Red Dragon Discussion Thread (1)

[Silmfeanor]

This is the only way a Dragon based Mars transit makes sense.

Could you for the love of pete please stop making statements like these?
They are just flat out wrong.

Also, read up the on the previous discussion before making posts. The essential thing about the red dragon idea was that you take a dragon with minimal changes and land it on mars with some payload because it's cheap and doesn't require a lot of work.

These are not "hey that's nice" - these are what makes them work. With your ideas, you might aswell build a totally new capsule that works better for propulsive entry. You're trying to make something work towards mars while only using the outer mold line of dragon ( one without SuperDraco's might I add ) and just cramming all sorts of stuff in there and saying "but it'll work!" - all the while butchering the very idea that might make Red Dragon work - if substantial problems are overcome.

Also, please provide sources for your numbers of weight.

[meekGee]

Well, what dwightlooi is doing is designing a Martian SSTO vehicle using Dragon as a starting point.

Definitely not a "minimum change" design, and not intended for max-value for minimum-investment mission.   That would be either a "land only" or an "circumfly and return" mission.

So perhaps this belongs in a separate thread, not the Red Dragon thread, since Red Dragon was defined in the context of a quick-and-simple mission.

dwightlooi - if we discuss this proposal on its merits, the first question is why design an SSTO around Dragon to begin with?  Since the modifications are more than minimal, and since of all companies, SpaceX does have the ability to design from scratch (and quickly), why not start with a blank slate?

I will give you that if you were to design an SSTO from scratch, you might end up with something not too far from what you sketched (fuel on the inside, unpressurized cargo on the outside) - and you wouldn't be hearing all the objections, since now everything would have been designed to work properly to begin with, not made to fit an existing vehicle.

[Joel]

Sorry for being ignorant, but what's the point of spending 2300 m/s of delta-v for going into LMO? I mean, can't you just aim straight at some point (preferably as low altitude as possible) on Mars and do aerobraking.

I mean, I understand that there could be a point of going into lunar orbit before landing on the moon, but on Mars?

[Kaputnik]

Still waiting on confirmation that the dry mass of a Dragon capsule is 3200kg.

[adrianwyard]

Unless someone is privy to unpublished info, or can spot flaws in the data that has been published, then I'm inclined to believe the SpaceX/Ames assessment over the (very varied) speculations here. They claim 1 t of payload is possible. Performance will be verified before Red Dragon flies.

So... arguing over various masses doesn't help answer the current question.

As far as hazard avoidance goes, the last I heard this was not planned. It will have no greater capability in this regard than other recent landers. The comparison was made to MPL - i.e. land where it's nice and flat.

As for payload power, I'm not sure what the plan is. For a true science mission, this could require significant changes, i.e. deployable arrays. But if the first mission is primarily EDL/SSR demo, then 1 t allows for some batteries. You can also cover the top (where the CBM is today) with solar cells, and the sensor bay door too (where the grapple fixture is today).

Here's a question: if the first one is indeed 99% EDL/SSR demo, then I think it will be heavily instrumented, and you'd really like real-time constant high data-rate comm back to Earth, or perhaps to the trunk still in orbit, or to other orbiters. Is that problematic enough to kill the proposal? (You could store the entry telemetry until after landing, but... see Beagle 2.)

[Jim]

Here's a question: if the first one is indeed 99% EDL/SSR demo, then I think it will be heavily instrumented, and you'd really like real-time constant high data-rate comm back to Earth, or perhaps to the trunk still in orbit, or to other orbiters. Is that problematic enough to kill the proposal? (You could store the entry telemetry until after landing, but... see Beagle 2.)

a.  the trunk is a dummy shell, it is not spacecraft
b.  It is not going to be in orbit, it will be reentering with the dragon
c.  UHF, which the orbiters use, is affected by ionization. 
d.  There is no real way to provide realtime high data rated telemetry.  MSL, MPL, MER used semaphores.

[adrianwyard]

All good points - thanks. sorry about the trunk idiocy.

So this is indeed an honest to goodness high risk for a minimal Red Dragon. If it makes it to the surface then it's a major advancement, if we don't hear from it then the whole project gets you very little.

[Kaputnik]

Unless someone is privy to unpublished info, or can spot flaws in the data that has been published, then I'm inclined to believe the SpaceX/Ames assessment over the (very varied) speculations here. They claim 1 t of payload is possible. Performance will be verified before Red Dragon flies.

So... arguing over various masses doesn't help answer the current question.

Believe SpaceX/AMES if you like. However the idea that Dragon can be half the weight of a Soyuz for a given size doesn't pass the sniff test, IMHO.

[QuantumG]

Believe SpaceX/AMES if you like. However the idea that Dragon can be half the weight of a Soyuz for a given size doesn't pass the sniff test, IMHO.

Ya know Soyuz has a lot of stuff in it right?

[Kaputnik]

Believe SpaceX/AMES if you like. However the idea that Dragon can be half the weight of a Soyuz for a given size doesn't pass the sniff test, IMHO.

Ya know Soyuz has a lot of stuff in it right?

Is any of that 'stuff' things that Dragon does not also have?
Remember the 3.2t mass that someone has bandied about is excluding the super-dracos or any payload.

[Robotbeat]

Believe SpaceX/AMES if you like. However the idea that Dragon can be half the weight of a Soyuz for a given size doesn't pass the sniff test, IMHO.

Ya know Soyuz has a lot of stuff in it right?

Is any of that 'stuff' things that Dragon does not also have?
Remember the 3.2t mass that someone has bandied about is excluding the super-dracos or any payload.

Yes. Dragon doesn't have legacy approaches to solving problems from half a century ago. Dragon has totally modern electronics and other systems and was designed during the age of modern computer design techniques, whereas Soyuz was not. Also, some systems scale up very well, but there may well be a "minimum mass" associated with the approach, where the mass needed for a 7-passenger vehicle is only, say, 20% greater compared to a 3 passenger one.

One big issue is that Soyuz uses hydrogen peroxide monopropellant, Dragon uses higher Isp propellants. Even bigger is the heatshield design... Dragon uses PICA-X which is an incredibly advanced ablative tweaked from PICA which was developed and used for Stardust, etc. Soyuz's heatshield also has to be able to easily be discarded right before landing, while SpaceX's is permanently attached during flight.

SpaceX and the Russians also have a different design philosophy. You can stand on Russian rocket stages while they are being assembled, while SpaceX's rocket stages are much more lightweight and are pressure-stabilized for flight loads.

[Kaputnik]

I grant you there are differences in approach and design.
There is still no citation for the 3.2t figure quoted earlier in the thread.

Whatever way you cut it there is very little mass to play with. Knowing the T:W of the super-dracos would help enormously in working this stuff out.

[DaveH62]

Not sure if anyone saw this article on a NASA inflatable heat shield test coming up. Seems like this could have a big impact on Mars landing, enabling a much larger heat shield than the launch faring. Based on the drawing in the article, it appears the shield is nearly 3 times faring width, or 10 meters. The area of the shield would go from about 40 square meters to over 300 square meters.
Interesting to know what this would do to the math for landing a heavier payload.

http://www.space.com/16615-nasa-inflatable-heat-shield-launching-saturday.html

[Robotbeat]

Not sure if anyone saw this article on a NASA inflatable heat shield test coming up. Seems like this could have a big impact on Mars landing, enabling a much larger heat shield than the launch faring. Based on the drawing in the article, it appears the shield is nearly 3 times faring width, or 10 meters. The area of the shield would go from about 40 square meters to over 300 square meters.
Interesting to know what this would do to the math for landing a heavier payload.

http://www.space.com/16615-nasa-inflatable-heat-shield-launching-saturday.html

Yeah, this would be an incredible advance enabling a Mars surface mission. If the inflatable heat shield works, you could land a pre-fueled (hypergolic) lander on the surface, taking a whole bunch of other questions off the table. It also allows you to land large base components relatively easily. It's more important than an HLV.

[StephenB]

Mars Science Lab IIRC from the video is slowed to ~1000 mph by its heat shield alone. I wonder what speed reduction could be achieved by this. Ten meters is over twice the diameter of the 4.5 meter MSL heat shield, and 4x the area. The MSL supersonic parachute is 16 m in diameter, by comparison.

[adrianwyard]

I think the physics dictates that atmospheric deceleration methods are always less effective on Mars than on Earth (there's < 1% of the atmosphere to do the braking). While IRVE+parachutes might work well for some applications on Earth, on Mars the thin atmosphere will leave even IRVE-derived/low ballistic coefficient vehicles with a rather high terminal velocity. The obvious way to get rid of this last bit of velocity is through rocket propulsion. But if your lander has rocket propulsion to deal with the last bit, then you might be able to achieve the same deceleration that an inflatable large-diameter heat-shield would give you by simply adding propellant of equivalent mass; a much less risky proposition.

I think is the logic that takes you to a 100% propulsive solution like Red Dragon.

And Red Dragon is conceived as a demo of this EDL concept with the minimum of changes to the LAS-enabled DragonRider that's being developed for commercial crew.

[douglas100]

Yeah, this would be an incredible advance enabling a Mars surface mission. If the inflatable heat shield works, you could land a pre-fueled (hypergolic) lander on the surface, taking a whole bunch of other questions off the table. It also allows you to land large base components relatively easily. It's more important than an HLV.

The illustration in Dave62's post was also on the Cygnus return thread where there was some discussion of this technology. Inflatable heat shield technology (IRDT) was tested on the first Soyuz Fregat flight in 2000 with partial success.

http://space.skyrocket.de/doc_sdat/irdt-1.htm

Totally agree this is a very promising technology (but a bit OT with regard to Red Dragon.)

[DaveH62]

Yeah, this would be an incredible advance enabling a Mars surface mission. If the inflatable heat shield works, you could land a pre-fueled (hypergolic) lander on the surface, taking a whole bunch of other questions off the table. It also allows you to land large base components relatively easily. It's more important than an HLV.

The illustration in Dave62's post was also on the Cygnus return thread where there was some discussion of this technology. Inflatable heat shield technology (IRDT) was tested on the first Soyuz Fregat flight in 2000 with partial success.

http://space.skyrocket.de/doc_sdat/irdt-1.htm

Totally agree this is a very promising technology (but a bit OT with regard to Red Dragon.)

You are probably correct. Interesting if they could use and jettison before firing super draco's but may actually add risk without adding much to landing mass.
Interesting to see the math though. With the 3.6 meter Dragon you would have nearly 10 times the surface of the Dragon PICA shield.

[Kaputnik]

I think the physics dictates that atmospheric deceleration methods are always less effective on Mars than on Earth (there's < 1% of the atmosphere to do the braking). While IRVE+parachutes might work well for some applications on Earth, on Mars the thin atmosphere will leave even IRVE-derived/low ballistic coefficient vehicles with a rather high terminal velocity. The obvious way to get rid of this last bit of velocity is through rocket propulsion. But if your lander has rocket propulsion to deal with the last bit, then you might be able to achieve the same deceleration that an inflatable large-diameter heat-shield would give you by simply adding propellant of equivalent mass; a much less risky proposition.

I think is the logic that takes you to a 100% propulsive solution like Red Dragon.

And Red Dragon is conceived as a demo of this EDL concept with the minimum of changes to the LAS-enabled DragonRider that's being developed for commercial crew.

A couple of points.

1) SpaceX don't need to buy in or develop inflatable heatshield technology. They could just fly a 5.2m PICA-X heatshield inside their standard PLF. As myself and several others have said from the start of this thread, it makes much more sense to reassemble Dragon technology into a dedicated Mars lander design, than it does to start adding things onto a stock Dragon.

2) Red Dragon, as currently proposed, is not really breaking new ground in the way that people are claiming. The propulsion is not to kick in until < mach 3. This is within the range of heritage parachute systems, which would be a more mass-efficient solution. So IMHO all this talk of Red Dragon being breakthrough technology is a bit off the mark; it does not produce as useful a system as people are claiming. You also have to remember that it will produce 7G on approach which is far too high for a deconditioned crew to handle.

[baldusi]

1) SpaceX don't need to buy in or develop inflatable heatshield technology. They could just fly a 5.2m PICA-X heatshield inside their standard PLF. As myself and several others have said from the start of this thread, it makes much more sense to reassemble Dragon technology into a dedicated Mars lander design, than it does to start adding things onto a stock Dragon.

Inside a standard fairing can only fit a 4.65m heatshield. The could develop a customized fairing, or even a 5m Red Dragon. But nothing of this would be "minimal changes".