SpaceX's Dragon cargo ship splashes down in Pacific | Hacker News Reader

SpaceX's Dragon cargo ship splashes down in Pacific

phys.org

113 pointsdnetesn20 comments

> SpaceX's Dragon is the only cargo carrier in use that can return gear to Earth.

Don't they mean the only American cargo carrier? I thought the Soyuz was the only capsule ferrying Astronauts to and from the station, at least until the Commercial Crew program gets to that point.

Soyuz returns three human beings in circumstances that could generously be called "very cramped". It carries no cargo.

The Russian cargo vehicle is named Progress, and it does not survive re-entry.

If it's anything like the first Apollo missions' capsules, it's pretty much three chairs tied back to back. There's barely enough room to sit in, I don't know how the astronauts didn't go crazy in it.

Yes - but no. It is similar - both have some aerodynamic shapes and carry three people - but that's about where similarities end. Soyuz return capsule is 2/3 of Apollo's by volume - which is restrictive. Shape is optimized for mass, so accelerations are less gentle.

Soyuz has another advantages over Apollo - like another module, separate from return capsule; together, those two modules provide livable volume 1.5 of Apollo's.

But for what we're talking Soyuz is more restrictive than Apollo.

The Soyuz is not a 'cargo carrier', it is a 'people carrier'. It does have a service module that can carry a very small amount of cargo on the way up, but that gets ditched and burn up on the way down. The return capsule just carries the astronauts and personal effects (and it's a tight fit at that).

SpaceX Dragon is the only vehicle currently flying that has significant downmass capability. European ATV, Japanese HTV, Russian Progress and Orbitak ATK's Cygnus all have destructive reentry, meaning after they are unloaded at the station, they are filled with junk and disintegrate, burn up and sink in the Pacific.

You can take stuff back from the station in the Soyuz when it lands with returning crew, but space and mass are very limited. For example, Soyuz can't bring back the -80°C freezer with blood, saliva and urine samples from the astronauts (those are used, among other things, to calibrate exercise and diet regimens that lead to the least calcium loss from their bones in microgravity).

Technically Soyuz can return a small amount of cargo, but it is extremely weight and volume limited. I couldn't find a precise figure, but it looks like it can return at most 50kg or so of cargo, in addition to crew.

Dragon can return about 2500kg in total (though it is quite volume limited), and has special facilities such as cargo racks that can support, for example, a powered freezer to hold scientific samples requiring such facilities.

None of the other operational vehicles -- Progress, Cygnus or HTV -- have any cargo return capability.

So the quote is correct in two respects: firstly, Soyuz isn't generally considered a "cargo vehicle"; and if you expand that definition, Soyuz can only carry an extremely small amount of a limited subset of possible return cargo that does not include the most interesting payloads such as frozen biological samples.

When the Commercial Crew vehicles become operational in the next couple of years they will also provide some cargo return capability, but that isn't their primary purpose and will be fairly limited under most circumstances.

The second round of the Commercial Cargo program -- CRS2 -- has selected Sierra Nevada Corporation's Dream Chaser in addition to Dragon and Cygnus. Dream Chaser is a spaceplane that will provide substantial cargo return capability by landing on a runway. This will subject the payload to lower g-forces than Dragon and allow for a very short interval between leaving the station and cargo offloading and processing on the ground. Such capabilites will be extremely useful for returning delicate and time-sensitive experiments.

So, until Dream Chaser becomes operational, almost all cargo return capability will be provided by Dragon; and right now, the cargo that is returned not on Dragon is on the order of a rounding error.

Thanks, that's interesting! Do you know if the future upgrades to Dragon with propulsive landing for the crew return will provide similar capabilities for fast landing at bases as the Dream Chaser?

First flights of Dragon 2 will splash down under parachute because NASA is nervous about propulsive landing. When propulsive landing happens (probably at CCAFS) we'll see how fast can the capsule be decontaminated (superdraco uses hydrazine fuel, will need something like this: https://www.wired.com/images_blogs/dangerroom/2011/11/120310...).

I'm curious how Dragon carried a docking adapter to ISS. Such things generally don't fit through hatches.

Dragon has an unpressurized "trunk" which it can use to carry stuff like this. Here's a picture (a rendering, looks like, but it gets the point across) of the adapter being removed from Dragon's trunk:

http://imgur.com/LAMS49w

The rear part (with the solar panels) is discarded before the capsule at the top returns to Earth.

Here are some photos of the trunk on the ground: http://www.spacex.com/news/2013/03/26/dragon-trunk

Quite a lot of space in there.

The BEAM was transported in the trunk as well. That couldn't have fit through any hatch either.

The NASA article[1] has a better write up and says:

While the crew will be able to move the supplies out of the interior, pressurized compartment of the Dragon without leaving the station, the robotic arm will be called on to pull the IDA from the trunk and maneuver it near the port where it will be connected. NASA astronauts currently living aboard the station will perform a spacewalk later this summer to make the final connection of the IDA to the Harmony module.

1. http://www.nasa.gov/feature/spacex-crs-9-carrying-crucial-po...

https://www.youtube.com/watch?v=pErRpkvtl-g

Timelapse of IDA-2 Removal from SpaceX Dragon Trunk [94 seconds]

> returning a load of NASA research from the International Space Station

Is it common practice to send down only, say, half of the results, while keeping the other half at the ISS for backup purposes?

ISS freezer is space limited. They might spread samples over different dragons for safety, if they have the space.

SpaceX is really setting itself up for interstellar travel. I am really proud of Elon Musk and SpaceX in general.

Well, saying that SpaceX is setting up for interstellar travel is like saying that me going kayaking is preparing me for transatlantic navigation... but mighty impressive nonetheless.

The first ocean navigators did use small rafts to do it. That's how they managed to go to Easter Island, for instance. So your affirmation confirms that SpaceX is preparing for interstellar travel.

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