totm nov 2023 SpaceX Discussion Thread

[RCgothic]

It takes what, an hour to load propellant before launch? There would certainly be collateral damage, but domino effect doubtful.

[YNM]

47 minutes ago, RCgothic said:

It takes what, an hour to load propellant before launch? There would certainly be collateral damage, but domino effect doubtful.

You'd need a different place for placing the rockets (apron) and the launching of rockets (liftoff/landing zone).Their distance have to be quite enourmous.

Not really possible with current configurations.

Not to mention planes don't fuel on the runway yet it's not too lethal to explode vs rockets that only fuels once in the "runway" yet having one hell of a destructive power.

Edited February 28, 2018 by YNM

[Green Baron]

No domino ? How disappointing ... :-)

I was only commenting on the artist's impression :-)

Edited February 28, 2018 by Green Baron

[RCgothic]

It is a cool artist's impression, even if it is unrealistically crowded. :-)

[wumpus]

19 hours ago, DDE said:

That's basically the Me-163 - or, if we dig into the Soviet files, the Bereznyak-Isaev BI-1, preceded by several of Korolev's rocket gliders. Nitric acid oxidizer, pretty advanced for its age, and it was starting ground tests by the time of Operation Barbarossa.

Wooden aircraft were nothing unusual back then, though.

I wouldn't expect wood to be the first choice for high performance aircraft.  Typically it was chosen because of scarcity (thanks to the war) of aluminum and other materials.  Of course plenty of aircraft designers were familiar with wood as canvas covered wood was an earlier favorite material for aircraft.

19 hours ago, Antstar said:

You couldn't pay me to get in that

In many ways fuming nitric acid is worse than NO2/N2O4/N2O5. And it IS hypergolic with wood... At least LOX requires an ignition source

The one I heard about killed a test pilot (I think on the second flight), but really wasn't closely connected with Korolev at all (the designers may have corresponded with him at the golag, but that was it).  Soviet weapon design tended to be dangerous for the operator and wildly dangerous (thus effective) to anyone it aimed at.  This really made sense when looking at the deaths due to the "Great Patriotic War", although reading through "Rockets and People" more people he knew seemed to die in the purges than the war (note he lived in areas that weren't overrun, that probably made the difference).

19 hours ago, sevenperforce said:

The Grumman concept:

["shuttle on shuttle" picture]

Vertical takeoff on rockets; horizontal landing on jets. The orbiter carries two crossfed drop tanks discarded at 300 m/s under orbital insertion.

While this looks good at first glance, anyone familiar with the death of SR-71 test pilot Ray Toric launching a top-mounted drone would realize that the second stage orbiter was a "burn or die" rocket, as clearing the carrier's tail is absolutely mandatory (granted, I have no idea where you would land if you could detach from the main jet without thrust, but presumably you *have* to detach or everyone on board dies).  While a "center sustainer to [nearly] orbit" might not be a terribly efficient design, there are safety features and why they have flown 99% of all humans to space (just counting Soyuz + Shuttle).

I like this design.  I'd love to see F-1 based (Kerolox) engines on the booster and RL-10 (hydrolox expander cycle) engines on the orbiter, but I have doubts that even a RL-10 can be sufficiently certain of lighting.  Of course, there are plenty of "nobody has ever survived the abort procedure on the simulator" points in the shuttle, I wouldn't want to go ahead with a design with such a flaw.  Maybe you could get the RL-10 reliable enough, or maybe the second stage fuel tanks would be small enough to justify hypergolics (the last 300m/s were always going to be hypergolics anyway, and stored within the orbiter).

Note that while Spacex has done an amazing job retrofitting the Falcon-9 to hoverslam (it was expected to be recovered by parachutes), I can't imagine anyone remaining on board during such a flight (witness the recent destruction of Falcon Heavy's center booster) and the tech in the 1970s likely required at least pilot assistance.  On the other hand BFG's upper stage may be designed that way (presumably with redundancy and hover abilities that the Falcon 9 will never have).

Edited February 28, 2018 by wumpus

[PB666]

4 hours ago, YNM said:

You'd need a different place for placing the rockets (apron) and the launching of rockets (liftoff/landing zone).Their distance have to be quite enourmous.

Not really possible with current configurations.

Not to mention planes don't fuel on the runway yet it's not too lethal to explode vs rockets that only fuels once in the "runway" yet having one hell of a destructive power.

If the base elevation was higher you could allow the launch gases to travel underground in a giant horseshoe. The H202 rockets are not too bad, but the SFRBs would have to be replaced by something 'quieter'.

 

[sevenperforce]

What do we think the chances are that SpaceX will ever have a Falcon 9 RTLS landing failure after entry burn shutdown?

[Rakaydos]

6 minutes ago, sevenperforce said:

What do we think the chances are that SpaceX will ever have a Falcon 9 RTLS landing failure after entry burn shutdown?

Forever is a long time, but since SpaceX wants to retire the Falcon 9 in an unreaonably short time (by conventional standards) the odds seem rather good that it wont happen.

Now, BFR landing failures after entry...

[sevenperforce]

12 minutes ago, Rakaydos said:

Forever is a long time, but since SpaceX wants to retire the Falcon 9 in an unreaonably short time (by conventional standards) the odds seem rather good that it wont happen.

Now, BFR landing failures after entry...

I'm inclined to agree. SpaceX will only RTLS when they have plenty of margin to do so, and any engine start problems would likely be detected during either the boostback or the entry burn, giving the stage plenty of time to redirect and ditch in the ocean. With additional TEA-TEB due to lessons learned from the FH core splashdown, I don't really see it as likely.

[StrandedonEarth]

10 minutes ago, sevenperforce said:

I'm inclined to agree. SpaceX will only RTLS when they have plenty of margin to do so, and any engine start problems would likely be detected during either the boostback or the entry burn, giving the stage plenty of time to redirect and ditch in the ocean. With additional TEA-TEB due to lessons learned from the FH core splashdown, I don't really see it as likely.

The booster already aims just offshore so that if the landing burn fails to start it splashes. The landing burn steers it to the landing pad

Edited February 28, 2018 by StrandedonEarth

[sevenperforce]

10 minutes ago, StrandedonEarth said:

The booster already aims just offshore so that if the landing burn fails to start it splashes. The landing burn steers it to the landing pad

That was what they did initially, but now that they're using 1-3-1 burns on RTLS, this may no longer be the case. The booster comes in with an AOA and flies an odd trajectory; despite numerous analyses over at NSF, no one is quite sure.

[YNM]

2 hours ago, PB666 said:

If the base elevation was higher you could allow the launch gases to travel underground in a giant horseshoe.

Doesn't change the fact if it explodes.

 

Again, rocketry is still nowhere as safe as airplanes or the even safer (in some sites) railways. Even if we class Airplanes as being not that safe, it's very hard to imagine having one of them struck the terminals at flying speed or as explosion debris. Rockets in an airplane environtment would cause one heck of a damage, or if we want to scale up you end up with a very big scale indeed (like VAB to KSC LC 39, compare with the usual runway/taxiway/taxiway/taxiway(apron)/apron succession in large airports).

Rockets also have a different problem : the space itself. As with space debris, I think launching something within an hour of each other is still a bit worrying (though given the usual 90m this means launching something at 30-60m interval looks "optimal"), as not everything has settled off. Not to mention the weather problem - I think that I'll only believe such a "dense" launching only when you can launch one in absolute rain and gusts, which means it has a very high accuracy whatever the external factors are.

But yeah, that's it. I don't say it's not possible, I only say if it was to be done we'd need a lot of change from the current situation.

 

If they'd let a "launch-spotting special" train in Vandenberg for the Minotaur while being entirely chill, and no PR disaster occurs, then maybe we're ready. Otherwise, lots of work needed.

Edited February 28, 2018 by YNM

[PB666]

5 minutes ago, YNM said:

Doesn't change the fact if it explodes.

 

Again, rocketry is still nowhere as safe as airplanes or the even safer (in some sites) railways. Even if we class Airplanes as being not that safe, it's very hard to imagine having one of them struck the terminals at flying speed or as explosion debris. Rockets in an airplane environtment would cause one heck of a damage, or if we want to scale up you end up with a very big scale indeed (like VAB to KSC LC 39, compare with the usual runway/taxiway/taxiway/taxiway(apron)/apron succession in large airports).

Rockets also have a different problem : the space itself. As with space debris, I think launching something within an hour of each other is still a bit worrying (though given the usual 90m this means launching something at 30-60m interval looks "optimal"), as not everything has settled off. Not to mention the weather problem - I think that I'll only believe such a "dense" launching only when you can launch one in absolute rain and gusts, which means it has a very high accuracy whatever the external factors are.

But yeah, that's it. I don't say it's not possible, I only say if it was to be done we'd need a lot of change from the current situation.

The collateral explosion damage issues are greatly decreased if one uses H2/02 since H2 is lighter than air and tends to rise (rise away from the launch site). Also both are cryogenics and less able to ignite by spurious spark.

If you read that Challenger report, the greatest apriori fear of the engineers from Morton Thiokol was that the SFRs would explode on the launch pad, they were amazed when it did not, almost all of the initial damage was caused by the SFR, even the big orange tank, after being penetrated was still largely intact, it wasn't until the SFR collided into the side of the orbiter that all hell broke loose. That overall risk is still there and hasn't gone away. Overall one can double gate the H2 or O2 and also kill all the engines on a liquid fueled rocket. If you are running side mounted fuel tanks (which I frequently do given the luxury of RS 68A's advanced thrust) you can seperate then H2 from the O2 storage tanks and the risk of the tanks exploding do to flame is zero.

The random probability of debris impacting a second rocket is negligible. Most of that debris comes from the S1-S2 coupling, which occurs at <3000 m/s. If we remember the equation F_centrifugal = V²/r then at 3000 m/s then resistence to gravity is only 1.40/9.8 g. If we imagine that the debris is at 140,000 meters. then it is still radially accelerating at ~8.3 m/s.  140,000 =  4.15T². It takes 183 seconds for the debris to clear the airspace (not considering friction). Initially friction acts against the horizontal (assuming that the separation occurs close to apogee) component of friction but later acts on the vertical component, if one assumes and +radial trajectory of say  1000 m/s then it takes only 125 seconds to clear apogee and another 125 seconds to return to the altitude that the stage separates, at this it is traveling at 1000 m/s and so again clears the area in less than 400 seconds (about 7 minutes). The typical acceleratrions due to friction forces above 100 km are micrometers per second on just about everything but a parachute. In addition lets assume that the second space craft launches along the same exit path. The problem with that analysis is that exit path once suborbital is a trajectory in celestial coordinate system, where as the second launch remains in a cartesian (longitudinal/latitudinal reference frame), that two reference frames are moving relative to each other. So that if the second flight launches bearing 090 and follows the prograde, its path is not behind the first rocket, but behind and offset from the first. The first rockets orbital reference frame is both moved in spacetime and offset, with the chance of collision no greater than any other objects in LEO. What would be riskier is if two rockets, one launched from Vandenburg and its S2-S3 debris (or late S1-S2 debris) crosses the Canavaral launch site as the second rocket launches. A due east launch from Boca-Chica will never cross Canavareal since it is 3.4 degrees south and its debris will always remain to the South of the latitude of Canaveral 

The only false assumption is that a rocket would travel strait up for the first 200 seconds of flight and then separate, however not even the New Horizon spacecraft, which never obtained an  earth orbit, did not S1-S2 separate on a completely vertical profile.

BTW if projectile are the concern its simple enough to use light weight chain-linked fencing as a catch system, if you are running up 100 rockets a year you can afford a projectile catch system that surrounds the rocket. Projectiles are not rotating bullets, the are typically going to slow down so rapidly they would never reach a second site.

[T-10a]

Wait, New Horizons didn't make orbit before zipping off to Pluto? TIL.

Edited February 28, 2018 by T-10a

[Antstar]

12 hours ago, Green Baron said:

No domino ? How disappointing ... :-)

I was only commenting on the artist's impression :-)

 

11 hours ago, RCgothic said:

It is a cool artist's impression, even if it is unrealistically crowded. :-)

I wish it was just an artists impression. Sadly, it is a still from that terrible (so terrible it was hilarious) movie Geostorm. You know, the one where they sent a whole shuttle up with only one guy on board. No wonder they had a climate problem, it was the CO2 footprint from all the shuttle launches

 

But in real life... Does KSC really have the room for more launchpads? It looks pretty crowded on the map already. Maybe they can try to improve on the time it takes to recondition for another launch instead. I have no idea what actually is involved in reconditioning a pad. I guess you have to check everything critical isn't broken, but as long as the rocket got away OK I would think there will not be much to fix?

Edited February 28, 2018 by Antstar
writing ksp instead of ksc :/

[magnemoe]

1 hour ago, Antstar said:

But in real life... Does KSC really have the room for more launchpads? It looks pretty crowded on the map already. Maybe they can try to improve on the time it takes to recondition for another launch instead. I have no idea what actually is involved in reconditioning a pad. I guess you have to check everything critical isn't broken, but as long as the rocket got away OK I would think there will not be much to fix?

You have the old missile row, it was originaly used for first generation ICBM before they was put into silos. 
Many are used for various launches today. https://en.wikipedia.org/wiki/List_of_Cape_Canaveral_and_Merritt_Island_launch_sites
As you see most are inactive, to launch BFR sized rockets they would probably need an serious rebuild, might be cheaper to build an new pad. 

[YNM]

8 hours ago, Antstar said:

Does KSC really have the room for more launchpads?

Yes, to the north.

6 hours ago, magnemoe said:

You have the old missile row, it was originaly used for first generation ICBM before they was put into silos. 

That's CCAFS for now, they're not connected to KSC and is effectively on a different island.

12 hours ago, PB666 said:

The collateral explosion damage issues are greatly decreased if one uses H2/02 since H2 is lighter than air and tends to rise (rise away from the launch site).

Depends on the design, the ET and CBC (D-IV) stores O2 over H2, the S-IVB stores H2 over O2.

 

Even with the practically spotless record on D-IV, they won't let a train near it XD Or is it because no-one has tried to ask ?

Edited March 1, 2018 by YNM

[Antstar]

13 hours ago, YNM said:

Doesn't change the fact if it explodes.

 

Again, rocketry is still nowhere as safe as airplanes or the even safer (in some sites) railways. Even if we class Airplanes as being not that safe, it's very hard to imagine having one of them struck the terminals at flying speed or as explosion debris. Rockets in an airplane environtment would cause one heck of a damage, or if we want to scale up you end up with a very big scale indeed (like VAB to KSC LC 39, compare with the usual runway/taxiway/taxiway/taxiway(apron)/apron succession in 

Well, in terms of casualties per capita per km, aeroplane is the safest I think.

Like all machines, the greatest danger of failure is during a (I think it's the technical term) change of state. Takeoff, landing. However I've definitely seen on the news that planes have many times had low speed taxiing collisions,  which can still be quite damaging to the plane.

For rockets, the *most common* failure mode is still when changing state - like the recent loss of the FH core. But spacex rockets have so many state changes during a launch they have introduced a bunch of new critical failure points.

And I agree, rockets have low structural integrity for unexpected force. And huge amounts of dense fuel AND oxidiser. So when a plane crashes at an airport usually no fire, if a fire, usually not an explosion.  For rockets, an explosion is the Usuall result of a failure of the fuselage

[Antstar]

13 hours ago, PB666 said:

The collateral explosion damage issues are greatly decreased if one uses H2/02 since H2 is lighter than air and tends to rise (rise away from the launch site). Also both are cryogenics and less able to ignite by spurious spark.

Snip

What about turbulence?  I know wings generate force perpendicular to direction of travel and are more susceptible to stalling with turbulent airflow. But a rocket launch must make for a heck of a huge atmospheric disruption

[sevenperforce]

6 hours ago, Antstar said:

What about turbulence?  I know wings generate force perpendicular to direction of travel and are more susceptible to stalling with turbulent airflow. But a rocket launch must make for a heck of a huge atmospheric disruption

Only very transiently.

[tater]

 

[sh1pman]

27 minutes ago, tater said:

 

Maybe they decided against the crazy hot recovery idea.

[wumpus]

9 hours ago, YNM said:

Depends on the design, the ET and CBC (D-IV) stores O2 over H2, the S-IVB stores H2 over O2.

O₂ over H₂ certainly would be more aerodynamically stable.  Doing it the other way sounds expensive.  The S-IVB presumably didn't fire in the atmosphere (I'm not sure about the Saturn IB, it was the second stage), so that much seems moot: the explosion would certainly kill the crew.  If you are near the ground, the lower stage are so much more of a problem that the S-IVB's configuration is meaningless.

[PB666]

59 minutes ago, sevenperforce said:

Only very transiently.

There are many forms of turbulence. Two types encountered Mach shock and sub Mach churning. At the launch site Mach shock is directed in the direction of exhaust gas travel. The venturi effect of the engines also concentrated around the engines. There is turbulence from the redirected exhaust plume but this is largely local. and velocity drops with the square of distance. Once the rocket is moving the flows are laminar with respect to the rocket up until about Mach 0.85 at which point bow shock starts to occur. There is considerable turbulence under the shock wave and this persists until the rocket is above 70 km (depending on its speed). Again if the rocket is 15 km when it hits max Q then sonic shock wave extends out at 45' angle downward to about 20 km on the ground, its likely someone on the ground would notice a slight boom. But the dispersion in a flat plane is E/d and E/d² depending on vertical dispersion

So we are not really concerned with what happens directly below the vehicle, because Newton's laws basically prevent a rocket from taking off from the same spot another rocket has just taken off from. So the next concern is the shock wave. The problem with sonic boom is that its much easier to detect when its coming at you relative to moving away. The nose cone of the rocket is not a sharp point but rolls, so that the shock wave evolves with speed. At Mach speed the rather flat bow shock angle quickly bends around and this is the danger with FH and other boosted rockets that the return of the bow-shock places large amount of momentum collisions on joints and other leading surfaces. Past experience with Mach aircraft indicate that with complex designs results are unpredictable. As the vehicle accelerates close to Max Q, the available energy is at its greatest, E = F * d. The shock wave is close to its greatest mass, and we can see that the plume of the rocket is no longer contained by the atmosphere, indicating that the shock wave joins below the plume. At this point the energy is redirected at angles that intercept the ground, but its still not confined to a plane.

The force is generally in the area of a = 1, M = 300,000 kg and distance traveled is 400 m/s, so that power is = 115 MW of power. Not all of this goes into the bow show, some goes into heating, some goes into sound. Assuming that all the energy is spread over a meter at 20km distance (imagine a ring of radius 20,000m) The ring has 5750 W square meter. Now we have to consider how many meters on the ground that travels, so it is travels 400 m/s its rounghly 560 m/s. So that the power is 5750/560 ~ 10 J of energy. If we assume again that the wave is traveling and we limit our calculation to a cubic meter of air (22.4 liters per mole, a mole weight 15 grams 1000 liters in a cubic meter, and air that is not at all moving, then there is 0.67 kg in a cubic meter= So 10 = 0.335 * V² that translates to a maximum change of V of 5.4 m/s. Note that as the space craft is turning east it is also moving the wave along the ground at higher horizontal velocities, this means that not

So that a typical aircraft taking off has a Vr of 50 to 80 m/s and as the aircraft is rotating it will generate more velocity as it rotates because the wheels have not lifted off the ground, so that typically by the time the wheels are weighed they aircraft is moving 5 to 10 m/s faster than minimum lift speed and velocity continues to climb. In most cases liftoff flaps will be set at "3" for commercial jets with a Vmax for the flap of 100 to 120 m/s. In addition, a poorly known fact about stalls, stalls are not caused by low speeds, but high angle of attack (>15'). If you have a craft with zero speed and you point its leading wing edges strait down, the craft will not stall (even though it is technically stalled).

 

 

So that in general  a horizontal pulse in any direction will not stall the craft, vertical pulses (as was learned in the late 1970's) can stall a craft during take off or landing. For the same reason. If you have a 20 m/s that comes at an angle perpendicular to the lifting (rotating) wing, then such a pulse can stall the wing and cause the plane to fall. This happened in the late 1970's due to the vertical windshear that occurs in the vicinity of microburst thunderstorms. As a consequence of LOC events in the great plains region, wind-shear sensors were mandated on commericial aircraft and doppler radars were placed near airports to prevent conditions that would result in wing stalling. 

https://en.wikipedia.org/wiki/Stall_(fluid_mechanics)

https://en.wikipedia.org/wiki/Angle_of_attack

https://en.wikipedia.org/wiki/Wind_shear#Impact_on_passenger_aircraft

 

[YNM]

11 hours ago, wumpus said:

O₂ over H₂ certainly would be more aerodynamically stable.  Doing it the other way sounds expensive.  The S-IVB presumably didn't fire in the atmosphere (I'm not sure about the Saturn IB, it was the second stage), so that much seems moot: the explosion would certainly kill the crew.

Interestingly, there were plans for for Saturn-Centaur that shows Centaur uses LH2 over LOX ; So is the DCSS (D-IV) with two separate tanks.

I guess there are a lot of reason, but none of them really meant to address / aleviate explosion.

Also, if H2 will rise faster than O2, wouldn't that meant the two shall meet if you put O2 over H2 ? ( @PB666 )

Edited March 2, 2018 by YNM