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#1160 by meekGee on 22 Jan, 2018 07:06
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I expect they will stabilise design and concentrate on volume production and launch. There is still likely to be follow on LV in early stages of development.
Yup. They just got to market first - so they need to capitalize.
And remember that the only other realistic competitor is 2x as expensive.
The more they fly, the faster they can bring the next version to market.
The T/W seemed pretty high. This argues for a stretch version as some point.
For a first flight - were the engines running at full thrust?
Unlike their competitor, this vehicle uses very new technology. This means that there is very likely room for major improvements.
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#1161 by ArbitraryConstant on 22 Jan, 2018 07:45
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Or they switch over to advanced capacitors, especially if they jettison them like the battery packs currently.
Doubt supercapacitors make sense in this application, the specific energy is just too low to make sense even if you eject more frequently. And the higher discharge speeds are unnecessary.
A lot can be inferred from the video. There was only one battery hot swap/jettison, about 4 minutes after staging. Yet it's no problem to discharge a high power lithium battery in under a minute. They could have done a larger number of hotswap/jettison events if they had wanted to even using lithium. From this I infer it's a critical event and possible LOM if it fails, hence undesirable to do a bunch of them.Ben Brockert: The upper stage exhaust was very sparky. That's usually only seen in solids, usually sparks in liquids means that some of the engine is eroding.
Wonder if that has anything to do with the 3D printed manufacturing.Ben Brockert: They really leaned on the upper stage. Long into the second stage burn they called 3km/s, not even half way to orbit.
Reminds me of SpaceX, they've tended to stage low and slow too, even before they were landing. Seems like that could be a consequence of using the same engines on both stages. I also note they end up with a 9:1 ratio and even something very like the SpaceX octoweb arrangement. I doubt they copied that without doing the math, seems like that's something of a golden ratio for a TSTO LEO-optimized launcher.
One consequence of using your first stage engine on your upper stage is that it's very high thrust for an upper stage, there is far less need for the first stage to protect the upper stage from gravity losses as is the case with eg the RL-10. And the ISP of the first stage engines isn't amazing, so maybe better to do more with the vac optimized engine as soon as possible.Unlike their competitor, this vehicle uses very new technology. This means that there is very likely room for major improvements.
One advantage of the electric cycle... you can get significant improvements just sitting around waiting for better batteries. -
#1162 by Bananas_on_Mars on 22 Jan, 2018 10:16
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I've been thinking wether the Rutherford engine allows for a true "run to depletion" because of the electric turbopump?
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#1163 by TrevorMonty on 22 Jan, 2018 13:34
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Relativity Space also plan to use 9+1 engine configuration, but they are exSpaceX staff.
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#1164 by ringsider on 22 Jan, 2018 14:19
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but they are exSpaceX staff.
You are not wrong but people put too much emphasis on that stuff. They were mostly short summer internships during their degree programs, then 1-2 years in very junior positions before they started Relativity:-
CTO
USC Bachelors degree 2010-2014
Blue Origin
Propulsion Intern (summer intern)
Dates Employed Jun 2013 – Aug 2013
Employment Duration 3 mos
SpaceX
In-Space Propulsion Intern (summer intern)
Dates Employed Jun 2014 – Sep 2014
Employment Duration 4 mos
Propulsion Development Engineer (full time)
SpaceX
Dates Employed Sep 2014 – Dec 2015
Employment Duration 1 yr 4 mos
CEO
USC Bachelors and Masters degrees 2008-2013
Turbomachinery Development (summer intern)
BLUE ORIGIN
Dates Employed May 2011 – Aug 2011
Employment Duration 4 mos
Propulsion Testing (summer intern)
BLUE ORIGIN
May 2012 – Aug 2012
Employment Duration 4 mos
Turbomachinery Development (summer intern)
BLUE ORIGIN
Dates Employed May 2013 – Aug 2013
Employment Duration 4 mos
Propulsion Development (full time)
BLUE ORIGIN
Dates Employed Jan 2014 – Dec 2015
Employment Duration 2 yrs
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It's not nothing, but it's also a bit of a stretch to put a huge emphasis on that aspect.
Jimmy Cantrell is another one who makes his links to SpaceX seem more than it really is. He left SpaceX because after a few months "he didn't believe in it", or some such. If you think about it Jimmy is actually more like Ron Wayne, the guy who sold his Apple stock for $800... -
#1165 by Lars-J on 22 Jan, 2018 16:29
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It is certainly interesting that we now have two operational rockets with a 9+1 engine configuration. But I suppose it makes the most sense if you only have the budget to create one engine.
It also shows that both providers and customers are now far more accepting of clustered engine approach. -
#1166 by imprezive on 22 Jan, 2018 16:32
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I expect they will stabilise design and concentrate on volume production and launch. There is still likely to be follow on LV in early stages of development.
Yup. They just got to market first - so they need to capitalize.
And remember that the only other realistic competitor is 2x as expensive.
The more they fly, the faster they can bring the next version to market.
The T/W seemed pretty high. This argues for a stretch version as some point.
For a first flight - were the engines running at full thrust?
Unlike their competitor, this vehicle uses very new technology. This means that there is very likely room for major improvements.
Who’s the competitor that’s 2x as expensive? I’m assuming either Vector or Virgin but both are similar in $/kg to RL. -
#1167 by edzieba on 22 Jan, 2018 17:22
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3. Here is a crazy idea. Changing prop in the middle of the upper stage burn. So start the US on a methalox fuel, but when getting closer to orbit and gravity losses are getting small, switch over to hydralox.
Tripropellant cycles are kind of "Devil in the Details" designs. Either you add another motorpump (probably eating up all your ISP gains) for the Hydrogen, or you have to deal with trying to flush the fuel lines and pump of RP-1/Methane before switching to Hydrogen or you end up with an unknown fuel mix. Plus you need a pump that can handle the transition from Liquid Methane (or RP-1) temperatures down to liquid Hydrogen temperatures without damage, or an engine that can handle the transition from liquid/liquid phase injection & combustion to liquid/gas phase.
Sure you lose thrust, but at that point in the burn, that doesn't matter if the ISP goes way up.
You would probably gain dry mass due to more complex tankage and extra piping though. But the pump might not care about the fuel change.
This would probably really help out if your going to GEO or further out. -
#1168 by john smith 19 on 22 Jan, 2018 18:30
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1. Sub cool the propellants like Space X.
Depends, if sub cooling is planned into the performance, or if a thrust upgrade to the engines is planned in. Basically anything within 3K of the NBP of LN2 has been within the Soa since the X33 programme. Anything lower (which SX seem to us) is going to be harder and more expensive.Quote from: BarryKirk2. With two motors and two pumps, both electric, one has to ask, how difficult it would be to change to a different propellant?
Probably not that difficult. Basically there's LH2 and everything else in terms of density and flowrate (LH2 is also the compressible liquid, completely unlike pretty much every other propellant).
Probably want to stick with KeroLox for the booster, at least initially, but how difficult would it be to change the US to Methalox?Quote from: BarryKirk3. Here is a crazy idea. Changing prop in the middle of the upper stage burn. So start the US on a methalox fuel, but when getting closer to orbit and gravity losses are getting small, switch over to hydralox.
Massive extra complexity on the pad and the vehicle. 3 tanks, not 2, trouble with GH2 permeation into a tank structure (not sure even NASA has solved that yet)
Sure you lose thrust, but at that point in the burn, that doesn't matter if the ISP goes way up.Quote from: BarryKirkYou would probably gain dry mass due to more complex tankage and extra piping though. But the pump might not care about the fuel change.
Wrong. The pump is the big one. LH2 (even desified) is < 1/10 the density of RP1LCH4 is (IIRC) about 460K/Kg^3, less than 1/6 the density of Methane, and (unlike every other propellant) it's compressible (so raising the pressure does not in fact raise the pressure, it causes the LH2 to shrink).
Which makes LH2 pump design a PITA, and only done if you really want the performance.
Actually you missed (in principle) the simplest trick, mixture ratio shifting. For each flight stage you run rich(er) with the most dense propellant (normally the Oxidizer) which runs slightly lower Isp but lightens the stage faster, IE it improves acceleration. That lowers gravity losses. Since the rocket already has an IMS measuring when to do this would be quite easy. Then it's a question of adding an actuator (actuators?) to the LOX (fuel?) side of the engine, then gradually dial it down as you gain height to trade thrust for Isp. This could b as simple as a two position valve or fully variable driven by a stepper motor.
I don't think anyone's done a full MR shift (or at least anyone who's said so). Fully implemented a rocket could barely get off the pad ( say 1.05g acceleration) then within seconds (after maximum propellant loss has burned off the most propellant for the least gain) start to shift to fuel rich, raising Isp.
BTW the terminology is confusing. In car engines "lean burn" means low fuel. Here you start "lean" then shift to fuel rich, yet your Isp (or "rocket MPG") goes up. This sounds very counter intuitive if you have a car background. -
#1169 by john smith 19 on 22 Jan, 2018 18:32
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Tripropellant cycles are kind of "Devil in the Details" designs. Either you add another motorpump (probably eating up all your ISP gains) for the Hydrogen, or you have to deal with trying to flush the fuel lines and pump of RP-1/Methane before switching to Hydrogen or you end up with an unknown fuel mix. Plus you need a pump that can handle the transition from Liquid Methane (or RP-1) temperatures down to liquid Hydrogen temperatures without damage, or an engine that can handle the transition from liquid/liquid phase injection & combustion to liquid/gas phase.
Unless of course you swap oxidizers, rather than fuels. -
#1170 by Davidthefat on 22 Jan, 2018 18:51
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Tripropellant cycles are kind of "Devil in the Details" designs. Either you add another motorpump (probably eating up all your ISP gains) for the Hydrogen, or you have to deal with trying to flush the fuel lines and pump of RP-1/Methane before switching to Hydrogen or you end up with an unknown fuel mix. Plus you need a pump that can handle the transition from Liquid Methane (or RP-1) temperatures down to liquid Hydrogen temperatures without damage, or an engine that can handle the transition from liquid/liquid phase injection & combustion to liquid/gas phase.
Unless of course you swap oxidizers, rather than fuels.
What kind of oxidizer would you use instead of LOX? -
#1171 by ZachS09 on 22 Jan, 2018 18:59
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How about hydrogen peroxide?
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#1172 by john smith 19 on 22 Jan, 2018 19:12
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author=ZachS09 link=topic=35300.msg1775496#msg1775496 date=1516651171]
How about hydrogen peroxide?
[/quote]
Actually on that basis you would run HTP in the booster, or early flight, and LOX in the later, or just the upper stage. Basically the same idea of the RP1/LH2 shift that Von Braun did with the Saturn V.
Air of course.Tripropellant cycles are kind of "Devil in the Details" designs. Either you add another motorpump (probably eating up all your ISP gains) for the Hydrogen, or you have to deal with trying to flush the fuel lines and pump of RP-1/Methane before switching to Hydrogen or you end up with an unknown fuel mix. Plus you need a pump that can handle the transition from Liquid Methane (or RP-1) temperatures down to liquid Hydrogen temperatures without damage, or an engine that can handle the transition from liquid/liquid phase injection & combustion to liquid/gas phase.
Unless of course you swap oxidizers, rather than fuels.
What kind of oxidizer would you use instead of LOX?
I was alluding to Reaction Engines SABRE engine, but merely as a way to point that it's easy to develop tunnel vision in this game, when IRL there are alternatives. -
#1173 by gin455res on 22 Jan, 2018 23:51
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Is an electrically-pumped-rocket thrust limited by electric motor size of the propellant with the greatest volume(, usually the oxidizer)?
And if so would the most powerful useful electric engine occur roughly when fuel and oxidizer volumes are approximately equal, and pump-sizes roughly equal?
Would 70% alcohol/lox be a good combination?
And can a pump be twice as big if it is composed of one impeller between two motors? The motors either side of the impeller shaft. -
#1174 by BarryKirk on 22 Jan, 2018 23:52
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All interesting ideas... Agreed that probably LH2 would be a non starter. Hadn't realized those devil details....
I like the idea of changing the mixture in mid burn... With separate electrically driven pumps, one can adjust the mixture any way you want.
So an Oxygen rich mixture would give you lots of thrust, but low ISP. Probably much easier to do oxygen rich since the only place you need to deal with hot oxygen is in the combustion chamber, and not the pump or turbo.
And later on fuel rich with methane at least would give you lots of lightweight stuff, for much higher ISP than stoichiometric mixtures. -
#1175 by john smith 19 on 23 Jan, 2018 00:04
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I like the idea of changing the mixture in mid burn... With separate electrically driven pumps, one can adjust the mixture any way you want.
Historically this has been done by bypass valves around the turbopumps, with them staying at a pretty constant speed. Mechanical engineers like to keep large lumps of metal spinning at high speed at a constant high speed. However in principle with power electronics ramping the motor speeds up or down should be fairly simple, and "throttle response" fairly fast provided the pump response at the different speeds is mapped carefully. Again stuff that works fine at constant speed has proven problematical at other speeds.Quote from: BarryKirkSo an Oxygen rich mixture would give you lots of thrust, but low ISP. Probably much easier to do oxygen rich since the only place you need to deal with hot oxygen is in the combustion chamber, and not the pump or turbo.
Don't go overboard on this. Engines that have done this are things like the J-2's on Saturn V & RL10 and SSME had a lot of ground tests (very flexible. Something like O/F from 4.5-6.0:1 in 0.1 unit increments).Quote from: BarryKirkAnd later on fuel rich with methane at least would give you lots of lightweight stuff, for much higher ISP than stoichiometric mixtures.
Fuel rich is SOP for all rocket engines, because the combustion products have lower molecular weight. -
#1176 by gongora on 23 Jan, 2018 00:09
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Multiple fuels? Switching fuels on the same stage in flight??? Getting rid of batteries? Why on Earth would Rocket Lab bother with any of that stuff. They designed a very nice little vehicle that seems to be able to get the job done at a very good price. Throwing a bunch of money at bizarre modifications to the vehicle really wouldn't make any sense. Can't we just be happy that someone brought a launcher to market that flies for less than 1/4 the price of any other active vehicles?
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#1177 by QuantumG on 23 Jan, 2018 00:12
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Pretty low funding too. Absurd valuation.
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#1178 by Lars-J on 23 Jan, 2018 00:42
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Multiple fuels? Switching fuels on the same stage in flight??? Getting rid of batteries? Why on Earth would Rocket Lab bother with any of that stuff. They designed a very nice little vehicle that seems to be able to get the job done at a very good price. Throwing a bunch of money at bizarre modifications to the vehicle really wouldn't make any sense. Can't we just be happy that someone brought a launcher to market that flies for less than 1/4 the price of any other active vehicles?
Right. It's as people have ignored every lesson illustrated by SpaceX over the last years (simplicity being a prime one!) and defaulted back to Rube Goldberg ideas to squeeze out a few percent more performance while adding massive costs. Brilliant!
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#1179 by Space Ghost 1962 on 23 Jan, 2018 01:34
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Pretty low funding too. Absurd evaluation.
Perhaps you mean ... valuation? And yes quite over the top. Most of the current crop of microlaunchers are that way.
Heh. The skys the limit
