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#280
by
TripD
on 24 Jun, 2017 01:40
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I have never understood why there was ever sat connections on the barge to begin with. The barge will ALWAYS have the support ship since it cannot get out to sea by itself. So why not just use a cheap omni or large angle sector antennas (90 or 120 degree) that point towards the support ship, and have the support ship do all the more delicate sat up/down links. Can anyone explain why they would not want to do it this way? Any drawbacks? This is one of the things I never quite understood...
I can only speak for myself. But every time I see the video cut out and then suddenly see the booster sitting on the deck makes be chuckle that the conspiracy theorists are going ballistic right then.
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#281
by
LouScheffer
on 24 Jun, 2017 01:41
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I hope they have a drone video of this landing.
A 'normal' single engine landing generates about twice the weight of the rocket, so net 1G up. Since the rocket is going about 300 m/s, it needs to start 4 km up and brake for 30 seconds.
A true three engine landing would generate 6x the weight, so 5G up. It would start at 900 meters(!), only 13x the height of the rocket itself (and roughly the height of the tallest skyscrapers) and scream to a stop in 6 seconds.
The real landing is probably 1-3-1 or 3-1, and probably not quite so extreme. But it should be sporty indeed.
And all of this to save 12 engine-seconds, or about 1.3 more seconds of first stage boost. Rockets are *really* low margin operations.
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#282
by
georgegassaway
on 24 Jun, 2017 06:52
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And all of this to save 12 engine-seconds, or about 1.3 more seconds of first stage boost.
Presuming that 12 seconds engine-seconds is a good number, since the single engine landing usually burns for about 30 seconds, that would reduce the fuel needed by about 40%.
Really is interesting to think about. The fuel saved is pretty much whatever would be burned for the Falcon booster to do a true "hover" for 12 seconds (or however many seconds if 12 is not correct). And yes, I know, the center Merlin can't throttle down low enough to hover, and they would not do a hover even if it could. This is a theoretical example for those who may have trouble grasping gravity loss (or gravity drag) and therefore why a 3-engine landing requires less fuel than a single engine landing (but is riskier).
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#283
by
Geron
on 24 Jun, 2017 07:04
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The new grid fins are 4*5 feet with claw like features, new metal and 100% reusable!! They are being placed in service within the next few flights, should be super cool to watch:)
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#284
by
Steven Pietrobon
on 24 Jun, 2017 08:25
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The new grid fins are 4*5 feet with claw like features, new metal and 100% reusable!! They are being placed in service within the next few flights, should be super cool to watch:)
I thought that was the size of the old fins. The new fins will be bigger than that.
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#285
by
gospacex
on 24 Jun, 2017 08:37
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I have never understood why there was ever sat connections on the barge to begin with. The barge will ALWAYS have the support ship since it cannot get out to sea by itself. So why not just use a cheap omni or large angle sector antennas (90 or 120 degree) that point towards the support ship, and have the support ship do all the more delicate sat up/down links. Can anyone explain why they would not want to do it this way? Any drawbacks? This is one of the things I never quite understood...
I can only speak for myself. But every time I see the video cut out and then suddenly see the booster sitting on the deck makes be chuckle that the conspiracy theorists are going ballistic right then.
New "SpaceX is fake" videos stopped appearing on UT.
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#286
by
Dante80
on 24 Jun, 2017 09:45
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42801/2017-038A: 212 x 65512 km x 24.06 deg.
42802/2017-038B: 210 x 65641 km x 23.91 deg.
Understanding that the payload mass for this one was 3,669kg, what would be the GTO-1800 theoretical equivalent? Does SES-10 still hold the equivalent mass record for GTO-1800 re-usable performance?
Was this a burn to depletion campaign? Given what was said by Elon, was this the most difficult (speed, distance) S1 recovery attempt or does SES-9 still hold the record for that?
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#287
by
guckyfan
on 24 Jun, 2017 10:18
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Perigee looks low enough. The
first 
second stage should decay quickly.
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#288
by
StuffOfInterest
on 24 Jun, 2017 10:32
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Perigee looks low enough. The first stage should decay quickly.
Umm, first stage decayed in about 10 minutes and then did everything it could to avoid smacking into the ocean. Second stage however will hopefully be returning in the not too distant future.
Sorry, couldn't resist.
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#289
by
LouScheffer
on 24 Jun, 2017 11:38
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42801/2017-038A: 212 x 65512 km x 24.06 deg.
42802/2017-038B: 210 x 65641 km x 23.91 deg.
Understanding that the payload mass for this one was 3,669kg, what would be the GTO-1800 theoretical equivalent? Does SES-10 still hold the equivalent mass record for GTO-1800 re-usable performance?
Was this a burn to depletion campaign? Given what was said by Elon, was this the most difficult (speed, distance) S1 recovery attempt or does SES-9 still hold the record for that?
Here are my guesses about this:
To go from a 180x180x28
o orbit to the one observed takes about 2830 m/s, and results in a GEO-1590 orbit. A minimal GTO (roughly GEO-1800), like SES-10, takes about 2462 m/s. So F9 supplied about 370 more m/s to BulgariaSat.
Using nominal assumptions (ISP=348, second stage empy mass 4.5t, fuel=111.5t) then this should be the same difficulty as putting 4.7t into a GEO-1800. So to me, this seems like they should have had more reserves than SES-10, not less.
Some possible explanations are (a) this was a targeted insertion, whereas SES-10 was a burn to depletion, or (b) they were not planning to three-use this booster anyway, and so decided to try a minimal landing and give all margin to the payload, or (c) this contract very specifically called for a GEO-1600 or better, and after margins for this were included, little was left for landing.
Elon stated this was the most difficult re-entry try yet. This seems backed up by the red-hot grid fins, and the 3 engine landing burn. But it looks like this was a choice, for perhaps one of the reasons above, and not dictated by absolute performance.
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#290
by
Ads
on 24 Jun, 2017 12:44
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When is footage of the landing likely to be available?
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#291
by
cscott
on 24 Jun, 2017 13:53
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When is footage of the landing likely to be available?
It usually gets posted shortly after the ASDS returns to port. And that takes a couple days (you can follow its progress in one of the ASDS threads).
EDIT: and yes, they *could* upload the video from the boat, or send a fast ship to courier it back, or even take it off the ASDS as soon as it's close enough to transfer crew, instead of waiting until the ASDS is tied up and berthed. Lots of ways they could get the footage faster. But that doesn't seem to be what happens, or if it does it doesn't seem to impact the timing of the public posting.
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#292
by
Machdiamond
on 24 Jun, 2017 14:06
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Can't wait for that video. I have a hunch it is going to be badass.
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#293
by
macpacheco
on 24 Jun, 2017 19:36
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Surprising are they not suitable for any more than one reuse?
Wrong takeaway.
This is a Block III stack, this was a launch right at the edge of the recoverable performance for such a stack.
If SpaceX could ONLY do launches that left the booster with enough performance margin, they could do a longer re-entry burn and save 1 or 2 extra seconds of fuel for the landing and recover the booster just fine.
At the same time, if this were a full Block V booster, it could deliver the same payload to orbit and have enough fuel reserves to recovery this without extra toastiness.
The other way to look at it is existing Block III boosters should be either expended (customer gets more performance, so it pays more for a booster that has limited future value, perhaps customer pays the price for a regular new booster with reuse) or flown to the limit like this (there's probably lots to be learned from this recovered booster, and even if the booster can't be refurbed as is, they perhaps can refurb and requalify the really expensive part of the booster = the engines).
either way, this is what I expect for Block III reflights. Re-re-flights likely will wait until full Block IV or full Block V stacks.
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#294
by
rickl
on 24 Jun, 2017 19:49
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I'd like to see them put Stage 1 telemetry on the left side of the screen and Stage 2 telemetry on the right. During first stage flight they would be identical, then diverge after first stage separation.
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#295
by
wannamoonbase
on 24 Jun, 2017 20:12
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I'd like to see them put Stage 1 telemetry on the left side of the screen and Stage 2 telemetry on the right. During first stage flight they would be identical, then diverge after first stage separation.
I agree, although I've really enjoyed the recent first stage telemetry. Especially noting when the atmosphere is thick enough to start decreasing the speed of the booster.
The first FH launch could have a lot going on. 2 RTLS feeds, 1 ASDS and the US. That would be footage and telemetry porn.
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#296
by
rickl
on 24 Jun, 2017 21:46
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The first FH launch could have a lot going on. 2 RTLS feeds, 1 ASDS and the US. That would be footage and telemetry porn.
We're gonna need a bigger screen!
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#297
by
TripD
on 25 Jun, 2017 03:37
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The first FH launch could have a lot going on. 2 RTLS feeds, 1 ASDS and the US. That would be footage and telemetry porn.
We're gonna need a bigger screen!
Retro man, retro!
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#298
by
manoweb
on 27 Jun, 2017 06:15
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I'd disagree with that. You can build a buoy with your uplink antenna on it, and run a cable back to the ASDS. Get your antenna far enough from the rocket that it doesn't lose signal. It's certainly within the means of SpaceX, just not worth the expense or the recovery team's labor deploying and retrieving it all the time.
Exactly. Or, forget the cable, some radio that uses a "not so directional" antenna.
Also, RP1 + LOX produces ionized gas - is this true?
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#299
by
RDMM2081
on 27 Jun, 2017 06:31
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I'd disagree with that. You can build a buoy with your uplink antenna on it, and run a cable back to the ASDS. Get your antenna far enough from the rocket that it doesn't lose signal. It's certainly within the means of SpaceX, just not worth the expense or the recovery team's labor deploying and retrieving it all the time.
Exactly. Or, forget the cable, some radio that uses a "not so directional" antenna.
Also, RP1 + LOX produces ionized gas - is this true?
I'm going to chime in and say I don't think the "antenna on a buoy on a cable" scheme is going to work either. I don't see any way that a <2m buoy (how big are buoys anyway?) in waves (no thrusters) moves any _less_ than a barge being impinged by rocket exhaust. I'm sure there is a way for the "remote antenna" concept to work, but it's probably not quite as simple as that.
second stage should decay quickly.