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

[simonbp]

I have a question:why use a launch vehicle with 8mT+ SSO capacity to launch a 500kg satellite?

Because it was once a F1E payload, then the rocket disappeared from SpaceX's plans. Plus this is a test flight.

Actually I think it was originally bought by MDA as Falcon 5 payload. A paper manifest I have from 2006 lists it as a Falcon 9 from Kwaj, but they were already discussing at the time launching from CCAFS and doing a massive dogleg.

[MP99]

Since the point of boost back is to kill the forward horizontal velocity component and replace it with enough horizontal component to reach the landing zone, the point of the test should be to kill enough forward motion to hit the atmospheric interface down range at the same speed as a boost back will hit the atmosphere at.

Yes, but that just shows that you are not understanding the point of this test.

Why?
1) Testing attitude control of first stage after staging;
2) Testing engine restart and performance;
3) Testing first stage reentry with the same parameters (only direction is different);
4) Testing attitude control for landing;
5) Testing low altitude-backward motion engine restart;
6) Testing landing software.
Something missing?

Did I respond to YOU? (does kevin-rf post under multiple aliases?)

No. Just countering kevin-rf's 'claim' that boost-back was an essential point of this test, that it had to hit the atmosphere at the same speed that a boost-back flight would. I'm sure they will try to get somewhat close, but a ballistic trajectory will most likely have a larger horizontal velocity than a "lofted" boost-back one.

MY claim is that surviving reentry is the point of this test. Everything else is gravy.

Make your mind up.

kevin-rf said there'd be no boost-back, and you refuted him.

Everyone else piled in and agreed there'd be no boost-back.

Now, you seem to be saying there will be no boost-back, so why did you disagree with kevin-rf???

cheers, Martin

Edit: or did you just mid-read kevin-rf's post in the first place?

[Lars_J]

Sigh. Everyone seems to be under te impression what the boost-back reentry speed will be, so therefore SpaceX will try to enter at that speed now.

But the crucial thing they are missing is that not even SpaceX knows what that will be yet - they are going to experiment and see what stresses the 1st stage can take. They are going to slowly get there by pushing margins.

This is why you cannot say that this flights booster will enter at boost-back velocity. It also depends on how lofted the ultimate boost-back trajectory will end up. 

[aero]

Sigh. Everyone seems to be under te impression what the boost-back reentry speed will be, so therefore SpaceX will try to enter at that speed now.

But the crucial thing they are missing is that not even SpaceX knows what that will be yet - they are going to experiment and see what stresses the 1st stage can take. They are going to slowly get there by pushing margins.

This is why you cannot say that this flights booster will enter at boost-back velocity. It also depends on how lofted the ultimate boost-back trajectory will end up. 

Mostly agree but it is also true that SpaceX is not operating in a knowledge vacuum. They know the theory, they know their plan, they know their simulation results, they have a nominal trajectory plan and they expect success. The test is to discover what parts of what they know is false or not sufficiently precise and where they have been to conservative in their preparations.

I hope they don't break their RP-1 tank on touchdown and cause an oil slick.

[kevin-rf]

Did I respond to YOU? (does kevin-rf post under multiple aliases?)

No, I only have one account, sorry...

I was pointing out this is a simple test, any test requires two additional restarts.

The first restart to kill enough forward velocity to be able to survive reentry. You do not kill your vertical velocity component.

The second restart is to slow the now reentered vehicle down enough so that it can hover over and then walk on water.

For boost back you really do not want to kill your vertical velocity.

Think about it.

If you zero out booth then you have to fly a ballistic trajectory back to the launch site.

If you only zero out the horizontal since you are still moving upward, you only have to build up enough horizontal speed to reach the launch site before you come back down into the atmosphere.

The second method requires less of a delta V.

As for the saying there is no boost back, that was from one of the many tweets about them walking on water down range for this launch. They have said it will be down range. With all the oil platforms, Vandenberg is a tougher location to do boost back too.

At this point today my mind is fried enough that I think I would have a better chance of finding two identical snowflakes than weeding through the trillions of unique posts to find it where SpaceX said that about the test. It's been a long day, pellet stove cleaned, new dishwasher installed, entertainment center relocated, spring planting done, now since you suggested it, seeing how many accounts I can create.

[averagespacejoe]

I know there is still three months till launch and this launch is filled with complexity with its many firsts... But is it appropriate to separate out the speculation about how the first stage may or may not come back (General Discussion)/(Party Thread) from actual hardware and reports (Updates)? Not sure if its too early for that.

[aero]

Has SpaceX said anything about the plan for the excess margin available for the US? The payload is what? Half a tonne? How high is the orbit and is there any excess margin? I guess that factors into the velocity at MECO and separation for this flight, doesn't it? They might have enough margin to attempt dropping the US into the atmosphere at survivable velocity. Just a thought.

I guess the US would be over land when it comes back around the first time.

[kevin-rf]

I guess the US would be over land when it comes back around the first time.

Shouldn't it be over the pacific and not California... The earth rotates towards the east.

[douglas100]

How high is the orbit and is there any excess margin?

http://mertensiana.phys.ucalgary.ca/quickfacts.html

There's lots of margin on this flight.

They might have enough margin to attempt dropping the US into the atmosphere at survivable velocity.

They could certainly drop it into the atmosphere but without a heat shield it wouldn't survive even if they burned all the remaining propellant.

[MP99]

Sigh. Everyone seems to be under te impression what the boost-back reentry speed will be, so therefore SpaceX will try to enter at that speed now.

But the crucial thing they are missing is that not even SpaceX knows what that will be yet - they are going to experiment and see what stresses the 1st stage can take. They are going to slowly get there by pushing margins.

This is why you cannot say that this flights booster will enter at boost-back velocity. It also depends on how lofted the ultimate boost-back trajectory will end up. 

There will be a slow down burn before reentry, so lofting of the boost back is irrelevant.

Cheers, Martin

[MP99]

I was pointing out this is a simple test, any test requires two additional restarts.

The first restart to kill enough forward velocity to be able to survive reentry. You do not kill your vertical velocity component.

The second restart is to slow the now reentered vehicle down enough so that it can hover over and then walk on water.

For boost back you really do not want to kill your vertical velocity.

Agree re not wanting to kill the vertical component on the boost-back (per your reasons below).

However, I don't think that necessarily applies for the reentry slow-down burn. At it's simplest, you just want to slow down enough not to break up, and orient the stage end-on when it hits the atmosphere.

I also wonder whether that burn will take place before there's any sensible atmosphere, or early in the reentry itself?

If before, then the stage would need to orient horizontal for your burn, then again to direction-of-flight for reentry.

If after, then the stage would have to be side-on to the airflow to do a horizontal-only burn.



If the stage just orients to direction-of-flight and does it's burn, then it will also be orientated correctly for reentry. Since this is simpler and requires less manoeuvres, they might even do this for their initial tests, then get more creative with the actual recoveries on land.



OTOH, if you kill most or all of the forward component of motion, then the stage would just drop vertically through the atmosphere, and that might make for easier targeting of the landing zone.

OTGH, could the stage orient itself for a little lift and make use of the forward velocity to extend / reduce the severity of reentry heating?

cheers, Martin

If you zero out booth then you have to fly a ballistic trajectory back to the launch site.

If you only zero out the horizontal since you are still moving upward, you only have to build up enough horizontal speed to reach the launch site before you come back down into the atmosphere.

The second method requires less of a delta V.

[FinalFrontier]

The fairing bothers me. IMO that is going to be the thing to watch out for on this flight.

That and the schedule. The pressure is on now for them to start flying more rapidly. It needs to go sometime in the next 4 months or so.

[MP99]

The fairing bothers me. IMO that is going to be the thing to watch out for on this flight.

Agree - successful insertion of the payload is many times more important than the post-staging recovery.

That and the schedule. The pressure is on now for them to start flying more rapidly.

Agree - critical.

It needs to go sometime in the next 4 months or so.

ISTM the exact date of the first 1.1 isn't particularly critical, but a quick ramp-up to high cadence is.

cheers, Martin

[ugordan]

Agree - successful insertion of the payload is many times more important than the post-staging recovery.

That's certainly not the impression one gets when looking at the general theme of this thread. Just one more proof that on this forum, it's all about the rocket.

[MP99]

Agree - successful insertion of the payload is many times more important than the post-staging recovery.

That's certainly not the impression one gets when looking at the general theme of this thread. Just one more proof that on this forum, it's all about the rocket.

It is the first v1.1 launch, and Elon did discuss the recovery attempt on this flight.

But, hard to argue your general point.

cheers, Martin

[cro-magnon gramps]

Agree - successful insertion of the payload is many times more important than the post-staging recovery.

That's certainly not the impression one gets when looking at the general theme of this thread. Just one more proof that on this forum, it's all about the rocket.

It is the first v1.1 launch, and Elon did discuss the recovery attempt on this flight.

But, hard to argue your general point.

cheers, Martin

this site has been built around the Engineering of Rockets and Space Craft. Their developments, trials and tribulations. There are many who post here, perhaps a significant majority perhaps, who are either Engineers in Rocketry or who have Engineering backgrounds who have used their knowledge to gain a level of expertise in that field, to good purpose. For better or worse, politics and the missions became secondary, perhaps for good reason also. As those two have proven to be explosive subjects and lead much acrimony and to many locked threads.

Cheers

Gramps

Now this is OT, and we should return to our discussion of the Rocket and the Mission,   

[Clyde]

This might be known already

http://www.parabolicarc.com/2013/03/28/musk-spacex-to-attempt-falcon-9-first-stage-water-landing/

but it seems to answer some questions asked in this thread.

[Chris-A]

Elon's twitter feed could be a good indication on how well the vacuum chamber testing goes. If a week or two goes by without anything, then it might be time to worry about the schedule.

[Garrett]

Elon's twitter feed could be a good indication on how well the vacuum chamber testing goes. If a week or two goes by without anything, then it might be time to worry about the schedule.

That might be true in a world without ITAR. But we're not living in such a world.

[pericynthion]

Elon's twitter feed could be a good indication on how well the vacuum chamber testing goes. If a week or two goes by without anything, then it might be time to worry about the schedule.

That might be true in a world without ITAR. But we're not living in such a world.

Bragging about a successful test is not prohibited by ITAR.