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2 hours ago, tater said:

E0jfCjnXMAUpYH9?format=jpg

 

 

Regarding RTLS for SH, Musk said a while ago that for F9, downrange recovery was a ~18% performance hit to LEO, and RTLS was a 40% hit.

In addition to the points you make, Starship doesn't need a re-entry burn and it saves a lot of dv by belly flopping. On top of that, I would expect it to have a greater engines-out cross-range ability than the Flacon 9. 

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Liftoff!

MECO/Sep/SES-1/Fairing all nominal

I thought that was gonna miss. Wow.

 

Landing

 

And not just landing, like a dead on bullseye.

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Right in the middle! Looks like it made an impressive translation to get there.

How long will the second stage stay in orbit? Would it still be up there after five or six orbits?

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1 hour ago, Deddly said:

I would expect Starship to have a greater engines-out cross-range ability than the Falcon 9. 

Well, that will help make sure that the impact point isn't in the middle of a city or something, but otherwise I'm not sure what the point is for "engines-out cross-range ability" when all that means is an ability to direct where the "BOOM!" happens.

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36 minutes ago, RCgothic said:

Yes, it is wasteful. Return to launch site comes with a hefty performance penalty as Superheavy has to reserve a sizeable amount of fuel for the boostback burn. Not two thirds or even half its fuel though, as relieved of the mass of the Starship Upper Stage it has a very much more favourable mass ratio.

It's notable that even with this performance penalty Starship Superheavy manages almost twice Saturn V's mass to LEO.

I can't remember if I've done the math on this before or not....

120 tonnes dry mass, 30 tonnes landing reserve prop, and 100 tonnes payload to LEO, so mf is 250 tonnes. 1200 tonnes prop at staging but that presumably includes those 30 tonnes in the header tanks so m0 is 1420 tonnes. So dV expended to LEO is 6473 m/s. We know that Starship needs all six engines to light at staging to help avoid overmuch gravity drag, which means a fairly lofted trajectory and some gravity drag losses -- probably as high as 600 m/s. So we can ballpark staging velocity at LEO - 5873 or roughly 2 km/s.

Superheavy needs to cancel its downrange velocity (but not its upward velocity) and head back to the pad. A lofted trajectory helps with this because it only needs enough speed to traverse the same distance during its hang time. We can assume that Superheavy, like Falcon 9, will have a landing burn that kicks off just after the vehicle goes subsonic, around 310 m/s, but just as Falcon 9 it will need about 200 m/s more to account for gravity drag during the landing burn.

In the NROL-108 mission, Falcon 9 needed about 550 m/s for the landing burn (it was a single-engine burn) and also burned all three engines for an entry burn for 28 seconds. It is 27 tonnes dry so that is 6 tonnes of prop for the landing burn, and a Merlin 1D has a mass flow rate of 305.4 kg/s so burning three of those for 28 seconds was about 25 tonnes, so total mass before the start of the boostback burn would have been 58 tonnes. Its boostback burn lasted 37 seconds and thus would have consumed 33.9 tonnes of propellant. Since the vacuum specific impulse of the SL Merlin 1D is 311 seconds,  the boostback burn provided about 1400 m/s (staging velocity was 1600 m/s but part of that was an upward component, because lofted trajectory).

The SL Raptors on Starship light up at 330 seconds and reach somewhere around 356 s by burnout. It won't need an entry burn. I'm estimating Superheavy at around 290 tonnes dry and 3690 tonnes wet, so it burns around 1700 tonnes (49% of its prop load) getting to Mach 2, another 1450 tonnes (43% of its prop load) getting to staging, about 229 tonnes (6.7% of its prop load) on the boostback, and about 49 tonnes (1.5% of its prop load) for the landing burn.

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41 minutes ago, mikegarrison said:

Well, that will help make sure that the impact point isn't in the middle of a city or something, but otherwise I'm not sure what the point is for "engines-out cross-range ability" when all that means is an ability to direct where the "BOOM!" happens.

You would prefer the BOOM to be in an uncontrolled location? But seriously, I think you know as well as I do that it is too early to judge whether the flip maneuvre is going to work reliably. All of the early landing attempts of Falcon 9 also crashed and exploded, and look what that resulted in in the end. Would have been a shame if they just scrapped the whole idea and said "What's the point of grid fins when all that means is an ability to direct where the explosion happens?" 

I still can't believe they nailed the belly flop and skydive maneuvre right from the first attempt. 

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1 minute ago, Deddly said:

You would prefer the BOOM to be in an uncontrolled location? But seriously, I think you know as well as I do that it is too early to judge whether the flip maneuvre is going to work reliably. All of the early landing attempts of Falcon 9 also crashed and exploded, and look what that resulted in in the end. Would have been a shame if they just scrapped the whole idea and said "What's the point of grid fins when all that means is an ability to direct where the explosion happens?" 

I still can't believe they nailed the belly flop and skydive maneuvre right from the first attempt. 

It's the "engines out" part that I was really referring to. Whether Falcon 9 or Starship, "engines out" is an unrecoverable failure.

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13 minutes ago, mikegarrison said:

It's the "engines out" part that I was really referring to. Whether Falcon 9 or Starship, "engines out" is an unrecoverable failure.

Engine-out is unrecoverable for Falcon 9.

Engine-out is fine for Starship as long as it happens at relight (not mid-landing-burn) and the failed engine doesn't frag the others.

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Posted (edited)

Engines off, then. Sorry, I didn't realise that "engines out" meant "engine failure" 

Edited by Deddly
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Posted (edited)
7 hours ago, RCgothic said:

Yes, it is wasteful. Return to launch site comes with a hefty performance penalty

Is it though?  I remember reading waaay back when that the real cost was losing the rocket engine - and that fuel was comparatively inexpensive 

 

-so a loss of performance but an economic gain? 

Edited by JoeSchmuckatelli
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31 minutes ago, Deddly said:

Engines off, then. Sorry, I didn't realise that "engines out" meant "engine failure" 

Ah. OK, yeah, I guess I'm used to airliners. "Engine out" has a pretty specific meaning there, and I just unthinkingly assumed you meant the same thing.

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Performance in this case is mass to space. Given the reality that even with Starship most all "mass to LEO" will in fact be residual propellant, it's just how many re-tanking flights are required to send a SS someplace past LEO.

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1 hour ago, Deddly said:

I still can't believe they nailed the belly flop and skydive maneuvre right from the first attempt. 

And that’s why I believe Spacex can get this down. Falcon 9 didn’t get that close on its first landing attempt. 

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1 hour ago, mikegarrison said:

Ah. OK, yeah, I guess I'm used to airliners. "Engine out" has a pretty specific meaning there, and I just unthinkingly assumed you meant the same thing.

This actually brings up a decent point. Starship depends on its engines to land. It's literally screwed if its engines don't turn on at the right moment and if they don't throttle correctly. Its fair to say that no spacecraft has a backup, but stuff like parachutes are hard to not get to work if they deploy correctly and they are a failsafe with most approaches. Complicated engines using cryogenic propellant and turbopumps haven't been extensively tested after a six month drift through deep space and there is really only one way to find out if an engine of this caliber can work properly but is it worth it? and even if it works landing on mars, would it work coming home? After possibly 3 years of mission time elapsing. 

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9 minutes ago, SpaceFace545 said:

Its fair to say that no spacecraft has a backup, but stuff like parachutes are hard to not get to work if they deploy correctly and they are a failsafe with most approaches.

Parachutes are far from 100% reliable, and wouldn't be enough to slow down all the way in the thin martian atmosphere.

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6 minutes ago, Spaceman.Spiff said:

Parachutes are far from 100% reliable, and wouldn't be enough to slow down all the way in the thin martian atmosphere.

I'm actually excited about the prospect of SX crashing a few prototypes into the Moon and Mars in my lifetime.  Because I'm confident that after a few - they'll stick the landing... And we are off to the races 

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2 minutes ago, JoeSchmuckatelli said:

I'm actually excited about the prospect of SX crashing a few prototypes into the Moon and Mars in my lifetime.  Because I'm confident that after a few - they'll stick the landing... And we are off to the races 

Indeed...they'll surely toss one off at Mars of their own volition as soon as they're capable of refueling. Then we'll get to see a picture of the crater from MRO.

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6 minutes ago, cubinator said:

Indeed...they'll surely toss one off at Mars of their own volition as soon as they're capable of refueling. Then we'll get to see a picture of the crater from MRO.

If they have the capability, maybe they can launch a new observation sat! 

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25 minutes ago, cubinator said:

Indeed...they'll surely toss one off at Mars of their own volition as soon as they're capable of refueling. Then we'll get to see a picture of the crater from MRO.

does spacex have any isru and surface habituation in the works? because if the musk date is accurate then those should be happening soon.

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7 minutes ago, SpaceFace545 said:

does spacex have any isru and surface habituation in the works? because if the musk date is accurate then those should be happening soon.

Actually yes. One, the first "hab" will be SS itself.

As for ISRU, they are building a few plants to make LOX from the air, and I think they have messed with extracting C from CO2.

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1 hour ago, Spaceman.Spiff said:

If they have the capability, maybe they can launch a new observation sat! 

Anything to pay for the fuel, eh?

"You pay half gas, and I'll get you to Mars orbit; just don't expect me to hang around... Bradbury expects me"

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I just saw the Starlinks from today...Incredible! I saw a perfect linear reflection of the Sun's diameter in the glint! I also saw second stage spinning in front of the group.

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Posted (edited)
Spoiler

Is the owner of the rightmost pickup sure that it's ok with his car and nothing leaks?

***  

1 hour ago, tater said:

This is supposedly an air separator (all the things together).

That net separates the fresh air from smoke? Wise.

Edited by kerbiloid
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