SpaceX Falcon 9 : Hispasat 30W-6 (1F) : March 6, 2018 - DISCUSSION

[speedevil]

Perhaps some ∆V could also be found from the second stage? If the webcast velocities are correct, we've occasionally seen S2 thrust at about 107% of the published figures. They've usually only maintained these levels for the first minute or so of the burn before throttling back to 94% or so. But if they did run harder for longer, they could reduce S2 gravity losses by quite a bit.

If there is that margin, I wonder if the same exists in non-vac engines.
Increasing the entry velocity to maximum, skirting the edge of thermal issues and delaying the burn as much as possible before a three engine 107% burn should get a little extra.

[LouScheffer]

Does anyone remember where the payload weights to re-entry success curve chart is? I've been looking for it for an hour (google-fu is lacking

The most useful chart for keeping track of GTO performance (in my opinion) is GTO performance, kept by stcks.  It has the name, mass, MECO speed, transfer orbit (if known), and remaining delta-V.  The name is very useful since then you can go back and watch the exact SpaceX launch webcast, and fill in missing details.

[LouScheffer]

Perhaps some ∆V could also be found from the second stage? If the webcast velocities are correct, we've occasionally seen S2 thrust at about 107% of the published figures. They've usually only maintained these levels for the first minute or so of the burn before throttling back to 94% or so. But if they did run harder for longer, they could reduce S2 gravity losses by quite a bit.

I don't think gravity losses on S2 are enough to make much of a difference.

Agree that gravity losses should be minimal.  At MECO, the apogee is already at orbital altitude.  So the second stage can just thrust horizontally while it coasts up to LEO, and does not need to fight gravity.

SpaceX could also gain a tiny amount by using a lower LEO.  Some of the Apollo missions used orbits as low as 160 km, if I recall correctly.

[Lars-J]

Some margin might come from the fairing, if they use Fairing 2.0 for this launch. (supposedly lighter, but I don't know the accuracy of that)

[Lar]

Does anyone remember where the payload weights to re-entry success curve chart is? I've been looking for it for an hour (google-fu is lacking)

Even for an "experimental" landing, there must still be high confidence for the Ti fins. I think it'll be further refinement of existing burns rather than hardware changes and their being confident of the exact limits they can push a booster too

I think there is a bit of "hysteresis here" ...
- use Al fins? for sure lose stage as they can't give the necessary control authority. But you only lost Al fins.
- use Ti fins? MAYBE you get the stage back (and the fins) but if you're wrong, you lose Ti fins.

Fun decision tree

[stcks]

Does anyone remember where the payload weights to re-entry success curve chart is? I've been looking for it for an hour (google-fu is lacking)

Even for an "experimental" landing, there must still be high confidence for the Ti fins. I think it'll be further refinement of existing burns rather than hardware changes and their being confident of the exact limits they can push a booster too

I think there is a bit of "hysteresis here" ...
- use Al fins? for sure lose stage as they can't give the necessary control authority. But you only lost Al fins.
- use Ti fins? MAYBE you get the stage back (and the fins) but if you're wrong, you lose Ti fins.

Fun decision tree

Fun indeed! Assuming this booster does have Ti fins then we know SpaceX have at least 3 sets of them now since the FH display booster at KSC still had them on and there were some (at least one) in the 39A HIF for the VIPs on Wednesday.

[John Alan]

Maybe we are overlooking the obvious... The launch was sold as ~ GEO-2100... 
The bird has enough delta-v as built, to make up the short fall we think it will have...

GS has said in the past [1] of customers looking at adding more Delta-V to the birds themselves.
They would do this, so they could make the F9 S1 recovered on ASDS launch price point.. 
This may just be the first one of those launches... 

[1] I do not have a link for this source... but I know she talked of this in the last 2 years...

On edit...
It's kinda like adding a 3rd stage...
Only it's just bigger fuel tanks and some structure mass to a normal GEO-1800 bird design... 

[LouScheffer]

We have seen block 4 before so unless this is a 4.5 or something I don't see the higher thrust part as all that likely.

I see no reason they need to switch the engines and the rest of the booster at the same time.   If I were SpaceX, I'd start making only the uprated engines as soon as they were qualified.   If that's before the rest of the block 5 is ready, no big deal.  Just stick them on the model 4 core and enjoy the benefits.  Exactly like they did with the titanium fins.

What's the alternative in this case?  Deliberately build less-useful engines? 

So my vote is a model 4.5 core.

Here is why I think this is a model 4.5 booster.   It's way out of family for any other GTO mission.  (Data from stcks F9 to GTO page.

[John Alan]

Take the above chart and extend the top out to GEO-2100... It fits just fine...   

I guess we will find out, when the initial orbit comes in from 3rd party tracking sources...
Better rocket... lower energy orbit... maybe a bit of both... 

[OneSpeed]

... At MECO, the apogee is already at orbital altitude.  So the second stage can just thrust horizontally while it coasts up to LEO, and does not need to fight gravity.

At MECO, S2 is flying at best at one third of orbital velocity. To maintain its apogee at orbital altitude, while accelerating at only around 1g, it needs to fly with a substantial AoA, and hence cosine losses. You can see this for yourself in the webcasts. It can only fly horizontally and maintain altitude once it has reached orbital velocity.

[jabe]

With the stage looking like it has titanium fins, per https://forum.nasaspaceflight.com/index.php?topic=44695.msg1791981#msg1791981,  may be worth doing salvage if they lose the stage.
anyone know the cost of those fins?
jb

[cppetrie]

With the stage looking like it has titanium fins, per https://forum.nasaspaceflight.com/index.php?topic=44695.msg1791981#msg1791981,  may be worth doing salvage if they lose the stage.
anyone know the cost of those fins?
jb

Time may be a more important factor. They are certainly expensive, but Elon’s remarks have also indicated they take a long time to make.

[lrk]

Another thing to note is that, when working on high-AoA reentry, the only way to try it to the full extent in the first place might be to use the titanium fins

There's also always the chance that, depending on exactly how it crashes on the ASDS (e.g. running out of fuel at the last second and tipping over), they might still get (at least some of) the fins back without recovering the booster

[IanThePineapple]

With the stage looking like it has titanium fins, per https://forum.nasaspaceflight.com/index.php?topic=44695.msg1791981#msg1791981,  may be worth doing salvage if they lose the stage.
anyone know the cost of those fins?
jb

It's not really their cost but more the time and labor needed to make them (So yes, cost is also a problem with those when you add in all the prices of the labor and machinery).

Titanium doesn't float on water AFAIK, so if they lose the stage there's a really good chance they lose the fins too. If the fins land fairly intact on the deck of OCISLY they may be salvageable, but most of the past landing failures have involved a large portion of the vehicle falling off the ship.

[jabe]

Titanium doesn't float on water AFAIK, so if they lose the stage there's a really good chance they lose the fins too. If the fins land fairly intact on the deck of OCISLY they may be salvageable, but most of the past landing failures have involved a large portion of the vehicle falling off the ship.

that is what i mean by salvagable..is it worth the effort to go diving for them?

[Lar]

Titanium doesn't float on water AFAIK, so if they lose the stage there's a really good chance they lose the fins too. If the fins land fairly intact on the deck of OCISLY they may be salvageable, but most of the past landing failures have involved a large portion of the vehicle falling off the ship.

that is what i mean by salvagable..is it worth the effort to go diving for them?

Given how far at sea they are I am going to guess no....

[jabe]

Given how far at sea they are I am going to guess no....

time to get my sea drone out  and prepped in case
going to be an interesting landing...

[Lars-J]

Titanium doesn't float on water AFAIK, so if they lose the stage there's a really good chance they lose the fins too.

Aluminum doesn’t float either.

[IanThePineapple]

Titanium doesn't float on water AFAIK, so if they lose the stage there's a really good chance they lose the fins too.

Aluminum doesn’t float either.

Yeah, I know most metals don't float, but I'm too tired to remember or look up whether Titanium floats or not...

[Yellowstone10]

Titanium doesn't float on water AFAIK, so if they lose the stage there's a really good chance they lose the fins too.

Aluminum doesn’t float either.

Yeah, I know most metals don't float, but I'm too tired to remember or look up whether Titanium floats or not...

It doesn't - density is about 4.5 g/cm³. The three metals with densities less than water are lithium, potassium, and sodium, but building floating structures out of those would be, shall we say, problematic.

Edit - melting points would be a problem too - Na melts at 98° C, potassium at 64° C, and lithium at 181 °C