What is an empty leg?
The term comes from air charter, where an aircraft repositioning without passengers is sold at a discount because the flight is happening either way. Space cargo has the same economics for a different reason: a launch vehicle is manifested to a mass and volume budget, and it almost never fills that budget exactly.
Residual capacity shows up in two ways. On a rideshare mission, slots go unsold before the manifest closes. On a dedicated mission, the primary payload sits well under what the vehicle can lift. Either way the launch is going regardless, so the marginal cost of carrying more is far below the cost of buying capacity on a launch of your own.
It is also perishable. Once the manifest closes, that capacity is gone — it does not roll over to the next flight.
The six steps
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Find capacity
Browse open availabilities and filter by what your payload actually needs.
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Check the fit
Review the dimensional envelope, power, thermal and data notes for that slot.
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Request a quote
Submit your cargo, organisation and compliance details.
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Provider review
The provider — and our compliance review — respond, typically within three business days.
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Booking
A booking exists once the provider confirms and payment is processed.
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Manifest & launch
Integration runs against the operator’s interface requirements through launch.
1. Find capacity
Browse open availabilities and filter on the things that actually decide whether your payload can fly: departure site, vehicle, destination, available mass in kilograms, available volume in cubic metres, and the launch window. Each listing carries the provider’s own figures and a booking deadline — the date the manifest closes, which is the deadline you are really racing.
Requests close at least 4 days before launch, even if a provider’s own posted deadline is later. That window is not padding: once a request is accepted, everything that has to happen before a payload can fly against a firm launch time has to fit inside it — cargo verification against the declared mass, dimensions and safety disclosures; export-control and identity authorisation; funds transfer and payment confirmation; and, where applicable, insurance arrangements. A booking made closer to launch than that cannot reliably complete all of it, so the window is enforced platform-wide rather than left to chance. A listing’s countdown on its detail page always reflects this floor, not just the provider’s stated deadline.
2. Check the fit
Open the leg detail page for the dimensional envelope, power, thermal and data notes, and the risk disclaimer that applies to that specific slot. If the numbers do not work, the constraint is usually volume or the deployment interface rather than mass.
3. Request a quote
Requesting a quote requires an account, because quotes are tied to a verified organisation. The request captures your cargo details, your organisation’s identity information, and your export-control and cargo-safety declarations. Pricing is by quote: residual capacity is priced against what is left and how close the manifest deadline is, so there is no published rate.
4. Provider review
Your request goes to the provider holding the slot, and to our compliance review in parallel. The provider decides — they are the party with the operator relationship and the interface documentation. Most providers respond within three business days.
5. Booking
A booking exists once the provider has confirmed and payment has been processed. Submitting a request is not a reservation, and neither is a quote you have received but not accepted.
6. Manifest and launch
From confirmation onward, integration runs between you and the provider against the operator’s interface requirements. Launch windows move; when we detect that a schedule has drifted, the affected listing is placed on hold and both parties are notified.
What you need before you start
- Cargo mass and dimensions you can stand behind — declared figures are certified as accurate at submission.
- Organisation details, including legal name, country of incorporation and registration number.
- Export-control answers. If your cargo is dual-use or ITAR-controlled, you will be asked for the licence number at request time. Being controlled does not disqualify cargo; failing to disclose it does.
- Physical safety disclosures for pressure vessels, stored energy, propulsion, propellants, pyrotechnics and restricted platings or finishes. This is a self-certification that routes your request to the provider for review, not a technical approval by us.
Who does what
CharterSpace.IO is a marketplace. We list capacity, run the quote request through identity and export-control screening, and route it to the right provider. We do not operate launch vehicles, we do not handle or insure cargo, and we are not a party to the contract of carriage.
The provider lists the capacity, quotes it, and carries it under their own terms. The launch operator retains sole and final authority over manifest composition, cargo acceptance, scheduling and mission execution.
Because of that split, we strongly recommend independent cargo insurance for any tendered payload. See the Risk Disclosure for the full picture, and the Prohibited Cargo Policy for what can and cannot be tendered.