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#20
by
sublimemarsupial
on 20 Feb, 2014 20:26
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#21
by
Wigles
on 20 Feb, 2014 21:09
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Elon has said that the Merlin 1D is currently only operating at 85%. Would this make up the 0.5t discrepancy?
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#22
by
Chris Bergin
on 20 Feb, 2014 21:35
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Done and done!
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#23
by
newpylong
on 21 Feb, 2014 00:52
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#24
by
LouScheffer
on 21 Feb, 2014 01:33
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SpaceNews reports that it is in fact riding uphill on Falcon 9, NOT Falcon Heavy. At 5.3 mt, its either not going to anywhere close to a traditional 1500 m/s GTO, or SpaceX is sandbagging their advertised capacity of 4.85 mt to GTO.
http://www.spacenews.com/article/satellite-telecom/39558updated-ses-books-falcon-9-for-2016-launch?utm_content=buffer96acd&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer
No the article says they will use thrusters to raise orbit. So robotbeat is right.
No, the article says "SES and Airbus Defence and Space said the satellite would employ chemical propulsion to raise its orbit from the Falcon 9’s drop-off point to final geostationary location, and electric propulsion to maintain itself stably in orbit once at its operating position."
So it is NOT using electrical thrusters to get into GEO, implying it *is* in a more or less traditional GTO orbit. So I suspect that SpaceX experience with the first two mission allows them to be confident of a larger payload. It doesn't take much; a very slightly better than minimum ISP, or slightly smaller residuals, or both, could easily account for the extra 450 kg.
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#25
by
Robotbeat
on 21 Feb, 2014 01:34
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Or they're just using more chemical propulsion to get into the initial orbit. Using electric propulsion for station-keeping may free up the chemical system for quick orbit insertion.
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#26
by
beancounter
on 21 Feb, 2014 03:13
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I think TrueBlueWitt ment if they use a Heavy instead.
I think TrueBlueWitt ment if they use a Heavy instead.
Actually, a GTO mission would be a worst case test of recovery of a second stage, since the thermal conditions would be extreme.
Wouldn't they have enough margin, given it's such a light load on a F9H, to propulsively brake to nearer LEO re-entry velocity prior to re-entry if they chose?
Hi. What's with the F9H? It's confusing. There's F9 v1.1 or just F9 and there's FH. Please use the appropriate designation.
Cheers,
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#27
by
SpaceDom
on 21 Feb, 2014 04:05
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Hi
I am not a specialist in trajectory but what happen in mass capacity if Falcon 9 V1.1 is launched from Boca Chica Beach Tx. ? Flight is in 2016, if Spacex take a decision quickly, the pad will be ready ?
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#28
by
Comga
on 21 Feb, 2014 04:54
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Hi
I am not a specialist in trajectory but what happen in mass capacity if Falcon 9 V1.1 is launched from Boca Chica Beach Tx. ? Flight is in 2016, if Spacex take a decision quickly, the pad will be ready ?
Welcome to the forum.
A Texas launch site is well out. 2016 is really pretty soon.
Check out how long it took to get the pad up and running at Vandenberg, and that didn't require SpaceX to create any launch support facilities like radar and telecom, never mind bringing in electric power, water, internet, etc.
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#29
by
Lars_J
on 21 Feb, 2014 05:07
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F9 not capable of 5 tons to GTO, so it has to be a FH.
The article says that the launch mass of the satellite will be 5 tons, which is 10% of the capability of FH. I suspect the bottom line is that Space News is wrong.
However, we should not discard a third possibility, that Elon is promising some enhanced variant of Falcon 9 to customers in a couple of years.
Some have speculated that SpaceX is "sandbagging" the true performance numbers for the F9v1.1 (when comparing to Nasa NLS II figures) - Or more likely, the numbers on the SpaceX might already take into account stage 1 reuse, as others have speculated. (Both the SES-8 and Thaicom-6 missions did apparently reserve some propellant for restart tests)
Now that those two GTO missions are done, they clearly know the true performance of the LV to a much greater degree than earlier - so if they are comfortable with a GTO payload of this size, presumably it can be done.
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#30
by
PerW
on 21 Feb, 2014 06:13
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Copy paste from @pbdes again:
"SpaceX: Falcon 9 can lift 5,300kg to GTO. Published 4,850kg max included 450kg we reserved for ourselves. So 5,300kg SES-10 fits on F9."
So i guess the first tweet about using FH was not right then? Interesting any how.
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#31
by
Kaputnik
on 21 Feb, 2014 07:48
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Does that include any margin for stage recovery, I wonder?
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#32
by
MikeAtkinson
on 21 Feb, 2014 08:14
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Does that include any margin for stage recovery, I wonder?
Probably not in my opinion.
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#33
by
Sohl
on 21 Feb, 2014 12:58
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Does that include any margin for stage recovery, I wonder?
Probably not in my opinion.
Mine too. Maybe go legless and set thrusters to full.
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#34
by
MP99
on 21 Feb, 2014 15:09
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Does that include any margin for stage recovery, I wonder?
Probably not in my opinion.
Doesn't sound like they're going to have much in the way of margins, even for an expendable flight.
SES may accept risk (small, I hope) of a bit of a shortfall in the dV-to-GTO if something goes wrong. Will be interesting to hear, as the launch approaches, whether this flight is at risk of under-performing in event of, eg, first stage engine out.
cheers, Martin
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#35
by
Mader Levap
on 21 Feb, 2014 19:36
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Well, SES engineers were "embedded" in some SpaceX team during that troubleshooting of second stage. I think SES knows real performance figures of F9 - and basis for them - very, very well.
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#36
by
Joffan
on 21 Feb, 2014 20:59
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(Both the SES-8 and Thaicom-6 missions did apparently reserve some propellant for restart tests)
Or perhaps the reserve was for engine-out and other contingencies - once the contingencies did not arise, it was then free for some restart testing.
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#37
by
Robotbeat
on 21 Feb, 2014 21:05
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If there is a performance shortfall, the satellite has a LOT of margin in the electric propulsion system... They'd lose many months thrusting, but as long as they get to a semi-stable orbit, if the Xenon tanks are full (about 350kg, I think?) they technically have enough to get basically all the way to GSO even from LEO (assuming they plan to do GTO to GSO relying on chemical propulsion, with a little chemical left over for margin... LEO ends at roughly 2000km, so they'd probably have to be close to that altitude at apogee for this to work...)... though it'd basically be out of fuel at that point, with reduced capacity solar arrays. It'd also take a really, really long time...
...my point is that even with engine-out or a performance short-fall, it wouldn't necessarily be a complete loss for SES (pretending for the moment that they don't have insurance... which they would have).
...They'd have to time the thrusting periods right, though, which would take a lot longer than just thrusting constantly, though... You really wouldn't want to do this operationally, at least not unless you had a bigger array and better thrusters.
EDIT:Such a performance shortfall happened in the past with an Ariane 5 partial failure, with an electric propulsion system that I believe shares heritage with SES's bird:
http://erps.spacegrant.org/uploads/images/images/iepc_articledownload_1988-2007/2003index/0096-0303iepc-full.pdfThe combination of chemical and electric propulsion eventually saved the mission. Electric propulsion adds a lot of flexibility and robustness to these sorts of missions.... As long as you get into orbit!
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#38
by
kevin-rf
on 21 Feb, 2014 23:35
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While it could make GSO if a performance shortfall occurs, overcoming a performance shortfall will consume Xenon and reduce the operational lifetime of the satellite. SEP is not free.
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#39
by
Robotbeat
on 22 Feb, 2014 04:19
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While it could make GSO if a performance shortfall occurs, overcoming a performance shortfall will consume Xenon and reduce the operational lifetime of the satellite. SEP is not free.
Isn't that exactly what I said?
