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Oh, I know the easiest NEO's are not far from LEO, but the bulk of them are tougher to reach, having more elongated orbits. That's why I suggested a pair of Falcon-Heavies, to reach the more difficult targets, and perhaps even travel from one to another to another to another ........ Plus, the spacecraft itself can be bigger, heavier, and more capable. If we're going to go prospect the NEO's, let's look at a whole bunch of them. They're all different, or that's the way it seems, anyway. More likely to find what we want by visiting many. I picked Falcon-Heavy for $800-1000/lb payload at max payload 53 tons. It's 2.5 to 3 times cheaper than Atlas-V 551/552 at $2400/lb at 25 tons. Thinking bigger is actually cheaper, in many ways!!!!
Radiation shielding: doesn't take very much dirt to shield solar particles. I was thinking equivalent to 20 cm thickness of water. At an effective sp.gr about 2 for "dirt", that's only about 10 cm of said "dirt". Cosmic rays, that's also about as good as it gets, unless you go with meters and meters of thickness, due to the secondary particle shower. There's going to be some sort of waste crap that can serve as "dirt" almost anywhere you go.
It's the career limit on cosmic rays you worry about for long-term exposure, since the thin shield only cuts it down crudely by a factor of 2. Otherwise, you have to have a really thick shield. Solar minimum GCR is 60 REM/year. Cut that in half to 30 with a thin shield. If the astronaut is already old enough to take the high career limit of 400 REM, it'll take over 10 years to accumulate, as long as he doesn't go outside. Younger people are allowed less, and cannot stay as long.
Refueling is "automated" with Progress, I know, but it's sort of a restricted case, and not everybody is doing it yet. Besides, overseeing the tasks, and making sure everything happens correctly with refueling, is a good excuse for astronauts to fly. So, why not?
.... choir boy's singing again.......
GW
Turns out that a drill rig and a steam generator might be really handy to have in space after all!
On really low-gravity places, your ice cavern will have to be deep enough inside for the basic strength of the ice to hold air pressure. You won't be able to rely on overburden weight to hold the pressure in. But, I see no real problem with that.
GW
How to reach an NEO with what we have this year or next, to support prospecting for mining? Hmmmmm.
How about launching two Falcon-Heavies? One has the unmanned spacecraft (whatever it is) that will go to the NEO. The other payload is nothing but a giant propellant tank made out of a Falcon second stage, but without engines. The vehicle with the NEO spacecraft keeps its second stage, using it to circularize in LEO at near-depletion of propellant. The second vehicle is just a refuelling tanker.
Once refueled in LEO, the spacecraft uses the refueled Falcon second stage as its propulsion for departure and rendevous, much like we used the Saturn S-IV-B stage decades ago. Except, I'd plan to use it for the rendezvous with the NEO, too, that's typically a significant delta-vee. Then the spacecraft itself can prospect the NEO, collect samples, and perhaps return.
I'm thinking we'll need men to oversee the refuelling transfer in LEO. Certainly to safely dock the two big "spacecraft" and make the fluid hookups. So, the tanker probably has a manned Dragon on its nose. Crew of 2?
This is not an idea for sending men to an NEO, just a prospecting robot. Sending men requires a different kind of vehicle, one resembling a manned Mars transfer vehicle. That's a different problem, but the same basic transfer vehicle assembled in LEO could serve. The difference is that you don't need a lander to visit NEO's.
GW
I looked closely at the video of the Armadillo Stiga-2 test with the ballute. It was a powered-inflation balloon deployed in vacuum just after apogee. Before the strap failed, it seemed to be stabilizing the tumble of the rocket, once it hit the thin air high up. I could see the air pressures ripple the surface of the ballute just a bit. This thing was indeed working.
I suspect without proof that the strap failed because of the heavy point mass of the nose cone bouncing around in the middle of the strap. Separate recoveries for rocket body and nose cone might have worked better. Very interesting test, though.
As I read the descriptions of the flight, peak velocity before leaving the air was about Mach 3.8. So, "re-entry" would have been in that same speed class. That's high enough to worry a little about aeroheating, but short enough to heat-sink your way through (the way the other suborbital tourist plane guys do). From a heating standpoint, I would choose Kevlar for the exposed fabrics, as it's good to about 290 F. But, you can't use it for shock-absorbing "structures", as it has almost no "give", at 1-2% elongation-to-failure. The stuff is very, very stiff/brittle under shock loads, that's why it's not used for parachutes. The other materials all fail under 210 F, some under 190 F.
Extending this type of decelerator for use during hypersonic entry is an intriguing idea. But heat protection will drive the issue. Perhaps a layered structure for both ballute and towline? The inner heat-protected part being something with a lot of elongation, like a nylon, sleeved in some way with tough Kevlar that holds a layer of some suitable ablating but hard char-forming rubber (Dow Corning 93-104 perhaps?). The inflation pressure for the ballute will have to be very high as well: re-entry dynamic pressures here on Earth are typically in the 5000 psf class. How one stands-off the tough ablative sleeving from the load-bearing but heat-vulnerable pieces thermally, I don't have a clue.
But it's a very interesting idea. I do smell a solution there. If it can work here on Earth, for sure it can be made to work on Mars.
GW
Louis:
You are correct about the possibility thrusted descent. I have a hunch that the canted thrusters on Dragon will be fluid dynamically stable for thrust during entry. I suspect that is in part why they are designed that way, in part just simple geometry without firing directly through a heat shield (although I believe that could be done, too). I wouldn't say killing all the velocity before entry was the wisest thing to attempt, but thrusting during hypersonic reentry could be a wise course, as long as not too many deceleration gees result.
The lander problem is less about descent (hard as that is on Mars) than it is the following ascent. Even with ISRU refueling on the surface, where would you put it in a Dragon? There's not enough space inside the heat shield-protected capsule for the fuel for a full thrusted descent, aerobraking of some kind must assist. The space where you could stash a lot of fuel would be in the trunk module, which you have to jettison before entry.
In fact, use the rocket equation and the required delta-vee yourself, at realistic mass fractions, and you find out that a chemical lander will have to be 3 or even 4 stages. You could get away with 3 (1 descent, 2 ascent) if you had a really big heat-protected ballute of some kind during a thrusted entry, with thrusted deceleration to M2.5-ish post-entry big chute deployment, and a final heavily-thrusted landing. You'll still need at least 2 stages to return to orbit. For a given payload of, say, 2 men and minimal equipment, the thing is still going to be huge. Remember, all such landers are dead-head payload that must be sent to Mars, even if not fueled for the trip.
300 sec-class Isp for storables, structural mass fractions in the 10% range for a throwaway vehicle, and the problem is very ridiculous, because each stage is the previous one's dead-head payload. Even at 450 sec-class Isp for LH2/LOX, it's still ridiculous, although you might get away with 2 stages, 1 descent, 1 ascent.
Compare that with 900 sec-class Isp with NERVA. 1 stage goes down and back up again, including a 30 degree plane change both ways, and no aerobraking assist, just rocket thrust all the way both ways. I used 20% structure for reusability, and 10% payload. 6 tons of men and equipment in a 60 ton fully-fueled lander. 6 tons returned, too. A real landing boat built tough, not some fragile throwaway toy like the Apollo LEM. You could carry a whopping lot more down, if you ISRU refueled on the surface.
Just wishing .....
GW
Louis:
No, I've never met the Armadillo guys. I went to their website and crawled around a bit, including looking at their Stiga-2 movie.
That test reminded me very strongly of the US Army Bumper-WAC test ca. 1950. Stiga-2 was a high-performance single stage sounding rocket. Bumper-WAC was a 2-stage rig made of a captured V-2 and an Army WAC-Corporal missile. Bumper-WAC actually reached about 200 miles (300 km) up. Same sort of profile. Neither had active roll control.
The ballute test was really intriguing. It was clearly deployed and inflated in vacuum just after apogee. I could see the air drag stabilizing the cluster somewhat, just before the strap failed. I have to wonder if the point mass of the nose cone bouncing around, midway out the strap, isn't why it failed.
Myself, I would have used separate ballutes for the main rocket body and the nose cone. Straps are more durable without extra point masses banging around. At least, that's been my experience.
GW
edit adding content
http://newmars.com/forums/viewtopic.php … 36#p160336
What I have seen regarding the SABRE engine is encouraging. There is still a lot more testing to do before it could possibly fly.
I'm not too enthusiastic about the Skylon airframe designs I have seen. With tip-mounted engines, the shocks shed by the engine inlet spikes will impinge the wing leading edges. Above about Mach 6, there are no known materials but ablatives that might possibly survive this, and any ablatives will have to be very thick and heavy, and single-use, if they can survive at all, which I doubt.
Reentry starts at Mach 25. I think the shocks will cut the wings off the bird during reentry. It may even have problems on ascent from about Mach 6 on up. Depends upon how fast they are flying when they exceed about 200,000 feet altitude.
I say what I say about shock impingement heating, because it amplified the already-horrific hypersonic heating by a factor of 7-ish, on the X-15 flight that was severely damaged by this. That was only Mach 6.7.
GW
Sabre engine, {if it can be made to work!} will solve many of the SSTO problems.
https://www.reactionengines.co.uk/news/ … conditions
If you trust NASA's findings on radiation exposures and risks, they had a report defining all that stuff, which was on the internet. It appears to date to about 1992. I abstracted the "meat" and put it together in a single terse article on my "exrocketman" site. To me it looks like the radiation issues can be handled fairly easily for voyages maybe up to several years, with very practical shielding made out of stuff you have to carry anyway. The shielding is primarily to save you from solar flare events. But, it will be career limit exposures to cosmic rays that ultimately limit the duration of such voyages. http://exrocketman.blogspot.com
GW
How are you guys imbedding graphics in these posts? I have no idea how to do anything except write text.
GW
Elon Musk/Spacex has nearly everything he needs to mount a private mission to Mars in about 10 years. It's something he's already said he wants to do, and he has the money to back it up.
In the next 2-4 years, he will have Falcon-Heavy and a manned version of Dragon flying. Those plus a Bigelow inflatable for the habitat module, and some sort of propellant tank module (fairly short development), are all that is needed to do a vehicle or vehicles assembled in LEO by docking that could take men to LMO. If he does it right, they'll have artificial gravity by spinning the vehicle end-over-end.
The real problem is a practical lander. He doesn't have one. No one does. Yet.
The lander and its propellant supply is a major dead-head payload item going to Mars (not coming back). Its size sets a major amount of what you have to assemble in LEO to go to Mars. Its design is a major enabling item for the design of the transit vehicle or vehicles.
If Musk is working on a lander design, he's pretty quiet about it. (One-way unmanned Dragons for probes and cargo can land, but cannot ascend back to orbit, so that ain't the manned lander design.)
The lander is a big deal. That's just hard numbers with the rocket equation, and fancy trick orbits won't fundamentally change that outcome. If Musk wants to go to Mars in the next 10 years, he'd better be working the lander issue. If Mars really is his goal, that's more important than a flyback reusable Falcon first stage.
GW
Louis:
I went and looked at Reaction Engines' web page, and crawled around a bit just looking. Things have changed since I first ran across them a few years ago.
Most or all of the essential engine component technologies are now funded development programs of this or that agency. If these component technologies can be made to work about as thought, then the system can really be built. Like most web sites, it's quite optimistic, but I saw enough "meat" to know for sure it's "real", meaning this thing might eventually fly. They do have a long way to go proving all the engine components. And then there's some airframe components that will have to be proven, most notably the heat shield.
A look at their web site was reminiscent of looking at XCOR Aerospace's site, except Reaction Engines is fairly big by comparison. Yet, I know that XCOR's Lynx suborbital tourist spaceplane is "for real", too. You should go visit their site.
I've sat in their Lynx mockup, and it's simple enough even I could fly that spaceplane. My contacts there tell me Lynx number 1 is being built this year on their hangar floor.
XCOR is about 30 guys and gals in one hangar at the Mojave, CA municipal airport. They've made their living so far selling rocket engines with the life, restart, and maintenance characteristics one expects from FAA-certified aircraft engines. They're definitely "for real", too. Watch them, I think they'll impress you next year.
Most of the rest of the flightline at that airport is owned by Burt Rutan / Scaled Composites. Last time I saw Burt in person was 1985. Didn't get to go visit him, when I visited XCOR recently (who's looking for ramjet help from me).
GW
Mark:
I looked at the link. That's the absorption-degas analog of the dry ice confined-heating self compression I had thought about. Very clever. I never knew adsorption had reached storage volumes that large. That's a good technique. Once it's near 17 psia, then ordinary compressors could take it to 2000 psi if need be.
The fuel-maker sounds intriguing, too. I've recently become a fan of methane-LOX here as a cleaner alternative to kerosene-LOX.
These items are the sort of gear that needs to get scaled up and taken along on the first mission or two, to get thoroughly checked-out and wrung-out of any hidden "gotchas". After that, it's ready for prime time, and the very thing we need.
You must be younger than I am, with more recent industry experiences and connections, to know of such things.
GW
There's ways to run electric wires safely in water. Your enclose-the-wires-dry inside a tube is one good way. I kinda like it.
Concentrating solar thermal is a good way to generate wet saturated steam. That's all we would need for heat. Plus, there's waste heat from the lights.
Most of the plumbing would be down in the pond, except for hot lines to and from the solar collector. Freezing should not be an issue as long as heat is being collected. Perhaps two collectors for the safety of redundancy.
I'm really liking this agricultural pond idea. It looks far easier than any kind of pressure domes or enclosures on the surface. But limited to "seafood" is not good enough. The surface enclosure / dry land plant approach needs a pressure solution too.
GW
Rune:
I've seen a lot of re-entering satellites, and I watched Columbia re-enter in pieces, although I didn't know it was Columbia until about 10 minutes later. Thinking back on what I saw, and watching the video footage others took over-and-over, I pretty well figured out what I saw.
The ship lost its wing to the foam impact damage at about M12 over the Texas-New Mexico border. (It was photographed over New Mexico at M15 intact but streaming debris from an obviously-failing wing.) It tumbled and immediately lost its other wing, vertical fin, and bay doors to the hypersonic wind blast.
2-3 seconds later the windshield caved in, ripping the top off the flight deck, and the 4 astronauts there were ripped out from under their seat belts in pieces. 3000-5000 psf q does that. No time to burn, just blunt wind blast pressure forces. Those 4 torn-apart astronauts were the body parts that rained down just east of Dallas, a little cooked, but not burnt.
We knew about the vulnerability of the windscreen to direct hypersonic stream impingement when I was a grad student in 1973. Found it in wind tunnel tests, and found the narrow range of AOA where the stream safely jumps over the cockpit, as a separated flow. Lose attitude control, you're dead.
When it was over Dallas at about M6 or 7, that's when I saw it from outside Waco, Texas, to my north about 100 miles slant range. The heavy engine thrust structure had already separated. It and the fuselage (cabin still attached) led the debris stream. The wings were fluttering along behind, along with the chunks of bay doors and the fin, and a whole cloud of smaller pieces, maybe 2 dozen or so. The fuselage and thrust structure were tumbling. I could not see them tumble, but they were leaving characteristically-braided contrails.
I watched it go eastward until the contrails dimmed as the hypersonics faded into "mere" supersonics. Between Dallas and Tyler, I saw the fuselage break up as a fan of pieces, leaving the cabin tumbling alone and still mostly intact, except for the lost flight deck roof. A contact at NASA confirmed to me that the three on the mid deck were still alive at that point, although I hope the gee-force pounding had beaten them unconscious. That's the last I saw of it, visually.
Seconds later the cabin decelerated to about M1/20kft, and was crushed by the rapidly-rising wind pressures again. My contact at NASA said that's when the 3 mid deck astronauts died by blunt force trauma, not upon impact with the ground seconds later. If stabilized so as not to tumble, it would not have crushed like that.
Clearly, lots of the structures survived the re-entry in recognizable condition. This includes uniform patches and plastic parts from the interior. No, this stuff doesn't burn up on re-entry the way all the "experts" always said it did all these years. There isn't time to burn, it decelerates quite rapidly. The pieces literally heat-sink their way through reentry on a transient.
As for crew survival, you separate the cabin from the cargo bay with a shaped charge, and stream an inflated drogue from the nose to take the spin off the cabin. If there’s enough warning time, the flight deck crew can evacuate down to the middeck. Otherwise, windshield failure and flight deck roof loss is very likely before the drogue can stabilize it. As it slows to “mere” supersonic speed, you blow the hatch. All survivors on the mid deck have but seconds to jump before impact, but that’s better than no chance at all.
It was the same with Skylab in 1979. Fragile thin-shell aluminum remained intact as one single radar return down to 40 nautical mile altitude, about halfway through reentry (around M12, just like Columbia). Minutes later, although the solar wings and telescope mount were gone, the main body was still in one piece when it completed reentry just off the western Australian coast.
It finally broke up over land at about M1/20kft, while ballistically falling into rapidly rising q at low altitudes as the path angle quickly steepened downward. Of 85-90 tons at reentry, they picked up 75 tons of debris in Australia. Nope, these things most definitely do not "burn up".
GW
As for chicken-and-egg problems, that has always obtained with new commercial ventures of any size at all.
You solve it by bootstrapping and "leverage" (really, financial cheating). Do things by increments, etc. Things eventually happen, it's just not nearly as fast as most of us would like.
Sometimes, you get public-private partnerships that help by financing some of it with tax money. Sometimes not (for the next few decades, I think not, conditions are just too strained right now to count on that).
Lately, I've been betting more on the likes of Spacex, XCOR, and several others. Now there's PRI looks promising, too. Vision is not yet dead among us. That's hopeful.
GW
Just singing like a canary, I guess.
Do y'all really think they'll find things like platinum in ore bodies rich enough to process in these NEO's? That's the sort of product with value down here. The volatiles would have value in LEO, not down here. At least to my way of thinking.
What about the stony minerals? Any use for them that anyone can see?
I'm not sure about the nickel-iron. Whether there's any value down here is questionable, I suppose, since we have so much recyclable steel. But for steel construction on the moon, Mars, and elsewhere, it could be quite valuable, once there's folks there on those places who need it. Not yet, but "soon".
GW
I dunno what a "solid state compressor" is, but I'm glad to hear there is one and that it works. Sounds like that "do it a different way" I suggested has "already been done". That's great news.
What kind of propellants did they make at Pioneer?
GW
I'm thinking electric lights just because Earth plants need visible light centered at green wavelength, plus a snit of UV, to survive well.
Steam is a very good way to transmit heat, though.
GW
Monopoly pricing is no surprise. Historically.
GW
Louis:
Both shuttle accidents showed pressure cabin separation from the rest of the debris (I witnessed this with my own eyes during Columbia's destruction, right from my front yard). Structurally, the weak point was the cabin to cargo bay joint, where the structure went from a closed tube to an open tube (no strength in the bay doors).
If you take the spin off the pressure cabin (pressurized or not, the crew should be in suits, who cares if it is punctured in some way), you can use the compartment between cockpit (two levels) and cargo bay as a sacrificial "heat shield", with nothing more than a stabilizing drogue from the nose.
Once the noisy hypersonics quiet down, you are are low-supersonic decelerating toward M1/20kft max q, and only dozens of seconds from impact. You quickly blow the hatch, and jump out on personnel chutes with an oxygen bottle. No wings, so we don't need the silly pole and tractor rocket motors.
We have known since WW2 that crews were unable to bail out from spinning airplanes due to centrifugal forces. In fact, that problem was the original rationale behind ejection seats.
But for a shuttle pressure cabin, a de-spin drogue is simply more practical.
We have also known since WW2 that bailout from a non-spinning airplane is easy. Just don't do it above about M1 or thereabouts, because of the nonsurvivable wind blast (known since the early 50's). Which transonic point is some 20kft on the typical ballistic re-entry trajectory, even for debris.
GW
Spacenut:
That conversion ratio vs reactor pressure curve you posted shows exactly what I am talking about. Yield is better the higher your reaction pressure, in a nonlinear fashion. Everything "falls off a cliff" between 0.1 and 1.0 atm. Mars is 0.007 atm in its open "air". Compression above 30:1 is a real problem, as I have already described.
All that says is "do it a different way".
I've never said not to do ISRU. But most of the pre-conceived notions of exactly how to do ISRU look like crap to me.
GW
A part of what y'all are debating here (costs of ground control) is something I have written posts about before. The result you get depends upon whether PRI uses the NASA model, the ULA model, or the Spacex model. If it takes the population of a major American city to support your launches and flights, when you add up all the contractors and vendors too, that's the NASA model, and it is precisely why a shuttle launch was $1.5 B. At 25 metric tons max payload, that's $27,000/lb.
On the other hand, there's Spacex, who for the first time in history uses the population of only a small Texas country town to support launches and missions. This is why Spacex is charging about $2500/lb for a 10.1-max metric ton payload on Falcon-9. Factor-ten better is no mean feat! Three cheers for visionary-led private enterprise!
There is a launch vehicle scale effect that applies here: bigger rockets should lead to lower per-lb payload costs when delivering max payload. Now, ULA's Atlas V, in the -551 and -552 configurations, is priced at 2400/lb at a max 25 metric ton payload size. (All of this is LEO from Canaveral.)
But, Falcon-Heavy is projected at 53 metric tons for $800-1000/lb on Spacex's website. Conclusion: ULA is too high for the payload size, they ought to be nearer $1500-1700/lb. Boeing and Lockheed-Martin are gigantic corporations, while Spacex is not. Does anybody else see the advantage of a small, lean company here? (Or the advantage of any for-profit company over a government agency?)
If you think and act like a Spacex, asteroid mining could actually be profitable. If you think and act like a ULA, maybe not. If you think and act like NASA, never. That's the real lesson of what we have seen for the last 50 years or so. It's hard to argue with numbers interpreted in the light of actual history.
Comments?
GW
RobS:
Unfortunately, the problem really isn't containment. That's just about an inch of steel in a gas bottle's wall at well above 2000 psig, and there's not very many of those bottles in real system, not compared to the mass of the compressor itself, even here.
The problem is the size and efficiency (more than one sense here, see also next paragraph) of the compressor. That machinery here is 30 to 70% energetically efficient, meaning throughput massflow x enthalpy rise (more or less proportional to compression ratio) compared to shaft power input. On Mars there is the same basic machinery friction to fight, but only about 0.6% of the throughput. So, the energy efficiency is way-to-hell-and-gone far lower there, unless you reduce compression ratio very, very, very drastically in proportion. Which trends toward very little product. Which trends toward not being usable. Not a picture I like.
There is also the problem of throughput x time-to-accumulate-a-given-mass compared to the mass of the compression machinery. This is proportional to inlet density ratio, no matter what else. On Mars, that's 0.6% of here. No compressor capable of filling a welding gas bottle at a useful pressure will ever be small on Mars. Laws of physics preclude it. If it ain't small, who's going to pay to ship it there? Another picture I don't like.
Sorry. Too much knowledge is a dangerous thing, just like too little.
But I am still very intrigued by thermal self-compression of CO2 and H2O in confined spaces. Low grade heat is cheap and lightweight, even on Mars.
GW
Actually, on the buried glacier, you start the pond construction by nothing more than pumping heat down a well drilled into the glacier. The bulldozer is for simply smoothing and adjusting the regolith cover. Melt out a cavity you can get into, then "hot fire hose" it to the shape and size you want. Add habitat with airlocks into the water and on the surface. Rig the lights. Add organic matter and transplanted Earth water plants. Voila: operating farmland on Mars.
GW
There seems to be lots of buried ice on Mars. Why not dig the ice-covered agriculture pond on a buried glacier? Then, the liquid and ice are in equilibrium, and you don't lose water as a groundwater current into dry regolith. Except for the cracks in the rock, digging ponds in bedrock does the same thing. These are all problems that can be solved.
I really don't see why acres and acres of Mars's surface cannot be quickly put into aquaculture production with no more sophisticated heavy construction machinery than a bulldozer operable in vacuum. There might even be a way to do a hydrogen peroxide-hydrocarbon piston engine to power it at high force levels.
This is not first mission stuff, but pieces of it should definitely be tried on the first mission or two, so that this technology will be ready for use on the mission that actually establishes a base of some kind.
GW
Well, passenger safety with a launch rocket such as Falcon-9 or Falcon-Heavy depends upon a good escape system. I think Spacex's use of the capsule itself fully powered as the escape vehicle, is a better idea than the old escape tower we used on Mercury and Apollo. You have coverage from ignition all the way to orbit. The tower didn't work after jettison.
With an airliner-like vehicle (such as Skylon), you have to make the craft "utterly reliable" so that no escape system is needed (sounds hauntingly familiar, like "make the ship unsinkable", right? Well, that's exactly what you have to do).
That's what we tried to do with shuttle, and failed. A fragile heatshield, exposed to debris impact in a side-mounted cluster, is two strikes against you right there. Add foam insulation that peels off, and you kill a crew. We did.
That's why Skylon is proposed as an unmanned cargo vehicle. Flying it like that for a while will uncover all the "gotchas", which can be fixed in a follow-on design that could be manned. That's actually the smart way to do it. Because of its unique engines, Skylon is really a feasibility demonstration vehicle. Until we've flown it for a while.
Any high-energy vehicle, be it a vertical launch rocket or some kind of spaceplane, will be risky. That is just plain unavoidable. But it can be managed and designed-for.
Feasibility of spaceflight itself is no longer in doubt. For passenger service, we need to get the safety-of-flight engineers in on the ground floor of all vehicle designs from now on. After 50+ years, we're finally doing that. They did it at Spacex, and I'm proud of them for it.
Actually, there was a way to have saved both shuttle crews, and it was not what they implemented. My idea was hindsight-only for Challenger, but afterward it was never done, which is why Columbia's crew died. I couldn't get NASA to listen to me. Outsider, "not invented here", and all that jazz. But to this day I still show spaceflight crew escape concepts on my resume as something I consult in.
GW