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SpaceX Vehicles and Missions => SpaceX Early Days Archive Section => Topic started by: Chris Bergin on 10/02/2013 03:24 pm

Title: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Chris Bergin on 10/02/2013 03:24 pm
New thread for the Merlin 1Ds.

Thread 1:
http://forum.nasaspaceflight.com/index.php?topic=26388.0

Resources:
Merlin 1D News Articles:
http://www.nasaspaceflight.com/?s=%22Merlin+1D%22

Remember to stay on topic and not to wander into different subjects (even if they are SpaceX related). We have lots of threads and you can even start splinter threads if the discussion warrants it.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Okie_Steve on 10/11/2013 05:43 pm
Something on another thread got me to wondering. What are the fundamental limits to throttling a kero-lox turbopump engine like the Merlin. I believe that pressure fed pintle engines can throttle much deeper. Is the 70% envelope on the Merlin-1D a fairly hard limit or just a design trade off? Anyone have any insight?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Elmar Moelzer on 10/11/2013 05:59 pm
Someone mentioned the possibility of flow separation if the M1D is throttled too low. From my limited understanding that among other things depends on the shape and size of the nozzle extension. So maybe it could be possible to throttle a M1d more deeply with a different nozzle design. That might mean less efficiency in other parts of the flight envelope though.
I am sure that someone with more rocket engine design knowledge will immediately jump in and correct me in 10...9...
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: cambrianera on 10/11/2013 06:07 pm
Something on another thread got me to wondering. What are the fundamental limits to throttling a kero-lox turbopump engine like the Merlin. I believe that pressure fed pintle engines can throttle much deeper. Is the 70% envelope on the Merlin-1D a fairly hard limit or just a design trade off? Anyone have any insight?

No insight, but some thinking.
To throttle your engine you reduce propellant flow; you can do this increasing pressure drop on the injector or reducing the RPM of the turbopump.
In the first case you have a net loss of energy, in the second you actually increase the percentage of propellant flowing through the combustion chamber (in GG cycle the propellant through GG and turbine is lost for thrust)

But turbomachinery doesn't like big variations of RPM, normally they are highly optimized for a small range.
Therefore throttling range only from 100% to 70%.
I believe SpaceX went this way.

Usual disclaimer, only speculation.

BTW: expert's opinion highly appreciated.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: baldusi on 10/11/2013 06:40 pm
Someone mentioned the possibility of flow separation if the M1D is throttled too low. From my limited understanding that among other things depends on the shape and size of the nozzle extension. So maybe it could be possible to throttle a M1d more deeply with a different nozzle design. That might mean less efficiency in other parts of the flight envelope though.
The Merlin 1D has the whole nozzle made of a structure that circulates RP-1 to cool it (it's called regeneratively cooled nozzle). It would look, from the extremely clean look of it and amazing T/W, that they have the inner and oute linings and use a corrugated separator in the middle. Then they would braze it. Like the NK-33. You can add an extension, that will have to be cooled differently (either ablatively, or film-cooled+radiatively, like the Vacuum version of the Merlin 1D). But you can't cut it easily. You'd have to modify or even get new tooling, and the pressure loss on the nozzle cooling circuit will be reduced, which I don't know how would impact the power balance on the engine. Thus, is not easy to reduce the thrust because of flow separation.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Okie_Steve on 10/11/2013 07:01 pm
Hmm, thanks for the food-for-thought. It sounds like applying various already-done-elsewhere ideas could address most of these. Route the turbopump output to the nozzle along the lines of the Merlin-Vac, use a double bell nozzle, recycle some of the pump output back to the input etc. I had not considered the reg-cooling but I suspect it's not a show stopper. Based on the immediate discussion it sounds to me like there's nothing really fundamentally limiting just that they applied the KISS principle to the tubopump design because the design trade offs for deeper throttling were not worth it.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: malu5531 on 12/12/2013 12:37 pm
While trying to understand Merlin 1D and in particular "Merlin 1D+"* in depth, I've iterated my calculations (http://tinyurl.com/merlin1d) a few times and have reached internal coherence and good balance with reality using the following characteristics/specs. 

Merlin 1D..Merlin 1D Vac..Merlin 1D+..Merlin 1D+ Vac
Chamber Pressure, MPa9.79.710.810.8
Pressure exhaust, bar0.430.030.4750.034
Throat area, m^20.0420.0420.0420.042
Nozzle area, m^20.97.220.97.22
Nozzle diameter, m1.073.031.073.03
Mixture ratio2.342.362.362.375
Mass flow chamber, kg229229253.5253.5
Mass flow gg, +%3.253.253.253.25
Net mass flow, kg236236262262
SL Thrust, klbf147 klbf165 klbf
SL Isp, s282 s286 s
Vac Thrust, klbf167 klbf181 klbf185 klbf200 klbf
Vac Isp, s320 s347 s321 s347 s

*) Merlin 1D+ is a nick-name for the engine Elon hinted during the SES8 teleconference; a 165 klbf SL "Merlin 1D"

Disclaimer; IANARS & many constants are read from analogue charts (http://www.braeunig.us/space/comb-OK.htm), so there are some wiggle room.
Nozzle diameter should probably be a few cm less.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Prober on 12/12/2013 01:16 pm
Someone mentioned the possibility of flow separation if the M1D is throttled too low. From my limited understanding that among other things depends on the shape and size of the nozzle extension. So maybe it could be possible to throttle a M1d more deeply with a different nozzle design. That might mean less efficiency in other parts of the flight envelope though.
The Merlin 1D has the whole nozzle made of a structure that circulates RP-1 to cool it (it's called regeneratively cooled nozzle). It would look, from the extremely clean look of it and amazing T/W, that they have the inner and oute linings and use a corrugated separator in the middle. Then they would braze it. Like the NK-33. You can add an extension, that will have to be cooled differently (either ablatively, or film-cooled+radiatively, like the Vacuum version of the Merlin 1D). But you can't cut it easily. You'd have to modify or even get new tooling, and the pressure loss on the nozzle cooling circuit will be reduced, which I don't know how would impact the power balance on the engine. Thus, is not easy to reduce the thrust because of flow separation.

The extension can be cut very easy.  Water jet can cut it without a problem.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: pagheca on 12/12/2013 01:41 pm
Hi everyone,

this question maybe obvious for many of you - please excuse me if this is the case but I'm just in learning mode.

As well known, the Merlin 1D engine can be throttled down from 100% to 60%.

The vacuum thrust of a rocket engine is proportional to the exhaust velocity and to the mass flow rate of the gas exhaust: dm/dt * V_exh.

In vacuum and if also the gravity drag is negligible, when a Merlin 1D engine is throttled down, is dm/dt only changing, OR also V_exh (aka Isp_vacuum) is affected someway, with a consequent reduction in the engine efficiency in using the available propellant?

If the second hypothesis is right (as I would say by looking at the physical principles the engine is based on), does someone know a reasonable way to write the relation Thrust(%) = f(%,dm/dt, V_exh)?

Thanks for any hint,

Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: cambrianera on 12/12/2013 03:18 pm
Someone mentioned the possibility of flow separation if the M1D is throttled too low. From my limited understanding that among other things depends on the shape and size of the nozzle extension. So maybe it could be possible to throttle a M1d more deeply with a different nozzle design. That might mean less efficiency in other parts of the flight envelope though.
The Merlin 1D has the whole nozzle made of a structure that circulates RP-1 to cool it (it's called regeneratively cooled nozzle). It would look, from the extremely clean look of it and amazing T/W, that they have the inner and oute linings and use a corrugated separator in the middle. Then they would braze it. Like the NK-33. You can add an extension, that will have to be cooled differently (either ablatively, or film-cooled+radiatively, like the Vacuum version of the Merlin 1D). But you can't cut it easily. You'd have to modify or even get new tooling, and the pressure loss on the nozzle cooling circuit will be reduced, which I don't know how would impact the power balance on the engine. Thus, is not easy to reduce the thrust because of flow separation.

The extension can be cut very easy.  Water jet can cut it without a problem.

I guess baldusi was suggesting that it's easy to add an extension (increasing the expansion) but not to cut the nozzle (decreasing the expansion).
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Elmar Moelzer on 12/12/2013 03:22 pm
And I was talking about a different/ new nozzle design, not just cutting or extending the current nozzle.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: cambrianera on 12/12/2013 03:24 pm
Two things about throttling:
-thanks to aero for this interesting link
http://www.ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20100033271_2010034521.pdf
the post
http://forum.nasaspaceflight.com/index.php?topic=33142.msg1130796#msg1130796
-in last GH1 flight, it's likely that throttling of merlin 1D went to about 60%.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Joffan on 12/12/2013 07:16 pm
Two things about throttling:
-thanks to aero for this interesting link
http://www.ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20100033271_2010034521.pdf
the post
http://forum.nasaspaceflight.com/index.php?topic=33142.msg1130796#msg1130796
-in last GH1 flight, it's likely that throttling of merlin 1D went to about 60%.

.. and that's 60% of whatever they were using as 100% lift-off thrust. If top thrust can be increased by (say) 10%, still leaving some margin, and the throttling back can still get down to the same low level, it would be about 55%.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: aero on 12/12/2013 08:32 pm
While trying to understand Merlin 1D and in particular "Merlin 1D+"* in depth, I've iterated my calculations (http://tinyurl.com/merlin1d) a few times and have reached internal coherence and good balance with reality using the following characteristics/specs. 

Merlin 1D..Merlin 1D Vac..Merlin 1D+..Merlin 1D+ Vac
Chamber Pressure, MPa9.79.710.810.8
Pressure exhaust, bar0.430.030.4750.034
Throat area, m^20.0420.0420.0420.042
Nozzle area, m^20.97.220.97.22
Nozzle diameter, m1.073.031.073.03
Mixture ratio2.342.362.362.375
Mass flow chamber, kg229229253.5253.5
Mass flow gg, +%3.253.253.253.25
Net mass flow, kg236236262262
SL Thrust, klbf147 klbf165 klbf
SL Isp, s282 s286 s
Vac Thrust, klbf167 klbf181 klbf185 klbf200 klbf
Vac Isp, s320 s347 s321 s347 s

*) Merlin 1D+ is a nick-name for the engine Elon hinted during the SES8 teleconference; a 165 klbf SL "Merlin 1D"

Disclaimer; IANARS & many constants are read from analogue charts (http://www.braeunig.us/space/comb-OK.htm), so there are some wiggle room.
Nozzle diameter should probably be a few cm less.


I have a question for you. If SpaceX were to try the D+, what would they do for propellant? Mass flow goes from 236 to 262 so the burns would be shorter on both stages. Sure, the Isp is up a little but in the wash, it really doesn't make much difference to payload capability. With more powerful engines, will they extend the length of the tanks by 10 % (a guess) to keep the lift-off T/W the same or will they just drive the engines harder for little benefit?

And by the way, does anyone know the actual propellant mass for the stages of the existing F 9? Simulating the F 9 is a trick because each time the Isp changes, the lift-off mass changes, or the dry weight of the stages changes to compensate.

I know the mixture ratio so if I knew the length of the tank I could estimate the propellant mass probably more accurately than using the fuel flow rate and burn time since fuel flow rate is a mystery anyway.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Elmar Moelzer on 12/12/2013 08:41 pm
I have a question for you. If SpaceX were to try the D+, what would they do for propellant? Mass flow goes from 236 to 262 so the burns would be shorter on both stages. Sure, the Isp is up a little but in the wash, it really doesn't make much difference to payload capability. With more powerful engines, will they extend the length of the tanks by 10 % (a guess) to keep the lift-off T/W the same or will they just drive the engines harder for little benefit?
If they did not need the center engine for breaking, the extra thrust of the 1D+ should allow them to just get rid of it and save the weight. I don't think an 8 engine layout would work... hmmm...

And by the way, does anyone know the actual propellant mass for the stages of the existing F 9? Simulating the F 9 is a trick because each time the Isp changes, the lift-off mass changes, or the dry weight of the stages changes to compensate.

I know the mixture ratio so if I knew the length of the tank I could estimate the propellant mass probably more accurately than using the fuel flow rate and burn time since fuel flow rate is a mystery anyway.
Not sure how accurate this is, but there are some numbers here:
http://www.spacelaunchreport.com/falcon9v1-1.html#components
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: aero on 12/12/2013 08:54 pm
Thanks for the link. It's an update from the old one that I've been referring to.


Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Joffan on 12/12/2013 08:56 pm
If SpaceX were to try the D+, what would they do for propellant? Mass flow goes from 236 to 262 so the burns would be shorter on both stages. Sure, the Isp is up a little but in the wash, it really doesn't make much difference to payload capability.

Yes, it does make a difference. The reason is that with higher thrust you get a quicker ascent and reduced gravity losses. So the answer is that they could increase the maximum payload even without changing the amount of propellant.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Elmar Moelzer on 12/12/2013 08:59 pm
Yes, it does make a difference. The reason is that with higher thrust you get a quicker ascent and reduced gravity losses. So the answer is that they could increase the maximum payload even without changing the amount of propellant.
But wouldn't that also increase the g forces on the payload?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: MikeAtkinson on 12/12/2013 09:02 pm
I have a question for you. If SpaceX were to try the D+, what would they do for propellant? Mass flow goes from 236 to 262 so the burns would be shorter on both stages. Sure, the Isp is up a little but in the wash, it really doesn't make much difference to payload capability. With more powerful engines, will they extend the length of the tanks by 10 % (a guess) to keep the lift-off T/W the same or will they just drive the engines harder for little benefit?

My guess is that they would "spend" the extra thrust in two ways:

Firstly, so that 8 M1D+ engines can give the thrust of 9 current M1D, they avoid having to keep a propellant reserve for the extra gravity losses during engine out. So no stretch of the 1st stage, and run the engines at less than their full thrust.

This would up the payload to LEO to about 16 tonnes and to GTO to about 5.5 tonnes [guesses, not run any simulations].


Secondly, a modest stretch of the 2nd stage [guesses, not run any simulations].

Together these would up the payload to LEO to about 20 tonnes and GTO to about 6.5 tonnes.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: mheney on 12/12/2013 09:21 pm
Another consideration is that, if you want to reuse the engines, you extend their life by not red-lining them.  When you optimize for cost rather than raw performance, SOP may well be to run the engines at 80% of theoretical max performance rather than pedal-to-the metal ...
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Joffan on 12/12/2013 10:25 pm
Yes, it does make a difference. The reason is that with higher thrust you get a quicker ascent and reduced gravity losses. So the answer is that they could increase the maximum payload even without changing the amount of propellant.
But wouldn't that also increase the g forces on the payload?

It could, but even if the g-force were restricted to the same maximum by throttling back, there would still be a significant gain. The high g-force is late in the ascent, where the gravity losses are already getting smaller. Getting off the pad up through max-Q is where you'd get the bulk of the gains.

---------
EDIT to add: If the craft were throttling back for max-Q already, it's possible that you would have to throttle back over a longer altitude range (starting lower/finishing higher) with the higher max thrust.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: macpacheco on 12/13/2013 12:25 am
Considering Elon's statement that they're only using 85% of available thrust, parsing that as a performance envelope not currently used for launches (perhaps only on the test stand):
 100% thrust today =   85% future maximum thrust
 117% thrust today = 100% future maximum thrust
   75% thrust today =   64% future maximum thrust
Not too shabby, ability to throttle from full thrust down to 2/3
Of course you can always wish for more

This has been discussed here:
http://forum.nasaspaceflight.com/index.php?topic=32998.0

The additional consideration is that should this extra thrust be fully available for full time use, this would call for a F9v1.2 with more fuel, increasing both non reuse payload and perhaps allowing for F9v1.2 S1+S2 reusability with the same F9R S1 reusability today, but even without more fuel, this would increase payload (both with and without S1 reusability, just less than with a version with more fuel)
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: cleonard on 12/13/2013 12:45 am
In general the exhaust velocity will decline as the engine is throttled down.  There are also second order effects.  Take a gas generator cycle engine.  Does the amount of fuel burned to pump the fuel change exactly the same as the throttling.  I doubt it.  It's likely close, but not exact.


Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: dante2308 on 12/13/2013 12:47 am
Hi everyone,

this question maybe obvious for many of you - please excuse me if this is the case but I'm just in learning mode.

As well known, the Merlin 1D engine can be throttled down from 100% to 60%.

The vacuum thrust of a rocket engine is proportional to the exhaust velocity and to the mass flow rate of the gas exhaust: dm/dt * V_exh.

In vacuum and if also the gravity drag is negligible, when a Merlin 1D engine is throttled down, is dm/dt only changing, OR also V_exh (aka Isp_vacuum) is affected someway, with a consequent reduction in the engine efficiency in using the available propellant?

If the second hypothesis is right (as I would say by looking at the physical principles the engine is based on), does someone know a reasonable way to write the relation Thrust(%) = f(%,dm/dt, V_exh)?

Thanks for any hint,

V_exh is not affected by thrust directly. There is a second order effect because you slightly lower the chamber pressure. This is my impression at least. I may be wrong.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: dante2308 on 12/13/2013 12:48 am
Ok well at least there is some agreement about using the term 'second order effect.'
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Robotbeat on 12/13/2013 03:45 am
Hi everyone,

this question maybe obvious for many of you - please excuse me if this is the case but I'm just in learning mode.

As well known, the Merlin 1D engine can be throttled down from 100% to 60%.

The vacuum thrust of a rocket engine is proportional to the exhaust velocity and to the mass flow rate of the gas exhaust: dm/dt * V_exh.

In vacuum and if also the gravity drag is negligible, when a Merlin 1D engine is throttled down, is dm/dt only changing, OR also V_exh (aka Isp_vacuum) is affected someway, with a consequent reduction in the engine efficiency in using the available propellant?

If the second hypothesis is right (as I would say by looking at the physical principles the engine is based on), does someone know a reasonable way to write the relation Thrust(%) = f(%,dm/dt, V_exh)?

Thanks for any hint,

V_exh is not affected by thrust directly. There is a second order effect because you slightly lower the chamber pressure. This is my impression at least. I may be wrong.
Thrust is proportional to chamber pressure (to first order), so you're right. Good old Sutton.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: ChrisWilson68 on 12/13/2013 04:17 am
Yes, it does make a difference. The reason is that with higher thrust you get a quicker ascent and reduced gravity losses. So the answer is that they could increase the maximum payload even without changing the amount of propellant.
But wouldn't that also increase the g forces on the payload?

As others have said, you can throttle down near the end of the burn to keep the maximum g load during the first stage burn the same.  But there's also a second stage burn, and, depending on the mass of the payload, the second stage burn could be giving the payload higher g forces than the first stage even with more first-stage thrust.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: MP99 on 12/13/2013 07:47 am
I have a question for you. If SpaceX were to try the D+, what would they do for propellant? Mass flow goes from 236 to 262 so the burns would be shorter on both stages. Sure, the Isp is up a little but in the wash, it really doesn't make much difference to payload capability. With more powerful engines, will they extend the length of the tanks by 10 % (a guess) to keep the lift-off T/W the same or will they just drive the engines harder for little benefit?

How much extra prop mass could fit within the existing tanking volume by densification (sub-cooling) of the O2?

Obviously this would require the bulkhead between the two tanks to be moved as the RP1 density is unchanged. Aerodynamics would be unaffected, but CoG, etc would be.

Sub-cooled O2 might also help with on orbit lifetime for the upper stage for GTO missions.

Cheers,  Martin

Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: MP99 on 12/13/2013 08:08 am
Found an answer.

http://www.grc.nasa.gov/WWW/RT/RT2001/5000/5870tomsik.html

Edit: Seems to be a dead link. Believe this is the same document:-
http://ntrs.nasa.gov/search.jsp?R=20050203875

Quote

This additional loaded mass of 16,100 lb represented on average an 8.9-percent increase in onboard LO2 propellant. Test results also confirmed the presence of thermally stratified oxygen layers inside the tank. These layers varied in the vertical direction from 122 °R for the colder, denser fluid at the bottom to 166 °R for the warmer, less dense LO2 near the top outlet of the STA tank.


(OK,  how many of you had even heard of Rankin as a temperature measure?)

At ~2.5:1,  I believe that's about 6.35% greater kerolox mass in the same total tank volume.

Cheers,  Martin
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Robotbeat on 12/13/2013 08:17 am
I've heard of Rankine! :) It's like the imperial version of Kelvin. Also, if you're going to subcool the LOx... We could always subcool the kerosene...
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: guckyfan on 12/13/2013 09:40 am
We could always subcool the kerosene...

Elon Musk does not like solid boosters. ;D

Maybe gel engines?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: baldusi on 12/13/2013 12:32 pm
I've heard of Rankine! :) It's like the imperial version of Kelvin. Also, if you're going to subcool the LOx... We could always subcool the kerosene...
Flows like frozen molasses. Or were you making a joke? Please put a smiley. In the internet you can't say something ridiculous enough not to be taken at face value.  ::)
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: pagheca on 12/13/2013 01:29 pm
V_exh is not affected by thrust directly. There is a second order effect because you slightly lower the chamber pressure. This is my impression at least. I may be wrong.

Thanks for your impression, but why a variation of the propellant flow is only "slightly" lowering the chamber pressure? How is the chamber pressure affected by a reduction in the propellant fed into it?

I searched a lot over the internet, for example by reading this http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19710019929_1971019929.pdf (http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19710019929_1971019929.pdf). I also looked at the Lunar Model Descent Propulsion System, that is someway similar in design to the Merlin, but couldn't find a single reference to the issue "how throttling a rocket engine impacts on the exhaust velocity?".

I was guessing that a rocket engine is essentially working by expanding adiabatically a gas. Now, if I apply the ideal gas law, pV=RT, by reducing p, being V fixed, T reduces LINEARLY. As T is related to the kinetic energy of the molecules expulsed by the nozzle, the exhaust velocity would in turn vary LINEARLY with the pressure, determined by the amount of propellant injected in the gas chamber.

I'm probably wrong here because T is dictated by the chemical reaction, and the chamber pressure is connected through a throat to the nozzle. So within certain limits, the pressure must build up until the gas is expelled through the throat, and the relation be less than linear.

However it is, I would really like to find a single reference explaining this and showing a plot of exhaust velocity vs. throttle to better understand the issue. It must be something very important for a powered descent on the Moon or to Earth.

It may also tell why it is better to use N<<9 engines at full throttle rather than M>N engines at reduced throttle (assuming you have enough throttle range to achieve the required total thrust), despite the fact that, as I suppose, a throttled engine is less stressed and therefore more reliable.

pagheca

p.s. frankly speaking, I do not understand why my original thread labelled "simulating a Merlin 1D throttling down" has been moved here. I'm a newbie here, so I fully accept the decision of the management, but by doing this the replies to my question, that is more a general one about the performances of rocket engines, are now mixed up with many many other posts and topics, making very difficult to follow the discussion. Moreover, I (and everyone reading here, I suppose) am receiving e-mail tell me that "A reply has been posted to a topic you are watching", even it concerns an issue I'm not at all interested in.Can someone please explain me the rationale behind this? Thanks. I wish to adhere the forum rules but I have to understand them first.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: pagheca on 12/13/2013 03:19 pm
I think that at last I found a reference confirming your impression was right, dante2308:

Only a few applications require a change in thrust during flight. Equations [...] show that the thrust is  directly proportional to the throat area At, the chamber pressure Pl, or the mass flow rate rh, but it is a weak function of CF, which in turn depends on k, the altitude, a pressure ratio, and A2/At. These equations show how the thrust may be varied and imply how other performance parameters may be affected by such variation. For liquid propellant rockets the mass flow to the chamber can be decreased (by throttling valves in  the propellant feed system) while the chamber geometry and the nozzle throat area are unchanged. The reduced mass flow will cause an almost linear decrease in Pl and thus an almost linear decrease of F. The combustion temperature does change slightly but it does not enter into the above relations. The specific impulse would also decrease slightly. (from http://web.mit.edu/e_peters/Public/Rockets/Rocket_Propulsion_Elements.pdf (http://web.mit.edu/e_peters/Public/Rockets/Rocket_Propulsion_Elements.pdf), page 96, paragraph 3.8.)
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: aero on 12/14/2013 03:13 am
Do the first stage Merlin D engines, as built, throttle?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Owlon on 12/14/2013 03:26 am
Do the first stage Merlin D engines, as built, throttle?

Yes. They are throttled down during a typical launch as the first stage approaches empty in order to limit acceleration. SpaceX has said they throttle to 70%, but some fellow NSFers say the most recent Grasshopper test must have throttled down to about 60%.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Hobbes-22 on 12/14/2013 09:32 am
On photos of various Merlin 1Ds, I've noticed two different turbopump exhausts:
One, angled to one side like the Merlin 1C was:
http://forum.nasaspaceflight.com/index.php?action=dlattach;topic=26388.0;attach=338595;image

The other is straight down:
http://2.bp.blogspot.com/-XNytk6p2UDk/Up7cbC4ckTI/AAAAAAAAbPQ/ode0klmkBaU/s1600/Captura-de-pantalla-2013-09-29-a-las-20.25.15.png

this reply in another thread (http://forum.nasaspaceflight.com/index.php?topic=32859.msg1103307#msg1103307 (http://forum.nasaspaceflight.com/index.php?topic=32859.msg1103307#msg1103307)) suggests that the straight-down version is the production version. Is that correct?

Of course this may be moot since this picture suggests the turbopump exhausts are hidden behind the bottom cover:
http://digitalvideo.8m.net/spacex/new/octaweb2.jpg

But is this a production rocket or just an unfinished engineering model?

I'm working on a 3D printable model of the F9 v1.1...
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: cambrianera on 12/14/2013 09:58 am
On photos of various Merlin 1Ds, I've noticed two different turbopump exhausts......(snip)

Your first pic is of M1D prototype (later used on GH1).
Other pics are of production M1D.
M1D prototype shares with M1C the thrust structure (then called quadrapod) and a big part of the TPA.
M1D production has a new thrust structure (smaller, to fit into the octaweb) and a new TPA (fixed to the CC).
I attach pictures of M1D prototype (first pic) and M1D production (second pic) on the same test stand.

BTW: it's better to attach pics rather to embed them, Chris is happier!
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: pagheca on 12/14/2013 12:17 pm
They are throttled down during a typical launch as the first stage approaches empty in order to limit acceleration.

Do you have any reference for this?
thanks
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: cambrianera on 12/14/2013 01:04 pm
They are throttled down during a typical launch as the first stage approaches empty in order to limit acceleration.

Do you have any reference for this?
thanks
Hmm, SpaceX Falcon9 main page reports this:
"The first stage engines are gradually throttled near the end of first-stage flight to limit launch vehicle acceleration as the rocket’s mass decreases with the burning of fuel."
http://www.spacex.com/falcon9
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Prober on 12/14/2013 01:15 pm


I'm working on a 3D printable model of the F9 v1.1...

Great news and looking forward to printing your model in the future  :)
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: pagheca on 12/14/2013 01:57 pm
Hmm, SpaceX Falcon9 main page reports this:
"The first stage engines are gradually throttled near the end of first-stage flight to limit launch vehicle acceleration as the rocket’s mass decreases with the burning of fuel."
http://www.spacex.com/falcon9

Ops... I someway missed this information. Available data from first v1.1 flight on altitude and velocity fit quite well with a full throttle simulation with a reasonable trajectory. However, I noticed that near the end data completely miss the model. Thanks to your hint I searched the internet and found that "After passing the T+2-minute mark, the Falcon 9 started to throttle back its engines to limit stress on the vehicle" (from http://www.spaceflight101.com/falcon-9-v11-cassiope-launch-updates.html). If this information is accurate, the fit for the first 2 mins can be used, by including a careful estimation of the gravity and aerodynamic drag, to evaluate the trajectory of the rocket, that is actually what I'm trying to do now.

thanks again

p.s. Yes, I imagine this has been already done by many others.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: ugordan on 12/14/2013 02:03 pm
Available data from first v1.1 flight on altitude and velocity fit quite well with a full throttle simulation with a reasonable trajectory.

Because MECO-1 happened earlier than on an expendable flight, roughly at the time it would normally start throttling down due to G limits. I would expect the SES-8 flight did involve throttling to some degree.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: pagheca on 12/14/2013 02:15 pm
Available data from first v1.1 flight on altitude and velocity fit quite well with a full throttle simulation with a reasonable trajectory.

Because MECO-1 happened earlier than on an expendable flight, roughly at the time it would normally start throttling down due to G limits. I would expect the SES-8 flight did involve throttling to some degree.

I'm not completely sure I understand what you mean. However, MECO happened at T+163 on this flight. 43 sec after throttling down started if the 2 min marker is taken for granted. However, a fit with the first 2 mins is enough to get some indication on the trajectory to be checked with available imaging.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: ugordan on 12/14/2013 02:21 pm
43 sec after throttling down started if the 2 min marker is taken for granted. However, a fit with the first 2 mins is enough to get some indication on the trajectory to be checked with available imaging.

Simple. The "after passing the 2 minute mark" is vague, it doesn't imply throttling immediately after 2 min nor would that be consistent with vehicle acceleration at that time.

Take v1.0 as an example, with a roughly similar split between stages. It shut down 2 engines some 15 seconds before MECO-2 so around 165 seconds or thereabouts. 15 - 20 seconds before running dry is roughly the time Cassiope staged.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: fatjohn1408 on 12/20/2013 10:04 am
Hi everyone,

this question maybe obvious for many of you - please excuse me if this is the case but I'm just in learning mode.

As well known, the Merlin 1D engine can be throttled down from 100% to 60%.

The vacuum thrust of a rocket engine is proportional to the exhaust velocity and to the mass flow rate of the gas exhaust: dm/dt * V_exh.

In vacuum and if also the gravity drag is negligible, when a Merlin 1D engine is throttled down, is dm/dt only changing, OR also V_exh (aka Isp_vacuum) is affected someway, with a consequent reduction in the engine efficiency in using the available propellant?

If the second hypothesis is right (as I would say by looking at the physical principles the engine is based on), does someone know a reasonable way to write the relation Thrust(%) = f(%,dm/dt, V_exh)?

Thanks for any hint,

Changing thrust settings will change the chamber pressure, the chamber temperature, the characteristic velocity and correspondingly the specific impulse. And in the process also the mass flow.
It will leave key characteristics unchanged, such as the exit area, throat area, the oxidizer-to-fuel ratio and thus the ratio of specific heats , the vandenkerkhove function, the exit to chamber pressure ratio and therefore the thrust coefficient.

Since the throat area and the thrust coefficient stay constant, a change in thrust leads to a linearly corresponding change in chamber pressure and from this pressure ratio, a change in chamber temperature can be found using Poisson’s equation

This leads in turn to a change in characteristic velocity and specific impulse.
At 50% throttle a decrease of specific impulse from 340s to 317s is to be expected

On top you can expect some losses due to combustion efficiency that gets lower with lower throttle in a pintle engine.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: pagheca on 12/20/2013 12:15 pm
[Changing thrust settings will change the chamber pressure, the chamber temperature, the characteristic velocity and correspondingly the specific impulse. And in the process also the mass flow.
It will leave key characteristics unchanged, such as the exit area, throat area, the oxidizer-to-fuel ratio and thus the ratio of specific heats , the vandenkerkhove function, the exit to chamber pressure ratio and therefore the thrust coefficient.

Since the throat area and the thrust coefficient stay constant, a change in thrust leads to a linearly corresponding change in chamber pressure and from this pressure ratio, a change in chamber temperature can be found using Poisson’s equation

This leads in turn to a change in characteristic velocity and specific impulse.
At 50% throttle a decrease of specific impulse from 340s to 317s is to be expected

On top you can expect some losses due to combustion efficiency that gets lower with lower throttle in a pintle engine.

Thanks for this comment.

This is more or less what I guessed. In particular I was tempted to apply the Poisson's equation. This would mean that throttling the system 50% makes it much less performant. And that 2 engines working at 50% are less savvy than a single one working at 100% in terms of fuel usage.

The problem is that I couldn't find any confirmation this is true. I only found a very old paper from 1955, telling a very different story.

Tomazic, William A. Rocket-engine throttling. UNT Digital Library. http://digital.library.unt.edu/ark:/67531/metadc61716/.

The paper is based on actual measurements performed on two different types of injection devices. I haven't followed  all the math yet, although is quite simple, but apparently, for a wide range of variation in the thrust, experimental data show that Vexh remain substantially constant.  Of course the paper is so old it doesn't mean very much, but I couldn't find anything better and the principles used today are the same.

More important, this fits with the impression that SpaceX mission profilers are not so concerned about using rockets at low throttle. For example: it's well known that during the final phase of the ascent, when the rocket has already used most of his fuel, a Falcon 9 v1.1 1st stage reduces the throttle rather than switching off more and more of his 9 Merlins 1D.

Also Space Shuttle and other LV's rockets are throttle down in some situation, when a more efficient solution would be to just switch them off. But the important point of the Merlin is that they are designed to allow a large number of restart, and that throttling happens at the end of the ascent, not - for example - during MaxQ, so that you would need to switch it on again later, that would be quite demanding in terms of reliability.

Why that? Maybe just because progressively throttling is more efficient, at the end of the day, because it allows to follow much more carefully the thrust demand than just switching off engines?

Cheers,

Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: deltaV on 12/20/2013 04:21 pm
I ran RPA lite with the following settings: 1000 psi chamber pressure, RP-1 and LOX with O/F=2.555, area ratio 50 with frozen equilibrium flow at area ratio 2. It gives theoretical vacuum ISP of 352.9 seconds at full throttle and 350.4 seconds at 50%, i.e., the vacuum ISP is more or less independent of throttle setting. Throttling does have a major effect on sea level performance (as expected), with 256.1 s at 50% and 278.9 s at 100%.

I believe Poisson's equation for adiabatic expansion is inappropriate here because that equation deals with adiabatic expansion that is also isentropic, which requires that work is extracted as the gas expands. If you think of the throttled engine chamber conditions as the original chamber conditions followed by a transformation, I think the appropriate transformation is an adiabatic but non-isentropic throttle-type pressure drop as seen in the Joule-Thomson effect. For ideal gases this leaves the temperature unchanged and for real gases the temperature change is small.

I seem to recall reading that the reason that higher chamber pressure slightly improves ISP is that higher chamber pressure pushes the equilibrium towards higher molecular weight products like H20 and CO2 and away from lower molecular weight ones like CO, OH-, and H+. In other words higher chamber pressure produces more complete combustion.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Robotbeat on 12/20/2013 05:26 pm
Well that may be true, The real reason that higher chamber pressure increases exhaust velocity is because you can get a higher expansion ratio.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: solartear on 12/20/2013 06:27 pm
Why that? Maybe just because progressively throttling is more efficient, at the end of the day, because it allows to follow much more carefully the thrust demand than just switching off engines?

IMO a big reason would be if another engine unexpectedly shutdown, as has happened with STS and Falcon9, then they just throttle up the remaining engines, with much shorter delay and avoiding the effects of restarting an engine in flight.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: pagheca on 12/20/2013 09:38 pm
IMO a big reason would be if another engine unexpectedly shutdown, as has happened with STS and Falcon9, then they just throttle up the remaining engines, with much shorter delay and avoiding the effects of restarting an engine in flight.

Yep. Good point... You may be right IMHO.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Hobbes-22 on 12/27/2013 01:26 pm
While trying to understand Merlin 1D and in particular "Merlin 1D+"* in depth, I've iterated my calculations (http://tinyurl.com/merlin1d) a few times and have reached internal coherence and good balance with reality using the following characteristics/specs. 

Merlin 1D..Merlin 1D Vac..Merlin 1D+..Merlin 1D+ Vac
Nozzle diameter, m1.073.031.073.03


I've tried to draw the Falcon 9 first stage with your diameter, but I can't get it to fit. A circle of 8 engines with a diameter of 1,07 m each is going to have an outer diameter of at least 3,8 m as drawn in my CAD program, and that's with the engine nozzles touching each other. But if you look at images of the launch, the engines do not protrude outside the first stage diameter. And there's a gap between the engines.

If I limit the outer diameter of the 8 engines to 3,66 m and allow some spacing between them, the nozzle diameter is around 96,5 cm (my drawing was in 1:144).

I've also tried measuring the diameter from the second photo. Ignoring the distortion, the space between the center engine and the outer engines is 0.452 times the diameter of the center engine. So the total diameter of the ring of 8 engines is (3 + (2*0.452)) times the diameter of one engine nozzle. If the total ring diameter is 366 cm, then one engine must be 93,5 cm in diameter.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: malu5531 on 12/31/2013 01:39 am
I fully agree, nozzle diameter should be something like ~93-94 cm. I'm not fully there with the model. I have a similar issue with the RD-0162, not sure yet if those are related or there is a more trivial problem with the 1D model (such as adjusting the chamber pressure a bit, since that info might be old). 

While trying to understand Merlin 1D and in particular "Merlin 1D+"* in depth, I've iterated my calculations (http://tinyurl.com/merlin1d) a few times and have reached internal coherence and good balance with reality using the following characteristics/specs. 

Merlin 1D..Merlin 1D Vac..Merlin 1D+..Merlin 1D+ Vac
Nozzle diameter, m1.073.031.073.03


I've tried to draw the Falcon 9 first stage with your diameter, but I can't get it to fit. A circle of 8 engines with a diameter of 1,07 m each is going to have an outer diameter of at least 3,8 m as drawn in my CAD program, and that's with the engine nozzles touching each other. But if you look at images of the launch, the engines do not protrude outside the first stage diameter. And there's a gap between the engines.

If I limit the outer diameter of the 8 engines to 3,66 m and allow some spacing between them, the nozzle diameter is around 96,5 cm (my drawing was in 1:144).

I've also tried measuring the diameter from the second photo. Ignoring the distortion, the space between the center engine and the outer engines is 0.452 times the diameter of the center engine. So the total diameter of the ring of 8 engines is (3 + (2*0.452)) times the diameter of one engine nozzle. If the total ring diameter is 366 cm, then one engine must be 93,5 cm in diameter.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Ben the Space Brit on 01/06/2014 10:26 pm
I might just not be looking in the right place, but has the Isp of Merlin-1D-VAC been confirmed or even reliably estimated yet?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Jason1701 on 01/06/2014 10:28 pm
I might just not be looking in the right place, but has the Isp of Merlin-1D-VAC been confirmed or even reliably estimated yet?

340 s in vacuum according to their website.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Proponent on 02/19/2014 11:16 am
I fully agree, nozzle diameter should be something like ~93-94 cm. I'm not fully there with the model. I have a similar issue with the RD-0162, not sure yet if those are related or there is a more trivial problem with the 1D model (such as adjusting the chamber pressure a bit, since that info might be old). 
I fully agree, nozzle diameter should be something like ~93-94 cm. I'm not fully there with the model. I have a similar issue with the RD-0162, not sure yet if those are related or there is a more trivial problem with the 1D model (such as adjusting the chamber pressure a bit, since that info might be old).

Chamber pressure need not enter into it In the 1D model*.  Thrust is

    F = q ve + Ae (pe - pa) ,

where pa is the ambient pressure.  Therefore the difference between sea-level (pa = pSL = 1 atm) thrust and vacuum (pa = 0) thrust is

    Fvac - FSL = Ae pSL ,

so

    Ae = (Fvac - FSL) / pSL .

If we take the total thrust of the Falcon 9's first stage at sea level and in vacuo from the Falcon 9 web page and divide by nine, we get single-engine thrusts of 653.9 and 741.3 kN, respectively.  For pSL = 101.325 kPa, we get Ae = 0.863 m2 and hence a diameter of 1.048 m, which agrees closely with the value you've calculated.  On the other hand, if we look at the web page for the Merlin engine itself, (http://www.spacex.com/news/2013/03/26/merlin-engines) we're told that the engine's vacuum thrust is just 716 kN.  This lower thrust gives an exit area of 0.613 m2 and a diameter of just 0.883 m.  This fits within the geometric limit found by Hobbes-22.

Now, it could be that this simple analysis violates some constraints imposed by your more extensive model.  I would think, though (and please correct me if I'm wrong), that the the other constraints have are pretty loose, given SpaceX's reluctance to give engineering specifics.



* Actually, I suppose that's not strictly true.  If we're going to assume that flow separation occurs once the pressure drops more than a certain amount below ambient, then the effective nozzle area would depend on chamber pressure.  Thus far, though, we've been assuming there's no flow separation.  As far as I know (which isn't very far), flow separation is usually avoided these days.  (The sustainer of the classic Atlas was over-expanded at sea level to the point that flow separation did occur, but that was back when men were men :) .)  Anyway, allowing for flow separation would tend to increase our estimate of the nozzle's size.  Since we're pretty close to the size allowed by geometry already, this suggests that separation does not occur.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: aero on 02/19/2014 09:49 pm
There is a picture up the nozzles of the Merlin C posted here.

http://forum.nasaspaceflight.com/index.php?topic=33598.msg1161838#msg1161838 (http://forum.nasaspaceflight.com/index.php?topic=33598.msg1161838#msg1161838)

It looks to me as though SpaceX has done something to suppress flow separation at sea level. I would call it a duel bell nozzle design except it looks like quadruple bell design would be more accurate.

I can see that the nozzles are uniformly divergent on the outside but on the inside it is different. What do you all think?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Lars_J on 02/19/2014 09:52 pm
There is a picture up the nozzles of the Merlin C posted here.

http://forum.nasaspaceflight.com/index.php?topic=33598.msg1161838#msg1161838 (http://forum.nasaspaceflight.com/index.php?topic=33598.msg1161838#msg1161838)

It looks to me as though SpaceX has done something to suppress flow separation at sea level. I would call it a duel bell nozzle design except it looks like quadruple bell design would be more accurate.

I can see that the nozzles are uniformly divergent on the outside but on the inside it is different. What do you all think?

What are you drawing *that* conclusion from? That is just an engineering drawing with different sub-component coloured differently. I think you are reading more into those colours that you should.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: aero on 02/19/2014 09:56 pm
There is a picture up the nozzles of the Merlin C posted here.

http://forum.nasaspaceflight.com/index.php?topic=33598.msg1161838#msg1161838 (http://forum.nasaspaceflight.com/index.php?topic=33598.msg1161838#msg1161838)

It looks to me as though SpaceX has done something to suppress flow separation at sea level. I would call it a duel bell nozzle design except it looks like quadruple bell design would be more accurate.

I can see that the nozzles are uniformly divergent on the outside but on the inside it is different. What do you all think?

What are you drawing *that* conclusion from? That is just an engineering drawing with different sub-component coloured differently. I think you are reading more into those colours that you should.

You're right. That's not a picture, my bad. Does anyone have a picture of the inside of a SpaceX rocket engine nozzle?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Lars_J on 02/19/2014 10:01 pm
There is a picture up the nozzles of the Merlin C posted here.

http://forum.nasaspaceflight.com/index.php?topic=33598.msg1161838#msg1161838 (http://forum.nasaspaceflight.com/index.php?topic=33598.msg1161838#msg1161838)

It looks to me as though SpaceX has done something to suppress flow separation at sea level. I would call it a duel bell nozzle design except it looks like quadruple bell design would be more accurate.

I can see that the nozzles are uniformly divergent on the outside but on the inside it is different. What do you all think?

What are you drawing *that* conclusion from? That is just an engineering drawing with different sub-component coloured differently. I think you are reading more into those colours that you should.

You're right. That's not a picture, my bad. Does anyone have a picture of the inside of a SpaceX rocket engine nozzle?

Here is one, with M1C's:

EDIT: added a M1D picture:
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: aero on 02/20/2014 12:12 am
yep - nothing there but light bouncing around.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: malu5531 on 02/24/2014 08:42 am
I'm having a discussion with Aero to figure this Merlin 1D/1D+ model (https://docs.google.com/a/infidyne.com/spreadsheet/ccc?key=0Av6Zu8Wm_3cqdFE2RnlSVEN2THFoVDdmSXp4eFNEV0E&usp=drive_web#gid=2) out.

It occurred to me that this particular document (https://docs.google.com/a/infidyne.com/spreadsheet/ccc?key=0Av6Zu8Wm_3cqdFE2RnlSVEN2THFoVDdmSXp4eFNEV0E&usp=drive_web#gid=2) was not shared before, where I try to model Merlin 1D+ at thrust levels 30-100% in order to figure out constraints on throttling due to low exhaust pressure.

If anyone have some insights in modelling rocket engines, we would appreciate some feedback if there is something we've missed / misunderstood. My understanding of rocket engines is limited to the knowledge found here (http://www.braeunig.us/space/).

In particular I'm wondering; when an engine is throttled I have assumed the Mach number will stay constant, i.e., this number characterise a particular nozzle/throat/chamber design - and using this number one can calculate the exhaust pressure if given the chamber pressure (see spreadsheet for 90% throttle, for example).
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Proponent on 02/24/2014 10:25 am
In particular I'm wondering; when an engine is throttled I have assumed the Mach number will stay constant, i.e., this number characterise a particular nozzle/throat/chamber design - and using this number one can calculate the exhaust pressure if given the chamber pressure (see spreadsheet for 90% throttle, for example).

That assumption isn't quite correct, because the Mach number will change as the ratio of specific heats changes, and that ratio, of course, changes with chamber pressure.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: MP99 on 02/24/2014 06:26 pm
In particular I'm wondering; when an engine is throttled I have assumed the Mach number will stay constant, i.e., this number characterise a particular nozzle/throat/chamber design - and using this number one can calculate the exhaust pressure if given the chamber pressure (see spreadsheet for 90% throttle, for example).

That assumption isn't quite correct, because the Mach number will change as the ratio of specific heats changes, and that ratio, of course, changes with chamber pressure.

It's my understanding that flow through the throat is always exactly sonic, IE exactly Mach 1.0.

Mass flow (density of the exhaust through the throat) is presumably determined by chamber pressure.

I presume downstream pressure is related to throat pressure and expansion ratio (assuming no evolution of the molecular makeup during transit of the nozzle). [Is this what's referred to as "frozen flow"?]

Edit: and I further presume that exhaust velocity is related to pressure at the throat?

Cheers, Martin
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Proponent on 02/25/2014 03:12 pm
It's true that flow at the throat is sonic.  But, of course, the absolute flow speed at the throat depends on throat temperature, which in turn depends on chamber temperature.

I haven't thought the problem through, but I think the approach would be to establish the area ratio of the nozzle, presumably by the above-discussed kremlinology on the available Merlin data.  Then, run a thermochemical code (e.g., RPA) for a variety of chamber pressures.  That will give a chamber temperature, molecular weight, and ratio of specific heats for each pressure.  Using the specific-heat ratio and the exit-to-throat area ratio, one can numerically determine the chamber-to-exit pressure ratio, and hence the exit pressure (going the other way, from pressure ratio to area ratio is easier: just plug the numbers into the formula, but to get an area ratio you have to solve the same equation numerically).  Once you've got the pressure ratio, it's easy to solve for all of the other quantities, including thrust and mass-flow rate.  Then you can tabulate these for various chamber pressures to establish the relationship between mass-flow rate and thrust, which I presume is ultimately what is of interest.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Hobbes-22 on 02/25/2014 03:40 pm
kremlinology on the available Merlin data

 ;D You know, that's exactly how I felt trying to gather data for my Falcon 9 scale model.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: baldusi on 02/25/2014 03:54 pm
Tom Muller had stated an expansion ratio of 16 for the 1D (14.5 for tge 1C). That might help.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: aero on 03/04/2014 03:50 am
Has anyone else considered that SpaceX may modify the Merlin D in order to achieve Elon's projected 15% increase in thrust (12 to 17 % depending on how you figure)?

I have been wondering if maybe, just maybe they might convert the Merlin D engine fueling system to a staged combustion cycle. That would give them the performance and it is not totally unreasonable now that they are gaining experience in staged combustion by working on the Raptor engine. Building a smaller staged combustion engine than the Raptor makes some sense, and building one for LOX/RP-1 seems logical since they are familiar with and have available everything that goes into building and testing LOX/RP-1 engines.

What do you think about a staged combustion Merlin D+?

Would it be possible/practical/acceptable to test a SC Merlin D + on the Falcon 9 while leaving 8 of the engines as is?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Lars_J on 03/04/2014 04:16 am
A "staged combustion Merlin" would be a whole new engine. Not much would be in common.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: guckyfan on 03/04/2014 04:34 am
I don't think a staged combustion RP-1 engine is likely at all. If they want to build a smaller SC-engine they would build a methane engine. It would make for a better upper stage engine of the Falcon 9 and gives experience for building the big one. I thought for a while they might do that but even that seems unlikely now.

Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Wigles on 03/04/2014 06:12 am
I wouldn't discount further changes to the 1D, possibly even a 1E model, due to the length of time they expect to continue operating the Falcon9 and F9R.

 But I doubt they would bother with an almost full redesign to include SC.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: aero on 03/04/2014 02:42 pm
A "staged combustion Merlin" would be a whole new engine. Not much would be in common.

Well, the rocket would be in common. Seems like a lot of commonality to me.

I know that the prop pumps are a very expensive part of the engine and they would need to change the turbine/pumps and routing, but would they need to change the feeds and engine attachments, nozzle? Would an SC cycle engine even fit into the space available?

I think an important consideration is their long term plan for retaining the Falcon 9 in their operational inventory which I don't know.


Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: cuddihy on 03/04/2014 03:50 pm
I believe an RP1 and Methalox SC engine are entirely different beasts- the RP-1 has to run ox-rich preburner as does the RD-180 due to coking whereas methalox can run fuel-rich preburner due to simpler metallurgy &turbine construction. Either way they both operate at higher chamber pressures, have radically different piping and turbine requirements. Basically it'd be like re-constructing a Mustang to run on batteries--can be done, but it would be clunky& heavier than just starting fresh.

All that said, I'm convinced SpaceX is likely to first design a "Merlin sized" SC Methalox vacuum engine for upperstage use prior to doing booster Raptors...but now thats drifting OT.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: baldusi on 03/04/2014 03:53 pm
A "staged combustion Merlin" would be a whole new engine. Not much would be in common.

Well, the rocket would be in common. Seems like a lot of commonality to me.

I know that the prop pumps are a very expensive part of the engine and they would need to change the turbine/pumps and routing, but would they need to change the feeds and engine attachments, nozzle? Would an SC cycle engine even fit into the space available?

I think an important consideration is their long term plan for retaining the Falcon 9 in their operational inventory which I don't know.
Would be two completely different engines with just (some) construction methods in common. For starters, they would have to use an oxygen rich preburner. So, the would go from burning 3% of the RP-1 to 100% of the Oxigen, which means the preburner will have to process 90 times more mass, in a highly corrosive oxygen environment. Then, the turbine will have to pass 90 times more mass, so it will have a lot more power. Since the pump has more power, but have a lot more pressure losses, the pump outlet pressure should be 2 to 3 times as high. And then the injector will have to mix gas (O2) with liquid (RP-1), instead of both liquid. And the main combustion chamber would work at least at 70% more pressure. Not to mention that they wouldn't have the GG exhaust.
So, I don't believe they could use anything save a few valves and may be some electronics. You can't get more different engines made by the same people with the same fuel.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Lars_J on 03/04/2014 04:02 pm
A "staged combustion Merlin" would be a whole new engine. Not much would be in common.

Well, the rocket would be in common. Seems like a lot of commonality to me.

But this is a *Merlin* thread. The rocket is called Falcon. The Falcon family could in theory have all different engines in a future version, but they wouldn't have to be called Merlin just because they are attached to a Falcon rocket. Does that make sense?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: MP99 on 03/04/2014 05:50 pm
Has anyone else considered that SpaceX may modify the Merlin D in order to achieve Elon's projected 15% increase in thrust (12 to 17 % depending on how you figure)?

I have been wondering if maybe, just maybe they might convert the Merlin D engine fueling system to a staged combustion cycle. That would give them the performance and it is not totally unreasonable now that they are gaining experience in staged combustion by working on the Raptor engine. Building a smaller staged combustion engine than the Raptor makes some sense, and building one for LOX/RP-1 seems logical since they are familiar with and have available everything that goes into building and testing LOX/RP-1 engines.

What do you think about a staged combustion Merlin D+?

Would it be possible/practical/acceptable to test a SC Merlin D + on the Falcon 9 while leaving 8 of the engines as is?

I understand that would have to be ox-rich (ORSC) with RP-1, and at higher temps than you get away with on with methane.

No, don't see it.

Makes much more sense that they've left some margin on the table for now, and even then perhaps that 112% is for expendable flights only.

Cheers, Martin
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: TrevorMonty on 03/04/2014 06:37 pm
They may yet produce a M1E version, being engineering driven company I'd be surprised if they didn't tweek the M1D. Reducing the manufacturing cost of engine is one reason to make a new version, 3D printing may add significant cost savings if they are not already using it.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: DJPledger on 03/04/2014 07:18 pm
They may yet produce a M1E version, being engineering driven company I'd be surprised if they didn't tweek the M1D. Reducing the manufacturing cost of engine is one reason to make a new version, 3D printing may add significant cost savings if they are not already using it.
Tom Mueller said a couple of years ago that there won't be a M1E. However the M1D is supposed to get a thrust upgrade to 165klbf at SL which has been discussed widely. SpaceX could have changed their mind over a possible M1E but I think it is still unlikely since SpaceX are moving on to their next gen. engine.

Is the TC of the production M1D additively manufactured? The TC of M1D has a matt finish which looks like the finish on the additively manufactured SD TC and the nozzle of M1D is shiny. The different finishes of the M1D TC and nozzle indicate different manufacturing processes being used for the TC and nozzle.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Mader Levap on 03/04/2014 11:35 pm
A "staged combustion Merlin" would be a whole new engine. Not much would be in common.
Well, the rocket would be in common. Seems like a lot of commonality to me.
Nonsensical argument. We are talking about comparing engines alone - Merlin 1D and mythical Merlin 1SC - and about commonality between them.
What rocket is attached to these engines is another matter, unrelated to comparison between engines.

So yes, forget about that. No staged combustion Merlin will happen.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: aero on 03/13/2014 07:21 pm
While looking for Merlin data I came across this interesting little chalk talk by Tom Mueller on the Merlin 1C. Have your note pad ready, he gives numbers for the C model. I wonder how much they carry over to the D?

http://www.livescribe.com/cgi-bin/WebObjects/LDApp.woa/wa/MLSOverviewPage?sid=n7SMWV6PdG7r (http://www.livescribe.com/cgi-bin/WebObjects/LDApp.woa/wa/MLSOverviewPage?sid=n7SMWV6PdG7r)

The article where I found the link is here:

http://blog.linuxacademy.com/space/under-the-hood-with-the-spacex-merlin-engine/ (http://blog.linuxacademy.com/space/under-the-hood-with-the-spacex-merlin-engine/)

JMO but I expect the numbers carry over reasonably well to the D model, better than the numbers that we don't have on the Merlin D.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Robotbeat on 03/13/2014 07:29 pm
Merlin 1D may be too large to easily print using a metal 3d printer. I believe they rely on other techniques, like explosive forming.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Elmar Moelzer on 03/13/2014 07:48 pm
Merlin 1D may be too large to easily print using a metal 3d printer. I believe they rely on other techniques, like explosive forming.
Maybe not the large parts, but I could see them print many of the smaller items.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Prober on 03/13/2014 11:25 pm
While looking for Merlin data I came across this interesting little chalk talk by Tom Mueller on the Merlin 1C. Have your note pad ready, he gives numbers for the C model. I wonder how much they carry over to the D?

http://www.livescribe.com/cgi-bin/WebObjects/LDApp.woa/wa/MLSOverviewPage?sid=n7SMWV6PdG7r (http://www.livescribe.com/cgi-bin/WebObjects/LDApp.woa/wa/MLSOverviewPage?sid=n7SMWV6PdG7r)

The article where I found the link is here:

http://blog.linuxacademy.com/space/under-the-hood-with-the-spacex-merlin-engine/ (http://blog.linuxacademy.com/space/under-the-hood-with-the-spacex-merlin-engine/)

JMO but I expect the numbers carry over reasonably well to the D model, better than the numbers that we don't have on the Merlin D.

You might wish to use the search functions @ the top.   This info has be talked to death ::) ::)
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: aero on 03/14/2014 02:27 am
Ok, I searched. The article has been linked before but I didn't see anything about the fuel and LOX tank pressures or the turbo pump output pressures. Things I found interesting are:

Tank pressure = 50 psi for both tanks,
turbo pump output pressure, LOX 1400 psi, RP-1 1500 psi
gg combustion temperature 1033 deg. F

Combustion chamber temperature 6000 deg. F
Mdot 350 lbm/s

And the description of how the gas generator works.

Yes, it was for the Merlin 1 C, but interesting anyway.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Prober on 03/14/2014 03:12 am
Ok, I searched. The article has been linked before but I didn't see anything about the fuel and LOX tank pressures or the turbo pump output pressures. Things I found interesting are:

Tank pressure = 50 psi for both tanks,
turbo pump output pressure, LOX 1400 psi, RP-1 1500 psi
gg combustion temperature 1033 deg. F

Combustion chamber temperature 6000 deg. F
Mdot 350 lbm/s

And the description of how the gas generator works.

Yes, it was for the Merlin 1 C, but interesting anyway.

a lot of very good information built up on this site, glad it worked for you.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: cambrianera on 03/15/2014 08:59 am
What about an expander cycle Mvac with LOX-CH4 propellants?
Some experience for injector and combustion with CH4 and some kg gained on payload.
Not something I would suggest otherwise, but SpaceX's drive for improved propulsion is out of ordinary.

Removed typo (thanks! :) )
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: aero on 03/17/2014 05:25 am
Does anyone (or  everyone but me) know what the area ratio is for the Merlin 1 D Vac engine. That is the upper stage engine?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: cambrianera on 03/17/2014 12:50 pm
Does anyone (or  everyone but me) know what the area ratio is for the Merlin 1 D Vac engine. That is the upper stage engine?

Found 117 for Mvac C.
http://forum.nasaspaceflight.com/index.php?topic=29476.msg959740#msg959740
http://forum.nasaspaceflight.com/index.php?topic=26388.msg959792#msg959792
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: drsnooker on 03/18/2014 12:43 am
I did not see this posted here. I apologize if I missed it somewhere, but it's taken by Steve J last thursday

http://www.flickr.com/photos/jurvetson/13160622333/in/photostream/
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: sublimemarsupial on 03/18/2014 12:53 am
I did not see this posted here. I apologize if I missed it somewhere, but it's taken by Steve J last thursday

http://www.flickr.com/photos/jurvetson/13160622333/in/photostream/

It should go in the MVacC thread, not this one, seeing as how its not an M1D (or even an MVacD). Its not really even an MVacC, its more like a franken-merlin, since it has the MVacC chamber, nozzle, sump, and extension, but the M1C gas generator exhaust system.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: docmordrid on 03/18/2014 12:55 am
I did not see this posted here. I apologize if I missed it somewhere, but it's taken by Steve J last thursday

http://www.flickr.com/photos/jurvetson/13160622333/in/photostream/

Merlin Blaster? Is someone being cute or is this a new variant for Falcon Heavy? Maybe the improved M1D with 100% thrust?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: drsnooker on 03/18/2014 12:56 am
I couldn't place it (all chromed up and everything) but his caption is one of 28 engines in the falcon heavy...
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: go4mars on 03/18/2014 01:53 am
What are the things in the background (under and to the right)?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: dorkmo on 03/18/2014 02:31 am
What are the things in the background (under and to the right)?

my guess is some sort of bent piping and wiring inventory holder waiting to be installed in the octoweb?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Lars_J on 03/18/2014 02:35 am
What are the things in the background (under and to the right)?

I'm no expert, but
 - just below is an "octaweb" assembly station,
 - and just to the right of that they appear to be assembling and/or doing electrical tests on M1D engines (three are lined up)
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: JBF on 03/18/2014 11:30 am
It's a display they have hanging up.  I want to say it's a 1A due to the thrust structure and GG exhaust, but I could be wrong.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: sublimemarsupial on 03/18/2014 02:16 pm
It's a display they have hanging up.  I want to say it's a 1A due to the thrust structure and GG exhaust, but I could be wrong.

Its not a 1A. Its up there purely to look pretty - its an MVacC thrust structure, chamber, nozzle, and nozzle extension with M1C (ie boost phase) gas generator and exhaust, likely just made up of spares they no longer have a use for other than decoration.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: corrodedNut on 03/18/2014 02:27 pm
It's a display they have hanging up.  I want to say it's a 1A due to the thrust structure and GG exhaust, but I could be wrong.

Its not a 1A. Its up there purely to look pretty - its an MVacC thrust structure, chamber, nozzle, and nozzle extension with M1C (ie boost phase) gas generator and exhaust, likely just made up of spares they no longer have a use for other than decoration.

I agree. It's a Franken-merlin.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: aero on 03/30/2014 09:27 pm
I ran my Falcon 9 launch simulation with throttle up on the 1 D Vac only. It puts 13,150 kg into a 185 km orbit  when throttled up from 106% to 110% giving 21 kg to 160 kg prop reserve.  Below that throttle setting all the prop is used and then some, but very little more than is available. At 100 % throttle the burn goes to 389 seconds where my program stops on prop limits, 154 kg beyond a full prop load, and 3 m/s short of orbit, though it is 250 meters above the 185 km orbital altitude.

This is with prop reserved  for first stage recovery, with stage 1 entering the stratopause at 1.07 km/s.

This says to me that the advertised numbers of 13,150 kg to orbit with stage 1 recovery is doable.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: mr. mark on 04/21/2014 04:43 pm
4 successful launches so far. That 36 engines Merlin 1D (non Vacuum) all running nominally with no failures. Far better than the Merlin 1C. Looks like they've got it right this time.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: RDMM2081 on 04/21/2014 04:50 pm
The video from the latest F9R-Dev1 test using a Merlin 1D also seems to demonstrate the new and improved throttling capabilities (seems like it achieves almost perfectly sustained hover for several seconds). 

http://forum.nasaspaceflight.com/index.php?topic=33892.msg1184601#msg1184601
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Comga on 04/21/2014 05:00 pm
The video from the latest F9R-Dev1 test using a Merlin 1D also seems to demonstrate the new and improved throttling capabilities (seems like it achieves almost perfectly sustained hover for several seconds). 

http://forum.nasaspaceflight.com/index.php?topic=33892.msg1184601#msg1184601 (http://forum.nasaspaceflight.com/index.php?topic=33892.msg1184601#msg1184601)

You cannot draw that conclusion without calculations like those done by Lourens (http://forum.nasaspaceflight.com/index.php?topic=33892.msg1185402#msg1185402) and others.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: ugordan on 04/21/2014 06:05 pm
Far better than the Merlin 1C.

How is that far better, given the current statistically insignificant sample size?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Comga on 04/22/2014 04:39 am
Far better than the Merlin 1C.

How is that far better, given the current statistically insignificant sample size?

ugordon has a valid question for you, RDMM2081.
"Engineering is done with numbers.  Everything else is just opinion."
Please make some attempt at calculating confidence intervals if you want to make an assertion we can agree to.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: RDMM2081 on 04/22/2014 05:19 am
Far better than the Merlin 1C.

How is that far better, given the current statistically insignificant sample size?

ugordon has a valid question for you, RDMM2081.
"Engineering is done with numbers.  Everything else is just opinion."
Please make some attempt at calculating confidence intervals if you want to make an assertion we can agree to.

I don't see any questions directed at me, looks like mr. Mark made the assertion about 1c vs 1d failure rates.  I agree with ugordan calling that into question based on the limited sample size.

Also in my previous post linking the video of the new F9R video, I was not claiming any trotting capabilities in excess of what Lourens and others have found, just commenting that it was nice to see it in action.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: TrevorMonty on 07/22/2014 12:35 am
 Does anybody know if SpaceX plan to redesign the Merlin to benefit from 3D printing.

Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Robotbeat on 07/22/2014 02:21 am
I'm not sure it would benefit. 3d printing generally makes poorer quality parts (ie grain structure, higher porosity and void content, rougher surface finish, poorer as-produced precision, etc) than traditional manufacturing and is severely size limited. It's nice because of complicated geometries being easier to fabricate and design-to-build cycle is shorter. A good fit for SuperDraco, not so much Merlin. No doubt some parts would make sense to 3d print, though.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: mvpel on 07/27/2014 03:36 am
I'm not sure it would benefit. 3d printing generally makes poorer quality parts (ie grain structure, higher porosity and void content, rougher surface finish, poorer as-produced precision, etc) than traditional manufacturing and is severely size limited.

Technology may have already outstripped your generalization, late last year.

First 3D-Printed Metal Gun Fires 50 Rounds and Counting (http://mashable.com/2013/11/11/3d-printed-metal-gun/)
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Robotbeat on 07/27/2014 04:30 am
I'm not sure it would benefit. 3d printing generally makes poorer quality parts (ie grain structure, higher porosity and void content, rougher surface finish, poorer as-produced precision, etc) than traditional manufacturing and is severely size limited.

Technology may have already outstripped your generalization, late last year.

First 3D-Printed Metal Gun Fires 50 Rounds and Counting (http://mashable.com/2013/11/11/3d-printed-metal-gun/)
Nope. Not relevant to anything I said. Of course you can 3d print a gun out of metal, doesn't make it better quality (precision, porosity, etc) than traditional manufacturing.

BTW, you can deal with a lot of these issues with a bit of post-processing. But that's cheating. ;)
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: su27k on 07/27/2014 04:45 am
d.  The multi engine scheme is just a marketing ploy.  More than a 2/3's of a Falcon 9 flight time has the same consequence from a engine failure as the EELV's.  It uses a single engine (which is also significantly different than the first stage engines) for second stage flight.

Was this significant difference between Merlin Vacuum and regular Merlin documented somewhere? I remember seeing this claim before but no details was given.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: TrevorMonty on 07/27/2014 04:56 am
The benefits of re engineering for 3D printing may not be worth costs and risk ie if it ain't broke don't fix it. With recent announcements of plans to make most flights have recoverable boosters.
Engine production rate should drop off in long run, even though flight rates increase.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: TrevorMonty on 08/01/2014 08:55 am
Looks like the Merlin 1D is going to be 3D printed, but as a piecemeal process.

http://forum.nasaspaceflight.com/index.php?topic=35319.0
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: AncientU on 08/01/2014 08:53 pm
I'm not sure it would benefit. 3d printing generally makes poorer quality parts (ie grain structure, higher porosity and void content, rougher surface finish, poorer as-produced precision, etc) than traditional manufacturing and is severely size limited. It's nice because of complicated geometries being easier to fabricate and design-to-build cycle is shorter. A good fit for SuperDraco, not so much Merlin. No doubt some parts would make sense to 3d print, though.

Sounds like SpaceX have data to the contrary.

Quote
Compared with a traditionally cast part, a printed valve body has superior strength, ductility, and fracture resistance, with a lower variability in materials properties. The MOV body was printed in less than two days, compared with a typical castings cycle measured in months.

And:
The benefits of re engineering for 3D printing may not be worth costs and risk ie if it ain't broke don't fix it. With recent announcements of plans to make most flights have recoverable boosters.
Engine production rate should drop off in long run, even though flight rates increase.

M-1D was already a production optimized engine... why change it unless the benefit is significant.
I suspect that 3-D printing will play a substantial role from here out... not just boutique part making here and there.  A majority 3-D printed power pack anyone?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: TrevorMonty on 08/01/2014 11:50 pm
Being able to flight prove changes on a single engine at low risk to the mission is a great innovation.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Robotbeat on 08/02/2014 12:30 am
I'm not sure it would benefit. 3d printing generally makes poorer quality parts (ie grain structure, higher porosity and void content, rougher surface finish, poorer as-produced precision, etc) than traditional manufacturing and is severely size limited. It's nice because of complicated geometries being easier to fabricate and design-to-build cycle is shorter. A good fit for SuperDraco, not so much Merlin. No doubt some parts would make sense to 3d print, though.

Sounds like SpaceX have data to the contrary.

Quote
Compared with a traditionally cast part, a printed valve body has superior strength, ductility, and fracture resistance, with a lower variability in materials properties. The MOV body was printed in less than two days, compared with a typical castings cycle measured in months.
well yeah, if you compare it to castings! Castings usually have inferior material properties to forged or rolled stock which is then machined or stamped or otherwise worked to shape.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Coastal Ron on 08/02/2014 01:31 am
M-1D was already a production optimized engine... why change it unless the benefit is significant.
I suspect that 3-D printing will play a substantial role from here out... not just boutique part making here and there.  A majority 3-D printed power pack anyone?

Yes, I think this first part is a pathfinder for them, both for improving the Merlin 1D and for ultimately producing the Raptor.  It helps to start with something that is a known so that you have a fallback in case something doesn't work out the way you hope.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: oldAtlas_Eguy on 10/23/2014 01:57 pm
SpaceX update, "SPACEX COMPLETES 100TH MERLIN 1D ENGINE":

http://www.spacex.com/news/2014/10/16/spacex-completes-100th-merlin-1d-engine

High-res photos attached

This is where this shoud be posted.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Prober on 10/23/2014 07:41 pm
SpaceX update, "SPACEX COMPLETES 100TH MERLIN 1D ENGINE":

http://www.spacex.com/news/2014/10/16/spacex-completes-100th-merlin-1d-engine

High-res photos attached

This is where this shoud be posted.

Congrats SX

now that's good PR
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: FutureSpaceTourist on 10/23/2014 10:22 pm
Quite an achievement. Not clear to me why SpaceX need a production rate of 5 engines per week this soon. Surely pad and payload availability mean they don't need more than 200 engines next year?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Robotbeat on 10/23/2014 10:47 pm
Quite an achievement. Not clear to me why SpaceX need a production rate of 5 engines per week this soon. Surely pad and payload availability mean they don't need more than 200 engines next year?
15 F9s and 3 Falcon Heavies and an in-flight abort F9. Though much of that will probably be for ramping up for 2016 (wouldn't be terribly surprised to see FH slip to 2016, but they'll need to start doing lots of tests in Texas starting in 2015). That's not completely unreasonable as a production goal. They doubled the number of launches from last year to this year and nearly doubled that from the year before. Wouldn't be impossible for them to hit 18 launches in 2016.

Consider they'll probably do 7 launches this year and a pad abort for a total of nearly 8 all from one launch site. By 2016, they'll probably be using 3 launch sites and possibly 4. 3 times 7 is 21. 4 times 8 is 32.

That's a lot of launches, so the bottleneck will likely not be the pads. Texas may be the bottleneck. But anything less than 5 engines a week COULD be nearly a bottleneck by the end of 2015.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: deruch on 10/27/2014 02:25 am
Quite an achievement. Not clear to me why SpaceX need a production rate of 5 engines per week this soon. Surely pad and payload availability mean they don't need more than 200 engines next year?
15 F9s and 3 Falcon Heavies and an in-flight abort F9. Though much of that will probably be for ramping up for 2016 (wouldn't be terribly surprised to see FH slip to 2016, but they'll need to start doing lots of tests in Texas starting in 2015). That's not completely unreasonable as a production goal. They doubled the number of launches from last year to this year and nearly doubled that from the year before. Wouldn't be impossible for them to hit 18 launches in 2016.

Consider they'll probably do 7 launches this year and a pad abort for a total of nearly 8 all from one launch site. By 2016, they'll probably be using 3 launch sites and possibly 4. 3 times 7 is 21. 4 times 8 is 32.

That's a lot of launches, so the bottleneck will likely not be the pads. Texas may be the bottleneck. But anything less than 5 engines a week COULD be nearly a bottleneck by the end of 2015.

Plus there may be a few used for future F9R-dev# vehicles.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Robotbeat on 10/27/2014 02:41 am
I'm not sure there will be more dev vehicle for Falcon 9. Dev2, maybe a dev3.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: deruch on 01/24/2015 04:45 am
In light of the below quoted tweet, I think this thread needs a bump.  Especially as I've seen a potential uprating of the M1D discussed in various places as a result.

Interesting to see that the launch of SES-9 may use the higher thrust Merlin 1D engines.

Peter B. de Selding @pbdes
SES: We may skip spring SpaceX launch slot & wait till mid-year to let someone else be 1st using Falcon 9 main engine in full-thrust regime.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: TrevorMonty on 01/24/2015 08:42 am
SpaceX have already done modifications to M1D, they flew one engine early last year with 3D printed part. With 9 engines they can afford to test fly a single upgraded engine a few times before committing to it with all 9 engines.

I would them to be a lot more cautious with upper stage engine.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: MP99 on 01/24/2015 09:59 am
In light of the below quoted tweet, I think this thread needs a bump.  Especially as I've seen a potential uprating of the M1D discussed in various places as a result.

Interesting to see that the launch of SES-9 may use the higher thrust Merlin 1D engines.

Peter B. de Selding @pbdes
SES: We may skip spring SpaceX launch slot & wait till mid-year to let someone else be 1st using Falcon 9 main engine in full-thrust regime.

My main question is whether (as I've speculated before), this also requires sub-cooling of the propellants?

The extra thrust will be a requirement to lift more prop, but are the two joined at the hip? If not, liftoff T:W would be over 1.3.

Antares flew with subcooled lox, so this is an area where SpaceX don't need to blaze a trail. Still, I look forward to hearing more about this.

Cheers, Martin
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: hkultala on 01/24/2015 12:30 pm
In light of the below quoted tweet, I think this thread needs a bump.  Especially as I've seen a potential uprating of the M1D discussed in various places as a result.

Interesting to see that the launch of SES-9 may use the higher thrust Merlin 1D engines.

Peter B. de Selding @pbdes
SES: We may skip spring SpaceX launch slot & wait till mid-year to let someone else be 1st using Falcon 9 main engine in full-thrust regime.

My main question is whether (as I've speculated before), this also requires sub-cooling of the propellants?

The extra thrust will be a requirement to lift more prop, but are the two joined at the hip? If not, liftoff T:W would be over 1.3.

Antares flew with subcooled lox, so this is an area where SpaceX don't need to blaze a trail. Still, I look forward to hearing more about this.

Cheers, Martin

More thrust with same amount of fuel means less gravity losses. So it will give some benefit. But also adding more fuel (by either bigger tanks of subcooling the fuel) easily gives about 3 times bigger benefit than just increasing the thrust. My factor 3 is based on stettson-harrison method.

ULA did increase the trust of Delta IV by changing from RS-68 to  RS-68A and not increase amount of fuel. This upgrade was needed to launch some big NRO payload about a year ago.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: TrueBlueWitt on 01/24/2015 04:12 pm
In light of the below quoted tweet, I think this thread needs a bump.  Especially as I've seen a potential uprating of the M1D discussed in various places as a result.

Interesting to see that the launch of SES-9 may use the higher thrust Merlin 1D engines.

Peter B. de Selding @pbdes
SES: We may skip spring SpaceX launch slot & wait till mid-year to let someone else be 1st using Falcon 9 main engine in full-thrust regime.

My main question is whether (as I've speculated before), this also requires sub-cooling of the propellants?

The extra thrust will be a requirement to lift more prop, but are the two joined at the hip? If not, liftoff T:W would be over 1.3.

Antares flew with subcooled lox, so this is an area where SpaceX don't need to blaze a trail. Still, I look forward to hearing more about this.

Cheers, Martin

More thrust with same amount of fuel means less gravity losses. So it will give some benefit. But also adding more fuel (by either bigger tanks of subcooling the fuel) easily gives about 3 times bigger benefit than just increasing the thrust. My factor 3 is based on stettson-harrison method.

ULA did increase the trust of Delta IV by changing from RS-68 to  RS-68A and not increase amount of fuel. This upgrade was needed to launch some big NRO payload about a year ago.

Makes me wonder if F9H will fly from the start with uprated Merlins and subcooled prop? Better to validate with final combination from the start.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: edkyle99 on 01/24/2015 05:28 pm
Makes me wonder if F9H will fly from the start with uprated Merlins and subcooled prop? Better to validate with final combination from the start.
If the Heavy boosters are longer, they will weigh more.  Perhaps full-thrust 1D was created for that reason.

 - Ed Kyle
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: ugordan on 01/24/2015 05:42 pm
If the Heavy boosters are longer, they will weigh more.  Perhaps full-thrust 1D was created for that reason.

Yes, but that still appears to be less mass than what a single core has to push with the loaded 2nd stage on top.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: MP99 on 01/24/2015 06:07 pm
Makes me wonder if F9H will fly from the start with uprated Merlins and subcooled prop? Better to validate with final combination from the start.

It is my strong belief that FH will never fly any other way. I suspect it's one of the things that has been holding up the maiden flight.

cheers, Martin
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: ArbitraryConstant on 01/24/2015 06:32 pm
If the Heavy boosters are longer, they will weigh more.  Perhaps full-thrust 1D was created for that reason.
Getting more thrust from the same engines helps you pretty much no matter what you're doing, no?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Herb Schaltegger on 01/24/2015 06:47 pm
If the Heavy boosters are longer, they will weigh more.  Perhaps full-thrust 1D was created for that reason.
Getting more thrust from the same engines helps you pretty much no matter what you're doing, no?

Not necessarily; not if it costs you ISP, or results in exceeding structural limits on your stage or g-limits on your payload.

Everything is a tradeoff.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Lars-J on 01/24/2015 08:00 pm
Makes me wonder if F9H will fly from the start with uprated Merlins and subcooled prop? Better to validate with final combination from the start.

It is my strong belief that FH will never fly any other way. I suspect it's one of the things that has been holding up the maiden flight.

cheers, Martin

Huh? What? As ugordan wrote, FH should still have a better T/W ratio at liftoff than F9v1.1...
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: MP99 on 01/24/2015 08:19 pm
Makes me wonder if F9H will fly from the start with uprated Merlins and subcooled prop? Better to validate with final combination from the start.

It is my strong belief that FH will never fly any other way. I suspect it's one of the things that has been holding up the maiden flight.

cheers, Martin

Huh? What? As ugordan wrote, FH should still have a better T/W ratio at liftoff than F9v1.1...

AFAICT, the sub-cooled / 112% F9 will have a higher liftoff T:W than previous flights, but I don't think this is necessarily ideal.

I suspect that F9 v1.1 was engineered so that it has the margin to fly sub-cooled. I assume this means they had to do engineering analyses on both setups.

The longer boosters on FH give the opportunity to rebalance T:W back to a preferred value, if they wish, and only analyse the sub-cooled variant.

Cheers, Martin
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: ArbitraryConstant on 01/24/2015 10:06 pm
Not necessarily; not if it costs you ISP, or results in exceeding structural limits on your stage or g-limits on your payload.
Fair enough, it's helpful provided you don't intentionally blow up the rocket. I took that to be implicit.

It seems like the impact of lower ISP would depend on the the impact on GLOW.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: deruch on 01/25/2015 02:11 am
Not necessarily; not if it costs you ISP, or results in exceeding structural limits on your stage or g-limits on your payload.
Fair enough, it's helpful provided you don't intentionally blow up the rocket. I took that to be implicit.
It seems like the impact of lower ISP would depend on the the impact on GLOW.

I posted the following in a different thread: http://forum.nasaspaceflight.com/index.php?topic=35480.msg1315177#msg1315177

pF = 50.41 -[0.026(TF -60) + 0.290(API -43.5)]

where:

pF= Fuel density (lb/ft3)
TF= Fuel temperature (oF)
API= American Petroleum Institute gravity (https://en.wikipedia.org/wiki/API_gravity) (degrees) [related to the specific gravity of petroleum products; from linked spec sheet in reply #106 on the Vandy thread, NASA's accepted range for RP-1 is 42.0 to 45.5]

It's from this paper:
Analysis of RP-1 Fuel Density For Operational Atlas Missiles (.pdf) (http://atlasbases.homestead.com/Analysis_of_RP-1_Fuel_Density_-_SAWE0323.pdf)
 
So, the density of RP-1 increases by 0.026lb/ft3 for every oF cooler it is (RP-1 freezing point @ -36 oF).  The number I've seen for the first stage is 38,000 gallons of RP-1.  With that amount of RP-1, the max increase is about 13,000lbs (100 degree change, say from +70 to -30 oF).  Basically, the increased weight isn't that much of an issue.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: MP99 on 01/25/2015 09:47 am
How much is that as a percentage of the RP-1? About 4%?

NASA did tests densifying lox, and found they could get an 8.9% increase in lox load at 122 Rankin. ;-)

Making either change without the other will change the Merlin mixture ratio.

The only guesses I can find for M1D mixture ratio are somewhat fuel rich, which will partly be the effect of the gas generator. It looks like sub-cooling both would make Merlin run less fuel rich, which would increase combustion temperatures. Could that be coped with by the greater regen cooling of the RP-1? Note, also, that the colder lox would absorb some of that extra energy.

This assumes they don't shift the bulkhead between the tanks for whatever is the ideal mixture ratio for M1D @ 112%. I guess that would only be a minor reconfiguration of the TEL? (And a fair bit of work to re-validate the stage structure.)

Cheers, Martin
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: guckyfan on 01/25/2015 10:02 am
It seems they have planned for subcooling from the beginning. Also RP-1 is the much smaller component of propellant. Is it possible they have planned the RP-1 tank large enough to cope?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: dror on 01/25/2015 06:20 pm
In light of the below quoted tweet, I think this thread needs a bump.  Especially as I've seen a potential uprating of the M1D discussed in various places as a result.

Interesting to see that the launch of SES-9 may use the higher thrust Merlin 1D engines.

Peter B. de Selding @pbdes
SES: We may skip spring SpaceX launch slot & wait till mid-year to let someone else be 1st using Falcon 9 main engine in full-thrust regime.
Is there \ could there also be a lower thrust version of M1-D ?
I was thinking maybe, if they upgrade the thrust levels of the outer 8 engines,  and seriously downgrade the thrust level of the inner engine,  they can get the same total thrust at lift of but with better chances of landing the core.
This goes against basic rocket engineering logic of maximizing performance ,  but can possibly serve spaceX better.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Lars-J on 01/25/2015 06:30 pm
In light of the below quoted tweet, I think this thread needs a bump.  Especially as I've seen a potential uprating of the M1D discussed in various places as a result.

Interesting to see that the launch of SES-9 may use the higher thrust Merlin 1D engines.

Peter B. de Selding @pbdes
SES: We may skip spring SpaceX launch slot & wait till mid-year to let someone else be 1st using Falcon 9 main engine in full-thrust regime.
Is there \ could there also be a lower thrust version of M1-D ?
I was thinking maybe, if they upgrade the thrust levels of the outer 8 engines,  and seriously downgrade the thrust level of the inner engine,  they can get the same total thrust at lift of but with better chances of landing the core.
This goes against basic rocket engineering logic of maximizing performance ,  but can possibly serve spaceX better.

No, that doesn't make sense. Why throw away the advantage of a single engine mass production and create a second line? If all the engines are uprated (above 100% thrust) and somehow also raise their lowest thrust setting, they'll most likely eat that difference and instead tweak the final landing burn.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: llanitedave on 01/25/2015 08:19 pm
In light of the below quoted tweet, I think this thread needs a bump.  Especially as I've seen a potential uprating of the M1D discussed in various places as a result.

Interesting to see that the launch of SES-9 may use the higher thrust Merlin 1D engines.

Peter B. de Selding @pbdes
SES: We may skip spring SpaceX launch slot & wait till mid-year to let someone else be 1st using Falcon 9 main engine in full-thrust regime.
Is there \ could there also be a lower thrust version of M1-D ?
I was thinking maybe, if they upgrade the thrust levels of the outer 8 engines,  and seriously downgrade the thrust level of the inner engine,  they can get the same total thrust at lift of but with better chances of landing the core.
This goes against basic rocket engineering logic of maximizing performance ,  but can possibly serve spaceX better.


What makes you think their chances of landing the core are too low now? They seem to be very close to success with surprisingly little learning curve so far.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: dror on 01/26/2015 06:05 am
In light of the below quoted tweet, I think this thread needs a bump.  Especially as I've seen a potential uprating of the M1D discussed in various places as a result.

Interesting to see that the launch of SES-9 may use the higher thrust Merlin 1D engines.

Peter B. de Selding @pbdes
SES: We may skip spring SpaceX launch slot & wait till mid-year to let someone else be 1st using Falcon 9 main engine in full-thrust regime.
Is there \ could there also be a lower thrust version of M1-D ?
I was thinking maybe, if they upgrade the thrust levels of the outer 8 engines,  and seriously downgrade the thrust level of the inner engine,  they can get the same total thrust at lift of but with better chances of landing the core.
This goes against basic rocket engineering logic of maximizing performance ,  but can possibly serve spaceX better.


What makes you think their chances of landing the core are too low now? They seem to be very close to success with surprisingly little learning curve so far.

Well,  you know,  I wish them well and good luck and I hope that won't be needed.
But I guess that if they can have a T/W closer to 1 then they will have better chances for successful landings.
We can hope that that won't be necessary but we haven't seen that work yet. All landings and hoverings must have been done with additional weight and at much lower velocities, IMO.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: dror on 01/26/2015 06:09 am

No, that doesn't make sense. Why throw away the advantage of a single engine mass production and create a second line? If all the engines are uprated (above 100% thrust) and somehow also raise their lowest thrust setting, they'll most likely eat that difference and instead tweak the final landing burn.
That makes sense only if reusability turns out to be impossible with full size M1Ds due to T\W >>1 .
Of course, we are not there yet.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: deruch on 02/01/2015 02:38 am
How much is that as a percentage of the RP-1? About 4%?

NASA did tests densifying lox, and found they could get an 8.9% increase in lox load at 122 Rankin. ;-)

Making either change without the other will change the Merlin mixture ratio.

The only guesses I can find for M1D mixture ratio are somewhat fuel rich, which will partly be the effect of the gas generator. It looks like sub-cooling both would make Merlin run less fuel rich, which would increase combustion temperatures. Could that be coped with by the greater regen cooling of the RP-1? Note, also, that the colder lox would absorb some of that extra energy.

This assumes they don't shift the bulkhead between the tanks for whatever is the ideal mixture ratio for M1D @ 112%. I guess that would only be a minor reconfiguration of the TEL? (And a fair bit of work to re-validate the stage structure.)

Cheers, Martin

Darn.  I wanted to compare performance on an F9v1.1 with M1D+ engines between 2 different usage strategies (a large stretch of my math/rocketry capabilities).  1) Use higher thrust to increase T/W and thereby lower gravity losses in early flight.  2) Use higher thrust to slightly stretch the 2nd stage, thereby resetting the T/W back to what it was prior to engine uprating.  But having to account for Prop/LOX densification and a potential rejiggering of the mix load has definitely pushed this out of the realm of possibility for me.  Not to mention a potential increase in Isp that might come with the improved thrust.  If anyone else want's to give it a go though, I would love to see what they come up with. 

(I'll probably still try a simplified version of the above analysis)
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: mvpel on 02/01/2015 03:35 am
Well,  you know,  I wish them well and good luck and I hope that won't be needed.
But I guess that if they can have a T/W closer to 1 then they will have better chances for successful landings.
We can hope that that won't be necessary but we haven't seen that work yet. All landings and hoverings must have been done with additional weight and at much lower velocities, IMO.

It's important to remember that the computer controlling the landing doesn't really care what the T/W ratio is, per se. It's just another item in a list of factors which govern the software's decisions about the landing operation.

Take, for example, the VersaLogic "Falcon" embedded system:

(http://www.versalogic.com/Products/Photos/EPU-2610-A-DS.jpg) (http://www.versalogic.com/products/ds.asp?productid=230)

It has a 1.6-gigahertz Intel Atom E6x0T processor (http://www.intel.com/content/www/us/en/intelligent-systems/medical-applications/atom-e6xx-series-datasheet.html#) and gigabit Ethernet, with up to two gigabytes of RAM, as well as integrated 3D graphics capabilities.

Now, let's suppose the booster's terminal velocity is 150m/s. That means for each clock cycle of this VersaLogic Falcon, a falling Falcon will have moved 0.0937 microns. The average thickness of a human hair is about a thousand times larger than this, and the Atom chip can execute up to two instructions per clock cycle (http://en.wikipedia.org/wiki/Intel_Atom_%28CPU%29#Bonnell_microarchitecture). And if you offload calculations to the GPU, the power available to you during those 0.0937 microns of travel is multiplied even further.

So while a booster falling through the atmosphere like a hypersonic spear looks overwhelmingly daunting to our plodding human perceptions, it is quite a leisurely pace as far as the guidance computer is concerned. And while the work that went in to devising the software for guiding a booster from near space down to a tiny platform in the middle of the ocean is a breathtaking work of mathematical and software art, it is just another day at the office for the computer systems tasked with following the instructions of that software.

The computer is not a human helicopter pilot who needs an eternity - in computer time - to figure out the landing maneuver, and it need not concern itself with the physical comfort of itself or any passengers. If the T/W is higher, it will just pull higher G's by triggering the landing burn later, and then twiddle its thumbs for a bit while it waits patiently for the Merlin to spin up, the same as before. (At launch, ignition is begun at T-3 seconds (http://www.spaceflight101.com/falcon-9-generic-countdown-timeline.html) - that's 4.8 billion clock cycles for a VersaLogic Falcon, and up to 9.6 billion instructions.) This persistent notion that the ability to hover, or a lower T/W, will make a difference to the landing operations arises from thinking about the maneuver in human terms, rather than machine terms.

And on the contrary, we have seen it work repeatedly, on each of the multiple occasions that the booster has made a soft touchdown in the Atlantic. The fact that it fell over and popped like a balloon afterward is irrelevant to the landing sequence. If there had been a barge underneath CRS-3 or OG-2, they'd have a booster on display outside Hawthorne today.

(And this is my 500th post on NSF. Yay!  ;D)
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: ChrisWilson68 on 02/01/2015 03:53 am
Now, let's suppose the booster's terminal velocity is 150m/s. That means for each clock cycle of this VersaLogic Falcon, a falling Falcon will have moved 0.0937 microns. The average thickness of a human hair is about a thousand times larger than this, and the Atom chip can execute up to two instructions per clock cycle (http://en.wikipedia.org/wiki/Intel_Atom_%28CPU%29#Bonnell_microarchitecture). And if you offload calculations to the GPU, the power available to you during those 0.0937 microns of travel is multiplied even further.

So while a booster falling through the atmosphere like a hypersonic spear looks overwhelmingly daunting to our plodding human perceptions, it is quite a leisurely pace as far as the guidance computer is concerned.

...

(And this is my 500th post on NSF. Yay!  ;D)

And a great post it was!  That's a good explanation of why a T/W ratio higher than 1 isn't really a problem that needs solving.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: meekGee on 02/01/2015 04:49 am
And one more factor - the computer does not feel fear of failure, and is infinitely confident.  It's just math.

Find a landing solution, and execute it.  You should see how the collision prevention systems in modern cars bring them to a stop 2" from an obstacle, as if nothing.   Or watch any demo on youTube how robotic systems shuffle parts around at blazing speeds.

Hovering is the equivalent of winding up 3 times before you try to jump.  It's psychological.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: IRobot on 02/01/2015 06:28 am
So while a booster falling through the atmosphere like a hypersonic spear looks overwhelmingly daunting to our plodding human perceptions, it is quite a leisurely pace as far as the guidance computer is concerned. And while the work that went in to devising the software for guiding a booster from near space down to a tiny platform in the middle of the ocean is a breathtaking work of mathematical and software art, it is just another day at the office for the computer systems tasked with following the instructions of that software.
The bottleneck is not the computer guidance calculation speed, it is the sensors integration time, which can be millions of times slower. Worst even are the actuators, in this case grid fins, engine gymbal, engine thruster and gas thrusters. These act very slowly to compensate.

So sensor + actuators speed, accuracy and precision eventually determines the landing accuracy, unrelated to CPU speed.

Still, I agree with the general principle you described, I just would not go that far on boasting CPU performance when that clearly is not the bottleneck.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: wannamoonbase on 02/01/2015 02:07 pm
Forgive me if this has been discussed.  I searched but didn't find my question.

With an updated 1D+ and its increased thrust, when in the flight profile would the engines throttle back to limit G loads?

My idea that the engines are working harder, but that the burn time of the first stage would be shortened. So there would be a partial trade off regarding engine wear.

I thought as well that nearly 1.7 million pounds of thrust that the booster wouldn't be at full throttle the whole time.  Again reducing the impacts of the additional thrust.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: oldAtlas_Eguy on 02/01/2015 03:07 pm
Forgive me if this has been discussed.  I searched but didn't find my question.

With an updated 1D+ and its increased thrust, when in the flight profile would the engines throttle back to limit G loads?

My idea that the engines are working harder, but that the burn time of the first stage would be shortened. So there would be a partial trade off regarding engine wear.

I thought as well that nearly 1.7 million pounds of thrust that the booster wouldn't be at full throttle the whole time.  Again reducing the impacts of the additional thrust.

You are off a llittle bit on the thrust.
-If current M1D is only 85% of the M1d+ then
    - Upgraded M1D SL thrust from 147klbf to 173klbf.
    - 9 M1D+ engines at SL is 1,556klbf.

BTW if the F9 could carry the extra fuel equivelent (supercooling prop) to the thrust increase then payload would increase from 13.5mt to 15.9mt LEO and 4.8mt to 5.6mt GTO.
alas supercooling the prop will gain payload performance but not as much as a vehicle stretch.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: JamesH on 02/01/2015 06:52 pm
So while a booster falling through the atmosphere like a hypersonic spear looks overwhelmingly daunting to our plodding human perceptions, it is quite a leisurely pace as far as the guidance computer is concerned. And while the work that went in to devising the software for guiding a booster from near space down to a tiny platform in the middle of the ocean is a breathtaking work of mathematical and software art, it is just another day at the office for the computer systems tasked with following the instructions of that software.
The bottleneck is not the computer guidance calculation speed, it is the sensors integration time, which can be millions of times slower. Worst even are the actuators, in this case grid fins, engine gymbal, engine thruster and gas thrusters. These act very slowly to compensate.

So sensor + actuators speed, accuracy and precision eventually determines the landing accuracy, unrelated to CPU speed.

Still, I agree with the general principle you described, I just would not go that far on boasting CPU performance when that clearly is not the bottleneck.

This. And as of right now ,do we know if the throttle response of the engines is fast, accurate and repeatable? That's the bit that I think is the slowest and most indeterminate. All the other stuff can be accurately timed (even if slow). If it takes 3s seconds +- 0.5s for the engine to respond to a throttle setting, you can use a 6502 processor and still be fast enough.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: IRobot on 02/01/2015 07:47 pm
Correct me if I'm wrong, but I think the most complex task for the F9 guidance computer is to recalculate a flight ascent profile on the fly, for example if one of the engines is under performing or simply died. And for that you need some calculation power.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: dror on 02/01/2015 08:37 pm
So while a booster falling through the atmosphere like a hypersonic spear looks overwhelmingly daunting to our plodding human perceptions, it is quite a leisurely pace as far as the guidance computer is concerned. And while the work that went in to devising the software for guiding a booster from near space down to a tiny platform in the middle of the ocean is a breathtaking work of mathematical and software art, it is just another day at the office for the computer systems tasked with following the instructions of that software.
The bottleneck is not the computer guidance calculation speed, it is the sensors integration time, which can be millions of times slower. Worst even are the actuators, in this case grid fins, engine gymbal, engine thruster and gas thrusters. These act very slowly to compensate.

So sensor + actuators speed, accuracy and precision eventually determines the landing accuracy, unrelated to CPU speed.

Still, I agree with the general principle you described, I just would not go that far on boasting CPU performance when that clearly is not the bottleneck.


Clearly landing with T/W >1 is not impossible, hovering is for cowards, computers are awesome.

With that logic only, nothing stops from landing a single engine core stage like atlas, falcon 1 or falcon 9 2nd stage.
Do you think that that is possible with good enogh computers, actuators and sensors?
Really, do you think its possible?

OTOH, using 9 engines gave spacex the ability to throttle deep enough and therefore to approach the ground slow enough and hopfully land.

So there must be some golden zone for landing T/W, depending on the electromechanic abilities of the LV,
And probably a smaller engine won't be necessary.





Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Billium on 02/01/2015 09:46 pm
Would this also increase Dragon payload mass to ISS or is Dragon payload constrained by other factors?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: docmordrid on 02/01/2015 10:00 pm
Would this also increase Dragon payload mass to ISS or is Dragon payload constrained by other factors?

Generally, Dragon payloads have been volume limited.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: moralec on 02/01/2015 10:10 pm

Well,  you know,  I wish them well and good luck and I hope that won't be needed.
But I guess that if they can have a T/W closer to 1 then they will have better chances for successful landings.
We can hope that that won't be necessary but we haven't seen that work yet. All landings and hoverings must have been done with additional weight and at much lower velocities, IMO.

It's important to remember that the computer controlling the landing doesn't really care what the T/W ratio is, per se. It's just another item in a list of factors which govern the software's decisions about the landing operation.

Take, for example, the VersaLogic "Falcon" embedded system:

(http://www.versalogic.com/Products/Photos/EPU-2610-A-DS.jpg) (http://www.versalogic.com/products/ds.asp?productid=230)

It has a 1.6-gigahertz Intel Atom E6x0T processor (http://www.intel.com/content/www/us/en/intelligent-systems/medical-applications/atom-e6xx-series-datasheet.html#) and gigabit Ethernet, with up to two gigabytes of RAM, as well as integrated 3D graphics capabilities.

Now, let's suppose the booster's terminal velocity is 150m/s. That means for each clock cycle of this VersaLogic Falcon, a falling Falcon will have moved 0.0937 microns. The average thickness of a human hair is about a thousand times larger than this, and the Atom chip can execute up to two instructions per clock cycle (http://en.wikipedia.org/wiki/Intel_Atom_%28CPU%29#Bonnell_microarchitecture). And if you offload calculations to the GPU, the power available to you during those 0.0937 microns of travel is multiplied even further.

So while a booster falling through the atmosphere like a hypersonic spear looks overwhelmingly daunting to our plodding human perceptions, it is quite a leisurely pace as far as the guidance computer is concerned. And while the work that went in to devising the software for guiding a booster from near space down to a tiny platform in the middle of the ocean is a breathtaking work of mathematical and software art, it is just another day at the office for the computer systems tasked with following the instructions of that software.

The computer is not a human helicopter pilot who needs an eternity - in computer time - to figure out the landing maneuver, and it need not concern itself with the physical comfort of itself or any passengers. If the T/W is higher, it will just pull higher G's by triggering the landing burn later, and then twiddle its thumbs for a bit while it waits patiently for the Merlin to spin up, the same as before. (At launch, ignition is begun at T-3 seconds (http://www.spaceflight101.com/falcon-9-generic-countdown-timeline.html) - that's 4.8 billion clock cycles for a VersaLogic Falcon, and up to 9.6 billion instructions.) This persistent notion that the ability to hover, or a lower T/W, will make a difference to the landing operations arises from thinking about the maneuver in human terms, rather than machine terms.

And on the contrary, we have seen it work repeatedly, on each of the multiple occasions that the booster has made a soft touchdown in the Atlantic. The fact that it fell over and popped like a balloon afterward is irrelevant to the landing sequence. If there had been a barge underneath CRS-3 or OG-2, they'd have a booster on display outside Hawthorne today.

(And this is my 500th post on NSF. Yay!  ;D)

++ to this post. And happy 500th.

Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: meekGee on 02/01/2015 10:24 pm
So while a booster falling through the atmosphere like a hypersonic spear looks overwhelmingly daunting to our plodding human perceptions, it is quite a leisurely pace as far as the guidance computer is concerned. And while the work that went in to devising the software for guiding a booster from near space down to a tiny platform in the middle of the ocean is a breathtaking work of mathematical and software art, it is just another day at the office for the computer systems tasked with following the instructions of that software.
The bottleneck is not the computer guidance calculation speed, it is the sensors integration time, which can be millions of times slower. Worst even are the actuators, in this case grid fins, engine gymbal, engine thruster and gas thrusters. These act very slowly to compensate.

So sensor + actuators speed, accuracy and precision eventually determines the landing accuracy, unrelated to CPU speed.

Still, I agree with the general principle you described, I just would not go that far on boasting CPU performance when that clearly is not the bottleneck.


Clearly landing with T/W >1 is not impossible, hovering is for cowards, computers are awesome.

With that logic only, nothing stops from landing a single engine core stage like atlas, falcon 1 or falcon 9 2nd stage.
Do you think that that is possible with good enogh computers, actuators and sensors?
Really, do you think its possible?

OTOH, using 9 engines gave spacex the ability to throttle deep enough and therefore to approach the ground slow enough and hopfully land.

So there must be some golden zone for landing T/W, depending on the electromechanic abilities of the LV,
And probably a smaller engine won't be necessary.

It's a lot simpler than that.  If you try to land an empty stage with 9 engines (or land an Atlas, or any of your other examples) then you'll exceed the allowed acceleration limit of the stage, and it will fail mechanically.  Having a 1:9 throttle really helps when the stage empty weight is only a few % of the takeoff weight.

It is true that with higher T/W, the avionics has to "work harder", but as has been pointed out above, it's really not an issue.  You can land at T/W=2 (a=1g), or T/W=3 (a=2g) and for the computers and actuators, this is slow-mo.

What's more (again as has been pointed out) - the less time you spend going low and slow, the better it is from the point of view of wind gusts.  The "scary" part of the landing is actually predicable.  Wind gusts are not, and you want to get the landing over and done with as quickly as possible, before they have time to affect your attitude.  (The rocket's attitude, not yours personally)

Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: ChrisWilson68 on 02/01/2015 10:41 pm
It's a lot simpler than that.  If you try to land an empty stage with 9 engines (or land an Atlas, or any of your other examples) then you'll exceed the allowed acceleration limit of the stage, and it will fail mechanically.  Having a 1:9 throttle really helps when the stage empty weight is only a few % of the takeoff weight.

It is true that with higher T/W, the avionics has to "work harder", but as has been pointed out above, it's really not an issue.  You can land at T/W=2 (a=1g), or T/W=3 (a=2g) and for the computers and actuators, this is slow-mo.

I completely agree with your point, but I have a minor quibble about how you present it here.  While T/W=2 does give 1g acceleration with respect to the surface of the Earth, the load on the structure of the rocket is 2g, and at T/W=3 the load is 3g.  When T/W=1, the rocket hovers and the load is 1g.  Since we're talking about the structural capacity of the rocket, I think that's the more useful number.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: ChrisWilson68 on 02/01/2015 11:00 pm
So while a booster falling through the atmosphere like a hypersonic spear looks overwhelmingly daunting to our plodding human perceptions, it is quite a leisurely pace as far as the guidance computer is concerned. And while the work that went in to devising the software for guiding a booster from near space down to a tiny platform in the middle of the ocean is a breathtaking work of mathematical and software art, it is just another day at the office for the computer systems tasked with following the instructions of that software.
The bottleneck is not the computer guidance calculation speed, it is the sensors integration time, which can be millions of times slower. Worst even are the actuators, in this case grid fins, engine gymbal, engine thruster and gas thrusters. These act very slowly to compensate.

So sensor + actuators speed, accuracy and precision eventually determines the landing accuracy, unrelated to CPU speed.

Still, I agree with the general principle you described, I just would not go that far on boasting CPU performance when that clearly is not the bottleneck.

This. And as of right now ,do we know if the throttle response of the engines is fast, accurate and repeatable? That's the bit that I think is the slowest and most indeterminate. All the other stuff can be accurately timed (even if slow). If it takes 3s seconds +- 0.5s for the engine to respond to a throttle setting, you can use a 6502 processor and still be fast enough.

The point about the speed of the processor is to point out that our intuition says it's impossibly hard to land a rocket like that because it's too fast for our human brains.  The point of the processor speed is that it's not too fast for the processor.

It's true that throttle response is not immediate.  But that's not necessarily a problem.  What matters is the comparison of the throttle response time to how quickly something unexpectedly changed.

If the computer had perfect information, throttle response time wouldn't matter.  The throttle could have a 10 minute delay and it wouldn't matter because the computer could just send the commands to the throttle 10 minutes before it wanted them to happen.

The question is how quickly things change and need to be compensated for.  Do the control inputs (throttle, gimbaling, fins, etc.) react quickly enough to compensate for winds and any other atmospheric changes?

We've seen with Grasshopper and F9R-dev1 that they do react quickly enough at low speeds.  How much more quickly would they have to react at higher vertical speeds?  Probably not a lot, if any, faster.  At low speeds they already have to deal with varying winds, and in the test videos it's clear the vehicles are rock-solid in those circumstances.

Trying to keep a vehicle hovering is really no different to a computer than trying to keep it on a pre-defined trajectory.  The computer can sense when it's drifting off the trajectory (including going higher or lower than intended along the path) just as easily as it can sense when it's moving off a fixed position in a hover.  There's no difference.

The one way that a hoverslam might be more demanding to the system than a hover is if the atmosphere is changing unexpectedly along its path, just because conditions at 500 feet are different than those at 300 feet.  But such changes are equivalent to unexpected wind changes while hovering, and the videos from the Texas test flights suggests those are easily compensated for.

All this discussion is somewhat moot anyway -- as has been said several times, we know it works just fine because they managed to do successful water landings twice.  Falcon 9's first stage has already been proven to be able to do a hoverslam landing.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: meekGee on 02/02/2015 12:19 am
It's a lot simpler than that.  If you try to land an empty stage with 9 engines (or land an Atlas, or any of your other examples) then you'll exceed the allowed acceleration limit of the stage, and it will fail mechanically.  Having a 1:9 throttle really helps when the stage empty weight is only a few % of the takeoff weight.

It is true that with higher T/W, the avionics has to "work harder", but as has been pointed out above, it's really not an issue.  You can land at T/W=2 (a=1g), or T/W=3 (a=2g) and for the computers and actuators, this is slow-mo.

I completely agree with your point, but I have a minor quibble about how you present it here.  While T/W=2 does give 1g acceleration with respect to the surface of the Earth, the load on the structure of the rocket is 2g, and at T/W=3 the load is 3g.  When T/W=1, the rocket hovers and the load is 1g.  Since we're talking about the structural capacity of the rocket, I think that's the more useful number.

That's what I meant.  T/W determines the structural load, and a determines how dror feels about the landing :)  (Cheers Mate!) and how responsive the control system has to be.

Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: cleonard on 02/02/2015 02:39 am
It seems like there is a lot of unfounded speculation that a uprated Merlin 1D is physically different than the model currently flying.  I don't think that is the case.  Isn't it just a case of running more propellant through the engine?  Nothing more than some simple code changes to the engine controller.

Now I do imagine that there are just about 100% for sure some minor tweaks to the M1D since it started flying, but I just don't think that there are any substantial changes for this soon to fly uprated engine.

Is there any info on what is being considered.  In the past there have been numbers up to 117%.  I have a feeling that they will be starting at 105% or maybe even 110%.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: ChrisWilson68 on 02/02/2015 03:02 am
It seems like there is a lot of unfounded speculation that a uprated Merlin 1D is physically different than the model currently flying.  I don't think that is the case.  Isn't it just a case of running more propellant through the engine?  Nothing more than some simple code changes to the engine controller.

In the same paragraph where you ding other people for unfounded speculation, you go ahead and indulge in speculation of your own that has no better foundation.

I don't think there's anything wrong with speculation, but don't attack other people for it and do it yourself.

Now I do imagine that there are just about 100% for sure some minor tweaks to the M1D since it started flying, but I just don't think that there are any substantial changes for this soon to fly uprated engine.

Is there any info on what is being considered.  In the past there have been numbers up to 117%.  I have a feeling that they will be starting at 105% or maybe even 110%.

From Spacenews:

Quote
“You know SpaceX is introducing into their manifest ... a modification of the current engine, with about a 20 percent increase in thrust," said Martin Halliwell, SES’s chief technical officer. "We’re making a decision internally as to whether we want to be the first to fly it.”

http://spacenews.com/ses-rethinking-being-first-to-fly-on-a-full-throttle-falcon-9/

A tweet, also from Spacenews, says:

Quote
SES: We may skip spring SpaceX launch slot & wait till mid-year to let someone else be 1st using Falcon 9 main engine in full-thrust regime.

This all adds up to 20% more thrust, starting in the spring of 2015.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: cleonard on 02/02/2015 03:30 am
SpaceX discussion threads are all about speculation until some confirming data comes out one way or another.   Sorry you took what I wrote as some kind of attack. 

Simple logic really.  There is not evidence one way or the other that there are hardware changes.  Making the assumption that the hardware is not substantially changed.  That really only leaves software changes that can achieve the effect.  Speculation down that path.

A few more open valve settings and the gas generator makes more gas turning the pump faster/harder leading to more propellant in the combustion chamber at a higher pressure.  The result?  More thrust at most likely the same or just slightly better isp.

OK that better isp is more specualtion.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: MP99 on 02/02/2015 08:07 am
It seems like there is a lot of unfounded speculation that a uprated Merlin 1D is physically different than the model currently flying.  I don't think that is the case.  Isn't it just a case of running more propellant through the engine?  Nothing more than some simple code changes to the engine controller.

Now I do imagine that there are just about 100% for sure some minor tweaks to the M1D since it started flying, but I just don't think that there are any substantial changes for this soon to fly uprated engine.

It's my suspicion that the higher thrust is dependent on propellant sub-cooling.

If so, it will be a more substantial system-wide set of changes, and especially ground handling, than just "turn the power up to 11".


Is there any info on what is being considered.  In the past there have been numbers up to 117%.  I have a feeling that they will be starting at 105% or maybe even 110%.


117% is just 1/85%.

165klb is 112% of today's published SL thrust level (147 klb).

If it was really 117%, that would be 173 klb, and it seems unlikely Elon would quote 165 klb if the true number was 173 klb.


I think these are the only hard numbers we have on the subject:-

Quote from:  http://shitelonsays.com/transcript/spacex-ses-8-pre-launch-conference-2013-11-24
With respect to the future potential for the rocket, I do think we've got.. I'm really happy with this rocket design. It's an incredibly capable vehicle. It's actually one of the biggest rockets in the world, it's worth noting, at about 1.3 million pounds of thrust, and we're only actually operating the engines at about 85% of their potential. Down the road, in future missions, we anticipate being able to crank them up to their full thrust capability, which would give about 165,000 pounds of sea-level thrust per engine. Anyway, it really is something that is, I think, going to serve really well for the commercial launch market, for government satellites and for Dragon, both crew and cargo. I believe its inherent reliability potential is better than any other rocket in the world. It will be up to us to show that it lives up to that reliability potential.

Cheers, Martin
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: ChrisWilson68 on 02/02/2015 09:06 am
165klb is 112% of today's published SL thrust level (147 klb).

If it was really 117%, that would be 173 klb, and it seems unlikely Elon would quote 165 klb if the true number was 173 klb.

I think these are the only hard numbers we have on the subject:-

Those aren't the only hard numbers we have.  Those are numbers from 2013.  In 2015, SES said a 20% increase in thrust, and they are a customer who is considering delaying a launch because of the changes, so they should know exactly what the real numbers are.

In 2013, Elon was likely less sure of what the numbers would be, and it's possible he was quoting the lower end of the range they expected.  If it was really a 12% increase, I really doubt SES would be going around saying 20%.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: MP99 on 02/02/2015 10:27 am
165klb is 112% of today's published SL thrust level (147 klb).

If it was really 117%, that would be 173 klb, and it seems unlikely Elon would quote 165 klb if the true number was 173 klb.

I think these are the only hard numbers we have on the subject:-

Those aren't the only hard numbers we have.  Those are numbers from 2013.  In 2015, SES said a 20% increase in thrust, and they are a customer who is considering delaying a launch because of the changes, so they should know exactly what the real numbers are.

In 2013, Elon was likely less sure of what the numbers would be, and it's possible he was quoting the lower end of the range they expected.  If it was really a 12% increase, I really doubt SES would be going around saying 20%.

Hmm, 112% vs 7-8% extra prop from densification + legs + grid fins and their hydraulics + a little extra drag seems a fairly balanced upgrade.

ISTM that 120% might need trajectory shaping to avoid higher max-Q - or that a noticeably higher max-Q is one of the issues that SES want to see proved out before they fly. Perhaps a lofted trajectory is OK for F9-R, and anything else will fly on FH-R anyway.

Is it possible that today's F9 actually has a sub-optimal T:W, so that the upgraded version is optimal?

If not, could there be a barrel stretch of F9US coming with this?

cheers, Martin
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: gongora on 02/02/2015 03:01 pm
If it was really a 12% increase, I really doubt SES would be going around saying 20%.

If it's closer to 17% though I could easily see someone outside the company rounding it up to 20% in a conversation.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Roy_H on 02/02/2015 03:08 pm
Is it possible that today's F9 actually has a sub-optimal T:W, so that the upgraded version is optimal?
cheers, Martin

That's my bet, I believe (without any proof) that this "higher thrust" was planned from the beginning for the 1D and has been throttled down for first set of flights just to be conservative and also waiting for tweeks like sub cooled fuel.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Norm38 on 02/02/2015 03:53 pm
Granted what I'm about to say doesn't hold for whole vehicle issues like prop loading or a higher Max Q.
But if customers are worried about higher stresses on the engines at higher power, and no one wants to go first....

Well there are 9 engines, and engine out capability, so do all 9 engines need to be run at the same power level?  If two engines opposite each other were run at the new full thrust while the others stayed put, then if an engine did happen to fail, the payload would still make orbit by sacrificing the fuel set aside for landing.  If everything works as planned, they have a validation and customers may feel better about going first on a full 9 engine upgrade.
I wonder if they're considering that?

Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: abaddon on 02/02/2015 04:39 pm
My guess (just that) is that SpaceX was planning on running the first uprated launch on a Dragon mission.  With the loss of Antares late last year, it wouldn't surprise me if NASA expressed discomfort with such a plan and asked SpaceX to do it with someone else.  SpaceX is now looking for someone else to go first and SES would rather have it be someone else, too...

I doubt they will run a mission with a subset of engines operating in the higher thrust regime, but I suppose if nobody will agree to go first, and that assuages anyone's concerns, it is possible.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: cambrianera on 02/02/2015 05:00 pm

It's my suspicion that the higher thrust is dependent on propellant sub-cooling.


Reducing pressure loss in cooling channels (and pipings, and injectors) it is possible to achieve higher chamber pressure with the same pump outlet pressure.
Higher chamber pressure means higher thrust.
Therefore it is possible that propellant subcooling has an effect on increased thrust, but the same can be true for 3D printed parts and/or other tweaks.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: MP99 on 02/02/2015 07:22 pm
Granted what I'm about to say doesn't hold for whole vehicle issues like prop loading or a higher Max Q.
But if customers are worried about higher stresses on the engines at higher power, and no one wants to go first....

Well there are 9 engines, and engine out capability, so do all 9 engines need to be run at the same power level?  If two engines opposite each other were run at the new full thrust while the others stayed put, then if an engine did happen to fail, the payload would still make orbit by sacrificing the fuel set aside for landing.  If everything works as planned, they have a validation and customers may feel better about going first on a full 9 engine upgrade.
I wonder if they're considering that?

I suspect that the increased thrust is dependent on sub-cooling of the prop, which would make that difficult.

cheers, Martin
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: cleonard on 02/02/2015 08:35 pm
Sub cooling also causes viscosity increase as well as density increase.   The increased viscosity means more pressure loss in the piping.   Not too much of an issue for the lox but it is more significant for the rp1 through all the small cooling channels.  I'll venture a guess that sub cooling means that more pumping power is needed.

I'm no turbo pump engineer,  but I will also speculate that increased viscosity also reduces cavitation margins unless tank pressure is increased.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: acsawdey on 02/02/2015 09:19 pm
I'm no turbo pump engineer,  but I will also speculate that increased viscosity also reduces cavitation margins unless tank pressure is increased.

The opposite effect also exists. Cavitation occurs when the static pressure drops below the vapor pressure of the fluid. Reducing the temperature reduces the vapor pressure, thus increasing the cavitation margin. Given that the vapor pressure of lox drops rapidly (10x reduction from 90K to 70K), the viscosity effect would have to be rather large.

(http://encyclopedia.airliquide.com/images_encyclopedie/VaporPressureGraph/Oxygen_Vapor_Pressure.GIF)
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: punder on 02/02/2015 09:37 pm
My guess (just that) is that SpaceX was planning on running the first uprated launch on a Dragon mission.  With the loss of Antares late last year, it wouldn't surprise me if NASA expressed discomfort with such a plan and asked SpaceX to do it with someone else.  SpaceX is now looking for someone else to go first and SES would rather have it be someone else, too...

I doubt they will run a mission with a subset of engines operating in the higher thrust regime, but I suppose if nobody will agree to go first, and that assuages anyone's concerns, it is possible.

If push comes to shove, they could put a mass simulator on top of the first stage and fly a suborbital flight, with an orbital mission profile, to test the new engines.  The mass sim would stage at the proper time, in the usual manner, but simply fall into the ocean.  The first stage would make a "routine" landing on Just Follow Read the Instructions.

I mean, propellant is cheap, right?   ;D  And, such a flight would be a perfect example of aviation flight test applied to orbital boosters.

Almost certainly one of the customers will be persuaded, perhaps with a discount, to allow the new engines on their flight.  So this is not likely to happen.  But it could happen.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: abaddon on 02/02/2015 09:39 pm
If push comes to shove, they could put a mass simulator on top of the first stage and fly a suborbital flight, with an orbital mission profile, to test the new engines.  The mass sim would stage at the proper time, in the usual manner, but simply fall into the ocean.  The first stage would make a "routine" landing on Just Follow the Instructions.

Hm... interesting idea... and I think you just described the DragonV2 in-flight abort test...
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: punder on 02/02/2015 09:44 pm
If push comes to shove, they could put a mass simulator on top of the first stage and fly a suborbital flight, with an orbital mission profile, to test the new engines.  The mass sim would stage at the proper time, in the usual manner, but simply fall into the ocean.  The first stage would make a "routine" landing on Just Follow the Instructions.

Hm... interesting idea... and I think you just described the DragonV2 in-flight abort test...

Ha ha!  You got me.  Well, close anyway.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Norm Hartnett on 02/02/2015 10:16 pm
<snip>

 The first stage would make a "routine" landing on Just Follow the Instructions.
<snip>


A small nit... the autonomous spaceport drone ship is named Just Read the Instructions nothing was actually said about following instructions.

;)
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: punder on 02/02/2015 11:13 pm
<snip>

 The first stage would make a "routine" landing on Just Follow the Instructions.
<snip>


A small nit... the autonomous spaceport drone ship is named Just Read the Instructions nothing was actually said about following instructions.

;)

And I call myself a Banks fan...  :-[  Will fix in my post.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: intrepidpursuit on 02/03/2015 07:41 am
Is it possible that today's F9 actually has a sub-optimal T:W, so that the upgraded version is optimal?
cheers, Martin

That's my bet, I believe (without any proof) that this "higher thrust" was planned from the beginning for the 1D and has been throttled down for first set of flights just to be conservative and also waiting for tweeks like sub cooled fuel.

I would agree. IMHO Musk's statements about the rocket being as long as it can be structurally are an indicator that there was energy left in the engines. If you need a certain tank size then you build for it. If the tank structural engineers come back and say, "we can't make it that big without making it wider" then you say, "well tell me how big you can make it." Once that design trade off is done you start thinking about how to squeeze more fuel into these volume limited tanks. That leads you to sub cooling.

They likely optimized the engines for the thrust they could take advantage of with the current tank design, but tuning it up to its maximum output after it was tuned down probably seems like it would not require significant changes to the engine. Certainly not changing the interfaces and attachment points. I am not a rocket engineer, but this theory does follow a likely engineering path.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Proponent on 02/03/2015 11:14 am
Sub cooling also causes viscosity increase as well as density increase.   The increased viscosity means more pressure loss in the piping.   Not too much of an issue for the lox but it is more significant for the rp1 through all the small cooling channels.  I'll venture a guess that sub cooling means that more pumping power is needed.

I wonder, though, whether the RP-1 might have warmed up quite a bit by the time it reaches the injectors.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Razer on 02/05/2015 09:11 pm
Do we know if the new Merlin 1D+ Engine would be mounted in the future on all Falcon 9, or will there be two versions falcon falcon 1D and 1D+ ?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: symbios on 02/05/2015 09:24 pm
Do we know if the new Merlin 1D+ Engine would be mounted in the future on all Falcon 9, or will there be two versions falcon falcon 1D and 1D+ ?

As I understand it from what I have read, Merlin 1D+ is the Merlin 1D with 165 klb instead of 147 klb of thrust. It is not a new engine and it is debated of how much change has actually been made on the Merlin 1D to get the new thrust.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: LastStarFighter on 02/05/2015 09:49 pm
Do we know if the new Merlin 1D+ Engine would be mounted in the future on all Falcon 9, or will there be two versions falcon falcon 1D and 1D+ ?

As I understand it from what I have read, Merlin 1D+ is the Merlin 1D with 165 klb instead of 147 klb of thrust. It is not a new engine and it is debated of how much change has actually been made on the Merlin 1D to get the new thrust.
I agree. My understanding was that they over built the engine to have extra margins. Now that they have lots of firings and data on the stresses they are releasing those margins because they are more comfortable.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: oldAtlas_Eguy on 02/06/2015 01:12 am
Do we know if the new Merlin 1D+ Engine would be mounted in the future on all Falcon 9, or will there be two versions falcon falcon 1D and 1D+ ?

As I understand it from what I have read, Merlin 1D+ is the Merlin 1D with 165 klb instead of 147 klb of thrust. It is not a new engine and it is debated of how much change has actually been made on the Merlin 1D to get the new thrust.
I agree. My understanding was that they over built the engine to have extra margins. Now that they have lots of firings and data on the stresses they are releasing those margins because they are more comfortable.

The real question is there an ISP increase. A 5 point increase would result in a 15% or more increase in payload capability.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: TripD on 02/06/2015 03:11 am
Quote
The increased viscosity means more pressure loss in the piping. 

Forgive this plebeian question.  At first glance, I would think that increased viscosity would decrease flow rate.  I can't see how this becomes a decrease in pressure.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Norm38 on 02/06/2015 03:44 am
As far as everything else, your moving such a huge amount of fuel in such a short time, you'd have to be inputing a crazy amount of heat from somewhere to warm the fuel load up a single degree.

Isn't that the basic definition of a rocket engine?  A machine that turns a crazy amount of fuel into a crazy amount of heat?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Burninate on 02/06/2015 04:13 am
Do we know if the new Merlin 1D+ Engine would be mounted in the future on all Falcon 9, or will there be two versions falcon falcon 1D and 1D+ ?

As I understand it from what I have read, Merlin 1D+ is the Merlin 1D with 165 klb instead of 147 klb of thrust. It is not a new engine and it is debated of how much change has actually been made on the Merlin 1D to get the new thrust.
I agree. My understanding was that they over built the engine to have extra margins. Now that they have lots of firings and data on the stresses they are releasing those margins because they are more comfortable.

The real question is there an ISP increase. A 5 point increase would result in a 15% or more increase in payload capability.
That's rather high, I think.

If the first stage averages 300s Isp, and the second stage averages 340s Isp, theoretical dV at 13,150kg payload is 10,084m/s.  Take that number, and find the payload to match it at 305s Isp for the first stage and 345s Isp for the second, and you get 14,077kg, a 7.5% increase to LEO.  Applying the same analysis to GTO using quoted payload figures of 4850kg, raises payload to 5423kg, an 11.8% increase to GTO.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: cscott on 02/06/2015 07:22 am
Quote
The increased viscosity means more pressure loss in the piping. 

Forgive this plebeian question.  At first glance, I would think that increased viscosity would decrease flow rate.  I can't see how this becomes a decrease in pressure.

http://en.m.wikipedia.org/wiki/Friction_loss

I'm not an plumbing expert, rocket or otherwise, but the above link leads me to believe that the convention is to describe frictional loss (like that caused by increased velocity) in terms of additional "height" that you need to pump a liquid.  That is, if you were pumping it "up 10 feet", then the frictional loss would be another "3 feet up" you effectively need to pump it in order to overcome the pipe friction.  So the frictional loss is thought of as a "extra pressure" required.  This might just be an analytic convenience, since in a rocket you perhaps have to keep the outlet pressure more or less constant and adjust the flow rate to compensate, I don't know.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: ChrisWilson68 on 02/06/2015 08:02 am
Do we know if the new Merlin 1D+ Engine would be mounted in the future on all Falcon 9, or will there be two versions falcon falcon 1D and 1D+ ?

As I understand it from what I have read, Merlin 1D+ is the Merlin 1D with 165 klb instead of 147 klb of thrust. It is not a new engine and it is debated of how much change has actually been made on the Merlin 1D to get the new thrust.
I agree. My understanding was that they over built the engine to have extra margins. Now that they have lots of firings and data on the stresses they are releasing those margins because they are more comfortable.

The real question is there an ISP increase. A 5 point increase would result in a 15% or more increase in payload capability.

I would guess that if there were an Isp increase, they would have mentioned that along with the mention of the thrust increase.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: wannamoonbase on 02/06/2015 03:28 pm
The real question is there an ISP increase. A 5 point increase would result in a 15% or more increase in payload capability.

Have a look at page 1 of this thread.  In the third post a table shows a 4 sec (1.4%) improvement in sea level ISP.

I don't know the legitimacy of the table, but in the absence of other data...
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: TripD on 02/06/2015 04:23 pm
@Cscott   Thanks. That makes sense.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: acsawdey on 02/06/2015 04:48 pm
If the first stage averages 300s Isp, and the second stage averages 340s Isp, theoretical dV at 13,150kg payload is 10,084m/s.  Take that number, and find the payload to match it at 305s Isp for the first stage and 345s Isp for the second, and you get 14,077kg, a 7.5% increase to LEO.  Applying the same analysis to GTO using quoted payload figures of 4850kg, raises payload to 5423kg, an 11.8% increase to GTO.

If the table on the first page can be trusted, the average increase in Isp will only be about 2s as there isn't much increase in vacuum Isp. I suspect the Isp increase comes from the higher chamber pressure resulting in the exhaust being less under-expanded at sea level. There was another post later on the first page where someone saw a similar relationship when they modeled throttling at sea level. There is no increase in Isp for the M1D-vac. So you're looking at 300 vs 302 for the first stage and no change for second stage.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: oldAtlas_Eguy on 02/06/2015 05:33 pm
If the first stage averages 300s Isp, and the second stage averages 340s Isp, theoretical dV at 13,150kg payload is 10,084m/s.  Take that number, and find the payload to match it at 305s Isp for the first stage and 345s Isp for the second, and you get 14,077kg, a 7.5% increase to LEO.  Applying the same analysis to GTO using quoted payload figures of 4850kg, raises payload to 5423kg, an 11.8% increase to GTO.

If the table on the first page can be trusted, the average increase in Isp will only be about 2s as there isn't much increase in vacuum Isp. I suspect the Isp increase comes from the higher chamber pressure resulting in the exhaust being less under-expanded at sea level. There was another post later on the first page where someone saw a similar relationship when they modeled throttling at sea level. There is no increase in Isp for the M1D-vac. So you're looking at 300 vs 302 for the first stage and no change for second stage.
If you also add the overall prop increase due to super cooling of ~1.5% to the 1st stage ISP increase of 2 points at sea level only which would be only an average of just 1 for atmospheric a vac operation of 1st stage, I wonder what you get for a payload increase with your model.

The second item is that if there is a sea level ISP increase then there should also be about the same or proportionately large vac ISP increase. This due to the fact that ISP is dependent on TC pressure. Higher pressure higher ISP. This implies that ISP will increase for vac operation as well.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: acsawdey on 02/06/2015 05:48 pm
If you also add the overall prop increase due to super cooling of ~1.5% to the 1st stage ISP increase of 2 points at sea level only which would be only an average of just 1 for atmospheric a vac operation of 1st stage, I wonder what you get for a payload increase with your model.

The second item is that if there is a sea level ISP increase then there should also be about the same or proportionately large vac ISP increase. This due to the fact that ISP is dependent on TC pressure. Higher pressure higher ISP. This implies that ISP will increase for vac operation as well.

The 2s increase is alread averaging 4s at sea level --> 1s vacuum from malu5531's post (http://forum.nasaspaceflight.com/index.php?topic=32983.msg1131598#msg1131598 (http://forum.nasaspaceflight.com/index.php?topic=32983.msg1131598#msg1131598)).

The other post I was referring to was this one from deltaV: http://forum.nasaspaceflight.com/index.php?topic=32983.msg1136160#msg1136160 (http://forum.nasaspaceflight.com/index.php?topic=32983.msg1136160#msg1136160)

He modeled 100% vs 50% throttling for the M1D. It seems like the same relationships should apply for 112% vs 100%, i.e. much larger Isp increase at sea level than vacuum.

Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: oldAtlas_Eguy on 02/06/2015 06:18 pm
If you also add the overall prop increase due to super cooling of ~1.5% to the 1st stage ISP increase of 2 points at sea level only which would be only an average of just 1 for atmospheric a vac operation of 1st stage, I wonder what you get for a payload increase with your model.

The second item is that if there is a sea level ISP increase then there should also be about the same or proportionately large vac ISP increase. This due to the fact that ISP is dependent on TC pressure. Higher pressure higher ISP. This implies that ISP will increase for vac operation as well.

The 2s increase is alread averaging 4s at sea level --> 1s vacuum from malu5531's post (http://forum.nasaspaceflight.com/index.php?topic=32983.msg1131598#msg1131598 (http://forum.nasaspaceflight.com/index.php?topic=32983.msg1131598#msg1131598)).

The other post I was referring to was this one from deltaV: http://forum.nasaspaceflight.com/index.php?topic=32983.msg1136160#msg1136160 (http://forum.nasaspaceflight.com/index.php?topic=32983.msg1136160#msg1136160)

He modeled 100% vs 50% throttling for the M1D. It seems like the same relationships should apply for 112% vs 100%, i.e. much larger Isp increase at sea level than vacuum.
I calculated the vac ISP from the thrust and flow rate which gives an ISP of 358s (200000/(2.2*253.5)) a gain of 11. Something is not correct in his numbers.
Edit sorry using the net  flow of 262 does give an ISP of 347s. So an increase in thrust but no ISP increase with increased TC pressure is still hard to believe.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: CraigLieb on 02/15/2015 04:03 pm
 I am wondering if there is any discussion regarding catastrophic failure modes that could cause one engine to take out a second engine on launch? The shuttle experience and even Apollo 13 imply that a small manufacturing defect, possibly from a sub-contractor and/or an out of bounds operating condition might lead to such an event.
With increased performance on the Merlin 1D+ engines they push the envelope closer to the boundaries of their design. What systems are most vulnerable to failures of this type, and what design elements protect or isolate each engine from the other to prevent loss of two engines, leading to mission failure? 
Becomes much more important with people onboard.

Are there any public sources on SpaceX risk analysis or reduction efforts?

Apologies if this topic has been covered and/or if the thread is wrong for a discussion.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: oiorionsbelt on 02/15/2015 04:58 pm
Each engine is shielded from the adjacent engines by Kevlar blankets.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Nomadd on 02/15/2015 05:39 pm
Quote
The increased viscosity means more pressure loss in the piping. 

Forgive this plebeian question.  At first glance, I would think that increased viscosity would decrease flow rate.  I can't see how this becomes a decrease in pressure.
Depends on where you measure pressure. It's like the idiots solution to low engine oil pressure, which is to add thicker oil. That might increase pressure at the pump and sensor, but it decreases oil flow and pressure at the outlets or the injectors in the rocket engine case.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: docmordrid on 02/16/2015 01:59 am
Each engine is shielded from the adjacent engines by Kevlar blankets.

And IIRC, armor plates.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Prober on 02/17/2015 02:34 am
Do we know if the new Merlin 1D+ Engine would be mounted in the future on all Falcon 9, or will there be two versions falcon falcon 1D and 1D+ ?

maybe 3 vers.  9FR being the 3rd.

This brings into question the whole expression of disgust by SX management regarding certification.  This thread becomes meaningful.... http://forum.nasaspaceflight.com/index.php?topic=34818.0.   The USAF can't be expected to certify a moving target can they?   
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Coastal Ron on 02/17/2015 03:11 am
Do we know if the new Merlin 1D+ Engine would be mounted in the future on all Falcon 9, or will there be two versions falcon falcon 1D and 1D+ ?

maybe 3 vers.  9FR being the 3rd.

This brings into question the whole expression of disgust by SX management regarding certification.  This thread becomes meaningful.... http://forum.nasaspaceflight.com/index.php?topic=34818.0.   The USAF can't be expected to certify a moving target can they?

Assuming the change in configuration is not caused by obsolescence of components or safety reasons, SpaceX could continue to produce their current engine and the improved one concurrently.  This does happen a lot in manufacturing, and I don't think it would be a big problem for them.

By doing that they could complete their certification for the current Falcon 9 configuration, and then work towards certifying the new engines at a later point.  And SpaceX management would have known about how the upgraded engine would affect their certification of the Falcon 9 long ago, so I don't think this will be an issue.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Lars-J on 02/17/2015 04:18 am
Do we know if the new Merlin 1D+ Engine would be mounted in the future on all Falcon 9, or will there be two versions falcon falcon 1D and 1D+ ?

maybe 3 vers.  9FR being the 3rd.

This brings into question the whole expression of disgust by SX management regarding certification.  This thread becomes meaningful.... http://forum.nasaspaceflight.com/index.php?topic=34818.0.   The USAF can't be expected to certify a moving target can they?
ULA makes small tweaks to their LVs quite frequently. Think the M1D thrust upgrade as RS-68 vs RS-68A, just to name an example.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: AncientU on 02/17/2015 12:19 pm
We don't know that M1D+ is operating outside of the flight qualification envelope of the original M1D.  Use to date has been throttled to 85% or so... Maybe nothing new is needed engine-wise to fly in the uprated mode.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: mhlas7 on 02/17/2015 05:56 pm
Do we know if the new Merlin 1D+ Engine would be mounted in the future on all Falcon 9, or will there be two versions falcon falcon 1D and 1D+ ?

maybe 3 vers.  9FR being the 3rd.

This brings into question the whole expression of disgust by SX management regarding certification.  This thread becomes meaningful.... http://forum.nasaspaceflight.com/index.php?topic=34818.0.   The USAF can't be expected to certify a moving target can they?
ULA makes small tweaks to their LVs quite frequently. Think the M1D thrust upgrade as RS-68 vs RS-68A, just to name an example.

How big of a change needs to be made before it is considered a new rocket and require re-certification? Could ULA argue that their BE-4 powered rocket is just an evolution of the Atlas V a not require re-certification?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Hauerg on 02/17/2015 06:00 pm
Considering a completely new - never flown in any rocket - engine and new fully cryogenic fuel this would be almost ridiculous.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: mhlas7 on 02/17/2015 09:37 pm
I realize it's ridiculous but what I'm trying to get at is where is the line drawn between an upgraded rocket and a new rocket? The air force must have a definition.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: abaddon on 02/17/2015 10:36 pm
Based on historic practices, the USAF will consider the Atlas V successor a new rocket but will be intimately involved with the development, so certification will mostly be a part of the development process.  I am not sure how this is going to work with the BE-4 as presumably the USAF is not intimately involved with its development.

That is off-topic for this thread, however.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: AJW on 02/18/2015 02:15 am
How big of a change needs to be made before it is considered a new rocket and require re-certification? Could ULA argue that their BE-4 powered rocket is just an evolution of the Atlas V a not require re-certification?

Quote
"While the new system will require certification, we're confident this new system will enable us to further reduce costs while continuing to provide the most affordable and reliable launch services to our customers," ULA spokeswoman Jessica Rye wrote in an email.

ULA does seem to understand that switching engines will require recertification, but that "further reduce costs" and "affordable" part did make me chuckle.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: deruch on 02/22/2015 03:10 am
Space News: SES Rethinking Being First To Fly a Full-throttle Falcon 9 (http://spacenews.com/ses-rethinking-being-first-to-fly-on-a-full-throttle-falcon-9/)

Quote
“You know SpaceX is introducing into their manifest ... a modification of the current engine, with about a 20 percent increase in thrust," said Martin Halliwell, SES’s chief technical officer. "We’re making a decision internally as to whether we want to be the first to fly it.”

120%? That's 175klb. I don't think we've seen anything over 112% before for the upgrade have we?  This is along with densification would allow enough margin for boost back even with com SATs? How they get to 53t Without cross feed for FH?

The various percentages mentioned for this upgrade/uprate are all mixed.  If you want to know where SES's quoted 20% comes from, take Elon's statement that previous launches have all been running the M1D @ 85%, a 20% increase over that is actually 102% (0.85x + 0.2*0.85x=1.02x) or close enough to 100% to make no difference in PR-speak.  The confusion is whether the "20%" you're talking about is of the nominal 100% or just of the originally quoted 85%.

The bigger problem is that none of the calculated numbers are very consistent.  Some are based on math using quoted percentages, some are based on using quoted thrust levels, some are a mixture of the two, etc.  The best thing to do is just to read what Elon actually said about the M1D+ and ignore all the percentages: 
Quote from: Elon Musk
"at about 1.3 million pounds of thrust, and we're only actually operating the engines at about 85% of their potential. Down the road, in future missions, we anticipate being able to crank them up to their full thrust capability, which would give about 165,000 pounds of sea-level thrust per engine."

165klb of SL thrust per M1D+.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: TrueBlueWitt on 02/22/2015 03:32 am
Space News: SES Rethinking Being First To Fly a Full-throttle Falcon 9 (http://spacenews.com/ses-rethinking-being-first-to-fly-on-a-full-throttle-falcon-9/)

Quote
“You know SpaceX is introducing into their manifest ... a modification of the current engine, with about a 20 percent increase in thrust," said Martin Halliwell, SES’s chief technical officer. "We’re making a decision internally as to whether we want to be the first to fly it.”

120%? That's 175klb. I don't think we've seen anything over 112% before for the upgrade have we?  This is along with densification would allow enough margin for boost back even with com SATs? How they get to 53t Without cross feed for FH?

The various percentages mentioned for this upgrade/uprate are all mixed.  If you want to know where SES's quoted 20% comes from, take Elon's statement that previous launches have all been running the M1D @ 85%, a 20% increase over that is actually 102% (0.85x + 0.2*0.85x=1.02x) or close enough to 100% to make no difference in PR-speak.  The confusion is whether the "20%" you're talking about is of the nominal 100% or just of the originally quoted 85%.

The bigger problem is that none of the calculated numbers are very consistent.  Some are based on math using quoted percentages, some are based on using quoted thrust levels, some are a mixture of the two, etc.  The best thing to do is just to read what Elon actually said about the M1D+ and ignore all the percentages: 
Quote from: Elon Musk
"at about 1.3 million pounds of thrust, and we're only actually operating the engines at about 85% of their potential. Down the road, in future missions, we anticipate being able to crank them up to their full thrust capability, which would give about 165,000 pounds of sea-level thrust per engine."

165klb of SL thrust per M1D+.

1.3m/.85=1.53m
 1.53m/9=170klb

Guess we'll just have to wait and see...

Edit:

Interesting page claiming to show Merlin progression
http://www.b14643.de/Spacerockets_2/United_States_2/Falcon-IX/Merlin/index.htm
 
[email protected] and SL ISP of 286

200klb M1DV+
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Robotbeat on 02/22/2015 03:37 am
"About 85%" from what I can tell implies no more precision than 82.5-87.5%.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Lars-J on 02/22/2015 03:40 am
Why is this still being discussed? If it is 165klb according to Musk - what else is there to argue?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Kabloona on 02/22/2015 03:59 am

Interesting page claiming to show Merlin progression
http://www.b14643.de/Spacerockets_2/United_States_2/Falcon-IX/Merlin/index.htm
 
165klb @10.8MPa and SL ISP of 286


How refreshing...someone else who actually  heard Elon say 165klb...
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: deruch on 02/22/2015 04:07 am
"About 85%" from what I can tell implies no more precision than 82.5-87.5%.

Especially when his "1.3 million pounds of thrust" divides out to 144.4klbs per M1D if you assume he was using exact numbers.  Everything was rounded for public consumption.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Lars-J on 02/22/2015 04:45 am

Interesting page claiming to show Merlin progression
http://www.b14643.de/Spacerockets_2/United_States_2/Falcon-IX/Merlin/index.htm
 
165klb @10.8MPa and SL ISP of 286


Neat - and M1D has now doubled the M1A thrust, while staying the same size. (Actually is effectively more compact, since the thrust structure and gimbaling mechanism is much more compact)
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: S.Paulissen on 02/22/2015 03:11 pm

Interesting page claiming to show Merlin progression
http://www.b14643.de/Spacerockets_2/United_States_2/Falcon-IX/Merlin/index.htm
 
165klb @10.8MPa and SL ISP of 286


Neat - and M1D has now doubled the M1A thrust, while staying the same size. (Actually is effectively more compact, since the thrust structure and gimbaling mechanism is much more compact)

If this can be taken at face value it is really interesting, because it's not been clear to me whether the extra thrust came from opening the throat or increasing chamber pressure and Ae.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Kabloona on 02/22/2015 03:20 pm

Interesting page claiming to show Merlin progression
http://www.b14643.de/Spacerockets_2/United_States_2/Falcon-IX/Merlin/index.htm
 
165klb @10.8MPa and SL ISP of 286


Neat - and M1D has now doubled the M1A thrust, while staying the same size. (Actually is effectively more compact, since the thrust structure and gimbaling mechanism is much more compact)

If this can be taken at face value it is really interesting, because it's not been clear to me whether the extra thrust came from opening the throat or increasing chamber pressure and Ae.

The extra thrust can be gained by upping chamber pressure and mdot, so there is no need to change physical dimensions of the throat and nozzle.

http://forum.nasaspaceflight.com/index.php?topic=32983.msg1131598#msg1131598
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Robotbeat on 02/22/2015 03:42 pm

Interesting page claiming to show Merlin progression
http://www.b14643.de/Spacerockets_2/United_States_2/Falcon-IX/Merlin/index.htm
 
165klb @10.8MPa and SL ISP of 286


Neat - and M1D has now doubled the M1A thrust, while staying the same size. (Actually is effectively more compact, since the thrust structure and gimbaling mechanism is much more compact)

If this can be taken at face value it is really interesting, because it's not been clear to me whether the extra thrust came from opening the throat or increasing chamber pressure and Ae.

The extra thrust can be gained by upping chamber pressure and mdot, so there is no need to change physical dimensions of the throat and nozzle.

http://forum.nasaspaceflight.com/index.php?topic=32983.msg1131598#msg1131598
Yeah, greater chamber pressure is more likely than changing throat area to me.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: TrueBlueWitt on 02/22/2015 04:16 pm
I'm curious and don't have time to run numbers on volume lost due to additional
Tank shrinkage if they do sub cool?  It would be a function of delta Temp * thermal expansion coefficient to the 3rd power.. Correct?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: ZachS09 on 02/22/2015 05:26 pm
Should SpaceX call this higher-thrust engine the Merlin 1E?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: ugordan on 02/22/2015 05:29 pm
Should SpaceX call this higher-thrust engine the Merlin 1E?

We obviously need a poll to decide that.









   




(No, we don't really...)
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Mongo62 on 02/22/2015 05:33 pm
Should SpaceX call this higher-thrust engine the Merlin 1E?

I would not think so. It appears that the higher thrust was intended from the beginning. They are setting the 'standard' throttle from ~85% of planned thrust to ~100%. The upgrade might be as simple as a change to the engine firmware.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: docmordrid on 02/22/2015 06:46 pm
How about just M1D+, as Norbert Brügge had it in his Merlin table (http://www.b14643.de/Spacerockets_2/United_States_2/Falcon-IX/Merlin/index.htm)? More than a D, less than an E. Just for our discussion purposes.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Skyrocket on 02/22/2015 07:10 pm
How about just M1D+, as Norbert Brügge had it in his Merlin table (http://www.b14643.de/Spacerockets_2/United_States_2/Falcon-IX/Merlin/index.htm)? More than a D, less than an E. Just for our discussion purposes.

I would not rely on designations from the Brügge website. He is unfortunately very creative in inventing his own designations ("Voskhod-U", "PSLV-G+" etc.).

I would not introduce a new engine designation, unless there is confirmation of it. AFAIK, the uprated M-1D is pretty identical to the current M-1D, just certified for higher thrust.

Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: ChrisWilson68 on 02/22/2015 07:49 pm
Should SpaceX call this higher-thrust engine the Merlin 1E?

I would not think so. It appears that the higher thrust was intended from the beginning. They are setting the 'standard' throttle from ~85% of planned thrust to ~100%. The upgrade might be as simple as a change to the engine firmware.

And don't forget prop densification by lowering its temperature.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: ZachS09 on 02/22/2015 08:35 pm
How about just M1D+, as Norbert Brügge had it in his Merlin table (http://www.b14643.de/Spacerockets_2/United_States_2/Falcon-IX/Merlin/index.htm)? More than a D, less than an E. Just for our discussion purposes.

I would not rely on designations from the Brügge website. He is unfortunately very creative in inventing his own designations ("Voskhod-U", "PSLV-G+" etc.).

I would not introduce a new engine designation, unless there is confirmation of it. AFAIK, the uprated M-1D is pretty identical to the current M-1D, just certified for higher thrust.

Being certified for higher thrust reminds me of the Space Shuttle Main Engine: its normal maximum was 100% until 1983 when 104.5% became the maximum.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: enzo on 02/22/2015 11:04 pm
Sorry if this is an obvious question. After the 1D+ has been tested and validated, would they continue to use the new higher thrust for typical missions? I.e. low-mass payload, enough fuel for RTLS. In other words, if the goal is to maximize engine lifespan, does logic dictate running the engines slower when possible?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Comga on 02/23/2015 12:10 am
I'm curious and don't have time to run numbers on volume lost due to additional
Tank shrinkage if they do sub cool?  It would be a function of delta Temp * thermal expansion coefficient to the 3rd power.. Correct?

I think not, but almost.
It should be Delta-Temp*Coeff_of_Thermal_exp times 3
The volume of a cylinder is Pi*R^2*L*(1+dT*CTE)^3.
If the last term is expanded you get  1+ 3*dT*CTE +3*(dt*CTE)^2 +(dt*CTE)^3
The terms with higher powers of dt*CTE are insignificant.
The derivative of the constant term is zero.
The derivative of the second term with respect to temperature  is 3*Pi*R^2*L*CTE.  To get the volume change multiply by dt.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: meekGee on 02/23/2015 01:50 am
I'm curious and don't have time to run numbers on volume lost due to additional
Tank shrinkage if they do sub cool?  It would be a function of delta Temp * thermal expansion coefficient to the 3rd power.. Correct?

I think not, but almost.
It should be Delta-Temp*Coeff_of_Thermal_exp times 3
The volume of a cylinder is Pi*R^2*L*(1+dT*CTE)^3.
If the last term is expanded you get  1+ 3*dT*CTE +3*(dt*CTE)^2 +(dt*CTE)^3
The terms with higher powers of dt*CTE are insignificant.
The derivative of the constant term is zero.
The derivative of the second term with respect to temperature  is 3*Pi*R^2*L*CTE.  To get the volume change multiply by dt.

I remember when I had that conversation with my dad as a kid...
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: MP99 on 02/23/2015 06:43 am
Should SpaceX call this higher-thrust engine the Merlin 1E?
It appears to be the same engine with increased prop flow.

Cheers, Martin
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: S.Paulissen on 02/23/2015 02:43 pm
Should SpaceX call this higher-thrust engine the Merlin 1E?

I would not think so. It appears that the higher thrust was intended from the beginning. They are setting the 'standard' throttle from ~85% of planned thrust to ~100%. The upgrade might be as simple as a change to the engine firmware.

And don't forget prop densification by lowering its temperature.

There is no thrust increase strictly from increased prop density, just stage mass ratio increases. 
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: HMXHMX on 02/23/2015 04:24 pm
Should SpaceX call this higher-thrust engine the Merlin 1E?

I would not think so. It appears that the higher thrust was intended from the beginning. They are setting the 'standard' throttle from ~85% of planned thrust to ~100%. The upgrade might be as simple as a change to the engine firmware.

And don't forget prop densification by lowering its temperature.

There is no thrust increase strictly from increased prop density, just stage mass ratio increases. 

Centrifugal pumps are volume-pumping machines at constant rpm so density increases do increase flow rate and thus thrust.  Stage mass fraction has no effect on thrust.  The turbopump power also has to be increased to accommodate the increased mass flow at constant volume.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: cambrianera on 02/23/2015 07:53 pm
And the T/W ratio should be over 170  :o
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: S.Paulissen on 02/23/2015 10:55 pm
Should SpaceX call this higher-thrust engine the Merlin 1E?

I would not think so. It appears that the higher thrust was intended from the beginning. They are setting the 'standard' throttle from ~85% of planned thrust to ~100%. The upgrade might be as simple as a change to the engine firmware.

And don't forget prop densification by lowering its temperature.

There is no thrust increase strictly from increased prop density, just stage mass ratio increases. 

Centrifugal pumps are volume-pumping machines at constant rpm so density increases do increase flow rate and thus thrust.  Stage mass fraction has no effect on thrust.  The turbopump power also has to be increased to accommodate the increased mass flow at constant volume.

Just to clarify, I was not claiming that mass ratio increases thrust, I was claiming mass ratio increases with prop density.  Sorry I was not clear.  All else, we agree on.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: tp1024 on 03/03/2015 11:45 pm
And the T/W ratio should be over 170  :o

Which means that the engines make up about 0.7% of the total mass of the stage, whereas the tanks are on the order of 3-4%. While high T/W ratios are great (and I'd love to see a 200 there), it really doesn't matter all that much. Reducing tank mass and residual fuel mass is much more important in terms of performance - and so is any increase in ISP, even if it means a lower T/W ratio.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: MarekCyzio on 03/04/2015 12:53 am
AviationWeek posted an interesting article on updated Falcon 9/Merlin 1-D

http://aviationweek.com/space/upgraded-falcon-9-may-need-additional-certification

Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: BobHk on 03/04/2015 05:21 am
Sorry if this is an obvious question. After the 1D+ has been tested and validated, would they continue to use the new higher thrust for typical missions? I.e. low-mass payload, enough fuel for RTLS. In other words, if the goal is to maximize engine lifespan, does logic dictate running the engines slower when possible?

I'll try to find the quote but Musk indicated one of the reasons for the increase in thrust specifically was to allow for reusability/landing 1st stage when F9 has higher orbit flights:

https://twitter.com/elonmusk/status/572257004938403840 (https://twitter.com/elonmusk/status/572257004938403840)

Quote
Upgrades in the works to allow landing for geo missions: thrust +15%, deep cryo oxygen, upper stage tank vol +10%

So its not really needed for typical leo...
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: cambrianera on 03/04/2015 09:05 am
And the T/W ratio should be over 170  :o

Which means that the engines make up about 0.7% of the total mass of the stage, whereas the tanks are on the order of 3-4%. While high T/W ratios are great (and I'd love to see a 200 there), it really doesn't matter all that much. Reducing tank mass and residual fuel mass is much more important in terms of performance - and so is any increase in ISP, even if it means a lower T/W ratio.

Tanks should be at 2.3-2.5%.
I agree that any increase in ISP is more important, in terms of performance, than a higher T/W ratio.
But I'm amazed no one is giving merits to SpaceX for achieving such record figures.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Prober on 03/04/2015 10:30 pm
AviationWeek posted an interesting article on updated Falcon 9/Merlin 1-D

http://aviationweek.com/space/upgraded-falcon-9-may-need-additional-certification

http://forum.nasaspaceflight.com/index.php?topic=32983.msg1332549#msg1332549

just saying :)
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: macpacheco on 03/05/2015 03:10 am
Is there any possibility that SpaceX has been slowly ramping up max throttle on the M1D at each launch ? Like adding 1% per launch. The weight of those GEO payloads vs DeltaV to GEO, any data suggesting that ? Of course, increasing throttle without any of the other changes would result in just reduced gravity losses, or a relatively small performance gain.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: pericynthion on 03/05/2015 04:38 am
I don't think the higher thrust levels are possible without propellant densification.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: ChrisWilson68 on 03/05/2015 05:02 am
Is there any possibility that SpaceX has been slowly ramping up max throttle on the M1D at each launch ? Like adding 1% per launch. The weight of those GEO payloads vs DeltaV to GEO, any data suggesting that ? Of course, increasing throttle without any of the other changes would result in just reduced gravity losses, or a relatively small performance gain.

No, that's not consistent with what SES was saying about possibly giving up their upcoming launch spot because they didn't want to be on the first F9 flight with upgraded thrust.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: ChrisWilson68 on 03/05/2015 05:08 am
Should SpaceX call this higher-thrust engine the Merlin 1E?

I would not think so. It appears that the higher thrust was intended from the beginning. They are setting the 'standard' throttle from ~85% of planned thrust to ~100%. The upgrade might be as simple as a change to the engine firmware.

And don't forget prop densification by lowering its temperature.
There is no thrust increase strictly from increased prop density, just stage mass ratio increases. 

Centrifugal pumps are volume-pumping machines at constant rpm so density increases do increase flow rate and thus thrust.  Stage mass fraction has no effect on thrust.  The turbopump power also has to be increased to accommodate the increased mass flow at constant volume.
That doesn't really sound like very good logic. RPM and amount of propellant moved are both functions of power to the pump. Increased density isn't what's causing more flow. Power is.

HMXHMX is correct.  He's talking about mass flow when he says "density increases do increase flow rate" at constant RPM.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: S.Paulissen on 03/05/2015 04:07 pm
Can't we all just say that we all are agreeing with each other but from different perspectives? 

He chooses to see the rocket as a pumping machine with a fixed RPM.

I choose to see it as a heat pump with a fixed amount of pumping power.

I feel that my view is closer to the reality of taking an identical rocket and stuffing cold propellant in it instead of warm propellant.  I'm sure he feels that his view is closer to the reality of taking a rocket and optimizing it for colder propellants.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: cambrianera on 03/05/2015 05:57 pm
Power required by pump (any kind) is:
(DeltaP*Q)/Eta
Pressure differential multiplied volume flow rate divided efficiency.

Engine thrust is related to mass flow rate.

Increasing density you have more mass flow (more thrust) with same volume flow (same pumping power).

This is without taking into account pump (and piping) efficiency, related to viscosity.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: sugmullun on 03/07/2015 02:41 pm

Pressure differential multiplied volume flow rate divided efficiency.
Engine thrust is related to mass flow rate.
Increasing density you have more mass flow (more thrust) with same volume flow (same pumping power).

It would seem that unless you changed the geometry of the combustion/thrust chambers, that it's going to take higher pressures and temperatures to increase the thrust, and so pumping power.
The same orifice, the same (or close) mach 1?, higher pressure...
Centrifugal pumps are not volume machines, but pressure machines with the power needed being that to maintain a pressure at a given flow. The pressure is generated by the centripetal? acceleration of the mass and then the force outward.
I wonder how all this relates to the "sweet spot" Musk mentioned long ago.

edit: drifted a little.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Zed_Noir on 03/07/2015 05:00 pm

Pressure differential multiplied volume flow rate divided efficiency.
Engine thrust is related to mass flow rate.
Increasing density you have more mass flow (more thrust) with same volume flow (same pumping power).

It would seem that unless you changed the geometry of the combustion/thrust chambers, that it's going to take higher pressures and temperatures to increase the thrust, and so pumping power.
The same orifice, the same (or close) mach 1?, higher pressure...
Centrifugal pumps are not volume machines, but pressure machines with the power needed being that to maintain a pressure at a given flow. The pressure is generated by the centripetal? acceleration of the mass and then the force outward.
I wonder how all this relates to the "sweet spot" Musk mentioned long ago.

edit: drifted a little.

AIUI there is no changes to geometry of the engine require. Since the engine was likely designed for extra flow from the start. Just that SpaceX was running the Merlins at 85% flow rate from the design maximum possible flow rate. SoaceX in the future will run the Merlins at 100% flow rate.

It might be still possible for SpaceX to squeeze out a few more percent flow rate above 100% in the future. Hmm that will result in an engine  thrust to weight ratio of over 170 to 1.  :o
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Kabloona on 03/21/2015 01:51 pm
So what's going on here? Elon said the M1D was merely being throttled up from 85% to 100% thrust.

Now Gwynne says the upgraded rocket will be "30% more powerful" and that the engine upgrade is being qual tested.

Quote
In March 16 and 17 appearances at the Satellite 2015 conference here, Shotwell said the new-version Falcon 9, which has yet to be named, will be about 30 percent more powerful than the rocket’s current version. -

Quote
Shotwell said the company stopped full qualification of the Merlin 1D engine’s capabilities to keep the first Falcon 9 v1.1 flights on schedule. But the qualification work has continued.

“We’ve gone back and gotten that performance on the engine to place it on the vehicle,” Shotwell said. “So we’ve got a higher-thrust engine. We’ve finished development on that and are going into qual [qualification testing].

http://spacenews.com/spacex-aims-to-debut-new-version-of-falcon-9-this-summer/

Since the article says the upgraded vehicle will debut this summer on the SES mission, it seems that Elon's "85 to 100%" throttle-up comment and this article's "30% more powerful" are referring to the same vehicle upgrade.

So how does a throttle-up from 85% to 100% translate into a "30% more powerful" rocket?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: S.Paulissen on 03/21/2015 02:13 pm
30% more powerful is meaningless without knowing what exactly they're referring to with the word 'power'.  There is no reason to think she's countermanding Elon.

She's clearly talking about payload capability of the rocket... and probably payload to LEO.

Aerospace 101 style rocket equation of new numbers confirms ~30% more payload to orbit with 285ISP for first stage, 345ISP for second stage, +10% second stage tank volume and +9% propellant mass (approximated the weighted average of 10% LOX density and 5% RP-1 density).  New GLOW is 525613kg.  T/W at lift off is ~1.16:1.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: baldusi on 03/21/2015 02:18 pm
Well, we don't know how much will it be uprated. Apparently, they will also add densification, which means better pmf, and increase the volume of the upper stage. It's not clear from the article, but if the new core was the Falcon Heavy's enlarged boosters (+10% volume, I've estimated before), then they are not only uprating the engine but adding a lot of propellant through densification and extra volume.
Besides, the real question is 30% extra performance to which orbit. Have they optimized the US for GTO, while before was optimized for LEO? Are they talking about the previous performance target (4,8tonnes to a 1,800m/s) delta-v, or from what they said they could push it without their reserves (5.15 tonnes to same orbit). But if they add 30% to GTO, they would be competing on the 5.5 to 6.2 tonne market. That cover over 80% of the market.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Robotbeat on 03/21/2015 02:37 pm
30% more payload to GTO seems most likely. If you improve the mass fraction (which propellant densification does) or the Isp (which increased thrust usually does), then you're improving payload to GTO more than you are to LEO (which is also improved, of course).
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Elmar Moelzer on 03/21/2015 02:46 pm
I am not expert, but does not reducing the thrust of an engine to below design optimum also reduce the Isp? So if they reduced the throttled the engine down to 85% thrust, they would also reduce the Isp a bit and throttling it up to 100% would improve Isp as well. Densification will do the rest of the 30% increase in performance. That is at least my idea of what is happening.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Robotbeat on 03/21/2015 02:48 pm
I am not expert, but does not reducing the thrust of an engine to below design optimum also reduce the Isp? So if they reduced the throttled the engine down to 85% thrust, they would also reduce the Isp a bit and throttling it up to 100% would improve Isp as well. Densification will do the rest of the 30% increase in performance. That is at least my idea of what is happening.
It's about the chamber thrust and the nozzle expansion ratio. In existing engines, usually if you increase the thrust, you do so by increasing the chamber pressure (there are other ways to do it, but usually it means you're essentially producing a new engine).
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Kabloona on 03/21/2015 03:38 pm
30% more powerful is meaningless without knowing what exactly they're referring to with the word 'power'.  There is no reason to think she's countermanding Elon.

She's clearly talking about payload capability of the rocket... and probably payload to LEO.

Aerospace 101 style rocket equation of new numbers confirms ~30% more payload to orbit with 285ISP for first stage, 345ISP for second stage, +10% second stage tank volume and +9% propellant mass (approximated the weighted average of 10% LOX density and 5% RP-1 density).  New GLOW is 525613kg.  T/W at lift off is ~1.16:1.

Thanks, that clears things up.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Paul_G on 03/21/2015 05:25 pm
There's a thought on the lower throttle limit....

If SpaceX are saying that come the summer, we will see launches at 100% of throttle, rather than the 85%ish that we are apparently seeing now, does this have an impact on the achievable lower throttle ranges - if SpaceX are saying they can throttle to 40% (or 60% based on how you interpret the Elon statement on throttle range), what was that 40 / 60% throttle based on - the current max - 85%, or the 100% throttle rating that is coming this summer?

Paul
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: SpunkyEnigma on 03/23/2015 04:05 am
Got an idea bouncing around in my head, but need some info to noodle on.

Does anyone have the dimensions of the M1Dvac with and without the bell attached?   Cylinder or box dimensions will work.  Include the thrust vectoring assembly as well, looking for everything below the tank essentially.

Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Zed_Noir on 03/23/2015 05:43 am
A rather cryptic tweet from Elon
Tweet (https://twitter.com/elonmusk/status/579861658337574912)

Quote
Elon Musk @elonmusk  ·  2h 2 hours ago
Falcon 9 lifting off with 1.3 mmmillion pounds of force

Is he rounding up the thrust of the F9 core from 1.26M lbf or did SpaceX manage to squeeze out another 40000 lbf of thrust with maybe a gain of a few seconds in impulse?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: docmordrid on 03/23/2015 06:17 am
Last I checked 147,000 x 9 = 1,323,000

Sounds like you're using the initial design goal of 140,000 lbf.  Once the M1D was qualified in 2012 it was stated to be 147,000 lbf.

At the SES-8 teleconference the 1.3 mlbf (147,000 ea) current value and an upgrade to 165,000 lbf was mentioned.

https://soundcloud.com/matthew-clarke-30/spacex-ses-8-pre-launch
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: deruch on 03/23/2015 06:54 am
A rather cryptic tweet from Elon
Tweet (https://twitter.com/elonmusk/status/579861658337574912)

Quote
Elon Musk @elonmusk  ·  2h 2 hours ago
Falcon 9 lifting off with 1.3 mmmillion pounds of force

Is he rounding up the thrust of the F9 core from 1.26M lbf or did SpaceX manage to squeeze out another 40000 lbf of thrust with maybe a gain of a few seconds in impulse?

I think the important bit of information in that tweet is the extra "mm" in "mmmillion."  I'm pretty sure it's a play on the fact that he is using his Dr. Evil photo for his twitter profile pic.  Basically, the tweet is just an excuse to make a referrence joke (https://www.youtube.com/watch?v=EJR1H5tf5wE). 
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Kabloona on 03/23/2015 02:03 pm
And Elon forgot to mention in his tweet that the launch was for the Republic of Kerplakistan...
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: oldAtlas_Eguy on 03/23/2015 04:00 pm
The 30% improved performance (payload wise) would increase the F9 to [approximations payload values to show scale of increases]:

                                LEO                   GTO
Reusable              13.3 -> 17        4.5 -> 5.8
Fully Expendable   16 -> 20           5.2 -> 6.7

To put it in competitive payload capability with an Atlas V:
GTO AV-521 vs F9R, AV-531 vs F9E
LEO AV -531 vs F9R, AV-551 vs F9E


The LEO capability may be even great enough to launch a BA330 on a fully expendable F9 flight vs having to use a FH.

The basic thing is that the new performance numbers means that any payload services sold that required the use of an F9E (no legs) can now be performed by a F9R (with legs).

Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Chris Bergin on 03/23/2015 04:17 pm
Sexy:

Tom Mueller ‏@lrocket  27m27 minutes ago
A fresh batch of Merlin 1Ds ready to take flight.

https://twitter.com/lrocket/status/580048775961432064

Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Razer on 03/23/2015 10:40 pm
Is the stage that will be used for SES-9 missions ?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: S.Paulissen on 03/25/2015 12:29 am
Looks like they mildly changed octoweb.  Perhaps lacking white 'covers'?

Credit: SpaceX, via parabolicarc.
http://www.parabolicarc.com/wp-content/uploads/2014/10/SpaceX_Merlin_1D_octoweb.jpg
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: edkyle99 on 03/25/2015 01:22 am
Looks like they mildly changed octoweb.  Perhaps lacking white 'covers'?

Credit: SpaceX, via parabolicarc.
http://www.parabolicarc.com/wp-content/uploads/2014/10/SpaceX_Merlin_1D_octoweb.jpg

Where? I don't see a difference.
Right.  The base of the first few v1.1 rockets was white, but then changed to black. 

 - Ed Kyle
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: S.Paulissen on 03/25/2015 05:24 am
The 30% improved performance (payload wise) would increase the F9 to [approximations payload values to show scale of increases]:

                                LEO                   GTO
Reusable              13.3 -> 17        4.5 -> 5.8
Fully Expendable   16 -> 20           5.2 -> 6.7

To put it in competitive payload capability with an Atlas V:
GTO AV-521 vs F9R, AV-531 vs F9E
LEO AV -531 vs F9R, AV-551 vs F9E


The LEO capability may be even great enough to launch a BA330 on a fully expendable F9 flight vs having to use a FH.

The basic thing is that the new performance numbers means that any payload services sold that required the use of an F9E (no legs) can now be performed by a F9R (with legs).

I wish we would specify a little more clearly what we mean with things like 'GTO'.  There are a lot of GTO orbits and they are not the same.  One of which is SpaceX's GTO -1800m/s which is not comparable to, say, Ariane 5 GTO -1500m/s capability.   I know you know the difference, but it would be nice, as a reader, to not have to interpret what you mean quite as heavily. :)
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: eweilow on 03/25/2015 06:45 am
Looks like they mildly changed octoweb.  Perhaps lacking white 'covers'?

Credit: SpaceX, via parabolicarc.
http://www.parabolicarc.com/wp-content/uploads/2014/10/SpaceX_Merlin_1D_octoweb.jpg

Where? I don't see a difference.
Right.  The base of the first few v1.1 rockets was white, but then changed to black. 

 - Ed Kyle
Could it be "unpainted" TPS?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Giovanni DS on 03/25/2015 08:00 am
Looks like they mildly changed octoweb.  Perhaps lacking white 'covers'?

Credit: SpaceX, via parabolicarc.
http://www.parabolicarc.com/wp-content/uploads/2014/10/SpaceX_Merlin_1D_octoweb.jpg

Where? I don't see a difference.
Right.  The base of the first few v1.1 rockets was white, but then changed to black. 

Would that require a new certification?

/jk
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Rebel44 on 03/25/2015 09:05 am
The 30% improved performance (payload wise) would increase the F9 to [approximations payload values to show scale of increases]:

                                LEO                   GTO
Reusable              13.3 -> 17        4.5 -> 5.8
Fully Expendable   16 -> 20           5.2 -> 6.7

To put it in competitive payload capability with an Atlas V:
GTO AV-521 vs F9R, AV-531 vs F9E
LEO AV -531 vs F9R, AV-551 vs F9E


The LEO capability may be even great enough to launch a BA330 on a fully expendable F9 flight vs having to use a FH.

The basic thing is that the new performance numbers means that any payload services sold that required the use of an F9E (no legs) can now be performed by a F9R (with legs).

I wish we would specify a little more clearly what we mean with things like 'GTO'.  There are a lot of GTO orbits and they are not the same.  One of which is SpaceX's GTO -1800m/s which is not comparable to, say, Ariane 5 GTO -1500m/s capability.   I know you know the difference, but it would be nice, as a reader, to not have to interpret what you mean quite as heavily. :)

If I understand that corretly, satelite needs to use more fuel t finalize its orbit, if launhed on F9, compared to Atlas V o Proton-M? How much is that expected to change after planned F9 upgrade?

thx
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: deruch on 03/25/2015 12:25 pm
The 30% improved performance (payload wise) would increase the F9 to [approximations payload values to show scale of increases]:

                                LEO                   GTO
Reusable              13.3 -> 17        4.5 -> 5.8
Fully Expendable   16 -> 20           5.2 -> 6.7

To put it in competitive payload capability with an Atlas V:
GTO AV-521 vs F9R, AV-531 vs F9E
LEO AV -531 vs F9R, AV-551 vs F9E


The LEO capability may be even great enough to launch a BA330 on a fully expendable F9 flight vs having to use a FH.

The basic thing is that the new performance numbers means that any payload services sold that required the use of an F9E (no legs) can now be performed by a F9R (with legs).

I wish we would specify a little more clearly what we mean with things like 'GTO'.  There are a lot of GTO orbits and they are not the same.  One of which is SpaceX's GTO -1800m/s which is not comparable to, say, Ariane 5 GTO -1500m/s capability.   I know you know the difference, but it would be nice, as a reader, to not have to interpret what you mean quite as heavily. :)

How exactly do you suggest we do that?  SpaceX's numbers are either with or without 30% reserves for reuse already baked in; with or without the full thrust Merlin 1Ds already baked in; with or without the rest of the upgrades Elon mentioned--subchilling and +10% US volume-- already baked in; to a GTO that is 1800m/s short of GEO or one closer to GEO than that (ABS/Eutelsat was to about -1600m/s); realistic or somewhat wishful thinking; etc.

Which of the above underlying assumptions are people using as a baseline starting point for their numbers?  I too would be happy to have some more explicitly defined conditions listed but I don't really see any practical way of doing that until SpaceX clears up some of the ambiguity surrounding their claimed capabilities.  Until we get a new set of payload numbers from SpaceX to use as a baseline, one with the underlying assumptions explicitly laid out, I just don't see us being able to achieve much clarity on the subject.  Just my $0.02
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: abaddon on 03/25/2015 12:29 pm
Which of the above underlying assumptions are people using as a baseline starting point for their numbers?  I too would be happy to have some more explicitly defined conditions listed but I don't really see any practical way of doing that until SpaceX clears up some of the ambiguity surrounding their claimed capabilities.  Until we get a new set of payload numbers from SpaceX to use as a baseline, one with the underlying assumptions explicitly laid out, I just don't see us being able to achieve much clarity on the subject.  Just my $0.02

Our best data has been and will continue to be actual performance.  The SES-9 launch should be very interesting.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: spacenut on 03/25/2015 02:11 pm
If they are going to run at 85% power, would not engine out allow them to throttle up to 100% to insert properly?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: S.Paulissen on 03/25/2015 02:23 pm
The 30% improved performance (payload wise) would increase the F9 to [approximations payload values to show scale of increases]:

                                LEO                   GTO
Reusable              13.3 -> 17        4.5 -> 5.8
Fully Expendable   16 -> 20           5.2 -> 6.7

To put it in competitive payload capability with an Atlas V:
GTO AV-521 vs F9R, AV-531 vs F9E
LEO AV -531 vs F9R, AV-551 vs F9E


The LEO capability may be even great enough to launch a BA330 on a fully expendable F9 flight vs having to use a FH.

The basic thing is that the new performance numbers means that any payload services sold that required the use of an F9E (no legs) can now be performed by a F9R (with legs).

I wish we would specify a little more clearly what we mean with things like 'GTO'.  There are a lot of GTO orbits and they are not the same.  One of which is SpaceX's GTO -1800m/s which is not comparable to, say, Ariane 5 GTO -1500m/s capability.   I know you know the difference, but it would be nice, as a reader, to not have to interpret what you mean quite as heavily. :)

How exactly do you suggest we do that?  SpaceX's numbers are either with or without 30% reserves for reuse already baked in; with or without the full thrust Merlin 1Ds already baked in; with or without the rest of the upgrades Elon mentioned--subchilling and +10% US volume-- already baked in; to a GTO that is 1800m/s short of GEO or one closer to GEO than that (ABS/Eutelsat was to about -1600m/s); realistic or somewhat wishful thinking; etc.

Which of the above underlying assumptions are people using as a baseline starting point for their numbers?  I too would be happy to have some more explicitly defined conditions listed but I don't really see any practical way of doing that until SpaceX clears up some of the ambiguity surrounding their claimed capabilities.  Until we get a new set of payload numbers from SpaceX to use as a baseline, one with the underlying assumptions explicitly laid out, I just don't see us being able to achieve much clarity on the subject.  Just my $0.02

Not a single word of that addresses my point that you need to clarify what orbit you're talking about.  Talk about SpaceX payload claims is irrelevant (and furthermore is not as impossible to figure as you suggest.)
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: corneliussulla on 03/26/2015 09:22 am
If the new engine pushes the Falcon heavy towards 60 tonnes to LEO, won't this make the $1 billion Per launch 70 tonne SLS look DOA. $150 mill for 60 tonnes.$1000 mill for 70 tonnes ummm

Does anyone know the figures for falcon heavy with updated engines to LEO
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: notsorandom on 03/26/2015 12:49 pm
If the new engine pushes the Falcon heavy towards 60 tonnes to LEO, won't this make the $1 billion Per launch 70 tonne SLS look DOA. $150 mill for 60 tonnes.$1000 mill for 70 tonnes ummm

Does anyone know the figures for falcon heavy with updated engines to LEO
Since cross feeding is no longer being used on the Falcon Heavy I suspect that the upgrades will be used to get it to its advertised lift capacity. SLS is not a good comparison to make. SLS will be capable of almost 90 tonnes from the start. The lift capacity is under reported. The program wanted room for mass growth should it happen, but it hasn't.

The better metric to use instead of payload to low orbit is payload to L2, TLI, TMI. Those are the likely destinations based on the current mission architecture concepts. The only official figures I could find for the Falcon Heavy were to LEO, GTO, or Mars. So the comparison will have to use Mars instead of the more likely L2 or TLI. The Falcon Heavy is capable of 13.2 tonnes to Mars. SLS will initially be able to do 20.2 to Mars, and 31.7 tonnes with the EUS which could be as soon as the 2nd or 3rd launch. SLS will have almost 2.5 times the lift capacity to BEO destinations. It will be able to send more on a Mars trajectory than any currently flying rocket can to LEO.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: SVBarnard on 03/26/2015 01:19 pm

Since cross feeding is no longer being used on the Falcon Heavy I suspect that the upgrades will be used to get it to its advertised lift capacity.

I am such a newb  but why is cross feeding no longer being used for FH? How do y'all know when it aint even launched yet, has spacex disclosed said design details so many months before it even debuts?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: notsorandom on 03/26/2015 01:56 pm

Since cross feeding is no longer being used on the Falcon Heavy I suspect that the upgrades will be used to get it to its advertised lift capacity.

I am such a newb  but why is cross feeding no longer being used for FH? How do y'all know when it aint even launched yet, has spacex disclosed said design details so many months before it even debuts?
It was mentioned in the thread about Gwynne Shotwell's comments at UC Berkeley. The LEO payload for Falcon Heavy is now 53 tonnes according to the website not 52 as it had been. So it looks like SpaceX is updating the official figures on the website and that they are at least somewhat current.
http://forum.nasaspaceflight.com/index.php?topic=36879.msg1337655#msg1337655
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: GreenShrike on 03/26/2015 02:31 pm
I am such a newb  but why is cross feeding no longer being used for FH? How do y'all know when it aint even launched yet, has spacex disclosed said design details so many months before it even debuts?

From what I understand, it's too little gain from too much engineering design work and additional mission risk. If the upcoming thrust and ISP improvements to the Merlin 1Ds and associated increased propellant storage (densification, stretching, etc), mean that FH can reach its stated goals without developing and gluing on the crossfeed system, then there's little reason to make the investment.

This is especially true when payloads requiring super-heavy lift are rather scant on the drawing boards. Should a client actually need the performance adding crossfeed would give the Falcon Heavy, however, I'm sure SpaceX would be willing to work something out.

Until then, SpaceX already has rather a lot of work needing its attention -- like getting the FH flying in the first place. ;-)
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: spacenut on 03/26/2015 03:18 pm
Also, the outer boosters could operate at full power (165,000 lb thrust) upgraded mode, while the core can operate at a lower thrust to burn longer thus higher staging for the second stage.  13 tons to Mars is not bad.  They could send several small ISRU and power production units prior to human landing at a much lower cost than SLS.  Even two Falcon Heavy launches, docked, for 26 tons.  One with a Mars booster, and the other with the lander ISRU equipment that could match SLS at a lower cost.   Or they could launch a 50 ton unit and refuel it with Falcon 9 or another heavy for 50 tons unit to Mars. 

With all the SLS/Direct-Jupiter talk several years ago, several people suggested the next logical step up was 50 tons to LEO using Atlas heavies with solids, or Delta IV heavies with crossfeed and solids, and or Atlas V phase two that would have used existing off the shelf technologies to upgrade to 50 tons instead of spending a lot of money on SLS.  Even Direct-Jupiter using existing shuttle technology off the shelf was a better choice to get some serious deep space exploration started. 

SpaceX engine upgrades, booster landings, etc, are incrementally improving space flight and exploration.  Nasa's since founding, has been one big project after another, just to eventually shut it down instead of incrementally improving what they have.  First Saturn V shut down, now Shuttle. 
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: guckyfan on 03/26/2015 04:02 pm
13 tons to Mars is not bad.  They could send several small ISRU and power production units prior to human landing at a much lower cost than SLS.  Even two Falcon Heavy launches, docked, for 26 tons.  One with a Mars booster, and the other with the lander ISRU equipment that could match SLS at a lower cost.   Or they could launch a 50 ton unit and refuel it with Falcon 9 or another heavy for 50 tons unit to Mars. 


13t is not bad. 2t landed with Red Dragon is also not bad but quite limited in scope.

The other option would require expensive development. Much more likely they invest that development capability in MCT.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Hauerg on 03/26/2015 04:15 pm
Not developing Xfeed would indicate that the MCT booster might indeed not see a 3 core, wouldn'it.
But then this might still be too far away to play a role in first iteration of FH design.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: MikeAtkinson on 03/26/2015 04:24 pm
It was mentioned in the thread about Gwynne Shotwell's comments at UC Berkeley. The LEO payload for Falcon Heavy is now 53 tonnes according to the website not 52 as it had been. So it looks like SpaceX is updating the official figures on the website and that they are at least somewhat current.
http://forum.nasaspaceflight.com/index.php?topic=36879.msg1337655#msg1337655

It was 53 tonnes on or before the 5th May 2011 according to my notes.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Rebel44 on 04/06/2015 07:33 pm
Correct me, if I am wrong, but deeply cooled LOX will also provide part of performace incrase for high energy orbits, because it will slow down LOX boil-off.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: freds on 04/06/2015 09:12 pm
Correct me, if I am wrong, but deeply cooled LOX will also provide part of performace incrase for high energy orbits, because it will slow down LOX boil-off.

Actually no, as there is no boil-off during the ascent. However it does mean more mass in a smaller storage space to then be thrown out the tail pipe so to speak.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: nadreck on 04/06/2015 10:12 pm
Correct me, if I am wrong, but deeply cooled LOX will also provide part of performace incrase for high energy orbits, because it will slow down LOX boil-off.

Actually no, as there is no boil-off during the ascent. However it does mean more mass in a smaller storage space to then be thrown out the tail pipe so to speak.

There is no boil off while the engine is running, but during the coast phases, and given the goal to support coast phase all the way to a GEO injection burn to support one specific class of DoD contracts, this will make some difference, how much I don't know.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: cartman on 04/12/2015 10:52 pm
Hans said today that the upgraded merlins will fly in the 4th mission after SPX-6, the engines now run at 80% and they will go to full performance. It will bring the payload a little up, better return to land and barge landings on payloads that are more demanding, no significant change on the outside of the vehicle.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: dkovacic on 04/13/2015 12:18 pm
This is strange - SES-9 is supposed to be the mission for upgrade Merlins. Before they could launch Turkmenisat-1, Orbcomm og2 and what? Jason-3? In flight abort?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: mheney on 04/13/2015 01:59 pm
CRS-7
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: deruch on 04/13/2015 09:50 pm
This is strange - SES-9 is supposed to be the mission for upgrade Merlins. Before they could launch Turkmenisat-1, Orbcomm og2 and what? Jason-3? In flight abort?

If you watch the briefing, you'll see that he's not very sure about exactly how many flights will be launched between.  He said that he only focuses on the 2 upcoming launches at any time, so anything beyond those he's not too sure on.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Kaputnik on 05/15/2015 10:17 pm
Also, the outer boosters could operate at full power (165,000 lb thrust) upgraded mode, while the core can operate at a lower thrust to burn longer thus higher staging for the second stage.

There is no performance benefit in running at anything less than maximum throttle. "Staging later" just means more gravity losses.

(Unless the engine has higher isp at lower throttle, but this is the opposite of what is usual)
(And of course there may be structural reasons for throttling down, but that's getting into a trade between vehicle dry mass and extracting full performance from the engines)
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: ChrisWilson68 on 05/15/2015 10:36 pm
Also, the outer boosters could operate at full power (165,000 lb thrust) upgraded mode, while the core can operate at a lower thrust to burn longer thus higher staging for the second stage.

There is no performance benefit in running at anything less than maximum throttle. "Staging later" just means more gravity losses.

(Unless the engine has higher isp at lower throttle, but this is the opposite of what is usual)
(And of course there may be structural reasons for throttling down, but that's getting into a trade between vehicle dry mass and extracting full performance from the engines)

Of course there's a performance benefit from running the center booster at less than maximum throttle -- the benefit is that more of the propellant in the center core only has to lift the mass of the core, not the side boosters.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Avron on 05/15/2015 10:44 pm
Also, the outer boosters could operate at full power (165,000 lb thrust) upgraded mode, while the core can operate at a lower thrust to burn longer thus higher staging for the second stage.

There is no performance benefit in running at anything less than maximum throttle. "Staging later" just means more gravity losses.

(Unless the engine has higher isp at lower throttle, but this is the opposite of what is usual)
(And of course there may be structural reasons for throttling down, but that's getting into a trade between vehicle dry mass and extracting full performance from the engines)


Also, the outer boosters could operate at full power (165,000 lb thrust) upgraded mode, while the core can operate at a lower thrust to burn longer thus higher staging for the second stage.

There is no performance benefit in running at anything less than maximum throttle. "Staging later" just means more gravity losses.

(Unless the engine has higher isp at lower throttle, but this is the opposite of what is usual)
(And of course there may be structural reasons for throttling down, but that's getting into a trade between vehicle dry mass and extracting full performance from the engines)

Of course there's a performance benefit from running the center booster at less than maximum throttle -- the benefit is that more of the propellant in the center core only has to lift the mass of the core, not the side boosters.



also Musk never goes to 100% , there is always some capacity. it ensures a desirable outcome - re Pareto 
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Okie_Steve on 05/16/2015 01:04 am
Now that we hope to be seeing the "full thrust" Merlin 1-D configuration fly soon I have to wonder how long they've been planning this. Back when the Merlin 1-D was first introduced, I believe it was Tom Mueller who said there would not be a 1-E, which generated some discussion here. I wonder if he had a hard time keeping a straight face. Given later statements about needing to qualify and fly even though they realized the engines had more to give I suspect it's been since day 1 and the stage 2 stretch has been sitting on the shelf waiting for quite a while. I do wonder how much tweaking it took to qualify the Merlin-1D at full thrust.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: wannamoonbase on 05/16/2015 08:18 am
Now that we hope to be seeing the "full thrust" Merlin 1-D configuration fly soon I have to wonder how long they've been planning this. Back when the Merlin 1-D was first introduced, I believe it was Tom Mueller who said there would not be a 1-E, which generated some discussion here. I wonder if he had a hard time keeping a straight face. Given later statements about needing to qualify and fly even though they realized the engines had more to give I suspect it's been since day 1 and the stage 2 stretch has been sitting on the shelf waiting for quite a while. I do wonder how much tweaking it took to qualify the Merlin-1D at full thrust.

Given SpaceX's practice of using operational flights as part of development, I think there was a notion but not enough data for known values from the start.  It was important for them to get flying and show progress and book some revenue.  The size of stretch would have depended on performance values possible.

The U.S. Stretch maybe a result of increased performance as well as improved first stage recovery options.

There is no need to call the motor anything more than a 1D.  It's the same equipment with higher rating.  Like moving the redline on a car from 6000 to 6800 rpm.  They just have more confidence and data to work with now.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: AncientU on 05/16/2015 12:04 pm
They didn't move thr red line... they just developed technology (fuel densification) that allowed operation at the original 100% red line instead of at 85% like v1.1.

Edit: Changed version number
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: S.Paulissen on 05/16/2015 01:33 pm
They didn't move thr red line... they just developed technology (fuel densification) that allowed operation at the original 100% red line instead of at 85% like v1.0.
Highly speculative statement.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: TrueBlueWitt on 05/16/2015 02:06 pm
They didn't move thr red line... they just developed technology (fuel densification) that allowed operation at the original 100% red line instead of at 85% like v1.0.

It is unclear that fuel densification is required for operation at "100%"..   Does densification reduce potential for cavitation? Was that a limiting factor?

Also curious how they will call out thrust level.  With shuttle it was relative to original baseline so "operating at 104%".  Will it be re-baselined at 100 for new max thrust, or relative to Merlin 1D as operating today?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: AncientU on 05/16/2015 02:17 pm
They didn't move thr red line... they just developed technology (fuel densification) that allowed operation at the original 100% red line instead of at 85% like v1.0.
Highly speculative statement.

Don't think so.  EM said that they were operating at 85% on v1.1 and their fineness ratio (?) was near maximum.  Operating at 100% would have required an even longer profile because they were constrained in diameter. Densification allowed more propellant in same stage geometry. Small stretch of second stage was a knob to turn to use additional payload capability.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: baldusi on 05/16/2015 05:03 pm
I wonder if they tested them at 100% for those GTO missions where they only did a couple of burns after MECO1. That would have been quite an opportunity to test the 100% thottle level.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: baldusi on 05/16/2015 05:09 pm
Now that we hope to be seeing the "full thrust" Merlin 1-D configuration fly soon I have to wonder how long they've been planning this. Back when the Merlin 1-D was first introduced, I believe it was Tom Mueller who said there would not be a 1-E, which generated some discussion here. I wonder if he had a hard time keeping a straight face. Given later statements about needing to qualify and fly even though they realized the engines had more to give I suspect it's been since day 1 and the stage 2 stretch has been sitting on the shelf waiting for quite a while. I do wonder how much tweaking it took to qualify the Merlin-1D at full thrust.
I believe that it was as related to the huge margin for thurst increase that Merlin 1D had, but also becuase of the Raptor development. Whatever comes after Falcon will be a thing out of science fiction books. If you have seen the simulations that Dimitry and Hyperion 5 did of a Falcon 9 M with Mini-Raptors, and you consider densification and stretched upper stage as a possibility, you're talking about 30tonnes to LEO and 10 to GTO from a single stick.
In other words, Tom knew that anything that came after the Merlin 1D was going to be CH4/LOX full staged technology.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: MikeAtkinson on 05/16/2015 08:54 pm
Now that we hope to be seeing the "full thrust" Merlin 1-D configuration fly soon I have to wonder how long they've been planning this. Back when the Merlin 1-D was first introduced, I believe it was Tom Mueller who said there would not be a 1-E, which generated some discussion here. I wonder if he had a hard time keeping a straight face. Given later statements about needing to qualify and fly even though they realized the engines had more to give I suspect it's been since day 1 and the stage 2 stretch has been sitting on the shelf waiting for quite a while. I do wonder how much tweaking it took to qualify the Merlin-1D at full thrust.
I believe that it was as related to the huge margin for thurst increase that Merlin 1D had, but also becuase of the Raptor development. Whatever comes after Falcon will be a thing out of science fiction books. If you have seen the simulations that Dimitry and Hyperion 5 did of a Falcon 9 M with Mini-Raptors, and you consider densification and stretched upper stage as a possibility, you're talking about 30tonnes to LEO and 10 to GTO from a single stick.
In other words, Tom knew that anything that came after the Merlin 1D was going to be CH4/LOX full staged technology.

And that any further enhancements to Merlin would be for manufacturability, reliability and maintenance which would not involve any major changes, but lots of minor, mostly invisible changes. Definitely not deserving of a 1E moniker.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: sanman on 05/16/2015 09:45 pm
What market will be served by the fuller-thrust Merlin, with the other changes (densified propellant, stretched stage, etc)?

Doesn't F9R do everything it's supposed to right now, mission-wise?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: deruch on 05/16/2015 09:57 pm
What market will be served by the fuller-thrust Merlin, with the other changes (densified propellant, stretched stage, etc)?

Doesn't F9R do everything it's supposed to right now, mission-wise?

Same market but with more possibilities for recovery of the 1st stage.  Right now, that is not possible for GTO comsat missions.  With the changes, it will be for sats up to X tonnes.  "X" yet to be revealed/determined.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: sanman on 05/16/2015 10:03 pm
Same market but with more possibilities for recovery of the 1st stage.  Right now, that is not possible for GTO comsat missions.  With the changes, it will be for sats up to X tonnes.  "X" yet to be revealed/determined.

Will these changes propagate to Falcon Heavy also? Once the new generation appears, does the previous generation go obsolete and get retired?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Lars-J on 05/16/2015 10:09 pm
Same market but with more possibilities for recovery of the 1st stage.  Right now, that is not possible for GTO comsat missions.  With the changes, it will be for sats up to X tonnes.  "X" yet to be revealed/determined.

Will these changes propagate to Falcon Heavy also? Once the new generation appears, does the previous generation go obsolete and get retired?

Falcon Heavy will likely fly with these enhancements from the beginning.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: guckyfan on 05/16/2015 10:17 pm
Will these changes propagate to Falcon Heavy also? Once the new generation appears, does the previous generation go obsolete and get retired?

Very likely one reason for Falcon Heavy delays was the desire to introduce it with the new features.

The old version will be retired. I think the last one with the old features has already been produced and any new core will have the new setup.

I do wonder though if they will use subcooling for all starts or only if required. Uneducated guess, only when required.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Burninate on 05/17/2015 06:32 am
The 30% improved performance (payload wise) would increase the F9 to [approximations payload values to show scale of increases]:

                                LEO                   GTO
Reusable              13.3 -> 17        4.5 -> 5.8
Fully Expendable   16 -> 20           5.2 -> 6.7

To put it in competitive payload capability with an Atlas V:
GTO AV-521 vs F9R, AV-531 vs F9E
LEO AV -531 vs F9R, AV-551 vs F9E


The LEO capability may be even great enough to launch a BA330 on a fully expendable F9 flight vs having to use a FH.

The basic thing is that the new performance numbers means that any payload services sold that required the use of an F9E (no legs) can now be performed by a F9R (with legs).
I'm afraid the math doesn't work like that.  The only figure for which they might achieve 30% increase is actual payload to GTO, and the only reason it's so large is that the upper stage dry mass is 4-5 tons, so a 15% increase in mass to GTO represents a ~30% increase in *payload* to GTO.

Because upper stage dry mass is much smaller in relation to payload to LEO, and also because whatever propulsive advantages are causing all this add capability to the LEO->GTO transition as well as ascent->LEO, payload to GTO grows much faster than payload to LEO, where the improvement is probably more like ~10%.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Okie_Steve on 05/19/2015 02:37 am
This got me to thinking, is the thrust being uprated on both the booster and vacuum engines? I don't remember seeing it specified and just improving the second stage would probably be the biggest help.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: guckyfan on 05/19/2015 04:56 am
This got me to thinking, is the thrust being uprated on both the booster and vacuum engines? I don't remember seeing it specified and just improving the second stage would probably be the biggest help.

The second stage engine is overpowered already. No need to upgrade unless it involves a sizable ISP increase too. The second stage upgrade is in the tank stretch.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: groundbound on 05/19/2015 05:10 am
This got me to thinking, is the thrust being uprated on both the booster and vacuum engines? I don't remember seeing it specified and just improving the second stage would probably be the biggest help.

The second stage engine is overpowered already. No need to upgrade unless it involves a sizable ISP increase too. The second stage upgrade is in the tank stretch.

But isn't an ISP increase implicit? How do you get more thrust without increasing the chamber pressure?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: ArbitraryConstant on 05/19/2015 06:20 am
But isn't an ISP increase implicit? How do you get more thrust without increasing the chamber pressure?
What if the preburner requires proportionally greater propellant?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Rebel44 on 05/19/2015 08:50 am
I would expect that fuel densification will be used for the second stage - it should reduce LOX boil off rate for long coast missons. With both fuel densification and incresed volume of second stage, uprating might make sense - it would slighly increase Isp + reduce gravity losses in first part of (second stage) flight - after that engines would be throttled anyway.

Please correct me, if I got it wrong.
/not-a rocket-scientist/
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Okie_Steve on 05/19/2015 03:56 pm
Since LOX and RP densify at different rates S2 needs the stretch to keep the ratio's correct. Unless they've been flying with one of the tanks partially full where do you put much extra propellant on S1? As I recall, RP is the limiting factor so stuffing in as much of that as you can and matching that with less or less chilled LOX limits how much more propellant can be loaded into S1. Given the relative importance of S2 performance for beyond LEO I'm guessing that only S2 will benefit much from densification. But, increased thrust on S1 will reduct gravity losses a bit and in this business every little bit counts. Will the S1 LOX be chilled to the same temperature as needed for S2 resulting in a partial fill or will it be chilled/densified less than S2 resulting in a full tank? No point in lifting extra oxidizer for the booster since it's job is over quickly and long term boil off is a non issue.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: baldusi on 05/19/2015 04:03 pm
But isn't an ISP increase implicit? How do you get more thrust without increasing the chamber pressure?
What if the preburner gas generator requires proportionally greater propellant?
I tried to calculate the isp of the uprated Merlin 1D Vac, but I found out that the gas generator (this is not staged combustion) dumped mass basically cancelled out the increase in Pc. A bigger expansion ratio would otherwise help, though.
BTW, I've estimated the new US T/W to be around 1.08+/-0.02. Which is surprisingly close to par to every single other US save Centaur and DIVUS 4m and 5m. BTW, Dual Centaur is around 0.84, so it would seem that for 2 stage rockets, 0.85~1.1 is the desirable T/W. What the Falcon 9 v1.1 has is an amazing pmf. Like in record breaking better than most LV first stage pmf. And the v1.2 (or what they will actually call it) will probably be better yet.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Okie_Steve on 05/19/2015 07:36 pm
Hmmm, how big a change would it be to adjust the relative s1 tanks to optimize for chilled prop?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: foltster on 05/19/2015 08:21 pm
Hmmm, how big a change would it be to adjust the relative s1 tanks to optimize for chilled prop?

There is discussion about this in other threads, I just can't find where right now.  Probably the General Falcon 9 thread somewhere.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: AncientU on 05/19/2015 09:10 pm
Hmmm, how big a change would it be to adjust the relative s1 tanks to optimize for chilled prop?

There is discussion about this in other threads, I just can't find where right now.  Probably the General Falcon 9 thread somewhere.
Discussion there was that it would only require repositioning the common bulkhead.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Kabloona on 05/19/2015 09:26 pm
Hmmm, how big a change would it be to adjust the relative s1 tanks to optimize for chilled prop?

There is discussion about this in other threads, I just can't find where right now.  Probably the General Falcon 9 thread somewhere.
Discussion there was that it would only require repositioning the common bulkhead.

Discussion here:

http://forum.nasaspaceflight.com/index.php?topic=36815.msg1347978#msg1347978
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: deruch on 06/25/2015 02:39 am
Cool picture of SpaceX spin forming a Merlin engine nozzle from SpaceX's Instagram acct.

https://instagram.com/p/4QVWKdl8Ux/
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: PahTo on 06/25/2015 03:57 pm

Great photo--thanks deruch.  The nozzle expansion looks huge--is this a Merlin Vac or is this just early in the process and they will "bring it in" to a smaller diameter?  (I realize they will "bring it in" regardless, but ...)
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: abaddon on 06/25/2015 04:31 pm

Great photo--thanks deruch.  The nozzle expansion looks huge--is this a Merlin Vac or is this just early in the process and they will "bring it in" to a smaller diameter?  (I realize they will "bring it in" regardless, but ...)

Merlin 1D nozzles are explosive formed.  This is a 1D-Vac extension.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: pospa on 06/25/2015 07:38 pm

Great photo--thanks deruch.  The nozzle expansion looks huge--is this a Merlin Vac or is this just early in the process and they will "bring it in" to a smaller diameter?  (I realize they will "bring it in" regardless, but ...)
Merlin 1D nozzles are explosive formed.  This is a 1D-Vac extension.
I don't think so. Explosively formed is inner and outer layer of combustion chamber with integrated cooling channels. Nozzle shouldn't be produced that way sice its made out of one layer of quite thin sheet of metal.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: blazotron on 07/08/2015 06:26 am
I found this exchange with Tom Mueller amusing.  I'm not a Quora expert, but it appears to be one of only two things he has posted so he must really have wanted to set the record straight!

"The Merlin 1D weighs 1030 pounds, including the hydraulic steering (TVC) actuators.  It makes 162,500 pounds of thrust in vacuum.  that is nearly 158 thrust/weight.  The new full thrust variant weighs the same and makes about 185,500 lbs force in vacuum.  You can do the math!  BTW, I believe most other engines don't include the thrust vector control actuators in their F/W numbers."

http://www.quora.com/Is-SpaceXs-Merlin-1Ds-thrust-to-weight-ratio-of-150+-believable

I've often wondered which engines include TVC actuators in their reported masses as we now know M1D does, and which engines consider them part of the stage systems?  RD-180 presumably includes them since they appear to be part of the engine/thrust structure assembly, but SSME presumably does not?  The frequently quoted 137:1 thrust-to-weight ratio of the NK-33, against which M1D is often compared, presumably also does not include TVC actuators as it had none in the configuration the NK-15 flew on the N1 vehicle, and which NK-33 was intended to replace.  Anyone know the story for LR-87-5 which is also claimed to have a very high thrust-to-weight ratio (although strangely does not usually make it into lists of high thrust-to-weight engines)?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Semmel on 07/08/2015 07:43 am
Why does it read "Former launch engineer at SpaceX"? Is Tom Mueller not with SpaceX any more?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: QuantumG on 07/08/2015 07:46 am
Why does it read "Former launch engineer at SpaceX"? Is Tom Mueller not with SpaceX any more?

That is weird. According to his LinkedIn profile (https://www.linkedin.com/pub/thomas-mueller/3b/451/209) his job title has changed but he's still at SpaceX.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: intrepidpursuit on 07/08/2015 05:38 pm
"The Merlin 1D weighs 1030 pounds, including the hydraulic steering (TVC) actuators.  It makes 162,500 pounds of thrust in vacuum.  that is nearly 158 thrust/weight.  The new full thrust variant weighs the same and makes about 185,500 lbs force in vacuum.  You can do the math!  BTW, I believe most other engines don't include the thrust vector control actuators in their F/W numbers."

http://www.quora.com/Is-SpaceXs-Merlin-1Ds-thrust-to-weight-ratio-of-150+-believable

Doing the math... That is a 180:1 thrust/weight ratio. That is insane! This is certainly more of a testament to improved manufacturing techniques since there are so few american liquid rocket engines developed in the last 2 decades, but whatever the reason the results are impressive.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: UberNobody on 07/08/2015 05:49 pm
180:1 thrust to weight...  Absolutely incredible. 

I guess that's what happens when you push the limits of RP-1 without switching to staged combustion.

I look forward to future progress with Raptor!
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: mme on 07/08/2015 07:49 pm
Why does it read "Former launch engineer at SpaceX"? Is Tom Mueller not with SpaceX any more?

That is weird. According to his LinkedIn profile (https://www.linkedin.com/pub/thomas-mueller/3b/451/209) his job title has changed but he's still at SpaceX.
I seem to recall there is more than one person named "Tom Mueller" that works (has worked) at SpaceX.  The Tom Mueller that is a founding employee of SpaceX was never a "launch engineer", he's always headed up propulsion (though his title may have changed.)

Edit: Nevermind.  There was another Tom Mueller online that claimed to work at SpaceX, but I should have followed the Quora link to the profile.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: llanitedave on 07/08/2015 08:35 pm
His title has changed.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: ClaytonBirchenough on 07/08/2015 09:22 pm
Why does it read "Former launch engineer at SpaceX"? Is Tom Mueller not with SpaceX any more?

That is weird. According to his LinkedIn profile (https://www.linkedin.com/pub/thomas-mueller/3b/451/209) his job title has changed but he's still at SpaceX.

Looks like a focus on Mars......Raptor? EDIT: i.e. does the nozzle maybe become under expanded?

Just speculation? Or did I miss something on his Linkedin?

And I wonder, is the 180:1 T/W ratio accompanied with a drop in performance?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: philw1776 on 07/09/2015 02:20 am
Why does it read "Former launch engineer at SpaceX"? Is Tom Mueller not with SpaceX any more?

That is weird. According to his LinkedIn profile (https://www.linkedin.com/pub/thomas-mueller/3b/451/209) his job title has changed but he's still at SpaceX.

Looks like a focus on Mars......Raptor? EDIT: i.e. does the nozzle maybe become under expanded?

Just speculation? Or did I miss something on his Linkedin?

And I wonder, is the 180:1 T/W ratio accompanied with a drop in performance?

No, the thrust is increased
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: cuddihy on 07/09/2015 02:30 am
180:1 thrust to weight...  Absolutely incredible. 

I guess that's what happens when you push the limits of RP-1 without switching to staged combustion.

I look forward to future progress with Raptor!

FFSC will likely have much lower T/W due to requirement for an additional preburner, turbine, and gas flow piping that raises mass considerably. Somewhat compensated by higher combustion pressure and higher ISP
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Llian Rhydderch on 07/09/2015 05:04 am
"The Merlin 1D weighs 1030 pounds, including the hydraulic steering (TVC) actuators.  It makes 162,500 pounds of thrust in vacuum.  that is nearly 158 thrust/weight.  The new full thrust variant weighs the same and makes about 185,500 lbs force in vacuum.  You can do the math!  BTW, I believe most other engines don't include the thrust vector control actuators in their F/W numbers."

http://www.quora.com/Is-SpaceXs-Merlin-1Ds-thrust-to-weight-ratio-of-150+-believable

Doing the math... That is a 180:1 thrust/weight ratio. That is insane! This is certainly more of a testament to improved manufacturing techniques since there are so few american liquid rocket engines developed in the last 2 decades, but whatever the reason the results are impressive.

Question:  Might SpaceX have changed manufacturing technique for the "full-thrust" Merlin 1D?  Perhaps 3D-printing the thrust chamber to reduce weight?  Sounds a bit crazy, but read on.

Musk said this week at the ISSRDC that they are 3D-printing LOTS of engine parts for Raptor, and we know they are doing so for Super Draco.  He emphasized lower weight as a result.  Link to the source, and summary of what he said, is in another NSF thread, here (http://forum.nasaspaceflight.com/index.php?topic=37839.msg1402002#msg1402002).

If SpaceX is perhaps simply changing the manufacturing technique of some parts of the Merlin 1D as part of the full-thrust engine, that would result in a crazy high thrust-to-weight ratio.


Edited to clarify.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: AncientU on 07/09/2015 12:45 pm
"The Merlin 1D weighs 1030 pounds, including the hydraulic steering (TVC) actuators.  It makes 162,500 pounds of thrust in vacuum.  that is nearly 158 thrust/weight.  The new full thrust variant weighs the same and makes about 185,500 lbs force in vacuum.  You can do the math!  BTW, I believe most other engines don't include the thrust vector control actuators in their F/W numbers."

http://www.quora.com/Is-SpaceXs-Merlin-1Ds-thrust-to-weight-ratio-of-150+-believable

Doing the math... That is a 180:1 thrust/weight ratio. That is insane! This is certainly more of a testament to improved manufacturing techniques since there are so few american liquid rocket engines developed in the last 2 decades, but whatever the reason the results are impressive.

Question:  Might SpaceX have changed manufacturing technique for the "full-thrust" Merlin 1D?  Perhaps 3D-printing the thrust chamber to reduce weight?  Sounds a bit crazy, but read on.

Musk said this week at the ISSRDC that they are 3D-printing LOTS of engine parts for Raptor, and we know they are doing so for Super Draco.  He emphasized lower weight as a result.  Link to the source, and summary of what he said, is in another NSF thread, here (http://forum.nasaspaceflight.com/index.php?topic=37839.msg1402002#msg1402002).

If SpaceX is perhaps simply changing the manufacturing technique of some parts of the Merlin 1D as part of the full-thrust engine, that would result in a crazy high thrust-to-weight ratio.


Edited to clarify.

The TM quote says that the weight remain the same.  Makes sense in that M1-D was only operating at 85% in v1.1. 
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: AncientU on 07/09/2015 12:49 pm
180:1 thrust to weight...  Absolutely incredible. 

I guess that's what happens when you push the limits of RP-1 without switching to staged combustion.

I look forward to future progress with Raptor!

FFSC will likely have much lower T/W due to requirement for an additional preburner, turbine, and gas flow piping that raises mass considerably. Somewhat compensated by higher combustion pressure and higher ISP

Two questions:
1. What was the previous record holder for gas gen T/W?
2. Couldn't SpaceX apply same techniques/technology to shatter the records for SC engines?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Dante80 on 07/09/2015 04:23 pm
180:1 thrust to weight...  Absolutely incredible. 

I guess that's what happens when you push the limits of RP-1 without switching to staged combustion.

I look forward to future progress with Raptor!

FFSC will likely have much lower T/W due to requirement for an additional preburner, turbine, and gas flow piping that raises mass considerably. Somewhat compensated by higher combustion pressure and higher ISP

Two questions:
1. What was the previous record holder for gas gen T/W?
2. Couldn't SpaceX apply same techniques/technology to shatter the records for SC engines?

1. Don't know about gas gen but I think that the absolute best TWR engine right now (for first stage at least) is the RD-275M, with a rating of something like 173 for vacuum thrust (and 158 for sl). For RP-1/LOX, the second best performer after merlin is NK-33. Both are SC engines.

2. New manufacturing techniques always help, but remember that one of SXs main goals is to produce engines with higher than normal margins for re-usability purposes. We will have to see.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: MP99 on 07/11/2015 09:19 am
I found this exchange with Tom Mueller amusing.  I'm not a Quora expert, but it appears to be one of only two things he has posted so he must really have wanted to set the record straight!

"The Merlin 1D weighs 1030 pounds, including the hydraulic steering (TVC) actuators.  It makes 162,500 pounds of thrust in vacuum.  that is nearly 158 thrust/weight.  The new full thrust variant weighs the same and makes about 185,500 lbs force in vacuum.  You can do the math!  BTW, I believe most other engines don't include the thrust vector control actuators in their F/W numbers."

http://www.quora.com/Is-SpaceXs-Merlin-1Ds-thrust-to-weight-ratio-of-150+-believable

I've often wondered which engines include TVC actuators in their reported masses as we now know M1D does, and which engines consider them part of the stage systems?  RD-180 presumably includes them since they appear to be part of the engine/thrust structure assembly, but SSME presumably does not?  The frequently quoted 137:1 thrust-to-weight ratio of the NK-33, against which M1D is often compared, presumably also does not include TVC actuators as it had none in the configuration the NK-15 flew on the N1 vehicle, and which NK-33 was intended to replace.  Anyone know the story for LR-87-5 which is also claimed to have a very high thrust-to-weight ratio (although strangely does not usually make it into lists of high thrust-to-weight engines)?
I've been out of the loop for a while, but those numbers (at least at the vac stage of the burn) are basically 114% thrust vs current.

Cheers, Martin
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: MP99 on 07/11/2015 09:20 am


180:1 thrust to weight...  Absolutely incredible. 

I guess that's what happens when you push the limits of RP-1 without switching to staged combustion.

I look forward to future progress with Raptor!

Conversely, don't most manufacturers quote T:W at sea level, not vac?

Cheers, Martin
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: PreferToLurk on 07/11/2015 11:20 pm
I found this exchange with Tom Mueller amusing.  I'm not a Quora expert, but it appears to be one of only two things he has posted so he must really have wanted to set the record straight!

"The Merlin 1D weighs 1030 pounds, including the hydraulic steering (TVC) actuators.  It makes 162,500 pounds of thrust in vacuum.  that is nearly 158 thrust/weight.  The new full thrust variant weighs the same and makes about 185,500 lbs force in vacuum.  You can do the math!  BTW, I believe most other engines don't include the thrust vector control actuators in their F/W numbers."

http://www.quora.com/Is-SpaceXs-Merlin-1Ds-thrust-to-weight-ratio-of-150+-believable

I've often wondered which engines include TVC actuators in their reported masses as we now know M1D does, and which engines consider them part of the stage systems?  RD-180 presumably includes them since they appear to be part of the engine/thrust structure assembly, but SSME presumably does not?  The frequently quoted 137:1 thrust-to-weight ratio of the NK-33, against which M1D is often compared, presumably also does not include TVC actuators as it had none in the configuration the NK-15 flew on the N1 vehicle, and which NK-33 was intended to replace.  Anyone know the story for LR-87-5 which is also claimed to have a very high thrust-to-weight ratio (although strangely does not usually make it into lists of high thrust-to-weight engines)?
I've been out of the loop for a while, but those numbers (at least at the vac stage of the burn) are basically 114% thrust vs current.

Cheers, Martin

Actually it is at least 4k lbf less than the spacex website currently states.  Though those figures are obviously rounded since they quote 1500000 lbf for the whole stage, and reaching such a round number by chance would be extraordinary.  It is also highly believable just because of the source, which isn't 100% certain to actually be THE Thomas Mueller, but the profile links to his facebook account, so if it isnt THE Thomas Mueller than he has a serious identity theft problem.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: cuddihy on 07/16/2015 02:24 am
Again, SC and especially FFSC is going to decrease, not increase T:W over GG.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: R7 on 07/16/2015 06:42 am
And switching from RP-1 to methane decreases T/W too. Overall propellant density drops, larger plumbing required and TP needs to do more work.

Merlin has stellar T/W because it has modest Isp for a modern kerolox engine. IIRC it has best Isp for GG kerolox engine but that's because its the first modern clean sheet design of that type since ... since ... the 60s? What was the last American kerolox GG engine that went to production? RS-27 (a H-1 touch up) ? The russians dont even bother with that type because they pushed SC kerolox technology about as far as it can be pushed already in the 60s/70s.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: wannamoonbase on 07/17/2015 04:14 am
The russians dont even bother with that type because they pushed SC kerolox technology about as far as it can be pushed already in the 60s/70s.

70s/80s, don't give them too much credit. What they accomplished was amazing but from the mid 60's onward they were 10 years behind the American program.  For example their shuttle program.  Also, how many liquid hydrogen engines have come out of USSR/Russia?

The excellence in Soviet technology, although impressive has not been unsurpassed because others simply have gone down a different path.

Edit: Spelling

Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Impaler on 07/19/2015 07:48 pm
The russians dont even bother with that type because they pushed SC kerolox technology about as far as it can be pushed already in the 60s/70s.

70s/80s, don't give them too much credit. What they accomplished was amazing but from the mid 60's onward they were 10 years behind the American program.  For example their shuttle program.  Also, how many liquid hydrogen engines have come out of USSR/Russia?

The excellence in Soviet technology, although impressive has not been unsurpassed because others simply have gone down a different path.

Edit: Spelling

But the Russians seems to have gone down the RIGHT path (hydrocarbon rather then hydrogen and solids), being much further along on a wrong track doesn't put you ahead, if anything it's a road block (due to vested interests) to actually getting to the right solution.  The Russians mistake was to try to do copy our path rather then sticking with their own.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: DanseMacabre on 07/19/2015 10:00 pm
The russians dont even bother with that type because they pushed SC kerolox technology about as far as it can be pushed already in the 60s/70s.

70s/80s, don't give them too much credit. What they accomplished was amazing but from the mid 60's onward they were 10 years behind the American program.  For example their shuttle program.  Also, how many liquid hydrogen engines have come out of USSR/Russia?

The excellence in Soviet technology, although impressive has not been unsurpassed because others simply have gone down a different path.

Edit: Spelling

But the Russians seems to have gone down the RIGHT path (hydrocarbon rather then hydrogen and solids), being much further along on a wrong track doesn't put you ahead, if anything it's a road block (due to vested interests) to actually getting to the right solution.  The Russians mistake was to try to do copy our path rather then sticking with their own.

On what basis are you stating that Kerolox is the "right" path over LH2/LOX? As I understand it, both have their uses in different situations.

I believe the choice of rocket fuel is simply a design decision based on the intended market and application of the launch vehicle.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: guckyfan on 07/20/2015 05:19 am
I believe the choice of rocket fuel is simply a design decision based on the intended market and application of the launch vehicle.

Correct. If you want to maximise cost to get the largest profit out of cost + contracts, first stages with LH plus solids are the path of choice.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Tev on 07/20/2015 07:09 am
The russians dont even bother with that type because they pushed SC kerolox technology about as far as it can be pushed already in the 60s/70s.

70s/80s, don't give them too much credit. What they accomplished was amazing but from the mid 60's onward they were 10 years behind the American program.  For example their shuttle program.  Also, how many liquid hydrogen engines have come out of USSR/Russia?

The excellence in Soviet technology, although impressive has not been unsurpassed because others simply have gone down a different path.

Edit: Spelling

Their excellence in kerolox SC engines has been surpassed by whom?
Overall they're clearly behind, but in this area (pretty much only one close to being ontopic) they haven't yet been beaten.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: oldAtlas_Eguy on 07/20/2015 04:33 pm
The following is a table summary of the M1D through its many forms. Please update and correct any errors in the values of the table.

EngineMerlin 1D (Design)Merlin 1D (Test article)Merlin 1D (Production)Merlin 1D (Plus)
SL Thrust140klbf?147klbf168klbf?
Vac Thrust155klbf?(better than expected)161klbf184klbf?
SL isp280s??282s282s?
Vac isp310s309s?311s311s?
T/W160?150+157?
Chamber Pressure1410psi? 1410psi?1410psi?
Expansion1616?16?(this shouldn’t vary much from design)16
Throttle range70-100%70%-100%?70%-100%70%-100%?
Engine weight 440kg??485kg?485kg?
Costs<M1C?-<M1C=M1D(Production)
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Rebel44 on 07/28/2015 09:53 pm
Some interesting new info

170klbf thrust at sea level and 210klbf in vacuum  :)

https://twitter.com/stephenclark1/status/626099566840918016

Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: mfck on 07/28/2015 10:06 pm
That looks like F9 1.0 with legs and Dragon 2.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: S.Paulissen on 07/29/2015 12:01 am
The following is a table summary of the M1D through its many forms. Please update and correct any errors in the values of the table.

EngineMerlin 1D (Design)Merlin 1D (Test article)Merlin 1D (Production)Merlin 1D (Plus)
SL Thrust140klbf?147klbf168klbf?
Vac Thrust155klbf?(better than expected)161klbf184klbf?
SL isp280s??282s282s?
Vac isp310s309s?311s311s?
T/W160?150+157?
Chamber Pressure1410psi? 1410psi?1410psi?
Expansion1616?16?(this shouldn’t vary much from design)16
Throttle range70-100%70%-100%?70%-100%70%-100%?
Engine weight 440kg??485kg?485kg?
Costs<M1C?-<M1C=M1D(Production)

I would be -very- surprised if the new thrust was achieved without a commensurate increase in ISP since they presumably are not redoing the thrust chamber to open the throat.  (I.e. they modestly increased chamber pressure.)  But that's just speculation.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: rcoppola on 07/29/2015 12:54 am
In the slides posted above, thanks for that btw, it shows a "Center Pusher" under the Mvac during stage sep.
I don't recall ever seeing that. I wonder if that was needed because of the new thrust profile and/or 2nd stage stretch. Was the bell extended along with the interstage requiring an additional guide or is it because the pushers along the interstage are no longer able to push the stretched 2nd stage without additional help. Or all of the above.

Has that ever been done before...this center line, internal pusher?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: llanitedave on 07/29/2015 12:58 am
That "Center Pusher" stage separation system is something I'd never heard of.  Is that the current technique?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: rcoppola on 07/29/2015 01:04 am
That "Center Pusher" stage separation system is something I'd never heard of.  Is that the current technique?
I don't think so. They currently use 4 pushers spaced around the perimeter of the interstage. I've never seen an indication of a center pusher, either in assembly photos or 2nd stage sep videos from mission launches.

Edit: I'm going to post over in the general vehicle thread. This isn't really thread specific and I'm really curious about this.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: ClayJar on 07/29/2015 02:24 am
In the slides posted above, thanks for that btw, it shows a "Center Pusher" under the Mvac during stage sep.
I don't recall ever seeing that. I wonder if that was needed because of the new thrust profile and/or 2nd stage stretch. Was the bell extended along with the interstage requiring an additional guide or is it because the pushers along the interstage are no longer able to push the stretched 2nd stage without additional help. Or all of the above.

Since the first graphic specifically says "Additional pusher to guide full thrust nozzle during stage separation", I'd say that the bell being extended and requiring an additional guide fits the description.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Prober on 07/29/2015 04:06 pm
In the slides posted above, thanks for that btw, it shows a "Center Pusher" under the Mvac during stage sep.
I don't recall ever seeing that. I wonder if that was needed because of the new thrust profile and/or 2nd stage stretch. Was the bell extended along with the interstage requiring an additional guide or is it because the pushers along the interstage are no longer able to push the stretched 2nd stage without additional help. Or all of the above.

Has that ever been done before...this center line, internal pusher?

maybe they are going for a composite nozzle,  or the reverse of the RL-10 on Delta to push the nozzle into lock.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: cambrianera on 07/29/2015 04:48 pm
@oldAtlas_Eguy:
T/W for M1D+ should be 175 instead of 157 (digit swap?).
Also the value of 1030 lb for M1D mass translates in 470 kg.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: wannamoonbase on 07/29/2015 10:17 pm
Some interesting new info

170klbf thrust at sea level and 210klbf in vacuum  :)

It will be interesting to see what happens to the specific impulse for the vacuum version.  210,000 is a 26,000 more than the expected number listed in the table.

Anyway have a guess?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: MP99 on 07/30/2015 12:43 am
I would be -very- surprised if the new thrust was achieved without a commensurate increase in ISP since they presumably are not redoing the thrust chamber to open the throat.  (I.e. they modestly increased chamber pressure.)  But that's just speculation.

Some of the energy in the prop has to be used to bring the liquids up from sub-cooled temperatures to the v1.1 temps. That has the potential to reduce Isp.

Cheers, Martin
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: TrueBlueWitt on 07/30/2015 12:49 am
Some interesting new info

170klbf thrust at sea level and 210klbf in vacuum  :)

It will be interesting to see what happens to the specific impulse for the vacuum version.  210,000 is a 26,000 more than the expected number listed in the table.

Anyway have a guess?

Not sure that's true.. the 210klbf in the NASA slide is for the M1Dvac(full thrust)  The guess at 184klbf would be for M1D(full thrust) in a vacuum.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: ArbitraryConstant on 07/30/2015 03:17 am
70s/80s, don't give them too much credit. What they accomplished was amazing but from the mid 60's onward they were 10 years behind the American program.
Were that the case losing access to 1980s Soviet engine technology would not be a crisis for American assured access to space.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: ChrisWilson68 on 07/30/2015 04:03 am
70s/80s, don't give them too much credit. What they accomplished was amazing but from the mid 60's onward they were 10 years behind the American program.
Were that the case losing access to 1980s Soviet engine technology would not be a crisis for American assured access to space.

No, that doesn't logically follow.

I'm not saying I agree that the Russian program was technologically behind the American in engine technology.  But hypothetically, even if the Russian program were technologically inferior, we could still have the Atlas V engine crisis simply because we chose to use Russian engines to keep Russian rocket engineers from being hired by Iran and North Korea and/or because it was cheaper.  Either way, we could become dependent on Russian engines for Atlas V because we chose to, not because we couldn't have built engines just as good or better ourselves.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: ArbitraryConstant on 07/30/2015 06:17 am
No, that doesn't logically follow.
Perhaps, but we can also see the outcome of attempts to do hydrogen boost and the technology gap for American attempts to do hydrocarbon boost, which rules out the other possibilities. These aren't equally valid technology tracks. Hydrocarbon boost is really better. The US finally getting credible ORSC hydrocarbon boost is probably the biggest advance in American spaceflight in generations, but even then it's not quite up to RD-180 standards. AR-1 and BE-4 look to be a regression in ISP.

Raptor might be the exception and truly represent unambiguous technological leadership, but that is completely decoupled from the rest of US space policy, that's basically Musk unilaterally deciding that American rocket propulsion technology peaked with RS-27 and going it alone.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: abaddon on 07/30/2015 01:41 pm
Were that the case losing access to 1980s Soviet engine technology would not be a crisis for American assured access to space.

It's only a "crisis" because the rocket was designed for the engine and slotting in a new engine that is not designed identically is a big effort.  And developing a new engine takes time.  Kicking that can down the road repeatedly has created this "crisis".

Regardless, that window is closing, and the not-so-distant future will see only one US LV provider (and a marginal one at that) relying on Russian engine technology.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: ArbitraryConstant on 07/30/2015 04:46 pm
It's only a "crisis" because the rocket was designed for the engine and slotting in a new engine that is not designed identically is a big effort.  And developing a new engine takes time.
Granted, but AFAICT AR-1 still has reduced ISP. More akin to an uprated NK-33. That's nothing to complain about but when the US resets and picks up where the Soviets were in the 1960s/70s and it's an improvement, it's really hard to believe the two technology bases are equal but different.

Of the primary hydrogen engines in play (SSME, RS-68, RL-10) I think only RL-10 really counts in making the case for American leadership here, and it's not a boost engine or remotely new, so it still looks like most propulsion work done post-Apollo didn't net out to much. SSME is a technological marvel but is really hard to fit into vehicles worth having.

Other areas, like the extremely refined stage build around the engine (Centaur) are where the US has a big advantage. Put a Russian engine on an American rocket and it's the best in the world if you can afford it. And the fact that the US completely dominates in-space capabilities (vast majority of successful Mars missions, monopoly beyond Jupiter).

Regardless, that window is closing, and the not-so-distant future will see only one US LV provider (and a marginal one at that) relying on Russian engine technology.
Yes, changing tracks and resetting to 1960s/70s Soviet technology is an improvement, and more than enough for viable launch capability. It may never be economical to replicate RD-180/191.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: oldAtlas_Eguy on 07/30/2015 10:36 pm
A note about the RL-10 and why it and the Centaur made the US so successful in interplanetary missions is that it had high reliability and a low dry weight with a high Delta-V capability that was needed for all those IP missions to be successful in the first place.

Now back to the M1D and specifically the M1D+. The M1D+VAC engine with 210klbf would mean that the engines needs to be able to throttle down to 50% in order to keep the max g's for the lighter GEO sat missions (3mt payload) to remain under 7g's.

So is there new values for the throttle ranges?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: The Roadie on 07/31/2015 01:30 am
Ballast would cut down the max G without new levels of throttling.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Herb Schaltegger on 07/31/2015 03:10 am
Ballast would cut down the max G without new levels of throttling.
Ballast on an upper stage sufficiently to reduce max g-loading makes zero sense. Payload is king, especially in high-energy missions like commercial GTO.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: guckyfan on 07/31/2015 05:59 am
Payload is king, especially in high-energy missions like commercial GTO.

Yes, the payload is king. What counts is its safe and sound delivery. What is the problem with ballast when doing this for a lightweight payload requires either a reengineering or ballast?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: ArbitraryConstant on 07/31/2015 06:46 am
Payload is king, especially in high-energy missions like commercial GTO.
Yes, the payload is king. What counts is its safe and sound delivery. What is the problem with ballast when doing this for a lightweight payload requires either a reengineering or ballast?
Why reengineering? They'd know the specs MVac 1D+ needed to hit from the outset. It's just engineering.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: guckyfan on 07/31/2015 06:59 am
Why reengineering? They'd know the specs MVac 1D+ needed to hit from the outset. It's just engineering.

the 1D+ is still a Merlin 1D basically. To lower throttle they would need to do a lot of reengineering. It is completely unnecessary if ballast can do the same.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: MP99 on 07/31/2015 07:45 am


Payload is king, especially in high-energy missions like commercial GTO.

Yes, the payload is king. What counts is its safe and sound delivery. What is the problem with ballast when doing this for a lightweight payload requires either a reengineering or ballast?

Suppose you turn a 3t payload into 5t payload + ballast.

The lighter payload allows enough margin to recover the first stage, so perhaps you've now made that impossible.

More importantly, Ariane launches from close to the equator, and drops the payload 1500 m/s short of GSO.

Falcon launches from Florida, and GTO leaves the payload 1800 m/s short of GSO. The extra prop the sat must expend reduces its lifetime on orbit.

F9 can launch to a super synchronous orbit (80,000 km) if the payload is small enough, which reduces the dV penalty on the payload. It can't do this if it's ballasted down.

So the answer to your "what is the problem" question is that it shortens the lifespan of the satellite once it reaches orbit. Which reduces the value of the launch, and therefore the price that can be charged.

Cheers, Martin
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: guckyfan on 07/31/2015 08:04 am

So the answer to your "what is the problem" question is that it shortens the lifespan of the satellite once it reaches orbit. Which reduces the value of the launch, and therefore the price that can be charged.

Cheers, Martin

No it doesn't. We are talking about very light satellites that get accelerated too much. That would be satellites that are well below F9 capabilities. Heavier satellites won't need ballast.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: ArbitraryConstant on 07/31/2015 08:22 am
the 1D+ is still a Merlin 1D basically. To lower throttle they would need to do a lot of reengineering. It is completely unnecessary if ballast can do the same.
Don't think that follows.

First it's not obvious that the changes would raise the minimum throttle point. They qualified it for higher pressure, not seeing why that would raise the minimum pressure, or if it did, that the increase would be proportional.

Second, couldn't the original MVac throttle even when M1C couldn't? Can't be that bad.

Third, isn't flow separation the main throttling constraint on 1D? Irrelevant for MVac 1D.

I'm sure ballast would be considered if necessary, but not seeing the obvious necessity.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: guckyfan on 07/31/2015 08:58 am
I'm sure ballast would be considered if necessary, but not seeing the obvious necessity.

I also don't see an obvious necessity. I just say they would use it over engine redesign.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: MP99 on 07/31/2015 02:17 pm

So the answer to your "what is the problem" question is that it shortens the lifespan of the satellite once it reaches orbit. Which reduces the value of the launch, and therefore the price that can be charged.

Cheers, Martin

No it doesn't. We are talking about very light satellites that get accelerated too much. That would be satellites that are well below F9 capabilities. Heavier satellites won't need ballast.

My highlight:-
The M1D+VAC engine with 210klbf would mean that the engines needs to be able to throttle down to 50% in order to keep the max g's for the lighter GEO sat missions (3mt payload) to remain under 7g's.

This is exactly the weight range that has already been put into SSO on earlier F9 flights. IIRC, this pushed F9 sufficiently that they did not have the margin to do all burns for first stage recovery.

cheers, Martin
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: oldAtlas_Eguy on 08/01/2015 08:09 pm
If there is a minimum operational pressure for the M1D or M1D+, it would be such that the same pressure level for the 75% throttle position of the M1D would be the same as the 60% throttle position on the M1D+. This would be the same throttle position for both the M1D(+) and M1DVAC(+) versions sets.

What this means is that for lighter payloads there has always been a minimum total payload weight such that either ballasting or secondary payloads are added to keep the g's within the level that the payload singed up for.

BTW the payload users guide specifies max g's at 7g's which is somewhat of an industry standard so that if you design your sat to meet that level and a few other environment values you have little limitation on which LV can be used.

So basically I believe we have identified that the M1D+ has a possible new throttle position related to the original minimum TC pressure point which on the M1D+ would be at 60%.

Edit: This is not to say that certain very light payloads have not been made to meet a higher g value so no basllasting would be used and higher delta V's could be achieved.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Prober on 08/14/2015 05:12 pm
Bumped into this enjoy!

Servo Motors Survive Space X Launch Conditions
Robust Servo Motors Survive Launch Conditions to Optimize Rocket Fuel Burn

http://www.micromo.com/applications/aerospace-defense/space-x-shuttle-launch

Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: guckyfan on 08/14/2015 09:42 pm
It is probably old. They use photos of the 1.0 with the tic tac toe arrangement.

Edit: still interesting.  :)
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: oldAtlas_Eguy on 08/14/2015 11:08 pm
It does give a confirmation that the mixture is tweaked in flight by the software.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Kabloona on 08/15/2015 10:09 pm
Bumped into this enjoy!

Servo Motors Survive Space X Launch Conditions
Robust Servo Motors Survive Launch Conditions to Optimize Rocket Fuel Burn

http://www.micromo.com/applications/aerospace-defense/space-x-shuttle-launch

That's a nice little window into SpaceX's design and procurement philosophy. Use commercial off the shelf non-aerospace components where possible, design with plenty of margin, do qual testing in-house. Those servo units probably cost them a small fraction of what an aerospace qualified unit from, say, Moog would cost.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Elmar Moelzer on 08/18/2015 02:04 am
Image of new Merlin (1D something?) version posted by SpaceX today:
https://instagram.com/p/6gYIwJl8ZH/
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Damon Hill on 08/18/2015 02:06 am
Wicked.   Paint, or anodizing?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Ohsin on 08/18/2015 03:49 am
Quote from: SpaceX
Upgraded Merlin rocket engine with special black coating for thermal testing

Attached
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Elmar Moelzer on 08/18/2015 05:34 am
Is this a significantly updated version of the Merlin engine (like a Merlin 1E), or is this just the Merlin 1D with full thrust. In the latter case I would have to wonder why they need to test its thermal properties. I would have assumed that they already tested all this a long time ago?
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Jarnis on 08/18/2015 05:50 am
Is this a significantly updated version of the Merlin engine (like a Merlin 1E), or is this just the Merlin 1D with full thrust. In the latter case I would have to wonder why they need to test its thermal properties. I would have assumed that they already tested all this a long time ago?

We have no idea how old this picture is... Could easily be many months ago.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Kaputnik on 08/18/2015 06:57 am
According to their Facebook page, this is "special black coating for improved thermal testing"
Whatever that means...
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: MATTBLAK on 08/18/2015 07:03 am
Is this a significantly updated version of the Merlin engine (like a Merlin 1E), or is this just the Merlin 1D with full thrust. In the latter case I would have to wonder why they need to test its thermal properties. I would have assumed that they already tested all this a long time ago?

We have no idea how old this picture is... Could easily be many months ago.


That picture is very near current.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Jet Black on 08/18/2015 07:53 am
Is this a significantly updated version of the Merlin engine (like a Merlin 1E), or is this just the Merlin 1D with full thrust. In the latter case I would have to wonder why they need to test its thermal properties. I would have assumed that they already tested all this a long time ago?

It depends on what the upgrades are. Additionally it is data for their own confidence and confidence of their customers.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: grythumn on 08/18/2015 03:39 pm
According to their Facebook page, this is "special black coating for improved thermal testing"
Whatever that means...

Probably wanted something with known emissivity to get accurate and consistent non-contact/IR temperature readings across different materials and surface finishes.

http://www.npl.co.uk/reference/faqs/what-is-emissivity-and-why-is-it-important-%28faq-thermal%29
http://www.tnp-instruments.com/sitebuildercontent/sitebuilderfiles/Infrared%20Thermometer%20and%20Emissivity.pdf

-Bob
EDIT: Add some URLs.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: sghill on 08/18/2015 06:17 pm
According to their Facebook page, this is "special black coating for improved thermal testing"
Whatever that means...

Maybe because the shiny chrome gets all sooty on the trip up, and they need to test it dirty for improved accuracy.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: freds on 08/18/2015 11:12 pm
Maybe because the shiny chrome gets all sooty on the trip up, and they need to test it dirty for improved accuracy.

Maybe they are looking ahead to reuse, the chrome can burn off where as this can simply be retouched up(grin)!

I have one of the pictures of the almost landing as my desktop and engines look fairly dark after use anyway.
 
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: russianhalo117 on 08/18/2015 11:57 pm
Quote from: SpaceX
Upgraded Merlin rocket engine with special black coating for thermal testing

Attached
center engine already had a partiall coating full is for all engines
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Okie_Steve on 08/19/2015 12:56 am
Ha, they say it is a thermal coating but they are really just going for that cool SR-71 look.

I told my wife I was lusting after an hourglass figure, she thought it was funny.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: S.Paulissen on 08/19/2015 12:58 am
The 'stand' of sorts the engine bell is in, is the same type of hold-down/support used for the Merlin 1d vac?  Is this method (at least the main) reason the M1D-vac needs the 'stiffener' ring that comes off in after the first few seconds of stage 2 firing?

EDIT:picture added
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: MechE31 on 08/19/2015 11:53 am
The 'stand' of sorts the engine bell is in, is the same type of hold-down/support used for the Merlin 1d vac?  Is this method (at least the main) reason the M1D-vac needs the 'stiffener' ring that comes off in after the first few seconds of stage 2 firing?

EDIT:picture added

MVAC nozzle is a soft Niobium nozzle that needs some help to prevent deformation.

M1D is not a soft metal. The stand is just to keep the engine upright and secure.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: S.Paulissen on 08/19/2015 01:51 pm
The 'stand' of sorts the engine bell is in, is the same type of hold-down/support used for the Merlin 1d vac?  Is this method (at least the main) reason the M1D-vac needs the 'stiffener' ring that comes off in after the first few seconds of stage 2 firing?

EDIT:picture added

MVAC nozzle is a soft Niobium nozzle that needs some help to prevent deformation.

M1D is not a soft metal. The stand is just to keep the engine upright and secure.

I was under the impression that the M1D was the metal niobium bell and that the Vac had a carbon-carbon nozzle extension.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: PreferToLurk on 08/19/2015 04:28 pm
The 'stand' of sorts the engine bell is in, is the same type of hold-down/support used for the Merlin 1d vac?  Is this method (at least the main) reason the M1D-vac needs the 'stiffener' ring that comes off in after the first few seconds of stage 2 firing?

EDIT:picture added

MVAC nozzle is a soft Niobium nozzle that needs some help to prevent deformation.

M1D is not a soft metal. The stand is just to keep the engine upright and secure.

I was under the impression that the M1D was the metal niobium bell and that the Vac had a carbon-carbon nozzle extension.

The carbon-carbon extension was put on hold after it became a pacing problem for the V1.1.  I have not heard any news related to it since.  M1DVac uses niobium currently.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: edkyle99 on 08/19/2015 04:40 pm
The 'stand' of sorts the engine bell is in, is the same type of hold-down/support used for the Merlin 1d vac?  Is this method (at least the main) reason the M1D-vac needs the 'stiffener' ring that comes off in after the first few seconds of stage 2 firing?

EDIT:picture added

MVAC nozzle is a soft Niobium nozzle that needs some help to prevent deformation.

M1D is not a soft metal. The stand is just to keep the engine upright and secure.

I was under the impression that the M1D was the metal niobium bell and that the Vac had a carbon-carbon nozzle extension.
My understanding is that Merlin Vacuum is not just a Merlin 1D with a nozzle extension.  I think it has a different base nozzle as well.  I'm not sure about the thrust chamber.

 - Ed Kyle
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: edkyle99 on 08/19/2015 04:49 pm
Is this a significantly updated version of the Merlin engine (like a Merlin 1E), or is this just the Merlin 1D with full thrust. In the latter case I would have to wonder why they need to test its thermal properties. I would have assumed that they already tested all this a long time ago?
Full thrust Merlin 1D.  They may have been awaiting a turbopump upgrade, or something similar, before being able to put full-thrust into development testing.  Also, this coating may be for a cluster firing on the first "v1.2" stage, or something.  Maybe.  Or maybe not.

 - Ed Kyle
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Lars-J on 08/19/2015 05:40 pm
The 'stand' of sorts the engine bell is in, is the same type of hold-down/support used for the Merlin 1d vac?  Is this method (at least the main) reason the M1D-vac needs the 'stiffener' ring that comes off in after the first few seconds of stage 2 firing?

EDIT:picture added

MVAC nozzle is a soft Niobium nozzle that needs some help to prevent deformation.

M1D is not a soft metal. The stand is just to keep the engine upright and secure.

I was under the impression that the M1D was the metal niobium bell and that the Vac had a carbon-carbon nozzle extension.
My understanding is that Merlin Vacuum is not just a Merlin 1D with a nozzle extension.  I think it has a different base nozzle as well.  I'm not sure about the thrust chamber.

 - Ed Kyle

Correct. The nozzle (even without the extension) has different geometry, and there are many other differences between the M1D and the M1D-Vac. (ducting of turbopump exhaust is just one of them)

Think of it as M1D and the M1D-Vac as two of an engine family - some part are shared, but there are more differences than the naming suggests.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: cambrianera on 08/19/2015 09:43 pm
Thermal imaging makes it possible to get a validation of CFD models (widely used for heat exchangers).
If this is the case, black coating is only for testing and is used to get good and constant emissivity (as pointed out by grythumn http://forum.nasaspaceflight.com/index.php?topic=32983.msg1417223#msg1417223)
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: HMXHMX on 09/19/2015 05:36 pm
Perhaps someone can help answer a question about the Merlin 1D Vac engine...

As I understand the current booster engine layout, the TPA is hard-mounted to the thrust structure (a la LR-79 or RS-27A) and pump outflow reaches the engine injector and cooling jacket via lines that include dual bellows.  Is the second stage layout similar?  Or does the TPA gimbal with the engine (since the turbine exhaust is dumped into the bell and not separately overboard as in earlier versions)?

From two images below I can't tell. 

Thanks to anyone who can clarify.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: cambrianera on 09/19/2015 06:11 pm
Until Merlin 1C the TPA assembly was mounted partially on the thrust structure (following combustion chamber only on 1 DOF); movement was compensated with bellows.
On Merlin 1D TPA gimbals completely with engine and this is true specially for 1D Vac, where TPA exaust goes into nozzle.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: cambrianera on 09/19/2015 06:28 pm
Picture show the struts linking the TPA to the thrust structure (Merlin 1C).
Movement is allowed in the direction of the arrows.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: cambrianera on 09/19/2015 06:49 pm
Three more pics:
-first one shows pump casing suspended to the thrust structure (M1C);
-second one shows M1D with TPA backpacked, TVC actuators are disconnected (no thrust structure in this picture);
-third shows M1D complete with thrust structure (upper plate to be integrated on octoweb).
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Prober on 09/19/2015 06:54 pm
Picture show the struts linking the TPA to the thrust structure (Merlin 1C).
Movement is allowed in the direction of the arrows.

uh oh, you said the magic word "struts", who wants to be the first with the questions?
 
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: HMXHMX on 09/19/2015 09:57 pm
Until Merlin 1C the TPA assembly was mounted partially on the thrust structure (following combustion chamber only on 1 DOF); movement was compensated with bellows.
On Merlin 1D TPA gimbals completely with engine and this is true specially for 1D Vac, where TPA exaust goes into nozzle.

Thanks very much.
Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
Post by: Dante80 on 09/21/2015 10:33 am
Some "new" (changed 20 days ago) numbers on the SpaceX website (http://www.spacex.com/falcon9).
  • Merlin 1D vac thrust is now 934kN / 210.000lbf, isp is now 348s, burn time is 397s
  • Merlin 1D FT thrust is now 756kN / 170.000lbf (SL) and  825kN / 185.500lbf (vac), burn time is 162s

  • From a first glance, it seems like the plan is to offload work from the first stage (18s less burning time) to make stage recovery easier.
    Also, any idea what would the TWR be now?
  • Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: cambrianera on 09/21/2015 12:29 pm
    From here : http://forum.nasaspaceflight.com/index.php?topic=32983.msg1401598#msg1401598
    You get weight 1030 lb.

    T/W 165 (sl) 180 (vac) !!!!!!!!

    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Dante80 on 09/21/2015 01:32 pm
    T/W 165 (sl) 180 (vac) !!!!!!!!

    Thats pretty nice (especially since high TWR makes a lot of sense for 1st stage propulsion). It also says there that the weight is with the thrust vector control actuators, and those are sometimes not counted on other engines when TWR results are published.

    Any idea how much those actuators would weigh?

    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: wannamoonbase on 09/21/2015 02:29 pm
    From a first glance, it seems like the plan is to offload work from the first stage (18s less burning time) to make stage recovery easier.
    Also, any idea what would the TWR be now?
    [/li]
    [/list]

    You need to look at more than the burn time.  Look at the velocity of the stage at engine shutdown.

    Yes SpaceX has increased density of the fuel and oxidizer, but that is probably not enough on it's own.  The increase in thrust is coming from putting more fuel through the engine in the same amount of time.

    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: dunderwood on 09/21/2015 03:37 pm
    Not sure where you're getting the info that the M1C, MVac or M1D turbopumps gimbal.  The M1DVac is the only one that does.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Dante80 on 09/21/2015 04:26 pm
    You need to look at more than the burn time.  Look at the velocity of the stage at engine shutdown.

    Yes SpaceX has increased density of the fuel and oxidizer, but that is probably not enough on it's own.  The increase in thrust is coming from putting more fuel through the engine in the same amount of time.

    You are absolutely right. Both S1 and S2 look to be lengthened (at least the according to the renders (http://i.imgur.com/etScOp3.jpg) in the spaceX site), and we know that there is more propellant in there (due to that, and also due to densification). The higher thrust means that the engines will burn more fuel for the same burn time, thus the stage could reach the same velocity when separation comes. 
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: oldAtlas_Eguy on 09/21/2015 04:30 pm
    Some "new" (changed 20 days ago) numbers on the SpaceX website (http://www.spacex.com/falcon9).
  • Merlin 1D vac thrust is now 934kN / 210.000lbf, isp is now 348s, burn time is 397s
  • Merlin 1D FT thrust is now 756kN / 170.000lbf (SL) and  825kN / 185.500lbf (vac), burn time is 162s

  • From a first glance, it seems like the plan is to offload work from the first stage (18s less burning time) to make stage recovery easier.
    Also, any idea what would the TWR be now?
  • Where did you find the ISP values? 348 was the earlier estimate for M1DVAC. Was there any actual ISP published so we can determine if the TC pressure has increased?
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: guckyfan on 09/21/2015 04:39 pm
    Where did you find the ISP values? 348 was the earlier estimate for M1DVAC. Was there any actual ISP published so we can determine if the TC pressure has increased?

    It is on the SpaceX website. Click on the interstage of Falcon 9. It opens a window with some data, including the ISP 348.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Dante80 on 09/21/2015 04:39 pm
    Where did you find the ISP values? 348 was the earlier estimate for M1DVAC. Was there any actual ISP published so we can determine if the TC pressure has increased?

    The current (for M-1D vac - FT) isp is listed here (http://www.spacex.com/falcon9). Just click on the "inside the interstage" button.

    Copying from the site.

    Quote
    Falcon 9's second stage is powered by a single Merlin vacuum engine nearly identical to the first-stage engines, but modified to operate in the vacuum of space. Like the main Merlin engines, the vacuum engine is designed and manufactured in-house by SpaceX. The engine is designed to burn for about six minutes, and can be shut down and restarted multiple times as needed to deliver different payloads into different orbits. SpaceX's Merlin vacuum engine has the highest vacuum specific impulse (isp)--a measure of engine efficiency--of any American liquid oxygen/kerosene engine with a vacuum isp of 348 seconds. The engine is housed inside the rocket's interstage.

    Regarding older isp numbers, I checked the site with the wayback machine. Here is a link from june 2015 (http://web.archive.org/web/20150519004028/http://www.spacex.com/falcon9). Quoting.

    Quote
    Falcon 9's second stage is powered by a single Merlin vacuum engine nearly identical to the first-stage engines, but modified to operate in the vacuum of space. Like the main Merlin engines, the vacuum engine is designed and manufactured in-house by SpaceX. The engine is designed to burn for about six minutes, and can be shut down and restarted multiple times as needed to deliver different payloads into different orbits. SpaceX's Merlin vacuum engine has the highest vacuum specific impulse (isp)--a measure of engine efficiency--of any American liquid oxygen/kerosene engine with a vacuum isp of 340 seconds.  The engine is housed inside the rocket's interstage.

    Seems like an increase of 8s vac isp.

    edit: Added the old and new renders for the M-1D vac. The top one is the old one.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: symbios on 09/21/2015 05:07 pm
    From 240 to 248 in ISP is like what? About ~12 % in fuel savings for the same Dv? According to spaceflight101.com they carried 92.670 kg of fuel on the second stage on the original F9 1.1.

    In this case since they have made the tanks larger and added densification... That should do a lot for payload mass to orbit.

    ...

    Copying from the site.

    Quote
    Falcon 9's second stage is powered by a single Merlin vacuum engine nearly identical to the first-stage engines, but modified to operate in the vacuum of space. Like the main Merlin engines, the vacuum engine is designed and manufactured in-house by SpaceX. The engine is designed to burn for about six minutes, and can be shut down and restarted multiple times as needed to deliver different payloads into different orbits. SpaceX's Merlin vacuum engine has the highest vacuum specific impulse (isp)--a measure of engine efficiency--of any American liquid oxygen/kerosene engine with a vacuum isp of 348 seconds. The engine is housed inside the rocket's interstage.

    Regarding older isp numbers, I checked the site with the wayback machine. Here is a link from june 2015 (http://web.archive.org/web/20150519004028/http://www.spacex.com/falcon9). Quoting.

    Quote
    Falcon 9's second stage is powered by a single Merlin vacuum engine nearly identical to the first-stage engines, but modified to operate in the vacuum of space. Like the main Merlin engines, the vacuum engine is designed and manufactured in-house by SpaceX. The engine is designed to burn for about six minutes, and can be shut down and restarted multiple times as needed to deliver different payloads into different orbits. SpaceX's Merlin vacuum engine has the highest vacuum specific impulse (isp)--a measure of engine efficiency--of any American liquid oxygen/kerosene engine with a vacuum isp of 340 seconds.  The engine is housed inside the rocket's interstage.

    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: oldAtlas_Eguy on 09/21/2015 06:49 pm
    The 2.4% increase is probably due to the longer M1DVAC nozzle, and not a TC psi increase. If that is the case then there is no increase in ISP for the M1D or if there is it is small of about 1-2.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: MP99 on 09/21/2015 08:54 pm
    Some "new" (changed 20 days ago) numbers on the SpaceX website (http://www.spacex.com/falcon9).
  • Merlin 1D vac thrust is now 934kN / 210.000lbf, isp is now 348s, burn time is 397s
  • Merlin 1D FT thrust is now 756kN / 170.000lbf (SL) and  825kN / 185.500lbf (vac), burn time is 162s

  • From a first glance, it seems like the plan is to offload work from the first stage (18s less burning time) to make stage recovery easier.
    Also, any idea what would the TWR be now?

  • The increase in thrust is greater than the increase in density of the propellants. If the tanks are the same size, stage will burn out quicker.

    Total vehicle T:W (and therefore the dV imparted by the first stage) will also depend on the mass of the upper stage and payload.

    Cheers, Martin
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Elmar Moelzer on 09/21/2015 09:12 pm
    I thought that decreasing the thrust of the engines (for the old Merlin 1D version) also decreased their ISP. So it would seem feasible that the full throttle version has a slightly higher ISP. But I might be remembering something wrong.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Dante80 on 09/21/2015 10:05 pm
    I thought that decreasing the thrust of the engines (for the old Merlin 1D version) also decreased their ISP. So it would seem feasible that the full throttle version has a slightly higher ISP. But I might be remembering something wrong.

    I think I read somewhere that the isp could be lower, since the propellant is coming to the engine at a lower temperature.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: ArbitraryConstant on 09/21/2015 10:59 pm
    I thought that decreasing the thrust of the engines (for the old Merlin 1D version) also decreased their ISP. So it would seem feasible that the full throttle version has a slightly higher ISP. But I might be remembering something wrong.
    It's possible chamber pressure and therefore expansion ratio has increased.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: baldusi on 09/23/2015 01:11 pm
    Open cycle engines like gas generator have an issue that above a certain level of Pc, you need to dump more propellant to run the turbines, and thus you increase the efficiency at the Mcc but the lose propellant to the turbines. I would not be surprised that the increase in ISP is more due to the expansion ratio than the Pc.
    Of course, the increased thrust would need the longer nozzle to keep the same nozzle exit pressure.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: acsawdey on 09/23/2015 02:36 pm
    Open cycle engines like gas generator have an issue that above a certain level of Pc, you need to dump more propellant to run the turbines, and thus you increase the efficiency at the Mcc but the lose propellant to the turbines. I would not be surprised that the increase in ISP is more due to the expansion ratio than the Pc.
    Of course, the increased thrust would need the longer nozzle to keep the same nozzle exit pressure.

    Just poking at this in RPA lite, it seems like you would get some gain from higher Pc at sea level with the same size nozzle. The exhaust is less overexpanded at sea level so you get increased Isp at low altitudes. The same effect reduces Isp when you throttle down at sea level -- exhaust becomes more overexpanded, flow separation makes the nozzle smaller, effectively.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Prober on 09/23/2015 03:37 pm
    From 240 to 248 in ISP is like what? About ~12 % in fuel savings for the same Dv? According to spaceflight101.com they carried 92.670 kg of fuel on the second stage on the original F9 1.1.

    In this case since they have made the tanks larger and added densification... That should do a lot for payload mass to orbit.

    ...

    Copying from the site.

    Quote
    Falcon 9's second stage is powered by a single Merlin vacuum engine nearly identical to the first-stage engines, but modified to operate in the vacuum of space. Like the main Merlin engines, the vacuum engine is designed and manufactured in-house by SpaceX. The engine is designed to burn for about six minutes, and can be shut down and restarted multiple times as needed to deliver different payloads into different orbits. SpaceX's Merlin vacuum engine has the highest vacuum specific impulse (isp)--a measure of engine efficiency--of any American liquid oxygen/kerosene engine with a vacuum isp of 348 seconds. The engine is housed inside the rocket's interstage.

    Regarding older isp numbers, I checked the site with the wayback machine. Here is a link from june 2015 (http://web.archive.org/web/20150519004028/http://www.spacex.com/falcon9). Quoting.

    Quote
    Falcon 9's second stage is powered by a single Merlin vacuum engine nearly identical to the first-stage engines, but modified to operate in the vacuum of space. Like the main Merlin engines, the vacuum engine is designed and manufactured in-house by SpaceX. The engine is designed to burn for about six minutes, and can be shut down and restarted multiple times as needed to deliver different payloads into different orbits. SpaceX's Merlin vacuum engine has the highest vacuum specific impulse (isp)--a measure of engine efficiency--of any American liquid oxygen/kerosene engine with a vacuum isp of 340 seconds.  The engine is housed inside the rocket's interstage.


    you sure the 2nd stage uses densified?
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: baldusi on 09/23/2015 04:17 pm
    Just poking at this in RPA lite, it seems like you would get some gain from higher Pc at sea level with the same size nozzle. The exhaust is less overexpanded at sea level so you get increased Isp at low altitudes. The same effect reduces Isp when you throttle down at sea level -- exhaust becomes more overexpanded, flow separation makes the nozzle smaller, effectively.
    You surely meant underexpanded, right? I concur with your assesment for a first stage engine. If the Merlin 1D Full Thrust is exactly the same as the previous (MCC, throat and nozzle dimensions), then it should has a bigger isp bias towards sea level performance. It might increase isp overall, but should be higher at sea level.
    But I was talking about the vacuum version, which has the enlarged nozzle. There's basically no atmosphere for it and thus is a vacuum analysis.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: acsawdey on 09/23/2015 05:19 pm
    Just poking at this in RPA lite, it seems like you would get some gain from higher Pc at sea level with the same size nozzle. The exhaust is less overexpanded at sea level so you get increased Isp at low altitudes. The same effect reduces Isp when you throttle down at sea level -- exhaust becomes more overexpanded, flow separation makes the nozzle smaller, effectively.
    You surely meant underexpanded, right? I concur with your assesment for a first stage engine. If the Merlin 1D Full Thrust is exactly the same as the previous (MCC, throat and nozzle dimensions), then it should has a bigger isp bias towards sea level performance. It might increase isp overall, but should be higher at sea level.
    But I was talking about the vacuum version, which has the enlarged nozzle. There's basically no atmosphere for it and thus is a vacuum analysis.

    I was going off of the terminology used in this figure in wikipedia:

    https://en.wikipedia.org/wiki/Rocket_engine#/media/File:Rocket_nozzle_expansion.svg (https://en.wikipedia.org/wiki/Rocket_engine#/media/File:Rocket_nozzle_expansion.svg)

    If this is backwards, perhaps we should tell them. In any case yes I agree that in vacuum Pc doesn't make much difference and the substantial Isp increase is almost all due to the bigger bell.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: cambrianera on 09/23/2015 05:25 pm
    Just poking at this in RPA lite, it seems like you would get some gain from higher Pc at sea level with the same size nozzle. The exhaust is less overexpanded at sea level so you get increased Isp at low altitudes. The same effect reduces Isp when you throttle down at sea level -- exhaust becomes more overexpanded, flow separation makes the nozzle smaller, effectively.
    You surely meant underexpanded, right? I concur with your assesment for a first stage engine. If the Merlin 1D Full Thrust is exactly the same as the previous (MCC, throat and nozzle dimensions), then it should has a bigger isp bias towards sea level performance. It might increase isp overall, but should be higher at sea level.
    But I was talking about the vacuum version, which has the enlarged nozzle. There's basically no atmosphere for it and thus is a vacuum analysis.
    He meant  probably overexpanded nozzle (but wrote overexpanded exhaust).
    About the increase of thrust of merlin 1D, I believe it was obtained optimizing the flow, without increase of turbine power.
    Optimizing the pumps, redesigning cooling channels, increasing diameter of pipes, you can minimize friction losses. The 15% gain seems consistent with this, and the good part is you need no extra propellant for turbine.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: acsawdey on 09/23/2015 06:07 pm
    He meant  probably overexpanded nozzle (but wrote overexpanded exhaust).
    About the increase of thrust of merlin 1D, I believe it was obtained optimizing the flow, without increase of turbine power.
    Optimizing the pumps, redesigning cooling channels, increasing diameter of pipes, you can minimize friction losses. The 15% gain seems consistent with this, and the good part is you need no extra propellant for turbine.

    Yes, overexpanded nozzle was what I meant.

    So the additional 15% thrust between M1D and "M1D FT" is due to reduced friction losses in the propellant flow? Does this imply a higher Pc at the same pump power? Or just larger mdot at the same pressure?
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: cambrianera on 09/23/2015 07:02 pm
    He meant  probably overexpanded nozzle (but wrote overexpanded exhaust).
    About the increase of thrust of merlin 1D, I believe it was obtained optimizing the flow, without increase of turbine power.
    Optimizing the pumps, redesigning cooling channels, increasing diameter of pipes, you can minimize friction losses. The 15% gain seems consistent with this, and the good part is you need no extra propellant for turbine.

    Yes, overexpanded nozzle was what I meant.

    So the additional 15% thrust between M1D and "M1D FT" is due to reduced friction losses in the propellant flow? Does this imply a higher Pc at the same pump power? Or just larger mdot at the same pressure?

    Please be careful, the "reduced losses" hypotesys is only my opinion.
    Anyway to get larger mdot passing from the throat of the combustion chamber you need higher pressure, and this is a fact.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: ArbitraryConstant on 09/23/2015 07:22 pm
    Optimizing the pumps, redesigning cooling channels, increasing diameter of pipes, you can minimize friction losses. The 15% gain seems consistent with this, and the good part is you need no extra propellant for turbine.
    SpaceX changing more than they let on again. :P
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Dante80 on 09/23/2015 11:03 pm
    Could the whole USAF cert thingy have anything to do with this (like the name for the new engine variant, the stage changes etc?)

    At some point, it just makes sense to call the thing Falcon 9 1.2/2.0 or merlin 1-E and be done with it. Judging from a slide we saw from SES, the rocket and the engine have changed enough.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: wannamoonbase on 09/23/2015 11:21 pm
    He meant  probably overexpanded nozzle (but wrote overexpanded exhaust).
    About the increase of thrust of merlin 1D, I believe it was obtained optimizing the flow, without increase of turbine power.
    Optimizing the pumps, redesigning cooling channels, increasing diameter of pipes, you can minimize friction losses. The 15% gain seems consistent with this, and the good part is you need no extra propellant for turbine.

    Yes, overexpanded nozzle was what I meant.

    So the additional 15% thrust between M1D and "M1D FT" is due to reduced friction losses in the propellant flow? Does this imply a higher Pc at the same pump power? Or just larger mdot at the same pressure?

    It's with looking at decreased viscosity at lower temperatures.

    Not sure what percentage improvement it would be, but it should be less for both fuel and oxidizer.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Herb Schaltegger on 09/23/2015 11:56 pm
    He meant  probably overexpanded nozzle (but wrote overexpanded exhaust).
    About the increase of thrust of merlin 1D, I believe it was obtained optimizing the flow, without increase of turbine power.
    Optimizing the pumps, redesigning cooling channels, increasing diameter of pipes, you can minimize friction losses. The 15% gain seems consistent with this, and the good part is you need no extra propellant for turbine.

    Yes, overexpanded nozzle was what I meant.

    So the additional 15% thrust between M1D and "M1D FT" is due to reduced friction losses in the propellant flow? Does this imply a higher Pc at the same pump power? Or just larger mdot at the same pressure?

    It's with looking at decreased viscosity at lower temperatures.

    Not sure what percentage improvement it would be, but it should be less for both fuel and oxidizer.

    It's been a long darn time since my undergrad classes in fluid mechanics, but it seems that I recall the viscosity of many (most?) liquids increases with lower temperature - admittedly, I haven't looked at either RP1 or LOX to see if that's the case.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: acsawdey on 09/24/2015 02:23 pm
    It's been a long darn time since my undergrad classes in fluid mechanics, but it seems that I recall the viscosity of many (most?) liquids increases with lower temperature - admittedly, I haven't looked at either RP1 or LOX to see if that's the case.

    This table of viscosity for oxygen shows LOX viscosity increases with decreasing temperature for all pressures in the relevant regime (0.1MPa to 10MPa). Dynamic viscosity nearly doubles between 90K and 70K while the increase in density is much more modest, so kinematic viscosity must also be increasing going from 90K to 70K.

    http://www.nist.gov/srd/upload/jpcrd395.pdf (http://www.nist.gov/srd/upload/jpcrd395.pdf)
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: wannamoonbase on 09/24/2015 05:58 pm
    It's been a long darn time since my undergrad classes in fluid mechanics, but it seems that I recall the viscosity of many (most?) liquids increases with lower temperature - admittedly, I haven't looked at either RP1 or LOX to see if that's the case.

    This table of viscosity for oxygen shows LOX viscosity increases with decreasing temperature for all pressures in the relevant regime (0.1MPa to 10MPa). Dynamic viscosity nearly doubles between 90K and 70K while the increase in density is much more modest, so kinematic viscosity must also be increasing going from 90K to 70K.

    http://www.nist.gov/srd/upload/jpcrd395.pdf (http://www.nist.gov/srd/upload/jpcrd395.pdf)


    My bad.

    Maybe it's different with gas giants.  I was thinking about the very high speed winds on Neptune discovered by Voyager 2 and the scientists saying the speed was possible before of the loss of friction at very cold temperatures.

    But yes, I should have thought about it, denser liquids would have more tightly packed molecules rubbing against each other increasing the viscosity.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: cambrianera on 09/24/2015 06:39 pm
    Superfluidity exists: https://en.wikipedia.org/wiki/Superfluidity

    But cannot be used in rocket motors  ;)
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: russianhalo117 on 09/25/2015 01:54 am
    Ill throw this milestone in:
    SpaceX vid of Static fire test at full thrust for flight
    https://www.youtube.com/watch?v=qbe1KNUBEEU
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: MP99 on 09/25/2015 08:10 am
    Open cycle engines like gas generator have an issue that above a certain level of Pc, you need to dump more propellant to run the turbines, and thus you increase the efficiency at the Mcc but the lose propellant to the turbines. I would not be surprised that the increase in ISP is more due to the expansion ratio than the Pc.
    Of course, the increased thrust would need the longer nozzle to keep the same nozzle exit pressure.

    Just poking at this in RPA lite, it seems like you would get some gain from higher Pc at sea level with the same size nozzle. The exhaust is less overexpanded at sea level so you get increased Isp at low altitudes. The same effect reduces Isp when you throttle down at sea level -- exhaust becomes more overexpanded, flow separation makes the nozzle smaller, effectively.

    I wonder if it makes sense to throttle down as the atmosphere thins during ascent, once you get into regime where the acceleration is already relatively high and gravity losses much lower? Assumes there is a point where Isp becomes more important than gravity losses (and that GG is in the regime that baldusi describes).

    Cheers, Martin
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: JamesH on 09/25/2015 12:11 pm
    Open cycle engines like gas generator have an issue that above a certain level of Pc, you need to dump more propellant to run the turbines, and thus you increase the efficiency at the Mcc but the lose propellant to the turbines. I would not be surprised that the increase in ISP is more due to the expansion ratio than the Pc.
    Of course, the increased thrust would need the longer nozzle to keep the same nozzle exit pressure.

    Just poking at this in RPA lite, it seems like you would get some gain from higher Pc at sea level with the same size nozzle. The exhaust is less overexpanded at sea level so you get increased Isp at low altitudes. The same effect reduces Isp when you throttle down at sea level -- exhaust becomes more overexpanded, flow separation makes the nozzle smaller, effectively.

    I wonder if it makes sense to throttle down as the atmosphere thins during ascent, once you get into regime where the acceleration is already relatively high and gravity losses much lower? Assumes there is a point where Isp becomes more important than gravity losses (and that GG is in the regime that baldusi describes).

    Cheers, Martin

    Don't they throttle back anyway as the mass of the stage reduces (fuel used up) to prevent excessive acceleration?
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: guckyfan on 09/25/2015 12:48 pm
    Do I understand correctly? Overexpanded first stage engines increase their ISP when throttled to be less overexpanded when the atmosphere gets thinner on altitude  compared to not throttled?
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: acsawdey on 09/25/2015 02:34 pm
    Do I understand correctly? Overexpanded first stage engines increase their ISP when throttled to be less overexpanded when the atmosphere gets thinner on altitude  compared to not throttled?

    I don't think you'll ever increase Isp by throttling. What happens is that if the nozzle exit pressure is kept >= ambient pressure, you don't lose more than a few % Isp by throttling down to that point. With M1D at 147k lbf you could start throttling somewhere around 3km altitude, and the higher pressure of the "full thrust" version moves that point to a lower altitude.

    Whether or not this is the best thing to do is a complex trade with drag force, gravity loss, and trajectory. It's almost certainly the case that the throttling at the end of the first stage burn to limit acceleration doesn't cost much Isp though.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: cambrianera on 09/25/2015 05:03 pm
    Throttling on merlin 1D is done dosing propellants to the turbopump.
    Likely at lower thrust not only the mass of propellants to TP is less, but also the percentage on total flow.
    Therefore is possible to have a slight increase in ISP.
    As ever IMHO.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: acsawdey on 09/25/2015 05:43 pm
    Throttling on merlin 1D is done dosing propellants to the turbopump.
    Likely at lower thrust not only the mass of propellants to TP is less, but also the percentage on total flow.
    Therefore is possible to have a slight increase in ISP.
    As ever IMHO.

    So if you meet the criteria I mentioned about the exit pressure, you may potentially gain Isp because you are spending less propellant running the gas generator. If you don't need the extra thrust, there isn't really any reason to crank up the chamber pressure beyond what is necessary to make full use of the nozzle expansion ratio at a particular ambient pressure.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Dante80 on 12/28/2015 09:44 am
    Here is a hypothetical question.

    Both M1-D+ and M1-D+ vac are turbopump-fed gas generator engines. In the vaccuum version, the pump exhaust is fed back to the nozzle, but in the S1 version it is not.

    Would it make sense to design a future variant of the S1 engine to also do that (like the F1 engine did for example)? What are the possible advantages or disadvantages of a variation like that (in engine complexity/mass/reliability/performance and octaweb complexity/mass)?

    Any help would be vastly appreciated, cheers. If there is a relevant prior discussion for this, linking it would help greatly. C:
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: ArbitraryConstant on 12/28/2015 05:22 pm
    Both M1-D+ and M1-D+ vac are turbopump-fed gas generator engines. In the vaccuum version, the pump exhaust is fed back to the nozzle, but in the S1 version it is not.

    Would it make sense to design a future variant of the S1 engine to also do that (like the F1 engine did for example)? What are the possible advantages or disadvantages of a variation like that (in engine complexity/mass/reliability/performance and octaweb complexity/mass)?
    Probably not. In fact the proposal for an updated F-1B engine would have done away with this as well, see http://arstechnica.com/science/2013/04/new-f-1b-rocket-engine-upgrades-apollo-era-deisgn-with-1-8m-lbs-of-thrust/

    It's done on F-1 to protect the nozzle extension, which MVac has but M-1D doesn't. Seems like the trades today for a first stage engine favor just going for simplicity rather than a larger nozzle.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: baldusi on 12/28/2015 07:30 pm
    The F-1 used the terribly expensive brazed tubes nozzle. Which was not only extremely expensive, but only road portable thanks to the nozzle extension. So you have cost and road transport as reasons for the nozzle extension.
    But the higher the MCC pressure the smaller (in proportion to thrust) for the first stage optimized nozzle. Merlin 1D had 1400psi (vs F-1 1kpsi), and Merlin 1D Full Thrust might have a bit more (probably 1,600psi). So in proportion they would need a smaller nozzle.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Jcc on 12/29/2015 12:34 pm
    Do we have specific info on the differences in the M1D FT version if any? Thanks!
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Jcc on 12/30/2015 11:37 am
    My guess is that there are no major differences between the FT and non-FT versions of the M1D. If true, then the engines recovered from the Jason S1, if recovered, together with any spares could be repurposed for a Full Thrust stage with minor refurbishment. If the combustion chamber is different, that would not be possible.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: sdsds on 12/30/2015 07:02 pm
    Has SpaceX been clear on the question of whether all M1-D engines can be qualified for full thrust flight, or only M1-D engines produced since a certain date, or?
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Jcc on 12/30/2015 08:44 pm
    Has SpaceX been clear on the question of whether all M1-D engines can be qualified for full thrust flight, or only M1-D engines produced since a certain date, or?

    Well, we can probably say that an engine is not qualified for full thrust until tested at full thrust, and earlier engines will need to be tested again, at least.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: sdsds on 12/30/2015 08:52 pm
    My understanding has been that every Merlin engine is first shipped to MacGregor and individually tested before being returned to Hawthorne for integration onto a vehicle. IMHO they must have tested some engines at full thrust before they committed to manufacturing the full thrust vehicle. I'm wondering if in fact they have been individually testing many/all of the engines intended for v1.1 vehicles at the full thrust level for quite some time now?
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Comga on 12/30/2015 08:55 pm
    Has SpaceX been clear on the question of whether all M1-D engines can be qualified for full thrust flight, or only M1-D engines produced since a certain date, or?

    We know that Musk doesn't like type designations, but they have labeled the Merlin engines 1A, 1B, 1C, and 1D.  To have two "flavors" of Merlin 1D with different thrusts would be very strange.
    A reasonable assumption, but only an assumption, is that engines sharing a single designation are more or less interchangeable.  My guess, but its only a guess, would be that the Jason F9-1.1 engines could be run at full thrust
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Coastal Ron on 12/30/2015 09:24 pm
    Has SpaceX been clear on the question of whether all M1-D engines can be qualified for full thrust flight, or only M1-D engines produced since a certain date, or?

    We know that Musk doesn't like type designations, but they have labeled the Merlin engines 1A, 1B, 1C, and 1D.  To have two "flavors" of Merlin 1D with different thrusts would be very strange.

    As I recall Musk said the Merlin 1D was capable of more power but that they weren't ready with all the improvements when they needed it for the initial V1.1 Falcon 9, so they ran it "derated" from it's full potential.  Of course now we know the full potential needed the colder RP-1 & LOX, so it could be the Merlin 1D is the same from a mechanical standpoint for any version of the V1.1, but that the software changes to account for whether they are using sub-cooled fuel.

    Quote
    A reasonable assumption, but only an assumption, is that engines sharing a single designation are more or less interchangeable.

    That is usually the norm, although in manufacturing you could still have design revision changes that limit interchangeability.

    Quote
    My guess, but its only a guess, would be that the Jason F9-1.1 engines could be run at full thrust

    As I wrote above, I think it's likely the engines would be capable of their full thrust, but since the Jason-3 1st stage will likely NOT be using sub-cooled fuel it won't be able to reach it's full potential thrust - just the thrust level of the previous V1.1 before the Orbcomm flight.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Comga on 12/30/2015 10:20 pm
    (snip)
    Of course now we know the full potential (power) needed the colder RP-1 & LOX,
    (snip)

    No.  We don't really know that either.
    Sub-cooling could be for just the increased density.  SpaceX has stated the benefit of increased propellant density.
    F9-FT needs sub-cooled P1 & LOX AND "Full Thrust" engines but we don't know that one leads to the other.
    Coincidence is not causality.
    We don't have that level of detail.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Fluke72 on 12/30/2015 10:54 pm
    My guess is that there are no major differences between the FT and non-FT versions of the M1D. If true, then the engines recovered from the Jason S1, if recovered, together with any spares could be repurposed for a Full Thrust stage with minor refurbishment. If the combustion chamber is different, that would not be possible.

    There are some differences on the FT version. I wish I could define them here but I can't. Eventually I am betting SX will release a picture (like we have seen of legacy M1Ds in various stages of build on the factory floor) and the visual clues will be obvious to the keen eye.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Jcc on 12/30/2015 11:44 pm
    (snip)
    Of course now we know the full potential (power) needed the colder RP-1 & LOX,
    (snip)

    No.  We don't really know that either.
    Sub-cooling could be for just the increased density.  SpaceX has stated the benefit of increased propellant density.
    F9-FT needs sub-cooled P1 & LOX AND "Full Thrust" engines but we don't know that one leads to the other.
    Coincidence is not causality.
    We don't have that level of detail.

    I think you are right, but part of the equation is higher thrust requires higher propellant consumption rate, and would run out of propellant too soon unless they carry more, either by stretching the stage or supercooling. Supercooling is better, because they can do so without adding the mass of a longer stage. They do both for S2 because the more powerful S1 can lift it, and that way they can boost a substantially bigger payload.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: oldAtlas_Eguy on 12/31/2015 02:26 am
    The question now that a set of M1DFT's have flow will we ever find out the real performance values for these engines?
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: guckyfan on 12/31/2015 08:15 am
    The question now that a set of M1DFT's have flow will we ever find out the real performance values for these engines?

    With SES-9 flown we will have a good indication what the real performance is as soon as we know which orbit is reached. That flight will require everything Falcon 9 FT can give. Some people will be able to calculate engine performance backward from that.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Okie_Steve on 12/31/2015 07:08 pm
    There are some differences on the FT version. I wish I could define them here but I can't. Eventually I am betting SX will release a picture (like we have seen of legacy M1Ds in various stages of build on the factory floor) and the visual clues will be obvious to the keen eye.
    One obvious candidate would be slightly large plumbing to deal the the higher mass flow. Pictures when they happen will be interesting.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: harrisoncassidy on 01/04/2016 09:50 am
    Can anyone give an update on information regarding the ablative coating of the M1D engines? I remember watching a video of the M1A a few years ago which was one of the first tests but I wondered if the technology has improved and what advancements in this area would aid to rapid reusability?
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Dante80 on 01/04/2016 09:56 am
    Can anyone give an update on information regarding the ablative coating of the M1D engines? I remember watching a video of the M1A a few years ago which was one of the first tests but I wondered if the technology has improved and what advancements in this area would aid to rapid reusability?

    M1-A used an ablatively cooled Carbon-fiber-reinforced polymer composite nozzle. From M1-C forward, the engine has a regenerative nozzle (using about a sixth of the total RP-1 fuel flow to cool the chamber and the nozzle).

    An ablative nozzle would not help a lot with rapid re-usability. You would either have to make the coating thick enough for multiple cycles (thus adding to engine weight and inspection time/costs), or replace it after every cycle (thus adding to manufacturing and swapping time/costs).
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Johnnyhinbos on 01/04/2016 04:32 pm
    I know back on Jan 16th, 2014 that SpaceX fitted and launched an additive printed Main Oxidizer Valve on one of the nine booster Merlin-1D engines. I was wondering if there's been any update on this 'test' and if they are now using this version of the MOV (and any other printed components) on the Merlin-1D?

    Source: http://www.spacex.com/news/2014/07/31/spacex-launches-3d-printed-part-space-creates-printed-engine-chamber-crewed
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Dante80 on 01/04/2016 04:53 pm
    I know back on Jan 16th, 2014 that SpaceX fitted and launched an additive printed Main Oxidizer Valve on one of the nine booster Merlin-1D engines. I was wondering if there's been any update on this 'test' and if they are now using this version of the MOV (and any other printed components) on the Merlin-1D?

    Source: http://www.spacex.com/news/2014/07/31/spacex-launches-3d-printed-part-space-creates-printed-engine-chamber-crewed (http://www.spacex.com/news/2014/07/31/spacex-launches-3d-printed-part-space-creates-printed-engine-chamber-crewed)

    I think I saw one here @10:00

    [youtube]O5bTbVbe4e4[/youtube]
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: bstrong on 01/04/2016 05:26 pm
    There are some differences on the FT version. I wish I could define them here but I can't. Eventually I am betting SX will release a picture (like we have seen of legacy M1Ds in various stages of build on the factory floor) and the visual clues will be obvious to the keen eye.

    Attaching some recent images from the Kloss photoshoot and the OG2 webcast in case some keen eyes can spot something in them.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Damon Hill on 01/04/2016 05:47 pm
    There are some differences on the FT version. I wish I could define them here but I can't. Eventually I am betting SX will release a picture (like we have seen of legacy M1Ds in various stages of build on the factory floor) and the visual clues will be obvious to the keen eye.
    One obvious candidate would be slightly large plumbing to deal the the higher mass flow. Pictures when they happen will be interesting.
    If the supercooled propellant is denser, then a greater weight of propellant can occupy the same volume.  So why should anything be larger, which increases weight, however slightly?  There may be changes in the engines that are less obvious--but if the engines were designed for supercooled propellants prior to this flight, perhaps not.  I'm guessing more turbopump power is needed to stuff the additional mass of propellant into the combustion chamber, and the lower temperature of the propellants may have an effect on combustion efficiency (and may help cooling the engine, making the performance margin possible).

    So there might be changes, yes, but I suspect they are subtle.

    --Damon
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: docmordrid on 01/04/2016 06:31 pm
    Landed M1D FT cluster up-close, plus a brightened version

    https://twitter.com/SpaceX/status/684094378021801984

    Brightened removed
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Silmfeanor on 01/04/2016 06:40 pm
    Landed M1D FT cluster up-close

    https://twitter.com/SpaceX/status/684094378021801984

    higher res, using the :orig tag.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Lars-J on 01/04/2016 06:48 pm
    Landed M1D FT cluster up-close, plus a brightened version

    A more accurate brighter version:
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: matthewkantar on 01/04/2016 08:03 pm
    Does anybody know what parts of the nozzles on the first stages engine are made of what? I think they have passages inside of them to circulate RP-1 for cooling, but they are so smooth and (when new) shiny on the outside. Is the whole nozzle niobium with channels in it? Is there an inner shell and an outer shell that covers the cooling channels? I think I remember some bits of of it are niobium, or a niobium alloy, what parts.

    The very bottom edge has some thickness, but no sign of there being any layers of anything.

    Matthew
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Fluke72 on 01/04/2016 08:16 pm
    The nozzles do have cooling passages. On one of the pics with them in the Octo you can sorta see the drain plugs (very small allen plug) near the bottom edge. As far as material and what flows in it I can't speak to that  ;)
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: acsawdey on 01/04/2016 08:27 pm
    A picture with some details of nozzle construction of the M1D. Channels are milled into the inner part seen in the foreground, outer shell seen on the other side of the aisle is attached.

    https://www.flickr.com/photos/jurvetson/8233308933/ (https://www.flickr.com/photos/jurvetson/8233308933/)
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: cambrianera on 01/04/2016 08:31 pm
    Does anybody know what parts of the nozzles on the first stages engine are made of what?

    Best candidate IMHO is stainless steel.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: acsawdey on 01/04/2016 08:39 pm
    Does anybody know what parts of the nozzles on the first stages engine are made of what?

    Best candidate IMHO is stainless steel.

    The picture I just posted looks like the inner layer with the channels milled in it is copper. Could be that the inner and outer layers are some kind of nickel superalloy for heat resistance. Which makes the overall construction not too different from the stainless/copper/stainless layering used in some cooking pots ...
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: cambrianera on 01/04/2016 08:49 pm
    Does anybody know what parts of the nozzles on the first stages engine are made of what?

    Best candidate IMHO is stainless steel.

    The picture I just posted looks like the inner layer with the channels milled in it is copper. Could be that the inner and outer layers are some kind of nickel superalloy for heat resistance. Which makes the overall construction not too different from the stainless/copper/stainless layering used in some cooking pots ...
    You are right, could be chrome plated copper.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Okie_Steve on 01/05/2016 02:38 pm
    There are some differences on the FT version. I wish I could define them here but I can't. Eventually I am betting SX will release a picture (like we have seen of legacy M1Ds in various stages of build on the factory floor) and the visual clues will be obvious to the keen eye.
    One obvious candidate would be slightly large plumbing to deal the the higher mass flow. Pictures when they happen will be interesting.
    If the supercooled propellant is denser, then a greater weight of propellant can occupy the same volume.  So why should anything be larger, which increases weight, however slightly?  There may be changes in the engines that are less obvious--but if the engines were designed for supercooled propellants prior to this flight, perhaps not.  I'm guessing more turbopump power is needed to stuff the additional mass of propellant into the combustion chamber, and the lower temperature of the propellants may have an effect on combustion efficiency (and may help cooling the engine, making the performance margin possible).

    So there might be changes, yes, but I suspect they are subtle.

    --Damon
    You just answered your own question. Denser=Thicker=More-Pumping-Loss. Either increase pump power or decrease pumping loss. If the turbopump is maxed out then slightly larger pipe are another answer.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Robotbeat on 01/05/2016 09:07 pm
    Pump power is more related to volume and pressure than to density. Or more precisely, it takes less energy to pump a given mass of propellant to a certain pressure if the density is greater.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Okie_Steve on 01/06/2016 01:05 am
    They are increasing the mass flow to make use of the FT so it is more like constant volume but increased density. No free lunch, something HAS to give a bit.

    Edit typo
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Jcc on 01/06/2016 03:37 am
    A few questions that perhaps the experts here can answer:
    - when the M1D or any similar engine throttles down, how is this throttling actually accomplished? Is it by reducing the RPM of the turbo pumps, partially  closing a valve or pintle, or combination?
    - how does it ensure the proper combustion ratio is maintained, despite a possible change in the LOX temperature during a flight, and resulting expansion? Does it dynamically adjust the flow of LOX volume to account for different density?
    The densification is about 10%, IIRC, which will have some effect on the energy used to pump it, but it seems the more significant effects of densification relate to controlling the combustion mixture.
    Not that I'm an expert or anything.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: sdsds on 01/06/2016 04:53 am
    - when the M1D or any similar engine throttles down, how is this throttling actually accomplished?

    I have no insight to offer into M1D, but for two SLS Engine Office engines, search for "throttle" in:
    https://blogs.nasa.gov/J2X/2013/08/06/inside-the-leo-doghouse-rs-25-vs-j-2x/
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: cambrianera on 01/06/2016 11:40 am
    A few questions that perhaps the experts here can answer:
    - when the M1D or any similar engine throttles down, how is this throttling actually accomplished? Is it by reducing the RPM of the turbo pumps, partially  closing a valve or pintle, or combination?
    - how does it ensure the proper combustion ratio is maintained, despite a possible change in the LOX temperature during a flight, and resulting expansion? Does it dynamically adjust the flow of LOX volume to account for different density?
    The densification is about 10%, IIRC, which will have some effect on the energy used to pump it, but it seems the more significant effects of densification relate to controlling the combustion mixture.
    Not that I'm an expert or anything.
    For M1D we know for sure (after CRS-6) that a bipropellant valve regulates the flow to the preburner, therefore effectively controlling the RPM of the turbopump.
    LOX/RP-1 ratio can be adjusted independently with another set of valves.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Fluke72 on 01/07/2016 09:28 pm
    only the center engine has a bi prop valve in order to throttle for landing ops...
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Lars-J on 01/07/2016 10:04 pm

    only the center engine has a bi prop valve in order to throttle for landing ops...

    Huh? Source?
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Coastal Ron on 01/07/2016 10:20 pm
    only the center engine has a bi prop valve in order to throttle for landing ops...

    Part of the flight profile requires throttling down all the engines, and then being able to throttle back up (especially if they lose an engine).  And according to Wikipedia for the Merlin 1D (https://en.wikipedia.org/wiki/Merlin_(rocket_engine_family)#Merlin_1D):

    "A new feature for the engine is the ability to throttle from 100% to 70%."

    What makes you think only the center engine throttles?
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: dorkmo on 01/07/2016 11:28 pm
    ^ "former SpaceX technician"

    good enough for me

    if only one engine throttles you still get a reduced 100 - 90%  range eh

    or

    do we think that the typical 1d can do 100-70 and perhaps the middle engine has a greater range?
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Jcc on 01/08/2016 12:44 am
    ^ "former SpaceX technician"

    good enough for me

    if only one engine throttles you still get a reduced 100 - 90%  range eh

    or

    do we think that the typical 1d can do 100-70 and perhaps the middle engine has a greater range?

    We did see some deep throttling in Grasshopper. Made folks wonder if the M1D could throttle more than advertised.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Herb Schaltegger on 01/08/2016 12:47 am
    ^ "former SpaceX technician"

    good enough for me

    if only one engine throttles you still get a reduced 100 - 90%  range eh

    or

    do we think that the typical 1d can do 100-70 and perhaps the middle engine has a greater range?

    We did see some deep throttling in Grasshopper. Made folks wonder if the M1D could throttle more than advertised.

    That still doesn't answer whether it's ONLY the center engine that throttles, and if so, what is the real benefit of the Falcon Heavy configuration? Throttling down only 1 engine of 9 in the core doesn't save THAT much prop, does it? Whereas throttling down all 9 to 70% or so will save quite a bit in such a "stage-and-a-half" configuration.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: dorkmo on 01/08/2016 01:26 am
    wikipedia says the 1d-vac can do 39%?
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Jcc on 01/08/2016 02:13 am
    wikipedia says the 1d-vac can do 39%?

    Which would be 61%, if true. That would be with reference to the non-full-thrust standard as well, I guess.

    We seem to be short on solid facts here.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: sdsds on 01/08/2016 04:30 am
    We seem to be short on solid facts here.

    We should all feel, "Welcome to the new world."

    I see no particular reason to doubt that the center engine has characteristics differentiating it from the others. Like deep throttling.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: ugordan on 01/08/2016 08:42 am
    That still doesn't answer whether it's ONLY the center engine that throttles, and if so, what is the real benefit of the Falcon Heavy configuration?

    If the information about the center engine on F9 is correct, then it looks like this is info that at least the center core engines on FH will all need to throttle, i.e. the core difference would be more than just tankage/octaweb structural factors.

    I had expected that the other engines even on F9 would need to throttle to limit G loads, but it turns out the max load at v1.1 burnout works out to around 4.8 Gs which is not that bad. That 2nd stage stretch compared to v1.0...
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Fluke72 on 01/08/2016 10:38 am
    Maybe I was not so clear but I didn't state the engines as a group don't have the ability to throttle up and down to a degree...only that E9, the center positioned engine has a actual added valve (the bi prop valve) and sensor package for throttling. The other positions may or may not have the same or lesser degrees of throttling as well. ;)
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Johnnyhinbos on 01/08/2016 01:04 pm

    Maybe I was not so clear but I didn't state the engines as a group don't have the ability to throttle up and down to a degree...only that E9, the center positioned engine has a actual added valve (the bi prop valve) and sensor package for throttling. The other positions may or may not have the same or lesser degrees of throttling as well. ;)
    So you are saying there are _four_ flavors of 1D engine? One for vacuum, one for center engine, one for two outer engines used for SSRP and one for the rest?

    I believe Both Musk and Shotwell have publicly stated their desire to minimize variants - for both manufacturing and system architecture perspectives.

    I suggest one and only one Marlin-1D SL flavor. It's restartable from an external (to engine) TEA/TEB system, and has the full throttle range afforded to a 1D.

    Let me ask this - it's commonly understood that engine start during launch is via GSE, correct? What's that architecture? It certainly doesn't have nine pairs of lines running from GSE to individual engines, right? So if you accept that, then you must also accept that the engine start plumbing to each engine comes from a single point on the rocket. (Let's call it a distribution manifold - see where this is going?). Now it's also accepted that three engines are also restarted via onboard systems. So does it make sense to have a entire second system for the restarts designed into certain engines, with all that extra unneeded redundancy and complication, or would it make more sense to utilize the same plumbing and manifold structure already in place for the GSE fed start for the relights?

    So the addition of valves to direct the relights to particular engine(s) provides a uniform architecture (only one flavor) and also provides opportunity to go to another outside opposing pair if the initial pair has issues relighting.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: JamesH on 01/08/2016 01:27 pm

    Maybe I was not so clear but I didn't state the engines as a group don't have the ability to throttle up and down to a degree...only that E9, the center positioned engine has a actual added valve (the bi prop valve) and sensor package for throttling. The other positions may or may not have the same or lesser degrees of throttling as well. ;)
    So you are saying there are _four_ flavors of 1D engine? One for vacuum, one for center engine, one for two outer engines used for SSRP and one for the rest?

    I believe Both Musk and Shotwell have publicly stated their desire to minimize variants - for both manufacturing and system architecture perspectives.

    I suggest one and only one Marlin-1D SL flavor. It's restartable from an external (to engine) TEA/TEB system, and has the full throttle range afforded to a 1D.

    Let me ask this - it's commonly understood that engine start during launch is via GSE, correct? What's that architecture? It certainly doesn't have nine pairs of lines running from GSE to individual engines, right? So if you accept that, then you must also accept that the engine start plumbing to each engine comes from a single point on the rocket. (Let's call it a distribution manifold - see where this is going?). Now it's also accepted that three engines are also restarted via onboard systems. So does it make sense to have a entire second system for the restarts designed into certain engines, with all that extra unneeded redundancy and complication, or would it make more sense to utilize the same plumbing and manifold structure already in place for the GSE fed start for the relights?

    So the addition of valves to direct the relights to particular engine(s) provides a uniform architecture (only one flavor) and also provides opportunity to go to another outside opposing pair if the initial pair has issues relighting.

    I don't think adding some sensors and one valve really construes a new variant. Still only two variants - Vacuum and the others. The centre engine just has a couple of extra bits to allow better throttling range/accuracy, which are not required on the others.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: abaddon on 01/08/2016 02:01 pm
    Here's my understanding, gleaned from reading this site for some time:

    -There are "restart kits" added to the engines that need them; only three of the engines have them (and 1D-Vac, obviously).
    -Ground start uses igniters and TEA-TEB supplied by the pad, that are not part of the rocket.
    -F9 has always throttled down to ~70(?)% thrust around max-Q to reduce aero loads on the rocket.
    -(New) The center engine has a unique biprop valve, presumably for better throttle control.  Presumably this is the valve that had the stiction issue and was fixed since the previous barge landing attempt.  I would also guess it is always 100% open during the primary mission, and is only used for the final landing burn.

    I don't have sources/links for any of this, but this is what I recall reading.  It all seems to hang together pretty well.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: cambrianera on 01/08/2016 04:26 pm
    Ok, I've found it:
    http://forum.nasaspaceflight.com/index.php?topic=31734.msg1080178#msg1080178

    The other pertinent piece of information I got, said offhand like it was public knowledge (and maybe it is, you tell me), is that the main reason for going with the octoweb over the tic-tac-toe layout is to reduce parts count. I asked what part count. I got a dumb look and then he said, oh, the Merlin 1-Cs, there was three different part numbers: corners, top/sides, and middle, but with octoweb all the engines are the same, even the center engine, which just throttles differently to the outside engines. This was apparent in the layout of the factory floor too, as there was no longer three engine assembly areas. My host pointed out where the old lines were removed.


    But this make me wonder: different piping layout and parts should qualify for a different part number.

    What has to be different between center and outside engines is not throttle, but gimbal.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: guckyfan on 01/08/2016 04:41 pm
    What has to be different between center and outside engines is not throttle, but gimbal.

    Not necessarily. Different available space for gimbal does not translate into different hardware, just software restrictions on its use.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Lars-J on 01/08/2016 04:54 pm
    What has to be different between center and outside engines is not throttle, but gimbal.

    No, they all gimbal. See this image, which highlights the gimbal actuators for the outer engines:
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: cambrianera on 01/08/2016 05:02 pm
    I said “gimbal has to be different“
    I did not say “hardware for gimbal has to be different“
    I did not say “no gimbal“

    Edited and rephrased
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Lars-J on 01/08/2016 05:05 pm
    Gimbal has to be different.
    (What is so difficult to understand in this?)

    Hint: not hardware for gimbal has to be different; not no gimbal.

    Gimbal limits, yes, but that might only be a software limit for the outer engines. And instead of hinting, say what you mean. (w/ source)
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Chris Bergin on 01/08/2016 05:15 pm
    Gentlemen, please! Be civil.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: cambrianera on 01/08/2016 05:24 pm
    Gimbal should be limited:
    -by software, the engine controller is fixed to the “thrust plate“, different between center and outboard engines.
    -by hardware, stroke limiting clamps are visible on actuators of outboard engines.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: JamesH on 01/08/2016 05:28 pm
    Gimbal should be limited:
    -by software, the engine controller is fixed to the “thrust plate“, different between center and outboard engines.
    -by hardware, stroke limiting clamps are visible on actuators of outboard engines.

    Doesn't make the engine 'different' surely? Just a different mount. All engines are still coming off the same production line.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Kabloona on 01/08/2016 05:34 pm
    stroke limiting clamps are visible on actuators of outboard engines.

    Those appear to be electrical harness clamps, not mechanical stops, which are typically internal to TVC actuators and not externally visible.

    Anyway, drifting off topic. The point is, there's no reason to doubt the statement that all F9 first stage engines are identical. The differences being discussed above (throttling, gimbal angle input limits) are all *external* to the engine itself.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: MechE31 on 01/08/2016 05:48 pm
    stroke limiting clamps are visible on actuators of outboard engines.

    Those appear to be electrical harness clamps, not mechanical stops, which are typically internal to TVC actuators and not externally visible.

    Anyway, drifting off topic. The point is, there's no reason to doubt the statement that all F9 first stage engines are identical. The differences being discussed above (throttling, gimbal angle input limits) are all *external* to the engine itself.

    They could also be ground handling stops to prevent unintended movement of the engines.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: ArbitraryConstant on 01/08/2016 06:26 pm
    That still doesn't answer whether it's ONLY the center engine that throttles
    I don't see that being a question in the first place. Back in the day when Merlin 1C couldn't throttle they had to throttle by shutting off two engines to keep the acceleration within limits. Throttling down one engine cannot provide reduction in thrust similar to shutting off two engines. Therefore all engines can throttle.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: guckyfan on 01/08/2016 09:24 pm
    That still doesn't answer whether it's ONLY the center engine that throttles
    I don't see that being a question in the first place. Back in the day when Merlin 1C couldn't throttle they had to throttle by shutting off two engines to keep the acceleration within limits. Throttling down one engine cannot provide reduction in thrust similar to shutting off two engines. Therefore all engines can throttle.

    Can we assume then that the center engine throttles more than the others?
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Fluke72 on 01/08/2016 09:35 pm
    Gimbal should be limited:
    -by software, the engine controller is fixed to the “thrust plate“, different between center and outboard engines.
    -by hardware, stroke limiting clamps are visible on actuators of outboard engines.

    those "limiting clamps" are temp installed to prevent movement of TVC actuators until flight and during shipping (or during testing).
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Silmfeanor on 01/08/2016 09:40 pm
    That still doesn't answer whether it's ONLY the center engine that throttles
    I don't see that being a question in the first place. Back in the day when Merlin 1C couldn't throttle they had to throttle by shutting off two engines to keep the acceleration within limits. Throttling down one engine cannot provide reduction in thrust similar to shutting off two engines. Therefore all engines can throttle.

    Can we assume then that the center engine throttles more than the others?
    They all are able to throttle; I assume the center one is more precise or has a faster response due to the added biprop valve, and gives faster feedback about the actual performance due to added instrumentation. This does not necessarily change anything about the engine structure itself, but is more like an added package only installed for the center engine.

    Or atleast, this seems to me to combine both having just 1 type of M1D and there being some additions to the throttling of the center engine.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: baldusi on 01/10/2016 10:48 am
    Normal way of throttling could be limiting the fuel or oxidizer flow to the TP. I think many gas generators do this. If this is how the Merlin 1D does it, it would always keep a fixed O/F ratio.
    The issue might be that you have an oxidizer that evaporates. And thus, if you can adjust the O/F you can make better use of the propellant reserves.
    Centaur and DIVUS do this regularly to optimize propellant usage. I could bet that the Vac version of the Merlin 1D does it to optimize for different mission profiles (a GTO transfer would have LOX boiloff).
    This valve might be the reason Merlin 1D Vac does 100% to 39% (data from F9 User Guide v2.0). It might also enable the center engine to also achieve better throttling capabilities. Albeit the core engine might be limited by the instabilities generated from an over-expanded nozzle.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: dkovacic on 01/18/2016 01:44 am
    Is there any known or expected difference between M1Dvac and M1D engines (except different nozzle)? In other words, would it be possible to take "worn out" engine from reusable S1, fit vacuum nozzle and mount it as S2 engine?
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Lars-J on 01/18/2016 02:29 am
    Is there any known or expected difference between M1Dvac and M1D engines (except different nozzle)? In other words, would it be possible to take "worn out" engine from reusable S1, fit vacuum nozzle and mount it as S2 engine?

    There are several differences, you cannot do this. The geometry of the nozzle (before nozzle extension) is very different, and on the vacuum model the turbopump exhaust is gimballed with the engine nozzle and injected into the nozzle. The M1DVac also has more thrust than the M1D.

    This is not M1D, but here is a picture showing the M1C (center) and M1C-Vac (right) - That should show you that there is MUCH more difference between these kinds of engines beside a nozzle extension.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Saabstory88 on 01/18/2016 02:31 am
    Is there any known or expected difference between M1Dvac and M1D engines (except different nozzle)? In other words, would it be possible to take "worn out" engine from reusable S1, fit vacuum nozzle and mount it as S2 engine?

    The thrust chamber / nozzle interface does not appear to be identical.

    http://www.spacex.com/sites/spacex/files/shiny_merlin_edited.jpg

    http://www.spacex.com/files/assets/img/merlinvac.jpg
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Llian Rhydderch on 01/18/2016 08:21 pm
    Is there any known or expected difference between M1Dvac and M1D engines (except different nozzle)? In other words, would it be possible to take "worn out" engine from reusable S1, fit vacuum nozzle and mount it as S2 engine?

    The thrust chamber / nozzle interface does not appear to be identical.

    http://www.spacex.com/sites/spacex/files/shiny_merlin_edited.jpg

    http://www.spacex.com/files/assets/img/merlinvac.jpg

    Yes, those two photographs are very helpful in showing for the Merlin 1D and Merlin 1Dvac the same sorts of differences that were shown above in the excellent post by Lars-J.

    Perhaps one of you, or another image-savvy editor, could make a side-by-side single image of those two, so that Lars-J's point could be well illustrated with the 1D technology.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Lars-J on 01/18/2016 11:15 pm
    Is there any known or expected difference between M1Dvac and M1D engines (except different nozzle)? In other words, would it be possible to take "worn out" engine from reusable S1, fit vacuum nozzle and mount it as S2 engine?

    The thrust chamber / nozzle interface does not appear to be identical.

    http://www.spacex.com/sites/spacex/files/shiny_merlin_edited.jpg

    http://www.spacex.com/files/assets/img/merlinvac.jpg

    Yes, those two photographs are very helpful in showing for the Merlin 1D and Merlin 1Dvac the same sorts of differences that were shown above in the excellent post by Lars-J.

    Perhaps one of you, or another image-savvy editor, could make a side-by-side single image of those two, so that Lars-J's point could be well illustrated with the 1D technology.

    Here's the best I could do. The angles are different, but I tried to size them such that the combustion chamber is the same size.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Saabstory88 on 01/19/2016 12:03 am
    Notice where the high pressure line from the RP-1 turbopump interfaces with the chamber wall. Those are likely the same distance on both engines. MVac even seems to have additional fuel cooled walls lower than this interface.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Llian Rhydderch on 01/19/2016 03:07 am
    Is there any known or expected difference between M1Dvac and M1D engines (except different nozzle)? In other words, would it be possible to take "worn out" engine from reusable S1, fit vacuum nozzle and mount it as S2 engine?

    The thrust chamber / nozzle interface does not appear to be identical.

    http://www.spacex.com/sites/spacex/files/shiny_merlin_edited.jpg

    http://www.spacex.com/files/assets/img/merlinvac.jpg

    Yes, those two photographs are very helpful in showing for the Merlin 1D and Merlin 1Dvac the same sorts of differences that were shown above in the excellent post by Lars-J.

    Perhaps one of you, or another image-savvy editor, could make a side-by-side single image of those two, so that Lars-J's point could be well illustrated with the 1D technology.

    Here's the best I could do. The angles are different, but I tried to size them such that the combustion chamber is the same size.

    That is a very useful graphic, Lars-J.  Very easy to see some of the major differences.

    I had not even been thinking of having pics of engines being fired, just side-by-sides of the two jpg photos that dkovacic had inserted into the discussion a few posts ago (shiny engines on the factory floor):

    http://www.spacex.com/sites/spacex/files/shiny_merlin_edited.jpg

    http://www.spacex.com/files/assets/img/merlinvac.jpg

    ... which would still look great in a side-by-side comparison image.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Lars-J on 01/19/2016 06:09 pm
    I had not even been thinking of having pics of engines being fired, just side-by-sides of the two jpg photos that dkovacic had inserted into the discussion a few posts ago (shiny engines on the factory floor):

    http://www.spacex.com/sites/spacex/files/shiny_merlin_edited.jpg

    http://www.spacex.com/files/assets/img/merlinvac.jpg

    ... which would still look great in a side-by-side comparison image.

    That last image is a M1C-Vac, not M1D-Vac. As you should be able to tell, the M1C-Vac is quite different than the M1D-Vac. That image of an M1DVac firing is the only public photo of the M1DVac that I have been able to find. (excluding rocket cam footage)

    If you can find a shiny M1D-Vac photo from the factory floor I would be happy to use it. :)
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Llian Rhydderch on 01/20/2016 02:48 am
    I had not even been thinking of having pics of engines being fired, just side-by-sides of the two jpg photos that dkovacic had inserted into the discussion a few posts ago (shiny engines on the factory floor):

    http://www.spacex.com/sites/spacex/files/shiny_merlin_edited.jpg

    http://www.spacex.com/files/assets/img/merlinvac.jpg

    ... which would still look great in a side-by-side comparison image.

    That last image is a M1C-Vac, not M1D-Vac. As you should be able to tell, the M1C-Vac is quite different than the M1D-Vac. That image of an M1DVac firing is the only public photo of the M1DVac that I have been able to find. (excluding rocket cam footage)

    If you can find a shiny M1D-Vac photo from the factory floor I would be happy to use it. :)

    Okay, thanks for clarifying.  I had understood that they were both M1D/M1Dvac engines from whomever originally posted the images. 
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Nomadd on 01/20/2016 02:59 am
     I told a SpaceX engineer I met a few days ago I could build them a variable geometry nozzle out of an old Buick Roadmaster hood and two used garage door openers to help increase the throttle range of the M1D. I'm pretty sure he was serious when he said they'd think about it.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: QuantumG on 01/20/2016 03:09 am
    I told a SpaceX engineer I met a few days ago I could build them a variable geometry nozzle out of an old Buick Roadmaster hood and two used garage door openers to help increase the throttle range of the M1D. I'm pretty sure he was serious when he said they'd think about it.

    That's some Northrop Grumman Lunar Lander Challenge engineering right there.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Lars-J on 01/20/2016 07:56 am
    I had not even been thinking of having pics of engines being fired, just side-by-sides of the two jpg photos that dkovacic had inserted into the discussion a few posts ago (shiny engines on the factory floor):

    http://www.spacex.com/sites/spacex/files/shiny_merlin_edited.jpg

    http://www.spacex.com/files/assets/img/merlinvac.jpg

    ... which would still look great in a side-by-side comparison image.

    That last image is a M1C-Vac, not M1D-Vac. As you should be able to tell, the M1C-Vac is quite different than the M1D-Vac. That image of an M1DVac firing is the only public photo of the M1DVac that I have been able to find. (excluding rocket cam footage)

    If you can find a shiny M1D-Vac photo from the factory floor I would be happy to use it. :)

    Okay, thanks for clarifying.  I had understood that they were both M1D/M1Dvac engines from whomever originally posted the images.

    How about this? I had to scale up the M1D-Vac image quite a bit, but I believe the relative size is very accurate. The nozzle extension is the red part. Hopefully this will kill further speculation that an M1D-Vac can be made by just adding a nozzle extension to an M1D.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: wardy89 on 01/20/2016 01:49 pm
    Earlier in this thread i remember seeing a picture of a merlin 1D with a black thermal coating for testing, https://forum.nasaspaceflight.com/index.php?topic=32983.msg1417111#msg1417111

    Looking at the pictures of the ORBCOMM-2 engines from the returned core it seems that this coating might well have made it all the way to the final version of the engine, do we know if this is the case?

    I don't remember reading anything more about it since seeing the picture on here, and don't recall any pre launch photos of the ORBCOMM-2 core showing the engines to confirm this.

    Edit: I know the general consensus is that the black coating was for better IR imaging on the test stand but looking at the images of the returned stage and how constant the black coating appears on the engines it just got me wondering.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Kabloona on 01/20/2016 04:48 pm
    Quote
    Looking at the pictures of the ORBCOMM-2 engines from the returned core it seems that this coating might well have made it all the way to the final version of the engine, do we know if this is the case?

    There's no need for black coating on flight engines and we know the OG2 engines didn't have it. Watch the SpaceX OG2 webcast on YouTube and at T-18:10 you'll see a top-down view of the stage with shiny nozzles at the bottom.

    What you're seeing in post-flight photos is soot.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Dante80 on 01/26/2016 07:06 pm
    https://www.youtube.com/watch?v=6glAvN5APh4 (https://www.youtube.com/watch?v=6glAvN5APh4)

    Hadn't seen that separation test around 0:36.

    Damn, that new nozzle is big! You can also see the added center pusher (in black).
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: kevinof on 01/26/2016 07:29 pm
    Hadn't seen that either and yes, that's a big nozzle. Like the sign they have up.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Dante80 on 01/26/2016 07:33 pm
    For reference, that image painted on the counter-weight is a Thwomp (https://www.google.gr/search?q=Thwomp&source=lnms&tbm=isch&sa=X&ved=0ahUKEwj0u43JqcjKAhWCOxQKHb_ZCF4Q_AUIBygB&biw=1120&bih=607) from the Super Mario videogames..


    Oh SpaceX.. ;D
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Lars-J on 01/26/2016 09:32 pm
    Hadn't seen that either and yes, that's a big nozzle. Like the sign they have up.

    According to my calculations based on image measurement, the nozzle is ~2.8m wide. It takes up ~78% of the 3.6m outside diameter of the interstage.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Herb Schaltegger on 01/26/2016 11:17 pm
    https://www.youtube.com/watch?v=6glAvN5APh4 (https://www.youtube.com/watch?v=6glAvN5APh4)

    Hadn't seen that separation test around 0:36.

    Damn, that new nozzle is big! You can also see the added center pusher (in black).

    I get "This video has been removed by the user." Anyone get a rip? Or at the least, explain what was in the video?

    Thanks.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Comga on 01/27/2016 02:29 am
    Hadn't seen that separation test around 0:36.

    Damn, that new nozzle is big! You can also see the added center pusher (in black).

    I get "This video has been removed by the user." Anyone get a rip? Or at the least, explain what was in the video?

    Thanks.
    Try over here. (http://forum.nasaspaceflight.com/index.php?topic=39182.msg1483572#msg1483572)
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: JBF on 01/27/2016 03:29 pm
    Does anyone have the current price/cost of the Merlin 1D?  DoD mentioned that the RD-180 costs ULA 30 million today and the last figure I heard about the 1D was 2 million each.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Prober on 01/28/2016 03:25 pm
    Does anyone have the current price/cost of the Merlin 1D?  DoD mentioned that the RD-180 costs ULA 30 million today and the last figure I heard about the 1D was 2 million each.


    9x2Mil = 1st stage 18mil
    1x ? = 2nd stage
    Total Finished F9 per EM 60 mil

    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: TomTX on 02/06/2016 12:44 pm

    Maybe I was not so clear but I didn't state the engines as a group don't have the ability to throttle up and down to a degree...only that E9, the center positioned engine has a actual added valve (the bi prop valve) and sensor package for throttling. The other positions may or may not have the same or lesser degrees of throttling as well. ;)
    So you are saying there are _four_ flavors of 1D engine? One for vacuum, one for center engine, one for two outer engines used for SSRP and one for the rest?

    I believe Both Musk and Shotwell have publicly stated their desire to minimize variants - for both manufacturing and system architecture perspectives.

    I suggest one and only one Marlin-1D SL flavor. It's restartable from an external (to engine) TEA/TEB system, and has the full throttle range afforded to a 1D.

    Let me ask this - it's commonly understood that engine start during launch is via GSE, correct? What's that architecture? It certainly doesn't have nine pairs of lines running from GSE to individual engines, right? So if you accept that, then you must also accept that the engine start plumbing to each engine comes from a single point on the rocket. (Let's call it a distribution manifold - see where this is going?). Now it's also accepted that three engines are also restarted via onboard systems. So does it make sense to have a entire second system for the restarts designed into certain engines, with all that extra unneeded redundancy and complication, or would it make more sense to utilize the same plumbing and manifold structure already in place for the GSE fed start for the relights?

    So the addition of valves to direct the relights to particular engine(s) provides a uniform architecture (only one flavor) and also provides opportunity to go to another outside opposing pair if the initial pair has issues relighting.

    Is it a plausible answer that the engines are throttled as a group and that only the center engine can individually throttle due to added biprop valve?
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: TomTX on 02/06/2016 12:50 pm
    Landed M1D FT cluster up-close

    https://twitter.com/SpaceX/status/684094378021801984

    higher res, using the :orig tag.

    Lots of asymmetrical accretion of crusties* both inside and outside the nozzles, plus more at the mounting - that should give a lot of useful information by pattern and compositional analysis.

    *First estimate is primarily mixed metal oxides, but I'd need to start with some FTIR  and ICP-MS (maybe LIBZ, if they have calibration curves for their materials. Manufacturer curves tend to be good on steel and aluminum alloys) to get an outline of composition.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Comga on 02/13/2016 10:25 pm
    The new user's guide covers both F9 and FH:  http://www.spacex.com/sites/spacex/files/falcon_9_users_guide_rev_2.0.pdf (http://www.spacex.com/sites/spacex/files/falcon_9_users_guide_rev_2.0.pdf)

    This says, on page 11, that the first stage engines can throttle to 70% (119 klbf vs 170 klbf @ sea level) but the second stage Merlin 2 Vac can throttle below 39% (81 klbf vs 210 klbf vacuum). 

    39% is pretty deep throttling!
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: S.Paulissen on 02/15/2016 04:15 pm
    Landed M1D FT cluster up-close

    https://twitter.com/SpaceX/status/684094378021801984

    higher res, using the :orig tag.

    Lots of asymmetrical accretion of crusties* both inside and outside the nozzles, plus more at the mounting - that should give a lot of useful information by pattern and compositional analysis.

    *First estimate is primarily mixed metal oxides, but I'd need to start with some FTIR  and ICP-MS (maybe LIBZ, if they have calibration curves for their materials. Manufacturer curves tend to be good on steel and aluminum alloys) to get an outline of composition.

    To my highly untrained eyes it looks like residue/ash from very slow burning kerosene (hypoxic environment) that was dripping down from the injector after shutdown.  (Notice that it's primarily on the two outboard engines probably of the three engine reentry burn.)  My explanation for why it's not on the center engine is that the center engine refired again for landing and had plenty of atmosphere to more cleanly burn off the kerosene at sea level.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Kabloona on 02/15/2016 04:20 pm
    Landed M1D FT cluster up-close

    https://twitter.com/SpaceX/status/684094378021801984

    higher res, using the :orig tag.

    Lots of asymmetrical accretion of crusties* both inside and outside the nozzles, plus more at the mounting - that should give a lot of useful information by pattern and compositional analysis.

    *First estimate is primarily mixed metal oxides, but I'd need to start with some FTIR  and ICP-MS (maybe LIBZ, if they have calibration curves for their materials. Manufacturer curves tend to be good on steel and aluminum alloys) to get an outline of composition.

    To my highly untrained eyes it looks like residue/ash from very slow burning kerosene (hypoxic environment) that was dripping down from the injector after shutdown.  (Notice that it's primarily on the two outboard engines probably of the three engine reentry burn.)  My explanation for why it's not on the center engine is that the center engine refired again for landing and had plenty of atmosphere to more cleanly burn off the kerosene at sea level.

    This has been discussed elsewhere. It's likely the oxides of aluminum and boron, residue from the TEA/TEB ignition fluid. The TEA/TEB ignition fluid is probably injected into all three engines at every restart event for simplicity of plumbing design, even though the landing burn uses only the center engine.

     The landing burn burns off the TEA/TEB residue in the center engine, but since the outer two engines are not used in the landing burn, the TEA/TEB residue from the landing burn restart remains in those two nozzles.

    http://forum.nasaspaceflight.com/index.php?topic=39257.msg1471588#msg1471588
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: S.Paulissen on 02/15/2016 04:24 pm
    This has been discussed elsehwhere. It's likely the oxides of aluminum and boron, residue from the TEA/TEB ignition fluid. The TEA/TEB ignition fluid is probably injected into all three engines at every restart event for simplicity of plumbing design, even though the landing burn uses only the center engine.

     The landing burn burns off the TEA/TEB residue in the center engine, but since the outer two engines are not used in the landing burn, the TEA/TEB residue from the landing burn restart remains in those two nozzles.

    Thanks for the information, that does make a lot of sense. You too TomTX. 
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Lars-J on 05/07/2016 01:43 am
    Elon tweeted this a few minutes ago:

    https://twitter.com/elonmusk/status/728753234811060224
    "@lukealization Max is just 3X Merlin thrust and min is ~40% of 1 Merlin. Two outer engines shut off before the center does."

    There had been some disagreement about the throttle range of the M1D - did it have a 40% range or could it throttle down to 40%? But this confirms it - it can throttle down to 40%. (A 60% range)
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: MP99 on 05/07/2016 10:39 am
    Elon tweeted this a few minutes ago:

    https://twitter.com/elonmusk/status/728753234811060224
    "@lukealization Max is just 3X Merlin thrust and min is ~40% of 1 Merlin. Two outer engines shut off before the center does."

    There had been some disagreement about the throttle range of the M1D - did it have a 40% range or could it throttle down to 40%? But this confirms it - it can throttle down to 40%. (A 60% range)
    40% to 112% is a 65% range. (Can't remember if that 112% is current for the "full but not 1.7 mblf thrust" engine?)

    Cheers, Martin
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Greg Pecchia on 05/14/2016 11:36 pm
    Any new info on the further improvement of the Merlin 1D?

    https://en.wikipedia.org/wiki/Merlin_%28rocket_engine_family%29#Merlin_1D

    In May 2016, SpaceX announced plans to further uprate the Merlin 1D by increasing vacuum thrust to 914 kN and sea-level thrust to 845 kN.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: wannamoonbase on 05/15/2016 01:02 pm
    Any new info on the further improvement of the Merlin 1D?

    https://en.wikipedia.org/wiki/Merlin_%28rocket_engine_family%29#Merlin_1D

    In May 2016, SpaceX announced plans to further uprate the Merlin 1D by increasing vacuum thrust to 914 kN and sea-level thrust to 845 kN.

    Edit: 10.8% increase in vacuum thrust.  Nice.
    A great summary.  I'd been looking forward to an evolutionary summary.

    It's very exciting to see the steady progression.  I'm a fan of the iterative develop, fly, develop, fly progression.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: gospacex on 05/28/2016 06:34 pm
    Looking at the photos of aft end... it's amazing outer engine bells can work while so closely spaced. With all the vibration, I swear it looks like this should not be possible :D
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: PahTo on 05/29/2016 05:42 am
    Looking at the photos of aft end... it's amazing outer engine bells can work while so closely spaced. With all the vibration, I swear it looks like this should not be possible :D

    FH should prove...interesting.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: ngilmore on 05/29/2016 06:18 am
    During the Thaicom-8 launch coverage for regular folks, one of the announcers gave very specific thrust numbers for the Merlin - something like, "it can throttle from 80,000 lbf to 210,000 lbf". I believe he gave even more digits of precision, that's my rough memory.

    I'm too lazy to rewatch it to get the exact quote.

    I'm sure you all were watching the Technical Broadcast and missed it.  ::)
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: wannamoonbase on 05/29/2016 06:31 am
    During the Thaicom-8 launch coverage for regular folks, one of the announcers gave very specific thrust numbers for the Merlin - something like, "it can throttle from 80,000 lbf to 210,000 lbf". I believe he gave even more digits of precision, that's my rough memory.

    I'm too lazy to rewatch it to get the exact quote.

    I'm sure you all were watching the Technical Broadcast and missed it.  ::)

    I remember that, I believe that was for the M-Vac, which if I recall has a larger throttle range than the first stage Merlin
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: mnelson on 05/30/2016 05:45 am
    During the Thaicom-8 launch coverage for regular folks, one of the announcers gave very specific thrust numbers for the Merlin - something like, "it can throttle from 80,000 lbf to 210,000 lbf". I believe he gave even more digits of precision, that's my rough memory.

    I'm too lazy to rewatch it to get the exact quote.

    I'm sure you all were watching the Technical Broadcast and missed it.  ::)

    I remember that, I believe that was for the M-Vac, which if I recall has a larger throttle range than the first stage Merlin

    You are both correct. It was 80,000 lbf - 210,000 lbf for the M-Vac. It is at 49:00 in the hosted webcast video which is T+27:32 on the countdown clock.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Kabloona on 05/30/2016 10:51 am
    During the Thaicom-8 launch coverage for regular folks, one of the announcers gave very specific thrust numbers for the Merlin - something like, "it can throttle from 80,000 lbf to 210,000 lbf". I believe he gave even more digits of precision, that's my rough memory.

    I'm too lazy to rewatch it to get the exact quote.

    I'm sure you all were watching the Technical Broadcast and missed it.  ::)

    I remember that, I believe that was for the M-Vac, which if I recall has a larger throttle range than the first stage Merlin

    You are both correct. It was 80,000 lbf - 210,000 lbf for the M-Vac. It is at 49:00 in the hosted webcast video which is T+27:32 on the countdown clock.

    Not both correct. That range of throttling (down to 40%) can also be achieved by the M1D according to a recent Elon tweet in reply to a question about the 3-engine landing burn. He said center engine throttles down to 40% for landing.

    Quote
    Elon Musk – Verified account ‏@elonmusk

    @lukealization Max is just 3X Merlin thrust and min is ~40% of 1 Merlin. Two outer engines shut off before the center does.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: rpapo on 05/30/2016 10:58 am
    Not both correct. That range of throttling (down to 40%) can also be achieved by the M1D according to a recent Elon tweet in reply to a question about the 3-engine landing burn. He said center engine throttles down to 40% for landing.
    I wonder how much the back-pressure in the bells from the 300mph+ descent affects this?
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Kabloona on 05/30/2016 11:31 am
    Not both correct. That range of throttling (down to 40%) can also be achieved by the M1D according to a recent Elon tweet in reply to a question about the 3-engine landing burn. He said center engine throttles down to 40% for landing.
    I wonder how much the back-pressure in the bells from the 300mph+ descent affects this?

    There isn't any "back pressure" after the engine restarts, so there's no aero effect on engine thrust or throttling.

    Exhaust flow after the nozzle throat is supersonic, which means no information about external pressure can flow upstream back into the nozzle. Conditions inside the engine/nozzle are exactly the same regardless of external atmospheric conditions (except for low ambient pressure that could cause flow separation inside the nozzle, but that's a different condition.) 

    If the stage is supersonic during retropropulsion, a bow shock will form outside the nozzle, but that's still downstream of the exit plane and so doesn't affect engine thrust. If subsonic, no bow shock, and same logic applies.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: rpapo on 05/30/2016 11:44 am
    There isn't any "back pressure" after the engine restarts, so there's no aero effect on engine thrust or throttling.

    Exhaust flow after the nozzle throat is supersonic, which means no information about external pressure can flow upstream back into the nozzle. Conditions inside the engine/nozzle are exactly the same regardless of external atmospheric conditions (except for low ambient pressure that could cause flow separation inside the nozzle, but that's a different condition.) 

    If the stage is supersonic during retropropulsion, a bow shock will form outside the nozzle, but that's still downstream of the exit plane and so doesn't affect engine thrust. If subsonic, no bow shock, and same logic applies.
    Thank you for the reminder of the implications of supersonic flow.  My still slightly sleepy mind was thinking along the lines of back pressure increasing the chance of flow separation further down the nozzle, and thereby reducing the throttleability of the motors.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: baldusi on 05/30/2016 12:53 pm
    Not both correct. That range of throttling (down to 40%) can also be achieved by the M1D according to a recent Elon tweet in reply to a question about the 3-engine landing burn. He said center engine throttles down to 40% for landing.
    I wonder how much the back-pressure in the bells from the 300mph+ descent affects this?

    There isn't any "back pressure" after the engine restarts, so there's no aero effect on engine thrust or throttling.

    Exhaust flow after the nozzle throat is supersonic, which means no information about external pressure can flow upstream back into the nozzle. Conditions inside the engine/nozzle are exactly the same regardless of external atmospheric conditions (except for low ambient pressure that could cause flow separation inside the nozzle, but that's a different condition.) 

    If the stage is supersonic during retropropulsion, a bow shock will form outside the nozzle, but that's still downstream of the exit plane and so doesn't affect engine thrust. If subsonic, no bow shock, and same logic applies.
    The supersonic flow is at the throat, not at the nozzle plane. So it might impact a bit and you could suffer from flow separation at the nozzle tip. Obviously not close to the throat.
    What the retroburn might cause is to increases the effective ambient pressure, and for that it would like a lower nozzle expansion to get optimum performance. But I'm not quite sure.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Dante80 on 05/30/2016 01:34 pm
    According to the info we have available.

    M9

    Thrust :.
    SL 845 kN - (190,000 lbf)
    Vac 914 kN - (205,500 lbf)

    Weight :. 467kg (1030 lb) together with the actuators.

    TWR :. SL 184.4, Vac 199.5

    Throttle range :. 338 kN - 914 kN (76,000 lbf - 205,500 lbf)

    MVac

    Thrust :. Vac 934 kN (210,000 lbf)

    Throttle range :. 356kN - 934 kN (80,000 lbf - 210,000 lbf)
     
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Robotbeat on 05/30/2016 02:03 pm
    Not both correct. That range of throttling (down to 40%) can also be achieved by the M1D according to a recent Elon tweet in reply to a question about the 3-engine landing burn. He said center engine throttles down to 40% for landing.
    I wonder how much the back-pressure in the bells from the 300mph+ descent affects this?
    The back pressure actually probably improves things. It's easier to light an engine at pressure than in vacuum.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: oldAtlas_Eguy on 05/30/2016 03:27 pm
    You have to realize that the SL low throttle thrust if it was a M1C would be 77% of the M1C SL. The exit plane area of the M1D and M1C is the same. What is different is the the M1D has a smaller throat and higher TC pressures. So throttling down to just below the exit plane velocities that an M1C had should work fine without much problems in SL pressure conditions.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Kabloona on 05/30/2016 06:51 pm
    Not both correct. That range of throttling (down to 40%) can also be achieved by the M1D according to a recent Elon tweet in reply to a question about the 3-engine landing burn. He said center engine throttles down to 40% for landing.
    I wonder how much the back-pressure in the bells from the 300mph+ descent affects this?

    There isn't any "back pressure" after the engine restarts, so there's no aero effect on engine thrust or throttling.

    Exhaust flow after the nozzle throat is supersonic, which means no information about external pressure can flow upstream back into the nozzle. Conditions inside the engine/nozzle are exactly the same regardless of external atmospheric conditions (except for low ambient pressure that could cause flow separation inside the nozzle, but that's a different condition.) 

    If the stage is supersonic during retropropulsion, a bow shock will form outside the nozzle, but that's still downstream of the exit plane and so doesn't affect engine thrust. If subsonic, no bow shock, and same logic applies.
    The supersonic flow is at the throat, not at the nozzle plane. So it might impact a bit and you could suffer from flow separation at the nozzle tip. Obviously not close to the throat.

    Nozzle throat is always choked *sonic* flow, not supersonic. Then as exhaust expands downstream of throat, it goes supersonic. So it is actually supersonic at the exit plane, but only sonic at throat.

    http://physics.stackexchange.com/questions/107191/why-do-rocket-engines-have-a-throat (http://physics.stackexchange.com/questions/107191/why-do-rocket-engines-have-a-throat)

    Edit: correction
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: cambrianera on 05/30/2016 08:52 pm
    Well, separation occurs if Pa>Pe, (ambient pressure larger than exit pressure) not the opposite.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Kabloona on 05/30/2016 09:25 pm
    Well, separation occurs if Pa>Pe, (ambient pressure larger than exit pressure) not the opposite.

    Yes, got my signs backwards. Corrected.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Robotbeat on 05/31/2016 01:31 am
    Well, separation occurs if Pa>Pe, (ambient pressure larger than exit pressure) not the opposite.
    True, though you can get away with a little Pa>Pe. I think Merlin 1D is slightly under-expanded on take-off.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: S.Paulissen on 05/31/2016 01:52 am
    You have to realize that the SL low throttle thrust if it was a M1C would be 77% of the M1C SL. The exit plane area of the M1D and M1C is the same. What is different is the the M1D has a smaller throat and higher TC pressures. So throttling down to just below the exit plane velocities that an M1C had should work fine without much problems in SL pressure conditions.

    Is there evidence for this? I've not seen that particular assertion before.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: obi-wan on 05/31/2016 04:24 am
    Well, separation occurs if Pa>Pe, (ambient pressure larger than exit pressure) not the opposite.
    True, though you can get away with a little Pa>Pe. I think Merlin 1D is slightly under-expanded on take-off.
    Almost all first stage engines are over-expanded at liftoff and under-expanded at MECO. At launch, Pa>Pe, and an oblique shock at the exit plane causes the flow to "neck down" as you always saw in the close-ups of SSMEs at ignition. (These oblique shocks also give rise to the classic "shock diamonds" in the exhaust.) Pa has to be more than twice Pe for the flow to actually be separated, which means the oblique shocks move up into the nozzle and the flow lines depart from the nozzle up inside, which is very inefficient and greatly to be avoided. First stage engines are ideally expanded (Pa=Pe) at only one altitude, and at that point the flow of the exhaust will perfectly match the exit angle of the nozzle. Above that altitude, the nozzle is under-expanded, and an expansion wave at the exhaust will cause the flow to bend outwards and form the large "fans" you see from about Max-Q to MECO. Upper stage engines are always under-expanded, because the nozzle would have to be infinitely long to match exit pressure to the vacuum ambient conditions. The nozzles are as long as practical to get the best performance in vacuum, though.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Comga on 05/31/2016 04:45 am
    According to the info we have available.

    M9

    Thrust :.
    SL 845 kN - (190,000 lbf)
    Vac 914 kN - (205,500 lbf)

    Weight :. 467kg (1030 lb) together with the actuators.

    TWR :. SL 184.4, Vac 199.5

    Throttle range :. 338 kN - 914 kN (76,000 lbf - 205,500 lbf)

    MVac

    Thrust :. Vac 934 kN (210,000 lbf)

    Throttle range :. 356kN - 934 kN (80,000 lbf - 210,000 lbf)

    There really isn't anything designated "M9", is there?
    Perhaps that's a typo for M1?
    And both sets of thrust values represent sligtly more than 60% reductions from max to min, showing throttling to about 37% and 38% for the M1 and M1Vac respectively.
    Either these are excessive or Musk rounded off when stating throttling to "40%".
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: mvpel on 05/31/2016 07:37 am
    And both sets of thrust values represent sligtly more than 60% reductions from max to min, showing throttling to about 37% and 38% for the M1 and M1Vac respectively.
    Either these are excessive or Musk rounded off when stating throttling to "40%".

    Elon, like me, has come to realize over the decades that when talking to regular people, saying things like "38.1%" in extemporaneous remarks makes you sound like a Vulcan, which is slightly off-putting in most situations. And so we think 38.1%, but very consciously say "40%" or "about 40%" instead, unless we're talking to a colleague who's more likely to be appreciative - or less preferably, impressed - rather than put off by that level of extemporaneous precision.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Dante80 on 05/31/2016 01:36 pm
    According to the info we have available.

    M9

    Thrust :.
    SL 845 kN - (190,000 lbf)
    Vac 914 kN - (205,500 lbf)

    Weight :. 467kg (1030 lb) together with the actuators.

    TWR :. SL 184.4, Vac 199.5

    Throttle range :. 338 kN - 914 kN (76,000 lbf - 205,500 lbf)

    MVac

    Thrust :. Vac 934 kN (210,000 lbf)

    Throttle range :. 356kN - 934 kN (80,000 lbf - 210,000 lbf)

    There really isn't anything designated "M9", is there?
    Perhaps that's a typo for M1?
    And both sets of thrust values represent sligtly more than 60% reductions from max to min, showing throttling to about 37% and 38% for the M1 and M1Vac respectively.
    Either these are excessive or Musk rounded off when stating throttling to "40%".

    M9 is how SpaceX internally call their first stage merlin engines. MVac is how they call their second stage merlin engines. Here is Musk on it (bottom of the e-mail).

    (http://i.imgur.com/waUJnnH.png)

    Regarding the thrust values. For MVac, this is the exact quote we got from the stream (80,000 lbf - 210,000 lbf). For M9, Musk has tweeted 40% of throttle @landing. This makes the lowest thrust output for M9 76,000 lbf, with the max being 190,000 lbf at launch, and 205,500 lbf at vacuum.The throttle range in that situation is exactly 40-100%.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: John Alan on 05/31/2016 02:22 pm
    Questions...
    Are they all in, all done at 190,000 sl-lbf... ??
    Have we now seen the final top thrust numbers planned on SpaceX Merlin series rocket engines... ??
    Will they run S1 at that 9 x 190K all the time off the pad... or only when needed... ??
    Will this now get them to the published 5500kg to GTO-1800 with ASDS recovery and S1 in reusable condition target shown on their website... ??
    ???
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Dante80 on 05/31/2016 02:36 pm
    Questions...
    Are they all in, all done at 190,000 sl-lbf... ??
    Have we now seen the final top thrust numbers planned on SpaceX Merlin series rocket engines... ??
    Will they run S1 at that 9 x 190K all the time off the pad... or only when needed... ??
    Will this now get them to the published 5500kg to GTO-1800 with ASDS recovery and S1 in reusable condition target shown on their website... ??
     ???

    I'll try to answer some of that.


    Are they all in, all done at 190,000 sl-lbf... ??
    Have we now seen the final top thrust numbers planned on SpaceX Merlin series rocket engines... ??

    No idea. They seem to keep upping performance as they get more data and knowledge on the engine and what it can do. It would not be absurd to think they will keep working on it with performance, cost and re-usability goals in mind.

    Will they run S1 at that 9 x 190K all the time off the pad... or only when needed... ??
    There is no reason to launch a vehicle @less than max thrust/throttle. Ever.

    Will this now get them to the published 5500kg to GTO-1800 with ASDS recovery and S1 in reusable condition target shown on their website... ??
    That is their official advertisement on their site, and what they are aiming for.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: philw1776 on 05/31/2016 02:44 pm
    Questions...
    Are they all in, all done at 190,000 sl-lbf... ??
    Have we now seen the final top thrust numbers planned on SpaceX Merlin series rocket engines... ??
    Will they run S1 at that 9 x 190K all the time off the pad... or only when needed... ??
    Will this now get them to the published 5500kg to GTO-1800 with ASDS recovery and S1 in reusable condition target shown on their website... ??
     ???

    I'll try to answer some of that.


    Are they all in, all done at 190,000 sl-lbf... ??
    Have we now seen the final top thrust numbers planned on SpaceX Merlin series rocket engines... ??

    No idea. They seem to keep upping performance as they get more data and knowledge on the engine and what it can do. It would not be absurd to think they will keep working on it with performance, cost and re-usability goals in mind.

    Will they run S1 at that 9 x 190K all the time off the pad... or only when needed... ??
    There is no reason to launch a vehicle @less than max thrust/throttle. Ever.

    Will this now get them to the published 5500kg to GTO-1800 with ASDS recovery and S1 in reusable condition target shown on their website... ??
    That is their official advertisement on their site, and what they are aiming for.

    And the reason you launch at max thrust is to mitigate propellant wasting gravity losses as much as possible. 
    There is a secondary benefit in that you also minimize the sudden impact of an engine loss.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: envy887 on 05/31/2016 03:21 pm
    Will they run S1 at that 9 x 190K all the time off the pad... or only when needed... ??
    There is no reason to launch a vehicle @less than max thrust/throttle. Ever.


    That's not entirely true. The pad might not be able to take that thrust level, or the reflected acoustical energy near the pad might damage the rocket/pad, or any number of similar reasons might limit the liftoff thrust. Musk stated that liftoff thrust will be less than "capable" in flight thrust. Whether that means there will be a throttle-up after liftoff isn't clear, but it seems possible.

    Quote
    Elon Musk ‏@elonmusk  Apr 30
    F9 thrust at liftoff will be raised to 1.71M lbf later this year. It is capable of 1.9M lbf in flight.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Rebel44 on 05/31/2016 03:29 pm
    Will they run S1 at that 9 x 190K all the time off the pad... or only when needed... ??
    There is no reason to launch a vehicle @less than max thrust/throttle. Ever.


    ..... Musk stated that liftoff thrust will be less than "capable" in flight thrust. Whether that means there will be a throttle-up after liftoff isn't clear, but it seems possible.

    Quote
    Elon Musk ‏@elonmusk  Apr 30
    F9 thrust at liftoff will be raised to 1.71M lbf later this year. It is capable of 1.9M lbf in flight.

    That is just the difference between performance of 9 Merlin engines at sea level and in vacuum*

    * based on published numbers at SpaceX website.

    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: envy887 on 05/31/2016 03:43 pm
    That is just the difference between performance of 9 Merlin engines at sea level and in vacuum*
    * based on published numbers at SpaceX website.
    That makes sense. FH will be throttling down the center core in flight, implying that it lifts off at or near open throttle, so a single F9 with 1/3 the thrust shouldn't have any pad issues at open throttle.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: oldAtlas_Eguy on 05/31/2016 08:49 pm
    You have to realize that the SL low throttle thrust if it was a M1C would be 77% of the M1C SL. The exit plane area of the M1D and M1C is the same. What is different is the the M1D has a smaller throat and higher TC pressures. So throttling down to just below the exit plane velocities that an M1C had should work fine without much problems in SL pressure conditions.

    Is there evidence for this? I've not seen that particular assertion before.
    For the same exit area and a higher expansion ratio  the throat has to be smaller. M1D has a significant larger expansion ratio over that of the M1C. Exit area/throat area = expansion ratio.
    M1C expansion ratio = ~12
    M1D expansion ratio = ~16
    [Exact figures are not published or either just the approximates]
    M1C TC pressure = ~1000 psi
    M1D TC preasure = >1400 psi

    From this thread discussion of tidbits of released SpaceX data as far back as 2011.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: cambrianera on 05/31/2016 09:07 pm
    Expansion ratio should be 14.5 for M1C and 16 for M1D.
    http://forum.nasaspaceflight.com/index.php?topic=26388.msg792218#msg792218

    "Revealing several new details of the 1D, Tom Mueller, propulsion engineering vice president, says the engine is designed to produce 155,000 lb. vacuum thrust and have a chamber pressure at “the sweet spot” of roughly 1,410 psia. “We’ve also increased the nozzle expansion ratio to 16 [compared with 14.5 on the Merlin 1C],” says Mueller"

    from Aviationweek aug 2011
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: MP99 on 05/31/2016 09:19 pm


    Will they run S1 at that 9 x 190K all the time off the pad... or only when needed... ??
    There is no reason to launch a vehicle @less than max thrust/throttle. Ever.


    And yet, SSME max thrust was 109%, but it launched at 104.5% because that was the maximum they were comfortable with unless the situation was so desperate that this was the lesser risk.

    Cheers, Martin
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Modal on 05/31/2016 09:48 pm


    Will they run S1 at that 9 x 190K all the time off the pad... or only when needed... ??
    There is no reason to launch a vehicle @less than max thrust/throttle. Ever.

    And yet, SSME max thrust was 109%, but it launched at 104.5% because that was the maximum they were comfortable with unless the situation was so desperate that this was the lesser risk.


    Why would NASA run the SSMEs at lower throttle? Was it because the thrust was angled, or because the SSMEs were way over expanded at SL?
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: TrueBlueWitt on 05/31/2016 09:51 pm


    Will they run S1 at that 9 x 190K all the time off the pad... or only when needed... ??
    There is no reason to launch a vehicle @less than max thrust/throttle. Ever.


    And yet, SSME max thrust was 109%, but it launched at 104.5% because that was the maximum they were comfortable with unless the situation was so desperate that this was the lesser risk.

    Cheers, Martin

    Which is why I asked earlier about the max thrust setting available in current(pre190klbf nominal) profile for M-1D? Is that setting available today if needed to prevent a LOM due to some other failures?
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: PahTo on 05/31/2016 10:30 pm

    Why would NASA run the SSMEs at lower throttle? Was it because the thrust was angled, or because the SSMEs were way over expanded at SL?

    MP99 touched on it--mission and system managers determined the SSME throttle level was the best for safety and performance (and in that order).  Indeed, some of the work being done now with engine controllers is to have more (safety) confidence in running the engines at max rating.

    EDIT--apologies for going OT, but hey, here's a SpX thread talking SSME/SLS...  :)
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: envy887 on 06/01/2016 12:56 pm

    Why would NASA run the SSMEs at lower throttle? Was it because the thrust was angled, or because the SSMEs were way over expanded at SL?

    MP99 touched on it--mission and system managers determined the SSME throttle level was the best for safety and performance (and in that order).
    ...

    Rocket engines are typically throttled by varying turbopump RPMs, so "wide open" throttle is really a limit on how fast the turbopumps can spin before they start going kabloomy. "Max throttle" is really "Max safe throttle", on both SSMEs and Merlins.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: John Alan on 06/01/2016 08:01 pm
    Questions...  ???

    Do you think the rotating assy in the turbopump is identical in the M9 and Mvac... ??

    Do you think it's possible there are minor changes/upgrades to such an assy from time to time... ??

    Do you think maybe it's not only software, but minor hardware changes to allow getting to the announced thrust reliably... ??

    Do you think the engines on the CRS-8 stage may not be just a flash upgrade to refly at upgraded levels... ??

    Myself... all 4 question are YES... they are earlier level designs and built last year during the RTF stand-down..,
    They may not fly again unless they get at least some upgrades... or may just be scrapped...

    My opinion... they have run test engines on the stand recently to over 225K+ sea level to validate where they are at on latest design changes and now feel good about releasing a 190K/205K M9 to match the already released 210K Mvac...
    I base this on what I understand GE does to validate jet engines... run them up at/over rpm redline till thrust is at least 10% over requirement... The GE90/115B holds a world record that surprised me...  :o
    https://en.wikipedia.org/wiki/General_Electric_GE90#GE90-115B (https://en.wikipedia.org/wiki/General_Electric_GE90#GE90-115B)
    http://www.geaviation.com/commercial/engines/ge90/

    But what do I know... Just waving my hands here and offering an opinion...  ;)
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: deruch on 06/07/2016 03:55 am
    Questions...
    Are they all in, all done at 190,000 sl-lbf... ??
    Have we now seen the final top thrust numbers planned on SpaceX Merlin series rocket engines... ??

    I would imagine that even if they are not currently considering increasing thrust goals in the future, they are still looking at ways to improve producibility of the engines.  And, if they come up with a way to significantly improve that, they will be willing to revisit their thrust levels again.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: matthewkantar on 07/02/2016 03:31 am
    Nice pic of some welds on a Merlin-1D on Instagram:

    link :https://www.instagram.com/p/BHVLJBGjXAe/?taken-by=spacex

    Enjoy, Matthew
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Adriano on 07/26/2016 07:31 pm
    When you throttle down an engine you reduce the chamber pressure and the efficiency of the engine quickly deteriorates. Correct? Much better shutting off one of the engines than throttling all engines down. Of course that raises the issue of restarting the engine...
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Adriano on 07/26/2016 07:41 pm
    Theoretically you ca actually increase the efficiency of a throttled down engine by decreasing the throat area to preserve the chamber pressure. That also increases the nozzle expansion and, if the original nozzle was under expanded in the flight conditions, the efficiency of the engine would actually increase...
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Adriano on 07/26/2016 07:52 pm
    For example we could modify the pintle by placing at its center a movable cone that can be moved into the throat reducing its area. The pintle architecture could e modified and use the fuel flow to cool the center cone and its support. We add complexity, but that may make sense in a reusable rocket.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Roy_H on 07/26/2016 07:55 pm
    When you throttle down an engine you reduce the chamber pressure and the efficiency of the engine quickly deteriorates. Correct? Much better shutting off one of the engines than throttling all engines down. Of course that raises the issue of restarting the engine...

    Yes, but there seems to be a strong aversion to shutting down even though there is lots of experience with re-starts. I think some day there will be enough confidence to do that.

    AFAIK no one has built a rocket engine with a variable throat size. Major challenge given the forces and temperatures involved.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: envy887 on 07/26/2016 08:32 pm
    When you throttle down an engine you reduce the chamber pressure and the efficiency of the engine quickly deteriorates. Correct?

    Partly correct. The chamber pressure decreases, but engine efficiency does not quickly deteriorate.

    The Merlin, for example, only loses about 15% of it's specific impulse when throttled to 40% thrust at sea level. When Merlin Vacuum is throttled to 30% of max thrust, it only loses about 1% of of it's specific impulse.

    Source: model of known Merlin parameters in RPA lite.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: wannamoonbase on 07/26/2016 08:51 pm
    When you throttle down an engine you reduce the chamber pressure and the efficiency of the engine quickly deteriorates. Correct?

    Partly correct. The chamber pressure decreases, but engine efficiency does not quickly deteriorate.

    The Merlin, for example, only loses about 15% of it's specific impulse when throttled to 40% thrust at sea level. When Merlin Vacuum is throttled to 30% of max thrust, it only loses about 1% of of it's specific impulse.

    Source: model of known Merlin parameters in RPA lite.

    The Vac number is impressive.  Really nice that they can manage thrust and not lose much efficiency. 

    Is it safe to assume a higher combustion chamber pressure Raptor would have more or less efficiency change with throttling?
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: baldusi on 07/26/2016 10:19 pm
    Define quickly. RD-180 loses 3sec of isp when doing 50% (yes, it's that good). Don't forget that you usually throttle by reducing the oxidizer flow. Since fuel is usually lighter, the O/F increases isp. And if you are in vacuum, the expansion give you a lower output pressure. So the performance loss is not as steep.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: envy887 on 07/26/2016 10:43 pm
    Higher chamber pressures will have lower throttling losses at sea level, because the throttled pressure is still much higher than sea level ambient. That's why the RD180 is so good.

    In vacuum it's really irrelevant; since there's no back pressure, chamber pressure has little effect on ISP.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Adriano on 07/27/2016 03:32 pm
    I think I get it. At altitude nozzles are under expanded and drive isp so pressure reduction does not reduce isp. At ground level instead pressure reduction result in over expanded nozzle and loss of isp. Does that mean rd180 nozzle is under expanded at ground level? Why give up isp from longer nozzle?
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: DOCinCT on 08/09/2016 08:52 pm
    Can someone provide basic physical specifications (length, width, weight) of the Merlin 1D and 1Dvac?
    I've pieced together some, but information via web search is hard to come by.
    (I'm doing some comparison to RS-25, RS-68A and J2X)
    Thanks
    Alan
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: symbios on 08/11/2016 10:11 am
    Did not see this here..

    From SpaceX facebook by Mike Hawes
    Quote
    Wow, so we've learned that SpaceX will be phasing out single engine testing at McGregor! (Gwynne, end of Q&A, Small Sat Conference)

    Have not seen the video of the conference yet.

    Edit: Just finished watching the video at about 1:01:46:
    Quote
    We are likely to go away from single engine tests on Merlin, you know, once we have finalized the design and show great decrease variability, i say, greater non variability, decrease variability
    My emphasis
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: AncientU on 08/11/2016 11:42 am
    Should be a nice decrease in costs and improvement in flow.

    Talk of dropping the static fire another simplification that is discussed -- no timing known, but could flow from the same logic.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: JamesH65 on 08/11/2016 11:59 am
    Should be a nice decrease in costs and improvement in flow.

    Talk of dropping the static fire another simplification that is discussed -- no timing known, but could flow from the same logic.

    So do they test all 9 at once on the stage at Macgregor? Or just in the static fire?
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Herb Schaltegger on 08/11/2016 12:32 pm
    Did not see this here..

    From SpaceX facebook by Mike Hawes
    Quote
    Wow, so we've learned that SpaceX will be phasing out single engine testing at McGregor! (Gwynne, end of Q&A, Small Sat Conference)

    Have not seen the video of the conference yet.

    Edit: Just finished watching the video at about 1:01:46:
    Quote
    We are likely to go away from single engine tests on Merlin, you know, once we have finalized the design and show great decrease variability, i say, greater non variability, decrease variability
    My emphasis

    Interesting that even with all the accumulated manufacturing and testing knowledge they've built up making many hundreds of Merlin engines, they still have much variability at all. I guess the constant design iterations along the way are to blame but still interesting that (apparently) acceptance testing is used to characterize the engines (individually? by lot?).
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: AncientU on 08/11/2016 12:48 pm
    Should be a nice decrease in costs and improvement in flow.

    Talk of dropping the static fire another simplification that is discussed -- no timing known, but could flow from the same logic.

    So do they test all 9 at once on the stage at Macgregor? Or just in the static fire?

    Think the idea is to continue to test full stage at McGregor with a goal of 48 hr turn-around.  Static fire on pad is what they will be skipping.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: AncientU on 08/11/2016 12:53 pm

    Interesting that even with all the accumulated manufacturing and testing knowledge they've built up making many hundreds of Merlin engines, they still have much variability at all. I guess the constant design iterations along the way are to blame but still interesting that (apparently) acceptance testing is used to characterize the engines (individually? by lot?).

    I would think by engine #300 they would be doing functional testing, not characterization.  Hopefully the variability is small with respect to the design margin, not anything that would be close to changing the operating parameters.  It is difficult to imagine that they have a 'reject' rate much over zero.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: guckyfan on 08/11/2016 01:09 pm
    It is difficult to imagine that they have a 'reject' rate much over zero.

    If they had, they would probably not think of skipping individual engine tests and do only a testfire of the whole core.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Lars-J on 08/11/2016 03:10 pm
    Did not see this here..

    From SpaceX facebook by Mike Hawes
    Quote
    Wow, so we've learned that SpaceX will be phasing out single engine testing at McGregor! (Gwynne, end of Q&A, Small Sat Conference)

    Have not seen the video of the conference yet.

    Edit: Just finished watching the video at about 1:01:46:
    Quote
    We are likely to go away from single engine tests on Merlin, you know, once we have finalized the design and show great decrease variability, i say, greater non variability, decrease variability
    My emphasis

    Interesting that even with all the accumulated manufacturing and testing knowledge they've built up making many hundreds of Merlin engines, they still have much variability at all. I guess the constant design iterations along the way are to blame but still interesting that (apparently) acceptance testing is used to characterize the engines (individually? by lot?).

    That's the *point*. Variability *has* dropped, so this is why they are getting to the point of skipping that step. I'm not sure why you read it and assume almost the opposite. In the meantime they are simply being thorough, something many people seem to assume they are not.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: wannamoonbase on 08/11/2016 04:16 pm
    Did not see this here..

    From SpaceX facebook by Mike Hawes
    Quote
    Wow, so we've learned that SpaceX will be phasing out single engine testing at McGregor! (Gwynne, end of Q&A, Small Sat Conference)

    Have not seen the video of the conference yet.

    Edit: Just finished watching the video at about 1:01:46:
    Quote
    We are likely to go away from single engine tests on Merlin, you know, once we have finalized the design and show great decrease variability, i say, greater non variability, decrease variability
    My emphasis

    Interesting that even with all the accumulated manufacturing and testing knowledge they've built up making many hundreds of Merlin engines, they still have much variability at all. I guess the constant design iterations along the way are to blame but still interesting that (apparently) acceptance testing is used to characterize the engines (individually? by lot?).

    I'm sure the variability is a small but present significant figures. 

    Perhaps it has something to do with the certification process that requires the design to be stable for 'X' units. 

    It's a great sign it's being discussed.  One more step in the way to efficiency that comes from a stable design.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: oldAtlas_Eguy on 08/12/2016 02:26 am
    They still have a little while to go since the FT+ engines should be now showing up for single engine tests. But in 6 months the SL versions tested (due to the 18/yr launch rate) will be ~81 engines. So a year from now after >160 SL engines they could feel confident that the single engine test step is not required. Prior to that after a dozen flights of the FT+ versions they could do away with the on-pad hot fire test. Its a matter of like you say decreasing the variation distribution between engines to the point that the differences even on a 3sigma+ engine vs a 3sigma- engine is not very much. Add to that the likelihood of the 1st stage testing decreasing in occurrence due to stage reuse and the effort involved with M1D engine testing will be greatly reduced a year from now. M1DVAC single engine testing is likely to follow by sometime after the SL stop doing single engine testing. Making the most testing being that of US.

    On another note is the statement of being able to cycle the test stand in <48hrs. So in a month they can test 15 engines. 9 engines in every 18 days. That supports a launch rate of 20 per year of new 1st stages.

    They continue to head in the direction of lowering cost per launch and increasing launch rate.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Herb Schaltegger on 08/12/2016 03:29 am
    Did not see this here..

    From SpaceX facebook by Mike Hawes
    Quote
    Wow, so we've learned that SpaceX will be phasing out single engine testing at McGregor! (Gwynne, end of Q&A, Small Sat Conference)

    Have not seen the video of the conference yet.

    Edit: Just finished watching the video at about 1:01:46:
    Quote
    We are likely to go away from single engine tests on Merlin, you know, once we have finalized the design and show great decrease variability, i say, greater non variability, decrease variability
    My emphasis

    Interesting that even with all the accumulated manufacturing and testing knowledge they've built up making many hundreds of Merlin engines, they still have much variability at all. I guess the constant design iterations along the way are to blame but still interesting that (apparently) acceptance testing is used to characterize the engines (individually? by lot?).

    That's the *point*. Variability *has* dropped, so this is why they are getting to the point of skipping that step. I'm not sure why you read it and assume almost the opposite. In the meantime they are simply being thorough, something many people seem to assume they are not.

    I read the quote, paying close attention to the bolded part. Seems future tense to me, or at best "imminent tense" if you will. Not past. Not sure why you read it and missed that part.

    Tl;dr - less condescension, more comprehension. Please and thank you.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Nomadd on 08/12/2016 03:46 am
     I've asked this before, but does it look like pre-launch hotfires will continue forever? They would mean double the beach closures, which I don't think too many people here realize yet.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: AncientU on 08/12/2016 11:24 am
    They still have a little while to go since the FT+ engines should be now showing up for single engine tests. But in 6 months the SL versions tested (due to the 18/yr launch rate) will be ~81 engines. So a year from now after >160 SL engines they could feel confident that the single engine test step is not required. Prior to that after a dozen flights of the FT+ versions they could do away with the on-pad hot fire test. Its a matter of like you say decreasing the variation distribution between engines to the point that the differences even on a 3sigma+ engine vs a 3sigma- engine is not very much. Add to that the likelihood of the 1st stage testing decreasing in occurrence due to stage reuse and the effort involved with M1D engine testing will be greatly reduced a year from now. M1DVAC single engine testing is likely to follow by sometime after the SL stop doing single engine testing. Making the most testing being that of US.

    On another note is the statement of being able to cycle the test stand in <48hrs. So in a month they can test 15 engines. 9 engines in every 18 days. That supports a launch rate of 20 per year of new 1st stages.

    They continue to head in the direction of lowering cost per launch and increasing launch rate.

    48 hours refers to full stage testing -- arrival at McGregor to departure.

    Individual engine testing is going away for M1-D.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: envy887 on 08/12/2016 01:30 pm
    I've asked this before, but does it look like pre-launch hotfires will continue forever? They would mean double the beach closures, which I don't think too many people here realize yet.

    Responsive launch is a SpaceX goal, and the static fire is a big chunk of the critical path for a short-notice launch.
    Right now they are firing each engine at least 4 times before liftoff: single testing, stage testing, static fire, and for a couple seconds before liftoff. As they decrease variability between firings they can go to fewer firings with higher confidence. It sounds like they are keeping the stage testing, and they will always light the engines for checkout a couple seconds ahead of liftoff, so the other two (single testing and static fire) will probably go away.

    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: meekGee on 08/12/2016 07:34 pm
    I've asked this before, but does it look like pre-launch hotfires will continue forever? They would mean double the beach closures, which I don't think too many people here realize yet.

    It might be that at some point, the static fire will be merged with the launch.  Sort of like a live pre-flight check. 

    Changes will be required, but I don't see anything in principle against it, and it will reduce the number of cryo cycles on the tanks.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: guckyfan on 08/12/2016 07:47 pm
    I've asked this before, but does it look like pre-launch hotfires will continue forever? They would mean double the beach closures, which I don't think too many people here realize yet.

    It might be that at some point, the static fire will be merged with the launch.  Sort of like a live pre-flight check. 

    Changes will be required, but I don't see anything in principle against it, and it will reduce the number of cryo cycles on the tanks.

    It will reduce the workload on the launch crew and help increase flight rate, one can hope.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: AncientU on 08/13/2016 01:24 am
    I've asked this before, but does it look like pre-launch hotfires will continue forever? They would mean double the beach closures, which I don't think too many people here realize yet.

    It might be that at some point, the static fire will be merged with the launch.  Sort of like a live pre-flight check. 

    Changes will be required, but I don't see anything in principle against it, and it will reduce the number of cryo cycles on the tanks.

    The first couple seconds of any launch are identically a 'static fire' -- there won't be two lightings of the fuse, just one.  If all engines check out, the propellant flow continues and the hold-downs get released.  If any engine is not up to power (or anything else is abnormal) the launch is aborted.  In other words, normal launch sequence will subsume static fire.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: enzo on 08/13/2016 03:41 pm
    Changes will be required, but I don't see anything in principle against it
    In other words, normal launch sequence will subsume static fire.
    The data review after static fire is done by humans, so are you both suggesting it is simple enough to be done by code? (Maybe it already is for the most part, I don't know.) If not then a simple AI will have to be developed and trained off prior data.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: AncientU on 08/13/2016 04:35 pm
    Changes will be required, but I don't see anything in principle against it
    In other words, normal launch sequence will subsume static fire.
    The data review after static fire is done by humans, so are you both suggesting it is simple enough to be done by code? (Maybe it already is for the most part, I don't know.) If not then a simple AI will have to be developed and trained off prior data.

    After building and repeatedly firing 300 or so Merlins, their performance has become a known entity -- static fire simply won't be needed.  The first seconds of engine firing will be monitored for abnormal conditions as currently done... then hold-downs will be released.

    I suspect the LRR will simply occur (possibly soon?) without benefit of a static fire; don't think there will be a second AI-based 'LRR' post first few seconds of firing.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: meekGee on 08/14/2016 12:58 am
    Changes will be required, but I don't see anything in principle against it
    In other words, normal launch sequence will subsume static fire.
    The data review after static fire is done by humans, so are you both suggesting it is simple enough to be done by code? (Maybe it already is for the most part, I don't know.) If not then a simple AI will have to be developed and trained off prior data.
    I think the static fire is different from the first two seconds of launch.

    First - as you say - there's data analysis to be done that even if automated, can take time.

    There must be some borderline cases where it's ok to go, but only after review.  So if the static fire was merged with the launch, you'd have missed a launch window.

    For a fully reusable first stage, lighting up twice should not be a big deal.

    What the static fire will be designed to catch are problems that developed during the previous launch and reentry.

    With a mature rocket, I don't see a reason not to do the static fire 20 minutes prior to liftoff.

    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: the_other_Doug on 08/14/2016 01:42 am
    It's not like it hasn't already been done -- sort of.

    I wish I could recall exactly which mission it was, but I recall quite well an occurrence where the Falcon 9 engines started up, then shut down just prior to the hold-downs coming off.  After a short analysis and quick fix, the count was recycled and the launch proceeded that night (IIRC), late but still within the launch window.

    That was about a two-second firing, and the rocket did just fine in flight.

    There was also, IIRC, a Falcon 1 launch in which the engine started up, shut down, and after a short analysis the count was recycled and the rocket launched successfully.

    So, if it came down to it, yes, you could conceivably fuel the rocket, run a 2-second firing, analyze your data, then proceed with your count.  For right now, I would bet that a part of the post-firing LRR includes a physical examination of the engines after the firing.  I imagine they would have to do without that, if they incorporated a static fire into the main launch countdown.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: jimvela on 08/14/2016 02:11 am
    It's not like it hasn't already been done -- sort of.

    I wish I could recall exactly which mission it was, but I recall quite well an occurrence where the Falcon 9 engines started up, then shut down just prior to the hold-downs coming off.  After a short analysis and quick fix, the count was recycled and the launch proceeded that night (IIRC), late but still within the launch window.

    I believe the F9 sequence you are describing was prior to subcooled LOX... 
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: the_other_Doug on 08/14/2016 02:15 am
    It's not like it hasn't already been done -- sort of.

    I wish I could recall exactly which mission it was, but I recall quite well an occurrence where the Falcon 9 engines started up, then shut down just prior to the hold-downs coming off.  After a short analysis and quick fix, the count was recycled and the launch proceeded that night (IIRC), late but still within the launch window.

    I believe the F9 sequence you are describing was prior to subcooled LOX...

    Yes, I'm positive it was.  I'm also pretty sure it was a Falcon 9 v1.1, prior to the current FT version that, we are told, should just be called Falcon 9... :)

    Anyone remember which mission it was?  I'm pretty certain it wasn't a CRS flight, they have very short launch windows.  Maybe Cassiopeia?  It was definitely pre-stage-recovery days.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Dante80 on 08/14/2016 09:37 am
    Not sure if this was posted earlier.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Jcc on 08/14/2016 03:47 pm
    IMO, static fires have been as much to test GSE and pad flow as the rocket itself, which have needed continual refinement. Others have use a " wet dress rehearsal" (WDR) which does propellant loading but not firing the engines, but SpaceX decided it was better to fire them also. When pad flow readiness is in doubt, WDR or static fire provides a buffer against scrubs on launch day, but as confidence increases, they could rely on the 3 second hold at launch, or potentially a hot fire earlier on launch day to verify vehicle readiness.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: mfck on 08/14/2016 08:52 pm
    Not sure if this was posted earlier.

    St. Merlin of Hawthorne.

    Canonized while alive, after repeatedly ascending to heavens and coming back.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: alang on 08/15/2016 08:00 am
    Probably discussed many times but I can't find it: is there any likelihood that sea level Merlin will burn redirected turbo pump exhaust in future?
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: mfck on 08/15/2016 09:22 am
    Probably discussed many times but I can't find it: is there any likelihood that sea level Merlin will burn redirected turbo pump exhaust in future?
    IANAE, but it does not seem worth the trouble at this point in engine design cycle all for a couple of seconds of ISP on an SL engine. They probably want to be done with R&D on this engine.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: cuddihy on 08/15/2016 10:27 am
    Well it's already ducted into the after part of the nozzle to provide cooling. That probably lets you burn the engine hotter overall, which means better MR, which gives you more Isp. So I think it's already maxed out in that regard.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: hkultala on 08/16/2016 05:04 am
    Well it's already ducted into the after part of the nozzle to provide cooling.

    Only in vacuum version of the engine. The 1st stage version has separate nozzle for the turbopump.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Dante80 on 08/16/2016 06:15 pm
    Probably discussed many times but I can't find it: is there any likelihood that sea level Merlin will burn redirected turbo pump exhaust in future?

    I think I read somewhere that the actual turbopump exhausts pay a role (due to their position and use) on some aspects of the octaweb assembly performance.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: russianhalo117 on 08/16/2016 09:34 pm
    Probably discussed many times but I can't find it: is there any likelihood that sea level Merlin will burn redirected turbo pump exhaust in future?
    That was a planned feature for Merlin-2 LRE before Raptor Development became a thing and Merlin-2 work was shelved indefinitely. Any Merlin-2 improvements they decide to move over to the Merlin-1 family would likely become Merlin-1E although there are no present plans for Merlin-1E LRE development.

    Advancements in 3-D Printing and other new/next generation manufacturing technologies will make these LRE advancement options easier to produce and cut dry mass and manufacturing complexity (turbo pump exhaust reuse was one of the manufacturing issues that came up with the ABMA/NASA MSFC development of the Rocketdyne F-1 LRE's and is the main reason why the F-1 LRE Family has never been selected for a project other Apollo Saturn V series).
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: kaoru on 08/17/2016 03:05 am
    Probably discussed many times but I can't find it: is there any likelihood that sea level Merlin will burn redirected turbo pump exhaust in future?

    I think I read somewhere that the actual turbopump exhausts pay a role (due to their position and use) on some aspects of the octaweb assembly performance.

    The answer is, quoting "Generator gas flows through a heat exchanger which heats up Helium gas for tank pressurization in flight before being dumped overboard through an exhaust. (http://spaceflight101.com/spacerockets/falcon-9-v1-1-f9r/)", obviously plays an extremely important role.  That role requires plumbing that has to have high tolerances/pressures (read heavy).  Moving the heat exchanger and adding mass for a diffuser of cooler and slower gas/exhaust is not practical.  The F1 did it only to provide cooling to the nozzle extension so it was worth it in that regard.

    Kaoru
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: deruch on 08/17/2016 07:23 am
    It's not like it hasn't already been done -- sort of.

    I wish I could recall exactly which mission it was, but I recall quite well an occurrence where the Falcon 9 engines started up, then shut down just prior to the hold-downs coming off.  After a short analysis and quick fix, the count was recycled and the launch proceeded that night (IIRC), late but still within the launch window.

    I believe the F9 sequence you are describing was prior to subcooled LOX...

    Yes, I'm positive it was.  I'm also pretty sure it was a Falcon 9 v1.1, prior to the current FT version that, we are told, should just be called Falcon 9... :)

    Anyone remember which mission it was?  I'm pretty certain it wasn't a CRS flight, they have very short launch windows.  Maybe Cassiopeia?  It was definitely pre-stage-recovery days.

    SES-8, though based on a perusal of the "SpaceX launch log" thread, I think your memory may be playing tricks on you a bit.  SES-8 got through start-up, but didn't release.  They then recycled and attempted a second countdown.  But that second countdown was scrubbed due to contamination of the ground side TEA-TEB.  It then launched successfully a few days later.  So, the gist of your point was still valid.  They got through engine start-up, held the launch, and then recycled to try again within the same window.  But it didn't launch on the second attempt either.  That's the only launch that I could find that might fit your memory.  It's also possible that the log didn't catch this somewhat unusual type of attempt.

    https://www.youtube.com/watch?v=zW1vobiEycI

    Somewhat interestingly, SES-9 did pretty much the same thing.  On the launch attempt with the wayward boat.  They recycled after the range fouling and got through start-up but held for low thrust.  They then considered another attempt in that same window, but couldn't because of the subcooled LOX warming too much.  But if they hadn't had to worry about the warmer LOX, I think they would have recycled and tried again.  I remember them taking a fair bit of time after the low thrust hold to finally scrub the attempt.
    Title: Re: SpaceX: Merlin 1D Updates and Discussion Thread 2
    Post by: Chris Bergin on 08/27/2016 04:35 pm
    Thread 3:
    https://forum.nasaspaceflight.com/index.php?topic=41014.0