Author Topic: What are advantages and disadvantages of powered and aerodynamic landing?  (Read 11105 times)

Offline antiquark

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Don't think anyone mentioned this yet, but wings are pretty reliable compared to rocket engines.  Wings are simple chunks of metal with few moving parts, whereas rockets are complicated chunks of metal with lots of moving parts.


Offline Robotbeat

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Don't think anyone mentioned this yet, but wings are pretty reliable compared to rocket engines.  Wings are simple chunks of metal with few moving parts, whereas rockets are complicated chunks of metal with lots of moving parts.


Columbia was a loss-of-crew-event because of wing failure (due to debris impact... wings present extra area which can be hit by debris).
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Offline Namechange User

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And engines can explode for any number of reasons.....

It's a trade that depends on many factors and one that definitively will not be answered on this thread.
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Offline antiquark

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Here's a thought experiment to put it into perspective: imagine you had a wingless space shuttle. What kind of engines, and how much fuel, would be needed for a vertical landing?

Offline Namechange User

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Why would anyone have a "wingless space shuttle"?  If it did exist, it wouldn't be the "space shuttle" anyway and therefore how many engines, amount of prop, etc would be a completely different context. 
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Offline deltaV

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Don't think anyone mentioned this yet, but wings are pretty reliable compared to rocket engines.  Wings are simple chunks of metal with few moving parts, whereas rockets are complicated chunks of metal with lots of moving parts.

On the other hand it's easier to design for engine-out than for wing-out.   ;)

Offline Namechange User

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Don't think anyone mentioned this yet, but wings are pretty reliable compared to rocket engines.  Wings are simple chunks of metal with few moving parts, whereas rockets are complicated chunks of metal with lots of moving parts.

On the other hand it's easier to design for engine-out than for wing-out.   ;)

But that whole argument of "wings get hit by debris" is a bias looking for justification. 

Yes, it happened in the past.  But windows get hit by birds on aircraft take-off.  There is a risk there but it gets mitigated by any number of ways.  Same with powered-landings.

So a particular tactical solution to the design is based partly on the strategic reason for the vehicles existance in the first place and the overall concept of operations.

It is ok to have more than one solution. 
« Last Edit: 02/22/2012 07:03 PM by OV-106 »
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Offline antiquark

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Just imagine you're designing a wingless spacecraft that has the same capabilities as a shuttle orbiter:

http://en.wikipedia.org/wiki/Space_Shuttle_orbiter

For example, the "wingless shuttle" would have a crew of 8, max payload of 55,000 lbs, payload bay that is 60 ft long, etc, etc.

Based on my crude calculations, it would need ~100,000 lbs of fuel for a rocket-powered landing. So actually wings might be more efficient in this case.



Offline A_M_Swallow

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{snip}

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?

The spacecraft could use a mixed system - engines to slow down from escape velocity to just under LEO velocity and use wings for the rest of the landing.  The wings would be replacing the parachutes.

This slow down would require a delta-V of about 3.23 km/s to trigger re-entry plus extra fuel for manoeuvring.

I will leave it to other people to decide if the extra mass is worth while.

Online douglas100

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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?

I am not artificially excluding the rest of the Solar System. The title "What are advantages and disadvantages of powered and aerodynamic landing?" is meaningless applied to bodies without an atmosphere. Such bodies are automatically excluded from such a discussion. And of course we are going to have to use powered landing for them.

I am only commenting on landing on Earth from LEO. As I said earlier, there are pros and cons on both sides but I still slightly favour wings.
« Last Edit: 02/22/2012 10:41 PM by douglas100 »
Douglas Clark

Online douglas100

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Actually, OV has it right:

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It's a trade that depends on many factors and one that definitively will not be answered on this thread.
Douglas Clark

Offline Robotbeat

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...
I am not artificially excluding the rest of the Solar System. The title "What are advantages and disadvantages of powered and aerodynamic landing?" is meaningless applied to bodies without an atmosphere. Such bodies are automatically excluded from such a discussion. And of course we are going to have to use powered landing for them.

And again, one of the advantages of using powered landings on Earth is that the knowledge can be extended to allow the same technique in other places, allowing you to get more return on your investment. That still counts as an advantage, even if you're using it primarily on Earth.

And of course I agree that some little web forum thread won't decide the issue (was that ever in doubt?).

Virgin Galactic and XCOR and Skylon (and others) are attempting the HTHL approach, SpaceX and Blue Origin and Masten (and others) are attempting the VTVL approach. I happen to think the VTVL approach is better (for orbital). But smart people are trying both ways.
« Last Edit: 02/22/2012 10:52 PM by Robotbeat »
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Offline Robotbeat

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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).
It kind of depends on the product, actually.

One thing you have to realize is that all aerospace engineers have to learn all about wings and aerodynamics, etc. They don't have to learn as much about rockets, etc. That's probably partly why you see so many people saying they like the look of wings, that they're cooler, etc... People (engineers and aerospace enthusiasts) are more familiar with wings. That doesn't mean wings aren't a better solution, just that you might want to take that into account to explain the popularity of wings in some circles.

The US Air Force (who deals largely with winged vehicles, obviously) commissions flyback boosters (i.e. horizontal landing). SDIO (DoD missile guys) did DC-X (vertical landing). When you have a hammer, everything looks like a nail.
« Last Edit: 02/22/2012 11:08 PM by Robotbeat »
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Offline Proponent

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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.

The idea with Dragon is that the same propellant supply is used for launch abort, for in-orbit maneuvering and de-orbit, and for landing.  At most two of those three will be done on any one flight.

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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.

The way powered descent and landing is usually envisioned is that the vehicle falls to a low altitude -- like a few kilometers.  No parachutes are used, but drag still slows the the vehicle to below the speed of sound.  Then the engines are lit for, say 30 seconds, during which time the vehicle decelerates at 1 G or so and touches down gently.  Thus, there's no need to ignite the engines at high altitude, and the time that they need to burn is actually pretty short.

I suppose it might be the case that a returning Falcon first stage would perform a braking burn a high altitude (over 100,000 ft) so as to re-enter the atmosphere more slowly (since Falcon first stage apparently have a hard time staying in one piece during Mach 10 re-entries), but the engine would surely then be extinguished (or maybe kept running at very low thrust) until landing.
 
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BTW:  Has there EVER been a spacecraft that has returned from Earth orbit using powered descent all the way to the surface?

So, no, no powered landing would involve continuous thrusting from orbit down to the ground.
« Last Edit: 02/23/2012 01:14 AM by Proponent »

Offline JohnFornaro

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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.

Of course, that was one sixth gee and no atmo, so not too comparable to an Earth landing. 

It's a complicated trade... I dont' know how to figure it.
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Offline Andrew_W

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Soyuz 1 hit the ground at less than 100mph with tangled drogue and reserve 'chutes. So if it's only terminal velocity you have to break against, you're probably talking about less than 10% of the re-entry mass needing to be propellant, wings would weigh more than that, heat shield is still required with both methods.
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Offline Robotbeat

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Soyuz 1 hit the ground at less than 100mph with tangled drogue and reserve 'chutes. So if it's only terminal velocity you have to break against, you're probably talking about less than 10% of the re-entry mass needing to be propellant, wings would weigh more than that, heat shield is still required with both methods.
...and wings which can survive reentry are not trivial.
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Offline nacnud

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IIRC I saw a web page that described some early designs of the Russian shuttle before it was decided to use the Buran design.

The preferred design was a lifting body that used rockets for landing, I'll try to find it again.


Offline antiquark

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IIRC I saw a web page that described some early designs of the Russian shuttle before it was decided to use the Buran design.

The preferred design was a lifting body that used rockets for landing, I'll try to find it again.



Found it!

http://www.astronautix.com/craft/buran.htm

"their preferred 1974 design was an unwinged spacecraft, consisting of a crew cabin in the forward conical section, a cylindrical payload section, and a final cylindrical section with the engines for maneuvering in orbit. This unwinged MTKVA would glide to the landing zone at low subsonic speed. The final landing maneuver would use parachutes for initial braking, followed by a soft vertical landing on skid gear using retrorockets."

Offline nacnud

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