Author Topic: "Used" Dragons  (Read 46968 times)

Offline baldusi

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Re: "Used" Dragons
« Reply #80 on: 05/23/2014 01:59 pm »

The plan is to fit VASIMR engines to ISS and power them from a 50kwhr battery to enable 15 min bursts at full thrust.

Using Dragon as free flying test platform with a 60kwhr battery should be able to achieve same result. Allow 24 HR between tests for batteries to recharge. They could even send it around the moon.
Assuming 5N of thrust and a 10tonne total weight, that would get 0.45m/s of delta-v per firing. Assuming 3kWh power budget, it would take 20hrs of sunlight between charges. You would have to launch either into an SSO orbit or polar to get constant power for a while. Else, you might not even get enough solar illumination for one firing per day. And it would take seven months to get 100m/s of delta-v. The whole point of testing a VASIMR in space is to validate a long firing, like you'd do on a missions where you might get 5,000m/s.

Offline Mader Levap

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Re: "Used" Dragons
« Reply #81 on: 05/24/2014 12:02 am »
About original topic of this thread: I don't think these dragons will be ever reused.
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Offline Lar

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Re: "Used" Dragons
« Reply #82 on: 05/24/2014 12:59 am »
It's funny how, when SpaceX opts for mass production instead of reusability, a lot of people start to tout the benefits of mass production. Streamlining the process, enhancing the design iteratively, etc...  ::)

We're not in "mass" production but we are in serial production. As of now each unit seems to be different than the last, and that's true for Dragons, first stages, and maybe even second stages. So far.

About original topic of this thread: I don't think these dragons will be ever reused.

Yes. These are too early. Once things settle down and there isn't variance from one to the next, that's when reuse is more likely, to my way of thinking.
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Online Coastal Ron

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Re: "Used" Dragons
« Reply #83 on: 05/24/2014 01:22 am »
It's funny how, when SpaceX opts for mass production instead of reusability, a lot of people start to tout the benefits of mass production. Streamlining the process, enhancing the design iteratively, etc...  ::)

Serial production of low-cost designs can lower overall costs, but reusability is still the ultimate solution.

And it's not unusual for 1st generation systems to not have all the features needed to fully realize the potential of a design.  In that light, think of the current Dragon as capable of reusability, but not optimal for a number of reasons.  And certainly they are proving out all their manufacturing processes on the 1st generation systems too, which benefits later versions.

And likely because SpaceX has continued to participate in the Commercial Crew program, they have not needed to pursue reusability for the 1st generation Dragons, and instead have focused all their internal resources on their 2nd generation Dragon.

Note:  I was typing this before dinner then finished afterwards, and I see Lar has covered the same topic, but I'll post what I wrote anyways.
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Offline llanitedave

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Re: "Used" Dragons
« Reply #84 on: 05/24/2014 02:17 am »
I think the Dragon and the trunk should be considered two separate entities.

No, it shouldn't.  Dragon has limited capabilities (mission life) once it sheds the trunk.

You're going to reuse the capsule.  Unless they extensively redesign the trunk, it's always going to be expended.
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Offline Llian Rhydderch

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Re: "Used" Dragons
« Reply #85 on: 05/24/2014 02:21 am »
I took clongton's statement just a bit diffferently.  Not that there are not now, currently, two different models of Dragon.  There clearly are:  the crew Dragon currently flying on CRS-3 (which is a "Dragon v2 v1.1" with upgraded power and avionics), and perhaps with others in the production pipeline (as we've seen) for future CRS flights); and the new SuperDraco-included Dragons that will be unveiled late this month, and will participate in the ground-abort test and launch-abort test in the coming months.

Dragon V2 is the docking and land-landing capable dragon initially intended for crew transport. CRS-3 dragon is upgraded but not a new main version. It have been called Dragon v1.5 on one occasion, but that seems a bit high a version number, since the only confirmed changes are improved power system that can provide much more power to payloads and more waterproof solutions for electronics boxes in the unpressurized but internal part of dragon. Perhaps the upgrades are much more extensive than what is confirmed -- It would probably be smart to "backport" much of the minor v1.x compatible changes intended for V2 back into v1.x cargo dragons to get them tested early, spread out the risks on more than one flight and avoid unnecessary parallel versions of subsystems.

edit: typos etc.

I do understand the major distinction between the cargo Dragon and the new, soon-to-be-unveiled, crew Dragon. I thought that Shotwell referred to the upgraded Dragon (new avionics and additional power for the NASA cargos) as "v2".  I could quite easily be wrong. (I was wrong, it is v1.1 I know I was surprised to hear her say that as I had been aware of the major upgrades for crew that had been planned for a long time.

What is SpaceX formally referring to the particular model of cargo Dragon that just flew on CRS-3?

I think we have the answer now, direct from Elon.

Elon just tweeted this to our very own QuantumG:
Quote
Elon Musk ‏@elonmusk 2h

@QuantumG Dragon V1.1 doesn't have a launch escape system. Probably comparable reliability to Shuttle, but we need to do better.
(emphasis added).

I think we can safely say that the descriptor for the Dragon model first flown on CRS-3, the one with upgraded avionics and a lot more power available for powered payloads, is Dragon v1.1.

The reveal on March 29th will be of the crew Dragon, aka DragonRider, aka Dragon Mk II, and on this forum often as Dragon v2.

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  Llian
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Offline Andy Smith

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Re: "Used" Dragons
« Reply #86 on: 05/24/2014 11:46 am »
Given the signed off capability of the dragon for proximity operations around the ISS, I would suggest that a "used" v1.1 dragon is used to berth an empty F9 second stage to the ISS. I.e. the second stage is not separated from the dragon.

From www.spacelaunchreport.com/falcon9v1-1.html the empty mass of the second stage is approx 6 tonnes, which should be within the capability of the dragon control system (www.spacex.com/dragon).

The extended length and different mass distribution would obviously need some consideration.

Once berthed, the ISS now has a fuel depot capability able to hold over 40 tonnes each of RP1 and LOX. Power to the second stage (for valve control and stage health monitoring) can be supplied via an umbilical from ISS to what would have been the standard pad umbilical connectors, likewise pump connections for loading fuel or taking it off could be done via it's existing pad connectors.

Subsequent missions to ISS which have spare mass available could carry fuel or oxidiser in standalone tanks in the trunk. The arm could then be used to move and connect them to the fuel depot for offloading.

Potentially if suitable relocation takes place, the Merlin could also provide ISS reboost and debris avoidance capability (given the 40% throttle capability), though whether a standard second stage / trunk / dragon configuration is structurally robust enough to handle that I don't know.

Online docmordrid

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Re: "Used" Dragons
« Reply #87 on: 05/24/2014 11:55 am »
How do you stop the RP-1 from gelling or stratifying? May be better off developing a disposable  Draco/SuperDraco (hypergolic) propulsion module with a PCBM.
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Offline Andy Smith

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Re: "Used" Dragons
« Reply #88 on: 05/24/2014 12:23 pm »
Thank you for your response. I can see that being a more efficient development if starting from scratch.

If it was actually possible to use the dragon / second stage this way then stratification and gelling could be avoided by pumping the RP1 between two identical second stage depots on a periodic basis.

I realise RP1 is not an ideal depot fuel, but perhaps stratification management is an acceptable trade-off for being able to deliver a capability based on existing infrastructure.

Regards



Offline Jim

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Re: "Used" Dragons
« Reply #89 on: 05/24/2014 12:27 pm »

1.  From www.spacelaunchreport.com/falcon9v1-1.html the empty mass of the second stage is approx 6 tonnes, which should be within the capability of the dragon control system (www.spacex.com/dragon).


2.  Once berthed, the ISS now has a fuel depot capability able to hold over 40 tonnes each of RP1 and LOX. Power to the second stage (for valve control and stage health monitoring) can be supplied via an umbilical from ISS to what would have been the standard pad umbilical connectors, likewise pump connections for loading fuel or taking it off could be done via it's existing pad connectors.


3.  Potentially if suitable relocation takes place, the Merlin could also provide ISS reboost and debris avoidance capability (given the 40% throttle capability), though whether a standard second stage / trunk / dragon configuration is structurally robust enough to handle that I don't know.


1.  Why would you think it can?  The CG issue makes it a non starter.  Pure translations on various axis would be next to impossible.

2.  The stage systems were designed for loading in a one g environment.  There is nothing to keep LOX from coming out the vents.  Also, high pressure helium is needed for the stage and then there is the orbital debris issue and the tanks  Also, just plugging into the umbilicals doesn't mean the stage can be controlled.  Software would have to be rewritten if possible to control the stage.


3.  Still too much thrust
« Last Edit: 05/24/2014 12:28 pm by Jim »

Offline TrevorMonty

Re: "Used" Dragons
« Reply #90 on: 05/27/2014 05:00 am »
One possible use is as environmental test lab attached to ISS. Could be configured for different pressures, gas mixtures, temperatures and humidity.

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