What goes up must come down – except in space. When a space mission is due to reenter Earth’s atmosphere the aim is that it does not survive the plunge to the ground in fragments large enough to potentially injure anyone.
Since April 2008 all ESA satellites – and launcher upper stages used to deploy them – due to be disposed of by atmospheric reentry at the end of their operational life must demonstrate that the risk from fragments surviving reentry to cause casualties on the ground is less than one in 10 000.
The concept involved is called ‘Design for Demise’: the intentional design of space system hardware so that it will completely burn up – or ‘ablate’ – during uncontrolled atmospheric reentry as a means of post-mission disposal.
This design methodology is especially required for uncontrolled reentry, which would otherwise pose a hazard to public safety, whether on the ground, in the air or on the sea.
Ensuring ‘Design for Demise’ requires knowledge of material properties. In the past spacecraft propellant tanks – made of high-melting point materials like titanium or stainless steel – have proved most likely to survive reentry. Leftover propellant may sometimes remain in these tanks, adding to the potential risk to life.
Any heavyweight space system making wide use of materials that would not be consumed during deentry may not comply with ESA debris mitigation requirements. In such cases, a design that allows disposal by controlled reentry becomes mandatory.
As part of ESA’s Clean Space initiative, the Agency has issued an Invitation to Tender aimed at companies interested in Design for Demise: ‘Characterisation of demisable materials.’ The ITT package is accessible via EMITS (Electronic Mailing Invitation to Tender System) for any registered company. Otherwise follow the link (http://www.esa.int/About_Us/Industry/Industry_how_to_do_business/ESA_s_Invitation_to_Tender_System_EMITS) to register.