sevenperforce

The high T/W ratio, coupled with dense fuel, greatly minimizes gravity drag losses. With a very dense fuel, you burn a larger proportion of your GLOW more quickly, reducing the total mass to orbit. A dense fuel also reduces overall size, cutting aerodynamic drag considerably in comparison to something like a hydrolox SSTO. The ISP of the Merlin 1D is where you're getting hung up, I think. To start with, I did add a mass penalty for the air augmentation ducts: 25% of engine mass, which is fairly conservative given that they are part of the vehicle structure. Yet those simple fixed ducts add considerably to the specific impulse. At launch, they give the Merlin 1Ds an effective exhaust velocity of almost 3,200 m/s; from Mach 0.1 to Mach 2 they give an effective exhaust velocity starting at 4,150 m/s and climbing to 4,570 m/s; from Mach 2 to Mach 8 it slowly declines to around 3,300 m/s and maintains this to orbit. The numbers I gave assumed that this range of specific impulses would effectively zero out gravity drag and atmospheric drag and result in a net average 348 seconds, but I can go back and run the numbers for each flight segment a little more tightly. It borrows slightly from Skylon, but with a vehicle TWR that starts at 1.4 and increases to well over 2 soon after launch, it's quite different. It's also not an airbreather; it's an AAR without the technological hurdles of airbreathing or rocket mode changes.

Sunset is fairly late here at this time of year. I was walking around outside at around 8:20 PM local time and it was still quite bright out; the sun had sunk just below the treeline to the west but the sky hadn't yet started to go gray at all...still pale blue. To my surprise, I was able to see Jupiter just southeast of the zenith, quite clear. It could have been imagination, but it seemed to have both angular size and a faint golden tinge. I have seen planets just after sunset, but never so high or when the sky is still so bright. What's the highest magnitude a planet can get, and is Jupiter's angular size ever visible with the naked eye? Was the gold tint just my eyes playing tricks on me, or was it perhaps Rayleigh scattering?

The v1.1 upper stage is larger than the v1.0 upper stage, and the v1.1FT upper stage was lengthened and ostensibly strengthened in comparison, so I doubt it has the same structural limits as 9v1.0 did. The SES-9 mission payload was about 110% of the stated v1.1 GTO payload, and that was after circularization in LEO, so presumably the increase would be closer to Gwen's claimed 15% payload increase. I think I calculated it at 15 and some-odd tonnes based on a variety of factors, but don't quote me on that; I may have been thinking of something else. On another note... Does anyone actually know how low SpaceX salaries are? I hear about how they take advantage of status and dreamers to pay less, but I'm trying to get an idea for what that looks like.

Wrong. LEO payload of F9 was about 10 tonnes; LEO payload of F9v1.1 was over 13 tonnes; payload of F9v1.1FT (we are getting DBZ with these names here) is unpublished but I have previously estimated it at 15-16 tonnes.

The superheated column of air rising off of the molten solid stuff (rock or metal) will sear your nerves away inside and out before you hit the surface.

Right when he got to the Leidenfrost effect I thought "Oh god no"

Like I said, presumably by pressurizing it and opening the hatch. Even unpressurized cargo in the trunk is typically brought out and then brought within an airlock if it is intended for use inside the ISS. The only reason to fly pressurized is if the cargo cannot be vacuum-hardened. Once on the ground, the Martian atmosphere provides air-cooling to components. I doubt the payload fairing will be required for planetary protection, but even if it is, the fins on the trunk are only there to provide stability during LES, which this wouldn't need. And power systems for the new navcom can be added separately in the form of payload.

The SpaceX suits will be compressive rather than overpressure-based.

Presumably by pressurizing it and then opening the hatch. The contract at the provided link states that the full up or down capacity can be fully depressurized. What's the current coolant design? New navcom, yes, but the existing trunk is just fine, the hatch is already automated, and the deployment mechanisms, planetary protection provisions, and auxiliary power systems are really just part of payload.

Not...really? I mean, it depends, but if you're merely removing the docking hatch and bolting a tube into the center of the cabin area, you can really put anything inside. Conveniently, the Dragon's TWR is tripled on Mars. Hydrazine+NTO can have a vacuum ISP of 339 s with the right nozzle; 4.1 km/s thus requires a mass ratio of 2.5:1. Should be entirely realizable.

I can't imagine that going pointy-end-down results in greater drag.

"the" unpressurized variant ? That would require a whole new design. I'm pretty sure that most of the equipment is designed with air cooling in mind and isn't vacuum hardened. The Dragon 1 already has the option of flying pressurized or unpressurized (final bullet, page 6 here). The Dragon V2 will have the same capability: it can fly with unpressurized cargo, pressurized cargo, or pressurized with crew. Page 5 of the House Subcommittee Statement by Garrett Reisman states, "Crew Dragon carries sufficient breathable gas stores to allow for a safe return to Earth in the event of a leak of up to an equivalent orifice of 0.25 inches in diameter. As an extra level of protection, the crew will wear SpaceX-designed spacesuits to protect them from a rapid cabin depressurization emergency event of even greater severity. The suits and the vehicle itself will be rated for operation at vacuum." So yeah, it's vacuum-hardened already. Like I said, Dragon V2 is over-designed for these express purposes. It will not need substantial redesign for its Martian debut. Well, it would be a completely new craft inside the Dragon body to be sure, but the Dragon V2 itself would still be substantially the same. I wonder if adding vacuum nozzle extensions to the SuperDracos would boost its isp enough to give it Martian SSTO capability with expanded internal auxiliary tanks.

Dragon V2 can absolutely be placed on a Martian aerobraking transfer trajectory by Falcon Heavy, without the need for a Raptor upper stage. I ran the numbers and it's well within margins. V2 isn't primarily a crew capsule; it's primarily a lander. It's designed with broad enough margins to land propulsively on Earth, the moon, Mars, or most other worlds with only minor modifications. I'm sure this will be the unpressurized variant. The aeroshell is pretty important, though. Falcon Heavy is not exactly a paper rocket. Falcon 9 has flown enough times that we can readily identify the performance range of FH.

Any reason why the two planets couldn't have active cores with stable field coupling? I talked to him a while back...he erroneously applied the Titus-Bode law to exoplanet systems and didn't factor in Hill spheres, so his systems aren't quite right.

The simplest and least controversial way to define interplanetary would be "starting at one planet's orbit and crossing another planet's orbit."

As long as the warhead survives to a relatively low altitude, the outside of the RV can be red-hot slag. I'm also guessing the warhead is still high hypersonic when it detonates. It certainly doesn't have to slow down to the parachute-safe speeds of a re-entry capsule. A capsule must slow from around 8 km/s to less than 1 km/s without melting. An ICBM is probably slowing from around 5 km/s to around 2 km/s.

Elon did specifically say that the Dragon V2 would be man-rated for LEO and lunar missions, but nothing outside of the Earth-moon system due to limited life support and space constraints.

I think the implication was that they were starving to death one by one.

Only a few days of power post-landing, since the trunk can't survive a landing. Then again, it won't be hard to add batteries or a fuel cell to the payload. The notion that this could be used for sample return, on the other hand, are quite ill-conceived. The Dragon V2 does not have nearly enough propellant for direct SSTO ascent from the Martian surface.

While wearing sunglasses, let's not forget.

Jupiter, ready or not, here we come!!! So next thing is to land on the sun right?

A binary planet is not unstable. Earth and the moon are essentially a binary planet.

Although the current definition uses an equation to determine a given object's likelihood of clearing its orbit. If Earth was a Jovian trojan, it would still be in the right zone and mass to fit the equation for clearing its orbit even though it wouldn't. So it would fit the definition for clearing an orbit but would not have cleared an orbit. Unless it was a double trojan, where the two objects are close in mass and 60 degrees separated in the same low-eccentricity orbit. Lissajou.

A blunt re-entry surface is ideal when you want high drag and low heating. An ICBM doesn't need high drag, and it only needs to survive long enough to get to the surface.

Think you missed a few points. Those aren't inlets for the engine; they are inlets for ram compression and exhaust reheat. Wrapping even a very simple exhaust shroud around an engine results in a pressure-induced flow that increases thrust by 15%; at speed it goes up to 50% augmentation if your engine can vary its mixture ratio, which the Merlin 1D can. Takeoff is emphatically not relying on lift; it's relying on thrust. Rolling takeoff is to build up airflow through the ducts to increase the vehicle T/W ratio to 1.5-1.8, enough to point the nose (relatively) straight up. As I mentioned, it has enough static thrust (1.4:1) to take off vertically, but horizontal takeoff helps reduce gravity drag and allows it to fly out of any airport that can take a LOX depot, which is good if you want to use it for suborbital flights. This is similar in overall shape and re-entry profile to Skylon, though with a less depressed flight trajectory, a better T/W ratio, and a smaller overall size. And sure, SSTOs aren't generally a brilliant idea. But that is kind of the point of this. SSTOs aren't built because there isn't a reason to build them. And here's an example to show why building them is in many ways the easy part.