Sto seguendo un interessante Thread su http://forum.nasaspaceflight.com/category-view.asp tra i sostenitori dello space shuttle e quelli del CEV. A parte il solito “bla,bla” se sia più “cool” una capsula o un veicolo alato,ho trovato particolarmente interessanti alcuni argomenti pro capsula .Riassumendo in sintesi:1-I voli spaziali presentano un indiscutibile ed ineliminabile margine di rischio,un architettura basata su un sistema complicato come quello dello Shuttle presenta molti più rischi di uno più semplice basato su una capsula stile Apollo.2-Gran parte dei compiti per i quali lo Shuttle è stato costruito si sono rivelati nel tempo troppo pericolosi o antieconomici.Oggi ci troviamo con un sistema disegnato per fare cose che non sono più richieste.4-Lo shuttle è una macchina brucia soldi perchè dopo ogni missione deve praticamente essere quasi ricostruito.L’orbiter è un veicolo complicatissimo; propio in ragione della sua riusabilità gran parte del bilancio va via per la manutenzione post volo . Una capsula presenta il vantaggio di un modulo di servizio “semplice” ed economico perchè a perdere.5-costruire dei satelliti pensati per una durata relativamente limitata e lanciarli con piccoli vettori è infinitamente più economico che inviarli nello spazio con missioni dello Shuttle,per poi farli riparare o recuperare dall’orbiter .6-Un astronave costruita per essere riutilizzata più è più volte è un sistema "rigido"incapace di evolvere nel design e nei sistemi di bordo.Il modulo di comando,o il modulo lunare dell’ Apollo presentava di missione in missione sensibili migliorie tecnologiche,evolvendo di continuo. Inserisco alcuni degli interventi originali più interessanti.
Space travel is not about what looks cool or what attracts the public, its about the very dangerous job of taking people into a truly horrific environment and trying desperately not to kill them while doing it.
I absolutely guarantee that there will be a loss of life on whatever vehicle we build to replace Shuttle - no matter what its design.
It’s not a question of IF, but WHEN.
All we can do is make sure we do everything possible to ensure that loss happens as far away in time as we possibly can.
The biggest lesson Challenger and now Columbia can possibly teach us is that space flight isn’t safe, and we should try everything to make sure it is as safe as possible. Shuttle has taught us that a very complicated system is far more dangerous than a very simple one.
And this is a lesson many of the real creators behind the VSE realised up-close and personal. Astronauts such as Owen Garriott were the real architects behind this Vision. Scott Horowitz, formerly of ATK, now back at NASA is another brain behind this philosophy - and there’s no coincidence that ATK were the ones who came up with the catch-phrase “Safe, Simple, Soon” running through the core of the VSE.
These guys want the safest possible system to fly in because they are ones who have quite litterally risked their own butts doing it, and they are the ones who’s close workmates died on those orbiters. They are the ones who also had to comfort the grieving families of those lost. They aren’t blinded by what looks cool - they know better than anyone else what really needs to be done.
Just because Shuttle looks fancy, doesn’t mean its good. Just because Klipper or OSP look cool, does not mean they are safe. They are all more complicated than a simple capsule, and thus there is more chance of something going wrong.
We’ve all become brainwashed by the last 40 years of spacecraft on Sci-Fi shows, but the safest tool for this job is the simplest one. With no over-complications, an Apollo-style capsule should be far safer than most other concepts.
And so the problem of what spacecraft design is truly the best was very carefully analysed. Go and read the ESAS report and you can see very quickly that an enormous amount of real analysis found that the Apollo capsule shape was an amazingly good design, probably even more ideal than people realised. Griffin is on record as having said how surprised the analysts were to find just how right the Apollo guys got it.
The conical capsule is the most ideal concept for the risky job of carrying crews into space atop a rocket, taking them to some location in space, and then bringing them back safely afterwards.
The TPS is the simpest possible, it requires no overly complex shapes, no risky seams, doesn’t need different materials and on a conical shape capsule it will orientate itself automatically to the ideal re-entry profile without any sort of controlled intervention.
The conical shape also weighs the least of virtually any option - which is an incredibly important factor.
And being a cone, it is ideally suited to being placed on top of the simplest possible rocket (the CLV is very simple too, and since the fixes after Challenger, its hardware looks to be very well proven too) with an escape system to get the crew away from any possible disaster.
While it would certainly be realy cool to have spaceships that look like the starship Enterprise, or the Pan-Am clipper from 2001; it just isn’t necessary to get the job done. And I just don’t think cool looking spaceships are worth a single life.
A few comments;
Firstly Shuttle SRBs travel thousands of miles across the continent for reload.
Secondly CEV LZ can be a desert in mid-west but I don’t see why it couldn’t be on sea a few dozen miles off the coast of KSC. Or Great Lakes. Or Lake Pontchartrain. BTW it’s not obligatory to send a costly navy carrier battle group to pick up a capsule from the sea, the SRB recovery ships could do the trick. Shuttle can land only on few runways in the world, miss them and it’s guaranteed loss of vehicle. A capsule can land almost anywhere. It might even do an emergency landing smack in the middle of some suburb. It may crunch a doghouse or put a serious dent on someones roof, people in the house have ample time to get into safety/rescue the dog because the parachuting capsule lands relatively slow, and by that time every local radio and tv channel is broadcasting ‘watch the sky, spacecraft going to landing here!!’. Once the craft hits the doghouse/roof the residents are happy because it was just a ten ton craft landing vertically at 16mph instead of hundred ton craft plowing horisontally at 200mph.
This gives much more freedom to plan missions, and it’s a major safety issue. Imagine a situation where CEV experiences malfunction on orbit and has to immediately do a reentry (crew health issue, micrometeor punctures airtank or something similar). The CEV can do that and has a good chance of succesful landing. It might land far away from nominal LZ, perhaps other side of the globe, but IMO the terrestrial part of the logistical problem of getting crew back from space is peanuts compared to dangers in reentry and landing.
Thirdly, related to above, a lesson from STS: crossrange capability. AFAIK Shuttle has never actually used the very challenging USAF requirement of doing just one polar orbit and land back to launchsite. But it dictated the specification for very high crossrange. The CEV has much inferior crossrange for two reasons; it’s not really needed … and a capsule needs it even less because of the relaxed LZ requirements.
And last is general comment of another lesson from STS: downmass capability. Another thing that is not really needed for the time being. It was supposed to make routine of bringing satellites back to earth for repair/rehaul. That falls apart for at least couple of reasons; you need two flights by complex and costly machine to do it, and most of the satellites that might benefit from such service are out of reach at GEO. In the long run it’s more practical and cheaper to just overengineer the satellites, launch them using cheap expendables and operate the sat until it breaks. The only real downmass requirement for a very long time will be people, results from experiments and samples. A capsule design can handle that perfectly well.
Disclaimer: I’m not anti-Orbiter zealot and would love to see something like X-33 fly some day, but IMO the ESAS ‘K.I.S.S.’ approach suits NASA the best right now, yielding maximum results with the limited resources(aka money) available The maintenance work required to make those re-usable components on STS fly again tends to be incredibly intensive and very expensive. Maintaining re-usable engines & such things between each mission requires a huge portion of the STS budget. There are hudreds of workers crawling all over each orbiter for weeks between flights, just attempting to prepare it for the next flight.
The SM seems to be being designed to be as simple as possible, and discarded. If it had to be recovered and designed for re-use multiple times, it would have to be significantly more complicated and require a large team of people inspecting, testing, repairing and servicing it each time it flies.
I think they must have concluded that such service work is too costly and it would be noticably cheaper and easier to just make the SM simply for one use and then just discard it at the end of the mission.
Another issue - if you re-use the same thing over and over again, it becomes a lot more difficult to change its design when you want to imporove it. Look at the Orbiters - they only recently all got the glass cockpits which airliners have been enjoying for many years. Evolutionary changes to the design are very slow to happen in a re-usable design. Conversely, in a disposable design, they can make changes on the production line and possibly even fly those improvements on the very next flight.
Look at the Lunar Module for a good example of a quickly evolving program.
The LM evolved continuously across just the 9 flight program. You could NEVER have done as many evolutionary changes which were done to get to J-missions if you had been using some sort of re-usable design. It was largely because the LM’s were disposable, that the evolutionary changes could occur so quickly in the program.
I’m actually looking forward to watching the evolutionary progression of the CEV, CLV, CaLV, LSAM and EDS projects. What they start out with in the early years is quite likely to get continually improved throughout the life of the program.