I know nothing about the fluid dynamics of upper atmosphere nor why the current design of the shuttle was determined to be the most effective to get back on the ground…but have made a few “assumptions”.
The wings of the shuttle were made only large enough to give it usable maneuverability in the lower reaches of the atmosphere to give it a chance to get lined up for a landing.
The wings aren’t large enough to give it enough lift in the thinner upper parts, so the heat tiles are in place along the leading edges and bottom in order to protect the craft as it plunges through the thinner, unmaneuverable air molecules. Rockets keep the angle of attack so that the bottom and forward part are exposed to this friction.
The resultant engineering of the shuttle, the size, weight air displacement and aerodynamic drag forces of take off into account to arrive at this “best of all worlds” final compromise of a design to survive launch, general hazards of space duty, rentry and landing it where wanted.
But just to question one aspect…how could re-entry be made safer?
How about: when the first twinges of resistant air is met, pop a huge chute. There might not even be enough air to get it fully deployed for a minute …but when it did it wouldn’t pop your neck or anything dangerous…just start to gradually slow you down. Let’s say it happens at 250,000 feet (+ or - 100k). The chute, attached to the rear, would naturally cause the shuttle to orient itself forward, at first, and then GRADUALLY downward, slowing as it went. The frictional forces would never (?) come into play as the chute is big enough to physically react to the gathering number of air molecules to exert evermore slowing force on the falling craft.
When an elevation has been reached to allow craft control with wing surfaces (let’s assume a wing surface 50% larger than current) at around 50,000 feet, cut the chute loose. The craft would not need to fall much further before it had complete aerodynamic control and could glide a couple hundred miles in any direction to reach a runway.
Pluses for this idea include:
NO DAMAGING HEAT i.e. no totally helpless moments when the craft is completely at the mercy of reentry forces.
Huge weight reduction possibilities with elimination of most of the tile…a gain for payload size.
Possible minuses:
What if the chute didn’t deploy or deploy correctly? I’m sure there are devices such as inflatable “helpers”, etc to assure this to a degree…
Could overshoot or undershoot the landing spot by a couple of thousand miles. Maybe fire retros at the correct “spot” shortly after the chute is deployed?
So, what do you think of this idea? What kind of holes do you see?
TP
“When I die I want to go peacefully like my grandfather. Not screaming and thrashing like all those people in his car”. Unk
Uh, don’t you suppose there are just a handful of folks at NASA who DO know about these things? Don’t mean to be nasty sounding, but you must be able to figure that there have been engineers working on the design of a reusable shuttle for at least 30 years. (Maybe 50 for all I know) I gotta figure that they’ve looked at a lot of possible designs, even those you’ve mentioned. Maybe, if you made one of your questions more specific, someone would give you a specific answer that would advance your understanding of these things.
The shuttle is going WAY too fast for a chute to be able to survive and slow it down. If you wanted to slow the shuttle down instead of using friction to slow it, you’d have to use a rocket, and then you’d need to carry as much fuel as it took to get the shuttle up there in the first place, which is quite a bit.
The Shuttle in orbit is travelling at over 15,000 mph, because that’s what it takes to achieve (and stay in) orbit. 100 tons of mass travelling at that speed has 2*10[sup]12[/sup] Joules of kinetic energy. That’s 600 megawatt-hours. To get back to the ground and stop, you have to either supply this much energy to reverse thrusters, or use “brake pads” that can dissipate this much energy. The thermal tiles on the Shuttle serve as the latter. It has to get hot; the whole point is to get rid of kinetic energy by turning it into heat.
And even if a parachute were possible, how do you figure it’s safer than wings with insulation tiles? It’s true that one fatal accident occurred as a result of failed insulation tiles, but another one occurred as a result of tangled up parachutes (Soyuz 1).
Thermal protection usually isn’t the hardest part of a spacecraft. It’s a weak point on the Shuttle only because it’s designed to be reusable (i.e. you can’t use materials that melt away as it’s heated), and built with 1970s technology. This article has some info on a newer, more robust thermal protection system.
In this case, the parachute will be subjected to the heat of re-entry, as it slows from orbital velocities. What material suitable for a parachute can hope to withsand that heat?
The relative velocity (something like 18000mph) of those air molecules is the problem.
If the shuttle is to glide a couple of hundred miles from an altitude of 10 miles, it will need a glide ratio around 20:1, as compared to the current shuttle’s 2:1. This would be a radical redesign and invoke many other problems and costs.
You may have the common misconception that the tiles are something like kitchen tiles. In terms of density, they are actually much more like styrofoam. Eliminating them would represent a meaningful weight savings, but perhaps not as large as you are thinking.
IIRC the shuttle is doing about Mach 25 or so when it hits the atmosphere…
According to this, that’s about 18,000 miles per hour… I’m not sure a chute could be made strong enough with current technology to either slow down the shuttle or even remain attached at that speed.
There arguably is a little lift but that has not much do do with the fact that all that kinetic energy has to be turned into something else, heat. No convenient way for the reeentry to just recharge the fuel cells instead of heating the tiles. Second it doesn’t need to be held in its orientation by rockets as the shape is a stable one with the center of mass ahead of the center of drag. Of course it needs to be put in that orientation by rockets since there isn’t any other way to maneuver above the atmosphere.
Don’t think that the shuttle isn’t the only possible design for reenetry but it isn’t as flawed as you seem to think.
Give the guy a break. There’s no harm in discussing the idea, even if it turns out not to be very good. At this point, NASA is not really in a position to say “we know best.”
A parachute made of the best available material would be ripped to shreds going 18,000 mph through the sea-level atmosphere. However, high up in the atmosphere, there is little air, so the drag is a lot less. One misconception is that the reentry heating is due to friction - not really true. I’m not a gas dynamicist, but my understanding is that most of the heating comes from compression in the region just upstream of the vehicle.
Could a parachute made of, say, silica fiber on the outside with some sort of structural reinforcement in a deeper layer, be feasible? There are many, many factors to consider, but I wouldn’t dismiss it out of hand.
Why does the shuttle have to move so fast? I know that to acheive and maintain orbit requires speed, but would it be possible to slow down before entering the atmosphere? (or is that what the fuel you mention would be used for?)
How does Burt Rutan and SpaceShip One do it? I know they don’t acheive orbit, but they don’t seem to have the fiery reentry that NASA’s spacecraft do/
NASA could send Jessica Alba up with the shuttle. My understanding is she would gain the power to project a big force field around the shuttle during re-entry.
Right - as noted, it would take approximately as much fuel to slow the shuttle down to flying speed as it took to accelerate it from that sort of speed to orbital speed.
They didn’t achieve orbit and thus didn’t need anything like orbital speed. Thus, a much smaller amount of energy to dissapate during descent.
As impressive as SpaceShip One is, it’s a big step from there to an orbital mission.
I’ve always wondered why you can’t use a small amount of fuel to gently spiral into the athmosphere. Is the boundary that well defined that either you’re orbiting or burning up? Would it require too much fuel to just start spiraling down in a controlled fashion until you’re in the upper athmosphere not going the orbital velocity anymore?
By spiralling I mean start the descent slowly controlling altitude and slowing down as much as possible in very thin athmosphere near orbit over several (if not dozens) of passes around the earth.
Let’s say you enter that narrow layer where air is just dense enough to slow you down gently, but not dense enoug that you need heat shields. What do you do when the braking force slows you down to, say, 80% of orbital speed? You’re still travelling at Mach 20, and centrifugal (orbital) force is not enough to keep you afloat. You’d plunge down further into the atmosphere, where air is dense enough to provide lift and heat you up.
Perhaps you could use rocket engines to keep you afloat, but then you’d be at the mercy of those engines working correctly. Heat shields are simpler and more reliable than engines.
An orbit is, roughly speaking, an ellipse, correct? A descent to the ground is that same ellipse with thrust and air resistence factored in which makes it some sort of a degenerate logarithmic spiral. So what parameters are needed to adjust how tight the spiral is(say 1/3rd of a pass around the earth before touchdown vs. 200 passes)? Does it require increasing your speed or using too much energy to get to the latter?
You can have as many loops on that spiral as you like, but most of your decrease in speed and in altitude is going to come in a small fraction of the last loop. In fact, while the Shuttle is “in orbit”, it’s really just making a lot of loops of such a spiral (though not the same spiral as the one it’s on while landing; it would take too long to wait for that).
By the way, Controvert, is that the best use you can think of for Jessica Alba? Personally, I’d much rather have her in some specific places on the Earth.
The original thought would have a chute able to be opened in near non-existent air without being “holed”. The thought is that there are relatively few molecules of air up in the reaches where the slightest sort of friction would be felt. Just for example lets say there are 100 molecules per square centimeter at 250,000 ft whereas closer to sea level every cubic centimeter has roughly 1 x 10 to the 20th, or 100,000,000,000,000,000,000 molecules (which is true).
If that chute could be deployed at a relative 18,000 mph, would those 100 molecules per sq centimeter “hole” the chute? That would kill the idea.
I would hope there would be SOME friction (compression?) to start applying a slight tug on the ship but not enough heat to damage the chute. This would very gently slow the forward movement causing it to fall slightly lower in orbit, encountering more molecules, thus more slowing. There is no sudden “wall” of heavy molecule count that will rip the chute or cause acute deceleration. It’s all gradual.
But if you all are saying that molecules of any small number hitting the chute at those high speeds are going to hole it, burn and shred it, then this exercise is over.
This I understand. However, I don’t want to remain at the same height - I want to land the spacecraft. Therefore, I want to slow down.
Suppose instead of orbiting, I’m in a spacecraft travelling in a straight line and arriving at the Earth. Is acheiving orbit (at some fantastic speed) required before I land on the planet, or can I just come straight down? (I understand that “down” is a relative term, but its meaning seems obvious in this context.) According to this site, the surface of the earth is moving at approximately 1041mph at the equator. At the poles, it is moving hardly at all. In addition, we are moving at 67000mph around the sun. So, what would a spacecraft from outside the solar system have to do to catch Earth and effect a landing?