SpaceX to reveal their manned DragonV2 capsule tonight

[magnemoe]

It's also using the wrong engines, because single stage to lunar orbit won't work with under 675 Isp. And that's with a fuel/mass fraction of almost 1, i.e. you don't get any payload whatsoever. It's also without doing anything else after arriving in lunar orbit - if you wanted the dV to land or return to Earth (or both), and still do it in a single stage, you'd need even more Isp; probably at least 900 for a land and return. And if you wanted some room for payload, you'd probably want to make it at least 1200. And, of course, all that from an engine that has enough sea level thrust to launch this gigantic mountain of fuel out of earth's atmosphere at terminal velocity.

Frankly, short of a gas-core nuclear lightbulb, I don't think mankind has the technology to pull something like that off And even that idea is a pure on-paper, speculative design concept, so it appears we won't be walking in sir Clarke's footsteps for a while yet. Single stage concepts sadly are brutally unforgiving in our "full size" solar system.

In case anyone's wondering, by the way, the SuperDracos have been quoted at 235 sea level Isp (they're hypergolic engines). Dunno about vacuum Isp, but I would be very interested if someone could find a source on that.

Question, does this kill off the idea of mining water and crack into H2/ O2 on moon, or at least make it far harder? Remember you need return without any payload. Still it looks like you at least need to use something like an nerva transfer stage from leo to moon orbit and a seperate lander.

[Exoscientist]

It's also using the wrong engines, because single stage to lunar orbit won't work with under 675 Isp. And that's with a fuel/mass fraction of almost 1, i.e. you don't get any payload whatsoever. It's also without doing anything else after arriving in lunar orbit - if you wanted the dV to land or return to Earth (or both), and still do it in a single stage, you'd need even more Isp; probably at least 900 for a land and return. And if you wanted some room for payload, you'd probably want to make it at least 1200. And, of course, all that from an engine that has enough sea level thrust to launch this gigantic mountain of fuel out of earth's atmosphere at terminal velocity.

Frankly, short of a gas-core nuclear lightbulb, I don't think mankind has the technology to pull something like that off And even that idea is a pure on-paper, speculative design concept, so it appears we won't be walking in sir Clarke's footsteps for a while yet. Single stage concepts sadly are brutally unforgiving in our "full size" solar system.

In case anyone's wondering, by the way, the SuperDracos have been quoted at 235 sea level Isp (they're hypergolic engines). Dunno about vacuum Isp, but I would be very interested if someone could find a source on that.

Clarke's idea was for a lunar SSTO. The delta-v to lunar orbit is less than 2,000 m/s, compared to over 9,000 m/s for the Earth. So it's long been known you can do a SSTO for a lunar lander, meaning actually the landing and take-off by that one single stage.

Bob Clark

[RuBisCO]

Question: are the SuperDraco even used for anything other than emergency separation and landings? Considering how small their nozzle is that engine was likely designed for insane thrust with no concern for ISP or extended operation. The SuperDraco has ~160% the thrust of the Lunar Lander Descent Engine, which operated on almost the same fuel yet was bigger than a person and had an ISP of 311.

Look there is no other way around it with conventional nozzles you have to go big in order to get high ISPs. And thus the superdracos as they presently are, make for poor lunar landing system. Stopping and landing a spacecraft falling at 80-120 m/s in a say 10 seconds flat is going to require just a few hundred m/s of deltaV, small enough to warrant not worrying about low ISP, but a lunar landing is going to need 1.7-2 km/s. A much larger nozzle will be needed to increase ISP. It would though make a fine Mars landing system.

Edited June 2, 2014 by RuBisCO

[Reddragon]

Superdraco is a methane engine. APS wasn't. I'm not sure but since it's going to be restartable, perhaps it could be used for more dramatic orbital maneuvers. Depends on the delta V though.

[RuBisCO]

Superdraco is a methane engine. APS wasn't. I'm not sure but since it's going to be restartable, perhaps it could be used for more dramatic orbital maneuvers. Depends on the delta V though.

It runs on methane? Citation please.

[Ayo99]

I wish I had money... but I don't

[Streetwind]

Question, does this kill off the idea of mining water and crack into H2/ O2 on moon, or at least make it far harder? Remember you need return without any payload. Still it looks like you at least need to use something like an nerva transfer stage from leo to moon orbit and a seperate lander.

Nah, that doesn't really matter. I mean, mining the stuff from near Earth asteroids is almost always going to be more economical in terms of access dV, but on the Moon you can have bigger mines (economies of scale are a thing).

More than half the dV required to take a ship from Earth surface to Moon surface and back to Earth surface is actually just the launch into LEO. If you have a space tug that merely moves stuff from the Moon to LEO, without having to launch out of that deep gravity well, then you're going to have a significantly easier time. Also keep in mind that the numbers given were for a single stage - if you allow for multiple stages, then you drastically reduce the effort it takes to get a high dV. And multiple stages don't mean no reusability. For example, having a dedicated lifter for Moon surface to Moon orbit and then a dedicated space tug for Moon orbit to Earth orbit is a two-stage system, and both stages are independent and fully reusable (assuming there's a fuel depot in at least one of the orbits for the tug to refuel at).

Clarke's idea was for a lunar SSTO. The delta-v to lunar orbit is less than 2,000 m/s, compared to over 9,000 m/s for the Earth. So it's long been known you can do a SSTO for a lunar lander, meaning actually the landing and take-off by that one single stage.

Bob Clark

You're late to the party - read what I wrote two posts above yours

Question: are the SuperDraco even used for anything other than emergency separation and landings? Considering how small their nozzle is that engine was likely designed for insane thrust with no concern for ISP or extended operation. The SuperDraco has ~160% the thrust of the Lunar Lander Descent Engine, which operated on almost the same fuel yet was bigger than a person and had an ISP of 311.

*snip*

Look there is no other way around it with conventional nozzles you have to go big in order to get high ISPs. And thus the superdracos as they presently are, make for poor lunar landing system. Stopping and landing a spacecraft falling at 80-120 m/s in a say 10 seconds flat is going to require just a few hundred m/s of deltaV, small enough to warrant not worrying about low ISP, but a lunar landing is going to need 1.7-2 km/s. A much larger nozzle will be needed to increase ISP. It would though make a fine Mars landing system.

It'll be used for orbital maneuvers such as the deorbit burn, or required adjustments after a suboptimal insertion.

The DragonV2 is a LEO taxi, it is not built to land on the Moon. If it was, it would have different engines (also see three posts above yours) and far, far more fuel.

Don't discount the SuperDracos right away though, they have 235 sea level Isp. Even without a vacuum nozzle, that's only going to go up in space, probably over 260. That's not that far away from the LM descent engine. It's closer than you think despite the lack of a nozzle due to modern alloys and manufacturing processes; the SuperDracons can run higher chamber pressures and temperatures, and have a more precisely controlled fuel and combustion flow, which increases efficiency.

Superdraco is a methane engine.

No it's not. It's a MMH/N2O4 hypergolic maneuvering thruster on steroids. In fact, it's quite similar to the space shuttle's OMS engine. Three times the thrust and no nozzle skirt, but same fuel mix and general purpose.

SpaceX's upcoming CH4/LOX engine is called Raptor, is projected at 363 vacuum Isp, and probably almost 8 times the thrust of the entire DragonV2 capsule.

Edited June 2, 2014 by Streetwind

[R0cketC0der]

Superdraco is a methane engine. APS wasn't. I'm not sure but since it's going to be restartable, perhaps it could be used for more dramatic orbital maneuvers. Depends on the delta V though.

Ummm... No? The Draco engine family(both the normal ones and superdracos) runs on MMH/N2O4.

[RuBisCO]

Well I'm sure the chamber pressure is fatastically higher than the old LM engine but without that huge nozzle it's not going to get the efficency needed to high delta-V operation: chamber pressure can only go so far, you can try that on a ISP caculator if you doubt me. De-orbit burns and small orbital corrections are not going to require more then a few hundred m/s, if not even a few dozen m/s, but the dracos can and do do that, and might I say comfortably. Just two superdracos firing would be over a G of impluse, and likely can't fired less then 4 at a time in order to be have thrust centered correctly, so that is over 2 Gs of impluse. Its going to take just a few seconds to do a de-orbit burn. 8 Dracos is going to be 2% of a G, with higher ISP and no 15% off-center, with a several minute de-orbit burn. If they focus on only landing for the SuperDracos they can use an atmosphere adjusted nozzle (if they are not already) for the superdraco and us the dracos for all orbital operations.

Edited June 2, 2014 by RuBisCO

[CaptRobau]

Could anyone explain why the trunk of the first version Dragon spacecraft, the one already flying, is slightly rotated. The LazTek version has it, as do real photos. Why isn't it perfectly symmetrical?

[Nibb31]

Could anyone explain why the trunk of the first version Dragon spacecraft, the one already flying, is slightly rotated. The LazTek version has it, as do real photos. Why isn't it perfectly symmetrical?

I know that the rotated trunk interferes with some people's OCD (including me), but when you think about it, it's basically a quite clever cost saving measure:

In arrangement a (Dragon V1), both left and right panels are the same. All panel segments are identical. The panel is thinner and has less moving parts.

In the arrangement b (which is similar to Soyuz), you have a left and right panel. Because the axis goes through the middle of the folded panel, the first segment has to be half size, which means that you have to source 2 different types of panels, which means twice the inventory, sourcing, higher manufacturing costs, etc. The arrangement also requires more hinges, including left and right side hinges, which increases the weight, the thickness of the folded panel, and the number of moving parts. More moving parts equals lower reliability.

Apparently Dragon V2 will have an even cheaper and simpler trunk with no folding/rotating panels. They probably figured that plastering the trunk with flexible panels (even if half of them are only used at a time) is lighter and cheaper and more reliable than maintaining the folding/rotating mechanism and covers.

Edited June 3, 2014 by Nibb31

[astropapi1]

It's a quite clever cost saving measure.

... How does it save money?

[Nibb31]

Sorry, I hadn't finished my crappy sketch when I hit reply. Edited.

Edited June 3, 2014 by Nibb31

[magnemoe]

I know that the rotated trunk interferes with some people's OCD (including me), but when you think about it, it's basically a quite clever cost saving measure:

http://i59.tinypic.com/2uhuxzr.png

In arrangement a (Dragon V1), both left and right panels are the same. All panel segments are identical. The panel is thinner and has less moving parts.

In the arrangement b (which is similar to Soyuz), you have a left and right panel. Because the axis goes through the middle of the folded panel, the first segment has to be half size, which means that you have to source 2 different types of panels, which means twice the inventory, sourcing, higher manufacturing costs, etc. The arrangement also requires more hinges, including left and right side hinges, which increases the weight, the thickness of the folded panel, and the number of moving parts. More moving parts equals lower reliability.

Apparently Dragon V2 will have an even cheaper and simpler trunk with no folding/rotating panels. They probably figured that plastering the trunk with flexible panels (even if half of them are only used at a time) is lighter and cheaper and more reliable than maintaining the folding/rotating mechanism and covers.

They probably found that the power use was so small they did not need so much solar cells.

Wonder if they will use dragon 2 for cargo too? however they might want to wear out the existing dragon 1 first.

[Nibb31]

Wear out? They are not reusing the Dragon V1s yet. I don't know if they will reuse them at this point.

As you can see, they are in a sorry state (and Dragon V2 will look like this after landing too). They have been dunked in seawater, scorched, parachutes blown, and would need complete refurbishing. It is probably still cheaper to build new ones until they have built up confidence with the reusability.

They will probably keep flying Dragon V1s for cargo, because they are the only vehicle at this point that can bring up and bring down ISPR racks, which is the main way of sending up new science experiments. ISPRs can only fit through CBM ports, so Dragon V2 cannot carry them.

To make a cargo version of Dragon V2, they would need to fit a CBM, but that would require a whole different nose arrangement.

Edited June 3, 2014 by Nibb31

[sojourner]

Elon stated that they would build both v1 Cargo and v2 crew for at least a few years.

[karolus10]

I guess that cargo version of dragon 2.0 (even with CBM) will be a good option as well if you can accept loosing the capsule on the way back, you can push harder with sending and landing one cargo capsule multiple times as you don't risk killing people during EDL.

Same convention may later occur with launch pricing of reused falcon IX rocket, as multiple reused stages may be cheaper to rent for exchange that something can more likely (slight change, but still it has less liability in comparison to brand new rocket) go wrong.

Edited June 3, 2014 by karolus10

[Nibb31]

I guess that cargo version of dragon 2.0 (even with CBM) will be a good option as well if you can accept loosing the capsule on the way back, you can push harder with sending and landing one cargo capsule multiple times as you don't risk killing people during EDL.

Crewed Dragon V2 will be flying before there is a cargo Dragon V2, so by that time, Dragon V2 should be quite robust.

[CaptainKipard]

I was impressed by the veil removal system.

[PlonioFludrasco]

An opinion from Russia, in an article I've just found:

http://www.popularmechanics.com/science/space/rockets/the-russian-ancestors-of-spacexs-new-dragon-16859356?click=pm_news

[Streetwind]

Interesting. I was aware of the ongoing development of the Russian next-gen manned capsule, but I was not aware how it looked or how far along it was.

[CaptainKipard]

An opinion from Russia, in an article I've just found:

http://www.popularmechanics.com/science/space/rockets/the-russian-ancestors-of-spacexs-new-dragon-16859356?click=pm_news

Capitalists have the best PR I guess. <- You can read that however you like.

[The Silent Majority]

Dunked in seawater

I was under the impression that they would not be dunked in seawater, all the other things apply though.

Does the V2 use parachutes?

EDIT: found it, the V2 has a backup system parachute system.

So the parachute will probably also not be blown out.

Also, according to Wikipedia, they will be not refurbished until after being flown again multiple times.

Edited June 6, 2014 by The Silent Majority

[Nibb31]

I was under the impression that they would not be dunked in seawater, all the other things apply though.

Does the V2 use parachutes?

The V1 landed with parachutes + splashdown. The V2 lands in the same way in launch abort mode.

The parachute lines rip open the skin of the capsule, so if they deploy the parachutes for launch abort or landing abort, then the capsule goes straight into refurbishment (depending on how well it survived the hard landing or splashdown).

[shynung]

The V1 landed with parachutes + splashdown. The V2 lands in the same way in launch abort mode.

The parachute lines rip open the skin of the capsule, so if they deploy the parachutes for launch abort or landing abort, then the capsule goes straight into refurbishment (depending on how well it survived the hard landing or splashdown).

Makes sense. Aborts are only done when something doesn't work right, in which all involved vehicles would go into refurbishment anyway.

Edited June 6, 2014 by shynung