Ag_of_08 said:

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They're going to hot stage instead of using sep an ullage motors. The whole point of hot staging is to eliminate the need for both those systems, and has been in use almost since the start of space flight.

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And how many of these historical rockets had to return to their launch sites, be captured by chopsticks, and be capable of being refueled and relaunched within a few hours even a few days?

How many rockets in history have ever RTLSd, or even been seen again after hitting the ocean at terminal velocity?

Otoh, how many times have they test fired small numbers of raptors at low thrust?

I don't know how far Raptors can be throttled down but Merlins are very limited. When your minimum thrust:weight ratio is greater than 1 as in the case of the F9, it makes landing the things an absolute engineering marvel.

Raptors can be throttled down way further than the Merlins

Starship and even superheavy will not "hoverslam" like falcon, the engines can throttle quite deeply.

Can they throttle that much at ignition though?

It's funny how a few pages back we were (mostly) lamenting the spin separation as a blogger's idea (tim dodd), but now this is somewhat 'hotly' debated. Tim actually had a whole video about the challenges of 'starting' a rocket motor and how complex that is.



Anyway, this seems like something that is relatively 'common' so hopefully it works better than we expected the spin separation to.

In flight ignition and its woes are actually why the first gen atlas does the weird 1.5 stage thing, and korolev insisted on parallel instead of serial staging.

Von Braun had a bit more of an obsession with serial staging and the....aesthetic of the rocket. By lighting them all on the ground, they knew up front if they would be burning...pad abort( unless its blowing up) is a better scenario than IFA, on no abort at all . Saturn 5 took a pretty big chance with the s1 to s2 staging, especially since it was still in atmosphere when it occurred. The ullage and separation was pretty complex, and highly mission critical.

Just speculation on my part from to much time in Rss/Ro on kerbal.... raptor will not be on/off power. It does take time to spin up, and even when the chamber lights, it takes time to come up to thrust. If the hot stage it the way most of them are, the interstage will already have released, and ignition should occur right before the g load eases, so the stage will pull away as soon as thrust starts to build. That should maintain ullage. I also highly doubt they light all the engines on stage sep, as long as they can establish enough positive thrust to pull it away they can light the others as the vehicles separates, even just a second or two behind would make all the difference. The big ass grid fins on the SH booster should also created drag and the whole thing will start decelerating when power rolls off, which will make separation even faster.

I'm not an engineer, but just looking at the vehicles that DO hot stage and the way the vehicle looks to be operating, I think the image a lot of people have of the whole Starship lighting off on the pad is not what a hot stage fire will look like.

Interesting article on the Mars Sample Return program, which has been in development since at least 2009, but a desire from the science community since the 80's.

https://arstechnica.com/space/2023/06/the-mars-sample-return-mission-is-starting-to-give-nasa-sticker-shock/

The projected cost have ballooned well beyond JWST, which benefits far more of the science community than studying Mars materials. A big part of the estimated $10B program price tag is due to JPL developing their own Mars lander rather than utilize one of the many different commercial companies, all who are actively developing many different lunar landers with varying mass payloads. This includes the latest proposals and landers for a new 1500kg Lunar Terrain Vehicle from Intuitive Machines.

Quote:

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The concern, says Paul Byrne, a planetary scientist at Washington University, is that Mars Sample Return risks becoming the planetary community's James Webb Space Telescope. For the better part of a decade, the Webb instrument consumed most of the astrophysics budget to the detriment of other projects.

Webb has been a phenomenal success now that it is in space, Byrne said. However, the Webb telescope has benefitted a very broad segment of the space science community, from astrophysicists to astronomers studying exoplanets to planetary scientists. It has observed all manner of phenomena, both locally in our Solar System and all the way to the edge of the Universe. The Mars sample return mission, while it may produce some spectacular science, will only benefit a fairly narrow segment of planetary scientists.

"It's the same scope as Webb in terms of cost but a much, much narrower scope in terms of science," Byrne said. "That's really problematic."

NASA is selling the sample return mission as a "life-detection mission," which may find evidence of life on Mars past or present. However, Byrne said most planetary scientists think the mission has only a very low chance of actually finding definitive evidence of life. And if the sample return mission does not, he said, the general public is likely to ask why NASA spent $10 billion to study the geological history of Mars.

...

NASA and policymakers do have some options if they want to control the costs of the Mars Sample Return mission.

Foremost among them is having a competition for the development of the large lander that is the centerpiece of the missionand which will probably comprise about half of the total cost.

"Why are we not putting out a call and having an industry competition for people like Lockheed Martin, SpaceX, Blue Origin, Astrobotic, Intuitive Machines, and whoever else?" one NASA source asked. "They're already building landers. Why can't we ask them what they could do? JPL hasn't even asked. We should be using a commercial, milestone-based approach."

Zurbuchen said that NASA's current administration should be seriously considering this alternative if the Mars Sample Return mission is to continue.

"If I were in charge, I would develop a commercial option for the lander and seriously consider taking it away from JPL," he said. "Recall, this would be the first stationary lander done out of JPL. All others were built by Lockheed and that was before new capabilities by SpaceX and others."

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Today is the first day of the year-long CHAPEA mission to study living on Mars. Coolest part of this is the use of ICON 3D printed structures with a Mars red dirt simulator. I'm guessing this is a bit more challenging than being on the real Mars in some ways, as there you get to see into the expanse of the planet and venture much further to study it.

NASAg03 said:

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Today is the first day of the year-long CHAPEA mission to study living on Mars. Coolest part of this is the use of ICON 3D printed structures with a Mars red dirt simulator. I'm guessing this is a bit more challenging than being on the real Mars in some ways, as there you get to see into the expanse of the planet and venture much further to study it.

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Hopefully they don't go native on us.

I can't imagine how bad that would suck. God bless those brave test subjects.

Looks good so far

— Elon Musk (@elonmusk) June 27, 2023

Ship 25 completes a six-engine static fire test at Starbase in Texas pic.twitter.com/wCCrh0RRNA

— SpaceX (@SpaceX) June 27, 2023

Ag_of_08 said:

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In flight ignition and its woes are actually why the first gen atlas does the weird 1.5 stage thing, and korolev insisted on parallel instead of serial staging.

Von Braun had a bit more of an obsession with serial staging and the....aesthetic of the rocket. By lighting them all on the ground, they knew up front if they would be burning...pad abort( unless its blowing up) is a better scenario than IFA, on no abort at all . Saturn 5 took a pretty big chance with the s1 to s2 staging, especially since it was still in atmosphere when it occurred. The ullage and separation was pretty complex, and highly mission critical.

Just speculation on my part from to much time in Rss/Ro on kerbal.... raptor will not be on/off power. It does take time to spin up, and even when the chamber lights, it takes time to come up to thrust. If the hot stage it the way most of them are, the interstage will already have released, and ignition should occur right before the g load eases, so the stage will pull away as soon as thrust starts to build. That should maintain ullage. I also highly doubt they light all the engines on stage sep, as long as they can establish enough positive thrust to pull it away they can light the others as the vehicles separates, even just a second or two behind would make all the difference. The big ass grid fins on the SH booster should also created drag and the whole thing will start decelerating when power rolls off, which will make separation even faster.

I'm not an engineer, but just looking at the vehicles that DO hot stage and the way the vehicle looks to be operating, I think the image a lot of people have of the whole Starship lighting off on the pad is not what a hot stage fire will look like.

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Rocket engines don't take time to spin up. They are up to power in under a second. They do take time to bleed in the fuel and chill in the ox. But once those pumps light, they reach their set RPM in a split second. It will start at a low power condition but I suspect it goes from off to that power setting in only a few hundred milliseconds. That's just how it is for rocket engines. A few hundred milliseconds is a long time on the rocket ignition timescales, but it's near instant by most people's standards. The whole sequence of events for the stage separation and engine ignition will probably appear to just happen at the same time.

Raptor ignition is complex and difficult but they've got it down now.

Three center Raptors of Booster will fire at ~50% thrust during hot staging

— Elon Musk (@elonmusk) June 27, 2023

Thx. But when can a rocket start actually throttling down? Don't they generally have to go to something like 50% power for a few seconds?

Also, woah.

NEWS 🚨: Astronomers have discovered the largest black hole ever, and it’s over 30 billion times the size of our sun

Reaching the “upper limit of how large a black hole can theoretically become” 😳 pic.twitter.com/2XwC3znzmf

— Latest in space (@latestinspace) June 27, 2023

nortex97 said:

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Thx. But when can a rocket start actually throttling down? Don't they generally have to go to something like 50% power for a few seconds?

Also, woah.

NEWS 🚨: Astronomers have discovered the largest black hole ever, and it’s over 30 billion times the size of our sun

Reaching the “upper limit of how large a black hole can theoretically become” 😳 pic.twitter.com/2XwC3znzmf

— Latest in space (@latestinspace) June 27, 2023

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Depends on the engine design.

Usually the power level will be determined by a flow metering valve. Wherever they set the valve is what power it will come to. They can have it start up at any power level. And they usually reduce throttle to lower maxQ (maximum dynamic pressure) but then increase the throttle again.

Not all rockets throttle. Solids for example just go, no throttling control.

nortex97 said:

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NEWS 🚨: Astronomers have discovered the largest black hole ever, and it’s over 30 billion times the size of our sun

Reaching the “upper limit of how large a black hole can theoretically become” 😳 pic.twitter.com/2XwC3znzmf

— Latest in space (@latestinspace) June 27, 2023

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I haven't heard there's an upper limit for the size of a black hole, but I have heard the universe could be the inside of a black hole.

That's a big black hole .. maybe it swallows the entire universe one day ?

bmks270 said:

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nortex97 said:

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Thx. But when can a rocket start actually throttling down? Don't they generally have to go to something like 50% power for a few seconds?

Also, woah.

NEWS 🚨: Astronomers have discovered the largest black hole ever, and it’s over 30 billion times the size of our sun

Reaching the “upper limit of how large a black hole can theoretically become” 😳 pic.twitter.com/2XwC3znzmf

— Latest in space (@latestinspace) June 27, 2023

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Depends on the engine design.

Usually the power level will be determined by a flow metering valve. Wherever they set the valve is what power it will come to. They can have it start up at any power level. And they usually reduce throttle to lower maxQ (maximum dynamic pressure) but then increase the throttle again.

Not all rockets throttle. Solids for example just go, no throttling control.

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Isn't it a lot more complicated than that though? Since Raptor is a full-flow staged combustion engine which is basically two closed cycle, cross feeding, gas-gas propellant paths.

If you throttled the fuel valve to the main chamber, it quickly moderates chamber thrust but the decrease in flow of the gaseous fuel line decreases flow through the turbine for the oxidizer power head. If you do that, the oxidizer flow is moderated which means the chamber thrust decreases even more in which case the control valve has to compensate so the throttle valve likely has a dance it does to change throttles to prevent control oscillation.

I am sure SpaceX has the timeline for changes in throttle figured out to keep operation smooth between throttle changes. But because this process is so delicate, won't you be increasing the probability of a mishap by starting the engines with a pre moderated fuel flow to begin with? They may already do this.

Genuinely curious about this.

Kceovaisnt- said:

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bmks270 said:

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nortex97 said:

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Thx. But when can a rocket start actually throttling down? Don't they generally have to go to something like 50% power for a few seconds?

Also, woah.

NEWS 🚨: Astronomers have discovered the largest black hole ever, and it’s over 30 billion times the size of our sun

Reaching the “upper limit of how large a black hole can theoretically become” 😳 pic.twitter.com/2XwC3znzmf

— Latest in space (@latestinspace) June 27, 2023

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Depends on the engine design.

Usually the power level will be determined by a flow metering valve. Wherever they set the valve is what power it will come to. They can have it start up at any power level. And they usually reduce throttle to lower maxQ (maximum dynamic pressure) but then increase the throttle again.

Not all rockets throttle. Solids for example just go, no throttling control.

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Isn't it a lot more complicated than that though? Since Raptor is a full-flow staged combustion engine which is basically two closed cycle, cross feeding, gas-gas propellant paths.

If you throttled the fuel valve to the main chamber, it quickly moderates chamber thrust but the decrease in flow of the gaseous fuel line decreases flow through the turbine for the oxidizer power head. If you do that, the oxidizer flow is moderated which means the chamber thrust decreases even more in which case the control valve has to compensate so the throttle valve likely has a dance it does to change throttles to prevent control oscillation.

I am sure SpaceX has the timeline for changes in throttle figured out to keep operation smooth between throttle changes. But because this process is so delicate, won't you be increasing the probability of a mishap by starting the engines with a pre moderated fuel flow to begin with? They may already do this.

Genuinely curious about this.

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Look at a Raptor flow diagram and give it some thought. At the end of the day you run all of the same parameters except lower mass flow and you'll have lower power. Setting the valves more closed will be lower mass flow through the turbine burners and lower pump power and flow rates.

There are two turbo pumps that dump the exhaust into the thrust chamber. You change what goes into the turbo pump combustors. Everything into those two combustors ends up in the main thrust chamber. But each also controls the pump power.

The EverydayAstronaut video at the top of the page goes through a very detailed explanation of the shuttle engine start up cycle over about 5 second span. Granted Raptor will likely spool up faster it's a very delicate dance with lots of moving parts.

nortex97 said:

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Thx. But when can a rocket start actually throttling down? Don't they generally have to go to something like 50% power for a few seconds?

Also, woah.

NEWS 🚨: Astronomers have discovered the largest black hole ever, and it’s over 30 billion times the size of our sun

Reaching the “upper limit of how large a black hole can theoretically become” 😳 pic.twitter.com/2XwC3znzmf

— Latest in space (@latestinspace) June 27, 2023

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Theoretically couldn't all matter in existence be sucked in to a black hole on a long enough timeline? Or would black holes colliding lead to more big bangs and expansion. If thats the case, what cycle are we in on the infinity timeline if contraction and expansion? What if this is the 39273627th time the universe has done this? Existence is weird.

BTW - the cadence out at Boca Chica makes me think they will be ready by late August, just waiting on clearance from the feds.

SpaceX continues to defy my expectations.

Sea Speed said:

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nortex97 said:

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Thx. But when can a rocket start actually throttling down? Don't they generally have to go to something like 50% power for a few seconds?

Also, woah.

NEWS 🚨: Astronomers have discovered the largest black hole ever, and it’s over 30 billion times the size of our sun

Reaching the “upper limit of how large a black hole can theoretically become” 😳 pic.twitter.com/2XwC3znzmf

— Latest in space (@latestinspace) June 27, 2023

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Theoretically couldn't all matter in existence be sucked in to a black hole on a long enough timeline? Or would black holes colliding lead to more big bangs and expansion. If thats the case, what cycle are we in on the infinity timeline if contraction and expansion? What if this is the 39273627th time the universe has done this? Existence is weird.

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This is way above my pay grade, but this article discusses the ISCO/limits as to how a black hole can accrete/add mass by sucking more in vs. it getting pushed out. "It depends" I guess on how fast it is spinning etc.

Theoretical physicists have been arguing/nerding out about their ideas as to what happens 'in' a black hole since it became an idea. I think Hawking changed his opinion on it something like 3 times quite famously. I don't even know if there's a current dominant theory about the Big Bang being…the other side of a black hole event horizon or not. Kinda fascinating but just too much for my little brain.

https://twitter.com/SpaceX

Key takeaway from the briefing is that the three were all very pleased with the flight, and endorsed suborbital research as something that fills a gap between terrestrial and orbital platforms.

— Jeff Foust (@jeff_foust) June 29, 2023

Sierra CEO gave a briefing hinting at 'horizontal take off/launch' in the future, which I read as "we're getting sick of waiting on ULA to figure out how to launch the Vulcan Centaur even one time.'

Quote:

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Speaking at the Jeffries Space Summit online investor conference June 27, Tom Vice, chief executive…


He said he expected Dream Chaser to be fully integrated with its launch vehicle, United Launch Alliance's Vulcan Centaur, in "the December timeframe" and launch in a window that extends into early February.

That timing, though, is dependent on the readiness of the Vulcan rocket. ULA announced June 24 it needed to make a "minor reinforcement" to part of the Centaur upper stage, delaying its first launch for an unspecified period. The first Dream Chaser will launch on the second Vulcan, after the inaugural launch that carries payloads for Astrobotic, Amazon and Celestis.

"We're watching the Vulcan very carefully," Vice acknowledged. "They've got to get up their first flight of Vulcan, turn the mission data analysis around and then we're on the second flight."
That launch is the first of at least seven Sierra Space will perform for NASA to transport cargo to and from the International Space Station. He said the company is in talks with potential non-NASA U.S. government customers as well as unspecified customers interested in free-flying science missions.
The company is also working on a second version that can carry both crew and cargo. Vice said that version will have 40% greater cargo capacity than the first version and can support a six-person crew.

The ability of Dream Chaser to glide back to Earth in a runway landing, rather than splash down in the ocean, is a key selling point to customers, he argued. "We just think that landing at runways around the world is a huge differentiator: low-g landing back on a runway for both time-critical cargo and science, but also just the way people are going to want to fly back and land."

Vice hinted that the company has longer-term plans for Dream Chaser that could possibly allow it to end dependence on other companies' launch vehicles. "We're thinking about investigating the right technologies in thermal and propulsion and materials that allows us to potentially think about the staging options that would allow us, for the first time, have horizontal takeoff," he said. He didn't offer a schedule for developing that version of Dream Chaser.

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Surely a carrier aircraft a la Virgin Galactic with a boost phase could work for Dreamchaser, to LEO anyway.

This video from inside the Virgin Galactic shot is cool as hell. Looks and sounds like something out of Star Wars.

Here's the Drop and Burn moment from the cockpit, best part is you can hear the passengers in the back. pic.twitter.com/Sv0vDG9PnU

— Scott Manley (@DJSnM) June 30, 2023

Also,

Isn't this spot in the sky absolutely black? So where is it?

OnlyForNow said:

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Also,

Isn't this spot in the sky absolutely black? So where is it?

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Black holes usually have a lot of stuff falling into them, which actually makes them pretty bright

Sea Speed said:

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nortex97 said:

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Thx. But when can a rocket start actually throttling down? Don't they generally have to go to something like 50% power for a few seconds?

Also, woah.

NEWS 🚨: Astronomers have discovered the largest black hole ever, and it’s over 30 billion times the size of our sun

Reaching the “upper limit of how large a black hole can theoretically become” 😳 pic.twitter.com/2XwC3znzmf

— Latest in space (@latestinspace) June 27, 2023

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Theoretically couldn't all matter in existence be sucked in to a black hole on a long enough timeline? Or would black holes colliding lead to more big bangs and expansion. If thats the case, what cycle are we in on the infinity timeline if contraction and expansion? What if this is the 39273627th time the universe has done this? Existence is weird.

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For any given distance to a black hole, there is an escape velocity. The larger the distance, the lower the escape velocity by 1/r^2. Since the universe is expanding there's going to be a point where objects at rest relative to the black hole have reached escape velocity. And beyond that, objects traveling towards the black hole can even achieve escape velocity.

I have no clue what you just said