Author Topic: Speculation on new Dragon features  (Read 123526 times)

Offline Lars_J

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Re: Speculation on new Dragon features
« Reply #40 on: 01/23/2011 05:15 am »
No, apparently the Dragon heat shield is not sized right for the much less dense martian atmosphere. It would have to be much bigger/wider to adequately brake a craft of Dragon's mass.

Offline blazotron

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Re: Speculation on new Dragon features
« Reply #41 on: 01/23/2011 05:33 am »
I'm pretty sure I heard/saw somewhere after the Dragon first flight that the attitude control system consists of 18 thrusters distributed in 4 independent modules around the service section.  Since the abort motors are apparently supplied by the same 4 modules, the natural configuration is to use symmetry of multiples of 4 (in this case 8 ) in the abort thruster architecture. 
« Last Edit: 01/23/2011 05:34 am by blazotron »

Offline meekGee

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Re: Speculation on new Dragon features
« Reply #42 on: 01/23/2011 05:52 am »
Oh, after the comment by zaitcev I'm already fine with 4 on an emotional level :), and yes, I agree on the practicalities of fuel tank distribution and preferred engine size mentioned before.

Based on that insight, do y'all think we can infer that if they are using 4 motors, then likely they plan to vector each one in 1 DOF?

Do you think they will vector each thruster, or just tilt the entire cluster?


Mars wise, I think that with SpaceX,  their future plans are much different than F9 and Dragon.  What they built to date was the minimum necessary to complete steps 1 (orbit) and 2 (ISS supply) so they can achieve credibility and move on.  This is why both these systems are so "minimalistic".  SpaceX can do much more, but they were disciplined in their priorities for the first development project, and good for them that they were.

In Elon's mind F9 and Dragon are ancient history by now, and he is deep into the next steps I'm sure. I have no doubt that they dabble already in anything from propellant stores, BEO propulsion, and Mars EDL.  It will be interesting to know who they hired from these fields.

This is part of the reason I am rooting for them so much. If you look at all other rocket players who've been in the field for so many decades now none of them had the combination of capability and drive that SpaceX does.
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Offline douglas100

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Re: Speculation on new Dragon features
« Reply #43 on: 01/23/2011 01:02 pm »
From meekGee

Quote
If you look at all other rocket players who've been in the field for so many decades now none of them had the combination of capability and drive that SpaceX does.

SpaceX's achievements have been impressive, but I disagree strongly with what you say here. So ULA has neither the drive nor capability of SpaceX? Has SpaceX got 4 operational launch pads (not counting Delta II)? A heavy lift launcher? Has it launched any large DoD or comsat missions? Does SpaceX operate high energy upper stages with a heritage of hundreds of flights? It will not have these capabilities for years, if ever.

Try and have a sense of proportion.
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Offline Jim

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Re: Speculation on new Dragon features
« Reply #44 on: 01/23/2011 01:04 pm »


In Elon's mind F9 and Dragon are ancient history by now, and he is deep into the next steps I'm sure. I have no doubt that they dabble already in anything from propellant stores, BEO propulsion, and Mars EDL.  It will be interesting to know who they hired from these fields.

This is part of the reason I am rooting for them so much. If you look at all other rocket players who've been in the field for so many decades now none of them had the combination of capability and drive that SpaceX does.

They just started to walk.  They don't have the resources for the those "next" steps.

Space x's next steps are to develop sustaining engineering and put together a substantiate string of successful launches.  Which without, Spacex doesnt exist, much less worry about propulsive landing
« Last Edit: 01/23/2011 07:52 pm by Chris Bergin »

Online Chris Bergin

Re: Speculation on new Dragon features
« Reply #45 on: 01/23/2011 07:52 pm »
After this post above, the thread turned into three pages about ULA.

So we've splint the thread and created two. This one stays on SpaceX - no excuses.

This thread:
http://forum.nasaspaceflight.com/index.php?topic=23902.0
Is the splinter about ULA vs SpaceX.
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Offline docmordrid

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Re: Speculation on new Dragon features
« Reply #46 on: 01/23/2011 08:28 pm »
THANK YOU!!
DM

Offline simonbp

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Re: Speculation on new Dragon features
« Reply #47 on: 01/23/2011 11:36 pm »
(Reposting this, as it got swallowed up in the flame war)

I can see them making a trunkless version with enhanced batteries for specific use for LEO station ferry missions using a two to three orbit rendezvous.
Sorta like the solar wingless ferry Soyuz.

Would there really be that much mass advantage to a solar-less version?

Quote
I can also see a propulsion module for lunar missions.
Other lunar modifications deletion of three to four seats adding a full WCS,improved galley,and various modifications for the deep space thermo environment.

So, if I assume the mass of the Dragon capsule is 10 tonnes, and the dry mass of the lunar-capable trunk/SM is 5 tonnes, and the Isp of the SM is 320 s (~current Kestrel or AJ-10), then for 1.5 km/s Delta V, the spacecraft would mass 24 tonnes, and 39 tonnes with 3.0 km/s.

The former (1.5 km/s) would be enough for just TEI from lunar orbit or L1, or both L2OI and TEI for L2. The latter (3.0 km/s) is enough for both capture and departure at L1 and lunar orbit. If the Isp is bumped up to 342 s (Merlin Vac), the masses go to 23.5 tonnes and 37 tonnes, respectively (so, not much difference).

Online Comga

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Re: Speculation on new Dragon features
« Reply #48 on: 01/24/2011 12:55 am »
(Reposting this, as it got swallowed up in the flame war)

I can see them making a trunkless version with enhanced batteries for specific use for LEO station ferry missions using a two to three orbit rendezvous.
Sorta like the solar wingless ferry Soyuz.

Would there really be that much mass advantage to a solar-less version?

More of a cost savings than a weight savings, I would guess.  Reduce the cost of the Trunk which is expended.  Batteries are possibly even a mass disadvantage, but would certainly be a hit to the down-mass.

Also, Dragon would probably have to be able to take power from the "LEO station" to avoid having the docking turn into a "Fire Drill" like teens at a traffic light.  The Shuttles can do this at the ISS, so the facility must exist there. 
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline Patchouli

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Re: Speculation on new Dragon features
« Reply #49 on: 01/24/2011 02:11 am »

More of a cost savings than a weight savings, I would guess.  Reduce the cost of the Trunk which is expended.  Batteries are possibly even a mass disadvantage, but would certainly be a hit to the down-mass.

Also, Dragon would probably have to be able to take power from the "LEO station" to avoid having the docking turn into a "Fire Drill" like teens at a traffic light.  The Shuttles can do this at the ISS, so the facility must exist there. 

I was thinking mostly a cost savings esp if re usability works out.
The larger battery pack likely would weigh more then the solar wings.
I was assuming it would be recharged off the LEO station and the batteries would have a nominal capacity of 48 hours with maybe a 12 hour reserve.
The mass increase may not be too great esp if improved batteries from electric cars are used.
I think Spacex is already using Lithium Ion technology which have about 2 to 3x the energy density for mass of nickle hydrogen batteries typically used in spacecraft and even double that of the Silver Zinc batteries in the Apollo LEM.
Pretty much the mass would be about half what normally would be expected.

It really would depend on how much excess payload F9 has for LEO missions and can they really max it out.
I suspect LEO Dragon missions may never max out the payload of the block II F9.
« Last Edit: 01/24/2011 02:24 am by Patchouli »

Offline douglas100

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Re: Speculation on new Dragon features
« Reply #50 on: 01/24/2011 03:03 pm »
The trunk provides cooling as well. Without it you would probably need more fluid for the flash evaporator. So this extra mass would have to be taken into account.

Also, I seem to remember in another thread that fast rendezvous results in unacceptably high rates of approach to the station and the consumption of more propellant. I wouldn't be surprised if that alone negated the mass advantage that a "trunkless" Dragon would have.
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Offline Lars_J

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Re: Speculation on new Dragon features
« Reply #51 on: 01/24/2011 03:54 pm »
Indeed. The trunk is a part of the operational Dragon spacecraft. It is not optional, other than for a quick 2-3 orbit test flight.

Online Comga

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Re: Speculation on new Dragon features
« Reply #52 on: 01/25/2011 03:19 am »
The trunk provides cooling as well. Without it you would probably need more fluid for the flash evaporator. So this extra mass would have to be taken into account.

Also, I seem to remember in another thread that fast rendezvous results in unacceptably high rates of approach to the station and the consumption of more propellant. I wouldn't be surprised if that alone negated the mass advantage that a "trunkless" Dragon would have.

Does the trunk really "provide cooling"? Is it really known?  Do we know where the fluid reservoir and pump are?  If they are within Dragon, only the radiators and some plumbing would be on the trunk.  Either way, those are probably a lot less expensive than solar panels, so it is less of an issue to continue to dispose of them.

On the other hand, three orbit rendezvous are possible, at the cost of flexibility and, I believe, payload due to the need for increased orbital maneuvering fuel.  It's another trade-off.  Can enough weight be saved by minimizing the cooling to compensate for the extra fuel, and would the cost savings be worth the loss in payload.
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline docmordrid

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Re: Speculation on new Dragon features
« Reply #53 on: 01/25/2011 04:21 am »
http://www.spacex.com/dragon.php

Quote
>
The Dragon spacecraft is comprised of 3 main elements:
>
....and the Trunk, which provides for the stowage of unpressurized cargo and will support Dragon’s solar arrays and thermal radiators.
>
« Last Edit: 01/25/2011 04:23 am by docmordrid »
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Offline Jorge

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Re: Speculation on new Dragon features
« Reply #54 on: 01/25/2011 01:44 pm »
The trunk provides cooling as well. Without it you would probably need more fluid for the flash evaporator. So this extra mass would have to be taken into account.

Also, I seem to remember in another thread that fast rendezvous results in unacceptably high rates of approach to the station and the consumption of more propellant. I wouldn't be surprised if that alone negated the mass advantage that a "trunkless" Dragon would have.

Does the trunk really "provide cooling"? Is it really known?

Yes.
JRF

Online Comga

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Re: Speculation on new Dragon features
« Reply #55 on: 01/25/2011 02:51 pm »
That's not the point, guys.  The issue is how much of the complexity of the cooling system is in the trunk, and how much is in the capsule.  To "provide cooling" some parts need to store and pump fluid, some need to exchange heat into the fluid, and radiators are needed to dump the energy from the fluid.  All that is obvious is that the trunk includes the radiators.

The discussion was about reducing cost by not discarding valuable systems.  The solar panels, with their triple junction cells and deployment and tracking mechanisms are complex and expensive.  If they could, under some circumstances, live with batteries, particularly ones that are recovered with the Dragon capsule, it is an opportunity for cost savings.   

On the other hand, the elements of the cooling system that are in the trunk may not be nearly as complex or expensive.  Fixed radiators in particular are way less expensive than deployed and mechanized solar panels.
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline douglas100

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Re: Speculation on new Dragon features
« Reply #56 on: 01/25/2011 11:23 pm »
I doubt you could operate the vehicle without radiators for any length of time. So you would keep the trunk but not mount solar panels.

What fraction of the cost of a flight would be saved by omitting the solar panels? Is it worth doing at all?
Douglas Clark

Offline Lars_J

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Re: Speculation on new Dragon features
« Reply #57 on: 01/25/2011 11:28 pm »
No. Not if you plan a mission longer than 2-3 orbits.

Offline douglas100

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Re: Speculation on new Dragon features
« Reply #58 on: 01/25/2011 11:32 pm »
I agree.
Douglas Clark

Offline Patchouli

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Re: Speculation on new Dragon features
« Reply #59 on: 01/26/2011 12:05 am »
The trunk provides cooling as well. Without it you would probably need more fluid for the flash evaporator. So this extra mass would have to be taken into account.

Also, I seem to remember in another thread that fast rendezvous results in unacceptably high rates of approach to the station and the consumption of more propellant. I wouldn't be surprised if that alone negated the mass advantage that a "trunkless" Dragon would have.

Does the trunk really "provide cooling"? Is it really known?

Yes.

I was assuming the trunk remains as it's also the the launch vehicle adapter it just simply remained attached to the second stage on the first test flight.

As for a 3 orbit rendezvous I think Spacex is actually planning on being able to do this when the vehicle is carrying seven people.
It's not crazy at all Apollo did it with Skylab and Boeing plans to do it with the CST-100.
I could not imagine them being like that for 2 days and I don't think Spacex has spacial compression technology like the Tardis.

The quick rendezvous seems to be more timing critical vs requiring alot of delta V it also requires the LV getting the initial orbit very close.
I even did one in orbiter with the shuttle.
The shuttle did have no payload other then the docking adapter. I also ended up leaving the ET in a 400x200km or so orbit.
The Crew only dragon is going to be generally lighter then a fully loaded cargo Dragon which is going to be stuffed with cargo.
This means the F9 second stage should be able to inject the vehicle into the ISS's orbit vs requiring several burns.
Not sure how accurate the model for Dragon is in orbiter but it's a lot easier to catch ISS quickly with it then the shuttle which took me several tries.

Now Apollo and Orion it's pretty easy I even managed a 1.5 orbit rendezvous with them.
But I ended up burning through about 60% of the fuel and doing stuff that simply would not be allowed like leaving the S-IVB in orbit and using the SPS within 10Km of the station.
« Last Edit: 01/26/2011 12:23 am by Patchouli »

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