Author Topic: What are advantages and disadvantages of powered and aerodynamic landing?  (Read 8791 times)

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.
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Online 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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Online 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 »

Online 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.
Sometimes I just flat out don't get it.

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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Online 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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Offline Archer

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Thank you for your answers!

I was thinking about transportation between factory in LEO (space station in LEO) and Earth, not other planets (I cannot imagine why we will have a lot of traffic from other planets/Moon soon).

Actually, I was trying to find out what types goods can be manufactured in space, which would justify such venture.
Surprisingly, I couldn't find any information about how much would be price of kg of something transported from LEO to Earth.
It seems that nobody ever made even a paper-spacecraft, designed to bring goods from orbit to surface; spacecraft that is designed to be launched empty (and refueled in orbit if it uses powered landing), and return with cargo.

With current launch prices, I guess, only mining gold and platinum from asteroids will close the business case, but if the price can be less than 100$ per kg down, we have more options.


The future is better than the past. Despite the crepehangers, romanticists, and anti-intellectuals, the world steadily grows better because the human mind, applying itself to environment, makes it better. With hands...with tools...with horse sense and science and engineering. (c) R. A. Heinlein

Offline Solman

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Thank you for your answers!

I was thinking about transportation between factory in LEO (space station in LEO) and Earth, not other planets (I cannot imagine why we will have a lot of traffic from other planets/Moon soon).

Actually, I was trying to find out what types goods can be manufactured in space, which would justify such venture.
Surprisingly, I couldn't find any information about how much would be price of kg of something transported from LEO to Earth.
It seems that nobody ever made even a paper-spacecraft, designed to bring goods from orbit to surface; spacecraft that is designed to be launched empty (and refueled in orbit if it uses powered landing), and return with cargo.

With current launch prices, I guess, only mining gold and platinum from asteroids will close the business case, but if the price can be less than 100$ per kg down, we have more options.




 I remember reading a book years ago by the British Interplanetary Society called "Man and the Planets" that mentioned using waveriders of such a simple design and low mass that they were disposable. They glided to a horizontal landing.

 The first thing to manufacture in space is perhaps spacecraft. After all - they are so valuable that it is worth the cost of launching them to orbit.

Steve

Offline gbaikie

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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).

As mentioned, it depends upon cost of rocket fuel in orbit. Or the cost of getting rocket fuel from earth. So with SpaceX and it's plan of lowering payload to $100 per lb- one essential has the cost of rocket fuel of whatever is left the rocket as less than $100 per lb [you don't need go somewhere to get it- because already available].

So if rocket fuel as cheap as $100 per lb, it favors using more rocket fuel to brake with.

As for thought experiment of a factory in space. I am guessing you mean something which doesn't high volume- making drugs or something with low mass but is valuable. So perhaps 10 tons per year shipped to earth per year? With increase possible, perhaps to say 100 tons per year?

And you want move worker up to space. And that seems to be the expensive part.

Generally, getting down from orbit is much cheaper than getting to orbit- say somewhere around 1/10th the cost or less.
If whatever you shipping from space to earth surface can withstand high gees- it's cheaper. 50 gees is a car accident. If payload can withstand over 100 gees, "landing" is more like a controlled crash. A controlled crash into a lake, could something with fairly high terminal velocity. And one major aspect is the accuracy of hitting say 10 sq kilometer area.
Normally, one want re-entry which is lifting body- to reduce gees [and heat- though heat isn't as challenging as gee loads].
« Last Edit: 02/26/2012 10:49 PM by gbaikie »

Offline Archer

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The first thing to manufacture in space is perhaps spacecraft. After all - they are so valuable that it is worth the cost of launching them to orbit.

Steve
Plants that build electronics costs billions on Earth, and market for satellites is very small. That's too much for a risky enterprise.

As for thought experiment of a factory in space. I am guessing you mean something which doesn't high volume- making drugs or something with low mass but is valuable. So perhaps 10 tons per year shipped to earth per year? With increase possible, perhaps to say 100 tons per year?
Exactly. I just don't know what small (both low mass and small dimensions) and expensive can be manufactured in space, that cannot be manufactured on Earth.
As far as I know only mining metals from asteroids can be profitable (if delivery from LEO to Earth surface is 100$/kg).

If whatever you shipping from space to earth surface can withstand high gees- it's cheaper. 50 gees is a car accident. If payload can withstand over 100 gees, "landing" is more like a controlled crash. A controlled crash into a lake, could something with fairly high terminal velocity. And one major aspect is the accuracy of hitting say 10 sq kilometer area.
Normally, one want re-entry which is lifting body- to reduce gees [and heat- though heat isn't as challenging as gee loads].
Good point about g-loads.
It seems that my factory will need 2 types of LEO-shuttles: one for workers (with gentle landing) and one hard-duty automated cargo truck.
« Last Edit: 02/28/2012 06:42 PM by Archer »
The future is better than the past. Despite the crepehangers, romanticists, and anti-intellectuals, the world steadily grows better because the human mind, applying itself to environment, makes it better. With hands...with tools...with horse sense and science and engineering. (c) R. A. Heinlein

Offline Jim

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 The first thing to manufacture in space is perhaps spacecraft. After all - they are so valuable that it is worth the cost of launching them to orbit.


No, it is because it is cheaper to do it on the ground.  A factory in orbit is expensive.  I content it will be cheaper to recover raw materials from space on the ground, re-manufacture and launch for many decades* before it will be cheaper to do it in space.

* as long as humans have to be present.
« Last Edit: 02/28/2012 07:23 PM by Jim »

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