152 posts in this topic

32 minutes ago, Darnok said:

What about something like this?

_80896032_80896031.jpg

Landing with those boosters wouldn't be easier than falcon 9 style?

The boosters seem to be reusable, but they carry a heavy mass penalty for no good reason. The core doesn't seem to be reusable.

What's the point?

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22 minutes ago, Nibb31 said:

The boosters seem to be reusable, but they carry a heavy mass penalty for no good reason. The core doesn't seem to be reusable.

What's the point?

The point is to carry less fuel for landing, than falcon 9 does.

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11 minutes ago, Darnok said:

The point is to carry less fuel for landing, than falcon 9 does.

By adding wings that weigh twice as much? Sure....

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25 minutes ago, sevenperforce said:

By adding wings that weigh twice as much? Sure....

It will take more fuel, but might have a chance of landing more often and more safely.  One huge difference is that falcon can use the fuel for other things.  Such as simply giving more mass the same delta-v, or perhaps avoiding a disaster in the Cygnus launch (ULA simply has huge margins.  Falcon-9 could have simply dipped into the landing reserve.  This craft would either need ULA's margins or simply fail).

It also isn't clear *where* they would land.  You would need fuel similar to space-x to get back to Florida (in addition to launching those wings).  Launching over land has worse issues.  They really don't look like they are meant for sea landings.  Also, I thought there was a reason that they couldn't use X-15 style wings (other than the unused cross-range spec) for the shuttle, my guess is that  when hitting the atmosphere wings perpendicular, the center of drag needs to go through the center of mass.  Such things make for interesting design problems.

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8 hours ago, sevenperforce said:

 

Staging simply offers a LOT of advantages, not all of which are readily apparent. You can use sea-level-optimized engines at sea level and vacuum-optimized engines in space.

 

You can do so too with SSTOs.

8 hours ago, sevenperforce said:

 

Perhaps even more importantly, you can have a lot of thrust at launch and less thrust up high. Hydrolox offers by far the highest specific impulse of any reasonably fuel combination, and mass ratio is insanely important for an SSTO, so let's use hydrolox. You need about 7,500 m/s of dV to get into orbit, so that's a propellant mass fraction of 84%. Totally manageable, right?

8 hours ago, sevenperforce said:

But there's something else to account for: drag. Gravity drag and aerodynamic drag. And here's where the lack of staging really kills you. Hydrogen engines have high specific impulse but crappy thrust, which means they are going to have far worse susceptibility to gravity drag than a beefier fuel combination like kerolox. A kerolox engine might need an extra 1.5 km/s to fight drag going up, but a hydrolox engine will need closer to 2 or 2.5 km/s to fight drag, bringing the propellant mass fraction up above 90%. And your hydrogen engines will need to be heavier than a kerolox engine of equivalent thrust, which will probably end up cutting your payload in half or worse.

Couple that with hydrogen's low density and high tankage volume, and you'll REALLY be wishing you had a kerolox engine and a kerolox tank strung alongside to help lift you the first half of the way. But if you have a kerolox engine and a kerolox tank strapped alongside, then it really only makes sense to drop them at some point so they can RTLS for reuse while your hydrolox stage rockets into orbit.

1.5 stages to orbit is SO much simpler than single-stage-to-orbit.

That's why tripropellant engines exist.

3 hours ago, sevenperforce said:

Replace the SRBs with Falcon-Heavy style kerolox boosters, but add auxiliary LH2 tanks

What's the point of using H2 on the boosters? You're only going to use them on the surface, you're better off using regular Rp-1 Lox, an you don't need to use crossfeed if you do. So much simpler.

3 hours ago, sevenperforce said:

truncated aerospike nozzle for altitude compensation

Or an SSME.

2 hours ago, Darnok said:

What about something like this?

_80896032_80896031.jpg

Landing with those boosters wouldn't be easier than falcon 9 style?

It should. Wings have a better landing success record than F9 landings :P

2 hours ago, sevenperforce said:

the center booster needs to be altitude-compensating with a truncated aerospike to act a heat shield,

Wait, wasn't it expendable in your design?

2 hours ago, sevenperforce said:

You don't need those useless fins

They aren't useless if you want to land horizontally.

1 hour ago, wumpus said:

perhaps avoiding a disaster in the Cygnus launch (ULA simply has huge margins.  Falcon-9 could have simply dipped into the landing reserve.  This craft would either need ULA's margins or simply fail).

F9 would just fail if the same thing happened as happened on the OA-6 mission, all the extra Delta V is on the 1st stage (and it was that stage that failed).

 

But that also brings the question- how about using parafoils to do a landing on a aircraft carrier (I think that would be too expensive) or by heli mid-air  recovery? Is heli recovery too risky? Or is it a viable near-term solution, comparable to F9 landings? I mean, the S-IC was once considered for the heli recovery

2 hours ago, Nibb31 said:

The boosters seem to be reusable, but they carry a heavy mass penalty for no good reason. The core doesn't seem to be reusable.

What's the point?

Reducing costs, via the reusable LRBs.

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2 hours ago, sevenperforce said:

By adding wings that weigh twice as much? Sure....

How much fuel (in tons) is needed for Falcon 9 to land back near landing pad?

How much does landing legs weight? How much weights landing gear?

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48 minutes ago, Darnok said:

How much fuel (in tons) is needed for Falcon 9 to land back near landing pad?

How much does landing legs weight? How much weights landing gear?

https://www.quora.com/How-much-additional-fuel-will-a-Falcon-9-first-stage-need-in-order-to-return-to-the-launch-pad

Apparently, there's a 30% payload penalty for RTLS landings.

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On April 4, 2016 at 11:33 AM, Spaceception said:

Not even on paper? I mean, I know going by paper isn't always completely correct, but it's a good ballpark.

really? I would say the on paper only credibility rate is quite low.

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1 hour ago, Darnok said:
5 hours ago, Darnok said:

What about something like this?

_80896032_80896031.jpg

Landing with those boosters wouldn't be easier than falcon 9 style?

How much fuel (in tons) is needed for Falcon 9 to land back near landing pad?

How much does landing legs weight? How much weights landing gear?

The solution is to design a side tank with a cheap engine, cheap fuel, and barely suitable wall.....otherwise known as a SRB. 

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26 minutes ago, PB666 said:

The solution is to design a side tank with a cheap engine, cheap fuel, and barely suitable wall.....otherwise known as a SRB. 

The idea was the reuse would be cheaper.

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9 minutes ago, fredinno said:

The idea was the reuse would be cheaper.

If the fuel is 80% of the cost why bother.

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Fuel (propellant) isn't 80% of the cost... isn't it about 1 percent or less?

Edited by Pipcard

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3 hours ago, fredinno said:

You can do so too with SSTOs.

That's why tripropellant engines exist.

 

Well, existed, more than exist. But yes, you can compensate for these things in an SSTO. I was just pointing out that these are automatically provided for with staging, but need to be specifically provided for in SSTO designs. 

3 hours ago, fredinno said:

What's the point of using H2 on the boosters? You're only going to use them on the surface, you're better off using regular Rp-1 Lox, an you don't need to use crossfeed if you do. So much simpler..

Oh, I had no intention of actually burning LH2 in the strap-on boosters. Those tanks are there solely to feed the core rocket, allowing it to have a full tank at staging. Hydrolox has such high tankage volume that dropping tanks is extremely advantageous; using the side boosters to carry the drop tanks back for reuse should offer a substantial advantage.  

4 hours ago, fredinno said:

Or an SSME.

It should. Wings have a better landing success record than F9 landings :P

Wait, wasn't it expendable in your design?

I'm not sure whether an SSME nozzle or an annular aerospike would be better for powered tail-first landings. An annular aerospike is more easily throttleable. 

Technically, winged autonomous landings of spaceplanes are 1 for 1 (Buran), just like tail-first autonomous RTLS landings of orbital-class boosters. 

And no, the core booster definitely wasn't expendable. If I was going to go expendable on anything, I would just say to go Falcon 9. The point was that rapid-turnaround 100% reuse could be readily realized using parallel staging, with almost all the same advantages as SSTO and none or few of the detriments. 

3 hours ago, Darnok said:

How much does landing legs weight? How much weights landing gear?

Assuming materials of equal strength are used, landing legs will always be substantially lighter than landing gear. Landing legs must bear the weight of the vehicle; landing gear must bear the weight of the vehicle AND transfer that weight to an axle AND to a set of wheels, all of which are heavy. 

 

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13 minutes ago, sevenperforce said:

Oh, I had no intention of actually burning LH2 in the strap-on boosters. Those tanks are there solely to feed the core rocket, allowing it to have a full tank at staging. Hydrolox has such high tankage volume that dropping tanks is extremely advantageous; using the side boosters to carry the drop tanks back for reuse should offer a substantial advantage.  

But that enormously increases complexity, and uses untested crossfeed. For a near-term RLV, it's hard enough making the RLV be cheaper.

13 minutes ago, sevenperforce said:

I'm not sure whether an SSME nozzle or an annular aerospike would be better for powered tail-first landings. An annular aerospike is more easily throttleable. 

SSMEs exist. Large aerospikes do not.

14 minutes ago, sevenperforce said:

And no, the core booster definitely wasn't expendable. If I was going to go expendable on anything, I would just say to go Falcon 9. The point was that rapid-turnaround 100% reuse could be readily realized using parallel staging, with almost all the same advantages as SSTO and none or few of the detriments. 

I would put wings on the core too, then. It's actually easier (I think), since you don't need jet engines, as you would for the boosters, you can use the same systems, and the Shuttle can give us data. The propulsive landings probably aren't much better for upper stages, since you still need a lot of weight either way, just to recover it.

You also should but a Centaur-G on the top for GEO missions.

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49 minutes ago, Pipcard said:

Fuel (propellant) isn't 80% of the cost... isn't it about 1 percent or less?

The solid fuel, oh no, not much more expensive. Solid fuel has aluminum in it.  I mean Space X could get the Mexicans to make the housing and float it across the riogrande, lol.

Here are some KSP dynamics,

Prelaunch a = 300,360

I built a 9.95 payload rocket and on a 40.3 ton rocket with a SSME on it, no booster it made a = 646.8 km

I added a very small attachment point added 4 sepratons to added 0.5t (5 second and separation) it made a = 672.5 km

Replaced the seps with 2 Flea - aking total mass = 46.8t (8 seconds, with an aero fuel on top giving about 15 seconds of burn time to engine) a = 1270 km

Increased main fuel tank added 4 hammer mass = 70.9 ton (side tanks add another 30 seconds of burn time to main engine) a = N/A escape velocity + 3700m/s  at 72km.

Replaced boosters with 2,2,2 asparagas mass = 81.3 to (side tanks add 70 seconds of burn time to main tank) escape velocity 70km alt v = 4700 m/s (requires a very aerodynamic payload to withstand maximum dynamic pressure)

Payload size remain constant, in the last three only the booster system changed.

The point-

Accelerate quickly to the spike - Disposable boosters primary use is to accelerate the rocket as fast as possible to maximum dynamic pressure.
Handle the pressure spike - They push the rocket against the greatest resistance to forward motion during the flight
Dispose of the mass tax created by the boosters after the spike- After which they are disposed of, allowing the main engines to efficiently take the craft into space.

Implicit in these three is they add critical kinetic energy, momentum, and altitude all of which act to make the main engine more efficiently and thus add more energy to the payload.

1. fast acceleration means less  gravitational losses while 'hoovering' over the launch pad. The differential between gravity and omega^2*r plotted against time acculates as waste, faster acceleration along the prograde to circularlize reduces this waste.
2. Increased altitude adds potential energy and decrease gravitational pull (an artifact of KSP is that gravity drops about 10 time more quickly than it does on earth for each unit of altitude gained). Reaching these more quickly lowers the gravity costs even more.

3. Increased velocity means dV added by the main engines substantially increases kinetic energy, which can be converted to potential energy by Apo affording a lower cost burn to circularize
4. the cost to get to initial apo in terms of main engine dV is lower, which it has more dV left at apo to circularize and do other stuff (like say carry more payload at the expense of fuel).

Even the smallest booster at launch can have the most profound effect if the main engines a scaled properly for high altitude climb. As we can clearly see, if separation of an orbit from the surface is the goal, boosters get the rocket to extreme heights without the need of stacked stage. Stacked stages need to increase by a factor of 5 for each lower stage added.

There is a bit of a declining utility in boosters if they aren't aerodynamic, because for the first 20 seconds they are accelerating, the force of drag is less than gravity but once the force of drag = gravity the moment of total force goes up with velocity rapidly, there is some advantage to asparagas because you can control speed and prevent escalating drag cost, but those cost are most apparent for a very short period of time.

 

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45 minutes ago, PB666 said:

The solid fuel, oh no, not much more expensive. Solid fuel has aluminum in it.  I mean Space X could get the Mexicans to make the housing and float it across the riogrande, lol.

Here are some KSP dynamics,

Prelaunch a = 300,360

I built a 9.95 payload rocket and on a 40.3 ton rocket with a SSME on it, no booster it made a = 646.8 km

I added a very small attachment point added 4 sepratons to added 0.5t (5 second and separation) it made a = 672.5 km

Replaced the seps with 2 Flea - aking total mass = 46.8t (8 seconds, with an aero fuel on top giving about 15 seconds of burn time to engine) a = 1270 km

Increased main fuel tank added 4 hammer mass = 70.9 ton (side tanks add another 30 seconds of burn time to main engine) a = N/A escape velocity + 3700m/s  at 72km.

Replaced boosters with 2,2,2 asparagas mass = 81.3 to (side tanks add 70 seconds of burn time to main tank) escape velocity 70km alt v = 4700 m/s (requires a very aerodynamic payload to withstand maximum dynamic pressure)

Payload size remain constant, in the last three only the booster system changed.

The point-

Accelerate quickly to the spike - Disposable boosters primary use is to accelerate the rocket as fast as possible to maximum dynamic pressure.
Handle the pressure spike - They push the rocket against the greatest resistance to forward motion during the flight
Dispose of the mass tax created by the boosters after the spike- After which they are disposed of, allowing the main engines to efficiently take the craft into space.

Implicit in these three is they add critical kinetic energy, momentum, and altitude all of which act to make the main engine more efficiently and thus add more energy to the payload.

1. fast acceleration means less  gravitational losses while 'hoovering' over the launch pad. The differential between gravity and omega^2*r plotted against time acculates as waste, faster acceleration along the prograde to circularlize reduces this waste.
2. Increased altitude adds potential energy and decrease gravitational pull (an artifact of KSP is that gravity drops about 10 time more quickly than it does on earth for each unit of altitude gained). Reaching these more quickly lowers the gravity costs even more.

3. Increased velocity means dV added by the main engines substantially increases kinetic energy, which can be converted to potential energy by Apo affording a lower cost burn to circularize
4. the cost to get to initial apo in terms of main engine dV is lower, which it has more dV left at apo to circularize and do other stuff (like say carry more payload at the expense of fuel).

Even the smallest booster at launch can have the most profound effect if the main engines a scaled properly for high altitude climb. As we can clearly see, if separation of an orbit from the surface is the goal, boosters get the rocket to extreme heights without the need of stacked stage. Stacked stages need to increase by a factor of 5 for each lower stage added.

There is a bit of a declining utility in boosters if they aren't aerodynamic, because for the first 20 seconds they are accelerating, the force of drag is less than gravity but once the force of drag = gravity the moment of total force goes up with velocity rapidly, there is some advantage to asparagas because you can control speed and prevent escalating drag cost, but those cost are most apparent for a very short period of time.

 

KSP ain't IRL :mad:

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1 hour ago, fredinno said:

But that enormously increases complexity, and uses untested crossfeed. For a near-term RLV, it's hard enough making the RLV be cheaper.

SSMEs exist. Large aerospikes do not.

I would put wings on the core too, then. It's actually easier (I think), since you don't need jet engines, as you would for the boosters, you can use the same systems, and the Shuttle can give us data. The propulsive landings probably aren't much better for upper stages, since you still need a lot of weight either way, just to recover it.

Untested crossfeed?

Odd that you would cite the SSMEs as better than alternatives while claiming crossfeed is untested when the Shuttle used crossfeed.

A large truncated annular aerospike offers a large surface area for a PICA-X heat shield to protect the booster during re-entry. 

There is no need for jet engines. Use an engine cluster and RTLS for a tail-first landing on the central engine. Make the central engine underexpanded if you desperately need hovering capability. The core booster will have a rougher re-entry due to its high velocity but staging gives us a wide fuel margin.

Wings require landing gear, which weighs more than landing legs. Wings require a runway, which requires additional fuel for maneuvering. 

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7 hours ago, fredinno said:

So those wings would weight more? How?

4 hours ago, sevenperforce said:

Assuming materials of equal strength are used, landing legs will always be substantially lighter than landing gear. Landing legs must bear the weight of the vehicle; landing gear must bear the weight of the vehicle AND transfer that weight to an axle AND to a set of wheels, all of which are heavy. 

 

But landing legs needs to keep booster vertically in balance, while landing gear is for horizontal position. And you don't need mechanism SpaceX uses to balance rocket during landing.

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12 hours ago, wumpus said:

It will take more fuel, but might have a chance of landing more often and more safely.  One huge difference is that falcon can use the fuel for other things.  Such as simply giving more mass the same delta-v, or perhaps avoiding a disaster in the Cygnus launch (ULA simply has huge margins.  Falcon-9 could have simply dipped into the landing reserve.  This craft would either need ULA's margins or simply fail).

It also isn't clear *where* they would land.  You would need fuel similar to space-x to get back to Florida (in addition to launching those wings).  Launching over land has worse issues.  They really don't look like they are meant for sea landings.  Also, I thought there was a reason that they couldn't use X-15 style wings (other than the unused cross-range spec) for the shuttle, my guess is that  when hitting the atmosphere wings perpendicular, the center of drag needs to go through the center of mass.  Such things make for interesting design problems.

Yes, don't think you can use the atmosphere to turn around and glide back with first stage. 
If you launch over land or has land at landing zone you don't need boost back and you also don't need wings. 
Benefit with the falcon 9 system is that lots of the landing fuel is also emergency reserve 

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9 hours ago, fredinno said:

KSP ain't IRL :mad:

I forgot to add - 5. By increasing altitude more quickly during the early flight phase it maintains fuel while diminishing drag.

Yeas, not RL. But since I make my own parts I can deal with some of the differences (like for instance having an SSME with 453 ISP). But the points are still valid, its a major reason that all the space programs use a launch stage or boosters.

The differences between KSP and RL

1. The orbit is 7900 m/s versus 2300 m/s
2. The surface moves 400 m/s versus 175 m/s
3. Earths R = 6371000 versus 600000. This means that for Earth the thermodynamic potential for reaching space at the same altitude is slightly higher (about 11%).
4. Earths atmosphere is thicker at the lower levels and drops out less quickly. Mount Everest is about 30,000 feet (9840 meters) but the atmosphere is a 1/3rd. Kerbin atmosphere drops 1/2.6 by 5000 meters, by 10000 meters it is around 1/6.5 (about half as then as Earth at the same altitude)

The result of the difference
1. The need for dV is greater, since the ISPs are about the same, this translate into the need for more stages on Earth.
2. The surface movement slightly reduces the dV thirst of Earth launch.
3. KSP based rockets start experiencing significant reduction of gravity the moment they take off, for an earth based rocket to experience the same difference it would need to travel 10.5 times as far away from the surface.
4. Earth based rockets have to be more streamlined and turn to horizontal less slowly than in the game.

The result in terms of staging.

A. If a rocket designed on Earth has just enough thrust to hold velocity at maximum dynamic pressure on earth meaning it rough has 2g of acceleration and with coefficient of drag it can accelerate to 0.90 Mach at 1 ATM (which mean that drag = force of gravity at that speed) then its surface relative acceleration will follow a path of roughly 1G to 0G with average acceleration of 0.75G. At the same time it would be burning fuel, to maintain that acceleration from launch it would need additional thrust or it would be wasting fuel. If a booster provides that thrust and then falls away at maximum dynamic pressure, that booster is providing the most possible benefit to the rocket
Reason - the time that a rocket spends over the launch pad trying to gain maximum allowable speed is the time that consumes the most fuel per distance traveled in flight.

Math -      Energy (work) = Force * distance traveled   The less distance traveled while applying a force, the less energy that is created.
                Energy(work)/Mass = Acceleration * distance. = Thrust/Mass * distance

Since an ideal rocket engine (that means not over powered and thus weight wasteful) reaches around 275 m/s at which point it no longer needs to accelerate until it loses drag force and fuel, and since  it takes about 40 seconds to reach this point and since a typical rocket has about 5 to 10 minutes of fuel at full throttle, that rocket at 40 seconds would have had  more weight than it needed to push at optimal altitude, its ISP would have been 5% lower.
IOW it would have had around 20 to 30% more weight than its engine could efficiently push at lift-off.

Theoretically it needs a booster(2) that can lift that 20 to 30% more weight and itself at 2g of force. Since you need 2 for balance that equates to 10 to 15% of the weight plus its own weight, and it roughly needs to burn for 40 seconds.

So if we just want to take care of 1 set  launch specific inefficiencies, the lack of optimal momentum and ISP at launch, we need to use boosters or a different first stage. Kerbal or not, the problem is the same.

The next problem is the circularization phase. Lets state the problem.

Suppose I want to place something in high earth orbit or in orbit around the moon. Once I have a circularized orbit, I don't need much of an engine at all, I can kick my orbit at pe several times to get altitude, so why would I carry a launch engine that gives my craft 100 m/s of acceleration once it has burn most of its fuel. Second question is why would I carry all those fuel tanks. Having dealt with the atmosphere and launch inefficiencies its time to think about circularization.

There are two basic problems, simplified to the ridiculous, heat and drag going horizontal and lack of horizontal motion going vertical. The primary issue is how much engine do you need to circularize, the answer is that in order to gain horizontal you have to have enough thrust to counteract a significant portion of gravity experienced. For example the sin of 30 degrees is 1/2, so if the engine generates 2 g of thrust it has enough g force to counteract gravity at 30' once drag has been reduced to the point that it does not cannibalize important momentum and 0.86 of its thrust can go into horizontal acceleration. Since it needs to be roughly 7900 m/s - 400 m/s or 7500 m/s and it can get 2 * 0.86 * 9.8 = 16.85 it needs to burn about 444 seconds at this force to reach its target. Note: it is important to state that vertical acceleration is important for two reasons - first to add thermodynamic energy to the orbit (which the craft keeps and uses) and second to waste, as little as possible, in fighting the war against gravity (u/(alt+surface radius) - omega^2*(alt+surface radius). To waste as little as possible we have to gain horizontal velocity rapidly and altitude less rapidly, the reason why circularization quickly is better than burning up.

However, as it burns the fuel its mass decreases and its engines become overpowering, but the problem is more profound according to omega^2*r once it reached Vo of 5925 it only needs 1/4 of its thrust to gain to maintain verticle speed irregardless of weight loss. This is about 333 seconds after maximum dynamic pressure for the engine which has already 40 seconds, which means the engine has been burning for a total of 373 seconds. Its ISP is 435 seconds in a vacuum, its time to shed that engine and tanks and go for a combo that produces 1/10th the thrust, with an engine weight of 1/20th and is efficient. Instead of an engine that can carry something at 5x*2g you need something that carries at 1x*g.     
Heres the point. Once gravity is sufficiently tamed ______ that is when  (u/(alt+surface radius) - omega^2*(alt+surface radius) is much closer to zero than surface gravity , its time to get shed  the antigravity gladiator and invest in a dV miser. Since the craft still has vertical momentum it can consume that momentum with a lower thrust engine and burn to horizontal. One other very important point also, that huge engine and stage tanks are traveling at 6000 m/s, it falls back to earth with no need for a decay burn. So there are three good reasons to have a second stage even if one has two boosters for the first stage.

 

 

 

 


 

Edited by PB666
corrected 1/2 with 1/4th

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5 hours ago, Darnok said:

So those wings would weight more? How?

But landing legs needs to keep booster vertically in balance, while landing gear is for horizontal position. And you don't need mechanism SpaceX uses to balance rocket during landing.

30% of the payload is not much in comparison to the rocket. Falcon 9v1.1 massed 506 tonnes on the launch pad with an LEO payload of 13 tonnes. 30% of the payload is just 0.77% of the mass of the loaded rocket. Good luck figuring out a way to put wings on a booster for under 1% of launch weight.

Landing legs have the support the same weight regardless of whether the booster is vertical or horizontal; the booster doesn't magically lose mass in the horizontal position. Landing gear for a horizontal landing requires the entire booster body to be strengthened to support radial stresses, while landing on the tail distributes stress axially, which is the direction the rocket is already designed to handle stress in. Finally, SpaceX uses no "mechanism" to balance the rocket; rather, they simply use the existing RCS cold gas thrusters required for attitude control during launch.

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24 minutes ago, sevenperforce said:

30% of the payload is not much in comparison to the rocket. Falcon 9v1.1 massed 506 tonnes on the launch pad with an LEO payload of 13 tonnes. 30% of the payload is just 0.77% of the mass of the loaded rocket. Good luck figuring out a way to put wings on a booster for under 1% of launch weight.

What gives me ~4 tons for both boosters wings?

 

24 minutes ago, sevenperforce said:

Landing legs have the support the same weight regardless of whether the booster is vertical or horizontal; the booster doesn't magically lose mass in the horizontal position.

Sure, but legs has to be larger and stronger, so rocket wouldn't tip over? While gear can be smaller, because you are landing with EMPTY tank horizontally and you need 3 gears not 4 legs.

 

24 minutes ago, sevenperforce said:

Landing gear for a horizontal landing requires the entire booster body to be strengthened to support radial stresses, while landing on the tail distributes stress axially, which is the direction the rocket is already designed to handle stress in. Finally, SpaceX uses no "mechanism" to balance the rocket; rather, they simply use the existing RCS cold gas thrusters required for attitude control during launch.

True, but we are talking about booster, not about core section where you have thrust on bottom and weight on top. Boosters are on sides, so their body has to be stronger for that kind of stresses.
Correct me if I am wrong, but IMO for boosters forces during take off are much larger than forces during horizontal landing with empty tank?

They are called grid fins... but they probably doesn't weight much.

I would go even further and use inflatable wings, if they would have less weight http://www.nasa.gov/centers/dryden/news/NewsReleases/2001/01-46.html

 

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7 minutes ago, Darnok said:

True, but we are talking about booster, not about core section where you have thrust on bottom and weight on top. Boosters are on sides, so their body has to be stronger for that kind of stresses.

Correct me if I am wrong, but IMO for boosters forces during take off are much larger than forces during horizontal landing with empty tank?

 

You are right the the forces are larger at take off, but it's the direction of the forces that's the issue. Any rocket stage is strong in one direction (regardless of whether it's a booster or a core stage) which is vertically. As soon as you introduce lateral loads they are considerably weaker, to the point where landing on its side could cause catastrophic issues if not strengthened appropriately.

Edited by Steel
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