161 posts in this topic

6 hours ago, Darnok said:

Next idea I've seen

Slide27.JPG

This seems the same as a Falcon 9R arrangement with an expendable upper stage, except that it has to carry a cargo bay up and back, and has useless wings.

26 minutes ago, Darnok said:

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.

Four legs or three legs, doesn't matter from a weight perspective. The Falcon 9 first stage could land with three legs easily; they would just be larger individually. Four legs is slightly more stable than three legs.

The tank is empty at vertical landing, too, so there isn't any difference there. Horizontal makes no difference either. The landing gear needs to be fairly wideset so that the rocket body won't tip over either way horizontally. Plus, you have to factor in control surfaces, and you need to be able to extend the gear from inside the body because landing gear cannot fold up aerodynamically.

29 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?

The side boosters couple so that their thrust is transferred through their central axis just like the core booster. Horizontal landing would introduce radial/lateral forces far greater than those experienced during takeoff, even though axial forces are comparatively minimal.

30 minutes ago, Darnok said:
1 hour ago, sevenperforce said:

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.

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

The grid fins are used for hypersonic aerodynamic control during and after re-entry. Landing stability during the suicide burn uses cold gas RCS.

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12 hours ago, sevenperforce said:

 

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

The Shuttle did not use crossfeed, the Shuttle lacked fuel tanks for the SSMEs. It just tunneled its fuel onto the orbiter's engines. That's not crossfeed, that's extra piping.

12 hours ago, sevenperforce said:

There is no need for jet engines

You need those for the lower stages when using wings, otherwise you drop too fast.

 

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9 minutes ago, fredinno said:

The Shuttle did not use crossfeed, the Shuttle lacked fuel tanks for the SSMEs. It just tunneled its fuel onto the orbiter's engines. That's not crossfeed, that's extra piping.

You need those for the lower stages when using wings, otherwise you drop too fast.

 

Like the shuttle brick-gliding in for a landing?

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31 minutes ago, fredinno said:

The Shuttle did not use crossfeed, the Shuttle lacked fuel tanks for the SSMEs. It just tunneled its fuel onto the orbiter's engines. That's not crossfeed, that's extra piping.

How sure are you? I am almost certain that the Shuttle had internal tanks for the SSMEs.

Watch this video of the External Tank separation -- there is no MECO before separation and the plume remains throughout.

EDIT: After reviewing more info it seems you're right; MECO came before separation. 

In any case, I was just presenting a potential design for full reuse.

Edited by sevenperforce
Correction

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4 hours 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.

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.

I've checked few things

http://spaceflight101.com/spacerockets/falcon-9-ft/

https://www.reddit.com/r/spacex/comments/32qh7a/how_much_deltav_does_the_first_stage_need_for/

Empty 1st stage weights ~22t
Someone calculated that you would need ~25 tons of fuel to boostback and landing in falcon 9 style on landing pad
"Legs + grid fins + associated plumbing and avionics likely weigh about 4 tonnes in total".

So we can add wings, landing gear, avionics and booster body could be stronger for horizontal landings.
Even we could put in some electric engines and batteries to have some level of thrust in atmosphere... and I am pretty sure all of this would weight less than 25 tons.

 

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7 minutes ago, Darnok said:

I've checked few things

http://spaceflight101.com/spacerockets/falcon-9-ft/

https://www.reddit.com/r/spacex/comments/32qh7a/how_much_deltav_does_the_first_stage_need_for/

Empty 1st stage weights ~22t
Someone calculated that you would need ~25 tons of fuel to boostback and landing in falcon 9 style on landing pad
"Legs + grid fins + associated plumbing and avionics likely weigh about 4 tonnes in total".

So we can add wings, landing gear, avionics and booster body could be stronger for horizontal landings.
Even we could put in some electric engines and batteries to have some level of thrust in atmosphere... and I am pretty sure all of this would weight less than 25 tons.

 

This shows the payload for a RLV flyback 1st stage reduces payload by 1/2: 

http://www.russianspaceweb.com/baikal.html

http://www.russianspaceweb.com/angara1.html

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1 minute ago, Darnok said:

I've checked few things

http://spaceflight101.com/spacerockets/falcon-9-ft/

https://www.reddit.com/r/spacex/comments/32qh7a/how_much_deltav_does_the_first_stage_need_for/

Empty 1st stage weights ~22t
Someone calculated that you would need ~25 tons of fuel to boostback and landing in falcon 9 style on landing pad
"Legs + grid fins + associated plumbing and avionics likely weigh about 4 tonnes in total".

So we can add wings, landing gear, avionics and booster body could be stronger for horizontal landings.
Even we could put in some electric engines and batteries to have some level of thrust in atmosphere... and I am pretty sure all of this would weight less than 25 tons.

 

The mass penalty to strengthen the booster for horizontal landing is severe. You're no longer just supporting a single column against a single stress; you're supporting wings (which aren't axisymmetric) and pitch stress and yaw stress. You're also supporting far heavier landing gear, and since it needs to retract inside the body, that's less space inside the body for fuel. The landing gear is heavier because the booster is heavier, and on and on in a punishing cycle. You have extra weight due to the need for control surfaces; unlike grid fins, the weight of movable aerodynamic control surfaces is significant, and you need a lot of control authority because of how small your wings are.

You'll easily triple the dry mass of your booster.

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I wonder if it would be useful to explore a smaller parallel-staged first stage with a larger SSTO-capable main spacecraft. Sort of a "launch assist" stage, but one which carries a substantial amount of fuel for crossfeed to the main spacecraft. Basically, the smaller parallel stage would compensate for gravity drag and aerodynamic drag while "gifting" the main spacecraft with a substantially decreased dV requirement for orbit, allowing it to sustain dramatically higher payload fractions.

The launch assist stage would need to be high-thrust, but would not need to reach particularly high altitudes or velocities compared to typical stacked first-stages, so recovery would be extremely easy.

Edited by sevenperforce

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In that case, it's not an SSTO.  But it's a good concept, just use high-powered SRBs with parachutes and StageRecovery

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22 minutes ago, linuxgurugamer said:

In that case, it's not an SSTO.  But it's a good concept, just use high-powered SRBs with parachutes and StageRecovery

And maybe even a drop tank, with a side-slung spaceplane, eh?

No, it wouldn't be an SSTO. But it would be closer. I wouldn't want to use SRBs, though; the whole point of an SSTO is rapid reuse, and SRBs are anything but. 

What about a triad of kerolox engine clusters wrapped in a shroud around the base of the core rocket, carrying LH2 tanks for crossfeed and forming a duct for air augmentation of the core engine? Even the simplest duct can increase thrust (and decrease thrust-specific fuel consumption) by 15% at start and by up to 50% during ascent. The ring would be dropped when its LH2 was depleted for a propulsive RTLS landing. The ascent would be short enough that it would be virtually refuel-and-refly.

Not unlike the Falcon 9 first stage, the core would be theoretically capable of zero-payload SSTO; the launch assist ring would serve merely to allow the core to carry a large payload into orbit. You could use launch assist rings of various sizes and capacities while retaining the same core stage for simplicity.

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Well, he said high thrust, short duration.  Subs, especially single segment, could be refurbished fairly quickly, and are cheap enough to allow a number of Srbs in storage

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12 minutes ago, sevenperforce said:

And maybe even a drop tank, with a side-slung spaceplane, eh?

No, it wouldn't be an SSTO. But it would be closer. I wouldn't want to use SRBs, though; the whole point of an SSTO is rapid reuse, and SRBs are anything but. 

What about a triad of kerolox engine clusters wrapped in a shroud around the base of the core rocket, carrying LH2 tanks for crossfeed and forming a duct for air augmentation of the core engine? Even the simplest duct can increase thrust (and decrease thrust-specific fuel consumption) by 15% at start and by up to 50% during ascent. The ring would be dropped when its LH2 was depleted for a propulsive RTLS landing. The ascent would be short enough that it would be virtually refuel-and-refly.

Not unlike the Falcon 9 first stage, the core would be theoretically capable of zero-payload SSTO; the launch assist ring would serve merely to allow the core to carry a large payload into orbit. You could use launch assist rings of various sizes and capacities while retaining the same core stage for simplicity.

Put the drop tank on the SRB and time it to empty when the SRB is finished, then drop it with SRB, since lf and Ox have to be separate place planes or fins into the tank that flare when the tank is released cause it to slow down more rapidly. then use a small amount of thrust to land it. Its recovered, problem of recovering SRB is solved, you have a little lf-0X on top to power a controlled landing.

 

 

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14 hours ago, sevenperforce said:

The mass penalty to strengthen the booster for horizontal landing is severe. You're no longer just supporting a single column against a single stress; you're supporting wings (which aren't axisymmetric) and pitch stress and yaw stress. You're also supporting far heavier landing gear, and since it needs to retract inside the body, that's less space inside the body for fuel. The landing gear is heavier because the booster is heavier, and on and on in a punishing cycle. You have extra weight due to the need for control surfaces; unlike grid fins, the weight of movable aerodynamic control surfaces is significant, and you need a lot of control authority because of how small your wings are.

You'll easily triple the dry mass of your booster.

Yes, most of the old reuseable first stages all the way to the Von Braun ideas used wings as its the most obvious. 
As you say its increase the demand on frame a lot and adds lots of other stuff like the wings.
An added downside is that for first stages wings are not as useful as you separate to high and fast too use the wings to turn around after separation. 

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Here's an idea. If Elon wants 100% stage reuse, why not offer a tandem launch with crossfeed? Call it Falcon TT.

Take a standard Falcon 9 FT first stage and replace one opposing pair of its outer engines with Merlin 1D Vacuum engines:

Falcon_TT.png

Strap it to a standard Falcon 9 first stage capped booster and add your payload on top.

Falcon_TT_2.png

On launch, fire all nine Merlin 1Ds on the strap-on booster and fire the seven SL-optimized Merlin 1Ds on the payload booster, keeping the pair of Merlin 1D Vacuum engines turned off. Crossfeed fuel from the strap-on booster to the payload booster up past Max-Q, then throttle down the engines on the payload booster while keeping the strap-on booster at full throttle.

Within moments, the vehicle will be high enough to ignite the vacuum-optimized engines at full throttle, downthrottling the other seven or even cutting off several of them entirely. Continue until the strap-on booster is down to its boostback and landing reserves, then separate. Allow the two Merlin 1D Vacuum engines to carry the remaining stage and payload all the way into orbit.

With the two vacuum-optimized engines, the stage will have a much higher remaining delta-v in orbit and can deliver its payload with enough remaining dV for an extended re-entry burn. It can RTLS without a boostback burn because it is already in orbit. It can touch down on the SL-optimized engine.

I think that would work, anyway.

22 minutes ago, Darnok said:

No one said it couldn't be done. It can just be done with higher payloads and lower booster cost if you stick with tail-first RTLS landings. Those StarBoosters would be insanely expensive.

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10 minutes ago, sevenperforce said:

Here's an idea. If Elon wants 100% stage reuse, why not offer a tandem launch with crossfeed? Call it Falcon TT.

Take a standard Falcon 9 FT first stage and replace one opposing pair of its outer engines with Merlin 1D Vacuum engines:

Falcon_TT.png

Strap it to a standard Falcon 9 first stage capped booster and add your payload on top.

Falcon_TT_2.png

On launch, fire all nine Merlin 1Ds on the strap-on booster and fire the seven SL-optimized Merlin 1Ds on the payload booster, keeping the pair of Merlin 1D Vacuum engines turned off. Crossfeed fuel from the strap-on booster to the payload booster up past Max-Q, then throttle down the engines on the payload booster while keeping the strap-on booster at full throttle.

Within moments, the vehicle will be high enough to ignite the vacuum-optimized engines at full throttle, downthrottling the other seven or even cutting off several of them entirely. Continue until the strap-on booster is down to its boostback and landing reserves, then separate. Allow the two Merlin 1D Vacuum engines to carry the remaining stage and payload all the way into orbit.

With the two vacuum-optimized engines, the stage will have a much higher remaining delta-v in orbit and can deliver its payload with enough remaining dV for an extended re-entry burn. It can RTLS without a boostback burn because it is already in orbit. It can touch down on the SL-optimized engine.

I think that would work, anyway.

No one said it couldn't be done. It can just be done with higher payloads and lower booster cost if you stick with tail-first RTLS landings. Those StarBoosters would be insanely expensive.

Nice idea, although I feel that although the re-usable first stage has some heat-shielding, it would be no-where near enough to survive a full re-entry. Also, the issue with cross-feed is that it's never been successfully demonstrated, and even the F9H will not have cross-feed in it's first iterations, so the capability is a few years (at least) away.

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Just now, Steel said:

Nice idea, although I feel that although the re-usable first stage has some heat-shielding, it would be no-where near enough to survive a full re-entry. Also, the issue with cross-feed is that it's never been successfully demonstrated, and even the F9H will not have cross-feed in it's first iterations, so the capability is a few years (at least) away.

Yeah, that's an issue. There are two other challenges I can see -- one is that adding a pair of vacuum engine nozzles might end up spraying some exhaust from the other engines onto the outside of the vacuum engines, which is less than ideal. Another challenge is changing center of mass/center of thrust because you don't have a balanced launcher. But those are solvable.

Crossfeed might not be necessary; your core booster is firing fewer engines than your strap-on booster, and can be downthrottled past maxQ. Plus, once altitude is high enough, the higher-thrust vacuum engines can be ignited and the other engines can be shut off entirely, which further decreases fuel consumption. So it might even work without crossfeed.

If so (or if crossfeed can be implemented), then it's quite possible that the booster would have enough remaining dV in orbit to burn off a good deal of speed prior to re-entry. Particularly because it can RTLS without a boostback burn, simply by doing AOA.

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Well, when I play KSP and try to design my own SSTO space plane, I realized I am spending a lot of time for little gain in saving to design it, and operating it is a whole another beast to tackle compares to rocket, whats with the long in-atmosphere flight path in near orbital speed. Rocket can be shot up to orbit with much less hassle, which is all we really need to get to space - going to orbit. When every single gram of mass matters, an SSTO is just pure luxury, considering you have to haul all the mass of one vehicle instead of ditching the ones you don't need anymore.

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8 minutes ago, RainDreamer said:

Well, when I play KSP and try to design my own SSTO space plane, I realized I am spending a lot of time for little gain in saving to design it, and operating it is a whole another beast to tackle compares to rocket, whats with the long in-atmosphere flight path in near orbital speed. Rocket can be shot up to orbit with much less hassle, which is all we really need to get to space - going to orbit. When every single gram of mass matters, an SSTO is just pure luxury, considering you have to haul all the mass of one vehicle instead of ditching the ones you don't need anymore.

Before 1.0 I used to make Jet powered launch platforms, once I got up to about 300 m/s and 15 k I would launch my rocket. This was particularly useful for launching telescopes and other objects with large profiles. Since a turbofan is just a propeller based craft that compresses air to create thrust they tend not to work well as the air thins. But the thing is that they can lift at any speed, so that if you have something really delicate, it gets you out of the messy atmosphere. Unfortunately in the game I can't land both the launch pad and the rocket. 10 or 15 of   PW4098 put the platform about 30 meters off the ground, at 100000 lbs of thrust per unit you could lift Just about any payload you want. The only limitation is that you need to keep it vertical and it would help to feed it oxygen as the air thins out. 

The reality on Earth is that the P&W4098 generates that level of thrust for takeoff, which means you need some air motion and thick air, and in addition cold air works best (it expands the most when heated). It has an effective ceiling of about 50,000 feet or 16km, but that is at full velocity, 50k feet is its coffin corner with no load, unless you are moving forward that stall height would be much lower, around 10-12,000 meters, and the maximum thrust at the output is a quarter or less in that range. You could engineer into the platform an air induction that feeds the turbofans air, but this adds mega-weight.

The basic reality is for jet power first stage on earth is that I can entirely replace it by putting my launch site on the side of a decently high mountain in Ecuador, and add a few boosters. Even if you landed the platform, the cost of fuel and structure in the boosters would be less. For one, you need RCS thrusters on the platform to keep it level. For most jet engines, despite the fact that they can generate an awful lot of thrust, the point in a flight were jet engines are most inefficient is when they trottle up to take off. This is because on the ground air is hotter (further away from 0K), and the compressor is really designed for sustained speed at around 500 kts at high altitude. 

For space craft that need a delicate launch. Launch from a high elevation, have a series of small boosters that are shed on the way up, control velocity with the main engine, launch entirely vertical and maintain, when the altitude is such that crossing the Mach barrier produces little hammer force on your flat forward facing surface throttle to full power and begin gravity turn.

 

 

 

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The best arrangement I can think of is essentially using a Skylon as a first stage. Just operate it the same way you would if it was an SSTO but with a payload (second stage) way too big to make orbit. Then the 2nd stage detaches and flies normally. 

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9 minutes ago, KerbonautInTraining said:

The best arrangement I can think of is essentially using a Skylon as a first stage. Just operate it the same way you would if it was an SSTO but with a payload (second stage) way too big to make orbit. Then the 2nd stage detaches and flies normally. 

I have yet to see any advantages in such a design over using something like the Falcon 9R as the first stage.

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4 hours ago, sevenperforce said:

Here's an idea. If Elon wants 100% stage reuse, why not offer a tandem launch with crossfeed? Call it Falcon TT.

Take a standard Falcon 9 FT first stage and replace one opposing pair of its outer engines with Merlin 1D Vacuum engines:

Falcon_TT.png

Strap it to a standard Falcon 9 first stage capped booster and add your payload on top.

Falcon_TT_2.png

On launch, fire all nine Merlin 1Ds on the strap-on booster and fire the seven SL-optimized Merlin 1Ds on the payload booster, keeping the pair of Merlin 1D Vacuum engines turned off. Crossfeed fuel from the strap-on booster to the payload booster up past Max-Q, then throttle down the engines on the payload booster while keeping the strap-on booster at full throttle.

Within moments, the vehicle will be high enough to ignite the vacuum-optimized engines at full throttle, downthrottling the other seven or even cutting off several of them entirely. Continue until the strap-on booster is down to its boostback and landing reserves, then separate. Allow the two Merlin 1D Vacuum engines to carry the remaining stage and payload all the way into orbit.

With the two vacuum-optimized engines, the stage will have a much higher remaining delta-v in orbit and can deliver its payload with enough remaining dV for an extended re-entry burn. It can RTLS without a boostback burn because it is already in orbit. It can touch down on the SL-optimized engine.

I think that would work, anyway.

NASA was thinking about something like this, but with wings...

astrrckt.jpg

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Just now, Darnok said:

NASA was thinking about something like this, but with wings...

astrrckt.jpg

Gorgeous photos.

The only reason they planned wings and turbofan engines was because they didn't have the computer control or deep throttling they needed for sitting down on the tail.

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9 minutes ago, sevenperforce said:

Gorgeous photos.

The only reason they planned wings and turbofan engines was because they didn't have the computer control or deep throttling they needed for sitting down on the tail.

Some descriptions and data
http://www.pmview.com/spaceodysseytwo/spacelvs/sld002.htm
http://www.pmview.com/spaceodysseytwo/spacelvs/sld052.htm
http://www.astronautix.com/lvs/reurrier.htm

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