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I have been reading a bit about the Orion spacecraft. I see they just did some sea recovery testing. It seems like in the post Space Shuttle era, NASA is going backwards. Is this a one off solution, or is there a solid rationale for moving away from controlled flight reentry?

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Please realize that capsules like the Orion fly a controlled aerodynamic re-entry. They are not dumb balls thrown into the atmosphere. They have low Lift/Drag ratio compared to winged air/spacecraft, but they use their lift nonetheless.

Wings for a precision runway landing are all fine and dandy, but they are simply dead mass for missions beyond Low Earth Orbit (LEO).

The same can be said for the wheels - unless you want a re-usable spacecraft, wheels are a nuisance.

Missions to Mars, asteroids, or the Moon intend to bring back the crew and samples only. Unlike complex spacecraft, samples are insensitive to high g-loads/shocks at landing. This leaves you with the safety of the crew as the ultimate factor in mission design.

Those missions will be infrequent and not exactly time-sensitive as far as search and recovery go. Thus, you can allow an hour or two before the crew is recovered.

The final choice (water or land) depends on the country and the structural limits of the spacecraft. Say, Russia historically had almost no aircraft carriers, a sturdy Soyuz reentry capsule design, and a large territory without too many man-made landing hazards - rivers, railroads, transmission lines, mountains, marshes (okay it's technically Kazakhstan, but whatever). Not so for the United States. Anyway, making safe landing into water is easier at interplanetary re-entry speeds (terminal braking solid rockets/engines also take away precious mass budget). For instance, the Orion lost its capability to land on the ground after a mass reduction campaign scratched away its air bags.

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    $\begingroup$ Sure, no point in sending wings and wheels across interplanetary distances, but you could say the same about parachutes and floatation devices i.e. all of the equipment required for direct return. Seems to me that that the most feasible human visit to Mars misson concepts assumed the existence of a "space shuttle" to bring crew from Earth surface to a vehicle assembled in-orbit; presumably the return trip would involve a "space shuttle" for the re-entry portion of the return trip, and if doing that, why not wings and wheels instead of parachutes and splashdowns? $\endgroup$ – Anthony X Aug 24 '13 at 14:09
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    $\begingroup$ @AnthonyX - how are you going to reduce the speed to get to your shuttle? You have to rendezvous with something in LEO, and this means propulsive maneuver and a waste of fuel instead of letting Earth's atmosphere run the show. $\endgroup$ – Deer Hunter Aug 24 '13 at 15:47
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    $\begingroup$ @AnthonyX: A set of parachutes and a flotation device can weight maybe 5-10kg. A functional set of wings and wheels under 100kg? Unlikely. $\endgroup$ – SF. Aug 24 '13 at 18:27
  • $\begingroup$ I think the advantage of wings and wheels is not weight but reusability - of the entire system that gets you to LEO. As for deceleration from Mars return trajectory, sure, atmospheric braking, but just to achieve LEO rendezvous rather than full re-entry. If you think about it, a Mars-Earth transfer vehicle will be very large and very heavy to support a crew for the months long journey; no need to soft-land all that mass when you're only bringing samples and crew home; why bring your "Earth lander" all the way to Mars and back? $\endgroup$ – Anthony X Aug 25 '13 at 2:28
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    $\begingroup$ Perhaps the onus for rendezvous maneouvers wouldn't have to be on the Mars return vehicle... just settle into a reachable parking orbit to which a "shuttle" could be launched for rendezvous after the parameters of the parking orbit are known. Are a couple of extra days in Earth orbit waiting for pickup such a big deal after an umpteen-month expedition? $\endgroup$ – Anthony X Aug 25 '13 at 22:55
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in the post Space Shuttle era, NASA is going backwards

This is based on the assumptions that because the Space Shuttle looked cool, it was (a) an effective spacecraft, and (b) an effective method of reentry. Both assumptions are entirely incorrect.

As a route to orbit, the Space Shuttle was significantly less effective than anything else. It was less robust and more expensive per launch than the Soyuz. It was way more expensive per launch than Ariane. Its initial design concept of being cheaply reuseable was entirely incorrect - it was more expensive to refurbish a Shuttle than it would have been to throw it away and build from scratch, because designing for "refurbishing" made it way more expensive. As a spacecraft, it was a complete dead end. Its only achievement as a spacecraft was to somewhat resemble an aeroplane, a requirement set by the USAF with no technical basis.

Not only was it a dead end, but it also caused some steps back in spaceflight generally. "Investment" in the Shuttle directly prevented many unmanned missions being run. Its long development time and overruns were the direct cause of the loss of Skylab, resulting in the ISS having to be started entirely from scratch. Its lifting capacity to orbit was also no better than Ariane or Soyuz, so building the ISS required many separate launches with relatively small components, compared to the much more capable Saturn-V rocket which launched Skylab as a single payload. It prevented development of any manned missions beyond LEO. And of course we have two major disasters over its operating life, the last of which left the US and its allies with no manned route to orbit.

Then we come onto its reentry abilities. The most obvious problem was with its heat tiles, which caused the loss of Columbia. Replacement of heat tiles is why it was so expensive to reuse, of course. But also its basic shape with wings was a massive design flaw for reentry, because the structure of the wing root is inevitably a weak point. As a safe way through reentry, it really wasn't.

And finally of course, the last few thousand feet to landing. The Shuttle famously was hard to steer, had a glide slope significantly worse than a parachute, and a landing speed of 200-300mph. It was so bad at landing that runways had to be specially built to handle its awful performance, and crews nicknamed it "the Flying Brick". Landing it was extremely high risk, because as a glider you only got one shot at the landing, and its performance meant that highly skilled pilots were needed to land it - which after all was why the USAF had specified that it had to have wings, to ensure their continued involvement in the program.

Now compare to a capsule landing in the sea (US design) or a deserted plain somewhere (Russian design). The capsule can be designed to "shuttlecock" to the correct position for reentry. The capsule heatshield is a continuous smooth surface, so there are none of the weak points of a wing root. Parachutes give inherent stability with no pilot intervention required, and with multiple parachutes you have built-in redundancy. In essence, the capsule and parachute design just works.

So NASA got it right the first time, and then spent 50 years screwing it up in the pursuit of something which looked cool and didn't actually work well. After billions of wasted dollars and one unnecessary disaster, they finally returned to something which just works. I don't see how that's going backwards.

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    $\begingroup$ " it was more expensive to refurbish a Shuttle than it would have been to throw it away and build from scratch" citation needed $\endgroup$ – Organic Marble Apr 3 at 20:19
  • $\begingroup$ Yeah, that seems extremely improbable (although a short-lifetime reusable-ish spaceplane isn't a nonsensical concept to me) $\endgroup$ – ikrase Apr 3 at 20:44
  • $\begingroup$ @OrganicMarble From en.wikipedia.org/wiki/Criticism_of_the_Space_Shuttle_program: "Fundamentally, it failed in the goal of reducing the cost of space access. Space Shuttle incremental per-pound launch costs ultimately turned out to be considerably higher than those of expendable launchers." If you don't need to reuse it, you don't build it how the Shuttle was built in the first place, and in fact you don't build a Shuttle at all. $\endgroup$ – Graham Apr 3 at 22:30
  • $\begingroup$ @Graham your claim is that building a new shuttle is cheaper than refurbing an existing one. I don't see support for that claim on Wikipedia. $\endgroup$ – Organic Marble Apr 3 at 22:34
  • $\begingroup$ Incidentally, which of the shuttle accidents do you consider "necessary"? $\endgroup$ – Organic Marble Apr 3 at 22:41
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Disregarding other concerns such as the practicality of spaceplanes:

If you are designing from scratch, and you just need to get a crew and/or a few hundred kg of cargo into space and back to the ground, and you are not trying to push for hardcore re-usability with fast turnaround, a capsule is vastly easier to design and to make safe and durable and robust than a spaceplane.

Most capsule-type reentry vehicles are controllable to some degree.

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