Poll

Should Briz be re-designed, or should Khrunichev focus on quality control?

Re-design
7 (20.6%)
Quality control
27 (79.4%)
Switch to another upper stage
0 (0%)

Total Members Voted: 34

Voting closed: 12/14/2012 04:35 PM

Author Topic: Fixing Briz  (Read 10429 times)

Offline Danderman

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Fixing Briz
« on: 12/10/2012 04:35 PM »
I am specifically not listing the variants of Briz, because they all share the common problem of the thing not working.

The question is how to fix it?

The easiest approach is to upgrade quality control.

The second approach is to look at the entire existing propulsion system, and see if there is a re-design that would enhance the reliability of the entire existing system.

A third approach is more challenging -

a) rework the avionics so that in the event that a main engine failure is detected, rather than immediate separation of the satellite, the entire unit should go into safe mode.

b) institute an uplink command channel so that the stage could be commanded from the ground.

c) replumb the system so that the "settling" thrusters could be fed from the main propulsion tank, and thus serve as a backup to the main engine. This would be arduous, both in design, construction and operations, but preferable to losing a satellite once a year.

Of course, any change to the existing system creates risks, but I suspect that the risk from the change would be less than the current risk.

Offline kevin-rf

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Re: Fixing Briz
« Reply #1 on: 12/10/2012 05:41 PM »
a) rework the avionics so that in the event that a main engine failure is detected, rather than immediate separation of the satellite, the entire unit should go into safe mode.

b) institute an uplink command channel so that the stage could be commanded from the ground.

As you point out in 'b', 'a' requires uplink and assumes the "problem" can be fixed by simple uplink before the Briz's batteries die. This assumes the Briz is shutting down for silly reasons and not an unsafe state that could lead to a very rapidly evolving and exciting situation. I do not believe that is the case. 

In the sense of the paying customer, salvaging the payload through immediate separation and getting it the heck away from the stage is the safest option in an off nominal situation. 

What they need is a fool proof way to safe the stage in the event of these situations. A RUD some months later is not a good way to safe the stage.
« Last Edit: 12/10/2012 05:45 PM by kevin-rf »
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Offline Danderman

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Re: Fixing Briz
« Reply #2 on: 12/10/2012 06:03 PM »
a) rework the avionics so that in the event that a main engine failure is detected, rather than immediate separation of the satellite, the entire unit should go into safe mode.

b) institute an uplink command channel so that the stage could be commanded from the ground.

As you point out in 'b', 'a' requires uplink and assumes the "problem" can be fixed by simple uplink before the Briz's batteries die. This assumes the Briz is shutting down for silly reasons and not an unsafe state that could lead to a very rapidly evolving and exciting situation. I do not believe that is the case. 

In the sense of the paying customer, salvaging the payload through immediate separation and getting it the heck away from the stage is the safest option in an off nominal situation. 

What they need is a fool proof way to safe the stage in the event of these situations. A RUD some months later is not a good way to safe the stage.

I would imagine that an abort system could differentiate between a true emergency, where the spacecraft should be separated immediately, and a condition where the engine is shutting down in a relatively safe manner. And, yes, the a+b+c I listed above are not separate options, but instead an integrate approach to the problem.

IIRC, Briz does not have a unified fuel system, so there is a separate prop tank system for the small thrusters. Creating that unified fuel system would make Briz a more robust system, at the risk of a thruster leak impacting the entire prop supply.

Offline Prober

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Re: Fixing Briz
« Reply #3 on: 12/10/2012 06:08 PM »
Isn't the Briz in the middle of a redesign?

This is how the Russian system tests with launches? 

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Online Galactic Penguin SST

Re: Fixing Briz
« Reply #4 on: 12/10/2012 06:10 PM »
Well do we know what's going on at Khrunichev? For some reason the Fregat upper stage build by Lavochikin, which uses an engine with more or less the same parts and design, never had any in flight failures since its first flight in 2000 (and only one small ground processing issue that led to a slightly off course mission in 2009). Why? QA issues? Or just that a space tug with a pump fed engine that must work for 9 hours + is just difficult to work with high reliability?
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Offline kevin-rf

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Re: Fixing Briz
« Reply #5 on: 12/10/2012 06:38 PM »
I would imagine that an abort system could differentiate between a true emergency, where the spacecraft should be separated immediately, and a condition where the engine is shutting down in a relatively safe manner. And, yes, the a+b+c I listed above are not separate options, but instead an integrate approach to the problem.

Your assuming that the engine can, and should be restarted after the shutdown. These engines do not shutdown for no reason, if they are shutting down there is a reason, and short of getting a cosmonaut up there with a wrench they should not be restarted.

Also, while a a single propellant supply may make sense, the settling thruster thrust is so low that for every mission you would have to completely redesign the flight software to handle two completely different thrusting modes. Include the stage and thrusters need to live long enough   to burn a full tank of propellant. This burn will take much longer than one with the main engine. You are adding cost and complexity to the upper stage to fix something that should not be an issue.

Btw a list of Briz failures over the last few years:

2006 February 28 - Arabsat - 4M

14 March 2008 - Ruptured plumbing, you can not continue to use the system after that.

3 February 2011 - Engine restart failed, not a Proton GEO launch. Brings up a point, could it have handle the extra weight you are asking for so it can do a save by thrusters?

17 August 2011 - failure due to an issue with programming around Gyro limitation (Clearly a case to be argued about changing out the gyro for one that does not have the weakness). The thrusters would not have helped. Actually, it burned all it's fuel.

6 August 2012 - FOD, clogged line. Chances of the thrusters also working?

« Last Edit: 12/10/2012 06:39 PM by kevin-rf »
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Online Chris Bergin

Re: Fixing Briz
« Reply #6 on: 12/10/2012 06:39 PM »
They always said with shuttle that redesigning/mods always risked making the issue bigger, so I'd go with better QA.

Offline Danderman

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Re: Fixing Briz
« Reply #7 on: 12/10/2012 07:08 PM »
Btw a list of Briz failures over the last few years:



14 March 2008 - Ruptured plumbing, you can not continue to use the system after that.

6 August 2012 - FOD, clogged line. Chances of the thrusters also working?



A well design integrated fuel system may have saved these two missions. For example, looking at the Soyuz spacecraft prop system, there are capabilities for completing entire missions missing the main engine.

Offline Danderman

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Re: Fixing Briz
« Reply #8 on: 12/10/2012 07:09 PM »
They always said with shuttle that redesigning/mods always risked making the issue bigger, so I'd go with better QA.

I suspect that if the same engine failed two or three times during Shuttle missions, causing LOM, then redesigns would be in order.

Offline kevin-rf

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Re: Fixing Briz
« Reply #9 on: 12/10/2012 07:16 PM »
A well design integrated fuel system may have saved these two missions. For example, looking at the Soyuz spacecraft prop system, there are capabilities for completing entire missions missing the main engine.

Raised eyebrow... considering the verniers run off the same turbo pump as the main engine, how? I suspect the gravity losses may eat you alive.

Or are you referring to the manned Soyuz spacecraft and not the rocket?
« Last Edit: 12/10/2012 07:17 PM by kevin-rf »
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Offline Stan Black

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Re: Fixing Briz
« Reply #10 on: 12/10/2012 07:17 PM »
 As far as I understand… in 1999 there was two failures of Proton-K due second stage engines. The first return to service was quick and followed shortly after by another failure. The failures were from old rockets. Turns out they already had a plan in place to enhance these engines for the Proton-M, and these improvements would also later be used in Proton-K. They just got forced to introduce them earlier, and re-fit already manufactured rockets.

 I wonder if the same thing is happening here. Briz-M is already to be improved for phase IV, the first having flown for Intelsat-22?

 But removing pages from the website; then giving quick explanations for the failures does not help.

Offline zaitcev

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Re: Fixing Briz
« Reply #11 on: 12/10/2012 08:02 PM »
6 August 2012 - FOD, clogged line. Chances of the thrusters also working?
The clogged or folded pressurization line was the topic of much speculation on forums, because the failed stage was worked upon and the line was replaced. Allegedly photos taken before the closeout showed undercomplement number of fasteners installed. However, IIRC, the final conclusion unexpectedly fingered an unnamed component made in Omsk. Allegedly, Omsk people did a quality job, but they understood the intent of designers improperly and so their part was materially different from one made in Fili. Several Briz-M missions flew with Omsk-made parts, but they were not pushed as hard and so the difference did not cause a failure. Fili was responsible for QC but it never occured for them to check the the specific deviation that occured. Or so I heard.

Offline Prober

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Re: Fixing Briz
« Reply #12 on: 12/10/2012 08:06 PM »
Well do we know what's going on at Khrunichev? For some reason the Fregat upper stage build by Lavochikin, which uses an engine with more or less the same parts and design, never had any in flight failures since its first flight in 2000 (and only one small ground processing issue that led to a slightly off course mission in 2009). Why? QA issues? Or just that a space tug with a pump fed engine that must work for 9 hours + is just difficult to work with high reliability?

You forgot about Lavochikin's work with Phobos Grunt.
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Offline Rocket Science

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Re: Fixing Briz
« Reply #13 on: 12/10/2012 08:16 PM »
A redesign for the sake of a redesign is a waste of resources. Then what’s to say if your redesign has failures due to QC. Start with basics of QC on the existing design and go from there...
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Online Galactic Penguin SST

Re: Fixing Briz
« Reply #14 on: 12/10/2012 08:34 PM »
You forgot about Lavochikin's work with Phobos Grunt.

Well a complex Phobos sample return mission is much more complex than "just" an upper stage.... (remember the software loop that the Russians think P-G got stuck on?)
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Offline kevin-rf

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Re: Fixing Briz
« Reply #15 on: 12/11/2012 01:16 PM »
It's not just rockets Russia is have quality problems with, http://www.flightglobal.com/blogs/the-dewline/2012/12/russias-su-34-fleet-found-to-h.html
 
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Offline spectre9

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Re: Fixing Briz
« Reply #16 on: 12/11/2012 01:49 PM »
Aerospace in Russia is hitting a wall it seems.

Soviet technology has lasted quite a while but now it's all starting to break down and lack of new investments are showing through.

I voted for better QA but that's because Proton is on the way out anyway.

Angara with a hydrolox upper stage is where Russia wants to go. Getting that right is important. If it makes it through development. Have we even seen Soyuz 2.1v yet? I know it hasn't launched but has it been seen in public?

Offline DFSL

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Re: Fixing Briz
« Reply #17 on: 12/11/2012 02:47 PM »
Have we even seen Soyuz 2.1v yet? I know it hasn't launched but has it been seen in public?

Erm... There were a couple of threads at this very forum showing pictures of the engine tests and the first rocket being fit-checked at its launchpad. Maybe you didn't see them?

Constant quality control issues seem to plague the Russian industry.

Online russianhalo117

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Re: Fixing Briz
« Reply #18 on: 12/11/2012 03:25 PM »
Aerospace in Russia is hitting a wall it seems.

Soviet technology has lasted quite a while but now it's all starting to break down and lack of new investments are showing through.

I voted for better QA but that's because Proton is on the way out anyway.

Angara with a hydrolox upper stage is where Russia wants to go. Getting that right is important. If it makes it through development. Have we even seen Soyuz 2.1v yet? I know it hasn't launched but has it been seen in public?
It is more an affect of the industries ratio of increasing retirement of senior knowledge to the use of recruitment and retention of green engineers/employees without experience. Their employees are retiring too fast to allow proper training of their replacements and that is serious problem.

Offline Danderman

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Re: Fixing Briz
« Reply #19 on: 12/14/2012 06:18 PM »
A less radical approach to fixing Briz would be to adopt a vehicle health management system that can assess the condition of the stack, and while shutting down the main engine, use the settling thrusters to generate additional Delta-V, if this can be done safely (ie the stack is stable and the main engine is not exploding).

Of course, it would be super if those settling thrusters could be plumbed to the main prop tanks, with some sort of pyro valve installed to make the connection, in the event of a main engine failure, but that might be asking too much. Without access to the main prop tank, the settling thrusters probably have no more than 50 kg of prop to expend.  However, saving the prop in the satellite is worth more than gold, per kilo saved.


« Last Edit: 12/14/2012 06:18 PM by Danderman »

Offline akula2

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Re: Fixing Briz
« Reply #20 on: 12/15/2012 06:27 AM »
I really don't know how many here are Engineers/Scientists. Briz-M is not unique just because it happens to be Soviet technology. Such things are quite common in other industries (west) too.

#1 Anyone remember how Air France 447 (Airbus A-330 happens to be most advanced in its design that time) vanished out of trace from Brazil?
#2 How about brand new Ferrari 458 Italia infamous hot fires (friend of mine lost one)
#3 Then there are Airbus A-380 engine problems (remember Qantas grounded them)
#4 If we go back to the US Air Force, anyone remembers how many SR-71s they lost (that too in non-combat accidents)?

Progress has impressive record but it's unfortunate that Briz-M problems are recurring, rather say becoming so predictable! IMO Mr. Putin should take charge of the Russian Space Agency.

Soviet technology still good enough, Soyuz/Progress proves this very much. In my experience, there is increased accuracy of GLONASS over GPS on some parameters.

Offline Jim

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Re: Fixing Briz
« Reply #21 on: 12/15/2012 01:47 PM »

#1 Anyone remember how Air France 447 (Airbus A-330 happens to be most advanced in its design that time) vanished out of trace from Brazil?

#4 If we go back to the US Air Force, anyone remembers how many SR-71s they lost (that too in non-combat accidents)?

Pilot errors

Offline akula2

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Re: Fixing Briz
« Reply #22 on: 12/15/2012 04:51 PM »
Pilot errors
Not all were/are pilot errors. There was a design deficiency in that illfated A-330 control system (side stick etc), complemented with a few complicated instruments/sensors (say Pitot Tube nightmare at high altitude).

Lockheed Martin knows very well dealing with numerous design errors/deficiencies in Systems/Software be it in F-22 or F-35

Offline Stephan

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Re: Fixing Briz
« Reply #23 on: 12/15/2012 05:13 PM »
Not all were/are pilot errors. There was a design deficiency in that illfated A-330 control system (side stick etc), complemented with a few complicated instruments/sensors (say Pitot Tube nightmare at high altitude).
It had nothing to do with the sidesticks.
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Offline Jim

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Re: Fixing Briz
« Reply #24 on: 12/15/2012 05:38 PM »
Pilot errors
Not all were/are pilot errors. There was a design deficiency in that illfated A-330 control system (side stick etc), complemented with a few complicated instruments/sensors (say Pitot Tube nightmare at high altitude).

Those examples were pilot errors and training deficiencies, especially the A-330.  Anyways, your examples were not applicable to Breeze.
« Last Edit: 12/15/2012 05:40 PM by Jim »

Online Galactic Penguin SST

Re: Fixing Briz
« Reply #25 on: 12/15/2012 05:42 PM »
.....and luckily the Briz stage isn't controlled by pilots on the ground.  ::)

Apparently the preliminary investigation points to the main engine turbopump as the culprit..... http://www.russianspaceweb.com/proton_yamal402.html 
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Offline kevin-rf

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Re: Fixing Briz
« Reply #26 on: 12/16/2012 12:07 PM »
If true, does that mean it still has four minutes of propellants on board and at some point in the future we will again see a violent debris producing event?

Considering the perigee is 3000 km, any debris will be up for a very, very long time.
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Offline Danderman

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Re: Fixing Briz
« Reply #27 on: 12/17/2012 02:19 AM »
If true, does that mean it still has four minutes of propellants on board and at some point in the future we will again see a violent debris producing event?

Considering the perigee is 3000 km, any debris will be up for a very, very long time.

All the more reason to plumb the settling thrusters into the main prop tanks; apart from being able to continue the mission, burning prop is the best way to empty a prop tank.

Offline kevin-rf

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Re: Fixing Briz
« Reply #28 on: 12/17/2012 03:32 AM »
Maybe not, the settling thrusters are usually pressure fed, meaning they most likely have much lower ISP. Also, with the exception on the final (be it fourth,fifth, or 100th burn), what orbit do you shoot for? Unless the failure happens (like the latest failure) near the end of the final burn, the mission will require the satellite saving itself to some degree. Remember two of the Briz failures where guidance issues and not engine/pressurization failures

Don't pressure fed systems usually operate ay higher pressure? Heavier dry mass then...
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Offline Jim

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Re: Fixing Briz
« Reply #29 on: 12/17/2012 03:42 AM »
If true, does that mean it still has four minutes of propellants on board and at some point in the future we will again see a violent debris producing event?

Considering the perigee is 3000 km, any debris will be up for a very, very long time.

All the more reason to plumb the settling thrusters into the main prop tanks; apart from being able to continue the mission, burning prop is the best way to empty a prop tank.


Not feasible with current propellant combination.  UDMH is not monoprop

Offline Danderman

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Re: Fixing Briz
« Reply #30 on: 12/17/2012 03:46 AM »
Maybe not, the settling thrusters are usually pressure fed, meaning they most likely have much lower ISP. Also, with the exception on the final (be it fourth,fifth, or 100th burn), what orbit do you shoot for? Unless the failure happens (like the latest failure) near the end of the final burn, the mission will require the satellite saving itself to some degree. Remember two of the Briz failures where guidance issues and not engine/pressurization failures

Don't pressure fed systems usually operate ay higher pressure? Heavier dry mass then...

First off, I am not suggesting that use of the settling thrusters by themselves should be able to achieve the final orbit, the goals would be to achieve some extra delta-V (as compared with the current off-nominal procedure), and to burn off the remaining prop. Using the avail tank pressure in the main prop tanks to feed the settling thrusters, especially once there is some acceleration, should be enough to accomplish the two goals.

As for the guidance failures, remember that these failures had the effect of shutting down the system. A simple uplink command channel could be used to mitigate the impact of the system dying because of guidance failures (not to stop the failure in process, but to recover some delta-V after the system were shut down from guidance problems).

Usually, the best practice is: if it ain't broke, don't fix it. However Briz IS broken. It needs to be fixed.

« Last Edit: 12/17/2012 03:50 AM by Danderman »

Offline Jim

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Re: Fixing Briz
« Reply #31 on: 12/17/2012 04:09 AM »
Maybe not, the settling thrusters are usually pressure fed, meaning they most likely have much lower ISP. Also, with the exception on the final (be it fourth,fifth, or 100th burn), what orbit do you shoot for? Unless the failure happens (like the latest failure) near the end of the final burn, the mission will require the satellite saving itself to some degree. Remember two of the Briz failures where guidance issues and not engine/pressurization failures

Don't pressure fed systems usually operate ay higher pressure? Heavier dry mass then...

First off, I am not suggesting that use of the settling thrusters by themselves should be able to achieve the final orbit, the goals would be to achieve some extra delta-V (as compared with the current off-nominal procedure), and to burn off the remaining prop. Using the avail tank pressure in the main prop tanks to feed the settling thrusters, especially once there is some acceleration, should be enough to accomplish the two goals.

As for the guidance failures, remember that these failures had the effect of shutting down the system. A simple uplink command channel could be used to mitigate the impact of the system dying because of guidance failures (not to stop the failure in process, but to recover some delta-V after the system were shut down from guidance problems).

Usually, the best practice is: if it ain't broke, don't fix it. However Briz IS broken. It needs to be fixed.



An uplink command channel is  far from simple.
A.  It is a major avionics change.  It is more than just adding a receiver.  The guidance system has to be able to accept the command.  That means computer changes and code changes
B.  having a receiver doesn't mean there is a transmitter in line of sight or in range to send the command
B.  still is a major conop change and it has to be planned and practiced and real time tools have to be developed to determine the course of action

Offline hop

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Re: Fixing Briz
« Reply #32 on: 12/17/2012 04:25 AM »
All the more reason to plumb the settling thrusters into the main prop tanks; apart from being able to continue the mission, burning prop is the best way to empty a prop tank.
If preventing the tanks from popping is the goal, vent valves timed to open N hours after the nominal end of mission would seem like a much more practical approach. Or depending on the details, something completely passive like a rupture disk might do the trick.

This entire premise of this thread seems rather silly to me. The response to a failure should be based on the results of the failure investigation. Given the number of recent failures, it's certainly fair to suggest the investigation should go beyond the immediate cause of the current failure and look at broader organizational and design issues.

If the root cause is poor quality control, adding more complexity to the vehicle seems unlikely to improve the overall success rate much. You might get more recovery options, but you also get more places to mess up.

While there might be merit to making a stage like Briz more recoverable, there would also be considerable cost in engineering, complexity, and possibly mass. If you have those resources to expend, the correct course would be to do trades to determine where you get the most value. I don't see an justification for assuming your proposal would automatically be the best choice.
« Last Edit: 12/17/2012 04:25 AM by hop »

Offline kevin-rf

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Re: Fixing Briz
« Reply #33 on: 12/17/2012 01:20 PM »
One thing I have never understood about the fuel choices here, how quickly do they boil off in vacuum. Some fluids do not immediately flash to gas when exposed to a vacuum. So does depressurizing the tanks and venting to vacuum result in the spent stage being coated with two different caustic sludges that burn on contact?
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Offline Prober

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Re: Fixing Briz
« Reply #34 on: 12/17/2012 01:40 PM »
Maybe not, the settling thrusters are usually pressure fed, meaning they most likely have much lower ISP. Also, with the exception on the final (be it fourth,fifth, or 100th burn), what orbit do you shoot for? Unless the failure happens (like the latest failure) near the end of the final burn, the mission will require the satellite saving itself to some degree. Remember two of the Briz failures where guidance issues and not engine/pressurization failures

Don't pressure fed systems usually operate ay higher pressure? Heavier dry mass then...

First off, I am not suggesting that use of the settling thrusters by themselves should be able to achieve the final orbit, the goals would be to achieve some extra delta-V (as compared with the current off-nominal procedure), and to burn off the remaining prop. Using the avail tank pressure in the main prop tanks to feed the settling thrusters, especially once there is some acceleration, should be enough to accomplish the two goals.

As for the guidance failures, remember that these failures had the effect of shutting down the system. A simple uplink command channel could be used to mitigate the impact of the system dying because of guidance failures (not to stop the failure in process, but to recover some delta-V after the system were shut down from guidance problems).

Usually, the best practice is: if it ain't broke, don't fix it. However Briz IS broken. It needs to be fixed.



Danderman is right, Britz is broken.    Britz IMHO, needs to default to release payload, and deorbit.   Mitigating more space trash should be an issue at this point.
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Offline hop

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Re: Fixing Briz
« Reply #35 on: 12/17/2012 08:15 PM »
Britz IMHO, needs to default to release payload, and deorbit.   Mitigating more space trash should be an issue at this point.
??? Huh? De-orbit requires the stage to be pretty much fully functional, in which case it should complete the mission. Briz would not have the dV to de-orbit late in the mission.

Passivating the things that create large debris clouds is a much more realistic (i.e. possible in the real world) option.

Offline woods170

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Re: Fixing Briz
« Reply #36 on: 12/17/2012 08:38 PM »
Usually, the best practice is: if it ain't broke, don't fix it. However Briz IS broken. It needs to be fixed.

Danderman is right, Britz is broken.   

No, Briz is not broken. What is much more likely is that the QA chain around Briz is broken. The design itself is sound, as proven by the fact that over 80 percent of the Briz missions had no failures whatsoever. The current failure rate of 18 percent is consistent with flaws in quality assurence.

Other indicator pointing to quality issues is random failures on other launch systems, such as the fairly recent failure of a Soyuz-U launcher, carrying a Progress spacecraft. That failure was a quality issue as well.

Offline Prober

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Re: Fixing Briz
« Reply #37 on: 12/17/2012 08:44 PM »
Details from another article...

Russian Rocket Failure Confirms Need to Fully Review Booster's Upper Stage

http://news.yahoo.com/russian-rocket-failure-confirms-fully-review-boosters-upper-190402799.html
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Offline kevin-rf

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Re: Fixing Briz
« Reply #38 on: 12/18/2012 01:09 AM »
From Prober's article
Quote
Palme and Kramer said that despite its premature shutdown, the Breeze-M stage that failed Dec. 9 completed the passivation procedures that the stage performs on all its missions and is not at risk of exploding in orbit.

Didn't they also make that claim with the recently RUD'd previous failure? Now saying, well this one dropped the drop tank, so it won't RUD... Glad the author took them to task with the claims.
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Offline Danderman

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Re: Fixing Briz
« Reply #39 on: 02/27/2013 11:23 PM »
If the problems with Briz-M are due to the long burn time of the engine required to go through the 15 tons of prop (it's a very small engine, so it has to burn for a long time to get satellites to GTO), then another approach would be to somehow affix small engines to the large auxiliary propellant tank (APT). Even  a series of 100 kg engines would significantly reduce Briz-M engine burn time.


Offline kevin-rf

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Re: Fixing Briz
« Reply #40 on: 02/28/2013 02:40 AM »
If the problems with Briz-M are due to the long burn time of the engine required to go through the 15 tons of prop (it's a very small engine, so it has to burn for a long time to get satellites to GTO), then another approach would be to somehow affix small engines to the large auxiliary propellant tank (APT). Even  a series of 100 kg engines would significantly reduce Briz-M engine burn time.

Unless they greatly increase the ISP, the increase mass fraction will adversely impact your system performance. Especially if the extra engines have lower ISP.
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Offline Danderman

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Re: Fixing Briz
« Reply #41 on: 02/28/2013 04:25 PM »
If the problems with Briz-M are due to the long burn time of the engine required to go through the 15 tons of prop (it's a very small engine, so it has to burn for a long time to get satellites to GTO), then another approach would be to somehow affix small engines to the large auxiliary propellant tank (APT). Even  a series of 100 kg engines would significantly reduce Briz-M engine burn time.

Unless they greatly increase the ISP, the increase mass fraction will adversely impact your system performance. Especially if the extra engines have lower ISP.

Yep, reliability at the expense of performance.

Offline Danderman

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Re: Fixing Briz
« Reply #42 on: 11/02/2013 06:08 PM »
OK, after checking various launch vehicle manuals, I have figured out the story concerning the Briz high pressure and low pressure prop tanks.

The Briz main engine is fed by a turbopump, which allows tank pressure for the main engine to be maintained at a relatively low pressure. This include the Briz main engine tanks and the APT as well.

There are also 4 small rocket engines (40 kg), which are pressure fed. Therefore, their prop tanks are maintained at relatively high pressure. Note that this "high pressure" is the same as the Russian segment of ISS prop system.

Therefore, it would be virtually impossible for the 4 small thrusters to feed from the large prop tanks, since there would not be enough pressure for effective thrust.

« Last Edit: 11/02/2013 06:09 PM by Danderman »

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