In the scenario dependence section of our methodology, we assume that deployment would begin with modified existing aircraft at high-latitudes and low altitudes (HiLLA) (see that uncertainty here). In order to reach the second stage – of subtropical deployment – new, purpose-built aircraft would need to be developed.
Metric
Time to develop, test, certify, and deliver a fleet capable of delivering ~1Mt/yr payload to 20km is over 10 years from first large-scale funding.
Uncertainty
The limited research that exists points to a timeline well below 10 years to develop a purpose-built aircraft that can achieve the characteristics detailed in our metric. Bingaman et al. (2020) estimate a timeline of 6 years and cost of $1 to $1.5 billion for all the steps of the timeline to a first airplane. John Langford, in his company Iris Aero’s unpublished study, estimates the timeline to produce an unmanned aircraft capable of achieving these characteristics to be 3 years at a budget of $120 million, with an additional 3 years and $1 billion to make it ready for mass production (at a cost of $20 million per plane (Levitan, 2026). Langford estimates that each plan would be capable of carrying 7.5 tons per flight, requiring 50 planes based on our above estimates. These aircraft would use existing Rolls Royce engines, currently used both in some commercial aircraft as well as the Global Hawk that has a similar flight ceiling (indeed, comparing the Iris Aero design with specifications for the Global Hawk, the former roughly replaces much of the fuel weight of a Global Hawk with the material payload as flights will be extremely short; this comparison provides confidence that the design is plausible, despite it not being a detailed design). Important to note is Smith (2024), which states the timeline for a first aircraft at over 10 years, however much of this time is a result of the long FAA certification process, which can be largely avoided by flying exclusively in non-commercial airspace. While there is clearly subjectivity in how much to weigh different people’s opinions, given the limited research and the fact that this has never been done before we choose to categorize the uncertainty as medium.
Decision relevance
This is hard to categorize as our definitions here are based on the start of HiLLA deployment. If this timeline was delayed, the length of the HiLLA deployment period could in theory be extended, but would likely cause a non-trivial bump in the overall deployment plan.
Further Information
To contextualize this challenge, a reasonable estimate for the number of aircraft needed can be made by assuming:
- We need to loft 1Mt/year of material (per definition of the metric; this is a reasonable scale for the beginning of deployment, corresponding to ~0.1C cooling).
- Each plane will be able to carry 7.5 tons per flight.
- Each plane can complete 8 flights per day. (Some commercial aircraft currently fly this often per day.).
- There are 350 operational days per year. This accounts for any roadbumps such as weather, maintenance, etc.
Based on the above assumptions, we would need a fleet of about 50 airplanes.
Once the first aircraft is ready for a test flight, a further several years for testing, certification, and low rate initial production (LRIP), is likely needed. After the initial 25 airplanes are produced, additional production should not be a limiting factor as we will be able to produce aircraft at a faster rate than deployment capacity requirement increase. For example, Boeing can currently build more than one 737 per day (Shepardson and Catchpole, 2025), although their process is much more streamlined than any new aircraft production will initially be.
References
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