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 · 2024-11-23 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 (2024-11-23 08:55:14)

tahanson43206 · 2024-11-23 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 · 2024-11-23 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 · 2024-11-23 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)

tahanson43206 · 2024-11-30 18:50:25

GW Johnson has prepared four documents that may be of interest to NewMars members.

These will be published in the exRocketman blog as well.

The topics are:

/SpaceTugs/Elliptical Orbit Capture.pdf
https://www.dropbox.com/scl/fi/pilp0r9x … slms0&dl=0

/SpaceTugs/On Pressure Vessels.pdf
https://www.dropbox.com/scl/fi/pxsr6v7d … x39iu&dl=0

/SpaceTugs/Options for Artemis Mission Alternatives.pdf
https://www.dropbox.com/scl/fi/owwf93im … t4yg9&dl=0

/SpaceTugs/Tug Assisted Arrivals and Departures.pdf
https://www.dropbox.com/scl/fi/a1xzjmuh … b564m&dl=0

I've been following along by email as GW worked his way through the thought process.

This work is a follow on to the early mentions of Space Tugs when he was working on the problem of how to deliver RobertDyck's Large Ship to Mars and to get it back home safely.

The focus now is much smaller and more immediate. The Artemis II flight is in preparation for a flight in late 2025. The heat shield mounted to the space craft is suspect, but NASA is (apparently) committed to flying with it despite the risk, due to the costs of doing anything. GW has been looking at a variety of ways to ease the Orion capsule into LEO, from which the existing heat shield can return to Earth safely.

The documents at the links above cover the problem to be solved, and offers solutions.

(th)

GW Johnson · 2024-12-01 09:52:46

First: all 4 links work.

Second: Artemis-2 flight with Artemis-1-type heat shield -- Reading between the lines somewhat, from akl the publications I have seen, NASA managers boiled their decision down to 3 options: (1) do nothing, just fly as-is, (2) do nothing to the heat shield, but modify the entry portion of the trajectory to reduce the heating a little, or (3) fix-or-replace the heat shield. Choice 3 meant another year's delay and a lot of extra costs, so they went with either 1 or 2, I think probably 2. That prioritizes money and schedule above astronaut's lives, but they have a demonstrated history of doing that, apparently never learning the lesson that there is nothing as expensive as a dead crew, especially one dead from a bad management decision. Whatever "fix" there might be for the Orion heat shield will go on Artemis-3 (the manned landing) which hasn't yet been built. The Artemis-2 heat shield was built back in 2020, according to some dated photos I have seen.

Third: I seriously doubt NASA managers would be open to finding a means to slow the Artemis-2 Orion down all the way into LEO to ease the entry heating. Whether that was among the options they might have considered is unknown, but my hunch says unlikely. Such a thing might be done with a crew Dragon sent along as a wingman (docking to Orion on the return), but would require a lot more dV out of the Super Draco's than could possibly be loaded, even into the "super trunk" variant they are looking at for ISS deorbiting. There's nothing that could fly right now that could do the job of 3.1 km/s dV with a whole Orion added to the crew Dragon mass, to get from approach speed down to circular orbit speed.

GW

Last edited by GW Johnson (2024-12-01 10:02:58)

tahanson43206 · 2024-12-03 09:20:09

For all ...

This post is reserved for links to two images prepared by GW Johnson in study of the Space Tug concept.

In this case, Dr. Johnson evaluated Starship as a potential Space Tug for the Artemis II mission.

It appears the concept would actually work. The Starship appears to be capable of pushing the entire Artemis upper stack onto the desired trajectory around the Moon. This would allow the Interim Second Stage to slow the flight 3.1 km/s to enter LEO. From there, the Orion capsule can safely return to Earth.

A benefit of this plan is that the Space Tug and the Artemis Interim Second Stage would remain in orbit for re-use or other purposes.

Update: GW created a pdf version of the above. I'll link it here shortly.

https://www.dropbox.com/scl/fi/201e8mv4 … 0bx48&dl=0

(th)

GW Johnson · 2024-12-03 16:48:43

The links work fine.

But if you read the article, you see that I did not do this study for using a tug with Artemis-2 in any way. NASA is going to fly that one with the bad heat shield, that much is clear.

Actually, since the Orion capsule is not reusable, I don't see much usefulness for trying to slow it into orbit coming back from the moon or anywhere else. It'll have a "fixed" heat shield from Artemis-3 onward, and the odds favor success flying with the bad one on Artemis-2, although the probability of a fatal burn-through is not as close to zero as it ought to be.

I did the study to find out what might be possible in the near term. For the orbital data I used, getting onto an interplanetary trajectory at 11.5 km/s requires 3.7 km/s dV from LEO at 7.8 km/s, unassisted. The tug could get it to 10.9 km/s and subsequently be recover itself from an ellipse apogeeing near the moon's orbit. The interplanetary craft dV from that tug assist point is only 0.6 km/s! Tug-assisted departure makes a big difference!

I think Starship might actually have its flap burn-through problem solved, and its heat shield pretty much determined, and also have demonstrated propellant transfer from 1 vehicle to another, in about a year, which is very near-term. That means a tug modification could be flying not that long afterward. And the mass capacity it could fling onto hyperbolic departure is astonishing: just short of 500 metric tons or thereabouts. Arrivals, not so much: nearer only 175 tons.

The real long pole in the tent is not modifying Starship or some other upper stage to be used as a space tug, it is having a good facility in LEO to assemble interplanetary payloads and then dock tugs to them, using remote-operated mechanical arms, plus a ready means and depot from which to refuel the tugs and fuel the interplanetary craft.

That won't happen on a 2-year timescale! If Gateway gets built at the moon, the assembly and propellant depot facility in LEO will never get built. There is not enough $ to do both.

But with a tug assisting departures and maybe arrivals, why would we need Gateway? THAT is the really telling question no one is asking.

GW

tahanson43206 · 2024-12-06 14:47:05

This post is reserved for a link to an article printed by the Waco newspaper, and published in their online edition.

GW Johnson wrote a long article about the leak in the Russian docking tunnel.

While the article brings the reader up to date on the problem and it's serious nature, unfortunately since International Relations are involved, there is not enough information available for the general public to have a sense of what might be done. GW has proposed an interesting solution, which would be to make an adapter that will fit onto existing US ports and allow Russian Progress vessels to dock.

That too, is something the incoming NASA Administrator might be able to consider.

The article: https://www.dropbox.com/scl/fi/25otv519 … cnqpa&dl=0

(th)

tahanson43206 · 2024-12-10 19:38:26

For GW Johnson...

It appears that kbd512 is irrevocably committed to the use of ion drive for his deep space transport.

Oldfart1939 arrived on the scene with what may be a workable solution.

Your design for the Space Tug on a free return orbit is preserved, if you are able to add a final boost using thermal nuclear propulsion.

What I'm thinking about here is a component that can provide the massive push to deliver the last 600-800 m/sec to the payload, and then slow itself so it drops back to an Earth return trajectory. This component would be independent of the Space Tug, but an add-on to put the customer on the desired trajectory while preserving the reusability of the Tug itself, as well as the nuclear thermal component.

Please evaluate this option.

(th)

kbd512 · 2024-12-10 23:07:33

GW,

Starship-3 is intended to carry 2,300t of propellant vs 1,200t, and will be equipped with 6X Raptor-3 Vac engines.

How much dead-head payload can I push with 2,300t of propellant?

Is it close to 952t?

Mass estimate for a CFRP hull variant of the my ITV design:
hull structure only CNM / 4X HRMs / PPM: 175t
life support systems: 50t
passengers: 50t
food: 162t (might be a bit high)
water: 95t
LLM (Mars lander / lifeboat): 75t (a reconfiguration of my SSTO concept)

That's 607t, but doesn't include power generation, engines, or fuel for mid-course corrections. I can get rid of a lot of mass if I don't have to power a VASIMR engine, but I add it all back and then some using chemicals. If I set my total payload mass to 650t, and provision the vehicle with 150t of NTO/MMH fuel with a 343s Isp, then I get 698.43s of Delta-V, which is enough to perform the mission. We could also use LOX/RP1, LOX/LCH4, LOX/LC3H8. Any of those combinations provide enough performance.

That said, the propellants will require 12.5 launches, which is $50,000 per person, assuming each launch actually costs $2M, which seems a little dubious at best. On top of that, another 2 launches are required to deliver the crew and consumables. That's a lot of launches.

tahanson43206 · 2024-12-11 07:11:30

For kbd512 re #471

It is encouraging to see the numbers you've put together for your transport. One number I don't see is the fee for the Space Tug. That will include the fuel for the service, plus amortized cost of the vehicle, plus operations costs such as salaries, and a profit for the funder.

I think a round number to consider for a comfortable, safe flight to Mars and return is $1,000,000 per passenger.

Can you make that work, if your passenger manifest is 500 and your crew is 50?

Or perhaps the 500 count is firm, so 450 passengers and 50 crew?

(th)

GW Johnson · 2024-12-11 22:58:45

A question or two: what is the tonnage that a tug needs to push from LEO into LLO (low lunar orbit), and still return to LEO unladen? Is it 900-some, or is it 600-some? Metric tons units of measure is what I am looking for.

Does all this need to go in one big chunk, or can it go in multiple smaller chunks? If it can go in multiple smaller chunks, what tonnages?

GW

tahanson43206 · 2024-12-12 10:10:44

For GW Johnson re #473

kbd512 appears to have invented a propulsion method based upon solar power that makes solar sailing look like a two person skiff compared to a deep ocean racer at full throttle.

I understand you are going to need time to try to catch up with his ideas, because they are coming out at a rapid pace.

It turns out I mis-read a number if kbd512's presentation, so the actual thrust is a bit lower than I thought.

The dV is modest.

The system ** does ** require use of a huge solar energy collection array, and all that solar energy has to be channeled into a very small volume to heat the hydrogen, but setting aside the engineering, I get the impression the physics might work.

(th)

tahanson43206 · 2024-12-12 20:31:34

This post is to provide a link to an article GW is working on for publication in the exRocketman blog early next year.

Comments from NewMars members are welcome.

https://www.dropbox.com/scl/fi/8ocyko8a … jpu5z&dl=0

The material will be familiar to regular NewMars readers.

It is organized for presentation to a general audience, so may be interesting to a few folks who might have missed the earlier work.

it appears that it is feasible to push large deep space vessels into a parking orbit around the Moon, from which they can depart under their own power without risk of falling back toward the Earth.

(th)

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