improve this answer | |
$\endgroup$
  • 3
    $\begingroup$ Falcon Heavy fairing is bigger. Per en.wikipedia.org/wiki/Falcon_Heavy - 13.2m height, 5.2m in diameter. If the estimated size of satellite (5 x 2.5) is accurate, it should be possible to fit 8 satellites in one fairing (not counting with weight limits). $\endgroup$ – CorwinCZ Nov 26 '19 at 16:20
  • $\begingroup$ Right, but obviously the fairing isn't exactly square - with 2.5mx5m rectangular prisms in a bullet-shaped fairing of 5.2mx13.2m, I'd be surprised if they could fit more than 4 of the buggers in a 2x2 configuration. $\endgroup$ – bracec Nov 26 '19 at 16:42
  • 1
    $\begingroup$ No no, I meant 2x2 in a vertical configuration. The whole issue is that the current fairing is only 5.2m wide, and you cannot put a 5m wide square peg in a 5.2m wide round hole. 2x2 vertical is the best you could do with the current fairing, although you could probably fit more if you made a custom fairing for the job. $\endgroup$ – bracec Nov 26 '19 at 17:12
  • 5
    $\begingroup$ @CorwinCZ Those dimensions are outer, not inner, and the length includes a tapered portion. Falcon 9 payload guide 2009 says the fairing is 5.2 m x 13.9 m, but payload envelope maximum diameter is 4.6m. (I'm guessing the 13.2 for FH in WP is a typo, or the fairing got shorter since 2009.) Full-width payload envelope length is 6.6m; at 11.4m it's down to 1.3m diameter. 4.6m is definitely not enough to get two side by side. $\endgroup$ – Russell Borogove Nov 26 '19 at 17:24
  • 2
    $\begingroup$ I found a different source showing a long fairing with 12.2m length at full-width, so two sats would fit nicely, but it tapers from there to the 16.5m so a third wouldn't be able to fit. quora.com/… $\endgroup$ – Russell Borogove Nov 26 '19 at 17:29

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.