How the ISS will end its life in orbit | Hacker News Reader

How the ISS will end its life in orbit

bbc.com

48 pointspmoriarty33 comments

This plan is an insane waste.

Other than Zarya and the other Russian built modules, the American, Japanese, and European ISS segments have held up quite well. Despite the intense thermal cycles and stress, these modules continue to operate with some repairs to sub-systems along the way. For example, Tranquility's Carbon Dioxide Removal Assemblies (CDRAs) has had two unrelated failures a decade ago (2013), but they've been repaired and the station continues to function. And it should function for at least another two decades.

We've spent so much money trucking these segments up the gravity well, and large parts of the structure are "fine," for an unknown quantity of fine. The primary structure, the Integrated Truss System https://en.wikipedia.org/wiki/Integrated_Truss_Structure, has been monitored constantly and hasn't experienced any significant degradation (or, degradation that has been made public). The modules may not be fresh off the assembly line, but they should continue to function.

My analysis is limited by the fact that I haven't been able to find a technical assessment of the central truss' lifetime, but currently there is no reason why it shouldn't continue to function far into the future as new modules are swapped in and out. The Truss itself is modular, and if push comes to shove, it is cheaper to start replacing segments than it is to build a new station

Here is a simple proposal.

We should send up thermal blankets, more radiators, and a better thermal management system to reduce thermal stress on the station via expansion & contraction. We should also develop secondary systems for each of the major sub-components that are nearing the end of life, and perform 1-to-1 swaps with existing systems (this has been done before!)

We should then boost the perigee up to at least 1,000km. As the density dropoff is exponential, the ISS will then last in this orbit for several hundred years.

The ISS should then be privatized (but managed by the USG + ESA), with different trusses, spaces being allocated to allow people to build on top of the ISS' infrastructure and experiment with in-orbit construction, manufacturing, and mass chemical synthesis in orbit for pharmaceuticals.

the problem is I don't think there is interest in privatizing the station. I think it was floated at one point, but Axiom and Blue Origin seem to be more interested in building their own stations.

especially when the prospect of being able to launch the entire orbital mass of the ISS on two expendable Super Heavy/Starship rockets is on the horizon.

also I don't know how hard it is to change the stations orbit inclination, but when they went from being Space Station Freedom to the ISS the orbit was changed to allow the Russians to be able to launch to it. That drastically reduced the amount the Shuttle could carry to the ISS. From my understanding Axiom and Blue Origin are both planning to optimize for launch from North America.

(only half joking) but how bad does it smell in those segments after decades of canned recycled air?

> how bad does it smell in those segments

Depends

ISS requires too much constant maintenance. No-one would be willing to operate it at what it costs NASA. Any future space stations want to learn from the lessons of ISS and build something that doesn't require constant work and monitoring to function, and with modern launch prices you can get the baseline capability up there for just a few years of ISS maintenance.

> We should then boost the perigee up to at least 1,000km.

This would expose the occupants to significantly more radiation, would it not? The Van Allen belts start at ~650 km, varying with latitude and solar weather.

You're absolutely right! The inner belt starts at,

> The inner Van Allen Belt extends typically from an altitude of 0.2 to 2 Earth radii (L values of 1.2 to 3) or 1,000 km (620 mi) to 12,000 km (7,500 mi) above the Earth.[3][13] In certain cases, when solar activity is stronger or in geographical areas such as the South Atlantic Anomaly, the inner boundary may decline to roughly 200 km[14] above the Earth's surface.

I found a graph that shows the dose rates at given altitudes for circular orbits, https://ars.els-cdn.com/content/image/3-s2.0-B97801281405810...

You quickly get into the centuries range as you approach a 800km perigee, see,

https://www.researchgate.net/figure/Orbital-decay-of-the-spa...

With the ISS' large cross section, it will experience more drag, but (and this is a guess) the reboost time would be measured in years and decades rather than months somewhere between 750km to 800km.

Maybe there's an altitude here that's safe and doesn't poison humans?

I also found a report of shielding required for given equatorial circular orbits at different altitudes, https://space.nss.org/wp-content/uploads/Orbital-Space-Settl...

    > Table 4 suggests that for settlements in low equatorial orbit (below 500 km), no shielding mass is required to meet the 20 mSv/year and only a tiny (equivalent to polyethylene 0.01 ton/m2) amount to meet the 6.6 mGy/year limit. The ISS has an average of about the equivalent of 200 kg/m2 aluminum shielding [Cucinotta 2013]. Thus the minimal shielding provided by a pressure hull, solar arrays, whipple shield, etc. should be sufficient to meet the pregnant woman threshold. This has radical implications for space settlement as discussed below.

    > There is a very high radiation level (mGy/year column) with no shielding at 600 km. This is mostly trapped protons that can be easily shielded as is seen from the rapid dropoff when small amounts of shielding are added.

Increased inclination (such as the ISS' orbit), means increased radiation exposure as they pass through the south atlantic anomaly.

> in March, Nasa asked Congress for funding to start development of a "space tug" that might be needed to perform the task – a spacecraft that can push the station back into the atmosphere. Kathy Leuders, head of Nasa's human spaceflight programme, later revealed it was estimated the tug vehicle would cost just shy of $1bn (£800m).

This part sounds insane. Use a docked Progress, Soyuz or Dragon to give it the right calculated nudges at a fraction of the cost. There is complexity, angular momentum and rotation in there I'm sure but NASA is good at rocket science, why develop a new vehicle.

Progress/Soyuz/Dragon don’t have the delta-V necessary to be able to de orbit 400 tonnes. It may be possible to refuel one of the repeatedly to achieve that over multiple burns, but that’s a complex job over months with multiple refuelling missions required and likely new hardware to support that.

One billion dollars is only 1/43rd of a Twitter. That sounds like a pretty good deal to me.

I guess that works if you feel Twitter is valued reasonably (or even has a positive value on a societal level with externalities). I don't work in tech so have a different view on the wild west of the tech industry than most on that here. Maybe a better comparison is cost of 30 ICE3 trains for 1 billion euros[1].

[1] https://www.globalrailwayreview.com/news/104428/deutsche-bah...

It's too bad moving it to a stable orbit would be so expensive, the ISS would make a great fixture for an orbital museum in a few hundred years. Instead, all that history is just going to burn up in the atmosphere.

I don't think folks realize just how low the ISS's low Earth orbit really is. They feather the solar panels when in earth shadow, to reduce aerodynamic drag!

You’d think that one of of the multi billionaires with rocket companies would attempt to save it. Would be great PR.

I don't know much about space or the ISS so this might be a naive question. But why wouldn't NASA persue a "ship of Theseus" approach? What I mean is the ISS is modular, why wouldn't it be feasible to keep taking on and decommissioning modules? I would assume this is because the ISS has a "core module" that all other modules tack on to, and that module is getting old? Right?

At this point the core structural module is the truss, which I believe is doing fine, being essentially an unpressurized aluminum skeleton. You could eject the pressurized components and bolt a whole new set onto it, but at that point you might as well build a new station, and let's be honest the part of the station everyone is sentimental about isn't the scaffolding

I think you could. the question is "is it it worth it?". the Station was built on the ground mostly in the 90s using 80s technology. I would think there are a lot of design decisions driven by 1980s technology that they are stuck with today. and its non-trivial to move an existing station away from that.

Also I don't think NASA really wants to keep going with a Space Station. from my understanding with the Axiom Commercial Space Station and the Orbital Reef station , NASA is happy to buy services on those stations rather than operate their own. like they are doing with Commercial Crew and cargo. Plus with Lunar Gateway and a possible Mars gateway station. I would imagine that there is a lot of know how and talent on the ISS engineering and operations teams that NASA would like to put to work on the moon and mars projects under Artemis.

It's only kinda modular. The core modules would be rather difficult to separate, and replacing them would probably cost as much or more than a new station. And many of them are Russian, which is a problem for a whole host of reasons.

The attitude control (Russian) modules and energy generation (USA) modules are getting very old, and showing signs of their age more every day. We've accomplished the mission of the ISS many times over, and to keep it aloft would essentially mean building a new one - exactly what they're doing with the Artemis Gateway. It's had a great run, and I'm among many who will be devastated when they finally deorbit it, but it's necessary at this point.

Is the prohibitive cost of boosting it to a higher orbit calculated based on currently available rockets?

I can imagine that if in the next few years Starship becomes functional and anywhere close to as cost effective as is planned, then that should drastically reduce the cost of boosting the ISS.

Instead of de-orbiting it towards earth, why don't they de-orbit it in the other direction, away from earth. Wouldn't that be safer?

The amount of energy needed to get out of earth's gravity well is incredibly high. It would be silly to try to boost a massive object like the ISS out.

Escape velocity energy from an orbit is sqrt(2) times the energy it takes to get to that orbit. But it’s more than ~41% more fuel, since you need more fuel to push the fuel, and more fuel than that to get it to orbit in the first place.

Much cheaper to let the atmosphere drag it down, which is something that is going to happen anyways.

So achieving escape velocity from geosynchronous orbit requires more delta v than from LEO?

I kind of see it, as the surface velocity of a GEO satellite is near zero yet the surface velocity of a LEO bird is measured in the thousands of KPH. However so much more energy was invested in raising the satellite so high up, I have a difficult time imagining that actually more energy is now required to bring it to escape velocity. Is not escape velocity at GEO altitudes lower than escape velocity at LEO?

This is done for GEO satellites, but as mentioned in other comments here, it's impossible for LEO satellites such as the ISS.

https://en.wikipedia.org/wiki/List_of_orbits

https://en.wikipedia.org/wiki/Graveyard_orbit

https://www.esa.int/ESA_Multimedia/Images/2008/03/Mitigation...

That would take way to much energy for little benefit. They expect the ISS to burn up in the atmosphere so there wouldn't be a safety issue to people/things on earth.

Much more expensive (in delta-v terms) to hit escape velocity, I’m guessing?

I really hope they load the thing up with cameras and have a live view of both the inside and outside as it burns up.

Wouldn't the reentry ioniztion mess with this?

Maybe that's a stupid question, but : why can't its lifetime be extended again ?

The article says "much of its hardware is decades old, which could eventually see the station become dangerous or even uncontrollable in orbit" but it's not very explicit about why we couldn't change some internal hardware / repair what needs to be repaired and keep the main overall structure for a longer lifetime ?

The Russians have already indicated an intention to pull out. Plus, current politics (perhaps, that should read "war") makes continuing to work with Russia troublesome. What is the consortium meant to do, purchase Russia's modules?

Uncouple Russian modules and burn them ?

I wonder why creating a "space tug" to deorbit the station is going to cost NASA $800M. Won't a regular second of third stage of any rocket in current wide use be sufficient? The only tricky part / payload would be an attachment to direct the impulse exactly at the center of mass.

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