I have some thoughts on human spaceflight and inappropriate risk aversion, over at Popular Mechanics.
16 thoughts on “To Boldly Go”
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I have some thoughts on human spaceflight and inappropriate risk aversion, over at Popular Mechanics.
Comments are closed.
Nice article, Rand. Agree heartily on the safety issue.
On the HLV issue, while the “minimum largest piece” size is unknowable as a philosophical absolute, surely there’s a minimum size below which it isn’t realistically practical for any type of human mission.
If 25 metric tons is too large, what is a reasonable minimum number in your opinion?
I don’t necessarily think that it’s too large, and if that’s the number, we don’t need a heavy lifter, because we can already almost do that with Atlas V (or a variant). I think that, ultimately, with some cleverness and innovation, we could do things in five-ton chunks (which isn’t a bad size for a reusable space transport). I know for sure that you could fund a lot of innovation for the cost of a heavy-lifter development.
I could see 5 tons, ultimately, with RLVs, because that number represents useful payload in the proper orbit, not total payload in a LEO launch orbit.
But what about the near term and using existing ELVs, where the number in discussion is not the useful payload in a proper orbit but the total payload in a LEO launch orbit?
I don’t understand the question. What is a “proper orbit” and what is a “LEO launch orbit”?
I am not sure that it is entirely productive to make the argument that we should be less risk adverse. NASA is very penny wise and pound foolish with regard to safety – safety concerns are a strong argument against NASA and for New Space.
Poor safety is one of the many reasons why NASA must get out of the launch vehicle business – they can only design over sized, overly complicated expensive low flight rate vehicles that can not be incrementally improved and that soon become dated. They are unsafe by fundamental design and soon end up killing a lot of people.
New Space low cost high flight rate developments are the obvious pathway to much greater safety. Greater safety is a feature of New Space as compared to NASA, not a bug.
A raw inflatable habitat shell five meters long by 3 meters in diameter with a large factor of safety masses around 50kg. Though there are simple ways of zipping one together from smaller sections if need be. Personally I would be inclined to make them bigger and add multiple shells for greater safety and shielding. For perspective, a couple of Falcon 1es could launch something with the habitat volume of the ISS.
I do not know what the “minimum largest piece” is for a space station – but habitat modules do not seem to be particularly limiting. If one could launch a person, then one could launch a habitat module.
So assuming propellant and habitat module depots, what is left that requires large launch vehicles? – Landing vehicles? Reentry vehicles?
What’s this about “former aerospace engineer”? Are you now just an aerospace engineering consultant?
As to the “largest minimum piece”, there are multiple ways to approach the problem. One is to design the piece and then determine what can launch it. The other is to look at the maximum currently available launcher capacity and use that as a constraint in designing the piece.
As an analogy, the Air Force has used C-130 transport planes for over 50 years. They’re good, rugged planes capable of operating out of small, rough fields but not exactly the biggest lifter available. If you want your new piece of military equipment to be carried on a C-130, you have a fixed set of constraints as to the size and weight. Violate those constraints and you’re faced with either needing a bigger plane (C-5 or C-17) or a bigger version of the C-130 (actually being studied). Since the Air Force operates some 600 C-130s and much smaller numbers of C-5s and C-17s, the cost of replacing the C-130s would be very high. That forces the developers of many new systems to make their designs smaller and lighter than they’d otherwise want if they need to equipment to be transportable by C-130.
For designers of space hardware, perhaps they should tailor their designs to fit existing boosters or those that will be available within a few years. Launching them “dry” and fueling them in orbit could be a solution.
For designers of space hardware, perhaps they should tailor their designs to fit existing boosters or those that will be available within a few years.
That would be the sensible thing to do. And is I expect what most everyone except NASA will do.
I suspect that the first generation of low cost reusable launch vehicles will be much smaller, maybe in the 500-1000kg class . But people, propellant and provisions, a large proportion of the market, should fit on them. Larger expendable launch vehicles might still serve as C-5 equivalents until the market gets big enough to justify the development of larger reusable launch vehicles.
I don’t understand the question. What is a “proper orbit” and what is a “LEO launch orbit”?
Proper orbit: one at sufficient or at least not poorly optimized altitude to do rdvz ops and (as any non-single launch op requires) and at a similarly useful inclination.
Launch orbit: most are pretty low, 200nm or less,
I’m just getting at the fact the rdvz associated hardware, fuel, and operational orbit requirements mean if you assume a 5 metric ton largest piece at the rdvz or depot, you probably need a 8-10 mt “payload” vehicle. And any RLV would have similar penalties associated with delivered payload. So in other words a 22 mt launcher would probably result in a 12-15 mt “largest piece”,which seems reasonable to me.
I suspect that the first generation of low cost reusable launch vehicles will be much smaller, maybe in the 500-1000kg class . But people, propellant and provisions, a large proportion of the market, should fit on them.
And this is what I was getting at. A 500-1000kg payload is not going to fit people on it, unless the on-orbit mass of the RLV is much much higher (If you use shuttle amounts it would need to be 10-15 mt orbital vehicle.)
A 500-1000kg payload is not going to fit people on it, unless the on-orbit mass of the RLV is much much higher (If you use shuttle amounts it would need to be 10-15 mt orbital vehicle.)
Payload definitions may vary and the shuttle is not the best of data points.
A perhaps 1-2 person reusable launch vehicle seems likely for the first prototypes – minimum development cost path.
Maybe reusability requires 2-3 times the effective raw payload of an an expendable launch vehicle with a blanket no returns, no life support policy.
Proper orbit: one at sufficient or at least not poorly optimized altitude to do rdvz ops and (as any non-single launch op requires) and at a similarly useful inclination. Launch orbit: most are pretty low, 200nm or less,
Where did you get those definitions from?
Gemini 6 and 7 demonstrated rendezvous at 161 nautical miles. Apollo 7 demonstrated rendezvous at 125 nautical miles.
Those were significantly below 200 nautical miles, what you call a “launch orbit” is sufficient for rendezvous ops.
Yeah, Ed, as long as it doesn’t need to wait in orbit for more than a few days that works. But then, that’s not a very “flexible” architecture if it depends on multiple, rapidly coordinated launches over a short period of time. Also not very realistic in an ELV world where 4 to 5 month delays are the norm.
I’m just trying to suggest that we apply the same basic rules with different architecture concepts in order to compare fairly.
For instance if you just compare HLV development costs to MLV development costs obviously HLVs come up short every time. The same is also true of MLV development costs vs SLV (<1000kg) development costs. So if you just take that fact we should be striving for an SLV-based commercial launch architecture.
But reality(and specifically the physics of getting to GEO) dictates that satellites are best developed as MLV-size payloads rather than SLV-sized.
So while I support Rand’s contention that there may not be a need for a government-designed HLV to continue human spaceflight, I’m not so sure that there isn’t a fairly large “largest piece” required, perhaps bigger than any simpler MLV (like a 401, 402, or F9) can launch.
Yeah, Ed, as long as it doesn’t need to wait in orbit for more than a few days that works.
What is “it,” and why does “it” need to wait in orbit for more than a few days? Why couldn’t a ferry vehicle simply come down to meet it?
But then, that’s not a very “flexible” architecture if it depends on multiple, rapidly coordinated launches over a short period of time.
By that logic, we don’t have a very “flexible” architecture for air or sea or ground transportation. All of those involve “rapidly coordinated launches over a short period of time.”
It appears you’re defining “flexible” to mean inflexible. A system that can launch frequently is not less flexible than a system which can only launch once or twice a year.
But reality(and specifically the physics of getting to GEO) dictates that satellites are best developed as MLV-size payloads rather than SLV-sized.
There is no such law of physics. Communications satellites are sized based on their owner’s desire for large power arrays and antenna apertures, not because of a law of physics that prevents launching smaller satellites to GEO.
Besides, we were talking about human spaceflight, not communications satellites. Stay on topic.
I’m not so sure that there isn’t a fairly large “largest piece” required, perhaps bigger than any simpler MLV (like a 401, 402, or F9) can launch.
I’m not sure the government doesn’t have a flying saucer fleet at Area 51 — but I see no evidence that it does. The “largest piece” falls in the same category as the saucer fleet. People talk about it, but no one can say exactly what it is or show evidence that it even exists.
Max Hunter used to say that the largest piece of space equipment that could not be disassembled for transport was an adult male astronaut. What is this “largest piece” that you think can’t be built up from parts?
One big issue I have with this commentary is the comment that “institutional obsession with safety”. NASA has never worried that much about safty. In Apollo era a astronaut wife was reassured that the crew of the first Apollo to circle the moon had nearly 50-50 odds of returning alive. With Shuttle they concealed the problems with the O-rings from crews for years. Choosing to risk lives (they did expect the problem to cost them a ship and crew sooner or later) in order to not embarras the agency. I.E. they choose to risk losing lives rather then risk bad press.
Having worked on space craft programs, NASA does not push for normal, much less higher then normal, safety and reliability. The shuttle is the safest spacecraft to ever go to orbit – but your a 100 times safer flying into combat in a current military aircraft. After a half century of flight to orbit – this hardly show a obsession with safety and reliability.
On the other, I strongly agree that going for a more challenging to develop, but far more capable, craft would be a big advantage.