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Red Dragon
Mongo
post Sep 17 2012, 05:17 PM
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That's the big question -- whether it would be more cost-effective to use a nearly stock Dragon, with its very low cost, to deliver a science cargo of several tonnes to the Martian surface, or to design a vessel specifically for Mars, which could deliver a substantially larger payload to Mars surface but at a much greater cost.

My guess is that a specially designed landing vehicle plus Falcon Heavy launcher could deliver maybe six tonnes of scientific payload to the Martian surface in a single package, but would cost as much as three separate two-tonne payload Red Dragon landers plus launchers.
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Kaputnik
post Sep 17 2012, 08:39 PM
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A 'nearly stock' Dragon would be aiming to deliver about 1t to the surface (not 'several tonnes'). The papers from AMES suggest an entry mass of about 7t, with 2t of that being the propellant burned in the last few seconds to reduce speed from Mach 2 to a soft landing. That leaves 5t to be landed, of which 4t is the capsule itself.
Now, that 4t figure for an empty Dragon equipped with landing gear and Super-Dracos is one that I find a little hard to digest. Bear in mind the far smaller Soyuz capsule, which has no large liquid fuelled engines or landing legs etc, is 3t. The Super Draco thrusters are going to have to pretty special indeed (i.e. have exceptionally high thrust:weight).
Not saying that this cannot work, obviously SpaceX and AMES think it can, but I think we should be aware of the margins that the system has.

Entry mass is proportional to the amount of drag that the vehicle can generate. A dedicated Mars lander would use the full 4.6m payload capacity of the FH, allowing, in theory, up to 60% greater entry mass than Red Dragon (i.e. over 11t). In addition, a dedicated platform could offer wider scope for different payloads, and could probably offer some mass savings by not carrying unnecessary hardware all the way to the surface.

I'm not saying that Red Dragon isn't a cool proposal- just I think some people are pinning too many hopes on it.
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Mongo
post Sep 17 2012, 09:30 PM
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Acording to SpaceX, the dry mass of a Dragon is 3,180 kg (albeit without landing structure).

The landed mass according to this proposal for Red Dragon EDL is stated as 5,180 kg

5,180 kg minus 3,180 kg is 2,000 kg

The "1,000 kg" figure being thrown about is a conservative estimate of landed payload, with a considerable safety margin. Depending on reentry trajectory and altitude of the surface, it can go higher (perhaps considerably higher, as seen in the above report).
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Kaputnik
post Sep 17 2012, 11:29 PM
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A 3180kg Dragon does not have, as far as I am aware, the Super-Draco engines included in that mass.

No data has been released on the mass of these engines. However, we do know that they will provide an a total axial thrust of 120,000lb; given that they are canted at an angle of at least 35 degrees, and probably more, the actual thrust produced must be in the region of 150,000lb or higher. A generous figure for thrust:weight ratio is about 50:1 (IMHO) which gives an engine mass of 1363kg, plus tank mass. The engine mass could easily be greater than this if they are canted at a steeper angle and/or if the T:W is lower. Admittedly the mass could be lower as well, but, again IMHO, not by much.

As you say, the landing gear and its deployment system also has to be accounted for.

If SpaceX have managed to squeeze the engines, tanks, and landing gear into a capsule the same weight as a Soyuz (which has none of those things), yet at the same time made it twice as big.... then I take my hat off to them!
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dtolman
post Sep 17 2015, 12:45 AM
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A few days ago Space.com posted a speculative article about a Mars sample return mission built off of the SpaceX Dragon 2 capsule, where it would rendezvous with the 2020 Mars Rover to pickup its return cargo. What makes it a bit more interesting, is that this does not appear to be a mission organized by the SpaceX corporation - instead the plan is from NASA's Ames Research Center as a feasibility study of a potential 2022 mission using cost reducing "off the shelf equipment" - with the added benefit of being simpler than other model missions they have considered.

To quote the relevant bits from the article:
In the Red Dragon study, the spacecraft would make a direct entry into the atmosphere of Mars. It would descend to the Red Planet's surface without a parachute system, using retro propulsion for a precision touchdown.

As currently envisioned, the sample-toting Red Dragon return vehicle would blast off the Martian surface (with the aid of the MAV) and head directly for Earth.

A study scenario sees a later mission, using a Dragon and launched by a Falcon Heavy, performing a rendezvous with the return vehicle in high Earth orbit. The mission would then retrieve the sample container and break the chain of contact with Mars by transferring the sample into a sterile and secure container.
...
Other recent Mars sample-return ideas would employ three Red Planet missions, requiring a lot of flight hardware and numerous interfaces.

EDIT: I meant to post this in the Past/Future forum - my apologies on the misplacement. - Merged with existing Red Dragon thread - Mod
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sittingduck
post Sep 18 2015, 09:38 AM
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I have a question concerning the CGI used to showcase Red Dragon. In this attached composite they used an image from Curiosity. I wanted to check whether or not they had scaled the Dragon correctly. Does anybody know what sol that image was made?
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eoincampbell
post Sep 18 2015, 03:33 PM
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Just beyond Dingo Gap sol 528


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'She drove until the wheels fell off...'
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sittingduck
post Sep 18 2015, 04:22 PM
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Thanks eoincampbell!

By my reckoning that places the craft ~93 meters away, and vertically spanning 6.5 in the NAVCAM image gives it a height of around 10.5 meters, quite a bit bigger than the actual height which is around 5 or 6 meters depending on source. Taking the largest value of 6.1 meters, this is how it would have really looked in that spot (attached).
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anticitizen2
post Jan 4 2016, 04:40 AM
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I am hearing that Red Dragon is more likely to get to mars than InSight, in 2018 or 2020. NASA is going to have the opportunity to 'instrument the hell out of it'. It is a fairly concrete effort within NASA, for something I've only heard rumors about before recently. Are we allowed to speculate or wish for a set of instruments? (Nobody say seismometer)

We probably won't have to wait more than a year to hear a lot more about the project, but I'm curious about what could be done.

I know sample return has been discussed, but on this timeline I think scientific instruments are more likely.
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stevesliva
post Jan 4 2016, 04:49 AM
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QUOTE (anticitizen2 @ Jan 4 2016, 12:40 AM) *
I am hearing that Red Dragon is more likely to get to mars than InSight, in 2018 or 2020. NASA is going to have the opportunity to 'instrument the hell out of it'.


As it stands now, it has to compete with Insight's sunk costs for that to happen.
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mcaplinger
post Jan 4 2016, 05:17 AM
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QUOTE (anticitizen2 @ Jan 3 2016, 08:40 PM) *
I am hearing that Red Dragon is more likely to get to mars than InSight, in 2018 or 2020.

Citation needed.


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Disclaimer: This post is based on public information only. Any opinions are my own.
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vjkane
post Jan 4 2016, 01:13 PM
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QUOTE (anticitizen2 @ Jan 3 2016, 08:40 PM) *
I am hearing that Red Dragon is more likely to get to mars than InSight, in 2018 or 2020. NASA is going to have the opportunity to 'instrument the hell out of it'. It is a fairly concrete effort within NASA, for something I've only heard rumors about before recently. Are we allowed to speculate or wish for a set of instruments? (Nobody say seismometer)

We probably won't have to wait more than a year to hear a lot more about the project, but I'm curious about what could be done.

I know sample return has been discussed, but on this timeline I think scientific instruments are more likely.

There's a lot of work needed to design and qualify systems that can reliably function for the months required for a Mars mission and then to ensure that the lander can function in the temperature extremes of Mars with just a few hours a day of good sun exposure.

To give a comparison, one of the engineers I correspond with tells me that the standard CubeSat deployment racks that work well in Earth orbit need to be redesigned to ensure reliability on a planetary mission where the deployment may occur months or years after launch. Think of every system on a Red Dragon mission, and every one needs to be rated and tested for a longer and environmentally more extreme mission than the Earth-orbiting Dragon spacecraft with a lifetime of days or weeks.

Red Dragon is an intriguing idea, but it's not something that that I think gets done quietly by some small team with some small budget. Space is hard.



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