Author Topic: What are advantages and disadvantages of powered and aerodynamic landing?  (Read 38853 times)

Offline Archer

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What are advantages and disadvantages of powered landing (future Dragon) and aerodynamic (Space Shuttle, Dream Chaser) landing types?

For example, let's assume I have a factory at LEO :), and I need to transport product from LEO to Earth, and also to move workers up and down (just a thought experiment).
« Last Edit: 02/21/2012 07:33 pm by Archer »
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Offline go4mars

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Wings are heavy, but provide more cross-range if that is needed. 
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Offline kevin-rf

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Doesn't this belong in the advanced concept section, as it applies to more than just spaceX?
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Offline Lee Jay

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What are advantages and disadvantages of powered landing (future Dragon) and aerodynamic (Space Shuttle, Dream Chaser) landing types?

Wings are orders of magnitude more efficient at generating lift than rocket fuel and engines are.

Offline AbeJ

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It seems to me to be a tough sell to justify carrying the mass of all the fuel needed for powered landing all the way up to LEO. 
I've also wondered about the extra heat shielding needed for the exhaust plume as the vehicle nears touchdown - especially for returning launch stages which don't have re-entry shielding, as has been proposed.
I think, for the scenario proposed here, aerodynamic would be the way to go - especially in a reusable form such as Dreamchaser.

Offline Robotbeat

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What are advantages and disadvantages of powered landing (future Dragon) and aerodynamic (Space Shuttle, Dream Chaser) landing types?

Wings are orders of magnitude more efficient at generating lift than rocket fuel and engines are.
Over long distances, maybe. But not for small amounts of lift just for landing, especially if you have the rocket engines and tanks and everything anyway. In that case, it's just a case of making the whole thing a little higher performing versus making your entire vehicle completely different with completely different load paths and different orientations, etc.

If you need 10-30 seconds of thrust to land, you need 10-30 seconds of fuel. If you need to land, your wings are still huge.

The trade is pretty close, though. Different folks are trying it different ways. I still sort of side with the vertical landing folks... Wings are dead weight in space.


May the best design win!
« Last Edit: 02/22/2012 03:23 am by Robotbeat »
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Offline Lee Jay

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Over long distances, maybe. But not for small amounts of lift just for landing, especially if you have the rocket engines and tanks and everything anyway.

In that case, nearly all of the delta-V comes from aerodynamics, and that's because wings (even they they are low-aspect-ratio ones like capsules) are more efficient than rocket fuel and engines.

Offline Proponent

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As has been said before, if you're flying very frequently, then the cross-range provided by wings is pretty valuable, because it potentially allows you to return to the launch site on each orbit.  With propulsive landing, however, you might have to wait a day for your orbital track to pass over the launch site.  I think it's going to be a while, though, before flight rates are high enough that an extra half day or so in orbit is a significant drag on the economics of an orbital transportation system.

There's also the question of launch abort.  SpaceX's Dragon shows how the landing system can double as a launch escape system.  Intact abort for a winged vehicle is potentially a little trickier, since for low-altitude aborts the winged vehicle is going to need a pretty powerful boost to get it and its wings up to flight speed.

Wings represent a large area requiring thermal protection on re-entry, which can be problematic as we saw with Columbia.  On the other hand, by presenting a large area on re-entry, the winged vehicle may get away with lower temperatures and hence cheaper, more durable materials over much of its wings than the a capusule would require over its smaller heatshield.

I guess I'm a powered-landing guy myself, but I think it's great that both approaches are being actively pursued (e.g., CST-100, Dragon, Orion for powered, Dream Chaser for winged).
« Last Edit: 02/22/2012 04:46 am by Proponent »

Offline colbourne

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Fuel is a low cost part of a space launch system. Musk reckons the re-usability of his craft will more than out weigh the extra fuel cost.

The choice between wings and rockets will vary between the various planets/moons being landed on.

If coming from orbital velocity, aerobraking saves a lot of fuel and wings can be required to make this feasible on some planets.

Designing a craft to land on Mars without a massive fuel requirement for this process should be a top priority as any weight saved in landing will make a huge difference to the take off mass from Earth.

Offline Robotbeat

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Over long distances, maybe. But not for small amounts of lift just for landing, especially if you have the rocket engines and tanks and everything anyway.

In that case, nearly all of the delta-V comes from aerodynamics, and that's because wings (even they they are low-aspect-ratio ones like capsules) are more efficient than rocket fuel and engines.
Yup, for high delta-v lift, there's an advantage. At low delta-v, there's a certain mass for wings. You just need a little bit of fuel, on the other hand, if you go propulsively.
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Offline douglas100

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The trade is pretty close, though. Different folks are trying it different ways. I still sort of side with the vertical landing folks... Wings are dead weight in space.

May the best design win!

Agree that the trade is close. I prefer wings for aesthetic reasons, but I also agree that vertical landing has its merits. (I thought the latest video of Xaero was very cool.)

I could even imagine both approaches being used in different contexts.
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Offline douglas100

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One advantage of wings that has been mentioned is a potentially softer landing for ISS crew after 6 months on orbit. The Soyuz landing is pretty brutal.
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Offline go4mars

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Away from Earth, wings are a disadvantage almost all the time.  SpaceX wants to have Mars capable hardware and systems (as much as possible).
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Offline Proponent

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One advantage of wings that has been mentioned is a potentially softer landing for ISS crew after 6 months on orbit. The Soyuz landing is pretty brutal.

But there's no reason a powered landing can't be gentle -- consider the Apollo LM, for example.

Offline grakenverb

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This looks extremely difficult for a whole variety of reasons.  I can see the first and second stages having enough fuel left to make the return journey, but I can't imagine that there would be enough room in the Dragon for the fuel required for powered descent.  I thought they would go with a combination of parachutes to slow Dragon, then the Super Dracos for the last 30 or 40 thousand feet.







BTW:  Has there EVER been a spacecraft that has returned from Earth orbit using powered descent all the way to the surface?
« Last Edit: 02/22/2012 06:06 pm by grakenverb »

Offline douglas100

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Away from Earth, wings are a disadvantage almost all the time.  SpaceX wants to have Mars capable hardware and systems (as much as possible).

I am taking the title of the thread to mean aerodynamic landing on Earth. There are other threads for discussing Mars landing techniques.
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Offline Robotbeat

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Away from Earth, wings are a disadvantage almost all the time.  SpaceX wants to have Mars capable hardware and systems (as much as possible).

I am taking the title of the thread to mean aerodynamic landing on Earth. There are other threads for discussing Mars landing techniques.
We're interested in going beyond Earth, so it's relevant if the same techniques can then be applicable for other worlds besides the Earth.

...for extremely high Mars entry speeds, wings with their higher hypersonic lift/drag (used "negatively") can help keep the entry craft from skipping off into space. But that's a pretty extreme example.
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Offline douglas100

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But there's no reason a powered landing can't be gentle -- consider the Apollo LM, for example.

That's true. The comment I made was based (I think) a claim made by SNC about Dream Chaser. And being Devil's advocate for a moment, and speaking against my own preference, powered landing has the advantage of not needing a runway-any reasonably level piece of terrain will do.

On the other hand, a winged landing means that all propellant on board can be burned or vented before landing, greatly reducing the risk of fire or explosion in the event of a hard impact. A powered lander must land with prop on board. I remember the DC-X trying to land on three legs, falling over and being engulfed in flame.

I think I still (slightly) favour wings...
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Offline douglas100

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...for extremely high Mars entry speeds, wings with their higher hypersonic lift/drag (used "negatively") can help keep the entry craft from skipping off into space. But that's a pretty extreme example.

It is. And wings cannot be used for landing on Mars by themselves, of course. So I hold to my point that if we are talking about aerodynamic landing (I take that to mean winged landing, not parachutes), we are talking about landing on Earth. (OK, we might mention Titan, in which case we might make the lander a seaplane.  :))

Aerodynamic maneuvering is a different matter and can in principle be carried at any Solar System  body (excluding the Sun!) which has an atmosphere.
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Offline Robotbeat

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...for extremely high Mars entry speeds, wings with their higher hypersonic lift/drag (used "negatively") can help keep the entry craft from skipping off into space. But that's a pretty extreme example.

It is. And wings cannot be used for landing on Mars by themselves, of course. So I hold to my point that if we are talking about aerodynamic landing (I take that to mean winged landing, not parachutes), we are talking about landing on Earth. (OK, we might mention Titan, in which case we might make the lander a seaplane.  :))

Aerodynamic maneuvering is a different matter and can in principle be carried at any Solar System  body (excluding the Sun!) which has an atmosphere.
The title asks:
"What are advantages and disadvantages of powered and aerodynamic landing?"
One of the advantages of powered landing (vs aerodynamic) is that it can be done at places other than Earth. To artificially exclude the rest of the solar system is to deny one of powered landing's best advantages. We're going to have to get good at powered landing anyway.

Another is that wings are generally pretty heavy and are only really very good at returning from LEO. Do we really want to be restricted to only returning from LEO?
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

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