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

[deltaV]

It seems to me, based on the knowledge gained from reading many expert posts (thank you!) on this forum, that one would never want to do a substantial portion of the plane-change burn at perigee, where the cost in delta-V is  higher than at apogee. To make good use of the very high apogee, it seems that you would want to complete zeroing out the inclination at apogee. For added efficiency, you would combine that with the perigee-raising burn, completing both at apogee. Then, at next perigee, burn retrograde and lower the apogee to GEO.

I can see other options to reflect spacecraft and/or orbital constraints, but I think that the plane change burn (or burns) would only occur at apogee. To do otherwise would waste the extra delta-V cost invested in getting to the super-sync orbit.

For the reasons you mentioned the majority of the plane change should be done at apogee. For best results however you shouldn't do 100% of the plane change there. The reason for this is that the cost of a burn that both lowers the apogee and lowers the inclination is not the sum of the costs of doing those two maneuvers separately. It turns out that adding a little inclination change to the apogee lowering burn comes almost for free.

Edit: a problem with similar behavior is minimizing x^2 + 10*y^2 subject to x + y = 1.  Think of x as the inclination change at apogee and y as the inclination at perigee. If you do the calculus x is bigger than y but both are non-zero.

[Kabloona]

Looks llke I was posting in the wrong thread ,, maybe this is the right place..

Re: SpaceX Falcon 9 v1.1 - SES-8 - November 25 - UPDATE THREAD
« Reply #172 on: Today at 06:15 PM »

Quote from: tigerade on Today at 05:41 PM
Jonathan Amos ‏@BBCAmos

Falcon-9 telecon tonight with SES CTO Martin Halliwell: Entry of @SpaceX to commercial launch market will "shake industry to its roots".



Since my last msg was "lost", let me re-phrase my reply... if this launch and the next go well, thats the #2 sat service provide aligning with Spacex and three in a row for F9 v.1.1 means the airforce et. al can use Spacex services.. now that must make ULA/LMT worried.. we are looking for proof that history is been made.. watch LC40
Modify message

Since you mentioned Halliwell....Spaceflight Now quotes him as praising SpaceX highly for their openness during the anomaly investigation and allowing SES folks to "embed" with SpaceX propulsion engineers. And he specifically said much different this experience was from working with other launch providers. Sounds like another convert. Hope the launch goes well for him.

[Garrett]

Not sure if this has been posted before, but the attached image of a F9 launching with an SES decal on the fairing can be seen on the front page of the SES website

[douglas100]

Isn't that part of the Ariane 5 service tower shown below and to the right of the F9???

[Rhyolite]

I got to go to the SES-SpaceX customer reception / press event yesterday afternoon.  Most of what was said there has been reported elsewhere but there are a couple of tidbits that seemed noteworthy.  First, Elon said that SES had given them permission to attempt to recover the stage on this flight but that SpaceX had chosen to reserve the margin for the flight.  He also said that even though they were not going to attempt to recover the stage on this flight, they were going to gather data on reentry and that the max Q on reentry was expected to be 4 times higher than on the previous v1.1 flight.

FWIW.

[guckyfan]

I got to go to the SES-SpaceX customer reception / press event yesterday afternoon.  Most of what was said there has been reported elsewhere but there are a couple of tidbits that seemed noteworthy.  First, Elon said that SES had given them permission to attempt to recover the stage on this flight but that SpaceX had chosen to reserve the margin for the flight.  He also said that even though they were not going to attempt to recover the stage on this flight, they were going to gather data on reentry and that the max Q on reentry was expected to be 4 times higher than on the previous v1.1 flight.

FWIW.

So they will at least use the thrusters to keep the stage aligned? Seems a good test. They will see at which Q force the stage will collapse. A good data point to have.

[donaldp]

The BBC has an article that appears to sum up what's involved and the importance of this flight.

http://www.bbc.co.uk/news/science-environment-25087861

[cambrianera]

I got to go to the SES-SpaceX customer reception / press event yesterday afternoon.  Most of what was said there has been reported elsewhere but there are a couple of tidbits that seemed noteworthy.  First, Elon said that SES had given them permission to attempt to recover the stage on this flight but that SpaceX had chosen to reserve the margin for the flight.  He also said that even though they were not going to attempt to recover the stage on this flight, they were going to gather data on reentry and that the max Q on reentry was expected to be 4 times higher than on the previous v1.1 flight.

FWIW.

Thanks for sharing!
I was wondering if SpaceX was going to try something similar, due the fact that F9 v1.1 has a lower staging velocity (2000 m/s instead of 3000 m/s).
Still difficult to get something intact, but as guckyfan says, a good data point.

[tigerade]

Great article on today's launch from BBC's Jonathan Amos:

http://www.bbc.co.uk/news/science-environment-25087861

"We've done everything we can possibly think of to maximise the reliability of this launch," said Elon Musk, the SpaceX CEO and chief designer.

"There's no stone that hasn't been turned over at least twice to maximise the probability of success. Being a rocket, there's still some chance of failure, but whatever happens we can be at peace that we've done everything we could think of, and SES's technical team has looked at it and they concur."

[Avron]

looking for link to the ksc cameras, hopefully one is online and targeted on LC40

[rocketfan42]

The view of LC40 from my hotel room at Ron Jon's Cape Caribe Resort in Cape Canveral (next to Jetty Park).

[Avron]

The view of LC40 from my hotel room at Ron Jon's Cape Caribe Resort in Cape Canveral (next to Jetty Park).

awesome.. thanks, she is vertical..

[Chris Bergin]

The view of LC40 from my hotel room at Ron Jon's Cape Caribe Resort in Cape Canveral (next to Jetty Park).

That's what I call a good first post. Welcome to the site's forum!


--
William's launch article going on shortly. Will post in the update thread.

[cro-magnon gramps]

The view of LC40 from my hotel room at Ron Jon's Cape Caribe Resort in Cape Canveral (next to Jetty Park).

That's what I call a good first post. Welcome to the site's forum!


--
William's launch article going on shortly. Will post in the update thread.

I call that epic posting ;-) now someone get that room number and we'll have a convention there when FH launches (or post our own camera person ;0 )

[MP99]

I got to go to the SES-SpaceX customer reception / press event yesterday afternoon.  Most of what was said there has been reported elsewhere but there are a couple of tidbits that seemed noteworthy.  First, Elon said that SES had given them permission to attempt to recover the stage on this flight but that SpaceX had chosen to reserve the margin for the flight.  He also said that even though they were not going to attempt to recover the stage on this flight, they were going to gather data on reentry and that the max Q on reentry was expected to be 4 times higher than on the previous v1.1 flight.

FWIW.

That gives me a good "in" for a few questions I was wondering.

If this F9 suffers a first-stage engine-out similar to F9 #004 (SpX-1 / CRS-1), that would presumably reduce the margins on the upper stage.

This sort of eventuality is obviously the sort of reason why they are retaining max margin for this flight. And there is no reason for that to lead to a no-go for the GTO injection burn (per 004's secondary).

But, in the event they have a shortfall that exceeds their margin, I was wondering:-

Q1 - if the u/s falls a little short of it's intended dV (but all else is OK), I presume that would that just place the sat at a lower apogee? IE the sat would need to expend some extra prop to get itself to GSO.

Q2 - I presume the injection is not a burn to exhaustion for the u/s?

Q3 - I presume there's no value in going to a higher apogee if they have lots of margin left? (I'm certain the answer is "they'll just go for the apogee they promised", but wanted to ask just in case.)

Q4 - would we expect the u/s to perform a disposal burn after s/c separation? If so, is it likely to position the stage to re-enter, or to push itself on the escape?

Q5 - how long would the u/s usually wait after s/c sep before doing it's disposal manoeuvre? (It's not listed in the press kit.)

Q6 - if no disposal manoeuvre takes place, how often would the u/s cross GSO / be a danger to other GEOsats?

Thanks, Martin

[Chris Bergin]

And I better link it in the other threads too....

William Graham's launch preview:
http://www.nasaspaceflight.com/2013/11/spacex-falcon-9-v1-1-milestone-ses-8-launch/

[Avron]

Musk and kids in the flame duct.. yesterday..  https://twitter.com/TalulahRiley/status/404865657637842946/photo/1

[mlindner]

Musk and kids in the flame duct.. yesterday..  https://twitter.com/TalulahRiley/status/404865657637842946/photo/1

That's just awesome in so many different ways.

[Okie_Steve]

...they were going to gather data on reentry and that the max Q on reentry was expected to be 4 times higher than on the previous v1.1 flight...

Does anyone know how the maxQ reentry loads compare to the launch loads. I'm wondering if it's more likely to crumple or burn up first before hitting the ocean. Of course whether it crumples or TPS fails what's left will "burn down, fall over, and sink into the swamp"

[LouScheffer]

Rather large acceleration for the second stage?

I was surprised the second burn was so short (1 minute).   Intuitively, this would seem to imply rather large accelerations, so I tried some numbers.  If my arithmetic is correct, going from a 200x200 km orbit to 200x80000 takes about 2830 m/sec delta v and even slightly more, since they are reducing the inclination as well.  Spread over 1 minute, this is 47 m/s every second, or 4.8 Gs average. 

The 1D, at full thrust has something like 801kN of thrust.  Making some linear approximations, to get 4.8G average, the mass must average about 17000 kg.  But over one minute, the engine will consume something like 15000 kg of propellant.  So it must start at something like 24500 kg and drop to 9500 kg at burnout.  But that low a mass would give about 8G at burnout, or more than 5Gs even at 70% throttle.

Now you should really use the rocket equation rather than a linear approximation, but the basic conclusion seems unavoidable - the accelerations must be quite large.  Do they throttle back to keep to 5 Gs or so?  Or can the satellite take more?  What would they do if they had a light payload to Earth escape - it would not seem they could throttle back enough to hold it to only 5 Gs...