Author Topic: Basic Rocket Science Q & A  (Read 271817 times)

Offline Burninate

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Re: Basic Rocket Science Q & A
« Reply #1040 on: 12/08/2015 08:34 PM »
Thank you both! I'm pretty sure now that I was not using the online calculator I had found correctly.

strangequark, that page is exactly what I really needed, thank you!

A 1.6% difference in density makes a lot more sense and that must be well within the tolerances of the NK-33 engine.

For future reference, anyone discussing the merits of LOX densification, etc.

LOX at -184 C = 1141.7 kg/m3 (just below boiling point)
LOX at -192 C = 1185.4 kg/m3
LOX at -196 C = 1204.3 kg/m3
LOX at -210 C = 1268.4 kg/m3
LOX at -217 C = 1299.0 kg/m3 (just above freezing point)
Boiling & freezing points at what pressure though?

Offline whitelancer64

Re: Basic Rocket Science Q & A
« Reply #1041 on: 12/09/2015 08:46 PM »
Thank you both! I'm pretty sure now that I was not using the online calculator I had found correctly.

strangequark, that page is exactly what I really needed, thank you!

A 1.6% difference in density makes a lot more sense and that must be well within the tolerances of the NK-33 engine.

For future reference, anyone discussing the merits of LOX densification, etc.

LOX at -184 C = 1141.7 kg/m3 (just below boiling point)
LOX at -192 C = 1185.4 kg/m3
LOX at -196 C = 1204.3 kg/m3
LOX at -210 C = 1268.4 kg/m3
LOX at -217 C = 1299.0 kg/m3 (just above freezing point)
Boiling & freezing points at what pressure though?

Oh, right, the boiling / freezing point also changes due to pressure. I should have mentioned in my previous post that each of the density numbers I listed is at 40 psi.

The calculator on the NIST page doesn't allow you to set temperatures less than -218.789 C, which is the freezing point of Oxygen at sea level air pressure (1 atm or 101.325 kPa). -182.96 C is the the boiling point at sea level air pressure. I just rounded up and down to the nearest degree C to get to just above and just below those points, my intention being to establish upper and lower boundaries for the density information.

It's safe to say that those two data points are not precisely accurate in regards to being just above or just below the freezing / boiling points at 40 psi, and I'm not sure how to figure it out, as I'm quite far outside of my knowledge base here, which is why I asked about it in the first place :D
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Offline Dante80

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Re: Basic Rocket Science Q & A
« Reply #1042 on: 01/04/2016 03:51 PM »
Here is a question.

Falcon9 has done three GTO missions, where the end orbit was super-synchronous.

12/03/13 Falcon 9 v1.1 F9-7  SES 8                 3.183 CC 40 295x80000x20.8 GTO+
01/06/14 Falcon 9 v1.1 F9-8  Thaicom 6             3.016 CC 40 295x90000x22.5 GTO+
03/02/15 Falcon 9 v1.1 F9-16 Eutelsat 115WB/ABS 3A 4.159 CC 40 400x63300x24.8 GTO+


If I understand correctly, the reason for that is that it makes circularizing to GEO for the payload easier.

I want to know how I can convert the above stats to a - X m/s equivalent. In other words, I want to find out how much dv the payloads had to use to get to their end orbits.

How can I do that?

Offline baldusi

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Re: Basic Rocket Science Q & A
« Reply #1043 on: 01/04/2016 04:25 PM »
Here is a question.

Falcon9 has done three GTO missions, where the end orbit was super-synchronous.

12/03/13 Falcon 9 v1.1 F9-7  SES 8                 3.183 CC 40 295x80000x20.8 GTO+
01/06/14 Falcon 9 v1.1 F9-8  Thaicom 6             3.016 CC 40 295x90000x22.5 GTO+
03/02/15 Falcon 9 v1.1 F9-16 Eutelsat 115WB/ABS 3A 4.159 CC 40 400x63300x24.8 GTO+


If I understand correctly, the reason for that is that it makes circularizing to GEO for the payload easier.

I want to know how I can convert the above stats to a - X m/s equivalent. In other words, I want to find out how much dv the payloads had to use to get to their end orbits.

How can I do that?
If you assume two burns from a super synchronous GTO, you can use my spreadsheet (it is done in LibreOffice). But I guess you could use it for sub synchronous, too. Normal GTO usually have a single burn and thus I'm not sure it will work. It should since it takes the delta-v requirements of two burns which should be the same. But I'm not sure.

BTW:
12/03/13 Falcon 9 v1.1 F9-7  SES 8                 3.183 CC 40 295x80000x20.8 GTO+ -> 1,511m/s
01/06/14 Falcon 9 v1.1 F9-8  Thaicom 6             3.016 CC 40 295x90000x22.5 GTO+ -> 1,504m/s
03/02/15 Falcon 9 v1.1 F9-16 Eutelsat 115WB/ABS 3A 4.159 CC 40 400x63300x24.8 GTO+ -> 1,594m/s
« Last Edit: 01/04/2016 04:27 PM by baldusi »

Offline Dante80

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Re: Basic Rocket Science Q & A
« Reply #1044 on: 01/04/2016 04:44 PM »
Here is a question.

Falcon9 has done three GTO missions, where the end orbit was super-synchronous.

12/03/13 Falcon 9 v1.1 F9-7  SES 8                 3.183 CC 40 295x80000x20.8 GTO+
01/06/14 Falcon 9 v1.1 F9-8  Thaicom 6             3.016 CC 40 295x90000x22.5 GTO+
03/02/15 Falcon 9 v1.1 F9-16 Eutelsat 115WB/ABS 3A 4.159 CC 40 400x63300x24.8 GTO+


If I understand correctly, the reason for that is that it makes circularizing to GEO for the payload easier.

I want to know how I can convert the above stats to a - X m/s equivalent. In other words, I want to find out how much dv the payloads had to use to get to their end orbits.

How can I do that?
If you assume two burns from a super synchronous GTO, you can use my spreadsheet (it is done in LibreOffice). But I guess you could use it for sub synchronous, too. Normal GTO usually have a single burn and thus I'm not sure it will work. It should since it takes the delta-v requirements of two burns which should be the same. But I'm not sure.

BTW:
12/03/13 Falcon 9 v1.1 F9-7  SES 8                 3.183 CC 40 295x80000x20.8 GTO+ -> 1,511m/s
01/06/14 Falcon 9 v1.1 F9-8  Thaicom 6             3.016 CC 40 295x90000x22.5 GTO+ -> 1,504m/s
03/02/15 Falcon 9 v1.1 F9-16 Eutelsat 115WB/ABS 3A 4.159 CC 40 400x63300x24.8 GTO+ -> 1,594m/s


Many thanks for that. I had excel, tried libre online, didn't work, installed it, saved as xls, uninstalled libre, restarted the PC, opened FF and...saw that you provided the numbers..T_T

Now, I'm thinking of uninstalling office and getting libre..XD

So...judging by the fact that S2 was burned to depletion, the Thaicom 6 mission gives us an estimate of 3,000kg to a GTO-1500 (equivalent) orbit for the v1.1 maxed out.
Lets see how the FT version does in SES9..C:
« Last Edit: 01/04/2016 04:55 PM by Dante80 »

Offline baldusi

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Re: Basic Rocket Science Q & A
« Reply #1045 on: 01/05/2016 02:07 PM »
Well, if its true that they have 30% more performance, 3.9tonnes should be doable and 4 tonnes may be doable. But this is just from the first launches. They stated they had some performance padding. In fact, NLS II states that the F9 v1.1 could do 5.6 tonnes to a 28.5deg GTO (1,804m/s).. And a 20.2Deg x 88,000km (1,500m/s) NLS II says 3,855kg.
If those numbers are true, then FT could do 5 tonnes to a 1,500m/s GTO!

Offline Dejv

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Re: Basic Rocket Science Q & A
« Reply #1046 on: 01/07/2016 05:55 PM »
Hi guys,

I am preparing for spaceflight mechanics exam and I am a little bit stuck with these questions. (see attach)

In the first question if we assume the perturbation is -1.7x10^-3 deg/day , and the burn is every 1000s (i.e. 86.4 times a day), then the maximal deviation from non-perturbed motion should be -1.97x10^-5 deg. I don't get it why there is the delta v then... is the slot calculated some other way (should it be in seconds..)?

In the second question, the perturbance is easily calculated, but i dont really know how to connect it with the Tsiolkovsky equation.

Thanks for any help!
(I am not aerospace/spaceflight student, I took this course only from pure interest)


Offline Stan-1967

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Re: Basic Rocket Science Q & A
« Reply #1047 on: 01/07/2016 06:23 PM »
1.  Can you drop the class

2.  The second part seems to be describing the pertubation from the ideal orbit with the given parameters.  So it seems like you need to set the rocket equation for deltaV equal to the amount of deltaV caused by the pertubation.

I may help you to know that in the rocket equation, exhaust velocity can be replaced by ISP x Gravity ( 4500 x 9.807 m/s^2) ln(mo/m1) and then solve for m1


Offline Dejv

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Re: Basic Rocket Science Q & A
« Reply #1048 on: 01/07/2016 07:12 PM »
1.  Can you drop the class

2.  The second part seems to be describing the pertubation from the ideal orbit with the given parameters.  So it seems like you need to set the rocket equation for deltaV equal to the amount of deltaV caused by the pertubation.

I may help you to know that in the rocket equation, exhaust velocity can be replaced by ISP x Gravity ( 4500 x 9.807 m/s^2) ln(mo/m1) and then solve for m1

1. no, i cant

2. well the perturbation is in rad/s, as i know the semimajor axis i can convert that to m/s. so i just pop that into rocket equation and thats it? shouldnt be the time somehow included there as well?

Yeah I know exh. velocity = g x Isp
« Last Edit: 01/07/2016 09:14 PM by Dejv »

Offline meetsitaram

Re: Basic Rocket Science Q & A
« Reply #1049 on: 01/25/2016 02:47 PM »
Hi Guys, can you suggest a good book that explains basics of rockets and space flight? I was searching on google and found:
Quote
Astronautics: The Physics of Space Flight - Ulrich Walter
Rocket and Spacecraft Propulsion - Martin J. L. Turner

Offline Zaum

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Re: Basic Rocket Science Q & A
« Reply #1050 on: 01/25/2016 07:58 PM »
Rocket Propulsion Elements - George Sutton, Oscar Biblarz

Covers the basics and a bit more. Very comprehensive.
You can probably see a preview on google books to check if it has what you're looking for.
« Last Edit: 01/25/2016 08:01 PM by Zaum »

Offline nicp

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Re: Basic Rocket Science Q & A
« Reply #1051 on: 02/21/2016 01:37 PM »
I have a really boring question.  ;)
Obviously liquid propellant rockets have valves. Valves for the pre-burner and for the main combustion chamber and a load of others.
I don't think I've ever seen a picture of a main oxidizer or fuel propellant - or perhaps I didn't recognize it.
I mean, take the F-1 - that's got to have some seriously meaty propellant valves. With bloody enormous actuators.

Or perhaps more interestingly, take the original Atlas. Those booster engines are gonna get dropped off, so you have a separation plane too.

So what kind of valves are they - obviously they need to be lightweight, but have to take a very high flow rate, etc..

Just my weird curiosity.. If this is covered elsewhere, apologies, I haven't noticed anything appropriate..
Where's my Guinness?

Offline AnalogMan

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Re: Basic Rocket Science Q & A
« Reply #1052 on: 02/21/2016 02:16 PM »
I have a really boring question.  ;)
Obviously liquid propellant rockets have valves. Valves for the pre-burner and for the main combustion chamber and a load of others.
I don't think I've ever seen a picture of a main oxidizer or fuel propellant - or perhaps I didn't recognize it.
I mean, take the F-1 - that's got to have some seriously meaty propellant valves. With bloody enormous actuators.

Or perhaps more interestingly, take the original Atlas. Those booster engines are gonna get dropped off, so you have a separation plane too.

So what kind of valves are they - obviously they need to be lightweight, but have to take a very high flow rate, etc..

Just my weird curiosity.. If this is covered elsewhere, apologies, I haven't noticed anything appropriate..

Just to give you some idea - here are a couple of slides showing the Main Fuel Valve for the shuttle SSME engine.

Offline mfck

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Re: Basic Rocket Science Q & A
« Reply #1053 on: 02/21/2016 09:59 PM »
Hi,

I have a Mechanical Engineering (probably) question

It is my understanding, that in most LVs and spacecraft pressure vessels are also a main structural element, due to mass-efficiency considerations. My question is whether there's a physical limit to scaling of such design before mass-efficiency dictates main structural element be external to the pressure vessel, or in other words, how big would your pressure vessel need to be, assuming habitable temperature, pressure and max load (5g?), before you have to unload to external structure to stay mass-efficient?

I am not sure it's even a valid question. Maybe a constraint should be no exotic materials as well?

Thanks

Offline sdsds

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Re: Basic Rocket Science Q & A
« Reply #1054 on: 02/22/2016 04:32 AM »
how big would your pressure vessel need to be [...] before you have to unload to external structure to stay mass-efficient?

I have no answer, but like your question! Is it possible the honeycomb isogrid or orthogrid integrated into many pressure vessel walls performs a function like what you describe? Does it matter if that structure is inside or outside the pressure vessel wall?

A completely unrelated question of my own: does the "residence time" requirement (in the sense of the characteristic length) for a combustion chamber change dramatically when the propellants are being injected as gases, e.g. in a full-flow staged combustion design?
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Offline R7

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Re: Basic Rocket Science Q & A
« Reply #1055 on: 02/22/2016 04:43 PM »
I have a really boring question.  ;)

(valves)

Not a boring question at all. AnalogMan already gave an example of ball valve. Other types used in rocket engines are at least poppet and butterfly valves. Here's a diagram of F-1 main LOX valve (the engine had two of them and also two similar main fuel valves). They are usually actuated using high pressure pneumatics or hydraulics.



More here: http://heroicrelics.org/info/f-1/f-1-main-lox-valve.html
« Last Edit: 02/22/2016 04:44 PM by R7 »
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Offline Remes

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Re: Basic Rocket Science Q & A
« Reply #1056 on: 02/22/2016 11:06 PM »
With bloody enormous actuators.

E.g. fuel Isolation valves are relatively simple. They only fully open or fully close. Most often they are driven pneumatically. Pressurized Helium drives a piston, the piston drives a rack/pinion which in turn runs the valve itself. Force equals pressure times area. So a big enough pneumatic cylinder gives plenty of power. A spring closes the valve.

The ball valve shown from the Space Shuttle is hydraulically driven (with a pneumatic emergency shutdown alternative system). Hydraulic systems work on higher pressures and have a much higher power density. So the Actuator housing must be more robust, but is still smaller than for pneumatic actuation. On L2 there is a manual for SSME, showing lots of details.

Modern engines more often get electric actuators. E.g. several motors are driving the ball type or poppet type valve. Most often they have an emergency pneumatic backup for shutdown. The actuators have a lower power density. But they are easier to install, to test, etc. as keeping the hydraulic system clean is not that easy.

Offline Remes

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Re: Basic Rocket Science Q & A
« Reply #1057 on: 02/22/2016 11:29 PM »
Does it matter if that structure is inside or outside the pressure vessel wall?
My best guess: If the grids go outwards, the distance between the grid corners become bigger. If they go inwards, they are becoming smaller and therefore provide more stiffness.

Here is a nice video about a buckling test.
https://www.youtube.com/watch?v=nUjpVBktTAI?t=203

Also inward pointing grids allow a easier attachment of sensors, pressure vessels, etc.

Offline R7

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Re: Basic Rocket Science Q & A
« Reply #1058 on: 02/27/2016 12:16 PM »
A completely unrelated question of my own: does the "residence time" requirement (in the sense of the characteristic length) for a combustion chamber change dramatically when the propellants are being injected as gases, e.g. in a full-flow staged combustion design?

For instance RD-170/RD-180 combustion chamber has characteristic length of 1079.6mm. I would not rate that as dramatic reduction. Gasification is just step one on the complex chain of combustion.

http://lpre.de/energomash/RD-170/index.htm
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Offline Oli

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Re: Basic Rocket Science Q & A
« Reply #1059 on: 03/05/2016 03:25 PM »

I find it curious that so many rockets do parallel staging. Apart from ground-starting the engines on the core there don't seem to be any obvious advantages. You save some thrust on the first stage (often little because the core uses hydrolox) but you lose some performance (more dry mass at separation, lower engine ISP).

Anything else?