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#626 2026-04-09 10:24:32
- GW Johnson
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- From: McGregor, Texas USA
- Registered: 2011-12-04
- Posts: 6,264
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Re: GW Johnson Postings and @Exrocketman1 YouTube videos
Today's "Daily Launch" from AIAA finally brings up the heat shield issue facing Artemis-2 as it heads to re-entry. The link was to a Scientific American article of some kind. Not all the supposed facts quoted in it were correct, but the concern over char cracking leading to the shedding of chunks of char was correctly pointed out.
Myself, I think the odds are good that the crew will come home just fine. Where I differ with NASA is that I think the same damage seen on Artemis-1 will happen to Artemis-2's heat shield, despite switching to a non-skip, single heating pulse entry. It might be less than what happened to Artemis-1, or it might not. But if ANY chunks at all get shed, then NASA was wrong and I was right!
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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#627 2026-04-22 06:43:19
- tahanson43206
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Re: GW Johnson Postings and @Exrocketman1 YouTube videos
This post is reserved for a set of files GW Johnson sent by email on Tuesday 2026/04/21
I'll return to this post later today, Wednesday 2026/04/22
Work plan:
1) three pdf's in HeatShieldArtemisII folder to Dropbox
The three pdf's were stored in Dropbox
2) Link three pdf's from Dropbox to this post
https://www.dropbox.com/scl/fi/sp0kxa1o … w1mzq&dl=0
Above is Entry By Hand Article using spreadsheet from Orbits Course
https://www.dropbox.com/scl/fi/udi4mzuk … 0ptpm&dl=0
See notes below for content
https://www.dropbox.com/scl/fi/auanvzc5 … nnabe&dl=0
Study of Orion heat shield after Artemis II flight
3) Add text from email to explain links
Test from email:
First: there is "Entry By Hand Article.pdf", which shows exactly how to
use my entry spreadsheet and do really interesting things with it. There
are slides and presentation notes for this.Second: there is "Entry Study.pdf", which shows results and comparisons
for a small probe with either a conical heat shield or a blunt heat
shield, at Earth from LEO and lunar return, and at Mars from direct entry
off a fast interplanetary trajectory. All of that gets compared to an
Apollo returning from the moon, or from low circular orbit, at Earth.There are slides and presentation notes for this, too.
Third: there is "Quick First Look at Orion.pdf, where I ran a spread of
entry angles for an Orion lunar return, trying to figure out how to use my
simple tools to at least bound what Artemis-2 really just did. No slides
yet, but there will be.If you want to post any of this stuff on the forums, be my guest.
Updates completed 2026/04/22 at 23:27 UTC
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#628 2026-04-28 12:17:27
- tahanson43206
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Re: GW Johnson Postings and @Exrocketman1 YouTube videos
This post offers a link to a document prepared by GW Johnson:
https://www.dropbox.com/scl/fi/s3r092rt … scnaw&dl=0
Preliminary Evaluation of Artemis II heat shield performance.
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#629 2026-05-16 07:35:48
- tahanson43206
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Re: GW Johnson Postings and @Exrocketman1 YouTube videos
This is what a post to LinkedIn by GW Johnson looks like:
<snip>
Gary Johnson’s picture
Gary Johnson posted: Entry Model Heat Shield Pressure This is the second of three postings about…
<snip>
GW Johnson is posting regularly on the Wordpress blog, occasionally on YouTube, occasionally on NewMars and lately on LinkedIn.
If anyone spots additional coverage of GW Johnson topics, please post a report here.
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#630 2026-05-16 12:55:41
- tahanson43206
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Re: GW Johnson Postings and @Exrocketman1 YouTube videos
Todo list for updates for GW Johnson:
1) spreadsheet update
Status: saved local
Todo: Dropbox and link to forum <done>
2) new pdf
Status: saved local
Todo: Dropbox and link to forum <done>
PDF document: Launch to Low Earth Orbit Study - Presentation
https://www.dropbox.com/scl/fi/3q2p3aj4 … 9h40b&dl=0
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#631 2026-05-23 06:14:31
- tahanson43206
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Re: GW Johnson Postings and @Exrocketman1 YouTube videos
For GW Johnson re Starship flight ...
There were a couple of nice touches by the Communications Team ..
1) There was a drone flying at the target site in the Indian Ocean.
It showed the Starship falling over slowly and then exploding with plenty of fireworks action
2) The cameras on the deployed simulated satellites showed the Starship in flight.
Naturally we saw the ** top ** of the Starship, since the deployment bay door was on top of the vehicle.
The views from inside the cargo bay were well done, including views from overhead, beside the slider, and aft of the slider.
3) The camera attached to one of the fins gave us a nice sense of the movement of the fin in flight.
According to reports there were 52 cameras on this mission, and perhaps more footage will become available.
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#632 2026-05-31 05:58:31
- tahanson43206
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Re: GW Johnson Postings and @Exrocketman1 YouTube videos
GW Johnson send me a link to a YouTube video about heat shields... The video is long because it covers a variety of heat shields, and it repeats itself quite a bit. Details are abundant. On balance I think it was worth my time. I played it without audio. GW played it with audio and reported that the AI voice mispronounced a few words.
URL here: I misplaced the link. I'll try to find it and will ask Dr. Johnson to send it again.
And! Here it is: https://www.youtube.com/watch?v=S5xuB5DVS8U
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#633 2026-06-05 11:49:29
- tahanson43206
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Re: GW Johnson Postings and @Exrocketman1 YouTube videos
For GW Johnson re post by HOP...
http://newmars.com/forums/viewtopic.php … 63#p239663
Your post seems to miss the point.... HOP was not talking about space elevator to the surface of Mars.
He was talking about passing mass between the Moons.
This is an advanced concept in orbital mechanics.
It will be interesting to see if you can recreate his calculations.
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#634 2026-06-17 18:15:57
- tahanson43206
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Re: GW Johnson Postings and @Exrocketman1 YouTube videos
This post contains an opinion piece by GW Johnson.
It starts from the post by Calliban about the recent SpaceX IPO,. and ends up offering a vision for a fully realized transportation system for Earth/Mars.
I regret not knowing how to reformat the file so that the arbitrary carriage returns from email are removed. There may be an easy way to do that, but if there is and I knew about it, I've forgotten.
Myself, I see little direct connection between what happens in the
"financial world" of stock trading, and what happens in the "real world"
of actually building hardware and doing things with it. The one is about
obtaining money, the other about building hardware. The actual connection
is only that hardware is expensive. Politics (which utterly controls and
permeates most of NASA) usually impairs both worlds (but especially the
real world), to the point of stopping or damaging a lot of real-world
hardware efforts. The politicians want for themselves the money needed to
build the hardware, simple as that. That assessment may be pessimistic,
but it is realistic.The original Mars mission plans were drawn up during the Apollo moon
mission efforts. They were not carried out because the cost was very high
and politics would not allow it. The very same pessimistic
politics-afflicted situation has prevailed for over half a century since
then, and it shows up in the per-launch price of SLS-Orion. After half a
century doing nothing but LEO stuff, NASA is proving to be far less
capable about going back to the moon at all, much less efficiently., than
it was in the 1960's.That leaves private outfits like Musk. Personally, he is far better at the
money, than he is about the hardware. I say that because SpaceX has ZERO
experience malking rough field landings with ANY of its rockets, and TESLA
is still afflicted with its self-driving software that kills people,
violent battery fires, and some other recalls here and there that should
not be. Plus, for a while there during the first Starship test flights,
he kept getting into trouble with the FAA by violating his launch license
terms, since he doesn't believe that other people's rules apply to him.The only strategic thing that Musk did that was right, was
understanding that costs to go to the moon and Mars must be
lowered drastically, in order to get the politicians out of the way,
since their only excuse not to go, was cost. A lot of others realized
that too, but Musk was the first one to come up with enough money to try
doing it.I think his Starship/Superheavy will be the same leap forward as a
surface-to-LEO transport that his Falcon-9 and Falcon-Heavy were before.
Getting first stage reusability by flying it back and landing has been a
huge success, enabled entirely by the low return speeds allowing entry
without a heat shield. Getting upper stage reusability has been very hard
indeed, because now the upper stage must be a fully-qualified entry
vehicle, plus it must have a means of landing, and those very seriously
compromise the design! Which inherently means a refueled Starship going
outside LEO is not the best design for those beyond-LEO jobs, although it
can do them! Plus, SpaceX has zero experience landing things on rough,
soft ground. Their Starship design so far reflects nothing credible yet,
regarding making landings on the moon or Mars.Going to Mars (and back) inexpensively requires 9 transportation
infrastructure elements: (1) low-cost surface-to-LEO heavy-lift transport
(we are getting there!), (2) low-cost surface to LMO modest-lift transport
(does NOT yet exist!), (3) elliptic departure/arrival at Earth using tug
assist, as reusable stage designs that only fly in space (does not yet
exist but very soon could), (4) the Earth station in LEO that assembles
and fuels interplanetary vehicles, and refuels the tugs (does not exist,
but most certainly could), (5) a proper orbit-to-orbit transport that only
flies in space, but that can be refueled and reused (and if crewed provide
both radiation protection and artificial gravity), which as yet DOES NOT
EXIST, but it certainly could, (6) elliptic departure/arrival at Mars
using tug assist, as reusable stage designs that only fly in space (does
not yet exist, but very soon could), (7) the Mars station in LMO that
services and fuels interplanetary vehicles, and refuels the tugs based
there (does not exist but certainly could), (8) propellant manufacturing
capability on Earth (already long-established), and (9) propellant
manufacturing capability on Mars (DOES NOT YET EXIST).You can get started at Mars with only items (1), (3), (4), (5), and (8),
aimed initially at establishing item (9), and then adding items (2), (6),
and (7). Most of the same things work for the moon, except that the
vehicle making the voyage from LEO to LLO need not be
interplanetary-capable, and if crewed, need not provide artificial
gravity, simply because the flight time is mere days. The Gateway halo
orbit about the moon was NASA's version of elliptic departure and arrival
at the moon, except they botched it by (1) compromising to an unstable
orbit trying get SLS/Orion into it with the propellant to return, and (2)
they failed to put the station in LLO, leaving it on the ellipse where the
surface is very hard to reach.Bear in mind that the vehicles used in items (1), (2), (3) (5), and (6) all
have vastly-different and conflicting design requirements. You do NOT want
to try to perform more than one vehicle function with any one vehicle
design, it will be needlessly too heavy, inherently. Adding greatly to
expense. And if it gets expensive, the politicians will stop you from
trying, as they have been doing for half a century now.Bear also in mind that the tank farm function of the LEO and LMO stations
(or any LLO station), items (4) and (7), require propellant transfer in
zero-gee without ullage thrusts or accelerations. For storables, that
already exists in the form of bladdered taks with the bladders squeezed by
modest gas pressure. For cryogenics, that capability only exists as
orbit-altering ullage thrusts or accelerations, although I have come up
with the vane tank as a likely-viable-in-the-short-term alternative,
meeting all the requirements for a tank farm at a station whose orbit MUST
NOT BE ALTERED by every single transfer operation.If you want to post this email as an evaluation on the forums, be my
guest. I may try to create a slide show out of this. It's a good outline
for one.GW
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#635 2026-06-20 18:01:32
- tahanson43206
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Re: GW Johnson Postings and @Exrocketman1 YouTube videos
This post is reserved for links to documents prepared by GW Johnson...
I put together two slide shows, complete with presentation notes (but no
documents), regarding getting low-cost Earth-Mars transportation. One is
for technical audiences, focusing upon the numbers (Earth-Mars
Transportation). The other is for non-technical audiences, focusing upon
the strategy (Rapid Progress Not Dead). Our NSS friends might be
interested. 2 ppt and 2 pdf files attached. Post them if you like.
I'll try to have links to the documents set up this weekend.
They are stored on the local hard drive for the moment.
And here they are:
1) https://www.dropbox.com/scl/fi/fuywx8s2 … u3p5e&dl=0
rapid progress not dead Powerpoint
2) https://www.dropbox.com/scl/fi/xfamdv1a … bnpyd&dl=0
Presentation Notes for Earth Mars Transit
3) https://www.dropbox.com/scl/fi/7178btq7 … mrp62&dl=0
Presentation notes for Rapid Progress Not Dead Yet
4) https://www.dropbox.com/scl/fi/ac82hqpn … zcmu2&dl=0
Earth Mars Transportation PowerPoint
Comments about these files are welcome.
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#636 2026-06-26 20:24:34
- tahanson43206
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Re: GW Johnson Postings and @Exrocketman1 YouTube videos
This post is about work GW Johnson is doing to protect cryogenic propellants from heating in space.
The target timeframe is 2 weeks (two), and the method in study is use of a combination of sturdy materials and highly insulating materials to survive high levels of acceleration as will be needed by Dr. Johnson's Space Tug designs.
There is a pdf and a presentation:
LH2 standoff concept is the theme:
https://www.dropbox.com/scl/fi/jrujmr1a … l90uz&dl=0
https://www.dropbox.com/scl/fi/zyjbwa0g … xalh8&dl=0
Comments are welcome.
This is a work in progress, and GW has not yet found the combination needed for the two week lifetime.
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#637 2026-06-28 12:15:11
- tahanson43206
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Re: GW Johnson Postings and @Exrocketman1 YouTube videos
Here are two more files generated by GW Johnson while investigating how to store cryopropellants for extended periods in space.
Presentation notes for Multiple Layers study:
https://www.dropbox.com/scl/fi/3u4zsptr … m0tmz&dl=0
Multiple layers study
https://www.dropbox.com/scl/fi/ketjczqm … 2no74&dl=0
Dr. Johnson will be available to take questions this evening, if anyone is curious to know more.
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#638 2026-07-05 11:32:35
- tahanson43206
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Re: GW Johnson Postings and @Exrocketman1 YouTube videos
This post is a first installment .... Dr. Johnson prepared a slide to help students to understand why it is advantageous to change orbits at apogee or perigee.
Here is the text ahead of the image. The image itself is on my local drive at 13:30 local time. It needs to be copied to the image server and linked to this forum.
:
Here's a sketch that shows why making changes to elliptical orbits has the
apoapsis or periapsis the preferred location for making those changes.
Attached png file. Might should be be added to some of the elliptical
orbit stuff in the orbits+ course materials linked from the forums.Think of it as the thrust force doing work upon the vehicle as it moves.
That work energy partitions between potential and kinetic energy,
depending upon its force orientation relative to the direction of gravity.
The thrust component that changes potential energy does NOT change
kinetic energy. Not changing KE, expressed as a required to desired speed
difference ratio, is the gravitational loss factor.That loss factor minimizes to 1.000 only where the speed direction is
perpendicular to the radius along which gravity acts. For an elliptical
orbit, that is only at the periapsis and the apoapsis. Those two points
are the preferred locations for making orbital changes, with minimal
gravitational loss. Making a speed change at periapsis affects apoapsis
radius, and vice versa. (For parabolic or hyperbolic orbits, there is
only the one point to make a change: the periapsis.)You can make changes anywhere along the orbit, but there are small
gravitational loss factors that ratio up the desired dV to the dV you must
use in the rocket equation. And the effects are no longer simple to
calculate.GW
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#639 2026-07-08 19:41:41
- tahanson43206
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Re: GW Johnson Postings and @Exrocketman1 YouTube videos
GW Johnson prepared three documents to help with study of orbital calculations. They were uploaded to Dropbox 2026/07/08, and linked to this post:
Answering Questions .. Departure and arrival using Space Tugs:
https://www.dropbox.com/scl/fi/0l4ey1u1 … huohf&dl=0
Elliptic Departure Arrival Operaiions
https://www.dropbox.com/scl/fi/qfntxhr5 … brn4k&dl=0
Extra Details about Orbits:
https://www.dropbox.com/scl/fi/b5v3uspo … k2ija&dl=0
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#640 2026-07-17 11:57:34
- tahanson43206
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Re: GW Johnson Postings and @Exrocketman1 YouTube videos
For GW Johnson!
Thanks for the report on the SpaceX test of Version 3 of the Starship vehicle combination.
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#641 2026-07-23 08:56:02
- GW Johnson
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- From: McGregor, Texas USA
- Registered: 2011-12-04
- Posts: 6,264
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Re: GW Johnson Postings and @Exrocketman1 YouTube videos
From AIAA’s “Daily Launch” email newsletter for 23 July 2026:
SPACE
After nearly 30 years, NASA realized this near-Earth asteroid is actually a comet. The discovery may help us defend the planet some day
Astronomers discovered that a near-Earth asteroid is actually a comet that could help scientists identify more hidden comets and improve planetary defense.
-----
My take on it:
Somewhere on these forums, some years ago, I opined that there really was no distinction between type C asteroids and comet cores, except that “comets” have ices mixed in, and the “asteroids” do not.
Nearly everything we have seen of small bodies beyond Saturn would classify as “comets”, and most things closer in have lost their ices to evaporation over geologic time, and so we classify them as “asteroids”.
There is the likelihood that ice content varied with formation distance from the sun, yes, but anything small that has remained in the same place over geologic time would have more or less found its equilibrium ice content. Inward of Saturn, that is likely pretty near zero.
The asteroid described in the article is a near-Earth asteroid, but it very most likely has not been in that orbit for eons of time. If it had, it would be dry of ices.
On the "asteroid defense" aspect:
If a body can be determined to have ices, then a beam of laser or maser energy could be used to heat those ices under a local surface spot, creating gas jets that might change the orbit over time. Exactly how that might be done is not known at this time.
This does require long warning time, something we do not have for most perturbed "comets" coming in by surprise from somewhere out near the Oort cloud or Kuiper belt.
GW
Last edited by GW Johnson (2026-07-23 09:04:13)
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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#642 2026-07-23 12:47:01
- tahanson43206
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Re: GW Johnson Postings and @Exrocketman1 YouTube videos
Here is the image that is supposed to go with Post #641
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#643 2026-07-28 14:37:39
- tahanson43206
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Re: GW Johnson Postings and @Exrocketman1 YouTube videos
For GW Johnson re update to new Spiral Launch topic.
The 70% figure just to reach circular orbit is good to know!
The option of using a maglev railroad to boost the vessel to that 70% velocity might be workable, but a small circularization burn with chemical propellant would still be required. If this method were used, then the amount of chemical propellant would be reduced to whatever amount is needed to lift the perigee up to the apogee altitude.
It might be possible to determine what percentage of the launch must be allocated to chemical propellant. I am guessing the amount needed will be at least 1% of the total, but that is just a guess.
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#644 2026-08-05 11:09:46
- tahanson43206
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Re: GW Johnson Postings and @Exrocketman1 YouTube videos
For GW Johnson re Silicon Oxygen as propellant ...
https://newmars.com/forums/viewtopic.ph … 74#p240774
The answer to your question is availability of raw material.
Silicon dioxide is available in abundance on the Moon and Phobos, and apparently elsewhere in the solar system.
The method should NOT be used on Earth or anywhere that living creatures might breath in the nanoparticles.
However, for propulsion of a massive ship such as RobertDyck's Large Ship, it should perform well and cost nothing (or very little) compared to anything shipped from Earth.
The return flight from Mars can be refueled from Phobos using Solar Power, without lifting anything at all from Mars.
However, the return flight needs to be planned so the exhaust goes to deep space and not back into the atmosphere of Mars.
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#645 2026-08-05 16:39:56
- GW Johnson
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- From: McGregor, Texas USA
- Registered: 2011-12-04
- Posts: 6,264
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Re: GW Johnson Postings and @Exrocketman1 YouTube videos
What is available "out there" is NOT silicon, but various forms of silica, the oxide of the mineral! It takes enormous energy to convert a pound of that stuff into the pure silicon necessary for combustion with oxygen! This stuff is not mine-able "for free" out there! It is NOT like coal or oil. Or natural gas. Or any other fossil fuel.
It will take something like 3-D printing of the fully-purified silicon, to create the microscopic passages through the mineral form that are required to get "efficient" combustion of silicon Si into silica, the silicon dioxide (SO2). That is NOT WITHOUT SERIOUS ENERGY COST!
And I have already opined on the problem of consensed forms not contributing to thrust and impulse from a nozzle. Liquids and solids are incompressible, and contribute NOTHING toward nozzle thrust production. PERIOD!
I simply do NOT see the "advantage" of trying to go this route. If it ain't "nearly free" for the taking, what is the point? And it ain't!
GW
Last edited by GW Johnson (2026-08-05 16:44:54)
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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#646 2026-08-07 10:54:19
- tahanson43206
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Re: GW Johnson Postings and @Exrocketman1 YouTube videos
This post is to display a link to a study done by GW Johnson about the inflatable heat shield concept tested by NASA.
https://www.dropbox.com/scl/fi/tzu7fwhd … tkpq7&dl=0
Attached is the pdf file for the latest version of my entry study for the LOFTID inflatable heat shield, that Bob Clark posted about. This version replaces anything I previously sent, being far more complete. If you decide to post it at all, it should go in my post #2358, in the "Starship is Go" thread, under "human missions".
Update: In private correspondence, GW Johnson asked several questions about LOFTID... here are two ...
1) What temperature was recorded in the backshell of the inflatable heat shield.
2) What covering was provided for interior
A related question would be...
Since this was a NASA project, all data should be available to the public.
? If so, where is it?
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#647 Yesterday 06:57:44
- tahanson43206
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Re: GW Johnson Postings and @Exrocketman1 YouTube videos
GW Johnson expressed interest in details of the LOFTID inflatable heat shield experiment in 2022. In particular, GW asked about measured temperatures behind the shield. I asked Gemini to look for information and it came up with what looks potentially helpful.
Thank you for your deep research, and for your careful presentation of facts and sources. Before we explore the options you offered, please prepare your detailed reports for our elderly forum. We use BBCode which is not the most advanced. The good news is we seem to support all standard text formatting and all colors. We are limited to just two fonts: normal and 'h' We do not recognize size or horizontal lines. We do support list for items that need to be set apart.
LOFTID Mission Overview & Engineering Summary
The Low-Earth Orbit Flight Test of an Inflatable Decelerator (LOFTID) was launched on November 10, 2022, aboard a United Launch Alliance (ULA) Atlas V rocket from Vandenberg Space Force Base. The primary objective of the launch was to deploy the NOAA/NASA JPSS-2 weather satellite. Following satellite separation, the Centaur upper stage initiated a planned de-orbit maneuver to execute a dedicated flight test of NASA's 6-meter (19.7-foot) Hypersonic Inflatable Aerodynamic Decelerator (HIAD).
The test demonstrated atmospheric re-entry from low-Earth orbit, proving the feasibility of large-scale inflatable heat shields for heavy-mass payload descent.
Structural Architecture & Thermal Materials
The inflatable structure and Thermal Protection System (TPS) were engineered to maintain structural rigidity under aerodynamic loading while isolating internal components from intense radiative and convective heating.
Torus Stack (Inflatable Structure): Formed from a series of concentric inflatable rings (tori) made of a high-strength para-aramid polymer weave. The assembled rings created a 70-degree blunt sphere-cone geometry held together by structural webbing tied to a rigid central hub.
Outer Thermal Shield: The exterior face exposed to the airflow was constructed from woven Silicon Carbide (SiC) ceramic fabric, capable of withstanding extreme surface temperatures while maintaining flexibility during packing and inflation.
Internal Insulation: Beneath the outer ceramic fabric, multiple layers of porous ceramic felts and aerogel-based insulation worked to restrict conductive heat transfer through the depth of the shield.
Gas Barrier: A continuous, heat-resistant polymer/silicone film layer was positioned behind the insulation layers to prevent hot gas penetration into the inner inflatable tori structure.
Peak Re-Entry Conditions
During entry into Earth's upper atmosphere at approximately 8 kilometers per second (Mach 25), the vehicle recorded the following key performance parameters:
Peak Deceleration: Approximately 9 Gs.
Peak Heat Flux: Approximately 40 Watts per square centimeter.
Front Surface Peak Temperature: Between 1,400°C and 1,600°C (2,550°F to 2,910°F) on the leading SiC face.
In-Depth Thermal & Backside Temperature Performance
Data collected by internal thermocouple arrays and fiber-optic temperature sensors revealed significant thermal attenuation across the shield profile:
Temperature Drop Across Insulation: The flexible thermal protection system dropped the thermal gradient by over 1,000°C across a depth of less than 2 inches (5 centimeters).
Backside / Gas Barrier Interface: The maximum operational limit for the synthetic structural tori and adhesives was set at 400°C (752°F). Sensor measurements during peak heating confirmed that temperatures at the gas barrier interface remained safely between 250°C and 350°C.
Internal Instrument Section: Behind the central rigid hub, ambient temperatures inside the vehicle body remained within standard operational limits for commercial payload electronics throughout re-entry, recovery, and splashdown.
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#648 Yesterday 07:31:55
- tahanson43206
- Moderator
- Registered: 2018-04-27
- Posts: 25,496
Re: GW Johnson Postings and @Exrocketman1 YouTube videos
For GW Johnson ... in reading over reports of NASA's work on inflatable shields, I spotted the signs of mental blocks in play.
As you know, mental blocks exist without human awareness. The block of interest here is captured in a single line of one of the recent reports. The reason for NASA to investigate inflatable heat shields was because no standard heat shield can be larger than the body of the shroud in which such a shield is lifted to space.
But of course, that is NOT the case for your design. Your design can be shipped in sections and assembled in space for flight.
Thus, your non-inflatable design can be as large as is needed.
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#649 Yesterday 09:20:52
- GW Johnson
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- From: McGregor, Texas USA
- Registered: 2011-12-04
- Posts: 6,264
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Re: GW Johnson Postings and @Exrocketman1 YouTube videos
If you look at about 700 F as quoted for the inflatable membrane interface, plus about 590 F drop through its insulation layer, also as quoted (1000 C), you get a backside surface temperature for the inflatable heat shield of about 1290 F. Which is NOT VERY FAR AT ALL from what I estimated with my crude little by-hand entry modeling technique (about 1300 F)!
Which proves my other point that even wake zone backside surfaces need heat protection, at entry speeds as low as 8 km/s, if they are not 2000-2500 F-capable superalloys.
The front surface quotation was 1400-1600 C (2550 F to 2910 F) is above my little estimate, as was the 9 gees. Silicon Carbide is a refractory re-radiator, not an ablative, so my surmise that their entry averaged a little steeper than the 2 degrees I analyzed, is therefore confirmed indeed! I could probably very closely duplicate their numbers at something in the 3 to 5 degree average angle range, but I am NOT going to waste my time doing it!
My main point is that going to very low ballistic coefficients, which LOFTID successfully did, does NOT relieve you of heat protection requirements during entry. Their 25 kg/sq.m corresponded to around 40 W/sq.cm, not far from what I estimated, and far below the ~200-ish W/sq.cm you get at ballistic coefficients nearer 300 kg/sq.cm.
But the re-radiation temperatures are still quite high! That's the temperature to 4th power variation of the Boltzmann equation for thermal radiation, inverted to yield a temperature that produces a certain re-radiation rate. It means for a factor-12 reduction in heating rate to be re-radiated, your surface re-radiation absolute temperature is crudely only 12^0.25 = 1.86 times smaller!
There is simply no way with any materials technologies that we have, including these new inflatable heat shields, that we are going to be able to delete the need for heat protection, by going to a very low ballistic coefficient. Thermal re-radiation physics and the well-established correlations for entry heating, simply will NOT allow that!
GW
Last edited by GW Johnson (Yesterday 09:33:53)
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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