GW Johnson Postings and @Exrocketman1 YouTube videos

GW Johnson · 2024-02-13 12:54:22

I have a slide set and some presentation notes for the 40 tons-of-cargo 1-way lander thing. I have not made a video of me presenting it. I have a written paper/document under construction, and about half done.

The 1-way lander was easy. It's about 80 tons at entry, and about 52 tons at touchdown.

A 1-way expendable transfer stage LEO to Mars direct entry off the interplanetary trajectory was also easy. Depart LEO on LOX-LH2, then use storables for 2 course corrections, plus likely the ullage solution for igniting the LOX-LH2 to depart.

A 2-way reusable transfer stage was much harder; it must use LOX-LH2 instead of storables once out of LEO, and that's a severe evaporation/boiloff risk, with 3.3 years on space before it can be recovered. Both used LOX-LH2 to depart. I retained storables for course corrections and ullage both ways.

In other news, I have posted about the ramjet book being available, on both "exrocketman" and LinkedIn. I already had sold and delivered 2, before posting the availability. Now there are 3 more "on the line", with all 3 "very likely".

All set for the trip to the conference at North Carolina State in March. Airline tickets bought and hotel reserved.

Been contacted by an engineer at an aerospace defense firm in Turkey, regarding integral boosters for ramjets. Looks like some consulting there, possibly.

And still there are the cactus tool business and the work on marketing the semi-towed countermeasure flare.

It's getting a bit busy around here.

GW

tahanson43206 · 2024-02-19 10:30:08

For GW Johnson!

Please provide a value to plug into the reference added to this post:
http://newmars.com/forums/viewtopic.php … 35#p159935

I'm looking for the dV of the space craft relative to Mars when the space craft is on a Hohmann orbit, and Mars is coming up from behind.

You've published this numerous times in the forum and elsewhere, but I'm trying to start a collection of facts that will be easy for everyone to find.

The number is on the order of 3-5 km/s ...

Update 2024/02/22 --- Thank you for your reply, which includes both the velocity difference as Mars comes up behind the Hohmann orbit vehicle, but also the pull of Mars on the space craft, which adds significantly to the velocity of the space craft with respect to Marsl

Quote goes here:

GW Johnson wrote:

Average Mars orbital speed is 24.121 km/s about the sun. At average planetary distances, the apohelion velocity on a Hohmann trajectory is about 21.499 km/s. The difference is the "Vfar" approximation for speed relative to Mars that is part of what sidesteps doing the 3-body problem: 2.622 km/s.
Mars gravity will accelerate the craft toward Mars as the two converge. Based on conservation of mechanical energy, the Vnear approximation is the square root of the sum of the squares of the Vfar value and Mars escape speed at the altitude of interest. This would be just barely less than the surface escape speed of 5.0282 km/s. Call it 4.955 km/s at 100 km altitude. This results in a "Vnear" of 5.606 km/s with respect to Mars at 100 km altitude.
The answer you asked for is 5.606 km/s wrt Mars at 100 km. That's essentially an atmospheric entry at somewhat over Mars escape speed at that altitude, and in fact bigger than surface escape speed. This estimate ignores the actual start of entry decel/heating, which begins at 135 km altitude. But it's in the ballpark, nonetheless.
GW

(th)

tahanson43206 · 2024-02-22 07:56:28

For GW Johnson re adjustments for 40 Ton Delivery topic.

There appears to be interest in both one-and-done and reusable delivery options.

Rather than split the topic, I've decided to ask contributors to specify which design they are working on.

The type of landing pad and strut design will differ between the two use cases.

There is a third category of design that may prove useful. That is a one-and-done with salvage option.

In that scenario, the landing platform with heat shield at the base, a frame of some kind, and the payload square in the center, would remain, while the rocket components would be unbolted and move to a location where they can be assembled into a vehicle capable of flight to orbit.

In any case, please indicate the category into which a particular post will fall.

(th)

tahanson43206 · 2024-02-22 08:28:38

For GW Johnson re Cycloid Study ....

Bearing in mind that this study is an update of a 50 year old concept, and that the materials needed do not yet exist, I remain interested in seeing the numbers for this concept applied to the 40 Ton Delivery problem.

There is a small difference between my vision of the Cycloid Delivery mechanism, and your description of the long cable with the balanced mass prescription.

I agree with your description of a balanced mass design, and also agree that the concept of release of a mass of equal size at the other end of the long cable would balance the release of the desired mass at the surface of the planet.

However, I have a different concept in mind. What I am thinking about is a hub with one spoke design. In that case, the hub is going to need to apply thrust along the spoke, so the hub pulls away from Mars, to prevent the payload from crashing into the planet.

The request I am offering for your consideration in this post, is to design the thrust mechanism that the payload will need to achieve the downward momentum it needs to reach the surface in 30 seconds. The animation is designed to show the action in seconds, and the actual Real Universe delivery time is 28.57 seconds, taking 100 km as the altitude and 3500 m/s as the orbital velocity at that altitude.

The time required for a 1/4 turn from 135 km would be greater, but the time available if the space craft is travelling at 5600 m/s would be less. I'll try to compute the time required later today.

It just occurred to me that I could improve the animation to show thrust occurring at the two times of interest. I'll think about doing that!

Whatever the time of a 1/4 turn is, the payload will need to be given an impetus downward by a rocket system designed for the purpose.

I would expect the hardware for the acceleration of the payload to remain attached to the cable so it can be reused.

An additional benefit of the payload end acceleration package is that it can reverse the rotation after it returns to the payload start point.

This ability would be most applicable to the orbital delivery system, as compared to the fly-by-from-Earth version.

(th)

tahanson43206 · 2024-02-25 11:20:33

For all ... GW Johnson has prepared a study of aerobraking from high orbit ...

The study consists of two documents.

Description of document 1: This is a two page document with the title: "Elliptic Capture"

Link to document 1: https://www.dropbox.com/scl/fi/qp68607k … glm46&dl=0

Description of document 2: This is a 3 page document with the title "Elliptic Capture 2"

Link to document 2: https://www.dropbox.com/scl/fi/cc46vuwr … tfgiv&dl=0

Here is GW's email comment:

I sat down and did an explanation of how "elliptic capture" really works from an orbital mechanics point of view. It's not quite what a lot of people seem to think. It can be done with suitable propulsive burns, or by some mix of aerobraking and propulsive burns. But, there will ALWAYS be some burns that must be made. The only question is how much?
Capture occurs at the high-velocity periapsis point, not at the low-velocity apoapsis point! The extended elliptic capture orbit will always be hard to reach from the surface or from low circular orbit, simply because its periapsis speed will always be very nearly escape speed at that altitude. And there are not-too-costly ways to modify that capture orbit a little.
But, if you aerobrake instead of doing a burn, to capture, there is always a requirement for a significant heat shield! The entry peak heating pulse always precedes the entry peak deceleration pulse. If you get any significant drag deceleration, you WILL get significant heating! There is no way around that. Despite what some so fervently wish.
This aerobraking elliptic capture thing is an easy thing to carry out at Earth, because of its predictable entry-altitude densities vs altitude. The risk at Earth has nothing to do with orbital mechanics, it is hard radiation exposure from the Van Allen belts. Any sort of elliptic orbit, that is extended-enough to do you much good, is going to take you through the Van Allen belts, simple as that.
Aerobraking elliptic capture is really risky at Mars because of the large and rather unpredictable entry-altitude density variations. At Mars, one simply must be prepared to make a significant deceleration burn just after your aerobrake deceleration pass, in the event the aerobraking in unexpectedly-thin "air" was insufficient to capture. If you must be prepared for that, then just why not avoid the uncertainty and the associated risk, and just burn to capture into an orbit, all outside the atmosphere? THAT has certainty and very little risk.

(th)

tahanson43206 · 2024-02-26 11:44:51

This post is about the challenges of trying to land on the Moon:

The document that goes with the image is to be added here:
https://www.dropbox.com/scl/fi/yg6agjub … jaetm&dl=0

(th)

tahanson43206 · 2024-03-04 18:15:39

This post is reserved for links to two new and one older presentation that may be of interest to NewMars members and non-Member readers.

I'll be linking the files from Dropbox, and adding text about the files later.

Title: Text paper for Big Mars Payloads (40 Ton topic)
File 1 link here: https://www.dropbox.com/scl/fi/6gumknmg … s7ikf&dl=0

Title: Launch Conv Bells - I ** think ** this is about rocket engine design
File 2 link here: https://www.dropbox.com/scl/fi/qtixtl3g … 3gob1&dl=0

Title: Launch to Low Earth Orbit
File 3 link here: https://www.dropbox.com/scl/fi/ur5yjl5h … rsgk0&dl=0

Here is an email from GW about the files...

On 3/4/24 19:24, Gary Johnson wrote:
> The "landing big things on Mars" thing has to do with that initiative in the thread. I just documented what I did, and how.
>
> The other 2 address recurring things I see on the forums regarding how best to get stuff from the surface up to LEO. There's a lot of enthusiasm from some correspondents for doing single stage to orbit, and from some others for doing various "trick" engines and nozzles to overcome the high dV requirements vs the lower dV capabilities, of all known chemical rocket propulsion. There would seem to be a segregation of fixed-bell rocket notions into only "sea level" and "vacuum-optimized" designs.
>
> Such is not true, and there is really no such thing as a "vacuum-optimized" design. I have offered a compromise design approach that very nearly approaches what can be done, even ideally. I do debunk the free-expansion nozzle as a "vacuum-optimized" design, and have some comments to offer about doing variable geometries like extendible-bell.
>
> GW

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tahanson43206 · 2024-03-14 13:46:05

For GW Johnson!

Knowing you're preparing for the upcoming Carbon Society conference, you may not have time to look at Calliban's question.

https://newmars.com/forums/viewtopic.ph … 94#p220394

When you get back, that excellent question will be waiting for you.

(th)

tahanson43206 · 2024-03-15 07:36:08

And speaking of the American Carbon Society ...

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Best wishes to GW Johnson for a smooth flight and productive session(s).

(th)

tahanson43206 · 2024-03-19 12:13:33

The Americah Carbon Society conference is underway....

https://www.americancarbonsociety.org/

If all has gone well, GW Johnson is on site.

(th)

GW Johnson · 2024-03-20 11:02:39

I'm back from the conference.

The trip out was a nightmare: the plane was 2.5 hours late, no explanation. I got to bed at 3:30 AM instead of 1 AM, and had to get up at 6AM. We had a long walking tour that afternoon. I was passing-out tired when I got back to the hotel at sundown.

Second day was good. They liked my talk on using the old by-hand design analyses as a concept screening tool to down-select to 1 or 2 best ones that then receive real design and design analysis efforts. The example was about designing entry heat protection, with the old 1953-vintage H. Julian Allen warhead entry dynamics and heating analysis embodied in a spreadsheet for almost-instantaneous results.

It allows you to afford real brainstorming and up your odds of getting a good design. I showed them how to get from peak gees and peak heating rate to the heat shield material selection criteria of pressure and surface temperature limits. Those calculations are almost trivially-easy, once you have peak gees and peak heating. Being able to do this also enables knowing when you have a GIGO problem with your software codes, which is fundamentally why shuttle Challenger was lost (what they analyzed was NOT what they built, as far as cold O-ring seals are concerned). That point made a hit with the crowd, so I suspect they have seen a lot of GIGO troubles with their fancy computerized stuff.

The other two presentations were done as poster presentations: the ceramic heat shield and the ramjet combustor ablative testing I did. Those went over well, too. As did many anecdotes about how I did such work.

There were some high-powered academics and scientists there, but they enjoyed talking with me, and seemed genuinely glad I was there. I was older than anybody else in attendance, and they seemed to appreciate the fact that I actually made carbon soot and char out of heat protection materials "in real life".

Will be in-and-out for next few days: had to see doc about infected finger this morning (it's much better but not done yet), and tomorrow I go back for a "nuclear heart stress test" on the treadmill. Then it's IRS tax time.

GW

Last edited by GW Johnson (2024-03-20 11:08:23)

tahanson43206 · 2024-03-25 15:09:04

For GW Johnson .... just FYI .... I met a Mom today who may be interested in looking at your Traditional Course ...

She was kind enough to let me pitch your course as possibly of interest to the school where her 12 year old son attends. She indicated there is a math teacher who might be interested in the course, and apparently there is some ability in the student population.

I'll let you know if there is any news from this opportunity.

In the mean time, please give some thought to how you would present the course to the teacher, if we can set up a meeting via Google Meeting or Zoom.

NewMars can support either venue.

(th)

GW Johnson · 2024-03-26 09:02:56

I presume you are referring to the orbits+ course. Traditional 2-body orbital mechanics, done with algebra. Followed by other algebra to evaluate the rocket equation. The logarithm and exponential functions used there are algebra-2 topics. If I remember correctly, the two-variable quadratic equations for ellipses are taught in both high school geometry and in algebra-2.

It is rare to see these more advanced things taught in algebra-1 anymore, not with the over-emphasis on teaching only to the standardized tests. Only the derivations of these equations are calculus, and I did not put derivations in the course, only the "how-to" to make the calculations, and "where to get" the input numbers.

The way to start this is to give the interested person the text documents for each lesson, which are complete with example problems, some worked, others to be worked (but with answers supplied). Each lesson's document is a sort of mini-textbook giving everything needed. If somebody then wants to teach this stuff to others, that's what the slides are for, a slide set corresponding to the document, one for each lesson. Since all this stuff is posted, they only need to know where to go, to obtain it all.

GW

tahanson43206 · 2024-03-27 10:48:42

For GW Johnson re Orbit Basics course ...

Thanks for thinking about how this material might be adapted for a 12 year old perspective.

For all ... please think about how you (or someone you know) might approach this interesting challenge.

If you wanted a work force of 1000 well trained space craft navigators in 10 years, you might start with 12 year olds and carry them through college, graduating with a Bachelor of Science / Engineering degree, and ready to go to work or on to advanced studies or both for some.

If you were planning to harvest asteroids such as Apophis, you'd want to have a work force that large to bring your chunks of asteroid material back to Earth vicinity for processing.

(th)

RGClark · 2024-03-30 07:10:40

GW Johnson wrote:

…
THAT is what it all boils down to: getting to the surface! Because THAT SURFACE is where the resources are, and THAT is where propellant and life support supplies will be manufactured! And that surface is where people have dreamed of going for some centuries now. Better to just belly up to the bar and simply do it right!
GW

Are you saying you can land a 150ton crew module on Mars? That would be about the size of the SpaceX Starship with provisions. What would be the size of the parachutes? What would be the speed needed to be cancelled out by propulsion? How much propellant would that take?

Bob Clark

tahanson43206 · 2024-03-30 08:14:13

For RGClark re #265

Haven't you read ** anything ** that GW has posted over the past several years?

He has published a series of videos on exRocketman1 at YouTube.

He has published multiple presentations hee in the forum, and at other sites.

The nature of your question implies to me you've read NONE of that material.

Had you read the parts about landing on Mars you would have known that parachutes are useless and not worth considering for anything more than the small probes landed so far.

(th)

GW Johnson · 2024-03-30 10:55:53

One can land anything of any size on Mars. The real question is only how much trouble will you have to go to, in order to do it.

Atmospheric entry is a question of hypersonic ballistic coefficient, speed at entry interface (about 135 km altitude on Mars), and the angle of entry trajectory below local horizontal at entry interface (which MUST be low, around 2 degrees). Speed is set by what you are doing (coming from low orbit, coming from high orbit, coming from Hohmann transfer, coming from a fast trajectory to Mars). It varies between about 3.6 km/s from low orbit to about 7.4 or 7.5 km/s coming from a fast trajectory to Mars.

Ballistic coefficient is mass at entry divided by product of the frontal blockage area, and the hypersonic drag coefficient that is based on that same area. Drag coefficient varies with shape, but only some. About the lowest would be 1.1 or 1.2 for a sphere or a dead-broadside cylinder. Most of the old space capsules were near 1.5, and the Mars probe heat shield shapes, nearly conical but blunted, were about 1.7. You want higher, so the ballistic coefficient is lower, and you decelerate a bit higher up.

Mass is proportional to volume, and the packing density for stuff is pretty invariant with size. That means mass is proportional to dimension cubed, all else equal. Blockage area is proportional to dimension squared, all else equal. That makes ballistic coefficient proportional to dimension cubed divided by dimension squared, or just proportional to dimension. Double the size, double the ballistic coefficient! But if you double the size, you make the mass 8 times larger! Looked at the other way, ballistic coefficient is then proportional to the cube root of mass, all else equal.

Ballistic coefficient is quite important at Mars, de to the thin air, which is quite distinct from our experiences entering here at Earth. At Earth, ballistic coefficient has little effect on the altitude at which the hypersonics end, because the densities that correspond to its variation are all located around 40-50 km up. Those same densities at Mars are at or very near the surface.

Our experiences landing things on Mars are associated with things massing a ton or less, with ballistic coefficients of 100 kg/sq.m or less. Most of these came out of hypersonics at or above 25 km above Mars's surface at local Mach 3. It takes a few seconds to slow to Mach 2.5, the max opening speed for a ringsail chute (the fastest available), then several seconds more to have the chute decelerate you subsonic, and "subsonic" on Mars is quite close to the speed of sound! You still have to decelerate from almost sonic, at about 240 m/s, to something survivable (around 1-2 m/s). And that's some combination of rocket retro-propulsion and shock-absorbing things like airbags. But rockets are ALWAYS involved!

The biggest things we ever landed are the two nuclear rovers, weighing in about 1 metric ton at entry, and ballistic coefficient right at 100 kg.sq.m. These came out of hypersonics closer to 20 km altitude than above-25 like the others. That required the Rube Golberg "skycrane" rocket braking systems to get the job done fast enough, AND not overload the launch vehicle payload capability for the trip from Earth. So it's complicated. That's from a tad faster than Hohmann, as direct entry, at about 5.5 km/s at entry interface.

If you come out lower than about 20 km at about 0.7 km/s (Mach 3 speed on Mars), there's only about 40 sec to impact on a 45-degree slant path. There is simply not time to deploy a chute (which won't survive opening at Mach 3), much less have it slow you by any appreciable amount, before you strike. If you have a ballistic coefficient over 100 kg/sq.m, you WILL come out lower than 20 km. That's just entry physics. Use my entry spreadsheet. You can run the trades for yourself. The velocity to be killed is 0.7 km/s, factored up by 1.5 to 2 to cover losses, and hover-and-divert budgets to avoid obstacles or hazards on the surface.

What that says is that above about the 1 ton mass of the nuclear rovers as entry vehicles, there's no point to attempting chutes. The obvious choice is rocket braking. Although SpaceX wants to attempt a supersonic lifting pull-up to reduce the speed that must be killed. The basic dV = 1.1-1.4 km/s, unless you can find some other way to slow down.

SpaceX's landing simulations show end of hypersonic at about 5 km and 0.7 km/s, pulling up in a lifting turn that decelerates to transonic at about 0.24 km/s at about 10 km, from which they have to kill about 0.24*(1.5-to-2) = 0.36-to-0.48 km/s speed with rocket braking.

Actually, I really doubt that Starship can generate enough lift to make that lifting pull-up possible. They will have to light the engines at end-of hypersonics, and use thrust to augment the lift, in order to make that decelerating pull-up. I think their rocket dV requirement will end up being higher than they thought. Closer to my estimate of 1.1 km/s min for direct rocket braking.

The pull-up does let you lower the thrust requirement, though. It's quite a bit higher for direct rocket braking right down the slant path.

As for 150 tons vs 1 ton, a gross estimate would be (100 kg/sq.m)*cube root of (150 ton/1 ton) = 531 kg/sq.m. That'll come out of hypersonics somewhere down near 5 km at 0.7 km/s, just like Starship. On the slant, you have about 7 km path length, to cover at the average of 0.7 km/s and 0 km/s, for about 20 sec to decelerated touchdown. That's an average deceleration of 700 m/s in 20 sec, or 35 m/s2. Or a tad over 3.5 gees! It's doable! But a rough ride, especially for people exposed to microgravity for multiple months getting there.

GW

Last edited by GW Johnson (2024-03-30 11:19:32)

RGClark · 2024-03-30 11:46:42

GW Johnson wrote:

…
As for 150 tons vs 1 ton, a gross estimate would be (100 kg/sq.m)*cube root of (150 ton/1 ton) = 531 kg/sq.m. That'll come out of hypersonics somewhere down near 5 km at 0.7 km/s, just like Starship. On the slant, you have about 7 km path length, to cover at the average of 0.7 km/s and 0 km/s, for about 20 sec to decelerated touchdown. That's an average deceleration of 700 m/s in 20 sec, or 35 m/s2. Or a tad over 3.5 gees! It's doable! But a rough ride, especially for people exposed to microgravity for multiple months getting there.
GW

So perhaps about 0.7km/s that needs to be cancelled out by rockets for a 150 ton lander. Even if the higher estimate of 1.1 km/s is needed, that’s not particularly difficult. I wonder why NASA considered landing large, crewed habitats on Mars such a daunting problem:

The Mars Landing Approach: Getting Large Payloads to the Surface of the Red Planet.
POSTED ON JULY 17, 2007 BY NANCY ATKINSON
Some proponents of human missions to Mars say we have the technology today to send people to the Red Planet. But do we? Rob Manning of the Jet Propulsion Laboratory discusses the intricacies of entry, descent and landing and what needs to be done to make humans on Mars a reality.

There’s no comfort in the statistics for missions to Mars. To date over 60% of the missions have failed. The scientists and engineers of these undertakings use phrases like “Six Minutes of Terror,” and “The Great Galactic Ghoul” to illustrate their experiences, evidence of the anxiety that’s evoked by sending a robotic spacecraft to Mars — even among those who have devoted their careers to the task. But mention sending a human mission to land on the Red Planet, with payloads several factors larger than an unmanned spacecraft and the trepidation among that same group grows even larger. Why?

Nobody knows how to do it.
https://www.universetoday.com/7024/the- … ed-planet/

Bob Clark

Last edited by RGClark (2024-03-30 11:48:14)

tahanson43206 · 2024-03-30 12:35:47

This post is intended to hold links to new files (including updated ones) created by GW Johnson in support of the Basic Ellipses course and various presentations.

The test that came with the files will be posted first, and the links to files will be added later:

I have upgraded the rocket performance spreadsheet used in the orbits+ course with (1) an altitude performance plotting capability, and (2) an easy and organized way to quickly report results. This probably ought to be posted where forums users can access it. There's actually 3 files, which ought to go in a folder together somehow. There's the Excel spreadsheet file "liquid rockets.xls", the user's manual file "user man.pdf", and the "engine sizing report.png" file that I made in Windows "Paintbrush". That last is where you directly paste an organized output block copied from the "r noz alt" worksheet, alongside a sketch of a rocket engine that makes clear the meaning of all the symbols. The user's manual is quite extensive and complete.

Here is the first file of three in this set. This is a spreadsheet:
https://www.dropbox.com/scl/fi/mcmgvky9 … iqvjk&dl=0

Here is a user manual for the liquid rockets spreadsheet:
https://www.dropbox.com/scl/fi/z01cwbeq … hpi33&dl=0

Here is an image that works with the spreadsheet:
https://www.dropbox.com/scl/fi/9scws7nh … wb7fi&dl=0

I will send you the entry dynamics and heating spreadsheet, and its user manual, separately. These could be posted for forums users to access and use, probably in a folder containing both items. I thought I had already sent that in the orbits+ course materials, but maybe not the user manual. Anyhow, a separate entry for users to find is probably better.

There are two files in this set. Here is a user manual for the entry spreadsheet:
https://www.dropbox.com/scl/fi/byivlgaw … j2gr4&dl=0

Here is the entry spreadsheet which covers heating:
https://www.dropbox.com/scl/fi/54iz1gut … uhlas&dl=0

(th)

tahanson43206 · 2024-03-30 13:10:52

I am open to suggestions on how best to offer the new files, and all the previous files and videos, to the public, as well as to NewMars members.

The forum software does not currently provide support for easy location of items of special interest.

kbd512 is in the process of updating our ancient FluxBB 1.5.11 software to run with modern PHP and MySQL. Hopefully that work will be ready for testing in a test facility in a few weeks. Once the updated software is thoroughly tested by SpaceNut and those NewMars members who wish to take part in testing, we will be able to ask Mars Society to install the software on the Dreamhost server.

When the dust settles after ** that ** major step, we will be able to consider changes to improve the software environment.

(th)

tahanson43206 · 2024-04-01 10:35:50

In the pdf at the link below, GW Johnson provides history on:

a) The standard size of railroad tracks in Europe and thus the USA...

b) The size of the V2 rocket

c) Details about why the Shuttle solid rockets were shipped by train in the US

https://www.dropbox.com/scl/fi/br3ymm93 … rdpgs&dl=0

(th)

tahanson43206 · 2024-04-02 12:14:07

For GW Johnson...

Your recent post in the Starship/Go topic seems (to me at least) to suggest a possibility to profit from the energy flowing around the recent test flight.

Is it possible to reverse-engineer the plan for the test orbit, using the tools you have developed and offered for free to anyone in NewMars (or anywhere for that matter)?

Taking the advertised launch mass, with fully loaded first and second stages, and the published flight path, is it possible to compute the parameters the engineers must have programmed to achieve their stated flight objectives?

GW Johnson wrote:

Two comments:
1. It did reach orbit. It just was an elliptical orbit that intersected the atmosphere or the surface near its perigee end. That's not what most people consider to be an "orbit", yet it is one. Every suborbital ICBM or probe rocket follows a similar path, just with (usually) a higher apogee. The theoretical perigee can be way inside the planet mathematically. The 2-D Cartesian small-scale approximation to this is the parabolic ballistic path, an inappropriate approximation at large scale (comparable to planet radius). But the real situation is 3-D spherical, and any path at max (perigee) speeds under escape is always elliptical mathematically.
GW

(th)

GW Johnson · 2024-04-03 08:44:54

The answer to the question is "yes". It takes iteration using the elliptic orbits spreadsheet from the course, and the apoapsis/periapsis two-endpoints worksheet.

Somebody quoted a an apogee altitude. I do not remember the number, but I do remember somebody said one. You put that in, plus a guess for the perigee altitude near the surface (could be above, or even below, the surface). Go with R-equatorial for a fairly low inclination orbit.

From the video, at about engine cutoff, there will be a listed speed and altitude. Vary the input perigee until you see a speed match at that altitude. There is an input for determining speeds at some desired input desired altitude, so put that desired altitude at engine cutoff in there. Vary the input perigee until you see a speed match at that engine cutoff altitude. The apogee speed should match, too. Adjust perigee altitude for the closest match of both speeds.

Can't really just use the R-V-q worksheet for a one-observation determination because we generally do not have a value for the angle q between R and V, except at apogee, where it is 90 degrees. The speed and altitude data as reported in the video may not be accurate enough to support a accurate orbit determination from just that one point. The two-point iteration solution in the other worksheet is a better solution that is more tolerant of data inaccuracies as read from their video. Which I presume to be considerably inaccurate, and probably significantly time-delayed.

GW

Last edited by GW Johnson (2024-04-03 08:52:19)

tahanson43206 · 2024-04-03 10:38:43

For GW Johnson re railroad technology....

As a follow up to your recent post about the history and technology of railroads, I stopped to look at a railroad car wheel assembly that is preserved as a memorial to the iron works that the father of US President George Bush (Senior) built in the city where I live. The factory itself is long gone, but the rail car wheel assembly is preserved nearby.

Your prediction was that I would find a slant when I looked at the rim of the wheels, and what I found was different.

The outer half of the rim is perfectly flat. That width looked (to my eye) to be close to what a standard US rail would look like. What is interesting to me, in light of your prediction, is that the inside half of the rim curved gently and then increasingly toward vertical, where the flange is found.

I was limited in time during that first visit, but I could return to take a photograph if there is any interest.

It would probably be possible to find an engineering drawing showing the cross section of that wheel, because I would imagine it is identical to millions running on US railroads today, and to ones still being manufactured.

In the context of Mars, I'd like to remind NewMars readers that GW's history shows that there is no physics or engineering reason to keep the gauge of track in common use on Earth, when setting up shop on Mars.

(th)

GW Johnson · 2024-04-03 12:14:15

My old 1987-vintage edition of Marks' Mechanical Engineer's Handbook has a huge section on railroad technology. One of the wheel designs I found shows a tapered inner rolling surface portion, then a flat middle rolling surface portion, then a radiused outer rolling surface portion transitioning into the flange. It's fairly common design, according to the article in that handbook. It also sounds an awful lot like what you are describing.

That same handbook article shows the AAR Plate B clearance limits diagram for rolling stock. Longer cars have tighter width limits, but that diagram goes with 53 feet long, unless I missed something. Most cars are that length or shorter.

GW

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