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SpaceX Discussion Thread

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10 hours ago, CatastrophicFailure said:

Upside is, the Falcon Heavy could launch a heavier block of solid lead than any one else in the business. :D

Only to GTO/LTO/M[ars]TO.  I think they are limited to the same mass to LEO as Falcon9 expendable due to weight support on the single Falcon9 booster (this may have changed after block 5, but I doubt it.  Falcon Heavy stopped being important to SpaceX during block 5's design).

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Just now, wumpus said:

Only to GTO/LTO/M[ars]TO.  I think they are limited to the same mass to LEO as Falcon9 expendable due to weight support on the single Falcon9 booster (this may have changed after block 5, but I doubt it.  Falcon Heavy stopped being important to SpaceX during block 5's design).

The standard, baseline payload adapter tops out at around 10-11 tonnes but a custom payload adapter can be ordered that will allow much heavier payloads. We don't know the structural limits of the upper stage but the TEL can erect something that's 25-30 tonnes easily. I don't assume Bridenstine has perfect working knowledge of FH's capabilities but he said that putting Orion, the ESM, and the ICPS on top of the upper stage would actually work but that replumbing the pad for hydrogen and reengineering wind tunnel tests would pose the biggest challenges. I don't think the NASA engineers who studied the possibility would have considered it if they had concerns about the upper stage's structural limitations.

If SpaceX had a reason to put a 60-tonne block of lead into LEO on FH, they would do it.

On 4/6/2019 at 5:42 PM, Rakaydos said:

Too clean to be reused. SpaceX has demonstrated that they arnt interested in clearing off soot for reused launches.

At least one of the nose cones is reused.

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14 hours ago, Flying dutchman said:

Yes i am aware of the staging and throttling sequence. I was refering to the rather high possible twr. Does this aid effeciency in any way or is this excessive? Because i just don't think it's neccesary. The engines are throttleable so i don't see any downsides. My question is: is there an upside?

There's absolutely an upside. Gravity is an incredibly harsh mistress. Gravity drag is the only thing that directly, linearly robs you of endpoint dV; if you have 100 m/s more gravity drag, then you stage at 100 m/s slower, and you reach final stage burnout (regardless of how many stages you have) at 100 m/s slower. Cutting gravity drag on the first stage provides a 1-to-1 boost to your final stage burnout velocity.

Gravity drag comes in units of m/s just like any other source of dV and is the product of gravitational acceleration (g) and time. Every second the rocket spends in its boost phase is 9.81 m/s of dV lost. If a higher TWR means you can shave 1 second off your ascent, you stage at 9.81 m/s faster. If you can shave 5 seconds off your ascent, you stage at 49.05 seconds faster.

During the first test flight, Falcon Heavy staged at T+373 seconds. If they can uprate the engines and increase TWR by just 2.5%, then they can stage at T+364 seconds instead, meaning they've shaved nine seconds off their ascent, which means around 92 m/s of dV gravity can't steal from them. The relationship between dV and mass fraction (all other things being equal) is logarithmic, so if the upper stage is trying to push a payload into GTO, starting with an extra 92 m/s is a significant advantage.

14 hours ago, insert_name said:

No, side boosters are going to be from this flight, central core is new

They hope to recover this center core, but since they haven't recovered a center core to date, they are building a new one for the next flight out of an abundance of caution. If they recover this core they will probably break it down and inspect it heavily before flying again. It is essentially a brand new rocket.

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19 minutes ago, sevenperforce said:

but since they haven't recovered a center core to date,

Well, they only had one launch to date, so it's a bit early to make such a statement?

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54 minutes ago, Delay said:

Well, they only had one launch to date, so it's a bit early to make such a statement?

I think the point is that they have not done a tear down on a center core (since it has different stresses than a regular core, tey'll want to go over it with a fine-tooth comb to understand how it deals with a launch/landing cycle.

Sensible, if true given the chance of a weather violation tomorrow.

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2 hours ago, sevenperforce said:

There's absolutely an upside. Gravity is an incredibly harsh mistress. Gravity drag is the only thing that directly, linearly robs you of endpoint dV; if you have 100 m/s more gravity drag, then you stage at 100 m/s slower, and you reach final stage burnout (regardless of how many stages you have) at 100 m/s slower. Cutting gravity drag on the first stage provides a 1-to-1 boost to your final stage burnout velocity.

Gravity drag comes in units of m/s just like any other source of dV and is the product of gravitational acceleration (g) and time. Every second the rocket spends in its boost phase is 9.81 m/s of dV lost. If a higher TWR means you can shave 1 second off your ascent, you stage at 9.81 m/s faster. If you can shave 5 seconds off your ascent, you stage at 49.05 seconds faster.

During the first test flight, Falcon Heavy staged at T+373 seconds. If they can uprate the engines and increase TWR by just 2.5%, then they can stage at T+364 seconds instead, meaning they've shaved nine seconds off their ascent, which means around 92 m/s of dV gravity can't steal from them. The relationship between dV and mass fraction (all other things being equal) is logarithmic, so if the upper stage is trying to push a payload into GTO, starting with an extra 92 m/s is a significant advantage.

They hope to recover this center core, but since they haven't recovered a center core to date, they are building a new one for the next flight out of an abundance of caution. If they recover this core they will probably break it down and inspect it heavily before flying again. It is essentially a brand new rocket.

This is not quite the while story, as you only get robbed of the full 9.81m/s per second if you're burning purely vertical. Once you start burning sideways gravity drag has less and less effect.

This is a trigonometric effect. Your thrust makes up the hypotenuse. Gravity drag is vertical. Your desired velocity vector is the difference.

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Posted (edited)
5 hours ago, Delay said:

Well, they only had one launch to date, so it's a bit early to make such a statement?

But it is a true statement. They haven’t had anything to look at yet. This one will boost back to near the coast, so it shouldn’t be too stressed (assuming it doesn’t run out of ignition fluids 

my bad, thought this was STP-2

Edited by StrandedonEarth

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Just now, RCgothic said:

This is not quite the while story, as you only get robbed of the full 9.81m/s per second if you're burning purely vertical. Once you start burning sideways gravity drag has less and less effect.

This is a trigonometric effect. Your thrust makes up the hypotenuse. Gravity drag is vertical. Your desired velocity vector is the difference.

Correct; I was simplifying. The majority of the gravity drag happens while the vehicle is still mostly-vertical...tautologically, of course.

It is still a huge impact. Adding fuel to the first stage is only a second-order improvement to final dV; adding thrust is first-order.

Just now, StrandedonEarth said:

But it is a true statement. They haven’t had anything to look at yet. This one will boost back to near the coast, so it shouldn’t be too stressed (assuming it doesn’t run out of ignition fluids 

Yeah someone is going to make sure it has extra.

I hadn't heard it was boosting back to near the coast -- is OCISLY positioned differently? Have they posted a near-coast NOTAM?

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Posted (edited)

And that's presumably for 4 seats and not 7! Tourism opportunities are there for less!

Edited by Ultimate Steve

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Posted (edited)
3 hours ago, sevenperforce said:

 

I hadn't heard it was boosting back to near the coast -- is OCISLY positioned differently? Have they posted a near-coast NOTAM?

Many pages back...

Apparently have to click the linked post to see the tweets. I was wrong, this FH is gonna go 967 km down range. STP-2 will almost RTLS

Edited by StrandedonEarth

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3 hours ago, sevenperforce said:

It is still a huge impact. Adding fuel to the first stage is only a second-order improvement to final dV; adding thrust is first-order.

As long as we’re getting tautological, let’s not forget there’s a diminishing-return effect of air drag right when you’re getting most of your gravity drag, too. -_-

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I looked on Spaceflight Now and it says that the FH launch has been pushed back to Wednesday because of the 70% no go weather report. At least the weather at the Cape appears to be good for the rest of the week.

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Posted (edited)

confirmed, launch slipped to Wednesday:

Ninja’d :ph34r:
 
3:36PDT/6:36EDT:TooMuchMath:36UTC
Edited by CatastrophicFailure

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Posted (edited)

...and apparently the Starhopper has been declawed... :o

1555633.jpg

 

Edited by CatastrophicFailure

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3 hours ago, MaverickSawyer said:

Huh. Issues with the engine?

It is a 300 bar engine. What did you expect?

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5 minutes ago, Xd the great said:

It is a 300 bar engine. What did you expect?

Guess you could say SpaceX has really set the bar high.

I'll show myself out.

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39 minutes ago, Ol’ Musky Boi said:

Guess you could say SpaceX has really set the bar high.

I'll show myself out.

Or maybe musk has a new version of the raptor engine.

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1 hour ago, Xd the great said:

Or maybe musk has a new version of the raptor engine.

Or he's decided to equip the Starhopper with a warp-drive for its next test.

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52 minutes ago, RealKerbal3x said:

Or he's decided to equip the Starhopper with a warp-drive for its next test.

At least the name would make sense.

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