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SpaceX Dragon spacecraft for low cost trips to the Moon.

Posted by: RGClark - Sat Oct 16, 2010 12:47 pm
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SpaceX Dragon spacecraft for low cost trips to the Moon. 
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Post Re: SpaceX Dragon spacecraft for low cost trips to the Moon.   Posted on: Sun Dec 19, 2010 5:47 pm
JamesHughes wrote:
May not be purely commercial, but it's lot more commercial than the current incumbents.


Not really. Boeing, LockMart, et al. all build what the customer wants and the market will bear. NASA and the USAF builds/designs very little hardware, its mostly farmed out to contractors. The likes of SpaceX and Orbital are just the newest kids on the block.

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How long before even the military realises it can put 10 times the hardware in orbit for the same launch cost and uses that to push down the prices of the current launches? Or goes with SpaceX?


Despite congressional soundbites, the military doesn't particularly care about costs. Its a peculiar situation of military necessity and one off and low rate (compared to commercial) production. They are mission, results oriented, and not cost sensitive. That does not translate over to commercial space, which is highly cost sensitive, so much so that cost is still well above demand, and why the big fish haven't even bothered.

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re: Conservative refinement. Nothing wrong with that.


Wasn't criticizing, just describing the reality of it behind the PR spin.


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Post Re: SpaceX Dragon spacecraft for low cost trips to the Moon.   Posted on: Sun Dec 19, 2010 11:09 pm
@JamesG, I think you missed the key point of JamesHughes'post:

JamesHughes wrote:
but as Musk himself said, he is in charge, chief architect etc, and what he wants to get done, gets done. No committee work! His purpose is to get humans in space, not to make money for shareholders, unlike the incumbents, and so far he is doing quite well at it with the conservative approach.


Elon Musk is in charge, and he gets stuff done :-)

Just look at all the things he is- and have been involved with!


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Post Re: SpaceX Dragon spacecraft for low cost trips to the Moon.   Posted on: Tue Jan 31, 2012 6:42 pm
SpaceX has said two Falcon Heavy launches would be required to carry a manned Dragon to a lunar landing. However, the 53 metric ton payload capacity of a single Falcon Heavy would be sufficient to carry the 30 mT (Earth departure stage + lunar lander system) described below. This would require 20 mT and 10 mT gross mass Centaur-style upper stages. This page gives the cost of a ca. 20 mT Centaur upper stage as $30 million:

Centaur IIA.
http://www.astronautix.com/craft/cenuriia.htm

A 10 mT Centaur-style stage would be somewhat less than this, so the total for both less than $60 million.

The 53 mT to LEO capacity of the Falcon Heavy would also allow large lunar cargo transport using two of the 20 mT gross mass Centaurs that already exist either using the Dragon to carry the cargo or by carrying somewhat more cargo just within a lightweight container.

An important cargo delivery to the Moon would be in-situ resource utilization (ISRU) equipment, specifically for producing propellant from the water discovered to lie within the shadowed craters near the lunar poles. Elon Musk has said a key goal of his is to mount a manned Mars mission within 1 to 2 decades. Such a mission could be mounted more cheaply if the large amount of propellant required did not have to be lofted from the Earth's deep gravity well but could be taken from the Moon.

Another important cargo delivery would be to carry a rover that could do a sample return mission from the near polar locations. Lunar orbiter observations suggest there may be valuable minerals concentrated in such locations:

SCIENCE -- October 21, 2010 at 2:05 PM EDT
Moon Blast Reveals Lunar Surface Rich With Compounds.
BY: JENNY MARDER
"There is water on the moon ... along with a long list of other compounds, including, mercury, gold and silver. That's according to a more detailed analysis of the chilled lunar soil near the moon's South Pole, released as six papers by a large team of scientists in the journal, Science Thursday."
http://www.pbs.org/newshour/rundown/201 ... water.html

If these tentative detections could be confirmed then that could possibly form a commercial market for flights to the Moon.

In this vein note there is even stronger evidence for large amounts of valuable minerals on asteroids. Observations suggest that even a small size asteroid could contain trillions of dollars (that's trillions with a 't') worth of valuable minerals:

Riches in the Sky: The Promise of Asteroid Mining.
Mark Whittington, Nov 15, 2005
http://voices.yahoo.com/riches-sky-prom ... -8776.html

It is quite important to note then that since the delta-V requirements to some near Earth asteroids is less than that to the Moon, that the sample return version of the lunar lander could also be used to return samples from the near Earth asteroids. If these asteroidal detections could be definitively confirmed by a sample return mission then that would provide further justification for private investment in lunar propellant production installations.

SpaceX expects to launch the first Falcon Heavy in 2013. Because the required Centaur stages already exist it is possible that a lunar lander could be formed from such mated together stages within this time frame at least for a unmanned cargo version.

It is important though that such a lander be privately financed. Because the required stages already exist I estimate a lander could be formed from them for less than a $100 million development cost. This is based on the fact that SpaceX was able to develop the Falcon 9 launcher for about $300 million development cost, and this required development of both the engines and the stages for a 300 mT gross mass and 30 mT dry mass launcher. But for this lunar lander, the engines and stages already exist for a total 40 mT gross mass and 4 mT dry mass system.

If the system were to be government financed then based on the fact that SpaceX was able to develop the Falcon 9 for 1/10th the development cost of usual NASA financed systems, the cost of the lander would suddenly balloon to a billion dollar development.

Note that while the evidence for valuable minerals in the lunar shadowed craters is not yet particularly strong, the evidence for such minerals in the asteroids is. So there is a strong financial incentive for forming such a lunar lander as it could also be used for the asteroidal lander.
But asteroidal mineral retrieval flights could be launched much more cheaply if the propellant could be obtained from the Moon. Then there is a strong financial incentive to produce ISRU installations on the Moon which would require lunar return missions from the shadowed crater regions to assess the best means of harvesting this lunar water for propellant. If such return missions also confirm the presence of valuable minerals in the shadowed craters then that would be like icing on the cake for justification of private investment in such missions.



Bob Clark



RGClark wrote:
The Orion spacecraft and Altair lunar lander intended for a manned Moon mission are large craft that would require a heavy lift launcher for the trip. However the Dragon capsule is a smaller capsule that would allow lunar missions with currently existing launchers.
The idea for this use would be for it to act as a reusable shuttle only between LEO and the lunar surface. This page gives the dry mass of the Dragon capsule of 3,180 kg:

SpaceX reveals first Dragon engineering unit.
DATE:16/03/07
By Rob Coppinger
http://www.flightglobal.com/articles/20 ... -unit.html

The wet mass with propellant would be higher than this but for use only as a shuttle between LEO and the Moon, the engines and propellant would be taken up by the attached propulsion system. With crew and supplies call the capsule mass 4,000 kg.
On this listing of space vehicles you can find that the later versions of the Centaur upper stage have a mass ratio of about 10 to 1:

http://www.friends-partners.org/partner ... pndexc.htm

The Isp's given for the RL-10A engines used on these stages are around 450 s, but an updated version with a longer, extensible nozzle has an Isp of 465.5 s:

RL10B-2.
http://www.pratt-whitney.com/StaticFile ... L10B-2.pdf

This page gives the delta-V's needed for trips within the Earth-Moon system:

Delta-V budget.
Earth–Moon space.
Image
http://en.wikipedia.org/wiki/Delta-v_bu ... Moon_space

The architecture will be to use a larger Centaur upper stage to serve as the propulsion system to take the vehicle from LEO to low lunar orbit. This larger stage will not descend to the surface, but will remain in orbit. A smaller Centaur stage will serve as the descent stage and will also serve as the liftoff stage that will take the spacecraft not just back to lunar orbit, but all the way to back to LEO. The larger Centaur stage will return to LEO under its own propulsion, to make the system fully reusable. Both stages will use aerobraking to reduce the delta-V required to return to LEO.
For the larger Centaur, take the gross mass of the stage alone as 30,000 kg, and its dry mass as 1/10th of that at 3,000 kg. For the smaller Centaur stage take the gross mass as 10,000 kg and the dry mass as 1,000 kg. The "Delta-V budget" page gives the delta-V from LEO to low lunar orbit as 4,040 m/s. In calculating the delta-V provided by the larger Centaur stage we'll retain 1,000 kg propellant at the end of the burn for the return trip of this stage to LEO: 465.5*9.8ln((30,000 + 10,000 + 4,000)/(3,000 +10,000 + 4,000 + 1,000)) = 4,077 m/s, sufficient to reach low lunar orbit. For this stage alone to return to LEO, 1,310 m/s delta-V is required. The 1,000 kg retained propellant provides 465.5*9.8ln((3,000 + 1,000)/3,000) = 1,312 m/s, sufficient for the return.
The delta-V to go from low lunar orbit to the Moon's surface is 1,870 m/s. And to go from the Moon's surface back to LEO is 2,740 m/s, for a total of 4,610 m/s. The delta-V provided by this smaller Centaur stage is 465.5*9.8ln((10,000 + 4,000)/(1,000 + 4,000)) = 4,697 m/s, sufficient for lunar landing and the return to LEO.
The RL-10 engine was proven to be reusable for multiple uses with quick turnaround time on the DC-X. The total propellant load of 40,000 kg could be lofted by two 20,000+ kg payload capacity launchers, such as the Atlas V, Delta IV Heavy, Ariane 5, and Proton.
The price for these launchers is in the range of $100-140 million according to the specifications on this page:

Expendable Launch Vehicles.
http://www.spaceandtech.com/spacedata/elvs/elvs.shtml

So two would be in the range of $200-$280 million. The Dragon spacecraft and Centaur stages being reusable for 10+ uses would mean their cost per flight should be significantly less than this. This would bring the cost into the range affordable to be purchased by most national governments.
Still, it would be nice to reduce that $200 million cost just to bring the propellant to orbit. One possibility might be the heavy lift launchers being planned by NASA. One of the main problems in deciding on a design for the launchers is that there would be so few launches the per launch cost would be too high. However, launching of the propellant to orbit for lunar missions would provide a market that could allow multiple launches per year thus reducing the per launch cost of the heavy lift launchers. For instance, the Direct HLV team claims their launcher would cost $240 million per launch if they could make 12 launches per year:

JULY 23, 2009
Interview with Ross Tierney of Direct Launch by Sander Olson.
http://nextbigfuture.com/2009/07/interv ... irect.html

This launcher would have a 70,000 kg payload capacity. However, if you removed the payload fairing and interstage and just kept the propellant to be launched to orbit in the ET itself and considering the fact that the shuttle system was able to launch 100,000+ kg to orbit with the shuttle and payload, it's possible the propellant that could be launched to orbit could be in the range of 100,000 kg. Then the cost per kg to orbit would be $2,400 per kg, or about a $100 million cost for the propellant to orbit.
Reduction of the per launch cost for the heavy lift launchers would then allow affordable launches of the larger spacecraft and landers for lunar missions.


Bob Clark

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Post Re: SpaceX Dragon spacecraft for low cost trips to the Moon.   Posted on: Thu Feb 02, 2012 7:14 am
You know, a lot of weight could be saved at launch by not sending the whole re-entry vehicle to lunar orbit, and back? During the Apollo missions, fully half of the mass was the conical capsule, which had to be accellerated to orbit, assembled, accellerated to escape velocity, parked, docked with after the ascent, then accellerated all the way back.

Now, we have a space station in orbit. Everything could be launched seperate from the crews, who assemble, and board it on orbit before heading out that way. SOme of it could even be automated to lunar orbit, then picked up when the crews get there.

There's little to be gained from sending quick visits to the surface, I would hope that our return would be the start of a more permanent instalation. While we could do it cheap, it would be more cost effective if we could Profit from the venture, like extracting Alluminum from the regolith for monopropellant, and/or building materials.

Instead, we seem to be planning this as if it's still the 1960s, and we haven't learned anything from half a century of space exploration. What we need is a dedicated vehicle, to efficiently shuttle personell, and cargo to, and from the lunar surface, and higher Earth orbits.

Then, we'd need to set up an infrastructure. Lunar sattelites, way stations, and communications relays to make this safe. Then we can mine the moon, and save increadible ammounts of money sending stuff to orbit. In 20 years, it would pay for itself, while paving the way for further exploration. Or, we can do it as a fast, and dirty publicity stunt, again.

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Post Re: SpaceX Dragon spacecraft for low cost trips to the Moon.   Posted on: Thu Feb 02, 2012 7:36 am
What we need the Orion capsule for is return to Earth. As light as we make it, it's just dead weight if we send it all the way to Lunar orbit, and back again. The heat sheild won't be used for the entire trip, once it acceives escape velocity, so it could be left off the intralunar shuttle entirely. (Not to mention the structural reinforcement to make it aerodynamic, and capable of withstanding the re-entry stresses.)

At the time of Apollo, the conical module was used as an abort, because a rescue mission would have been impossible, but now, we have a permanent installation to send such a rescue to, or from. With the same launch mass, we could instead send cargo, such as habitats to be left there, supplies for extended, or even permanent instalations, and mining equipment to turn a profit.

This would allow us to design a much lighter craft for the actual mission of going to, and from the moon. It wouldn't have to be aerodynamic, so a mass efficient sphere for the habitat volume wouldn't need to be very robust, and may even be partially inflated. (Bigalo, I'm looking at you.) Once on the lunar surface, these modules could be interconnected into a station for the arriving crews to start mining, or whatever we're there to do.

A conical shape is fine for aerodynamics, and in orbit, but once we get to the surface, it's not all that hot for standing up in. The inflatible habitats would be more comfortable if they were cylindric with a 2m ceiling height, or so. They could even be stacked, or inflated in, and buried by lunar dust for some protection from radiation, and possible space debris.

Concentric docking rings on each end may even allow them to be stacked, while forcing down further with some sort of tunneling equipment. Flexible tunnels could interconnect them for a shirt-sleeve environment, eventually to a small mining town. I envision using heat to fuse the ubiquitous dust into tunnels, that may eventually be pressurised as more habitat volume.

The engines would also be free to use an efficient dedicated space design, instead of a heavier overpowered trans-atmospheric hybrid. Long slow burns would use a lot less fuel than the short hard thrusts used in the original lunar transfers, with the entire mission a lot lighter, which would mean a lot less fuel to send up in the first place.

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Post Re: SpaceX Dragon spacecraft for low cost trips to the Moon.   Posted on: Thu Feb 02, 2012 10:31 am
RGClark wrote:
SpaceX has said two Falcon Heavy launches would be required to carry a manned Dragon to a lunar landing. However, the 53 metric ton payload capacity of a single Falcon Heavy would be sufficient to carry the 30 mT (Earth departure stage + lunar lander system) described below. This would require 20 mT and 10 mT gross mass Centaur-style upper stages.


That should say 40 mT gross mass for the (Earth departure stage + lunar lander) system that was described in the original post in this thread with 30 mT and 10 mT Centaur-style stages.


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Single-stage-to-orbit was already shown possible 50 years ago with the Titan II first stage.
Contrary to popular belief, SSTO's in fact are actually easy. Just use the most efficient engines
and stages at the same time, and the result will automatically be SSTO.
Blog: http://exoscientist.blogspot.com


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Post Re: SpaceX Dragon spacecraft for low cost trips to the Moon.   Posted on: Thu Feb 02, 2012 10:38 am
RGClark wrote:
It is important though that such a lander be privately financed. Because the required stages already exist I estimate a lander could be formed from them for less than a $100 million development cost. This is based on the fact that SpaceX was able to develop the Falcon 9 launcher for about $300 million development cost, and this required development of both the engines and the stages for a 300 mT gross mass and 30 mT dry mass launcher. But for this lunar lander, the engines and stages already exist for a total 40 mT gross mass and 4 mT dry mass system.
If the system were to be government financed then based on the fact that SpaceX was able to develop the Falcon 9 for 1/10th the development cost of usual NASA financed systems, the cost of the lander would suddenly balloon to a billion dollar development.



Nice article here:

SpaceX Might Be Able To Teach NASA A Lesson.
May 23, 2011
By Frank Morring, Jr.
Washington
Quote:
“I think one would want to understand in some detail . . . why would it be between four and 10 times more expensive for NASA to do this, especially at a time when one of the issues facing NASA is how to develop the heavy-lift launch vehicle within the budget profile that the committee has given it,” Chyba says.
He cites an analysis contained in NASA’s report to Congress on the market for commercial crew and cargo services to LEO that found it would cost NASA between $1.7 billion and $4 billion to do the same Falcon-9 development that cost SpaceX $390 million. In its analysis, which contained no estimates for the future cost of commercial transportation services to the International Space Station (ISS) beyond those already under contract, NASA says it had “verified” those SpaceX cost figures.
For comparison, agency experts used the NASA-Air Force Cost Model—“a parametric cost-estimating tool with a historical database of over 130 NASA and Air Force spaceflight hardware projects”—to generate estimates of what it would cost the civil space agency to match the SpaceX accomplishment. Using the “traditional NASA approach,” the agency analysts found the cost would be $4 billion. That would drop to $1.7 billion with different assumptions representative of “a more commercial development approach,” NASA says.

http://www.aviationweek.com/aw/gener...p36-324881.xml


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Contrary to popular belief, SSTO's in fact are actually easy. Just use the most efficient engines
and stages at the same time, and the result will automatically be SSTO.
Blog: http://exoscientist.blogspot.com


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Post Re: SpaceX Dragon spacecraft for low cost trips to the Moon.   Posted on: Thu Feb 02, 2012 3:02 pm
Space is all about nitpicky details...

Psiberzerker wrote:
At the time of Apollo, the conical module was used as an abort, because a rescue mission would have been impossible, but now, we have a permanent installation to send such a rescue to, or from.


The ISS is not in an orbit that is conducive to departing or receiving tranfers to the Moon or elsewhere. The timing is tricky. Even if you match orbits, if you're out of phase and out of time or fuel, even by a few kilometers/minutes, the rescuees and refuge might as well be on other sides of the universe. The most efficient Earth-return transfer utilizes aero-braking on the Earth's atmosphere, so even if you aren't going to plunge in and re-enter, you need a heat shield to accomplish this. Apollo 13 would have ended tragically if it had been configured differently.

Quote:
This would allow us to design a much lighter craft for the actual mission of going to, and from the moon.


I agree with you though that we should invest in actual "ships" for venturing beyond LEO.
Quote:
(Bigalo, I'm looking at you.) Once on the lunar surface, these modules could be interconnected into a station for the arriving crews to start mining, or whatever we're there to do.


Bigalo advocates assembling the entire "facility" in orbit and then landing it all in one piece.

Quote:
A conical shape is fine for aerodynamics, and in orbit, but once we get to the surface, it's not all that hot for standing up in.

Orion is big enough to stand up in.


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Post Re: SpaceX Dragon spacecraft for low cost trips to the Moon.   Posted on: Fri Feb 10, 2012 8:43 pm
Interest tidbit from Elon Musk, talking about the Dragon capsule, and general reusability of the Falcon stack.

"There is no question in my mind that it will work, It’s just a question of how quickly the testing progresses. We expect to do several vertical-takeoff, vertical-landing (VTVL) flights this year and hopefully go supersonic in the fourth quarter."

Sounds like fun!

More details

http://www.popularmechanics.com/science ... =pm_latest


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Post Re: SpaceX Dragon spacecraft for low cost trips to the Moon.   Posted on: Mon Feb 13, 2012 11:32 am
JamesHughes wrote:
Interest tidbit from Elon Musk, talking about the Dragon capsule, and general reusability of the Falcon stack.

"There is no question in my mind that it will work, It’s just a question of how quickly the testing progresses. We expect to do several vertical-takeoff, vertical-landing (VTVL) flights this year and hopefully go supersonic in the fourth quarter."

Sounds like fun!

More details

http://www.popularmechanics.com/science ... =pm_latest



From the article:

Elon Musk on SpaceX’s Reusable Rocket Plans.
February 7, 2012 6:00 PM
Quote:
The key, at least for the first stage, is the difference in speed. "It really comes down to what the staging Mach number would be," Musk says, referencing the speed the rocket would be traveling at separation. "For an expendable Falcon 9 rocket, that is around Mach 10. For a reusable Falcon 9, it is around Mach 6, depending on the mission." For the reusable version, the rocket must be traveling at a slower speed at separation because the burn must end early, preserving enough propellant to let the rocket fly back and land vertically. This also makes recovery easier because entry velocities are slower.
However, the slower speed also means that the upper stage of the Falcon rocket must supply more of the velocity needed to get to orbit, and that significantly reduces how much payload the rocket can lift into orbit. "The payload penalty for full and fast reusability versus an expendable version is roughly 40 percent," Musk says. "[But] propellant cost is less than 0.4 percent of the total flight cost. Even taking into account the payload reduction for reusability, the improvement is therefore theoretically over a hundred times."

http://www.popularmechanics.com/science ... =pm_latest

Then for the Falcon 9, the payload would be reduced from 10 mT to 6 mT. If the reduction in payload really is this high, then maybe it would be better to recover the first stage at sea. The loss in payload is coming from the reduction in the speed of staging as well as the need to retain a portion of the fuel for the return to base. Recovering at sea would not have these disadvantages because you could let the first stage make its usual trajectory at returning to the sea but use just small amount of propellant for the final slowdown before the sea impact.
In this article Musk does mention that returning back to the launch point allows the turnaround time at least for the first stage to be just hours. But will we really need that short a turnaround time at this stage of the game? A turnaround time of a few days would seem to be sufficient.
Perhaps the idea that retrieval at sea would be so expensive comes from the experience of the shuttle with the SRB's. But these were quite large and heavy at ca. 90 mT dry compared to that of the Falcon 9 first stage at less than 15 mT. Also, it is well known the labor costs for the shuttle were greatly inflated compared to a privately funded program.
The only additional requirement is that you would need a cover that could be extended to cover the engine section and would be watertight.



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Contrary to popular belief, SSTO's in fact are actually easy. Just use the most efficient engines
and stages at the same time, and the result will automatically be SSTO.
Blog: http://exoscientist.blogspot.com


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Post Re: SpaceX Dragon spacecraft for low cost trips to the Moon.   Posted on: Tue Feb 14, 2012 11:24 am
And what about corrosion due to sea water? Then you need a ship with a crew that sails back and forth, there are more range issues to contend with, you have to crane the rocket onto the ship and off it again, carry it across land from the sea port back to the space port...

Flying back seems a lot simpler to me, and simplicity is good. Even if it's economically not quite worth it to fly back compared to a sea recovery, the reduction in risk may be worth it.

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Post Re: SpaceX Dragon spacecraft for low cost trips to the Moon.   Posted on: Wed Feb 15, 2012 2:05 pm
Lourens wrote:
And what about corrosion due to sea water?


There is 80 odd years of marine environment mitigation in aviation.

Quote:
Then you need a ship with a crew that sails back and forth, there are more range issues to contend with, you have to crane the rocket onto the ship and off it again, carry it across land from the sea port back to the space port...


Depends on if you have the precision to plop in just off shore from you launch/turn-around point.

Quote:
Flying back seems a lot simpler to me, and simplicity is good. Even if it's economically not quite worth it to fly back compared to a sea recovery, the reduction in risk may be worth it.


Sea landing is relatively safer and simpler than ground landing which is why it was chosen for the early US program.


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Post Re: SpaceX Dragon spacecraft for low cost trips to the Moon.   Posted on: Thu Feb 16, 2012 9:57 am
Sure, keeping your steel barge from rusting away from underneath you is a known art. But relatively fragile space hardware, on a weight budget? And I think the point of the sea recovery is that you don't waste fuel flying back, so it wouldn't be a precision splashdown just off the coast. Also the Russians have been doing land landings successfully from the start...

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Post Re: SpaceX Dragon spacecraft for low cost trips to the Moon.   Posted on: Thu Feb 16, 2012 11:53 am
RGClark wrote:
Then for the Falcon 9, the payload would be reduced from 10 mT to 6 mT. If the reduction in payload really is this high, then maybe it would be better to recover the first stage at sea. The loss in payload is coming from the reduction in the speed of staging as well as the need to retain a portion of the fuel for the return to base. Recovering at sea would not have these disadvantages because you could let the first stage make its usual trajectory at returning to the sea but use just small amount of propellant for the final slowdown before the sea impact.
In this article Musk does mention that returning back to the launch point allows the turnaround time at least for the first stage to be just hours. But will we really need that short a turnaround time at this stage of the game? A turnaround time of a few days would seem to be sufficient.
Perhaps the idea that retrieval at sea would be so expensive comes from the experience of the shuttle with the SRB's. But these were quite large and heavy at ca. 90 mT dry compared to that of the Falcon 9 first stage at less than 15 mT. Also, it is well known the labor costs for the shuttle were greatly inflated compared to a privately funded program.
The only additional requirement is that you would need a cover that could be extended to cover the engine section and would be watertight.

Bob Clark


There is also the time issue. Drop in to the sea, you are talking some weeks before the stage is ready to go again (get fish out of the engines etc). Land it back at base, you could be ready the next day (I think Musk gave figures). That could be worth the 4t reduction in payload, for a much higher flight rate. Fuel is also a minimal cost compared to the hardware, so the reduction in payload is also a good tradeoff.


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Joined: Mon Dec 18, 2006 11:15 pm
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Location: Columbus, GA USA
Post Re: SpaceX Dragon spacecraft for low cost trips to the Moon.   Posted on: Thu Feb 16, 2012 12:18 pm
But then you start chasing your tail. The weight of landing gear and aerodynamic controls, requires more propellant mass, which requires larger tanks, which requires more thermal protection mass, which raises gross weight, which means more mass for landing gear and structure. Which leads to so on and so forth. So you either wind up with a monster like the STS or an impractically small payload (like the X-37B most likely).

Lourens wrote:
Sure, keeping your steel barge from rusting away from underneath you is a known art. But relatively fragile space hardware, on a weight budget? And I think the point of the sea recovery is that you don't waste fuel flying back, so it wouldn't be a precision splashdown just off the coast. Also the Russians have been doing land landings successfully from the start...


No, think naval aircraft and seaplanes.

In the early days reentry and orbital dynamics weren't fully understood, also there wasn't the methods or fuel for controlled reentries, so a big ocean is a convenient landing spot. The Russians, without large naval fleets steaming around all of the world's oceans, but with large open plains (and a cavalier safety attitude) opted for ground landing. It would not have been "practical" for NASA to launch and land from Eastern Colorado & Nebraska.

Ground landings are also very hard on the vehicle compared to water. Not conducive to re-useability.


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