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I heard in a few places downmass is a limiting factor in the ISS national lab capacity. Is that true?

According to NASA's pricing plan, it actually costs more to get downmass than upmass. Why is that?

David Hammen
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nadav zilberman
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    To get a mass down from ISS you need a capsule with heat shields and parachutes. All that should be brought up from ground too the ISS before. So downmass should be more expensive than downmass. – Uwe Jan 01 '23 at 20:56
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    @Uwe - only if the capsule mass is more than the payload it can safely deorbit. That's the part that confuses me - looking at e.g. the Apollo CM, structure+heatshield+recovery+RCS mass was (barely) less than 50% of the capsule weight. (From https://en.wikipedia.org/wiki/Apollo_command_and_service_module -> 2681.2/5560 kg). And that had to withstand a lot harder reentry. – TLW Jan 02 '23 at 18:32
  • I've edited the question to link directly to NASA as opposed to spacenews.com as the latter obtained the information it posted directly from the former. – David Hammen Jan 07 '23 at 10:44
  • Note that trash disposal is not free. The price NASA charges commercial entities for upmass and trash mass are identical, $20K per kg. Downmass costs $40K per kg. – David Hammen Jan 07 '23 at 10:47

2 Answers2

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For ISS, download payload is significantly more limited than upload. Being a scarcer resource, download mass is priced accordingly.

Spacecraft Upmass to ISS Downmass from ISS Notes
Cargo Dragon 3,307 kg 2,507 kg (+800 kg of trash) Trash is stored in the "trunk" which burns up
SoyuzTMA 100 kg + crew 50 kg + crew

Upload capacity is determined primarily by the launch vehicle. A bit more lift means a bit more cargo. But download is limited by the design of the re-entry vehicle. Overloading = instability and burn-through.

Downmass price is aimed at commercial users who want to download manufactured products, verses those who don't. And those users who want their equipment returned in one piece rather than trashed. There is a limited supply of up, down and trash so the price of each resource should be determined by demand. This ensures efficient use of resources. Or so say the "dismal scientists" in economics.

Woody
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    The Cargo Dragon can also take 800 kg of trash in its disposable trunk. A very important capability. – Schwern Jan 01 '23 at 23:56
  • @Schwern ... interesting. How do they decide what gets disposed of that way as opposed to just chucking it out the airlock? – Woody Jan 02 '23 at 00:05
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    There is (almost) no air in space and (almost) no drag. The ISS is moving horizontally at 27,600 km/h around the Earth in orbit. If you chuck something out the airlock, let's say at 100 km/h, it will now orbit slightly lower at 27,500 km/h and be hazardous space junk. You have to slow it down a lot until its low enough to be slowed by atmospheric drag. Same reason we can't just "throw" our trash into the Sun; you have to cancel the Earth's 100,000 km/h orbital velocity around the Sun. See Can An Astronaut Throw Something From Orbit To Earth. – Schwern Jan 02 '23 at 00:22
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    @Woody Most of the cargo freighters (HTV, Cygnus, Progress, etc.) have/had 0 downmass, and are used to dispose of trash. – Jacob Krall Jan 02 '23 at 01:21
  • I'm really tempted to revert the @Schwern edit. It's not downmass if it doesn't make it down to Earth. Otherwise you could also count whatever you can shove into the ascent module of the Soyuz as downmass, since that's also destroyed on re-entry. – Erin Anne Jan 02 '23 at 01:23
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    @ErinAnne You can't pile infinite weight in a vehicle that's going to be destroyed--it has to have enough propellant to deorbit whatever you put in it. – Loren Pechtel Jan 02 '23 at 01:52
  • @ErinAnne .... I agree. The OP asks about the cost of downloading mass, not taking out the garbage. – Woody Jan 02 '23 at 05:09
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    I think as long as it's made clear the difference between downmass and trash, it's a useful addition to the answer; both are similar issues facing the ISS. As Woody's comment demonstrates, I don't think people consider the trash problem. You can't just throw either out the airlock, you need a vehicle and propellant to deorbit both downmass and trash. The difference is one reaches the ground intact and the other does not. But it isn't my answer. – Schwern Jan 02 '23 at 05:10
  • @Schwern The ISS is quite low, so the space junk wouldn't last for very long. Maybe a year until it deorbits? – gerrit Jan 02 '23 at 16:16
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    This post doesn't seem to answer the question: How much does it cost? How much NASA charges might not be the same as how much it actually costs. – gerrit Jan 02 '23 at 16:17
  • @gerrit ... the question in the OP title of cost was answered by the link in the OP. The posted answer was a response to the question in the body of the question: why is the charge for downmass higher than upmass? The title needs an edit. – Woody Jan 02 '23 at 16:31
  • @gerrit;@Schwern ... you are correct about short time for de-orbit of trash. A tool bag which was "dropped" from ISS (not ejected) was tracked until it re-entered 9 months later. – Woody Jan 02 '23 at 16:34
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    @gerrit You pay $x for a launch that includes some upmass, some downmass, and some trash disposal. There's no inherently correct way to allocate that cost into 3 parts. Do you divide everything evenly by kg? Do you say trash is free since it's a technical limitation that it burns up? Do you allocate the cost of the Soyuz launch abort system solely to humans, not the upmass? – user71659 Jan 02 '23 at 20:58
  • I think to make this truly complete, it should include: Up (?) and Down (0) and Trash (?) of each of the other vehicles used to deliver people and/or stuff to ISS. Then add columns showing the vehicle cost, launch cost, total cost and possibly (which is where it gets really fuzzy) total cost/(Up + Down). – manassehkatz-Moving 2 Codidact Jan 02 '23 at 21:07
  • @manassehkatz-Moving2Codidact ... sounds good. Fill your boots, as they say, and post an answer. – Woody Jan 02 '23 at 23:02
  • @user71659... I think the downmass price is aimed at commercial users who want to download manufactured products, verses those who don't. And those users who want their equipment returned in one piece rather than trashed. There is a limited supply of up, down and trash so the price of each resource should be determined by demand. This ensures efficient use of resources. Or so say the dismal scientists. – Woody Jan 02 '23 at 23:11
  • @Woody Sure, market forces set a price, but in the specific comment from gerrit I was replying to, he directly asks for cost. It particularly a valid question for government agencies which often need to know cost, e.g. because they can't turn a profit or they need to bill say the DoD's budget, so I'm sure there's some NASA allocation policy and model somewhere. – user71659 Jan 03 '23 at 02:29
  • If NASA has public prices for up/downmass for experiments run on the ISS that's probably the best we can do. – Dan Is Fiddling By Firelight Jan 03 '23 at 18:41
  • @user71659 Trash disposal is not free. NASA charges commercial entities $20K per kg for trash mass, half of what it charges for downmass. – David Hammen Jan 07 '23 at 10:55
  • Regarding the price of each resource should be determined by demand: NASA is not a commercial entity. For a long time, NASA subsidized commercial ventures in the hope that organizations would take advantage of those subsidized costs. Now that there is some demand for those services, NASA is trying to charge more in line with what providing those services cost NASA, but obviously as very rounded charges. – David Hammen Jan 07 '23 at 12:25
  • @DavidHammen Again, he's not asking for price, he's asking for cost. They are different things. – user71659 Jan 07 '23 at 19:32
  • @user71659 In a way, they are not different things. The prices that NASA charges commercial payloads for upmass, trash mass, and downmass are the costs of those resource to the commercial entity. In other sense, they are different things, but in that sense what you are asking for is privileged information that those who do know cannot disclose. – David Hammen Jan 07 '23 at 19:48
  • @DavidHammen No. First, the price charged to companies was below cost "The pricing policy... did not reflect full reimbursement for the value of NASA resources; it was intended to stimulate the market..." In many user fee situations, the gov't is allowed to charge commercial users what a commercial entity would charge. Second, price has to include full NASA/gov't overhead. Third, they're government, it's public. We know how much they're paying for a flight, the cost allocation model shouldn't be secret. – user71659 Jan 07 '23 at 20:07
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I heard in a few places downmass is a limiting factor in the ISS national lab capacity. Is that true?

That is true. NASA has two contractors (Northrop Grumman and SpaceX) plus other additional vehicles that can carry payload to the ISS, but only two of them (SpaceX and Russia) can bring material back to the surface of the Earth. Those vehicles that can return material to the surface can also dispose of trash, as can the Cygnus, the Automated Transfer Vehicle, the H-II Transfer Vehicle, and the Progress. Downmass is a precious resource.

According to NASA's pricing plan, it actually costs more to get downmass than upmass. Why is that?

Because downmass is a precious resource. With a few exceptions, everything that goes up to the ISS must come down, with the "coming down" as either trash or return. NASA appears to have arbitrarily split the cost of going up and coming down as trash (which is incinerated during reentry) 50-50, at \$20K per kg each way. Downmass is limited, so it is charged an extra \$20K per kg.

David Hammen
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