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#326 2024-07-02 18:48:49

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 18,189

Re: GW Johnson Postings and @Exrocketman1 YouTube videos

For GW Johnson...

RGClark just opened a new topic about an Italian company that is (apparently) planning to use a rocket fuel that produces a greater ISP than any rocket created by humans to this point.

My recollection is that among your many publications is one that shows that an ISP greater that 450 can produce desirable results.

If you have a moment or two, please add a post to  RGClark's new topic.

Please don't say that the new rocket is not possible with known technology, because clearly the company will be using technology that is new and far beyond anything achieved in the past several thousand years.

Instead, please show what the ISP of the new rocket fuel must be to achieve the desired result.

I assume the ISP must be greater than 450, but perhaps no more than 650?

(th)

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#327 2024-07-03 15:10:32

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 5,620
Website

Re: GW Johnson Postings and @Exrocketman1 YouTube videos

Tom:

I found the link in the SSTO section,  and followed it to something posted on X that said and showed NOTHING,  which in turn led to a posted article elsewhere,  about European space.  Specifically,  a new start-up in Italy.

In that article there was not one single word or number about the Isp they achieved,  only a burn time of 11 sec!  There were words about a stage length of 4.2 m long,  and a payload of 13 kg.  And that is all there was!  They have not yet flown at all. There was absolutely nothing (!!!) in the article about what their propellant might be.

What I showed with my bounding calculations was that anything over about 450 s could indeed be an expendable (only!!!) SSTO at a competitive payload fraction,  at an inert mass fraction in the 4-5% range.  There is not now,  and never will be,  anything reusable from orbit in that inert mass fraction range!  You need a heat shield and more structural beef to bring it back from orbital speeds. Those are heavy!  End of issue!

I used inert fractions in the 10-15% range (should probably be nearer 20%),  and showed you must have well over 600-700 sec Isp to do the orbit and return in a single stage,  even at 0% payload fraction!  Which is entirely unattractive from a business earnings standpoint!

I'm pretty sure those results of mine are correct,  and I'm also pretty sure any claims otherwise are BS,  marketing hype,  or plain advertising fraud,  pure and simple (of which there is a lot out there on an internet entirely unpoliced for truth,  especially X of late).  Those 3 terms are synonyms,  by the way.

GW

Last edited by GW Johnson (2024-07-03 15:17:51)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#328 2024-07-03 19:38:23

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 18,189

Re: GW Johnson Postings and @Exrocketman1 YouTube videos

For GW Johnson re #327

Thank for confirming that your calculations show that an SSTO is possible using ISP of 450, for an expendable vehicle.

Thank you for reminding the members that a SSTO that can return for re-use would need an ISP over 600.

The members of this forum who are enthused with SSTO have an opportunity to find a fuel with ISP of 600 or more.

***
In the SpinLaunch topic I have invited SpaceNut to find a web site that can compute the ballistic flight of the SpinLaunch rocket, from initial release through apogee.  My hope is that if SpaceNut can find such a program, it will allow computation of apogee and velocity Eastward at apogee.  If you have that information, am I correct in thinking your spreadsheet can compute the second and third stage phases of the flight.  If all goes well, we'll know enough to be able to work backward from the goal to 200 kg in LEO, to the mass of the fully fueled capsule before launch.

(th)

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#329 2024-07-08 19:35:30

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 18,189

Re: GW Johnson Postings and @Exrocketman1 YouTube videos

For all ... NewMars members and readers...

I am happy to be able to report that the hot links from the Big Things On Mars video are now working.

Dr. Johnson has replaced the defective links, and the YouTube software is allowing his links to be displayed as hypertext.

Go to YouTube.com/exRocketMan1 to see the working links.

Please note that the number of views is showing as 109. That's a respectable number for a technically challenging topic.

(th)

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#330 2024-07-10 06:09:08

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 18,189

Re: GW Johnson Postings and @Exrocketman1 YouTube videos

images prepared by GW Johnson for solid rocket topic...

Solid rocket adapted for SpinLaunch:
LLrPLKc.png

Thrusted decoy:
hxjQpvh.png

Apollo Saturn Ullage motor:
qZ0A7Vc.png

(th)

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#331 2024-07-11 09:44:59

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 5,620
Website

Re: GW Johnson Postings and @Exrocketman1 YouTube videos

Re: pictures in post 330 just above.

The first one is what a conventional solid rocket design in a cylindrical case would look like with a propellant grain shaped exactly like a pool of liquid for sideways gee.  At 1000's of gees,  the solid propellant would indeed flow viscously into such a shape.  It cannot stand up by itself at such extreme gee.  I don't like this design because it has very low cross-sectional loading of propellant,  leading to a very poor low ratio of propellant to total loaded motor weight,  and thus a high inert fraction,  compounded by the structural robustness required for the case itself to resist extreme lateral gee. 

The second one is a design that I did for a thrusted entry decoy for warheads about 1988.  It is entirely unsuitable for extreme-gee conditions in any direction,  but shows that very unique and challenging problems can really be solved with out-of-the-box design thinking.  Almost nobody in the industry would have attempted this,  but I showed in subscale lab motor tests that the round-the-corner grain design actually works,  and overcast technology was already well-known to work. 

The third one is a sketch representing a very simple production small motor used for ullage on the old Saturns during Apollo.  With the case beefed up,  it could serve as an extreme-gee motor of high cross-sectional loading,  for axially-directed extreme gee,  because the propellant charge is the same shape as a liquid pool.  But this is oriented the wrong way for spin launch as we understand it.

GW

Last edited by GW Johnson (2024-07-11 09:47:58)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#332 2024-07-12 21:18:12

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 5,620
Website

Re: GW Johnson Postings and @Exrocketman1 YouTube videos

Wasn't sure where to post this. 

I saw a report that Ariane-6 flew,  but there was a problem getting the whole mission done.  The upper stage has some sort of APU (auxiliary power unit) whose exhaust supplies the ullage thrust necessary to light the engine for subsequent burns,.  They got up there and did one relight,  but after that the APU failed,  and so the other relights could not happen.  Partial success.

GW


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#333 2024-07-15 11:20:17

tahanson43206
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Registered: 2018-04-27
Posts: 18,189

Re: GW Johnson Postings and @Exrocketman1 YouTube videos

For GW Johnson re gent with Aerospace background.

This gent was indeed employed in aerospace right out of college in the 60's, and he wrote FORTRAN programs in connection with jet engine design and air flow. However, the industry cut back and laid him off, so he went with other employers and never looked back. 

I'll keep watching/listening to see if there might be others who are more directly involved in aerospace engineering.

(th)

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#334 2024-07-19 08:16:49

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 5,620
Website

Re: GW Johnson Postings and @Exrocketman1 YouTube videos

Sounds like he knows something about compressible aerodynamics,  then.  He'd probably like what I did for the rocket engine estimator spreadsheet.  There's nozzle compressible flow underlying it.

GW


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#335 2024-07-19 17:21:11

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 18,189

Re: GW Johnson Postings and @Exrocketman1 YouTube videos

For GW Johnson!

Thanks for noting my interview with the gent with aerospace experience out of college. 

I got the impression he made two decisions that are factors in his current interests... first, he hired on with IT companies doing non-aerospace work ... I missed the details but the focus was probably finance. The other is that he went into management.

My impression is that his youthful interest in aerospace would be difficult to rekindle.  I think our best path forward is to keep looking.

Meanwhile, best wishes for success with your most recent ventures in several areas.

I have all the hardware I need to bring one of the large wired systems back online.  It's just a case of finding and making the time.

(th)

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#336 2024-07-19 17:51:18

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 18,189

Re: GW Johnson Postings and @Exrocketman1 YouTube videos

For GW Johnson!

Regarding "Weekly Reader" (which I remember from elementary school)...

In 2012, Weekly Reader ceased operations as an independent publication and merged with its new owner, Scholastic News, due primarily to market pressures to create digital editions as well as decreasing school budgets.

Weekly Reader - Wikipedia

Wikipedia
https://en.wikipedia.org › wiki › Weekly_Reader
People also ask
Is Weekly Reader still around?
Who publishes weekly Readers?

Say Goodbye to 'Weekly Reader'

The Atlantic
https://www.theatlantic.com › archive › 2012/07 › kiss-...
Jul 23, 2012 — Scholastic has owned Weekly Reader, a magazine aimed at children and what can only be described as a grammar school must-read, for about six ...

Weekly Reader: An Important Part of Classrooms for Many ...

America Comes Alive
https://americacomesalive.com › ... › Communications
Weekly Reader has supplemented classroom work by bringing current news to elementary school children. It has existed since 1928.

Classroom Magazines & News for All Grades | Scholastic ...

Scholastic
https://classroommagazines.scholastic.com
Scholastic Magazines+ covers the latest topics to enhance instruction in math, science, reading, social studies, and more. Bring learning to life!
Scholastic Magazines+ · Shop Scholastic News · Shopping Cart Icon · Support

Weekly Reader Publishing

Wikipedia
https://en.wikipedia.org › wiki › Weekly_Reader_Publi...
Weekly Reader Publishing was a publisher of educational materials in the United States that had been in existence for over 100 years.

Longstanding Classroom Magazine, Weekly Reader, Stops ...

Education Week
https://marketbrief.edweek.org › 2012/07
Jul 25, 2012 — The consolidated magazine will be called Scholastic News Weekly Reader and will be published weekly in print during the school year, Roome said.

The last Weekly Reader?

CNN
https://www.cnn.com › 2012/07/25 › the-last-weekly-re...
Jul 25, 2012 — Weekly Reader, now owned by Scholastic, will cease independent publication this school year. by Donna Krache, CNN. (CNN) The Weekly Reader title ...

Throwback Thursday: Remember Weekly Readers?

The Flourishing Academic
https://flourishingacademic.wordpress.com › 2022/11/10
Nov 10, 2022 — While not the epitome of classroom reading material, the Weekly Reader still offers a useful catalyst for pedagogical discussion.
Free 2–5 day delivery · 14-day returns

Landmark publication Weekly Reader to shut down

New York Post
https://nypost.com › 2012/07/23 › landmark-publicatio...
Jul 23, 2012 — Weekly Reader, a staple in American classrooms for a century, has some hard news for its young readers: it's shutting down.

So long Weekly Reader . . . | Science ...

Science News
https://www.sciencenews.org › blog › science-the-public
It will now begin “combining the features of Weekly Reader into the Scholastic classroom magazines,” says Cathy Lasiewicz, with Scholastic in New York City. “ ...

(th)

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#337 2024-07-20 18:09:29

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 18,189

Re: GW Johnson Postings and @Exrocketman1 YouTube videos

For GW Johnson.... I asked ChatGPT4o to write a little Python program to show the performance of a SpinLaunch projectile if the mass is increased while the cross section is held constant...

import numpy as np
import matplotlib.pyplot as plt

# Constants
g = 9.81  # acceleration due to gravity (m/s^2)
rho = 1.225  # air density at sea level (kg/m^3)
Cd = 0.5  # drag coefficient (assumed)
dt = 0.01  # time step (s)

def projectile_motion(m, A, v0, angle, altitude):
    angle = np.radians(angle)
    v0x = v0 * np.cos(angle)
    v0y = v0 * np.sin(angle)
   
    x, y = 0, altitude
    vx, vy = v0x, v0y
    positions = [(x, y)]
   
    while y >= 0:
        v = np.sqrt(vx**2 + vy**2)
        Fd = 0.5 * Cd * rho * A * v**2
        ax = -Fd * vx / (m * v)
        ay = -g - (Fd * vy / (m * v))
       
        vx += ax * dt
        vy += ay * dt
        x += vx * dt
        y += vy * dt
       
        positions.append((x, y))
   
    return np.array(positions)

def plot_trajectory(positions, label):
    plt.plot(positions[:,0], positions[:,1], label=label)
    plt.xlabel('Distance (m)')
    plt.ylabel('Height (m)')
    plt.title('Projectile Motion with Drag')
    plt.legend()
    plt.grid(True)

# Example usage
m1 = 300  # mass of projectile (kg)
m2 = 2000  # mass of projectile (kg)
A = 0.1  # cross-sectional area (m^2)
v0 = 5000 * 0.44704  # launch velocity (m/s) - converted from mph to m/s
angle = 45  # launch angle (degrees)
altitude = 0  # launch altitude (m)

positions1 = projectile_motion(m1, A, v0, angle, altitude)
positions2 = projectile_motion(m2, A, v0, angle, altitude)

plot_trajectory(positions1, f'Mass = {m1} kg')
plot_trajectory(positions2, f'Mass = {m2} kg')
plt.show()

# Calculate apogee and range
apogee1 = np.max(positions1[:,1])
range1 = positions1[-1,0]
apogee2 = np.max(positions2[:,1])
range2 = positions2[-1,0]

print(f'Mass = {m1} kg -> Apogee: {apogee1:.2f} m, Range: {range1:.2f} m')
print(f'Mass = {m2} kg -> Apogee: {apogee2:.2f} m, Range: {range2:.2f} m')

I'm not in a position to run the program right now, but if there is a NewMars member who can run Python, please download the little program and publish the results.

GW is currently looking at 300 Kg mass for the projectile,l and I am recommending a mass of 2000 kg, which is the mass of payload, third stage and second stage.

(th)

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#338 2024-07-20 18:14:46

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 18,189

Re: GW Johnson Postings and @Exrocketman1 YouTube videos

I asked ChatGPT4o if the first version of the program accounts for decreasing air density with altitude and it did not.

Here is a revised version that does compute the decreased atmospheric density, using an exponential model:

import numpy as np
import matplotlib.pyplot as plt

# Constants
g = 9.81  # acceleration due to gravity (m/s^2)
rho0 = 1.225  # air density at sea level (kg/m^3)
Cd = 0.5  # drag coefficient (assumed)
dt = 0.01  # time step (s)
H = 8500  # scale height for Earth's atmosphere (m)

def air_density(altitude):
    """Calculate air density at a given altitude using an exponential model."""
    return rho0 * np.exp(-altitude / H)

def projectile_motion(m, A, v0, angle, altitude):
    angle = np.radians(angle)
    v0x = v0 * np.cos(angle)
    v0y = v0 * np.sin(angle)
   
    x, y = 0, altitude
    vx, vy = v0x, v0y
    positions = [(x, y)]
   
    while y >= 0:
        v = np.sqrt(vx**2 + vy**2)
        rho = air_density(y)
        Fd = 0.5 * Cd * rho * A * v**2
        ax = -Fd * vx / (m * v)
        ay = -g - (Fd * vy / (m * v))
       
        vx += ax * dt
        vy += ay * dt
        x += vx * dt
        y += vy * dt
       
        positions.append((x, y))
   
    return np.array(positions)

def plot_trajectory(positions, label):
    plt.plot(positions[:,0], positions[:,1], label=label)
    plt.xlabel('Distance (m)')
    plt.ylabel('Height (m)')
    plt.title('Projectile Motion with Drag')
    plt.legend()
    plt.grid(True)

# Example usage
m1 = 300  # mass of projectile (kg)
m2 = 2000  # mass of projectile (kg)
A = 0.1  # cross-sectional area (m^2)
v0 = 5000 * 0.44704  # launch velocity (m/s) - converted from mph to m/s
angle = 45  # launch angle (degrees)
altitude = 0  # launch altitude (m)

positions1 = projectile_motion(m1, A, v0, angle, altitude)
positions2 = projectile_motion(m2, A, v0, angle, altitude)

plot_trajectory(positions1, f'Mass = {m1} kg')
plot_trajectory(positions2, f'Mass = {m2} kg')
plt.show()

# Calculate apogee and range
apogee1 = np.max(positions1[:,1])
range1 = positions1[-1,0]
apogee2 = np.max(positions2[:,1])
range2 = positions2[-1,0]

print(f'Mass = {m1} kg -> Apogee: {apogee1:.2f} m, Range: {range1:.2f} m')
print(f'Mass = {m2} kg -> Apogee: {apogee2:.2f} m, Range: {range2:.2f} m')

If a NewMars member has the ability to run Python, please show the results for the 300 kilogram projectile and the 2000 kilogram one, launched at 45 degrees at 5000 mph (or whatever the metric equivalent may be).

(th)

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#339 2024-07-20 20:01:34

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 18,189

Re: GW Johnson Postings and @Exrocketman1 YouTube videos

I found a laptop that had Python installed, and ran the program developed by ChatGPT4o as reported above.

The program produced a graph which is definitely encouraging. It shows that when the mass of the projectile is increased, while everything else remains the same, the apogee is much higher.

I will attempt to deliver the image via imgur.com

CUJI9gU.png

(th)

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#340 2024-07-21 11:10:53

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 18,189

Re: GW Johnson Postings and @Exrocketman1 YouTube videos

GW Johnson sent a PDF file of his latest round of work on the SpinLaunch venture....

In the PDF at the link below, GW shows that if the launch is upgraded to 5500 mph, and the device adheres to the mass, cross section and length that he has chosen, the vehicle will cross over the 37 mile altitude and still have some momentum for the second stage to work with. The mass GW has chosen is 3500 lbm, which is substantially less than the mass ChatGPT4o estimated would be required to put a 200 kg payload into orbit.

Despite the smaller mass, GW's design does achieve the altitude needed for the second stage to take over.

For readers (like me) who might not be familiar with "lbm", here is a Google definition:\

0.453 592 37 kg

That means GW's estimate of 3500 lbm would be 1585 kg, well below the 2000 that ChatGPT4o "thought" would be needed.

That 1585 kg needs to include the payload of 200 kg, the propellant and casing, the auxiliary hardware to allow the rocket to function after dealing with 10,000 G, the carrier for the package, and the control electronics to manage the rocket burns and navigate the vehicle to a docking with the destination.

However, 1385 kg is a lot to work with, so we can stay tuned to see if GW can put the package together.

Here is the link to the PDF:

link goes here: https://www.dropbox.com/scl/fi/p8t4m1cj … okgyf&dl=0

(th)

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#341 2024-07-22 13:38:13

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 18,189

Re: GW Johnson Postings and @Exrocketman1 YouTube videos

For GW Johnson re SpinLaunch studies...

First, thank you ** very ** much for spending so much time and thought in exploration of this subject!

While the payloads delivered to LEO are currently showing as less than the (arbitrary) goal of 200 kg, the fact that you are getting ** anything ** to orbit using both liquid and solid propellant is a testament to your skill as a designer.  Since you have purposefully erred on the side of caution, I am (reasonably) optimistic that further refinement of your design will yield improvements.

One thing we can be sure of... as the mass of the projectile increases, while the drag remains the same, the projectile will travel higher and arrive at the desired altitude of 37 miles with greater velocity than is possible with a lower mass.

There is (most likely) an upper limit to the tensile strength of the throw arm, but at this point I don't think we (not at SpinLaunch) have much of an idea of what that limit might be.

A severe constraint on the performance of the secondary stages is the ISP of the propellants chosen.

The ISP of 245 for a particularly difficult-to-work-with solid fuel appears (to me at least) to be about as far as we can go in that direction.

It seems to me (based only on what I can glean from the documents you have shared) that you have set aside for now the tricky question of how to retain the interior shape of the grain when it is exposed to 10,000 lateral G's.  We have discussed making the plug for the nozzle a little solid fuel rocket of it's own. We have discussed surrounding the plug cylinder with water, in order to retain the shape of the grain as cast, but there may be a better choice for that part of the system, and potentially that part might contribute to the thrust needed to put the payload into orbit.

Your work with liquids makes use of hypergolic fluids (as I understand your text) and that certainly makes sense for a variety of reasons, but since we are starved of ISP in the early going, it might be interesting to see what could be done with LOX and LH2. The volume they would require might preclude their serious consideration.  You have indicated (as I interpret your text) that a ratio of 1 diameter to 10 length of the projectile is about the longest that might be considered for a practical device. The mass of the projectile is hovering around 2 tons or 4000 pounds, and that mass is advantageous for punching through the drag, but it implies a massive swing arm and all the attendant features that allow the projectile to be held against 10,000 G's and released at the correct time.

All in all, it certainly seems clear why the SpinLaunch concept is regarded with skepticism by some folks in (or not in) the aerospace community.

(th)

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#342 2024-07-23 08:23:54

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 18,189

Re: GW Johnson Postings and @Exrocketman1 YouTube videos

For GW Johnson....

ChatGPT4o is a higher level program than the free version you might have read about.  I have explained your skepticism, and it is willing to work with you (with me as intermediary) in an attempt to bring your two models into alignment.

In the present circumstance you have divided the problem into five stages, and you and ChatGPT4o should be able to work on all five stages separately, while keeping in mind that together they accomplish the mission objective.  The five stages are mutually interdependent, and they interact with each other.

You can think of ChatGPT4o as a ** very ** smart spreadsheet. I don't think it will care, and it might help you to allow this powerful tool to help you approach closer and closer to a proposal we can offer SpinLaunch.

Here is an offer from ChatGPT4o...

Aligning Approaches: AI Model vs. Engineer's Model

1. Verify Initial Conditions and Assumptions:

  • Initial Altitude and Velocity: Ensure both models start with the same initial conditions (37 miles altitude and residual velocity).

  • ISP and Drag Coefficient: Confirm consistent use of specific impulse (ISP) and drag coefficients for the solid fuel approach.

2. Compare Stage Configurations:

  • Stage Configurations: Examine the stage configurations in both models. Verify staging strategy and mass of each stage.

  • Mass Breakdown: Ensure total mass breakdown and payload fraction are comparable.

3. Cross-Check Calculations:

  • Delta-V Calculations: Compare delta-V calculations for each stage, including thrust profiles and burn times.

  • Losses Accounted For: Ensure atmospheric drag and gravity losses are accounted for similarly.

4. Detailed Step-by-Step Comparison:

  • Side-by-Side Comparison: Create a step-by-step comparison of each model’s calculations from SpinLaunch release to final orbit insertion.

  • Identify Discrepancies: Identify discrepancies in intermediate values like velocities, altitudes, and remaining mass.

5. Parameter Sensitivity Analysis:

  • Sensitivity Analysis: Conduct a parameter sensitivity analysis to understand how changes affect final outcomes.

  • Critical Assumptions: Identify critical assumptions or simplifications that might differ.

6. Collaborative Review:

  • Present Results: Present AI model and engineer’s model side-by-side to the team.

  • Encourage Discussion: Invite collaborative discussion to reconcile differences.

7. Iterative Refinement:

  • Refine AI Model: Use feedback from the engineer to iteratively refine the AI model.

  • Improve Accuracy: Incorporate insights or corrections to improve reliability.

(th)

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#343 2024-07-23 08:28:28

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 18,189

Re: GW Johnson Postings and @Exrocketman1 YouTube videos

For GW Johnson re post #342

ChatGPT4o has suggested agreeing upon the velocity and direction of the projectile at 37 miles as a starting point.

Since you have found a solution that puts the projectile at 37 miles with some residual velocity, please provide the velocity and angle of movement that your spreadsheet solution shows.  The projectile starts at 45 degrees and it will have dropped by some amount when it reaches 37 miles. Hopefully your spreadsheet can tell you what that angle is, and what velocity the projectile has at that altitude.

(th)

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#344 2024-07-23 10:06:45

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 5,620
Website

Re: GW Johnson Postings and @Exrocketman1 YouTube videos

The 3rd and 4th studies I did presumed a 3000 lb object 22.45 inches diameter.  The 3rd study showed apogee at 56.5 km altitude and 1.0 km/s speed (all horizontal at apogee,  by definition!!!).  It launched from the slinger at 45 degrees and 5000 mph.  The 4th study threw exactly the same object from the slinger at 45 degrees and 5500 mph (10% faster).  It achieved apogee at 65.5 km altitude and 1.08 km/s speed. 

The two altitudes bracket your 37 stature miles = 59.5 km,  and the two speeds are almost the same at 1.0 to 1.08 km/s.  Altitudes in that range are high enough to neglect air drag for the ascent to orbit,  and the radial change is low enough to reduce gravity loss for the ascent from that apogee to orbit.  These data were in the plots that I sent you in the 3rd and 4th documents.

The notion is to eject the payload and rockets from the carrier vehicle and fire the main rocket stages,  all right at apogee conditions.  The transfer ellipse is the apogee altitude as the ellipse min altitude 59.5 km (give or take a smidge),  and ellipse max altitude 300 km (give or take a bit).  We have to get from from 1.0-1.08 km/s to the transfer perigee speed with the main rocket burns,  then wait for it to reach transfer apogee to circularize with a final small burn. 

I am assuming a tug goes and retrieves it,  relieving it of needing to burn for rendezvous and docking.  I also do not assume a deorbit burn for disposal,  which presumes "something ese" deals with that issue.

This scenario is in fact what I have been using for the initial bounding calculations attempting to size NTO-MMH and solid rockets to do this job.  The ideal dV without losses is 6.95 km/s to get onto the transfer orbit,  and 0.08 km/s to circularize at 300 km altitude.  The loss I figured as 2% of surface circular orbit speed.  I tried limiting them to 3000 kg = 6600 lbm,  knowing the larger size might give me a bit more altitude,  or alternatively let me lower the slinger launch speed and gees.  Maybe I should lower that to 3000 lbm,  or maybe I should look at 6600 lbm slung vehicles.  I do not yet know.

The liquid did fairly well as a two-stage item making 3 burns (the second stage relights to circularize.  The solid I first tried as a 3-stager,  with two main stages for the burns onto the transfer orbit,  plus a very small solid motor to circularize. It did not do very well,  being lower Isp. I got better results with a 4-stager,  that being 3 solid stages to get onto the transfer ellipse,  plus a very small motor to circularize.  The results I got at 3000 kg just scale up or down with payload size.  The velocity requirements do not scale.

I still don't believe any of this,  not having done any design layouts and checking the requirements to survive the sling,  as well as do the propulsion job.

GW

Last edited by GW Johnson (2024-07-23 10:12:49)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#345 Yesterday 21:22:00

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 18,189

Re: GW Johnson Postings and @Exrocketman1 YouTube videos

For GW Johnson...

I found an article from 2014 about Dr. John Hunter...

I thought you might be interested in his prediction for the exit velocity of his planned device:

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Above & Beyond

The Man Who Wants to Shoot the Moon
A Q&A with John Hunter

Duncan Geere
April 10, 2014  22 min read

An illustration of a rocket hurtling towards the Moon.

John Hunter is a man who knows about space guns. During the mid-90s he was in charge of Project SHARP, a gas gun capable of shooting objects at a significant fraction of escape velocity from Earth. In the late 2000s he founded Quicklaunch, a company aiming to commercialize similar technology.

He left Quicklaunch in 2012, so we took the opportunity to find out what he’s working on next. He told us about almost meeting space gun pioneer Gerald Bull, Elon Musk’s chances of success with SpaceX, how space guns can replace rockets, and why he’s the only person who can build one.

spacer
Let’s start at the beginning: What is a space gun and how does it work?

A space gun is very simple geometry. It’s basically a tube and the only difference between it and a regular gun is it uses hydrogen as opposed to gunpowder. If you go to physics 101, you know that gases can expand at a certain rate. It turns out that rate is a function of the sound speed, which is a function of the molecular weight of the gas. Air has a molecular weight of 28 or 29, as it’s largely nitrogen. Gunpowder has a molecular weight of 22, but it’s very, very hot–so that’s why it gets extra performance, because it’s so damn hot–the sound speed goes as the square root of temperature. But it turns out that helium and hydrogen are far, far lighter than air. Helium has a molecular weight of four and hydrogen has a molecular weight of two as it’s diatomic. So they have extraordinarily high sound speeds, particularly hydrogen.

So a gas gun is a tube made of steel where you evacuate the cylinder and you have the projectile in an appropriate shape for atmospheric exit, and you basically release the hounds–you let the hydrogen push this thing down the barrel.

I was a theoretical physicist for the first nanosecond of my career, and then I got involved in actually building stuff because I got tired of no one ever building anything. It was apparent to me after some time at Livermore National Laboratory that we needed more guys that build stuff and fewer guys that would just think deep thoughts. So I stopped thinking deep thoughts and started building stuff.

It turned out that a hydrogen gas gun is something that I could teach you how to do in 30 minutes. There’s about 10 rules: Here’s how you deal with steel, here’s how you deal with hydrogen, here’s how you deal with controls, and so on. Get some engineers and you could build a system very straightforwardly.

What would you generally use one of these guns for in the context of space exploration?

Well, I favor that application because I’ve always been concerned about arms races. It turns out that hydrogen guns are not really weaponizable, because you can’t fire them every 10 seconds. If you want a weapon, you want something that you can shoot every 10 seconds, or every minute in the case of some big, big systems.

So it’s sorta good in the sense that you can only fire these things probably once an hour. For high performance, you’ve got to pull a vacuum on the barrel, you’ve got to clean it out very, very carefully, you’ve got to keep the barrels aligned, and so on. They’re not trivial to maintain. Did that answer your question?

What I’m trying to get at is why are they superior to, say, a rocket for getting something to space?

Oh, certainly, it’s because of the reusability issue. If you could reuse a rocket a hundred times, or a thousand times, then you would never want to use a gun. The rockets are made out of metals and some composites. They have typically a three or four percent payload fraction–these are SpaceX-type numbers. So if you could reuse this thing time and time again–the first stage, second stage, third stage–you’d only pay for them once. And you’d pay a little bit of money to maintain them, right?

The problem is, that doesn’t work. Because typically you kick your first stage off, and it’s traveling maybe Mach 10 when it departs from the second stage–and trying to recover that first stage is a bear. I’ve shot things at high Mach numbers and you just don’t recover them at those speeds. On the other hand, Elon Musk is trying to do this, and I’ve always been impressed by this guy–so if anyone can pull it off, he’ll pull it off. I’ve been out of the field of shooting big guns for over 10 years, but he’s going to run into an issue recovering high-Mach number objects. It’s a very difficult issue.

So here’s where the gun comes in–the gun is essentially the first stage. We’re launching these things at–in my case it looks like six kilometers per second [3.7 miles per second] is a really nice number. At six kilometers per second, you don’t have significant barrel erosion, and the vehicle survives the exit of the atmosphere easier because all the bad things go at high powers of velocity. So the faster the thing comes out of the barrel, the more you’ve got to worry about as it goes towards some space depot. Six kilometers per second is a good number.

So we have this gun, it launches things repeatedly at six kilometers per second–think of that as the first stage, so the first stage essentially becomes infinitely reusable.

So you’re essentially putting a rocket into a gun?

Yes–it’s a single-stage rocket now instead of a two-stage. The first stage becomes reusable, because the gun is the first stage.

How did you get interested in this subject in the first place?

I was hired at Livermore to build magnetic guns. I had a background in theoretical physics, and I knew about magnetics–the standard stuff you learn in graduate school. This was during the Star Wars era, so launching stuff into space. I worked for a forward-thinking guy named Lowell Wood, who was a weapons lab guy but was extremely talented–he now consults for Bill Gates and those guys. Lowell was my boss, and he was a genius who was a little quirky, personality-wise. He and I didn’t always get along–eventually I left his group, though we actually became better friends after I left. But I was hired to build magnetic launchers.

A year into my soujourn there, in 1988, I ran into the head of the lab at a cocktail party–John Nuckolls. Nuckolls had heard about my work–I was looking at superconductors and generators and all sorts of exotic gizmos, and he said: “This is fantastic John, because our gas guns only get seven or eight kilometers per second [4.3 or five miles per second].” I replied: “What’s a gas gun?” I was one of the uninformed masses at the time about gas guns, but thank God I’m an alcoholic, otherwise I never would have met this guy at the cocktail party! I’m only partially kidding there.

So John Nuckolls told me that gas guns existed, and they used gas guns at these laboratories because there’s no other way to get to high speeds. Livermore was a weapons lab in those days. Now it’s become an environmental-type lab with a bit of weapons stuff on the sides. They use these guns to test equations of state of metals–when you hit, say uranium on steel, what happens there? What happens to these materials under stresses and pressures and things like that.

There was some classified fusion stuff, which was the thermonuclear stuff, and then we had the unclassified fusion, which was like the NOVA laser and the NIF laser and those kind of things. Livermore needed to know how materials behave under immense pressure, and so the only way to get that pressure was to slam things into each other at high speed. And the only way to do that was a hydrogen gas gun.

They had two or three little gas guns at Livermore, but when I heard about this stuff I immediately got permission from Lowell to build one that was about 30 centimeters [11.8 inches] long, and it mocked up a particular weapon that our enemies–in those days of the Cold War–were using. I got it to work, and I was shocked because I got experimental results within a month, and it worked within one percent of my code predictions!

Where I come from, in quantum chromodynamics and string theory, and these arcane things, no one ever gets an answer that works. It’s very unsatisfying if you ever want to get results. Sadly, 30 years later, still nothing has been calculated. It’s been a disaster in my opinion. But I was tickled pink that ordinary, one-dimensional fluid dynamics calculated these results so accurately.

That was done within one month, and I used that as leverage to get permission to build a second gun that was three meters [9.8 feet] long. We got that to work within two months–which shocked Livermore, because they’d been working on a similar system for three years. When they heard I was progressing on this one, they sped up and got their first shot the same day I got my first shot. I gave them some motivation!

That gun ultimately managed eight kilometers per second [five miles per second], which far surpasses any real gun that’s historically ever been made–electric guns never came close to the gas gun for performance, and still don’t. It’s such a simple geometry and methodology. But then Lowell and I got mad at each other–I got ticked off at Lowell and left the group. I walked out.

I went to another division, which was lasers. They sent me there, but then I made a presentation at the lab about gas guns, and I came in number two out of more than a hundred presentations, and I got $800,000 to build a 122-meter [400-foot] system. This was the one I was going to use to put things in space, five kilograms [11 pounds] at a time. That was called Super-HARP.

How did SHARP differ from past space gun projects, like the original project HARP?

The original Project HARP was run by this guy called Gerald Bull, who had a very colorful past and was eventually executed by some people–let’s just say most likely from an area near Tel Aviv. He made the mistake of going out late at night, and ignoring two painters that snuck up behind him and put a few rounds in the back of his head. He was a very talented aerodynamicist and what made him special was he was a guy who would really build the hell out of things.

A photo of a large artillery-style gun aimed upwards, with a plane flying overhead.
He got into artillery, and he made some improvements in our long-range artillery in the United States, I’m told. He did things involving base bleed, and exotic projectiles, for conventional 16-inch guns. But then he was pretty talented and he was able to raise money to do project HARP–the one in the mid-60s. He went to Barbados, and he went to Yuma, and he set the world record for altitude out of Yuma–it was the Y28 shot in 1966. I was in Yuma Proving Grounds two years ago and that gun is still there–and it’s in really good shape–so you could go to Yuma now with a little bit of cash and do another series of shots with that powder gun. It’s a nice system. That’s only 120 miles [193 kilometers] from where I am right now!

So Mr. Bull built this powder gun–he took two ordinary 16-inch guns, he smooth-bored them out because at high speeds you tear the rifling out, put thin liners in, and then attached them together with flanges. Then he was able to work on the gunpowder burn, using big grains that burn slowly. He did everything right, went through a whole lot of experimentation, got it to work rather well, and did a lot of shots out of Barbados. He was probing the ionosphere for some of his customers–primarily I think it was the U.S. Army in those days. Then he went to Yuma and did some more shots. He was working in conjunction with the ballistics research laboratory, the U.S. Army, and Canada in those days.

So then that thing ended in the late 1960s, and he went on to making money with Space Research Corporation. My impression was he crossed wires with the CIA, spent a few months in the slammer, got a little bit embittered, and took SRC to Brussels. The rest is history–he got zapped–and they put me in all the books as the evil guy that got away. I’m only one-tenth as evil as they think. Maybe 20 percent.

So did you ever meet or speak to Bull?

No, I came really close. I was going to call him a month before he got shot. I heard he was doing some stuff, and I had intended the name SHARP to be complimentary. Maybe I’m sorta weird, but I was thinking Super High Altitude Research Project would make people recall his earlier work, so I suggested we call ours Super HARP. Maybe he thought I was belittling him, because I heard through the author of one of the books that I drove him nuts–that he didn’t like the fact that I used his name and added an “S” to it. Then he thought I had a billion dollars of funding, because there was a typographical error in an Aviation Week article. I only had a few million.

So Bull apparently didn’t like me because of this–I was going to call him up and be nice to him, explain things, but one of my consultants told me not to do it. He said that Bull is dealing weapons on the international market–if you call him up, you’re going to get Livermore involved, which is a government-funded agency. My consultant was right about that, so I didn’t call him, and a month later he’s dead. That’s as close as I got to Gerald Bull.

Later on I met his collaborator, Murphy, and we exchanged pleasantries–he autographed a book for me. Bull and Murphy wrote a nice book called the Paris Guns–a nice coffee-table book, I’d recommend it if you can still get them. It tells the whole history of the Germans’ 1917 gun.

The one that become the V-3 cannon?

It never really became the V-3–it was just to rain terror on the poor Parisians–a weapon of mass destruction. They killed about a person per round–they shot a few hundred rounds and killed a load of kids and churchgoers and so on. It was just the Germans trying to intimidate Paris in those days.

But then the V-3, which was in the Second World War, was a different beast. It was a side-injected system with powder; it was supposed to fire 90 miles across the English Channel. Strangely enough, Joseph P. Kennedy Jr. was killed on a mission to destroy the V-3–he was on a glider that had a lot of explosives in it, but the thing blew up in mid-air. I heard the gun had timing issues. It was supposed to give a bit of extra oomph, but it was dismantled at the end of the war.

A raggedy gun lies on an upwards slope of a hill, covered in rotted canvas.
Project Babylon was dismantled at the end of the first Gulf War.
So you had no relationship with Bull?

I just respected his work. I never knew what kind of person he was, and later on I read that he had a bit of an unusual personality–but he was a damn good scientist.

But you weren’t aware of any of the Project Babylon work?

No, not until after it had already happened. After it happened I ended up helping our guys dismantle it–my engineer and I helped our side because there was a question of what would happen if the thing was pointed in a different direction. In the Middle East, every third project is called Project Babylon. They apparently like that word. There were 120 different Project Babylons all babbling in different directions. It was like a tower of Babylons.

But I did help some of our guys, nameless guys, on that topic with my main engineer–we nailed it.

So going back to Project SHARP, what happened to that? How did that all end?

Well, Project SHARP got some internal funding from Livermore–the $800,000 I mentioned before. Then in the second year they liked the project so they gave us another $800,000. Then the Strategic Defence Initiative Organisation kicked in half a million, these were the Star Wars guys. Then later on the Air Force kicked in some money for hypersonic scramjet testing–so those were our funding sources.

We did 20 or 30 shots, in total, with every shot taking a couple of days of preparation and a day or two afterwards to clean things up, because this was a giant gun–it wasn’t made for shooting every hour. I built the thing so cheap and so quickly that it didn’t have capability to reload fast. We used human beings and trolleys–we tried to use the wheel wherever we could.

It was pretty unusual that we pulled it off, because in that era people were building systems similar in size and they were coming in at $30 million. They’d build 10 percent and run out of money. We built SHARP for $2.3″”$2.5 million, which was pretty phenomenal, because I tried to avoid as much bureaucracy as I could, so I kept the manpower costs down and the hardware costs up. We were focusing on getting a lot of steel in place. So as soon as I got my first check for $800,000, I started ordering steel as opposed to more studies. Most theoretical scientists just want to study things until they can retire and smoke their pipe all the way to the grave. I just wanted to put hardware in the ground and get the thing going.

We were doing shots for the air force–lethality tests during the first Iraq War, when we were concerned Saddam was going to be nerve-gassing Tel Aviv and places like that. We wanted to see if we could destroy his warheads, because he was thinking of putting nerve agents on SCUD missiles. We ended up doing some shots on simulated warheads that were quite effective–we were killing these things at Mach 9. That was one of our clients–we did five or 10 shots doing that.

Then we segued into doing shots for the air force on hypersonic engines–hydrogen-burning engines. During those days, people postulated you could have very high-Mach number aircraft–well above Mach 3, we’re talking Mach 12, Mach 20, these fantastic numbers. In reality, I’m not as sanguine on the prospects of civil transport above, say, Mach 2, because it turns out that the level of difficulty goes up as a high power of the velocity. I’d be shocked if we ever got civil transport above Mach 2 or Mach 3. We had the Concorde and the Tu-144, and so on, but there’s all kinds of difficulties–the guys have to wear spacesuits because of the heating issues. If you make a mistake at high Mach numbers, it tends to be fatal. Whereas you can recover at low Mach numbers. But in those days there was interest in doing civil transport at high speed, and we were part of that.

We did tests shooting scramjets at high Mach numbers. It was one of these classic government programs where they just wanted to study it forever and keep making money, but people were reticent to actually do testing. Because when you do testing you can actually fail–which is embarrassing. Better to study things forever. I was scolded by the head of the program because we did tests and got real data. We got the first free-flight data above Mach 7 in the world with these engines. He reprimanded me for doing this work for the air force, even though he didn’t fund me, because I think it embarrassed him. “Here are these guys, going out without permission and getting real data!” As opposed to just studying materials for the next 20 years. They’ll spend $5 million studying halfnium diboride to coat the outer layers of the wings, as opposed to just flying the *bleep.* Pardon my French.

We were getting better and better at collecting data, but we never showed thrust. We couldn’t confirm or deny that we were getting thrust–high-speed photographs were taken, but the thing was only flying 30 meters [90 feet] before it vaporized, because it would run into a sandbag. That’s why I said Elon is going to have some issues recovering, because he’s going to have to collect his first stages as they come down, tumbling through the atmosphere, but he’s got to slow them down from Mach 9 to Mach 0 to recover them. I never had any luck doing that, but I didn’t have his resources, and I didn’t have a lot of atmosphere to work with, so who knows? He might pull something off that I couldn’t figure out.

The project ended because I got bored. I was doing a shot every six months towards the end, the funding dropped down to a trickle. So I got bored and decided to take my kids to San Diego to see their grandparents so they would see them while they were still alive. I left the project in the hands of my collaborators. They did a couple more shots, and I came in as a consultant on a few more shots, but then the funding turned off and so there was a dead period–no shots from 1998 through maybe 2000. Then in 2000, just before 9/11, there was some interest in the stuff through DARPA. Long story short, they were able to take the supergun–SHARP–to Vandenberg Air Force Base for storage for potential shots, but the funding never materialized.

Then 9/11 came along and everything changed–in terms of R&D, this country lost almost a decade because of that. I got wrapped around the axle, too–I had a nephew in the battle of Fallujah, so I ended up going and working on armor for a year or two, which was a righteous cause because you don’t want your guys to be killed by these other folks. We might have been successful and pulled off some funding and done some shots into space, but who knows–you can’t go back in time.

A long thin artillery-style gun lying along the base of a valley, firing a projectile into a solid block with smoke pouring from the end of the gun.
Project SHARP firing in Livermore National Laboratory.
Then in 2010 you founded Quicklaunch, right?

Yeah–it might have been 2009. I was one of the three founders of Quicklaunch. There was the three of us that had been involved with the supergun stuff, so we all kicked in some cash and some sweat equity, and pursued that. I don’t want to say anything out of line, so I’ll just say that you have to be able to get along with people, and everyone’s got to be willing to do their fair share.

Can you talk about the idea behind the company and how you were planning to make money from it?

Let’s say I was a third party. Let’s say I had a totally clean sheet of paper, I’d say: Well–this is a reusable first stage. You know what the cost of the space gun is–if you do the math, after a couple of lines of algebra, you know how long it takes to amortize the gun. Maybe it’s 10,000 shots, maybe it’s a thousand shots, some number in there–because you’re reusing this thing, so at some point it’s all paid off because you’re dividing by n. Say the gun’s a million dollars, and you do a thousand shots, then that’s a thousand dollars a shot.

You also have to circularize the orbit. You launch out of the atmosphere–say at a 30-degree launch angle, so you burn through a lot of atmosphere. You burn three or four inches of nose off the forebody of the vehicle, you get an aeroshell made out of carbon/carbon. As Elon showed, these ablatives can be anything–an ablative material to protect the nosecone is not exotic. Some of the earliest ablatives were just wood–people used oak, cork, anything. Even steel can work. Anything’s an ablative. But carbon/carbon is pretty nice. Water is even better, so you can do exotic, weird things with that. You can do ablation, no problem.

Then you can do a rocket motor that takes high G-forces–that’s been done before. So that’s the second part of the technology pyramid. You can do either a liquid or a solid–solids are much easier to build than liquids, they don’t have the internal plumbing issues that you have with a liquid. The problem with solids is turning them off. I like hybrid motors. They all work.

That’s inside the projectile, right?

Correct, that’s inside the projectile. You launch that at six kilometers per second, and you lose half a kilometer per second [.3 miles per second] going through the atmosphere. But your total delta-V budget is about nine kilometers per second [5.6 miles per second] to get it to low Earth orbit, so you need to add three with the rocket motor. When all the smoke clears, you have a payload fraction that’s close to 20 percent–of the original weight of the vehicle inside the barrel. That’ll fly through the air, it’s easy to calculate the shocks off this thing and it’ll survive the atmosphere. You’ll burn a little bit of the nose off of it.

Once it gets to 100 kilometers [62 miles] of altitude, you blow the aeroshell off because that’s the part that absorbed the heat and gets trashed by the atmosphere. Then you have a nice, pristine little rocket that’s gravitationally coasting to 300 or 400 kilometers [186 to 249 miles] above the Earth. When it gets close, you turn the rocket motor on and then it supplies the remaining push to to get the rest of the way into a nice orbit–a circular or elliptical or whatever orbit you want.

What’s so great about this stuff to me is that it’s so simple compared to the stuff I used to do. The equations of motion–Newton’s laws–are so nice. You can get a little spreadsheet and work them out in three minutes. It’s all quite understandable–that’s what I like about it.

6 km/s is equal to (per Google) 13421.6 miles per hour.

Your job sure would be easier if you had that much push at the time you start your first stage.

The article itself is from 2014 ... https://www.howwegettonext.com/qa-dr-john-hunter/

You might enjoy reading about his experiences in Star Wars and after.


Note: The copy from the article captured more than I'd planned, but FluxBB took it so I'll leave it there.

(th)

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#346 Today 09:46:47

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 5,620
Website

Re: GW Johnson Postings and @Exrocketman1 YouTube videos

It's unclear to me,  but it sounds like he's using hot hydrogen at pressure to push the projectile,  not combusting.  He does evacuate the barrel,  because you only want to push the projectile out of the barrel,  not it plus a mass of air, too.

I think his estimate of half a km/s velocity loss is too low.  My slinger launch drag loss numbers run much higher than that.  More than 2/3 of the muzzle velocity gets lost in the first 10 seconds.  Then you're in the thin air and it loses very little from there.  It's why the velocity-time plots are shaped the way they are.

His estimates of SpaceX first stage entry speeds at Mach 9 or 10 are quite wrong.  The staging velocity is actually quite low: ~2 km/s,  which is only about Mach 6 or 7,  and it takes place essentially exoatmospheric.  They do an entry burn to slow speeds down to around Mach 2.5 to 3.5 for hitting the atmosphere,  heat-sinking their way through the brief heating pulse with their aluminum Falcon cores.  Steady state,  aluminum is only good for Mach 2.5 speeds.  The boost-back burn is a slow arcing trajectory with an entry speed Mach 3 to 4. That's too high for aluminum.

You'll note that Starship/Superheavy has a similar staging speed and altitude,  but does no entry burn,  because stainless steel can take the heat steady-state at Mach 3.5.  The boost-back burn puts it on a slower arcing trajectory,  specifically to limit entry speed to something the bare steel can take.

He's looking at a gun trajectory that apogees-out at orbital altitude,  something not seen with the slinger.  Note also how he talks about the extreme heating and the ablative required to survive it.

Yes,  my 2-D Cartesian trajectory spreadsheet could model such projectiles,  given a muzzle velocity and a launch angle.  It is the same as what I was doing for the slinger,  just more extreme.

GW

Last edited by GW Johnson (Today 09:50:15)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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