Falcon Heavy for moon shot

[sevenperforce]

1 hour ago, fredinno said:

Batteries are too massive.

Solar cells might get ripped off during reentry, posing a danger to the crew.

Fuel cell compartments would need significant modifications to the vehicle, even if you just placed it on top (and removed the docking port)

The modifications would be enough to call this Dragon V3. It's not worth it for a 1-time flight.

Flush-mounted solar panels in the upper aeroshell would not be a problem in re-entry. 

Not to beat a dead horse, but why do you keep saying that modifications "would make this a Dragon V3" when I quoted Elon specifically talking about modifying the V2 platform to use for the Moon or Europa or any other world?

I mean, I love getting pushback because it helps me identify things I might not have considered; I'm just not sure why you're fixed on (relatively minor) retrofitting as the problem.

[Nibb31]

Real life engineering isn't KSP. None of the modifications you are proposing are anywhere near "minimal". It would be a totally different vehicle.

For example, flush-mounted panels mean that the structure of the aeroshell is completely different, with holes in it. Its resistance to thermal and aero loads needs to be reassessed.

Mounting tanks on the inside means that you need to redesign the pressure vessel, including new plumbing, holes, and again, studies about the physical forces that are going to impact that new structure. It's not a "simple mod". How do you even fit those 2m tanks through the door without redesigning the way the pressure vessel is built?

In the end, you'd be better off scrapping the entire vehicle and starting from scratch.

Edited March 16, 2016 by Nibb31

[fredinno]

2 hours ago, sevenperforce said:

Flush-mounted solar panels in the upper aeroshell would not be a problem in re-entry. 

Not to beat a dead horse, but why do you keep saying that modifications "would make this a Dragon V3" when I quoted Elon specifically talking about modifying the V2 platform to use for the Moon or Europa or any other world?

I mean, I love getting pushback because it helps me identify things I might not have considered; I'm just not sure why you're fixed on (relatively minor) retrofitting as the problem.

V3 would be a modification of V2 in the same way F9 FT is a modification of V1.1.

[DerekL1963]

2 hours ago, sevenperforce said:

I'm just not sure why you're fixed on (relatively minor) retrofitting as the problem.

Because the alterations you're proposing aren't even "relatively" minor.   They're significant alterations to major components of the vehicle.

[sevenperforce]

9 hours ago, Nibb31 said:

Real life engineering isn't KSP. None of the modifications you are proposing are anywhere near "minimal". It would be a totally different vehicle.

For example, flush-mounted panels mean that the structure of the aeroshell is completely different, with holes in it. Its resistance to thermal and aero loads needs to be reassessed.

Mounting tanks on the inside means that you need to redesign the pressure vessel, including new plumbing, holes, and again, studies about the physical forces that are going to impact that new structure. It's not a "simple mod". How do you even fit those 2m tanks through the door without redesigning the way the pressure vessel is built?

In the end, you'd be better off scrapping the entire vehicle and starting from scratch.

That's not what Elon suggested.

8 hours ago, DerekL1963 said:

Because the alterations you're proposing aren't even "relatively" minor.   They're significant alterations to major components of the vehicle.

There are various options; the only necessary things are the addition of an auxiliary tank and the installation of nozzle extensions.

[Frybert]

9 hours ago, Nibb31 said:

Real life engineering isn't KSP.

This quote should be stickied somewhere.

[Nibb31]

1 hour ago, sevenperforce said:

That's not what Elon suggested.

He also suggests freaking colonies on Mars, and nuking Mars to terraform it, and yet we all know that none of that is going to happen during his lifetime. His PR suggested reusable upper stages, reusable Dragon V1, powered Dragon V2 landings, Falcon Heavy crossfeed, and none of that is happening either...

He has delivered on other stuff, sure, but I really wish people would stop taking Musk's tweets as the voice of <insert your favorite deity here>.

Some of what he has to say is decent information. A lot of what he says is starry eyed wishful thinking. And most of what his companies actually come up with in the end arrives late or gets abandoned along the way, because real-engineering is much harder than tweeting.

Quote

There are various options; the only necessary things are the addition of an auxiliary tank and the installation of nozzle extensions.

Nozzle extensions on Dragon's Super Dracos would require a pretty serious redesign of the shape of the capsule, since they are designed with short nozzles precisely so that they stay out of the airflow. That is absolutely not "minor", and neither is fitting an auxiliary tank inside an existing pressure vessel.

Edited March 16, 2016 by Nibb31

[DerekL1963]

1 hour ago, sevenperforce said:

10 hours ago, DerekL1963 said:

Because the alterations you're proposing aren't even "relatively" minor.   They're significant alterations to major components of the vehicle.

There are various options; the only necessary things are the addition of an auxiliary tank and the installation of nozzle extensions.

It doesn't matter if there are five options or fifteen, or whether they're optional or necessary - none of them are minor.  None, zero, zip, nada.   They're significant alterations to the form, fit, and function of major components of the vehicle.

[sevenperforce]

26 minutes ago, Nibb31 said:

He also suggests freaking colonies on Mars, and nuking Mars to terraform it, and yet we all know that none of that is going to happen during his lifetime. His PR suggested reusable upper stages, reusable Dragon V1, powered Dragon V2 landings, Falcon Heavy crossfeed, and none of that is happening either...

And most of what his companies actually come up with in the end arrives late or gets abandoned along the way, because real-engineering is much harder than tweeting.

Nozzle extensions on Dragon's Super Dracos would require a pretty serious redesign of the shape of the capsule, since they are designed with short nozzles precisely so that they stay out of the airflow. That is absolutely not "minor", and neither is fitting an auxiliary tank inside an existing pressure vessel.

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.

[tater]

Seems goofy with even a cursory examination. Saturn V delivered 2.6X as much mass to LEO (140,000kg) as Falcon Heavy is supposed to. Pretty much all that mass was sent to the moon, and mass was a huge concern, even with 140 tons to play with. Why would we expect SpaceX to need vastly less mass than Apollo to do the same thing, much less a direct approach instead of LOR?

[Rakaydos]

18 minutes ago, tater said:

Seems goofy with even a cursory examination. Saturn V delivered 2.6X as much mass to LEO (140,000kg) as Falcon Heavy is supposed to. Pretty much all that mass was sent to the moon, and mass was a huge concern, even with 140 tons to play with. Why would we expect SpaceX to need vastly less mass than Apollo to do the same thing, much less a direct approach instead of LOR?

If my understanding of the mission architecture is right, Apollo used a less efficient (but safer) trajectory. Instead of a free return orbit, circularization, landing and rendezvous, this proposal  calls for a transfer to lagrange, a fall straight to the moon, and a crash burn to land, followed by a direct ascent.

[sevenperforce]

47 minutes ago, tater said:

Seems goofy with even a cursory examination. Saturn V delivered 2.6X as much mass to LEO (140,000kg) as Falcon Heavy is supposed to. Pretty much all that mass was sent to the moon, and mass was a huge concern, even with 140 tons to play with. Why would we expect SpaceX to need vastly less mass than Apollo to do the same thing, much less a direct approach instead of LOR?

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.

[fredinno]

3 hours ago, sevenperforce said:

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.

You forgot the fuel cells and H2 O2 tanks.

[sevenperforce]

3 minutes ago, fredinno said:

You forgot the fuel cells and H2 O2 tanks.

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.

[fredinno]

7 minutes ago, sevenperforce said:

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.

It is, but at that point, it would no longer be Dragon V2, but a specialized lunar lander.

[Nibb31]

1 hour ago, sevenperforce said:

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.

He was also confident about the other stuff I mentioned. But it's not gonna happen.

1 hour ago, sevenperforce said:

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.

Detachable nozzles, in themselves, would be a major development. Has it ever been done? How do you design them to be detachable, resist the heat and vacuum, and make them fit into the existing design? It's far from a non-issue.

Oh, and once you're on the Moon, what do you do? You are aware that Dragon isn't designed to be depressurized or to support spacesuits, aren't you? You can't EVA from it. Adding that capability would also be far from trivial.

[sevenperforce]

23 minutes ago, fredinno said:

It is, but at that point, it would no longer be Dragon V2, but a specialized lunar lander.

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.

15 minutes ago, Nibb31 said:

Detachable nozzles, in themselves, would be a major development. Has it ever been done? How do you design them to be detachable, resist the heat and vacuum, and make them fit into the existing design? It's far from a non-issue.

Oh, and once you're on the Moon, what do you do? You are aware that Dragon isn't designed to be depressurized or to support spacesuits, aren't you? You can't EVA from it. Adding that capability would also be far from trivial.

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.

[fredinno]

16 minutes ago, sevenperforce said:

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.

Yeah... no. The computer equipment and everything inside would have to be redesigned to support vaccum conditions, or they would break on EVAs.

Also, LOR is more efficient, and Dragon V2 is heavy due to needing to survive reentry, so any lunar lander would be a new design.

[sevenperforce]

15 minutes ago, fredinno said:

Also, LOR is more efficient, and Dragon V2 is heavy due to needing to survive reentry, so any lunar lander would be a new design.

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.

16 minutes ago, fredinno said:

The computer equipment and everything inside would have to be redesigned to support vaccum conditions, or they would break on EVAs.

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.

[fredinno]

10 minutes ago, sevenperforce said:

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.

Depressurised reentry would be for a short period of time. EVAs are much longer, hours instead of minutes.

And any lunar landing is almost certain to be done via Orion/SLS, using EOR of 2 SLSs and LOR to send 4 people down to the Lunar Surface, possibly for up to 10-15 days, so I don't see why FH speculation is really necessary.

[sevenperforce]

1 minute ago, fredinno said:

Depressurised reentry would be for a short period of time. EVAs are much longer, hours instead of minutes.

And any lunar landing is almost certain to be done via Orion/SLS, using EOR of 2 SLSs and LOR to send 4 people down to the Lunar Surface, possibly for up to 10-15 days, so I don't see why FH speculation is really necessary.

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. 

[fredinno]

Just now, sevenperforce said:

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. 

And who's paying for that? NASA has their own BLEO systems for a reason.

And considering the constant delays of Falcon Heavy and Dragon V2, they aren't far off in terms of development time- first launch is off by 2 years for SLS.

[sevenperforce]

5 minutes ago, fredinno said:

And who's paying for that? NASA has their own BLEO systems for a reason.

And considering the constant delays of Falcon Heavy and Dragon V2, they aren't far off in terms of development time- first launch is off by 2 years for SLS.

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. 

[More Boosters]

This reminds me of when in KSP I'd make it to the moon in an oversized rocket and then try with a smaller, more "efficient" rocket and end up short.

[sevenperforce]

2 minutes ago, More Boosters said:

This reminds me of when in KSP I'd make it to the moon in an oversized rocket and then try with a smaller, more "efficient" rocket and end up short.

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.