Author Topic: A Dragon derived general purpose Mars lander?  (Read 55609 times)

Offline charliem

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Re: A Dragon derived general purpose Mars lander?
« Reply #120 on: 06/12/2012 10:39 pm »
To hear about the technical challenges still ahead for Dragon look from min 50:20 into the video.

Well Go4mars, all this talking by people with much better access to the real specs gives me hope, but let's try not to be too optimistic.

After all the main obstacle to reach Mars is not technology, but money ... :-\

Offline Robotbeat

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Re: A Dragon derived general purpose Mars lander?
« Reply #121 on: 06/12/2012 10:43 pm »
Technology is still a pretty big one, to be honest. Mars is really, really hard. Even if you throw a trillion dollars into it.
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Offline Robotbeat

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Re: A Dragon derived general purpose Mars lander?
« Reply #122 on: 06/12/2012 11:32 pm »
...
- The SuperDraco engines will start only 800 m from the surface, while the capsule is doing 2.24 km/s. Deceleration will reach 7 g.
...
Actually, that's Mach 2.24, NOT 2.24 km/s! Huge difference! Easy mistake, though. :)

Mach 2.24 is less than 1km/s.
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Offline charliem

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Re: A Dragon derived general purpose Mars lander?
« Reply #123 on: 06/12/2012 11:59 pm »
...
- The SuperDraco engines will start only 800 m from the surface, while the capsule is doing 2.24 km/s. Deceleration will reach 7 g.
...
Actually, that's Mach 2.24, NOT 2.24 km/s! Huge difference! Easy mistake, though. :)

Mach 2.24 is less than 1km/s.

Thanks Robotbeat, you're right. I'll edit it right away.

Online meekGee

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Re: A Dragon derived general purpose Mars lander?
« Reply #124 on: 06/13/2012 12:09 am »
When converting Mach 2.4 to km/s, are those local Mach numbers?

Regarding sticking the landing, while I think that's possible on Earth (saves propellant, reduces the influence of wind), it is less likely on Mars - the final terrain is not known and definitely not obstacle free, gravity losses are less, and wind influence is less.

But otherwise - Yeeeha!
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Offline jabe

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Re: A Dragon derived general purpose Mars lander?
« Reply #125 on: 06/13/2012 12:40 am »
the final terrain is not known and definitely not obstacle free,
curious,
define "not known"...MRO has pretty good resolution..Apollo had worse resolution maps then what we have for mars..
jb

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Re: A Dragon derived general purpose Mars lander?
« Reply #126 on: 06/13/2012 01:20 am »
the final terrain is not known and definitely not obstacle free,
curious,
define "not known"...MRO has pretty good resolution..Apollo had worse resolution maps then what we have for mars..
jb

If you're coming to land on a pad on Earth, it's flat concrete with a homing beacon.

With all of MRO's capabilities, it has a roughly 1 m resolution, enough to get a good understanding of 5 m ground features.  The laser altimeter is worse.


Sure, Apollo was worse, but we're not yet at the point where we can stick the landing without surveying the surface from the landing craft and reacting to the findings.

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Offline billh

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Re: A Dragon derived general purpose Mars lander?
« Reply #127 on: 06/13/2012 02:05 am »
The SuperDraco engines will start only 800 m from the surface, while the capsule is doing mach 2.24.

D***!

Offline Robotbeat

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Re: A Dragon derived general purpose Mars lander?
« Reply #128 on: 06/13/2012 02:18 am »
The SuperDraco engines will start only 800 m from the surface, while the capsule is doing mach 2.24.

D***!
You should watch the presentation. It's really not TOO bad. In the proposed flight profile that the second speaker presented, the Dragon would enter a "constant descent velocity" mode at ~40m above the surface and descend at 2.4m/s until landing, kind of like MSL. That means it's okay if the altimeter (or range-finder) is off by a couple dozen meters.
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Offline charliem

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Re: A Dragon derived general purpose Mars lander?
« Reply #129 on: 06/13/2012 02:36 am »
When converting Mach 2.4 to km/s, are those local Mach numbers?

I think so.

You can calculate the speed of sound from temperature and atmosphere composition. For the martian atmophere is: ss = sqr (247.42*T)   (T in ēK, ss in m/s).

At 3 km below MOLA the mean temperature is 245 ēK so the average speed of sound should be around 246 m/s (it swings quite a bit from day to night, summer to winter, and even with dust storms).

So the Dragon capsule has to start its SuperDraco engines at ~550 m/s, 800 m before crashing, and decelerate at 7 g ... what a ride!!

Offline Robotbeat

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Re: A Dragon derived general purpose Mars lander?
« Reply #130 on: 06/13/2012 02:39 am »
When converting Mach 2.4 to km/s, are those local Mach numbers?

I think so.

You can calculate the speed of sound from temperature and atmosphere composition. For the martian atmophere is: ss = sqr (247.42*T)   (T in ēK, ss in m/s).

At 3 km below MOLA the mean temperature is 245 ēK so the average speed of sound should be around 246 m/s (it swings quite a bit from day to night, summer to winter, and even with dust storms).

So the Dragon capsule has to start its SuperDraco engines at ~550 m/s, 800 m before crashing, and decelerate at 7 g ... what a ride!!

To be honest, I'd bet they mean Mach 1 = 343m/s.
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Offline charliem

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Re: A Dragon derived general purpose Mars lander?
« Reply #131 on: 06/13/2012 02:49 am »
For those who think that turning Dragoncrew in a general purpose mars lander is a wacky idea, I wonder what they'll think about this group of people presentation (the most "interesting" part is from min 17:00)?

http://www.livestream.com/marsconcepts2012_hep/video?clipId=pla_cd665151-0af9-4099-a2b4-d6ceee9e084c

Offline billh

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Re: A Dragon derived general purpose Mars lander?
« Reply #132 on: 06/13/2012 02:54 am »
Depending on which of you is right about what Mach 1 is on Mars, that means the engines start firing only 1 or 2 seconds before impact would occur! And the entire deceleration at 7gs would take place in 4 or 5 seconds. That's steely-eyed missile man stuff, for sure.

Offline charliem

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Re: A Dragon derived general purpose Mars lander?
« Reply #133 on: 06/13/2012 03:29 am »
So the Dragon capsule has to start its SuperDraco engines at ~550 m/s, 800 m before crashing, and decelerate at 7 g ... what a ride!!

Those numbers can't be right. I've rechecked them against the presentation and this time it's not my mistake.

In one of the slides we can read: "* Performs a direct transition to powered flight at Mach 2.24 800 m above ground utilizing SuperDraco thrusters".

That speed can't be vertical, because then a simple v=sqr(2.h.a) says that the minimum distance to brake from 550 m/s to zero at 7 gees is 2200 meters, so the only possibility that remains is a very very shallow descent.

???

Offline Downix

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Re: A Dragon derived general purpose Mars lander?
« Reply #134 on: 06/13/2012 04:18 am »
I don't know.  But just about every type of factory occasionally has surplus inventor to deal with.  Cars, toys, furniture...

It sounds like this is the production model for SpaceX, though I'm not saying I know for sure either way.

No, production is order based.

In modern facilities, correct.  But the production capacity is there.  So the incremental cost to make one more article for internal consumption is low, especially when flex-scheduled to a time when orders are low.
Boeing set up the Decatur factory for Delta IV to produce 48 Delta IV cores a year, so having such production capacity is nothing new.  The issue is lack of demand, which is what resulted in the ULA merger in the first place.
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Offline go4mars

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Re: A Dragon derived general purpose Mars lander?
« Reply #135 on: 06/13/2012 04:39 am »
Boeing set up the Decatur factory for Delta IV to produce 48 Delta IV cores a year, so having such production capacity is nothing new.
I wonder how things might have been different if Boeing had produced 48 cores for a few years instead (stockpiling the extras). 

I suggest that the production cost per rocket could have been lower, that it could have had a lot of commercial use, that lead-times to launch could have decreased, and that the long-term profit could have been higher. 

Just because Boeing did it a certain way (which made some sense in the context of their main target customer and from a quality perspective), doesn't mean it is the best or only way of doing things.
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Offline Robotbeat

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Re: A Dragon derived general purpose Mars lander?
« Reply #136 on: 06/13/2012 04:41 am »
So the Dragon capsule has to start its SuperDraco engines at ~550 m/s, 800 m before crashing, and decelerate at 7 g ... what a ride!!

Those numbers can't be right. I've rechecked them against the presentation and this time it's not my mistake.

In one of the slides we can read: "* Performs a direct transition to powered flight at Mach 2.24 800 m above ground utilizing SuperDraco thrusters".

That speed can't be vertical, because then a simple v=sqr(2.h.a) says that the minimum distance to brake from 550 m/s to zero at 7 gees is 2200 meters, so the only possibility that remains is a very very shallow descent.

???

+1, there's an inconsistency somewhere. Forgetting about gravity, that works out to be about a 70 degree angle.
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Online meekGee

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Re: A Dragon derived general purpose Mars lander?
« Reply #137 on: 06/13/2012 05:27 am »
Boeing set up the Decatur factory for Delta IV to produce 48 Delta IV cores a year, so having such production capacity is nothing new.  The issue is lack of demand, which is what resulted in the ULA merger in the first place.

So in this case, IF Boeing wanted to self-fund their own Mars mission, and IF Boeing was vertically integrated, then the cost to them would have been lower than the price of a launcher.

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Online MATTBLAK

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Re: A Dragon derived general purpose Mars lander?
« Reply #138 on: 06/13/2012 06:07 am »
They could do a Mars mission launch campaign from 'mass-produced' Delta IV-H if the funding and demand were there. Upgrading the D-4H to lift nearly 50 tons to orbit would be relatively simple (in Rocket Science terms) and 'relatively' cheap. With enough launchpads, D4-H's and Falcon Heavies could be launched in 'salvos' to assemble a mission each 26 month launch window.

Other challenges are the interplanetary Hab Modules - coming and going from Mars - and all their ancilliary needs including radiation protection, the Ascent Vehicle and surface systems including power, Crew Rover vehicles and scientific tools and equipment.

I'd love to see someone do a *New* detailed paper on a Mars mission architecture using available boosters - D4-H - and soon-to-be-available Falcon Heavy. Then, do a rational, credible design for all the other gear as mentioned above, do a sober cost analysis - which always gets laughs or starts arguments - then also build in 'Plan B' and 'Plan C' options...

So many Mars Mission designs have come before!! Some are mostly credible, others only partly so. Nothing seems to divide 'Space Cadets' (like me) more passionately than how to do a Mars mission. Start with a (relatively) clean sweep, crunch the numbers and come forward with a new, rebranded 'Man On Mars' mission design that has looked hard at the 40+plus years of studies done before and incorporates what has been learned. If it stands up well to the 'Giggle factor' and gets a two-thirds or more majority of positive opinion; then it will be a triumph.

Get people to Mars: Near Earth Asteroids are interesting but people and especially TV Hosts/comedians may confuse it with an old Bruce Willis movie and bore quickly. I'd love to see a (basic) Moonbase, but unless Mars is the ultimate goal, people will lose interest.

EDIT: Actually, this isn't a bad start - http://marssociety.org.au/sites/default/files/library/willson-et-al.pdf

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« Last Edit: 06/13/2012 06:18 am by MATTBLAK »
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Offline Lampyridae

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Re: A Dragon derived general purpose Mars lander?
« Reply #139 on: 06/13/2012 07:15 am »
- As we know Dragon needs to prove a number of its [yet] theoretical capabilities, but my personal impression about the Nasa personnel doing the presentations is that they are non as skeptical as some over here ... ;D

Interesting, so Dragon can manage a re-entry through a CO2 atmosphere? I wonder how cost effective it is compared to standard entry options such as MSL. Pity that it's limited to only 1mT, but it's a stepping stone to a large manned Mars lander.



EDIT: different image for MSL heatshield, original was way too big.
« Last Edit: 06/13/2012 07:16 am by Lampyridae »
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