Okay, I see where you're going with this. That does make sense; I should have seen it earlier. Even capsules have to worry about L/D...
Your argument about Mach 25 was still nonsense.
Also, you'd have to worry about whether or not the wings were actually going to see significant aero loads in an off-nominal condition. A light structure would rip off if you actually tried to fly with it rather than just massaging the trajectory (and it occurs to me that you might get more lift (definitely more drag), though not much maneuverability, with just the stage broad side on - you couldn't use weak wings broad side on at a speed high enough for the cross range improvement to be noticeable).
...after further consideration, I still don't like it. I think they'd have to be pretty heavy. But this is pre-analysis, so in principle I could be convinced.
It's not like no one has ever proposed scissor wings on a flyback booster before. But the design tends not to be an afterthought on a conventional rocket stage.
Space X to build reusable launch vehicle
Well the thing is that they would not have to be much more durable than the parachute suggested by others...Also, you'd have to worry about whether or not the wings were actually going to see significant aero loads in an off-nominal condition. A light structure would rip off if you actually tried to fly with it rather than just massaging the trajectory (and it occurs to me that you might get more lift (definitely more drag), though not much maneuverability, with just the stage broad side on - you couldn't use weak wings broad side on at a speed high enough for the cross range improvement to be noticeable).
As you are saying the wings only have to give it a slightly more horizontal trajectory and orient the stage in a way that gives it the most drag/lift.
You dont have to maneuver much with it either, most of that is done with the engines.
Dont think of it as flying, more of a controlled falling. Thinking about how much crossrange basejumpers get out of a wingsuit, the wings just would not have to be very big.
You dont need much crossrange anyway. About 1:1, probably even less since the engines can do the rest. They will have to do some of that anyway if they want to do a pinpoint landing.you couldn't use weak wings broad side on at a speed high enough for the cross range improvement to be noticeable)
In the case of the F9 first stage even a tiny, small improvement reduces the amount of fuel it needs for the return to the launchpad considerably.
I know others have, which is why I picked up Kitemans idea there.It's not like no one has ever proposed scissor wings on a flyback booster before.
Last edited by Skipjack on Mon Oct 31, 2011 6:52 pm, edited 1 time in total.
Parachutes don't have to be "durable" because they're in tension. A wing root has to take shear, and lots of it.
Also keep in mind that if the angle of attack is nonzero, the wings are going to take at least their fair share of the drag corresponding to their share of the front-facing area - more if they aren't stalled... and terminal velocity is one gee...
Also keep in mind that if the angle of attack is nonzero, the wings are going to take at least their fair share of the drag corresponding to their share of the front-facing area - more if they aren't stalled... and terminal velocity is one gee...
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GIThruster
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Skipjack wrote:As you are saying the wings only have to give it a slightly more horizontal trajectory and orient the stage in a way that gives it the most drag/lift.
Not so sure. . . Separation is about 100km downrange and the wings won't work above 100km. Add the coast during breaking and you're left with a need for better than 1:1 average glide. That requires a significant wing. Shuttle glides 1:1 at about 60 km, but much higher lower down (all wings will experience this change) of about 4.5:1 at final approach. To get 100km cross-range from something like a cylinder, you need a serious wing.
"Courage is not just a virtue, but the form of every virtue at the testing point." C. S. Lewis
I never said that shuttle could not do polar. What I am saying is that it is either one or the other. Even X-37 has not been able to transition into a polar with its Massive changes in orbit.
And as you know, you can launch polar from anywhere, it is just how much push verses payload. Again, as you know,the lower latitude pads just require less push for load when you use the planet's spin as an assist.
But I would like to see the mission that does anything useful for things on the ground during re-entry. What would be the point, and what useful thing could be accomplished that you could not do from on-orbit without the distraction of trying to stay alive while "driving" a white hot brick to the dirt?
And as you know, you can launch polar from anywhere, it is just how much push verses payload. Again, as you know,the lower latitude pads just require less push for load when you use the planet's spin as an assist.
But I would like to see the mission that does anything useful for things on the ground during re-entry. What would be the point, and what useful thing could be accomplished that you could not do from on-orbit without the distraction of trying to stay alive while "driving" a white hot brick to the dirt?
The U.S. likes to launch over water, or at least uninhabited territory. Location matters.
There was a plan, apparently, to put up a polar-orbiting satellite (or steal a Soviet one) in a single orbit, and land back at base. Since the target orbital track wouldn't pass back over the base, the Shuttle needed enough cross range to make up the difference. Nobody claimed there would be black ops conducted during reentry.
Of course, it also helps to be able to target multiple landing sites without having to wait a long time for your orbit to align; the mission doesn't need to be black for that.
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As for changing from equatorial to polar, you'd actually use about 30% less delta-V just landing the thing and relaunching into the desired orbit. Of course, Shuttle couldn't actually do equatorial from either launch site, but the delta-V required to go to polar orbit from a Kennedy orbit is about the same as that required to launch to polar orbit from the ground.
There was a plan, apparently, to put up a polar-orbiting satellite (or steal a Soviet one) in a single orbit, and land back at base. Since the target orbital track wouldn't pass back over the base, the Shuttle needed enough cross range to make up the difference. Nobody claimed there would be black ops conducted during reentry.
Of course, it also helps to be able to target multiple landing sites without having to wait a long time for your orbit to align; the mission doesn't need to be black for that.
...
As for changing from equatorial to polar, you'd actually use about 30% less delta-V just landing the thing and relaunching into the desired orbit. Of course, Shuttle couldn't actually do equatorial from either launch site, but the delta-V required to go to polar orbit from a Kennedy orbit is about the same as that required to launch to polar orbit from the ground.
Last edited by 93143 on Mon Oct 31, 2011 8:40 pm, edited 4 times in total.
I could see a west coast launch with an east coast recovery, but man, that would be a FAST mission. It would also beg the question, what is the point?
A lot of russian birds are in molniya and that would be a really hard capture. They use the molniya due to being a high latitude nation.
High inclination and polars are good for ISR, lots of fast ground coverage. But ground station can be a challenge as it is running on a tangent. Equaltorial or low inclination are better for ground station links. The birds with high data to pass get longer looks to the dishes. This is also another advantage of molniya, you can pick your slow leg for data link, and many russian comm birds do exactly this.
Kepler is unforgiving, and we have yet to put up something with enough energy density to flaunt his laws like an episode of Star Trek.
A lot of russian birds are in molniya and that would be a really hard capture. They use the molniya due to being a high latitude nation.
High inclination and polars are good for ISR, lots of fast ground coverage. But ground station can be a challenge as it is running on a tangent. Equaltorial or low inclination are better for ground station links. The birds with high data to pass get longer looks to the dishes. This is also another advantage of molniya, you can pick your slow leg for data link, and many russian comm birds do exactly this.
Kepler is unforgiving, and we have yet to put up something with enough energy density to flaunt his laws like an episode of Star Trek.
...yeah, I don't think a Molniya would have been feasible; the speed at perigee is way too high. Shuttle couldn't have caught it. It would have to have been in LEO.
It should be noted that the satellite kidnapping scheme is the second version of the story I've heard. The first time, the story I got was that Shuttle was supposed to put up American satellites in polar orbit, short notice once-around. I suppose a fast retrieval of a friendly spysat might also have been plausible... you know, there's a guy on NSF who would know; maybe I should search his posts...
Also keep in mind that polar orbits have very harsh radiation environments. A Shuttle in a polar orbit would have to get down pretty quickly regardless of the mission objectives.
It should be noted that the satellite kidnapping scheme is the second version of the story I've heard. The first time, the story I got was that Shuttle was supposed to put up American satellites in polar orbit, short notice once-around. I suppose a fast retrieval of a friendly spysat might also have been plausible... you know, there's a guy on NSF who would know; maybe I should search his posts...
Also keep in mind that polar orbits have very harsh radiation environments. A Shuttle in a polar orbit would have to get down pretty quickly regardless of the mission objectives.
Most ground surveillance type flights are either high inclination or polar.
A snatch mission is perfectly feasible, just needs a high energy budget. And if you are going after anything with any kind of legs, and the other guy knows it, you might as well go home.
I don't see why shuttle couldn't have done a snatch. Especially given the relative retardedness of non-US states to do space tracking. If there is an area the US is way ahead it is space surveillance. Of course they may put two and two together after they lose contact, but the ability to prove what happened is another thing entirely, especially back in shuttle's heyday.
Be an interesting book to read. Something on the lines of Robert Ballard and his "Titanic" cover mission or the Glomar Explorer.
A snatch mission is perfectly feasible, just needs a high energy budget. And if you are going after anything with any kind of legs, and the other guy knows it, you might as well go home.
I don't see why shuttle couldn't have done a snatch. Especially given the relative retardedness of non-US states to do space tracking. If there is an area the US is way ahead it is space surveillance. Of course they may put two and two together after they lose contact, but the ability to prove what happened is another thing entirely, especially back in shuttle's heyday.
Be an interesting book to read. Something on the lines of Robert Ballard and his "Titanic" cover mission or the Glomar Explorer.
As I said, it only needs to glide PART of the distance.Not so sure. . . Separation is about 100km downrange and the wings won't work above 100km. Add the coast during breaking and you're left with a need for better than 1:1 average glide. That requires a significant wing. Shuttle glides 1:1 at about 60 km, but much higher lower down (all wings will experience this change) of about 4.5:1 at final approach. To get 100km cross-range from something like a cylinder, you need a serious wing.
It does not have to glide all the way. Personally, I am convinced that it does not have to at all and that it can just flay back with its engines. From the video that is what SpaceX thinks as well.
But, I was saying that any ability to glide even part of the way will help with saving fuel. Of course you wont have much air to glide on high up in the atmosphere, but parachutes wont help you there either.
Once you reach 60km, things get a bit better though and even the shuttle brick gets a 1:1 glide ratio.
Dont forget that in contrast to the shuttle, an almost empty first stage is very bouyant. Add a bit of directional impulse from the engines (something that the shuttle does NOT have during descent) and the world looks very differently.
This is why I think that Kitemans idea was not that far out. But as I said, I dont think they will need that at all. I think that with the planned upgrades to the first and second stage, they will have enough performance reserves to fly the first stage back and do a powered landing.
Shuttle used thrusters for reentry attitude control until the control surfaces got enough bite. Not a good use for OMS, although it might have made an interesting last-ditch mode. RCS is redundant enough.Skipjack wrote: Add a bit of directional impulse from the engines (something that the shuttle does NOT have during descent) and the world looks very differently.
I found this table for air density versus altitude.
If it is accurate it means good and a bad news.
The good news is that a cylindrical body of the shape and mass of an empty Falcon 9 first stage has a terminal velocity of only about 200 m/s (falling engines first). That means the amount of propellants needed for the final maneuver is even less than the 2 tonnes I calculated before, more like 1.2-1.4 t (if performed in the minimum time).
The bad news is that above 40 km the terminal velocity is so high that at the relatively low speed the stage falls it hardly suffers any braking, so from 100 km to 40 km it keeps accelerating to near 2.2 km/s, and then it has to lose all that in the few seconds that takes to get to the 10 km level (T/V ~335 m/s).
The kinetic energy to get rid of is huge, more than 45,000 MJ. If completely turned into heat it would elevate the temperature of a block of 20 t of aluminum more than 2,500 K, and with steel is even worse.
I wonder how much from that is taken away by the air, and how much is radiated, and how fast.
If it is accurate it means good and a bad news.
The good news is that a cylindrical body of the shape and mass of an empty Falcon 9 first stage has a terminal velocity of only about 200 m/s (falling engines first). That means the amount of propellants needed for the final maneuver is even less than the 2 tonnes I calculated before, more like 1.2-1.4 t (if performed in the minimum time).
The bad news is that above 40 km the terminal velocity is so high that at the relatively low speed the stage falls it hardly suffers any braking, so from 100 km to 40 km it keeps accelerating to near 2.2 km/s, and then it has to lose all that in the few seconds that takes to get to the 10 km level (T/V ~335 m/s).
The kinetic energy to get rid of is huge, more than 45,000 MJ. If completely turned into heat it would elevate the temperature of a block of 20 t of aluminum more than 2,500 K, and with steel is even worse.
I wonder how much from that is taken away by the air, and how much is radiated, and how fast.
"The problem is not what we don't know, but what we do know [that] isn't so" (Mark Twain)
So I guess the question is whether the improved performance of the 1D can allow the remaining fuel to provide enough delta-v to counter that acceleration between 100 and 40 km. If it works, I would think it should be able to divert the stage back towards the launch pad at the same time.
So, it comes down to available and required delta-v again.
So, it comes down to available and required delta-v again.