Author Topic: Red Dragon Discussion Thread (1)  (Read 559281 times)

Offline douglas100

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Re: Red Dragon
« Reply #160 on: 09/09/2011 01:20 pm »

So why not just make a new heatshield, about 5m diameter to fit inside the Falcon PLF, and make a proper Mars lander of around two or three tonnes. No new technology required.

Exactly.
Douglas Clark

Offline go4mars

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Re: Red Dragon
« Reply #161 on: 09/09/2011 02:13 pm »
So why not just make a new heatshield, about 5m diameter to fit inside the Falcon PLF, and make a proper Mars lander of around two or three tonnes. No new technology required.

The premise of this thread is that dragon could be used to deliver a science payload to the surface of Mars. Not to design a new 2 or 3 tonne lander, but to figure out how Elon might be planning to make dragon do the task. 

"This would possibly be several tons of payload — actually, a single Dragon mission could land with more payload than has been delivered to Mars cumulatively in history," -Elon

In that vein...

Would it work to have a large (12+ meter diamter) trunk-stowed ballute pop out for the primary deceleration?  Once subsonic, deploy the dragon parachutes to get up off the trunk/ballute, then super-dracos for the final touchdown? 

Can the solar panels be retracted back to the trunk once extended?

Perhaps the trunk might even be recoverable more or less intact (the ballute could act as an airbag potentially).  Then the solar panels could re-deploy and the trunk could be used as a solar-powered (unpressurized) storage shed.
« Last Edit: 09/09/2011 04:00 pm by go4mars »
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Offline Nathan

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Re: Red Dragon
« Reply #162 on: 09/09/2011 08:44 pm »
Thanks kaputnik. I've seen that reference previously and the problem I have with it and all of the other studies coming out of NASA is that nowhere do they say anything about entry masses in the 10 to 15tonne range.
I think my reference to the extra heat shield was actually zubrin's article rather than any associated with e Ames study so can be dismissed I think in relation to the red dragon mission.

I just don't see spacex making major changes to the capsule itself. Which leads me to think that the parachute will be modified in some way. Perhaps with a hypersonic decelerator followed by subsonic chute.
I do agree that all the calculation I run show a capsule too dense but I'm using Braun et al's work on the subject and not a detailed analysis of the spacex capsule itself.
I also agree that a larger htshield would assist but again don't see changes to the capsule as being in the offering since red dragon sounds like it will be done with the stock standard crewed version of the dragon.

It occurs to me that we don't actually know the payload mass for the red dragon mission. It could be 100kg for all we know which would lower the entry mass etc significantly. It could also be that the capsule will land at the lowest point on mars (in Hellas) to allow extra time to slow down.

I'm hoping Chris can write find out and write an article on the subject.

Given finite cash, if we want to go to Mars then we should go to Mars.

Offline Zed_Noir

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Re: Red Dragon
« Reply #163 on: 09/10/2011 12:17 am »
Wonder if the Dragon capsule can do additional atmospheric braking maneuvers like the shuttle.

Have the Dragon on a lot of banking turns to shredded delta V with RCS.

Since the heat shield is rated for Mars return to Earth supposedly. Can the Dragon fly through the Martian while doing banking turns until it's speed dropped below supersonic? Maybe even going around Mars several times along the equator.

Offline DaveH62

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Re: Red Dragon
« Reply #164 on: 09/10/2011 02:57 am »
Wonder if the Dragon capsule can do additional atmospheric braking maneuvers like the shuttle.

Have the Dragon on a lot of banking turns to shredded delta V with RCS.

Since the heat shield is rated for Mars return to Earth supposedly. Can the Dragon fly through the Martian while doing banking turns until it's speed dropped below supersonic? Maybe even going around Mars several times along the equator.

Can they approach in an elliptical orbit and decelerate in a series of orbital passes? Is this too time consuming or dangerous?
Could the process be improved by firing Draco's at the low point of each orbit?

Offline Kaputnik

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Re: Red Dragon
« Reply #165 on: 09/10/2011 02:31 pm »
SpaceX are good at doing the things other people did already, but cheaper. Aerocapture is not playing to their strengths.
Propellant cross feed.
[/quote]

Not in the same league. ULA will do a prop x-feed vehicle if you ask (and pay) them to. And SpaceX haven't actually achieved this yet anyway.

Aerocapture is potentially an extremely chalenging manoeuvre. Over the past four decades of orbital missions to Mars, in every instance a larger LV has been used to allow propulsive capture, and nobody has ever attempted to save mass by using Aerocapture. SpaceX can, potentially, offer cheap heavy lift, so it makes more sense to utilise this strength than to try to do aerocapture.
"I don't care what anything was DESIGNED to do, I care about what it CAN do"- Gene Kranz

Offline Kaputnik

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Re: Red Dragon
« Reply #166 on: 09/10/2011 03:04 pm »
So why not just make a new heatshield, about 5m diameter to fit inside the Falcon PLF, and make a proper Mars lander of around two or three tonnes. No new technology required.

The premise of this thread is that dragon could be used to deliver a science payload to the surface of Mars. Not to design a new 2 or 3 tonne lander, but to figure out how Elon might be planning to make dragon do the task. 
Well if you use a Dragon (10t), it weighs about 4.5t to start with; closing the deceleration gap propulsively requires around 3t of propellant; then you need the landing gear etc. Suddenly a 2 or 3 tonne lander doesn't seem such a bad option after all.

Quote
"This would possibly be several tons of payload — actually, a single Dragon mission could land with more payload than has been delivered to Mars cumulatively in history," -Elon
I would love to know how he proposes to achieve this. There is something missing in our information, because as currently designed a Dragon would be lucky to land its empty self on Mars, let alone land a large payload.

Quote
Would it work to have a large (12+ meter diamter) trunk-stowed ballute pop out for the primary deceleration?  Once subsonic, deploy the dragon parachutes to get up off the trunk/ballute, then super-dracos for the final touchdown? 

Can the solar panels be retracted back to the trunk once extended?

Perhaps the trunk might even be recoverable more or less intact (the ballute could act as an airbag potentially).  Then the solar panels could re-deploy and the trunk could be used as a solar-powered (unpressurized) storage shed.

A large ballute could well be the answer but who is going to develop it? Maybe if you fast-forward ten years Musk might be working on this sort of thing in the context of US recovery, but at the moment what they know is PICA-X rigid heatshields.

I don't understand this insistence on using a Dragon to land on Mars. Your ideas are such a large divergence from the craft that it would be easier to design something specifically for the task.

Anyway, if Musk is serious about mankind becoming a multi-planet species, he would do well to design a dedicated and otpimised Mars lander because he is going to need rather a lot of them.
"I don't care what anything was DESIGNED to do, I care about what it CAN do"- Gene Kranz

Offline Kaputnik

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Re: Red Dragon
« Reply #167 on: 09/10/2011 03:06 pm »
Wonder if the Dragon capsule can do additional atmospheric braking maneuvers like the shuttle.

Have the Dragon on a lot of banking turns to shredded delta V with RCS.
The Dragon is a 0.3 l/d vehicle, and this is already factored in when I did ome BOTE calculations of how it would fare in Mars entry.
"I don't care what anything was DESIGNED to do, I care about what it CAN do"- Gene Kranz

Offline Kaputnik

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Re: Red Dragon
« Reply #168 on: 09/10/2011 03:09 pm »
Can they approach in an elliptical orbit and decelerate in a series of orbital passes? Is this too time consuming or dangerous?
Could the process be improved by firing Draco's at the low point of each orbit?

They probably could take a number of passes through the atmosphere- this is aerobraking, and is used on most Mars missions, so is well understood. No need to waste propellant firing the Dracos at periapsis.

But all it lets you do is get down to a low circular orbit so that you enter at minimum velocity- and that is already presumed when working out how Dragon will fare in Mars entry.
"I don't care what anything was DESIGNED to do, I care about what it CAN do"- Gene Kranz

Offline Patchouli

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Re: Red Dragon
« Reply #169 on: 09/10/2011 03:42 pm »
Can they approach in an elliptical orbit and decelerate in a series of orbital passes? Is this too time consuming or dangerous?
Could the process be improved by firing Draco's at the low point of each orbit?

They probably could take a number of passes through the atmosphere- this is aerobraking, and is used on most Mars missions, so is well understood. No need to waste propellant firing the Dracos at periapsis.

But all it lets you do is get down to a low circular orbit so that you enter at minimum velocity- and that is already presumed when working out how Dragon will fare in Mars entry.

I think a low cost solution would be to store a paracone in the trunk.
http://www.astronautix.com/craft/paracone.htm

Parachutes should no longer be needed as the paracone should slow it enough the super dracos can handle the rest.
Instead have more propellant in place of the chutes.
« Last Edit: 09/10/2011 03:44 pm by Patchouli »

Offline yamato

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Re: Red Dragon
« Reply #170 on: 09/13/2011 11:57 am »
We´ve seen in this discussion, that it is not simple to decelerate propulsively in hypersonic airflow. But does it apply only to a rocket in the centre of the base (heatshield), ejecting the gases right into the stagnation point, or does it apply also to side rockets aka Dragon? Dragon actively uses its thrusters during the reentry (I guess that´s the reason of its unique precision landing), so ejecting rocket gases during hypersonic flight must be somehow possible.
As we´ve seen in the discussion, Dragon has too bad L/C for mars and it should hit the ground still being supersonic. Elon claims that it can not only land on mars, but it can land with significant payload. The only way I see is cheating - using propulsive deceleration (and maybe some extended fuel tanks). Are we sure that side thrusters cannot be used in hypersonic airflow?

Offline Kaputnik

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Re: Red Dragon
« Reply #171 on: 09/13/2011 01:22 pm »
But are they not simply firing the thrusters to rotate the dragon, which will have an off-centre CG and will therefore generate lift in a certain direction. This is how Apollo worked.
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Offline go4mars

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Re: Red Dragon
« Reply #172 on: 09/13/2011 01:40 pm »
Quote
Would it work to have a large (12+ meter diamter) trunk-stowed ballute pop out for the primary deceleration?  Once subsonic, deploy the dragon parachutes to get up off the trunk/ballute, then super-dracos for the final touchdown? 

A large ballute could well be the answer but who is going to develop it? Maybe if you fast-forward ten years Musk might be working on this sort of thing in the context of US recovery, but at the moment what they know is PICA-X rigid heatshields.

It could also be a steerable doughnut ballute stored in the trunk.  Once it becomes subsonic, dragon chutes could fire up through the ballute hole and pull dragon off (through the ballute hole).  Then propulsive landing at the very end. 

If it is still intact, the doughnut ballute could have secondary surface uses.

http://www.theregister.co.uk/2009/04/17/doughnut_ballutes_go_to_mars/

http://www.docstoc.com/docs/2256026/Summary-of-Ultralightweight-Ballute-Technology-Advances  This one has an interesting little slideshow(from > 5 years ago).
« Last Edit: 09/13/2011 01:42 pm by go4mars »
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Offline yamato

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Re: Red Dragon
« Reply #173 on: 09/13/2011 02:24 pm »
But are they not simply firing the thrusters to rotate the dragon, which will have an off-centre CG and will therefore generate lift in a certain direction. This is how Apollo worked.

But this still is firing a rocket engine into hypersonic airflow. Doesn´t it have any impact on capsule stability?

Offline Kaputnik

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Re: Red Dragon
« Reply #174 on: 09/13/2011 07:48 pm »
But are they not simply firing the thrusters to rotate the dragon, which will have an off-centre CG and will therefore generate lift in a certain direction. This is how Apollo worked.

But this still is firing a rocket engine into hypersonic airflow. Doesn´t it have any impact on capsule stability?

Not into the flow, but firing at a tangent to the circumference of the capsule. The MSL landing video has a good illustration of this. Since it is only rotating the capsule around the vertical axis, only a small force is required, so there is no effect on stability.

"I don't care what anything was DESIGNED to do, I care about what it CAN do"- Gene Kranz

Offline go4mars

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Re: Red Dragon
« Reply #175 on: 09/13/2011 07:52 pm »
But are they not simply firing the thrusters to rotate the dragon, which will have an off-centre CG and will therefore generate lift in a certain direction. This is how Apollo worked.

But this still is firing a rocket engine into hypersonic airflow. Doesn´t it have any impact on capsule stability?

Not into the flow, but firing at a tangent to the circumference of the capsule. The MSL landing video has a good illustration of this. Since it is only rotating the capsule around the vertical axis, only a small force is required, so there is no effect on stability.

Is there a chance that the rockets would fire pointed at a given angle (near horizontal or even slightly up) to be started with less supersonic airstream issues, then once roaring, be shifted more to a downward orientation? 
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Offline Robotbeat

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Re: Red Dragon
« Reply #176 on: 09/13/2011 08:06 pm »
SpaceX are good at doing the things other people did already, but cheaper. Aerocapture is not playing to their strengths.
Propellant cross feed.
They've announced it, but haven't done it.
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Offline mr. mark

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Re: Red Dragon
« Reply #177 on: 11/07/2011 09:07 pm »
New article about Dragon mission to Mars including detail of a late October meeting.

http://www.nature.com/news/2011/111107/full/479162a.html

Offline simonbp

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Re: Red Dragon
« Reply #178 on: 11/07/2011 11:50 pm »
So, they're shooting for an ice drill mission, thus the name "Icebreaker". The PI is Chris McKay, who was deeply involved in the Phoenix mission, and is a long-time advocate of deep ice as the place to look for life on Mars. A drill is perfect for such a mission, as it requires no mobility (thus minimal mods to the aeroshell), but is perennially too massive to land with a Phoenix/MPL style lander. By the sound of it, they are going for the next round of Discovery proposals, which should be interesting...

Offline go4mars

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Re: Red Dragon
« Reply #179 on: 11/08/2011 02:29 am »
Looks like we might not hear much about this until the planetary mission competition in 2013.  My 'curiosity' is certainly piqued. 

I was hoping this would propose to go a lot deeper than 1 meter, but I guess KISS ha$ it$ merit$. 
« Last Edit: 11/08/2011 02:33 am by go4mars »
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