GW Johnson Postings and @Exrocketman1 YouTube videos

tahanson43206 · 2024-07-29 01:18:20

As a follow up, I gave the suggestions from Gemini to ChatGPT4o, and it came back with a detailed set of specifications to create a complete web site to support the basic orbital mechanics course GW Johnson is offering via our forum.

I have saved the suggestions from ChatGPT4o, and expect to have time to work on them in August.

According to Gemini, there are ** no ** sites on record that implement the vision of animation of GW Johnson's work.

It would appear this would be a worthwhile undertaking.

(th)

GW Johnson · 2024-07-29 08:45:34

Responding to the question about the definition of "impulsive". It is a "fuzzy" thing. But here is what I recommend.

"Impulsive" burns need to approximate instantaneous velocity changes, in the sense that (1) the radius from central body center does not change during the burn by more than something like 1 part in a thousand, and/or (2) the burn time is under about 5 parts in a hundred the duration of the orbital period. As a rule-of-thumb for lower Earth orbits, the vehicle should accelerate faster than 0.1 or 0.2 gees, preferably nearer 0.5 gees.

The first criterion prevents the added energy from partitioning into potential energy instead of kinetic energy, which is gravity loss. The second criterion is more of a practical thing. An "impulsive" burn at perigee or apogee of an orbit with a period near 90 minutes needs to occur within a single handful of minutes, to stay "near" that perigee or apogee.

GW

GW Johnson · 2024-07-29 09:08:30

Not sure where to put these. From AIAA’s “Daily Launch” for Monday 7-29-2024:

Debris survives reentry:
AVIATION WEEK NETWORK
SpaceX To Shift Dragon Splashdowns To West Coast

In an effort to stem the chance that debris from discarded Dragon capsule trunk sections could reenter over populated areas, SpaceX will shift splashdown and recovery operations to the West Coast, the company said July 26. The decision follows the recovery of a piece of Dragon debris in Australia in 2022, indicating that—contrary to computer modeling—parts of the capsule’s discarded trunk can survive reentry heating.

My take on it: I have pointed out for years now that virtually nothing actually "burns up" on re-entry. Debris WILL make it through and crash to the surface, somewhere. Even from very insubstantial construction. Example: the Australians said they picked up about 75 tons of debris from Skylab that crashed in 1979 upon western Australia. Skylab was said by NASA to be about 85-90 tons at its entry. Not much at all burned up! Despite its shell being an aluminum S-IV Saturn stage.
-------
The end of Atlas-5:
SPACENEWS
ULA prepares for final military launch of Atlas 5 rocket

United Launch Alliance (ULA) is set to launch its final Atlas 5 rocket for the U.S. military on July 30. The classified payload, designated USSF-51, is scheduled to lift off at 6:45 a.m. Eastern from Space Launch Complex 41 at Cape Canaveral Space Force Station, bound for geostationary Earth orbit.

GW

tahanson43206 · 2024-07-29 11:31:36

For GW Johnson re #352

Thanks for details about planning for "impulsive" burns at perigee or apogee...

From the sounds of things, ChatGPT4o's default of 60 seconds is reasonable.

Thanks too, for mention of the G force produced by the burn. I had not thought that far ahead, so appreciate the reminder.

I'm looking forward to seeing if the tips provided by ChatGPT4o for a web based animation of your course material is something I can pull off.

What I am imagining is an interaction where the student can set up each burn at perigee or apogee, click "go" and watch the simulated spacecraft complete the next orbit. I'm hoping we can persuade the software to show the equations and the numbers as they drive the animation.

(th)

tahanson43206 · 2024-08-01 18:42:13

This post is for Void and anyone else in our membership who might be willing to tackle Rocket Science if the pathway is made simple enough. GW Johnson heard my comparison of his existing work to like an F16, when his audience is just barely able to fly a Cessna 150.

In the PDF at the link below, GW has attempted to prepare the reader to use the Basic Orbits spreadsheet, by introducing individual cells, and describing procedures to follow to obtain interesting and useful results.

Void, GW is continuing to praise your creative idea of building landing ring/cushions to fit around the Starship to achieve a successful vertical landing on an unprepared surface. This idea may be patentable, but at $1000 to request a preliminary reservation to request a patent, and $5,000 for the most basic of patents, it is unlikely you or I will attempt it. However, GW has already placed multiple patents on record. One was his alone, and the rest were team efforts.

I would like to invite you to at least look at this peace offering from GW, to see if you might be able to build up a head of steam to tackle it. If you ** are ** willing to tackle it, I would be a willing classmate, and potentially we might enlist one more member. Who that might be I have no idea, but certainly with 1000 members of record the potential that one would like to participate is non-zero.

SpaceNut... please keep upgrading all those innocent "banned" members to InActive status as rapidly as you have time. Every "banned" member who is not upgraded is lost to us. Who would make the effort to contact this forum, if the member finds he or she has been banned? They have no way of knowing the "banning" was an emergency measure to defeat hackers.

https://www.dropbox.com/scl/fi/icrjpdez … mx4yd&dl=0

Above is a link to: User Manual for Orbit Basics Excel Spreadsheet.

For GW ... please find a link to the spreadsheet and send it via email or by a post in this topic, so I can add it to this post.

The version of the orbits spreadsheet that the manual was written for is located at the link below, which was copied from post #20 in the "orbital mechanics class traditional" thread under "interplanetary transportation", in the Acheron labs" section. -- GW
https://www.dropbox.com/scl/fi/cxtpsx2n … nmkmv&dl=0
PS - I tested the link, it works.

The next step is for one or more members of NewMars forum to follow the links and begin study of the material.

In case there is someone not currently enrolled as a member, if you would like to take part in this initiative, please see the Recruiting topic for procedure.

(th)

GW Johnson · 2024-08-02 07:59:58

The version of the orbits spreadsheet that the manual was written for is located at the link below, which was copied from post #20 in the "orbital mechanics class traditional" thread under "interplanetary transportation", in the Acheron labs" section. -- GW

https://www.dropbox.com/scl/fi/cxtpsx2n … nmkmv&dl=0

PS - I tested the link, it works.

Last edited by GW Johnson (2024-08-02 08:01:17)

tahanson43206 · 2024-08-03 07:57:17

For GW Johnson re Void's Invention of Doughnut lander cargo concept...

In correspondence and here in the forum, you have indicated Void's idea would appear to be worth serious consideration for a lunar landing of a tall thin spaceship such as Starship. The design of a doughnut shaped cargo carrier to be fitted to a Starship after it reaches Earth Orbit would include a means of attaching the carrier firmly to the Starship, so that it will remain in place during burns, and more importantly, will be able to sustain the forces that would be imposed upon it by the Starship if the regolith was uneven at a landing site.

***
In a separate correspondence, or perhaps in a post, you indicated that at first glance, you did not think Void's idea would be as useful on Mars. I would like to offer an alternative way of looking at Void's idea for Mars...

The doughnut shape might lend itself to a useful function as part of aerobraking maneuver, since the cross sectional area of the combined ship and doughnut would be much greater than that of the Starship alone.

In saying that, I recognize your many times repeated caution that the atmosphere of Mars is so slim the accuracy of navigation to achieve aerobraking without missing the planet entirely, or plowing into the surface is ** very ** difficult to achieve.

However, Void's idea has one ** very ** significant benefit for Mars...

If we go with your recommended landing method of direct retro-propulsion, then moving cargo out of the Starship (or other vehicle such as your design) and into the cargo doughnut means the rocket can be loaded with more propellant, and that propellant can assist with landing and provide for return to orbit.

(th)

GW Johnson · 2024-08-03 09:32:03

Aside from the large deceleration forces that lead to large forces in the members connecting the doughnut to the main vehicle, there is a serious and very-fatal shock impingement heating risk. The doughnut, and the members that secure it, plus the main vehicle, all shed bow shock waves during hypersonic entry. Doesn't matter which way the thing faces. If any of those shock waves impinge upon any adjacent structure, that adjacent structure overheats to destruction in a matter of a single handful of seconds, max.

This effect has been known since the Mach 6.7 flight of the X-15A-2 back about 1968. It is EXACTLY why no successful entry vehicle has EVER had parallel-mounted nacelles of any kind. It is EXACTLY why no hypersonic aircraft will ever resemble the layout of the SR-71. And id it EXACTLY why the Skylon airframe concept cannot survive entry without massive changes.

The doughnut concept makes a whole lot more sense for the airless moon, not very much for Mars, whose thin atmosphere is enough to cause severe hypersonic heating at orbital entry speeds.

GW

tahanson43206 · 2024-08-03 10:05:21

for GW Johnson re #358

Thanks for helping us take a step forward to visualize Void's doughnut shaped cargo carrier.

As I read your text, you are thinking about the doughnut mounted on the exterior of the rocket hull without a shield of any kind.

That is exactly appropriate for a Lunar or other airless body landing. The rigging in that case has to be strong enough to hold up against force exerted by the hull if the regolith is uneven or sloping at the landing site.

I am not talking about the Lunar configuration. The doughnut and the rocket body would be safely protected behind an ablative shield of the required size.

Is there any limit to the size of a saucer shaped ablative shield?

If not, then the Mars lander you have already designed can be equipped with a doughnut cargo carrier, and you will have instantly solved the elevator problem that our friends in Germany were worried about.

After aerobraking, the center of the heat shield would eject, exposing the rocket engines, and they would complete the vertical landing.

After landing, the entire doughnut assembly would disconnect from the delivery rocket, and it could return to orbit, with fuel in the tanks due to placing cargo outside.

If Void were willing to do some of his artwork for us, he could show the saucer shaped heat shield first in descent, followed by the rocket body enclosed in the cargo doughnut.

This image might be helpful for those who are attempting to follow the discussion.

(th)

GW Johnson · 2024-08-03 16:29:59

Standing the vehicle and doughnut upon a heat shield might work, given some sort of insulation and high-temperature skin for the doughnut and vehicle. That is a heavy solution, though. More so at Earth than at Mars. The worst case entry speed at Mars is about 7.5 km/s, pretty close to orbital entry speed (8 km/s) here at Earth. You are talking exposure of doughnut and vehicle to gas near 7500-8000 K in such circumstances, but without the harsh scrubbing effects. Mercury and Gemini did that as bare metal afterbodies, but with serious insulation between those exposed afterbody skins and the pressure shell of the cabin.

GW

tahanson43206 · 2024-08-03 17:25:22

For GW Johnson re #360

Thanks for considering the saucer shaped heat shield idea.

The heat shield would take the brunt of the heating, so I assume ??? your concern is that hot gases would swirl behind the heat shield and into the low pressure region where the cargo and ship are hiding.

This problem has been successfully addressed for many decades.

It is possible (indeed likely) I just don't understand something important.

Perhaps the technique that has protected capsules returning to Earth from orbit or from the Moon only works at small scale?

Or perhaps the concern might be the length of the rocket, which might well extend into the wake of the oncoming atmosphere, after it exits the heat shield?

In any case, this is an interesting discussion and I hope it may be useful for Mars mission planners.

(th)

GW Johnson · 2024-08-04 09:47:59

What happens on leeside separated-flow surfaces has the same driving temperature as the heat shield out front, but a far lower heat transfer coefficient, because the weakly moving fluid does not scrub the surface. Scrubbing raises heat transfer coefficients, quite dramatically. By around a factor of 10 between separated wakes and heat shield front sides in terms of heating rates. Heating rate is the area times the heat transfer coefficient times the driving temperature difference.

That wake zone heating rate reduction makes the wake-zone heating rate more nearly the same as the heat re-radiation rate of "dark" surfaces at practical temperatures near 1000-2000 F. That is true for Earth entry up to about 8 km/s, but no faster: the gas temperatures get too high, in turn driving up heating by convection rates, and re-radiation cannot keep up at the surface temperatures that known materials can withstand. The re-radiation is proportional to absolute surface material temperature raised to the 4th power!

That balance of effects is why the old Mercury and Gemini capsules had ablative heat shields, but bare metal backside surfaces. They never exceeded about 8 km/s at entry, and re-radiation could keep pace with the convective input, albeit only for rather exotic alloys. You can do it with stainless steel these days, at least in large sizes. However, there must be some sort of high temperature-capable insulation between that hot leeside skin and the capsule pressure shell within. The hot skin re-radiates both directions, if there is not. You cannot do this with fiberglass, it melts at 900 F. Has to be mineral wool capable of withstanding 1500-2000 F.

Apollo came back from LEO at the same 8 km/s speeds, but from the moon much faster (about 10.9 km/s). With convective heating proportional to velocity cubed, and plasma radiation (from about 9 km/s on up) even a higher power, the total heating is way more than factor 2.5+ greater. Apollo had the ablative heat shield, but it had the same ablative as a thinner layer all over its backside surfaces, too.

In addition to the higher driving temperatures far-outracing the re-radiation effect, the more brightly-glowing plasma sheath is becoming pretty much opaque to thermal re-radiation, cutting off that method of cooling entirely by about 11 km/s speeds.

You can estimate (crudely) the gas driving temperatures for convection, anywhere around the capsule including backside separated wake zones, quite simply. The effective gas temperature in degrees K is numerically equal to the flight speed in m/s. That's about a 10%-good estimate. Actual values are higher or lower by up to 10%, because of varying ionization-level effects. Yet, at 8 km/s = 8000 m/s bringing about 8000 K gas temperatures, who really cares about 10% error? The real point is, it's overwhelming. At 11 km/s, it's pretty near 11,000 K, etc.

There are no materials that can stand such exposures steady-state. Only on a short transient, and only if cooled somehow, by re-radiation and/or ablation. Above about 9-10 km/s, only by ablation. Theoretically, transpiration cooling might also work, but it has never been flown, and so is unproven as of yet.

GW

Last edited by GW Johnson (2024-08-04 09:53:33)

tahanson43206 · 2024-08-04 11:26:37

For GW Johnson re #362

http://newmars.com/forums/viewtopic.php … 51#p225551

SearchTerm:HeatShield Heat Shield operation at various temperatures

In particular, this post includes explanation of the use of ablative material on the back side of the Apollo Moon Return vehicle to deal with hot gases flowing from the front of the capsule, around the rim, and into the region behind the vehicle.

For GW:

Picking up on your explanation of how the Apollo capsules were designed to survive Moon return, was the Orion capsule designed in the same or a similar way?

And ... is it safe to assume that if SpaceX attempts to return from the Moon directly, it must have ablative material around the entire vehicle?

And ... is it safe to assume that if ** anyone ** tries to return from Mars depending upon aerobraking, they will be subject to the same principles, except to a more extreme degree?

(th)

GW Johnson · 2024-08-04 14:08:12

To answer your questions ---

Picking up on your explanation of how the Apollo capsules were designed to survive Moon return, was the Orion capsule designed in the same or a similar way? YES

And ... is it safe to assume that if SpaceX attempts to return from the Moon directly, it must have ablative material around the entire vehicle? YES

And ... is it safe to assume that if ** anyone ** tries to return from Mars depending upon aerobraking, they will be subject to the same principles, except to a more extreme degree? YES

GW

tahanson43206 · 2024-08-04 19:30:33

For GW Johnson re #364

Thank you for those definitive answers!

***
kbd512 came up with a name I'd like to pass along: Xyla Foxlin
American engineer and entrepreneur

Please Google that lady. She graduated from Case Western. She has nearly half a million followers.

kbd512 thinks the kind of person we are looking for would be about 1 in 10,000.

With a population of 8 billion, that would be 800,000 potential persons with the needed set of abilities and interests.

However, that number would include all ages and all nations.

The number of candidates in the US who are below 20 would be some small fraction of that larger number.

(th)

GW Johnson · 2024-08-05 15:48:53

I looked at the gal Kbd512 came up with. Impressive for one so young.

GW

New Mars Forums

Announcement

#351 2024-07-29 01:18:20

Re: GW Johnson Postings and @Exrocketman1 YouTube videos

#352 2024-07-29 08:45:34

Re: GW Johnson Postings and @Exrocketman1 YouTube videos

#353 2024-07-29 09:08:30

Re: GW Johnson Postings and @Exrocketman1 YouTube videos

#354 2024-07-29 11:31:36

Re: GW Johnson Postings and @Exrocketman1 YouTube videos

#355 2024-08-01 18:42:13

Re: GW Johnson Postings and @Exrocketman1 YouTube videos

#356 2024-08-02 07:59:58

Re: GW Johnson Postings and @Exrocketman1 YouTube videos

#357 2024-08-03 07:57:17

Re: GW Johnson Postings and @Exrocketman1 YouTube videos

#358 2024-08-03 09:32:03

Re: GW Johnson Postings and @Exrocketman1 YouTube videos

#359 2024-08-03 10:05:21

Re: GW Johnson Postings and @Exrocketman1 YouTube videos

#360 2024-08-03 16:29:59

Re: GW Johnson Postings and @Exrocketman1 YouTube videos

#361 2024-08-03 17:25:22

Re: GW Johnson Postings and @Exrocketman1 YouTube videos

#362 2024-08-04 09:47:59

Re: GW Johnson Postings and @Exrocketman1 YouTube videos

#363 2024-08-04 11:26:37

Re: GW Johnson Postings and @Exrocketman1 YouTube videos

#364 2024-08-04 14:08:12

Re: GW Johnson Postings and @Exrocketman1 YouTube videos

#365 2024-08-04 19:30:33

Re: GW Johnson Postings and @Exrocketman1 YouTube videos

#366 2024-08-05 15:48:53

Re: GW Johnson Postings and @Exrocketman1 YouTube videos

Board footer