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Here's a notion for a quick habitat using something similar to a Bigelow inflatable. Have your equipment on a core structure to which the inflatable "shell" is already packaged around. This core has hard ends where the legs are. It sits on its side on those legs and inflates as an off-centered cylinder such that there is more volume above than below. The airlocks are also on the ends. You unpack your equipment inside, just mount nothing on the inflatable wall. Through something resembling an air mattress over it and inflate to not quite 7 mbar, as insulation and a meteroid shield. Throw an opaque tarp over that, and stake it all down. Voila: instant inflatable habitat, with all the gear already inside. Land it as a pallet and just set it up like a giant tent. There's probably a vertical-axis version, but stairs would be less convenient inside.
GW
Impaler: I dunno precisely how much a different entry orbit affects the heating drag. But, unless you're coming in at around escape velocity or more, it wouldn't be a lot different than any other entry. I used the surface circular orbit velocity as "representative" in my calculations: escape/square root of 2. From almost any closed orbit at low altitude the entry interface speed would be close to this figure.
From what I read, the heat shield on the Spacex Dragon is rated for a "free return" from Mars at some 50,000 ft/sec, beyond Earth escape velocity (about 36,000 fps) by quite a margin. Just a crude guess says such a shield might survive entry from LEO (about 25,000 fps) maybe 4 times before you ablate through it. KE proportional to speed squared, heating proportional to KE.
GW
All that I said in post no. 18 being what it is, I think the sense of Robert Dyck in post no. 1 is correct. We need a cheaper way to fly, one that is more or less independent of oil prices. If that's some nuclear engine, then so be it.
I'm not sure how this might be done at less than transoceanic ranges. But crossing ocean basins is flying across a fair fraction of the Earth's circumference. Once you're in that ballpark, an old science fiction idea rears its head as the best way to do things. Why not fly ballistic outside the Earth's atmosphere? The old "antipodes rocket" idea of Robert Heinlein. Actually, it makes good sense.
Once the range to be covered approaches half the Earth's circumference, the cost of accelerating high supersonic-to-hypersonic out of the atmosphere approaches the cost of cruising high subsonic over the same range. The cost of cruising supersonic over that same kind of range will never be as low, in my opinion, because of supersonic drag levels and supersonic aeroheating levels.
For a long range mission across an ocean basin, consider what it takes to reach Mach 3 to 6 on a short transient (minutes). Then look at sustained Mach 2 to 3 cruise (hours) vs that ballistic ascent into space. While you're coasting in vacuum, you can cool off by radiation. There is no drag. But cruising in the atmosphere at Mach 2 to 3 is very hot, and is done at very high drag.
Honestly, I have never understood why anyone would want to cruise supersonic in the atmosphere, when coasting in vacuum is so much easier to do. But, that's just me.
GW
Rune:
I used the data from the Glenn Research Center links you sent me to put together a sort of model of the Mars atmosphere for entry purposes. Extending the Glenn model to 100+ km altitudes is not very good, because the lapse rate is most likely wrong way up there. But the pressure is probably ballpark correct, and the density profile I got is conservatively too dense. Below around 28 km altitudes, it's probably not too bad a model.
I am still defeated by the notions of posting illustrations on this forum. I know those links you gave me are in English, but I do not share a dictionary with the writers of those instructions. So, I posted the model with the curves I got over at my "exrocketman" site: http://exrocketman.blogspot.com
All the guys:
This kind of model is a prerequisite to figuring out a landing scheme for landing large masses on Mars, either one-way or two-way. The bulk of the hypersonic deceleration should be taking place close to (or perhaps at, or even under) the 28 km I identified, and the chute supersonics and subsonics should be well below this altitude. At least it's a start.
I can rough out vehicles using pencil and paper from data like this, but it's just crude, order-of-magnitude stuff. Anything trustable in detail would require a trajectory code, which I don't have. Here's a first cut atmosphere model for those of you who might have such codes.
I'm going to dig out my pencil and solve this damned lander problem once and for all. One-way chemical, two-way chemical, and two-way nuclear thermal. This is going to take a while. Expect nothing quickly.
GW
Re: nuke B-36
It was the NB-36, not B-36N. This was a variant of an original 6-engine piston-prop design, not the intended design-that-didn't-work. There was a nuke turbojet engine design that they wanted to fly in it, but never did. They did fly a simple reactor and generated heat in flight. No real power output in usable form, though. That reactor flew inside a containment vessel tested to 500 mph impact against solid rock, on the rocket sled track at Holloman AFB, NM. The all-jet version of the B-36 came later, as the YB-60 8-engine prototype built and flown for the competition that resulted in the B-52, which in turn originally on paper was a turboprop resembling the Tupolev "Bear".
B-36 originally flew about 1945 or 1946 as a prototype with a single-tire main gear. Then B-36, B-36B, and B-36C flew configured with a 4-tire main gear truck (for safety's sake, since a blowout on the single tire design meant loss of aircraft and crew). All of these variants were 6 engine piston-prop, using the R-4360 4-row 28 cylinder radial engines of around 4000 SHP. From B-36D-on it was a 10-engine airplane: the same 6 piston-prop pushers, plus 4 early turbojets in two twin-engine pods, each out near the wingtip. B-36 is the ship with passages inside the wings out to the engines for in-flight maintenance.
I do not know which model of the B-36 was converted to NB-36 for the nuke flight tests. But I know they never actually flew the nuke turbojet. I don't know how much testing the nuke turbojet got on the ground, if any.
Re: nuke ramjet cruise missile
The Project Pluto cruise missile was a Mach 3 cruise, but very low altitude, ramjet. LTV Aerospace was airframe prime plus the inlet and nozzle guy, and AEC was to supply the reactor core. My father remembers this project, he was there when they did it, and told me what he knew. He didn't work on that one, though. Too busy designing the F-8 Crusader, among many other things. The shock wave alone was lethal to those on the ground, much less the spewed radiation. It would have killed more folks on the ground flying around, than with any warhead it could carry, and it carried a megaton-range fusion nuke.
This Pluto nuke ramjet thing got direct-connect tested on the ground at the Jackass Flats facility in Nevada on the old nuclear test site, adjacent to the nuclear rocket test facility. Some, but not all, of that gear is still out there, from both projects. Unlike NERVA, the Pluto guys were operating their reactor at a 10 deg F (5 deg C) margin above meltpoint for the reactor core supports. They had really bad erosion problems, never solved, unlike NERVA.
Re: earlier cruise missiles and jet aircraft
The V-1 Buzz Bomb of WW2 is often called the first cruise missile, but it was not. That distinction goes to a gyro-controlled pilotless biplane in WW1, which was Oliver Sperry's very first working automatic flight control and guidance system.
Gunther Diedrich at Argus Engine Works corrected some of the defects in Paul Schmidt's pulsejet tube to build the valved engine for that missile. He gave up work on a promising valveless pulsejet design to do that work for the Luftwaffe. The valve life averaged 45 minutes. Average flight time from France to London was 43 minutes. BTW, Luftwaffe test pilot Hanna Reisch (yep, a female!) was the first pilot to survive flight test flying the V-1. 6 died before her. She only died a few years ago. (I probably misspelled her name.)
Neither was the first jet engine to be flown a German turbojet in WW2. There was an Italian afterburning ducted fan that flew about 1939, but it was not the first, either. The very first jet powered flight took place in France in 1910 (yep, before WW1!!!), and it was accidental. Henri Coanda built two biplanes powered by an afterburning ducted fan, and accidentally took off and flew during a high speed taxi test. He crashed, but survived. The aircraft didn't. The surviving example still exists in a museum in France way outside Paris, BTW. It crashed because he had not yet trained himself to be a pilot.
We stand on the shoulders of the giants who preceded us. Sometimes it is really worthwhile to know who they were and what they did.
GW
Error correction: in post 121 above, I misremembered what I read about Curiosity's landing. The not-quite terminal velocity hanging on the chute approaching 2 km altitude from above is 100 m/s not 300 m/s. I have since calculated a soundspeed using the Glenn RC Mars atmosphere model, and it's right at 243 m/s from 2 km to the surface. That's 0.41 Mach for a terminal velocity at their chute mass loading, which is pretty near all that we can do. Compare that to terminal velocities in the 20-30 mph range for cargo and round personnel chutes here on Earth (0.026 to 0.039 Mach).
Rune: I'm glad you pointed me to that Glenn RC site. I have used it to generate profiles of temperature, pressure, density, and soundspeed to high altitudes on Mars. Below roughly 28 km, it looks pretty good. Above that, in the free-molecule flow regime (extreme low densities, too much mean free path length), the temperatures look anomalously low compared to Earthly profiles, which get very hot in the ionosphere. The soundspeeds look all wrong. I don't think I'd rely on that model for calculating entry drag and lift, the Mach numbers would look all wrong. Above 115 km, it predicts temperatures below absolute zero, so I cut that off as 4 deg K min.
Twinbeam: I think what we're talking about is not as different as it sounded at first. After having pored over that atmosphere model and using it to calculate Newtonian-flow stagnation pressures at circular-orbit velocity, I'm showing around 2 mbar pressure on the heatshield with vacuum behind, at beginning of entry, in the vicinity of 122-140 km altitude. I don't trust these numbers as accurate, but they are crudely representative.
Early in entry, while density is low, drag forces (and lift) are low. This lift and drag deficit could be made up with retro thrust through (or around) the heatshield, because flying tipped for lift points the rocket a bit downward, and that's what you were talking about. The only thing to "argue" about is how far to tip the heatshield.
Getting enough lift to flatten the entry trajectory up high has real benefits. It's best to do this as far from the surface as possible, for flight safety purposes.
Later, in mid entry trajectory, there's enough density and speed to fly fairly flat with little thrust at all.
Finally, late in the entry trajectory as Mach decreases under about 3 or 4, you have the density, but not the speed squared effect to have much drag or lift. Again, flying tipped for lift, using rocket retro thrust to make up the drag and lift deficits, could have real benefits. It keeps the trajectory flat and away from the surface. You'd like this to be around 10-20 km, maybe.
For one thing, you could pop the chutes at a lower, safer Mach, and do it higher up. That way, more of the descent could take place transonically to subsonically on the chute. You could use very little retro thrust, or even none. Save fuel.
Terminal velocities at reasonable chute mass loadings seem to be around half a Mach at 0-2 km on Mars. Heavily loaded chutes would still be supersonic. So chutes alone will never land anything of significant size on Mars. That's just plain rocket braking, from about 2 km or so altitude, at relatively high thrust.
Essentially, that's what Curiosity will do, except they are not making up deceleration deficits during entry or chute descent. Their final rocket braking scheme is a little complicated, but makes sense for a one-way probe of large mass.
GW
Answering TwinBeam in post number 117 above:
I think I understand what you were proposing. Using rocket thrust as lift to hold the entry vehicle in a flat trajectory long enough to slow down. Yes, that would work. However, if you have a blunt heatshield facing into the slipstream, and you tip the top edge forward a few degrees, you can generate a lift force comparable in magnitude to your drag force during the real hypersonics. That's lift without rocket thrust at all. It works down to around Mach 4-ish, with most any blunt shapes.
Depending upon whether we are entering at escape-class speeds, or orbital speeds, the Mach number is very definitely hypersonic. Here on Earth at orbital entry speeds, the initial hypersonic Mach number is around 25 as the vehicle grazes into sensible aero effects somewhere close to 90 km altitude. It was 36 coming back from the moon.
These are definitely some sort of free molecule slip flow aerodynamic conditions, not continuum flow, as the mean free path between air molecules up there is pretty close to 3 cm. I think most folks use some sort of modified Newtonian flow model, and an awful lot of correlations and Mollier diagrams to account for heat transfer and ionization effects.
From what I read about Curiosity, it enters at around 6 km/sec, "flies" on a tipped heat shield until the hypersonics are well over, presumably a little under Mach 3, pops a chute, and then sheds the heat shield. The chute takes it sort-of barely subsonic, but in that thin "air", the terminal velocity (drag = weight speed) is about 300 m/sec, which is close to speed of sound, unlike chutes here at home. From there it's rocket braking. They chose a skycrane rig to do the rocket braking.
As for lift during hypersonic braking, the tipped heat shield lift will be low initially, high up. Then in the middle of the deceleration deeper in the "air", there is lots of lift as the wind pressures are large at high speed and higher density. Late in the run, in the Mach 3-to-5 range, there is density, but not much speed, so lift forces are falling into insignificance again, and the trajectory inherently steepens. Rocket thrust lift would be advantageous here. And in the deceleration from below-Mach 4 to around-Mach 2.5, there is no aero lift, so rocket thrust lift could help there, too. Below Mach 2.5 is when you pop the chute.
GW
TwinBeam:
As I understand it, anything over a couple of tons mass cannot be slowed by sequential aerobraking enough to do a thrust touchdown, not without hitting dirt first. The "air" there is too thin to help enough for deceleration, but too thick to ignore in terms of entry aeroheating. That couple of tons is the entire vehicle mass at touchdown, not just the payload it contains.
A two or three ton limit is fine for small one-way probes, but they already smacked into the wall with the new Curiosity rover. That's what the complicated "skycrane" rig is supposed to address. Sure is a lot of stuff. Complicated stuff risks failure, and throwing away all that "skycrane" sure put some extra mass into what we had to shoot to Mars. I'd almost bet my idea both saves mass and reduces risk.
But any vehicle that might land 2-6 men is going to mass dozens of tons at touchdown, several to many dozen tons if it's not going to be a one-way trip. The dead-head payload crew cabin going back up might be about like a Spacex Dragon, and that's around 10 tons by itself. The ascent booster will be 10-20 times as big, with anything but nuke propulsion. That's around half a hundred to a hundred tons you have to land in the one vehicle. And we haven't included any sort of habitat or survival equipment, although that can be sent down one-way in separate smaller landers, given a beacon to home on. A 1-ton rover car will likely be close to the 2-ton lander limit, all by itself. It's hard to send down lots of tonnage if you're restricted to 2-3 total tons of landed mass per vehicle.
Anything with a blunt heat shield can be flown tipped slightly off-axis to generate a lift force, which can be used to adjust the trajectory to be whatever you need. No need for rocket thrust to do that lift job. We started using that with Gemini back in 1965. It works just fine. The lift force is comparable to the drag force, but on Mars supports 38% of the weight. You'll probably have to tip off-axis a bit more to compensate for the lower density better.
But, with Mars's too-thin "air", you're down to a small handful of km from the surface before the entry hypersonics are even over. You can pop a chute at about Mach 2.5-ish, but on Mars, if you're over the 2-3 ton limit, you'll strike before you can decelerate subsonic. Steepen the trajectory to hit denser "air" earlier, and you just hit the ground sooner. The trajectory has to be very shallow to work at all on Mars. It's already just about "flat horizontal". Plus, once you pop a chute, there's effectively no lift, and it steepens very quickly to near-vertical. That's just chutes. Ballutes would be no different.
So, to me, it appears there is a deficit in the aero-deceleration available at Mars. We need more, but it just ain't there to be had. No one can figure out how to make chutes and ballutes work during the hypersonics, so the only other option I see is adding a little rocket retro thrust. To my knowledge, no one has run the numbers for how much, but I bet it's low thrust during the hypersonics, and during the chute decel from supersonic to subsonic. Then throttle up and do a rocket touchdown.
GW
There's two things that haven't quite been done yet: (1) firing significant retro thrust into the oncoming slipstream at hypersonic speeds, and (2) firing significant retro thrust into the oncoming slipstream while hanging from a chute, at supersonic and transonic speeds. The Soyuz thing is like the battle tank: very subsonic.
Yet neither of these is particularly daunting, unless you are so over-bureaucratized as to attempt nothing that has not been done before. The key to firing engines through ports in a heat shield is no throughflow: a sealed engine compartment. Had shuttle Columbia's wing structure been sealed cell spaces inside, she would have brought her crew home safe in spite of the leading edge hole.
The key to retrofire while on a chute at Mach 2 is plume mixing with slipstream before it hits the chute, so that the chute is not damaged by hot gas. Not too much thrust, and stand the chute off well behind the vehicle on a heat-protected strap or cable. Easy enough.
Curiosity didn't really need a hovering skycrane. That kind of thing will never land men and habitats on Mars. Ridiculously big and complicated and wasteful.
GW
The real trouble with landing on Mars is that, once you're over a ton or two in sizes around 3+ meters across, there's not enough "air" for your heat shield to slow you into the supersonics before you're too low; it's mostly an a = F/m problem, the lower gee doesn't help that problem to any significant degree. Then, further, once you're only supersonic where a chute can be opened, there's not enough "air" for the chute to slow you into subsonic before you hit ground; again, it's mostly an a = F/M problem and the lower gee doesn't help.
Yes, a really huge vehicle might do rocket braking outside the "air", or all the way down, but it will be quite enormous, and likely 2 stages just to land if chemical. There is some aerobraking to be had, that can very significantly reduce the size of the vehicle, just not nearly as much aerobraking as is available here on Earth. There's a reason we were testing parachutes at over 100,000 feet altitudes for Viking.
The real "out of the box" solution is to do rocket braking at low thrust during the entry hypersonics, and during the chute deceleration to subsonic, so that you are ready for a high-thrust landing from a suitable altitude, instead of from below the surface! (ha ha)
The idea is to use some rocket thrust to make up the aerobraking deceleration deficit. You'd like to be way subsonic and just about fully stopped, as your path inclines to vertical, just hundreds to a thousand meters or so off the surface. At that point you shed the chute as a stability risk, and just ride the thrust down, the last several seconds.
We've never fired retro thrust in hypersonics before, although we have fired attitude control thrusters during entry on every single spacecraft we have ever flown. Dragon will do it with its Super Draco thrusters, canted about 45 degrees out the sides. I think you could fire right through ports in the heat shield, if you sealed the "engine room" for no through-flow, and you canted about 10-15 degrees for plume stability.
No one has used combined rockets and chutes since the Russians used that to land battle tanks from aircraft ca. 1960. But that does not mean we cannot do it today. Of course we can. That's a lot easier than the hypersonics problem, and even the hypersonics don't scare me off.
I'm not yet sure what the aero-deceleration deficit looks like on Mars. I suspect it's a function of vehicle size and mass. But, I see no fundamental reason at all why the "big lander" problem cannot be solved. And in a lot less than 10 years. So what if it hasn't been done before?
After all, we went from nothing to an Apollo LEM in about 5 years, never having done a vacuum landing of any kind but once before (Surveyor 3).
Solve this problem, and you will be capable of landing anything from 2-3 tons on up to any size whatsoever, and in the most economical manner possible.
We should have done it for the new Curiosity rover. Then we'd already be a leg-up on sending men to the surface of Mars.
But, we didn't. Budget constraints once again ruled out doing something really smart.
GW
Solids are cheap and easy enough not to reuse. Especially for a kick motor application. They've been used since the early 60's as kick motors.
GW
Thanks, Rune. The Martian atmosphere data really will come in handy, I think. In both sets of units.
As for BBcode, I know those were English words, mixed with a bunch of acronyms, but that's about it. We do not share a common dictionary. Still lost as regards images.
Slide rules were sticks you added lengths with, marked logarithmically down the sticks, but labeled normally. It was a mechanical analog hand calculator. We used them for about 300 years before electronic calculators appeared. I designed my first airplane and my first half a dozen supersonic missiles with a slide rule.
GW
Interesting thought experiment. Sure makes the premise behind H. G. Wells's "War of the Worlds" sound silly.
GW
"I don't even wear boots fighting prickly pear cactus anymore, damn near go barefoot"
One of the topics here is what kind of environment is suitable to live in, on Mars. The first explorers are going to live in tin cans and glorified pup tents, for sure. Folks who stay are going to need something better, because of the mismatch between an un-terraformed Mars and what humans need long-term.
Up above somewhere Louis said:
"People live in all sorts of God forsaken environments on Earth."
I thought that both funny and appropriate, since I live in Texas. We here in the US had a Civil War general on the Union side, Sherman, who said that if he was faced with the choice, he'd rent out Texas and live in Hell. Life here was too tough for him. This from the guy who burned Atlanta and brought modern-style war-against-civilians to this world for the first time.
A few years ago out here on my farm, we had a plague of grasshoppers. I counted 100+ per square foot; you could not see the ground for them. Big things, 2+ inches long, some of them over 4 inches. They killed some of my trees by eating the bark off them, and tried to eat the siding off my house. Since then, things like that, just not quite as bad, have happened multiple times, including this year.
In Egypt long ago, Pharoah was a wimp: he gave up too soon because of various plagues, including "locusts", meaning grasshoppers eating everything in sight. We rural Texans are a tough bunch. I'm still here, still growing grass for the cows, and still growing peaches and figs. I actually like it here. No snow to shovel.
The people who go to Mars to stay, will have to be tough indeed. But there really are people like that.
That's not to say that tin cans will be adequate, but it's a start.
GW
Hi Louis:
Actually, I rather doubt anybody who really needs any of these ideas is seeing much of this stuff. (Although, that's how one outfit ran across me, so the odds aren't infinite against.) Life in large organizations gets focused inward fairly strongly. The larger, the worse it is. A.K.A. "not invented here".
I have dreamed up a concept for a chemical lander, but I haven't run any numbers to size out the pieces of it, yet. In the next several days, I'll get that done, and post it in illustrated form over at http://exrocketman.blogspot.com. I still haven't a clue how to show illustrations here, although I've seen others do it.
(My slide rule was never this difficult to figure out.)
After a while, I'll do the same thing for a nuke lander, using old NERVA data. And I'll post that as well. I already know one piece of the answer: the chemical lander will be a lot larger and heavier for the same total dead-head payload deliverable to Mars. That's the penalty one pays for chemical vs nuke Isp. More crap to shoot up to LEO and assemble, plus shooting it 1-way to Mars.
PS - does anybody have a decent figure for the altitudes above Mars where hypersonic entry begins and where speed is down to around Mach 2.5-ish? Or does anybody have a good temperature vs altitude "standard" profile for Mars?
GW
"gas core and pulse propulsion !!"
Nice posts, Bob.
GW
John Hunter, that's the one I remember. His paper was right before mine, in the very same session.
It's an angled launch into a transfer ellipse. He was proposing a light gas gun floating in the ocean. At apogee, you need a kick motor to circularize. At 100+ gees, that kick motor is more likely a solid propellant motor than a liquid. I've worked on solid designs good to 20,000 gees. The trouble is, delivered impulse is less precise than one would like for the mission at hand, because it is fixed.
There must have been some sort of attitude thruster design on the old Sprint ABM, another 100+ gee system. A simple solid kick motor to rough-circularize, followed by detailed trim with that 100+ gee thruster design, could do the job we are talking about here.
Tanks tough enough to haul propellant up in a light gas gun launch, would likely be tough enough to survive re-entry with very minimal provisions. Now we are looking at a reusable propellant delivery tank! Imagine that.
GW
The more I think about it, the more sure I am that landing heavy items on Mars is a thing we can do far easier than we-the-community seem to think currently.
I think it takes low-thrust rocket braking during entry to the end of the hypersonics, followed by low-thrust rocket braking while your chute or ballute takes you subsonic, then high-thrust rocket braking for the final touchdown, probably without the chute, which would be pulling to one side, an instability factor. The idea is to use rocket thrust to make up the deceleration deficit that is inherently due to the extremely-thin Martian atmosphere, in both aero-deceleration phases.
I think the basic solution for rocket braking during entry hypersonics is multiple nozzles canted at around 10 or 15 degrees. That puts enough plume angle into the oncoming stream to make plume trajectory repeatable and steady-state. These engines fire right through open ports in the heat shield near its center, whatever that structure is. The "room" in which these engines are located needs to be sealed gas-tight behind the heat shield, so that there is no flow through that space. That no-throughflow feature is critical. That engine room space will pressurize like a pitot tube to the stagnation pressure during entry, but it will not heat to stagnation temperatures, as long as there is no throughflow. There is no better heat insulator than a static gas column, no matter what NASA says. We in the industry knew better. They didn't (see the segment joint designs in the shuttle SRB’s).
Myself, I'd separate the engines by "blast walls" of some sort, so that an explosion in one engine does not take out adjacent engines. Loss of an engine then means only that the remaining engines throttle up, but differentially, so that the same thrust is maintained, while thrust moments are still zeroed. This would apply to any chemical system, or to any nuclear thermal rocket system.
For the range between Mach 2.5-ish and subsonic, when chutes or ballutes are deployed, as long as the retro thrust remains fairly low, the plume massflow is small compared to the slipstream massflow, so that the aerodecelerators do not see a very-hot mixed flow field oncoming out behind the craft. Kevlar is good to about 290-300 F. Nothing magic there. You shed these aerodecelerators for final touchdown. Chutes or ballutes can be recovered after landing for re-use, by-the-way.
The final touchdown is then just standard rocket braking at throttled-up higher thrust. No different than Viking or the Apollo LEM.
How big a thing do you want to fly, and do you want it to be one-shot or reusable? I think we can do it, regardless.
As for ascent, if it's not reusable, leave the heat shield and any aeroshell surfaces at the landing site. Aeroshell surfaces can double as ramps for unloading content, by the way. The very same engines could serve for ascent, if the separable core has propellant tanks and a payload or crew cabin. Leave the descent tanks on the heat shield.
If it's nuke and reusable, just re-fold the unload ramps into an aeroshell, and just fly the whole thing back up.
I'd recommend a more-or-less conical shape, wider than it is tall, for at least the chemical one-shot version, with a slim core on the central axis for ascent. A fully-reusable nuke vehicle could be roughly as wide as it is tall. These sorts of shapes can prevent tip-over in a rough landing. Suspenders-and-belt.
Wild thoughts way outside the box, from an old rocket and ramjet guy who used to do wild-thoughts-outside-the-box for a living. It was called new product development work. Especially for products others thought impossible.
GW
No list is perfect, for sure. But the launch and orbital assembly thing is pretty much a demonstrated item now, after learning how to do it with 25 ton modules delivered by the shuttle. That was about $27,000/pound. Atlas-V-HLV can deliver 29 tons at about $2500/pound now, according to what I read. Pretty soon, Falcon-Heavy will be delivering 53 tons at near $1000/pound.
An ISS under these circumstances would be closer to $10B than the $100B we paid. So why not think of building whatever-we-need the same way, with what we have for launch rockets that double as commercial launchers, so that in turn there is a routine reason for their existence. To me, that seems the smarter solution, by far.
That is what NASA's old Constellation program should have been, but never even came close to being. Their thinking was way too corrupted by the perceived need to preserve existing contractors doing what they previously did during shuttle, and by illogical mandates from a Congress not competent to make those detail decisions (by definition).
If you think outside the box of the Apollo model (one mission-one launch, and one mission-one landing), then the orbit-to-orbit transit vehicle model, with landers as needed, immediately pops out as the most practical way to do this manned exploration thing (or some of the unmanned, for that matter). And it's not new: the same ideas were proposed by the Germans (von Braun, et al) ca. 1930's, 1940's, and 1950's. In the inner solar system, the very same transit vehicle can take you to orbit or rendezvous with any planet or moon or NEO inside the main asteroid belt. The same lander design would work on Mars, the moon, or Mercury, the only places we even need one.
One transit vehicle design, one lander design, do it modular to tailor the propellant supply to the particular mission, the other components being "common" universal designs. Now assemble them in LEO out of modules sized to fit rockets you have anyway, and reuse the hell out of whatever you can return home with (habitat and engines at least). What's so hard about that concept? And it is not, I repeat not, "Battlestar Galactica". We're talking an assembly far smaller than ISS for these missions.
Habitat modules (inflatable or otherwise) we can build, weve been doing it since 1973. Capsules we have or can build as crew return (or emergency return) vehicles. Engines (chemical, nuke, electric, etc) we have or could very soon have. Artificial gravity can be had during coast by spinning the ship end over end, and we know how to live in zero gee already.
Short-term zero gee is no problem. Radiation? Try 20+ cm worth of water around the designated shelter, as the water and wastewater tanks you already know you gotta have anyway. Make that shelter the flight deck, so critical maneuvers can be flown, no matter what. No problems or show-stoppers there. Just routine design and development testing.
The lander is the toughie. If we are serious about going to Mars, that is the critical enabling technology. We ought to be working on it. No one is, to my knowledge, but I am no insider. I think I know how to do it. There's no real show-stoppers, but it does require some combined techniques we haven't yet done together. Separately, yes; together, no. Not so very big a hurdle, that.
The artificial gravity is a major design constraint (how big a stack-up at whatever spin rate is tolerable?). Somebody ought to be looking at that seriously in LEO. We've had 40 years to do it, and no one has. The medical centrifuge of the ISS was cancelled. Very bad move. I suspect that the min therapeutic partial gee is a nonlinear function of required mission duration. But that's just a hunch.
The supple spacesuit is not being seriously worked, either. There’s a funded effort at MIT for a mechanical counterpressure suit design, but no major development effort at a real contractor who might actually build the thing. Yet, we have known since 1969 that this thing would work. It’s been relegated to academic research, and saddled with an unnecessary design constraint that today’s materials still cannot reach. How stupid is that?
All of the public policy and NASA program objectives I have seen, for decades now, says the government program does not really want to go to Mars (a radical departure from the NASA of the 1960's). I rather think they're afraid to go to Mars, because they cannot accept any significant risk any more. If they could, Spacex's Dragon would carry an astronaut a lot quicker than they plan to allow. When Glenn went up in his Mercury-Atlas in Feb. 1962, the Atlas was not yet man-rated, and ultimately it never really was man-rated. It just happened to work for 4 manned flights. Enough flights, and we would have killed somebody. It is just harsh statistics.
We were lucky with Mercury, but it worked. The Titan for Gemini wasn't any closer to man-rated, either. And the Saturns for Apollo certainly weren't man-rated, not by today's standards, and never were. Today it’s entirely different. I think they’re (NASA) gun-shy because of 3 lost crews. There’s demonstrably nothing as expensive as a dead crew, and now, no one in control of that agency is willing to do anything that might risk the loss of another one. Yet, we all know it will occasionally happen. It's just a matter of time and circumstance. Statistics.
There's a multiplicity of political and cultural problems holding us back here, but not so very much any technical obstacles anymore. See what I mean?
GW
There's something wrong with the format in this thread. Everything recent is indented out of view to the right. There is no way to scroll over to read or respond.
I could not figure out how to post a bitmap image here, so I posted it at http://exrocketman.blogspot.com. It shows the layout and structural equations for a pressure dome structure retained by gravity.
GW
This is a good discussion amongst folks with differing viewpoints. Too bad it is not taking place nationally in any meaningful way when NASA and the rest are getting their objectives set.
I rather like Louis's list. It's a good startpoint.
1. Launch
2. Orbital assembly
3. Long exposure to zero G and one third G
4. Protection from cosmic radiation/solar flares in transit and on Mars
5. Transit mode
6. Life support in transit
7. EDL for Mars
8. Return from Mars
9. Life support on Mars
10. Mars ISRU
and to it I would add one more item:
11. a supple, mobile space suit
I think that with orbital assembly, launch is no longer the problem it once was, and prices are coming down fast.
If you want a really good mission to do before going to Mars, try determining how much fractional gee is therapeutic in LEO.
Another would be a satellite outside the Van Allen belts with a radiation counter inside 20 cm thickness of water. It would give a good test of halving the cosmic ray risk, and on those erratic opportunities, a test of how good the 20 cm of water really is against solar flares. More of a design concept validation test, based on what we already know.
A third would be to check out frozen food storage and cooking under the presumption of artificial gravity for maybe 5 year missions in flightweight hardware designs. That can be done right here on the ground.
If you want to talk about validating missions, these would be necessary milestones along the way to a goal. With Apollo, we had a specific goal to land men on the moon and return them safely. That goal does not need to be specific as long as it is to send men to other celestial bodies to explore. Mars is an obvious choice among many that will come within range over time as we get more capable.
But, to say that visiting an NEO or a Martian moon is a necessary prerequisite to landing on Mars is setting up an unnecessary obstacle. The same vehicle that can take you from LEO to an NEO can take you to Mars orbit, or Venus orbit, or even orbit about Mercury, maybe even the asteroid belt with a bit hotter propulsion retrofitted to it. You look at an orbit-to-orbit transit vehicle, and it naturally becomes one design that does all those jobs. That's the analog to the caravel ship, or the clipper ship, or the DC-3, or the B-747.
Landing on Venus is a bit out of the question, but the same lander that can set down on Mars would work on Mercury, the moon, or even the moons of Jupiter and Saturn. And more. To visit small asteroids or moons, simple rendezvous with a propulsive backpack suffices, since the gravity is negligible. You don't need the big lander. Again, anything that will work on Mars will likely work on the other destinations. That's the analog to the barges and lighters that unloaded the caravels and later sailing ships, when no deepwater dock was available. It's pretty much all the same design problem; Mars makes a good set of design criteria and conditions.
The long pole in the tent is probably that lander, but we ought to be working on hotter propulsion, always.
GW
Nearly all round chutes have a peak vent, since before WW2. That vent lets them have a stable flow field so they don't oscillate around wildly behind the load they support.
The big slot around the girth does more-or-less what the multiple circumferential slots in a ribbon chute do: allow (reefed) opening in supersonic flow without "fatal" opening shock that blows the canopy to tatters. Both provide effective porosity.
The netting near the opening is a material that contributes to overall drag coefficient once the canopy is open and stable. I've used it in the form of grocery store grape bag netting as a tubular stabilizing drogue (sort of like a porous wind sock) all the way from 100 mph to Mach 1.4.
GW
Oops, forgot. The Earth's land is largely explored and settled now. There are only two places left where cultures can go to explore and colonize: (1) the deep sea, and (2) space. Both are very worthy and viable destinations, and I love what we have done in both arenas. In the "short" term, we need to be doing both IMHO. In the longer term, the sea is finite while space is infinite. So what does that tell you about long term objectives?
GW
Well, I’m glad to see I provoked some very relevant discussion with that over-long post of mine. Sorry about the length, but it’s really hard, actually impossible, to reduce something that complex to a sound bite. (Actually, I hate sound bites.)
One issue I seem to have provoked some discussion on, is “when-to-go”. One of my points in that long post was that the longer you wait (and your technology and experiences accrue), the easier and more reliable an exploratory voyage becomes. So, how long do you wait? There’s no definite (or easy) answer. But, if you wait too long, you never go (we’ve seen that before, too).
There’s a problem with never going or ceasing to go, another lesson taught by history. Cultures that cease to explore, will fade to obscurity, or even die. It just takes a while for the dead dinosaur to fall over. Example 1: China quit voyaging around the Indian Ocean and Western Pacific. Within a few centuries, China was no longer a regional power, and hasn’t been again, until recently. Example 2: About 280 AD, Rome began pulling back from exploration and colonization (we might all disagree with their subjugative methods, but the point is, they quit), starting in Britain. That’s what Hadrian’s Wall was really all about. By 2 centuries later, they had split their empire in two, and the western half had already fallen. (It took another millennium for the eastern half to end: big dinosaur.) That’s just two examples, there’s more.
I don’t have an answer about when it’s “best” to go to Mars, or even what “best” means in that context. It’s not a rational thing, anyway. I do know it was feasible at very high risk in the 1980’s. It’s easier, and a whole lot more likely now, that we could send a crew to Mars and get them home in good health. Personally, I’d say go as soon as you think you think you can get them home healthy maybe 98+% of the time, because of the “nothing is more expensive than a dead crew” problem we have already seen. But that’s just me. I think we’re just about there, if we design the mission, vehicles, and equipment right. (“Designs-done-right” are the topics of other discussions we have been having.)
I’d like to see what the rest of y’all would recommend for the answer and “rationale” (remember, this isn’t a logical thing, it’s a cultural thing) to the question “when do we go to Mars?”
GW
I think the enabling-technology boundary you are discussing here is not a sharp boundary. It depends very strongly on how much hardship and risk one is willing to endure, once the thing is feasible at all.
500 years ago it was possible for the very first time to cross the mid-Atlantic with ships from Europe. Magellan even took a fleet trans-Pacific, but about half his ships and men were lost, including Magellan himself. It took months to cross the Atlantic, years to cross the Pacific. Crews were dying of diseases like scurvy, and of spoiled food, all the time.
300 years ago the same Atlantic voyage took weeks, the Pacific took only months, and they had banished scurvy with citrus fruit. The ships were better and faster. Explorations and colonizations became far easier, so there were more of them. That's the way it worked.
We had the basic rocketry and capsules and a lander to go to the moon by the late 60's. In the 1970's, there was considerable experience with space station living with Skylab and the Salyuts. The remaining challenge that was recognized was a lander vehicle for Mars. The microgravity disease and radiation dangers went largely unrecognized or ignored back then. Long-term food storage and cooking was still unresolved.
But, from a simple technological feasibility standpoint, it had become possible to send men to the surface of Mars in the 1980's. That very mission had been on NASA's books for the 1983 opposition in the late 60's, and had been pushed back to the 1987 opposition at the time Apollo was cancelled and all manned flight beyond LEO forbidden in 1972.
In hindsight, we know the crew would more likely have died than survived, of microgravity disease, if not radiation. But we had an agency and an astronaut corps willing to go, back then. I know, that 1987 mission was my target via naval aviation and flight test school. It all went by the boards in 1972.
We know a lot more today, and have a lot more relevant experiences under our belt. There is a well-known work-around for microgravity disease, although most people still believe you have to build some "Battlestar Galactica" monstrosity to employ it. No, you don't. Nor do you need complicated cable crap, or gigantic space trusses, or any of that junk.
The same 20 cm thickness of water shielding that protects from solar flares also halves the cosmic ray exposure, without secondary showers. The "biggie" that we now have is experience at LEO assembly via docked modules - that's what's required to build the ship or ships that take men to Mars. We did that, it's called the ISS.
We still lack a viable lander. But that could be done, in about 5 years if a national priority. (That's just how we did the Apollo lander.) Mars is very hard to land big things upon, but there is a solution. It's called low-thrust rocket braking during hypersonic entry, followed by low-thrust rocket braking during chute or ballute descent, followed by a throttle-up to high-thrust rocket braking for the touchdown. You have to burn all the way down, at one thrust level or another. Multiple slightly-canted engines solves the retro plume instability problem during the hypersonics. The rest is tinkertoys we already have, we just never put them together for that application before.
If it were a national priority, if we as a people actually had the collective will, we could easily send men to the surface of Mars before 2020, and very likely get them home safely, not some "sometime in the 2030's” or later (which really means “never”, by the way). At today's launch prices, which are about 15 times cheaper than the shuttle, I do believe we could likely do it for under $100B.
We are in the analogous situation now relative to Mars, as were sailors 300 years ago trying to cross the Pacific. 300 not 500 years ago, when it was much more likely to fail. But it is still difficult and dangerous. No doubt about that.
I do not see the sanity of going all that way to Mars and not landing. What's the point? This is not a technical or science thing, this goes to the very heart of who and what we are. And what we have been, ever since that first migration out of Africa, maybe a million years ago, before we even became the species we are today.
Nope. If we go at all, we land. That's not even a proper topic for debate.
But on the other hand, I don't see the sanity of being hung up on the one trip - one landing model we used for Apollo. There's no such restriction on designs that rely on orbital assembly in LEO. Make several landings while at Mars, and visit the moons, too! But, you don't have to build "Battlestar Galactica" to do this, contrary to what most folks seem to believe.
You build a modest manned transit ship, and you build modest vehicles that take landers and the landing propellants, separately. You rendezvous all this fleet in Mars orbit, and then go to work exploring multiple sites, with rover cars that have drill rigs on them.
You go to find out “what all is there?” and “where exactly is it?”, and you try out your best “live-off-the-land” equipment while you’re there. That’s what we’ve always done, ever since that first migration out of Africa. Unless you get that done on the first visit to Mars, then any future base or colony will be “iffy” at best, and more likely fail. Same is true anywhere else we might go, too.
GW