SpaceX Dragon 2 Updates and Discussion - Thread 3

[clongton]

From CRS-20 pre-launch press conference:
https://twitter.com/jeff_foust/status/1236042796924121089

Koenigsmann says there are two more tests to go on Crew Dragon parachutes, testing “corner cases” in its operation.

What are "corner cases"?

[matthewkantar]

From CRS-20 pre-launch press conference:
https://twitter.com/jeff_foust/status/1236042796924121089

Koenigsmann says there are two more tests to go on Crew Dragon parachutes, testing “corner cases” in its operation.

What are "corner cases"?

A corner case would be something out on the fringes of the bell curve. Not expected but possible sets of circumstances that need to be accounted for.

[Johnnyhinbos]

From CRS-20 pre-launch press conference:
https://twitter.com/jeff_foust/status/1236042796924121089

Koenigsmann says there are two more tests to go on Crew Dragon parachutes, testing “corner cases” in its operation.

What are "corner cases"?

I think it’s demonstrating the ability to turn hard left or right...

(I’m kidding)

[Khadgars]

Really looking forward to seeing Crew Dragon with crew on it, going to be wonderful sight to see!

[RDoc]

From CRS-20 pre-launch press conference:
https://twitter.com/jeff_foust/status/1236042796924121089

Koenigsmann says there are two more tests to go on Crew Dragon parachutes, testing “corner cases” in its operation.

What are "corner cases"?

In software testing there are main use cases, kind of what you expect users to do, then there are various flavors of weird uses (often by weird users). Corner cases are very unusual uses, such as going down a normal use path, then branching off suddenly to do something that doesn't make sense.

I imagine that's the same kind of thing in this kind of testing. A string of different events happening that are possible but unlikely.

[XenIneX]

What are "corner cases"?

To lean into the metaphor:

Let's say you've got a little Roomba-looking robot in a closed room, and you want it to do something when it hits a wall.  When it hits the north wall, it does THIS, and when it hits the east wall, it does THAT... etcetera, etcetera.  So, you set up a condition for each wall, and you're good to go, right?

Well, what happens when it hits a corner?  What's it do when it, technically, hits two walls simultaneously?  Should it do both things at once, or neither, or do them in a particular order?


It's a pretty common trap in programming; particularly when you've got things which are conditional on two different, discontinuous functions.  You have to make sure you're not leaving a hole in the logic where they meet.  If you don't, your code ends off in no-man's-land, and you have no idea what went wrong.

[LouScheffer]

What are "corner cases"?

In Electrical Engineering, corner cases are combinations of conditions that occupy the corner of the operating envelope.   For example, suppose you have a chip that is supposed to operate with a supply voltage of 1.5-2.0 volts, and at a temperature of -50 to 110 degrees C.  If you plot these on a plane with one axis voltage and the other temperature, these conditions form a rectangle, and the chip should work at any conditions in this rectangle (commonly called 'operating area').

So a corner condition is one that is literally at a corner of the operating area (say 1.5 volts and -50 C).  In this example there are 4 corner cases.  In real life there can be many more - if you add another parameter (say clock speed can be 100-150 MHz) then you have 8 corners, and so on with 2^N corners for N variables.

I don't know if the meaning is precisely the same in parachute testing, but I bet the spirit is - make sure it can work under any foreseeable conditions.

[Wolfram66]

What are "corner cases"?

... Snip....

Aero and Aerospace it refers to the corners of the operational envelope. Speed, angle of attack, lift, spin or tumbling.
Outside of which leads to LOC. To high, too fast and tumbling or too low , too fast and upside down. Extremely unlikely conditions, but you need to test for it.

[A8-3]

Hi,

I'm sure this is explained somewhere but please indulge me. It's prompted by the article "SpaceX launches final Dragon 1 mission to the ISS". Does this mean that all future Dragon missions to the ISS will dock not berth? Isn't berthing somewhat preferable for cargo delivery(i thought the hatch opening was larger), or doesn't it really make that much difference?

[gongora]

All future Dragon missions will dock.  All of the other cargo ships on the USOS side of the station will still berth, and they all have larger cargo volume than Dragon, so anything really big can just go up on a different vehicle.

[duh]

What are "corner cases"?

In Electrical Engineering, corner cases are combinations of conditions that occupy the corner of the operating envelope.   For example, suppose you have a chip that is supposed to operate with a supply voltage of 1.5-2.0 volts, and at a temperature of -50 to 110 degrees C.  If you plot these on a plane with one axis voltage and the other temperature, these conditions form a rectangle, and the chip should work at any conditions in this rectangle (commonly called 'operating area').

So a corner condition is one that is literally at a corner of the operating area (say 1.5 volts and -50 C).  In this example there are 4 corner cases.  In real life there can be many more - if you add another parameter (say clock speed can be 100-150 MHz) then you have 8 corners, and so on with 2^N corners for N variables.

I don't know if the meaning is precisely the same in parachute testing, but I bet the spirit is - make sure it can work under any foreseeable conditions.

=============================================================================================
True for as far as it goes. However, as a sidelight, it makes the basic assumption that the performance at the corners is the worst for each of the parameters.
Say for example that the situation involves water over the temperature range of 33 deg F ( I don't want to get into the question of whether the water
has frozen or not) and 211 deg F at standard atmospheric pressure.

If the concern is where is the water most dense, it is not at 32 deg F or 211 deg F. Apparently it is at 40 deg F. The point is that testing the corners in and
of itself does not guarantee that the worst possible condtions have always been test. Usually the worst conditions are tested with the corner cases but
not always.

Now you can send me to my corner so that I stop writing with the possibility of taking this thread away from the corners of the corner case discussion :-)

[pathfinder_01]

Hi,

I'm sure this is explained somewhere but please indulge me. It's prompted by the article "SpaceX launches final Dragon 1 mission to the ISS". Does this mean that all future Dragon missions to the ISS will dock not berth? Isn't berthing somewhat preferable for cargo delivery(i thought the hatch opening was larger), or doesn't it really make that much difference?

Yes they will dock and not berth. There are a few items that need a larger hatch but most cargo items will fit through the smaller opening. As part of the CRS2 contracts the companies were allowed to offer solutions that could dock and not berth. For CCREW all spacecraft had to dock in addition other CCREW requirements and design changes prevented Space X from using the larger hatch in Dragon 2 so Dragon 2 is limited to docking. Also,as part of the CRS2 contract Dragon 1 is still on offer if for some reason NASA should want it but it is expected that all cargo from here on out for Space X will use Dragon 2. The other providers Cygnus and Dream Chaser will still berth.

[Johnnyhinbos]

Sorry -  you are correct! duh -   

(As water cools further, it rises to the surface, and thus ice forms there, rather than on the bottom!)
But I didn't manage to hide all traces of my mistake before MATTBLANK spotted it!

Er - and this is definitely getting off topic, but as water (liquid) cools it gets more dense. It's only when it experiences a phase change to solid (ice) does it indeed become less dense and float. This is a fairly unique property of water and is indeed a key factor for why life exists on this planet.


I'm going ice diving next weekend. Yet I dive in tropical waters literally on a daily basis for my job - and diving is my profession. All else being equal, guess which requires more weight - 75F water or 33F water...

[DistantTemple]

Sorry -  you are correct! duh -   

(As water cools further, it rises to the surface, and thus ice forms there, rather than on the bottom!)
But I didn't manage to hide all traces of my mistake before MATTBLANK spotted it!

Er - and this is definitely getting off topic, but as water (liquid) cools it gets more dense. It's only when it experiences a phase change to solid (ice) does it indeed become less dense and float. This is a fairly unique property of water and is indeed a key factor for why life exists on this planet.


I'm going ice diving next weekend. Yet I dive in tropical waters literally on a daily basis for my job - and diving is my profession. All else being equal, guess which requires more weight - 75F water or 33F water...

My bold
See: http://www1.lsbu.ac.uk/water/density_anomalies.html
Not exactly - as water cools towards 4C it gets denser and sinks, (or conversely hot water rises like it does in heating systems.) But at 4C it is at its densest. As it cools further, 3C, 2C 1C it again rises. This means that the coldest water is in the surface, and thus ice then forms at the surface, not on the bottom of lakes etc. It is one of the (many) remarkable things about water that makes life work as we know it!
Yes Ice is a step change less dense still. But without this quirk, we might get ice forming on the bottom, then ripping the lakebed up as it then broke for the surface.
This is good physics, despite being O/T. I don't think methane, nitrogen or oxygen liquids behave like this.

[Lars-J]

Hi,

I'm sure this is explained somewhere but please indulge me. It's prompted by the article "SpaceX launches final Dragon 1 mission to the ISS". Does this mean that all future Dragon missions to the ISS will dock not berth? Isn't berthing somewhat preferable for cargo delivery(i thought the hatch opening was larger), or doesn't it really make that much difference?

Someone can correct me, but I don’t believe Dragon 1 ever delivered a payload that was large enough to actually require the larger berthing hatch, so it won’t really be any real loss of essential capability.

If needed Cargo Dreamchaser can still deliver larger cargo, when it comes online.

[Alexphysics]

Hi,

I'm sure this is explained somewhere but please indulge me. It's prompted by the article "SpaceX launches final Dragon 1 mission to the ISS". Does this mean that all future Dragon missions to the ISS will dock not berth? Isn't berthing somewhat preferable for cargo delivery(i thought the hatch opening was larger), or doesn't it really make that much difference?

Someone can correct me, but I don’t believe Dragon 1 ever delivered a payload that was large enough to actually require the larger berthing hatch, so it won’t really be any real loss of essential capability.

If needed Cargo Dreamchaser can still deliver larger cargo, when it comes online.

I think there was really one relatively large cargo item that I can remember Dragon sending back to Earth and it was one of the few LEE's on the Candarm2. They brought it down for refurbishment on one of the recent cargo trips. Impressive something like that could fit inside Dragon. Some people who have actually went into one of those capsules say it is like a TARDIS LOL

[obi-wan]

Hi,

I'm sure this is explained somewhere but please indulge me. It's prompted by the article "SpaceX launches final Dragon 1 mission to the ISS". Does this mean that all future Dragon missions to the ISS will dock not berth? Isn't berthing somewhat preferable for cargo delivery(i thought the hatch opening was larger), or doesn't it really make that much difference?

Someone can correct me, but I don’t believe Dragon 1 ever delivered a payload that was large enough to actually require the larger berthing hatch, so it won’t really be any real loss of essential capability.

If needed Cargo Dreamchaser can still deliver larger cargo, when it comes online.

I think there was really one relatively large cargo item that I can remember Dragon sending back to Earth and it was one of the few LEE's on the Candarm2. They brought it down for refurbishment on one of the recent cargo trips. Impressive something like that could fit inside Dragon. Some people who have actually went into one of those capsules say it is like a TARDIS LOL

They also brought Robonaut 2 down for repairs and upgrades in a cargo Dragon. (It went up in a shuttle.) When it is relaunched it is going up in a Cygnus because it can’t fit through the IDA on Dragon 2.

[Coastal Ron]

I'm sure this is explained somewhere but please indulge me. It's prompted by the article "SpaceX launches final Dragon 1 mission to the ISS". Does this mean that all future Dragon missions to the ISS will dock not berth? Isn't berthing somewhat preferable for cargo delivery(i thought the hatch opening was larger), or doesn't it really make that much difference?

Someone can correct me, but I don’t believe Dragon 1 ever delivered a payload that was large enough to actually require the larger berthing hatch, so it won’t really be any real loss of essential capability.

If needed Cargo Dreamchaser can still deliver larger cargo, when it comes online.

The change to Dragon really affects NASA's ability to return large payloads from the ISS, not get them to the ISS - they still have Cygnus, the JAXA HTV, and the upcoming Dream Chaser for taking bulk cargo up.

[Alexphysics]

Hi,

I'm sure this is explained somewhere but please indulge me. It's prompted by the article "SpaceX launches final Dragon 1 mission to the ISS". Does this mean that all future Dragon missions to the ISS will dock not berth? Isn't berthing somewhat preferable for cargo delivery(i thought the hatch opening was larger), or doesn't it really make that much difference?

Someone can correct me, but I don’t believe Dragon 1 ever delivered a payload that was large enough to actually require the larger berthing hatch, so it won’t really be any real loss of essential capability.

If needed Cargo Dreamchaser can still deliver larger cargo, when it comes online.

I think there was really one relatively large cargo item that I can remember Dragon sending back to Earth and it was one of the few LEE's on the Candarm2. They brought it down for refurbishment on one of the recent cargo trips. Impressive something like that could fit inside Dragon. Some people who have actually went into one of those capsules say it is like a TARDIS LOL

They also brought Robonaut 2 down for repairs and upgrades in a cargo Dragon. (It went up in a shuttle.) When it is relaunched it is going up in a Cygnus because it can’t fit through the IDA on Dragon 2.

Do you think it can fit through Cygnus hatch? Cygnus hatch isn't like Dragon 1's hatch, it is smaller and doesn't take up the entire CBM like D1 does

[Lars-J]

Hi,

I'm sure this is explained somewhere but please indulge me. It's prompted by the article "SpaceX launches final Dragon 1 mission to the ISS". Does this mean that all future Dragon missions to the ISS will dock not berth? Isn't berthing somewhat preferable for cargo delivery(i thought the hatch opening was larger), or doesn't it really make that much difference?

Someone can correct me, but I don’t believe Dragon 1 ever delivered a payload that was large enough to actually require the larger berthing hatch, so it won’t really be any real loss of essential capability.

If needed Cargo Dreamchaser can still deliver larger cargo, when it comes online.

I think there was really one relatively large cargo item that I can remember Dragon sending back to Earth and it was one of the few LEE's on the Candarm2. They brought it down for refurbishment on one of the recent cargo trips. Impressive something like that could fit inside Dragon. Some people who have actually went into one of those capsules say it is like a TARDIS LOL

They also brought Robonaut 2 down for repairs and upgrades in a cargo Dragon. (It went up in a shuttle.) When it is relaunched it is going up in a Cygnus because it can’t fit through the IDA on Dragon 2.

Thanks - I stand corrected.