SpaceX Falcon 9 FT - ORBCOMM-2 - Dec. 21, 2015 (Return To Flight) DISCUSSION

[joek]

Another way that a Blue successful landing might influence the decision is strengthening the pro-land constituency inside NASA, AF, and FAA.

Any similarity between what BlueO and SpaceX are attempting--and the associated risks--are at best superficial.  Any decision-maker (e.g., USAF range and FAA) undoubtedly understands the difference and I hope and expect would not be swayed by cosmetic similarities.

However landing on a barge is far harder than landing on land, and SpaceX has already shown that the most difficult part about landing is horizontal accuracy, which landing on land addresses.

Does not matter if landing on a barge is harder or easier.  The only relevant question is the risk to life and property.

So, because SpaceX built a barge, they now have to land on it in order to have clearance to land on land. Right.

SpaceX has to show it is safe to land on land.  An offshore landing is one way to retire risk; no more and no less.

If T-0 is during off-hours, there would be a better chance of a landing attempt being granted at CCAFS. The test would have minimal impact of daily operations ... IMHO

Unlikely.  Areas will be cleared during launch period, and RTLS would be a minor extension to that period.  Risk to life might be marginally minimized (but not something anyone would bet their career on); risk to property would be the same; PR fallout would be the same.

[Robotbeat]

...

So, because SpaceX built a barge, they now have to land on it in order to have clearance to land on land. Right.

SpaceX has to show it is safe to land on land.  An offshore landing is one way to retire risk; no more and no less.
...

Actually, the implication is that it's THE way to retire risk, since the original poster was implying they wouldn't be allowed to land unless a barge landing was previously successful.

But honestly, the barge landings WERE successful. They showed the rocket can be guided to a small landing pad. The fact that the rocket tipped over afterward is basically irrelevant to public safety since the public and public infrastructure isn't anywhere near the actual landing pad (there's a significant buffer around the pad).

[johnnyhinbos01]

By the way - though I've watched the available videos of the barge landing attempts a thousand times, it's been a while and I just watched them again - I am absolutely amazed how SpaceX was able to guide this massive hunk of metal through body surfing and engine relights all the way back to a tiny scrap of a target and basically touch down right on the X. It's dumbfounding that they could do that. Watch the most recent video again. I mean, the booster is giant coming down on that barge. Truly amazing.

I think SpaceX has conclusively proven they have a mature enough system to at least bring their property (booster) back to their property (LX-1 ?). What they choose to do with it at that point (recycle it slowly or much much more rapidly) I don't think the USAF or FAA really gives two...

[joek]

But honestly, the barge landings WERE successful. They showed the rocket can be guided to a small landing pad. The fact that the rocket tipped over afterward is basically irrelevant to public safety since the public and public infrastructure isn't anywhere near the actual landing pad (there's a significant buffer around the pad).

No, they were not "successful"; simply hitting a target is *not* sufficient.  By that metric it should be safe to test any number of weapons systems in closer proximity to public areas.

That the rocket tipped over "after it landed" is far from irrelevant.  It crashed on landing.  By that metric any launch which got off the pad and was subsequently immolated would also be irrelevant.

By what reasoning do you determine that "public infrastructure isn't anywhere near the actual landing pad"; or more precisely, public infrastructure (or people) are not at risk?  Got an MPL calculation or model in your pocket you would like to share?

If not, then please stop stating opinion as if it was fact.

[cscott]

SpaceX struts are made of steel. 

Any specific reason why they chose steel over aluminum?

Steel *is* stronger; just the strength costs weight.

There is also materials compatability: the stainless steel alloy they were using is LOX-safe and strong (not brittle) at cyro LOX temps.

[guckyfan]

But honestly, the barge landings WERE successful. They showed the rocket can be guided to a small landing pad. The fact that the rocket tipped over afterward is basically irrelevant to public safety since the public and public infrastructure isn't anywhere near the actual landing pad (there's a significant buffer around the pad).

No, they were not "successful"; simply hitting a target is *not* sufficient.  By that metric it should be safe to test any number of weapons systems in closer proximity to public areas.

...............

If not, then please stop stating opinion as if it was fact.

It was successful in the sense that they demonstrated the reliable ability to reach their targets, showing there is little risk in allowing them RTLS.

Please stop stating opinion as if it was fact.

[Earendil]

Indeed, F9 reached pre-determined coodrinates many times.. When did Bezos do this prior to his  success?
SO why was he allowed to attempt a landing and SX is not?

[Kabloona]

SO why was he allowed to attempt a landing and SX is not?

You're comparing apples and oranges. SpaceX already had similar permission for their Grasshopper testbed program in Texas and was planning to do higher altitude hops similar to Blue's at Spaceport America, but their plans changed.

RTLS at a Government launch site is an entirely different situation, where the booster is flying back from hundreds of miles downrange with a huge radius of potential impact points if its guidance system were to go astray. New Shepard and Grasshopper were going straight up with limited propellants and thus limited ability to stray from their privately-owned test sites. And in Blue's case it helps if you own 290,000 acres of empty scrubland. There's not much out there to hit if things go wrong. Contrast that with Cape Canaveral/KSC/Cocoa Beach, where there are plenty of buildings and people relatively near the landing site. The risk equation is much different.

[OneSpeed]

SpaceX struts are made of steel. 

Any specific reason why they chose steel over aluminum?

Steel *is* stronger; just the strength costs weight.

There is also materials compatability: the stainless steel alloy they were using is LOX-safe and strong (not brittle) at cyro LOX temps.

Yes, as is the Aluminium-Lithium alloy used by SpaceX for the tank walls and domes. It's just not a reason to pick one over the other. There are other reasons though, like fatigue.

[cambrianera]

If they were using threaded connection, that's a good reason to use steel.
While threaded aluminium (and titanium) components are commonly used in motorsport and aerospace, threads on steel are considered more reliable.
What baffles me is that using high performance fibers (like dyneema) you can have the same strenght for one tenth of the mass; that's worth something, specially on second stage.

[MP99]

What baffles me is that using high performance fibers (like dyneema) you can have the same strenght for one tenth of the mass; that's worth something, specially on second stage.

Would you want to embed that inside a LOX tank?

Cheers, Martin

[Robotbeat]

But honestly, the barge landings WERE successful. They showed the rocket can be guided to a small landing pad. The fact that the rocket tipped over afterward is basically irrelevant to public safety since the public and public infrastructure isn't anywhere near the actual landing pad (there's a significant buffer around the pad).

No, they were not "successful"; simply hitting a target is *not* sufficient....

Yes it is. They don't care if the rocket ends up in a reusable state afterward, they only care about the risk to the uninvolved public.

Let's suppose they WERE successful in landing. Does that mean that every landing will be successful? Nope!

What the regulators care about is risk to the general public. That means guided to a safe area with the reliable capability to terminate the flight in case it begins to threaten straying out of that area. Just like for launch.

[cambrianera]

What baffles me is that using high performance fibers (like dyneema) you can have the same strenght for one tenth of the mass; that's worth something, specially on second stage.

Would you want to embed that inside a LOX tank?

Cheers, Martin

Why not?
It has amazing cryo properties.
As to flammability, do you realize that SpaceX is already embedding carbon fiber inside LOX tank?
Lot of mitigation factors can be considered.

[Kaputnik]

What baffles me is that using high performance fibers (like dyneema) you can have the same strenght for one tenth of the mass; that's worth something, specially on second stage.

Would you want to embed that inside a LOX tank?

Cheers, Martin

Why not?
It has amazing cryo properties.
As to flammability, do you realize that SpaceX is already embedding carbon fiber inside LOX tank?
Lot of mitigation factors can be considered.

Do we know that the strut operates only in tension? I would speculate that the strut may need a degree of stiffness that dyneema obviously cannot provide.
Suitable terminals would also be required at the metal-polymer connection point, which would be metal, and which would go some way towards negating the mass savings.

[Dante80]

By what reasoning do you determine that "public infrastructure isn't anywhere near the actual landing pad"; or more precisely, public infrastructure (or people) are not at risk?  Got an MPL calculation or model in your pocket you would like to share?

If not, then please stop stating opinion as if it was fact.

The only fact that we know at this point in time is that ORB-2 might get a RTL permission without having priorly demonstrated 100% successful landing from orbit - on either a barge or a private facility. Everything else really is opinion based. And that goes for your assumptions too man.

In any case, we are going to know pretty soon. Getting the permission is one aspect of the RTL question, the other is whether SX would keep wanting to go for it on this launch (which is non trivially burdened with RTF as well as a first launch of a new LV variant). Lets see how this unfolds..

[MP99]

What baffles me is that using high performance fibers (like dyneema) you can have the same strenght for one tenth of the mass; that's worth something, specially on second stage.

Would you want to embed that inside a LOX tank?

Cheers, Martin

Why not?
It has amazing cryo properties.
As to flammability, do you realize that SpaceX is already embedding carbon fiber inside LOX tank?
Lot of mitigation factors can be considered.

Did not know that.

OK, thanks.

cheers, Martin

[cambrianera]

What baffles me is that using high performance fibers (like dyneema) you can have the same strenght for one tenth of the mass; that's worth something, specially on second stage.

Would you want to embed that inside a LOX tank?

Cheers, Martin

Why not?
It has amazing cryo properties.
As to flammability, do you realize that SpaceX is already embedding carbon fiber inside LOX tank?
Lot of mitigation factors can be considered.

Do we know that the strut operates only in tension? I would speculate that the strut may need a degree of stiffness that dyneema obviously cannot provide.
Suitable terminals would also be required at the metal-polymer connection point, which would be metal, and which would go some way towards negating the mass savings.

Did you realized the difference between strenght/mass ratio of steel and dyneema?
More than ten times.
Which way a terminal (if needed at all) would negate this kind of mass savings?

[joek]

What the regulators care about is risk to the general public. That means guided to a safe area with the reliable capability to terminate the flight in case it begins to threaten straying out of that area. Just like for launch.

Thank you for restating, although our conclusions and definition of "sufficient" appear to differ.
Are there significant differences between RTLS and what has been demonstrated?  Yes.
Does that mean a successful barge landing is required before allowing RTLS?  No.
That prior efforts are sufficient to convince the Range and FAA that RTLS is safe is opinion, not fact.

[rcoppola]

One last thing wrt land landing with this RTF.

The last attempt was primarily foiled by a stuck valve causing the stage to overshoot, it tried to compensate...etc, boom. It's fair to say they have mitigated that potential issue as they have with Hydraulics, etc. But that valve response was off by all of 2 seconds or less. Landing this stage is an epic battle of precision. A battle they have not yet won. A battle, if I was the Range, would prefer to keep at sea until it was.

[Jim]

It has amazing cryo properties.
As to flammability, do you realize that SpaceX is already embedding carbon fiber inside LOX tank?
Lot of mitigation factors can be considered.

Where?