Falcon Heavy for moon shot

[sevenperforce]

All right, so I had been noticing the low impulse on the SuperDraco engines on the Dragon V2 and surmised in another thread that adding attachable vacuum exhaust extenders could bring the impulse high enough for the Dragon V2 o serve as the second stage all on its own.

That's probably not going to work. But I thought of something that would. 

The Dragon V2 will carry 1,388 kg of onboard propellant. However, the crewed version can accommodate 7 with its 10 cubic meter volume. If the crew were reduced to two and their living size was increased by 50%, this would free up 5.7 cubic meters of space for an auxiliary internal tank. The propellant combination used for the SuperDraco engines is quite dense, at 1200 kg per comic meter.

So that is an extra 6.84 tonnes of fuel. Add 200 kg for the tanka to the vehicle dry mass and assume your two-man crew and their consumables mass 1,103 kg (a third of the nominal payload capacity for the Dragon), and you end up with a non-fuel mass of 5.5 tonnes and a loaded mass of 13.7 tonnes. With the 336 second specific impulse, that's a dV of 3.01 km/s.

What's that good for? Well, Falcon Heavy was originally quoted at 53 tonnes to LEO, but with the Full Thrust modifications this will probably come up to about 10% higher, or 58.3 tonnes to LEO. LEO to the lunar surface is a dV of 5.93 km/s; the Falcon Heavy should be able to drop off around 15 tonnes to the lunar surface as a crasher stage. 

So a FH can lift a retrofitted Dragon V2 to the moon and then allow the Dragon to return to LEO (or simply Earth aeropcapture) under its own power. 

Thoughts?

Edited March 13, 2016 by sevenperforce

[lobe]

The delta-v seems a little tight. Isn't the total for a moon landing and return 3 km/s?

[fredinno]

32 minutes ago, lobe said:

The delta-v seems a little tight. Isn't the total for a moon landing and return 3 km/s?

Also, the Dragon V2 does not have provisions for a long duration lunar mission. Never mind that this is a direct ascent style mission, and will thus consume even more fuel than conventional lunar missions. 

 

You'd likely need a drop tank for this, again, putting us back on the crossfeed problem.

Never mind this isn't a realistic proposal anyways. NASA will build any lunar missions via dual launch SLS, and SpaceX has no interest in the moon.

[Scotius]

At this point you would be building practically new ship - with new internal structure, plumbing, modifications to life support systems, maneuvering systems etc. Not very practical.

[sevenperforce]

8 hours ago, lobe said:

The delta-v seems a little tight. Isn't the total for a moon landing and return 3 km/s?

The dV each way between LLO and the lunar surface is 1.87 km/s, meaning that a lander in LOR needs over 3.7 km/s. Definitely above what we could squeeze into the Dragon V2. 

However, the dV from LLO to an Earth aerobraking trajectory is less than 1 km/s. So if you can get down to the lunar surface using a crasher stage, your ascent vehicle needs only 2.7 km/s to get all the way back to Earth (as long as it has a heat shield for braking).

8 hours ago, fredinno said:

Also, the Dragon V2 does not have provisions for a long duration lunar mission. Never mind that this is a direct ascent style mission, and will thus consume even more fuel than conventional lunar missions. 

You'd likely need a drop tank for this, again, putting us back on the crossfeed problem.

Never mind this isn't a realistic proposal anyways. NASA will build any lunar missions via dual launch SLS, and SpaceX has no interest in the moon.

The Dragon is billed as having a two-week minimum crewed endurance so I can't imagine a lunar landing would be a problem. And like I said above, direct ascent to Earth only requires 2.7 km/s if you can zero out lunar orbit velocity by using your transfer module as a crasher stage. No drop tank required. The only potential issue is power for the Dragon on the moon and on the return trip; they would have to use an extended battery because they would shed the trunk with its solar panels before landing.

And if SpaceX is billing the Dragon V2 for Mars missions, demonstrating a manned lunar landing with a reusable landing and return vehicle would be exactly up their alley. 

6 hours ago, Scotius said:

At this point you would be building practically new ship - with new internal structure, plumbing, modifications to life support systems, maneuvering systems etc. Not very practical.

Modifications to the inside are minimal. The two-man crew allows the existing life support systems to suffice. No changes to maneuvering systems would be anticipated. 

[fredinno]

7 hours ago, sevenperforce said:

The dV each way between LLO and the lunar surface is 1.87 km/s, meaning that a lander in LOR needs over 3.7 km/s. Definitely above what we could squeeze into the Dragon V2. 

However, the dV from LLO to an Earth aerobraking trajectory is less than 1 km/s. So if you can get down to the lunar surface using a crasher stage, your ascent vehicle needs only 2.7 km/s to get all the way back to Earth (as long as it has a heat shield for braking).

The Dragon is billed as having a two-week minimum crewed endurance so I can't imagine a lunar landing would be a problem. And like I said above, direct ascent to Earth only requires 2.7 km/s if you can zero out lunar orbit velocity by using your transfer module as a crasher stage. No drop tank required. The only potential issue is power for the Dragon on the moon and on the return trip; they would have to use an extended battery because they would shed the trunk with its solar panels before landing.

And if SpaceX is billing the Dragon V2 for Mars missions, demonstrating a manned lunar landing with a reusable landing and return vehicle would be exactly up their alley. 

Modifications to the inside are minimal. The two-man crew allows the existing life support systems to suffice. No changes to maneuvering systems would be anticipated. 

Ignoring that Elon isn't planning t use Dragon, Falcon, etc. for Mars, and his plans have nothing to do with the moon.... I can see a circumlunar SpaceX flight as a sort of a prestige flight, but not any more. Remember that the Falcon Heavy has horrible BLEO performance compared to SLS due to its low isp upper stage.

[Streetwind]

17 hours ago, sevenperforce said:

What's that good for? Well, Falcon Heavy was originally quoted at 53 tonnes to LEO, but with the Full Thrust modifications this will probably come up to about 10% higher, or 58.3 tonnes to LEO. LEO to the lunar surface is a dV of 5.93 km/s; the Falcon Heavy should be able to drop off around 15 tonnes to the lunar surface as a crasher stage. 

You'll need to be careful with assumptions like this.

For starters, the 53 tons to LEO are a fully expendable figure. Falcon Heavy is probably never going to fly fully expendable, at least if SpaceX statements are to be believed. And if it does, the customer must be prepared to pay quite a bit extra; the prices on the SpaceX website (which by the way are PR examples and may not have anything to do with real prices) have "reusability factored in".

Then, that 53 ton figure could only be achieved when utilizing crossfeed mode. Development of that was practically abandoned over a year ago already, as the vehicle keeps getting delayed more and more, and the technology offers less of a price/performance advantage as simply getting the thing flying regularly does. It's unlikely at this point that FH will ever fly with crossfeed enabled.

Finally, it may be able to take 53 tons "to LEO", but to what orbit exactly? A 150x150 km temporary equatorial parking orbit for a hypothetical launch from Guiana Space Center? We don't know, because SpaceX never clarified this. No launch provider ever does, really. And there's probably a pretty good reason for that, namely that it's a useless orbit that maximizes a theoretical payload that doesn't need to go anywhere. For a company like SpaceX, which rides strongly on its public fame, this will be doubly true. To go to the Moon, however, you need to get into a specific orbit with a specific inclination, and that's going to reduce your payload.

For a more realistic assessment, I would expect a Falcon Heavy, with partial reuse, to be able to put around 25 metric tons into a low Earth orbit that's suitable for performing a translunar injection burn. Fully expendable, mabye 35 at best. And you'd probably have to fork an easy quarter million over for that (rocket + launch campaign total, spacecraft not included). No specific maths to back this up; just gut feeling, based on the grand total of what I've read about FH over the years.

So yeah, Dragon V2 free return around the Moon? Perfectly doable, the heatshield is even rated for it already, and the ISS lifeboat requirements ensure that it has enough life support too. Land and return? Highly unlikely.

 

Edited March 13, 2016 by Streetwind

[DerekL1963]

12 hours ago, sevenperforce said:

Modifications to the inside are minimal. The two-man crew allows the existing life support systems to suffice. No changes to maneuvering systems would be anticipated. 

You're planning on adding a nearly seven ton tank - and you think the modifications to the inside would be minimal?

[sevenperforce]

10 hours ago, DerekL1963 said:

You're planning on adding a nearly seven ton tank - and you think the modifications to the inside would be minimal?

Compared to designing a direct ascent lander capable of Earth re-entry without staging? Yeah, I'd call designing, building, and installing a couple of tanks (each less than 2 m across) is minimal.

15 hours ago, fredinno said:

Ignoring that Elon isn't planning t use Dragon, Falcon, etc. for Mars, and his plans have nothing to do with the moon.... I can see a circumlunar SpaceX flight as a sort of a prestige flight, but not any more. Remember that the Falcon Heavy has horrible BLEO performance compared to SLS due to its low isp upper stage.

Yeah, the low-isp upper stage is why a direct ascent on hypergols results in a lower launch mass than LOR.

SpaceX has no plans for colonizing the moon, but they certainly have contracts for lunar missions. A demonstration mission, landing a two-man crew on the moon and returning them using existing hardware would go very far toward convincing investors that a Mars shot is worth investing in. SpaceX would not only become the first private company to land men on another world, but Dragon V2 would become the first manned spacecraft in history to land on more than one world. While, I might add, still being reusable.

15 hours ago, Streetwind said:

You'll need to be careful with assumptions like this.

For starters, the 53 tons to LEO are a fully expendable figure.

Yeah, I was expecting that.

15 hours ago, Streetwind said:

That 53 ton figure could only be achieved when utilizing crossfeed mode. Development of that was practically abandoned over a year ago already, as the vehicle keeps getting delayed more and more, and the technology offers less of a price/performance advantage as simply getting the thing flying regularly does. It's unlikely at this point that FH will ever fly with crossfeed enabled.

Finally, it may be able to take 53 tons "to LEO", but to what orbit exactly? A 150x150 km temporary equatorial parking orbit for a hypothetical launch from Guiana Space Center? We don't know, because SpaceX never clarified this. No launch provider ever does, really.

For a more realistic assessment, I would expect a Falcon Heavy, with partial reuse, to be able to put around 25 metric tons into a low Earth orbit that's suitable for performing a translunar injection burn. Fully expendable, mabye 35 at best.

I read that the quoted 53-tonne-to-LEO figure was for a 200x200 km 26-degree orbit from Boca Chica, though I don't recall how solid a source it was.

But that's okay, because we do have a solid source, if we do the math ourselves. That 53-tonne figure was the original stated specification for Falcon Heavy when it was first announced in early 2011. It was accompanied by a quote of 12 tonnes to GTO. But by 2013, the quoted GTO payload had come up to 21.2 tonnes...and that is before the Full Thrust modifications.

That quote for GTO is useful for two reasons: first, any inclination changes necessary for TLI would be comparable to those required for GTO, so we can ignore that. Second, we know about what perigee SpaceX uses for GTO when maximizing payload, because they used it with SES-9 just a week and a half ago -- it's roughly 200 km.

So a fully-expendable Falcon Heavy can deliver 21.2 tonnes to GTO on a 200x35,786 km orbit. That orbit has a perigee speed of 10.25 km/s, while the 200x200 km parking orbit has a constant orbital speed of 7.784 km/s, corresponding to a dV of 2.47 km/s. The upper stage has a dry mass of 3.9 tonnes, so to execute a 2.5 km/s burn with a 21.2 tonne payload would require 51.7 tonnes of fuel. Looks like that originally-quoted 53-tonne figure was a little low. Remember, this is all before the Full Thrust upgrades.

Assuming 13.7 tonnes for our Dragon V2 , an upgraded expendable Falcon Heavy should therefore be able to loft it to a 200x200 orbit with 59.2 tonnes of fuel left in the upper stage. That's a dV of 5.02 km/s.

Enough? It should be. Extending the apogee out to EML-1 at 346,016 km requires a perigee speed of 10.96 km/s, eating up 3.18 km/s. With the right transfer trajectory, this will result in lunar capture with a free fall to the lunar surface and an impact velocity of 2.24 km/s, slightly under lunar escape velocity.

The upper stage can reignite its engine and burn retrograde to engine-out a few dozen km above the lunar surface, reducing the vehicle's speed to 396 m/s. The Dragon V2 can ignite its engines and break away, leaving the Falcon upper stage to crash-land while it makes a propulsive landing.

Cutting it close? Sure. But with the Full Thrust upgrades this should be absolutely doable.

[fredinno]

35 minutes ago, sevenperforce said:

Compared to designing a direct ascent lander capable of Earth re-entry without staging? Yeah, I'd call designing, building, and installing a couple of tanks (each less than 2 m across) is minimal.

Yeah, the low-isp upper stage is why a direct ascent on hypergols results in a lower launch mass than LOR.

SpaceX has no plans for colonizing the moon, but they certainly have contracts for lunar missions. A demonstration mission, landing a two-man crew on the moon and returning them using existing hardware would go very far toward convincing investors that a Mars shot is worth investing in. SpaceX would not only become the first private company to land men on another world, but Dragon V2 would become the first manned spacecraft in history to land on more than one world. While, I might add, still being reusable.

Yeah, I was expecting that.

I read that the quoted 53-tonne-to-LEO figure was for a 200x200 km 26-degree orbit from Boca Chica, though I don't recall how solid a source it was.

But that's okay, because we do have a solid source, if we do the math ourselves. That 53-tonne figure was the original stated specification for Falcon Heavy when it was first announced in early 2011. It was accompanied by a quote of 12 tonnes to GTO. But by 2013, the quoted GTO payload had come up to 21.2 tonnes...and that is before the Full Thrust modifications.

That quote for GTO is useful for two reasons: first, any inclination changes necessary for TLI would be comparable to those required for GTO, so we can ignore that. Second, we know about what perigee SpaceX uses for GTO when maximizing payload, because they used it with SES-9 just a week and a half ago -- it's roughly 200 km.

So a fully-expendable Falcon Heavy can deliver 21.2 tonnes to GTO on a 200x35,786 km orbit. That orbit has a perigee speed of 10.25 km/s, while the 200x200 km parking orbit has a constant orbital speed of 7.784 km/s, corresponding to a dV of 2.47 km/s. The upper stage has a dry mass of 3.9 tonnes, so to execute a 2.5 km/s burn with a 21.2 tonne payload would require 51.7 tonnes of fuel. Looks like that originally-quoted 53-tonne figure was a little low. Remember, this is all before the Full Thrust upgrades.

Assuming 13.7 tonnes for our Dragon V2 , an upgraded expendable Falcon Heavy should therefore be able to loft it to a 200x200 orbit with 59.2 tonnes of fuel left in the upper stage. That's a dV of 5.02 km/s.

Enough? It should be. Extending the apogee out to EML-1 at 346,016 km requires a perigee speed of 10.96 km/s, eating up 3.18 km/s. With the right transfer trajectory, this will result in lunar capture with a free fall to the lunar surface and an impact velocity of 2.24 km/s, slightly under lunar escape velocity.

The upper stage can reignite its engine and burn retrograde to engine-out a few dozen km above the lunar surface, reducing the vehicle's speed to 396 m/s. The Dragon V2 can ignite its engines and break away, leaving the Falcon upper stage to crash-land while it makes a propulsive landing.

Cutting it close? Sure. But with the Full Thrust upgrades this should be absolutely doable.

Investors have no reason to invest in Mars as there is no profit in it. Moon missions will do nothing for it.

I can see the low modifications Moon flyby and Moon orbit missions, but Moon landings need a lot more changes. What happens if the dust damages the heat shield at the bottom of the Dragon V2? More modifications necessary. What about a cargo hold to do anything useful on the moon? You guessed it, more modifications. What about landing legs extending beyond the drop tank? Yet more modifications. And all those mods will need new aerodynamic models to launch on FH. It's a losing battle.

[DerekL1963]

56 minutes ago, sevenperforce said:

14 hours ago, DerekL1963 said:

You're planning on adding a nearly seven ton tank - and you think the modifications to the inside would be minimal?

Compared to designing a direct ascent lander capable of Earth re-entry without staging? Yeah, I'd call designing, building, and installing a couple of tanks (each less than 2 m across) is minimal.

0.o  Yeah, silly apples to the thing least like apples you can imagine comparisons are so useful.

Seriously, the effort required to design a ludicrously specified vehicle is completely and totally irrelevant to the question at hand - the difficulties involved in converting a capsule as specified.   Just because x is simpler than y does *not* means that x is in and of itself simple.

[sevenperforce]

21 minutes ago, fredinno said:

Investors have no reason to invest in Mars as there is no profit in it. Moon missions will do nothing for it.

Call it "buy-in" rather than investment, then. Demonstrating that it's possible to land the same manned spacecraft on multiple worlds is a huge, huge step.

4 minutes ago, DerekL1963 said:

1 hour ago, sevenperforce said:

Compared to designing a direct ascent lander capable of Earth re-entry without staging? Yeah, I'd call designing, building, and installing a couple of tanks (each less than 2 m across) is minimal.

0.o  Yeah, silly apples to the thing least like apples you can imagine comparisons are so useful.

Seriously, the effort required to design a ludicrously specified vehicle is completely and totally irrelevant to the question at hand - the difficulties involved in converting a capsule as specified.   Just because x is simpler than y does *not* means that x is in and of itself simple.

My point is that if it's simpler to modify an existing capsule than it is to design a purpose-built craft, without significant performance reductions (let alone prohibitive ones), then we have demonstrated a really critical step towards reusability and flexibility in interplanetary expansion. And we should do it.

30 minutes ago, fredinno said:

I can see the low modifications Moon flyby and Moon orbit missions, but Moon landings need a lot more changes. What happens if the dust damages the heat shield at the bottom of the Dragon V2? More modifications necessary. What about a cargo hold to do anything useful on the moon? You guessed it, more modifications. What about landing legs extending beyond the drop tank? Yet more modifications. And all those mods will need new aerodynamic models to launch on FH. It's a losing battle.

I can't imagine that lunar dust would be more dangerous to heat shields than plummeting through the atmosphere at fifteen thousand miles per hour. I mean, we would definitely want to do testing to make sure, but it seems like a really minor problem.

The crewed model of the Dragon V2 already has a cargo hold, IIRC.

There is no drop tank. The ship would use the same landing legs for touchdown that it will use on Earth.

The only added aerodynamic modeling would be for the attachable vacuum nozzle extensions. Everything else is standard, with the exception that crew capacity has been dropped in exchange for mounting those auxiliary tanks in the cabin.

I'm not saying it wouldn't take extensive research and effort. And yeah, it would have a hefty price tag...probably a quarter billion. But those aren't reasons not to do it.

[Rakaydos]

Before Dragon V2, Dragonlab would probably be a better testbed for this. It's aready designed to be customizable, to match the customers desired expiriments, so adding extra fuel tanks for earth return shouldn't be an issue.

Practice precision lunar landing by visiting a historic Apollo site and take pictures.

[sevenperforce]

3 minutes ago, Rakaydos said:

Before Dragon V2, Dragonlab would probably be a better testbed for this. It's aready designed to be customizable, to match the customers desired expiriments, so adding extra fuel tanks for earth return shouldn't be an issue.

Practice precision lunar landing by visiting a historic Apollo site and take pictures.

Dragonlab does not have engines.

[fredinno]

25 minutes ago, sevenperforce said:

Dragonlab does not have engines.

It does, but not powerful enough, it is based off Dragon V1.

1 hour ago, sevenperforce said:

Call it "buy-in" rather than investment, then. Demonstrating that it's possible to land the same manned spacecraft on multiple worlds is a huge, huge step.

My point is that if it's simpler to modify an existing capsule than it is to design a purpose-built craft, without significant performance reductions (let alone prohibitive ones), then we have demonstrated a really critical step towards reusability and flexibility in interplanetary expansion. And we should do it.

I can't imagine that lunar dust would be more dangerous to heat shields than plummeting through the atmosphere at fifteen thousand miles per hour. I mean, we would definitely want to do testing to make sure, but it seems like a really minor problem.

The crewed model of the Dragon V2 already has a cargo hold, IIRC.

There is no drop tank. The ship would use the same landing legs for touchdown that it will use on Earth.

The only added aerodynamic modeling would be for the attachable vacuum nozzle extensions. Everything else is standard, with the exception that crew capacity has been dropped in exchange for mounting those auxiliary tanks in the cabin.

I'm not saying it wouldn't take extensive research and effort. And yeah, it would have a hefty price tag...probably a quarter billion. But those aren't reasons not to do it.

Please show me the Delta V calculations please, then I'll believe the Dragon can get to the Moon sans drop tank.

Also, if we put the V2 on the moon sans cargo hold, then we can use its landing legs, if we use it with the cargo hold, then we need new landing legs...

Also, the V2's solar panels will need to be redesigned to face the Sun, they won't under their current configuration due to being all on one side.

[sevenperforce]

32 minutes ago, fredinno said:

It does, but not powerful enough, it is based off Dragon V1.

It has Draco thrusters, but those are RCS, not propulsive engines.

32 minutes ago, fredinno said:

Please show me the Delta V calculations please, then I'll believe the Dragon can get to the Moon sans drop tank.

In my first post, I explained how installing removable nozzle extensions and an auxiliary fuel tank in the cabin could give the Dragon V2 about 3,010 m/s of dV. In this post, I explained how Falcon Heavy could put the Dragon a few km above the surface and drop velocity down under 400 m/s; with the 10% payload increase from Full Thrust, this would bring velocity down to 70 m/s. The Falcon upper stage would break away and crash while the Dragon would separate from its trunk and make a propulsive landing, burning an estimated 200 m/s of dV (allowing a couple of minutes of hover).

This leaves the ship with 2,810 m/s. According to this table, you only need 2,740 m/s for a direct ascent return from the moon if you can aerobrake on the way back.

37 minutes ago, fredinno said:

Also, if we put the V2 on the moon sans cargo hold, then we can use its landing legs, if we use it with the cargo hold, then we need new landing legs...

Also, the V2's solar panels will need to be redesigned to face the Sun, they won't under their current configuration due to being all on one side.

I wasn't talking about the trunk; I was talking about the internal cargo hold. I could be wrong about that, though.

The solar panels are an issue I mentioned above; it would either need to be fitted with additional solar panels or use additional batteries, since it would discard the trunk (with its solar panels) prior to landing.

If you're skeptical about whether SpaceX would actually be able to make these modifications, or be interested in interplanetary missions with Dragon V2 and Falcon Heavy, try this on for size:

Quote

Mr. Musk expanded on plans to utilize the SuperDracos for use during landings on the surfaces of other planets.

"Dragon 2 is capable of transporting scientific payloads to anywhere in the solar system, with a liquid or solid surface, with or without an atmosphere. So Dragon is really a crew transport and science delivery platform,” he added.

“Dragon, with the heat shield, parachutes and propulsive landing capability, is able to land on a planet that has higher entry heating, like Mars. It can also land on the Moon, or potentially conduct a Europa mission. When the destination doesn’t have an atmosphere, you can remove the parachute and the heat shield and replace that with additional propellant – so you’d have quite a lot of propellant for (propulsive) landing.”

So I'm not proposing anything they haven't considered, at least in piecemeal. I'm just putting it all together to show that a direct ascent moon shot is entirely within the system's reach.

[Rakaydos]

1 hour ago, sevenperforce said:

Dragonlab does not have engines.

If SpaceX can get the crasher stage to work right, can DragonLab land in lunar gravity under RCS alone? Ignoring return for now, just as a delivery platform, say for a rover charging base or something, for long term robotic exploration.

[fredinno]

59 minutes ago, sevenperforce said:

It has Draco thrusters, but those are RCS, not propulsive engines.

In my first post, I explained how installing removable nozzle extensions and an auxiliary fuel tank in the cabin could give the Dragon V2 about 3,010 m/s of dV. In this post, I explained how Falcon Heavy could put the Dragon a few km above the surface and drop velocity down under 400 m/s; with the 10% payload increase from Full Thrust, this would bring velocity down to 70 m/s. The Falcon upper stage would break away and crash while the Dragon would separate from its trunk and make a propulsive landing, burning an estimated 200 m/s of dV (allowing a couple of minutes of hover).

This leaves the ship with 2,810 m/s. According to this table, you only need 2,740 m/s for a direct ascent return from the moon if you can aerobrake on the way back.

I wasn't talking about the trunk; I was talking about the internal cargo hold. I could be wrong about that, though.

The solar panels are an issue I mentioned above; it would either need to be fitted with additional solar panels or use additional batteries, since it would discard the trunk (with its solar panels) prior to landing.

If you're skeptical about whether SpaceX would actually be able to make these modifications, or be interested in interplanetary missions with Dragon V2 and Falcon Heavy, try this on for size:

So I'm not proposing anything they haven't considered, at least in piecemeal. I'm just putting it all together to show that a direct ascent moon shot is entirely within the system's reach.

OK. Dragon has minimal internal cargo hold, it doesn't need one. That's a major internal modification necessary. You also need an external cargo hold to hold rovers, experiments, etc.

[fredinno]

Also, exposing the heat shield for days on end, not to mention high speed lunar dust on landing and take off, is a horrible idea- even a small hole from a rock will jeapordize the crew. It was one of the major concerns during Apollo 13, and similar things lead to columbia. 

Also, Your sun-traking solar panels will be ripped off by the engine exaust, so you need to use fuel cells. Allin all, the modifications make this unrealsitic, considering Elon doesn't care about the moon, and the only reason would be to show you can do it, and publicity.

[sevenperforce]

1 hour ago, Rakaydos said:

If SpaceX can get the crasher stage to work right, can DragonLab land in lunar gravity under RCS alone? Ignoring return for now, just as a delivery platform, say for a rover charging base or something, for long term robotic exploration.

A crasher stage is just a fancy term for staging during descent. It can really only be used if there is no atmosphere; you don't want to do stage separation during atmospheric re-entry. You also need a final descent engine with hover capability (and if you plan to leave, it needs to be an engine you don't mind restarting).

The Dragon 1 doesn't have a vehicle T/W ratio great enough for hover using RCS, so it's a no go. But the Dragon V2 has manned and unmanned configurations. They can absolutely strip off the parachute and heatshield and use it to land a rover or supplies or anything else. 

In fact, it would make a lot of sense to do exactly that, as a dry run for a manned landing. They could outfit a "disposable" Dragon V2 with additional payload to exactly match the launch mass for a manned mission, allowing them to test staging, lunar hover, and landing.

38 minutes ago, fredinno said:

OK. Dragon has minimal internal cargo hold, it doesn't need one. That's a major internal modification necessary. You also need an external cargo hold to hold rovers, experiments, etc.

The internal cargo hold is fine. An external one would be nice, but experiments wouldn't really be the point of the mission. As I discussed above, they could do a dry run first and include a rover that way if they really wanted to.

19 minutes ago, fredinno said:

Also, exposing the heat shield for days on end, not to mention high speed lunar dust on landing and take off, is a horrible idea- even a small hole from a rock will jeapordize the crew. It was one of the major concerns during Apollo 13, and similar things lead to columbia. 

Also, Your sun-traking solar panels will be ripped off by the engine exaust, so you need to use fuel cells. Allin all, the modifications make this unrealsitic, considering Elon doesn't care about the moon, and the only reason would be to show you can do it, and publicity.

You keep insisting that there is no concern for the moon, but I don't think that is true. The article I linked above has Elon specifically talking about using the Dragon V2 for landing payloads on the moon.

The integrity of the heat shield would absolutely be a critical mission design element. I'm sure that they would run a whole suite of tests and experiments and simulations. If necessary, they could use a lightweight disposable blast shield that dropped off during ascent. 

Added solar panels wouldn't be in the path of the engine exhaust. They could retrofit the outer/upper skin with one and sun-track using RCS on the return, or they could simply use a fuel cell. 

[fredinno]

20 hours ago, sevenperforce said:

A crasher stage is just a fancy term for staging during descent. It can really only be used if there is no atmosphere; you don't want to do stage separation during atmospheric re-entry. You also need a final descent engine with hover capability (and if you plan to leave, it needs to be an engine you don't mind restarting).

The Dragon 1 doesn't have a vehicle T/W ratio great enough for hover using RCS, so it's a no go. But the Dragon V2 has manned and unmanned configurations. They can absolutely strip off the parachute and heatshield and use it to land a rover or supplies or anything else. 

In fact, it would make a lot of sense to do exactly that, as a dry run for a manned landing. They could outfit a "disposable" Dragon V2 with additional payload to exactly match the launch mass for a manned mission, allowing them to test staging, lunar hover, and landing.

The internal cargo hold is fine. An external one would be nice, but experiments wouldn't really be the point of the mission. As I discussed above, they could do a dry run first and include a rover that way if they really wanted to.

You keep insisting that there is no concern for the moon, but I don't think that is true. The article I linked above has Elon specifically talking about using the Dragon V2 for landing payloads on the moon.

The integrity of the heat shield would absolutely be a critical mission design element. I'm sure that they would run a whole suite of tests and experiments and simulations. If necessary, they could use a lightweight disposable blast shield that dropped off during ascent. 

Added solar panels wouldn't be in the path of the engine exhaust. They could retrofit the outer/upper skin with one and sun-track using RCS on the return, or they could simply use a fuel cell. 

You would need to use a fuel cell, and add landing legs to the "Service module" (which would replace the trunk) containing the power module and an external cargo bay.

I need a source for the internal cargo bay. All the pics I've seen of Dragon V2 imply it would be a major internal modification.

All this would imply a pretty major development program, and likely mean a Dragon V3 would be in order, thus making an endeavor much more expensive. I'm sure it would work if Elon wanted to, but it's not going to be a one off mission- it's too expensive for that.

[sevenperforce]

17 minutes ago, fredinno said:

You would need to use a fuel cell, and add landing legs to the "Service module" (which would replace the trunk) containing the power module and an external cargo bay.

I need a source for the internal cargo bay. All the pics I've seen of Dragon V2 imply it would be a major internal modification.

All this would imply a pretty major development program, and likely mean a Dragon V3 would be in order, thus making an endeavor much more expensive. I'm sure it would work if Elon wanted to, but it's not going to be a one off mission- it's too expensive for that.

Yeah, either a fuel cell or aeroshell-mounted solar panels would be necessary, as I mention above.

No service module or external cargo bay; thus, the legs it already has are fine.

The article I linked above demonstrates that Elon expects modifications to the V2 platform as a matter of course.

[fredinno]

5 hours ago, sevenperforce said:

Yeah, either a fuel cell or aeroshell-mounted solar panels would be necessary, as I mention above.

No service module or external cargo bay; thus, the legs it already has are fine.

The article I linked above demonstrates that Elon expects modifications to the V2 platform as a matter of course.

Where do you put the fuel cells then? Inside? Do you realise how dangerous that can be?

[sevenperforce]

37 minutes ago, fredinno said:

Where do you put the fuel cells then? Inside? Do you realise how dangerous that can be?

They'd have to do an engineering feasibility analysis to determine whether it would be more mass- and cost-effective to install additional solar cells in the aeroshell, to add solid-state batteries, or to install a sealed fuel cell compartment with an external exchanger duct. 

[fredinno]

1 hour ago, sevenperforce said:

They'd have to do an engineering feasibility analysis to determine whether it would be more mass- and cost-effective to install additional solar cells in the aeroshell, to add solid-state batteries, or to install a sealed fuel cell compartment with an external exchanger duct. 

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.