Author Topic: SpaceX Dragon V2 Updates and Discussion  (Read 540571 times)

Offline Lars-J

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Re: SpaceX Dragon V2 Updates and Discussion
« Reply #540 on: 02/27/2015 08:24 PM »
Some interesting new information from the Garrett Reisman pre-congressional-hearing written statement released today:

http://science.house.gov/sites/republicans.science.house.gov/files/documents/HHRG-114-SY16-WState-GReisman-20150227.pdf

Some interesting information within...

Crew Dragon:
Quote
Crew Dragon is comprised of three main structural elements: the nosecone, which protects the vessel and the docking adaptor during ascent and reentry; the spacecraft, which houses the crew and pressurized cargo, as well as the service section (containing avionics, directional thrusters, parachutes, and other infrastructure); and the trunk, which will support Crew Dragonís solar arrays and radiators, as well as providing aerodynamic stability during aborts.

- Trunk fins for abort stability is confirmed.

Quote
Dragonís passively stable shape generates lift as it reenters the Earthís atmosphere supersonically. I In addition to the 8 SuperDraco engines onboard Crew Dragon, its 16 Draco thrusters provide 2-fault tolerant roll control during reentry for precision guidance on course for a soft touchdown on land. Additionally, a movable ballast sled allows the angle of attack to be actively controlled during entry to further provide precision landing control. The rew Dragonís SuperDraco engines are divided into four quads, each with two SuperDracos and 4 Draco engines. The SuperDracos will activate to provide precision land landing capability. Nominally, only two quads are used for on-orbit propellant with the Dracos and two quads are reserved for propulsive landing using the SuperDracos. For aborts or onorbit faults, all four quads are available for Draco or SuperDraco operations, increasing flexibility, robustness, and performance in these
critical situations.

- The movable ballast sled is a new information! I wonder where it is located?
- 50% of the propellant is reserved for landing. (nominally, but can be used for other purposes)

Quote
Crew Dragon carries sufficient breathable gas stores to allow for a safe return to Earth in the event of a leak of up to an equivalent orifice of 0.25 inches in diameter. As an extra level of protection, the crew will wear SpaceX-designed spacesuits to protect them from a rapid cabin depressurization emergency event of even greater severity. The suits and the vehicle itself will be rated for operation at vacuum.

- Presumably this means that the interior electronics will be vacuum rated?

Quote
Notably, the Cargo Dragon and Falcon 9 are scheduled to fly together at least 9 more times before the first Crew Dragon manned test flight in 2017. The Falcon 9 itself is scheduled to launch more than 50 times prior to the first Dragon crew mission

EDIT: more...

Quote
Since submitting the CCtCap proposal in January 2014, SpaceX has continued to enhance the Crew Dragon design to improve safety, operational flexibility, and reliability. These improvements include: the ability to perform precision propulsive land landing with full fault tolerance; increased propellant tank capacity for improved mission performance and to support propulsive landing; a movable ballast system to allow for high precision landings; life support system components moved from the trunk into the capsule service section to increase reliability; and consolidated avionics components to decrease complexity. The near doubling of the propellant tank capacity significantly increases the available impulse of the LAS allowing the capsule to travel further away from a failing launch vehicle. Additionally, the migration of life support consumables into the capsule allows the capsule to maintain pressure during the entire descent phase assuming a worst-case leak. Active center of gravity control allows for lift vector modulation for precise landings that ultimately enable fast access to the
returning crew either on land or in the water.

- The current iteration of the Dragon v2 design has close to double the propellant of the first proposal (similar to Cargo Dragon I assume)
- Crew consumables appear to be stored in the pressurized volume? (or in the unpressurized service ring?)
- Again a reference to the movable ballast sled

Quote
Precision propulsive land landing will be certified in parallel with parachute to water landing for Crew Dragon. This will allow the teams to stay on schedule and ensure U.S. crew transportation safely and reliably in 2017. Land landing will become the baseline for the early post-certification missions; in the meantime, precision water landing under parachutes has been proposed as the baseline return and recovery approach for the first few flights of Crew Dragon.

- For schedule reasons, the first few flights will do water landing.
- But propulsive land landings have not been abandoned :)


Pad 39A:
Quote
SpaceX is investing over $60 million in LC-39A to modernize the complex for Crew Dragon, Falcon 9
and Falcon Heavy. Construction on the hangar has begun and will be completed later this year. Taking advantage of the existing launch tower, SpaceX will add a crew gantry access arm and white room to allow for crew and cargo ingress to the vehicle. The existing Space Shuttle evacuation slide-wire basket system will also be re-purposed to provide a safe emergency egress for the Dragon crew in the event of an emergency on the pad that does not necessitate using the Crew Dragonís launch abort system.

- Crew access arm will be added to the existing tower
- Shuttle slide-wire escape baskets will be used
« Last Edit: 02/27/2015 08:40 PM by Lars-J »

Offline kevinof

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Re: SpaceX Dragon V2 Updates and Discussion
« Reply #541 on: 02/27/2015 08:37 PM »
Will be interesting to see what the interior of the Dragon 2 is like now compared to the original reveal. My guess is that it will be a lot more "cramped" with lots more equipment and systems installed.

It is interesting that there is a movable ballast system. Did/Does any other capsule have such a system?

Offline Lars-J

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Re: SpaceX Dragon V2 Updates and Discussion
« Reply #542 on: 02/27/2015 08:41 PM »
Will be interesting to see what the interior of the Dragon 2 is like now compared to the original reveal. My guess is that it will be a lot more "cramped" with lots more equipment and systems installed.

Yes, clearly. But shhhh... don't say it too loud, you'll be shouted down as an unbeliever for not thinking that was a flight-ready interior.  ;)

Offline kevinof

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Re: SpaceX Dragon V2 Updates and Discussion
« Reply #543 on: 02/27/2015 08:45 PM »
Oops. too late.

It's great that they are still pushing ahead with propulsive landings. That's great to see.

Will be interesting to see what the interior of the Dragon 2 is like now compared to the original reveal. My guess is that it will be a lot more "cramped" with lots more equipment and systems installed.

Yes, clearly. But shhhh... don't say it too loud, you'll be shouted down as an unbeliever for not thinking that was a flight-ready interior.  ;)

Offline deruch

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Re: SpaceX Dragon V2 Updates and Discussion
« Reply #544 on: 02/28/2015 01:34 AM »
Some interesting new information from the Garrett Reisman pre-congressional-hearing written statement released today:

http://science.house.gov/sites/republicans.science.house.gov/files/documents/HHRG-114-SY16-WState-GReisman-20150227.pdf

Some interesting information within...

Quote from: Reisman's Statement
Crew Dragonís seats are being designed with advanced occupant protections that draw on lessons learned from the Space Shuttle Columbia accident investigation reports, as well as the latest in automotive occupant protection technologies.

-2 of the recommendations from the Aeromedical investigation of the Columbia accident (.pdf) were "6. The design of the seat restraint systems should include considerations to preclude restraint-induced injuries during dynamic motion (e.g., NASCAR racing-type straps). 7. The suit-seat-restraint system should provide support for the head-neck complex (e.g., conformal helmets, head and neck restraint-type devices)."  The second one of those sounds something like the HANS device employed in race cars.  In light of this, maybe it's not so surprising that the seats from the unveiling looked so much like car seats.

Quote
Crew Dragon can suffer a failure within its system and still operate safely during the majority of the ascent.  (emphasis added)

-I thought this was an interesting point.  They've said that the SuperDraco LAS can provide safe abort the whole ride up.  But, if there's a failure within that system, they end up with at least some black zone.  I assume this is around the max drag point where they'd need the most effort to escape an exploding stage.  NB: This is not a criticism of the system or SpaceX's previous statements.  I'm actually impressed that they are still able to safely abort most of the time with a failure in the system.
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Offline deruch

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Re: SpaceX Dragon V2 Updates and Discussion
« Reply #545 on: 02/28/2015 02:05 AM »
video of the hearing:

Shouldn't reality posts be in "Advanced concepts"?  --Nomadd

Online meekGee

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Re: SpaceX Dragon V2 Updates and Discussion
« Reply #546 on: 02/28/2015 02:36 AM »
Some interesting new information from the Garrett Reisman pre-congressional-hearing written statement released today:

http://science.house.gov/sites/republicans.science.house.gov/files/documents/HHRG-114-SY16-WState-GReisman-20150227.pdf

Some interesting information within...

Crew Dragon:
Quote
Crew Dragon is comprised of three main structural elements: the nosecone, which protects the vessel and the docking adaptor during ascent and reentry; the spacecraft, which houses the crew and pressurized cargo, as well as the service section (containing avionics, directional thrusters, parachutes, and other infrastructure); and the trunk, which will support Crew Dragonís solar arrays and radiators, as well as providing aerodynamic stability during aborts.

- Trunk fins for abort stability is confirmed.

Quote
Dragonís passively stable shape generates lift as it reenters the Earthís atmosphere supersonically. I In addition to the 8 SuperDraco engines onboard Crew Dragon, its 16 Draco thrusters provide 2-fault tolerant roll control during reentry for precision guidance on course for a soft touchdown on land. Additionally, a movable ballast sled allows the angle of attack to be actively controlled during entry to further provide precision landing control. The rew Dragonís SuperDraco engines are divided into four quads, each with two SuperDracos and 4 Draco engines. The SuperDracos will activate to provide precision land landing capability. Nominally, only two quads are used for on-orbit propellant with the Dracos and two quads are reserved for propulsive landing using the SuperDracos. For aborts or onorbit faults, all four quads are available for Draco or SuperDraco operations, increasing flexibility, robustness, and performance in these
critical situations.

- The movable ballast sled is a new information! I wonder where it is located?
- 50% of the propellant is reserved for landing. (nominally, but can be used for other purposes)

Quote
Crew Dragon carries sufficient breathable gas stores to allow for a safe return to Earth in the event of a leak of up to an equivalent orifice of 0.25 inches in diameter. As an extra level of protection, the crew will wear SpaceX-designed spacesuits to protect them from a rapid cabin depressurization emergency event of even greater severity. The suits and the vehicle itself will be rated for operation at vacuum.

- Presumably this means that the interior electronics will be vacuum rated?

Quote
Notably, the Cargo Dragon and Falcon 9 are scheduled to fly together at least 9 more times before the first Crew Dragon manned test flight in 2017. The Falcon 9 itself is scheduled to launch more than 50 times prior to the first Dragon crew mission

EDIT: more...

Quote
Since submitting the CCtCap proposal in January 2014, SpaceX has continued to enhance the Crew Dragon design to improve safety, operational flexibility, and reliability. These improvements include: the ability to perform precision propulsive land landing with full fault tolerance; increased propellant tank capacity for improved mission performance and to support propulsive landing; a movable ballast system to allow for high precision landings; life support system components moved from the trunk into the capsule service section to increase reliability; and consolidated avionics components to decrease complexity. The near doubling of the propellant tank capacity significantly increases the available impulse of the LAS allowing the capsule to travel further away from a failing launch vehicle. Additionally, the migration of life support consumables into the capsule allows the capsule to maintain pressure during the entire descent phase assuming a worst-case leak. Active center of gravity control allows for lift vector modulation for precise landings that ultimately enable fast access to the
returning crew either on land or in the water.

- The current iteration of the Dragon v2 design has close to double the propellant of the first proposal (similar to Cargo Dragon I assume)
- Crew consumables appear to be stored in the pressurized volume? (or in the unpressurized service ring?)
- Again a reference to the movable ballast sled

Quote
Precision propulsive land landing will be certified in parallel with parachute to water landing for Crew Dragon. This will allow the teams to stay on schedule and ensure U.S. crew transportation safely and reliably in 2017. Land landing will become the baseline for the early post-certification missions; in the meantime, precision water landing under parachutes has been proposed as the baseline return and recovery approach for the first few flights of Crew Dragon.

- For schedule reasons, the first few flights will do water landing.
- But propulsive land landings have not been abandoned :)


Pad 39A:
Quote
SpaceX is investing over $60 million in LC-39A to modernize the complex for Crew Dragon, Falcon 9
and Falcon Heavy. Construction on the hangar has begun and will be completed later this year. Taking advantage of the existing launch tower, SpaceX will add a crew gantry access arm and white room to allow for crew and cargo ingress to the vehicle. The existing Space Shuttle evacuation slide-wire basket system will also be re-purposed to provide a safe emergency egress for the Dragon crew in the event of an emergency on the pad that does not necessitate using the Crew Dragonís launch abort system.

- Crew access arm will be added to the existing tower
- Shuttle slide-wire escape baskets will be used

Sensational new information support the far-fetched notion that SpaceX actually does analysis and ground testing :)

But, seriously now - any idea what this sled is?  "Movable ballast" - ballast against what?  Is this for changing the location of the cg under some test condition?

I tried googling it, but it's hard to wade through the references to fluorescent lighting and sailing boats.
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Offline DavidH

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Re: SpaceX Dragon V2 Updates and Discussion
« Reply #547 on: 02/28/2015 02:38 AM »
Some interesting new information from the Garrett Reisman pre-congressional-hearing written statement released today:

http://science.house.gov/sites/republicans.science.house.gov/files/documents/HHRG-114-SY16-WState-GReisman-20150227.pdf

Some interesting information within...

Crew Dragon:
Quote
Crew Dragon is comprised of three main structural elements: the nosecone, which protects the vessel and the docking adaptor during ascent and reentry; the spacecraft, which houses the crew and pressurized cargo, as well as the service section (containing avionics, directional thrusters, parachutes, and other infrastructure); and the trunk, which will support Crew Dragonís solar arrays and radiators, as well as providing aerodynamic stability during aborts.

- Trunk fins for abort stability is confirmed.

Quote
Dragonís passively stable shape generates lift as it reenters the Earthís atmosphere supersonically. I In addition to the 8 SuperDraco engines onboard Crew Dragon, its 16 Draco thrusters provide 2-fault tolerant roll control during reentry for precision guidance on course for a soft touchdown on land. Additionally, a movable ballast sled allows the angle of attack to be actively controlled during entry to further provide precision landing control. The rew Dragonís SuperDraco engines are divided into four quads, each with two SuperDracos and 4 Draco engines. The SuperDracos will activate to provide precision land landing capability. Nominally, only two quads are used for on-orbit propellant with the Dracos and two quads are reserved for propulsive landing using the SuperDracos. For aborts or onorbit faults, all four quads are available for Draco or SuperDraco operations, increasing flexibility, robustness, and performance in these
critical situations.

- The movable ballast sled is a new information! I wonder where it is located?
- 50% of the propellant is reserved for landing. (nominally, but can be used for other purposes)

Quote
Crew Dragon carries sufficient breathable gas stores to allow for a safe return to Earth in the event of a leak of up to an equivalent orifice of 0.25 inches in diameter. As an extra level of protection, the crew will wear SpaceX-designed spacesuits to protect them from a rapid cabin depressurization emergency event of even greater severity. The suits and the vehicle itself will be rated for operation at vacuum.

- Presumably this means that the interior electronics will be vacuum rated?

Quote
Notably, the Cargo Dragon and Falcon 9 are scheduled to fly together at least 9 more times before the first Crew Dragon manned test flight in 2017. The Falcon 9 itself is scheduled to launch more than 50 times prior to the first Dragon crew mission

EDIT: more...

Quote
Since submitting the CCtCap proposal in January 2014, SpaceX has continued to enhance the Crew Dragon design to improve safety, operational flexibility, and reliability. These improvements include: the ability to perform precision propulsive land landing with full fault tolerance; increased propellant tank capacity for improved mission performance and to support propulsive landing; a movable ballast system to allow for high precision landings; life support system components moved from the trunk into the capsule service section to increase reliability; and consolidated avionics components to decrease complexity. The near doubling of the propellant tank capacity significantly increases the available impulse of the LAS allowing the capsule to travel further away from a failing launch vehicle. Additionally, the migration of life support consumables into the capsule allows the capsule to maintain pressure during the entire descent phase assuming a worst-case leak. Active center of gravity control allows for lift vector modulation for precise landings that ultimately enable fast access to the
returning crew either on land or in the water.

- The current iteration of the Dragon v2 design has close to double the propellant of the first proposal (similar to Cargo Dragon I assume)
- Crew consumables appear to be stored in the pressurized volume? (or in the unpressurized service ring?)
- Again a reference to the movable ballast sled

Quote
Precision propulsive land landing will be certified in parallel with parachute to water landing for Crew Dragon. This will allow the teams to stay on schedule and ensure U.S. crew transportation safely and reliably in 2017. Land landing will become the baseline for the early post-certification missions; in the meantime, precision water landing under parachutes has been proposed as the baseline return and recovery approach for the first few flights of Crew Dragon.

- For schedule reasons, the first few flights will do water landing.
- But propulsive land landings have not been abandoned :)


Pad 39A:
Quote
SpaceX is investing over $60 million in LC-39A to modernize the complex for Crew Dragon, Falcon 9
and Falcon Heavy. Construction on the hangar has begun and will be completed later this year. Taking advantage of the existing launch tower, SpaceX will add a crew gantry access arm and white room to allow for crew and cargo ingress to the vehicle. The existing Space Shuttle evacuation slide-wire basket system will also be re-purposed to provide a safe emergency egress for the Dragon crew in the event of an emergency on the pad that does not necessitate using the Crew Dragonís launch abort system.

- Crew access arm will be added to the existing tower
- Shuttle slide-wire escape baskets will be used

Sensational new information support the far-fetched notion that SpaceX actually does analysis and ground testing :)

But, seriously now - any idea what this sled is?  "Movable ballast" - ballast against what?  Is this for changing the location of the cg under some test condition?

I tried googling it, but it's hard to wade through the references to fluorescent lighting and sailing boats.
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Offline Herb Schaltegger

Re: SpaceX Dragon V2 Updates and Discussion
« Reply #548 on: 02/28/2015 02:44 AM »

But, seriously now - any idea what this sled is?  "Movable ballast" - ballast against what?  Is this for changing the location of the cg under some test condition?

I tried googling it, but it's hard to wade through the references to fluorescent lighting and sailing boats.

It's not ballast "against" anything, except gravity (well, acceleration). You put a mass (tungsten, probably, or possibly lead) on a system of rails and move it to move the center of gravity. The differential between center of gravity and center of pressure will directly affect the coefficient of lift and and hence the trajectory of the reentry. Apollo's CG was fixed and the reentry trajectory was "flown" by rotation in order to create wide but very shallow turns (smaller scale versions of the shuttle's well-known entry S-turns). Dragon will evidently do the same thing, but CG is adjustable with this ballast sled system.
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Offline the_other_Doug

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Re: SpaceX Dragon V2 Updates and Discussion
« Reply #549 on: 02/28/2015 02:47 AM »
But, seriously now - any idea what this sled is?  "Movable ballast" - ballast against what?  Is this for changing the location of the cg under some test condition?

I tried googling it, but it's hard to wade through the references to fluorescent lighting and sailing boats.

I bet it's for the newest SpaceX design -- a Dragon that can also function as a submersible boat.  ;)

Seriously, this is the first I've heard of the Dragon V2 having "active CG control" as a part of its entry control suite.  Good idea, but they'll need to make very sure the sled mass can't easily break free from restraints and move freely -- if there is enough play in its motion, that could result in an uncontrollable situation.

With the talk about moving crew provisioning from the trunk into the cabin (i.e., air supplies), I wonder if that, or other relatively massive supplies or devices, will be the mass (or part of it) attached to this sled?  I'd say that whatever the mass is, it ought to be something more than just dead weight.  I'd think it would be a waste of the payload capacity of the vehicle to take up a lot of its weight and mass margin with a big sled covered with simple lead weights.
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Offline Robotbeat

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Re: SpaceX Dragon V2 Updates and Discussion
« Reply #550 on: 02/28/2015 02:48 AM »

And where are you going to dispose of the trunk?  El Paso?

Drop it in the Pacific Ocean. Dragon can fly 10 minutes without it plus the time from atmospheric contact to landing.

How? The trunk has no propulsion on its own. You either do a deorbit burn with it or you leave in orbit.

You are right. They could leave it in orbit but then it would descend anywhere without control.

This is simple to solve. Just do 2 deorbit burns. The first one with the trunk attached and the second without. Trunk lands in the ocean (perhaps the Gulf... are we still talking landing in Texas?) and Dragon on land.
« Last Edit: 02/28/2015 03:43 AM by Robotbeat »
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Offline darkenfast

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Re: SpaceX Dragon V2 Updates and Discussion
« Reply #551 on: 02/28/2015 03:01 AM »
Will be interesting to see what the interior of the Dragon 2 is like now compared to the original reveal. My guess is that it will be a lot more "cramped" with lots more equipment and systems installed.

It is interesting that there is a movable ballast system. Did/Does any other capsule have such a system?

There's a section that (as far as I know), we've never seen on V2.  Its the disk-shaped area under the deck of the "cabin".  It's about seven feet in diameter and about two feet deep.  A good look at that would answer a lot of questions.

Offline dglow

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Re: SpaceX Dragon V2 Updates and Discussion
« Reply #552 on: 02/28/2015 03:15 AM »
There's a section that (as far as I know), we've never seen on V2.  Its the disk-shaped area under the deck of the "cabin".  It's about seven feet in diameter and about two feet deep.  A good look at that would answer a lot of questions.

I can't wait for the artful cross-section digram of Dragon 2. I grew up with one of the Shuttle Orbiter taped to my bedroom wall. :D

Online meekGee

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Re: SpaceX Dragon V2 Updates and Discussion
« Reply #553 on: 02/28/2015 03:52 AM »

But, seriously now - any idea what this sled is?  "Movable ballast" - ballast against what?  Is this for changing the location of the cg under some test condition?

I tried googling it, but it's hard to wade through the references to fluorescent lighting and sailing boats.

It's not ballast "against" anything, except gravity (well, acceleration). You put a mass (tungsten, probably, or possibly lead) on a system of rails and move it to move the center of gravity. The differential between center of gravity and center of pressure will directly affect the coefficient of lift and and hence the trajectory of the reentry. Apollo's CG was fixed and the reentry trajectory was "flown" by rotation in order to create wide but very shallow turns (smaller scale versions of the shuttle's well-known entry S-turns). Dragon will evidently do the same thing, but CG is adjustable with this ballast sled system.

Oh - thanks.   I misread it...

Yes, I've heard of that, in military reentry vehicles.  Also, IIRC during MSL's "seven minutes of terror" video, there was a graphic that alluded to that, but I don't remember other information.

Good - it's elegant.

I suppose it also takes care of trim issues due to payload distribution - you can have some leeway if the system can correct for it.

DavidH - the trick is to lower the bar as much as possible, and then stumble over it.   Or just the second half.

EDIT:

In the first few seconds, it shows what I interpreted as the vehicle being moved inside the aeroshell.  No exactly how you'd do it in a Dragon, but still.

« Last Edit: 02/28/2015 03:55 AM by meekGee »
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Offline cosmicvoid

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Re: SpaceX Dragon V2 Updates and Discussion
« Reply #554 on: 02/28/2015 03:57 AM »
Is this "ballast" necessarily solid?  It could be a fluid system, perhaps to pump water to/from 1 of 4 quadrant tanks.
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Offline Lars-J

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Re: SpaceX Dragon V2 Updates and Discussion
« Reply #555 on: 02/28/2015 04:08 AM »

Is this "ballast" necessarily solid?  It could be a fluid system, perhaps to pump water to/from 1 of 4 quadrant tanks.

Calling it a ballast "sled" seems to imply it is solid.

Offline bstrong

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Re: SpaceX Dragon V2 Updates and Discussion
« Reply #556 on: 02/28/2015 05:33 AM »
With the talk about moving crew provisioning from the trunk into the cabin (i.e., air supplies), I wonder if that, or other relatively massive supplies or devices, will be the mass (or part of it) attached to this sled?  I'd say that whatever the mass is, it ought to be something more than just dead weight.  I'd think it would be a waste of the payload capacity of the vehicle to take up a lot of its weight and mass margin with a big sled covered with simple lead weights.

How about a Li-ion battery pack? It seems to ballast a Model S nicely.

Offline somepitch

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Re: SpaceX Dragon V2 Updates and Discussion
« Reply #557 on: 02/28/2015 05:38 AM »

Is this "ballast" necessarily solid?  It could be a fluid system, perhaps to pump water to/from 1 of 4 quadrant tanks.

Calling it a ballast "sled" seems to imply it is solid.

Would seem a waste to use some solid, otherwise useless mass - I wonder if they'll do something fancy like have the batteries as a moveable mass on the sled. Would that be possible?

Offline Nomadd

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Re: SpaceX Dragon V2 Updates and Discussion
« Reply #558 on: 02/28/2015 06:15 AM »
Is this "ballast" necessarily solid?  It could be a fluid system, perhaps to pump water to/from 1 of 4 quadrant tanks.

No chance. You definitely don't want ballast to be "moveable" as in partly filled tanks. That sort of moveable ballast is what capsizes ships and tips half full tanker trucks on ess curves. My wildass guess would be a weight on two jack screws, although, hydraulics would probably be faster.

Offline obi-wan

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Re: SpaceX Dragon V2 Updates and Discussion
« Reply #559 on: 02/28/2015 06:25 AM »
MSL/Curiosity had to have a CG on centerline because it was spin-stabilized during cruise. One ballast mass was ejected before entry to provide asymmetrical CG for lift, used to improve landing targeting. The second was ejected to allow the aeroshell to hang straight under the parachute for Skycrane separation.

There's really no reason to move the CG, as you can mitigate the effect of the lift by rolling around the velocity vector to produce zero net lift. (This is how Soyuz achieves a ballistic entry following a guidance failure.) A CG shift would move the stagnation point, and vary the ablation pattern on the heat shield. It also affects aft wake heating on the sides of the spacecraft. I wonder if the CG shift is necessary to reduce wake heating on the SuperDraco pods? It really looks like there would be wake impingement on the pod structure, particularly on the side closest to the CG...

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