Author Topic: Red Dragon Discussion Thread (2)  (Read 387854 times)

Offline guckyfan

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Re: Red Dragon Discussion Thread (2)
« Reply #900 on: 08/21/2017 09:37 pm »
Dragon 2 will have a ballast sled that lets them control the AOA during descent. So they do indeed have aerodynamic control features.

I wonder if this is one of the features they drop, now that powered landing is off.

Offline woods170

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Re: Red Dragon Discussion Thread (2)
« Reply #901 on: 08/22/2017 06:16 am »
You forgot accuracy, which I suspect is one of the primary reasons Dragon v2 landing was abandoned. Chaotic aerodynamic forces during reentry alter the post-reentry trajectory and this will vary the landing point quite dramatically (for example, Soyuz landings are often kilometers away from their targeted landing site), and Dragon doesn't have any aerodynamic control features to direct the capsule to a precise landing point like the Falcon 9 does. They could use thruster firings, but my suspicion is that they realized they couldn't reserve enough fuel for both worst-case scenario trajectory corrections and the landing burn.
The reason that Soyuz sometimes lands many miles off has nothing to do with "chaotic aerodynamic forces during reentry", but everything with lack of precision timing of the reentry burn as well as lack of precision management of the reentry burn profile.

On a system with proper systems, such as the current cargo Dragon, it's no big deal to do precision parachute landings. Cargo Dragon usually lands within a kilometer from the pre-positioned recovery ship. The only reason it isn't any closer is for safety reasons: you don't want all that mass to land on your head.
Precision parachuting into a radius of just a few hundred feat is no big deal actually as the both the US Amry and US Navy can tell you. And SpaceX has already accomplished that parachuting accuracy.
« Last Edit: 08/22/2017 08:42 am by woods170 »

Offline woods170

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Re: Red Dragon Discussion Thread (2)
« Reply #902 on: 08/22/2017 06:50 am »
I'd like to speculate on why NASA rejected the powered land landing concept for Dragon, which is the reason (excuse) for delaying (canceling) Red Dragon.

Performance: the weight of landing propellant, tanks, pipes, engines, and legs is bigger than that of parachutes and their deployment hardware. Any thruster failure has to be compensated by throttling back other thrusters (or cutting one al al N-1). So full thrust cannot be used in the nominal landing profile. All this extra weight is subtracted at 1 for 1 from the return payload.
The design of Crew Dragon was baselined with powered landings in mind, including a pre-determined return payload capacity.
NASA did not suddenly demand a higher return payload capacity. Return payload capacity is not the reason why SpaceX gave up on powered landings.


Reliability: Each thruster and landing leg is an individual failure point, but you can survive failure of one drogue and one main parachute in the Apollo/Orion system.
The system as designed was in fact very reliable. The Super Draco's were paired in pods. In each pod a Super Draco could fail and then Crew Dragon still could safely land, propulsively. Well before initiating the final landing burn the Super Draco's would be ignited shortly to check them working properly. If that "check burn" turned up any failures there was sufficient time left to deploy the parachute system.
Also, the landing legs were not required to deploy to safely set Crew Dragon down on the ground. The landing legs would have provided extra cushioning upon touch-down. But total failure of the legs to deploy would only result in a harder landing, but one that would not result in fatalities or major injuries.
Partial failure of the legs to deploy would result in Crew Dragon toppling-over upon touch-down. Again: nothing major as this is perfectly survivable without injuries. Soyuz topples over all the time without any harm done to the crew. That is what seats-and-restraints are for.

Safety: You need to open doors in the heat shield for the thrusters and legs. The five doors on the belly of the Shuttle were a source of obsessive worry throughout that program. Recall that when COLUMBIA's wing started to heat up, the mission controllers assumed immediately that a main gear door had failed. Shuttle ops veterans now occupy high management positions in the manned space program; they probably regard any head shield penetration as unacceptable.
Heatshield penetrations are perfectly acceptable and safe when well-engineered. In case you had not noticed: Orion has six heatshield penetrations. Those are structural supports for the CM. The Apollos CM had them as well. Cargo Dragon also has them where the capsule is attached to the trunk. The attachment point runs thru the heatshield for all three designs.
Doors in heat shields are not exceptional either. The design of a major hatch in the heat shield of capsules was flight-proven on Gemini B for the MOL progam. Multiple doors in the primary TPS, two of them closing in-flight, were proven on every single space shuttle mission that reached orbit.
In short: doors or penetrations in the primary heat shield were not the reason why SpaceX gave up on powered landings.

I've never understood the obsession with vertical powered landings on Earth. Since we have thick air and soft warm oceans here, it seems silly not to use them as free shock absorbers. Musk would probably argue that the time involved with bringing the spacecraft back to the launch site would prevent the high flight rates he fantasizes about, but obviously this is not a factor in ISS crew exchange operations.
Crew Dragon never was about high fligh-rates. Powered landing was about setting the ship down on land, in stead of landing in the water. Landing the capsule on land offers a host of advantages over water landings. That's why both Boeing and SpaceX chose to do landings on land. Boeing chose the airbag-cushion system that was originally envisioned for Orion. SpaceX went with powered descent.

The real reason why SpaceX gave up on powered landings is that qualifying the powered descent feature turned out to be much (as in MUCH) more cumbersome, and thus much more expensive, than SpaceX had previously anticipated. The requirements set by NASA, and the resulting engineering and testing required to certify powered landings simply did not fit within the available budget.
Remember, SpaceX is "doing" Crew Dragon for "just" $2.6 billion, compared to the $4.2 billion that Boeing is getting. SpaceX already has a perfectly functioning parachute system as well as a proven track-record of water landings AND water recovery. Compared to what it would have cost to qualify and certify for powered landings it was simply cheaper to adapt Crew Dragon for sea landings only given that initial flights of Crew Dragon were going to land in water anyway (NASA never agreed to powered landings for the initial missions but was open to eventually certifying powered landings once Crew Dragon had a few missions under it's belt).
« Last Edit: 08/22/2017 01:02 pm by woods170 »

Offline tdperk

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Re: Red Dragon Discussion Thread (2)
« Reply #903 on: 08/22/2017 01:20 pm »
I'd like to speculate on why NASA rejected the powered land landing concept for Dragon, which is the reason (excuse) for delaying (canceling) Red Dragon.

Performance: the weight of landing propellant, tanks, pipes, engines, and legs is bigger than that of parachutes and their deployment hardware. Any thruster failure has to be compensated by throttling back other thrusters (or cutting one al al N-1). So full thrust cannot be used in the nominal landing profile. All this extra weight is subtracted at 1 for 1 from the return payload.
The design of Crew Dragon was baselined with powered landings in mind, including a pre-determined return payload capacity.
NASA did not suddenly demand a higher return payload capacity. Return payload capacity is not the reason why SpaceX gave up on powered landings.

And since the reason seems to be the cost of doing to NASA's specs in time for commercial crew, and a powered landing obviously has enough the utility to justify it, I believe SpaceX will go ahead and get it done on their own time to their own satisfaction--unless a fully reusable ITS concept system is fairly near term, and then they'll go with that instead.

Offline tdperk

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Re: Red Dragon Discussion Thread (2)
« Reply #904 on: 08/22/2017 01:26 pm »
I've never understood the obsession with vertical powered landings on Earth.

Then I honestly must believe you do not understand math.  Water immersion and salt water in particular make replenishment for re-use difficult.  Replenishment for re-use is far less expensive than either build new or re-manufacture for re-use.

That last sentence is where the math comes in.

Offline Jim

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Re: Red Dragon Discussion Thread (2)
« Reply #905 on: 08/22/2017 01:36 pm »

And since the reason seems to be the cost of doing to NASA's specs in time for commercial crew, and a powered landing obviously has enough the utility to justify it, I believe SpaceX will go ahead and get it done on their own time to their own satisfaction-

Wrong.  Unsupported statement.  How do you know it is "NASA's specs".  How about it is just too expensive (maybe you don't understand the math) for anybody, since the only way to properly qualify it is to launch it?  There is no way to get a propulsive flight weight capsule high enough to TLYF.
« Last Edit: 08/22/2017 01:41 pm by Jim »

Offline yg1968

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Re: Red Dragon Discussion Thread (2)
« Reply #906 on: 08/22/2017 02:15 pm »
My guess is that propulsive landing isn't worth doing for only 6 flights. SpaceX had already stated that it wouldn't do it for the first few flights. The question then becomes, is it worth doing for just 3 or 4 flights? The answer seems to be no.
« Last Edit: 08/22/2017 02:16 pm by yg1968 »

Offline guckyfan

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Re: Red Dragon Discussion Thread (2)
« Reply #907 on: 08/22/2017 03:30 pm »
My guess is that propulsive landing isn't worth doing for only 6 flights. SpaceX had already stated that it wouldn't do it for the first few flights. The question then becomes, is it worth doing for just 3 or 4 flights? The answer seems to be no.

Including cargo there are more flights.

Offline whitelancer64

Re: Red Dragon Discussion Thread (2)
« Reply #908 on: 08/22/2017 03:41 pm »
You forgot accuracy, which I suspect is one of the primary reasons Dragon v2 landing was abandoned. Chaotic aerodynamic forces during reentry alter the post-reentry trajectory and this will vary the landing point quite dramatically (for example, Soyuz landings are often kilometers away from their targeted landing site), and Dragon doesn't have any aerodynamic control features to direct the capsule to a precise landing point like the Falcon 9 does. They could use thruster firings, but my suspicion is that they realized they couldn't reserve enough fuel for both worst-case scenario trajectory corrections and the landing burn.
The reason that Soyuz sometimes lands many miles off has nothing to do with "chaotic aerodynamic forces during reentry", but everything with lack of precision timing of the reentry burn as well as lack of precision management of the reentry burn profile.

On a system with proper systems, such as the current cargo Dragon, it's no big deal to do precision parachute landings. Cargo Dragon usually lands within a kilometer from the pre-positioned recovery ship.

Citation needed.

Quote
The only reason it isn't any closer is for safety reasons: you don't want all that mass to land on your head.
Precision parachuting into a radius of just a few hundred feat is no big deal actually as the both the US Amry and US Navy can tell you. And SpaceX has already accomplished that parachuting accuracy.

Citation needed.
"One bit of advice: it is important to view knowledge as sort of a semantic tree -- make sure you understand the fundamental principles, ie the trunk and big branches, before you get into the leaves/details or there is nothing for them to hang on to." - Elon Musk
"There are lies, damned lies, and launch schedules." - Larry J

Offline Arch Admiral

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Re: Red Dragon Discussion Thread (2)
« Reply #909 on: 08/23/2017 12:09 am »
You people who cite earlier programs like MOL, Soyuz, and Shuttle as evidence for what NASA managers consider acceptable in 2017 need to get real. Safety standards have risen at NASA just like everywhere else. Also, the political base for manned space flight has shrunken so much since The Good Old Days that a single fatal accident might well end the government program for good. I don't say I agree with this, but it is the reality that NASA management has to consider.

Offline deruch

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Re: Red Dragon Discussion Thread (2)
« Reply #910 on: 08/23/2017 03:19 am »
As an additional consideration, SpaceX now has a pretty good understanding of how much work it is taking them to refurbish and recertify Dragon 1 capsules after they get immersed in salt water.  So, maybe it is turning out to be less problematical (read: costly) than they had originally expected?  In which case, the cost driver for land landings maybe isn't such a big factor for the crewed capsules.  Though this thought does maybe "over-downplay" the difference of having the SuperDraco system get dunked for D2s.
Shouldn't reality posts be in "Advanced concepts"?  --Nomadd

Offline TomH

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Re: Red Dragon Discussion Thread (2)
« Reply #911 on: 08/23/2017 06:50 am »
As an additional consideration, SpaceX now has a pretty good understanding of how much work it is taking them to refurbish and recertify Dragon 1 capsules after they get immersed in salt water.  So, maybe it is turning out to be less problematical (read: costly) than they had originally expected?  In which case, the cost driver for land landings maybe isn't such a big factor for the crewed capsules.  Though this thought does maybe "over-downplay" the difference of having the SuperDraco system get dunked for D2s.

They don't have to open the hatch on the Dragon 1s, which protects the interior from saline. Could a Dragon 2 sit  with the hatch closed until after the capsule has been removed from the salt water and sprayed off? Opening the hatch in the open water would make it a lot easier for saline to get into the interior.

Offline woods170

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Re: Red Dragon Discussion Thread (2)
« Reply #912 on: 08/23/2017 07:01 am »
You people who cite earlier programs like MOL, Soyuz, and Shuttle as evidence for what NASA managers consider acceptable in 2017 need to get real. Safety standards have risen at NASA just like everywhere else. Also, the political base for manned space flight has shrunken so much since The Good Old Days that a single fatal accident might well end the government program for good. I don't say I agree with this, but it is the reality that NASA management has to consider.
Emphasis mine.
The same argument was heard after Challenger and Columbia. But US HSF is still very much alive and still very much in the lead. Another fatal accident will, IMO, not kill US HSF. The US general public will never accept a situation where the only people flying in space are from Europe, Japan, Russia and China (but not the USA).
« Last Edit: 08/23/2017 07:01 am by woods170 »

Offline woods170

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Re: Red Dragon Discussion Thread (2)
« Reply #913 on: 08/23/2017 07:27 am »
On a system with proper systems, such as the current cargo Dragon, it's no big deal to do precision parachute landings. Cargo Dragon usually lands within a kilometer from the pre-positioned recovery ship.

Citation needed.
SpaceX explained how they were going to get Cargo Dragon to land so accurate back in 2010. It's all about active steering during the non-parachute phase of re-entry and descent.
http://www.spacex.com/press/2012/12/19/spacexs-dragon-spacecraft-successfully-completes-high-altitude-drop-test

And it has worked beautifully so far. I've heard from multiple of my sources at SpaceX that the accuracy usually is exactly as advertised in the link above.
Also: I guess you've never seen the images and footage of Dragon-under-chutes taken from the recovery ship.

The only reason it isn't any closer is for safety reasons: you don't want all that mass to land on your head.
Precision parachuting into a radius of just a few hundred feat is no big deal actually as the both the US Amry and US Navy can tell you.

Citation needed.
About precision autonomous parachuting systems for the US armed forces:
https://en.wikipedia.org/wiki/Joint_Precision_Airdrop_System.
Stated accuracy: 50 to 75 meters (164 to 246 feet).
« Last Edit: 08/23/2017 07:49 am by woods170 »

Offline JAFO

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Re: Red Dragon Discussion Thread (2)
« Reply #914 on: 08/23/2017 04:34 pm »
You forgot accuracy, which I suspect is one of the primary reasons Dragon v2 landing was abandoned. Chaotic aerodynamic forces during reentry alter the post-reentry trajectory and this will vary the landing point quite dramatically (for example, Soyuz landings are often kilometers away from their targeted landing site), and Dragon doesn't have any aerodynamic control features to direct the capsule to a precise landing point like the Falcon 9 does. They could use thruster firings, but my suspicion is that they realized they couldn't reserve enough fuel for both worst-case scenario trajectory corrections and the landing burn.
The reason that Soyuz sometimes lands many miles off has nothing to do with "chaotic aerodynamic forces during reentry", but everything with lack of precision timing of the reentry burn as well as lack of precision management of the reentry burn profile.

On a system with proper systems, such as the current cargo Dragon, it's no big deal to do precision parachute landings. Cargo Dragon usually lands within a kilometer from the pre-positioned recovery ship.

Citation needed.

Quote
The only reason it isn't any closer is for safety reasons: you don't want all that mass to land on your head.
Precision parachuting into a radius of just a few hundred feat is no big deal actually as the both the US Amry and US Navy can tell you. And SpaceX has already accomplished that parachuting accuracy.

Citation needed.

Chariots for Apollo  https://www.hq.nasa.gov/office/pao/History/SP-4205/ch11-6.html

TindallGram from Bill Tindall to Jerome B. Hammack.

"The craft flew an entry curve to a point over northeast China, slanted to the southeast, and landed on target in the mid-Pacific. So accurate was the landing that it worried one of the chief mission planners and data watchers in Houston. Bill Tindall wrote to Jerome B. Hammack, head of the Landing and Recovery Division:
Jerry, I've done a lot of joking about the spacecraft hitting the aircraft carrier, but the more I think about it the less I feel it is a joke. There are reports that the C Prime command module came down right over the aircraft carrier
[stationed at 165 degrees 02.1' west longitude and 8 degrees 09.3' north latitude] and drifted on its chutes to land [at 165degrees 1.02' west and 8 degrees 07.5' north, only 4,572 meters] away. This really strikes me as being too close. . . . The consequence of the spacecraft hitting the carrier is truly catastrophic. . . . I seriously recommend relocating the recovery force at least [8 to 16 kilometers] from the target point."



Note: this TindallGram was written over 50 years ago, back in the days of unguided ring parachutes and before the days of ram air parachutes and GPS. Mr. Tindall states that the "There are reports that the C Prime command module came down right over the aircraft carrier" but subsequently drifted to land 4,52 meters away for landing.  Modern remote supply delivery has an accuracy within a couple hundred meters of a designated LZ, so I imagine a spacecraft using 21st century technology would be able to considerably improve on the Apollo-era accuracy.

"Ford, Dragon, 0.0, I have the ball."
« Last Edit: 08/23/2017 06:18 pm by JAFO »
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Offline whitelancer64

Re: Red Dragon Discussion Thread (2)
« Reply #915 on: 08/23/2017 04:56 pm »
Landing within 4.5 kilometers of the targeted landing site isn't really what I'd call pinpoint accuracy. It's similar to what Soyus has achieved.

https://forum.nasaspaceflight.com/index.php?topic=19141.msg1095791#msg1095791

Anyway, I had forgotten about the movable steering sled planned for Dragon v2, which does allay the landing accuracy concern I had had. It means that one of the other points Arch Admiral brought up must have been (or combined to be) the reason(s) why propulsive landing was cancelled for Dragon v2.
"One bit of advice: it is important to view knowledge as sort of a semantic tree -- make sure you understand the fundamental principles, ie the trunk and big branches, before you get into the leaves/details or there is nothing for them to hang on to." - Elon Musk
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Offline tdperk

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Re: Red Dragon Discussion Thread (2)
« Reply #916 on: 08/23/2017 07:33 pm »

And since the reason seems to be the cost of doing to NASA's specs in time for commercial crew, and a powered landing obviously has enough the utility to justify it, I believe SpaceX will go ahead and get it done on their own time to their own satisfaction-

Wrong.  Unsupported statement.  How do you know it is "NASA's specs".

Because SpaceX reported this this:

Quote
" “It was a tough decision,” he said when asked about propulsive landing capability during a question-and-answer session. “Technically it still is, although you’d have to land it on some pretty soft landing pad because we’ve deleted the little legs that pop out of the heat shield.”

SpaceX planned to transition from splashdowns, which is how the current cargo version of the Dragon returns to Earth, to “propulsive” landings at a pad at some point after the vehicle’s introduction. Certification issues, he said, for propulsive landings led him to cancel those plans.

“It would have taken a tremendous amount of effort to qualify that for safety, particularly for crew transport,” he said. "  <--  http://spacenews.com/spacex-drops-plans-for-powered-dragon-landings/

Please note he did not say it would be hard to design or build it, but only hard to qualify it.  It's not reading into it too much to think is it the specs vs. payment offered of the only paying customer which made the effort unreasonable, when plainly not dunking the ship in salt water is better if it can be avoided.

How about it is just too expensive (maybe you don't understand the math) for anybody, since the only way to properly qualify it is to launch it?

I know math and English well, and know with respect to the latter the words not chosen to be used mean as much as what are used.  Looks like an all-up flight would be in the neighborhood of $180~200mn to test from orbit, per spitballing.

I would not be shocked--unless they have near term plans to replace the Crew Dragon with something else entirely--if in the next several years they went ahead and did propulsive landings with the Crew Dragon for all customers but NASA, which organization is welcome to pay for as much replaced and refurbished hardware as it likes.

Welcome other than how the taxpayers feel about it.
« Last Edit: 08/23/2017 07:35 pm by tdperk »

Offline Jim

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Re: Red Dragon Discussion Thread (2)
« Reply #917 on: 08/23/2017 07:58 pm »

Please note he did not say it would be hard to design or build it, but only hard to qualify it.  It's not reading into it too much to think is it the specs vs. payment offered of the only paying customer which made the effort unreasonable, when plainly not dunking the ship in salt water is better if it can be avoided.


Wrong interpretation.  NASA "specs" have nothing to do with it.  It can't be cheaply qualified to anybody's specs, short of having no qualification program.  "hard to qualify it" means it is costly and not that specs are the issue.

I would not be shocked--unless they have near term plans to replace the Crew Dragon with something else entirely--if in the next several years they went ahead and did propulsive landings with the Crew Dragon for all customers but NASA, which organization is welcome to pay for as much replaced and refurbished hardware as it likes


That is completely inane.  Spacex or other customers are not going to pay for X number (about as many parachute drop tests for Dragon 1) of $180~200m flights to qualify the capability.   It is dead and gone.

Replacing and refurbishing hardware from water landings is cheaper than qualifying propulsive landings.

Just another case of unsupported NASA bashing
« Last Edit: 08/23/2017 08:10 pm by Jim »

Offline tdperk

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Re: Red Dragon Discussion Thread (2)
« Reply #918 on: 08/23/2017 08:42 pm »

Please note he did not say it would be hard to design or build it, but only hard to qualify it.  It's not reading into it too much to think is it the specs vs. payment offered of the only paying customer which made the effort unreasonable, when plainly not dunking the ship in salt water is better if it can be avoided.


Wrong interpretation.  NASA "specs" have nothing to do with it.  It can't be cheaply qualified to anybody's specs, short of having no qualification program.  "hard to qualify it" means it is costly and not that specs are the issue.

I would not be shocked--unless they have near term plans to replace the Crew Dragon with something else entirely--if in the next several years they went ahead and did propulsive landings with the Crew Dragon for all customers but NASA, which organization is welcome to pay for as much replaced and refurbished hardware as it likes


That is completely inane.  Spacex or other customers are not going to pay for X number (about as many parachute drop tests for Dragon 1) of $180~200m flights to qualify the capability.   It is dead and gone.

Replacing and refurbishing hardware from water landings is cheaper than qualifying propulsive landings.

Water landings requiring rebuild are cheaper than how NASA wants propulsive landing qualifications done.  I'm glad you agree.

What is not merely innane but insane is to write is you think they had the idea it wouldn't need to be qualified.

The nature of the specifics of the qualifications are at what is at issue.

Just another case of unsupported NASA bashing.

Actually I think there was an IG report that said the chief cause of the delays in CC was the length of time it took NASA to complete a review of data for a stage gate.  So possibly NASA is not being intelligently cautious.

There's also the fact NASA reported the Falcon development cost 1/10th what it would cost NASA to do, quite possibly it can fairly cost 1/10th what NASA told SpaceX to spend on the matter, and Musk isn't willing to burn money uselessly.

He may well do it for one 10th the cost on his own dime for his own purposes--or maybe he has something else in mind entirely.
« Last Edit: 08/23/2017 09:00 pm by tdperk »

Offline JamesH65

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Re: Red Dragon Discussion Thread (2)
« Reply #919 on: 08/24/2017 01:06 pm »
SpaceX have quite a few old boosters hanging around. Fuel costs around $300k. Lots of other costs of course. But really, would it be that expensive to have a Dragon 2 propulsive landing test flight on a refurbished booster? If I am reading the above posts correctly, people are saying test flights would be over $100M each. That seems excessive.

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