# What is the fuel cost of deorbiting a kilo of space junk?

Removing debris from LEO requires a significant delta-V which most schemes propose to accomplish via rocket propulsion.

Source

The ratio of launch fuel to payload mass is often given as 9:1 for LOE.

What is the equivalent fuel:debris mass ratio for de-orbiting?

The obvious answer is “it depends”. Orbital altitude (particularly periapsis altitude), ballistic coefficient and time to deorbit are all relevant.

For this question, consider a “typical” deorbiting task:

1. circular orbit 700km altitude
2. ballistic coefficient 50 kg/m2
3. target time to deorbit 25 years

The fuel:debris mass ratio is important when comparing the cost of non-propulsive deorbiting schemes such as tethers, light sails and drag chutes.

• based on the chart in your other question it looks like the fuel cost is zero, am I missing something? Commented Oct 30, 2022 at 23:50
• @BrendanLuke15 ... Yes, you are right. Everything de-orbits... eventually. But most of the junk above 700km will take more than 25 years to do so. And in that time, they may have collisions which fragment them into more pieces of junk. Current standards recommend all new satellites have a de-orbit plan for less than 25 years. Junk has no plan so it may need to be helped. Surgeons have a saying, "All bleeding stops.... eventually." But, like deorbiting, sooner is better. Commented Oct 31, 2022 at 2:40
• 9:1 fraction - isn't payload fraction confused with propellant fraction here? Propellant, indeed, is about 90 % of rocket's mass. But rockets also have several stages, and stages get most of the rest mass. Payload to LEO is usually 3-4 % or less. Commented Oct 31, 2022 at 12:09
• @Heopps ... published figures are confusing to me because they often include the dry weight of the top stage, which makes it to orbit but isn't really "payload". The ratio I'm interested in for the context of this question is "what is the fuel cost to launch a kilo of fuel to LEO?". I want to compare this with the fuel cost to deorbit junk since the deorbit fuel needs to be launched to LEO. Commented Oct 31, 2022 at 15:45
• @Woody I mean based on the chart a 50kg/m^2 object at 700 km has a deorbit time of ~25 years already Commented Oct 31, 2022 at 23:41