SgtSomeone

Why undock and burn up cargo modules?

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I've tried my hand at building a few stations in KSP and each time after using up the stored fuel (usually orbital tugs), I'll send up a fuel resupply ship to refuel. But every time after I transfer the fuel from the resupply ship to the station, I realize that if I left the resupply ship there I'll have added to the total fuel storage capability. Bonus points if my resupply ship has two docking ports and then I can chain them.

Obviously I'm not suggesting I'm smarter than NASA (relevant XKCD!), but after spending all that money manufacturing and hurling that Progress or Cygnus into orbit (not including Dragon because they need it's return-to-earth payload ability), why not treat them as new station modules that happen to bring food/water as well?  You could double station capacity with a year's worth or resupply vessels. Trash disposal doesn't require a pressurized and armored ship; you could just load a plastic bag with a firecracker (or real-life equivalent of a Seperatron) to de-orbit. Additional power shouldn't be a problem; they all bring their own Solar panels already. 

Or do I have this wrong and there have been stations made up of successive visiting vessels? 

Edited by SgtSomeone

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Every ship that docks at the ISS uses up a valuable docking port. There are a lot of them, sure, but they'd get filled up pretty quickly if every supply ship stayed there. The only way around this is to design the supply ships with an extra docking port of their own, and that's not worth the trouble or the expense. The station doesn't need the extra space, so it's better to just build the supply ships cheap and ditch them into the atmosphere afterward.

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6 minutes ago, Mitchz95 said:

Every ship that docks at the ISS uses up a valuable docking port. There are a lot of them, sure, but they'd get filled up pretty quickly if every supply ship stayed there. The only way around this is to design the supply ships with an extra docking port of their own, and that's not worth the trouble or the expense. The station doesn't need the extra space, so it's better to just build the supply ships cheap and ditch them into the atmosphere afterward.

This, docking ports are far cheaper in KSP than real life. 
Add that the modules are not designed to be used on an permanent basis, but has an life length. 
 

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4 minutes ago, magnemoe said:

This, docking ports are far cheaper in KSP than real life. 
Add that the modules are not designed to be used on an permanent basis, but has an life length. 
 

More than that. The ISS has a balance, if they chain supply vessels it will change the center of gravity and cost more in dV required to station keep.

There is an KSP addon called recyling bin as part of the EL launchpad pakage, I simply shove my supply drones into the recycling bin. Out comes metal and I can build a satellite with them.

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17 minutes ago, magnemoe said:

This, docking ports are far cheaper in KSP than real life. 
Add that the modules are not designed to be used on an permanent basis, but has an life length. 
 

Is there a significant difference between the docking ports for resupply ships, and the ports holding the modules together? (i.e Columbus and Destiny)

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2 hours ago, SgtSomeone said:

Is there a significant difference between the docking ports for resupply ships, and the ports holding the modules together? (i.e Columbus and Destiny)

I don't think so. The same docking ports are used, and the original docking port for the artif. G module were used for Cargo.

3 hours ago, SgtSomeone said:

I've tried my hand at building a few stations in KSP and each time after using up the stored fuel (usually orbital tugs), I'll send up a fuel resupply ship to refuel. But every time after I transfer the fuel from the resupply ship to the station, I realize that if I left the resupply ship there I'll have added to the total fuel storage capability. Bonus points if my resupply ship has two docking ports and then I can chain them.

Obviously I'm not suggesting I'm smarter than NASA (relevant XKCD!), but after spending all that money manufacturing and hurling that Progress or Cygnus into orbit (not including Dragon because they need it's return-to-earth payload ability), why not treat them as new station modules that happen to bring food/water as well?  You could double station capacity with a year's worth or resupply vessels. Trash disposal doesn't require a pressurized and armored ship; you could just load a plastic bag with a firecracker (or real-life equivalent of a Seperatron) to de-orbit. Additional power shouldn't be a problem; they all bring their own Solar panels already. 

Or do I have this wrong and there have been stations made up of successive visiting vessels? 

It's cheaper to dump them, and the station is not designed for the extra modules. They would need power, and be designed with useful things inside (like labs) that would reduce cargo capacity.

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2 hours ago, SgtSomeone said:

Is there a significant difference between the docking ports for resupply ships, and the ports holding the modules together? (i.e Columbus and Destiny)

It's not necessarily module ports vs spacecraft ports, it's American vs Russian ports. Russian ports use a probe and drogue kind of system, where the docking spacecraft has a pointed cone extending forward that's guided into a funnel where 2 vehicles can latch together. American docking ports have the latches, but not any type of guiding mechanism. All U.S. orbital segment modules and spacecraft (excluding the space shuttle) must be gently guided into the correct position by the Canadarm.

 

Edited by LMRaptor

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Waste.

They cannot dump it into space, then it's dangerous. 

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Because they actually contains waste when wasted away.

Well, apart from additional mass -> more energy requirement and limited docking ports.

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8 hours ago, SgtSomeone said:

Is there a significant difference between the docking ports for resupply ships, and the ports holding the modules together? (i.e Columbus and Destiny)

There are 3 (soon 4) different types of ports on the ISS.

- CBM (Common Berthing Mechanism). These connect the US  modules ( and the ESA and JAXA modules) together. They cannot be used for docking but require berthing, with a robotic arm. They are wider and allow standard ISPR rack modules to go through. The US modules use this, and so do some cargo vehicles: Dragon, HTV. It cannot be used by crew vehicles because they couldn't undock autonomously in an emergency.

- Probe and drogue: This is the Russian docking system for Progress, Soyuz, ATV. It's only on the Russian side and allows to refuel Zarya, which is the service module of the station. 

- APAS: This was a Russian docking system, but was used for the Shuttles (the Shuttles had APAS docking ports installed for the Shuttle-Mir program). The advantage of APAS is that it is androgynous. I think APAS also connects some Russian modules together too.

- NDS: NASA docking system, this is based on an international standard and is to replace APAS. New commercial crew vehicles (and some cargo vehicles) will use this. There are two adapters that are to be delivered by Dragon to the station to go on top of the two APAS ports on the US side. One was destroyed in the CRS-7 explosion.

And all the reasons for disposing of old cargo vehicles are correct:

- To dispose of waste (you can't just open an airlock and chuck out the waste)

- Because the vehicles have a shelf life

- Because they aren't suitable for habitation. They lack air recirculation, life support, climate control, etc...

Edited by Nibb31

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Pfff. Sheeple. Its for Chemtrails.

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I also doubt their plumbing and tankage is built to withstand multiple cycles of having fuel pumped in and out. They're tanker trucks, not fuel storage tanks. 

Its also worth noting that the ISS produces A LOT of waste, if I remember correctly. Used clothes, waste from food packages, etc. This needs to be dealt with somehow.

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10 hours ago, Nibb31 said:

1) To dispose of waste (you can't just open an airlock and chuck out the waste)

2) Because the vehicles have a shelf life

3) Because they aren't suitable for habitation. They lack air recirculation, life support, climate control, etc...

15 hours ago, Mitchz95 said:

*snip* 4) The station doesn't need the extra space, so it's better to just build the supply ships cheap and ditch them into the atmosphere afterward.

(numbers added by me)
1) A number of people mentioned waste, but I'm not sure it's a valid reason. I get that you can't just toss waste into space, but surely it doesn't need a full pressurized/armored vessel. You could haul up multiple inflatable garbage-bag-like modules with small deorbit motors in a single shipment. 
2) What determines a vehicle's 'shelf life'? I know the Soyuz have them, but I thought that was more about re-entry capability expiring rather than becoming unspaceworthy. 
3) It wouldn't seem that hard to add. We know they can habitated because astronauts are in there while they unload cargo. It shouldn't be that much more stress to add the additional air re-circulation fans and tie in the HVAC system? 
4) Doesn't the station always need extra space? I could see why launching new modules wouldn't be worth it, but these are already there!
 

15 hours ago, magnemoe said:

This, docking ports are far cheaper in KSP than real life. 

I guess it mostly comes down to this, though I wonder if the common berthing mechanism will bring those costs down, or if there would be a way to make them cheap enough to do this. 

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1 hour ago, SgtSomeone said:

(numbers added by me)
1) A number of people mentioned waste, but I'm not sure it's a valid reason. I get that you can't just toss waste into space, but surely it doesn't need a full pressurized/armored vessel. You could haul up multiple inflatable garbage-bag-like modules with small deorbit motors in a single shipment. 

That would be basically a whole new spacecraft design (including engines, avionics, power, attitude control, docking system) that you would have to send up empty for the sole purpose of handling garbage. Not worth the cost.

1 hour ago, SgtSomeone said:

2) What determines a vehicle's 'shelf life'? I know the Soyuz have them, but I thought that was more about re-entry capability expiring rather than becoming unspaceworthy. 

Batteries, consumables, coolants, solar panels, seals, gaskets, filters, insulation, etc... Any part that is certified for a specific on-orbit life or a specific number of thermal/mechanical cycles. Visiting vehicles are designed to be expendable. Making them permanent would require redesigning them, which would increase their cost. And then you would run out of docking ports for the next vehicles and you would be swamped with trash.

1 hour ago, SgtSomeone said:

3) It wouldn't seem that hard to add. We know they can habitated because astronauts are in there while they unload cargo. It shouldn't be that much more stress to add the additional air re-circulation fans and tie in the HVAC system? 

That would take up weight and room that is dedicated to cargo. Then you would have to outfit the inside to give it any use.

1 hour ago, SgtSomeone said:

4) Doesn't the station always need extra space? I could see why launching new modules wouldn't be worth it, but these are already there!

Not really. More space means more load on the ECLSS.

1 hour ago, SgtSomeone said:

I guess it mostly comes down to this, though I wonder if the common berthing mechanism will bring those costs down, or if there would be a way to make them cheap enough to do this. 

The CBM is the current large berthing system. The new system is LIDS, NDS, IDSS, IDA (it changes its name every couple of years), which is smaller and designed for the new crop of visiting vehicles. I doubt it will be cheaper. Note that Dragon plans to reuse the its docking adapter, whereas the other vehicles jettison it for reentry.

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