Red Dragon

[dwightlooi]

Sorry, that's ridiculous in every possible way. The inside of a capsule cannot be pressed into service as a hypergolic tank. You just turned Dragon inside out.

Exactly, you turn the Dragon inside out. It's a specialty variant for Mars transport missions

And why not? It is airtight, and can be pressurized -- exactly what the Hypergolic tanks needs to be. Sure bare aluminum is not compatible with a corrosive oxidizer, but neither is the aluminum in a Titan rocket's body. That's why you coat it on the inside with an appropriate barrier material.

In fact, not doing so is ridiculous. Let's look at the Dragon Spacecraft as is...

(1) You have a spacecraft whose dominant volume is a pressure vessel which is useless in a Mars mission because there is no reason anything going to mars is going to need to be pressurized, much less enough space for 7 humans plus life support equipment. So you basically have a spacecraft which is 75% useless volume and mostly dead weight.

(2) There isn't enough space for adequate propellant in the Dragon for Mars Capture and/or orbit insertion if you do not use the pressure vessel as a fuel tank.

(3) If you do not use on-board Hypergolics and the Dragon's own thrusters for Mars Capture and Orbit insertion. You are going to need to use either the upper stage or a new trans Mars propulsion stage for it. The former is not going to work because the Falcon upper stage uses LOX as the oxidizer and LOX is a cryogenic liquid. You can't keep that from boiling off during the 6~9 month trip. That is why all the interplanetary missions do not use LH2/LOX or RP-1/LOX propulsion for destination burns. They use storable liquids or solids. If you don't use the upper stage then you need a new propulsion stage for Mars Capture. That's a heck of a lot more work than improvising with the Dragon itself, and if you are going to essentially build something from the ground up why even use the Dragon with its big fat pressure vessel? Why not just build a spacecraft like a typical Mars probe?

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


NOTE: ALL THE DELTA Vs add up. You eliminate the need for worry about a Mars Capture stage in the mission. You have plenty of propellants to insert youself into whatever desired orbit right down to LMO. You have enough to land with after an aerobraking re-entry.

[Jim]

It is frickin ridiculous and absurd and unworkable

1. It is only designed to be pressurized to 15psia.  Not the 100's required for a pressurized prop system.

2. Again where do the avionics go?  They reside in the pressure vessel.

[Jim]

Yeah, right.  Tell me some other fairytale spacecraft designs.

No, like this...

Worse than fairytale

Parachute container is too small for rover

[dwightlooi]

It is frickin ridiculous and absurd and undoable

1. It is only designed to be pressurized to 15psia.  Not the 100's required for a pressurized prop system.

2. Again where do the avionics go?  They reside in the pressure vessel.

(1) Use a small accumulator tank and a check valve. Pressurize the Accumulator only.

(2) Externally, in an unpressurized space. Just like Falcon 9 Avonics or interplanetary probe avionics.

[dwightlooi]

Yeah, right.  Tell me some other fairytale spacecraft designs.

No, like this...

Worse than fairytale

Parachute container is too small for rover

The alternative is worse.

The alternative is a Dragon which doesn't have enough fuel.

The alternative is some kind of new Mars Capture propulsion stack. If you do that, why bother with the Dragon?

[Jim]

It is frickin ridiculous and absurd and undoable

1. It is only designed to be pressurized to 15psia.  Not the 100's required for a pressurized prop system.

2. Again where do the avionics go?  They reside in the pressure vessel.

(1) Use a small accumulator tank and a check valve. Pressurize the Accumulator only.

(2) Externally, in an unpressurized space. Just like Falcon 9 Avonics or interplanetary probe avionics.

1.  Huh?  wrong.  What is going to be the max burn duration.  Read up on prop system design.
2.  This is a dragon, it uses dragon avionics

[Jason1701]

Mars capture is not needed. Mars landers do not go into orbit before landing.

[adrianwyard]

OK, dwightlooi, are you are saying the SpaceX/NASA mission descriptions we've seen to date are incorrect? They claim a DragonRider can do a direct entry and get 1 tonne to the surface with standard tanks.

If so, this is already on the list. The propulsion side could the deal-killer due to straightforward tank sizing issues, or something unpredicted and problematic with using them in supersonic flow.

Both these can be verified with a DragonRider in Earth's upper atmosphere.

[manboy]

No landing hazard avoidance is planned.

I wonder if ALHAT could be placed in the GNC payload bay and have it open when Dragon is low enough in altitude.

[Kaputnik]

The Dragon weighs 3.2 tons (w/o the trunk).

Where does that figure come from?
What have SpaceX done to make a capsule about the same mass as a Soyuz but more than twice the size? Are the Russians building theirs out of lead or something?!


@ Adrian- one other point on the list- electrical power. Do we know if Dragon is supposed to supply the power to the payload, or does this come out of the one tonne payload itself? On a more practical note, have AMES or SpaceX elaborated on what type of power generation would be used?

[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.)