Red Dragon Discussion Thread (1)

[guckyfan]

How much pressurized volume will the Red Dragon provide? Says 7m3 payload here but am still unsure if this volume is pressurized or not.

EDIT: Been thinking about this, and I suppose it could be pressurized because the standard Dragon has this capability and modifying it would defeat the purpose of the Red Dragon mission...

But that was the point made in the Red Dragon paper. You can make a much bigger exit port because it would not have the need of full pressure. Lower pressure then may make it necessary to rework the avionics as a thin atmosphere would not cool it as efficiently as a dense one.

[Lobo]

Red Dragon is an interesting concept to land a crew.

Couple Red Dragon with something like Boeing's SEP-MTV concept could be interesting.

Prior to the crew arriving, a Dragon-Mars Ascent Vehicle is landed on Mars with a Methane Propulsion Module, but no LAS system.  it expends it's methane fuel landing, but has a tank of LH2 and a Sabatier rector on it to refuel itself on the surface.
A Hab module or modules would have to be sent ahead of time too.

Launch the crew in Dragon to the SEP-MTV.  Have the SEP-MTV take the capsule to Mars.  The crew descends to the Surface in the Dragon Capsule. 
After the mission, the crew boards the Dragon-MAV which has refueled itself and launches it back up to the SEP-MTV.  It docks and is taken back to Earth.  The Dragon-MAV is then used to return the crew to Earth via a water landing (since it didn't have the LAS system to save weight, and it's not really needed for Mars Ascent). 

This process could then be recycled.  The Dragon that launches the crew from Earth is the same one that lands them on Mars, and the Dragon that launches them from Mars lands them on Earth. 
A nice way to get dual use out of some hardware.  The Hab on the SEP-MTV is used for spacious transit habitat. 

It needs to be supplimented with other hardware.  The SEP-MTV could ferry the Dragon-MAV and the Hab Module (and maybe some other equipment landers, depending on how much landed mass you are talking about) and drop it off on Mars and come back for another component and do it again. 

An interesting thought would be to piggyback the Dragon-MAV on top of the Surface Hab lander.  If the Hab lander is anything like Zubrin's "tuna can" concept, the Dragon-MAV could be attached to the top, and the whole stack can use a single aershield for descent.  Once far enough down, the shield would be jettisoned, the Dragon-MAV would detatch and let the hab fall away.  Both landers would then do a propulsive landing a short distance from each other.  Now you have your base ready for the crew to come on the next SEP-MTV trip on a Dragon Capsule. 
The Hab could perhaps use a parachute to keep it's engines and fuel needed for touchdown to a minimum.  But the Dragon-MAV should have pleanty of fuel for a fully propulsive touchdown, as it's fuel tanks will be sized to launch itself back up all the way to the SEP-MTV.  I'd think the ascent would require a lot more fuel than the propulsive descent.
I'd -think- anyway.

Another interesting idea would be (if it had enough fuel), for the Dragon-MAV and it's larger fuel tanks and engines, riding on top of the Hab and shield on the way down, could have a long teather connecting it to the hab.  After the shield is jettisoned and they are slowing for touchdown, the Dragon-MAV unspools the teather letting the Hab descent low below it, while it does a propulsive brake and drops the Hab off.  Then it does it's own touchdown.  it'd have to be setup so the plume from the methane engines didn't melt the teather, and so the thrust didn't damage the Hab.  But, again, the Dragon-MAV would have sufficient fuel capacity so that it can get itself back up to the SEP-MTV at the end of the mission after it refueles itself, so I'm thinking if those tanks are full, only a portion of that fuel will be needed to land itself.  So if it can act as the "skycrane" if it has enough fuel.  It might not, but I like the idea of the double duty of having both landers share a single shield, and both landers use a single propulsion system

[ClaytonBirchenough]

Red Dragon is an interesting concept to land a crew.

Couple Red Dragon with something like Boeing's SEP-MTV concept could be interesting.

Prior to the crew arriving, a Dragon-Mars Ascent Vehicle is landed on Mars with a Methane Propulsion Module, but no LAS system.  it expends it's methane fuel landing, but has a tank of LH2 and a Sabatier rector on it to refuel itself on the surface.
A Hab module or modules would have to be sent ahead of time too.

Launch the crew in Dragon to the SEP-MTV.  Have the SEP-MTV take the capsule to Mars.  The crew descends to the Surface in the Dragon Capsule. 
After the mission, the crew boards the Dragon-MAV which has refueled itself and launches it back up to the SEP-MTV.  It docks and is taken back to Earth.  The Dragon-MAV is then used to return the crew to Earth via a water landing (since it didn't have the LAS system to save weight, and it's not really needed for Mars Ascent). 

This process could then be recycled.  The Dragon that launches the crew from Earth is the same one that lands them on Mars, and the Dragon that launches them from Mars lands them on Earth. 
A nice way to get dual use out of some hardware.  The Hab on the SEP-MTV is used for spacious transit habitat. 

It needs to be supplimented with other hardware.  The SEP-MTV could ferry the Dragon-MAV and the Hab Module (and maybe some other equipment landers, depending on how much landed mass you are talking about) and drop it off on Mars and come back for another component and do it again. 

An interesting thought would be to piggyback the Dragon-MAV on top of the Surface Hab lander.  If the Hab lander is anything like Zubrin's "tuna can" concept, the Dragon-MAV could be attached to the top, and the whole stack can use a single aershield for descent.  Once far enough down, the shield would be jettisoned, the Dragon-MAV would detatch and let the hab fall away.  Both landers would then do a propulsive landing a short distance from each other.  Now you have your base ready for the crew to come on the next SEP-MTV trip on a Dragon Capsule. 
The Hab could perhaps use a parachute to keep it's engines and fuel needed for touchdown to a minimum.  But the Dragon-MAV should have pleanty of fuel for a fully propulsive touchdown, as it's fuel tanks will be sized to launch itself back up all the way to the SEP-MTV.  I'd think the ascent would require a lot more fuel than the propulsive descent.
I'd -think- anyway.

Another interesting idea would be (if it had enough fuel), for the Dragon-MAV and it's larger fuel tanks and engines, riding on top of the Hab and shield on the way down, could have a long teather connecting it to the hab.  After the shield is jettisoned and they are slowing for touchdown, the Dragon-MAV unspools the teather letting the Hab descent low below it, while it does a propulsive brake and drops the Hab off.  Then it does it's own touchdown.  it'd have to be setup so the plume from the methane engines didn't melt the teather, and so the thrust didn't damage the Hab.  But, again, the Dragon-MAV would have sufficient fuel capacity so that it can get itself back up to the SEP-MTV at the end of the mission after it refueles itself, so I'm thinking if those tanks are full, only a portion of that fuel will be needed to land itself.  So if it can act as the "skycrane" if it has enough fuel.  It might not, but I like the idea of the double duty of having both landers share a single shield, and both landers use a single propulsion system

Dragon does not have near enough delta v for a Mars ascent and modifying the Dragon to have a methane ascent/descent propulsion would defeat the point of the Red Dragon concept entirely.

Anyone know/can do simulations to find how much payload can be landed at - 7km MOLA? The Red Dragon is said to be able to land 1000 kg at -1.3km MOLA. So basically, I'm wondering how much payload can be landed in the Hellas Basin (Hellas Planitia).

In addition, I have attached a document that may help and provide more insight into the Red Dragon Mars Mission if it has not been posted already.

[Garrett]

Musk: Version two of Dragon, which should be ready in three years, should be able to do it. ...full article http://www.wired.com/wiredscience/2012/10/ff-elon-musk-qa/all/

Assuming that Elon is referring to the 5 meter version, purported by the MarsOne thread

"January 2016 is only three years one month and a couple of weeks away.   Can SpaceX really have the 5m Dragon variant ready to go by then?"     ~"Pretty much"

, which may or may not be one and the same as crew dragon, how would downmass capability for red dragon (Mars) increase?  Linearly, etc.?   It will have a crappier mass to heat shield surface area ratio (I suspect), but could potentially haul a lot more dragon juice along (and/or more potent NOFBX).

I assume we haven't been talking about red dragon as a 5 meter capsule all along, but am not certain given the timeframe.  Might be analogous to the "merlin block 2 performance" that we kept reading about...  Is Red Dragon = dragon 2?  Might explain a few things about current dragon's deficiencies highlighted on this thread. 

The scale drawings I have seen all show current Dragon dimensions.  I am not aware of any suggestion of a scaled up version in connection with Red Dragon.

The Red Dragon proposal has always presumed propulsive landing using super Dracos. Only Dragon 2 fits that description.
(see slide 5 in this presentation: http://digitalvideo.8m.net/SpaceX/RedDragon/karcz-red_dragon-nac-2011-10-29-1.pdf)

[go4mars]

The graph on page ten shows Red Dragon coming down to 20 km elevation, then "bouncing" back up over 45 km elevation before landing.  So it looks like the plan is to obliquely skim/punch through to shed speed.  What would stop them from exaggerating this technique?  (20 km instead of less)

[StephenB]

The graph on page ten shows Red Dragon coming down to 20 km elevation, then "bouncing" back up over 45 km elevation before landing.  So it looks like the plan is to obliquely skim/punch through to shed speed.  What would stop them from exaggerating this technique?  (20 km instead of less)

I know you used the word oblique. I'm wondering, is the elevation gained due primarily to lift or to hitting the atmosphere at an oblique angle (the atmosphere being a curved surface) and passing into a thinner part of the atmosphere due to the angle?

[go4mars]

graph on page ten shows Red Dragon coming down to 20 km ... back up over 45 km elevation before landing. 

is the elevation gained due primarily to lift or to hitting the atmosphere at an oblique angle (the atmosphere being a curved surface) and passing into a thinner part of the atmosphere due to the angle?

I imagine it's mainly the latter, but maximized in effect as much as possible by lift and drag (to stay in the atmosphere as long as possible). 

So my question is intended to be along the lines of: "Is it G-force that limits the depth of the initial plunge?"
It seems to me that the limit can't be concern about skipping off the atmosphere at a low angle of attack.  It could have the same initial entry angle, just with a longer path through thicker atmosphere if it came down very close to the surface instead of only passing through initially 20 km up. I assume this initial angle is roughly tangent to the curve of Mars.  Why not go lower if it increases landed mass?

With a move like they show, it should even be possible to aim the initial pass through an area of lower elevation than the intended destination. 
Am I thinking about this the right way?   

[StephenB]

One factor is probably daily variation in Mars' atmospheric density. From this site on nasa.gov:

At any given location on Earth, the air pressure can vary about 10% whereas on Mars it can vary by as much as 50%.

That sounds like a lot of variation to engineer around.

[smoliarm]

One factor is probably daily variation in Mars' atmospheric density. From this site on nasa.gov:

At any given location on Earth, the air pressure can vary about 10% whereas on Mars it can vary by as much as 50%.

That sounds like a lot of variation to engineer around.

Not really. IIRC, normal atmospheric pressure on Mars is less than 1/100 atm,
which is called 'fore-vaccum' by engineers of vacuum equipment
http://en.wikipedia.org/wiki/Turbomolecular_pump

So this "50% variation" is a variation of vacuum quality so to speak. It wont create any structural issues like variation from 1 atm to 1.5 atm.

[Lars_J]

Structural issues isn't the problem... It is the accuracy of the landing, and making sure that your craft has sufficient margin to handle both extremes during re entry.

[StephenB]

Structural issues isn't the problem... It is the accuracy of the landing, and making sure that your craft has sufficient margin to handle both extremes during re entry.

It would be nice if they could make adjustments on the fly if the density is lower or higher than optimal on landing day.

[go4mars]

... making sure that your craft has sufficient margin to handle both extremes during re entry.

So 20 km might be the notional average.  If atmospheric density is presumed lower upon entry, skim down any amount up to 20 km lower, and if density is higher than expected on arrival, presumably go higher than 20 km (or maybe 20 km is the upper limit for a given downmass). 

To me that suggests active control after entry (whether through thrusters or control surfaces (tabs) or both). 

[baldusi]

Sounds to me more like a skip entry. I.e. a small bounce on the atmosphere to kill horizontal velocity (they are coming at interplanetary speed). Is sort of a semi aerocapture. The latter is, probably, the most important EDL development to be made in Mars.

[go4mars]

Sounds to me more like a skip entry. I.e. a small bounce on the atmosphere to kill horizontal velocity (they are coming at interplanetary speed). Is sort of a semi aerocapture. The latter is, probably, the most important EDL development to be made in Mars.

Totally agree.  But why 20 km instead of something lower (where added friction and time in atmosphere could mean more landed mass)?         

Maybe it does come down to landing accuracy after all. 

[simonbp]

The pull-up is relatively high up in order to allow for the spacecraft to bleed off more horizontal velocity before it fires the rockets. It's effective translating horizontal kinetic energy into both lift and drag. But the lift is so low that they have to start rather high up to avoid hitting the ground before they slow down enough. The scale height of the martian atmosphere is ~11 km, so the pressure is still about 1/10 of the surface.

MSL flew a similar lifting trajectory, and I bet that's what this trajectory was based on.

[go4mars]

The scale height of the martian atmosphere is ~11 km...

What does scale height mean?

[Robotbeat]

The scale height of the martian atmosphere is ~11 km...

What does scale height mean?

It's the height it takes for the density (or pressure... we're usually assuming isothermal) to change by a factor of "e" in the simple exponential atmosphere model.

[go4mars]

MSL flew a similar lifting trajectory, and I bet that's what this trajectory was based on.

I wonder how much change to landed mass is possible when MAVEN brings in the error bars.

[adrianwyard]

Red Dragon has come up in the "Manned Mars Lander" where different EDL options are being considered:
http://forum.nasaspaceflight.com/index.php?topic=33224.msg1125139#msg1125139

I've mocked up some additions that may (or may not) improve upon the basic Red Dragon design:

[mlindner]

Chop the big flat surface off the bottom...