You are not logged in.
Actually, Rob, I quite agree with you. Just don't expect anything out of "old space", and if I were you, I wouldn't expect anything out of NASA. Their track record since 1972 is actually NOT going anywhere but LEO, and the SLS/Orion/Artemis/Gateway thing is going to kill at least 1 crew, because there's nobody left who knows how to go further without killing somebody. All the ones who knew are long dead or retired. Which lack and that inevitable dead crew will put an end to NASA's space efforts as we know it. Today's NASA is very most definitely NOT the NASA of 1958-1972! Congress pretty much did them in, after 1972.
That puts it on "new space", and what I see there is some outfits more successful than others, but all of them in it up to their eyebrows just trying to fly things reliably. A lot of them won't be successful, because of the great difficulties. None of them are seriously working making propellants in situ, and none of them can work nuclear power, that being a government monopoly. There is some life support work going on, but not nearly enough.
For SpaceX, they got the Falcons going, then turned them into semi-reusable vehicles, and now they're in up to their eyebrows trying to make Starship/Superheavy work right! They are NOT putting any significant efforts into power supplies, life support, or making in situ propellants, because they can't! They are in way too deep at chronic overtime 70-80 hours/week, and they only hire people under 45 years old, who can put up with that for only a very few years. Which is EXACTLY why (1) they have high turnover, and (2) they keep having to learn from mistakes they made, while not learning from the mistakes made by others. That's been their pattern since they started.
I'm not complaining about the lack of progress in these mission-killing areas, I'm just observing. And I do not like what I see. For many years now.
If NASA were any good today, they'd be leading the necessary efforts toward propellant manufacture, power supplies, and life support with a bunch of contracts with "new space". But they can't, Congress won't let them, instead spending most of the money on pork-barrel projects that keep "old space" getting rich off corporate welfare while not actually accomplishing very much.
Without an effective NASA to lead the way, nothing useful is going on toward those 3 mission-killing lacks. THAT is what I observe!
GW
Rob:
Well, rocket vehicles are an operational, flying technology. Done "right" with adequate development and testing behind them, you can bet lives on them. I was looking at only deployable technologies that you can bet lives upon. That is why I was looking at the "impossibility" of how to land a fully-fueled Mars Ascent Vehicle! In practice, you do it as a multi-stage thing, where only the upper stage(s) are the actual ascent vehicle. Sort of like the Apollo LM. But as a craft that must fly in an atmosphere (both ways).
The propellant production on Mars is simply not an operational, ready-to-deploy technology. It will take years and (at least) $10M's to make it ready to bet lives upon. That can be done, but it doesn't happen quickly, not if done "right".
It is always one hell of a long way from small scale feasibility demonstrations to an operational technology that you will be betting lives on. "Long way" means large amounts of both efforts/resources and time. I see nobody scaling this up and trying to shake the bugs out of it. And you can bet your life that those bugs are there! The time to find them and root them out is NOT while your survival depends upon that equipment on Mars!
THAT is the long pole in the tent for any of the mission concepts that requite making propellant on Mars. And that includes SpaceX as well as any of the Mars Direct notions. To my way of thinking, it is a very long pole indeed! That has been known for a long time, and yet I see nobody actually working that problem, when it is the real "killer".
GW
To answer your questions ---
Picking up on your explanation of how the Apollo capsules were designed to survive Moon return, was the Orion capsule designed in the same or a similar way? YES
And ... is it safe to assume that if SpaceX attempts to return from the Moon directly, it must have ablative material around the entire vehicle? YES
And ... is it safe to assume that if ** anyone ** tries to return from Mars depending upon aerobraking, they will be subject to the same principles, except to a more extreme degree? YES
GW
That's a good plan, except for one thing: there are no feasible Mars Ascent Vehicle designs floating around as yet. These things have to be sent there fully fueled (somehow), landed, and still be viable on the surface for up to years at a time. NOBODY really has such a thing.
GW
With fewer and fewer flights available to the ISS for delivering crews, and with mounting losses on the Starliner program to cover its flaws that showed up in tests, I am unsurprised that Boeing might cancel the program and leave crew delivery to SpaceX. Costs are rising, far faster than any possible revenue, which is actually shrinking as the number of remaining flights drops. If all you care about is money (and reputation be damned), that is the "smart" thing to do.
GW
What happens on leeside separated-flow surfaces has the same driving temperature as the heat shield out front, but a far lower heat transfer coefficient, because the weakly moving fluid does not scrub the surface. Scrubbing raises heat transfer coefficients, quite dramatically. By around a factor of 10 between separated wakes and heat shield front sides in terms of heating rates. Heating rate is the area times the heat transfer coefficient times the driving temperature difference.
That wake zone heating rate reduction makes the wake-zone heating rate more nearly the same as the heat re-radiation rate of "dark" surfaces at practical temperatures near 1000-2000 F. That is true for Earth entry up to about 8 km/s, but no faster: the gas temperatures get too high, in turn driving up heating by convection rates, and re-radiation cannot keep up at the surface temperatures that known materials can withstand. The re-radiation is proportional to absolute surface material temperature raised to the 4th power!
That balance of effects is why the old Mercury and Gemini capsules had ablative heat shields, but bare metal backside surfaces. They never exceeded about 8 km/s at entry, and re-radiation could keep pace with the convective input, albeit only for rather exotic alloys. You can do it with stainless steel these days, at least in large sizes. However, there must be some sort of high temperature-capable insulation between that hot leeside skin and the capsule pressure shell within. The hot skin re-radiates both directions, if there is not. You cannot do this with fiberglass, it melts at 900 F. Has to be mineral wool capable of withstanding 1500-2000 F.
Apollo came back from LEO at the same 8 km/s speeds, but from the moon much faster (about 10.9 km/s). With convective heating proportional to velocity cubed, and plasma radiation (from about 9 km/s on up) even a higher power, the total heating is way more than factor 2.5+ greater. Apollo had the ablative heat shield, but it had the same ablative as a thinner layer all over its backside surfaces, too.
In addition to the higher driving temperatures far-outracing the re-radiation effect, the more brightly-glowing plasma sheath is becoming pretty much opaque to thermal re-radiation, cutting off that method of cooling entirely by about 11 km/s speeds.
You can estimate (crudely) the gas driving temperatures for convection, anywhere around the capsule including backside separated wake zones, quite simply. The effective gas temperature in degrees K is numerically equal to the flight speed in m/s. That's about a 10%-good estimate. Actual values are higher or lower by up to 10%, because of varying ionization-level effects. Yet, at 8 km/s = 8000 m/s bringing about 8000 K gas temperatures, who really cares about 10% error? The real point is, it's overwhelming. At 11 km/s, it's pretty near 11,000 K, etc.
There are no materials that can stand such exposures steady-state. Only on a short transient, and only if cooled somehow, by re-radiation and/or ablation. Above about 9-10 km/s, only by ablation. Theoretically, transpiration cooling might also work, but it has never been flown, and so is unproven as of yet.
GW
Standing the vehicle and doughnut upon a heat shield might work, given some sort of insulation and high-temperature skin for the doughnut and vehicle. That is a heavy solution, though. More so at Earth than at Mars. The worst case entry speed at Mars is about 7.5 km/s, pretty close to orbital entry speed (8 km/s) here at Earth. You are talking exposure of doughnut and vehicle to gas near 7500-8000 K in such circumstances, but without the harsh scrubbing effects. Mercury and Gemini did that as bare metal afterbodies, but with serious insulation between those exposed afterbody skins and the pressure shell of the cabin.
GW
Just bear in mind that these are projections for designs not yet built and tested. Not even Starship-1 has met the pre-build predictions for it. Things ALWAYS turn out different than expected in flight test. That is EXACTLY why we flight test.
GW
Aside from the large deceleration forces that lead to large forces in the members connecting the doughnut to the main vehicle, there is a serious and very-fatal shock impingement heating risk. The doughnut, and the members that secure it, plus the main vehicle, all shed bow shock waves during hypersonic entry. Doesn't matter which way the thing faces. If any of those shock waves impinge upon any adjacent structure, that adjacent structure overheats to destruction in a matter of a single handful of seconds, max.
This effect has been known since the Mach 6.7 flight of the X-15A-2 back about 1968. It is EXACTLY why no successful entry vehicle has EVER had parallel-mounted nacelles of any kind. It is EXACTLY why no hypersonic aircraft will ever resemble the layout of the SR-71. And id it EXACTLY why the Skylon airframe concept cannot survive entry without massive changes.
The doughnut concept makes a whole lot more sense for the airless moon, not very much for Mars, whose thin atmosphere is enough to cause severe hypersonic heating at orbital entry speeds.
GW
Void:
I like your idea of a sort of ring of cargo containers as the rough-field landing pad, for one-way cargo deliveries. I like it for airless worlds like the moon. I really don't think you could do entry with it at a world with an atmosphere like Mars.
I will say that I see quite a disconnect between concepts of early exploratory and experimental landings, and the process of building a colony. You cannot do those at the same time, nor can you do those with the same vehicles, not effectively, anyway.
Early exploratory landings should be small crews in small vehicles at multiple candidate locations, leaving behind enough hardware to become an experimental station should the site actually prove attractive. The idea is to find the best site for the colony, BEFORE you start to build it. These are very short stays.
The experimental landings are also small crews in modest vehicles, with a lot of hardware as cargo. These go only to the best one or two sites found by the exploratory landings. You add the cargo hardware to what was left at the site by the exploratory landing to create a base suitable for much longer stays, where you experiment with how to actually live off the land, but with deliveries from Earth to back you up if your experiments fail (and some will !!!).
Once you actually know how to live off the land "for sure", and you know the best site for the colony "for sure", ONLY THEN do you send lots of hardware and people in very big vehicles, to create that colony.
Anything else is getting the cart before the horse: a guaranteed recipe for failure. History says so.
GW
I've downloaded the pdf of the report. Will have to look closely at it. Thanks.
GW
Tom has loaded a link to the user's manual that I recently wrote for the latest version of the orbital mechanics spreadsheet into "GW Johnson postings and @exrocketman1 youtube videos" under "meta new mars". That link I copied and pasted just below. That latest version of the orbits spreadsheet has a link posted in post 20 of this thread, also copied and posted below. I put them here together for convenience. -- GW
user's manual, orbits spreadsheet
https://www.dropbox.com/scl/fi/icrjpdez … mx4yd&dl=0
orbits spreadsheet
https://www.dropbox.com/scl/fi/cxtpsx2n … nmkmv&dl=0
PS - I tested the links. They work.
The version of the orbits spreadsheet that the manual was written for is located at the link below, which was copied from post #20 in the "orbital mechanics class traditional" thread under "interplanetary transportation", in the Acheron labs" section. -- GW
https://www.dropbox.com/scl/fi/cxtpsx2n … nmkmv&dl=0
PS - I tested the link, it works.
The notion persists of a stolen 2020 election, despite 60+ court cases and all the other evidence since, saying ABSOLUTELY NOT!
I suggest that y'all quit taking internet BS from your favorite echo chambers at face value. About 99% of what I find "out there" proves to be utter BS. Mostly for profit, I might add. PLEASE go do some real, actual fact-checking before y'all spout any more of this CRAP! We have too much of it already!
Despite what you apparently believe, much of the mainstream media actually can be trusted to some extent, because of journalistic standards. The most notable exception is Fox "News", whose founder said long ago it was NOT news, it was right-wing entertainment! Nothing has changed since, except the virulence of the lies, which has increased. I have tracked it!
You should note that (1) I am a political independent who despises both the far right and the far left (and DESERVEDLY so!!!), and (2) I have not participated in this particular thread in a very long time, precisely because it is so fully consumed in far-right BS!
And I probably will avoid it for a very long time to come! Because I always get flamed for pointing out the real truths. And THAT ought to tell y'all something worthwhile!
GW
Void:
I'm still thinking about your "reverse staging" notion for some sort of 1-way lunar cargo transport. I really like the idea of using some sort of cargo "doughnut" as the landing "legs", to be left on the moon. I'm not at all sure we need to do lunar orbit rendezvous, it may actually be easier and more practical to just bite the bullet and fly direct from LEO to the lunar surface, and back to LEO.
If you make the propellant drop tanks long and thin, there is a small cluster that could return the core from the moon to LEO. Around that you add a layer or two to supply the propellants for a direct landing of the core and cargo. Around that is another layer or two that supplies the propellant to depart LEO fully assembled.
The LEO departure tanks could conceivably be returned to LEO by some sort of tug, from circulating on the transfer orbit to and from the moon. The lunar landing tanks would get ejected onto the lunar surface after landing, and stay there, for some other use there. The return tanks would definitely get returned to LEO, where they could be refilled and re-used.
The core is the engine set, a module with guidance and control equipment plus the power to run it, and the return tanks, plus an optional capsule if a crewed mission. As assembled in LEO, it would be that core covered laterally by layers of drop tanks comprising the landing set and the LEO departure set. Such tanks could be sent up pre-loaded to LEO in clusters by something large but economical like Starship/Superheavy. Definitely NOT SLS!
The cargo "doughnut" that doubles as "landing legs" is actually the most difficult concept. It cannot be a real circular doughnut shape, or it cannot easily be sent up to LEO. But it could be straight cylindrical segments with angled docking mounts, that could be assembled into a large segmented "ring" by docking modules together on orbit. These things could actually somewhat resemble shipping containers. The durability of such a thing makes it usable as "landing legs".
The thing to remember about landing legs is that the span of the pattern needs to equal or exceed the height of the center-of-gravity of the landing vehicle. That is where laterally-ejected drop tanks really "shines"! Starship/Superheavy is inherently unstable on rough ground, anywhere, precisely because it is tall and thin.
All in all, I kinda like your concept. For the moon. Mars is a different problem.
GW
Void:
Ah, now I understand. Thanks.
This is an old idea. If you have engines capable of many burns reliably, it makes very good sense. In the early days, we did not have engines that could even be re-started once, which is why this idea was not used long ago. That has changed very much in recent years.
The way around having to disconnect and reconnect the stack in order to discard empty tanks is also very old: cluster them in parallel and not series. Eject them straight out to the side. Just like the drop tanks off an airplane. This works very easily for something assembled by docking, in low Earth orbit.
In point of fact, this very staging technique was proposed in the Walt Disney 1958-ish flick about going to the moon.
GW
Void:
I don't know what the terminology "inverse staging" means.
GW
The suit contamination risk depends upon how much, and how long it has been exposed to vacuum. Gases would not be much of a problem, only liquids on the suit surface, which may be porous. And they evaporate quickly in vacuum when exposed to sunlight.
GW
Cannot argue with that assessment, SpaceNut.
GW
Void:
It's the same NTO and any-hydrazine propellants used in the old Apollo LM. Most of it comes out as combustion product gases to begin with, of which ammonia is the most toxic. Any unburnt, unevaporated liquids will evaporate rather quickly in the vacuum, whenever sunlit. I suppose some traces might get into the lunar regolith, but there would be very, very little. Probably not much of threat, especially to inherently-suited people.
Just best guesses on my my part.
GW
Not sure where to put these. From AIAA’s “Daily Launch” for Monday 7-29-2024:
Debris survives reentry:
AVIATION WEEK NETWORK
SpaceX To Shift Dragon Splashdowns To West Coast
In an effort to stem the chance that debris from discarded Dragon capsule trunk sections could reenter over populated areas, SpaceX will shift splashdown and recovery operations to the West Coast, the company said July 26. The decision follows the recovery of a piece of Dragon debris in Australia in 2022, indicating that—contrary to computer modeling—parts of the capsule’s discarded trunk can survive reentry heating.
My take on it: I have pointed out for years now that virtually nothing actually "burns up" on re-entry. Debris WILL make it through and crash to the surface, somewhere. Even from very insubstantial construction. Example: the Australians said they picked up about 75 tons of debris from Skylab that crashed in 1979 upon western Australia. Skylab was said by NASA to be about 85-90 tons at its entry. Not much at all burned up! Despite its shell being an aluminum S-IV Saturn stage.
-------
The end of Atlas-5:
SPACENEWS
ULA prepares for final military launch of Atlas 5 rocket
United Launch Alliance (ULA) is set to launch its final Atlas 5 rocket for the U.S. military on July 30. The classified payload, designated USSF-51, is scheduled to lift off at 6:45 a.m. Eastern from Space Launch Complex 41 at Cape Canaveral Space Force Station, bound for geostationary Earth orbit.
GW
From AIAA’s “Daily Launch” for Monday 7-29-2024:
Life on Mars?
THE NEW YORK TIMES
NASA Did Not Say It Found Life on Mars. But It’s Very Excited About This Rock
Scientists working with NASA’s Perseverance rover state emphatically that they are not claiming to have discovered life on Mars. But many would regard a rock that the rover just finished studying as “Most Likely to Contain Fossilized Microbial Martians.” The rock possesses features that are reminiscent of what microbes might have left behind when this area was warm and wet several billion years ago, part of an ancient river delta. The scientists clarified that they did not spot anything that they thought might be actual fossilized organisms.
------
By the way, that description of the traces matches exactly what the scientists found in the Allan Hills 84001 meteor from Mars, found decades ago in Antarctica. They announced they'd found fossils, and were repudiated for it at that time. Looks like the robot rover may have found confirmation they were actually right!
GW
If this souped-up Dragon could be launched by Falcon-Heavy, then it provides a way to use an existing rocket to send a manned capsule to low lunar orbit and back. Something SLS/Orion cannot do. Just substitute a crewed Dragon for the cargo Dragon, and use the same oversize service module. Add a small lander, and you could quickly reprise Apollo.
GW
From AIAA’s “Daily Launch” for Monday 7-29-2024:
ARS TECHNICA
NASA nears decision on what to do with Boeing’s troubled Starliner spacecraft
Astronauts Butch Wilmore and Suni Williams have been in space for 51 days as engineers on the groundwork through problems with Starliner's propulsion system. On Thursday, NASA and Boeing managers said they still plan to bring Wilmore and Williams home on the Starliner spacecraft. This weekend, Boeing and NASA plan to fire the spacecraft's thrusters in orbit to check their performance while docked at the space station. “I think we’re starting to close in on those final pieces of flight rationale to make sure that we can come home safely, and that’s our primary focus right now," Steve Stich, manager of NASA's commercial crew program, said
GW
Responding to the question about the definition of "impulsive". It is a "fuzzy" thing. But here is what I recommend.
"Impulsive" burns need to approximate instantaneous velocity changes, in the sense that (1) the radius from central body center does not change during the burn by more than something like 1 part in a thousand, and/or (2) the burn time is under about 5 parts in a hundred the duration of the orbital period. As a rule-of-thumb for lower Earth orbits, the vehicle should accelerate faster than 0.1 or 0.2 gees, preferably nearer 0.5 gees.
The first criterion prevents the added energy from partitioning into potential energy instead of kinetic energy, which is gravity loss. The second criterion is more of a practical thing. An "impulsive" burn at perigee or apogee of an orbit with a period near 90 minutes needs to occur within a single handful of minutes, to stay "near" that perigee or apogee.
GW