Author Topic: Red Dragon Discussion Thread (2)  (Read 195598 times)

Offline Kaputnik

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Re: Red Dragon Discussion Thread (2)
« Reply #20 on: 03/10/2014 10:44 PM »
My knowledge of celestial mechanics is quite limited so I may be missing something, but I was expecting the dV of a F9H+Dragon to be able to rendezvous with a sample container on a fairly wide range of trajectories. Is that not the case? To be clear, I'm assuming you know the precise trajectory of the container months in advance, and have the dV to choose to meet up in many places along the way (not just HEO/LEO). If necessary you could launch early, use slingshots, and if necessary use them again afterwards and take your time making it back to Earth.

In an extreme case, you could send the return Dragon on a free return trajectory all the way to Mars and meet up with the container as it begins its' journey toward Earth. The Dragon would perform the mid course corrections. In fact, that scenario may allow the max conceivable return mass.

On a related note: one possible use of a large-mass sample return capability would be a full intact core from a drill.

You can have all the dV in the world, and you can still be in the wrong place/time.
The incoming sample capsule is going to have higher energy than an object in Earth orbit. Therefore, to rendezvous with it, your spacecraft must have escaped Earth orbit. It cannot be travelling in the same direction as the incoming craft- unless it leaves orbit, stops, and comes back. That is a crazy amount of dV. Maybe it would be possible via a Lagrange point.
Your second idea actually makes more sense. Probably a minimal extra cost to the return spacecraft to make it capable of the flyby mission.
« Last Edit: 03/10/2014 10:45 PM by Kaputnik »
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Offline Robotbeat

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Re: Red Dragon Discussion Thread (2)
« Reply #21 on: 03/11/2014 01:40 AM »
Well, in the paper itself it looks like the sample return rocket does a Earth orbit insertion burn, captured into an elliptical Earth orbit. Then, another Dragon capsule does a rendezvous to return the sample to Earth. If it were up to me, I'd just do a direct reentry to Earth like Stardust or whatever.
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Online Zed_Noir

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Re: Red Dragon Discussion Thread (2)
« Reply #22 on: 03/11/2014 02:51 AM »
Well, in the paper itself it looks like the sample return rocket does a Earth orbit insertion burn, captured into an elliptical Earth orbit. Then, another Dragon capsule does a rendezvous to return the sample to Earth. If it were up to me, I'd just do a direct reentry to Earth like Stardust or whatever.

Than you will not get much samples back if you have to include EDL element along with the tiny storage volume available with the EDL element.

Offline Robotbeat

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Re: Red Dragon Discussion Thread (2)
« Reply #23 on: 03/11/2014 02:54 AM »
Well, in the paper itself it looks like the sample return rocket does a Earth orbit insertion burn, captured into an elliptical Earth orbit. Then, another Dragon capsule does a rendezvous to return the sample to Earth. If it were up to me, I'd just do a direct reentry to Earth like Stardust or whatever.

Than you will not get much samples back if you have to include EDL element along with the tiny storage volume available with the EDL element.
Sample is going to be small. Doesn't need anything other than a capsule for EDL. Just use a crushable cone and maybe you could avoid even a parachute. PICA is very light (used on Stardust sample return and similar to that used on SpaceX's Dragon).
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Offline AJW

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Re: Red Dragon Discussion Thread (2)
« Reply #24 on: 03/11/2014 03:54 AM »
I have still never understood why the recent rovers did not include a simple tray for collecting samples.  A Red Dragon could have met Curiosity, transferred the tray, and relaunched with a sample set taken across a vastly larger area and years of sampling.  Just seemed short sighted.

Offline Robotbeat

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Re: Red Dragon Discussion Thread (2)
« Reply #25 on: 03/11/2014 04:03 AM »
They will put a sample collector on a later rover well before a sample return. The problem is payload mass. Scientific payload is at a huge premium (the rover itself is much more massive than the scientific payload), and they really want a canister system than will take time to develop properly. It would likely be wasted if they chose not to land there or it would lock them into a site before they had a good rationale for sample return.

http://spacecraft.ssl.umd.edu/akins_laws.html
Akin's Laws:
"13. Design is based on requirements. There's no justification for designing something one bit "better" than the requirements dictate."
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Offline arachnitect

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Re: Red Dragon Discussion Thread (2)
« Reply #26 on: 03/11/2014 04:53 AM »
I have still never understood why the recent rovers did not include a simple tray for collecting samples.  A Red Dragon could have met Curiosity, transferred the tray, and relaunched with a sample set taken across a vastly larger area and years of sampling.  Just seemed short sighted.

This was proposed at one point and actually got pretty far along ...but didn't make it.

IIRC (and this is how rumors start...) it wasn't the domain of a PI; it was being funded out of some administration slush fund. I think it was supposed to be more of a technology and operations training tool and wasn't really well enough engineered and thought out to be worth retrieving.

Offline AJW

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Re: Red Dragon Discussion Thread (2)
« Reply #27 on: 03/11/2014 05:02 AM »
With a sample tray, collection could have occurred with no commitment to retrieve.  The return mission could have moved samples into a new container for return transport, so no need to wait .  Choices are now limited to sending another rover (MSL cost $2.5 billion), or to include a sample collection rover with the Red Dragon (weight restrictions), and then having to wait for the collection process.  If the sample collect mission fails, your options are once again limited.

What is the best option now for sample collection to be returned by a Red Dragon?


Offline Robotbeat

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Re: Red Dragon Discussion Thread (2)
« Reply #28 on: 03/11/2014 05:35 AM »
How much mass and/or space should be devoted to such a sample tray? 1kg? 2kg? MSL had a budget for about 84kg of scientific instruments. That's the actual payload, so the 1 or 2kg comes out of that. Considering the mission is about $2.5billion, that's about $30 million per extra kilogram you put on there. You better be sure you're going to use that capability, or that's $30 million down the drain.
« Last Edit: 03/11/2014 05:37 AM by Robotbeat »
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Offline adrianwyard

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Re: Red Dragon Discussion Thread (2)
« Reply #29 on: 03/11/2014 05:45 AM »
If a rover based on Curiosity does fly in 2020 (which is a real NASA plan*, unlike any Red Dragon mission to date) and it includes a sample cache mechanism, then it would have more than a year on the surface to fill the cache and then be ready for the 2022 retrieval mission described in this paper. So actually no time has been wasted.

The mechanism used to transfer the cache to the MAV would need to be sorted out fairly soon. Presumably the rover would make its way to the (Red Dragon) landing site, a robotic arm would retrieve the cache, and the rover would then retreat to a safe distance.

I suppose in a perfect world Curiosity would have flown with a cache, and Falcon Heavy, and deep-space Red Dragon might conceivably be developed hitch-free and be ready to perform a mission like this as early as 2018, but at this point even 2022 is wishful thinking.

* http://mars.jpl.nasa.gov/mars2020/news/whatsnew/index.cfm?FuseAction=ShowNews&NewsID=1490. Note the mention of soil sample return.


 
« Last Edit: 03/11/2014 06:01 AM by adrianwyard »

Offline Lampyridae

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Re: Red Dragon Discussion Thread (2)
« Reply #30 on: 03/11/2014 07:28 AM »
http://solarsystem.nasa.gov/docs/7B.4_Karcz_Feasibility%20of%20a%20Dragon-derived%20Mars%20lander%20for%20scientific%20and%20human-precursor%20missions.pdf

Scalability is mentioned several times in this presentation. One wonders if a 6m diameter "super red" version of Dragon would be able to deliver 5-8 tonnes or if changing aerodynamics and area densities throw it out the window.
« Last Edit: 03/11/2014 07:29 AM by Lampyridae »
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Offline Kaputnik

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Re: Red Dragon Discussion Thread (2)
« Reply #31 on: 03/11/2014 10:08 AM »
Cube-square law works against larger vehicles. They have to become wider and flatter to maintain the same ballistic coefficient.

FWIW from my understanding, those super dracos must be pretty darn special to pull this mission off. If you plug in the T:W and ISP of a 'normal' pressure-fed hyperbolic bi-prop thruster, taking account of the lack of nozzle expansion as well as cosine losses, the one tonne payload can be eaten up significantly just accounting for the mass of the engines. I would hope that they have studied reducing the number of super dracos from eight to four, but it's hard to get an idea of the nature of analysis done so far.
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Offline adrianwyard

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Re: Red Dragon Discussion Thread (2)
« Reply #32 on: 03/11/2014 03:42 PM »
http://solarsystem.nasa.gov/docs/7B.4_Karcz_Feasibility%20of%20a%20Dragon-derived%20Mars%20lander%20for%20scientific%20and%20human-precursor%20missions.pdf

Scalability is mentioned several times in this presentation. One wonders if a 6m diameter "super red" version of Dragon would be able to deliver 5-8 tonnes or if changing aerodynamics and area densities throw it out the window.
I think retropropulsion in general is understood to be one of the few EDL approaches that scales up to big masses, not specifically Red Dragon-based solutions.

That said, it is hard to resist speculating what Red Dragon could do with a lower ballistic coefficient (bigger heat shield). I mocked up some guesses on how it would look further back in this thread. I'll include a couple of images here. In short: if you add a 5m shield, and keep the needed fairing attached, you get the area of a 6.6m shield, i.e three times that of the standard Dragon. (And less work for the retropropulsion to do if you detach the shield.)

http://forum.nasaspaceflight.com/index.php?topic=33224.msg1125139#msg1125139
See also: http://forum.nasaspaceflight.com/index.php?topic=33224.msg1125139#msg1125139
« Last Edit: 03/11/2014 11:46 PM by adrianwyard »

Offline solartear

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Re: Red Dragon Discussion Thread (2)
« Reply #33 on: 03/11/2014 06:56 PM »
Would the ascent rocket use the Dragon as a launch platform? Eject the main door and slightly raise the rocket to keep it safe from blowback. I assume launching through the top of Dragon will be a close fit even with an enlarged opening.

Online Zed_Noir

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Re: Red Dragon Discussion Thread (2)
« Reply #34 on: 03/11/2014 10:50 PM »
Would the ascent rocket use the Dragon as a launch platform? Eject the main door and slightly raise the rocket to keep it safe from blowback. I assume launching through the top of Dragon will be a close fit even with an enlarged opening.

My guess is the MAV will operated quite similar to a silo based cold gas launched ballistic missile. It will be ejected from the vertical launch silo inside the Dragon with a gas generator powered piston through a frangible cover. The MAV motor will then ignited a few seconds later in the air after the piston is discarded.

Online guckyfan

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Re: Red Dragon Discussion Thread (2)
« Reply #35 on: 03/12/2014 07:58 AM »
Would the ascent rocket use the Dragon as a launch platform? Eject the main door and slightly raise the rocket to keep it safe from blowback. I assume launching through the top of Dragon will be a close fit even with an enlarged opening.

My guess is the MAV will operated quite similar to a silo based cold gas launched ballistic missile. It will be ejected from the vertical launch silo inside the Dragon with a gas generator powered piston through a frangible cover. The MAV motor will then ignited a few seconds later in the air after the piston is discarded.

I am not sure that is necessary. As solartear mentioned, there is the open side hatch to vent exhaust gases.

Online Zed_Noir

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Re: Red Dragon Discussion Thread (2)
« Reply #36 on: 03/13/2014 12:50 AM »
Would the ascent rocket use the Dragon as a launch platform? Eject the main door and slightly raise the rocket to keep it safe from blowback. I assume launching through the top of Dragon will be a close fit even with an enlarged opening.

My guess is the MAV will operated quite similar to a silo based cold gas launched ballistic missile. It will be ejected from the vertical launch silo inside the Dragon with a gas generator powered piston through a frangible cover. The MAV motor will then ignited a few seconds later in the air after the piston is discarded.

I am not sure that is necessary. As solartear mentioned, there is the open side hatch to vent exhaust gases.
Why would you add in internal ducting or erected some sort launcher outside. When it is a lot simpler to installed a plain vertical cylinder. Besides the cylinder also stores the MAV until launched.

Offline Lar

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Re: Red Dragon Discussion Thread (2)
« Reply #37 on: 03/13/2014 02:29 AM »
Nod.

Theoretically after the MAV launches who cares about the Dragon, its work is done. The only worry is that launching from a cylinder inside somehow has exhaust impingement issues or something similar. And I don't see that. No need for complex systems to have the launcher be outside the Dragon.
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Offline sghill

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Re: Red Dragon Discussion Thread (2)
« Reply #38 on: 03/13/2014 12:33 PM »
Nod.

Theoretically after the MAV launches who cares about the Dragon, its work is done. The only worry is that launching from a cylinder inside somehow has exhaust impingement issues or something similar. And I don't see that. No need for complex systems to have the launcher be outside the Dragon.

This post got me to thinking that leaving the Dragon on the Martian surface has some biological contamination issues that need to be addressed.  Here's my question: Can a Dragon even be manufactured to the non-contamination tolerances required for a Martian surface visit, or would changing the manufacturing process to the extent necessary to avoid contamination drive up the price so much that a whole different vehicle design is cheaper? 

The internal components simply weren't designed with decontamination in mind, and there are a whole heck of a lot of components in a Dragon.
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Offline Lars_J

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Re: Red Dragon Discussion Thread (2)
« Reply #39 on: 03/13/2014 02:17 PM »
If we plan on visiting Mars, contamination WILL happen. And if colonization is a serious intent, then contamination as a concern should just be ignored.

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