SpaceX Falcon Heavy Demo - Discussion and Speculation

[JH]

Mars has enough of an atmosphere that it doesn't function like vacuum for electrical currents.

[rpapo]

Also, doesn't a vacuum conduct electricity?

No.  But a near vacuum can, depending on what remains in that near vacuum.

[Robotbeat]

Mars is not a plasma, it is a CO2 atmosphere. Shorts are not an issue.

[oldAtlas_Eguy]

Mars is not a plasma, it is a CO2 atmosphere. Shorts are not an issue.

Modern digital motors are brushless. That is how they can be very very high operational lifetimes without maintenance. There are no sparks, gaps, or open surfaces. These motors are also the preferred motors for use in heavy moisture environments (like cars).

[AncientU]

Also, doesn't a vacuum conduct electricity?

No.  But a near vacuum can, depending on what remains in that near vacuum.

Yes, this is so.  At around 10^-3 to 10^-4 Torr*, high voltage circuits can experience an unquenched plasma discharge.  Higher pressure quenches that (CO₂ is specifically used as a quench gas) and lower has too rarified an environment for triggering/sustaining a plasma.

*In these units, Mars is at 5 Torr, so nicely higher in pressure and atmosphere is conveniently a quench gas

[tvg98]

Another update to Falcon Heavy's payload: http://www.spacex.com/falcon-heavy

Payload to LEO: 63,800 kg
Payload to GTO: 26,700 kg
Payload to Mars: 16,800 kg
Payload to Pluto: 3,500 kg

[CuddlyRocket]

Its less about the air pressure and more about the temps. Those batteries and motors won't work in the cold.

Takes a long time for things to cool off in space.

Especially when you have electric currents producing heat!

Batteries and motors are not monolithic point-sources, nor do they have uniform thermal conductivity throughout. There would be locally very hot and locally very cool points, potentially in close proximity one to on another.

It's why (to give just one easy example) even though half of every low-Earth orbit is in shade, parts of the ISS have shell heaters running to prevent surface moisture condensation against the pressure vessel, while at the same time radiators are operating to keep the cabin air and hardware cooling loops conditioned.

Real engineering is more complicated than a one-liner on a forum.

Who'd a' thunk it! 

What a one-liner can do - on a forum or in real engineering for that matter - is point out an obvious flaw in an argument. In this case that "those batteries and motors won't work in the cold".

As for the Tesla, its battery pack is a sealed unit containing internal cooling systems and heaters to deal with local temperature variations. Likewise, the drive unit has a cooling system; it doesn't have a heating system since the heating effect of the currents passing through it are more than adequate.

Now, none of that means that the Tesla battery and drive unit will work in space (though I wouldn't be shocked to discover that Elon had imposed such a requirement, despite the seeming over-engineering implied - he's always thinking ahead!); but it's not at all obvious that it won't.

[Comga]

Another update to Falcon Heavy's payload: http://www.spacex.com/falcon-heavy

Payload to LEO: 63,800 kg
Payload to GTO: 26,700 kg
Payload to Mars: 16,800 kg
Payload to Pluto: 3,500 kg

Surely one of out compulsive, I mean thorough, posters has collected these values over the years and created a plot of them versus time. To that analyst: please post that graph!

[oldAtlas_Eguy]

A BTW the Mars increase is 23% so if the TLI was 18mt the new one is 22.2mt. This is high enough to possibly get a BA330 to EML2.

[Confusador]

Another update to Falcon Heavy's payload: http://www.spacex.com/falcon-heavy

Payload to LEO: 63,800 kg
Payload to GTO: 26,700 kg
Payload to Mars: 16,800 kg
Payload to Pluto: 3,500 kg

They updated the pricing page with that info as well, but left the standard $90M recoverable number at 8,000 kg.

[Herb Schaltegger]

As for the Tesla, its battery pack is a sealed unit containing internal cooling systems and heaters to deal with local temperature variations. Likewise, the drive unit has a cooling system; it doesn't have a heating system since the heating effect of the currents passing through it are more than adequate.

And unless those cooling systems are vacuum-rated and can support 100% of the heat load through radiation, it'll overheat ...

Too much hand-waving in this thread.

[spacenut]

The fairing isn't big enough to carry a Bigelow 330 module.  I started a thread on what was the possibility of a larger fairing.  A 330 to the moon would help build a station at L1, orbiting, or otherwise.  If they can increase the size of the fairing, a lot of lunar work could be done with FH.  Mars as well. 

[oldAtlas_Eguy]

The fairing isn't big enough to carry a Bigelow 330 module.  I started a thread on what was the possibility of a larger fairing.  A 330 to the moon would help build a station at L1, orbiting, or otherwise.  If they can increase the size of the fairing, a lot of lunar work could be done with FH.  Mars as well.

Has there been any info about the larger faring design that SpaceX has and whether they could demo this faring on the FH demo flight?

You are correct the FH needs a larger faring. F9 could use one as well because it has outgrown it's existing one for larger LEO payloads. The existing faring is barely large enough for 13mt payloads. With the FH able to send to the Moon or Mars the same size payloads that the F9 can send into LEO a larger faring is a must have. It is also more expensive and would increase the incentive for recovery.

[JBF]

The fairing isn't big enough to carry a Bigelow 330 module.  I started a thread on what was the possibility of a larger fairing.  A 330 to the moon would help build a station at L1, orbiting, or otherwise.  If they can increase the size of the fairing, a lot of lunar work could be done with FH.  Mars as well.

Has there been any info about the larger faring design that SpaceX has and whether they could demo this faring on the FH demo flight?

You are correct the FH needs a larger faring. F9 could use one as well because it has outgrown it's existing one for larger LEO payloads. The existing faring is barely large enough for 13mt payloads. With the FH able to send to the Moon or Mars the same size payloads that the F9 can send into LEO a larger faring is a must have. It is also more expensive and would increase the incentive for recovery.

At 6mil a pop for the smaller fairing, they may be trying to get reuse figured out before finalizing a design on a larger one.

[rpapo]

Taken from the FH mission 3 thread:

At some point leading up to MaxQ, the torques between the three boosters will attempt to tear apart the stack.

Please clarify my ignorance.  I have heard on these forums several times now about torques being present between the cores of the Falcon Heavy stack.  There was a reference to startup torques requiring a staggered ignition of the engines.  Given that these rockets are symmetrical, I fail to see where this "torque", or twisting force, is coming from.  Why would there be such, apart from random vibrations of the ignited motors?

[Space Ghost 1962]

Taken from the FH mission 3 thread:

At some point leading up to MaxQ, the torques between the three boosters will attempt to tear apart the stack.

Please clarify my ignorance.  I have heard on these forums several times now about torques being present between the cores of the Falcon Heavy stack.  There was a reference to startup torques requiring a staggered ignition of the engines.  Given that these rockets are symmetrical, I fail to see where this "torque", or twisting force, is coming from.  Why would there be such, apart from random vibrations of the ignited motors?

LREs don't "combust" uniformly, more like loosely controlled chaos. Also, they are all gimballed, and the gimbals have certain variation/misalignment/compliance as well. Now, imagine you've got 3 sets of 9 each resultant vectors, each pulling/pushing/pitching/yawing/rolling at the thrust structures, which in turn are linked together. Oh, and also add in roll for each of these three groups as well. And axial thrust oscillations of each mass/thrust group per booster. (These forces are nontrivial, a significant percentage of the engine's thrust.)

You're goal is to keep the aggregate thrusts mostly aligned (for performance), and the thrust structures (plus combinations) from twisting/shearing/pivoting such that aggregate peak loads don't fatigue/fracture the thrust structures. You've got a big problem if multiple ones just happen to synchronize and pull apart (or together) in phase. You can't just assume that the randomness of the vectors will solve the problem for you.

And I haven't gone into the resonance effects of these long fluid filled cylinders, the effects of deep cryogens, the placement of separation hardware, the need to have certain passive behavior on shutdown, and still more (like fluid displacement, sloshing(!), and altitude). You've got limited controls to affect this and certain latencies to when the signaled control actually affects the deviation. It's like playing an enormous pipe organ, offsetting vector accumulations with an induced opposing "note"/phase to diminish the deviation. Gradually.

If combustion/engines were ideal, this would be considerably easier and like how you seem to believe it would work. Rest assured its a bit more than that.

(If it were easy, you'd see more clustered vehicles.)

[rpapo]

(If it were easy, you'd see more clustered vehicles.)

Thank you for the elaboration, though that still sounds like an exercise in dealing with a wide spectrum of vibrations, not with a net torque.  The only consistent torque I can think of, in this case, is the one which would tend to drive the noses of the side cores into the side of the center core.

Not to oversimplify things too much, though I was taught (Mechanical Engineering, 1978) that to come to any resolution to a real-life dynamic stress problem you need to try and simplify the problem.  What makes or breaks your analysis, though, is how carefully you select which portions of the problem to simplify or ignore. 

[Space Ghost 1962]

(If it were easy, you'd see more clustered vehicles.)

Thank you for the elaboration, though that still sounds like an exercise in dealing with a wide spectrum of vibrations, not with a net torque.  The only consistent torque I can think of, in this case, is the one which would tend to drive the noses of the side cores into the side of the center core.

Look, it's a big problem and a small post. Now, to constant torques, realize that everything is bent just a little, that CG//CP is a little off, and that you have levers in things. You have constant torques from these mis-alignments/etc (BTW, this slows you down in vehicle integration as well, finding/"fixing" them.)

Not to oversimplify things too much, though I was taught (Mechanical Engineering, 1978) that to come to any resolution to a real-life dynamic stress problem you need to try and simplify the problem.  What makes or breaks your analysis, though, is how carefully you select which portions of the problem to simplify or ignore.

Yes.

Some you solve statically/design. Some you compensate for by creatively wasting performance. Some you judge to be "anti-resonant" - those "cure" themselves.

[Jcc]

(If it were easy, you'd see more clustered vehicles.)

Thank you for the elaboration, though that still sounds like an exercise in dealing with a wide spectrum of vibrations, not with a net torque.  The only consistent torque I can think of, in this case, is the one which would tend to drive the noses of the side cores into the side of the center core.

Look, it's a big problem and a small post. Now, to constant torques, realize that everything is bent just a little, that CG//CP is a little off, and that you have levers in things. You have constant torques from these mis-alignments/etc (BTW, this slows you down in vehicle integration as well, finding/"fixing" them.)

Not to oversimplify things too much, though I was taught (Mechanical Engineering, 1978) that to come to any resolution to a real-life dynamic stress problem you need to try and simplify the problem.  What makes or breaks your analysis, though, is how carefully you select which portions of the problem to simplify or ignore.

Yes.

Some you solve statically/design. Some you compensate for by creatively wasting performance. Some you judge to be "anti-resonant" - those "cure" themselves.

Can't the constant torques due to misalignments be countered by gimballing the engines on the side boosters? I can see strain gauges at the connection points providing data for the adjustments.

[Jim]

Can't the constant torques due to misalignments be countered by gimballing the engines on the side boosters? I can see strain gauges at the connection points providing data for the adjustments.

No, that is not needed and anyways would be a kludge fix.