GW Johnson Postings and @Exrocketman1 YouTube videos

GW Johnson · 2024-11-09 08:41:40

To fill the LOX tank before the vehicle topples would take an opening about the same size as the diameter. I don't think there's any practical way to do that. You only have a single handful of seconds to get the job done.

GW

tahanson43206 · 2024-11-09 09:29:36

For GW Johnson re #451

Thank you for considering the question of admitting water to the vehicle to stabilize it while keeping it afloat.

It appears that trying to fill the oxygen tank, or even just admit ** some ** water into the tank is unlikely to succeed,

The rate of release of air inside the body of the vehicle would be a factor, if an opening at the top of the vehicle were provided.

I'm back from looking at several video's, and there was no evidence of an opening at the top of Starship in any of them.

There ** is ** another strategy that might allow the Starship to survive rotation from vertical to horizontal at landing... If the vehicle had some horizontal velocity, then as the ship's stern enters the water, it would drag, and the ship would tip in the direction of movement. If the direction were controlled so that the back of the ship hits the water, that part of the ship would be least elevated in temperature.

(th)

tahanson43206 · 2024-11-17 11:24:12

For GW Johnson re Void idea/suggestion in post: http://newmars.com/forums/viewtopic.php … 69#p227869

In one of his creative modes, Void explored the possibility that a Starship might be able to achieve LEO without a payload. His proposal seems to be that the ship itself would be (or could be) a useful "payload".

The material used to construct the ship is of very high quality. Void's idea seems to be to remove the engine compartment and return that to Earth. That reminds me of the Vulcan idea, of parachuting the engines back to Earth. In Void's case (if I understand correctly), the engines would be brought back by ships designed for that purpose.

My question for you is: Can a Starship deliver itself to LEO, if there is no payload other than itself?

How low would the orbit be, if it is even possible?

Void has hinted that a Space Tug of some kind might retrieve the empty rocket. The fuel for that operation would need to be delivered by a separate vehicle.

Is it simply more efficient to use a Super Heavy to give the Starship the boost it needs and call it a day?

Fuel and oxidizer are needed to place the vehicle in a higher orbit. Is this a situation where the fuel consumption is the same, or does one system have an advantage over the other?

The challenge of the Space Tug matching orbit with the single stage is non trivial. That problem is solved by just using the Super Heavy.

The ship to bring the engine compartment back to Earth would necessarily be larger than Starship, because the engine compartment is contained in a cylindrical section that is the same diameter as Starship. Fuel would have to be invested in delivering the return ship to orbit, and maneuvers would be needed to collect the engine compartment to be returned.

By the time you add up all the fuel expenses, I'm wondering if the two stage method works out as the most cost effective.

If Void's basic idea (as I understand it) is to use the Starship that reaches orbit as a component of a structure, then the engines would ** still ** need to be returned even if a Super Heavy is used to boost the ship to where it needs to go. So in that case, the special return vehicle would be needed, and it would need fuel.

If we consider Void's basic idea as delivery of components to LEO to build a large structure, than the cylindrical shape is not obligatory. In other words, the girders to make a square structure in space could be welded to the cylindrical walls of the Starship, so that the entire system could be simply bolted into place.

If we have anyone in the group with the skills and software needed to make drawings of what such a configuration might look like, it sure would be interesting to see it.

(th)

GW Johnson · 2024-11-18 12:31:23

Question: could a “Starship” without any payload reach LEO without a “Superheavy” booster?

Answer: it’s complicated. But it is very likely not possible.

Details:

As being currently flown, which is not yet fully fitted out, the inert mass of “Starship” is somewhere in the vicinity of 120 metric tons. These notions of getting that down to something in the 50-90 ton range are utter bullshit! That inert will grow, if anything. But let’s use it anyway. That same configuration has tanks that can hold a max of 1200 metric tons of propellant. That puts the vehicle at just about 1320 metric tons mass, ready for ignition with no payload.

To get efficient launch kinematics and not waste propellant by climbing too slowly, the very-well-verified rule-of-thumb is that you need thrust/weight = 1.5 at launch (basically half a standard gee above the local pull of gravity). For 1320 metric tons mass, that is 1980 metric tons-force of thrust that you need at liftoff on Earth.

As currently flown, “Starship” has a total of 6 Raptor engines, those being 3 sea level and 3 vacuum variants. These are Raptor 2’s for which the sea level variant has a sea level thrust somewhere in the vicinity of only about 200 metric tons-force. The vacuum variants cannot be used at sea level; they are on the verge of bell separation and with a much-reduced thrust. Raptor-3 is reputed to be nearer 250 metric tons-force sea level thrust in the sea level variant. There might be room to mount 9 engines in the “Starship” engine bay, if all 9 were sea level variants. The inner 3 would gimbal, but the outer ring of 6 could not gimbal.

If these 9 sea level engines were Raptor-2, total takeoff thrust would be 9*200 = 1800 metric tons-force, only a little bit short of the rule-of-thumb. If they were instead Raptor-3’s, total thrust would be nearer 9*250 = 2250 metric tons-force, more than enough. So you could successfully launch with either Raptor model, but you would get significantly better overall performance results at the higher thrust level of the Raptor-3 sea level design. Especially if inert mass grows, as I think it will.

As you burn off propellant on the way up, you will need to shut some engines down, or else overstress the structure with too much acceleration gee. 9 Raptor-3’s at 1/3 thrust on a dry-tanks 120 metric tons is still too high at 6.25 gees thrust-induced acceleration, near-horizontal and exo-atmospheric. The 3 gimballing center engines, at half-thrust, would produce about 3.1 gees, which is much more realistic. And don’t forget: at reduced thrust, Isp is always somewhat lower. You really have to look at this thrust stuff, otherwise, the rocket equation will lie to you, because of a GIGO problem!

The ascent-averaged Isp of the Raptor-2 (or -3) would be in the 350-360 sec Isp class. Call it 360 s just to be optimistic about what Raptor-3 will eventually be capable of! That puts the effective ascent-averaged exhaust velocity pretty near 3.53 km/s. For the rocket equation, that puts the no-payload mass ratio at 1320/120 = 11.00, producing a deliverable dV = 8.46 km/s. That has to cover the theoretical energy needed, plus at least the drag and gravity losses. (There’s also rendezvous and deorbit to worry about, plus maybe a landing burn.)

Now, estimate the dV and losses: conveniently, Earth circular orbit speed at the surface is 7.913 km/s. That’s a good measure of the energy we have to achieve going to low circular orbit (say near 200-300 km altitude), in a low-inclination eastward direction. It is also a good basis for figuring the losses. If we achieve launch thrust/weight near or above 1.5, gravity losses will be only on the order of 5% of surface circular, or 0.396 km/s. The “Starship” shape is aerodynamically pretty clean and of a nice L/D ratio, so the drag losses can be low, near 5% of surface circular, also 0.396 km/s. So the energy and losses total so far to 8.705 km/s, already greater than what the stage design can deliver (which is only 8.46 km/s)!

Conclusion: it won’t work!!! It cannot work!!! But even if it did, you would reach orbit with dry tanks. You would be unable to rendezvous with anything, which budgets somewhere around another 0.1 km/s as a minimum, so what good would that be as something delivered on-orbit? And you would also be incapable of doing a de-orbit burn, to dispose of this massive launched hardware safely, which is just about another 0.1 km/s from low circular orbit. How unethical would not being able to safely dispose of this thing be?

The real velocity requirement with losses would include both the rendezvous and deorbit burns, for a total of just about 8.905 km/s (or maybe a bit more) that your rocket equation delivery must meet. And that would be for a crash landing after deorbiting. You need even more, if you actually intend to land the thing and reuse it. Say, at or just above 9.1-9.3 km/s.

Only if you believe in the bullshit numbers for incredibly low inert mass, can you reach a mass ratio that could deliver near 9.2 km/s dV (or even only 8.9!!) at an ascent-averaged Isp of 360 s. I do not believe in crap like that! And with my background, I ought to know. I have never, not in all my life, seen a vehicle inert mass that did not grow during development and testing. They ALWAYS grow!

GW

Last edited by GW Johnson (2024-11-18 12:33:10)

GW Johnson · 2024-11-19 12:09:57

Here's one from AIAA's "Daily Launch" for Tuesday 11-19-2024 that is not worth the price of the paper it was written on.

The New York Times
SpaceX Starship’s Sonic Boom Creates Risk of Structural Damage, Test Finds

SpaceX’s new Starship rocket far exceeds projected maximum noise levels, generating a sonic boom so powerful it risks property damage in the densely populated residential community near its South Texas launch site, new data suggests. The measurements — of the actual sound and air pressure generated by the rocket during its fifth test launch last month — are the most comprehensive publicly released to date for Starship, the largest and most powerful rocket ever constructed.

My take:

I went and looked at the linked NYT article. Whoever wrote it was totally technically ignorant and confused the thrust noise made at launch with the sonic booms heard when the booster comes back. The sonic booms are never that loud, but the launch thrust noise is! There are no sonic booms heard at launch, period! The vehicle is subsonic until a handful of miles up and a handful of miles downrange eastward, out over the Gulf.

Coming back, the booster approaches some handful of miles up on 13 engines, and at much lower altitude on only three engines. That's all the thrust it needs to decelerate subsonic at a mile or two up, and then come down to land at roughly thrust equal to weight, with 3 engines, running throttled. You might hear a weak double boom for the sonic boom, and a stronger noise signal from the 13 engines as it reaches subsonic about a mile or so up, unless the thrust noise covers up the sonic boom. The 3 engines at touchdown are no noisier than any of the earlier Starship-only tests landing, which is also only thrust equal to weight on 3 engines, throttled.

It's the launch on 33 engines at full thrust, that is the real noise generator! I warned about this being a problem before they ever got started trying to test things there, if you will recall. At around 12-15 million pounds of thrust, about twice the Saturn-5, this thing is about as "thrusty" as the smaller end of the old "Nova" paper designs Von Braun brought with himself when he went to NASA in 1958 from the Army at Huntsville, AL. NASA could not use any of the "Nova" designs, as the launch noise level was thought to be too dangerous, for the 3-mile clearance they had to populated areas. Note that the launch pad at Boca Chica is only 5 miles from the Brownsville, TX, city limits. And there's many houses closer than that, and I am not referring to those few that were right next to the office building at Starbase. Not to mention civilians in Mexico, too.

Why would anybody be surprised when someone finally flagged the noise risk? I warned of this years ago! The writeup breaking this news is a piece of crap, but the data it refers to are quite real! I totally expected this! All I wondered was why this did not come up sooner!

GW

Last edited by GW Johnson (2024-11-19 12:15:11)

tahanson43206 · 2024-11-20 07:32:42

For GW Johnson re testing of new FluBB web site...

Please log into the new system at http://newmars.com/new/

Please post a message there to confirm you were able to log in, and to report your observations.

(th)

tahanson43206 · 2024-11-21 07:20:39

For GW Johnson re new web site...

Thanks for logging in and confirming the new site looks "normal" to you!

(th)

GW Johnson · 2024-11-22 10:06:10

From AIAA’s “Daily Launch” for Friday 11-22-2024, a short paragraph linking to a longer article published on Ars Technica:

ARS TECHNICA

NASA is stacking the Artemis II rocket, implying a simple heat shield fix

The Space Launch System rocket that will dispatch four astronauts on the first Moon mission in more than 50 years passed a major milestone Wednesday. NASA said ground teams inside the Vehicle Assembly Building (VAB) at Kennedy Space Center in Florida lifted the aft assembly of the rocket's left booster onto the mobile launch platform. Using an overhead crane, teams hoisted the left aft booster assembly—already filled with pre-packed solid propellant—from the VAB transfer aisle, over a catwalk dozens of stories high and then down onto mounting posts on the mobile launcher.

My take on it, after reading the linked article:

NASA managers have apparently decided to risk the crew with the evidently-defective heat shield design, and just modify the entry trajectory a bit to reduce peak heating as the “fix”, so that they can stack the rocket and fly as soon as possible before the “stacked lifetime” limit occurs. This would be the only way to fly during 2025 or early 2026. They are very close-mouthed about exactly what the “fix” to the heat shield really is, so that is what tells me they have decided to fly with what they have already installed on this Orion capsule.

They have decided to go ahead and risk manned flight with a poor heat shield design, in order to fly sooner and avoid the costs of a longer delay. And so they do not want that decision publicized, in case something bad happens. Where have we seen this pattern before?

Meanwhile, I have been in contact with David E. Glass at NASA, who is a real thermal protection engineer. I provided to him a copy of my original letter to Bill Nelson, with the 4 figures showing exactly how to put the hex into the bonded Avcoat tiles that they really want to use. I also provided to him two photos from ramjet combustor insulation tests I ran 3 decades ago, which show more-or-less the same cratering damage mechanism that they saw on the Artemis-1 heat shield, if there is only a weak tie between char and virgin beneath, under high fluid shear force conditions. These photos were from the presentation I took to the American Carbon Society meeting at NCSU last April.

Glass tells me that the NASA heat shield engineers trying to “fix” this problem now have all the materials that I sent to him. But I have heard nothing back from anyone, as of yet. But my contact was only just last week.

GW

tahanson43206 · 2024-11-22 10:16:49

For GW Johnson re #458

If the decision is made to use your recommended solution, would the rocket have to be unstacked?

That would seem necessary, unless the stage with the shield is not yet stacked.

***
RobertDyck just posted a link to a paper/article by NASA about 1960's fly-by mission concepts. I found this;

The crew would, however, continue to fire the thrusters in brief bursts, slowly increasing the spin rate and keeping cable tension constant. When the cables reached full extension, the CSM and MM/PC would be 158 feet (48.1 meters) apart, completing four rotations per minute. This would provide the crew in the MM with acceleration that they would feel as gravity roughly equal to the pull of gravity on Mars (0.4 G). Providing the crew with Mars-level gravity complemented the flyby mission biomedical research program; data on human response to Mars-level gravity would clear the way for long stays on the surface of Mars in the 1980s.

While your recent proposal of a 4 RPM habitat may not have had this earlier work as a direct antecedent, I do think it is interesting that the earlier concept chose the same RPM without having any field tests to validate it.

However, I bring this to your attention as an example of something that could be done with existing equipment and a bit of clever cable deployment design work.

***
In a separate topic, I have been attempting to explore the idea of shipping girders and curved panels to LEO as exterior add-ons to the existing Starship. If this could be done, then the lifting Starship could be returned to Earth and re-used. A set of girders could be used to make a sturdy frame for testing of the 4 RPM idea.

(th)

tahanson43206 · 2024-11-22 13:51:30

For GW Johnson re landing cargo pods....

Here is another interesting idea from Void:

So, I have already suggested that Moon ships could have one time landing legs made of Plastics, maybe wood.

The above appeared in a post created today, 2024/11/22, on one of Void's many topics.

I am bringing it to your attention because you have already folded one of Void's ideas into your lander designs, with cargo carried to the surface on fold-out legs that then detach while the delivery rocket returns to orbit. It just occurred to me that those drop-off legs need to be able to withstand blastoff wind and debris.

The idea of making the entire leg out of wood may not be practical, but perhaps significant parts of the cargo enclosure could be made of plastic or wood, and the result would be delivery of these materials to the surface of the destination object. Carbon on the Moon would be quite valuable, while the Hydrogen would be quite valuable on Mars.

(th)

GW Johnson · Yesterday 08:51:46

The impression I got from the Ars Technica article was that there is a time limit on how long the rocket can be stacked before it must be used. I saw no reason in the article as to why that is true, it was just stated as a given. Once the stages and SRB's are stacked, the Orion-and-service module-and fairing adapter "spacecraft assembly" is added.

That spacecraft assembly also apparently takes a lot of time to put together. I gathered from the story that there is not time to disassemble it and install a revised heat shield on the Orion, and then reassemble it, once the rocket stacking begins. Apparently, both processes have long schedules (which helps to partially explain the incredibly-high per-launch cost).

The Ars Technica article presumes that since rocket stacking has begun, there will be no heat shield revision to the Orion in the spacecraft assembly. The only other two options were a slight entry trajectory revision, or do nothing at all.

-- GW

Last edited by GW Johnson (Yesterday 08:55:14)

tahanson43206 · Yesterday 09:26:02

For GW Johnson re #461

Thanks for this update on the Artemis launch preparations!

The process can be stopped at any time by a single word from Bill Nelson.

Your letter about the alternative has been blocked once, but you have a better ball carrier this time. You't thrown an accurate pass. Now it is up to the ball carrier.

What seems clear is that is that the NASA team and the contractors want the Artemis flight to proceed before it gets cancelled by Elon Musk or anyone else on the Trump team.

If the heat shield has not yet been bolted into the assembly so that it cannot be replaced, there may be an opportunity to replace it. However, the pressure to build the replacement would be intense. It might be worth thinking about how to replace the existing shield with your design in a week (for example). The only way I can think of is to create the special panels in parallel. To the extent you've thought about the actual process, you may have imagined a single work station turning out a panel one every hour or so. A one week replacement window would require enough of your special purpose machines and enough personnel to accomplish the replacement in a week. The personnel to do the work could be all the NASA personnel and contractor personnel who are soaking up taxpayer dollars while twiddling their thumbs.

It would be up to you to offer a plan for parallel, coordinated manufacture of all those panels. There may be an order for assembly of the panels. For example, it may be preferable to start at the peak of the shield and work out, instead of starting at the exterior and working in. Starting at the peak has the advantage of needing fewer panels, so the work force can get up to speed as the size of the area to be covered increases.

The advantage of your conceptual design is that the panels can be examined by X-Ray after they have cooled and been scraped. That procedure would help to prevent voids, even though your recommended process is designed to prevent voids in the first place. It would be good to know there are no voids with a secondary confirmation.

Ultra-sound might work for that examination as well, and it might be less expensive due to lesser safety standards.

(th)

tahanson43206 · Yesterday 09:32:19

For GW Johnson as a follow up....

To save time, the shield must be replaced in the place where it is now. If the shield is on NASA property now, that is where the replacement needs to be done.

Does anyone know the timeline that is driving the Artemis launch preparations?

(th)

tahanson43206 · Yesterday 10:45:14

For GW Johnson re Congress vs Presidential Leadership....

What you call micromanaging was an attempt to keep the American space program running in the absence of presidential leadership.

There is NO SUBSTITUTE for leadership.

Congress is a committee. Occasionally strong leadership shows up there, but for the most part leadership there is absorbed by the environment.

There is NO SUBSTITUTE for leadership at the Presidential level in the United States, but that leadership must be supported by Congress.

We've SEEN strong presidential leadership in areas not related directly to space, and where that leadership was supported by Congress, positive results have followed. An example is the national highway system, but there are many more.

It will be interesting to see what happens in the next four years. Unfortunately, global conflict is a more than wispy possibility.

We had 70 years of relative stability after World War II, but the need for violent conflict appears to be strong in the human psyche.

(th)

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