Blue Origin Thread (merged)

[Camacha]

4 minutes ago, PB666 said:

You can calculate it guess at the weight, thats going to approximate the pressure on the nose cone. 1g to fight gravity, 1g to fight drag, 1g to accelerate.

I do not think you can calculate it like that. The dynamic pressure is a function of speed, air pressure/density and probably drag. Some kind of variable that signifies force per square area should be the result.

[softweir]

18 hours ago, Camacha said:

Does anyone happen to know what the maximum dynamic pressure is on the Falcon 9? I have been looking for it, but cannot find it.

To be honest, we don't know. This is the sort of detail launch operators don't normally share.

[PB666]

1 hour ago, Camacha said:

I do not think you can calculate it like that. The dynamic pressure is a function of speed, air pressure/density and probably drag. Some kind of variable that signifies force per square area should be the result.

Why did you ask then, call up space X and ask them. Max Q is not a dynamic equilibrium, its a transient state.

Maximum pressure is near Mach 1, if you go to the hosted video they call it out at 1250 km/hour, 1235 km/hour is mach 1 at sea level.

Max Q occurred at 11.1 km altitude, pressure is about 1/3 ATM. Mach 1 at this altitude varies

but it was probably close to -50'C around 1100 meters per second. To give you an idea how fast the rocket was accelerating, between 20:08 to 20:18 in the video it accelerated 250 kph or 25 km/hs = 6.94 +/- 0.3 m/s^2 . That is to say gravity is 9.8m/s, its is surface relative acceleration at 6.94 m/s and on top of that there is drag.

After max Q the rocket accelerated as fast as 500 m/s per 6 seconds or 23 m/s  during that period it traveled upward 1 km/second. and a the end of the period it was traveling 6025 kph. This contrast to the start of the flight in which it was traveling 200 kph over 20 sec or about 10 km/hs which converts to 2.9 m/s. The stated thrust at liftoff is 6,804,000 N. Thus acceleration should have been 1.16 im guesing at the sampling end it could be 1.23, there for the rockets total weight is 10% lower than the maximum.  594,000 kg x .9 = 535000. Burn time is 162 seconds, though thrust tapers around 2 minutes into flight as total G force (about 1/2 g and acceleration 23 m/s places max acceleration about 3g)

Vacuum ISP is 348. Rocket burned 90% of first stage by 2 minutes and 38 seconds. It reached max Q 1 :44. This should give you the information you need to figure it out. Since maximum ISP is 348, and starting thrust is 6804000 and vacuum thrust is 7426000 the launch ISP is 318. At 11,000 meters the ISP should be 338 or so.

Now you can calculate, need more help?

 

 

 

 

 

[Camacha]

24 minutes ago, PB666 said:

Max Q is not a dynamic equilibrium, its a transient state.

I do not think I ever claimed either. Most of us will know what Max Q - I was simply hoping someone would have a factual number or a specification. Much is known about the Falcon 9, so it is a little surprising this is not. Calling SpaceX is not an option, since Mr. Musk is not in my Rolodex

Edited April 15, 2016 by Camacha

[codepoet]

I was wondering about the interstage. As I recall on earlier flights (v1.1?) the interstage fairing was expendable, and I recall that one made the news when it washed up on the Scilly isles. However please photos of the recent barge unloading show the interstage still attached to the first stage. Am I reading that correctly?

[Nibb31]

The interstage might have been expendable at one point, but now it contains the hydraulics for the grid fin actuators and maybe the avionics, so it stays attached to the first stage. 

[Nibb31]

12 hours ago, Kryten said:

Still, windows are important for the experience they're trying to sell, and windows the size of the ones they're planning are a big change to the structure.

Agreed, especially large windows that survive the landing impact. Even with the retro-rockets, it's going to be brutal.

 

[PB666]

5 hours ago, Camacha said:

I do not think I ever claimed either. Most of us will know what Max Q - I was simply hoping someone would have a factual number or a specification. Much is known about the Falcon 9, so it is a little surprising this is not. Calling SpaceX is not an option, since Mr. Musk is not in my Rolodex

Gee, I have to do everything. Had you followed my instructions you would have a time stamp, a velocity stamp and an altitude. From that you could have derived this.

Note m/s is wrong (x-axis), I converted back to the original units for the graph, its km/h . Done so because the original call out was done at 1250 kph.

Gravity is known, we already deduced acceleration for the period at around 6.8 and we can see that were we should be is around 11.5

So, there are one of two things you can tell from that.

1. There was no throttle down and about 4.5 meters per second times mass of drag force was present

2. There was a throttle down in order to avoid those high levels of acceleration in which case what you would have seen was a fall in acceleration

So if we add all the forces. Force 1 = gravity 9.8 m/s, Force 2 & 3 are 11.5. The total force is 21.3 m/s, a bit below the 30 I predicted, its hard to guess at these things remembering what you saw on a video 6 days ago.

Can we now guess that force?

The original tack off condition was, with a bit better math extrapolated to take off , 2.5 m/s + 9.81 = 12.3 m/s, the original thrust was 6804000, we can guess the mass was 553,000 kg. That was for an ISP of 318

We then had an ISP of 338 thus thrust is 7231kN. We have a total mass of 340,000kg  so now we can estimate the forces (data trimmed to second digit for obvious reasons)

Gravity - 3,300,000
velocometric acceleration - 2,400,000
drag or engine throttle down - 1,530,000

So now you have a nose cone. Right, so my guess its between 2 and 22.5 meters in radius, this gives it a surface area of 12.5 to 16.25 sq. meters.

If you then take the drag force and divide you have the Maximum pressure around 120,000 N per square meter () 12 N per square cm, = 17 PSI. ATM is 14 PSI as MSL.

Assuming that SpaceX has a better engineering team than V program in germany, the critical problem is now moved down to the docking port and its bracing. Assuming that it is about 3 cm thick on its railing, and that you have and it radius is around 1.5 to 2 meters, the area of the railing is around 0.37 meters, this means the force pressure on the railing (including magnets and what not electronics is going to be about 4 million N/meter sq.

As you break Mach 1 most of the pressure is on the nose piece, however do to their non-Sears-Haack shape the is wave pressure on the launch vehicle, as speed increase that travels past the powerplant and thus you get soot all over the launch phase and, you start acceleration.

If you want to get a better answer than this I suggest you send a few bottles of French wine and Russian caviar to the launch engineers at Canaveral.

 

 

[tater]

BO said their capsule lands at 0.58 m/s. That's a drop test of 1.7 cm. On dust-like dirt (I know, it looks just like my yard, lol).

Edited April 15, 2016 by tater

[Camacha]

10 hours ago, PB666 said:

Gee, I have to do everything.

I only asked to post the dynamic pressure, if you happened to know the factual number. While it is fun to produce a guesstimate, there are too many assumptions to attach too much value to the number. You get a sticker for effort, though

[PB666]

33 minutes ago, Camacha said:

I only asked to post the dynamic pressure, if you happened to know the factual number. While it is fun to produce a guesstimate, there are too many assumptions to attach too much value to the number. You get a sticker for effort, though

Dynamic pressure is dynamic its not a factual number. The instantaneous and imprecise value is what we would call a subjectively-defined quantum statistic, it is a point in a confidence range of values, usually defined by a mean and standard deviation, skewing and kurtosis. In this particular case you would be looking at forces on the lip of the docking port that are not due to non-inertial motion, that itself would be a range of forces, because there are local fluctuations of pressure on the nose cone, particularly after the turn to horizontal has begun and there are a collection of time points that statistically could have been Max-Q at any one of these points.

Many players in the game have difficulty because they are all but oblivious to drag. Here is a graphic to help on player deal with his flex problem, it exhibits perfectly the problem of maximum dynamic pressure.

The cause of bending rockets (in 1.0) was drag not thrust per say. IOW, if I cheat this rocket into space, and set the gimble on the rocket below 20%, the rocket can fire through its first stage and survive. non-axial drag forces cause flexing at the segment joints. Since rockets in KSP are only attached at their nodes or attachment points, they have extraordinary segmental flexibility, drag is the enemy of these types of design. Its good however to demonstrate that small differences in the angle of attack cause differential drag on the forward surfaces, the more pointy and flexible a rocket is, the more susceptible it is to this type of problem, since all rockets need to turn to make orbit, the effects of drag even in aerodynamic rockets cannot be avoided, in fact it can be worse. The situation above, the un-cabled rocket tries to fly in different direction than its controller is pointed. Gimbling only makes matters worse (this is a low gimbling engine) because in introduces resonance, the resonances destroy the rocket. The rocket is also doomed because it is difficult to avoid Max-Q forces unless you reach a very high altitude at which point all the early stage fuel would be spent, flight dynamics reveals that it is unstable above 80 m/s at 2000m and so max-Q whatever the force is at an indicated airspeed of 60 kts. (about the speed of a super-cub). In this case Max Q is an IAS were above my ship could enter harmful resonances, it is a speed that will vary with altitude. I don't really care what the pressure is as long as I stay below it. (actually in the bottom panels above I fix the flex and resonance with cabling, still has a dynamic limit but much higher)

The relevance is this, if you go and watch the CRS-8 launch, you will see that Max Q is at a predetermined velocity, 1250 m/s,  where they expected it to be, and if you look at the graph there are many points that could qualify as Max-Q.

If you care about your designs the plot effort is worth it, not on every part but a sampling of parts used in rockets with different composite CoD. This is not the first time that I have plotted drag.  The design below was built to facilitate the launch of a 2 heavy fusion reactors (mounted on the Karmony modules, hey kerbals not fraid of a few stray neutrons).

Note: Another major complaint was about the fairings, people were having problems with them during flight, above two sets of fairings are used, flight dynamic are a major issue for fairing release when powered up, this particular rocket has to reduce its engines to near zero to jettison the fairings, but jettison did not damage other rocket parts, this is because the fairings are protected from drag forces by cabling (third full panel from left) to keep the fairing from flexing too much and sustaining damage in flight. In the game aerodynamic forces can damage fairings causing them not to release correctly (or at all).
The problem with fairings is that they encourage combinations of parts that are thick on top and thin on the bottom, even in RL, this would cause flexibility problems. Bracing is needed under the fairing to prevent sway during flight, again, pretty much all due to aerodynamics.

[Camacha]

18 hours ago, PB666 said:

Dynamic pressure is dynamic its not a factual number.

It is, in the sense that you need to design for an actual number. Otherwise your craft will fall apart if you exceed the pressure, or you will have over-engineered your craft. For instance, if you want to design a fairing, you will need to know the peak dynamic pressure. Note that we are discussing actual rockets, not KSP ones.

To be honest, I do not know why you want to complicate matters. The effort you put into your posts is appreciated, but most of it is not or not really related and only confuses matters. I guess the answer is we don't know, which is a valid answer.

[tater]

BEAM installed.

[Mitchz95]

Do we know when they're planning to "inflate" it? Also, do we know when SpaceX launches next?

[CatastrophicFailure]

3 minutes ago, Mitchz95 said:

Do we know when they're planning to "inflate" it? Also, do we know when SpaceX launches next?

IIRC somewhere near the end of May. 

Some things in space do NOT move fast...

[tater]

They said May 26 at the post-launch press conference.

[Cuky]

According to this site next SpaceX launch is on April 28th. Falcon 9 with JCSAT 14 as payload

[KerbonautInTraining]

9 hours ago, Cuky said:

next SpaceX launch is on April 28th

Aw, if it were one day earlier I'd be getting the best birthday present ever

[KerbonautInTraining]

 

1 minute ago, Kryten said:

On 4/13/2016 at 2:00 PM, Motokid600 said:

 

13 hours ago, CatastrophicFailure said:

 

32 minutes ago, KerbonautInTraining said:

 

Kryten.exe has stopped working

[DuoDex]

2 minutes ago, KerbonautInTraining said:

 

Kryten.exe has stopped working

seems to work fine...

[Dfthu]

19 minutes ago, DuoDex said:

seems to work fine...

Broken for me too.

[Kryten]

10 hours ago, Cuky said:

 

 

The quotes are just blank, not broken as such. I had to post that (and the one above, sorry) because I can't find any way to delete quote boxes on android, and once I've deleted everything outside a quote box I can't select anything outside the quote box again. 

 

 

I should note the problem is with Google's 'Android' operating system, I'm definitely not an actual android. If anybody says anything otherwise they're a dirty liar.

[CatastrophicFailure]

18 minutes ago, Kryten said:

 

I should note the problem is with Google's 'Android' operating system, I'm definitely not an actual android. If anybody says anything otherwise they're a dirty liar.

Much as I hate to miss an opportunity to slander and malign Android,  the problem is the same with us Apple-flavored kool-aid drinkers.  

New forum just does NOT like mobile...

or Exxon...

[Mad Rocket Scientist]

17 hours ago, Mitchz95 said:

Do we know when they're planning to "inflate" it? Also, do we know when SpaceX launches next?

For spacex info, take a look at this amazing site: https://spacexstats.com/

 

[Falcon Coupe]

3 hours ago, Kryten said:

 

The quotes are just blank, not broken as such. I had to post that (and the one above, sorry) because I can't find any way to delete quote boxes on android, and once I've deleted everything outside a quote box I can't select anything outside the quote box again. 

 

 

I should note the problem is with Google's 'Android' operating system, I'm definitely not an actual android. If anybody says anything otherwise they're a dirty liar.

I am able to delete quote boxes on my Android phone. To do this, tap on the title area of the quote box itself and you'll see some editing things around the edge of the box, then press the delete button on your keyboard. I hope this helps so you're no longer accused of being an android!