sevenperforce
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Posts posted by sevenperforce
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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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5 minutes ago, todofwar said:
Always thought this one: https://en.wikipedia.org/wiki/Liquid_fly-back_booster was worth a second look. Basically, slap some wings and engines on your boosters so they fly themselves back when they're done. I actually got this to work using the FMRS mod in Kerbal.
This is basically what I expected to see:
"The thing that shocked me was that at the beginning, this reusable flyback booster was just a cylinder with engines and little wings, just a turbo fan in the back. And three years later these were complete Airbuses in terms of size with four engines in each of them."
Your designs really really burgeon.
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9 minutes ago, Matuchkin said:
There is footage. A Soyuz astronaut took it while his vehicle was reentering.
Personally, I even saw color-footage from Stalingrad.
Footage from Shuttle re-entries as well...even one from Columbia's last mission, though it ended well before the breakup.
But no footage from something not intended to survive re-entry.
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Hey all,
I've been playing the Demo for a while now, and there's a challenge I'd like to propose. Can you make it into orbit and back using only solid-fueled boosters (specifically, the RT-5 and the RT-10) without a parachute?
Rules:
- You don't have to use Demo, obviously, but you have to limit to the Demo toolbox. No mods.
- It has to be manned.
- The capsule must return intact.
- You have to reach a stable orbit outside of the atmosphere before returning.
- I was thinking more "can you do it" than a particular winner, but we can say that whoever can do it with the lowest launch mass wins.
I'll try it too. Good luck!
EDIT: @*MajorTom* proved this was possible by making a glider and ditching it into the ocean, which wasn't what I had expected but is definitely a win! So good job. For further submissions, I'll additionally specify that a soft landing on land is required, with or without landing legs. This is supposed to be an exercise in suicide burns, haha.
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On 4/6/2016 at 9:06 PM, PB666 said:
Or another way to think of it.
When you travel about the sun you have potential and kinetic energy, imagine if you could borrow temporarily some potential energy and turn it into kinetic energy, and then give it back, you could not do this because to give potential means you lower altitude.
Crossing a planets SOI does this, you give up some of your potential energy momentarily and take kinetic energy (not to the star but to the planet), but when you fire your engines you gain alot more kinetic energy because you are going faster (work = force * distance traveled), then when you leave the SOI you give back the kinetic energy loan and take back the potential energy and get to keep all the extra kinetic energy.
Which you can do because burning close to the planet leaves your exhaust with much less gravitational potential energy, allowing you to keep that extra kinetic energy.
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16 minutes ago, Nibb31 said:
That sort of price is pure fantasy, with or without reusability.
Not realistic either. Cost of a launch <> Cost of launch vehicle.
The biggest part in the launch cost is the workforce. The actual hardware is only a minor part of the total launch cost, and the manufacturing cost of the first stage is only a part of the total hardware cost. There is also infrastructure, logistics, testing, payload integration, and all sorts of administrative overhead. Reusing first stages does little to reduce the workforces or any of those other costs, and SpaceX has already managed to price themselves 50% cheaper than their competition, so expecting reusability to further decrease launch prices by more that 10% is wildly optimistic.
That's why I still have a warm place in my heart for small SSTO concepts, despite how difficult they would be to design. Launch vehicle costs can be brought quite low by reusing separate stages, but the only way to significantly decrease workforce is to go to a single launch vehicle with minimal refurbishment.
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7 hours ago, fredinno said:
This thread should be pinned.
Hear, hear.
Here.
23 minutes ago, Wingman703 said:Anyone know what the profile is looking like for this launch? RTLS? Barge landing? I'm assuming RTLS due to the success with the last one but don't know for sure.
Yeah, as others have said, it's a barge landing.
With the BEAM in the trunk weighing them down, I think they would be cutting awfully close on a RTLS. It wouldn't make sense to attempt a risky RTLS when they have a very good chance of sticking the barge landing. Another barge landing failure, while disappointing, would not be the end of the world. A RTLS failure would be devastating; it would make the former landing look like a fluke while potentially messing up FAA approval for future attempts.
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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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That's silly.
"Our planned heavy-lift launcher will match your operating medium-lift launcher in per-kilogram costs!" Apples and oranges.
Never mind that Falcon Heavy is much further along than Ariane 6.
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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:
Strap it to a standard Falcon 9 first stage capped booster and add your payload on top.
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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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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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.
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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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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.
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6 hours ago, Darnok said:
Next idea I've seen
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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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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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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4 hours ago, fredinno said:
...where do you get the development money for [carbon nanotube weave]? Is demand high enough?
I'm not suggesting we develop carbon nanotube weave merely to build vacuum airships. Carbon nanotube weave will be developed for numerous applications as soon as it can be. Everybody needs that stuff.
5 hours ago, fredinno said:Explain Heisenburg.
Okay, so on certain scales, it is not possible to determine the position and momentum of a particle simultaneously. The uncertainty in the product of position and momentum is approximately equal to the Planck constant. This is because particles are actually wave functions and exist across all space with a defined expectation value.
Or were you talking about Walter White?
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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
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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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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9 minutes ago, Exoscientist said:
A landing where you crash and burn is not a successful landing.
No one suggested it was.
But alleging that the suicide burns are the source of their difficulty when in fact stability was the source of the two normal-condition landing failures is quite incorrect.
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10 minutes ago, Spaceception said:
I believe sevenperforce posted the exact same rocket 12 minutes before you did
Indeed. Though not quite the exact same. You don't need those useless fins, the center booster needs to be altitude-compensating with a truncated aerospike to act a heat shield, and you need to have LH2 and LOX crossfeed from the side boosters to the center booster (which themselves need to be kerolox). And everything needs landing legs.
You could do it with a single booster, I suppose, but then you do end up with some COM/COT issues.
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14 minutes ago, Exoscientist said:
Suicide-burn is the appropriate description for the Falcon 9 landing technique, not the "hover-slam" term SpaceX has been using.
Since the F9 can not hover, it is inappropriate to include the word "hover" in the landing description. A more appropriate name, aside from suicide-burn, would be "land-or-slam", since without hovering ability you only get one chance at it. You stick the landing on the first try or you crash and burn.
SpaceX needs to stop trying to reinvent the wheel, and investigate means of giving the F9 hovering capability.
They could put a massively underexpanded Merlin 1D in the center of the cluster, but it would result in a performance hit. And honestly they haven't had trouble with the suicide burns. The first two barge landing failures were tip-over, indicating stability problems. The last attempt, a three-engine suicide burn, had a vanishingly low probability of success from the very beginning, made harder by poor landing conditions.
They haven't actually attempted a normal-condition barge landing with the F9FT yet; both tip-overs were on the F9v1.1 model.
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The Shuttle is actually not too far from the optimum layout for getting to orbit and back with some degree of fast and simple reusability. It was just way, way too big to be reused quickly, and the requirement of an internal cargo bay meant that an external disposable drop tank was unavoidable.
If your goal is 100% reuse with short turnaround time, then your best bet is to build a VERY downscaled version of the Shuttle. Replace the SRBs with Falcon-Heavy style kerolox boosters, but add auxiliary LH2 tanks. Replace the Shuttle with a core hydrolox booster and give it a truncated aerospike nozzle for altitude compensation. Put a Dragon V2 style capsule on top (or a payload with a fairing, if you like). At launch, crossfeed the core booster from the side-booster LOX tanks and the auxiliary LH2 tanks up to side booster separation. Side boosters RTLS with vertical landing; the core carries the capsule into orbit, circles once or twice, and then deorbits, using its truncated aerospike as a heat shield to aerobrake to a vertical landing RTLS. Capsule (if applicable) re-enters separately and lands propulsively.
On the one hand, that's four separate vehicles instead of just one. But any problems or extended repair time is now relegated to a single component, so that re-use of the other components is unhindered. With the extremely good specific impulse of hydrolox and the very high thrust of kerolox, the propellant mass fraction would be extremely low, meaning the launch vehicle could be quite small and thus easier to recertify and reuse.
SSTOs galore
in Science & Spaceflight
Posted
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.