Merlin-1

Автор Salo, 24.04.2011 12:14:31

« назад - далее »

0 Пользователи и 1 гость просматривают эту тему.

Alex_II

ЦитироватьAlex Degt пишет:
Коты и буровые робочие к людям не относятся...
И чё? Урря-поцреоты вообще по биологической классификации относятся к поцам, и ничего - тебя ж еще не погнали с форума до сих пор... А "кот" - это звучит гордо ;)
И мы пошли за так, на четвертак, за ради бога
В обход и напролом и просто пылью по лучу...

Leonar

ЦитироватьMax Andriyahov пишет:
42269, а что значит 135897?
Вот и мне интересно, что значит 42269

Старый

#922
Leonar,
а у меня что получается?
всё нормально, имя, никаких номеров
1. Ангара - единственная в мире новая РН которая хуже старой (с) Старый Ламер
2. Назначение Роскосмоса - не летать в космос а выкачивать из бюджета деньги
3. У Маска ракета длиннее и толще чем у Роскосмоса
4. Чем мрачнее реальность тем ярче бред (с) Старый Ламер

Max Andriyahov

ЦитироватьLeonar
я еще не привык к этому сайту - так у меня ваш ник отобразился в комменте. ищу фак по форуму пока.

Salo

https://thephysicsofspacex.wordpress.com/2016/07/10/comparing-upper-stage-rocket-engines/
ЦитироватьComparing Upper Stage Rocket Engines              
Posted on July 10, 2016 by Tom Myers      
                 
This post follows our comparison of first stage engines, which can be found here. As a reminder, in 2014 Elon Musk said [1]:
"Right now, I'd say, engines are our weakest point at SpaceX."
To expand this quote a little:
"Right now, I'd say, engines are our weakest point at SpaceX, but they will become as strong as the structures and avionics in the next generation... our weakest point is engines with respect to specific impulse, but not with respect to thrust-to-weight. We actually have the highest thrust-to-weight of any engine, I think maybe ever, but our specific impulse, the efficiency of the engine is about 10% worse than a staged-combustion engine using the same propellant."
Since engine design is so fundamental to the performance of the rockets SpaceX launch, it's worth explaining what Musk said in a little more detail, in this case regarding upper stage engines. As background, SpaceX have their name on three families of upper stage engine – the (now obsolete) Kestrel, used in the Falcon 1, the Merlin 1D Vac (in use for the Falcon 9), and the still-in-development Raptor. The first two are fueled by kerosene and liquid oxygen (a combination known as kerolox), while the latter will use methane and liquid oxygen (methalox) [2].
So what defines a 'good' upper stage engine? The purpose of such an engine is to get a payload which is already above the atmosphere into its desired orbit. The Tsiolkovsky ideal rocket equation describes this process accurately:
total change in velocity = exhaust velocity * log (initial mass/final mass)
(where log refers to the natural logarithm, specifically). A good engine in terms of raw performance therefore has a high exhaust velocity (usually referred to as specific impulse, which is just exhaust velocity divided by the acceleration due to gravity), and a low mass. In the real world, an engine also needs enough thrust to reach orbit before gravity pulls the rocket back below the atmosphere, but not so much thrust that the stack is damaged by the acceleration in the later part of the burn (many engines, including the Merlin series, have the ability to throttle, which can help mitigate this). Plotted after the next paragraph are the specific impulse, mass and thrust of SpaceX's two flight-tested engine families, against most of the other rocket engines to have seen orbital flight.
Since the Raptor has not yet flown, and thus its specifications could still change, it is not included in the chart. In fact, no methane/liquid oxygen engine has ever made it to the launchpad for us to compare the Raptor to. In lieu of this, we have estimated theoretical upper limits for methalox and similar fuels, by simply assuming perfect conversion of all the stored chemical energy into kinetic energy. Our calculation can be found here: it finds that hydrogen/liquid oxygen (hydrolox) has a maximum of 532.5s, kerolox has 470.2s, and methalox has 458.7s. It should be noted that these are not necessarily achievable limits, and that real rocket engines will have lower efficiencies. These limits are plotted as vertical bars alongside the aforementioned data [3].
 

Starting with the upper limits, we can see that practical hydrolox and kerolox engines operate at about 100 seconds below their upper limits – by extension, we should expect methalox engines like the Raptor to behave similarly. The methalox upper limit is a little lower than that of kerolox, but it would be wrong to conclude that Raptor will have a lower specific impulse than the Merlin family. For one, the Raptor will use the more efficient staged combustion cycle (versus the Merlin's gas generator cycle), and for another, methane burns a little hotter than kerosene, which allows a given engine to get closer to its theoretical maximum efficiency [4]. A better conclusion would be that methane will behave a lot more like kerosene than hydrogen (but is hardly a drop-in replacement).
The first graph (mass vs specific impulse) shows us an intriguing fact about the Kestrel – it is in fact the lightest kerolox engine ever to make orbit, by more than a factor of two: 52 vs 121kg for the next lightest engine, the RD-0109. The RD-0109 is also notable for being the engine that first put a human (Yuri Gagarin) into space. Having a low mass is a significant benefit on the last stage – every kilogram shaved off the engine is an additional kilogram of payload, regardless of destination. It should also be noted, though, that the Kestrel was pressure-fed, which introduces additional complexity (hence: weight) to the tank, which the RD-0109 and others would not have to deal with.
It can also be seen that for all the enormous complexity of the space shuttles main engines [5], their specific impulse is quite similar to other liquid hydrogen engines. However, it should be noted that unlike other hydrolox engines, they were reused, and had to work within the atmosphere as well as outside it.

The thrust vs specific impulse graph shows an unusually high thrust for the Merlin family, even when compared to much larger launch systems (note that the Shuttle uses three main engines, and Saturn V used five on the second stage and one on the third stage). This is probably due to the Merlin's heritage, being originally designed as a first stage engine on the Falcon 1, and later being adapted for upper stage use on the Falcon 9. On the first stage, high thrust is important to reduce gravity losses; these are less significant on the second stage and so most dedicated second stage engines have lower thrust as a consequence. Ion engines (electric propulsion) have vastly lower thrusts than the chemical engines discussed here, but are still capable of performing some of the same tasks as these engines.
This can also be seen in the Kestrel's very low thrust – it was a dedicated upper-stage engine, with a small payload, and thus did not need to push the payload with a great deal of force.

In the quote at the start, Musk mentioned the high thrust-to-weight ratio as one of the Merlin's strongest points. Our analysis confirms that the engines do indeed have the highest thrust-to-weight of all the upper stages we surveyed; and this was true even before some of the upgrades SpaceX has made to the thrust over the lifetime of the Merlin. Thrust-to-weight ratio is arguably the most important performance parameter after specific impulse (as it corrects for the size and scale of the engine), and the value seen is a testament to the skill of SpaceX's engineers.
In addition to all of this, the Merlin 1D has never failed in 21 flights (CRS-7 was a tank overpressure event, unrelated to the performance of the engine), and costs comparatively little – around $1 million each [6]. All in all, remarkable for SpaceX's "weakest point". 
 
References:
[1] At MIT's Aero/Astro Centennial – see link for full transcript.
[2] Tom Mueller, SpaceX's Vice President of Propulsion, has confirmed this will be the case (see linked tweet).
[3] Raw data here as a pdf, and here in a csv format. Data sourced from astronautix.com, and occasionally Wikipedia, spaceflightnow or SpaceX's offical website. Data are individual rocket engines (as opposed to clusters) which have seen flight. We excluded manuvering thrusters, ullage motors, and ion thrusters from the analysis.
[4] From the r/SpaceX community FAQ, under 'Why use methane and not RP-1?'. See this, and the previous question, for a fuller discussion of methalox combustion.
[5] Look at the diagram on the last page of the linked presentation as a quick demonstration of just how complicated those engines are.
[6] According to a former SpaceX employee, anyway.
"Были когда-то и мы рысаками!!!"

Seerndv

#925
- оно тут было? 



P.S. Поскольку ветки по TR-107 не нашёл, то сюда наверное.
Свободу слова Старому !!!
Но намордник не снимать и поводок укоротить!
Все могло быть еще  хуже (С)

Salo

#926
https://www.instagram.com/p/BJgEqUGjCTn/
Цитировать
spacex After each rocket landing we gain the chance to inspect hardware that has survived the rigors of getting to space and back like this Merlin engine from a recently landed first-stage. By doing this, we gain new knowledge that helps move us closer towards achieving full and rapid reusability.
"Были когда-то и мы рысаками!!!"


Seerndv

Спасибо, этого я не видел.
Свободу слова Старому !!!
Но намордник не снимать и поводок укоротить!
Все могло быть еще  хуже (С)

Apollo13

NASA'S COMMERCIAL CREW PROGRAM: UPDATE ON DEVELOPMENT AND CERTIFICATION EFFORTS

ЦитироватьSpaceX has also experienced ongoing issues with stress fractures in turbopumps that must be resolved prior to flight.
"SpaceX испытывала постоянные проблемы с усталостными трещинами (?) в турбонасосах, которые должны быть решены до полета"

Seerndv

ЦитироватьApollo13 пишет:
NASA'S COMMERCIAL CREW PROGRAM: UPDATE ON DEVELOPMENT AND CERTIFICATION EFFORTS
ЦитироватьSpaceX has also experienced ongoing issues with stress fractures in turbopumps that must be resolved prior to flight.
"SpaceX испытывала постоянные проблемы с усталостными трещинами (?) в турбонасосах, которые должны быть решены до полета"
- и эти люди занялись многоразовостью и Марсом?  Маск - мегаавантюрист.  :(
Свободу слова Старому !!!
Но намордник не снимать и поводок укоротить!
Все могло быть еще  хуже (С)

Сергей

ЦитироватьApollo13 пишет:
"SpaceX испытывала постоянные проблемы с усталостными трещинами (?) в турбонасосах, которые должны быть решены до полета"
               
                  
Вопрос-уточнение - может это последствия сварки трением вала ТНА из разнородных материалов и дело не в усталости материала, а в граничных условиях между разнородными материалами??

Kap

#932
ЦитироватьSeerndv пишет:
- и эти люди занялись многоразовостью и Марсом
У Кометы то-же были усталостные трещины. Повторно использовать это не мешало - проблемы возникали при где-то тысячном полете.
ЦитироватьSeerndv пишет:
Маск - мегаавантюрист.
Вы так говорите как будто это что-то плохое. Авантюристом Маск стал в тот момент когда взялся писать платежную систему - на тот момент востребованность этого продукта была совсем не очевидна. В противном случае этим бы занялся тот же Майкрософт и не дал "мафии пэйпэл" ни каких шансов.

Apollo13

ЦитироватьСергей пишет:
ЦитироватьApollo13 пишет:
"SpaceX испытывала постоянные проблемы с усталостными трещинами (?) в турбонасосах, которые должны быть решены до полета"
               
                  
Вопрос-уточнение - может это последствия сварки трением вала ТНА из разнородных материалов и дело не в усталости материала, а в граничных условиях между разнородными материалами??
Никакой другой информации в отчете нет.

Kap

ЦитироватьApollo13 пишет:
Никакой другой информации в отчете нет.
А гугл по запросу "stress fractures" отправляет в медицинскую экнциклопедию. Но рискну предположить что та же фигня что у Кометы - искусственное старение при производстве. Однако, практика показывает что три (или уже 4?) повторных прожига на полное время Мерлин переживает.

Apollo13

http://uk.reuters.com/article/us-space-spacex-idUKKBN15H307

 
ЦитироватьSpaceX says fix underway for rocket turbine wheel cracking

SpaceX's final version of the Falcon 9 rocket, which Elon Musk aims to launch before the end of the year, will fix a potential problem with cracks in its turbopumps, the company said on Thursday. Its statement followed a report that the U.S. Government Accountability Office will flag turbine wheel cracks in the rocket's turbopumps as a safety issue. NASA, the U.S. space agency, and the Air Force are among SpaceX's customers.

The GAO's preliminary findings were reported by the Wall Street Journal on Thursday.

In an email to Reuters, SpaceX said it has "qualified our engines to be robust to turbine wheel cracks. However, we are modifying the design to avoid them altogether," said spokesman John Taylor.

In addition to flying cargo to the International Space Station, SpaceX has NASA contracts to begin flying astronauts to the orbiting research laboratory as early as 2018.

"SpaceX has established a plan in partnership with NASA to qualify engines for manned spaceflight," Taylor said.

GAO investigators found that the Falcon 9 turbopumps, which are part of the system that delivers propellants to the engine, have blades that are prone to cracking, the newspaper said.

SpaceX last month resumed flights following a 4-1/2-month investigation into why a rocket blew up as it was being fueled for a routine pre-launch test in Florida.

The cause of the accident was traced to a burst canister of helium in the rocket's second stage liquid oxygen tank. It was unrelated to the issue with the rocket's turbopumps.

The accident was SpaceX's second since the Falcon 9 debuted in June 2010. The company's next launch is targeted for Feb. 14.

(Reporting by Irene Klotz; Editing by Dan Grebler)

Not

ЦитироватьKap пишет:
ЦитироватьApollo13 пишет:
Никакой другой информации в отчете нет.
А гугл по запросу "stress fractures" отправляет в медицинскую экнциклопедию. Но рискну предположить что та же фигня что у Кометы - искусственное старение при производстве. Однако, практика показывает что три (или уже 4?) повторных прожига на полное время Мерлин переживает.
Эта фигня возникает в лопатках ТНА, которые относительно плавно нагреваются, но резко охлаждаются при останове двигателя.

Salo

Merlin-1D, Draco и Superdraco:
https://imgur.com/a/f0hzh#opqnbx2
"Были когда-то и мы рысаками!!!"

h4lf

Кстати, а как справились с трещинами на лопатках в SSME (RS-25)?
Хотя и с ними летали...

Apollo13

ЦитироватьВасилий Афанасьев пишет:
Кстати, а как справились с трещинами на лопатках в SSME (RS-25)?
Хотя и с ними летали...
Тут что-то есть

http://enginehistory.org/SSME/SSME6.pdf