sevenperforce

Those are (exotic) atoms, but not elements. Muonic atoms are metastable bound states of a particle and its antiparticle; hadronic atoms are elemental ions which have been charge-balanced by accepting baryons or leptons other than electrons. They don't count as elements because they have completely different energy structures than the elements that make up the periodic table. In theory, you could argue that a muonic atom like protonium (the metastable bound state of a proton and an antiproton) is merely a hydrogen ion and an antihydrogen ion, but that's not quite right. Being in an energy-bound state means they have different mass than if they were apart. We don't say that Helium-4 is "merely two deuterium atoms". Neutronium is a phase state of fermions, basically the same way that ice is a phase state of water or quark-gluon plasma is a phase state of quarks and gluons. It's not an element in any sense.

I'm not sure whether anyone told Elon this. He may be under a different impression. But in all seriousness, I don't see why SpaceX wouldn't conduct a few manned flights independent of NASA. They seem to have big plans for the Dragon platform and will want to demonstrate flexibility and independence from NASA. The trunk on the Dragon V2 is large enough to carry a small sat for deployment to offset launch costs. There's got to be some market for human spaceflight. Obviously there will be the handful of tourist launches: four or five people willing to drop 25 million each to spend a few hours in orbit, etc. Can't expect those to last, though. Surely there's some other reason....

Yeah, I wasn't thinking NASA per se. The whole concept would be more of a capability demonstration for SpaceX. If Elon really wants to put a colony on Mars, he needs to prove something dramatic. Like this. The guys on Apollo 13 were hella lucky. The LM was never planned for use as an emergency lifeboat; it was assumed that any failures significant enough to cripple the CM beyond repair would be immediately fatal. The explosion happened in what was basically the only place that would wreck the CM without explosively depressurizing it or ruining the other two modules. Damage to the re-entry capsule or to the LM would have also been fatal; there would have been no possibility of a rescue mission. The biggest concern is delta-V. And with the exception of the crasher stage burn, my mission profile has abort options with dV and secondary engines to spare at every point.

From what I've read it seems to be a pretty rapid process...not like the rocket will blow on the launch pad or anything, but reusing even once is risky.

The Saturn V was far more efficient than the Falcon Heavy, based on ISP. It used liquid hydrogen upper stages. But the mission profile was not very efficient.

NASA is not necessarily the only supplier of astronauts.

We don't consider comets to have atmospheres. That's basically what we are talking about here. Again, it's semantics. If you want to define an atmosphere as any gas particles near the surface of a celestial body, fine, but the fact remains that there is a clear divide between bodies with persistent, gravitationally-bound gaseous atmospheric envelopes and bodies without anything like that. I'd also wager that the exosphere on Mercury is highly ionized and is thus more plasma than gas.

I imagine we will see at least one unmanned propulsive landing on a droneship with abort-to-splashdown as an option, followed by a couple of unmanned RTLS landings and then a crewed RTLS landing.

FH has crappy BLEO performance, I know. But that's all the more impressive if they can pull off a manned lunar landing. Funding would be needed, sure, but we're talking less than a billion total. Hell, Elon might go himself...if not for the landing, for a preliminary free-return loop.

Precisely my point.

Yeah, a dual-oxidizer variable-ratio tripropellant liquid rocket engine would take a lot of R&D for sure. Thankfully, there is already a lot of experience with using HTP to run turbopumps for rocket engines, so that's a step in the right direction.

I'm not saying that modification wouldn't be needed for lunar EVA from the Dragon V2; I'm just saying it would be less extreme than you're suggesting because the Dragon is already at least somewhat vacuum-hardened. Compared to SLS/Orion, Falcon Heavy and the Dragon V2 are practically operational. If SpaceX can support a DA lunar landing with existing platforms for what would likely be a tenth the cost of an SLS/Orion EOR-LOR, years before SLS first launches, I imagine they'd seriously consider it.

Semantics. Most, I think, would require a thin collection of gas to have meaningfully measurable pressure and temperature in order to be considered an atmosphere.

Methinks you mean one proton and one electron. Hydrogen comes in three isotopes: protium, with one electron and one proton; deuterium, with one electron, one proton, and one neutron, and tritium, with one electron, one proton, and two neutrons. I suppose you can imagine a 1+ deuterium ion with just one proton and one neutron....

I'd be interested to see the math showing that a two-man lunar landing could be pulled off using an expendable Falcon Heavy and LOR. If the crew is suited above, the Dragon V2 can survive depressurized re-entry with an orifice up to 1/4". So the equipment inside must be vacuum-hardened already.

The isp of kerosene/peroxide is 319 s with an oxidizer/fuel ratio of 7.07, compared to 353 s for kerolox at an oxidizer/fuel ratio of 2.56. So for any case where you're replacing LOX with peroxide, you'll lose about 10% of your isp but you approximately double your T/W ratio. So if an engine can be designed to run on a variable mixture of LOX and HTP, it will be perfect for an SSTO application. The combination of lower pressure, higher altitude, and nonzero launch velocity results in a pretty substantial gain. Kerosene at sea level gets roughly 300 s of impulse, so that 250 m/s represents almost 10% of your launch mass right out of the gate. Plus, gravity drag is cancelled and you can use a vacuum-optimized engine bell with an initial isp of about 336 s. Due to gravity drag and lower isp, getting from 0-1 km/s takes literally twice as much propellant as getting from 250 m/s to 1 km/s if you start at 8 km up. Individual hydrogen atoms slip through metal-metal bonds like butter. When they meet, they form H2 molecules, which expand and form cracks. Thus, metal LH2 tanks are pretty much strictly single-use affairs. Yeah, I like toying around with odd fuel/oxidizer combos. Some don't work. But like I said above, the lower isp of H2O2 is compensated for by 15% higher impulse density and twice as much thrust, making it ideal for the first "stage" in a tripropellant-fueled SSTO.

It's the dV considerations that are the biggest challenge, really. But if we can demonstrate that those can be overcome, building a lunar lander based off of the Dragon V2 platform is actually worth investigating. Extensible nozzles are well-developed. Designing a detachable one would be challenging, but not prohibitively so. There's a difference between on-orbit EVA and landed EVA. The moon has enough gravity that you don't need an MMS or tethers or anything like that, and compression spacesuits will absolutely be worn in the V2. It can support depressurized re-entry for small breaches. So yeah, it should be able to support EVA as long as there is enough space and mass budget for a couple of repressurizations.

That's why I said "various options" -- there would be a range of possibilities, including aeroshell-mounted solar panels and solid-state batteries. Obviously, an actual manned lunar mission of ANY kind would result in a huge number of engineering analyses and models and simulations. That's a given. I'm more interested in the dV calculations and orbital dynamics approach showing whether this mission is actually possible in the first place.

Still works well enough for RTLS. Going to see whether layered stack decouplers can be used as an ablative heat shield in Demo.

What Rakaydos said. The Saturn V had to deliver three astronauts, a lunar module, a command module, and a return capsule to LLO, with the lunar module including separate descent and ascent stages. For such a complicated architecture, LOR is the only way to go. This profile, on the other hand, has only a single manned module for transfer, descent, landing, ascent, return, and re-entry. It only has to take two engine clusters and a single RCS system (the Merlin 1D Vacuum on the Falcon Heavy upper stage plus the SuperDracos and Dracos on the Dragon) beyond LEO, compared to four engine clusters and three RCS systems for the Apollo missions (transfer engine, CM engine, descent engine, ascent engine, CM RCS, LM RCS, and re-entry capsule RCS). There is no extra space/dV for rovers or other unnecessary equipment (although a rover could be landed in an unmanned, no-return test mission). Apollo used three circularization burns on the initial missions and four on the later ones; this profile uses none (a precise launch window would be chosen with the lowest possible transfer perigee). And yet safety is not significantly compromised. Hohmann transfer to EML-1 is virtually free-return. The only risk is right after passing EML-2; if the Falcon upper stage fails to fire, you might be screwed. The Dragon has enough dV for abort to LLO but not enough to get back home; you'd want a second Falcon Heavy standing by for an unmanned rescue mission if that happened. But as long as your crasher stage fires properly, you have plenty of fuel in your Dragon for abort and return.

I see the radar altimeter but it is analog and not clear enough to read accurately.

Been following this up with Grasshopper-style tests of high-thrust suicide landings, taking off vertically at random throttle and burn times, then calculating predicted apogee altitude and dividing by T/W ratio to get burn start altitude. Finally got it perfectly. The lump rising in my stomach as I plummeted, seemingly too fast to stop, and then the plume of fire rising under me when the speed indicator dropped to zero. Hitting X to kill the engines and seeing the dust clear. Really really satisfying.

I'm well aware that Elon has a tendency to over-fancify, but he seemed pretty confident that the Dragon V2 had been designed as a platform for a variety of mission configurations. Which isn't too crazy of an idea, I don't think. Fitting the auxiliary tank is probably the biggest challenge. The extended nozzles would cause some airflow turbulence on launch, so they'd have to model that for sure, but the nozzles would be discarded prior to Earth re-entry so that's not an issue.

Point being that we would not necessarily see them in the spectra of neutron star collisions because they are fairly rare events compared to supernovae.

That's not what Elon suggested. There are various options; the only necessary things are the addition of an auxiliary tank and the installation of nozzle extensions.