Dragon v2 or Orion

[tater]

I'm not sure reentry speed should be on that list. The tested orion heat shield is not even what they'd actually use at this point. The other stuff is what I was looking for (radhard, etc). I have yet to see much on mission duration except for the 21 days statement for Orion duration (which is basically lunar/cislunar at best). How much of the life support, etc requires the service module, because otherwise we are comparing a capsule to a CM/SM combo.

Again, D2 is not designed for a vague, non-mission BEO, so it would be sort of stunning if it was even close in many comparisons. I think a lot of the issue is the hype of "the spacecraft that will take us to Mars" nonsense that was on every news site when EFT-1 flew.

[A1Ch1]

This is like asking what's better, an A320 or a 777? They're designed to do different things. You don't fly a 777 from LA to SF and you don't fly an A320 from LA to Frankfurt. The question needs to specify what the vehicle will be tasked with to judge which is better.

[Voyager275]

Orion seems to be NASA's last hope for a crew vehicle. And also it doesn't have a full schedule(SLS test) while v2 has planned flights to ISS. For BEO I'm pretty sure SpaceX has a plan for Mars using v2 or another craft.

[Jonboy]

Better in what direction ? I'll take the structure: both are safe, dragon might be lighter thanks to no tiles on it's top. Orion might be roomier.

Proof that it's safe: both survived reentry. Or, for a worser one, think of this: does DragonV2's any safer than Soyuz ? Both returns succesfully.

We only see the hardware to this date for Orion; only a small part of the software also for Dragon (I believe there's no internal display yet on Dragon). You can't tell something well until you see it.

Orion had an unmanned orbit and reentry test, SpaceX doesn't plan to do an orbital test of DragonV2 until 2016. Both Launch Escape Systems have been tested successfully, though.

I prefer DragonV2's LES, because it is integrated into the capsule, which removes the need for staging. Plus DragonV2 has redundancy for landing. It can land safely on either the SuperDracos or parachutes.

[Frybert]

To beat a dead horse:

Whats better? A big rig or a taxi cab?

[tater]

I think the analogies like the one above are frankly wrong. I'd really like hard stats on how much radiation is mitigated, for example (for both). Without a "storm cellar," or unless Orion is uniformly built to those standards, a solar flare during a single, nominal 21 day (claimed duration) mission could end an astronaut's career (or life, rarely). Any requirement for a shielded hab to dock with would give the same capability to any craft docked. NASA says that Orion's shelter is to pile supplies up in the aft of the capsule. I'm pretty sure they can do the same on D2. Rad hard electronics are not that complicated to swap out for, frankly. I'm totally unsure on redundancy within the capsules, though, and if a service module is assumed, then a SM trunk could obviously be added to dragon.

The real question is what percentage of the money spent in total on Orion would need to be spent to make D2 work for the Orion missions postulated. If that is less than total Orion spending at all, Orion was a bad deal.

[Kibble]

The real question is what percentage of the money spent in total on Orion would need to be spent to make D2 work for the Orion missions postulated.

BLEO mission-capable capsules have very different requirements and standards than LEO. It wouldn't just be "modifying" Dragon to make it work - I'm sure qualifications would require major changes to the basic design, particularly radiation shielding. Orion is already developed, and ready for its unique and awesome task.

[tater]

What awesome task?

btw, it looks like they are still thinking about what radiation shielding they will actually use.

Also, ready for its awesome task implies they could launch soon. It's not at all ready for anything. Not the capsule, not the SM which doesn't exist, and not the launch vehicle to put it on a transfer anywhere interesting.

WRT manned flight I have to agree with Zubrin on one point, they need to set a short term goal, then do it. Making something that maybe is good for something is exactly what we've been doing post Apollo.

Edited June 3, 2015 by tater

[Kibble]

What awesome task?

Being a critical role in flying human beings beyond low Earthling orbit, facilitating deep-space EVA activities, primary habitation space for short-duration missions, and protection during high-velocity reentry.

[tater]

That's a cute sound bite, but it's not a mission. Constellation, erm, Orion, is a moon rocket. The TPS would have to be redesigned even for the proposed asteroid mission (which is a dumb mission, that only exists as something for Orion to do, a robot would be far more cost effective). That's according to LockMart, BTW. Mars? LOL. Not without a redesign---though I'm sure LockMart would be happy to do both redesigns for a few billion each).

It requires SLS, and SLS cannot possibly hit target costs because there are no payloads. It needs a high launch rate… of huge payloads, otherwise it will be the only thing NASA can do. What are the payloads?

A moon rocket? I'm down with that. Fund a lunar exploration program. THAT would be the mission. Everything to that goal (which would let them use Orion as-is). Building it, "because" is silly.

[Nibb31]

I pretty much agree with your analysis about Orion. Whatever spin NASA puts on it regarding Mars and asteroids, Orion is a spacecraft that was initially designed for cislunar flight, and that is reflected by most of its actual requirements and capabilities.

But that certainly doesn't change the fact that Dragon was designed as a LEO taxi, not an exploration vehicle. Again, spacecraft are not Lego. You can't just swap out shirtsleeve environment systems and replace them with hardened systems. You can't just recertify systems that are designed for a 6-month loiter time in LEO to a 3-year loiter time in deep space. You can't just bolt on EVA capability, a radiation shelter or a service module. If you do those things, you end up with a totally different vehicle with a whole new set of requirements and a separate design and certification process. The whole powered landing thing makes sense for a reusable taxi, but it's just detrimental dead weight if you have to carry that extra fuel and hardware all the way to the Moon, Mars, or wherever you're going and back.

So SLS-Orion doesn't have a well-defined BEO mission, but then again neither does Dragon. It will not be going to Mars either, or at least not in anything resembling its current form.

Edited June 3, 2015 by Nibb31

[Rune]

Better for what ?

Which is better, a Land Rover or a Mini? Same thing, it depends on the mission.

Dragon and CST are like the Mini, designed for short and frequent commutes in relative comfort. Orion is a Land Rover, designed for extreme environments and longer journeys with higher versatility and robustness.

You can go shopping in a Land Rover and you can cross the Kalahari in a Mini, but neither are the best vehicles for the job.

Orin can't do a lunar mission without a service module that won't be built. Orion can't go to Mars without a habitat and propulsion stage that are yet to be proposed. Orion's heatshield is heavier for a worse performance. Orion's shape is mass-inefficient, and the only reason it uses it is that the aerodynamic models were worked out durign Apollo (that is the official reason, I suspect it's just because it looks like Apollo this way). What is it exactly that makes Orion a "Land Rover"? The heavy-duty environmental systems that are yet to be built and tested and could be bolted onto any other capsule? Because those aren't up to a trip of more than a few days either.

No, for the same amount of additional development and hardware (transfer stages, habitats and such), Dragon would be able to accomplish every damn mission Orion is supposed to, only for a fraction of the mass and cost. Just because it is inherently more mass-efficient due to design considerations (better shape and heatshield, basically). It does pay some mass inefficiency for having an integrated escape system, but thanks to it being hypergolic, just the engine weight.

'K, that's from the beginning because, obviously, TL;DR. Now let's start by the end:

I pretty much agree with your analysis about Orion. Whatever spin NASA puts on it regarding Mars and asteroids, Orion is a spacecraft that was initially designed for cislunar flight, and that is reflected by most of its actual requirements and capabilities.

But that certainly doesn't change the fact that Dragon was designed as a LEO taxi, not an exploration vehicle. Again, spacecraft are not Lego. You can't just swap out shirtsleeve environment systems and replace them with hardened systems. You can't just recertify systems that are designed for a 6-month loiter time in LEO to a 3-year loiter time in deep space. You can't just bolt on EVA capability, a radiation shelter or a service module. If you do those things, you end up with a totally different vehicle with a whole new set of requirements and a separate design and certification process. The whole powered landing thing makes sense for a reusable taxi, but it's just detrimental dead weight if you have to carry that extra fuel and hardware all the way to the Moon, Mars, or wherever you're going and back.

So SLS-Orion doesn't have a well-defined BEO mission, but then again neither does Dragon. It will not be going to Mars either, or at least not in anything resembling its current form.

Those comments regarding "6 moths loiter time in LEO vs 3-year loiter time in deep space" depend entirely on what design requirements those tasks actually entail, and what was built into the capsules' components. Orion certainly wan't designed for a 3-year loiter time either. Just like Soyuz was never designed to stay up more than a couple of weeks (heck, it didn't have solar panels at first!), that capability was retrofitted into it exactly how you say can't be done: recertifying the design after an engineering analysis to see what components needed upgrading and/or replacing.

Edit of the edit, because this is golden, let's go by parts:

The requirements that Dragon is lacking for BEO missions are:

- Radiation shielding

Orion's "radiation shielding" is a joke. It's a tin can, same as everything else we have ever flown. A few mms of aluminum and a NASA study on radiation doses do not a radiation shield make.

- Hardened electronics

That can be achieved by using custom circuits like Orion does, or by having massive redundancy to handle the bitflips and burnouts like Dragon does. And it's still a matter of bolting a few kgs of equipment anyhow.

- Redundant systems

Just as redundant as any other manned spacecraft, that is, just as redundant as the NASA human spaceflight rules say. Dragon follows those guidelines, even the cargo version.

- Life support duration

That is funny. Three weeks vs two. Huge difference! And of course you can't change Dragon's by, say, reducing the crew number to Orion's four and packing extra supplies.

- Mission duration

Agin, the quoted one for either is 21 days nominal mission vs 2 years stowed in the brochure as someone else posted. Who comes out on top again?

- Reentry speed

Dragon's heatshield was designed for Mars reentry speeds, and the material outperforms compared with the Apollo legacy stuff. I expect D2 to handle higher reentry speeds safely.

- Navigation systems

Now you are just grasping at straws. Navigation is done from the ground much more precisely through the radio link.

- Communication systems

Because that is totally a thing that can't be added in the trunk as a subsystem easily.

- EVA capability

By depressurizing the cabin? Granted, D2's electronics are not vacuum-rated (not to say they can't be switched with ones that are), but seriously, what kind of serious mission would use the return capsule as an airlock?

Dragon systems are not certified with the same requirements. It is optimized to be economical for short trips to the ISS and back. You might be able to modify each system to meet the requirements for BEO exploration missions, but you would need to go through the entire design and certification process again and you would end up with a very different vehicle.

Just like you wold have to do with an Orion, as it is designed right now. The thing is very much not ready to serve as the manned capsule for a Mars mission, it is just a downgraded Apollo with a smaller service module after all.

Rune. But hey, let Lockheed continue burning billions on a redundant, overweight vehicle.

Edited June 3, 2015 by Rune

[Nibb31]

Orin can't do a lunar mission without a service module that won't be built.

The SM definitely is being built, by ESA, and it is part of Orion. Orion = CM + SM.

Dragon doesn't have a service module at all, so it can't go to the Moon.

Orion can't go to Mars without a habitat and propulsion stage that are yet to be proposed.

Neither can Dragon.

Orion's heatshield is heavier for a worse performance.

Worse performance than what? Dragon? We don't know about Dragon's reentry capabilities because they haven't been tested.

Orion's shape is mass-inefficient, and the only reason it uses it is that the aerodynamic models were worked out durign Apollo (that is the official reason, I suspect it's just because it looks like Apollo this way).

The "Apollo" shape is dictated by the ability to steer the capsule during reentry while keeping the sidewalls out of the plasma flow. Orion and Apollo are actually lifting bodies, that can bleed off speed by manoeuvering during reentry and performing a skip reentry. The steeper sidewalls on Dragon mean that it can't be steered as much, resulting in a lower L/D ratio, less cross-range, and more importantly less capability to bleed off excess speed.

What is it exactly that makes Orion a "Land Rover"? The heavy-duty environmental systems that are yet to be built and tested and could be bolted onto any other capsule? Because those aren't up to a trip of more than a few days either.

21 days for 4 people, which is enough for a lunar sortie or a trip to EML1. Dragon has life support for 7 days, which isn't enough to go to the Moon and back with any margin.

- Systems on Orion are hardened, redundant, and designed for on orbit service/repair, manual control, vacuum operation, multiple mission modes, BEO navigation, BEO comms, etc...

- Dragon systems are not hardened, designed for a shirtsleeve environment and are geared towards regular automatic LEO taxi flights with minimal training.

- Depress/Repress capability, support for EVA suits, and handrails/EVA fixtures are a requirement for contingency (crew transfer in case of a docking failure) and baseline operations (ARM) on exploration missions. Dragon does not support support EVA, therefore it requires an additional airlock module.

- Solar panels are orientable, which allows to orient the spacecraft independently from power production requirements (for thermal control, propulsion, scientific observation, EVA requirements, or other mission-specific requirements). Dragon v2 needs to spend most of its time with the trunk panels towards the Sun.

And no, you can't just "bolt" systems into another spacecraft. Spacecraft are not Legos. Spacecraft are built around their systems, not the other way round.

No, for the same amount of additional development and hardware (transfer stages, habitats and such), Dragon would be able to accomplish every damn mission Orion is supposed to, only for a fraction of the mass and cost.

Once you add a service module with equivalent dV and flight duration, extended life-support, deployable solar panels, EVA gear, and an airlock that are required for BEO exploration missions you would have pretty much the same, if not more, mass as Orion.

Just because it is inherently more mass-efficient due to design considerations (better shape and heatshield, basically). It does pay some mass inefficiency for having an integrated escape system, but thanks to it being hypergolic, just the engine weight.

A BEO Dragon would not have SuperDracos because it would be stupid to carry along that extra weight for no good reason. Until we get to a point where Earth-Moon trips become routine, propulsive landing and reusability make no sense for exploration missions.

Edited June 3, 2015 by Nibb31

[Rune]

The SM definitely is being built, by ESA, and it is part of Orion. Orion = CM + SM.

Yup, and the ESA's SM is totally capable of cismunar flights, right? I mean, it's not as if it was downgraded from the original proposal to only handle LEO missions and have insufficient dV for a lunar return... Oh wait, it did. Well, same function as Dragon's internal propellant then, and you save a staging event.

Dragon doesn't have a service module at all, so it can't go to the Moon.

Even with the fattest service module you can think of, even with one rated for lunar return, Orion can't go to the Mun either on its own, because every capsule needs a transfer stage to move around. But it helps the transfer stage if your capsule is lighter. And before you invoke the EDS stage Orion is supposed to always launch with, have in mind I could also invoke a restartable upper stage like Falcon's, on top of a booster that can do a direct shot to Luna like FH.

Neither can Dragon.

Which is my point, they are pretty much the same, only one masses about half than the other. It wouldn't make sense to carry a heavy Orion all the way to Mars and back, when a lighter Dragon would do.

Worse performance than what? Dragon? We don't know about Dragon's reentry capabilities because they haven't been tested.

Basic tests in the lab on rigs under applicable conditions, among other things. That was known ever since SpaceX developed PICA X, mostly by the NASA techs that compared it with the stuff they had on hand, like the older PICA and AvCoat. But if you want to grasp at operational use straws, Orion's heatshield has never been tested on a relevant reentry either, and Dragon's heatshield has had quite a few orbital test to figure out ablation rate. Bottom line? PICA X comes out on top for mass/protection with respect to AvCoat. Which is reasonable, since the latter was formulated on the sixties, and the former was specifically designed as an improvement.

21 days for 4 people, which is enough for a lunar sortie or a trip to EML1. Dragon has life support for 7 days, which isn't enough to go to the Moon and back with any margin.

- Systems on Orion are hardened, redundant, and designed for on orbit service/repair, manual control, vacuum operation, multiple mission modes, BEO navigation, BEO comms, etc...

- Dragon systems are not hardened, designed for a shirtsleeve environment and are geared towards automatic LEO taxi flights.

- Depress/Repress capability, support for EVA suits, and handrails/EVA fixtures are a requirement for contingency (crew transfer in case of a docking failure) and baseline operations (ARM) on exploration missions. Dragon does not support support EVA, therefore it requires an additional airlock module.

And no, you can't just "bolt" systems into another spacecraft. Spacecraft are no Legos. They are built around those systems, not the other way round.

Spacecraft get modified all the time. If you have the room, and the power/thermal budget, yes, you can bolt on new systems with the proper engineering analysis. Even complicated manned systems get regular upgrades, look at shuttle or Soyuz. In fact, look at Soyuz mostly, that thing is probably one of the most successful spacecraft of all time, if not the most, and it has seen so many versions with different equipment that I can't even come up with a ballpark number off the top of my head. There was the lunar version, the one for LEO without solar panels, the one rebuilt for taller american astronauts, the glass cockpit upgrade that replaced all avionics....

I know Orion uses some of its extra mass in having more equipment that provides extra capabilities. I also know most of it is redundant and/or useless to serve the role of a crew return vehicle in an interplanetary expedition, or the LEO taxi role. It just makes it suited to recreate Apollo missions, and we should go that route. IMO, of course.

Oh, and the depress/repress ability is nice in case of contingencies, I'll admit that. I would even admit that Dragon would require quite the big engineering pass to be modified for that (lots of not obvious systems require an atmosphere to do stuff like dissipate heat). But, again, that is a contingency use, I don't think NASA baselines Orion as the airlock module in any DRM other than ARM, and that is quite the travesty anyhow (modified ACES suits for EVAs, because Orion won't support big capable spacesuits with decent backpacks, for example, that is just looking for trouble). And it could be added if the need is great, probably at the expense of crew capacity (extra supplies to pressurize, and room to keep the suits). I wouldn't, and just take the risk and try to offset it somewhere else in the mission, to save on complexity of a spacecraft that has a very limited role in most missions (basically, getting the crew up to LEO and reentering them).

Once you add a service module with equivalent dV and flight duration, extended life-support, orientable solar panels (so that spacecraft orientation is independant from power generation), EVA gear, and an airlock that are required for BEO exploration missions you would have pretty much the same, if not more, mass as Orion.

But you don't need those! Those are exactly the functions the transfer stage and habitat should perform. Unless you want to recreate Apollo, an architecture of direct shots without transfer vehicle, and then you are stuck to cismunar missions. On a trip to Mars anywhere else with a decent long duration habitat and transfer stage, those things are dead weight that subtracts from payload.

A BEO Dragon would not have SuperDracos because it would be stupid to carry along that extra weight for no good reason. Until we get to a point where Earth-Moon trips become routine, propulsive landing and reusability make no sense for exploration missions.

A BEO Dragon would probably retain the SuperDracos, because changing the design structurally so much would mean a new capsule, basically, and the astronauts would still need an escape capability during launch. Yes, they would pay the penalty of lugging a few tens of kilograms, maybe more than a hundred, in extra propulsion hardware. Still a few tons to catch up to Orion.

In fact, I don't think you get the point I am trying to make generally. You don't want a heavy and over-capable cismunar-capable capsule to perform BEO flights. You want a light one, that can handle the return and stay dormant while the rest of the hardware does its BEO thing and is as light as it is feasible. And then with the true BEO hardware (hab and transfer stage), you can do Lunar missions for spare change, or as tests of the true interplanetary ones.

Rune. Just look at why Orion was designed, and what it's supposed to be used for. It makes no sense, even before you look at the price tag.

[Nibb31]

Just look at why Orion was designed, and what it's supposed to be used for. It makes no sense, even before you look at the price tag.

Orion was designed to go to the Moon, and that is all it is ever going to do. Anybody who seriously thinks that NASA is going to Mars in the next 30 years is delusional at this point. There is no habitat or MTV or Mars lander and there is no funding to build them. SLS and Orion are all we're getting, so they are going to have to include the exploration mission life-support and operational capabilities if we want to ever leave LEO.

NASA was banned from mentioning the Moon in its PR because the current administration cancelled Constellation, which is why they are desperately talking about using Orion for hypothetical and unfunded Mars and asteroid missions. After the next US election, things are going to change, because whether they like it or not, they are going to have find a use for SLS-Orion and the Moon is really the only place they can go.

For Lunar missions, either Apollo-style (LOR) or using an EML gateway and a reusable lander, Orion is perfectly adequate. Dragon isn't, and it needs a lot of extra hardware in order to acquire the same capability.

For ARM missions, the EVA capability is a baseline requirement because there is no extra mission module. But I know this is a circular argument, because with Orion there is no purpose for the ARM mission.

For Mars missions, all Dragon can do is get the crew to a larger MTV and back, and I agree that is all that is needed. It doesn't even need to go all the way to Mars if you include the dV for EOI on return. However, carrying that dV all the way to Mars and back is likely going to be heavier than carrying a crew capsule all the way to Mars and back. But I agree that you don't need an Orion for Mars.

Edited June 3, 2015 by Nibb31

[Kryten]

NEO is more practical than the moon at this point. Given current experience in the industry, habitats are going to be easier than landers.

[Kibble]

it was downgraded from the original proposal to only handle LEO missions and have insufficient dV for a lunar return... Oh wait, it did. Well, same function as Dragon's internal propellant then, and you save a staging event.

This is wrong. ESM was designed to be, and is still capable of, putting Orion on TEI from the Moon. You also don't save a staging event anyway, Dragon is not designed to launch without the trunk!

Orion can't go to the Mun either on its own, because every capsule needs a transfer stage to move around. But it helps the transfer stage if your capsule is lighter. And before you invoke the EDS stage Orion is supposed to always launch with, have in mind I could also invoke a restartable upper stage like Falcon's, on top of a booster that can do a direct shot to Luna like FH.

ICPS is also restartable. In fact, Falcon 9 upper stage is only rated for two restarts with its chemical ignition system, while RL10 can restart any time as long as the tanks are pressurized. Orion on System Block I can orbit the Moon and come back.

Orion's heatshield has never been tested on a relevant reentry either, and Dragon's heatshield has had quite a few orbital test to figure out ablation rate

You are way underestimating the importance of L/D ratio during Lunar return. Without that capability, a capsule can easily miss its reentry corridor, and the astronauts will die.

But you don't need those! Those are exactly the functions the transfer stage and habitat should perform.

That entirely depends on what mission architecture you use. Which mission architecture is "best" is an opinion.

In fact, I don't think you get the point I am trying to make generally. You don't want a heavy and over-capable cismunar-capable capsule to perform BEO flights. You want a light one, that can handle the return and stay dormant while the rest of the hardware does its BEO thing and is as light as it is feasible.

You don't want a BLEO-capable capsule for BLEO flights? Tell that to the only ever flown piloted BLEO missions in human history, Apollo! Or to the next-closest to flown BLEO capsule, Soyuz 7K-LOK, which massed 10 Mg. And even then, Blok-D was used for LOI. Falcon 9 second stage can't do LOI.

[Rune]

Orion was designed to go to the Moon, and that is all it is ever going to do. Anybody who seriously thinks that NASA is going to Mars in the next 30 years is delusional at this point. There is no habitat or MTV or Mars lander and there is no funding to build them. SLS and Orion are all we're getting, so they are going to have to include the exploration mission life-support and operational capabilities if we want to ever leave LEO.

NASA was banned from mentioning the Moon in its PR because the current administration cancelled Constellation, which is why they are desperately talking about using Orion for hypothetical and unfunded Mars and asteroid missions. After the next US election, things are going to change, because whether they like it or not, they are going to have find a use for SLS-Orion and the Moon is really the only place they can go.

For Lunar missions, either Apollo-style (LOR) or using an EML gateway and a reusable lander, Orion is perfectly adequate. Dragon isn't, and it needs a lot of extra hardware in order to acquire the same capability.

For ARM missions, the EVA capability is a baseline requirement because there is no extra mission module. But I know this is a circular argument, because with Orion there is no purpose for the ARM mission.

For Mars missions, all Dragon can do is get the crew to a larger MTV and back, and I agree that is all that is needed. It doesn't even need to go all the way to Mars if you include the dV for EOI on return. However, carrying that dV all the way to Mars and back is likely going to be heavier than carrying a crew capsule all the way to Mars and back. But I agree that you don't need an Orion for Mars.

So, stated as such, we are in complete agreement. Now if NASA could get themselves a reasonable, sustainable mandate with adequately funding, and the freedom to spec their own ships... a man can dream, right?

I would only add, that for lunar missions, the stage that got you into LOI can perfectly well be designed to take you back, you are not pushing chemical mass ratios that much (around 5km/s from LEO departure orbit). Thus, you could use the same simple capsule as you would anywhere else, from LEO taxi service to hypothetical Jovian missions on hypothetical nuclear-powered Battlestars.

This is wrong. ESM was designed to be, and is still capable of, putting Orion on TEI from the Moon. You also don't save a staging event anyway, Dragon is not designed to launch without the trunk!

I stand corrected, I thought the ATV-derived service modules had considerable less dV than the original LockMart design, mostly because the lunar missions had been dropped with Constellation (damn it,! I always start writing "munar" first nowadays... KSP much?). Then again, I hadn't thought about ARM, that also need some dV to get back, even if a distant lunar retrograde orbit is much closer to Earth than LLO.

ICPS is also restartable. In fact, Falcon 9 upper stage is only rated for two restarts with its chemical ignition system, while RL10 can restart any time as long as the tanks are pressurized. Orion on System Block I can orbit the Moon and come back.

Yup, both capsules require a in-space transfer stage. I reckon if used right, it could save the capsule having to carry any propellant other than for minor maneuvering and docking. I also reckon with the money spent on Orion, we could build a decent full-size EDS with a few nice extras like loiter, docking and stacking capability, instead of relying on ancient Centaur-derived stages that underutilize the planned-to-be biggest booster in history. Redirecting money from Orion into Boeing's ACES and its derived propellant depots, for example, would be a step in the right direction.

You are way underestimating the importance of L/D ratio during Lunar return. Without that capability, a capsule can easily miss its reentry corridor, and the astronauts will die.

Dragon's overall shape is based on that of Soyuz, and Soyuz's shape was dictated by a lunar return from the earliest design stage. The concept you are looking for, ballistic coefficient, has to do with density, not shape.

That entirely depends on what mission architecture you use. Which mission architecture is "best" is an opinion.

Lunar-designed architecture is pretty specific, yes. Much of the architecture for other places would be more universal and reusable, such as transfer habitats and transfer stages. Speaking very roughly, the only destination-specific hardware is the lander and the surface equipment, which are the only things a lunar mission requires, other than the launchers. This is my biggest jab at luna as a proving ground, it teaches you nothing about long-duration interplanetary flight (and thus, it doesn't force you to develop anything for it).

You don't want a BLEO-capable capsule for BLEO flights? Tell that to the only ever flown piloted BLEO missions in human history, Apollo! Or to the next-closest to flown BLEO capsule, Soyuz 7K-LOK, which massed 10 Mg. And even then, Blok-D was used for LOI. Falcon 9 second stage can't do LOI.

I argue for wasting the least amount of mass in bringing the crew up and down Earth's atmosphere. The simplest a return capsule can be, the more mass can be spent on stuff actually useful during the trip. Also, price tag. Plus the sheer lack of necessity, two other similar capsules are already funded (and considering time remaining to first crewed flight, further along their development path) in the US.

Rune. What is a capsule for, after all?

[Zucal]

Basic tests in the lab on rigs under applicable conditions, among other things. That was known ever since SpaceX developed PICA X, mostly by the NASA techs that compared it with the stuff they had on hand, like the older PICA and AvCoat. But if you want to grasp at operational use straws, Orion's heatshield has never been tested on a relevant reentry either, and Dragon's heatshield has had quite a few orbital test to figure out ablation rate. Bottom line? PICA X comes out on top for mass/protection with respect to AvCoat. Which is reasonable, since the latter was formulated on the sixties, and the former was specifically designed as an improvement.

I agree with some of your other points, but with this one..

There are so many factors in consideration with a BEO reentry. Orion's current heat shield cannot yet handle a lunar or Mars return, but that's a comparatively simple matter of swapping out the heat shield. The size, shape, lifting capacity, temperature, etc. all contribute, and saying "PICA-X is better" does not a safe reentry make.

[Rune]

I agree with some of your other points, but with this one..

There are so many factors in consideration with a BEO reentry. Orion's current heat shield cannot yet handle a lunar or Mars return, but that's a comparatively simple matter of swapping out the heat shield. The size, shape, lifting capacity, temperature, etc. all contribute, and saying "PICA-X is better" does not a safe reentry make.

If you compare two heatshields made to withstand a given reentry, the one made with PICA-X comes out lighter. That's basically why the original PICA was made, and SpaceX improved on it on the -X at the same time they got over the patent issue. Is that not enough of a metric to say that PICA-X is the better heatshield material? That's what I said:

Bottom line? PICA X comes out on top for mass/protection with respect to AvCoat.

Now why Orion was chosen to use the same identical material as Apollo, when a NASA-approved alternative was already there, still baffles me. Like the basic capsule shape, I assume it's for propaganda reasons, because it makes no engineering sense.

Rune. And to think Lockheed's original CEV Orion CEV Orion proposal actually made sense... it looked like a modern, more capable Soyuz.

Edited June 3, 2015 by Rune

[xenomorph555]

My view is like many have said; different purposes means they cannot be thrown into the "x vs y" competition, and besides neither has flown manned, Dragon-1 might end in a tragic accident that tarnish's everyone's view on.

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Like the basic capsule shape, I assume it's for propaganda reasons, because it makes no engineering sense.

Are you claiming that the Apollo/flat style capsule makes no sense?

[Rune]

Are you claiming that the Apollo/flat style capsule makes no sense?

I'm claiming "lightbulbs", like the Soyuz or the Dragon, are more mass/volume efficient. Same internal volume, less structural mass. That is known since the Soyuz, and it's not really me saying it. Cones make a (very slightly) gentler reentry, mostly on ballistic trayectories. Lifting bodies continue the trend towards more mass per unit of volume and gentler reentries, only they sit in a much "liftier" spot, conics/biconics are barely any different. Surely nothing you haven't heard of in the typical Apollo/Soyuz comparison?

My view is like many have said; different purposes means they cannot be thrown into the "x vs y" competition, and besides neither has flown manned, Dragon-1 might end in a tragic accident that tarnish's everyone's view on.

If Dragon crashes and kills everyone inside in the most public and spectacular fashion, it will still be a sound design. The blame then would fall squarely on the engineering implementation of said design, you can always muck that up.

Rune. Considering the recent experience in new spaceship construction of the respective engineering teams, it would surprise me a lot. But it could happen.

Edited June 3, 2015 by Rune

[xenomorph555]

Rune. Considering the recent experience in new spaceship construction of the respective engineering teams, it would surprise me a lot. But it could happen.

Yes, then again I wasn't expecting the SS2 accident last year, although that was a pilot failure, not the ship itself.

[Zucal]

If you compare two heatshields made to withstand a given reentry, the one made with PICA-X comes out lighter. That's basically why the original PICA was made, and SpaceX improved on it on the -X at the same time they got over the patent issue. Is that not enough of a metric to say that PICA-X is the better heatshield material? That's what I said:

I'm not disagreeing with you there. As a standalone, PICA-X has better heat flux resistance than AV-COAT, Orion's heat shield material. However, what I'm saying is that you can't say Dragon 2 is BEO-reentry ready just because its heatshield is.

Now why Orion was chosen to use the same identical material as Apollo, when a NASA-approved alternative was already there, still baffles me. Like the basic capsule shape, I assume it's for propaganda reasons, because it makes no engineering sense.

Orion has the same shape as Apollo because they were both designed for extremely similar missions, and similar reentry profiles. There's only so many shapes a capsule can be, and even fewer for the higher reentry velocities you're talking about. It's not propaganda. As for the heat shield, AV-COAT was chosen over PICA because PICA is brittle and needs to be put on in tiles, complicating the application process and increasing the risk, as you either need to apply it damn carefully or use a filler. AV-COAT can be applied in a single sheet, so it was chosen because although slightly less capable, it was less complex and safer.

[Rune]

I'm not disagreeing with you there. As a standalone, PICA-X has better heat flux resistance than AV-COAT, Orion's heat shield material. However, what I'm saying is that you can't say Dragon 2 is BEO-reentry ready just because its heatshield is.

Orion has the same shape as Apollo because they were both designed for extremely similar missions, and similar reentry profiles. There's only so many shapes a capsule can be, and even fewer for the higher reentry velocities you're talking about. It's not propaganda. As for the heat shield, AV-COAT was chosen over PICA because PICA is brittle and needs to be put on in tiles, complicating the application process and increasing the risk, as you either need to apply it damn carefully or use a filler. AV-COAT can be applied in a single sheet, so it was chosen because although slightly less capable, it was less complex and safer.

I just did a comment on Orion's shape. Let's all remember the good old Zond, it's uncontrolled reentries and the controlled, atmosphere-hopping level of precision that put it on par with Apollo when the Soviets got their guidance right. The cone was just easier to work out aerodynamically, and the Americans had the booster to be lazy in some design points. I mean, look at the size of the SM's engine. The whole Saturn design is a bit rushed and kludged together, with some items incredibly optimized, yet others were just what was available at the time.

As for today's reason for using AvCoat, if I had to be slightly malevolent, I'd say the engineers that apply it by hand burning countless man-hours get nice paychecks, and 10% on top as company profit. On the other hand SpaceX, with it's machine-built* PICA-X heatshields, offers the cheapest ride to orbit. I just don't buy the official explanation, with Dragon standing next to it and Elon publicly commenting how their designed-for-lunar-reentries heatshield is getting less erosion than they expected and reusing it seems likelier than ever.

Though probably the real reason is managerial fear of the new. That one is SO like NASA these days, ignoring the technology developed by themselves in their quest to revive their good old days with the least risk possible.

*(not totally sure about that, but certainly not that labour-intensive because they just don't have the people)

Rune. That is even sadder, at least the malevolent reason is ballsy.