SpaceX Dragon 2 Updates and Discussion - Thread 3

[Coastal Ron]

I think you are making the Dragon landing more complicated than it really is.  The Dragon is heavy about 5 Metric Tons. Dragon is descending under 3 or 4 parachutes; no steering. It's unguided.  Dragon on it's final 500 meters will be drifting at some fraction of the wind speed. If the wind is 10 Kts dragon might be going 5 Kts.  Dragon has a considerable inertia with respect to wind gusts due to it's mass. In addition Dragon is landing in open ocean which reduces wind gusts to more of a constant wind.  The towing vessel should be able to keep the dragon centered Port starboard. (Right to Left) The large boat carries a small support boat a RIB (Rigid hull Inflatable Boat).  The RIB will take position perpendicular to the target and give adjustments to the towing vessel to keep Dragon centered Fore Aft ( Front to Back)

Such a system could not rely on human judgement, it would need a computer controlled three-dimensional positioning system that could anticipate how quickly each moving body (i.e. lead boat, landing pad, positioning craft, & spacecraft) could change their speed and direction.

Could such a system work? I would like to think so, but for right now I really don't have a clue what that round bouncy thing will be used for, so I'll wait for our NSF members to do more digging... 

[oiorionsbelt]

If D2 misses the "Bouncy Castle" all is nominal.
 What's the worst that can happen if it doesn't hit it just right to catch it?

[Roy_H]

If D2 misses the "Bouncy Castle" all is nominal.
 What's the worst that can happen if it doesn't hit it just right to catch it?

Hitting the tow ship.

[GWH]

I think you are making the Dragon landing more complicated than it really is.  The Dragon is heavy about 5 Metric Tons. Dragon is descending under 3 or 4 parachutes; no steering. It's unguided.  Dragon on it's final 500 meters will be drifting at some fraction of the wind speed. If the wind is 10 Kts dragon might be going 5 Kts.  Dragon has a considerable inertia with respect to wind gusts due to it's mass. In addition Dragon is landing in open ocean which reduces wind gusts to more of a constant wind.  The towing vessel should be able to keep the dragon centered Port starboard. (Right to Left) The large boat carries a small support boat a RIB (Rigid hull Inflatable Boat).  The RIB will take position perpendicular to the target and give adjustments to the towing vessel to keep Dragon centered Fore Aft ( Front to Back)

Wouldn't the reaction time on port/starboard movements be quite slow given a tow line of any particular length?
I would expect forward velocity (fore/aft, parallel to direction of Dragon drift) to be quite easy to maintain, but perpendicular movements (starboard/port) to be more difficult. Or am I misunderstanding your directions?

An alternative arrangement could be two boats travelling in parallel, each with a tow line attached to a corner of the tug.
Starboard/port adjustments could be made by shortening line length on either side. 
An exaggerated view would look like this, boats are U's, O is the landing pad. Ideally the cables would be as close to perpendicular as possible.

U      U
   \  /
    O

From my experience of catching a drifting model rocket out of midair while driving an ATV, I have 100% confidence in Space X's ability to pull this off 

[whitelancer64]

I noticed that in the recent pictures of the interior, there where just four seats in the Dragon 2 Trainers. I do remember earlier pictures showing up to three additional seats. Were those nixed? When this was done? Or is it that there is a planned flexibility to make the interior with more seats in case needed?

Four seats has always been the base configuration for NASA flights.

Wasn't there talk of something to enable a single Dragon to evacuate a 7 person crew?

They would have to remove the cargo areas and the toilet, and then install 3 more seats in order to do that.

I don't believe they have to remove cargo area and toilet. It is a NASA requirement that they have 7 seats available for emergency evacuation. I assume this means that 3 spare seats will be stored on the ISS. This requirement applies to both the Dragon and Starliner.

I'm not aware of that being a NASA requirement.

[Doesitfloat]

Comment about flight computers.

Is Dragon using a SpaceX flight computer similar to the Cargo Dragon?  Their system if I remember is a "fault tolerant design" meaning the computer system has 3 to 5 independent computers that constantly check each other for errors. This system allows for the computers to perform more functions than a single hardened computer. The additional functions could be color displays instead of monochrome and touchscreens with digital switches.  SpaceX has shown this system to be robust enough to visit the ISS on all their Demonstration and CRS Missions.


Starliner is using a legacy hardened flight computer. The system uses a smaller computer. Functions not controlled by the computer can be monitored and controlled by dedicated circuits (Circuits feed data to computer but are not controlled by it).

Thus the difference between the Dragon with big touchscreens and Starliner with lots of switches.

[docmordrid]

Comment about flight computers.

Is Dragon using a SpaceX flight computer similar to the Cargo Dragon?  Their system if I remember is a "fault tolerant design" meaning the computer system has 3 to 5 independent computers that constantly check each other for errors.
>

Article about Dragon 1's computers, which likely have done nothing but get more robust.

AvWeek 2012...

Not sure about its accuracy, but a redditor claimed the Crew Dragon UI is done in Chromium and WebGL.

[oiorionsbelt]

Comment about flight computers.

Is Dragon using a SpaceX flight computer similar to the Cargo Dragon?  Their system if I remember is a "fault tolerant design" meaning the computer system has 3 to 5 independent computers that constantly check each other for errors.
>

Article about Dragon 1's computers, which likely have done nothing but get more robust.

AvWeek 2012...

Not sure about its accuracy, but a redditor claimed the Crew Dragon UI is done in Chromium and WebGL.

Thanks for that link, it was good to read it again.
 Wonder what generation they are on 12 years later?

[oiorionsbelt]

If D2 misses the "Bouncy Castle" all is nominal.
 What's the worst that can happen if it doesn't hit it just right to catch it?

Hitting the tow ship.

How likely is that?  Seems, as though a fast boat could "easily" get out of the way of a capsule descending under parachutes. Wrong?

 Lets say the boat can get out of the way of the capsule, is hitting the raft thingy on the edge a problem for the capsule?

[Roy_H]

I noticed that in the recent pictures of the interior, there where just four seats in the Dragon 2 Trainers. I do remember earlier pictures showing up to three additional seats. Were those nixed? When this was done? Or is it that there is a planned flexibility to make the interior with more seats in case needed?

Four seats has always been the base configuration for NASA flights.

Wasn't there talk of something to enable a single Dragon to evacuate a 7 person crew?

They would have to remove the cargo areas and the toilet, and then install 3 more seats in order to do that.

I don't believe they have to remove cargo area and toilet. It is a NASA requirement that they have 7 seats available for emergency evacuation. I assume this means that 3 spare seats will be stored on the ISS. This requirement applies to both the Dragon and Starliner.

I'm not aware of that being a NASA requirement.

Well, I tried to search for proof but was unsuccessful. I stand by my statement however as I remember it being stated many years ago when Dragon contract first announced. Do you think it is just a coincidence that both Starliner and Dragon have 7 seat capability?

The only reference I found was "With a new American spacecraft also offering another four to seven seats, the station can host more astronauts than its current complement of six. That means more science on the station since more people would be available for research duties." from https://www.nasa.gov/content/new-craft-will-be-americas-first-space-lifeboat-in-40-years/

[jpo234]

Regarding Crew Dragon interface: Found this on LinkedIn (Molly McCormick):

• Population Analysis and Anthropometrics:
- Performed statistical analyses of NASA astronaut population anthropometric database.
- Extrapolated and communicated to Crew Dragon Design Team the critical human design concerns and worst-case dimensions.
• Human Mechanics:
- Determined Dragon-specific ranges of motion and fields of view based on susbystem design, mission phase, procedural requirements, and nominal or off-nominal operations.
- Working individually with subsystem/hardware REs to ensure all crew interfaces support biomechanical and operational restrictions.
• Digital human modeling
- Generated and currently maintaining extensive digital manikin database in NX for native use in Crew Dragon models.
- Provided digital reach and view envelopes for subsystem REs to verify operational impacts.
- Assembled and routed spacesuit engineering components in digital model.
• Verification and Validation:
- Responsible engineer for NASA requirements covering limitation of crew injury, control placement, habitable space sizing, anthropometric accommodations, body waste management, and post-landing procedures.
- Author and RE of comprehensive Spacecraft Worksite Analysis to verify that the crew can safely and reliably fit, access, reach, view, operate, inhabit, or otherwise interact with all interfaces in Dragon.
- Ongoing interface with NASA Human, Health, and Performance subject matter experts.
- Trained as Communications Mission Control Operator

[gongora]

Well, I tried to search for proof but was unsuccessful. I stand by my statement however as I remember it being stated many years ago when Dragon contract first announced. Do you think it is just a coincidence that both Starliner and Dragon have 7 seat capability?

I've never seen anything indicating NASA wanted a 7 seat configuration, and have seen no indication that either vehicle would be reconfigured on orbit for additional seats.

[DigitalMan]

Well, I tried to search for proof but was unsuccessful. I stand by my statement however as I remember it being stated many years ago when Dragon contract first announced. Do you think it is just a coincidence that both Starliner and Dragon have 7 seat capability?

I've never seen anything indicating NASA wanted a 7 seat configuration, and have seen no indication that either vehicle would be reconfigured on orbit for additional seats.

My recollection is 7 seats is what SpaceX and others initially talked about, but when the commercial crew development contracts with NASA were signed it was only for 4 seats.  I also have never seen an indication NASA wanted a 7 seat configuration.

[whitelancer64]

I noticed that in the recent pictures of the interior, there where just four seats in the Dragon 2 Trainers. I do remember earlier pictures showing up to three additional seats. Were those nixed? When this was done? Or is it that there is a planned flexibility to make the interior with more seats in case needed?

Four seats has always been the base configuration for NASA flights.

Wasn't there talk of something to enable a single Dragon to evacuate a 7 person crew?

They would have to remove the cargo areas and the toilet, and then install 3 more seats in order to do that.

I don't believe they have to remove cargo area and toilet. It is a NASA requirement that they have 7 seats available for emergency evacuation. I assume this means that 3 spare seats will be stored on the ISS. This requirement applies to both the Dragon and Starliner.

I'm not aware of that being a NASA requirement.

Well, I tried to search for proof but was unsuccessful. I stand by my statement however as I remember it being stated many years ago when Dragon contract first announced. Do you think it is just a coincidence that both Starliner and Dragon have 7 seat capability?

The only reference I found was "With a new American spacecraft also offering another four to seven seats, the station can host more astronauts than its current complement of six. That means more science on the station since more people would be available for research duties." from https://www.nasa.gov/content/new-craft-will-be-americas-first-space-lifeboat-in-40-years/

Yes, they were both initially designed for a 7 seat capacity, but when the Commercial Crew contracts were awarded NASA only required 4 seats, and the extra area was filled with cargo space.

The cargo areas would need to be removed in order to have more seats.

[oldAtlas_Eguy]

One of the reasons for the 7 seat design was for the economics for commercial HSF. It costs the same to develop and launch a 4 seater as it does a 7 seater. This makes the commercial price per seat for a commercial buyer at 50% than the NASA prices. Pilot + 6 passengers vs pilot and 3 passengers. This applies for all of the proposed CC systems Dragoon 2, Starliner, Shepard, and Dream Chaser. Which is why they all went for a design goal for 7 persons due to the space available on a volume and weight optimized systems on the available launchers.

But NASA never needed more than 4 seats (initially only 3 with option to grow to 4 based on max personnel support levels that ISS can handle). But having a capability of 7 can offer options for NASA in the future. In a world of commercial Space Station replacement of ISS that is not restricted to just 7 max occupants that ability of supporting transport of 7 at a time will be very usefull and result in significant cost savings in operating a 2X larger space station for same operations costs.

[TripleSeven]

One of the reasons for the 7 seat design was for the economics for commercial HSF. It costs the same to develop and launch a 4 seater as it does a 7 seater. This makes the commercial price per seat for a commercial buyer at 50% than the NASA prices. Pilot + 6 passengers vs pilot and 3 passengers. This applies for all of the proposed CC systems Dragoon 2, Starliner, Shepard, and Dream Chaser. Which is why they all went for a design goal for 7 persons due to the space available on a volume and weight optimized systems on the available launchers.

But NASA never needed more than 4 seats (initially only 3 with option to grow to 4 based on max personnel support levels that ISS can handle). But having a capability of 7 can offer options for NASA in the future. In a world of commercial Space Station replacement of ISS that is not restricted to just 7 max occupants that ability of supporting transport of 7 at a time will be very usefull and result in significant cost savings in operating a 2X larger space station for same operations costs.

this is Lori G. at work ... its the airmail contract ...well a percentage of it...

[envy887]

One of the reasons for the 7 seat design was for the economics for commercial HSF. It costs the same to develop and launch a 4 seater as it does a 7 seater. This makes the commercial price per seat for a commercial buyer at 50% than the NASA prices. Pilot + 6 passengers vs pilot and 3 passengers. This applies for all of the proposed CC systems Dragoon 2, Starliner, Shepard, and Dream Chaser. Which is why they all went for a design goal for 7 persons due to the space available on a volume and weight optimized systems on the available launchers.

But NASA never needed more than 4 seats (initially only 3 with option to grow to 4 based on max personnel support levels that ISS can handle). But having a capability of 7 can offer options for NASA in the future. In a world of commercial Space Station replacement of ISS that is not restricted to just 7 max occupants that ability of supporting transport of 7 at a time will be very usefull and result in significant cost savings in operating a 2X larger space station for same operations costs.

Dragon's size is dictated by its multipurpose role and cost optimization.

Cargo is bulkier than Crew, and Dragon is already volume-limited for Cargo. There is no cost savings to building and operating a smaller 4-person Crew vehicle when you have to have a large Cargo vehicle with 95% of the same abilities anyway.

Any consideration for the commercial market are secondary at best, as that market is purely speculative.

[TripleSeven]

One of the reasons for the 7 seat design was for the economics for commercial HSF. It costs the same to develop and launch a 4 seater as it does a 7 seater. This makes the commercial price per seat for a commercial buyer at 50% than the NASA prices. Pilot + 6 passengers vs pilot and 3 passengers. This applies for all of the proposed CC systems Dragoon 2, Starliner, Shepard, and Dream Chaser. Which is why they all went for a design goal for 7 persons due to the space available on a volume and weight optimized systems on the available launchers.

But NASA never needed more than 4 seats (initially only 3 with option to grow to 4 based on max personnel support levels that ISS can handle). But having a capability of 7 can offer options for NASA in the future. In a world of commercial Space Station replacement of ISS that is not restricted to just 7 max occupants that ability of supporting transport of 7 at a time will be very usefull and result in significant cost savings in operating a 2X larger space station for same operations costs.

Dragon's size is dictated by its multipurpose role and cost optimization.

Cargo is bulkier than Crew, and Dragon is already volume-limited for Cargo. There is no cost savings to building and operating a smaller 4-person Crew vehicle when you have to have a large Cargo vehicle with 95% of the same abilities anyway.

Any consideration for the commercial market are secondary at best, as that market is purely speculative.

No...by your own def...you dont know or seem to grasp what Lori G was trying to accomplish.  you are not saying much

sorry

[HVACMan]

Since the Dragon has cold gas thrusters, couldn't those be used to assist in the landing to help it hit the inflatable recovery pad?  Perhaps even using the SuperDracos when it is still far enough away from the pad to not burn it if there was some severe wind currents.

[Alexphysics]

Since the Dragon has cold gas thrusters, couldn't those be used to assist in the landing to help it hit the inflatable recovery pad?  Perhaps even using the SuperDracos when it is still far enough away from the pad to not burn it if there was some severe wind currents.

Dragon doesn't have cold gas thrusters.