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Missions To Mars (HSF) / Re: Scaling Agriculture on Mars
« Last post by Vultur on Today at 04:31 AM »
Well, if you use a crater, that then reminds me of what I said before - can you fill it with some heavy gas that won't easily dissipate? There's been plenty of discussion about sulfur hexafluoride (SF6) as a breathing gas for humans which is heavy enough that it could be used to fill up craters, etc.  But if you're talking about a heavy gas that's meant to be tolerable to plants, then maybe you've got more choice on what kind of gas you can use?

Does anybody know of any candidates? How about some heavy hydrocarbon gas?

There are just not many very heavy gases. Heavy hydrocarbons aren't gases (unless there is some weird exception); boiling points increase as you add carbon atoms. Butane and butene are gases at room temperature, pentane and pentene have boiling points a little above room temperature, above that it's not even close.

Sulfur hexafluoride is probably about as good a candidate as you'll find. Xenon is a very rare element and has more intense narcotic/anesthetic properties than SF6. (Most gases have this to some degree, but with e.g. nitrogen it only becomes a problem at well above atmospheric partial pressure - the nitrogen narcosis or 'rapture of the deep' experienced by divers - while xenon has actually been used as an anesthetic. According to this source (http://www.ncbi.nlm.nih.gov/pubmed/8175542) SF6 is 8.5x as narcotic as nitrogen, while xenon seems to be 25.6x as narcotic (http://www.biomed.cas.cz/physiolres/pdf/56%20Suppl%201/56_S39.pdf).

Selenium, tellurium, and tungsten hexafluoride are totally unsafe (toxic/extremely corrosive).


What about in comparatively low-altitude depressions like Hellas Basin, where triple-point of water is believed to be possible?

It definitely does occur (though briefly); Curiosity weather data show pressures consistently above the triple point of water, and daily high temperatures sometimes rise above the triple point (Sol 737, the most recent on the http://marsweather.com/data site, shows 3 C high, -74 C low, 777 Pa pressure) And the ground temperature in the sun around noon/early afternoon should be higher than the air temperature.

However, the partial pressure of water vapor in the atmosphere is near zero, so even during these brief
times liquid water would evaporate, though not boil.

The best hope of "Mars-adapted" higher plants I think would be using thermogenic cells (like skunk cabbage uses to melt snow in spring) in the roots to melt subsurface ice where the pressure of the soil/regolith would keep it from evaporating as quickly. But this would not provide that much water (thus slow growth) and would require very advanced genetic engineering.

Quote
Just looking at the general shape/structure of cactus plants, their typical globe shape seems to suit the pressure hull idea

Since plants must exchange gas with the atmosphere to get CO2 (and excrete O2) I don't think the pressure hull idea is very workable. They would have to somehow pump CO2 in through the stomata against a pressure gradient.
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Commercial Crew Vehicles / Re: Flying Crew on a Cargo Dragon
« Last post by QuantumG on Today at 04:29 AM »
You have it completely backwards. The money from NASA is their bread and butter. The commercial market is the gravy.
There has been a lot of NASA money, which has given them a huge boost, but it's also a very limited and a very political market, and the money comes with a lot of hoops to jump through.

It was great for SpaceX to get the Dragon money from NASA, which they used to develop Falcon 9, but as you point out, doing it with NASA meant they couldn't do it the way they wanted, which is half the reason they're doing Dragon V2.
[/quote]

Again, you have it completely backwards. Dragon v2 is being developed because they can't do it their way. Dragon v2 will be the result of the ongoing negotiation with NASA to meet their ever-changing requirements.

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Commercial Crew Vehicles / Re: Flying Crew on a Cargo Dragon
« Last post by Nindalf on Today at 04:25 AM »
Falcon launch rates are insufficient for SpaceX's backlog, never mind a new regular service.  They've been constrained by their launch capabilities, and not payload availability, for years.

They have a backlog because NASA gets priority.
Well, that sure explains their backlog of resupply Dragon launches...

Quote from: Nindalf
As for the funding, I don't think it matters all that much.  The Commercial Crew money is gravy for SpaceX, not make or break.  I figure they're already pretty much paid up for developing Dragon V2, and they're doing well in the commercial market, as long as they can clear their backlog.

You have it completely backwards. The money from NASA is their bread and butter. The commercial market is the gravy.
There has been a lot of NASA money, which has given them a huge boost, but it's also a very limited and a very political market, and the money comes with a lot of hoops to jump through.

It was great for SpaceX to get the Dragon money from NASA, which they used to develop Falcon 9, but as you point out, doing it with NASA meant they couldn't do it the way they wanted, which is half the reason they're doing Dragon V2.

Now they're doing well on commercial contracts, which is straightforward business with people who don't want to look over their shoulders and tell them how to design their vehicles.  If the Commercial Crew money doesn't come through, they're going to go right ahead with DragonFly and do their test flights when they get their reusability working, without ever bothering with this idea of building a new Dragon V2 for each mission and landing it with a parachute as their primary landing option.  Like the first couple of Falcon 1s failing, it's not going to matter much in the long run, as long as other things go well.

The crewed Dragon V1 would only have been an important option for routine operations if SpaceX got their Falcon launch rate up sooner, and didn't accumulate this backlog.  The Falcon 9 delays effectively gave them the time they needed to develop Dragon V2.

Quote from: Nindalf
When people say that the original Dragon couldn't carry crew, I'm drawn to argue with that on the technical merits, but I also think it's pretty much a moot point.

Then why are you commenting on this thread?
Do you often quote answers to questions you're asking?
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For example, the 500 km baseline gives you 30 pixels or about 425 km per pixel looking at an Earth sized planet at that distance. So you would need a baseline of about 210,000 km for 1 km per pixel and about 210,000,000 km (1.4 AU) to get down to 1 m. Place the mirrors in orbit between Earth and Mars. That simple calculation is better than just saying it's solar system sized.
Now how big do those mirrors need to be?

To get the same SNR, you will need roughly the same number of photons from each of those 1m pixels as the 425 km pixels get in the NASA concept, so you need the corresponding increase in collecting area. That's a factor of ~180 billion.

Yeah, that sounds about right. Spy satellite resolution at interstellar distances is way over the top. :)

You could make a good quality globe using about 40 km pixels or about 10 times the NASA concept. That would require 100 times the collecting area. Taking advantage of space construction, 6 100 meter telescopes should do it.

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From the update thread:
Ariane 62 configuration

The Ariane 62, with two P120 solid boosters, will be used mainly in single-launch configurations.

http://www.esa.int/spaceinimages/Images/2014/10/Ariane_62_configuration

Image credit: ESA

Hmmm... That launch vehicle (1st image) does look very familiar. A close cousin of the Japanese H-IIA? (second image)

- The Ariane 6 "62" configuration is a close match to the H-IIA.
- The Ariane 6 "64" (four solids) is a close match to the H-IIA 204 model (replaced by H-IIB).
Generally, but the Ariane 6 boosters would carry nearly twice as much propellant as the SRB-A boosters.  Also, H-2A uses a different diameter core than H-2B while Ariane 6 will use the same core for both "62" and "64".  Thanks to the more powerful boosters the "64" would only use one main core engine rather than the two engines used by H-2B.

 - Ed Kyle
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SpaceX General Section / Re: SpaceX Dragon V2 Updates and Discussion
« Last post by manboy on Today at 04:11 AM »
I don't remember where the reference is but I DO remember that both the crew and cargo versions of Dragon v2 WILL eventually have propulsive-only landing as the nominal landing mode. That is, of course, after all testing and certifications are completed. It is anticipated that the parachutes will be rarely, if ever, used. It was either Elon or Gwynne that said that, but I am leaning toward Gwynne. I remember it so well because I rewound the video to listen to it again - twice. Nominal landing for both crew and cargo operational spacecraft will be via propulsive landing.

I think that is still the plan and that is why most of the Dragonfly test flights will be without parachutes. But Reisman made it seem like full-propulsive landing was a "down the road" kind of improvement. I am guessing that means that SpaceX will not try to get full-propulsive landing certified for crew (at least not at first). 

Every video they have produced and shown on the Dragon returning shows full propulsive landing - no chutes.
That's incorrect. Here's a video showing propulsion landing with parachutes in July 2012.
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That's possible, but they presumably knew about the patent back in July when they made the statement about solid surface landings for #14 and #15. So what changed between July 22 and September when Hans made those comments?

The filing challenging the patent.

http://spaceref.biz/company/spacex/spacex-challenges-patent-filed-by-blue-origin.html
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For example, the 500 km baseline gives you 30 pixels or about 425 km per pixel looking at an Earth sized planet at that distance. So you would need a baseline of about 210,000 km for 1 km per pixel and about 210,000,000 km (1.4 AU) to get down to 1 m. Place the mirrors in orbit between Earth and Mars. That simple calculation is better than just saying it's solar system sized.
Now how big do those mirrors need to be?

To get the same SNR, you will need roughly the same number of photons from each of those 1m pixels as the 425 km pixels get in the NASA concept, so you need the corresponding increase in collecting area. That's a factor of ~180 billion.
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Hans says that the barge is only in "trade study" status and is a "possibility for the future" but is not going to be one of the next missions.
I'd guess they're hung up on the Blue Origin patent.

That's possible, but they presumably knew about the patent back in July when they made the statement about solid surface landings for #14 and #15. So what changed between July 22 and September when Hans made those comments?
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Hans says that the barge is only in "trade study" status and is a "possibility for the future" but is not going to be one of the next missions.
I'd guess they're hung up on the Blue Origin patent.

...which is not entirely a bad thing for them.  The patent gives them a good reason why they have to boost it back toward land, which is what they prefer to be doing anyway, without demonstrating a barge landing first, which is probably what the range and FAA would prefer.
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