RCgothic
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Posts posted by RCgothic
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1 hour ago, MetricKerbalist said:
Hi everyone,
Actually, this discussion clarified a few things in my mind.
Let me summarize, and get things nailed down.
Let's say that we were at Kennedy Space Center, and let's agree to call its latitude 28 °.
Case 1: A rocket is standing upright on the launchpad
Inclination: 28 °
Pitch: 90 °
Heading: ?Case 2: A rocket is lying on the ground with its nose pointed towards Tallahassee
Inclination: 28 °
Pitch: 0 °
Heading: 300 ° or North 60 ° West
Case 3: A rocket is lying with its aft side on the ground and its nose propped up 30 ° pointed towards London
Inclination: 28 °
Pitch: 30 °
Heading: 40 ° or North 40° EastCase 4: A rocket is suspended vertically from its aft side and its nose pointed straight down
Inclination: 28 °
Pitch: -90 °
Heading: ?Could anyone please confirm the three parameters for all four cases. Note, however, that I have a question mark regarding the heading on Case 1 and Case 4.
Thank you.
Stanley
Correct. In cases 1 and 4 the heading/azimuth is undefined. The rocket is not pointing in any compass direction.
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When discussing orbits, pitch relative to virtual horizon is more generally useful.
The KSP Navball also uses this convention.
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Yes, with 3 the core stage might as well be stretched as well. But I believe 2 would work well enough, outside perhaps the very lightest and heaviest payloads.
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9 minutes ago, MetricKerbalist said:
Hi @mikegarrison,
First, I appreciate your response.
I guess I don't understand this, but I am always trying to learn.
Could you or someone else please be so kind as to define these three terms -- and in particular the difference among them?
Thank you for your consideration.
Stanley
Orbital inclination - the angle of the orbital plane to the plane of the equator.
Pitch angle - the angle of the rocket with respect to the virtual horizon (to the rocket's current horizontal plane with respect to earth).
Heading - the compass direction.
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Pretty sure Raptor could do the job from a *performance* perspective.
The *slightly*lower thrust can be compensated by SRBs on takeoff and the *much* higher ISP of the Raptor would then more than make up for it. <327s for BE-4 Vs 350s for Raptor at SL.
But you can't just mix and match rocket engines, even with similar fuels and performance values. It'd take an extensive redesign.
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Trans-shipping of Cargo is going to be important if they're going to reuse LSS for lunar downmass. Got to restock it somehow.
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Personally I'd err towards Late August.
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They weigh and cost a lot more, and the weight doesn't matter because generally the wings on a jet is holding them up and they're fully reusable.
Using them in a rocket, ISP is optimal at SL and in a vacuum, so a small bit of ISP is gained just before the first stage separates. But late in the burn it's carrying way too much dry tank mass. The engines also have to shut or throttle down to stay within structural limits and become additional dead mass.
Comparatively, the Two Stage design has slightly worse ISP just before separation. It is also carrying more more engine and staging mechanism mass, but only early in the flight where that matters less. Later where it matters most it has less tank mass, fewer engines, and the engines weigh comparatively less than a compensating design.
Two stage still wins.
You want a compensating engine when you are constantly moving between different altitudes, throttle settings, and not trying to minimise dry mass. A rocket has just two regimes, one of which it stays in very briefly (SL), and dry mass is very important. It's a better optimization to go with a staging event
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As far as we're aware this a permanent integration tower. It'll get some cladding to tidy it up at some point.
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8 hours ago, Exoscientist said:
By using alt.comp. on existing engines and lightweight tanks can can also double the payload to orbit. As a byproduct of that you also get an SSTO with the first stage that can more cheaply launch the smaller payloads, not needing the upper stage.
In SpaceX's particular case, that's just traded expending a cheap 2nd stage for expending the entire first stage. And the first stage also costs more than usual because of advanced!materials. That's not a good trade.
If utilising different engines and lightweight materials would make a big difference to turn a regular rocket into an SSTO (and note that several of them technically can already SSTO with extremely small payloads but never do), it would also make a big difference to a TSTO as well.
The only possible way an SSTO makes sense is if you want to reuse everything. And to reuse everything, everything needs a heat shield. Everything needs enough control authority for re-entry. All the extras need to be taken to orbit and back (eating potential payload).
Whereas to fully reuse a TSTO only the upper stage needs the extra bits, and the first stage can be much more lightweight.
SpaceX in particular aren't daft, and for starship they've taken the single best way to get to orbit fully reusable with a lot of payload. If SSTO made more sense, they'd have done that.
Finally, note that although SSMEs and RL10 are extremely efficient *engines*, their propellant tanks are larger, more insulated, more expensive, and heavier than the tanks required for alternative propellants. Storing hydrogen is hard.
Engine efficiency gives a linear benefit to the rocket equation. Mass fraction gives an exponential benefit. Depending on the application it can be better to optimise dry mass fraction than engine efficiency. A hydrogen powered stage might get more mass from LEO to the moon, but because of the better mass fraction a methane powered stage could send more mass from LEO out of the solar system entirely.
This is just one example to show why rockets don't always use "the best" even if they could. Hydrogen usually needs side boosters to get off the ground. Aluminium orthogrid may be lighter than steel, but it's more expensive, more time consuming to produce, and needs more heat shield than welded steel, for instance.
"Best" can mean many different things. Throwing better engines and materials on a rocket doesn't necessarily improve it if it makes the whole thing more expensive than the benefit.
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The only edge case I can think of is of the SSTO is landing somewhere fuel is available but a booster stage for a TSTO isn't.
If there's a booster available, TSTO is always better. If there's no fuel available then it's not rapidly reusable as SSTO Twice (without refuelling) isn't a thing on Earth.
Bit niche.
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What is the point of an SSTO? Cheap access to orbit? An expendable 2 stage will *always* be cheaper than the advanced engineering required for an SSTO.
Reuse? A reusable TSTO will always have more margin available than an equivalently engineered SSTO. Always.
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If it were economical someone would be doing it.
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I really don't see everything being readied by end of July. There's still so much to go.
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That's sure to set back the orbital launch attempt. Darn.
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Yes, the physics of KSP include discontinuities. When a spacecraft moves from one sphere of influence to another (defined by a simple radius on a per body basis) it experiences a sudden switch.
In real life there is no discontinuity and things like libration points exist where the forces cancel out. Orbits are no longer pure ellipses when you consider n bodies either. This would be extremely resource intensive to calculate for a dynamic situation such as a game.
Patched conics is a good approximation for performance reasons, but it is not fully realistic.
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Mark Watney had better not get stuck on Mars.
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And basically rebuilt between flights. That's not "cheap frequent access to space" in my book.
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How many sections does it need to be the highest structure in South Texas?
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Observers think first part of the catch mechanism has been installed on the launch tower. It's a super-heavy duty winch, very much excessive for an elevator.
The crane winch for lifting Superheavy/Starship onto the pad is expected to be in the crane up top. Due to rotation of the crane beam it'd be seriously unusual to try and articulate cables through that rotating joint. Therefore this isn't that.
I'm not sure I agree that the arms will be used to stack Superheavy and Starship on the launch pad. That'd be a very much more complicated mechanism than a linear catch with rotation to the pad performed by a crane on the top of the tower.
SpaceX Discussion Thread
in Science & Spaceflight
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