Needless to say, NASA does not use EA math in its budgeting ;-)
The world’s major space agencies abandoning the biggest thing we ever put into space in an uncontrolled deorbit is a politically untenable option (and the project represnts only around a third of the estimated $3bn annual budget to keep the ISS operational, although there’s an argument this spend has more ROI...). That’s even more the case against a backdrop of increasing calls for more regulation around everyone else’s launches and orbits and deorbits to prevent collisions in space[1]
The potential risk to human life of uncontrolled ISS reentry therefore isn’t the only factor in the decision and probably not even the main one, though I don’t think the deorbiting of generally orders of magnitude smaller stuff gives much of a guide to the magnitude of that risk.[2] (There are of course also other arguments against spending money on this project, such as the desirability of maintaining the ISS, the possibility of raising it to a graveyard orbit for future reuse/recycling instead of destroying it; and other arguments in favour such as the likelihood at least some of SpaceX’s R&D can be deployed to more productive projects in future). Space agencies usually aren’t especially rigorous in analysing cost effectiveness anyway, but cost-per-life saved is a pretty minor factor in why such contracts are awarded. Space funding is industrial policy targeting notionally large medium term returns from technology, not evidence-based philanthropy trying to find the most cost effective way to remedy problems.
this potentially compounds, with each debris impact creating more orbital debris, with the theoretical possibility of rendering some orbits unusable in future. Avoiding this scenario might still seem wasteful from the point of view of a Ugandan farmer whose neighbourhood could be fed for years on the research budgets being devoted to maintaining congestion-free orbits, but rather a lot of the developed world depends on access to satellite technology and I suspect even some NGOs in Uganda make some use of GPS and satcomms.
but that risk is probably still low, assuming even with it rentering via gradual orbital decay, operators would still have sufficient ability to control reentry using onboard thrusters to direct it to scatter it’s debris over thousands of kms that’s mostly ocean or sparsely populated, as with Skylab...
I love your comment about it being “politically ” untenable you might be right on the money there—even though of course there’s nothing about that in NASA discourse
The reason I wrote this post was because at least in the public facing materials I read, public human safety on earth was NASA’s only reason for doing a controlled vs random re-entry. Of course you could well be right that other considerations are more important than public safety that they’re not talking about but that’s all they list on their site—the full blurb is here below. They don’t mention the possibility of uncontrolled re-entry causing debris, nor the possibility of a collision on the way down. I assumed (like you said) this was because they would still have relative control of the re-entry using the boosters on the station.
”The U.S. Government specifies that re-entering spacecraft must meet or exceed a 1-in-10,000 likelihood of public risk due to debris. An inability to meet this specification requires the spacecraft to conduct a controlled deorbit, which is a standard industry practice for spacecraft that exceed the U.S. Government’s safe re-entry requirements unless the spacecraft operates near a disposal orbit, such as a geosynchronous orbit. An uncontrolled deorbit occurs when a spacecraft enters the atmosphere without navigational or propulsive control and is only acceptable when the debris impact risk to the public is small (i.e., a small spacecraft or the structure breaks into small pieces and has a small debris footprint). The International Space Station requires a controlled re-entry because it is very large, and uncontrolled re-entry would result in very large pieces of debris with a large debris footprint, posing a significant risk to the public worldwide. Ensuring the space station is well maintained continues to be the safest operational approach while also planning for deorbit at the space station’s end of life.
The use of existing space station propulsion systems, such as the Roscosmos Progress vehicles, would provide an alternative to an uncontrolled re-entry prior to the arrival of the U.S. Deorbit Vehicle (USDV). However, these systems do not provide sufficient margin to lower the public risk to an acceptable level. The USDV will provide this margin to lower the public risk to U.S. Government standards. ”
Read more on the agency’s International Space Station Deorbit Analysis Summary white paper. ”
I completely agree that keeping low orbit clear of debris is critcally important and probably worth far more than a few billion dollars, but they only discussed that being an issue if either the ISS was destroyed at its current orbit, and as also being a big risk also if they tried to elevate it to a higher orbit.
Just to clarify on the orbital debris problem: it’s not just the risk of the ISS specifically hitting things on the way down (which is non-zero but at the same time not that likely: the ISS is too big to overlook and will move in a reasonably predictable manner so things will generally adjust their orbits in advance to move out the way, and most of them have higher orbits anyway). It’s also that when operators of thousands of other satellites[1]- from Starlink to university cubesats—are being advised/required to have specific end-of-life deorbiting strategies to avoid creating more orbital debris, all of which cost them money in terms of additional man hours and launch mass, and lots of research dollars are being spent on addressing the problem of orbital debris, the world’s major space agencies can hardly state their end of life strategy for the ISS is as long as everyone else gets out the way and then when it breaks apart in the upper atmosphere the pieces land somewhere like Australia or the sea it probably won’t do any real harm. It’s really bad politics to demand everyone else is a responsible citizen whilst shrugging your shoulders about the fate of your flagship. And nearly all the alternatives—especially those discussed in the white paper—would cost more.
And yes, in the scope of the operations of the ISS $843m isn’t even that big a number, which I realise may seem obscene in a country where that sum of money would buy the entire population a couple of malaria nets
(FWIW I still think you can [i] make a good case that the project is premature, the wrong approach or poor value for money and [ii] make a good case that SpaceX has done unusually well in turning pork-barrel projects into useful, value-for-money services and may do so again despite the project being premature, the wrong approach and/or poor value for money)
Needless to say, NASA does not use EA math in its budgeting ;-)
The world’s major space agencies abandoning the biggest thing we ever put into space in an uncontrolled deorbit is a politically untenable option (and the project represnts only around a third of the estimated $3bn annual budget to keep the ISS operational, although there’s an argument this spend has more ROI...). That’s even more the case against a backdrop of increasing calls for more regulation around everyone else’s launches and orbits and deorbits to prevent collisions in space[1]
The potential risk to human life of uncontrolled ISS reentry therefore isn’t the only factor in the decision and probably not even the main one, though I don’t think the deorbiting of generally orders of magnitude smaller stuff gives much of a guide to the magnitude of that risk.[2] (There are of course also other arguments against spending money on this project, such as the desirability of maintaining the ISS, the possibility of raising it to a graveyard orbit for future reuse/recycling instead of destroying it; and other arguments in favour such as the likelihood at least some of SpaceX’s R&D can be deployed to more productive projects in future). Space agencies usually aren’t especially rigorous in analysing cost effectiveness anyway, but cost-per-life saved is a pretty minor factor in why such contracts are awarded. Space funding is industrial policy targeting notionally large medium term returns from technology, not evidence-based philanthropy trying to find the most cost effective way to remedy problems.
this potentially compounds, with each debris impact creating more orbital debris, with the theoretical possibility of rendering some orbits unusable in future. Avoiding this scenario might still seem wasteful from the point of view of a Ugandan farmer whose neighbourhood could be fed for years on the research budgets being devoted to maintaining congestion-free orbits, but rather a lot of the developed world depends on access to satellite technology and I suspect even some NGOs in Uganda make some use of GPS and satcomms.
but that risk is probably still low, assuming even with it rentering via gradual orbital decay, operators would still have sufficient ability to control reentry using onboard thrusters to direct it to scatter it’s debris over thousands of kms that’s mostly ocean or sparsely populated, as with Skylab...
Thanks so much David nice one!
I love your comment about it being “politically ” untenable you might be right on the money there—even though of course there’s nothing about that in NASA discourse
The reason I wrote this post was because at least in the public facing materials I read, public human safety on earth was NASA’s only reason for doing a controlled vs random re-entry. Of course you could well be right that other considerations are more important than public safety that they’re not talking about but that’s all they list on their site—the full blurb is here below. They don’t mention the possibility of uncontrolled re-entry causing debris, nor the possibility of a collision on the way down. I assumed (like you said) this was because they would still have relative control of the re-entry using the boosters on the station.
”The U.S. Government specifies that re-entering spacecraft must meet or exceed a 1-in-10,000 likelihood of public risk due to debris. An inability to meet this specification requires the spacecraft to conduct a controlled deorbit, which is a standard industry practice for spacecraft that exceed the U.S. Government’s safe re-entry requirements unless the spacecraft operates near a disposal orbit, such as a geosynchronous orbit. An uncontrolled deorbit occurs when a spacecraft enters the atmosphere without navigational or propulsive control and is only acceptable when the debris impact risk to the public is small (i.e., a small spacecraft or the structure breaks into small pieces and has a small debris footprint). The International Space Station requires a controlled re-entry because it is very large, and uncontrolled re-entry would result in very large pieces of debris with a large debris footprint, posing a significant risk to the public worldwide. Ensuring the space station is well maintained continues to be the safest operational approach while also planning for deorbit at the space station’s end of life.
The use of existing space station propulsion systems, such as the Roscosmos Progress vehicles, would provide an alternative to an uncontrolled re-entry prior to the arrival of the U.S. Deorbit Vehicle (USDV). However, these systems do not provide sufficient margin to lower the public risk to an acceptable level. The USDV will provide this margin to lower the public risk to U.S. Government standards. ”
Read more on the agency’s International Space Station Deorbit Analysis Summary white paper. ”
I completely agree that keeping low orbit clear of debris is critcally important and probably worth far more than a few billion dollars, but they only discussed that being an issue if either the ISS was destroyed at its current orbit, and as also being a big risk also if they tried to elevate it to a higher orbit.
Just to clarify on the orbital debris problem: it’s not just the risk of the ISS specifically hitting things on the way down (which is non-zero but at the same time not that likely: the ISS is too big to overlook and will move in a reasonably predictable manner so things will generally adjust their orbits in advance to move out the way, and most of them have higher orbits anyway). It’s also that when operators of thousands of other satellites[1]- from Starlink to university cubesats—are being advised/required to have specific end-of-life deorbiting strategies to avoid creating more orbital debris, all of which cost them money in terms of additional man hours and launch mass, and lots of research dollars are being spent on addressing the problem of orbital debris, the world’s major space agencies can hardly state their end of life strategy for the ISS is as long as everyone else gets out the way and then when it breaks apart in the upper atmosphere the pieces land somewhere like Australia or the sea it probably won’t do any real harm. It’s really bad politics to demand everyone else is a responsible citizen whilst shrugging your shoulders about the fate of your flagship. And nearly all the alternatives—especially those discussed in the white paper—would cost more.
And yes, in the scope of the operations of the ISS $843m isn’t even that big a number, which I realise may seem obscene in a country where that sum of money would buy the entire population a couple of malaria nets
(FWIW I still think you can [i] make a good case that the project is premature, the wrong approach or poor value for money and [ii] make a good case that SpaceX has done unusually well in turning pork-barrel projects into useful, value-for-money services and may do so again despite the project being premature, the wrong approach and/or poor value for money)
most of which were launched in the past few years, which is why history isn’t a reliable guide...