SpaceX Falcon 9 v1.1 - SES-8 - DISCUSSION THREAD

[ugordan]

I still don't understand your point.

Sigh.

Falcon 9 and Atlas V will fly the same trajectories for GTO missions. Falcon 9 will do the same things, as Atlas if they have known prelaunch excess performance, such as inclination reduction, super or sub synchronous injection.

The point is F9 cannot do all the same trajectories as Atlas if it only has two engine starts available. If I'm reading the following Atlas 401 graph correctly, the knee in the performance curve is the point where a 3-burn insertion becomes higher performing than 2-burn.

Image 2 - Falcon 9 doesn't have a 3rd burn available by default, it would need the delta-V kit (red), otherwise you can see where the blue line takes you.

Whether any U.S. vehicle ever flies that 3-burn profile or if it's just left to the payload to reduce inclination AND circularize, I'm not getting into that. I'll take your word for it. Probably higher performance with payload apogee kick motors anyway as you're not also boosting the stage dry weight.

[Jason1701]

Falcon 9 US has two restarts, not starts.

[yinzer]

I take it the injection would be to a GTO which is 1500 m/s short of GEO (valid assumption?).

Doubtful.  Look at previous GTO parameters for launches from the Cape - 1500 m/s to GEO is not a particularly popular choice.

When I say cost I mean the delta-V requirement for a degree of inclination change. Obviously this is more costly deeper into the gravity well.

Not always.  If you are generating a large in-track delta-V, cosine effects make generating a small cross-track delta-V very cheap.  A common exercise in orbital mechanics textbooks is to calculate the optimal approach for a two-burn transfer from 27.0 degree LEO to equatorial GEO, and the optimum is not to do the entire plane change at apogee.

If I'm reading the following Atlas 401 graph correctly, the knee in the performance curve is the point where a 3-burn insertion becomes higher performing than 2-burn.

I don't know how you're reading the graph.

The sharp knee in the Atlas graph happens when you run into your payload's apogee cap and have to start raising the perigee of your transfer orbit to reduce delta-V to GEO.

Looking at the SpaceX performance graphs does suggest that the "Delta-V mission kit" allows a third burn of the second stage to take place at apogee.

[ugordan]

I take it the injection would be to a GTO which is 1500 m/s short of GEO (valid assumption?).

Doubtful.  Look at previous GTO parameters for launches from the Cape - 1500 m/s to GEO is not a particularly popular choice.

Fair enough. The typical EELV profile from the Cape is what started me thinking about the whole difference between two burns and 3 burns and what it buys you.

If you are generating a large in-track delta-V, cosine effects make generating a small cross-track delta-V very cheap.  A common exercise in orbital mechanics textbooks is to calculate the optimal approach for a two-burn transfer from 27.0 degree LEO to equatorial GEO, and the optimum is not to do the entire plane change at apogee.

I can understand that and even though I've never done that exercise myself, intuitively it would seem to me that it's still optimal to do the majority of the plane change at apogee, purely on account of the massive velocity difference between apogee and perigee.

The sharp knee in the Atlas graph happens when you run into your payload's apogee cap and have to start raising the perigee of your transfer orbit to reduce delta-V to GEO.

Hmm, I'll have to revisit this then.

[Jim]

If I'm reading the following Atlas 401 graph correctly, the knee in the performance curve is the point where a 3-burn insertion becomes higher performing than 2-burn.

Again, Atlas, especially 401's, don't do three burns.  Centaurs are not equipped for those long duration missions.  Three burns would only occurr on heavy missions and maybe vehicles with 4 or 5 solids.

[Antares]

Or in a case with multiple spacecraft in different orbits (STP-1)
http://forum.nasaspaceflight.com/index.php?topic=6900.msg117850#msg117850

[Galactic Penguin SST]

OK two years after the last post, it's time to bump this thread! With the launch scheduled within a month of the CASSIOPE flight, and the first v1.1 first stage has already been shipped to Texas, is it reasonable to expect at least the first stage for this flight to be shipped from California soon?

[Chris Bergin]

Changed the title to realign.

[Jason1701]

OK two years after the last post, it's time to bump this thread! With the launch scheduled within a month of the CASSIOPE flight, and the first v1.1 first stage has already been shipped to Texas, is it reasonable to expect at least the first stage for this flight to be shipped from California soon?

I believe so. The tank is done, and the engines are probably mostly integrated by now. But they may wait to ship it until the first flight stage is off the test stand.

[AnjaZoe]

With the start of SES-8 now delayed from July to October as reported in another thread here, will SES patiently wait (I would expect more shift in delay) or switch to a back-up launcher? Being SES, I would be surprised if they hadn't a plan B in their pockets...

Zoe

[Galactic Penguin SST]

With the start of SES-8 now delayed from July to October as reported in another thread here, will SES patiently wait (I would expect more shift in delay) or switch to a back-up launcher? Being SES, I would be surprised if they hadn't a plan B in their pockets...

Zoe

Which one!? I don't recall seeing this over the past few days..... 

[pippin]

SES' strategy usually is to launch spare sats before they really need them so they have orbital spares. They will not be in an immediate hurry to get this particular bird up there.

[AnjaZoe]

Sorry, the October date is announced for Orbcomm, SES-8 for August. My fault (and egg in the face). I still wouldn't bet for an August launch though.
Look for the Space-X missions section for the announcement.

@pippin: that strategy is not uncommon, however it might come with some penalties or compensations, but what do I know about the contract between SES and Space-X ;-)

Zoe

[pippin]

Sure, didn't want to argue that. My point was just: they might not need to look for a backup launch provider, saving some money when the bird finally goes up might be the better option for SES.

[Prober]

SES' strategy usually is to launch spare sats before they really need them so they have orbital spares. They will not be in an immediate hurry to get this particular bird up there.

believe this firm had a very tight contract with SpaceX.

[input~2]

SES announces SES-8 launch in August
http://www.ses.com/4233325/news/2013/15245628

[Salo]

Not anymore SES 8 in the list of upcoming launches.
http://www.ses.com/4233127/upcoming-launches

[smoliarm]

Not anymore SES 8 in the list of upcoming launches.
http://www.ses.com/4233127/upcoming-launches

Strangely enough, SES-8 is still in their fleet listing -- and there it is listed as  already functional sat in orbit
(see the screenshot below)

Last fall SES announced the backup option for SES-8 (Ariane) in case Spacex can not launch on time. So far there were no word they switch to Ariane, and as of last week they still had this sat scheduled for launch with Spacex in August.

http://forum.nasaspaceflight.com/index.php?topic=29893.msg953590#msg953590

“If there are delays we will have a backup, in this case the Ariane 5,” Bausch said. “If we see a delay in Falcon 9 for SES-8, we would need to inform Arianespace six months ahead..."

So, may be this discrepancy on their site just indicate they choose the backup option and talks with Arianespace are underway.

Alternatively, (optimistically) this may be due to their negotiations with Spacex on delay to Q4 2013.

[Salo]

http://www.ses.com/4233127/upcoming-launches

Q3

ASTRA 5B
SES-8

[Salo]

From Dan Leone(@Leone_SN) on Twitter

@CSA_ASC says notional launch date for #CASSIOPE space weather satellite is Aug. 14 - little later than expected - on @SpaceX Falcon 9 1.1.

SES-8 NET September.