Deorbit ISS vs. Preserve ISS as raw materials for ISM?

Question

Recent news:

NASA Seeks Proposals from US Industry for Station Deorbit Spacecraft (ISS)

NASA has released a request for proposal from U.S. industry for the U.S. Deorbit Vehicle (USDV), a spacecraft meant to safely deorbit the International Space Station as part of its planned retirement.

UNH Researchers Awarded Close to $3 Million to Develop Sustainable In-Space Manufacturing (ISM)

The UNH researchers will collaborate with scientists from Purdue University and Baylor University, with support from NASA and Astroport Space Technologies, to explore ISM and the concept to set up “in-space factories” to reclaim and retrieve space resources to use in assembling and fabricating space-related hardware.

I am wondering if spending ~$1B to deorbit ISS isn't a little short-sighted. Would it be more prudent to invest in raising the ISS orbit (perhaps with an eye toward a likely orbit for a future ISM facility)? This would preserve the approximately 450,000 kg of very-space-craft-appropriate ISS mass for future manufacturing recycled/refined/reused materials.

I understand that ISM is in the very early stages and is likely to not be realized in the next couple of decades.

What would such a plan look like and how much would it cost to preserve ISS?

NOT keep ISS running. Just to preserve the mass. Put it in the "junkyard."

For example, would be more or less expensive in the near-term to preserve or deorbit ISS? (I understand that a high-energy, short-duration burn is required for successful deorbit, while raising the orbit would not have a significant limitation on duration.)

What parking orbit would you choose and how would you get ISS there? Refuel ISS? Send a tug?

What would the cost be to replace the de-orbited ISS mass with new raw material to supply an ISM facility at some point in the future? Where would it come from and how would you get it there?

Answer 1

Quoting from FAQ: The International Space Station Transition Plan:

Decommissioning by boosting an object to a higher “graveyard” orbit to extend orbital lifetime is often done with smaller satellites operating near geostationary orbits (~36,000 km in altitude). This is not a realistic target for space station decommissioning because of the large mass of the space station and distance from its operational altitude to a “graveyard” orbit. Existing propulsive assets (spacecraft) do not have the capability to raise the space station’s altitude to such a high target.

With current capability, it would be possible to raise the station’s altitude enough to slightly extend the orbital lifetime, but not escape low Earth orbit. This disposal method carries a high risk to future operations in low Earth orbit since the station could not be refueled for debris avoidance maneuvers. A debris strike on space station poses critical risk to astronauts, could render the station uncontrollable, or create additional debris that would present a risk to other missions. Alternative propulsive methods to escape Earth’s gravitational pull have been explored, but these options would require new hardware, a large amount of additional propellants, and would impose large additional cost burdens for the development, test, and deployment of these methods. Ultimately, this decommissioning strategy would only increase risk of station being struck by orbital debris and delay the uncontrolled re-entry of the space station to a later date.

Answer 2

This answer only addresses part of the "how could it be done?" side of the question rather than the "why/would it be worthwhile?"

The $1bn pricetag is presumably for an assured delivery to the south Pacific, expending most of the de-orbit propellant in much less than one rev. The boost-up to graveyard has no such time constraints. It would be reasonable to consider nearby graveyard zones, e.g. 2000km as this would buy a lot of time.

• For such a target orbit the continuous thrust delta-V will be is going to be about of the order of 1km/s.
• Assuming a high Isp of 4000s then a dead mass of 450 tonnes would require 12 tonnes of propellant (less if the Russian segment had already been detached).
• If the thrust level were 1N the transfer would take 15 years, though that is simply a reference point and a higher thrust would be proportionally shorter.
  • Drag varies a great deal over the solar cycle, 0.02N to ~1N according to What is the ISS drag? - , so its obvious that scheduling w.r.t the solar cycle will make a big difference
• I don't recall what the power availability on the space station is but as another reference point, 200kW could probably produce 4N or so at 4000s Isp. i.e. this is before bringing along any new solar arrays

Obviously there are some problems with raising the space station through a zone with a higher spatial density of debris and that this might be a stronger driver, possibly the strongest - obviously that depends on the probabilities of major release of further debris; I've just set out some figures for the energy involved in the transfer.

Answer 3

The three million dollar research grant that you mentioned has something of a questionable premise when it says that the goal is to "explore ways to recycle and reuse that cosmic debris to create a sustainable in-space manufacturing (ISM) industry." While this sounds great on the surface, there would likely be a problem with the idea of developing the ability to reuse old space hardware as a way to "create a sustainable in-space manufacturing (ISM) industry".

Since their premise in my opinion is not valid, for reasons which I will explain below, this means that the complexity and cost of safely keeping ISS in orbit until then is likely not going to be worth it, especially if it would cost more to preserve it then to deorbit it. If this is the case then the answer to the question whether ISS should be preserved for use as raw material for ISM instead of being deorbited would be no.

The problem with their approach is that it would rely on existing and future space debris as one of the main sources of material, combined as they said with ISRU materials mined from the Moon. The first problem is that space debris is scattered all over the place in different orbits and would be difficult to collect together in a central location for processing. It's certainly not impossible, but that's only the beginning of the challenges. The next one being that once collected it's going to be difficult, labor intensive, and potentially risky to safely disassemble the old satellites, rocket stages etc. and separate them into the various needed materials. This would be difficult and somewhat risky if done by astronauts during EVA. In theory the pieces could be brought into a pressurized "hangar" where astronauts could work on disassembling it, although in some cases there would be concerns about toxic fluids and gases.

Robots of course could be used for some parts of the process, like moving pieces from one location to another. However due to the wide variety in space hardware design, the actual disassembly and sorting of materials will likely require direct hands on human involvement for the foreseeable future. Especially since other than exceptions like ISS and Hubble, most space hardware was not designed to be disassembled in space.

A big problem could be that the quality and quantity of materials that are obtained from space debris may not be a good match with what is needed for a particular manufacturing process. Especially considering that at least current 3D printing technology for example is very specific in its materials requirements.

And then there is the legal aspect of the approach, since pretty much all space "junk" is owned by someone. So each party will have to be negotiated with independently. Many if not most countries and organizations may not be too keen on having someone getting an intimate look at their hardware, even if it is older. This legal issue is already a potential problem even for deorbiting programs being considered that would go around and send old debris into controlled Earth reentry.

And finally there is the inescapable fact that recycling old hardware is likely going to be a very costly prospect, and this has to be compared with the cost of launching the same materials from Earth, which was one of your questions. This of course can only be estimated, but I think @ChristopherJamesHuff explained the problem pretty clearly in a comment which I have slightly paraphrased:

You also have to consider what it would cost to just launch exactly the materials you need to exactly the orbit you'd need. It's likely to actually involve less launched mass than the tugs and refueling launches needed to move (debris) somewhere, then move the recycled materials to where you need them, even ignoring the cost of the orbital processing equipment needed to scrap the decommissioned (hardware) and turn its materials into something useful.

In the end the first in-space manufacturing industries will likely rely on a combination of ISRU resources and materials launched from Earth, where the exact type and quantity of material can be controlled. While there will eventually probably be a place for the recycling of existing space hardware, that is very far down the road in my opinion, making it too expensive and potentially risky to other satellites and spacecraft to preserve ISS just for the chance that its raw materials might be useful one day.

Answer 4

You also have to consider what it would cost to just launch exactly the materials you need to exactly the orbit you'd need. It's likely to actually involve less launched mass than the tugs and refueling launches needed to move the ISS somewhere, then move the recycled materials to where you need them, even ignoring the cost of the orbital processing equipment needed to scrap the decommissioned ISS and turn its materials into something useful.

Propellant requirements are linear with payload but exponential with delta-v. Say the specific impulse is 330 s (MMH/N2O4). A 4 km/s trip to a high disposal orbit will take about 1200 t of propellant. You could launch materials for two brand new ISS-class LEO space stations (with a good deal left over afterward) for what it'd take just to put the ISS in a disposal orbit for later salvage.