SpaceX Falcon 9 v1.1 - CASSIOPE - September, 2013 - GENERAL DISCUSSION THREAD

[Lars_J]

Interesting insights into SpaceX's support for media with this launch (ie none). And the general problem perhaps too.

http://www.americaspace.com/?p=41515

There might be something to it, but I would also take much of what Jason Rhian @ americaspace.com writes about SpaceX with a grain of salt. His posting history with regards to SpaceX has been somewhat hostile at times.

This is the first launch from a new pad, not yet 100% complete. As we get closer to launch, we should see more pictures. Also, in the past, a lot of the pictures from CRS launches have been shared by NASA - who is not a customer on this flight.

[PattiM]

re: sinking...   Well, if there is ~50% gas left in the tanks as they sink, the increasing overpressure as they sink will crush them.  It's not built like a submarine.  How thick are the tank walls?

[Robotbeat]

I don't see how they could sink if there's gas in them.

[PattiM]

Any words yet on actual launch date?   

[Chris Bergin]

Any words yet on actual launch date?   

Not yet. Probably after the WDR (which is tomorrow per L2). As with all launches, it's always a NET (No Earlier Than). NET September 9 or 10 right now.

[Robotbeat]

Any words yet on actual launch date?   

No earlier than September 10th:

Sources say the first launch of SpaceX's Falcon 9 v1.1 from Vandenberg is NET Sept. 10. That's a five-day slip from the previous target.

https://twitter.com/StephenClark1/status/372505876713590784

(This was on L2 before twitter, just to give a little mini-advertisement of L2...)

[Longhorn John]

L2 note of that slip was exactly 42 hours before that tweet! L2 is amazing

[PattiM]

I don't see how they could sink if there's gas in them.

There just needs to be slightly less gas than needed to displace a mass of water equivalent to the mass of the metal.  Aluminum is about 3x denser than water, so I guess the tanks would have to be pretty full of water to sink.  Still, due to the compressibility of air, floating when they're just about to sink is an unstable equilibrium.  Coupling with wave motion could also cause problems, such as structural instability leading to tank breach.

[smoliarm]

re: sinking...   Well, if there is ~50% gas left in the tanks as they sink, the increasing overpressure as they sink will crush them.  It's not built like a submarine.  How thick are the tank walls?

>>if there is ~50% gas left in the tanks as they sink
If 50% of tanks volume are still filled with gas - the stage stays afloat for good. It has total displacement of ca. 450 tons. Its dry weight is only about 25 tons.

>>How thick are the tank walls?
about 1 inch, but I could not find a reference.
Also, the thickness is different for LOX tank and for RP-1 tank

[Robotbeat]

I doubt they're 1 inch thick solid aluminum alloy.

[smoliarm]

I doubt they're 1 inch thick solid aluminum alloy.

Of course not, I did not mean this. The tank walls are not simple solid sheets.
On SpaceX site, in archives about 2009-2010 -- there was a nice detailed post on tank structure, but with their new site design I can't find it
The walls of lower (RP) tank are (as I recall) a bit thicker than 1", but they aren't solid, it is a kind of isogrid (or rib-stringer structure).
Anyway, if you take tanks dimensions (3.7 x ~40 m), calculate area for walls and 3 bulkheads, use Al-Li SG=2.65 g/cm3 and assume some tank weight - you can calculate average effective thickness. It will be something from 15 to 20 mm depending on weight assumed.

[cambrianera]

For F9 v1.0 wall thickness was 5 mm; RP1 tank had additional stir friction welded stringers (joined with rivets between sections of the tank).
Tank domes are probably thicker (about 12mm).
F9 v1.1 seems to have some differences, my opinion is SpaceX changed stringer‘s joining method to save worktime.

[Noborry]

re:sinking.
To sink it, you would need to fill something *more* than 95 % of the tank volume with water.
At that point, you can be assured the gaping hole the water would have needed to enter by is a greater worry than crushing due to compression of the tiny bit of remaining air.

[yg1968]

Here is something new to chew on while we wait....


https://s3.amazonaws.com/public-inspection.federalregister.gov/2013-20726.pdf

Here is an article based on your link. It's proof that other journalists read this website.
http://www.spacenews.com/article/launch-report/36960spacex-to-test-reusable-booster-technology-during-launch-of-canadian

[ChrisWilson68]

Interesting insights into SpaceX's support for media with this launch (ie none). And the general problem perhaps too.

http://www.americaspace.com/?p=41515

There might be something to it, but I would also take much of what Jason Rhian @ americaspace.com writes about SpaceX with a grain of salt. His posting history with regards to SpaceX has been somewhat hostile at times.

This is the first launch from a new pad, not yet 100% complete. As we get closer to launch, we should see more pictures. Also, in the past, a lot of the pictures from CRS launches have been shared by NASA - who is not a customer on this flight.

The article has a lot of complaining about events in the past.  The only thing that's recent seems to be that for the Cassiope launch, media can view it as guests of the Air Force instead of as guests of SpaceX.  SpaceX says it's engaging less with the media on this launch at the request of its customer, MDA, and MDA didn't respond to requests for comment.

I fail to see how any of that is on SpaceX.

[Prober]

re:sinking.
To sink it, you would need to fill something *more* than 95 % of the tank volume with water.
At that point, you can be assured the gaping hole the water would have needed to enter by is a greater worry than crushing due to compression of the tiny bit of remaining air.

re:sinking  rethink  if the weight of the engines and tank are angled down; it will displace the water and sink even with a pressurized tank
 
check out how a submarine works.

[Lobo]

A 'bad omen'? By what connection? A rocket once failed to clear its launch pad?

I'll be honest guys, this flight has me the most concerned out of all of SpaceX's so far.

More than the first F9 flight? The first Dragon to ISS? The first few F1 flights? Have you forgotten those, or worse - think SpaceX have forgotten?

Yes, more than those.

It is precisely because I remember them that makes this one more nerve-wracking. And if this flight is not nerve-wracking for you, then you are not aware of what is at stake here. This is literally a make-it-or-break-it shift for SpaceX. I am not concerned because I feel they will fail, but because failure *at this point* would be catastrophic for them precisely due to their previous steps. Note my first element, the launch insurance. This is a huge part of my nerves. Once upon a time I worked for an insurance underwriter. If this launch fails, SpaceX will be instantly toxic. The cost to launch on a SpaceX vehicle will skyrocket because the cost to insure the payload will skyrocket. This in turn will price them out of the market.

This has happened before, look at the issues SeaLaunch has undergone after their failures. Already the launch insurance industry is on-edge after the Proton failure just a few weeks ago. A rate jump from the current 7% to 25% or higher is not unheard of *and is perfectly normal after a launch failure of a new system*. On a $400 million satellite, having to pay 25% instead of 7% is an additional $72 million per launch, suddenly making the Atlas V at $50 million more than the Falcon 9 suddenly much more cost effective.

And don't forget, SpaceX already burned one insurance policy from its failure to deliver its secondary payload to the proper orbit.

My nerves are due to knowing this. SpaceX has delt with government contracts, which do their own underwriting. This launch is commercial, it is being underwritten by an independent underwriter, which means much more pressure on them, and with every other factor in place, this puts them with their feet to the fire.

Well, hopefully they feel pretty confident about launching their first F9v1.1 with a payload, rather than having a test launch first.  I'm assuming they wanted to save a test launch to save the company money, but hopefully that doesn't come back to bite them in the rear.

[Lobo]

My prediction would be earth escape, mostly because it doesn't leave the 2nd stage in orbit as debris. Additionally, with the light payload, my guess is there's plenty of propellant to attain a minimum c3. Any additional burn time simply adds energy to the orbit, which doesn't really matter.

What if SpaceX will perform a TMI with a small payload with the upper stage? Something containing a simple camera, solar panels, cold gas thrusters and high gain antenna? I believe the performance should be enough to do this.

It's been announced that, beside CASSIOPE, there will be 5 secondary payloads. Four are known, which leaves a fifth "unknown";

Payload	Mass
CASSIOPE	490 kg
CUSat-1	41 kg
CUSat-2	41 kg
DANDE	50 kg
POPACS, 3U	4 kg
Unknown (Mars probe?)	~200 kg
Mounting hw	~174 kg
Total	~1000 kg

My calculations, shows this might be possible with the following Delta-V margins;

Orbit	Payload, kg	Dv from 300 circ	Dv margin, m/s
300x1500 80°	676 kg	2250 m/s	~94 m/s
300x60000000 80°	200 kg	3200 m/s	~531 m/s	Passes Mars orbit

http://tinyurl.com/CassiopeMars
(Disclaimer; IANARS + guesstimates; please correct me if I'm wrong)

Note; The sattelite could not enter into orbit around Mars, only a possible fly-by in case Mars "happens" to be close enough to use residual delta-v in upper stage to "take aim" early in flight, which might be possible considering the time is almost right for optimal TMI.

Why would this be done? To measure performance of Upper Stage, and snap some pics for Musk to tweet casually next year.

Is Mars and Earth aligned correctly right now for a Mars flyby trajectory?

[ChrisWilson68]

Well, hopefully they feel pretty confident about launching their first F9v1.1 with a payload, rather than having a test launch first.  I'm assuming they wanted to save a test launch to save the company money, but hopefully that doesn't come back to bite them in the rear.

Cassiope is kind of a test launch.  It's a lot smaller and less valuable than the typical Falcon 9 payload.

[llanitedave]

re:sinking.
To sink it, you would need to fill something *more* than 95 % of the tank volume with water.
At that point, you can be assured the gaping hole the water would have needed to enter by is a greater worry than crushing due to compression of the tiny bit of remaining air.

re:sinking  rethink  if the weight of the engines and tank are angled down; it will displace the water and sink even with a pressurized tank
 
check out how a submarine works.

The submarine submerges by opening valves at the top of the ballast tanks to allow air to escape as the water enters from the bottom.  The bottom of the ballast tank is always open.  As long as the tank valves are shut, no air escapes, so no water gets in.

If the Falcon 9 tank is floating engines down, even if it's possible for water to enter the tanks through the engine piping (assuming the valves are no longer sealed, or don't shut against reverse pressure), as long as there is no hole in the top of the tank, the water entry will be limited by internal pressure, and the tank will remain afloat.