-
#80 by Steven Pietrobon on 17 Jan, 2014 03:12
-
Yes. I think all lunar landers (manned and unmanned) have been hypergolic.
For the actual propulsion just before landing, yes that is true. Surveyor did use a solid stage (a Thiokol TE-364 motor) in a staged descent with the actual landing using storable propellants (monomethyl hydrazine hydrate or MMH-H2O and MONO-10 or 90% N2O4 and 10% NO). The planned Soviet LK lander was to use a Block D kerolox stage in staged descent, with the LK lander itself using UDMH and N2O4 for the actual landing. -
#81 by sanman on 17 Jan, 2014 03:13
-
In some thread someone commented that cryogenic restart capability is impinged upon by the fact that when you burn off some of your cryo propellants, some of the remaining propellants will be more likely to go into vapor phase. Has anybody ever tried a bladder approach, whereby the propellant container shrinks in volume to keep the remaining propellant compressed? Obviously the elastic force of your bladder has to exceed the vapor pressure of the volatile.
Centaur upper stage uses stainless steel balloon tank, which doesn't have any structural integrity on its own. LH2/LOX are pumped to keep balloons inflated.
...
I guess balloon tanks might also help in keeping fuel settled down, by deflating when fuel is consumed (speculating).
Yeah, an elastic bladder would keep contracting as propellant is used up.
What about glassy amorphous metal alloys? For example, there are certain metal alloys which have highly elastic properties. If you could make balloon tanks out of such elastic alloys and then pump them up full of LOX and LH2 so that they were under tension, they could then contract as the propellants were consumed.
http://phys.org/news/2011-07-japanese-material-scientists-superelastic-alloy.html -
#82 by baldusi on 17 Jan, 2014 03:21
-
H2 is liquid at about 20K, LOX is around 93K. At those temperatures, very little materials are elastic. Not to mention the bad manners of the H2 molecules to get everywhere they can, generating embritelment and free H2 everywhere.
-
#83 by hop on 17 Jan, 2014 04:09
-
I guess balloon tanks might also help in keeping fuel settled down, by deflating when fuel is consumed (speculating).
No, the centaur "balloon" tanks are pressure stabilized, meaning they use pressure to maintain their shape, they aren't like elastic balloons. Non-cryogenic systems often do have an internal bladder, but as baldusi says, this is harder with cryogenics. -
#84 by AJA on 17 Jan, 2014 09:02
-
In some thread someone commented that cryogenic restart capability is impinged upon by the fact that when you burn off some of your cryo propellants, some of the remaining propellants will be more likely to go into vapor phase. Has anybody ever tried a bladder approach, whereby the propellant container shrinks in volume to keep the remaining propellant compressed? Obviously the elastic force of your bladder has to exceed the vapor pressure of the volatile.
This issue isn't restricted to cryogenics. ANY fuel tank'll face this issue. Turn a bottle of water upside down.. the efflux isn't smooth -- precisely because water falling out results in a vacuum at the top of the bottle... and periodically, the atmospheric pressure breaks surface tension in the lower free surface enough to allow some air to form a bubble and gush in.
So what do they do? They take the lightest gas known - compress it vastly, and tack it on to the rocket. They add a valve whereby this gas is slowly vented into the fuel tanks as the tank drains. (As long as the rocket's thrusting and undergoing acceleration, there is a well defined free surface within the tank) This keeps the pressure on top of the liquid, and "should" keep flow smooth (given other favourable circumstances). When you work out the arithmetic, you also make sure to set the super-incumbent gas pressure in the empty (or at-cutoff) fuel tank, catered to entirely by your pressurant gas - is greater than the vapour pressure of your propellant at the ambient temperatures likely to be encountered. The greater you make it, the lower the boil-off (but lower payload fraction).
Anyway, you do all that, and then you realise all sorts of things are catching fire, and exploding. So you swap out the lightest known gas, with the second lightest known gas
, while singing -- about your first iteration at a solution --
TL;DR - They use Helium to pressurise the tanks as they're evacuated.
Balloon tanks would be awesome, but aside from material concerns and challenges, you'd also have dynamic stability issues... how d'you ensure isotropic contraction? No one here has had a party balloon they inflated and let go of - fly straight and true Then again, those party balloons don't have active guidance.
-
#85 by baldusi on 17 Jan, 2014 10:46
-
Two points:
1) On your H2 tank, you can use the lightest gas. But normally this is done by heating a tiny bit just enough to get gaseous H at enough pressure (I think it's around 0.33MPa/50psi or so).
Membranes are used, but mostly on spherical or nearly so tanks. Think of a how would you put a membrane on a very thin and long tank, like the first stage tanks. You'd waste a lot of mass and the membrane would have to move from the top to the bottom, probably rubbing against itself. And elastomers are not known for their low coefficient of friction.
On a related note when a membrane is used, the other side of the tank is pressurized with He from a bottle with a regulator. This gives a constant pressure for pressure fed engines and work in any direction. The valves from the bottle to the tank was what got stuck during SpaceX's CRS-2, and that's why they couldn't activate the RCS. The tank's lacked the He that actually gave the pressure to the pressure fed engines. -
#86 by sanman on 17 Jan, 2014 13:37
-
Balloon tanks would be awesome, but aside from material concerns and challenges, you'd also have dynamic stability issues... how d'you ensure isotropic contraction? No one here has had a party balloon they inflated and let go of - fly straight and true
Then again, those party balloons don't have active guidance.
Well, the tank doesn't itself have to be the superstructure or fuselage of the rocket. The tank can be a flexible internal enclosure inside the superstructure. Maybe it could be a flexible accordion type of structure, to ensure it contracts in one axial direction. Boron Nitride, by the way, has shown itself capable of forming a quasi-hexagonal mesh similar to that in Graphene and Carbon Nanotubes, but the BN structure is capable of buckling in an accordion-like manner, in a linear direction. That's one reason why BN nanotubes are being researched for tank armor, because this buckling characteristic offers energy-absorbing or damping properties. It seems like these intrinsic properties would still be available even at cryogenic temperatures.
http://www.academia.edu/2718708/Compressive_Buckling_of_Boron_Nitride_Nanotubes_with_Hydrogen_Storage
-
#87 by AJA on 17 Jan, 2014 19:17
-
Well, the tank doesn't itself have to be the superstructure or fuselage of the rocket. The tank can be a flexible internal enclosure inside the superstructure. Maybe it could be a flexible accordion type of structure, to ensure it contracts in one axial direction.
What about the evacuated space between the inside of your aero-shell and the outside of your flexible tank wall? Aero-shells need to be pressurised to maintain their shape and rigidity. What's going to keep your aero-shell from collapsing because of the pressure differential? Also, why would your flexible tank continue to passively shrink when there's an evacuated zone outside it? Any active system that performs mechanical work to squeeze the balloon is going to cost mass. What's that? You'd use Helium? Uhh....
Unless you want to think about entraining ambient air, that's what you'd probably converge on. But capturing ambient air would require you to siphon some off, and would cost you drag, shock, vibration, heating, and is still entrained mass that you're going to be carrying uphill. Not to mention the aerodynamic problems caused by the flow, when it encounters a possibly anisotropic shrinking tank.
In any case, I wasn't talking about the problems with the aerodynamic interactions as much as I was referring to the mass distribution upsets caused by the deviations in the contraction of the balloon; throwing the rocket off balance, and moving its centre of gravity around unpredictably. That would be a GNC nightmare.QuoteBoron Nitride, by the way, has shown itself capable of forming a quasi-hexagonal mesh similar to that in Graphene and Carbon Nanotubes, but the BN structure is capable of buckling in an accordion-like manner, in a linear direction. That's one reason why BN nanotubes are being researched for tank armor, because this buckling characteristic offers energy-absorbing or damping properties. It seems like these intrinsic properties would still be available even at cryogenic temperatures.
That paper measures the change in the buckling behaviour of Boron nanotubes... when the nanotubes are subjected to an external compressional load. It says nothing about the direction of such buckling (accordion etc.), or the reversibility. This way.. you can buckle ANY material to shrink the volume, provided you ensure that it doesn't open up cracks that allow the LH2 out.
Plus, they're measuring the buckling in ISOLATED BN NANOtubes. Not BN Nanotubes packed so closely enough to form a seal impenetrable to Hydrogen molecules. But let's assume that a ring of BN nanotubes, spaced far enough apart to still exhibit the properties of nanotubes, rather than form a bulk solid structure -- i.e. stacked like the pillars of Stonehenge are still able to trap Hydrogen in the inner area because of a phenomenal adsorption power. Let's also assume that you can stack successive Stonehenges on atop the other to form a macroscopic cylinder -- or you're able to get a nanotube that's several metres in length; forgetting the difficulties of manufacturing a MULTI-STOREY structure out of NANO-tubes. (Boron Nitride btw -- atleast in the Wurtzite mineral form -- is harder than diamond and possibly the hardest substance known to man. Well...short of the exotic matter in stellar cores I guess).
For this structure to work as balloon tank, you'd have to ensure that the shrinkage happened only from top down... and that all your nano-tubes are aligned, and that it happens in the same direction, as opposed to the bottom half the tank shrinking down, and the top half shrinking up -- leading to a tear. You'd have to ensure this on a microscopic scale.
But...if you did all that though, I'll tell you one more thing you could do. You could get rid of all the wiring that needs to pass through that stage. The Boron Nitride nanotubes could act as fibre-optics! -
#88 by sanman on 17 Jan, 2014 23:43
-
Gee, I didn't know that propellant tank pressurization inflates the aeroshell. Why would you even need that in space though, where there's no external ambient pressure? I thought that's the only relevant context for this discussion - trying to restart your cryo engine in space.
-
#89 by vyoma on 22 Jan, 2014 15:04
-
Here are two insightful articles on GSLV Mk2, GSLV Mk3, and Indian and Russian cryogenic engines.
An interview with S. Ramakrishnan, Director, VSSC:
http://www.frontline.in/cover-story/will-be-able-to-repeat-the-success/article5590227.ece
An interview with K. Radhakrishnan, Chairman, ISRO:
http://www.frontline.in/cover-story/gslv-mkiii-the-next-milestone/article5596588.eceQuoteWhat elements of the Mark II cryogenic engine and stage, which fired GSLV-D5, still retain the legacy of Russian engine technology and design? How much of it is truly indigenous and how much of it relies on the Russian heritage?
Basically, both engines use the “staged combustion cycle”. That is one approach compared with gas generator cycle, which we are using for the C20 engine to be used in GSLV MkIII. There are several other differences, conceptually also, especially the igniter system that we are using, which is totally different from what has been used in the Russian engine. [In MkII liquid oxygen (LOX) and gaseous hydrogen (GH2) are ignited by pyrogen-type igniters in the pre-burner as well as in the main and steering engines during initial stages, as against pyrotechnic ignition in the Russian engine.] But in the staged combustion cycle, similarities can be found in the way the engine is started and the steering engines are used for controllability. -
#90 by vyoma on 01 Oct, 2015 06:15
-
http://timesofindia.indiatimes.com/city/hyderabad/IICT-develops-polymer-for-Isros-cryogenic-engine/articleshow/49164649.cmsQuote
HYDERABAD: In a significant development in rocket science, the Indian Institute of Chemical Technology (IICT) has developed a polymer for use in cryogenic rocket by the Indian Space Research Organisation (Isro).
Use of polymer instead of aluminium or other alloys in fuel plumbing and tubes in the cryogenic engine drastically reduces the overall weight of the rocket. The advantage of it is that the rocket can carry a higher payload. The weight of fuel plumbing and tubes made of polymer is just 10 per cent of those made of aluminium or other alloys.
"As of now, Isro is importing the polymer from the US. But we now have developed the Fluorinated Ethylene Propylene (FEP) polymer," said Shekharam Tammishetti, senior principal scientist and head, polymers and functional materials division, CSIR-IICT. He told TOI that the technology will be transferred to Isro.
In the cryogenic engine, the fuel that is used is oxygen and hydrogen. When the two elements are burnt together, they produce a lot of energy. At that temperature, only FEP polymer can withstand the heat. -
#91 by russianhalo117 on 01 Oct, 2015 06:18
-
http://timesofindia.indiatimes.com/city/hyderabad/IICT-develops-polymer-for-Isros-cryogenic-engine/articleshow/49164649.cms
FEPvis made in Houston and is transported under train car lease designation DOWXQuoteHYDERABAD: In a significant development in rocket science, the Indian Institute of Chemical Technology (IICT) has developed a polymer for use in cryogenic rocket by the Indian Space Research Organisation (Isro).
Use of polymer instead of aluminium or other alloys in fuel plumbing and tubes in the cryogenic engine drastically reduces the overall weight of the rocket. The advantage of it is that the rocket can carry a higher payload. The weight of fuel plumbing and tubes made of polymer is just 10 per cent of those made of aluminium or other alloys.
"As of now, Isro is importing the polymer from the US. But we now have developed the Fluorinated Ethylene Propylene (FEP) polymer," said Shekharam Tammishetti, senior principal scientist and head, polymers and functional materials division, CSIR-IICT. He told TOI that the technology will be transferred to Isro.
In the cryogenic engine, the fuel that is used is oxygen and hydrogen. When the two elements are burnt together, they produce a lot of energy. At that temperature, only FEP polymer can withstand the heat. -
#92 by vyoma on 30 Oct, 2015 12:45
-
Quote
From 2016 onwards, there will be two missions every year using the Mk-II version of the Geosynchronous Satellite Launch Vehicle (GSLV Mk-II), ISRO chairman A S Kiran Kumar said on the sidelines of a function organised by the High Energy Materials Society of India (HEMSI) here on Thursday.
http://www.newindianexpress.com/cities/thiruvananthapuram/GSLV-Mk-IIs-May-Provide-High-octane-to-ISRO-Missions/2015/10/30/article3104691.ece1 -
#93 by vyoma on 30 Oct, 2015 12:46
-
Can mods please change this topic title to: GSLV MkII & cryo stage discussion thread
-
#94 by input~2 on 30 Oct, 2015 14:34
-
Can mods please change this topic title to: GSLV MkII & cryo stage discussion thread
Done! -
#95 by vyoma on 04 Sep, 2016 22:12
-
#96 by vyoma on 05 Sep, 2016 21:45
-
VSSC, ISRO recently issued a tender (Aug 2016) for supplying CFRP elements for GSLV MkII cryogenic stage: http://www.isro.gov.in/sites/default/files/tenders/pt197.pdfQuote
This RFQ provides the details of realization of various CFRP elements required for cryo upper stage of GSLV launch vehicle. These are made of carbon epoxy prepreg and Aluminium honeycomb core materials and is fabricated by hand layup and Autoclave curing.
-
#97 by sanman on 07 Sep, 2016 18:26
-
Since SpaceX has achieved such great improvements through propellant densification, I wonder if ISRO has looked at this as a way to improve its launch vehicle performance? Anybody know?
-
#98 by vineethgk on 08 Sep, 2016 03:45
-
GSLV has a 20-year past and a long way aheadQuote
From now on the target is for two GSLV launches a year, which means a launch every six months. It took us a year between the last one and this. We want to improve that
QuoteThere is an increasing demand for the GSLV. We are looking at possible opportunities for it to provide commercial launches, just as the PSLV has done.
Yes, even for full launches. A few discussions are going on. We have to wait for the talks to firm up. -
#99 by worldtimedate on 09 Sep, 2016 05:18
-
Quote
Asked whether the space organisation is now comfortable with the indigenous cryogenic stage, a complex system compared to solid and earth-storable liquid propellant rocket stages, S. Somanath, Director, Liquid Propulsion System Centre, ISRO, said the scientists were very confident about it.
The cryogenic stage has settled into a system today. After the failure of the first stage, we identified the problems, conducted very detailed analysis and studies. Lots of tests were done simulating actual conditions, and they were very successful. We have mastered the technology, Mr. Somanath said.
He said ISRO was developing another engine, C-25, that will be twice as powerful as the current one.
ISRO now expects the GSLV to pick up business like the PSLV.
Source :
ISRO eyes Venus mission
--- [ --- ]
, while singing -- about your first iteration at a solution --