[1] http://www.spacesafetymagazine.com/aerospace-engineering/spa...
Even simple cylinders can be lifting bodies. Shuttle and Falcon 9 both have a L/D of 1.[1] On Falcon 9 the first stage acts as a lifting body, using the grid fins to "trim" the big cylindrical body making it act like a wing.
In the SpaceX landing videos you can see the stage pitch up on reentry. This is no accident. Upward lift = more atmosphere traveled through = more drag = less landing fuel needed = more payload to orbit. A nice optimization by the SpaceX team!
>you don't actually need wings by the way, it's kind of a common misconception around, you just need some lift over drag number, or lift vector - and steer back to the launch pad --- Elon Musk[2]
[1] https://spaceflightnow.com/2017/04/04/musk-previews-busy-yea...
[2] http://shitelonsays.com/transcript/npc-luncheon-with-elon-mu...
This space plane and the shuttle shouldn't be derided for gliding into landing. Not using fuel while landing saves precious cargo capacity. If the main argument against them is that they can't land on the moon, I don't understand why a future craft couldn't both glide into an atmosphere and use thrusters in a vacuum in to land.
Those wings are also a lot of mass, and hence take away from payload. In fact, propulsive landing always takes less mass than wings in the limit of large craft size. (You can see this by taking an equivalent limit, the limit of thin atmosphere; for sufficiently thin atmosphere, the amount of surface area you need to brake diverges but the amount of fuel to stop propulsively is fixed.) In this sense, propulsive landings naturally succeed wings as crafts get larger.
Elegance in engineering is fulfilling the requirements in the simplest, cheapest way possible.
Thanks for your comments.
People pay for a similar experience! ;)
You need a big rocket to slow down and land. At which point it's a very different machine.
> The Dragon-2 has enough power and fuel to land and ascend back to lunar orbit. The Dragon's SuperDraco has higher performance than the Apollo Lunar Module. Apollo LM descent engines has 10,000 lbf thrust, and 3,500 lbf thrust for ascent (the lander part is left behind). The Dragon's SuperDraco has 16,000 lbf thrust. The Dragon also uses computers to control throttle and land (much more fuel efficient). Hence, the Dragon-2 has enough power and fuel to land and ascend back to lunar orbit even if it carries all it's parts during ascent. However, it may need to cut crew from 7 to 3 to loose more weight for fuel.
(Plus, I said "more SpaceX" as in "capsules with powered descent", not "SpaceX's exact current models as already implemented"...)
Estimates are that the Dragon v2 has about 400m/s dV. This is around what it would need for controlled landing or abort. It takes around 1720m/s just to get to the stationary Lunar surface from Lunar orbit; If a Falcon upper stage detaches during the leg of the mission between Earth and Luna, the necessary delta V for the rest of the mission will be around 5080m/s. This is a lot. You would have to build another fairly large vehicle to accomplish this mission - Dragon v2 would be an afterthought.
At the very least, they'd need to consider the dry weight and fuel load to make a fair comparison - maybe they did so offscreen but it's not mentioned anywhere in the post.
Maybe it has been designed to work as a technology platform for deriving a lunar lander. But the Dragon 2 design is just not capable of doing it, not even close.
Work in progress..Well along in progress.
And especially interested on what the options for the problem scenarios look like (e.g. burning off too much or not enough velocity).
Not even close. Dragon has something like 450m/s of dv to use. Getting from the surface of Mars to orbit takes 3800. Orbital capture requires around 2000m/s. Without aerobraking, it couldn't enter Mars orbit, let alone land.
Remember, the initial shuttle design was actually viewed as an improvement by real rockets scientists even if the project ballooned into ridiculous territory there really is a lot of value in those short stubby wings.
"The militarily specified 1,085 nmi (2,009 km; 1,249 mi) cross range requirement was one of the primary reasons for the Shuttle's large wings, compared to modern commercial designs with very minimal control surfaces and glide capability." https://en.wikipedia.org/wiki/Space_Shuttle
There were a lot of other requirements and stakeholders that were part of the planning process, and any of them who didn't understand that espionage was a critical component were left wondering why anyone would design such an expensive, impractical failure; Why every stage of the process where it seemed to be unworkable, someone said "Yeah, don't worry about that" and poured money on the problem. Aside from direct requirements, we also encouraged the Soviet Union to spend lavishly copying our design.
By the time the USSR unexpectedly broke up, Energia had just (unsuccessfully) flown a test run with a giant Polyus laser weapon. Mission accomplished, right? But we didn't then want all of the Soviet scientists to spread to the winds and start building ICBMs for anyone who could pay. We needed them to stay in Russia until Russia could become a solvent, stable state.
So we said "What sort of international cooperative effort could we use a whole bunch of Shuttle AND Soyuz flights for?" and designed (or adapted) a space station around that requirement. We decided to revamp Reagan's ill-fated "Space Station Freedom" program into the ISS.
That's the only reason we didn't retire the Space Shuttle long before the Columbia.
I get a lot of "Nobody seriously thought this", but the high cross-range required of single-orbit-and-land is the long pole in the tent that stretches the rest of the requirements; It's not a reasonable tradeoff unless espionage was a use-case that could not be ruled out.
Without the requirement to land a large cargo bay with an extreme cross-range, the optimal design looks nothing like the Shuttle. The Shuttle cost an order of magnitude more than that optimal design.
The driving requirement was to act as a successor to the SR-71. Launch, make a single reconnaissance pass over the Soviet Union, and then utilize the cross-range capability to land immediately so that the film could be developed. But by the time the Shuttle was actually built, spy satellites equipped with digital cameras had improved so much that it became moot.
We had effective unmanned film camera platforms in space long before we had CCDs, long before the Shuttle was contemplated.
> During the 1950s, a Soviet hoax had led to American fears of a bomber gap. In 1968, after gaining satellite photography, the United States' intelligence agencies were able to state with certainty that "No new ICBM complexes have been established in the USSR during the past year."[10] President Lyndon B. Johnson told a gathering in 1967:
>> I wouldn't want to be quoted on this ... We've spent $35 or $40 billion on the space program. And if nothing else had come out of it except the knowledge that we gained from space photography, it would be worth ten times what the whole program has cost. Because tonight we know how many missiles the enemy has and, it turned out, our guesses were way off. We were doing things we didn't need to do. We were building things we didn't need to build. We were harboring fears we didn't need to harbor.[10]
I thought the link to the x-37c was interesting but I can't find anything that suggests it is anything more than a proposal at this point.
Edit: I would argue that the huge mass of the (STS) oribiter was pretty much its greatest problem, and could be largely attributed to the requirement that the whole thing must be reusable. Not only was it problematic to bring all that mass down, but consider this: the system could bring almost as much mass to orbit as the Saturn V rocket [3], but almost all that capacity was consumed by the orbiter, leaving "just" 27,500 kg for payload. Of course, that is still a huge payload capacity, and the orbiter itself could, to an extent, be considered useful payload.
[1] https://en.wikipedia.org/wiki/Space_Shuttle_Columbia_disaste...
[2] https://www.nasa.gov/mission_pages/shuttle/launch/sound-supp...
[3] The maximum takeoff weight of a space shuttle orbiter was around 109,000 kg (https://en.wikipedia.org/wiki/Space_Shuttle_orbiter#Shuttle_...) while the maximum LEO payload of the Satrurn V was around 140,000 kg (https://en.wikipedia.org/wiki/Saturn_V).