Explainer · Research proposal
What is a Space Debris Credit?
A Space Debris Credit is a proposed record of a verified reduction in orbital debris risk. This film explains the idea in about three and a half minutes: why some objects matter more, how risk is measured, what would earn a credit, and what is still open.
About 3½ minutes, English, with captions and a transcript below. Every figure comes from working paper WP-04 and the open reference code. Nothing shown is an official rating or an issued credit.
How a claim works
Verify, score, credit
A claim moves through three steps, and each one can be inspected. The lifecycle runs claimed, under review, verified, issued, retired. Rejected and revoked are final (rule C7).
Step 1
VERIFY
Two independent sources confirm what happened. If they disagree, a third-party audit starts and no unit is issued until it ends.
Rules D1 · D2
Step 2
SCORE
The change in risk, ΔR, is computed with its uncertainty. A unit is counted from the cautious low estimate and rounded down.
Rules C1 · C14
Step 3
CREDIT
The unit is written to a public registry with a tamper-evident chain. Retirement is one-way, and a unit cannot be counted twice.
Rules C8 · C9 · E2
The baseline
Doing what the law requires earns nothing
A credit recognises improvement beyond what would have happened anyway. That counterfactual is the baseline, and it includes everything the law already requires (rules C3 and C4). Without it, an operator could be rewarded for what it must do regardless, and the scheme would stop reducing risk.
Here is one object from the working paper, worked through. It is an illustration, not a claim.
- Object
- Zenit-2 No. 1-87 stage 2, a rocket body of 9,000 kg at 626 to 634 km. Rank 1 of the abandoned objects by R.
- Risk today
- R = 159.5, within a range of 10.8 to 246.2.
- Baseline
- It stays in orbit. Its estimated lifetime is 44.6 years, longer than the 25-year horizon.
- If it were removed
- ΔR = R before − R after. The cautious bound uses the low end of the range.
- Units
- ⌊ cautious ΔR ÷ ΔR₀ ⌋. The size of ΔR₀ is an open question in the consultation, so no unit count is shown.
Method WP-04 · GCAT, 11 October 2026. Illustration only: no removal is planned or claimed, and no unit exists.
The numbers
What the numbers mean
Several counts appear in the paper, the lab and the film. They describe different groups, so here is how they nest.
Catalogued objects with an apogee below 2,000 km. All of them are used to estimate how crowded each orbit is, which sets the collision chance Pc.
Method WP-04 · GCAT, 11 October 2026Intact objects among them: satellites and rocket stages, not fragments. 832 have no known mass, so they are counted but not ranked.
Method WP-04 · GCAT, 11 October 2026Intact objects with a known mass. These are the ones ranked by R.
Method WP-04 · GCAT, 11 October 2026Abandoned objects among the ranked ones. The 50 with the highest R hold 46.4% of their risk, and 48 of those 50 are rocket bodies.
Method WP-04 · GCAT, 11 October 2026The reduction from removing the ten highest-R abandoned objects, against the median of 10,000 random draws of ten. The cautious low estimate still beats 99.5% of the draws.
Method WP-04 · GCAT, 11 October 2026 · 10,000 drawsQuestions
What people ask first
Is this carbon credits for space?
It borrows the safeguards: define a claim, check the evidence, and record it so it cannot be counted twice. The analogy stops there. Orbital risk is not measured in tonnes of carbon, and its effects differ by orbit, object and time. A payment would not make an unsafe mission acceptable, and an unsafe action earns no credit (rule C12).
Who pays for a credit?
Nobody yet, because no credit exists. The Rulebook does not presuppose a market (rule F1). It lists options: voluntary retirement, licensing obligations, deposits and bonds, orbital-use fees, insurance and procurement criteria, and public purchase of removal. Whether units could ever be transferred is an open question.
Who checks a claim?
Accredited verifiers, assessed for competence, independence and data handling. A verifier cannot be the claimant. Where possible two independent sources must confirm the outcome, and a disagreement starts a third-party audit before any unit is issued (rules D1 and D2).
What is the difference between a rating and a credit?
The exposure rating (SDER) describes how much debris risk a mission carries and how sure we are about it. A credit records a verified reduction in that risk. They are separate: a rating is not a credit, and the rating has a known flaw, so units are sized by ΔR, not by the rating.
What does R actually measure?
R = M × L × Pc: mass, times the share of the next 25 years the object stays in orbit, times its chance of colliding with another catalogued object in that time. It is a proxy for how much debris an object could create. It is not a probability of disaster, and a high R is not a removal order.
What if the numbers are wrong?
Every input carries a stated range, and units are counted from the cautious low estimate. The Rulebook provides for disclosure, correction and appeal (rules B7 and D4), and publishes the reasons for accepting or rejecting a change to the rules (rule G1).
This is a proposed framework. No official rating, issued credit, certification or tradable market exists, and the Rulebook is a consultation draft that is not in force.
Read the transcript
The commons
Orbit is a shared road. The satellites behind our phones, weather forecasts and navigation all travel it. When a mission ends, whatever it leaves behind stays. Above about eight hundred kilometres, an abandoned rocket stage can circle Earth for a century or more. And if two objects collide, each can become thousands of fragments. Today, nobody is paid to remove a dead stage. This film explains one proposed way to change that: Space Debris Credits. It is a research proposal. No credit exists yet.
Where the risk sits
Not every object matters equally. In the open GCAT catalogue, eighteen thousand and thirty-six intact objects in low Earth orbit have a known mass. Of the two thousand eight hundred and forty-five that are abandoned, just fifty hold forty-six percent of the debris risk. Most of them are old rocket stages. In the model, removing the ten worst abandoned objects takes out eighty times more risk than removing ten at random. So the first job is to measure risk, and to say how sure we are.
Measuring risk
The research uses a deliberately simple measure. R equals M times L times Pc. M is the object's mass. L is the share of the next twenty-five years that it stays in orbit. Pc is its chance of colliding with another catalogued object in that time. Take Envisat: nearly eight tonnes, at seven hundred and sixty kilometres. Its R is about one hundred and forty-three, within a range from nineteen to five hundred and forty. A five kilogram cubesat scores almost nothing. R is a proxy for how much debris an object could create. It is not a probability of disaster.
The baseline
Now, what should earn a credit? Only an improvement beyond what would have happened anyway. This is called the baseline. If the law already requires an operator to deorbit a satellite, doing so earns nothing. But removing an abandoned stage that would otherwise stay for decades lowers R. That drop is called delta R. One unit would stand for a verified reduction of a fixed amount of delta R. It is counted from the cautious, low estimate, and rounded down.
Verify, score, credit
A claim follows three steps. First, verify. Two independent sources must confirm what happened, and any disagreement triggers an audit. Second, score. The change in R is computed, and its uncertainty is kept. Third, credit. Only then is a unit issued, and written to a public registry that is chained so it cannot be quietly edited. A unit can be retired once, and it can never be counted twice.
Honest limits
This is a proposal, not a rule. Nothing here is in force, and no rating or credit has been issued. The model leaves out debris smaller than about ten centimetres, which no public catalogue tracks. The exposure rating still has placeholder weights, and it puts a five kilogram cubesat in the same band as a nine tonne rocket stage. We publish that flaw because the Rulebook is a consultation draft. Explore the numbers in the lab, read the Rulebook, and challenge it.