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Crew Dragon Docks with ISS

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Re: Crew Dragon Docks with ISS

#71

What's with the gradient shadow? The space station shadow crossed the module, and it was blurry. I thought shadows in space were knife-sharp. The nose-cone shadow was. Its not the stream resolution, is it? Other knife-sharp features were visible. Maybe the space station is fuzzy? Maybe the module material blurs shadows? What am I missing?

Shadows in space aren't, in general, any sharper than on Earth. The "penumbra" of a shadow -- the blurry, partially-shaded region -- is basically a simple geometric effect, caused by the light source being partially obscured. The penumbra's size is approximately equal to the product of the light source's angular size and the distance from the shadow-casting object to the illuminated surface. (Diffraction has some effect as well, but only on very small scales that aren't particularly relevant here.)

The sun has almost exactly the same apparent angular size from either Earth's surface or LEO, because it's almost exactly the same distance away. But since that angular size is only about half a degree, shadows observed at short distances appear fairly sharp, either on Earth or in space.

What you may be thinking of is that, in many cases, shadows are darker in space, because the sky is dark, even in broad daylight. There's no atmospheric scattering to provide indirect, ambient illumination of regions that are shaded from direct sunlight. But there can still be indirect lighting from other surfaces.

For example, in photos of Apollo astronauts on the moon, shaded regions of the astronauts' spacesuits are still fairly-well illuminated by light bouncing off the lunar surface. But shadowed regions of the surface itself appear almost pitch-black, because the only thing they can "see" is the dark sky.

Re: Crew Dragon Docks with ISS

#72
post #14

Earlier quoted context omitted.

How does this get us closer to getting people to Mars?

Can’t tell if serious or troll. Successful human spaceflight on reusable hardware > lower cost to orbit of personnel > increased economic activity in orbit > construction of manufacturing facilities > scale up of materials, capability, endurance and knowledge > ability to construct and launch Mars ships and supply a colony Or something like that.

The problem of getting to Mars is bigger than “just do more spacey stuff in space” though. There are some massive physical limits, in terms of fuel efficiency, that make it really really hard to get there and come back. That’s the main challenge and I don’t think SpaceX moved us particularly closer on that point.

I’m in my forties and I don’t expect to see us on Mars in my lifetime, except on some poetic suicide mission (nice sidestep of euthanasia laws: “I’m not dying, I’m going to Mars!”). We might make something a bit more useful out of the Moon, though, if we don’t screw up too much.

Re: Crew Dragon Docks with ISS

#73
post #15

SpaceX runs basically as a giant R&D program that also happens to accomplish useful things as byproducts of its approach (with the miracle of insurance to cover costs if things get explody). Every flight is data for incremental improvement. If you think of all SpaceX has ever done was try to get to this point, with somewhere around 80 flights on the Falcon 9, but for a variety of mission buyers (NASA, USAF, Commercia…

SpaceX developments have a clearly defined goal with most engineering and production decisions made according to mission + cost constraints. The space shuttle development had dramatically changing requirements from multiple stakeholders (cheap launches, crossrange capability, recovery of military satellites, etc.) with production facilities based on jobs in voting districts. As impressive as the space shuttle was from an engineering perspective, from an economic and safety standpoint it was a complete desaster.

Re: Crew Dragon Docks with ISS

#74
post #36

I recall Elon was hoping to get an order of magnitude reduction in cost per launch, but Wikipedia claims it costs $160 million per launch versus the Soyuz price of $76 million per astronaut. That would “only” be a 3x reduction with a crew of seven, but they’ve configured for a crew of four, which is a hair under 2x. I wonder how reuse affects the math, and what they’ll be able to do to lower those prices further. Obv…

I would be interested to see the quote. Was he hoping for a 10-fold drop right off the bat for the first mission or rather for that drop "à un moment donné". I imagine the costs will continue to go down with time for the base model as things become more reusable, R&D costs drop, and more business comes their way.

Re: Crew Dragon Docks with ISS

#75
post #15

SpaceX runs basically as a giant R&D program that also happens to accomplish useful things as byproducts of its approach (with the miracle of insurance to cover costs if things get explody). Every flight is data for incremental improvement. If you think of all SpaceX has ever done was try to get to this point, with somewhere around 80 flights on the Falcon 9, but for a variety of mission buyers (NASA, USAF, Commercia…

All true, however, (splitting hairs, yes), the reason FH9 can best the shuttle boosters is because they had to carry the shuttle itself, which was around 50 tons.

Turns out it is a lot more useful to (potentially) reuse the first stage than to carry a lot of additional weight to reuse the last stage.

Re: Crew Dragon Docks with ISS

#76
post #15

SpaceX runs basically as a giant R&D program that also happens to accomplish useful things as byproducts of its approach (with the miracle of insurance to cover costs if things get explody). Every flight is data for incremental improvement. If you think of all SpaceX has ever done was try to get to this point, with somewhere around 80 flights on the Falcon 9, but for a variety of mission buyers (NASA, USAF, Commercia…

> a single company that started a decade ago as a side project for a guy who was trying to make electric cars after making money on the internet.

I believe this is backwards, SpaceX was created first and it was implied in the biography that it's more as if Tesla was the side project.

Re: Crew Dragon Docks with ISS

#77

What's with the gradient shadow? The space station shadow crossed the module, and it was blurry. I thought shadows in space were knife-sharp. The nose-cone shadow was. Its not the stream resolution, is it? Other knife-sharp features were visible. Maybe the space station is fuzzy? Maybe the module material blurs shadows? What am I missing?

Where do you mean? If it's a shadow caused by the light of the Earth it will be very fuzzy due to the size of the light source. Even shadows from the sun will be fuzzy if the shadowing object isn't close to the shadowed surface, as the sun is no further away than on Earth, and hence much bigger than the point light source needed for perfectly sharp shadows.

If you mean the contrast between lit and shadowed areas, LEO is quite different from e.g. the moon, as even though it's out of the atmosphere, there's a lot of ambient light from the huge close Earth below.

Re: Crew Dragon Docks with ISS

#78

What's with the gradient shadow? The space station shadow crossed the module, and it was blurry. I thought shadows in space were knife-sharp. The nose-cone shadow was. Its not the stream resolution, is it? Other knife-sharp features were visible. Maybe the space station is fuzzy? Maybe the module material blurs shadows? What am I missing?

[deleted]

Re: Crew Dragon Docks with ISS

#79
post #37

They mentioned something about the suit pressure for one of them being lower than expected and asked them to check for "white teeth" on 3 zippers, which they reported seeing on all 3. Can anyone explain what that is?

They did a leak check and one of their suits wasn't 100% sealed so it had a lower pressure differential to the capsule during their tests meaning there was a seal that wasn't completely sealed. The teeth thing is that they use different colored teeth on zippers so they can see visually when they've closed the zipper fully. They said it was still within the margin of keeping them protected during an emergency though.

Re: Crew Dragon Docks with ISS

#80

What's with the gradient shadow? The space station shadow crossed the module, and it was blurry. I thought shadows in space were knife-sharp. The nose-cone shadow was. Its not the stream resolution, is it? Other knife-sharp features were visible. Maybe the space station is fuzzy? Maybe the module material blurs shadows? What am I missing?

shadows are not blurry because of atmosphere. It's because of non-point light sources. The sun is not a point, but a disc.
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