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SpaceX may want to use their own Dragon, instead of launching Dream Chaser. There are advantages. If you launch Dream Chaser on Falcon Heavy, with a cargo pod, the cargo pod has an APAS docking hatch on one end to attach to Dream Chaser, the cargo pod has a CBM hatch on the other to "berth" with ISS.
CBM is the large square hatch, large enough for an entire rack for installation in a station module. However, the CBM does not have shock absorbers, so a Shuttle or modern spacecraft can't dock itself. Shuttle docked to APAS, which has shock absorbers for a 115 metric tonne Shuttle (with full propellant tanks and cargo), but the hatch is small and round. It's big enough for an astronaut in a white EMU spacesuit, and big enough for drawers from a science rack, but not big enough for a rack itself. The Multi-Purpose Logistics Module would be picked up by Shuttle's arm and berthed to a CBM hatch. Dream Chaser was built with an APAS hatch on its back end, small and round. It was expected to dock at the same port that Shuttle used to use. But the cargo version will "berth" the same way as Dragon or Cygnus. So the cargo pod has an APAS hatch at one end to attach Dream Chaser, and a CBM hatch at the other to berth with the station.
If you tried to do this with Dragon, the cargo pod would also require RCS thrusters. But Dragon has it's hatch on top, not the bottom. So Dragon would not be attached to the cargo pod. Dream Chaser would. Dragon could detach, and berth to a separate CBM hatch, but that requires two docking manoeuvres. If this was launched with crew, then crew in Dragon could not access the cargo pod until after it's attached to station, after Dragon is detached and docked separately to station. With Dream Chaser, crew can pass through the cargo pod to station.
Furthermore, since Dream Chaser launched on Falcon Heavy could carry as much launch mass as Shuttle, that means it could deliver new modules to station. So the Centrifuge Accommodation Module could be delivered this way.
By the way, the Dragon mission that failed was supposed to carry an adapter for the APAS hatch that Shuttle used. The adapter was for future crew spacecraft: crew Dragon, CST-100 Starliner, Orion, or crew Dream Chaser. I don't have technical details, but did notice drawings for the hatches on modern spacecraft do not include the "soft capture" ring with shock absorbers that Shuttle used. You don't need shock absorbers for a 115 metric tonne Shuttle when docking an 11 tonne capsule.
Last edited by RobertDyck (2016-05-03 22:12:32)
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Nice information RobertDyck as always to fill in the blanks on Dreamchaser. It would appear that Dreamchaser would be best suited to getting its own launcher for it to ride on in veiw of the Atlas V rocket engines issue and most likely higher ULA costs for Vulcan....I hope I got that right....
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Dream Chaser on Antares 200-series? Orbital ATK proposed replacing their AJ26 engines (refurbished NK-33) with a pair of RD-181 engines. The RD-181 is designed specifically for Antares, adapted from RD-191. It's a single chamber rocket engine. Antares 100-series was rated to lift 6 metric tonnes to LEO, it lifted Cygnus. That's a bit light for Dream Chaser, but Antares 200-series uses engines with more thrust and better Isp. However...
Wikipedia: Antares
While the 200 series uses the RD-181 by adapting the originally ordered 100 Series stages (KB Yuzhnoye/Yuzhmash, Zenit derived), it requires under throttling the RD-181 engines, which reduces performance. Thus, the 300 series will use a new first stage core designed for the full thrust and performance of the RD-181 engine.
Second stage
The second stage is an Orbital ATK Castor 30-series solid-fuel rocket, developed as a derivative of the Castor 120 solid motor used as Minotaur-C's first stage. The first two flights of Antares used a Castor 30A, which was replaced by the enhanced Castor 30B for subsequent flights.Third stage
Antares offers two optional third stages, the Bi-Propellant Third Stage (BTS) and a Star 48-based third stage. BTS is derived from Orbital Sciences' GEOStar spacecraft bus and uses nitrogen tetroxide and hydrazine for propellant; it is intended to precisely place payloads into their final orbits. The Star 48-based stage uses a Star 48BV solid rocket motor and would be used for higher energy orbits.
So Antares 300-series? I have an issue with solid rocket as primary propulsion for a manned spacecraft. Their BTS isn't an option, it's a bit small for use as a second stage, and fuel is actually hydrazine; not MMH or even UDMH, but pure hydrazine. That's hypergolic so I don't think safe for a manned launch. But if they can get Antares 200-series to deliver Cygnus, perhaps Antares 300-series could launch Dream Chaser.
Still, Falcon 9 would mean everything but the upper stage is reused.
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I mentioned using Falcon Heavy with Dream Chaser to deliver the Centrifuge Accommodation Module to ISS. Actually, there's an even simpler method. Since the module would require RCS thrusters to manoeuvre close to ISS, you could just add the service module from Cygnus. It has all the autopilot stuff to rendezvous with ISS. Would still need RCS thrusters, not just those on the service module. An entire station module is a lot bigger than Cygnus. But with additional thrusters under control of the service module, it could. Then the station arm could grab it and berth to a CBM port, just like an oversized Cygnus.
I suggested doing this with a Bigelow inflatable. It could be done with a metal hull module too, just with more thrusters for the additional mass.
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Sure would be nice if any centrifugal unit was sent but it seems that Nasa is still trying to deny that its needed.
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Research into reduced gravity is part of the "raison d'être" of ISS. Many medical experts have pointed out we have no long term medical data for Lunar or Mars level gravity. I seriously believe that Mars gravity is sufficient to completely prevent microgravity health effects. Lunar gravity might be enough, because it would allow convection and other fluid flow within the body. But that's just a guess. One space medicine doctor told me effects on the 6 astronauts who did set foot on the Moon were "contaminated" by high-G acceleration during launch from Earth, high-G atmospheric entry, and zero-G during transit to/from the Moon. So we just don't know.
The centrifuge on that module would be too small for a human. Wikipedia: Centrifuge Accommodations Module
Expose a variety of biological specimens that are less than 24.5 in (0.62 m) tall to artificial gravity levels between 0.01g and 2g.
That could accommodate a wide variety of specimens: mice, rats, rabbit, dog. The first living being the Russians launched into space in the 1950s was a dog. First suborbital hops, then after Sputnik, into orbit. Pick your subject, this could provide actual data.
I met one Mars Society member through the Mars Homestead project, and at Mars Society conventions. Dr. Richard Sylvan was an oncologist, that's a medical doctor who specializes in cancer. He was one of America's leading oncologists. Unfortunately he had cancer himself, and worked with another oncologists on his own treatments. One side effect of those treatments was osteoporosis. He was extremely interested in the Centrifuge Accommodations Module, because he hoped it would find a way to treat his own osteoporosis. I gave him my hypothesis of osteoporosis, but unfortunately if I'm right that would not pertain to medically induced osteoporosis, so wouldn't help him. He was disappointed. Unfortunately he died. His death was announced through the Mars Homestead email list. It didn't say his cause of death: cancer, complications from his treatment, or other. But I keep thinking we should name that module for him.
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I look at actions (money is involved) not words (talk is cheap). I think based on actions for many years that NASA really, really doesn't want to send men anywhere but cis-lunar space on missions of 2 to 4 weeks duration. They only want to reprise Apollo and similar, with men. If that were not true, then we would be building something other than a botched reprise of a Saturn moon rocket with shuttle technology, and something more than Apollo-on-steroids for a cramped capsule to ride in.
And most importantly, they would have been working on artificial gravity, having already found that about a year and half, maybe 2, is the most microgravity exposure that an astronaut might endure successfully and recoverably. There are no missions beyond the moon that short.
We could now (not 20 years ago) build a spinning free-flyer annex to ISS affordably. Modify 4 Bigelow 330's with interior decks, and add a center hard airlock/docking/solar panel module with some spin-up/spin-down flywheels. This cluster as a linear baton is around 25-30 meters long. Spin it at 8 rpm (tolerable with training), and you have one gee at the ends, and every value of partial gee down to zero in the center. You have a space big enough for a crew to live and work in. You could find out in a couple of years exactly how much partial gee is "enough", to support maybe the next century of solar system exploration.
Assume for the sake of argument each of these 5 modules will cost $100M to build as flyable items. Assume for the sake of argument that it costs around $100M to launch each one. Let the ISS crew catch them and dock them. So, you get your partial gravity research facility for human experiments, plus about 1300+ more cubic meters of space station, and you get your answer for how much partial gee is enough, for grossly $1B, under 1% of the original construction cost for the ISS.
If NASA was serious about sending men beyond the moon, they'd already have been working on this issue. Or, they'd be chomping at the bit to try an idea like this. If I can sit down and come up with ideas like this in under half an hour, how come they haven't already done so?
Well, THAT'S why I say they really don't want to send men to Mars.
Musk does.
I hope his people see this.
GW
Last edited by GW Johnson (2016-05-07 09:27:26)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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Perhaps someone can see what's wrong with this proposal of a SSTO. It's too obvious to not have been thought of before:
High performance engines that you would need to get high thrust at sea level should have high chamber pressure. Such engines need to be turbopump driven to generate these high pressures. Such engines though cost hundreds of millions in development costs, an expensive prospect for something as theoretical and controversial as an SSTO.
Pressure-fed engines on the other hand are easy and low cost to produce. In fact amateurs or small commercial concerns such as Armadillo Aerospace, Masten Space, and Garvey Space have made such engines and rocket stages. These are always low chamber pressure engines. You could make a high chamber pressure pressure-fed engine but then the propellant tanks would also require such high pressures, and this would result in the tanks being too heavy for a SSTO.
BUT how about this method to generate the high pressures in the engine for a pressure-fed system that at the same time has the relatively low pressure tanks of turbopump systems: the long cylindrical propellant tanks produce additional pressure at their bottoms from the weight of the propellant. Suppose we then have a pipe leading down from the bottom at 1/10th the diameter of the tank, so 1/100th the cross-sectional area. Shouldn't this result in the pressure within the pipe being 100 times that of the pressure within the tank?
So even if the pressure in the tank is only, say, 2 bar, typical of turbopump systems, the pressures in the pipes leading into the engines can be 200 bar. Correct?
But what about when the propellant becomes more and more burned off resulting in smaller and smaller weight to cause the pressure at the bottom? As the propellant gets burned off the weight decreases so the T/W goes up and so does the acceleration. Then the effective "weight" of the propellant also goes up, maintaining the same pressure at the bottom. You may want to throttle the engine though to limit the structural loads on the craft. But another consideration is that high up at near vacuum conditions high chamber pressure and thrust are not so important. What is important is high Isp, which can be done by using altitude compensation such as an aerospike.
A couple of problems though. Shouldn't this already be happening with the rockets used now? In that case why are turbopumps being used at all?
Secondly, the propellant tanks in rockets are pressurized aside from the increased pressures observed at the bottom due to gravity. So shouldn't this in itself without any consideration of the propellant weight or thrust or acceleration allow the reduced pipe diameter to have increased pressure inside the pipes?
Thirdly, there is the issue of Pascal's Principle:
http://hyperphysics.phy-astr.gsu.edu/hbase/pasc.html
This says that a pressurized liquid equalizes pressure throughout the vessel whether at wider or narrower parts of the vessel. In that case shouldn't the pressure be the same even in the narrower pipe?
Bob Clark
Old Space rule of acquisition (with a nod to Star Trek - the Next Generation):
“Anything worth doing is worth doing for a billion dollars.”
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Pascal's Law does apply, as long as flow rates are near zero. Pressure in the pipe equals pressure in the tank. Only the forces exerted on parts scale with cross section area. Pressure DOES NOT VARY with area in a liquid. That's solids only.
When flow rates are large, pressures in the feed pipe will be less than tank pressure by the friction losses. Pressures in the injection space will be less than pressures in the feed pipe for the same reason. There's a huge drop across the injector plate, regardless. Engine chamber pressure will be around half or less the tank pressure, if pressure fed. No way around that.
GW
Last edited by GW Johnson (2016-05-29 18:41:15)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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I look at actions (money is involved) not words (talk is cheap). I think based on actions for many years that NASA really, really doesn't want to send men anywhere but cis-lunar space on missions of 2 to 4 weeks duration. They only want to reprise Apollo and similar, with men. If that were not true, then we would be building something other than a botched reprise of a Saturn moon rocket with shuttle technology, and something more than Apollo-on-steroids for a cramped capsule to ride in.
Maybe. Under GWB's VSE, NASA was supposed to send astronauts back to the moon. That's probably part of it. And yes, a lot of people at NASA wanted to go back to the moon.
And most importantly, they would have been working on artificial gravity, having already found that about a year and half, maybe 2, is the most microgravity exposure that an astronaut might endure successfully and recoverably. There are no missions beyond the moon that short.
They're paying for mega rockets and mega capsules. There's no funding left for other, more useful space exploration technologies like CL-ECLSS, AG, MCP suits, and radiation exposure mitigation. No mega rocket or mega capsule is going to assist in any way with human exploration of Mars and only the ignorant and gullible general public would ever believe such nonsense. NASA's contractors and NASA think that if they repeat the lie often enough, people will believe it.
We could now (not 20 years ago) build a spinning free-flyer annex to ISS affordably. Modify 4 Bigelow 330's with interior decks, and add a center hard airlock/docking/solar panel module with some spin-up/spin-down flywheels. This cluster as a linear baton is around 25-30 meters long. Spin it at 8 rpm (tolerable with training), and you have one gee at the ends, and every value of partial gee down to zero in the center. You have a space big enough for a crew to live and work in. You could find out in a couple of years exactly how much partial gee is "enough", to support maybe the next century of solar system exploration.
We could certainly attach four BA-330's to ISS and rotate them, but if we're not going to send four connected BA-330's twirling through interplanetary space, that experiment may not have much applicability to the spacecraft that would make the journey.
Assume for the sake of argument each of these 5 modules will cost $100M to build as flyable items. Assume for the sake of argument that it costs around $100M to launch each one. Let the ISS crew catch them and dock them. So, you get your partial gravity research facility for human experiments, plus about 1300+ more cubic meters of space station, and you get your answer for how much partial gee is enough, for grossly $1B, under 1% of the original construction cost for the ISS.
The only thing we know with certainty is that humans don't have any gravity-related physiological issues when subjected to 1G. You're talking about a really expensive experiment that we can easily determine the results of once humans land on the surface of Mars. I think that the astronauts should be spun up to 1G for the transit there and back.
If NASA was serious about sending men beyond the moon, they'd already have been working on this issue. Or, they'd be chomping at the bit to try an idea like this. If I can sit down and come up with ideas like this in under half an hour, how come they haven't already done so?
1. SLS
2. Orion
Well, THAT'S why I say they really don't want to send men to Mars.
Musk does.
I hope his people see this.
GW
You could be right, but I want to see what the next administration directs NASA to do before finalizing my opinion on this matter.
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Funding aside for the support from the next administration, we are still caught in the bloat of the army of Nasa and of contractor welfare system that is.
We will need to direct pay Space x and others to get what man wants and that is a working, living presence that supports its own activities once started.....The population that is in space needs to be able to create a funding trail in order to keep self suficient in making business in space work....
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Pascal's Law does apply, as long as flow rates are near zero. Pressure in the pipe equals pressure in the tank. Only the forces exerted on parts scale with cross section area. Pressure DOES NOT VARY with area in a liquid. That's solids only.
When flow rates are large, pressures in the feed pipe will be less than tank pressure by the friction losses. Pressures in the injection space will be less than pressures in the feed pipe for the same reason. There's a huge drop across the injector plate, regardless. Engine chamber pressure will be around half or less the tank pressure, if pressure fed. No way around that.
GW
Thanks for the response. I think you're right about Pascal's Principle coming into play to make the pressure the same even in the reduced diameter pipe.
How about some variations on the idea: Pascal's Principle applies to liquids. Suppose the fuel is stored as solid particles. Would Pascal's Principle still apply in that case?
Or suppose it is stored as a non-Newtonian fluid such as a gel, like yogurt or Jello. Would it apply in that case?
Bob Clark
Old Space rule of acquisition (with a nod to Star Trek - the Next Generation):
“Anything worth doing is worth doing for a billion dollars.”
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Only in a true solid does Pascal's Law not at least approximately apply. Stress (a pressure) in a solid bar varies with cross section area, because it is force that must be conserved to satisfy Newton.
In liquids, as long as there is no flow, pressure is conserved (satisfying Newton on a control volume), so that force varies locally with cross section. Still approximately true for thixotropic stuff.
Not so sure about applying Pascal's Law to a pile of particles. Although in a crude sense it is true, or else the angle of repose of a sand pile would be higher than 40 degrees.
For gels I suppose the "truth" is an intermediate concept. But I don't know. Never worked with stuff like that.
Closest thing to it was rocket propellant too thick to flow under its own weight. We had to pressure-extrude the stuff into vacuum to avoid void formation. We treated it like Pascal's Law applied, and it seemed to work for us.
GW
ps - any word on unique nozzles?
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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Only in a true solid does Pascal's Law not at least approximately apply. Stress (a pressure) in a solid bar varies with cross section area, because it is force that must be conserved to satisfy Newton.
In liquids, as long as there is no flow, pressure is conserved (satisfying Newton on a control volume), so that force varies locally with cross section. Still approximately true for thixotropic stuff.
Not so sure about applying Pascal's Law to a pile of particles. Although in a crude sense it is true, or else the angle of repose of a sand pile would be higher than 40 degrees.
For gels I suppose the "truth" is an intermediate concept. But I don't know. Never worked with stuff like that.
Closest thing to it was rocket propellant too thick to flow under its own weight. We had to pressure-extrude the stuff into vacuum to avoid void formation. We treated it like Pascal's Law applied, and it seemed to work for us.
GW
ps - any word on unique nozzles?
Thanks for that. On the unique nozzles I just responded by email.
Bob Clark
Old Space rule of acquisition (with a nod to Star Trek - the Next Generation):
“Anything worth doing is worth doing for a billion dollars.”
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Yet another idea for an altitude compensating nozzle attachment to existing engine nozzles:
Altitude compensation attachments for standard rocket engines, and applications, Page 3: stretchable metal nozzles.
http://exoscientist.blogspot.com/2016/0 … s-for.html
The altitude compensating nozzle known as the aerospike has been known since the 60's. The problem is it would require the engine to be designed for it from the start, since for one thing it would need a toroidal combustion chamber. A change like this would be an expensive change for an already existing engine, and you might as well just design a new engine from the start.
Therefore I have been investigating ways of getting the altitude compensation just by making an attachment to an already existing engine's nozzle. Here is another method. The idea behind it is that metal becomes much more malleable at high temperatures. Then you would allow this nozzle extension to reach the temperatures where it can be stretched much more easily, but below the melting point, so it is still solid. To effect the nozzle stretch you could either use extensible actuator rods or high pressure gas injected into hollow nozzle walls.
Bob Clark
Old Space rule of acquisition (with a nod to Star Trek - the Next Generation):
“Anything worth doing is worth doing for a billion dollars.”
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Bob:
If there is already an expansion bell, at least part of it is already regeneratively cooled. Further downstream, such bells often can be "uncooled" except by thermal radiation. For example, much of the altitude nozzle extension on the Merlin that Spacex uses in its Falcon second stages is an uncooled shell. It glows, but it doesn't melt. The pressure loads are much lower there, so you can afford low strength in a hot material.
The recovery temperature in the boundary layer adjacent to the nozzle extension is crudely just about chamber temperature, all the way to the exit. It is the difference between that recovery temperature and the temperature of the shell material that drives heat transfer to the material from the hot gas. Film coefficients way out in the bell are on the order of half those in the throat, reducing the heat load a bit further.
Thermal radiation works at the 4th power of absolute material temperature, and gets factored by the average spectral emissivity in that particular color temperature band. I would think you could use a stainless steel at around 1200-1500 F, coupled with a very black external coating (like a furnace or oven part ceramic paint), for your vacuum nozzle extension structures. Titanium is no better than carbon steel, both are pretty useless structurally above 800-1000 F.
I dunno about expanding inflatables, but you could certainly build some sort of folding or telescoping item that way.
My two-spike concept could use those same material cooling strategies, and involves no changing of any geometry at all. Any luck with that idea? Its only downside is that you take off all of the bell starting at the throat, so some of the two-spike structure must be regeneratively cooled.
GW
Last edited by GW Johnson (2016-06-27 08:38:46)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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The original topic with the transpiring heatshield and the composite tanks
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