sevenperforce
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Posts posted by sevenperforce
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It looks absolutely terrific. The shoulder motion is…amazing.
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On 4/13/2024 at 12:07 PM, tater said:
Might need a print of this.
https://cosmicbackground.io/pages/total-eclipse
Got a framed one for my son to commemorate our road trip.
Absolutely incredible.
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On 4/5/2024 at 8:58 AM, Spaceception said:
Okay, that looks amazing
Looks like a behemoth! Reminds me of the early Raptor 1s with all the extra tubing and such.
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Liftoff of MAXAR-1!
MECO and stage separation. MVac ignition is good and these ground tracking shots are gorgeous.
Re-entry burn startup and shutdown look good! Continuing to see the short nozzle on the MVac burning hot.
Tracking camera showing re-entry.
20th entry burn by this booster.
Landing burn startup!
And that's a successful RTLS landing! Seriously, 20 reuses of a single airframe is impressive. Insanely.
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On 4/14/2024 at 10:13 PM, DAL59 said:
With all the tile issues SpaceX has been having (and the shuttle before them), should they have stuck to the evaporation cooling idea? Or just making the entry half of the starship out of a high melting point material (though this would reduce payload capacity).
Time will tell whether evaporative cooling would have been a better idea.
There is no material with a sufficiently high melting point, a sufficiently low thermal conductivity, and a sufficiently high strength to weight ratio to serve as the entry half of the starship and still be able to make orbit.
3 hours ago, tater said:(3 hours 20 min right now)
We've got the webcast starting!
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8 minutes ago, Exoscientist said:
SpaceX should withdraw its application for the Starship as an Artemis lunar lander, Page 3: Starship has radically reduced capability than promised.
https://exoscientist.blogspot.com/2024/04/spacex-should-withdraw-its-application.htmlSpeculation -- most of it already rebutted many times -- from beginning to end.
8 minutes ago, Exoscientist said:Elon suggests the current version V1 would be capable of 40 to 50 tons to orbit. This is bad because SpaceX sold NASA on the idea the Starship HLS could serve as an Artemis lander based on 150 tons to orbit reusable
As you know, Elon was talking about the dev version that was intentionally launched with underfilled tanks to a non-orbital trajectory.
His suggestion that this was still capable of 40-50 tonnes to orbit suggests that Starship dev is well on track to meet goals...goals that, I must add, do not depend on the performance of any dev version.
8 minutes ago, Exoscientist said:If they intend to use version V2 then this is bad because it would require further qualification flights for the larger version
SpaceX has done zero qualification flights to date, as they are still in development of their launch vehicle. Since all qualification flights are in the future, there are no "further" qualification flights needed.
8 minutes ago, Exoscientist said:A good Chief Engineer should be scrupulously forthright. He would not refer to the little 5 or 10 second static burns SpaceX does for the SuperHeavy or Starship as "full duration". A true Chief Engineer would be aware that "full duration" in the industry is short for "full mission duration".
As an attorney with a particular certification in securities law, I can tell you that being "scrupulously forthright" is much more important for officers and board members of a corporation than it is for engineers (or whatever you imagine a "Chief Engineer" to be), and that your particular quibble over the way that static fires are described is nowhere near the ethical line for misrepresentations.
8 minutes ago, Exoscientist said:These static fires in the industry are conducted at the full length and the full thrust of an actual flight and are meant to give confidence to potential customers that the engines can perform as expected for the promised capabilities of the launchers.
Where SpaceX deviates from industry standards, they do so openly and intentionally. You might as well complain that Apple deviated from industry standard by introducing an iPhone without a removable battery. Sure, people didn't like it, but it certainly didn't stop it from begin successful. Besides, you have presented no evidence that SpaceX has failed to share information with its potential customers about the duration and thrust levels of its static fires.
8 minutes ago, Exoscientist said:The FAA had great concerns in the Raptor reliability after the first test flight. In the "corrective actions" they required of SpaceX prior to a second Starship test flight, at the top of the list was correcting the tendency of the Raptor of leaking fuel and catching on fire while in flight.
Those were items C11-C20, so not the top of the list. Additionally, your phrasing -- "tendency of the Raptor of..." -- does not reflect the FAA's corrective action statement. More importantly, all of these were corrected to the FAA's satisfaction.
8 minutes ago, Exoscientist said:I have argued multiple, independent lines of evidence suggest SpaceX intentionally reduced the throttle of the Raptors
Each of which have been debunked.
8 minutes ago, Exoscientist said:Did SpaceX throttle down the booster engines on the IFT-2 test launch to prevent engine failures?
No.
8 minutes ago, Exoscientist said:SpaceX has said the Starship RUD was due to an intentional LOX dump they performed to keep that flight as suborbital. However, many knowledgeable observers doubted the LOX dump alone would have caused a RUD.
So NASA and the FAA were fooled, then?
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On 4/8/2024 at 2:30 PM, Exoscientist said:
If they intend to use version V2 then this is bad because it would require further qualification flights for the larger version and
Given that they have not started any qualification flights, this does not appear to be a problem, now does it?
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Just now, JoeSchmuckatelli said:
I was excited to see these - unfortunately they're not showing up
They didn't show up for me either, but if you right-click the image and hit "open in new tab" then they are visible.
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13 hours ago, Superfluous J said:
At a winery? If so I may have been standing nearby
Nope, but it sounds like other people had a similar idea! This was at a public park in Terre Haute, IN.
My Tiktok livestream of the ceremony caught this shot of the moonshadow whooshing overhead at the end of totality. Try to pay attention to the sky rather than the sun and you can see it:
The setting and ceremony was really beautiful, and we had a great time.
We catered our own wedding so I did eclipse tarts that all show varying levels of partiality:
Some video of the eclipse etc:
https://www.tiktok.com/t/ZPRTnu1Yd/
https://www.tiktok.com/t/ZPRTn3QRd/
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21 minutes ago, NFUN said:
those by definition have no event horizons...
I meant naked in the sense of having no accretion disk, not in the sense of a naked singularity.
In any event: I am blown away. Unable to really express it. It’s the most amazing thing I’ve ever seen, by far. Doubly amazing because we were getting married during it.
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18 hours ago, Kerb24 said:
I cannot put into words how amazing that was. My mind is still struggling to process it.
It was what you would imagine it would look like to be a god staring into the event horizon of a naked black hole.
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On 3/25/2024 at 4:47 PM, cubinator said:
Now THAT's a diamond ring to remember!
Speaking of rings, we forged our own wedding bands from a 125-year-old gold coin (with additional space themes as expected):
https://www.tiktok.com/t/ZPRTqKkke/
(if you feel like helping us celebrate at all, we’ve got a honeymoon fund here.)
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Radian has an update:
Wow! They have finally gotten enough capital to pay for a NEW RENDER!
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11 hours ago, tater said:
That's gorgeous to see!
It's very curious to me that neither turbopump is being placed inline with the engine. An inline approach (Raptor, BE-4, RD-191) would seem like the simpler, more lightweight design. Granted, other single-chamber engines with dual-shaft (separate turbines) turbopumps (RS-25, RS-68, YF-100, Vulcain, YF-20, YF-77) have both turbopumps off-axis, but that feels like it has almost always been due to other design constraints. Maybe it's an engine length issue? Something to do with how they are handling gimbal?
I wonder if the gimbal is happening halfway down the nozzle rather than up at the top. The structure of the top of the engine looks pretty gimbal-unfriendly, and these highlighted bits around the nozzle extension look suspiciously like gimbal mounts:
(Notable that those are clearly Lapsa's kids which is just awesome.)
Putting the gimbal halfway down the engine bell is....definitely different. Probably lower control authority, among other things. But I suppose it could really reduce weight in other places.
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15 hours ago, Exoscientist said:
He has an obvious error at item 4 -- "orbital" velocity. There is no indication whatsoever that Starship failed to reach its intended velocity or trajectory.
That is a debatable point because Elon did say there was an 80% chance of the Starship reaching orbit on this flight:
There was a 0% chance of Starship reaching true orbit because that was not the design trajectory. If Starship had reached true orbit, then something had to go very, very wrong. So obviously Elon was not talking about true orbit; he was saying that there was an 80% chance of Starship making it successfully through staging and the full-duration second-stage burn to its intended SECO.
Otherwise you're saying that when Elon says "80% chance" he is actually saying that the mission only has a 20% chance of success.
15 hours ago, Exoscientist said:But there still remains the question of why didn’t IFT-3 reach orbital velocity? In the case of IFT-2 they vented LOX reducing the velocity it was capable of, and Elon even said if they had a payload and had not vented LOX they would have reached orbit.
But they didn’t vent LOX on IFT-3 and SpaceX said they had a full propellant load and from the view of the propellant gauges the propellant was virtually expended in both stages. So why were they not able to reach orbit even though carrying 0 payload?
I've already painstakingly explained this to you. The very sentence where SpaceX says they had a "full propellant load" they also state the total amount of propellant and it is significantly lower than the actual full capability of Starship, meaning that it was a "full propellant load for this mission" not a "full propellant load for the maximum design capacity".
Or would you argue that the BE-4 engines on the Vulcan Cert-1 mission must have been operating at above their stated thrust levels because Vulcan reached "full propellant load" and an actual full propellant load is too heavy for two BE-4s to lift? (Obviously not; Bruno specifically said that they underfilled the tanks, just like SpaceX specifically quoted a total propellant amount lower than the maximum design capacity).
And even if they HAD a "full propellant load" (which they did not), that doesn't mean they would have accidentally entered a true orbit. Burning for a high apogee achieves orbital velocity without fully circularizing. You've played KSP, right? Haven't you ever accidentally burned too early or burned at the wrong angle and ended up depleting your props with a high apogee before you finish circularizing? Plus, burning at lower throttle can achieve the same thing. They were targeting a specific re-entry zone for a reason.
8 hours ago, Exoscientist said:I’ve suggested that SpaceX intentionally ran the Raptors on IFT-2 and IFT-3 at reduced power, i.e., thrust, to improve reliability.
Even if there was evidence that the Raptors were run at reduced power during IFT-2 or IFT-3, this wouldn't necessarily imply a reliability issue; it can also be done to achieve a full-duration burn time with a decreased propellant load in order to avoid entering a true orbit.
You know, the thing that they explicitly said they were doing.
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On 3/30/2024 at 4:35 PM, tater said:
Instead of trying to launch 3 rockets within <4.5 hours, they should do the prudent industry thing and spread these 3 launches over at least one Quarter. This just isn't "how it's done."
Departing from industry standard. Tsk tsk. And they expect to get government contracts?!
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1 hour ago, Exoscientist said:
Common Sense Skeptic, a well-known critic of SpaceX presents an argument that considering all the mission objectives IFT-3 should not be regarded as a successful test:
Appreciated a short synopsis. There's no way I was listening to a whole big post.
With respect to the booster engine landing burn relight: once grid fin control was lost, the booster return was expected to be a failure. If you'll recall, the CRS-16 mission suffered a similar fate when one of its grid fins entered a hydraulic stall and stuck hard-over. There, the single engine tried valiantly to correct for the problem, but it was already off-nominal. This is the same situation. Engine relight depends on a number of factors, including vehicle stability, and so once you are spinning out of control you don't expect engine relight to work.
He has an obvious error at item 4 -- "orbital" velocity. There is no indication whatsoever that Starship failed to reach its intended velocity or trajectory.
He then says that the payload door demo was not successful because the vehicle started to spin once the payload bay vented to space. That doesn't make any sense. It's clear that Starship lost attitude authority (likely due to frozen propulsive vents); whether or not it lost attitude authority doesn't impact the success of the payload door demo. He subsequently says "we have no indication that the test took place" and claims that this is because we did not see any graphical change in the LOX levels, which is also nonsensical; there was no indication that the GUI was supposed to show this. This should be a questionmark, not a failure.
Finally, he claims that because the re-entry time was three minutes different from the estimate from some random person on the internet, this meant it did not re-enter where it was supposed to re-enter. I shouldn't have to explain how silly THAT is.
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19 hours ago, farmerben said:
I just tested with 50 TWR vessel on Minimus. Going straight up uses 248 dV to escape the SOI. Changing to a near horizontal trajectory and burning in a straight line uses almost the same amount of dV.
However, throttling down and taking a gradual spiral used 279 dV.
Once you are past escape velocity, you no longer need to worry about gravity turns. Minmus has such low gravity that with substantial T/W you can achieve escape velocity within the first few seconds of launch, obviating the need for a gravity turn.
Note here that you are still achieving an orbit; it's just an orbit with a periapsis under the surface of Minmus.
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3 minutes ago, zolotiyeruki said:5 hours ago, Exoscientist said:
SpaceX repeating the same mistakes over and over again does not make those mistakes correct.
Just to be clear, what "mistake" is SpaceX repeating over and over again?
Not monitoring this forum more closely and therefore missing exo's advice, apparently.
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13 minutes ago, Ultimate Steve said:
Hmm, looks like they did. Memory is a weird thing.
The RVacs are designed to have flow separation just barely starting around the very edge of the nozzle at sea level. The nozzle is reinforced at the edge which helps keeps this from causing issues. Part of this was to save weight, part of this was to make them easier to static fire at sea level.
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I will be getting married in Terre Haute, Indiana during the eclipse.
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I'm so very excited to see what they've come up with.
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1 hour ago, .50calBMG said:
Just because they said fully fueled doesn't mean 100% full. There's plenty of rockets that will partially fuel the tanks for certain variants or flight profiles. Fully fueled in this case could just mean "fully fueled for this mission profile"
Yep, that's precisely what they meant.
Superheavy takes 3,400 tonnes of propellant while Starship takes 1,200 tonnes of propellant. Fully loaded, that would be a total of 4,600 tonnes of propellant. Yet SpaceX said "fully loaded with more than 4500 metric tons of propellant"; we can therefore pretty readily deduce that "fully fuelled for this mission profile" meant 100 tonnes LESS propellant in Starship than in an orbital mission profile.
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On 3/22/2024 at 4:32 PM, kerbiloid said:
First Luna crafts were sent (in)to the Moon without intermediate LEO.
https://en.wikipedia.org/wiki/Luna_1"Without intermediate LEO" doesn't mean that the rocket was launched vertically straight up all the way to the moon. The Luna 8K72 three-stage rocket (2.5 stages by US accounting) still executed a normal gravity turn, etc.; it just didn't stop off in a parking orbit. The Blok E upper stage burned continuously from stage separation all the way through to translunar injection. The RD-0109 engine most likely used a pyrotechnic igniter like the RD-0110 that came after it, so it was not designed to be restarted for that mission, requiring a single continuous burn.
You never burn straight up all the way.
On 3/22/2024 at 4:32 PM, farmerben said:If you have TWR of 1.5 or so, then the vertical approach is way less efficient. With TWR greater than 3 the amount wasted is very small.
With T/W ratio of more than 3, you begin losing substantial amounts of Δv to aerodynamic drag. I don't believe there is any situation where thrust to weight balance makes a vertical launch more efficient. You're not really "losing" anything at all by entering a stable orbit first, except perhaps a very tiny amount of Oberth advantage.
On 3/23/2024 at 8:30 AM, darthgently said:the DV req'd for that horizontal velocity isn't free either and keeps you in the atmo longer
This is the wrong way of thinking about it. While the Δv required for horizontal velocity isn't free, it's not wasted, either. The Δv you spend getting to orbit is preserved as your orbital velocity, which is then added to your eventual injection burn.
The only thing that is "wasted" is thrust spend pointing at the ground, resisting gravity.
Gravity turns are designed specifically to start the pitchover such that drag will be minimized. MaxQ happens very early in flight; drag after MaxQ is negligible. So "keeps you in the atmo longer" is not an issue.
On 3/23/2024 at 9:23 AM, farmerben said:The inclination difference is no big deal. It's easy to adjust inclination after leaving the atmosphere.
Not really, no. You want to change your inclination while moving at the lowest possible velocity. When you choose a particular launch direction, you are picking your inclination at a velocity of zero, which is optimal.
Burning out of the atmosphere and then changing directions is a huge waste of Δv.
On 3/23/2024 at 9:23 AM, farmerben said:Nobody claimed the vertical approach would save dV. But if the difference is not significant, what advantages does it have?
The difference is significant.
On 3/23/2024 at 9:23 AM, farmerben said:One of the big advantages in game is you can have oversized payloads without a fairing. The aerodynamics hurt you less.
If you are going fast enough to make up for the gravity drag losses, you will run into aerodynamics issues much sooner.
Artemis Discussion Thread
in Science & Spaceflight
Posted
Well, it's NOT a lander to and from low lunar orbit.
If you mean that the numbers are off-base for a minimal lander that WOULD be going to and from low lunar orbit...that depends on what you mean by minimal.
The ascent element denoted above needs to get from the lunar surface to Gateway. Technically, going between LLO and the Gateway should only cost 730 m/s, but the ascent element above has additional Δv to handle phasing and other issues for abort situations. Assuming the minimal mass of 9 tonnes above and hypergolics at ~318s, we're looking at a notional 5.4 tonnes of propellant. (This means a dry mass of 3.6 tonnes.) Reducing the required Δv to the bare 1.87 km/s to go from the lunar surface to LLO allows the total props to drop to just 3 tonnes, trimming the ascent element to a wet mass of 6.6 tonnes. Let's say the reduced tankage weight and getting rid of reusability/refillability can trim it to 3.2 tonnes dry and 5.9 tonnes wet. The Apollo LM ascent module had a dry mass of 2.15 tonnes, so ~49% dry mass growth for double the crew is pretty good. No reason to think this "can't be correct".
With an ascent module wet mass of 5.9 tonnes (compared to the 4.7 tonnes of the LM), using the gross mass ratio of the LM descent and ascent elements, you'd need a descent module of 12.9 tonnes, for a total gross mass of 19 tonnes. That's what the above figures suggest for a minimal lander going to and from low lunar orbit. 19 tonnes.
Of course that wouldn't satisfy any of the program requirements of Artemis.